Sorption behavior of heavy metal pollutants onto shales and correlation with shale geochemistry

Abstract

The sorption of lead (II) and cadmium ( II) on seven shales belonging to the Proterozoic Vindhyan basin, central India, and a black cotton soil, Mumbai, India, was studied and compared with sorbent geochemistry. The sorption equilibrium studies were conducted under completely mixed conditions in batch reactors ( pH = 5.0 and ionic strength = 0.01 M) at room temperature. The Freundlich model provided better fits to the experimental data compared to Langmuir model. High cadmium and lead sorption was observed for the calcareous shales with greater than 5% CaCO(3). The Freundlich isotherm parameter relating to sorption capacity, i.e., K(F), yielded a strong correlation with the calcium carbonate and calcium oxide content across the various geosorbents studied. The observed sorption pattern may be attributed to complex formation of CaCO(3) with Pb(2+) and Cd(2+) leading to surface precipitation. Moreover, the Ca(2+) present in the sorbents may also involve in ion exchange reaction with lead and cadmium.