Concurrent sorption of Ni²⁺ and Cu²⁺ by Chlorella vulgaris from a binary metal solution

Abstract.

Kinetics and capacity of Ni²⁺ and Cu²⁺ sorption by Chlorella vulgaris were studied using single and binary metal solutions at various concentrations of these metal ions. The second-order rate law best described the kinetics of metal sorption from both single and binary metal systems. C. vulgaris preferentially sorbed Cu²⁺ over Ni²⁺ in the binary system. In comparison to the single metal system, the amounts of Ni²⁺ and Cu²⁺ sorbed at equilibrium (q _e) were respectively 73% and 25%, and the initial rate of sorption (h) was ca. 50% in the case of the binary metal system. The test metals inhibited sorption of each other, thereby indicating competition between Ni²⁺ and Cu²⁺for sorption onto non-specific binding sites. The present study showed that C. vulgaris has specific as well as non-specific sites for the binding of Ni²⁺ and Cu²⁺. Participation of these sites for sorption depended on the ratio of Ni²⁺ and Cu²⁺ in solution. The maximum metal sorption capacity of C. vulgaris was 6.75 mmol g^–1 from the binary metal solution at the tested biomass concentration (100 mg dry weight l^–1). Total metal sorption was enhanced with increasing total concentration of both the metals up to 1.6 mM, beyond which a decrease occurred. Two-dimensional contour plots were successfully used for the first time for the evaluation of metal sorption potential.