Modified clay as soil amendment for remediation: Studies of leaching and sorption kinetics

Soil contamination with metals and metalloids is serious environmental problem nowadays, caused mainly by intensive anthropogenic activities such as industry, traffic or mining. Soil remediation regarding metals and metalloids in polluted sites includes methodologies based on chemical precipitation, ion exchange, carbon adsorption, membrane filtration, adsorption and co-precipitation. Soil amendments that affect metal immobilization can be used for remediation of soil. Use of clay, natural (raw) or modified, as a soil amendment is one of the most perspective soil remediation methodologies due to the efficiency and cost effectiveness. Clay consists of crystalline-hydrated aluminosilicates and it has high exchange capacity that is important property for the process of binding of metals and metalloids. Efficiency of clay as an immobilization agent for metal binding was tested by sorption and batch leaching tests. Sorption capacity for raw and modified clay samples was experimentally tested under various pH and temperature conditions. Samples of modified clay as a sorbent were tested for sorption of Pb as monocontaminant and at complex contamination of metals. Clay modification was done by using Ca and Na salts, HNO₃ (protonated forms), Fe-oxyhydroxide, hydroxyapatite. Higher sorption capacity was observed for clay modified with hydroxyapatite and Ca salts. Sorption capacity increased with a rise of temperature at the optimum pH 5.0-5.5. Immobilization of metals with cheap soil amendments such as clay in situ is effective method for reduction of environmental hazards with low and medium target concentrations of metals or metalloids at relatively stable environmental conditions. Increased efficiency of a soil amendment can be reached by using clay modified with hydroxyapatite.