Abstract
Bioavailability of Pb in contaminated soils can be highly decreased by conversion of labile Pb species into pyromorphite Pb5(PO4)3Cl, induced by amendment with a phosphate source. However, PO43− can be specifically adsorbed on goethite α-Fe(OH)3 present in soils. We demonstrate that despite the stability of phosphate ions adsorbed on goethite surface, the reaction between goethite-adsorbed phosphates and aqueous lead in the presence of Cl− results in crystallization of pyromorphite. Two morphological forms of pyromorphite formed on goethite were observed: 1) incrustations, indicating direct reaction of Pb and Cl ions with PO43− adsorbed on goethite surface, and 2) aggregates of pyromorphite crystals indicating that the reaction with PO43− ions took place in the volume of the solution. This suggests that precipitation of pyromorphite is faster than desorption of phosphates and that aqueous Pb may serve as a sink for phosphate ions by shifting the equilibrium and inducing PO43− desorption.
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