MTA-AUS 2014

CONEXPO-CON/AGG VIP SHOW GUIDE contains Floor Plans and a complete listing of companies exhibiting at the ConExpo-Con/Agg 2014 trade show in Las Vegas March 3-7, 2014. It also contains 2014 forecasts for the Aggregate, Concrete and Cement industries

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64 VDMA | 2014 VDMA MINING SUPPLEMENT VDMA Mineral Processing: X-ray Ore Sorting Lightens the Load on the Mill Long recognized as a market leader in magnetic separation, Steinert has also branched into sensor-based sorting systems. The company supplies electromagnet drums, eddy current separators and induc- tion, and X-ray and near-infrared (NIR) sorting systems. The com- pany recently supplied an X-ray sorting system to the Wolfram Camp mine in northern Queensland, which produces tungsten, molybde- num and bismuth concentrates. In 2008, open-cut mining and ore processing through a new concentrator commenced operation; how- ever, the plant operated for less than three months when technical difficulties coupled with a shortage of working capital, further com- pounded by the global financial crisis, resulted in a suspension of operations. Wolfra m Camp Mining Pty Ltd. was acquired by the cur- rent owners in 2011 and they embarked on a plant modification and expansion program. The process plant was designed to treat ore from an open-pit mine at a rate of 150,000 metric tons per year (mt/y), through a process comprising: • Two-stage crushing; • Ball-mill grinding in closed circuit with a screen; • Bulk sulphide flotation, followed by selective flotat ion of molyb- denite into a concentrate; and • Flotation tailings treated in a gravity circuit comprising centri- fugal jigs and shaking tables producing a +60% wolframite concentrate. The plant modification program improved ball mill screening; added cyclones, spirals and shaking tables; and removed centrifugal jigs, drying, and magnetic and electrostatic separation. Limited test work had been carried o ut by the previous owners into X-ray ore sorting and indications were that a high proportion of barren material could be rejected with minimum loss of valuable minerals. This offered a process route to increase annual tonnage treatment by rejecting a significant amount of waste ahead of the grinding and downstream process plant. Pilot ore sorting was carried out at the site, which confirmed earlier find ings, then an arrangement was entered into with Steinert to lease a commercial capacity ore sorter for on-site trials that further con- firmed the amenability to X-Ray ore sorting and culminated in acqui- sition of a new unit that was commissioned in March 2013 and incorporated into the Wolfram Camp Process. Now a sub-standard grade ROM material is upgraded to economic grades. With all the im- provement s implemented successfully, the plant doubled its capacity to 300,000 mt/y. The X-ray sorting technology was developed in Germany, and Stein- ert in Cologne and its field offices in Australia, South Africa, Brazil and the U.S. are helping mining operations by applying this technology. "The system at Wolfram Camp uses a flat conveyor to feed ma- terial in a single particle layer to the X-ray scanners," said Johan van Zyl, product manager-mining for Steinert Australia. "The con- veyor runs at about 2.5 m/s through the X-ray system, which scans each individual particle and determines if it is a wanted or un- wanted. It makes that decision by measuring the average atomic density of the particles, which is a function of the mineral. A com- puter subjects each particle to an algorithm. The particles follo w the normal arcing trajectory over the end of the conveyor. Under the particle stream, a series of air jets, which are controlled by the com- puter, locate the individual wolframite particles and blast them out of the stream with a compressed air pulse." From a health and safety standpoint, the X-ray system is no dif- ferent than those used for security screening airports, van Zyl ex- plained. "It's a very low dose of X-ray radiation," van Zyl said. "The machine is screened using mild steel and lead in such a way that there is no leakage. Most countries do, however, require the units to be registered with the relevant health and safety au- thorities. The mining company also needs to have a radiation officer on site." This technology has been available for 30 years or more, but ad- vances as far as mi croprocessors enable the processing to happen at a speed that allows decent throughput, van Zyl explained. "There also has been several advances mechanically with air valve tech- nology," van Zyl said. "When the technology was first tested, the throughput was so low that the system was not economical." This technology lends itself to high-value base and precious metals, such as tungsten, nickel sulphid es, gold, platinum, dia- monds and other gem stones. Steinert has recently tested the X-ray sorting system on diamonds. "We can separate the kimberlite from waste rock and reduce the size of the stream being processed," van Zyl said. "The technology does not necessarily need to target the Steinert's X-ray ore sorter eliminates waste rock ahead of the liberation process.

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