A. Xenidis et al., Stabilization of oxidic tailings and contaminated soils by calcium oxyphosphate addition: The case of Montevecchio (Sardinia, Italy), J SOIL CONT, 8(6), 1999, pp. 681-697
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.