SORPTION AND DESORPTION OF Pb2+ AND Cu2+ IN DIFFERENT TUNISIAN SOILS

Sorption and retention are the major processes for the accumulation of potentially toxic trace elements and its study is of great importance to understand the fate of trace elements in soils. Sorption and retention capacities of five Tunisian soils and the soil mineral influence were studied by Pb2+ and Cu2+ batch sorption experiments and scanning electron microscope (SEM) analysis. It has been shown that sorption and retention of Pb2+ are most influenced by cation exchangeable capacity (CECe), clay contents, Mn oxides and carbonate contents, whereas Cu2+ sorption and retention are most influenced by the total organic carbon (TOC) and carbonate contents. The alkalinity of the majority of soils due to their carbonate contents lead to increase of both Pb2+ and Cu2+ precipitation and high sorption capacity. The sorption irreversibility is higher in soils of highest alkalinity, TOC, CECe, and clay contents. The Energy Dispersive Spectrometer (EDS) semi-quantitative analysis performed by SEM demonstrates that calcite contents decreased when soils were treated with Pb2+ giving rise to a new crystalline phase and mostly amorphous phases with high Pb2+ fixing capacity. Hematite and calcite preferentially retain Cu2+.