Biosorption is a relatively new process that has proven very promising in the removal of contaminants from aqueous effluents. Microorganisms as well as plant- and animal-derived materials have been used as biosorbents by many researchers. Biomaterial immobilization and chemical modification improves the adsorption capacity and stability of biosorbents. Biosorption experiments over Cu(II), Cd(II), Pb(II), Cr(III), and Ni(II) demonstrated that biomass Cu(II) adsorption ranged from 8.09 to 45.9 mg g−1, while Cd(II) and Cr(VI) adsorption ranged from 0.4 to 10.8 mg g−1 and from 1.47 to 119 mg g−1, respectively. Mechanisms involved in the biosorption process include chemisorption, complexation, surface and pore adsorption-complexation, ion exchange, microprecipitation, hydroxide condensation onto the biosurface, and surface adsorption. Chemical modification and spectroscopic studies have shown that cellular components including carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties have metal binding properties and are therefore the functional groups in the biomass. Column studies using support matrices for biomass immobilization such as silica, agar, polyacrilamide, polysulfone, alginates, cellulase, and different cross-linking agents have been performed to improve the biomass adsorption capacity and reusability. In this review, the salient features of plant-derived materials are highlighted as potential phytofiltration sources in the recovery of toxic heavy and precious metals.
Metal-binding studies for a de novo designed calcium-binding protein
