Green and effective remediation of heavy metals contaminated water using CaCO3 vaterite synthesized through biomineralization

Heavy metal pollution has attracted significant attention due to its persistent presence in aquatic environments. A novel vaterite-based calcium carbonate adsorbent, named biogenic CaCO3, was synthesized utilizing a microbially induced carbonate precipitation (MICP) method to remediate heavy metal-contaminated water. The maximum Cd2+ removal capacity of biogenic CaCO3 was 1074.04 mg Cd2+/g CaCO3 with a high Cd2+ removal efficiency greater than 90% (initial Cd2+ concentration 400 mg/L). Furthermore, the biogenic CaCO₃ vaterite, induced by microbial-induced calcium carbonate precipitation (MICP) process, demonstrated a prolonged phase transformation to calcite and enhanced stability. This resulted in a sustained high effectiveness (greater than 96%) following six consecutive recycling tests. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the semi-stable vaterite type of biogenic CaCO3 spontaneously underwent dissolution and recrystallization to form thermodynamic stable calcite in aquatic environments. However, the presence of Cd2+ leads to the transformation of vaterite into CdCO3 rather than undergoing direct converting to calcite. This transformation is attributed to the relatively low solubility of CdCO3 compared to calcite. Meanwhile, the biogenic CaCO3 proved to be an efficient and viable method for the removal of Pb2+, Cu2+, Zn2+, Co2+, Ni2+ and Mn2+ from water samples, surpassing the performance of previously reported adsorbents. Overall, the efficient and promising adsorbent demonstrates potential for practical in situ remediation of heavy metals-contaminated water.