Concentration effects of EDTA and chloride on the retention of trace metals in clays

This study investigates the heavy-metal retention potential of complexing agents in a clay soil with different constituents. The organic and inorganic effects, respectively, of EDTA and sodium chloride were considered. Kaolinite and kaolinite mixtures [including kaolinite mixed with silica gel and calcium carbonate (KS, KC, KSC)] were exposed to two types of trace-metal solution, namely lead and zinc with increasing amounts of chloride and EDTA concentrations. The retention of each mixture was measured. It was demonstrated that with increasing concentrations of a complexing component such as EDTA, the retention of trace metals significantly decreased in all types of soil model. The results were also verified through SEM and XRD analyses. Moreover, increases in chloride concentration affected the trace-metal retention in kaolinite with a low affinity for adsorption. This retention varied with the soil constituents, cation exchange capacity (CEC), specific surface area (SSA) and pH of the soil solution. (C) 2000 Elsevier Science B.V. All rights reserved.