Study on the adsorption of cadmium and zinc by chlorella vulgaris

Abstract

The ability of algae to accumulate heavy metals from the surrounding environments is a widely recognized phenomenon that has a number of important implications. The metal binding characteristics of Chlorella vulgaris were investigated. Metal uptake by intact algal cells was found to consist of two processes ; (1) a fast, metabolism-independent surface reaction and (2) metabolism-dependent slow uptake. The effect of environmental variables on cadmium and zinc uptake was examined, and a striking pH effect for bioaccumulation was observed with metal adsorption being exerted an influence on by ionic strength in some degree. These results suggested that an ion-exchange mechanism accounts for the majority of metal adsorption. Equilibrium parameters governing the metal adsorption process were obtained by Scatchard analysis of both the cadmium and zine binding data. Carboxyl groups and aming groups of Chlorella vulgaris were modified for understanding of the effect of these fuctional groups on metal binding. Carboxyl-modified algae ahowed major decreases in Cd and Zn binding. Amine-modified algae also displayed some decreases in both metal adsorption, however, as exceeding a certain extent, the acetylation of amine groups increased metal uptake on the contrary. These results indicate that carboxyl groups on algal cells are responsible for a great portion of Cd and Zn binding, and that amine groups play auxiliary role as well.