More effective immobilization of divalent lead than hexavalent chromium through carbonate mineralization by Staphylococcus epidermidis HJ2

Heavy metals are the most common pollutant of soil and water, and are being the center of attention due to their toxicity and carcinogenic nature for environment and human health. Microbially induced carbonate precipitation (MICP) is one of well-known processes in recent years for metals immobilization; however, it could have preference for divalent metal ions as MICP directly precipitates calcium ions. Thus, the present research mainly focused on the MICP for the remediation of divalent Pb(II) and hexavalent Cr(VI) in solution using ureolytic Staphylococcus epidermidis. The urease activity led to the metal removal in MICP process, and the removal efficiency of Pb(II) and Cr(VI) was up to 86% and 76.8% (with initial metals concentration 25 mg l−1), respectively. The FTIR spectra revealed number of peaks indicative of CO3 bonding and formation of carbonate compounds in MICP samples; however, such peaks were clearly identified in MICP-Pb than MICP-Cr(VI) due to direct precipitation or immobilization ability of similar valency (Ca2+ and Pb2+). The SEM images also showed the deposition contained metals produced by co-precipitation with calcium clearly. The results showed significant difference in terms of Cr(VI) – and Pb(II) – immobilization, and MICP depicted clear efficacy or preference in the immobilization of divalent over multivalent metal ions.