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

Sr-90 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. Sr2+ 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 CO32- (r = 0.779, p < 0.01) in the mineral. However, mineralization experiments induced by chemicals showed that Sr2+ 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 Sr2+ 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.