Soil metal interactions and investigation of extractive metal removal pathways

Abstract

The aim of this work was to interprete the interaction of zinc with soils varying in composition and investigate methods for the removal of zinc from soil. The adsorption behaviour of zinc was evaluated with isotherms, kinetic studies and sequential fractionation. The findings derived from isotherms were in consistence with the results of sequential extraction experiments, suggesting the presence of more than two sites participating in the adsorption of zinc. Thus, it was presented that high affinity sites with high binding energies like iron and manganese oxides and carbonates were occupied at lower zinc concentrations, and low affinity sites with low binding energies like exchangeable sites at higher zinc concentrations. The removal of zinc with naturally occurring humic and fulvic acids was found to be low. The reason of this could not be explained by the number of functional groups involved in the extractions. The adsorption of humic and fulvic acid was proposed as the mechanism hindering the removal of zinc. The removal of zinc with synthetic chelating agents such as EDT A and DTPA increased with increasing EDT A and DTP A concentrations, revealing efficiencies over 100 %. These observations were well explained with the stoichiometric molar ratios and the pH dependent speciation of EDT A and DTP A. Sequentia.l extraction experiments helped to understand from which soil fraction zinc was taken by humic acid, EDT A and DTP A. Thus, humic acid preferred to remove zinc adsorbed by the exchangeable sites of soils, whereas EDT A and DTP A took the zinc associated with carbonates and iron and manganese oxides.