Bioleaching in stirred tank reactors to process Kupferschiefer-type ore: current status and perspectives
Résumé
In Europe, most of the primary resources with high or moderate metal grade, reasonable accessibility and easy to process are exhausted. European primary resources still available for exploitation have more complex mineralizations (e.g. polymetallic and polymineral, carbon rich), or low metal contents; they also have higher levels of toxic impurities such as arsenic, antimony and mercury, penalizing current pyrometallurgical technologies. As existing processes and technologies are often not profitable for these types of unconventional resources, new process options still need to be developed in order to overwhelming the complexity of the ore composition while remaining cost effective. In this context, bioleaching is more and more considered as a promising technology. Even though heap and dump bacterial leaching of sulphidic minerals are well established and the bacterial treatment of refractory gold concentrate using stirred tank reactors (STR) is an industrial reality, the European mineral industry is still sceptical and reluctant to adopt biohydrometallurgical techniques. Heap leaching is often considered as un-adapted due to space constraints, slow leaching kinetics and low recovery rate. The possibility of using STR for the treatment of other metals than refractory gold, such as copper sulphides, has already been demonstrated but improvements are still needed to achieve economic viability.
The Kupferschiefer deposits host the largest known copper reserve in Europe [1]. These black shale type ores are currently exploited in Poland through pyrometallurgical smelting. In Germany exploration campaigns were recently leaded in order to assess and prepare future exploitation of this ore deposit type. The main copper-bearing minerals are: chalcocite, bornite, chalcopyrite and covellite. This type of ore is also characterized by high amounts of carbonate and organic carbon as well as potentially rich with arsenic (volatile in pyrometallurgical processes). In the last years the ores are characterized by increased As and C contents, and lower Cu contents. It leads to a lower quality concentrate as well as operating and environmental issues during smelting. In this context, several European research projects have been dedicated to the development of new bioleaching approaches as alternative and complementary routes to the conventional smelting methods for the processing of Kupferschiefer ores (BioShale in EC-FP6, ProMine in EC-FP7, BIOMOre). By using a multi-scale approach from molecular techniques to bench-scale small pilot continuous tests, Cu recovery from this type of ores using bioleaching was demonstrated to be technically feasible and efficient. The stirred tank bio-reactor (STR) was shown as the best process option when compared to heap leaching due to the high content of carbonate in the ore.
This paper gives an overview of the work performed on this topic in the last decade. The R&D challenges necessary to tackle in order to improve the process economy will be analysed and compared. It will also discuss the new insights and future developments brought by ECOMETALS, a German and French joint research project, for the integration of bioprocess options in the metallurgical treatment of Kupferschiefer ores.
Domaines
Génie des procédés
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