……And Noah he often said to his wife when he sat down to dine, “I don’t care where the water goes if it doesn’t get into the wine. G.K. Chesterton.
I had the privilege of attending the International Conference on Hydrometallurgy at the Misty Hills Conference Centre. It did justice to the close proximity to the ‘Cradle of Humankind’ and a good choice for the association with the SA mining and metallurgical industry who had provided the ‘Cradle’ for hydrometallurgy.
Noteworthy in many presentations was the degree of international cooperation and participation in developing a project for a challenging ore deposit in a number of countries. The interaction involving specialist research teams, process development groups, equipment manufacturers and environmental specialists is a good illustration of how pieces of a jigsaw puzzle can be selected and put together to form what could be a viable new mine. It was particularly fascinating to learn that a commercially orientated organization, such as Mintek is aiming to become, can take a leading role on a transparent and nonconfidential basis with international funding for exploiting a deposit in Spain.
Hydrometallurgy is a modern age technology. Although the first application was conceived overseas, its first major commercial debut occurred in South Africa only a century ago. It had a huge impact on a dying industry and resuscitated what was to become one of the largest mining and metallurgical empires in the world’s history. I am, of course, referring to the MacArthur Forrest cyanidation process for gold recovery.
This precocious infant with a golden spoon in its mouth took another quantum leap into adulthood about 50 years later with the inauguration of the giant uranium extraction operation on 17 of the largest hydrometallurgical plants in the world, conceived and commissioned in a period of less than a decade thanks to an unprecedented cooperative effort nationally and internationally.
I was, as a new graduate, involved. There could not have been a more exciting introduction to the magic of ion exchange, solvent extraction, pressure leaching and the other technologies that remain as the cornerstones of the science and engineering of recovery of metals from solution.
Another great step forward also achieved prominence in South Africa with the evolution of bioleaching for treatment of refractory gold ores. This started off as a somewhat incidental investigation of the action of Thiobacillus ferrooxidans in producing acid in the pyrite in mine dumps around Johannesburg. What followed over many decades was a remarkable evolution from the strange discipline of microbiology into a sophisticated hydrometallurgical process with a huge impact on the economics of gold from refractory ores and a new approach to base metal recovery from low-grade sulphidic ores. The many papers describing applications in commercial opportunities show that bioleaching is now a mature technology. The fundamental work on mechanisms and modelling of kinetics, which were a feature of
many previous conferences has borne fruit.
It is indeed fitting that this international conference took place during the 75th anniversary of Mintek. It was at the Government Metallurgical Laboratory, the forerunner of Mintek, where much of the development work on uranium was conducted. Hydrometallurgy has remained a feature of the work of this research organization since.
As pointed out by several speakers, there has been an increasing demand for the hydrometallurgical approach. High-grade ore deposits that justify smelting have become a rarity. Low-grade deposits will be the main source of strategic commodities. Atmospheric and terrestrial pollution, low energy and water demands are the order of the day, as emphasized in many of the presentations. There were several references to the global recession and the low prices of copper, nickel and cobalt, the backbone of
base metal economics. Thus many of the exciting projects described at the conference are in jeopardy, creating a perception that the future is bleak in the short term.
Undoubtedly many of the promising new mines and plants will be put on hold. But while there is a downturn on new expansions, there is no shortage of new challenges. The prospects for further development work in Southern Africa can be rated as strategically important. There can now be no doubt that global warming is biting into the quality of life of its inhabitants and fossil fuels must be replaced to an increasing extent by nuclear power. This means uranium (the resources of which are not as plentiful as previously thought) achieves a renewed prominence.
As is well known, there are large low-grade resources in Namibia and along the western areas of Africa. There is still a lot of uranium to be recovered from the gold resources of South Africa, including the waste dumps that abound. This will represent a challenge for the low-cost and zero-waste potential of hydrometallurgy.
I feel certain the next big step forward will revolve around WATER. Certainly this will be the case in Africa and probably also in Australia. The ‘Noah’ approach to not caring what happens to the water is well on the way out, and there were many references to the need to recycle water and to avoid the build-up of impurities in doing so. Thus the precipitation of the valuable and toxic metals using lime and even magnesia complicate this recycle, and the recovery of reagents such as the acid for leaching.
Several of the papers at this conference point to the need for the development of a resin-in-pulp (RIP) process for handling leach slurries to recover substantially all the water. The resin-in-pulp technique is also ideal for the precipitation of metal hydrates without the addition of contaminating precipitants. RIP is in itself a challenge to overcoming the resin losses by abrasive particles in slurries, breakage in valves and pumps, and high velocity impacts. I have a feeling that such new equipment is just around the corner and with a number of other new concepts could usher in a repetition of the previous golden days of ion exchange.
I also foresee an expansion of the areas of application of the hydrometallurgical approach. Clean coal is one obvious example, but there are others such as fertilizers and water treatment where the experience in metallurgical microbiology could be invaluable. But there is a recession and mining and metallurgical commodities are hard hit. Sponsored work is going to be at a premium for the foreseeable short term. But maybe in order to at least maintain our technical manpower infrastructure, we should accept that this is the time for government with industry to sponsor work in hydrometallurgy on a broad front. If one speculates on future directions, this will mean close cooperation with departments of agriculture and energy.
But the focus will, I am sure, be on water, particularly as regards the many resources in desert areas, where water will assume an unusually high value. The days of even allowing a wet filter cake to dry by uselessly evaporating water on a slimes dam are numbered. I learn from a presentation to the Johannesburg Branch that the planned Trek Koppies uranium mine in Namibia will be deriving water from a sea water desalination plant.
At water costs of the order of thousands of cents per cubic metre, Noah’s fears from antiquity could be realized in this modern age in the form of some of the water finding its way via photosynthesis into food crops and vineyards and even into alcohol as biofuel!.
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