Stabilization of oxidic tailings and contaminated soils by calcium oxyphosphate addition: the case of Montevecchio (Sardinia, Italy)

摘要

The effectiveness of an in situ heavy metals fixation technique aimed at converting contaminants to low solubility and low bioavailability forms, eliminating the risk posed by oxidic tailings and contaminated soils, was investigated. Calcium oxyphosphate salt (Ca(H2PO4)2 H2O) was used as a stabilizing agent for oxidic tailings and contaminated soils originating from Montevecchio, Sardinia, Italy. Stabilization was effected by mixing the contaminated soil or oxidic tailing sample with calcium oxyphosphate salt at various doses. The effectiveness of stabilization was evaluated by US Environmental Protection Agency Toxicity Characteristic Leaching Procedure (TCLP) standard toxicity testing. Complementary EDTA extraction tests and biological tests using beans (Phaseolus vulgaris) as plant indicator were carried out. The toxicity of Pb and Cd was reduced below TCLP regulatory limits at calcium oxyphosphate doses higher than 0.7 and 0.2% w/w for soils and tailings, respectively. Lead solubility according to the EDTA test decreased with phosphate dose for both materials tested. Lead uptake by plant leaves and roots from the soil sample decreased with the phosphate addition, while Cd uptake remained almost constant. An adverse effect on plant growth andZn uptake was observed for calcium oxyphosphate dose up to 1.1% w/w. Based on the results, a remediation scheme for oxidic tailings and contaminated soils is proposed.