Integrated assessment of the liquid and solid phases of lead-contaminated soils remediated with phosphate

•The assessment of liquid and solid soil phases explain the Pb and P-remedied behavior.•The best molar ratio to reducing Pb in solution was 6:5 P:Pb.•The chloropyromorphite formation was quickly and consequently Pb soil remediation. The speciation of the ion activity in a soil solution is an important tool for modeling chemical equilibria to understand the mechanisms of mineral formation and stability. Consequently, it may be used to assess the efficiency of remediation processes. This study aims to assess the changes in a soil solution and their effects on the formation of chloropyromorphite in the solid phases of soils with contrasting textures that have been contaminated with Pb and remediated with phosphates. Two soils (loam Oxisol and clay Ultisol) both with a pH 5.8 and 7.0 were contaminated with two Pb doses (one and five times the dose corresponding to the maximum adsorption of Pb in each soil) and remediated with increasing doses of phosphates evaluated at 30, 60 and 311 days after the Pb incubation. Visual MINTEQ® software was used to simulate the main species of Pb and P in soil solutions, and chloropyromorphite formation was observed using electron microscopy and X-ray diffractometry. For both soils, chloropyromorphite formation and Pb2+ and H2PO4− inner sphere adsorption in clay minerals strongly influenced the pH of the solution. A 99.5% decrease in the level of Pb in solution was observed in the presence of P, and a higher level of chloropyromorphite formation was observed in the loam Oxisol. The theoretical models of chloropyromorphite stability in soil solutions efficiently predicted its formation and stability. As the incubation time increased, the equilibrium between the soil solution and chloropyromorphite formation was more evident. The integrated assessment of the liquid and solid phases increases the comprehensiveness and accuracy of studies of soil contaminated with Pb and remediated with P. Therefore, we recommend the application of 1.2 mol of P for each mol of Pb.