In Situ Chemical Stabilization of lead Using Phosphate Compounds in a Calcareous Contaminated Soil

The objective of this study was to investigate the in situ stabilization of lead in a contaminated soil in the precense of P. A complex soil sample from 0-5 cm depth of the road side of Tehran- Qom was collected. In order to study the effect of P-treatment on the in situ stabilization of lead, a factorial experiment based on completely randomized design with three treatments of Diammonium phosphate (DAP), Triple Superphosphate (TSP) and 1:1 ratio acid phosphoric and phosphate rock at 3, 6 and 9 molar ratios of P/Pb, was conducted. Results of variance analysis and average comparison showed that among three phosphorous treatments, the highest transformation of soil Pb from the non-residual fractions (SS,SE,CA,Fe-Mn form and Pb in OM) to the residual fraction occured in DAP treatment and the lowest one in acid phosphoric and phosphat rock (P<0.01) treatment. Also results showed that the acid phosphoric phosphat rock, TSP and DAP could transform 18.3, 21.4 and 33.1% of the total nonresidul fractions into residual form. Results of X-ray Diffraction (XRD) analysis and comparison of treated soil with control, showed that adding phosphorous to soil resulted in the formation of pyromorphite mineral and DAP showed the highest peak intensity among three treatments.‌