Modeling the competitive adsorption of Pb, Cu, Cd, and Ni onto a natural heterogeneous sorbent material (Italian Red soil)

The use of Italian Red Soil as an alternative low-cost sorbent material has been investigated for heavy metal removal in multicomponent systems. Pb, Cu, Cd, and Ni adsorption was studied at fixed pH (6.0) and constant ionic strength (0.1 mol L-1 by NaNO3) by a flowthrough reactor setup performing monocomponent and binary adsorption tests and sequential extraction. The whole set of experimental data was represented by a competitive model based on the surface complexation concept. High Pb and Cu adsorption was largely due to a surface complexation mechanism, whereas lower Cd and Ni adsorption was due to cation-exchange reactions. Sequential extraction results independently substantiated the different adsorption behavior. Pb and Cu adsorption was not significantly affected by the presence of the other metals, whereas Cd and Ni strongly compete with each other and were displaced in the presence of Pb and Cu. Red Soil was effective in the removal of heavy metals from contaminated aqueous streams in competitive conditions if compared with other low-cost sorbents.