Materials handling
various ores and minerals into valuable material and waste – or material that simply isn’t worth the cost of processing. Several such technologies are being implemented within the industry today, from colour sorting and near-infrared (NIR), both frequently used for industrial minerals, to X-ray transmission (XRT), which is most commonly used for base metals, precious metals and non-ferrous metals. Paul Bracher, managing director at IMS Engineering, is well aware of the potential benefits offered by sensor sorting. IMS Engineering began offering sensor sorters for the mining industry in the early 2000s, starting with a basic colour sensor. It now offers some of the latest technologies available today – but one in particular stands out in terms of value for the industry. “If you look at the number of sensors that are currently available, dual energy XRT is relatively robust and well-known,” Bracher says. It’s also less sensitive to dust and particle size distribution differences than other sensor sorters. “It can measure trace elements within a particle, which often wasn’t possible before. It slices the particle up into pixels, and you can look at each particle individually and make a determination of what you’re really looking for. “For example, if you have a coal sample and you’re destoning coal, that coal gets separated when you do sensor sorting. There’s coal and stone in one particle. It splits it up and says, ‘Okay, what percentage is stone? And what percentage is coal?’” The waste material is then separated from the ore and removed from the process, increasing the grade of the ore while reducing the costs that otherwise would have been spent processing the waste material.
Another key advantage of XRT, according to Dr Mathilde Robben, key account manager at TOMRA Sorting Mining, is that it’s a dry process. “With XRT, you don’t need to wash upfront to gain a clean surface because it looks through the particles,” she explains. “For colour sorting, the surface of the material needs to be clean and representative, because if we want to see red rocks, for example, then you don’t want to have a layer of dust or clay on top.” Other sorters – like NIR, for example – may find their results influenced by surface contaminants on the material and, like colour sorting, also require washing. As XRT does not call for washing upfront, it makes it easier to obtain a product for preconcentration, which results in reduced handling downstream, an increase in the grade of the mill feed material, and a reduction in haulage and the various energy costs.
Beyond that, though, removing washing from the process offers a number of knock-on benefits. “Washing is always a problem because you have to deal with the water,” Bracher says. “You usually then have contaminants or mud or something in the water, and so you have to settle it, separate it out
World Mining Frontiers /
www.nsenergybusiness.com
and recycle it again. Whereas if you do it dry and you can screen it dry, you don’t have any of that.” Other mining operations might benefit from a combination of different types of sensors, Bracher suggests. This can be useful when processing high- value ore, when a series of sensors might offer a more comprehensive separation of waste materials and valuable commodities. Diamond mines frequently have issues with kimberlite – once it’s been mined, the ore is extremely valuable, so mining operations want to ensure it’s not included in the waste material. “One of the big reasons why you’re seeing bigger diamonds being discovered now is you’re able to detect them much earlier on and also without them being crushed or sized,” Bracher says. “We have special crushing technology that avoids diamond damage, and using a sensor sorter is a very good process for making sure you don’t damage precious minerals.”
Further benefits
The advantages of sensor sorters extend far beyond reducing fine tailings, cutting water and energy costs, and creating more efficient processing. They can also help solve one of the main issues affecting the modern mining industry. The past decade has seen a number of high-profile tailings dam collapses, and the resultant destruction and death has left a black mark on the industry as a whole. It’s also led to increasing awareness on the need to reduce wet tailings from mining operations as much as possible. To do this, sensor sorters are used to preconcentrate the mined matter, which removes barren material early in the process and at as coarse a particle size as possible, and thereby reducing downstream comminution and processing. “If we talk about reduced tailings, then it really means that we are preconcentrating,” Robben explains. “So, because we’re taking the coarse particle size waste out upfront, the material that goes into conventional processing is reduced and you end up with less fine tailings at the end.”
“For colour sorting, the surface of the material needs to be clean and representative, because if we want to see red rocks then you don’t want to have a layer of dust or clay on top.”
Dr Mathilde Robben
Preconcentrating is also invaluable when dealing with stockpiled material that would otherwise have been considered waste and dumped. “Often with old dumps, it’s very difficult to use them. But in a gold operation that we were doing, they could take those dumps and double the grade,” says Bracher. Indeed, at Kensington gold mine in Alaska, the grade was reportedly increased by as much as sixfold.
33 4-7%
Of global greenhouse emissions are produced by the mining industry.
McKinsey
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