Stability of autunite - final product of uranium immobilization by hydroxyapatite

One of the most important questions concerning efficacy of in situ remediation is: how stable is the final solid phase product incorporating the contaminant. To answer this question about remediation by hydroxyapatite (HAP) of soil contaminated by uranium, stability of autunite was examined. In this analysis we compared stability of HAP and autunite, representing the final product of this remediation process. Stability of solid phases was determined according to a theoretical criterion, based on the calculation of the ion-ion interaction potential, representing the main term of the cohesive energy. The obtained results demonstrate that transformation of HAP into autunite by acquisition of uranium is followed by a significant increase of the system stability. Immobilization of uranium into a highly stable autunite form significantly decreases its mobility and bioavailability in this way preventing contamination of groundwater and the food chain. These results point out apatite technology as a suitable approach for in situ remediation of soil contaminated with depleted uranium. (author)