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If anything, the recent Minerals Engineering ’02 conference held in Western Australia highlighted the need for continued research and development funding across the global mining sector.
Organised by the UK-based Minerals Engineering International (MEI) in association with Australia’s CSIRO, the three-day event attracted an array of delegates from the international engineering and metallurgical communities, all of whom, it seemed, had one common goal. Basically, that was to reduce mineral production costs (through increased operating efficiencies) in an environmentally acceptable manner.
Rubbing shoulders with PhD students completing cutting edge research, university academics from campuses world-wide and representatives from various R&D-orientated groups were industry professionals from the likes of Finland’s Outokumpu Oy (a co-sponsor of the conference), Australian diversified mining house WMC Resources Ltd, WA-based junior copper and coal miner Straits Resources Ltd, New South Wales gold producer Newcrest Mining Ltd and leading Canadian ore processor Lakefield Oretest.
Given this broad cross section of delegates, the organisers were particularly mindful that all of the speakers received equal limelight. In his opening address, MEI’s Barry Wills said the number of papers were limited so there would be no parallel sessions or keynote addresses. “All of our speakers are keynote speakers, delivering in plenary sessions,” he explained. “Secondly, I have always taken the view that, although the technical sessions are of prime importance, delegates interacting and socialising in a relaxed, informal atmosphere is also vital.”
Part of this strategy involved long morning coffee breaks and lunches in which attendees were encouraged to network. However, following the amount of information crammed into the opening five minute poster presentations, it became apparent that the extra time was also useful in assisting with the mental digestion of the many details mentioned during the short talks.
Speaking first, Willie Coetzee from the South African-based Cape Technikon outlined a study designed to overcome the shortcomings found in previous research on the extensive use of ion exchange resin and the kinetics of such processes. He said a number of factors such as diffusivity, reaction probabilities and collision probabilities - were lumped into a single activity coefficient for each species, while his model also utilised assumptions regarding dynamic equilibrium and re-absorption of counter ions. Electrolyte solutions containing copper, nickel and cobaltic sulphates were contacted with an ion exchange resin to test the developed model. “It has been shown that the activity approach to ion exchange could effectively be applied when ion exchange resins are contacted with multi-component base metal solutions,” Coetzee explained. “Furthermore, this model is currently applied to resin-in-column configurations and it is believed that this method will simplify the RIP design procedure often used in the metallurgical industry.”
Ritva Tuunila, from the Lappeenranta University of Technology in Finland, looked at the efficient production of ultra fine mineral powders and how grinding processes could be optimised to reduce energy costs. In her study, Tuunila observed the effect of a pin stirrer type and its rotation speed on the grinding rate and on the energy consumption of grinding using four pin stirrers and, for a point of comparison, one type of disc stirrer (this was carried out using limestone). The results showed that the stirrer with long pins and the stirrer with short pins set in four equal lines gave the more cost-effective results. While pleased with her results, Tuunila told the conference that more research was still needed.
Neilesh Syna, a post graduate student from the University of Sydney, effectively introduced the issue of environmental responsibility when he looked at the possible substitution of thiourea for cyanide as well as using activated bagasse as an absorbent for the gold thiourea complex. A fibrous by-product of sugarcane milling, bagasse was activated by both physical and chemical techniques. “Bagasse is commonly used by the sugar industry for generation, and it’s used inefficiently,” Syna explained. “We made carbon using physical and chemical methods, we conducted bagasse absorption tests and we also did the carbon characterisations. “The carbon that we made by physical activation methods showed absorption capacities in the order of 318 milligrams of gold/gram, while the chemical one which used a variety of acids and salts with the best being chloride - returning 188 mg g/g. “We also tested some commercial carbons as well and they exhibited a range of 188-322 mg g/g. “As you can see, the carbons we made are fairly comparable in the sense that they lie in the range given by the commercial absorbents. “We found out that the carbon pH is an important factor because the gold thiourea Co-ordination seems to change a bit with pH, and we also found that high surface area is important with gold thiourea absorption.”
Colin Sprake of Canadian-based Falcon Concentrators Inc described how his company was looking to increase the recovery of fine particles by eliminating flotation or cyanidation while maximising gravity potential. Pre-concentration and scavenging of fine material, he said, were becoming as important as rich ore bodies were being depleted and the valuable mineral being recovered was becoming a lot finer. Furthermore, reprocessing of old tailings had also become more economically attractive using high G-force pre-concentration techniques. Falcon has installed gravity-only recovery sheets at three of its plants around the world. At a gold mill in Peru, Sprake explained, batch concentrators were used only within the grinding circuit. “It’s unique in many ways,” he said. “Firstly, it treats the entire mill discharge through gravity and, while at a low tonnage, they screen at 210 microns. “One hundred percent of the gold is -38 microns in size. They still use cyanidation for cyclone overflow, but that’s mainly because the shaking table after the gravity has proved to be inefficient with these very fine gold particles. What they are now doing to hopefully eliminate the final leach or the leach circuit is actually install a Gekko in-line leach reactor to keep the gravity concentrate and maximise the recovery from the gravity circuit.
Another Falcon-built gold plant, this time at Vetrenskoe in Russia, allowed the miner to use a batch concentrator as an in-grinding circuit and treat the higher mill discharge. Two stages of continuous concentrators on cyclone overflow treat a product of PAD 75 microns, thus maximising the recovery from the cyclone overflow. “The two products are tabled from the batch circuit and continuous circuit on separate tables to maximise gravity recovery and assure the efficient performance of the shaking tables within the gold room, and these concentrates are then shipped directly to the smelter,” Sprake said. “The nice thing about this circuit is its running now for around four months and the clients have achieved in excess of 85% recovery by gravity.”
The MEI conference was also a forum for R&D groups like the Commonwealth-funded CSIRO to peddle its latest technological developments, Mike Millen telling delegates about the organisation’s new integrated particle size analysis system for deployment on the grinding circuits of mineral processing plants. Millen said it was built around an ultrasonic particle size analyser and included a slurry sampling station and de-aeration unit to remove air from the slurry before particle size analysis. “The technique has been around for quite a while and it has been used in some particle analysers that are on the market,” he explained said. “We also make measurements on what we call the trouser tide, and that’s basically the time it takes to get across the slurry from the transmitter to the receiver on the other side. From that we measure the velocity, and we also make a standard measure for the variation of the solids loading in the slurry. One of the drawbacks with this methodology is that you have to know your slurry pretty well.”
It was the first time MEI had held one of its conferences in WA. The event attracted around 80 delegates from 17 countries.
Mark Fraser, Minerals Gazette. Email: firstname.lastname@example.org
(This article appears in the October 2002 edition of Minerals Engineering ‘02’s official publication, Minerals Gazette).
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