Sorption of toxic metal ions by solid sorbents: a predictive speciation approach based on complex formation constants in aqueous solution

Heavy metal pollution constitutes one of the more compelling environmental problems. The use of biomass sorption has been proposed as an alternative to conventional methods for metal ion removal from wastewater, and the research on this topic has become very important. In this paper, after an overview on the conventional methods a brief survey of the chemical features of biosorbents is presented. Following the speciation studies briefly outlined in the previous literature we present here a speciation and simulation study of the behaviour of sorbing materials toward metal ions. This simulation is based on simple assumptions, which link solution complex formation equilibria to the two-phase sorption phenomena. Using a sorbent characterized by different surface groups as a model and lead as representative of toxic metal ions, this simulation allows us to draw some particular aspect of data collection and data treatment. Several aspects are presented which can be of great utility in designing rational data acquisition procedures and in drawing a correct interpretation of the results, but most of all a method is presented that can be profitably employed by people working in sorption research on their own systems.