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

The effectiveness of an in situ heavy metals fixation technique aimed at co nverting contaminants to low solubility and low bioavailability forms, elim inating the risk posed by oxidic tailings and contaminated soils, was inves tigated. Calcium oxyphosphate salt (Ca( H2PO4)(2). H2O) was used as a stabi lizing agent for oxidic tailings and contaminated soils originating from Mo ntevecchio, Sardinia, Italy. Stabilization was effected by mixing the conta minated soil or oxidic tailing sample with calcium oxyphosphate salt at var ious doses. The effectiveness of stabilization was evaluated by USEPA TCLP standard toxicity testing. Complementary EDTA extraction tests and biologic al tests using beans Phaseolous vulgaris as plant indicator were carried ou t. The toxicity of Pb and Cd was reduced below TCLP regulatory limits at ca lcium oxyphosphate doses higher than 0.7 and 0.2% w/w for soils and tailing s, respectively. Lead solubility according to the EDTA test decreased with phosphate dose for both materials tested. Lead uptake by plant leaves and r oots from the soil sample decreased with the phosphate addition, while Cd u ptake remained almost constant. An adverse effect on plant growth and Zn up take was observed for calcium oxyphosphate dose up to 1.1% w/w. Based on th e results, a remediation scheme for oxidic tailings and contaminated soils is proposed.