Enhancing pyromorphite formation in lead-contaminated soils by improving soil physical parameters using hydroxyapatite treatment.

During chemical immobilization in soil, enhancement of insoluble phases is required to prevent toxic metal from leaching into the surrounding environment. Understanding the effects of physicochemical parameters of soil on the reaction between lead and hydroxyapatite is important to enhance the formation of the insoluble pyromorphite-lead phase. However, the combined effect of soil physical parameters on pyromorphite formation and compressive strength has not been reported.

Formation of a lead-insoluble phase, pyromorphite, by hydroxyapatite during lead migration through the water-unsaturated soils of different lead mobilities.

This study combined the original unsaturated-column-percolation test with X-ray diffraction (XRD) analysis to understand how lead is transformed into lead-insoluble phase and immobilized by hydroxyapatite during lead migration in the water-unsaturated soil of different lead mobilities. The amounts of lead migrated from the soils without hydroxyapatite ranged from 4 to 46%, depending on the lead mobilities of soils. On the other hand, those of soils with hydroxyapatite were greatly suppressed by > 95% as compared with those without hydroxyapatite.

Simultaneous lead and antimony immobilization in shooting range soil by a combined application of hydroxyapatite and ferrihydrite.

This study investigated whether a combined application of hydroxyapatite and ferrihydrite could immobilize lead and antimony in shooting range soil in which the level of lead contamination is markedly higher than that of antimony. In addition, we evaluated the stability of lead and antimony immobilized by the combined application with varying soil pH. The levels of water-soluble lead and antimony for the combined application were lower than those of single applications of hydroxyapatite or ferrihydrite, indicating that the combined application could suppress the levels of water-soluble lead and antimony by 99.