Microbially-Induced Carbonate Precipitation by Carbonic Anhydrases: A Novel Approach for Lead-Zinc Tailings...

The mining industry's rapid growth has intensified environmental pollution, particularly from lead-zinc tailings (LZT), which threaten soil and water quality due to heavy metal contamination. Heavy metals like lead (Pb), mercury (Hg), and cadmium (Cd) pose significant risks to ecosystems and public health. This study investigates the use of carbonic anhydrase (CA)-producing bacteria, which can convert carbon dioxide (CO₂) into bicarbonate (HCO₃^-) without generating harmful byproducts. The potential of these bacteria for remediating LZT through microbial-induced carbonate precipitation (MICP) was explored. Three bacterial strains with high CA activity were isolated, with one strain, identified as Bacillus sp., exhibiting the highest enzyme production at 12.29 U/L. Optimal conditions for bio-calcification were determined to be a calcium ion concentration of 50 mM and a pH of 8.5, leading to significant reductions in Pb (65%) and Zn (58%) bioavailability after treatment. The bio-mineralization process was effective even under environmental stress, including freeze-thaw and dry-wet cycles, demonstrating substantial decreases in heavy metal mobility and the formation of stable carbonate minerals, confirmed through XRD and SEM-EDS. Post-treatment analysis revealed over 80% of heavy metals were immobilized as carbonate minerals, effectively mitigating the risks associated with LZT. This study highlights the innovative use of CA-producing bacteria for bioremediation in challenging environments, suggesting future research should focus on scaling this approach for broader applications in contaminated sites.