Strength and leaching characteristics of stabilized ionic rare earth tailings by microbially induced calcium carbonate precipitation

Ion-adsorbed rare earth mining generates extensive tailings sites with compromised structural integrity and heavy metal contamination. This study employed microbially induced carbonate precipitation (MICP) with Sporosarcina pasteurii to solidify and stabilize ion-adsorbed rare-earth tailings. The effects of treatment method, cementation solution (CS) concentration, and heavy metal contamination level on strength characteristics and heavy metal leaching behavior were investigated. Results showed that the unconfined compressive strength (UCS) of samples treated by cyclic grout immersion correlated positively with calcium carbonate (CaCO3) content, reaching a maximum of 770 kPa at 1.00 mol/L CS. Surface CaCO3 content increased with heavy metal concentration, while average CaCO3 content initially increased, then decreased with rising CS concentration. MICP treatment significantly reduced heavy metal leaching. For tailings with initial heavy metal concentrations below 500 mg/kg, leaching concentrations were suppressed below 5 mg/L across all CS concentrations tested. Microstructural analysis revealed that amorphous aggregates composed of calcite, heavy metals, and carbonate coprecipitates served as the primary cementing phase, with heavy metal stabilization achieved through precipitation, adsorption, and CaCO3 encapsulation. These findings demonstrate that MICP technology effectively enhances the mechanical strength of rare earth tailings while immobilizing heavy metals, offering a promising approach for tailings remediation. Further research is needed to address scalability, long-term durability, and performance variability across different tailings types.