Modeling Multi-Metal Ion Exchange in Biosorption

Abstract

Some types of dead microbial or seaweed biomass are capable of effectively binding heavy metals often through ion exchange. This biosorption can be used for purification of metal-bearing effluents. A recently developed two-site model for the ion exchange between divalent metal ions and protons in biosorption was extended to describe multi-site and multi-ion system behavior. A model case for two ion exchange sites and three ions was compared to the experimental data for the sorption of Cd, Cu, and Zn by protonated Sargassum fluitans biomass in systems containing two metal ions and protons at different pH values. The equilibrium constants were comparable to those obtained for systems where, in addition to protons, only one metal ion was present. This opens the possiblity of predicting the sorption performance for three-cation systems from equilibrium constants determined in two-cation systems. There was no interference between the sorbed species except for competition for the same sorption sites. The model was able to predict the equilibrium binding of all three ions as a function of pH and of the final metal concentrations. Only two equilibrium constants, which were valid for any pH and in the presence of any competing ion, were necessary for predicting the binding of each metal ion. The complete equilibrium state (final concentration and binding) can be predicted as a function of the initial state for a pH titration in the simultaneous presence of two metal ions when the equilibrium constants are used in the chemical equilibrium program MINEQL+.

Incorporation of selectivity factor in modeling binary component adsorption isotherms for heavy metals-biomass system

“…This denotes that the binding of metal ions onto rice straw predominantly occurred by surface complexation or chelation mechanism (as evidenced from FTIR results) and ion exchange in lesser extent. For the latter mechanism, it was found to be predominant in the biosorption using algae or seaweed biomass, as verified in several studies [24][25][26].…”

Advances in the biosorption of heavy metals

“…Ion exchange process apparently plays an important role in biosorption and this is reflected in appropriately different equilibrium models proposed for biosorption based on ion exchange principles (Schiewer, 1996;Schiewer and Volesky, 1995;Schiewer and Volesky, 1996;. A steep initial slope of a sorption isotherm indicates a sorbent which has a high capacity for the sorbate in the low residual (final, C f ) concentration range (high affinity).…”

Desorption of lanthanum, europium and ytterbium from Sargassum

“…L −1 ). The proton uptake was calculated according to [15] by the difference between the final and initial pH values and the amount of nitric acid used to adjust the pH of the sorption system.…”