Quantitative analysis and equilibrium models of selective adsorption in multimetal systems using a bacterial biosorbent

This study investigated the behavior of selective adsorption on the biomass of Pseudomonas aeruginosa PU21 (Rip64) with solutions containing Pb, Cu, and Cd. Experiments were designed to quantitatively justify the biosorption preference of the biomass for the three metals. The multimetal adsorption equilibria were described by three models, two of which originated from single-component Langmuir isotherm, and the third one was established empirically. The multimetal adsorption results show that lead and copper significantly inhibited the adsorption of cadmium, while the effects of Cd on the adsorption of Cu and Pb were limited Lead was found to exhibit a slightly higher inhibition effect on Cu when the two adsorbate coexisted. The data obtained from the ion-exchange systems indicate that Pb and Cu appreciably replaced the preadsorbed Cd ions from the biosorbent, but the competition of Pb and Cu for the adsorption sites was comparative. For three-metal biosorption with equal initial molar concentrations, the relative surface coverage of Pb, Cu, and Cd on the biomass was approximately 55, 40, and 5%, respectively. A modified Langmuir-type model (Model 2), which took account of the heterogeneity and specificity of the adsorption sites, described the experimental results better than the traditional Langmuir isotherm (Model 1) did. Of the three models examined, the empirical one (Model 3) showed the best fits for the two-metal adsorption data, whereas Model 2 had better prediction for the ternary adsorption results. In Model 3 the parameters determined from binary systems can be extrapolated to predict the adsorption equilibria of three-metal adsorption systems satisfactorily.