Formation of pyromorphite by hydroxyapatite in soil during lead migration through water-unsaturated soils

Abstract

Chemical immobilization using a hydroxyapatite is one of the promising approach to soil with high level lead (Pb) contamination. To enhance the effectiveness of Pb immobilization by the hydroxyapatite, it is important to understand that how Pb reacts with the hydroxyapatite and forms insoluble Pb phases in the soil pore. This study conducted the up-flow-unsaturated column percolation test with the combined application of X-ray diffraction (XRD) analysis to understand the relation between the amount of Pb migrated and Pb transformed into pyromorphite in the water-unsaturated soil with regarding to the distance of Pb migration. The XRD analysis could quantify the amounts of Pb as pyromorphite formed during the water percolation test. Pb existed as water-soluble gradually migrated from the soil in the layer to the soil in the next layer with the water percolation despite the presence of hydroxyapatite. In opposite, the formation of pyromorphite was favor in the soil near the inflow side.