Bioleaching of mine tailings using acidophilic bacteria and organic acids

Fine-grained tailings from ore processing represent a considerable raw material potential and could be used in the cement industry, as base and surface sealing material for landfills or for dam construction. Those mine tailings are mostly deposited wet in so-called tailings ponds. Storage involves a certain environmental risk, for example mobilization of heavy metals and dam failures with catastrophic consequences. To prevent such environmental disasters in the future and to make these raw materials reusable again, a remediation concept for tailings ponds is therefore necessary. Bioleaching is to be used to modify the composition of the material to meet certain guidelines for its use in the construction industry. For this purpose, various acidophilic bacteria such as Sulfobacillus acidophilus DSM 10332, Leptospirillum ferrooxidans DSM 2705 and other acidophilic consortia were tested. In addition, the yeast Yarrowia lipolytica DSM 3286 was cultivated for the production of citric acid and the bacterium Bacillus licheniformis DSM 13 was cultivated for the production of γ-polyglutamic acid. The bioleaching with these organic acid supernatants and 10 % tailing concentration showed the most promising results to date. The culture supernatant containing 30 g/L citric acid was able to leach 43 % of Pb, 37 % of Zn, 8 % of Ca, 4 % of Mn and 3 % of Fe. Further research and a combination of different processes such as flotation and chemical leaching will also be necessary to optimize the extraction capacities. The authors acknowledge the financial support by the Federal Ministry of Education and Research of Germany in the framework of “Resource Efficient Circular Economy – Construction and Mineral Material Cycles (ReMin)”