Abstract

Over 70% of the world’s metals supply is extracted from sulfide minerals, resulting in large volumes of biogeochemically reactive waste possessing high concentrations of sulfur compounds. Increased demand for critical metals exacerbates these sulfur associated environmental risks, underscoring the vital need for more effective and sustainable management tools that can meet stewardship goals. At the global scale, many existing tailings storage facilities (TSF), remain at risk of causing deleterious sulfur related receiving environment (RE) impacts such as acid mine drainage, toxicity and contamination. These ongoing risks reflect that mines currently lack robust monitoring and treatment tools for all the possible reactive sulfur compounds that may pose RE risks, as well as understanding of the microbial sulfur cycling and associated sulfur and acidity outcomes that occur in TSF.

Results from a case study from the industry-academic partnered Mine Wastewater Solutions (MWS; 2016-2021) research project that integrated geochemical and molecular and experimental microbiological investigation of 4 base metal mine TSF will be presented.  Results identified the presence of a discrete suite of sulfur oxidizing bacteria (SOB), many of them novel, at all mines, indicative of the broader relevance of these results and opportunities for biological S management strategies associated with their manipulation. All three known sulfur oxidation pathways were dynamically present in these TSF SOB communities under differing conditions, indicating the adaptability and comprehensive flexibility of these SOB communities to process sulfur via an array of possible reactions. Thus, TSF acidity generation and sulfur compound occurrence and distribution will be SOB pathway dependent; which in turn is dependent on water physico-chemical and geochemical characteristics.

Results reveal that common TSF management conditions aimed at preventing AMD, namely, lower [O₂] and circumneutral pH values, (based on abiotic modeling) favour SOB specifically associated with the occurrence of higher sulfur compound concentrations. Thus, while these conditions result in less acidity generation on site, they increase the risk of sulfur impacts to downstream RE and non-compliance, as recalcitrant sulfur compounds in TSF wastewaters are not completely destroyed with currently available static, chemical and energy intensive water treatment technologies. The implications and possibilities presented by these emerging results to reduce S risks on site will be discussed. Results from this industry-academic collaborative research underscore the value of such upstream investigation that identify new opportunities to radically improve water stewardship through biologically informed development of more effective system-based sulfur monitoring tools and adaptive management approaches.