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| CSIRO | SOLVE | Issue 5 Nov 05 | |
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ARTICLE
MINERALS PROCESSING: Spinner Becomes a Screen Star
By Rebecca Thyer
‘Blinding’ – blocked screens – is a constant frustration for mineral processors. A new rotary tumbler may be the answer. Giant sieves – huge screens up to 3 m wide and 6 m long – are used by the world’s mining industries to separate minerals for processing. However, the efficiency of screens is regularly tested when material blocks a screen’s holes, reducing its operating surface and causing downtime as the screen is unblocked.
The tumbler, christened the ‘Rotary Classifier’, was developed by Dr Guy Metcalfe and Dr Kurt Liffman and their team at CSIRO Manufacturing and Infrastructure Technology. The Rotary Classifier separates granular material by tumbling material in a tilted vessel at various speeds, causing avalanches in the surface. This moves particles of a smaller size or higher density towards the centre and particles of larger size or lower density radially outward, allowing different materials to be extracted at selected locations. John Noordhoek, general manager of RCR Tomlinson’s Bunbury operation, explains that screens are needed to separate minerals, and all processing plants in industry have them: “But blinding is a huge problem. Once a screen becomes blocked, it reduces screening efficiency and increases processing time.” He says the Rotary Classifier development could overcome this problem and improve production efficiencies. “Building a commercial-scale pilot plant will allow us to prove the technology works. Early testing looks positive, so the potential out there for a screen-replacement product is huge.” The Rotary Classifier’s ability to process the large volumes required by the iron ore industry on a much smaller footprint than traditional screens is also a drawcard, as is its dry processing capabilities. Dr Metcalfe says the Rotary Classifier’s dry separation ability is an unexpected benefit. “Dry processing is becoming more and more important. It was not the reason we started looking at the fundamentals of granular materials, but it has become a huge selling point for the technology,” he says. The Rotary Classifier’s ability to process the large volumes required by the iron ore industry on a much smaller footprint than traditional screens is also a drawcard. Liquids are currently used to segregate material by density, with heavier materials sinking and lighter ones floating. However, a dry separation process is advantageous in two ways – using less water will be crucial to mining industries in environments such as Australia, where water is not available or is costly, and less energy will be used to pump water to and around a plant. Dr Liffman says the technology will be of immediate importance to the iron ore industry, where more minerals will be obtained in an environment where limited or no water is available. “Some processors are already talking about having to pump in sea water, desalinating it and then using it for separation processes, a costly process. However, if we can prove that dry separation works, industry could be clamouring to use it.” Dr Metcalfe says that CSIRO’s growing knowledge of granular materials has made dry separation possible. “Granular materials are almost a different state of matter to fluids and gases, and the big scientific question has always been – how do they move? “Once we uncovered some of the mysteries of granular materials we started thinking about how this information can be applied. The immediate answer was the minerals industry, because of the high volumes needing to be processed. “However, other possible applications are in the grains industry and the construction industry, which both separate a lot of granular material. It could also benefit the chemical industry, because 60 per cent of the inputs they use are granular.” APPLICATION CSIRO’s new Rotary Classifier separates granular material by tumbling the material in a tilted vessel at various speeds
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This is called ‘blinding’ and is a common industry problem. However, a Western Australia-based mining equipment company is testing a potential solution in the form of a rotary tumbler. RCR Tomlinson Ltd plans to have a pilot tumbler in operation by early 2007 before scaling up a full system.
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