Covellite (Bio)-Leaching with Amino Acids

Covellite is one of the main copper sulfides found in Kupferschiefer [1]. Besides that there are also indications of secondary covellite formation during leaching processes of related sulfides [2]. Therefore, understanding of covellite dissolution in the context of Kupferschiefer bioleaching is of great importance. However, conventional bioleaching employing acidophilic microorganisms is impeded due to its high acid neutralizing capacity. The Use of neutrophilic bacteria secreting metabolites capable of metal interactions may circumvent this problem. Thus, we synthesized an artificial covellite [3] and subjected it to both chemical and biological leaching. Parameters considered important for covellite dissolution involve e.g. type and concentration of leaching agent, pH, and temperature, presence of other metals or solid phases with adsorptive capacities. First results from batch assays revealed that amino acids might be suitable leaching agents. Physicochemical parameters, which determine leaching success, differ between different amino acids. We found that covellite dissolution is strongly pH dependent for glutamic acid, aspartic acid and arginine, whereas for glutamine and asparagine this could not be shown. The different behavior is currently attributed to the differences in stability of the formed copper-amino acid complexes. In addition pH determines chemical speciation of leaching agent which in turn is a key factor in complex formation. Growth of bacteria sometimes is heavily influencing pH and thus leaching success. Knowledge of these crucial parameters and how they interact, allows for optimization of the leaching process. Furthermore, it is planned to produce amino acids in-situ, by e.g. Corynebacterium glutamicum, to ensure an economical feasible process.

1. Kutschke, S., et al., Bioleaching of Kupferschiefer blackshale – A review including perspectives of the Ecometals project. Minerals Engineering, 2015. 75: p. 116-125.
2. Kostudis, S., et al., Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria. Minerals Engineering, 2015. 75: p. 38-44.
3. Xin, M., K. Li, and H. Wang, Synthesis of CuS thin films by microwave assisted chemical bath deposition. Applied Surface Science, 2009. 256(5): p. 1436-1442.