Lead-contaminated soils with contrasting texture remediated with phosphate: chemical fractionation and chloropyromorphite stability

Pb can be stabilized in soil as Pb-P mineral. The aims of this study were to access the distribution of Pb in organic and mineral fractions of contrasting texture of soil Pb-contaminated and remediated with P and Cl and to evaluate the stability of chloropyromorphite in these soils. A clay loam Oxisol (sandstone) and a clayey Ultisol (basalt) were used in a factorial experiment, with three replications: two soils, two Pb contamination levels, two soil pH values, and four P doses. The Pb concentrations were determined in seven soil phases. Release kinetics of Pb were performed with 0.1 mol L⁻¹ pH 2.5 citric acid. The transfer of soil Pb to chloropyromorphite was dependent on the level of contamination in the clay loam Oxisol. In the lowest P dose (molar ratios P:Pb 3:5), the main source was the Pb complexed in the organic matter and in the highest P dose (molar ratios P:Pb 12:5) was the Pb adsorbed by inner sphere in gibbsite and kaolinite. The release of Pb in the citric acid was dependent on the texture and mineralogy of the soils. Pb recovery applied to the clay loam Oxisol was around 100% (biphasic kinetic), while for the clayey Ultisol, the recovery ranged from 43 to 52% (single-phase kinetic). Remediation of Pb-contaminated soils with P and Cl is more efficient in clayey and oxidic soils since chloropyromorphite formation is faster and its solubilization is slower, an important combination in environmental terms.