CommodasUltrasort at Electra Mining as TOMRA Sorting Solutions

1 Trennung wertvoller mineralischer Erze vom tauben Gestein • Separation of valuable minerals ore from waste rock

2 Sortierung von Diamanten • Diamond sorting

3 Sortieranlage PRO Secondary XRT in einem südafrikanischen Kohlebergwerk • PRO Secondary XRT sorter in a South African coal mine

CommodasUltrasort, the mining division of internationally renowned Norwegian-listed, TOMRA Systems ASA, exhibited at Electra Mining (10.-14.09.2012 in Johannesburg/South Africa) under its new name TOMRA Sorting Solutions and presented its full portfolio of sensor sorting technologies. These, depending on application, are incorporated into three main product lines:

• ROM series of belt sorters – suited to coarse primary ROM material up to 300 mm

• Industrial Processing (PRO) Series – comprising chute-fed free fall sorters for primary, secondary and tertiary ROM material

• Gemstone (GEM) Series – comprising sophisticated wet-dry sorters for diamonds, emeralds, tanzanite and other gemstones

Lütke von Ketelhodt, General Manager of TOMRA Sorting Solutions South Africa, is pleased with the name change as it unequivocally identifies his operation as part of the world’s biggest and most technologically advanced sensor-based sorting company. “TOMRA Sorting Solutions provides sensor-based sorting solutions in the recycling, food and mining industries. Over the past 20 years it has installed more than 10 000 sensor based systems in more than 80 markets worldwide. This includes more than 180 sensor-based sorting machines in mining and mineral processing applications throughout the world, successfully sorting a variety of minerals and ores including coal, industrial minerals, platinum, gold, diamonds and tanzanite,” says von Ketelhodt.

There are some excellent results on mines in South Africa. One of these is a chrome mine operating in the western region of the Bushveld Igneous Complex (BIC), the largest chrome and platinum source in the world, where TOMRA Sorting Solutions showed that its X-ray Transmission (XRT) sorting technology produces outstanding results in the separation of lumpy chrome ore from waste rock (Fig. 1). The TOMRA Sorting Solutions XRT chute sorter has been operating on a full production plant at the mine processing 70 t/h at +90 % availability. After blasting and trucking, the ROM is crushed and screened and the -60 mm +20 mm material reports to the XRT sorter with the rest reporting to a conventional beneficiation plant. The feed grade into the XRT sorter averages approximately 32 % chrome and the process upgrades the saleable product to 36 % or better at 97 % efficiency.

Another TOMRA Sorting Solution success has been on one of the largest diamond mines in the world based in the southern African region. Here a pilot study between March and August 2011 on a TOMRA Sorting Solutions prototype XRT belt sorter and fed material with various throughputs and of various size ranges and produced a total recovery greater than 98 %. The pilot was requested by the mine as they were seeking a new recovery method for large diamonds prior to tertiary crushing (Fig. 2).

The main advantage of TOMRA Sorting Solutions’ XRT technology in this application is that it sorts on an atomic density rather than according to physical characteristics or properties such as relative density and luminescence. As the luminescence properties are not always consistent in diamonds, a technology was required that would recognise all diamonds regardless of their physical properties. “Our XRT is able to see the atomic make-up of each particle going through the detection zone of the machine. Therefore, a diamond, which consists of covalently bonded atoms forming so-called ‘diamond molecules’, appears in a distinct light-grey x-ray image,” explains von Ketelhodt. He adds that tests have been undertaken which compare high-throughput XRL technology and the TOMRA Sorting Solutions’ XRT high-throughput technology. It was found that that the TOMRA Sorting Solutions’ technology detected 100 % of the diamonds.

Coal is another area in which TOMRA Sorting Solutions has made a significant mark. Recently, on a leading South African coal mine, the company showed that with its PRO Secondary X-ray transmission (XRT) sorter, coarse raw coal (-100 mm +60 mm) with an average ash of 37.3 % was reduced to 17.8 %, the ash content of the discard was high at 77.5 % and the Abrasive Index was significantly reduced. The sorter improved the coal CV from 17.9 Mj/Kg to 25.0 Mj/Kg as well as the sulphur content, which was reduced by half (Fig. 3).

Von Ketelhodt says that the results obtained from the test are significant in terms of the potential of XRT sorting for coal mines. “In the process we also proved that our PRO Secondary XRT sorter is capable of processing up to 150 t/h of coarse raw coal and effectively removing the bulk of the contaminant stone in the raw coal with all the associated benefits. I believe this technology will become standard on coal mines in future, and especially in the new coal fields opening up in arid areas like the Waterberg,” he says. He adds that with XRT technology, no slurry is produced, resulting in reduced groundwater pollution due to acid drainage and salt accumulation in water circuits. Also it is less capital intensive because it does not require the extensive infrastructure and water handling requirements associated with dense medium separation.