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Article

Efficiency of Rice Bran for the Removal of Selected Organics from Water: Kinetic and Thermodynamic Investigations

Mubeena Akhtar,^† M. I. Bhanger,^† Shahid Iqbal,^† and S. Moosa Hasany*^§

National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan, and Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan

J. Agric. Food Chem., 2005, 53 (22), pp 8655–8662

DOI: 10.1021/jf058060h

Publication Date (Web): October 8, 2005

†

University of Sindh.

Corresponding author (e-mail hasany@pinstech.org.pk; fax +92-51-9290275; telephone +92-51-9290279).

Pakistan Institute of Nuclear Science and Technology.

Abstract

The sorption efficiency of indigenous rice (Oryza sativa) bran for the removal of organics, that is, benzene, toluene, ethylbenzene, and cumene (BTEC), from aqueous solutions has been studied. The sorption of BTEC by rice bran is observed over a wide pH range of 1−10, indicating its high applicability to remove these organics from various industrial effluents. Rice bran effectively adsorbs BTEC of 10 μg mL^-¹ sorbate concentration from water at temperatures of 283−323 ± 2 K. The effect of pH, agitation time between solid and liquid phases, sorbent dose, its particle size, and temperature on the sorption of BTEC onto rice bran has been studied. The pore area and average pore diameter of rice bran by BET method are found to be 19 ± 0.7 m² g^-¹ and 52.8 ± 1.3 nm. The rice bran exhibits appreciable sorption of the order of 85 ± 3.5, 91 ± 1.8, 94 ± 1.4, and 96 ± 1.2% for 10 μg mL^-¹ concentration of benzene, toluene, ethylbenzene, and cumene, respectively, in 60 min of agitation time using 0.1 g of rice bran at pH 6 and 303 K. The sorption data follow Freundlich, Langmuir, and Dubinin−Radushkevich (D−R) models. Sorption capacities have been computed for BTEC by Freundlich (32 ± 3, 61 ± 14, 123 ± 28, and 142 ± 37 m mol g^-¹), Langmuir (6.6 ± 0.1, 7.5 ± 0.13, 9.5 ± 0.22, and 9.4 ± 0.18 m mol g^-¹), and D−R isotherms (11 ± 0.5, 16 ± 1.3, 30 ± 2.2, and 33 ± 2.5 m mol g^-¹), respectively. The Lagergren equation is employed for the kinetics of the sorption of BTEC onto rice bran and first-order rate constants (0.03 ± 0.002, 0.04 ± 0.003, 0.04 ± 0.003, and 0.05 ± 0.004 min^-¹) have been computed for BTEC at their concentration of 100 μg mL^-¹ at 303 K. Studies on the variation of sorption with temperatures (283−323 K) at 100 μg mL^-¹ sorbate concentration gave thermodynamic constants ΔH (kJ mol^-¹), ΔG (kJ mol^-¹), and ΔS (J mol^-¹ K^-¹). The results indicate that the sorption of organics onto rice bran is exothermic and spontaneous in nature under the optimized experimental conditions selected. This sorbent has been used successfully to accumulate and then to determine benzene, toluene, and ethylbenzene in wastewater sample.