Characterization and optimization of Ni and Cu sorption from aqueous solution by Chlorella vulgaris

Sorption of Ni and Cu by Chlorella vulgaris showed the second-order rate kinetics. Change in biomass concentration altered the kinetic parameters of sorption. When biomass concentration was increased from 5 to 1000 mg l −1, the initial rates of sorption of Ni and Cu were reduced by about five- and three-times, respectively. The metal sorption capacity of the test alga was studied taking different concentrations of Ni and Cu at different biomass concentrations as well as different pH. The sorption of test metals fitted better in Freundlich than the Langmuir model thereby indicating multi-layer adsorption of Ni and Cu onto C. vulgaris. The K f and Q max both decreased with increase in biomass concentration thereby suggesting that the metal sorption capacity of the test alga was impaired at higher biomass concentrations. The maximum sorption of Ni and Cu occurred at pH 5.5 and 3.5, respectively. Heat-killed cells showed a greater potential of metal sorption than the live cells. The test alga was subjected to different pre-treatments to enhance its metal sorption capacity; acid (HCl and HNO 3) pre-treatments were most effective. The maximal removal of Ni and Cu, 93 and 96%, respectively, occurred from solutions having their 2.5 mg l −1 concentration. Thus C. vulgaris has a great potential for removing Ni and Cu especially when concentrations of these metals are low in the external environment.