Effects of the Sr/Ca ratio on the bioremediation of strontium based on microbially-induced carbonate precipitation

90 Sr is a radionuclide that poses a potential threat to ecosystem security, and Sr bioremediation based on microbially-induced carbonate precipitation (MICP) usually affected by Ca. Experiments of carbonate mineralization induced by Enterobacter sp. JC-1 in solution with different Sr/Ca molar ratios were performed to explore the effect of Sr/Ca ratio on microbially-induced carbonate precipitation. X-ray diffraction patterns indicated that strain JC-1 induced the formation of calcite (Sr/Ca < 1) and strontianite (Sr/Ca = 1), and the increase in the d (104) and d (012) of calcite indicated that Sr entered the calcite lattice. The normalized distribution coefficient of Sr (D Sr ) in the minerals indicated that a higher Sr/Ca ratio promoted Sr incorporation into minerals. Sr 2+ removal showed a V-shape (initial decrease and subsequent increase) with an increase in Sr/Ca ratio, which had no correlation with the D Sr , but was positively correlated with the mass of CO 3 2- (r = 0.779, p < 0.01) in the mineral. However, mineralization experiments induced by chemicals showed that Sr 2+ removal was positively correlated with D Sr (r = 0.785, p < 0.01), which suggested that MICP was not simple chemical process. The moles of carbonate in minerals revealed that a higher Sr/Ca ratio influenced the ability of bacteria to generate carbonate. The Sr 2+ removal was due to the combined effect of microbial growth and the D Sr . In conclusion, this study revealed the relationship of Sr/Ca ratios between the solution and minerals, which has reference value for the explanation of the formation mechanism of carbonate mineral and Sr bioremediation. • The Sr 2+ removal in solution is influenced by both microbial metabolism (CO 3 2- production) and D Sr of minerals. • MICP-based Sr remediation can be driven by ammoniation using Enterobacter sp. • XRD patterns revealed that Sr is incorporated into carbonate minerals by replacing Ca in the lattice; • Sr/Ca ratio of calcite had a linear relationship (R 2 =0.99539, p <0.05) with Sr/Ca ratio in solution;