Development of a Biomineralization-Enhanced Immobilization Remediation Technology for Pb-Contaminated Soil Based on Coupling Maifanite and Bacillus mucilaginosus

Immobilized microorganism technology offers a promising approach for remediating heavy metal-contaminated soils. This study developed a novel bio-mineral composite (B-AM) by coupling acid-modified maifanite (AM) with Bacillus mucilaginosus to enhance lead (Pb) immobilization. Comparative experiments demonstrated that B-AM outperformed conventional amendments, including oyster shell, pristine maifanite, AM and B. mucilaginosus in Pb immobilization. The B-AM treatment optimized soil pH, improved soil fertility with increases in available potassium (1.06-fold) and available phosphorus (1.28-fold). Additionally, B-AM transformed Pb into more stable fractions, reducing labile Pb fractions by 52.52% while increasing the residual fraction by 88.36%. These improvements resulted in an 83.24% reduction in Pb accumulation and a 63.95% increase in the fresh root weight of radish. Mechanistic insights revealed that the enhanced remediation performance stems from both the individual contributions of AM (adsorption capacity) and B. mucilaginosus (biosorption and biomineralization) and their synergistic interaction. Specifically, AM acts as a carrier and pH buffer, promoting microbial proliferation and reducing Pb remobilization from cell lysis. The resulting sustained microbial activity further leads to the formation of stable Pb minerals. Collectively, our results establish a theoretical and practical basis for using B-AM to remediate Pb-contaminated soils.