Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The Kupferschiefer is one of the most important sources of copper and silver in Europe, with resources located mainly in Poland and Germany. Mineralization is stratabound and hosted by sedimentary rocks comprising of sandstone, black shale, and carbonate rocks. Because Kupferschiefer-type ores are typically complex and very fine-grained, alternative approaches for metal recovery, such as bioleaching, are becoming an attractive alternative to flotation.
The focus of this study was a detailed monitoring of mineralogical changes through time during bioleaching of sandstone-hosted Cu-mineralization from two Polish Cu-mines. The change of modal mineralogy, mineral associations, microbial activity and copper recovery of a copper bearing sandstone during bioleaching with Acidithiobacillus ferrooxidans DSM 14882 was investigated. A series of 18 batch cultures and 18 abiotic controls in shaking flasks with a solid content of 6 wt.% was prepared and sampled every 3 to 4 days over a period of 18 days. Mineralogical analysis of leaching residues was done by mineral liberation analysis (MLA) and X-Ray powder diffraction (XRD), while chemical analysis of dissolved copper and ferric/ferrous iron was carried out with ion chromatography (IC).
The investigated sandstone ore contained 2.5 wt.% copper, mainly bound to the copper minerals chalcocite (Cu₂S, 1.3 wt.%), covellite (CuS, 1.0 wt.%) and bornite (Cu₅FeS₄, 0.9 wt.%). After 18 days the copper extraction was 84% for biotic samples and therefore significantly higher compared to abiotic controls (52%). MLA data showed that biotic dissolution was faster for all three copper ore minerals. The results of detailed mineralogical analysis indicate a passivation by jarosite during the leaching process, especially caused by ammoniojarosite. It was possible to trace progressive changes of each copper sulphide over the entire bioleaching process and calculate dissolution/formation rates by means of MLA data.