β-tricalcium phosphate enhanced biomineralization of Cd2+ and Pb2+ by Sporosarcina ureilytica HJ1 and Sporosarcina pasteurii HJ2

Abstract

Microbiologically induced CaCO3 precipitation (MICP) has been proposed as a potential bioremediation method to immobilize contaminating metals. In this study, carbonate mineralizing bacteria HJ1 and HJ2, isolated from heavy metal contaminated soil, was employed for Cd2+ and Pb2+ immobilization with or without β-tricalcium phosphate addition. Compared with the only treatments amended with strains, the combined application of β-tricalcium phosphate and HJ1 improved the immobilization rates of Cd and Pb by 1.49 and 1.70 times at 24h, and the combined application of β-tricalcium phosphate and HJ2 increased the immobilization rates of Cd and Pb by 1.25 and 1.79 times. The characterization of biomineralization products revealed that Cd2+ and Pb2+ primarily immobilized from the liquid phase as CdCO3 and PbCO3, and the addition of β-tricalcium phosphate facilitated the formation of Ca4.03Cd0.97(PO4)3(OH) and Pb3(PO4)2. Also, the calcium source was related to the speciation of carbonate precipitation and improved the Cd and Pb remediation efficiency. This research demonstrated the feasibility and effectiveness of MICP combined with β-tricalcium phosphate in immobilization of Cd and Pb, which will provide a fundamental basis for future applications of MICP to mitigate soil heavy metal pollutions. Environmental ImplicationMicrobially induced calcium carbonate precipitation is a biomineralization process involving calcium carbonate precipitation and possible co-precipitation of Cd, Pb and other heavy metals. In this study, the β-tricalcium phosphate addition enhanced the bacterial immobilization effect, strains HJ1 and HJ2 could use the β-tricalcium phosphate, which could accumulate and react with Cd2+ and Pb2+ to form metal precipitates, mainly in the form of CdCO3, Ca4.03Cd0.97(PO4)3(OH), PbCO3 and Pb3(PO4)2 that were immobilized and removed. Our investigation shed light on the potential of applying the β-tricalcium phosphate-assisted MICP method to remedy Cd- and Pb-rich soils and water bodies.