As sulfide minerals are mined and processed for base metal recovery, iron sulfides are rejected as waste tailings. When exposed to air, water, and microbes, these sulfide-laden waste tailing are oxidized to sulfuric acid producing acid mine drainage. There is a tremendous legacy cost to clean up Canadian mine sites impacted by acid mine drainage. However, the value of the nickel stored in existing tailings in Sudbury, ON is estimated to be in the billions of dollars. Thus, there is financial and environmental incentive to improve mine waste management.
Selenium release is another environmental concern for the mining industry. Selenium (Se) is an analog of sulfur (S) and a minor but more toxic component of sulfide minerals. Metal and coal mines in Canada released ~20 tonnes of Se to water in 2012.
With the tremendous advances in molecular biology tools, sequencing technology, and ensuing “omics” revolution, bioprocesses are no longer “black boxes”. Acid mine drainage ecology has now been characterized and provides us with a broad understanding of the dominant microorganisms in these communities. This information provides us with a toolkit to engineer improved mining processes by manipulating individual microbes or entire communities.
We propose to develop microbial driven processes to stabilize S and Se in their neutral elemental forms with simultaneous base metal recovery. Conventional approaches stabilize S and Se in their most reduced state (as sulfide or selenide). Our new approach has technical and economic advantages, and also challenges. While microbial processes contribute significantly to the oxidation and reduction of S and Se, arresting these reactions at elemental S and Se while liberating metals of commercial value requires a better understanding of rate-controlling reactions and the microbes involved in these conversion processes.