Thursday, 13 February 2014

The Future of Biohydrometallurgy for Gold Processing

In opening Biohydromet '12, MEI Consultant Dr. Chris Bryan, of the University of Exeter, spoke about the history of biohydrometallurgy, from the ideology of the early 80's, where it was going to revolutionise mining and replace pyrometallurgy completely, to the abrupt dose of reality in Corale Brierley's IBS 2005 keynote address "we need to wake up to the fact that this is, and only ever will be, a niche technology", and the need for pragmatism. Chris remarked that biohydrometallurgy has a poor reputation in certain circles, as a technology that is too unpredictable, but he highlighted that it is often used as an avenue of last resort on ores that are untreatable with other methods.
Biohydromet '14 is something to look forward to as it comes at a time when rapid advances in our understanding of the science of microorganisms may in effect have awoken biohydrometallurgy from its long slumber, and it now looks as though it might start to realise its true potential and provide real benefits to the minerals industry. A glance at the timetable for June's meeting confirms this view.
Biohydrometallurgy's greatest success has been in the treatment of refractory gold ores, the first industrial scale plant being started at the Fairview Mine at Barberton, South Africa, in 1986. Since then, biooxidation operations have been commissioned in a number of countries, such as Australia, Brazil, Ghana, Peru, China, Uganda, USA, Kazakhstan, Uzbekistan and Russia. A number of commercial bioreactor processes have been developed, such as BIOX®, which will feature on the 3rd morning of Biohydromet '14.
Researchers at Australia's highly esteemed CSIRO will be presenting three papers at Biohydromet '14 and one of the authors, Dr. Anna Kaksonen has co-authored an excellent review on the role of microorganisms in gold processing and recovery, which has recently been published in Hydrometallurgy. The paper shows how several microbial processes are relevant for gold leaching and recovery. Some of these may be applicable for in situ or in place leaching of low grade gold ores, which the industry will increasingly depend on into the future. Other microbial processes need to be considered as potential risks for lixiviant stability and gold recovery. The understanding of these processes will enhance future industrial applications of biotechnology and lixiviant use by the minerals industry.


  1. I should be more careful what I say! However, ~10 years ago none of us would have predicted that copper production by bioleaching would represent something like 15+% of the global production today. With 80% of the world's copper resource going forward being low-grade chalcopyrite, copper production using microorganisms may represent more than 20% of the global production in the not too distant future -- assuming we figure out how to effectively bioleach it.
    Corale L. Brierley, USA

    1. Dear Corale,
      thanks for your comment and insight.

      I've been trying to independently verify the 15+% number and was wondering if you (or any other kind community member) could thus highlight a couple of key players that are currently using bioleaching for copper production at industrial scale?
      Thanks, K. Brune, UK

    2. The following might be useful?

    3. ... and in the following article from 2008, 7% global Cu production is attributed to bioleaching - I guess this figure has been revised since. The table in here will also be very useful to show you some existing Cu heap leaching operations.

  2. Looking forward to your keynote at Biohydromet '14, Corale. Will be interesting to hear your views on the mines of the future and how advances in biohydrometallurgical processing might be commercially used.

  3. Barry, Thanks for the interesting subjects. I agree with Corale in that it is a niche. But the question I have for the bacterial proponents is how do you eliminate the bacteria? ARD is a significant problem. The Cu industry has used bacteria. But nobody has been able to turn them off.
    Steve Dixon, Goldcorp, USA

  4. Indeed, I guess my point is that bioleaching is riding a roller-coaster. It rode a wave of high expectations during the 80's, but, in my humble opinion(!), it didn't meet those (largely unreasonable) expectations and its reputation suffered as a result. However, I hope I didn't come across too negatively - as Corale points out, a significant proportion of the world's copper (up to 25% by some sources, but even 15% is huge) is produced by heap and dump bioleaching. Biooxidation of refractory gold ores accounts for 3% of world gold production. Again, a significant figure.

    I think the future for biomining is bright - it is being considered seriously for application to other primary resources - such as chalcopyrite and enargite - and secondary resources such as industrial waste streams. The increasing complexity and decreasing grade of the world's resources necessitates the development and application of hydrometallugical tools such as biomining. The arsenic content of many ore bodies I think is one area where bio can excel. Moreover, bioleaching usually

    The point that I was making at Biohydro 2012 was that it has the potential to be a very powerful tool in the mineral processing tool box. However, we must be pragmatic - it is one tool of many. The risk is that overstating its capabilities and applicability will simply damage its reputation in the long term; let's get off the roller-coaster.

    There is a lot of work to do: we understand very little of the actual biology that drives the process and there are issues with predictability as a result. For example, as far as I'm aware we still don't know how Sulfobacillus spp oxidise iron.

    To see real progress we need much more engagement with industry. What I’d like to see is industry coming to such conferences and presenting their challenges and opportunities. Of course, there are fundamental differences between academia and industry. We are driven by the creation and dissemination of knowledge via scientific papers, PhD and masters theses etc. Industry is driven by deliverables and achieving end points. However, we are all solution-driven and there are good examples out there of industry-academic links.

    At the same time, the academic body really needs to up its game. There are a lot of mediocre papers out there. Many are poorly designed and executed with basic flaws that simply should not happen. The industrial or academic rationale is often missing or poorly articulated – work can be academically useful while being less immediately relevant to industry and vice-versa, and that is fine. However, there is a fair amount of work out there that does not link to either – for example simple shake flask tests (often with no replicates) using putatively pure cultures at low pulp densities which are little more than first stage amenability tests for a particular ore. Shake flasks of course have their uses, and are essential for testing a wide array of conditions, but they must be used appropriately and the caveats recognised.

    Of course, there are many institutions out there who produce very high quality and elegant bodies of work. The future of biohydrometallurgical development (again, in my humble opinion) lies in the interface between academia and industry – producing bodies of work that are both academically stimulating while industrially relevant.

  5. I agree that biohydro is, and always will be, a niche approach. I also agree with Steve Dixon in the after problems. I was recently told by a representative of the Quebec Environment Ministry not to even broach bio for refractory gold because unless we could guarantee 100% that the bacteria would not escape back into the environment, then she would not approve it. This I think is one of two big problems with bio, the potential for associated ARD.

    The other problem is that for arsenical ores, despite many claims, there is almost no conclusive evidence that the residues are in fact stable. In theory, they might be, but as we found out many years ago at Imperial College, with John Monhemius and Peter Swash, the residues were a lot less stable than expected. The reason for this is that the oxidation rates of arsenic and iron are different, and therefore most of the arsenic is surface adsorbed. Work on this phenomenon continues at McGill, where a lot of interesting discoveries have come to light over the past few years.

    Bryn Harris

    1. I've been meaning to pick up on this comment for a while, but it's just popped up in my twitted feed and reminded me.

      To refuse a permit for bioleaching on the basis that the organisms might escape and cause AMD is pretty naïve. AMD is caused by organisms naturally occurring in the sulfidic mine wastes. In fact, some of the most effective bioleaching cultures have their origins in mine wastes. The exposure of sulfides to oxygen and moisture is the biggest factor in AMD generation; the organisms will already be there.


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