Zinc Biosorption by Seaweed Illustrated by the Zincon Colorimetric Method and the Langmuir Isotherm

Heavy metals are major pollutants in marine, ground, industrial, and even treated waters. Sorption of heavy metals onto live or dead biological materials (biosorption) is a potential method of removing toxic metals. Zinc and two algae, Ulva sp. and Gymnogongrus torulosus, were evaluated in this study. A linear zinc calibration curve in the range 1–8 mg L^-1 was obtained using the zincon colorimetric method. In the biosorption assays, a rapid zinc uptake was observed and kinetic curves stabilized after 60 minutes. Experiments using initial zinc concentrations of 50 mg L^-1 showed that 20% and 60% of zinc ions were removed from solution by Ulva sp. and Gymnogongrus torulosus, respectively. Results obtained from varying initial zinc concentrations allowed data fitting to Langmuir model with a good correlation. The maximum zinc uptake capacity and affinity constant obtained for Gymnogongrus torulosus were higher than those for Ulva sp. Maximum zinc uptake capacities were 42.8 x10^-3 and 26.8 x10^-3 for Gymnogongrus torulosus and Ulva sp., respectively, while the affinity constants were 0.084 L mg^-1 and 0.019 L mg^-1, respectively. An interesting and simple experiment was developed to show the potential of algae in biosorption processes.