The influence of clay mineralogy on the retention of heavy metals in acidic environments

The role of clay soil fractions in partitioning heavy metals in acidic environments is evaluated in this study. The distribution of heavy metals in the clay soils, used in this study, is evaluated using batch equilibrium tests and selective sequential extraction techniques. Pure kaolinite, a kaolinite-mixture with carbonates (KC) or silica gel (KS), and kaolinite mixed with both silica gel and carbonates (KSC) were exposed to two types of heavy metal contaminant solutions. Contaminant concentrations in the solutions were varied for various test series where retention capacities of the test soils were determined. Selective sequential extractions was conducted for all the contaminant- retention tests series. Results obtained indicate a maximum retention of KSC for both heavy metals with increasing acid concentrations. This is attributed to its high buffer capacity at a pH above 5.5. Dissolution of carbonates at low pH levels appears to be responsible for the decreased amounts of heavy metals retained by the carbonate phase at low pH values. The amounts of heavy metals retained in the exchangeable phase of KS, are higher than those in other soils because of the much higher CEC of silica gel