Phosphate-induced lead immobilization from different lead minerals in soils under varying pH conditions 2017-11-27

Xinde Cao, Lena Q. Ma, Satya P. Singh, Qixing Zhou

Abstract

This study investigated phosphate-induced lead immobilization from different Pb minerals in soils under varying pHs. Four soils were used, including one Pb-contaminated soil (NC-Soil) and three soils spiked with litharge (PbO), cerrusite (PbCO₃), or anglesite (PbSO₄), referred to as PbO-soil, PbCO₃-soil, and PbSO₄-soil, respectively. The soils were equilibrated with KCl and Ca(H₂PO₄)₂*H₂O under pH of 3-7. At low pH (3 and 5), Pb solubility followed PbO-soil > PbCO₃-soil > PbSO₄-soil; while at pH = 7, it was PbSO₄-soil > PbO-soil > PbCO₃-soil. Phosphate decreased Pb dissolution time from >180 to <60 min and reduced soluble Pb by 67-100%. This was mostly via transformation of Pb minerals into chloropyromorphite [Pb₅(PO₄)₃Cl]. Our results indicated that P addition can effectively transform various Pb minerals into insoluble chloropyromorphite in soils. This transformation was more significant at acidic condition (e.g., pH <= 5). Among the three Pb minerals tested, PbSO₄ was the most effectively immobilized by P, followed by PbO and PbCO₃. This study clearly demonstrated the importance of the form of Pb contamination and soil pH in determining the effectiveness of Pb immobilization in soils.

Published by Elsevier Ltd.