Download Hi-Res ImageDownload to MS-PowerPointCite This:ACS Omega 2019, 4, 22, 19723-19734

Upgrading Low-Grade Iron Ore through Gangue Removal by a Combined Alkali Roasting and Hydrothermal Treatment

Yuuki Mochizuki
Yuuki Mochizuki
Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
More by Yuuki Mochizuki
http://orcid.org/0000-0003-1977-413X
and
Naoto Tsubouchi*
Naoto Tsubouchi
Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
*E-mail: [email protected]
More by Naoto Tsubouchi
http://orcid.org/0000-0001-8236-8252

Cite this: ACS Omega 2019, 4, 22, 19723–19734

Publication Date (Web):November 11, 2019

https://doi.org/10.1021/acsomega.9b02480

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Abstract

In this study, a combination of alkali roasting and hydrothermal treatment is used as a method of gangue (Si, Al, and P) removal from iron ores as a means to upgrade low-grade iron ore (limonite) into a high-grade iron ore with low gangue content, low porosity, and high Fe and Fe₂O₃ content to enhance the sustainable development of iron and steel industries. The effects of the combined treatments (NaOH hydrothermal treatment and H₂O/NaOH hydrothermal treatment of the alkali roasted sample), the iron ore type, their physical properties, and their calcination/roasting temperatures on the removal extent of gangue are investigated. The extent of Si, Al, and P removal by subjecting iron ores to a 5 M NaOH hydrothermal treatment at 300 °C reached 10–91%, 39–70%, and 38–76%, respectively. When the iron ores are roasted with NaOH at 350 °C, α-FeOOH in limonite transfers to NaFeO₂. On the other hand, for alkali roasted iron ores that inherently contain Fe₂O₃, Fe₂O₃ and Na₂CO₃ are also observed after the roasting treatment. Higher Al and P removal extents are observed for H₂O leaching at room temperature in the prepared roasted samples (Roasting/H₂O_RT) as compared to NaOH hydrothermal treatment, whereas that of Si is low for all samples, except the iron ore with the highest Fe content. After the H₂O leaching process, the Fe form is found to be in the amorphous form for all samples, except for the iron ore sample of the highest Fe content. The reason for this is thought to be due to the large amount of unreacted Fe₂O₃ with NaOH during the roasting process. The specific surface area significantly increases after the Roasting/H₂O_RT treatment in all samples due to the dehydration of goethite (α-FeOOH → Fe₂O₃ + H₂O) during the roasting treatment and gangue removal during H₂O leaching. When the roasted samples are supplied for hydrothermal treatment by H₂O at 300 °C (Roasting/H₂O_SC), the removal rate of Si and P increases as compared with the Roasting/H₂O_RT treatment. The influence of temperatures of calcination and the roasting treatment on the extent of gangue removal in 5 M NaOH hydrothermal, Roasting/H₂O_RT, and Roasting/H₂O_SC treatments is small. When NaOH hydrothermal treatment is carried out on the samples that have undergone the Roasting/H₂O_RT treatment, a gangue removal extent of above 70–97% was achieved, except for the iron ore with the lowest P content, which had the largest loss of ignition and the lowest Fe content. In addition, it is revealed that low-grade iron ore with a high pore properties, α-FeOOH content, and gangue content can be upgraded to a high-grade iron ore with a low pore property (low specific surface area and pore volume), high Fe₂O₃ content, and low gangue content using the above method. Therefore, this method is promising as a method for upgrading low-grade iron ore.

Introduction

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A recent concern is the limited reserves and the rapid depletion of high-grade iron ore, which is utilized in the ironmaking process, due to an increase in steel demand in emerging countries. In addition, high-grade ore becomes higher in gangue (Si, Al, and P) and lower in Fe contents, year by year. For this reason, in the future, the iron and steel-making industry must actively use low-grade iron ore, such as limonite, which has a large amount of goethite (α-FeOOH) or gangue components. However, limonite has a large amount of combined water, and its low strength is not suitable for utilization in a blast furnace; the increasing gangue in the iron ore is directly related to the increase in production of iron and steel-making slag. Therefore, the increasing gangue in iron ore also increases the reducing agent ratio (coke usage) and decreases the tapping ratio (pig iron amount) for the blast furnace method. In other words, this increases energy consumption, CO₂ emissions, and iron production costs and decreases iron productivity for the ironmaking process, which is attributed to the increasing gangue in iron ore. It is therefore essential to develop a technology for an upgrading method for low-grade iron ore, which can be achieved by lowering the gangue content and raising the Fe content, for the sustainable development of the iron and steel industry, and the method has been sought after.

It is well-known that Si, Al, and P in iron ore exist as quartz, alumina, kaolinite, aluminosilicate, chlorite, ferric silicate, fayalite, apatite species (fluoroapatite, hydroxyapatite, apatite etc.), (1−6) other P species, (7) etc. The gangue removal, especially concerning P, through chemical and physical methods has been investigated by many researchers. (1−24) It is revealed that chemical leaching is an effective method for P removal from iron ore or calcined/alkali roasted iron ores. (3,7−17) However, in the chemical leaching reports described above, there are only a few studies focusing on removal of Si and Al. (14,15) In addition, although chemical leaching methods using sulfuric acid, hydrochloric acid, and nitric acid against iron ore or calcined/alkali roasted iron ore are effective for the removal of high P content, (3,10,11,13,15,17) there are problems such as low Si and Al removal as well as the loss of Fe. In the above reports of P removal, (1−24) the investigations were carried out against only one type of iron ore with high P contents, and statistical data acquisition for the removal of gangue from iron ore with different chemical components, physical properties, and different countries of production has not been done. It is therefore important to develop a technology capable of collectively removing gangue components, in particular the high levels of Si and Al content and P affecting the brittleness of the final product from iron ores; the development of technologies concerning these products, which vary in type and are produced in different countries, is vital for sustainable development in iron and steel-making industries worldwide.

Our research group has been investigating the removal of gangue from several types of iron ore having different chemical compositions and physical properties, which is produced in the different countries, and found that hydrothermal treatment with NaOH is an effective solution for gangue removal. (25) The removal extent of Si, Al, and P ranged at 10–92%, 38–70%, and 37–78%, and it depends on the types of iron ore. In the present study, we examine the removal of gangue (Si, Al, and P) from iron ores with a combination of alkali roasting and hydrothermal treatment to attain a higher removal extent of gangue than hydrothermal treatment with NaOH only because it has been reported that a combination of NaOH alkali roasting and water leaching at RT to100 °C is effective in the removal of gangue. (14)The effects of the combination of each treatment (leaching at room temperature and hydrothermal treatments of a roasted sample), type of iron ore, physical properties, and calcination temperature on the removal extent of gangue were investigated to develop an upgrading method for producing high-grade iron from low-grade iron ore (limonite).

Results and Discussion

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Removal of Gangue Component during Hydrothermal Treatment with NaOH

Table 1 shows the chemical composition, pore properties, and iron forms of the iron ore used in this study. Table 2 summarizes the yield, gangue removal extent, pore properties, and Fe forms in the iron ores treated with a hydrothermal method using 5 M NaOH at 300 °C. (25) The yields ranged from 80 to 87%, and a decrease was observed due to the dehydration of limonite and gangue removal. The removal extent of Si, Al, and P ranged between 10–92%, 39–70%, and 38–78%, respectively, and showed a large trend for BRH, which has the highest Fe content, Fe₂O₃ form, and the lowest loss of ignition (LOI) in the iron ores used in the present study. When the relationship among the gangue components was investigated, positive and negative correlations were found in Al versus P, Al versus Si, and P versus Si. (25) The iron forms (α-FeOOH) in the original iron ore changed to Fe₂O₃ after the samples had been treated. Both the specific surface area and pore volume values of the original iron ore (2–80 m²/g and <0.01 to 0.20 cm³/g) decreased to <1 to 15 cm²/g and <0.01 to 0.10 cm³/g, respectively, for all samples obtained after treatment. This decrease means that the sintering of Fe species after dehydration of α-FeOOH in the iron ores occurs through NaOH hydrothermal treatment, irrespective of the iron ore type, because significantly decrease in specific surface area, pore volume, and changing of Fe forms were not observed in the hydrothermal treatment using distilled water. (25) Here, decrease in specific surface area and pore volume for treated samples measured by the N₂ adsorption method shows occurrence of Fe species sintering. Now, although the reason why NaOH causes Fe sintering is not clear, it may be due to the morphological change of Fe species caused by the reaction between Fe species and NaOH. From the equilibrium calculation results, it was estimated that the gangue removal occurs due to a reaction of Si, Al, or P and NaOH solution during the hydrothermal treatment accompanied with a rearrangement of the Fe structure. (25) In conclusion, although the NaOH hydrothermal treatment is effective in gangue removal from high-grade iron ore, some are not effective for the low-grade ore.

Table 1. Chemical Composition, Pore Properties, and Iron Forms of the Iron Ore Used in This Study

		composition (%)
sample	country	total Fe	Si	Al	P	loss of ignitiona (%)	specific surface areab (m²/g)a	pore volume (cm³/g)c	Fe formd
INL	Indonesia	48	2.4	3.0	0.006	14	80	0.20	α-FeOOH (m)
ALY	Australia	55	2.0	1.0	0.048	12	25	0.12	α-FeOOH (m)
ALR	Australia	57	3.0	1.5	0.044	11	20	0.04	α-FeOOH (m)
MLL	Malaysia	59	1.1	1.8	0.053	11	15	0.03	α-FeOOH (m)
ILS	Indonesia	60	1.0	2.3	0.060	10	20	0.04	α-FeOOH (m)
WAL	Australia	63	2.4	2.1	0.083	8	10	0.03	α-FeOOH (m), Fe₂O₃ (w)
BRH	Brazil	67	2.3	0.5	0.029	1	2	<0.10	Fe₂O₃ (m)

^{^a}

Heated at 1000 °C in air.

^{^b}

Calculated by the BET method.

^{^c}

Calculated by the BJH method.

^{^d}

Designated by XRD: w (weak) and m (medium).

Table 2. Summaries of the Yields, Extent of Gangue Removal, Pore Properties, and Fe Forms in Iron Ores Subjected to 5 M NaOH Hydrothermal Treatment at 300 °C

		removal extent (%)
sample	yield (%)	Si	Al	P	specific surface area (m²/g)a	pore volume (cm³/g)b	Fe formc
INL	80	10	39	38	10	0.10	Fe₂O₃ (m)
ALY	84	58	43	70	10	0.04	Fe₂O₃ (m)
ALR	84	57	42	60	15	0.03	Fe₂O₃ (m)
MLL	83	43	56	68	5	0.03	Fe₂O₃ (m)
ILS	83	30	67	78	5	0.02	Fe₂O₃ (m)
WAL	86	42	46	42	2	<0.01	Fe₂O₃ (m)
BRH	87	92	70	69	<1	<0.01	Fe₂O₃ (m)

^{^a}

Calculated by the BET method.

^{^b}

Calculated by the BJH method.

^{^c}

Designated by XRD: m (medium).

Effect of Alkali Roasting on Gangue Removal with Distilled Water Leaching at Room Temperature

Figure 1 shows extent of gangue removal from NaOH-roasted iron ores prepared at 350 °C, which is the temperature that the dehydration reaction occurs for limonite, and treated with H₂O at room temperature (Roasting/H₂O_RT treatment). The characterization results of Roasting/H₂O_RT samples are listed in Table 3 and Figure 2. The results of the iron ore prepared by calcination up to 350 °C in air are also listed in Table 3 for comparison. The extent of removal of Si, Al, and P were 4–72%, 43–75%, and 32–78%, respectively, and the order of the samples were ILS = MLL < INL < ALY < WAL < ALR ≪ BRH for Si, ALR = INL < WAL < ALY < MLL < ILS < BRH for Al, and INL ≪ ALR < BRH = ALY = WAL < MLL = ILS for P. Here, the largest extent of gangue removal was found for BRH, which is classified as a high-grade iron ore in the samples used in the present study. The order of the extent of gangue removal components increased as Si ≪ Al < P. It is therefore revealed that the Roasting/H₂O_RT treatment is effective for gangue removal, especially for Al and P removal. Comparable results have been reported by another research group. (14) Although Roasting/H₂O_RT treatments are effective for gangue removal, the extent of Si and Al removal was lower than that of the 5 M NaOH hydrothermal treatment (Table 2). This difference may show that the gangue removal mechanism is different between both treatments. In addition, this difference occurs due to occurrence of gangue removal by the Roasting/H₂O_RT treatment. On the other hand, for a comparison between the specific surface area of a calcined sample in air at 350 °C and Roasting/H₂O_RT samples (Table 3), the latter samples provided higher values than the former samples, and it tended to increase with the order of increasing LOI values. However, pore volumes were similar for both samples. Although the reason is not clear, the agglomeration of pores may occur during the treatment. It was suggested that the decreasing yield and increasing specific surface area occur due to gangue removal. Figure 2 presents the XRD patterns of the samples before and after H₂O treatment at room temperature for comparison. The distributed peaks of Fe₂O₃ were observed for all calcined samples at 350 °C in air (Table 2). For roasted samples, the peaks that are attributable to NaFeO₂ were detected for all samples (Figure 2, left), and existing Na₂CO₃ was also observed only for BRH and WAL, whose Fe₂O₃ was observed in the original samples before treatment (Table 1). (25) In addition, the SiO₂ peaks and unknown peaks disappeared for roasted samples. The NaFeO₂ and Na₂CO₃ peaks observed for roasted samples almost disappeared after H₂O leaching treatment (Figure 2, right), and these XRD patterns consisted of a broad profile, except for BRH, which provided the Fe₂O₃ peaks. The reason for this was thought to be due to the large amount of unreacted Fe₂O₃ with NaOH during the roasting process. The melting point of NaOH is approximately 320 °C, and NaOH became molten until 350 °C during the NaOH roasting sample preparation. In addition, the dehydration of α-FeOOH in limonite and the development of the pore structure occur until 350 °C. (25,26) Therefore, it was suggested that the limonite dehydration reaction had occurred, at the same time, as the molten NaOH penetrated the pores produced by dehydration and reacted with the iron ore constituents. (25) The formation of Na₂CO₃ may derive from an exposure of NaOH in the laboratory atmosphere, which is nonreacted NaOH with an iron ore composition. According to the equilibrium calculation results, eq 1 is favorable by a thermodynamic equilibrium calculation at RT to 350 °C.

(1)

(2)

Figure 1. Extent of gangue removal in iron ores treated with the Roasting/H₂O_RT treatment.

Figure 2. XRD patterns of NaOH roasted iron ore at 350 °C (left) and iron ores after the Roasting/H₂O_RT treatment (right). (a) BRH, (b) WAL, (c) ILS, (d) MLL, (e) ALR, (f) ALY, and (g) INL.

Table 3. Summaries of the Yields, Pore Properties, and Fe Forms in Iron Ores Treated with the Roasting/H₂O_RT Treatment

	calcination at 350 °C in air				roasting at 350 °C	roasting/H₂O_RT treatment
sample	yield (%)	specific surface area (m²/g)a	Pore volume, (cm³/g)b	Fe formc	Fe formc	yield (%)	specific zurface area (m²/g)a	pore volume (cm³/g)b	Fe formc
INL	90	130	0.19	Fe₂O₃ (m)	NaFeO₂ (m)	82	175	0.15	n.d.d
ALY	90	100	0.12	Fe₂O₃ (m)	NaFeO₂ (m)	84	155	0.11	n.d.d
ALR	92	80	0.05	Fe₂O₃ (m)	NaFeO₂ (m)	84	100	0.04	n.d.d
MLL	91	85	0.04	Fe₂O₃ (m)	NaFeO₂ (m)	85	100	0.04	n.d.d
ILS	91	85	0.05	Fe₂O₃ (m)	NaFeO₂ (m)	85	105	0.05	n.d.d
WAL	95	50	0.04	Fe₂O₃ (m)	NaFeO₂ (w), Fe₂O₃(w)	85	60	0.03	n.d.d
BRH	99	3	<0.01	Fe₂O₃ (m)	NaFeO₂ (vw), Fe₂O₃(m)	89	15	0.01	Fe₂O₃ (s)

^{^a}

Calculated by the BET method.

^{^b}

Calculated by the BJH method.

^{^c}

Designated by XRD: vw (very weak), w (weak), m (medium), and s (strong).

^{^d}

Not detected.

Gibbs standard free energies (ΔG) of eqs 1 and 2 are the same. Therefore, the existing pore may be affecting the formation of NaFeO₂ during the preparation of the roasting samples because for BRH, which has an Fe₂O₃ form and low pore properties, Fe₂O₃ and Na₂CO₃ were observed in roasted samples. For eqs 1 and 2, the produced NaFeO₂ is hydrolyzed by H₂O addition to the Fe₂O₃ and NaOH solution. However, the clear diffraction peaks of Fe₂O₃ were not found in Roasting/H₂O_RT samples, except for BRH. This result shows that the rearrangement of Fe species occurs due to the reaction between NaOH and Fe species during the roasting process because NaFeO₂ and amorphous Fe are observed in Figure 2. According to previous reports, Si, Al, and P exist in iron ores as quartz (SiO₂), alumina (Al₂O₃), aluminosilicate (e.g., Al₂O₃·SiO₂), fayalite (Fe₂SiO₄), kaolinite (Al₂Si₂O₇·2H₂O), apatite species (e.g., Ca₅(PO₄)₃OH or Ca₂(PO₄)₂CaF₂)), iron phosphate (Fe₃PO₇), etc. (1−9,27,28) Based on these reports, the equilibrium calculation was performed to investigate the gangue removal mechanism through the Roasting/H₂O_RT treatment. For the calculation, assuming the Si, Al, or P species mentioned above reacts with NaOH according to the eqs 3–19. The Gibbs standard free energies of ΔG at 0–350 °C for eqs 3–19 are listed in Table 4.

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

Here, FePO₄ was used instead of Fe₃PO₇ because the latter specie does not exist in the HSC Chemistry5.1 (Outokumpu Research Oy) database, and eqs 12–15 were a referenced equation from ref. (11) The reactions of eqs 3–12 and 19 (denoted as rearrangement reactions) are supported by thermoequilibrium calculations, and the produced Na-Si, Na-Al, and Na-P compounds have the property of being water-soluble at room temperature. Therefore, a high removal extent of Al and P for the Roasting/H₂O_RT treatment may be observed by the rearrangement of gangue components. On the other hand, the extent of Si removal was low for all samples, except for BRH. This reason may be due to a large portion of Si exists in an iron ore other than SiO₂ or kaolinite. Furthermore, low extent of Si removal may be caused by a production of water-insoluble Si species, such as CaSiO₃. Although, eq 20 is favorable by thermoequilibrium, the water solubility of the produced CaSiO₃ is exceptionally low being 0.01 g/100 mL H₂O at 20 °C. Equation 21 is also supported by thermoequilibrium for calculation at 150–350 °C, but at a lower temperature (20–150 °C), the reaction of eq 20 occurs easier than eq 21.

(20)

(21)

Table 4. Equilibrium Calculation Results Using the Estimated Gangue Components

eq no.	reaction	ΔG_0–350°C (kcal/mol)
3	SiO₂ + 2NaOH = Na₂SiO₃ + H₂O(g)	–18 to −27
4	Al₂O₃ + 2NaOH = 2NaAlO₂ + H₂O(g)	–5 to −14
5	2SiO₂ + Al₂O₃ + 2NaOH = 2NaAlSiO₄ + H₂O(g)	–31 to −43
6	6SiO₂ + Al₂O₃ + 2NaOH = 2NaAlSi₃O₈ + H₂O(g)	–39 to −53
7	Al₂O₃·SiO₂ (A) + 4NaOH = Na₂SiO₃ + 2NaAlO₂ + 2H₂O(g)	–23 to −41
8	Al₂Si₂O₇·2H₂O + 6NaOH = 2Na₂SiO₃ + 2NaAlO₂ + 5H₂O(g)	–33 to −80
9	Al₂Si₂O₇·2H₂O + 2NaOH = 2NaAlSiO₄ + 3H₂O(g)	–22 to −56
10	FePO₄ + 4NaOH = NaFeO₂ + Na₃PO₄ + 2H₂O(g)	–42 to −64
11	Fe₂SiO₄(F) + 2NaOH = Na₂SiO₃ + H₂(g) + Fe₂O₃	–17 to −18
12	Ca₅(PO₄)₃OH + 9NaOH + 5SiO₂ = 3Na₃PO₄ + 5CaSiO₃ + 5H₂O(g)	–51 to −97
13	Ca₅(PO₄)₃OH + 3NaOH = 3NaPO₃ + 5CaO + 2H₂O(g)	145 to 126
14	Ca₅(PO₄)₃OH + 9NaOH = 3Na₃PO₄ + 5CaO + 5H₂O(g)	55 to 11
15	Ca₅(PO₄)₃OH + 3NaOH + 5SiO₂ = 3NaPO₃ + 5CaSiO₃ + 2H₂O(g)	37 to 18
16	3Ca₃(PO₄)₂CaF₂ + 8NaOH = 6NaPO₃ + 2NaF + 10CaO + 4H₂O(g)	302 to 266
17	3Ca₃(PO₄)₂CaF₂ + 20NaOH = 6Na₃PO₄ + 2NaF + 10CaO + 10H₂O(g)	128 to 36
18	3Ca₃(PO₄)₂CaF₂ + 8NaOH + 10SiO₂ = 6NaPO₃ + 2NaF + 10CaSiO₃ + 4H₂O(g)	88 to 50
19	3Ca₃(PO₄)₂CaF₂ + 20NaOH + 10SiO₂ = 6Na₃PO₄ + 2NaF + 10CaSiO₃ + 10H₂O(g)	–90 to −180

The rearrangement reaction for the formation of the insoluble Si form and inherently Si form in iron ore may influence the low removal extent of Si using the Roasting/H₂O_RT treatment. According to a previous report, it is well accepted that P in limonite exists as an adsorption form into limonite, this replaced the form with a part of Fe oxide, and apatite species. (7−9,27) In addition, it is believed that the apatite-type P has been demonstrated to be easily removed by chemical leaching, (12,14,17,29) whereas simple chemical leaching is ineffective for the goethite matrix-associated P. (10) Some hypothesis has been proposed for P associated with the goethite matrix; P exists in solid solution with goethite, (30) and P in goethite exists in the form of grattarolaite (Fe₃PO₇) via the replacement of a surface hydroxyl group by a P ligand. (10,28) Moreover, it is considered that P in goethite has been found to be much less soluble than P in hematite, and a heat treatment (such as roasting or alkali roasting) prior to leaching is necessary to obtain a high extent of P removal. (23) In the present study, the Roasting/H₂O_RT treatment provides higher P removal than the NaOH hydrothermal treatment for many of the iron ores used. For P removal in iron ore using a combination of roasting, alkali roasting/chemical leaching, or magnetic separation, it has been reported that an occurrence of structural rearrangement (changing of hematite to goethite for a calcination/reaction in the gangue component to form an acid-soluble form for the calcination/reaction with the alkali and gangue mineral during roasting, which then forms an acid soluble form for alkali roasting) produces acid-soluble Si, Al, or Si-Al species containing P and damaging the ore structure, and these treatments promote the removal of P (10,24,31) by using acid leaching. As shown in Table 4, the Fe, Si, Al, and P rearrangement reactions occur easily in NaOH roasting conditions. The high gangue extents of removal from roasted samples were achieved through H₂O treatment because water-soluble Al and P are produced by NaOH roasting. Figure 3 illustrates the relationship between Si, Al, and P removal. Although there is some scattering, the negative and positive correlations were observed for Si versus Al and Al versus P in all samples, except for INL. This correlation suggests that P exists as an associated-Al form, beside the apatite species, etc., and this Al-associated P might be existing as Fe oxide replaced or associated with limonite in iron ore. From these results, it was found that the Roasting/H₂O_RT treatment is an effective method for upgrading several kinds of low-grade iron ore, from the viewpoint of gangue removal, especially Al and P removal, irrespective of the producing countries. However, as seen in Table 3, the specific surface area increases significantly from the original values (2–80 m²/g) or calcined sample values (3–130 m²/g) to 15–175 m²/g. Figure 4 shows the comparison between the specific surface area of the original sample calcined at 350 °C in air and Roasting/H₂O_RT samples. The specific surface area in Roasting/H₂O_RT samples is larger than those of calcined samples. It is considered that the increasing specific surface area occurs due to the removal of gangue for Roasting/H₂O_RT and the rearrangement of the Fe species. Thus, it is necessary for the method of high Fe crystallization and low pore properties of iron ores to completely develop an upgrading method.

Figure 3. Relationship between the amounts of gangue removal of Si, Al, and P with the Roasting/H₂O_RT treatment.

Figure 4. Extent of increasing specific surface area of the iron ores after the Roasting/H₂O_RT treatment.

Removal of Gangue by Combination of Alkali Roasting and H₂O Hydrothermal Treatments

In this section, a hydrothermal treatment with H₂O against NaOH roasting samples was carried out because relatively significant extent of gangue removal was observed by using the NaOH hydrothermal treatment and Roasting/H₂O_RT treatment as shown in Table 2 and Figure 1. H₂O was used for the hydrothermal treatment of the roasted sample, and the mixture was heated at 300 °C for 30 min (denoted as Roasting/H₂O_SC). Here, as is mentioned above, it was thought that NaFeO₂ or nonreacted Na species (Na₂CO₃ and NaOH) in roasted samples are hydrolyzed to Fe₂O₃ and NaOH solutions by the addition of H₂O to the roasting samples. In other words, the hydrothermal treatment of roasted samples was carried out in a Na-containing solution containing a water-soluble gangue component at room temperature. The results are shown in Figure 5. The extent of Si, Al, and P removal ranged between 16–95%, 39–80%, and 30–90%, respectively, and the extent of P removal from all samples reached above 60%, except for INL. The order in which the extent increased is INL < ILS < MLL = WAL < ALR = ALY ≪ BRH for Si, INL = ALR < WAL < ALY < MLL < ILS < BRH for Al, and INL ≪ WAL < BRH < ALR < MLL < ILS = ALY for P, and BRH showed a large tendency of removal extent in all samples. The orders to which the extent of removal among the gangue components examined increased as Si < Al < P, and it was found that this treatment method is more effective for Al and P removal than the Roasting/H₂O_RT treatment. Figure 6 illustrates the relationship between Si, Al, and P removal amounts. Although there is some scattering, the negative and positive correlations were observed for Si versus Al, Si versus P, and Al versus P in all samples, except for INL. The correlation constant between Si versus Al increased due to increasing extent of Si removal, compared with Figure 3. This result may show that Si exists as nonassociated form with Al and P and supports the hypothesis about the P form, such as P exists with an Al-associated form, as is mentioned above. Table 5 summarizes the yields, pore properties, and Fe forms in Roasting/H₂O_SC samples. The yield decreased to 80–89%, and the order closely corresponded with that of LOI. The specific surface area decreased from 15–175 m²/g of Roasting/H₂O_RT samples to <1 to 15 m²/g for Roasting/H₂O_SC samples treated at 300 °C. Similar decreases were observed for the pore volume and NaOH hydrothermal treatment (Table 2). Although the amorphous Fe was observed from almost all Roasting/H₂O_RT samples, the Fe form was Fe₂O₃ for all Roasting/H₂O_SC samples. These results show that sintering Fe species and crystallization were also occurring during hydrothermal treatment with a Na-containing solution. Figure 7 shows the difference between the extent of gangue removal from Roasting/H₂O_SC and Roasting/H₂O_RT samples to investigate the effect of hydrothermal treatment on gangue removal. As seen in Figure 7, the extent of Si removal tended to increase for Roasting/H₂O_SC samples, and a slight increase in the extent of P removal was found for all samples, except for WAL and INL. The slight decrease of the Al extent occurs due to analytical errors. In conclusion, this combination of treatment can improve Si and P removal in the Roasting/H₂O_RT treatment. It is considered that the removal of Si and P by a Na-containing solution occurs due to a reaction between Si or P species and Na species to form a water-soluble species during hydrothermal treatment. (25)

Figure 5. Extent of gangue removal in iron ores treated with the Roasting/H₂O_SC treatment.

Figure 6. Relationship between the amounts of gangue removal of Si, Al, and P with the Roasting/H₂O_SC treatment.

Figure 7. Difference of the extent of gangue removal from the Roasting/H₂O_SC to the Roasting/H₂O_RT treatment.

Table 5. Summaries of the Yields, Pore Properties, and Fe Forms in Iron Ores Treated with the Roasting/H₂O_SC at 300 °C Treatment

sample	yield (%)	specific surface area (m²/g)a	pore volume (cm³/g)b	Fe formc
NL	80	15	0.07	Fe₂O₃ (m)
ALY	81	10	0.08	Fe₂O₃ (m)
ALR	84	12	0.06	Fe₂O₃ (m)
MLL	82	14	0.05	Fe₂O₃ (m)
ILS	84	10	0.04	Fe₂O₃ (m)
WAL	85	5	0.02	Fe₂O₃ (m)
BRH	89	<1	<0.01	Fe₂O₃ (m)

^{^a}

Calculated by the BET method.

^{^b}

Calculated by the BJH method.

^{^c}

Designated by XRD: m (medium).

In the present work, the hydrothermal treatment temperature of 300 °C was mainly used because the NaOH solution damages (causes corrosion) the SUS reactor in repeating experimental trials. However, it is important to clarify the effect of temperature on the behavior of gangue removal in the Roasting/H₂O_SC treatment. Therefore, the ALY roasted sample was made for hydrothermal treatment at each temperature to clarify the effect of hydrothermal temperature on gangue removal. Figure 8 presents the temperature dependency on the extent of gangue removal from an ALY roasted sample against temperature. The extent of Al and P removal at room temperature (Roasting/H₂O_RT treatment) was as high as 60 and 70%, respectively, whereas that of Si was as low as 15%. When the temperature was raised to 100 °C, the extent of P removal reached 85%, whereas those of Al and Si were constant with those of room temperature. Although the extent of P and Al removal did not change up to 300 °C, that of Si increased along with increasing temperature and reached 70% at 350 °C. In addition, the removal of Al increased at 300–350 °C and attained 75% at 350 °C. These results mean that Roasting/H₂O_SC treatment above 300 °C is more effective for further gangue removal than for temperatures below 300 °C if it is possible to use a corrosion-resistant reactor. Although the relationship between the amounts of Si, Al, and P removal was investigated, clear correlations were not found as seen in Figures 3 and 6. Table 6 summarizes the yields, pore properties, and Fe forms corresponding with the result of Figure 8. In addition, the changes in XRD patterns of the Roasting/H₂O_SC samples against hydrothermal temperature are shown in Figure 9 and summarized in Table 6. The yield of Roasting/H₂O_SC of ALY ranged from 80 to 84% and decreased with increasing temperature. This decreasing occurs due to the removal of gangue. Although the specific surface area (155 m²/g) of the Roasting/H₂O_RT ALY sample was constant until 200 °C, a drastic decrease was observed at 250–350 °C, and these values were lowered to 15 m²/g. On the other hand, the amorphous Fe form observed in Roasting/H₂O_RT was changed to Fe₂O₃ above 250 °C due to the crystallization effect of the NaOH and hydrothermal treatment, and the peak intensity increased with increasing temperature. Therefore, it is concluded that this combination of treatments above 300 °C is effective for gangue removal, crystallization of Fe, and decreasing pore of porous and amorphous Fe in iron ores obtained using the Roasting/H₂O_RT treatment.

Figure 8. Temperature dependency on the extent of gangue removal from ALY during the Roasting/H₂O_SC treatment.

Figure 9. Changes in the XRD pattern of the Roasting/H₂O_RT-treated ALY samples during the Roasting/H₂O_SC treatment. (a) Room temperature, (b) 100 °C, (c) 150 °C, (d) 200 °C, (e) 250 °C, (f) 300 °C, and (g) 350 °C.

Table 6. Summaries of the Yields, Pore Properties, and Fe Forms in ALY Treated with the Roasting/H₂O_SC Treatment at Different Temperatures

temperature (°C)	yield (%)	specific surface area (m²/g)a	pore volume (cm³/g)b	Fe formc
RT	84	155	0.11	n.d.d
100	84	150	0.10	n.d.d
150	84	150	0.10	n.d.d
200	83	130	0.13	Fe₂O₃ (w)
250	82	110	0.14	Fe₂O₃ (m)
300	81	15	0.16	Fe₂O₃ (s)
350	80	15	0.16	Fe₂O₃ (s)

^{^a}

Calculated by the BET method.

^{^b}

Calculated by the BJH method.

^{^c}

Designated by XRD measurement: w (weak), m (medium), and s (strong).

^{^d}

Not detected.

Effect of Calcination and Roasting Temperatures on Gangue Removal

To clarify the effect of calcination/roasting temperatures on gangue removal, each treatment (NaOH hydrothermal, Roasting/H₂O_RT, and Roasting/H₂O_SC treatment) was carried out against ALY samples (calcined and NaOH roasted at 350, 600, and 900 °C, respectively). The result is shown in Figure 10. Table 7 and Figure 11 list the yields, pore properties, and Fe forms of samples before and after each treatment. When the prepared ALY calcined at 350, 600, and 900 °C in air were supplied for 5 M NaOH hydrothermal treatment (Figure 10a), the extent of Si removal tended to increase with increasing calcination temperature, whereas that of Al and P were constant. The change of the Fe form in samples before and after the NaOH hydrothermal treatment was not observed as shown in Figure 11a,b. The specific surface area of all samples after the NaOH hydrothermal treatment decreased from 25–100 to 10–20 m²/g. For the Roasting/H₂O_RT treatment, all the extent of gangue removal tended to increase with increasing NaOH roasting temperature, as seen in Figure 10b. The peaks of attributable NaFeO₂ completely disappeared in all samples after the Roasting/H₂O_RT treatment (Figure 11c,d). In addition, the specific surface area increased to 80–155 m²/g, compared to calcined samples (25–100 m²/g), respectively. A slight increase in the extent of Si and Al removal was observed for the Roasting/H₂O_SC treatment with NaOH roasting temperature, as shown in Figure 10c. The amorphous Fe form obtained in the Roasting/H₂O_RT sample was changed to Fe₂O₃ by the Roasting/H₂O_SC treatment (Figure 11e), and the specific surface area (80–155 m²/g) of the Roasting/H₂O_RT-treated samples decreased to 10–15 m²/g. According to previous work, it is believed that a calcination/alkali roasting treatment is effective for the transformation of leaching solvent-insoluble gangue in an iron ore form to a soluble form by a reaction in the gangue component or alkali compound during heat treatment, resulting in an increased extent of removal during the leaching process. (16,24) In this study, the increasing Si, Al, and P extent of removal with calcination and roasting temperature were observed. It is, therefore, through the transformation (rearrangement of the structure) of gangue with calcination and the roasting treatment, which also occurs similar to the report mentioned above in the present study, and the resulting extent of gangue removal increased during each of these methods. On the other hand, it may be determined that the effect of pore properties on gangue removal is smaller than that of the calcination/roasting temperature for rearrangement because the specific surface area of the sample prepared at 900 °C, which showed the highest extent of removal for almost all treatments, is low as well as the original ALY. Although it is concluded that nonalkali and alkali roasting treatments are effective for the removal of gangue from iron ore, a dramatic improvement with calcination/roasting at 600 and 900 °C was not found in this case. The low-temperature treatment is more favorable than the high-temperature treatment for the actual process; therefore, we used 350 °C as the main treatment temperature in this study.

Figure 10. Effect of (a) calcination and (b, c) roasting temperatures on the extent of gangue removal from ALY with NaOH hydrothermal (a), Roasting/H₂O_RT (b), and Roasting/H₂O_SC (c) treatments at 300 °C.

Figure 11. XRD patterns of ALY samples obtained after the NaOH hydrothermal, Roasting/H₂O_RT, and Roasting/H₂O_SC treatments at 300 °C corresponding to the results of Figure 10. ALY at 350 °C (left), 600 °C (center), and 900 °C (right). (a) Calcination in air, (b) 5 M NaOH hydrothermal-treated sample, (c) Roasted sample, (d) Roasting/H₂O_RT sample, and (e) Roasting/H₂O_SC sample.

Table 7. Summaries of the Yields, Pore Properties, and Fe Forms in Calcined or Roasted ALY Treated with the 5 M NaOH Hydrothermal, Roasting/H₂O_RT, or Roasting/H₂O_SC Treatments at Different Temperatures

pretreatment	treatment of gangue removal	temperature (°C)	yield (%)	specific surface area (m²/g)a	pore volume (cm³/g)b	Fe formc
calcination	none	350	90	100	0.12	Fe₂O₃ (m)
		600	89	55	0.14	Fe₂O₃ (s)
		900	88	25	0.10	Fe₂O₃ (s)
	NaOH hydrothermal	350	81	10	0.04	Fe₂O₃ (m)
		600	84	20	0.10	Fe₂O₃ (s)
		900	83	15	0.07	Fe₂O₃ (s)
NaOH roasting	none	350		n.ad	n.ad	NaFeO₂ (w)
		600		n.ad	n.ad	NaFeO₂ (s)
		900		n.ad	n.ad	NaFeO₂ (s)
	leaching by H₂O (Roasting/H₂O_RT)	350	82	155	0.11	n.d.e
		600	81	125	0.07	n.d.e
		900	81	80	0.05	n.d.e
	H₂O hydrothermal (Roasting/H₂O_SC)	350	81	10	0.08	Fe₂O₃ (m)
		600	79	15	0.06	Fe₂O₃ (s)
		900	79	10	0.05	Fe₂O₃ (s)

^{^a}

Calculated by BET method.

^{^b}

Calculated by BJH method.

^{^c}

Designated by XRD : w (weak), m (medium), s (strong),

^{^d}

Not analysis.

^{^e}

Not detected.

Removal of Gangue by Combination of Alkali Roasting and NaOH Hydrothermal Treatments

As shown in Figure 5, the extent of Si removal was as low as below 50% by using the Roasting/H₂O_SC at 300 °C treatment, and that of Al also was below 70%. Therefore, in this section, the effect of the combination of alkali roasting and 5 M NaOH hydrothermal treatments (Roasting_H₂O_RT/NaOH_SC) on gangue removal was investigated to attain a high gangue removal. Figure 12 shows the gangue removal extent of iron ores used by Roasting_H₂O_RT/NaOH_SC at 300 °C treatment. This combination provided 65–97% of Si and Al removal extents, and the extent of P removal also reached above 80% for all samples, except for INL, which has the lowest P content and the largest LOI. The highest removal extent was observed for BRH, which has a high Fe content, Fe₂O₃ form, low LOI, and low pore properties of iron ores used in this study. Figure 13 illustrates the relationship between the amounts of Si, Al, and P removal by the Roasting_H₂O_RT/NaOH_SC at 300 °C treatment. For only Al versus P, a positive correlation was observed. Figure 14 shows the correlation between the amounts of Si, Al, and P removal obtained in Figures 1, 5, and 11 and Table 2. Although there is some scattering, a good positive correlation was observed for Al versus P, whereas the relationship was not found for Si versus Al and Si versus P. It was therefore strongly estimated that P exists as associated with Al in the iron ore. Table 8 summarizes the yields, pore properties, and Fe forms. The yield decreased to 79–88% and occurred due to the gangue removal. The Fe forms of amorphous Fe observed in the Roasting/H₂O_RT samples transferred to Fe₂O₃ in all samples. The specific surface area (15–175 m²/g) of Roasting/H₂O_RT also drastically decreased to 8–30 m²/g. Although the specific surface area was greater than those of other treatments due to high extent of gangue removal, the specific surface area was lower than the original iron ores. Therefore, it is concluded that the low-grade ores used were upgraded using the Roasting_H₂O_RT/NaOH_SC treatment. Figure 15 presents the effect of the 5 M NaOH hydrothermal treatment on gangue removal calculated by the difference between the extent of gangue removal for the Roasting_H₂O_RT/NaOH_SC treatment and the Roasting/H₂O_RT or Roasting/H₂O_SC treatment. From the difference between the Roasting_H₂O_RT/NaOH_SC treatment and the Roasting/H₂O_RT treatment (Figure 15a), the removal extent of Si, Al, and P increased by 25–75%, 15–45%, and 10–30%, respectively. This increase may occur by the increasing contact area between the Na-containing solution and iron ore compositions during hydrothermal treatment because the specific surface area increased due to the dehydration reaction of α-FeOOH and gangue removal for the Roasting/H₂O_RT treatment. On the other hand, from the difference of the extent of gangue removal from the Roasting_H₂O_RT/NaOH_SC treatment to that of the Roasting/H₂O_SC treatment (Figure 15b), the extent of Si, Al, and P removal increased by 5–50%, 10–50%, and 2–20%, respectively, for the Roasting_H₂O_RT/NaOH_SC treatment. For the latter difference (Figure 15b), the increase in the extent of P removal was lower than that of former (Figure 15a). These results show that the Roasting_H₂O_RT/NaOH_SC treatment is more effective for Si and Al removal than that of the Roasting/H₂O_RT and Roasting/H₂O_SC treatments. Now, although the reason why the extent of gangue removal increased by using the Roasting_H₂O_RT/NaOH_SC treatment compared with the Roasting/H₂O_SC treatment at 300 °C, the secondary reaction among gangue components removed by the H₂O treatment at room temperature of NaOH roasting samples, which remained in the solvent during the Roasting_H₂O_RT/H₂O_SC treatment at 300 °C, may occur during hydrothermal treatment of the Roasting/H₂O_SC treatment. On other words, it may be important to positively remove the gangue eluted by the water treatment of the roasted ore and then perform a hydrothermal treatment by adding a fresh NaOH solution again, such as the use of a flow-type reactor. The clarity of the detail will be the subject of future work.

Figure 12. Extent of gangue removal of iron ores treated with the Roasting_H₂O_RT/NaOH_SC treatment at 300 °C.

Figure 13. Relationship between the amounts of gangue removal of Si, Al, and P with the Roasting_H₂O_RT/NaOH_SC treatment at 300 °C.

Figure 14. Relationship between the amounts of gangue removal of Si, Al (a), and P (b) with each treatment carried out in Figures 1, 5, and 12 and Table 2.

Figure 15. Difference between the extent of gangue removal from the Roasting_H₂O_RT/NaOH_SC to (a) Roasting/H₂O_RT or (b) Roasting/H₂O_SC treatment at 300 °C.

Table 8. Summaries of the Yields, Pore Properties, and Fe Forms in ALY Treated with the Roasting_H₂O_RT/NaOH_SC Treatment at 300 °C

sample	yield (%)	specific surface area (m²/g)a	pore volume (cm³/g)b	Fe formc
INL	79	30	0.11	Fe₂O₃ (m)
ALY	80	20	0.12	Fe₂O₃ (m)
ALR	83	20	0.07	Fe₂O₃ (m)
MLL	82	15	0.03	Fe₂O₃ (m)
ILS	83	15	0.07	Fe₂O₃ (m)
WAL	82	15	0.06	Fe₂O₃ (m)
BRH	88	8	0.01	Fe₂O₃ (m)

^{^a}

Calculated by the BET method.

^{^b}

Calculated by the BJH method.

^{^c}

Designated by XRD measurement: m (medium).

Conclusions

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In the present study, we have examined the removal of gangue (Si, Al, and P) from iron ores by a combination of alkali roasting and hydrothermal treatments to attain a higher extent of gangue removal than hydrothermal treatment with NaOH only. The effects of the combination of each treatment (leaching at room temperature and hydrothermal treatments of the roasted sample), iron type, physical properties, calcination temperature on the extent of gangue removal were investigated to develop an upgrading method for producing high-grade iron from low-grade iron ore (limonite). Some findings are listed below.

(1)	When the iron ores used in the present study were roasted with NaOH at 350 °C, α-FeOOH in limonite transferred to NaFeO₂. On the other hand, for roasted iron ores, which inherently contained Fe₂O₃ in iron ore, Fe₂O₃ and Na₂CO₃ were observed after the roasting treatment.
(2)	The higher extent of Al and P removal than NaOH hydrothermal treatment was observed in H₂O leaching at room temperature of the prepared roasted samples (Roasting/H₂O_RT), whereas that of Si was low for all samples, except for BRH. After H₂O leaching, the Fe form was amorphous for all samples, except for BRH.
(3)	The specific surface area significantly increased after the Roasting/H₂O_RT treatment for all samples due to the dehydration of α-FeOOH during the roasting treatment and gangue removal during H₂O leaching.
(4)	When roasted samples were supplied for the hydrothermal treatment of H₂O at 300 °C (Roasting/H₂O_SC), the extent of Si and P removal increased compared to the Roasting/H₂O_RT treatment.
(5)	The calcination and roasting temperatures influenced the extent of gangue removal more during the NaOH hydrothermal, Roasting/H₂O_RT, and Roasting/H₂O_SC treatments, and the effect on the pore properties of the iron ore is lower than those of the pretreatments above.
(6)	When the NaOH hydrothermal treatment was carried out against the samples after the Roasting/H₂O_RT treatment, an extent gangue removal of above 70% was reached, except for P in INL.

Experimental Section

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Sample

Seven types of iron ore (BRH, WAL, ILS, MLL, ALR, ALY, and INL) produced in various countries (Brazil, Indonesia, Malaysia, and Australia) were used. The fraction size is <150 μm. Table 1 shows the chemical and physical composition and Fe forms of iron ores used. In X-ray diffraction analysis for iron ores, Fe forms were α-FeOOH for all samples, except for BRH and WAL, and the peaks of SiO₂ and nonidentified species were also detected for BRH, ILS, MLL, ALR, and ALY. (25)

Hydrothermal Treatment

The hydrothermal treatment was carried out with an SUS316 made batch reactor (length, 100 mm; o.d., 24 mm; thickness, 2 mm). The details of the experimental procedure have been reported in ref (25). About 2.5 g of a sample and 7 mL of solvent were first added into the reactor, the reactor was then pressurized with high-purity He (99.9995%) to check for leakage and to replace the atmosphere in the reactor. After the atmosphere in the reactor was replaced with enough He, the reactor was heated to 150–350 °C in a fluidized sand bath for 30 min. The change of pressure in the SUS reactor corresponded with the general vapor pressure curve of water. After a holding period of 30 min, the reactor was rapidly quenched in a water bath. The solid and liquid phases were separated using the filtrate method, and the former was repeatedly washed with distilled water until the pH of the filtrate becomes neutral. The yield of the treated samples was calculated based on the weight loaded into the reactor, and finally, the treated weight was obtained after each treatment and listed by iron ore basis (original sample basis). The distilled water or 5 M NaOH was used for the hydrothermal treatment. Here, a slight loss of solid phase occurs due to the sintering of the Fe species, which is strongly adhered to the inner wall and the Fe of the reactor, during hydrothermal treatment. In addition, almost no elution of iron was observed in all treatment.

Alkali Roasting

A NaOH fraction <150 μm, crushed and sieved, was used for the alkaline roasting of the iron ores. NaOH (1.44 g) was physically mixed with the iron ores at room temperature, and the mixture was then heated at 10 °C/min up to 350, 600, or 900 °C in air. It is well-known that dehydration of α-FeOOH in limonite occurs above 300 °C, and the maximum specific surface area is observed at 350 °C. (25,26) When the temperature was raised to 600 °C, the highest pore volume is found, whereas the specific surface area decrease, and at 900 °C, both values decrease. (25) In this study, the above temperatures were selected to investigate the effect of pore properties on gangue removal. The leaching and hydrothermal treatments of the prepared NaOH roasting samples were carried out as follows: (1) the sample was leached with 7 mL of distilled water at room temperature for 30 min under a N₂ atmosphere. The recovery of the solid phase was the same as that in Hydrothermal treatment section. (2) The sample and 7 mL of H₂O were added into the SUS reactor, and the mixture was heated with the same conditions as mentioned in Hydrothermal treatment section. Here, the NaOH solution concentration in the SUS reactor with the addition of H₂O was adjusted to 5 M NaOH. (3) The sample was first leached with distilled water in the same manner as (1) mentioned above. Following this, then the sample, which was recovered and dried at 108 °C for 12 h in N₂, and 7 mL of 5 M NaOH were added into the SUS reactor, and the reactor was then heated in the same manner as that in Hydrothermal treatment section. In the present study, treatments of (1), (2), and (3) were denoted as Roasting/H₂O_RT, Roasting/H₂O_SC (subcritical), and Roasting_H₂O_RT/NaOH_SC, respectively.

Characterization

The characterization was carried out by using the N₂ adsorption analysis (Quantachrome, Nova1200e) and conventional powder diffraction (Shimadzu, XRD6000) methods. The detail of the measurement condition has been described in our previous report. (25) Each element (Fe, Si, Al, and P) content in the sample before and after treatment was measured by an alkaline fusion method according to the Japanese Industrial Standard method (JIS M8214), which employs the inductively coupled plasma optical emission spectroscopy (Thermo Scientific, iCAP 6300 Duo) method. (25,32)

Author Information

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Corresponding Author
- Naoto Tsubouchi - Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan; http://orcid.org/0000-0001-8236-8252; Email: [email protected]
Author
- Yuuki Mochizuki - Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan; http://orcid.org/0000-0003-1977-413X
Notes
The authors declare no competing financial interest.

Acknowledgments

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The authors acknowledge the supply of iron ores from Kobe Steel Ltd., Mitsubishi Chemical Corp., Nippon Steel Corp., and JFE Steel Corp. in Japan.

References

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This article references 32 other publications.

1
Zhu, D.; Wang, H.; Pan, J.; Yang, C. Influence of mechanical activation on acid leaching dephosphorization of high phosphorus iron ore concentrates. J. Iron Steel Res. Int. 2016, 23, 661– 668, DOI: 10.1016/S1006-706X(16)30103-0
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Wu, F.; Cao, Z.; Wang, S.; Zhong, H. Novel and green metallurgical technique of comprehensive utilization of refractory limonite ores. J. Cleaner Prod. 2018, 171, 831– 843, DOI: 10.1016/j.jclepro.2017.09.198
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Novel and green metallurgical technique of comprehensive utilization of refractory limonite ores
Wu, Fangfang; Cao, Zhanfang; Wang, Shuai; Zhong, Hong
Journal of Cleaner Production (2018), 171 (), 831-843CODEN: JCROE8; ISSN:0959-6526. (Elsevier Ltd.)
Limonite ores are a common and widely distributed refractory iron oxide ores in the world. In this paper, in view of the growing development of steel and iron industry, the depletion of easy-processing iron ores and growing environmental concerns, a novel and green technique route was proposed to comprehensive utilize limonite ores by asynchronously recovering various valuable elements. The technique route included three stages: recovery (enrichment) of Fe and Mn by removal of impurities (Al and Si phases) via microwave-assisted roasting-acid leaching process using alkali lignin and Na2CO3-Na2SO4 binary sodium salts as roasting additives, where Na2SO4 was favorable for the aggregation and growth of iron-rich grains, Na2CO3 could enhance the activation of Al and Si phases and then improve the acid leaching of Al and Si, and alkali lignin has a favorable effect on the leaching; recovery of Si by ripening the acid leached liquor, where Si was enriched and extd. in the form of silica gel through the polymn. of silicic acid; and stepwise recovery of small amt. of leached Fe and Mn as well as Al by neutralizing and pptg. of filtrate from the 2nd stage using NaOH soln. and NaHCO3 soln. as pptg. reagents, resp. The final Na2SO4 and Na2CO3 filter liquor could be recycling used in the roasting process by evapn. pretreatment, achieving zero pollution and zero waste. By performing acid leaching process on the roasted ore treated at 200 °C, 600 W for 30 min in the presence of 5% alkali lignin, 5% Na2CO3 and 5% Na2SO4, an iron conc. assaying 57.08% Fe with the corresponding iron recovery ratio of 92.04% and yield of 64.66% was obtained from the refractory limonite ore contg. 40.10% Fe, 8.69% Mn, 9.40% Al, and 6.92% Si. Besides, Mn was simultaneous enriched in the iron conc. with a Mn recovery ratio of 71.73% and a Mn grade of 9.64%. Simultaneously, 84.11% of Si and 80.26% of Al existed in the limonite ore were extd., and leaching ratios of Fe and Mn were only 7.96% and 28.27%, resp. Subsequently, silica gel contg. 93.31% SiO2 and Al(OH)3 ppt. contg. 41.59% Al2O3 and Mn-Fe ppt. with 33.08% Fe and 14.83% Mn were successfully stepwise obtained by the last two stages. The proposed technique with the advantages of mild reaction conditions and discharge reducing, meeting the demands of green metallurgy, would potentially be a feasible route for the utilization of limonite ores, easing the shortages of iron and promoting the sustainable development of steel and iron industry.
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Yu, J.; Guo, Z.; Tang, H. Dephosphorization treatment of high phosphorus oolitic iron ore by hydrometallurgical process and leaching kinetics. ISIJ Int. 2013, 53, 2056– 2064, DOI: 10.2355/isijinternational.53.2056
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3
Dephosphorization treatment of high phosphorus oolitic iron ore by hydrometallurgical process and leaching kinetics
Yu, Jintao; Guo, Zhancheng; Tang, Huiqing
ISIJ International (2013), 53 (12), 2056-2064CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
Dephosphorization process of high phosphorus oolitic iron ore by acid leaching and leaching kinetics were investigated in the paper. The high phosphorus ore samples (51%T.Fe, 0.52%P) used in this work were analyzed by SEM-EDS and XRD, which showed their oolitic structure and mineral phases. Among the three kinds of acids (H2SO4, HCl and HNO3), sulfuric acid was the most appropriate one for dephosphorization, and structure changes after leaching were also investigated through the SEM and EDS anal. The effects of acidity, particle size, stirring speed and temp. were researched in detail. Through acid leaching, phosphorus could be removed effectively, and iron loss was negligible, which was also studied by thermodn. calcn. The exptl. data could be well described by the unreacted shrinking core model and rate controlling step was found to be chem. reaction between apatite and acid. The apparent activation energy was calcd. as 45.02 kJ/mol.
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Guo, L.; Gao, J.; Zhong, Y.; Gao, H.; Guo, Z. Phosphorus removal of high phosphorous oolitic iron ore with acid-leaching fluidized-reduction and melt-separation process. ISIJ Int. 2015, 55, 1806– 1815, DOI: 10.2355/isijinternational.ISIJINT-2015-135
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Phosphorus removal of high phosphorous oolitic iron ore with acid-leaching fluidized-reduction and melt-separation process
Guo, Lei; Gao, Jintao; Zhong, Yiwei; Gao, Han; Guo, Zhancheng
ISIJ International (2015), 55 (9), 1806-1815CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
A process with acid leaching followed by hydrogen-based fluidized redn. and melt sepn. is presented for recovering DRI (direct reduced iron) from high-phosphorus oolitic hematite in this study, and the aim of this study is to provide theor. and tech. basis for economical and rational use of high phosphorus oolitic iron ores. The reducibility of the ore can be improved by acid leaching, which is caused by the formation of voids in the ore particles after acid leaching and enhancing the internal gas diffusion. The phosphorus content in the DRI is still relative high even though there is no carbon in DRI, and it can be decreased to 0.087 wt% (raw ore 1.2 wt%) with the optimum condition in this study. It is proved that P exists in the DRI recovered from melt sepn. in the form of P2O5 inclusions or FexP as solid solns., while not in the form of Ca3(PO4)2 inclusions. Finally, a combined flowsheet for the treatment of high phosphorus oolitic iron ore is designed in this study.
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Tang, H.-Q.; Liu, W.-D.; Zhang, H.- Y.; Guo, Z.- C. Effect of microwave treatment upon processing oolitic high phosphorus iron ore for phosphorus removal. Metall. Mater. Trans. B 2014, 45, 1683– 1694, DOI: 10.1007/s11663-014-0072-5
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5
Effect of Microwave Treatment Upon Processing Oolitic High Phosphorus Iron Ore for Phosphorus Removal
Tang, Hui-Qing; Liu, Wei-Di; Zhang, Huan-Yu; Guo, Zhan-Cheng
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science (2014), 45 (5), 1683-1694CODEN: MTBSEO; ISSN:1073-5615. (Springer)
Influence of microwave treatment on the previously proposed phosphorus removal process of oolitic high phosphorus iron ore (gaseous redn. followed by melting sepn.) has been studied. Microwave treatment was carried out using a high-temp. microwave reactor (Model: MS-WH). Untreated ore fines and microwaved ore fines were then characterized by X-ray diffraction (XRD), SEM (SEM), energy dispersive spectroscopy (EDS), and thermogravimetric anal. (TGA). Thereafter, expts. on the proposed phosphorus removal process were conducted to examine the effect of microwave treatment. Results show that microwave treatment could change the microstructure of the ore fines and has an intensification effect on its gaseous redn. by reducing gas internal resistance, increasing chem. reaction rate and postponing the occurrence of sintering. Results of gaseous redn. tests using tubular furnace indicate both microwave treatment and high redn. temp. high as 1273 K (1000 °C) are needed to totally break down the dense oolite and metalization rate of the ore fines treated using microwave power of 450 W could reach 90 pct under 1273 K (1000 °C) and for 2 h. Results of melting sepn. tests of the reduced ore fines with a metalization rate of 90 pct show that, in addn. to the melting conditions in our previous studies, introducing 3 pct Na2CO3 to the highly reduced ore fines is necessary, and metal recovery rate and phosphorus content of metal could reach 83 pct and 0.31 mass pct, resp.
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Cai, X.; Qian, G.; Zhang, B.; Chen, Q.; Hu, C. Selective liberation of high-phosphorous oolitic hematite assisted by microwave processing and acid leaching. Minerals 2018, 8, 245– 258, DOI: 10.3390/min8060245
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6
Selective liberation of high-phosphorous oolitic hematite assisted by microwave processing and acid leaching
Cai, Xianyan; Qian, Gongming; Zhang, Bo; Chen, Qiushi; Hu, Chenqiang
Minerals (Basel, Switzerland) (2018), 8 (6), 245/1-245/13CODEN: MBSIBI; ISSN:2075-163X. (MDPI AG)
The release of valuable minerals from the assocd. gangues is called liberation. Good liberation is essential to the subsequent sepn. stage. Selective liberation is advantageous to improve the degree of liberation. Oolitic hematite is one of the typical refractory iron ores in China, and its resources are abundant. However, owing to its fine dissemination and complex mineralogical texture, the conventional grinding processes are inefficient in improving the selective liberation of oolitic hematite. In this study, microwave processing and acid leaching were used to assist the liberation of oolitic hematite. The assisted liberation of the oolitic hematite mechanisms of microwave processing and acid leaching were studied by using scanning electron microscope (SEM), X-ray diffraction (XRD), BET sp. surface area detection method (BET) and the transflective microscope method. The results indicated that microwave processing can reduce the mech. strength of oolitic hematite and improve the liberation of hematite, and acid leaching can improve the microwave-assisted liberation efficiency and reduce the content of phosphorus in the grinding product. Compared to direct grinding, the liberation of hematite increased by 54.80% in the grinding product, and esp., the fractions of -0.038-mm and 0.05-0.074 mm increased significantly; however, there was no obvious change in other grain sizes, and the dephosphorization ratio reached 47.20% after microwave processing and acid leaching. After the two stages, the iron grade and recovery of the magnetic sepn. product increased by 14.26% and 34.62%, resp., and the dephosphorization ratio reached 88.59%. It is demonstrated that microwave processing and acid leaching comprise an efficient method to improve the liberation of hematite and the dephosphorization ratio of oolitic hematite. The two-stage treatment can achieve selective liberation of oolitic hematite, which is beneficial to the following magnetic sepn.
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Pereira, A. C.; Papini, R. M. Processes for phosphorus removal from iron ore - a review. Rem: Rev. Esc. Minas 2015, 68, 331– 335, DOI: 10.1590/0370-44672014680202
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Wang, H. H.; Li, G. Q.; Zhao, D.; Ma, J. H.; Yang, J. Dephosphorization of high phosphorus oolitic hematite by acid leaching and the leaching kinetics. Hydrometallurgy 2017, 171, 61– 68, DOI: 10.1016/j.hydromet.2017.04.015
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Dephosphorization of high phosphorus oolitic hematite by acid leaching and the leaching kinetics
Wang, H. H.; Li, G. Q.; Zhao, D.; Ma, J. H.; Yang, J.
Hydrometallurgy (2017), 171 (), 61-68CODEN: HYDRDA; ISSN:0304-386X. (Elsevier B.V.)
It is highly difficult to remove phosphorus from high phosphorus oolitic hematite by the usual dressing process. Acid leaching is an effective method for the dephosphorization of high phosphorus oolitic hematite. The acid leaching expts. were conducted to study the effect of acid concn., temp., leaching time, solid-liq. (S/L) ratio and the stirring speed on the dephosphorization of the high phosphorus oolitic hematite. The results demonstrate that hydrochloric acid is the best selection for leaching acid for the dephosphorization, and treatment of the sample in 0.2 mol/L hydrochloric acid at 298 K for 10 min with the S/L ratio of 0.03 g/mL and a stirring speed of 300 rpm is optimum. Thus, the dephosphorization can reach 90% with < 0.18% iron loss. We also investigated the hydrochloric acid leaching kinetics. There were two distinct stages in the leaching process for dephosphorization, and the kinetics of both stages followed a shrinking core model. The apparent activation energy for leaching in leaching stage one (initial 10 min) and stage two (10-60 min) was estd. to be 2.51 kJ/mol and 5.59 kJ/mol, resp. The results demonstrated that leaching of the two stages was controlled by acid diffusion through the solid product layer. The leaching with iron dissoln. was mostly controlled by chem. reaction between Fe2O3 and acid.
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Cheng, C. Y.; Misra, V. N.; Clough, J.; Muni, R. Dephosphorisation of western Australian iron ore by hydrometallurgical process. Miner. Eng. 1999, 12, 1083– 1092, DOI: 10.1016/S0892-6875(99)00093-X
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Dephosphorisation of Western Australian iron ore by hydrometallurgical process
Cheng, C. Y.; Misra, V. N.; Clough, J.; Mun, R.
Minerals Engineering (1999), 12 (9), 1083-1092CODEN: MENGEB; ISSN:0892-6875. (Elsevier Science Ltd.)
More than 80% of Western Australian iron ore contains an av. of 0.15% phosphorus, and attracts a penalty due to its high level of phosphorus when it is exported. At the current rate of mining, identified premium grade iron ore with low phosphorus content (<0.05%) will be depleted in 30 yr. The development of an economical dephosphorisation process is crit. for the future success of the Western Australian iron ore industry. In the current work, effective dephosphorisation of Western Australian iron has been demonstrated. Sulfuric acid was chosen as the leachant on the basis of its availability and low cost. The iron ore sample used in this study typically contained 0.126% phosphorus, was from the Pilbara region of Western Australia. After roasting at 1250°C, lump ore (P80 5.6 mm), pellet 1 (grinding to 100% -1.5 mm before pelletization) and pellet 2 (grinding to 100% -0.15 mm before pelletization) were leached in solns. with different sulfuric acid concns. After leaching for 5 h at 60°C in 0.1 M sulfuric acid soln., 67.2%, 69.0% and 68.7% of the phosphorus was leached from the above three samples, resp. The phosphorus content was reduced from 0.126% to 0.044%, 0.055% and 0.042% resp. The dissoln. of iron during leaching was negligible. The optimum sulfuric acid concn. was 0.1 M in terms of acid cost and iron loss. The acid consumption cost is as low as $A 0.47/ton.
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Rezvani Pour, H.; Mostafavi, A.; Shams Pur, T. S.; Ebadi Pour, G.; Haji Zadeh Omran, A. Removal of sulfur and phosphorous from iron ore concentrate by leaching. Physicochem. Probl. Miner. Process. 2016, 52, 845– 854, DOI: 10.5277/ppmp160226
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Jin, Y.-s.; Jiang, T.; Yang, Y.-b.; Li, Q.; Li, G.-h.; Guo, Y.-f. Removal of phosphorus from iron ores by chemical leaching. J. Cent. South Univ. Technol. 2006, 13, 673– 677, DOI: 10.1007/s11771-006-0003-y
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11
Removal of phosphorus from iron ores by chemical leaching
Jin, Yong-shi; Jiang, Tao; Yang, Yong-bin; Li, Qian; Li, Guang-hui; Guo, Yu-feng
Journal of Central South University of Technology (English Edition) (2006), 13 (6), 673-677CODEN: JCSTFT; ISSN:1005-9784. (Central South University Press)
Alkali-leaching and acid-leaching were proposed for the dephosphorization of Changde iron ore, which contains an av. of 1.12% for phosphorus content. Sodium hydroxide, sulfurized, hydrochloric and nitric acids were used for the prepn. of leach solns. Phosphorus occurring as apatite phase could be removed by alkali-leaching, but those occurring in the iron phase could not. Sulfuric acid is the most effective among the three kinds of acid. 91.61% Phosphorus removal was attained with 1% sulfuric acid after leaching for 20 min at room temp. Iron loss during acid-leaching can be negligible, which was ≤0.25%. The pH value of soln. after leaching with 1% sulfuric acid was ∼0.86, which means acid would not be exhausted during the process and it could be recycled, and the recycle of sulfuric acid soln. would make the dephosphorization process more economical.
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Zhang, Y.; Muhammed, M. The removal of phosphorus from iron ore by leaching with nitric acid. Hydrometallurgy 1989, 21, 255– 275, DOI: 10.1016/0304-386X(89)90001-7
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12
The removal of phosphorus from iron ore by leaching with nitric acid
Zhang, Yu; Muhammed, Mamoun
Hydrometallurgy (1989), 21 (3), 255-75CODEN: HYDRDA; ISSN:0304-386X.
The apatite content (∼1%) is removed (>95%) by leaching the ore with HNO3. The Fe loss is <0.05% while the alkali metal content is greatly reduced (>60%). The quality of the ore, as a sinter feed, was slightly improved upon leaching. The characteristics of the percolation leaching operation by 2-8M HNO3 soln. were studied. The principal reaction of apatite dissoln. is 1st order with respect to H ions and is step-limited by diffusion. The dissoln. of Fe is sensitive, more than that of the apatite, to the initial acidity of leach solns. The variation of the flow velocity has a similar effect on the dissoln. of apatite and Fe. An overall leach-rate equation is established.
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Xia, W.; Ren, Z.; Gao, Y. Removal of phosphorus from high phosphorus iron ores by selective HCl leaching method. J. Iron Steel Res, Int. 2011, 18, 1– 4, DOI: 10.1016/S1006-706X(11)60055-1
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13
Removal of phosphorus from high phosphorus iron ores by selective HCl leaching method
Xia, Wen-tang; Ren, Zheng-de; Gao, Yi-feng
Journal of Iron and Steel Research International (2011), 18 (5), 1-4CODEN: JISIF4; ISSN:1006-706X. (Journal of Iron and Steel Research)
The selective HCl leaching method was used to remove phosphorus from high phosphorus iron ores. The hydroxyapatite in high phosphorus iron ores was converted into sol. phosphate during the process of HCl leaching. The effects of reaction time, particle size, hydrochloric acid concn., reaction temp., liq.-solid ratio and stirring strength on the dephosphorization ratio were studied. The dephosphorization ratio can exceed 98% under the conditions of reaction time 30 - 45 min, particle size <0.147 mm, hydrochloric acid concn. 2.5 mol/L, reaction temp. 25°, liq.-solid ratio 5 : 1 and stirring strength 5.02-12.76/s. After dephosphorization reaction, the content of phosphorus in iron ore complied completely with the requirements of steel prodn.
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Fisher-White, M. J.; Lovel, R. R.; Sparrow, G. J. Phosphorus removal from goethitic iron ore with a low temperature heat treatment and a caustic leach. ISIJ Int. 2012, 52, 797– 803, DOI: 10.2355/isijinternational.52.797
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Phosphorus removal from goethitic iron ore with a low temperature heat treatment and a caustic leach
Fisher-White, Michael John; Lovel, Roy Randall; Sparrow, Graham Jeffrey
ISIJ International (2012), 52 (5), 797-803CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
The phosphorus in high-phosphorus (>0.1% P) iron ores from the Pilbara area of Western Australia is mainly assocd. with the goethite fraction of the ore. Phys. sepn. methods and simple leaching processes do not remove sufficient phosphorus from the ores to meet market specifications of 0.075% P. Processing to disrupt the goethite structure to make the phosphorus amenable to leaching is necessary. Phosphorus assocd. with the goethite in high-phosphorus iron ores can be removed to 0.075% P using a heat treatment at 300-350°C for 1 h with 10 wt% NaOH, followed by a water leach. Heating at higher temps., up to 500°C, with heating times of 0.5 h to 4 h, gave no improvement in phosphorus removal. Similar phosphorus removal was achieved by heating the ore at 300-350°C for more than 0.5 h and leaching with 1-5 M NaOH at the b.p. for 3 h. The concn. of sodium hydroxide required depended on the amt. of phosphorus to be removed. Heating for up to 2 h or at higher temps. up to 750°C did not improve the amt. of phosphorus removed in the caustic leach. The temp. of the leach had a significant effect on the amt. of phosphorus removed with less phosphorus being removed below the b.p. of the leach liquor. The heat treatment at 300-350°C is considered to dehydroxylate the goethite to form a hematite intermediate phase, "protohematite", from which the phosphorus is dissolved during the leach step.
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Fisher-White, M. J.; Lovel, R. R.; Sparrow, G. J. Heat and acid leach treatments to lower phosphorus levels in goethitic iron ores. ISIJ Int. 2012, 52, 1794– 1800, DOI: 10.2355/isijinternational.52.1794
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15
Heat and acid leach treatments to lower phosphorus levels in goethitic iron ores
Fisher-White, Michael John; Lovel, Roy Randall; Sparrow, Graham Jeffrey
ISIJ International (2012), 52 (10), 1794-1800CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
Phosphorus assocd. with goethite in high-phosphorus (>0.10 mass% P) iron ores was lowered to below 0.075 mass% P with a heat treatment at 300 or 350°C for 1 h followed by a sulfuric acid (H2SO4) leach. This phosphorus removal was assocd. with a sample wt. loss of 10-20 mass% due to dissoln. of iron oxides. After heating at 900°C for 1 h, a sulfuric acid leach resulted in similar phosphorus removal but with dissoln. of less than 3 mass% of the sample. The wt. losses in the leach are assocd. with phase changes of the phosphorus-contg. goethite phase during heating. Heating at 300 or 350°C resulted in conversion of the goethite into an intermediate hematite phase (protohematite), while heating at 900°C gave a dense hematite phase. Compared with goethite in the ore, the more porous protohematite phase was more sol. in the sulfuric acid resulting in dissoln. of iron with the phosphorus, while the dense hematite phase was much less sol. and little iron was dissolved in the leach. Leaching at 25 mass% solids for 3 h at 60°C, at a pH of 0.5 or lower, gave significant lowering of phosphorus levels. Leaches were with 0.1-1M H2SO4; the concn. of acid required depended on the amt. of phosphorus to be removed. Recycling of the acid leach liquor four times did not show evidence for pptn. of phosphorus and resulted in leach solns. with up to 1 g/L P and 134 g/L Fe.
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Muhammed, M.; Zhang, Y. A hydrometallurgical process for the dephosphorization of iron ore. Hydrometallurgy 1989, 21, 277– 292, DOI: 10.1016/0304-386X(89)90002-9
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16
A hydrometallurgical process for the dephosphorization of iron ore
Muhammed, Mamoun; Zhang, Yu
Hydrometallurgy (1989), 21 (3), 277-92CODEN: HYDRDA; ISSN:0304-386X.
The dephosphorization of Fe ore consists of an integrated treatment for the removal of the P from the ore by leaching and further processing of the leach soln. H3PO4 is extd. by isoamyl alc. (iAmOH) and stripped by HNO3 soln. H3PO4 is concd. by evapn. where most of the HNO3 is removed. The remaining HNO3 is extd. by Me iso-Bu ketone. The raffinate from the H3PO4 extn. is treated by H2SO4 for the regeneration of the spent HNO3. HNO3 is extd. by iAmOH and concd. by distn. before reuse in further leaching. Evidence on the tech. feasibility of the process was established. The process is economically viable.
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Ionkov, K.; Gaydardzhiev, S.; Correa de Araujo, A.; Bastin, D.; Lacoste, M. Amenability for processing of oolitic iron ore concentrate for phosphorus removal. Miner. Eng. 2013, 46-47, 119– 127, DOI: 10.1016/j.mineng.2013.03.028
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17
Amenability for processing of oolitic iron ore concentrate for phosphorus removal
Ionkov, K.; Gaydardzhiev, S.; Correa de Araujo, A.; Bastin, D.; Lacoste, M.
Minerals Engineering (2013), 46-47 (), 119-127CODEN: MENGEB; ISSN:0892-6875. (Elsevier Ltd.)
Beneficiation routes aimed at dephosphorisation of oolitic gravity magnetic conc. and involving a combination of roasting, re-grinding, magnetic sepn. and water and acid leaching are investigated. Roasting was carried out at 900 °C for 1 h without or with lime or sodium hydroxide as roasting additives. When additives were used, cement phases of Si-Al-Na-Ca-O type were detected as well as the mineral giuseppettite. During the thermal process sodium silicate is liquefied and the newly formed phases coat the oolites and penetrate inside the cracks. Energy Dispersive Spectroscopy anal. has indicated that the zone surrounding the oolites consists of Na, Al and Si phases with part of phosphorus being captured there. As a result of the alk. roasting, goethite is partly transformed to magnetite and this redn. is reinforced with an increase in sodium hydroxide dosage. Investigation of redistribution of phosphorous shows that it could be only partly sepd. if leaching is not accompanied by re-grinding and phys. sepn. The recommended dosage of the reductive agent for the final flowsheet is 8 mass% ratio to conc. Grinding to a mean size of 0.040 mm, with water and acid leaching and double magnetic sepn. creates conditions to obtain a high-quality iron conc. with 65.97% Fe and recovery of 92.43%, with simultaneous decrease in the phosphorus content from 0.71% to 0.05%.
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Li, G.; Zhang, S.; Rao, M.; Zhang, Y.; Jiang, T. Effects of sodium salts on reduction roasting and Fe-P separation of high-phoshorus oolitic hematite ore. Int. J. Miner. Process. 2013, 124, 26– 34, DOI: 10.1016/j.minpro.2013.07.006
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18
Effects of sodium salts on reduction roasting and Fe-P separation of high-phosphorus oolitic hematite ore
Li, Guanghui; Zhang, Shuhui; Rao, Mingjun; Zhang, Yuanbo; Jiang, Tao
International Journal of Mineral Processing (2013), 124 (), 26-34CODEN: IJMPBL; ISSN:0301-7516. (Elsevier B.V.)
Effects of sodium salts on redn. roasting and Fe-P sepn. of high-phosphorus oolitic hematite ore were studied in the process of coal-based direct redn. followed by wet magnetic sepn. Various parameters, including reducing temp. and time, type and dosage of sodium salts, grinding fineness of magnetic sepn. feed and magnetic field intensity were investigated. The results of redn. and Fe-P magnetic sepn. are significantly improved by the addn. of sodium sulfate and borax, in comparison with those in the absence of additives. A magnetic conc. with total iron grade of 92.7% and phosphorus content of 0.09% was obtained from an oolitic hematite ore contg. 48.96% iron and 1.61% phosphorus when reduced in the presence of 7.5% sodium sulfate and 1.5% borax and wet magnetic sepd. under the proper conditions. The results of optical microscopy and X-ray diffraction (XRD) analyses of reduced pellet reveal that metallic iron grains exist in sizes of 10-20 μm and are assocd. with gangue minerals closely when reduced in the absence of sodium salts. By contrast, the oolitic structure is destroyed and metallic iron grains grow markedly to the mean size of 50 μm when reduced in the presence of sodium sulfate and borax. Sodium salts are capable of destroying the oolitic structure via reacting with gangues, enhancing the redn. of iron oxide and promoting the growth of metallic iron grains during redn., which is beneficial for Fe-P sepn. of the oolitic hematite ore.
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19
Omran, M.; Fabritius, T.; Elmahdy, A. M.; Abdel-Khalek, N. A.; Gornostayev, S. Improvement of phosphorus removal from iron ore using combined microwave pretreatment and ultrasonic treatment. Sep. Purif. Technol. 2015, 156, 724– 737, DOI: 10.1016/j.seppur.2015.10.071
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Improvement of phosphorus removal from iron ore using combined microwave pretreatment and ultrasonic treatment
Omran, Mamdouh; Fabritius, Timo; Elmahdy, Ahmed M.; Abdel-Khalek, Nagui A.; Gornostayev, Stanislav
Separation and Purification Technology (2015), 156 (Part_2), 724-737CODEN: SPUTFP; ISSN:1383-5866. (Elsevier B.V.)
Most of the past studies examd. the effects of ultrasonic treatment on the removal of phosphorus, silica and alumina minerals from iron ores. In the present work, the effect of combined microwave pretreatment and ultrasonic treatment on the efficiency of disintegration and removal of phosphorus and other gangue minerals assocd. with iron ores was studied. Three different iron ore samples have varying total iron concn. (TFe) and P2O5 content and mineralogical textures were studied. Microwave pretreatment generated intergranular fractures between the gangues (fluorapatite and chamosite) and oolitic hematite. These intergranular fractures improved liberation of iron ore, and accelerated ultrasonic disintegration and removal of phosphorus and gangue minerals from oolitic hematite. Microwave pretreatment increases the efficiency of ultrasonic disintegration and removal of particles by ∼20% compared to untreated sample. The results of ultrasonic treatment are quite promising. Significant increase in iron grade and redn. in phosphorus and alumina content of enriched product can be obtained. Depending on the sample texture and phosphorus distribution, ∼59% phosphorus removal can be obtained.
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20
Wang, H.; Li, G.; Yang, J.; Ma, J.; Khan, B. S. The behavior of phosphorus during reduction and carburization of high-phosphorus oolitic hematite with H₂ and CH₄. Metall. Mater. Trans. B 2016, 47, 2571– 2581, DOI: 10.1007/s11663-016-0709-7
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20
The Behavior of Phosphorus During Reduction and Carburization of High-Phosphorus Oolitic Hematite with H2 and CH4
Wang, Henghui; Li, Guangqiang; Yang, Jian; Ma, Jianghua; Khan, Babar Shahzad
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science (2016), 47 (4), 2571-2581CODEN: MTBSEO; ISSN:1073-5615. (Springer)
High-phosphorus oolitic hematite has not been widely utilized due to high content of phosphorus. Ca3(PO4)2 is the main component contg. phosphorus in high-phosphorus oolitic hematite. In the present work, the thermodn. was studied for Ca3(PO4)2 redn. by H2 gas and then carburization by CH4 gas. The results show that phosphorous in Ca3(PO4)2 cannot be reduced from gangue during the redn. of hematite and the formation of iron carbide at the temp. from 923 K to 1073 K (650 °C to 800 °C), in H2 and CH4 atmosphere. Redn. and carburization expts. were carried out. And phosphorus in reduced and carburized specimens was analyzed by EDS and wet chem. method. The results confirmed that phosphorous cannot be reduced during the prepn. of iron carbide from this iron ore. So the metallic iron or iron carbide can be prepd. without the redn. of phosphorous at relatively low temp., which can be a new route of utilizing high-phosphorus oolitic hematite. After fine milling-magnetic sepn., the 99.47 pct of Fe3C-contg. material was recovered, but the dephosphorization rate reached to 19.37 pct only.
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21
Gao, J.; Guo, L.; Guo, Z. Separation of P phase and Fe phase in high phosphorus oolitic iron ore by ultrafine grinding and gaseous reduction in a rotary furnace. Metall. Mater. Trans. B 2015, 46, 2180– 2189, DOI: 10.1007/s11663-015-0400-4
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Separation of P Phase and Fe Phase in High Phosphorus Oolitic Iron Ore by Ultrafine Grinding and Gaseous Reduction in a Rotary Furnace
Gao, Jintao; Guo, Lei; Guo, Zhancheng
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science (2015), 46 (5), 2180-2189CODEN: MTBSEO; ISSN:1073-5615. (Springer)
Due to the oolitic structure of the high phosphorus iron ore and the closely wrapping of apatite and hematite phases, an approach using jet mill was utilized to grind the ore to ultrafine 0.01 to 0.001 mm, which realizes the dissocn. of apatite phase and hematite phase. Then in a lab. scale rotary furnace, high phosphorus ores of different sizes were reduced by reducing gas at sub-m.p. temps. (973 to 1173 K [700 to 900 °C]). In the rotating inclined reactor, the ore particles reacted with the reducing gas coming from the opposite direction in a rolling and discrete state, which greatly improved the kinetic conditions. In this study, the reaction rate increases significantly with the decrease of particle size. For the ultrafine high phosphorus iron ores, the metalization ratio can reach 83.91 to 97.32 pct, but only 33.24 to 40.22 pct for powders with the size of 0.13 to 0.15 mm. The reduced particles maintained their original sizes, without the presence of sintering phenomenon or iron whisker. Hence, two kinds of products were easily obtained by magnetic sepn.: the iron product with 91.42 wt pct of Fe and 0.19 wt pct of P, and the gangue product with 13.77 wt pct of Fe and 2.32 wt pct of P.
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Jang, K.-o.; Nunna, V. R. M.; Hapugoda, S.; Nguyen, A. V.; Bruckard, W. J. Chemical and mineral transformation of a low grade goethite ore by dehydroxylation, reduction roasting and magnetic separation. Miner. Eng. 2014, 60, 14– 22, DOI: 10.1016/j.mineng.2014.01.021
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Chemical and mineral transformation of a low grade goethite ore by dehydroxylation, reduction roasting and magnetic separation
Jang, Kyoung-oh; Nunna, Venkata R. M.; Hapugoda, Sarath; Nguyen, Anh V.; Bruckard, Warren J.
Minerals Engineering (2014), 60 (), 14-22CODEN: MENGEB; ISSN:0892-6875. (Elsevier Ltd.)
The utilization of abundant low grade goethite (α - FeOOH) ores is potentially important to many countries in the world, esp. Australia. These ores contain many detrimental impurities and are difficult to upgrade to make suitable concs. for the blast furnace. In this paper, chem. and mineral transformations of a goethite ore were studied by dehydroxylation, redn. roasting in CO and CO2 gas mixts., and magnetic sepn. The goethite sample was taken from a reject stream at an iron ore mine from the Pilbara region, Western Australia. The roasting temp. range investigated was 400-700 °C. Chem. and mineralogical anal. was conducted using XRF, XRD, optical microscope, EPMA, and SEM. Magnetic sepn. was conducted using a Davis tube tester and a high intensity magnetic separator. The results show that redn. roasting can remove moisture and impurities but does not significantly change the Fe content in the feed. However, redn. roasting transforms goethite to hematite and eventually maghemite which can be recovered by magnetic sepn., allowing upgrading. Further studies are needed to optimize the redn. roasting and correlate it with the magnetic sepn. to maximize the efficiency of iron upgrading.
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Zhu, D.; Chun, T.; Pan, J.; Lu, L.; He, Z. Upgrading and dephosphorization of Western Australian iron ore using reduction roasting by adding sodium carbonate. Int. J. Miner., Metall. Mater. 2013, 20, 505– 513, DOI: 10.1007/s12613-013-0758-8
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Zhu, De-qing; Chun, Tie-jun; Pan, Jian; Lu, Li-ming; He, Zhen
International Journal of Minerals, Metallurgy and Materials (2013), 20 (6), 505-513CODEN: IJMMLM; ISSN:1674-4799. (Springer)
The technol. of direct redn. by adding sodium carbonate (Na2CO3) and magnetic sepn. was developed to treat Western Australian high phosphorus iron ore. The iron ore and reduced product were investigated by optical microscopy and SEM. It is found that phosphorus exists within limonite in the form of solid soln., which cannot be removed through traditional ways. During redn. roasting, Na2CO3 reacts with gangue minerals (SiO2 and Al2O3), forming aluminum silicate-contg. phosphorus and damaging the ore structure, which promotes the sepn. between iron and phosphorus during magnetic sepn. Meanwhile, Na2CO3 also improves the growth of iron grains, increasing the iron grade and iron recovery. The iron conc., assaying 94.12wt% Fe and 0.07wt% P at the iron recovery of 96.83% and the dephosphorization rate of 74.08%, is obtained under the optimum conditions. The final product (metal iron powder) after briquetting can be used as the burden for steelmaking by an elec. arc furnace to replace scrap steel.
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Yang, M.; Zhu, Q.; Fan, C.; Xie, Z.; Li, H. Roasting-induced phase change and its influence on phosphorus removal through acid leaching for high-phosphorus iron ore. Int. J. Miner., Metall. Mater. 2015, 22, 346– 352, DOI: 10.1007/s12613-015-1079-x
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International Journal of Minerals, Metallurgy and Materials (2015), 22 (4), 346-352CODEN: IJMMLM; ISSN:1674-4799. (Springer)
In the present study, roasting-induced phase change and its influence on phosphorus removal via leaching has been investigated for high-phosphorus iron ore. The findings indicate that phosphorus in the ore is assocd. with goethite and exists mainly in amorphous Fe3PO7 phase. The phosphorus remains in the amorphous phase after being roasted below 300°C. Grattarolaite (Fe3PO7) is found in samples roasted at 600-700°C, revealing that phosphorus phase is transformed from the amorphous form to cryst. grattarolaite during roasting. Leaching tests on synthesized pure grattarolaite reveal a low rate of phosphorus removal by sulfuric acid leaching. When the roasting temp. is higher than 800°C, grattarolaite is found to react with alumina to form aluminum phosphate, and the reactivity of grattarolaite with alumina increases with increasing roasting temp. Consequently, the rate of phosphorus removal also increases with increasing roasting temp. due to the formation of acid-sol. aluminum phosphate.
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Cited By

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Jianping Jin, Xinran Zhu, Pengchao Li, Yanjun Li, Yuexin Han. Clean Utilization of Limonite Ore by Suspension Magnetization Roasting Technology. Minerals 2022, 12 (2) , 260. https://doi.org/10.3390/min12020260
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Abstract
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Figure 1
Figure 1. Extent of gangue removal in iron ores treated with the Roasting/H₂O_RT treatment.
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Figure 2
Figure 2. XRD patterns of NaOH roasted iron ore at 350 °C (left) and iron ores after the Roasting/H₂O_RT treatment (right). (a) BRH, (b) WAL, (c) ILS, (d) MLL, (e) ALR, (f) ALY, and (g) INL.
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Figure 3
Figure 3. Relationship between the amounts of gangue removal of Si, Al, and P with the Roasting/H₂O_RT treatment.
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Figure 4
Figure 4. Extent of increasing specific surface area of the iron ores after the Roasting/H₂O_RT treatment.
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Figure 5
Figure 5. Extent of gangue removal in iron ores treated with the Roasting/H₂O_SC treatment.
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Figure 6
Figure 6. Relationship between the amounts of gangue removal of Si, Al, and P with the Roasting/H₂O_SC treatment.
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Figure 7
Figure 7. Difference of the extent of gangue removal from the Roasting/H₂O_SC to the Roasting/H₂O_RT treatment.
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Figure 8
Figure 8. Temperature dependency on the extent of gangue removal from ALY during the Roasting/H₂O_SC treatment.
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Figure 9
Figure 9. Changes in the XRD pattern of the Roasting/H₂O_RT-treated ALY samples during the Roasting/H₂O_SC treatment. (a) Room temperature, (b) 100 °C, (c) 150 °C, (d) 200 °C, (e) 250 °C, (f) 300 °C, and (g) 350 °C.
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Figure 10
Figure 10. Effect of (a) calcination and (b, c) roasting temperatures on the extent of gangue removal from ALY with NaOH hydrothermal (a), Roasting/H₂O_RT (b), and Roasting/H₂O_SC (c) treatments at 300 °C.
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Figure 11
Figure 11. XRD patterns of ALY samples obtained after the NaOH hydrothermal, Roasting/H₂O_RT, and Roasting/H₂O_SC treatments at 300 °C corresponding to the results of Figure 10. ALY at 350 °C (left), 600 °C (center), and 900 °C (right). (a) Calcination in air, (b) 5 M NaOH hydrothermal-treated sample, (c) Roasted sample, (d) Roasting/H₂O_RT sample, and (e) Roasting/H₂O_SC sample.
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Figure 12
Figure 12. Extent of gangue removal of iron ores treated with the Roasting_H₂O_RT/NaOH_SC treatment at 300 °C.
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Figure 13
Figure 13. Relationship between the amounts of gangue removal of Si, Al, and P with the Roasting_H₂O_RT/NaOH_SC treatment at 300 °C.
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Figure 14
Figure 14. Relationship between the amounts of gangue removal of Si, Al (a), and P (b) with each treatment carried out in Figures 1, 5, and 12 and Table 2.
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Figure 15
Figure 15. Difference between the extent of gangue removal from the Roasting_H₂O_RT/NaOH_SC to (a) Roasting/H₂O_RT or (b) Roasting/H₂O_SC treatment at 300 °C.
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This article references 32 other publications.
1. 1
  Zhu, D.; Wang, H.; Pan, J.; Yang, C. Influence of mechanical activation on acid leaching dephosphorization of high phosphorus iron ore concentrates. J. Iron Steel Res. Int. 2016, 23, 661– 668, DOI: 10.1016/S1006-706X(16)30103-0
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  Novel and green metallurgical technique of comprehensive utilization of refractory limonite ores
  Wu, Fangfang; Cao, Zhanfang; Wang, Shuai; Zhong, Hong
  Journal of Cleaner Production (2018), 171 (), 831-843CODEN: JCROE8; ISSN:0959-6526. (Elsevier Ltd.)
  Limonite ores are a common and widely distributed refractory iron oxide ores in the world. In this paper, in view of the growing development of steel and iron industry, the depletion of easy-processing iron ores and growing environmental concerns, a novel and green technique route was proposed to comprehensive utilize limonite ores by asynchronously recovering various valuable elements. The technique route included three stages: recovery (enrichment) of Fe and Mn by removal of impurities (Al and Si phases) via microwave-assisted roasting-acid leaching process using alkali lignin and Na2CO3-Na2SO4 binary sodium salts as roasting additives, where Na2SO4 was favorable for the aggregation and growth of iron-rich grains, Na2CO3 could enhance the activation of Al and Si phases and then improve the acid leaching of Al and Si, and alkali lignin has a favorable effect on the leaching; recovery of Si by ripening the acid leached liquor, where Si was enriched and extd. in the form of silica gel through the polymn. of silicic acid; and stepwise recovery of small amt. of leached Fe and Mn as well as Al by neutralizing and pptg. of filtrate from the 2nd stage using NaOH soln. and NaHCO3 soln. as pptg. reagents, resp. The final Na2SO4 and Na2CO3 filter liquor could be recycling used in the roasting process by evapn. pretreatment, achieving zero pollution and zero waste. By performing acid leaching process on the roasted ore treated at 200 °C, 600 W for 30 min in the presence of 5% alkali lignin, 5% Na2CO3 and 5% Na2SO4, an iron conc. assaying 57.08% Fe with the corresponding iron recovery ratio of 92.04% and yield of 64.66% was obtained from the refractory limonite ore contg. 40.10% Fe, 8.69% Mn, 9.40% Al, and 6.92% Si. Besides, Mn was simultaneous enriched in the iron conc. with a Mn recovery ratio of 71.73% and a Mn grade of 9.64%. Simultaneously, 84.11% of Si and 80.26% of Al existed in the limonite ore were extd., and leaching ratios of Fe and Mn were only 7.96% and 28.27%, resp. Subsequently, silica gel contg. 93.31% SiO2 and Al(OH)3 ppt. contg. 41.59% Al2O3 and Mn-Fe ppt. with 33.08% Fe and 14.83% Mn were successfully stepwise obtained by the last two stages. The proposed technique with the advantages of mild reaction conditions and discharge reducing, meeting the demands of green metallurgy, would potentially be a feasible route for the utilization of limonite ores, easing the shortages of iron and promoting the sustainable development of steel and iron industry.
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  Dephosphorization treatment of high phosphorus oolitic iron ore by hydrometallurgical process and leaching kinetics
  Yu, Jintao; Guo, Zhancheng; Tang, Huiqing
  ISIJ International (2013), 53 (12), 2056-2064CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
  Dephosphorization process of high phosphorus oolitic iron ore by acid leaching and leaching kinetics were investigated in the paper. The high phosphorus ore samples (51%T.Fe, 0.52%P) used in this work were analyzed by SEM-EDS and XRD, which showed their oolitic structure and mineral phases. Among the three kinds of acids (H2SO4, HCl and HNO3), sulfuric acid was the most appropriate one for dephosphorization, and structure changes after leaching were also investigated through the SEM and EDS anal. The effects of acidity, particle size, stirring speed and temp. were researched in detail. Through acid leaching, phosphorus could be removed effectively, and iron loss was negligible, which was also studied by thermodn. calcn. The exptl. data could be well described by the unreacted shrinking core model and rate controlling step was found to be chem. reaction between apatite and acid. The apparent activation energy was calcd. as 45.02 kJ/mol.
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4. 4
  Guo, L.; Gao, J.; Zhong, Y.; Gao, H.; Guo, Z. Phosphorus removal of high phosphorous oolitic iron ore with acid-leaching fluidized-reduction and melt-separation process. ISIJ Int. 2015, 55, 1806– 1815, DOI: 10.2355/isijinternational.ISIJINT-2015-135
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  4
  Phosphorus removal of high phosphorous oolitic iron ore with acid-leaching fluidized-reduction and melt-separation process
  Guo, Lei; Gao, Jintao; Zhong, Yiwei; Gao, Han; Guo, Zhancheng
  ISIJ International (2015), 55 (9), 1806-1815CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
  A process with acid leaching followed by hydrogen-based fluidized redn. and melt sepn. is presented for recovering DRI (direct reduced iron) from high-phosphorus oolitic hematite in this study, and the aim of this study is to provide theor. and tech. basis for economical and rational use of high phosphorus oolitic iron ores. The reducibility of the ore can be improved by acid leaching, which is caused by the formation of voids in the ore particles after acid leaching and enhancing the internal gas diffusion. The phosphorus content in the DRI is still relative high even though there is no carbon in DRI, and it can be decreased to 0.087 wt% (raw ore 1.2 wt%) with the optimum condition in this study. It is proved that P exists in the DRI recovered from melt sepn. in the form of P2O5 inclusions or FexP as solid solns., while not in the form of Ca3(PO4)2 inclusions. Finally, a combined flowsheet for the treatment of high phosphorus oolitic iron ore is designed in this study.
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5. 5
  Tang, H.-Q.; Liu, W.-D.; Zhang, H.- Y.; Guo, Z.- C. Effect of microwave treatment upon processing oolitic high phosphorus iron ore for phosphorus removal. Metall. Mater. Trans. B 2014, 45, 1683– 1694, DOI: 10.1007/s11663-014-0072-5
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  5
  Effect of Microwave Treatment Upon Processing Oolitic High Phosphorus Iron Ore for Phosphorus Removal
  Tang, Hui-Qing; Liu, Wei-Di; Zhang, Huan-Yu; Guo, Zhan-Cheng
  Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science (2014), 45 (5), 1683-1694CODEN: MTBSEO; ISSN:1073-5615. (Springer)
  Influence of microwave treatment on the previously proposed phosphorus removal process of oolitic high phosphorus iron ore (gaseous redn. followed by melting sepn.) has been studied. Microwave treatment was carried out using a high-temp. microwave reactor (Model: MS-WH). Untreated ore fines and microwaved ore fines were then characterized by X-ray diffraction (XRD), SEM (SEM), energy dispersive spectroscopy (EDS), and thermogravimetric anal. (TGA). Thereafter, expts. on the proposed phosphorus removal process were conducted to examine the effect of microwave treatment. Results show that microwave treatment could change the microstructure of the ore fines and has an intensification effect on its gaseous redn. by reducing gas internal resistance, increasing chem. reaction rate and postponing the occurrence of sintering. Results of gaseous redn. tests using tubular furnace indicate both microwave treatment and high redn. temp. high as 1273 K (1000 °C) are needed to totally break down the dense oolite and metalization rate of the ore fines treated using microwave power of 450 W could reach 90 pct under 1273 K (1000 °C) and for 2 h. Results of melting sepn. tests of the reduced ore fines with a metalization rate of 90 pct show that, in addn. to the melting conditions in our previous studies, introducing 3 pct Na2CO3 to the highly reduced ore fines is necessary, and metal recovery rate and phosphorus content of metal could reach 83 pct and 0.31 mass pct, resp.
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6. 6
  Cai, X.; Qian, G.; Zhang, B.; Chen, Q.; Hu, C. Selective liberation of high-phosphorous oolitic hematite assisted by microwave processing and acid leaching. Minerals 2018, 8, 245– 258, DOI: 10.3390/min8060245
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  Selective liberation of high-phosphorous oolitic hematite assisted by microwave processing and acid leaching
  Cai, Xianyan; Qian, Gongming; Zhang, Bo; Chen, Qiushi; Hu, Chenqiang
  Minerals (Basel, Switzerland) (2018), 8 (6), 245/1-245/13CODEN: MBSIBI; ISSN:2075-163X. (MDPI AG)
  The release of valuable minerals from the assocd. gangues is called liberation. Good liberation is essential to the subsequent sepn. stage. Selective liberation is advantageous to improve the degree of liberation. Oolitic hematite is one of the typical refractory iron ores in China, and its resources are abundant. However, owing to its fine dissemination and complex mineralogical texture, the conventional grinding processes are inefficient in improving the selective liberation of oolitic hematite. In this study, microwave processing and acid leaching were used to assist the liberation of oolitic hematite. The assisted liberation of the oolitic hematite mechanisms of microwave processing and acid leaching were studied by using scanning electron microscope (SEM), X-ray diffraction (XRD), BET sp. surface area detection method (BET) and the transflective microscope method. The results indicated that microwave processing can reduce the mech. strength of oolitic hematite and improve the liberation of hematite, and acid leaching can improve the microwave-assisted liberation efficiency and reduce the content of phosphorus in the grinding product. Compared to direct grinding, the liberation of hematite increased by 54.80% in the grinding product, and esp., the fractions of -0.038-mm and 0.05-0.074 mm increased significantly; however, there was no obvious change in other grain sizes, and the dephosphorization ratio reached 47.20% after microwave processing and acid leaching. After the two stages, the iron grade and recovery of the magnetic sepn. product increased by 14.26% and 34.62%, resp., and the dephosphorization ratio reached 88.59%. It is demonstrated that microwave processing and acid leaching comprise an efficient method to improve the liberation of hematite and the dephosphorization ratio of oolitic hematite. The two-stage treatment can achieve selective liberation of oolitic hematite, which is beneficial to the following magnetic sepn.
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7. 7
  Pereira, A. C.; Papini, R. M. Processes for phosphorus removal from iron ore - a review. Rem: Rev. Esc. Minas 2015, 68, 331– 335, DOI: 10.1590/0370-44672014680202
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8. 8
  Wang, H. H.; Li, G. Q.; Zhao, D.; Ma, J. H.; Yang, J. Dephosphorization of high phosphorus oolitic hematite by acid leaching and the leaching kinetics. Hydrometallurgy 2017, 171, 61– 68, DOI: 10.1016/j.hydromet.2017.04.015
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  Dephosphorization of high phosphorus oolitic hematite by acid leaching and the leaching kinetics
  Wang, H. H.; Li, G. Q.; Zhao, D.; Ma, J. H.; Yang, J.
  Hydrometallurgy (2017), 171 (), 61-68CODEN: HYDRDA; ISSN:0304-386X. (Elsevier B.V.)
  It is highly difficult to remove phosphorus from high phosphorus oolitic hematite by the usual dressing process. Acid leaching is an effective method for the dephosphorization of high phosphorus oolitic hematite. The acid leaching expts. were conducted to study the effect of acid concn., temp., leaching time, solid-liq. (S/L) ratio and the stirring speed on the dephosphorization of the high phosphorus oolitic hematite. The results demonstrate that hydrochloric acid is the best selection for leaching acid for the dephosphorization, and treatment of the sample in 0.2 mol/L hydrochloric acid at 298 K for 10 min with the S/L ratio of 0.03 g/mL and a stirring speed of 300 rpm is optimum. Thus, the dephosphorization can reach 90% with < 0.18% iron loss. We also investigated the hydrochloric acid leaching kinetics. There were two distinct stages in the leaching process for dephosphorization, and the kinetics of both stages followed a shrinking core model. The apparent activation energy for leaching in leaching stage one (initial 10 min) and stage two (10-60 min) was estd. to be 2.51 kJ/mol and 5.59 kJ/mol, resp. The results demonstrated that leaching of the two stages was controlled by acid diffusion through the solid product layer. The leaching with iron dissoln. was mostly controlled by chem. reaction between Fe2O3 and acid.
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9. 9
  Cheng, C. Y.; Misra, V. N.; Clough, J.; Muni, R. Dephosphorisation of western Australian iron ore by hydrometallurgical process. Miner. Eng. 1999, 12, 1083– 1092, DOI: 10.1016/S0892-6875(99)00093-X
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  9
  Dephosphorisation of Western Australian iron ore by hydrometallurgical process
  Cheng, C. Y.; Misra, V. N.; Clough, J.; Mun, R.
  Minerals Engineering (1999), 12 (9), 1083-1092CODEN: MENGEB; ISSN:0892-6875. (Elsevier Science Ltd.)
  More than 80% of Western Australian iron ore contains an av. of 0.15% phosphorus, and attracts a penalty due to its high level of phosphorus when it is exported. At the current rate of mining, identified premium grade iron ore with low phosphorus content (<0.05%) will be depleted in 30 yr. The development of an economical dephosphorisation process is crit. for the future success of the Western Australian iron ore industry. In the current work, effective dephosphorisation of Western Australian iron has been demonstrated. Sulfuric acid was chosen as the leachant on the basis of its availability and low cost. The iron ore sample used in this study typically contained 0.126% phosphorus, was from the Pilbara region of Western Australia. After roasting at 1250°C, lump ore (P80 5.6 mm), pellet 1 (grinding to 100% -1.5 mm before pelletization) and pellet 2 (grinding to 100% -0.15 mm before pelletization) were leached in solns. with different sulfuric acid concns. After leaching for 5 h at 60°C in 0.1 M sulfuric acid soln., 67.2%, 69.0% and 68.7% of the phosphorus was leached from the above three samples, resp. The phosphorus content was reduced from 0.126% to 0.044%, 0.055% and 0.042% resp. The dissoln. of iron during leaching was negligible. The optimum sulfuric acid concn. was 0.1 M in terms of acid cost and iron loss. The acid consumption cost is as low as $A 0.47/ton.
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10. 10
  Rezvani Pour, H.; Mostafavi, A.; Shams Pur, T. S.; Ebadi Pour, G.; Haji Zadeh Omran, A. Removal of sulfur and phosphorous from iron ore concentrate by leaching. Physicochem. Probl. Miner. Process. 2016, 52, 845– 854, DOI: 10.5277/ppmp160226
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11. 11
  Jin, Y.-s.; Jiang, T.; Yang, Y.-b.; Li, Q.; Li, G.-h.; Guo, Y.-f. Removal of phosphorus from iron ores by chemical leaching. J. Cent. South Univ. Technol. 2006, 13, 673– 677, DOI: 10.1007/s11771-006-0003-y
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  11
  Removal of phosphorus from iron ores by chemical leaching
  Jin, Yong-shi; Jiang, Tao; Yang, Yong-bin; Li, Qian; Li, Guang-hui; Guo, Yu-feng
  Journal of Central South University of Technology (English Edition) (2006), 13 (6), 673-677CODEN: JCSTFT; ISSN:1005-9784. (Central South University Press)
  Alkali-leaching and acid-leaching were proposed for the dephosphorization of Changde iron ore, which contains an av. of 1.12% for phosphorus content. Sodium hydroxide, sulfurized, hydrochloric and nitric acids were used for the prepn. of leach solns. Phosphorus occurring as apatite phase could be removed by alkali-leaching, but those occurring in the iron phase could not. Sulfuric acid is the most effective among the three kinds of acid. 91.61% Phosphorus removal was attained with 1% sulfuric acid after leaching for 20 min at room temp. Iron loss during acid-leaching can be negligible, which was ≤0.25%. The pH value of soln. after leaching with 1% sulfuric acid was ∼0.86, which means acid would not be exhausted during the process and it could be recycled, and the recycle of sulfuric acid soln. would make the dephosphorization process more economical.
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12. 12
  Zhang, Y.; Muhammed, M. The removal of phosphorus from iron ore by leaching with nitric acid. Hydrometallurgy 1989, 21, 255– 275, DOI: 10.1016/0304-386X(89)90001-7
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  The removal of phosphorus from iron ore by leaching with nitric acid
  Zhang, Yu; Muhammed, Mamoun
  Hydrometallurgy (1989), 21 (3), 255-75CODEN: HYDRDA; ISSN:0304-386X.
  The apatite content (∼1%) is removed (>95%) by leaching the ore with HNO3. The Fe loss is <0.05% while the alkali metal content is greatly reduced (>60%). The quality of the ore, as a sinter feed, was slightly improved upon leaching. The characteristics of the percolation leaching operation by 2-8M HNO3 soln. were studied. The principal reaction of apatite dissoln. is 1st order with respect to H ions and is step-limited by diffusion. The dissoln. of Fe is sensitive, more than that of the apatite, to the initial acidity of leach solns. The variation of the flow velocity has a similar effect on the dissoln. of apatite and Fe. An overall leach-rate equation is established.
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13. 13
  Xia, W.; Ren, Z.; Gao, Y. Removal of phosphorus from high phosphorus iron ores by selective HCl leaching method. J. Iron Steel Res, Int. 2011, 18, 1– 4, DOI: 10.1016/S1006-706X(11)60055-1
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  13
  Removal of phosphorus from high phosphorus iron ores by selective HCl leaching method
  Xia, Wen-tang; Ren, Zheng-de; Gao, Yi-feng
  Journal of Iron and Steel Research International (2011), 18 (5), 1-4CODEN: JISIF4; ISSN:1006-706X. (Journal of Iron and Steel Research)
  The selective HCl leaching method was used to remove phosphorus from high phosphorus iron ores. The hydroxyapatite in high phosphorus iron ores was converted into sol. phosphate during the process of HCl leaching. The effects of reaction time, particle size, hydrochloric acid concn., reaction temp., liq.-solid ratio and stirring strength on the dephosphorization ratio were studied. The dephosphorization ratio can exceed 98% under the conditions of reaction time 30 - 45 min, particle size <0.147 mm, hydrochloric acid concn. 2.5 mol/L, reaction temp. 25°, liq.-solid ratio 5 : 1 and stirring strength 5.02-12.76/s. After dephosphorization reaction, the content of phosphorus in iron ore complied completely with the requirements of steel prodn.
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14. 14
  Fisher-White, M. J.; Lovel, R. R.; Sparrow, G. J. Phosphorus removal from goethitic iron ore with a low temperature heat treatment and a caustic leach. ISIJ Int. 2012, 52, 797– 803, DOI: 10.2355/isijinternational.52.797
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  14
  Phosphorus removal from goethitic iron ore with a low temperature heat treatment and a caustic leach
  Fisher-White, Michael John; Lovel, Roy Randall; Sparrow, Graham Jeffrey
  ISIJ International (2012), 52 (5), 797-803CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
  The phosphorus in high-phosphorus (>0.1% P) iron ores from the Pilbara area of Western Australia is mainly assocd. with the goethite fraction of the ore. Phys. sepn. methods and simple leaching processes do not remove sufficient phosphorus from the ores to meet market specifications of 0.075% P. Processing to disrupt the goethite structure to make the phosphorus amenable to leaching is necessary. Phosphorus assocd. with the goethite in high-phosphorus iron ores can be removed to 0.075% P using a heat treatment at 300-350°C for 1 h with 10 wt% NaOH, followed by a water leach. Heating at higher temps., up to 500°C, with heating times of 0.5 h to 4 h, gave no improvement in phosphorus removal. Similar phosphorus removal was achieved by heating the ore at 300-350°C for more than 0.5 h and leaching with 1-5 M NaOH at the b.p. for 3 h. The concn. of sodium hydroxide required depended on the amt. of phosphorus to be removed. Heating for up to 2 h or at higher temps. up to 750°C did not improve the amt. of phosphorus removed in the caustic leach. The temp. of the leach had a significant effect on the amt. of phosphorus removed with less phosphorus being removed below the b.p. of the leach liquor. The heat treatment at 300-350°C is considered to dehydroxylate the goethite to form a hematite intermediate phase, "protohematite", from which the phosphorus is dissolved during the leach step.
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15. 15
  Fisher-White, M. J.; Lovel, R. R.; Sparrow, G. J. Heat and acid leach treatments to lower phosphorus levels in goethitic iron ores. ISIJ Int. 2012, 52, 1794– 1800, DOI: 10.2355/isijinternational.52.1794
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  15
  Heat and acid leach treatments to lower phosphorus levels in goethitic iron ores
  Fisher-White, Michael John; Lovel, Roy Randall; Sparrow, Graham Jeffrey
  ISIJ International (2012), 52 (10), 1794-1800CODEN: IINTEY; ISSN:0915-1559. (Iron and Steel Institute of Japan)
  Phosphorus assocd. with goethite in high-phosphorus (>0.10 mass% P) iron ores was lowered to below 0.075 mass% P with a heat treatment at 300 or 350°C for 1 h followed by a sulfuric acid (H2SO4) leach. This phosphorus removal was assocd. with a sample wt. loss of 10-20 mass% due to dissoln. of iron oxides. After heating at 900°C for 1 h, a sulfuric acid leach resulted in similar phosphorus removal but with dissoln. of less than 3 mass% of the sample. The wt. losses in the leach are assocd. with phase changes of the phosphorus-contg. goethite phase during heating. Heating at 300 or 350°C resulted in conversion of the goethite into an intermediate hematite phase (protohematite), while heating at 900°C gave a dense hematite phase. Compared with goethite in the ore, the more porous protohematite phase was more sol. in the sulfuric acid resulting in dissoln. of iron with the phosphorus, while the dense hematite phase was much less sol. and little iron was dissolved in the leach. Leaching at 25 mass% solids for 3 h at 60°C, at a pH of 0.5 or lower, gave significant lowering of phosphorus levels. Leaches were with 0.1-1M H2SO4; the concn. of acid required depended on the amt. of phosphorus to be removed. Recycling of the acid leach liquor four times did not show evidence for pptn. of phosphorus and resulted in leach solns. with up to 1 g/L P and 134 g/L Fe.
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16. 16
  Muhammed, M.; Zhang, Y. A hydrometallurgical process for the dephosphorization of iron ore. Hydrometallurgy 1989, 21, 277– 292, DOI: 10.1016/0304-386X(89)90002-9
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  16
  A hydrometallurgical process for the dephosphorization of iron ore
  Muhammed, Mamoun; Zhang, Yu
  Hydrometallurgy (1989), 21 (3), 277-92CODEN: HYDRDA; ISSN:0304-386X.
  The dephosphorization of Fe ore consists of an integrated treatment for the removal of the P from the ore by leaching and further processing of the leach soln. H3PO4 is extd. by isoamyl alc. (iAmOH) and stripped by HNO3 soln. H3PO4 is concd. by evapn. where most of the HNO3 is removed. The remaining HNO3 is extd. by Me iso-Bu ketone. The raffinate from the H3PO4 extn. is treated by H2SO4 for the regeneration of the spent HNO3. HNO3 is extd. by iAmOH and concd. by distn. before reuse in further leaching. Evidence on the tech. feasibility of the process was established. The process is economically viable.
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17. 17
  Ionkov, K.; Gaydardzhiev, S.; Correa de Araujo, A.; Bastin, D.; Lacoste, M. Amenability for processing of oolitic iron ore concentrate for phosphorus removal. Miner. Eng. 2013, 46-47, 119– 127, DOI: 10.1016/j.mineng.2013.03.028
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  Amenability for processing of oolitic iron ore concentrate for phosphorus removal
  Ionkov, K.; Gaydardzhiev, S.; Correa de Araujo, A.; Bastin, D.; Lacoste, M.
  Minerals Engineering (2013), 46-47 (), 119-127CODEN: MENGEB; ISSN:0892-6875. (Elsevier Ltd.)
  Beneficiation routes aimed at dephosphorisation of oolitic gravity magnetic conc. and involving a combination of roasting, re-grinding, magnetic sepn. and water and acid leaching are investigated. Roasting was carried out at 900 °C for 1 h without or with lime or sodium hydroxide as roasting additives. When additives were used, cement phases of Si-Al-Na-Ca-O type were detected as well as the mineral giuseppettite. During the thermal process sodium silicate is liquefied and the newly formed phases coat the oolites and penetrate inside the cracks. Energy Dispersive Spectroscopy anal. has indicated that the zone surrounding the oolites consists of Na, Al and Si phases with part of phosphorus being captured there. As a result of the alk. roasting, goethite is partly transformed to magnetite and this redn. is reinforced with an increase in sodium hydroxide dosage. Investigation of redistribution of phosphorous shows that it could be only partly sepd. if leaching is not accompanied by re-grinding and phys. sepn. The recommended dosage of the reductive agent for the final flowsheet is 8 mass% ratio to conc. Grinding to a mean size of 0.040 mm, with water and acid leaching and double magnetic sepn. creates conditions to obtain a high-quality iron conc. with 65.97% Fe and recovery of 92.43%, with simultaneous decrease in the phosphorus content from 0.71% to 0.05%.
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18. 18
  Li, G.; Zhang, S.; Rao, M.; Zhang, Y.; Jiang, T. Effects of sodium salts on reduction roasting and Fe-P separation of high-phoshorus oolitic hematite ore. Int. J. Miner. Process. 2013, 124, 26– 34, DOI: 10.1016/j.minpro.2013.07.006
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  18
  Effects of sodium salts on reduction roasting and Fe-P separation of high-phosphorus oolitic hematite ore
  Li, Guanghui; Zhang, Shuhui; Rao, Mingjun; Zhang, Yuanbo; Jiang, Tao
  International Journal of Mineral Processing (2013), 124 (), 26-34CODEN: IJMPBL; ISSN:0301-7516. (Elsevier B.V.)
  Effects of sodium salts on redn. roasting and Fe-P sepn. of high-phosphorus oolitic hematite ore were studied in the process of coal-based direct redn. followed by wet magnetic sepn. Various parameters, including reducing temp. and time, type and dosage of sodium salts, grinding fineness of magnetic sepn. feed and magnetic field intensity were investigated. The results of redn. and Fe-P magnetic sepn. are significantly improved by the addn. of sodium sulfate and borax, in comparison with those in the absence of additives. A magnetic conc. with total iron grade of 92.7% and phosphorus content of 0.09% was obtained from an oolitic hematite ore contg. 48.96% iron and 1.61% phosphorus when reduced in the presence of 7.5% sodium sulfate and 1.5% borax and wet magnetic sepd. under the proper conditions. The results of optical microscopy and X-ray diffraction (XRD) analyses of reduced pellet reveal that metallic iron grains exist in sizes of 10-20 μm and are assocd. with gangue minerals closely when reduced in the absence of sodium salts. By contrast, the oolitic structure is destroyed and metallic iron grains grow markedly to the mean size of 50 μm when reduced in the presence of sodium sulfate and borax. Sodium salts are capable of destroying the oolitic structure via reacting with gangues, enhancing the redn. of iron oxide and promoting the growth of metallic iron grains during redn., which is beneficial for Fe-P sepn. of the oolitic hematite ore.
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19. 19
  Omran, M.; Fabritius, T.; Elmahdy, A. M.; Abdel-Khalek, N. A.; Gornostayev, S. Improvement of phosphorus removal from iron ore using combined microwave pretreatment and ultrasonic treatment. Sep. Purif. Technol. 2015, 156, 724– 737, DOI: 10.1016/j.seppur.2015.10.071
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  19
  Improvement of phosphorus removal from iron ore using combined microwave pretreatment and ultrasonic treatment
  Omran, Mamdouh; Fabritius, Timo; Elmahdy, Ahmed M.; Abdel-Khalek, Nagui A.; Gornostayev, Stanislav
  Separation and Purification Technology (2015), 156 (Part_2), 724-737CODEN: SPUTFP; ISSN:1383-5866. (Elsevier B.V.)
  Most of the past studies examd. the effects of ultrasonic treatment on the removal of phosphorus, silica and alumina minerals from iron ores. In the present work, the effect of combined microwave pretreatment and ultrasonic treatment on the efficiency of disintegration and removal of phosphorus and other gangue minerals assocd. with iron ores was studied. Three different iron ore samples have varying total iron concn. (TFe) and P2O5 content and mineralogical textures were studied. Microwave pretreatment generated intergranular fractures between the gangues (fluorapatite and chamosite) and oolitic hematite. These intergranular fractures improved liberation of iron ore, and accelerated ultrasonic disintegration and removal of phosphorus and gangue minerals from oolitic hematite. Microwave pretreatment increases the efficiency of ultrasonic disintegration and removal of particles by ∼20% compared to untreated sample. The results of ultrasonic treatment are quite promising. Significant increase in iron grade and redn. in phosphorus and alumina content of enriched product can be obtained. Depending on the sample texture and phosphorus distribution, ∼59% phosphorus removal can be obtained.
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20. 20
  Wang, H.; Li, G.; Yang, J.; Ma, J.; Khan, B. S. The behavior of phosphorus during reduction and carburization of high-phosphorus oolitic hematite with H₂ and CH₄. Metall. Mater. Trans. B 2016, 47, 2571– 2581, DOI: 10.1007/s11663-016-0709-7
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  The Behavior of Phosphorus During Reduction and Carburization of High-Phosphorus Oolitic Hematite with H2 and CH4
  Wang, Henghui; Li, Guangqiang; Yang, Jian; Ma, Jianghua; Khan, Babar Shahzad
  Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science (2016), 47 (4), 2571-2581CODEN: MTBSEO; ISSN:1073-5615. (Springer)
  High-phosphorus oolitic hematite has not been widely utilized due to high content of phosphorus. Ca3(PO4)2 is the main component contg. phosphorus in high-phosphorus oolitic hematite. In the present work, the thermodn. was studied for Ca3(PO4)2 redn. by H2 gas and then carburization by CH4 gas. The results show that phosphorous in Ca3(PO4)2 cannot be reduced from gangue during the redn. of hematite and the formation of iron carbide at the temp. from 923 K to 1073 K (650 °C to 800 °C), in H2 and CH4 atmosphere. Redn. and carburization expts. were carried out. And phosphorus in reduced and carburized specimens was analyzed by EDS and wet chem. method. The results confirmed that phosphorous cannot be reduced during the prepn. of iron carbide from this iron ore. So the metallic iron or iron carbide can be prepd. without the redn. of phosphorous at relatively low temp., which can be a new route of utilizing high-phosphorus oolitic hematite. After fine milling-magnetic sepn., the 99.47 pct of Fe3C-contg. material was recovered, but the dephosphorization rate reached to 19.37 pct only.
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21. 21
  Gao, J.; Guo, L.; Guo, Z. Separation of P phase and Fe phase in high phosphorus oolitic iron ore by ultrafine grinding and gaseous reduction in a rotary furnace. Metall. Mater. Trans. B 2015, 46, 2180– 2189, DOI: 10.1007/s11663-015-0400-4
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  Separation of P Phase and Fe Phase in High Phosphorus Oolitic Iron Ore by Ultrafine Grinding and Gaseous Reduction in a Rotary Furnace
  Gao, Jintao; Guo, Lei; Guo, Zhancheng
  Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science (2015), 46 (5), 2180-2189CODEN: MTBSEO; ISSN:1073-5615. (Springer)
  Due to the oolitic structure of the high phosphorus iron ore and the closely wrapping of apatite and hematite phases, an approach using jet mill was utilized to grind the ore to ultrafine 0.01 to 0.001 mm, which realizes the dissocn. of apatite phase and hematite phase. Then in a lab. scale rotary furnace, high phosphorus ores of different sizes were reduced by reducing gas at sub-m.p. temps. (973 to 1173 K [700 to 900 °C]). In the rotating inclined reactor, the ore particles reacted with the reducing gas coming from the opposite direction in a rolling and discrete state, which greatly improved the kinetic conditions. In this study, the reaction rate increases significantly with the decrease of particle size. For the ultrafine high phosphorus iron ores, the metalization ratio can reach 83.91 to 97.32 pct, but only 33.24 to 40.22 pct for powders with the size of 0.13 to 0.15 mm. The reduced particles maintained their original sizes, without the presence of sintering phenomenon or iron whisker. Hence, two kinds of products were easily obtained by magnetic sepn.: the iron product with 91.42 wt pct of Fe and 0.19 wt pct of P, and the gangue product with 13.77 wt pct of Fe and 2.32 wt pct of P.
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22. 22
  Jang, K.-o.; Nunna, V. R. M.; Hapugoda, S.; Nguyen, A. V.; Bruckard, W. J. Chemical and mineral transformation of a low grade goethite ore by dehydroxylation, reduction roasting and magnetic separation. Miner. Eng. 2014, 60, 14– 22, DOI: 10.1016/j.mineng.2014.01.021
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  Chemical and mineral transformation of a low grade goethite ore by dehydroxylation, reduction roasting and magnetic separation
  Jang, Kyoung-oh; Nunna, Venkata R. M.; Hapugoda, Sarath; Nguyen, Anh V.; Bruckard, Warren J.
  Minerals Engineering (2014), 60 (), 14-22CODEN: MENGEB; ISSN:0892-6875. (Elsevier Ltd.)
  The utilization of abundant low grade goethite (α - FeOOH) ores is potentially important to many countries in the world, esp. Australia. These ores contain many detrimental impurities and are difficult to upgrade to make suitable concs. for the blast furnace. In this paper, chem. and mineral transformations of a goethite ore were studied by dehydroxylation, redn. roasting in CO and CO2 gas mixts., and magnetic sepn. The goethite sample was taken from a reject stream at an iron ore mine from the Pilbara region, Western Australia. The roasting temp. range investigated was 400-700 °C. Chem. and mineralogical anal. was conducted using XRF, XRD, optical microscope, EPMA, and SEM. Magnetic sepn. was conducted using a Davis tube tester and a high intensity magnetic separator. The results show that redn. roasting can remove moisture and impurities but does not significantly change the Fe content in the feed. However, redn. roasting transforms goethite to hematite and eventually maghemite which can be recovered by magnetic sepn., allowing upgrading. Further studies are needed to optimize the redn. roasting and correlate it with the magnetic sepn. to maximize the efficiency of iron upgrading.
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23. 23
  Zhu, D.; Chun, T.; Pan, J.; Lu, L.; He, Z. Upgrading and dephosphorization of Western Australian iron ore using reduction roasting by adding sodium carbonate. Int. J. Miner., Metall. Mater. 2013, 20, 505– 513, DOI: 10.1007/s12613-013-0758-8
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  Upgrading and dephosphorization of Western Australian iron ore using reduction roasting by adding sodium carbonate
  Zhu, De-qing; Chun, Tie-jun; Pan, Jian; Lu, Li-ming; He, Zhen
  International Journal of Minerals, Metallurgy and Materials (2013), 20 (6), 505-513CODEN: IJMMLM; ISSN:1674-4799. (Springer)
  The technol. of direct redn. by adding sodium carbonate (Na2CO3) and magnetic sepn. was developed to treat Western Australian high phosphorus iron ore. The iron ore and reduced product were investigated by optical microscopy and SEM. It is found that phosphorus exists within limonite in the form of solid soln., which cannot be removed through traditional ways. During redn. roasting, Na2CO3 reacts with gangue minerals (SiO2 and Al2O3), forming aluminum silicate-contg. phosphorus and damaging the ore structure, which promotes the sepn. between iron and phosphorus during magnetic sepn. Meanwhile, Na2CO3 also improves the growth of iron grains, increasing the iron grade and iron recovery. The iron conc., assaying 94.12wt% Fe and 0.07wt% P at the iron recovery of 96.83% and the dephosphorization rate of 74.08%, is obtained under the optimum conditions. The final product (metal iron powder) after briquetting can be used as the burden for steelmaking by an elec. arc furnace to replace scrap steel.
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24. 24
  Yang, M.; Zhu, Q.; Fan, C.; Xie, Z.; Li, H. Roasting-induced phase change and its influence on phosphorus removal through acid leaching for high-phosphorus iron ore. Int. J. Miner., Metall. Mater. 2015, 22, 346– 352, DOI: 10.1007/s12613-015-1079-x
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  Roasting-induced phase change and its influence on phosphorus removal through acid leaching for high-phosphorus iron ore
  Yang, Min; Zhu, Qing-shan; Fan, Chuan-lin; Xie, Zhao-hui; Li, Hong-zhong
  International Journal of Minerals, Metallurgy and Materials (2015), 22 (4), 346-352CODEN: IJMMLM; ISSN:1674-4799. (Springer)
  In the present study, roasting-induced phase change and its influence on phosphorus removal via leaching has been investigated for high-phosphorus iron ore. The findings indicate that phosphorus in the ore is assocd. with goethite and exists mainly in amorphous Fe3PO7 phase. The phosphorus remains in the amorphous phase after being roasted below 300°C. Grattarolaite (Fe3PO7) is found in samples roasted at 600-700°C, revealing that phosphorus phase is transformed from the amorphous form to cryst. grattarolaite during roasting. Leaching tests on synthesized pure grattarolaite reveal a low rate of phosphorus removal by sulfuric acid leaching. When the roasting temp. is higher than 800°C, grattarolaite is found to react with alumina to form aluminum phosphate, and the reactivity of grattarolaite with alumina increases with increasing roasting temp. Consequently, the rate of phosphorus removal also increases with increasing roasting temp. due to the formation of acid-sol. aluminum phosphate.
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  Mochizuki, Y.; Tsubochi, N. Removal of gangue component in low grade iron ore by hydrothermal treatment. Hydrometallurgy Accepted.
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  Naono, H.; Nakai, K. Thermal decomposition of γ-FeOOH fine particles. J. Colloid Interface Sci. 1989, 128, 146– 156, DOI: 10.1016/0021-9797(89)90393-7
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  Thermal decomposition of iron hydroxide oxide (γ-FeOOH) fine particles
  Naono, H.; Nakai, K.
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  γ-FeOOH nuclei were grown in acidic medium. The particles have the well-developed (010) surface giving the surface homogeneity. Thermal decompn. was carried out in vacuo at 130-500°. With the progress of decompn., the homogeneity of the (010) surface of γ-FeOOH disappears rapidly and microporous γ-Fe2O3 is formed in the γ-FeOOH matrix. Porous textures of the decompd. samples were investigated by electron microscopy and gas adsorption. Microporous γ-Fe2O3 consists of slit-shaped micropores 0.9 nm in width and plate-like crystallites 2.4 nm in thickness, which are regularly arranged parallel to the needle axis of acicular particles. At > 200°, the microporous texture is destroyed and a mesoporous or macroporous texture results. The mechanism of the thermal decompn. of γ-FeOOH fine particles is discussed based on the formation of the microporous texture and the previously established topotactic relation between γ-FeOOH and γ-Fe2O3.
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  MacRae, C. M.; Wilson, N. C.; Pownceby, M. I.; Miller, P. B. The occurrence of phosphorus and other impurities in Australian iron ores. Proceedings iron ore conference, Australasian Institute of Mining and Metallurgy, 2011, 281– 289.
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  About 90% of the titanium deposits in China are located in the Panzhihua area. The dissoln. of Panzhihua ilmenite ore in sulfuric acid was investigated. The kinetic expts. were carried out with an initial acid/ilmenite wt. ratio of 500:15, sulfuric acid concn. of 15.4 M and temp. 100-198°. The leaching kinetics can be described by a shrinking-core model. Both surface reaction and diffusion through the product layer promote the leaching rate. The kinetics can be expressed by an equation which is given. The apparent activation energy was estd. to be 72.6 kJ/mol. This kinetic relationship was used to simulate non-isothermal and the pseudo-adiabatic expts. under industrial conditions. The simulated values were consistent with the exptl. data.
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Upgrading Low-Grade Iron Ore through Gangue Removal by a Combined Alkali Roasting and Hydrothermal Treatment

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Abstract

Introduction

Results and Discussion

Removal of Gangue Component during Hydrothermal Treatment with NaOH

Effect of Alkali Roasting on Gangue Removal with Distilled Water Leaching at Room Temperature

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Removal of Gangue by Combination of Alkali Roasting and H2O Hydrothermal Treatments

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Effect of Calcination and Roasting Temperatures on Gangue Removal

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Removal of Gangue by Combination of Alkali Roasting and NaOH Hydrothermal Treatments

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Conclusions

Experimental Section

Sample

Hydrothermal Treatment

Alkali Roasting

Characterization

Author Information

Acknowledgments

References

Cited By

Abstract

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References

STEP 1:

STEP 2:

Removal of Gangue by Combination of Alkali Roasting and H₂O Hydrothermal Treatments