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Green approach of chemical immobilization of lead in metal - contaminated soils of NCT of Delhi using rock phosphate

Mamta Chhabra Sharma, Reena Saxena, Sandeep K.Sharma, Suneeti Singh

In Chemical immobilization, an in situ remediation method, inexpensive chemical e.g., rock phosphate is used to reduce contaminant solubility in contaminated soil. We investigated the effectiveness of rock phosphate (RP), to reduce extractability and gastrointestinal (GI) bioavailability in two Cd- and Pb- contaminated soils from industrial sites in NCT of Delhi. The effect of soil treatment on metal extractability was evaluated by TCLP and on human GI availability of Pb from soil ingestion by the Physiologically Based Extraction Test (PBET). Rock phosphate GIavailable Pb in both gastric and intestinal solutions was, 23 and 92%, respectively. Rock phosphate decreases risk from exposure to Pb via the soil ingestion pathway. Leachability of metals in treated soil was measured by using a combination of batch and bench tests to evaluate the immobilization capability of applied treatments. For efficient immobilization, pH reduction with H3PO4 became necessary to dissolve carbonate-bound metals and make them readily available for the geochemically stable metal phosphate formation.