Impact of organic acids on copper minerals in Kupferschiefer ore

The Central European Kupferschiefer constitutes one of the most important natural copper sources in Europe (Borg et al. 2012). The Kupferschiefer sensu strictu challenges conventional exploitation due to its organic load, complex mineralogy and fine dispersion of ores. Thus alternative beneficiation strategies are investigated. Bioleaching – the use of microorganisms or microbial metabolites for metal solubilisation from ore material – may serve as an efficient and environmentally benign approach. Among others leaching with microbially produced organic acids provided good results (Anjum et al 2010). In previous studies (Kostudis et al. 2015) leaching of copper from Kupferschiefer sensu strictu (Polkowice Mine, Lubin, Poland) using glutamic acid was examined. It was shown that copper is primarily released from chalcocite (Cu2S) being the main copper mineral in the shale sample. However, decrease in chalcopyrite (CuFeS2) and bornite (Cu5FeS4) content by 40 % and 37 %, respectively, has also been reported as well as formation of secondary minerals such as covellite (CuS). As the Kupferschiefer sensu strictu is constituted very complexly investigation of the single main copper minerals without the matrix is worthwhile. Thus the current study addresses the influence of organic acids on chalcocite, bornite and chalcopyrite. Experiments were performed using strewn slides prepared as thick sections. Ore samples of chalcopyrite, bornite and chalcocite were provided from Ashio/Japan; Butte/Montana/USA and Henderson Mine/Namaqualand/South Africa, respectively. The samples (fig. A) were analysed prior to and after leaching with citric and glutamic acid using mineral liberation analysis (MLA) consisting of combined SEM and ED X-ray spectrometry and a specific software for automated data acquisition (fig. B), micro-Raman spectroscopy (fig. C), and atomic force microscopy (fig. D). The presentation shows results of comprehensive mineralogical analysis of both pristine and processed copper ores.