The Asia Miner

OCT-DEC 2017

The ASIA Miner - Reporting Important Issues to Mining Companies in the Asia Pacific Region

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46 | ASIA Miner | Volume 14 • Issue 4 | 2017 Supplier News REPURPOSING technology to suit coal mining is becoming a speciality for engi- neers at New Acland Coal (NAC). In our latest venture, NAC has taken technolo- gy originally designed to sort rubbish and given it a new application in coal sorting. Using X-ray sorter technology originally developed for waste recycling industries, NAC engineers are able to eject reject material from raw coal before it enters the coal preparation plant (CPP). Previously the technology has been used to separate mechanical compo- nents of wrecked automotive bodies from various components of domestic house- hold garbage. NAC CPP manager Robert Rashleigh said the technology had also been ap- plied to ore sorting. "While this technology is currently used in processing metalliferous ores like tung- sten and nickel, our trial has shown that it can also process New Acland coal with good results," he said. "Should we move forward I believe this would be the first time the technology is installed in a coal mine in Australia and we are excited by the initial results of the trial." Pilot scale testing of the technology was carried out at STEINERT Australia in Bay- swater, Melbourne, using coal sourced from NAC. The process is relatively simple in prac- tice. A stream of sized material is fed to the X-Ray sorter, spreads out on a wide horizontal conveyor and passes between the X-Ray source and a detector. Inside the sorter, the X-Ray beam passes up- ward through the moving stream and differentiates particles of coal and stone, based on an adjustable sorting algorithm. As the stream discharges over the end of the conveyor, compressed air jets placed across the direction of flow are ac- tivated. Individual particles of target ma- terial are ejected out of the falling stream by the air impulse and separated from the flow. Either species can be ejected from the falling stream. Dual energy X-Ray transmission scan- ners are used to measure the amount of X-Ray radiation absorbed within each par- ticle at two different energy levels. There- by, it is possible to calculate the average atomic density of each measured area by the controlling software, independent of the effect that particle thickness or size have on the absorption of X-Ray radiation. Thus, the sorter can distinguish a coal particle from a stone particle with a very high degree of accuracy. However, for the sorter to be able to determine what is coal and what is reject material it had to learn the difference. In 2015, NAC sent a selection of hand- picked samples to Melbourne that includ- ed discrete coal and stone, taken from the raw coal stockpile. These samples were placed in the source beam so that the machine could be 'trained' to recog- nise coal and stone. The characteristics of the individual sam- ples were read by the machine while sta- tionary in the detector beam. From these readings, the machine's separation algo- rithms were developed and these were used as the basis of separation when the pilot work was undertaken. In December 2016 bulk raw coal sam- ples, in the order of six tonnes each, were collected from the NAC run of mine (ROM) pad to be used in the pilot scale project. The bulk material was screened in the laboratory to produce test portions -150+50mm and -50 +25mm with 1.5 tonnes and 1.3 tonnes respectively being sent to Melbourne. Although the -25mm was not treated, 25mm is an arbitrary size and the X-Ray sorter can treat small- er sized material. The relatively large test amounts were used to give more reliable outcomes. The prime target outcome of the pilot trial was to remove stone from generally poor quality ROM coal and at the same time en- sure that no significant quantity of recover- able coal was lost. To achieve this, a high cut point was tar- geted when upgrading CPP feed in order to minimise coal loss to reject. The sorting algorithm derived from the 2015 NAC test samples was used in the pilot trial and the stone was ejected from the falling stream. The algorithm was adjusted to reject only the highest mineral content particles so that coal loss to reject would be minimal. The first drum of -50+25mm was fed through the machine and the separated streams visually examined. While initial separation appeared to be ef- fective, there were small amounts of stone in the product and clean coal in the rejects which appeared to be misreported material. These particles were hand-picked from their respective streams and re-fed individually to the machine. In all cases, the particles reported correct- ly. This indicates that the sorter was detect- ing and ejecting the material type effectively, but that there was another physical mech- anism causing the material to misplace. These hand-picked particles were retrieved and returned to the streams to which they initially reported. For the -150+50mm test portion, the first drum was fed to the sorter using the existing sorting algorithm. As for the -50+25mm ma- terial, stone was ejected from the stream. The initial separation was visually unsat- isfactory with significant amounts of coal and reject misreporting to their alternate streams. In a similar manner to that of the first test sample, pieces of stone were removed from the product and individually re-fed to the sorter. In all cases, the material reported correctly. These hand-picked pieces were returned to the product stream. The sorting algorithm was adjusted and the material was recombined and re-fed. An improved separation resulted, but there remained some coal-bearing material in the reject, some of it as inter-banded compos- ite material. Ideally, further adjustment to the sorting al- gorithm would have been made in order to reduce the amount of coal loss. However, From junk pile to stockpile with STEINERT By New Acland Coal principal process engineer Michael Rodgers

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