Thursday, 5 January 2012

High Temperature Bioleaching

It has long been recognized that thermophilic, iron- and sulfur-oxidizing microorganisms can efficiently oxidize mineral sulfides at 65°C-85°C. They may be active in some ore leaching heaps or dumps at elevated temperatures but they have not yet found premeditated application in commercial mineral processing at these temperatures. One of the questions in potential process development is the choice of microbial culture.

The first thermophiles with potential for mineral sulfide processing at temperatures above 65°C were revealed during the mid 1960s in the USA, and later renamed as Acidianus species. The first demonstrations of rapid processing of copper concentrates were made with Sulfolobus metallicus at about 70°C in the early 1980s and more efficient leaching at higher temperature (about 80°C) was demonstrated in the early 1990s at Warwick University (UK) with species which remain un-named. These un-named strains were tested in continuous leaching of copper concentrates in the mid to late 1990s and used at pilot scale in the HIOX process at BRGM (France) and in the BioCOPTM Process at BHP Billiton (South Africa), the latter process reaching a commercial scale demonstration with Alliance Copper Ltd. in Chile in 2003. Meanwhile, concentrate processing with thermophiles had also been developed by Mintek (South Africa) and continued with pilot scale work through the EU BioMinE project up to 2008 using cultures dominated by Acidianus species at 70°C.

Paul Norris
With this background availability of a variety of thermophiles, MEI is pleased to announce that Dr. Paul Norris, of the University of Warwick, UK, will review the characteristics of several different cultures in a keynote lecture at Biohydrometallurgy ’12 in Falmouth in June. He will consider two aspects: the past developments with bioreactors; and ore heap leaching, where high temperature would be desirable (for chalcopyrite dissolution) or is inevitable (because of the rate of exothermic mineral sulfide oxidation, such as with the Talvivaara operation in Finland). The Talvivaara operation, the first commercial bioleaching operation in Europe, is the subject of another keynote lecture by Marja Riekkola-Vanhanen, who is the Senior Technology Adviser for the Talvivaara Mining Company, Finland. The problems associated with maintaining a well functioning heap will be discussed in the third keynote, to be presented by Prof. Sue Harrison of the University of Cape Town, South Africa.

The technical programme for this conference will be drafted later this month, so it is not too late to submit an abstract.

2 comments:

  1. Alliance Copper demonstration plant near Chuquicamata in Chile was shut down few months after starting because it cannot be economical for chalcopyrite concentrates. The plant used five large reactors lined with acid resisting bricks, residence time was 4 days, supply of oxygen was excessive, and material handling of lime to neutralize the acid generated and precipitate ferrous hydroxide created a large disposal problem. When compared with pressure leaching: one reactor would be enough, residence time only 4 hours, oxygen consumption is one third, no disposal problem because elemental sulfur and ferric oxide are formed. References: [1] F. Habashi, “Chalcopyrite: Bioleaching versus Pressure Hydrometallurgy,” pp. 17–22 in Proceedings International Conference: Metallurgy of the XXI Century. State and Development Strategy. Institute of Metallurgy and Mineral Beneficiation, Almaty, Kazakhstan 2006.
    [2] F. Habashi, “Chalcopyrite — Atmospheric versus Pressure Leaching,” Metall 61(5) 303–307 (2007).
    Fathi.Habashi@arul.ulaval.ca

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  2. My understanding is that there were other problems that led to the shut down of the plant. I seem to remember it was more about political problems between the partners than technical issues. I'm talking from memory, but a presentation I saw about it suggested that from a technical view it was a success (i.e. it met its stated objectives, which were not necessarily economic). I need to try and remember who it was that gave the presentation. I think there was more controversy here than a simple performance assessment...

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