Deep in situ biomining (DISB) offers the potential for exploiting metal-rich ore bodies that are currently difficult or non-economic to access, with far less environmental impact than current deep or opencast mining practices. DISB is being developed within the EU Horizon 2020 project “BIOMOre”, which targets a calcareous sedimentary copper ore, kupferschiefer, which is a widespread subterranean rock stratum in central and north-western Europe. Laboratory tests on the two main copper-bearing fractions of kupferschiefer, sandstone and black shale, showed that, besides requiring basic minerals to be removed ahead of indirect bioleaching (to avoid the formation of ferric carbonates), both contained significant amounts of chloride minerals (chiefly halite) which could have a major negative impact on DISB. A sequential three-phased protocol was developed, involving (i) leaching with water, which removed most of the chloride, (ii) leaching with sulfuric acid, which removed most of the residual chloride and carbonate minerals, and (iii) indirect bioleaching with an acidic ferric iron lixiviant. The latter was produced in a laboratory-scale ferric iron-generating bioreactor dominated by the iron-oxidizing acidophilic prokaryotes Leptospirillum ferriphilum, Sulfobacillus thermosulfidooxidans and Ferroplasma acidophilum. The iron oxidizing capacity of this bioreactor was not impaired by the concentrations of chloride present during the leaching phase in which it was used. Sequential leaching was applied successfully using a “composite” (sandstone plus black shale) ore column, which mimicked the flow circuit in a DISB, and included a bleed stream where soluble copper was removed from the pregnant leach solutions generated by sulfide precipitation. Water leaching was shown to cause partial disintegration and lowering of the resistance of the sandstone fraction to crushing.
Bibliographical note© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
- Acid leaching
- Copper ore
- Indirect bioleaching