Monday, 28 July 2014

Biooxidation research challenges

Last month's Biohydromet '14 ended with an excellent panel discussion on the future of biohydrometallurgy, chaired by MEI Consultants Patrick D'Hugues of BRGM France and Sue Harrison of University of Cape Town, with panellists Pieter Van Aswegen of PMet Consulting, South Africa, Paul Norris of University of Exeter, UK, and Jim Brierley of Brierley Consultancy, USA.
Pieter, Patrick, Paul, Jim, Chris Bryan and Sue
This one hour session covered many important aspects of the future role of biohydrometallurgy, some of which are highlighted below.

Pieter van Aswegen began by highlighting some of the challenges for biooxidation and some of the aspects which could make it a very serious competitor to pressure oxidation, which is the preferred technique in North America for the treatment of refractory gold ores.
Solids content has always been one of the major limitations for biooxidation, and in the past if more than 2000 tpd of concentrate were treated, pressure oxidation was the most economic method. Initially 10% solids was used, but in 1989 Fairview gold mine in South Africa increased to 20% solids, making biooxidation a viable alternative. Today the largest plant is in Uzbekistan with 1000m3 tanks treating 2000 tpd of concentrates, and developments in new agitators and impellers have allowed the start up of recent plants in Tanzania using 40% solids for high gas dispersion applied in cyanide destruction operations.
A major constraint on solids content is the bacteria, and how robust they are at 30% solids and above. He felt that very little work has been done on this, but it is important to aim for 20-30% solids, as this reduces capital costs due to smaller tanks and lower retention times. Lower retention times can be achieved by using thermophiles, but these are not as robust as mesophiles, which limits solids content to around 15% in most cases. Pieter's message to researchers was therefore not to be conservative, and to make real efforts to aim for 20-30% solids. Rob Hille remarked that the University of Cape Town team has been working on this for the past 2 years with Biomin, using mesophilic and thermophilic bacteria at 31% solids.
Pieter also highlighted another challenge for biooxidation of gold ores, the reduction of cyanide consumption, which is much higher than with pressure oxidation, due to the generation of elemental sulphur which consumes cyanide. Typically 10-40 kg/t of cyanide is consumed in biooxidation, compared with around 2 kg/t in pressure oxidation. Some work is being done using thermophiles in the final tanks to oxidise the elemental sulphur in order to reduce overall cyanide consumption.
Barrie Johnson of Bangor University pointed out that the high cyanide consumption in biooxidation could restrict the implementation of this technology in some countries, as cyanide usage is banned, and a major target for bio and hydrometallurgists should be to continue to look for alternatives to cyanide, as if this could be removed from the circuit biooxidation would have more widespread use.

Paul Norris spoke on behalf of the academics, and made the important point, discussed previously on the blog, that researchers should be aware of the wealth of past work which is out there. Biomet conferences have been held in various parts of the world for about 38 years now, and there have been hundreds of papers published, so there is always a danger of reinventing and recycling material which has been effectively hidden in the early literature.
He stressed that academics should continue to search for more useful microorganisms, as there are areas in which those currently available are inadequate for industrial use, solids tolerance in stirred tanks, discussed by Pieter, being a notable area, particularly at high temperature. It is important that workers in the wide range of countries represented at Biohydromet '14 look at relevant natural and mining sites in their countries. It is not difficult to find new microorganisms and then to screen them to assess their effectiveness.

Looking further ahead, Jim Brierley felt that future mines might utilise some form of a process similar to the hydrofracturing technology developed by petroleum engineers to release shale gas, thus opening up a buried resource. Benefits could include reducing the footprint of mining and development of new technologies for extraction of critical earth resources.
Could this be the future for the minerals industry? It would need a new mind-set, and how would we manage it to make it work? Biohydrometallurgists would play an important role in advancing new technologies, but obviously not working alone in developing such in situ technology- it would need the involvement of metallurgists, geologists, rock engineers and others. To prepare for this we should be researching how microorganisms behave under high hydrostatic pressures, anaerobic and other conditions yet to be defined. This would be a complex technology only applicable for use with highly specific amenable ore bodies and would need to meet all economic, environmental, safety and societal concerns.

Biohydrometallurgy is a rapidly evolving field, and we look forward to seeing how things have progressed, both technologically and socially, at Biohydrometallurgy '16. But in the meantime I invite comment- what do you feel about the role of biotechnology in future mining operations?

Thursday, 24 July 2014

Cornish Mining Sundowner- July

A good crowd this evening at the Chain Locker, despite the late afternoon showers which drove us indoors, despite the heat.

The next Sundowner will be Thursday August 21st, and as always, there is an open invitation to anyone who is in the Falmouth area at that time.

Monday, 21 July 2014

1st Call for Abstracts- Precious Metals '15 and Nickel Processing '15

Abstracts are now invited for two of MEI's small specialised conferences, which will run back to back in May next year. As with all MEI Conferences, papers accepted for presentation will be published in a Proceedings flash drive, available at the conference, and then authors will be invited to submit edited papers to Elsevier Science after the event for peer-review and publication in a special issue of Minerals Engineering. Both conferences are certified for Continuous Professional Development.
May is a great time to be in Cornwall, so plan ahead and aim to spend some time exploring this beautiful area of the world.
Falmouth Bay

Precious Metals '15 will deal with all aspects of the processing of gold and PGM ores, such as flotation, bio and hydrometallurgy and the associated environmental issues. Prof. Jacques Eksteen of Curtin University, Australia, will present the keynote lecture "Innovations in the processing of difficult and low grade gold ores".
The aim of Nickel Processing '15 is to bring together researchers and plant operators, to discuss all aspects of the physical and chemical processing of nickel ores, copper-nickel ores and laterites, and nickel concentrates, including:
• Froth Flotation and other beneficiation methods
• Bio and Hydrometallurgy
• Pyrometallurgy
• Environmental aspects of nickel processing and smelting
The keynote lecture "The future of nickel production - the outlook for nickel sulphide and laterite resource development" will be given by Dr. Andrew Mitchell, Principal Nickel Analyst with Wood Mackenzie, UK.

If you would like to present a paper at either of these meetings, please submit your short abstract by the end of November of this year. If your company is interested in exposure via sponsorship, details for Precious Metals '15 can be found here, and here for Nickel Processing '15.

Sunday, 20 July 2014

Nchanga Copper Mine 1970

While sorting out some old 8mm home movies, I came across a short clip of the Nchanga mine and concentrator, taken in 1970.

Although nowhere need HD quality, it may be of interest to anyone who worked on the mine during that era, and I have now transferred this to YouTube. It shows ore being transported from the huge Nchanga open pit (now no longer in operation) to the massive primary gyratory crusher (still in operation), and then rod and ball mill grinding at the East Mill.  At the West Mill, ore is seen arriving from underground, and the old flotation banks, dewatering and concentrate shipment can also be seen.

Things have moved on a lot in the intervening decades, as I saw during my return to Nchanga two years ago.

Friday, 18 July 2014

Gerald G. Hatch, 1922-2014

Sad to read on MEI Online of the death of one of Canada's great metallurgists, Gerald Hatch, founder of the engineering firm Hatch Limited, which has grown from six people in 1958 to over 11,000 employees in 65 offices worldwide.

If you knew Gerald, we invite you to add comments to this post to record your appreciations and memories.

Book Review: Hydrometallurgy: Fundamentals and Applications

I thank Sadegh Safarzadeh, Associate Editor of Hydrometallurgy, and Assistant Professor at South Dakota School of Mines and Technology, USA for supplying a review of this new text book.

Authored by Professor Michael L. Free, Hydrometallurgy: Fundamentals and Applications provides an in-depth understanding of the fundamentals of hydrometallurgical science and engineering. The book consists of 12 chapters including Introduction, Chemical Fundamentals of Hydrometallurgy, Speciation and Phase Diagrams, Rate Processes, Metal Extraction, Separation of Dissolved Metals, Metal Recovery Processes, Metal Utilization Environmental Issues, Process Design Principles, General Engineering Economics, General Engineering Statistics, and several useful appendices, including laboratory calculations.

The book has been prepared in 432 pages and published in 2013 by John Wiley and Sons, New Jersey. This textbook is arguably the first of its kind, in the sense that it compiles the fundamentals, applications, reference information and analytical tools on the topic of Hydrometallurgy.

The lack of an inclusive textbook for hydrometallurgy has been felt over the past years. While many of the books published so far are invaluable sources for hydrometallurgy, there was no single book that covered all of the aspects in hydrometallurgy from science to engineering. At the same time, these books appeared to be excellent on some topics, but weak on the other topics. In his book, Professor Free has given equal importance to each of the fundamental topics in hydrometallurgy. Among the important topics that are often weakly written in many related books, if not neglected, are the biochemical and electrochemical reaction kinetics, flowsheet development, and environmental hydrometallurgy. These topics are all covered in this textbook. At the end of each chapter, there is a set of problems that are directly related to the contents of the preceding chapter(s). This book is suitable for both undergraduate and graduate students in the field of mineral processing and extractive metallurgy. Also, it is recommended for mineral processing engineers who work in industry.

Professor Michael Free is with the department of Metallurgical Engineering at the University of Utah. He is a well-known hydrometallurgist, with significant contributions to electrometallurgy, engineering pedogogy, and web-based teaching.

We invite further comments on this volume.