Sorption of cadmium, nickel, and zinc in mono- and multimetal systems

The sorption behaviour of Cd, Ni, and Zn was studied in monometal, as well as in multimetal competitive systems (binary and ternary). Metal sorption was described using the SRS equation, a multicomponent Freundlich-type isotherm curve fit model. It was found that Zn was more strongly bound than Cd and Ni, with the order of reduced sorption being Zn > Ni > Cd. Specific sorption onto clay lattice edges, as determined by the first hydrolysis product of the metals, seems to have been the mechanism that explained metal retention. It was also found that competition suppressed the sorption of all three metals. However, Zn was affected much less than Cd and Ni, probably because it was the most strongly retained metal of the three. The SRS equation successfully predicted the competitive sorption of the metals, as the observed experimental data were correlated satisfactorily with the predicted data (R2 = 0.95).