Microbially induced carbonate precipitation as an innovative technology for achieves efficient Sr²⁺ bioremediation

Microbes have demonstrated remarkable potential for Sr²⁺ bioremediation under both laboratory and in situ conditions. However, the mechanism for efficient biological removal of toxic elements remains elusive. This study systematically investigated the efficacy and underlying mechanisms of Sr²⁺ immobilization through microbially induced carbonate precipitation (MICP) using Sporosarcina pasteurii in a simulated contaminated system. Experimental results revealed that the strain achieved simultaneous and efficient immobilization of both Sr²⁺ and Ca²⁺ within 72 h, with removal efficiencies exceeding 99.95 %. Solution chemistry analysis identified high concentrations of carbonate and bicarbonate ions, generated through bacterial ureolysis, as the key drivers of the efficient precipitation process. XRD, EDS, and XPS analyses confirmed the incorporation of Sr²⁺ into crystal lattices of calcite and strontianite crystal lattices through isomorphic substitution. Intriguingly, the Sr/Ca molar ratio (0.4-0.6) in early-stage precipitates was substantially different from that in the initial solution. Complementary analyses using FTIR and 3D-EEM fluorescence spectroscopy further demonstrated that bacterial-secreted organic matter selectively regulated the preferential precipitation of Ca²⁺. As a result, the strain's exceptional mineralization capacity effectively compensated for this preferential effect, ensuring efficient Sr²⁺ immobilization. This study demonstrates the application advantages of microbes in MICP technology, providing critical insights for the remediation of radioactive contamination as well as a promising strategy for carbon sequestration of microbe-derived organic matter.