Microbially induced calcite precipitation in As- and Sb- containing low sulfide tailings to mitigate neutral contaminated mine drainage: A comparison of bioaugmentation and biostimulation approaches

Desulfurization is a mine waste management strategy involving sulfides removal. While low sulfide filtered tailings do not generate acid mine drainage, their effluents can be contaminated with metals and metalloids at neutral pH. This study investigates the potential of microbially induced calcite precipitation (MICP) to immobilize As and Sb in low sulfide filtered tailings as a long-term management option using two approaches: bioaugmentation (BA) using Sporosarcina pasteurii , and biostimulation (BS) of indigenous microbial communities. Laboratory-scale experiments were conducted under varying urea and Ca 2+ concentrations (0.5–1.0 M) and temperatures (5–20 °C) to simulate conditions relevant to mine sites. BS consistently outperformed BA with respect to urea hydrolysis, carbonate precipitation, and As immobilization. Urea hydrolysis and carbonate precipitation were 12–56% lower in BA-based MICP compared to sand controls, possibly because of microbial inhibition by As, Sb, and co-occurring elements in tailings. Mineralogical analyses confirmed the formation of calcite lattice with encapsulated As-bearing loellingite. Taxonomic analyses revealed a loss of alpha-diversity under BA treatments, dominated by Sporosarcina spp. In contrast, BS-based MICP retained higher residual microbial diversity, enabling complementary immobilization pathways potentially occurring through non-ureolytic MICP, nucleation mediated by extracellular polymeric substances, and As oxidation. BS-based MICP immobilized up to 88% of As, decreasing As concentrations in leachates below Canadian criteria, and was more effective at low temperature. However, MICP enhanced Sb mobility by 24–75%, particularly under alkaline conditions or with BS, highlighting persistent environmental risks associated with Sb in biocemented tailings. Further research should focus on the evaluation of the long-term stability of biocemented tailings under dynamic redox conditions, wet/dry cycles, and optimization of indigenous microbial growth in BS-based MICP.