Remediation of heavy metal contaminated soil in mining areas with vaterite-type biological calcium carbonate

In recent years, research on the remediation of heavy metal contaminated soil by microbially induced carbonate precipitation (MICP) technology has yielded significant findings. However, when utilizing MICP for remediation in situ, urea and calcium chloride may produce high concentrations of NH4+ and Cl-, which subsequently cause secondary pollution. If the biological calcium carbonate (Bio-CaCO3) produced by MICP is employed as a highly efficacious adsorbent, secondary pollution can be avoided while remediating heavy metal pollution. In this study, vaterite-type Bio-CaCO3 was prepared under the regulation of sophorolipids, and the remediation effect and mechanisms for heavy metal contaminated soil were investigated. The results demonstrated that sophorolipids facilitate the formation and stabilization of vaterite-type Bio-CaCO3. The addition of vaterite-type Bio-CaCO3 could notably increase the content of soil organic matter, enhance soil urease activity, and reduce soil catalase activity. On the 30th day of remediation with vaterite-type Bio-CaCO3, the active state content of Pb and Cd in the soil exhibited a decrease of 41.23 % and 35.00 %, respectively. Additionally, the exchangeable state content demonstrated a reduction of 6.61 % and 8.48 %, while the carbonate-bound state exhibited an increase of 12.05 % and 13.89 %, respectively. The principal mechanisms for the remediation of heavy metal contaminated soil by vaterite-type Bio-CaCO3 may be attributed to ion exchange, chemical precipitation, physical adsorption, and complexation reactions. The analysis of the microbial community structure demonstrated that vaterite-type Bio-CaCO3 could enhance the abundance of multiple genera with urease-producing genes, including Pseudomonas, Staphylococcus, and Bacillus while maintaining the soil biodiversity. This study provides a new idea for the remediation of heavy metal contaminated soil around the mining area and offers technical support for the construction of green mines.