Effect of phosphate-mineralized bacteria on multi-metals migration behavior in vanadium tailing slags: Coexistence of immobilization and mobilization

Biomineralization techniques have been utilized to remediate heavy metals (HMs) contaminated environments. However, the effect of microbial-induced phosphate precipitation (MIPP) on HMs behavior in vanadium tailing slags has not been revealed. This study is the first to report the influence of MIPP on multiple HMs including Cd, Cu, Pb and Zn in the slags with and without soil mixing. The results showed that MIPP exhibited excellent ability for Cd immobilization, Cd immobilization rate reached 43.41% under the optimal parameters within 7 days. Cd immobilization performance was significantly improved and sustained after the slags were covered with soil, resulting from better colonization of phosphate mineralizing bacteria in slag-soil mixtures. Surprisingly, DTPA-Cu, Zn and Pb contents in slags were all increased to varying degrees after MIPP treatment. Leaching solution mineralization tests further suggested that MIPP significantly reduced the concentration of Cd²⁺, Pb²⁺, Ca²⁺, Mg²⁺ and Al³⁺, but barely changed Cu²⁺ and Zn²⁺ concentrations. Characterization analysis confirmed that formation of phosphates including Cd(PO₄)₂ and dissolution of minerals including PbZnSiO₂ were the reason for HMs immobilization and mobilization in vanadium tailing slags. This study provides new insights for understanding biomineralization technology and using MIPP to remediate HMs contaminated mine waste.