Effect of phosphate treatment on the solubility of lead in contaminated soil

Abstract

Lead-contaminated soil was used for treatment testing with phosphate-based additives. Reactions controlling leached lead concentrations from soil before and after phosphate treatment were evaluated. The concentration of lead from untreated soil is controlled by a desorption reaction from hydrous metal oxides. Phosphate addition reduced lead solubility in the acidic pH range, but not in the alkaline range. The addition of chloride further reduced lead solubility. The phosphate-treated soil released lower concentrations of lead in simulated digestion tests.

Evaluating the applicability of regulatory leaching tests for assessing the hazards of Pb-contaminated soils

“…8) significantly reduced the leachability of Pb by all leachates in both soil types. This is due to the formation of lead phosphate precipitates, which are more insoluble compared to other lead precipitates, agreeing with the findings of other researchers [9,10,12,13,[33][34][35]. The similarities in leaching profiles for all leachates, despite the differences in pH, are due to the generally insoluble nature of the Pb-phosphate compounds over the range of final pH values obtained in this study.…”

“…It is immediately apparent that phosphate stabilization provided the greatest reduction in Pb leaching from both soils over the pH range studied, possibly due to the formation of stable Pb phosphate precipitates. Work by Wang et al [5] showed a greater than 87% reduction in the TCLP extractable concentrations of Pb from soil upon the addition of CaHPO 4 while similar findings on the use of phosphate stabilization have been observed by many other researchers [5,9,10,13,38,39]. Fig.…”

“…During cement stabilization, the contaminants in the soil can be retained either through adsorption onto the cement matrix, through precipitation as metal hydroxides due to the alkaline pH of cement, or through Pb incorporation into the cement matrix [6,7]. Phosphate stabilization has been widely used for wastes containing Pb as it involves the formation of very stable lead phosphate precipitates [8][9][10][11][12][13][14]. Pyromorphite compounds (Pb 5 (PO 4 ) 2 X; X = halide or hydroxide) have been the most common group of Pb phosphates detected in these studies [9][10][11], in addition to other Pb phosphate compounds such as drugmanite (Pb 2 (Fe,-Al)(PO 4 ) 2 (OH) 2 ) and plumbogummite (PbAl 3 (PO 4 ) 2 (OH) 5 ·H 2 O) [10].…”

Lead bioaccessibility in topsoils from lead mineralisation and urban domains, UK

“…Table 1 shows that the median P concentration in the Rookhope soils is a factor of 2.7 less than in the Derbyshire soils. A comparison of the solubility of Pb in soils with the addition of phosphate (Stanforth and Qiu, 2001) shows that the solubility is markedly reduced at pH 6, which is similar to the pH of the UBM stomach and intestine extraction (6.3). The SLR modelling, does not, however, indicate P as being significant in controlling the BSI-Pb.…”

Remediation of Metal-Contaminated Soil by Organic Metabolites from Fungi II—Metal Redistribution

“…Lead associated with other soil fractions is more mobile and, consequently, poses more threat to the environment and human health since it can easily be leached out from soils and reach surface waters and groundwater (Huang et al 2006). The purpose of numerous studies has been to stabilize lead by various immobilization techniques rather than attempting to mobilize the nonactive lead fractions (Ruby et al 1994;Stanforth and Qiu 2001;Chen et al 2003;Huang et al 2006). There are, however, potential risks when using immobilization and/or stabilization techniques, since the contaminants can once again become mobilized, due to processes not foreseen.…”