IN-SITU FORMATION OF LEAD PHOSPHATES IN SOILS AS A METHOD TO IMMOBILIZE LEAD

Considerable evidence, both theoretical and experimental, supports the assertion that lead phosphates are the most stable environmental soil lead form and that they may form rapidly when adequate phosphate is present. This study demonstrated that the weathering of galena to insoluble lead phosphates in soils at a port facility historically used for shipment of ore concentrates is due to the presence of adequate soil phosphate. Geochemical modeling indicated that the addition of a phosphate amendment to Pb-bearing soil would result in lead phosphate formation with an estimated aqueous lead solubility of 0.1 mu g/L in soil. Assessment of the potential lead bioavailability from ingestion of pyromorphite, which will be controlled by lead mineral dissolution in the acidic environment of the human stomach, indicated limited bioaccessibility of lead. The study results suggest that in situ lead stabilization through phosphate amendment may provide a cost-effective method for reducing the leaching, migration, and bioavailability of lead from soils.