Extracting residues from mining waste

The objective of the research project "Extracting residues from mining waste" was the efficient use of mining residues by application of innovative technologies. The investigation focused on flat-shaped Kupferschiefer dumps, which have been deposited in a time span from 1870 to 1945 in the Mansfeld area of Sachsen-Anhalt, Central Germany. The examined dumps consist mainly of barren limestone and significant volumes of (at the time) low-grade Kupferschiefer ore with up to 1.3 per cent copper and substantial quantities of other metals. The joint project has investigated how and to what extent the metals can be extracted.

The mineralogical-petrographic characterization and detailed documentation and exploration of the dumps serve as fundamental parameters for the processing of the dump material. The evaluation of geochemical analyses revealed that significant amounts of copper and silver as well as considerable amounts of lead and zinc are contained in the low-grade Kupferschiefer ore. In order to recover these valuable metals, an innovative processing scheme has been developed.

In a first step, the barren wallrock was separated by sensor-based sorting from the mineralized dump material, which achieved a significant enrichment of the metal content for the subsequent ore processing. The pre-sorted material was comminuted and subsequently different flotation methods were applied. It has been shown that the low-grade Kupferschiefer ore can be best flotated if it is comminuted to a grain size of less than 100 µm and this pre-concentrate can be processed selectively by hydrometallurgical treatment.

Leaching procedures on roasted as well as on non-roasted pre-concentrates were applied to extract the metals. The use of waste acids from other industrial use in the leaching process was also investigated and has proven to improve cost efficiency. Initial microbial leach tests were investigated parallel to the conventional processing route of copper ores and have achieved higher metal recovery rates. However, data on industrial scale bioleaching has not been demonstrated yet to have similar positive effects on efficiency and should be investigated further.

Copper and silver can be extracted economically by integrated processing of Mansfeld Kupferschiefer dump material. Within the proposed holistic utilisation concept of the dump material, the remaining mineral residues can be supplied to and used by the building material industry.