Immobilization and migration of arsenic during the conversion of microbially induced calcium carbonate to hydroxylapatite.

Coprecipitation with calcium carbonate (CaCO) could decrease the bioavailability of arsenic (As). However, in a phosphate-rich environment, some CaCO will be converted to hydroxylapatite (HAP). Currently, the behavior of carbonate-bound As during conversion is unclear. Therefore, we prepared bio-induced CaCO in an As solution and converted it to HAP. The results showed that a high concentration of arsenate promoted vaterite precipitation and the conversion of CaCO to HAP. The dissolution data verified the low solubility of As in HAP, though its As-bearing CaCO precursor released up to 88.19% As during the conversion. Furthermore, HPLC-ICP-MS data showed partial oxidation of arsenite to arsenate, suggesting that CaCO and HAP's structure favored the incorporation of arsenate. Our results demonstrated that the stability of heavy metal-bearing CaCO should be considered, and the role of HAP in the immobilization of heavy metals such as As should not be overestimated.