Improved management of base metal mine tailings impoundment and receiving environment sulfur risks: Nature-based solutions

Sulfur oxidation intermediate (SOI) compounds represent a risk of delayed acidity generation, oxygen depletion, and metal mobilization in mine receiving environment (RE) waters, as current on-site wastewater monitoring methods often underreport their presence, and treatment strategies fail to effectively eliminate all SOI compounds. Currently, typical mine tailings impoundment (TI) wastewater management is focused on acid mine drainage (AMD) preventative strategies (i.e. low dissolved oxygen and high pH) which can inadvertently promote the activity of sulfur oxidizing bacteria (SOB) that regenerate the SOI pool, increasing SOI persistence through treatment. The objectives of this study were to establish SOB enrichments from the TIs and REs of four Canadian base metal mines and investigate links between acidity, sulfur speciation, and SOB community composition. Experimental results revealed that despite differences in TI and RE parent water SOB community diversity and relative abundance, Halothiobacillus spp. was enriched from all parent waters with detectable thiosulfate (S₂O₃^2-) and dominated six of the eight SOB enrichments (17.8% to 88.8% relative abundance). Enrichments dominated solely by Halothiobacillus spp. demonstrated complete oxidation of S₂O₃^2- to sulfate (SO₄^2-), while enrichments with mixed Halothiobacillus spp. and Thiobacillus spp./Sulfuriferula spp. communities demonstrated incomplete oxidation and/or disproportionation and regeneration of the SOI pool. These results highlight the potential of Halothiobacillus spp. as a biological treatment candidate for managing on-site sulfur associated risks, providing nature-based solutions for sustainable mine wastewater management. The integration of biological wastewater treatment strategies assists in closing a gap in current management practices improving treatment efficacy and sustainability across mining environments.