November 2007

New sorting system breathes life into talc mine

By C. Hersey

Ore and waste rock piles being produced by the optical ore sorter

A new technology’s in town, one that separates the good from the bad, and in doing so has saved the life of at least one mining company. An optical ore sorting system, aptly named ‘Automated Ore Sorting,’ has been set up by Terra Vision at the Sherritt Dynatec Minerals Division mine site (historically known as Canada Talc). Talc was discovered on a farm in Madoc, Ontario, in the 1880s. It first came into production in 1896, and, having gone through a few names and owners, has since mined over 800,000 tons of high-grade talc. Without the help of this revolutionary sorter, the well-known mine may have faced closure.

The need for the optical ore sorter came about when Sherritt Dynatec Minerals’ time came to undergo a little construction. For a variety of reasons, their underground workings were shut down and their headframe needed to be rebuilt. Unfortunately, delivery of the new headframe took quite a bit longer than they had expected, and the mine found itself unable to provide for the mill: ore-less and empty-handed.

Luckily, Terra Vision to the rescue. Under sub-contract, Terra Vision began sorting the waste. Old material, discarded as waste and deemed useless, is now being sorted over again. Ore is recovered and then sent to the mill, thus saving the mine from shutting down. Before the sorter came along, everything was done by hand, and the tonnages were obviously much too low, which is why Terra
Vision was called in.

The system, which is containerized (for shipping purposes), was ordered on May 7. It was delivered to Quebec City by CommoDaS GmbH on May 15, containerized by Terra Vision, and delivered to Madoc on May 22. Sorting began a week later. The technology is fairly simple. “Automated ore sorting is a complementary technology that applies a variety of sensors, including cameras and/or conductivity, magnetic susceptibility, and dual energy X-ray transmission sensors, to control the mechanical separation of ore from gangue on an individual rock-by-rock basis. The system separates the rocks by diverting individual rocks with a bank of high-pressure air jets. The air jets are controlled by a high speed image/data processing unit coupled to sensors that are scanning the entire width of the chute.”

This means that the machine looks at each rock individually with a camera and makes a decision as to whether or not it meets the ore criteria. While some systems sort based on texture, the system set up for Sherritt Dynatec sorts based on colour. These systems can be configured for applications ranging from precious gem sorting (+1 mm) up to coarsely crushed ore (-12 inch) with throughputs up to 350 tons an hour.

Terra Vision president Matthew Kowalczyk said that the setup process and optimization for the machine is fairly simple. Terra Vision has a contract to both supply and supervise the sorter. Training for the operators is minimal; once the system is set up for a permanent installation, operator intervention is limited to starting and stopping the processing line and adjusting one or two parameters. Parameters, alarms, and warnings are presented to the operators in a simple touch screen interface.

This automated ore sorting technology, though extremely beneficial, is actually quite a rarely heard-of concept in North America. Outside of the diamond industry, Sherritt Dynatec is using the first-ever optical ore sorter for minerals in Canada. The technology
actually started in the recycling industry in Europe. While ore sorting comes in many forms, ranging from the hand-sorting of waste dumps by individuals to advanced statistical methods based on bulk sampling and chemical assays, the latter has proven to be the most useful and can be applied in various situations using various methods. The automated optical ore sorting equipment can be applicable to not only industrial mineral projects, but also to base metal and precious metal projects. In the case of mill feed pre-concentration, profits can be increased by separating it into high- grade, low-grade, and waste fractions. Environmental risks and costs can also be reduced by sending waste rock to the appropriately designed dumps.

For newer mines, ore sorting can result in a higher cash flow, which could be used to pay off the capital cost of the mill more quickly, said Kowalczyk. For older mines, sorting can “increase the profitability of their operations by only hauling or hoisting ore that is well above the economic cutoff to the processing centre.” In addition, said Kowalczyk, “not only are direct processing costs reduced, but data gathered during the sorting process, such as particle size and description of the composition of the sorter output, can be fed forward, in realtime, to mill operators so that downstream operations can be optimized.” It’s a win-win situation.

Like any process out there, there are of course improvements to be made. Kowalczyk said some of the screening and washing at this installation can be improved to increase the throughput to the machine. They are currently running at about 20 tons per
hour, but with a few adjustments, could run up to 40 tons per hour (feed preparation currently limits the throughput).

Automated ore sorting has been around for over 15 years, and only now are we reaping its benefits here in North America. In the long run, the idea is to eventually integrate the sorter into Sherritt Dynatec’s regular ore sorting process, and not just use it as a temporary solution. Ultimately, the system will ensure that they can constantly provide high-quality talc to the mill. For now though, dumps that were previously considered waste are currently the only source of ore for the mill. This technology allows them to sort their waste piles, send them to the mill, and most importantly, avoid shutdown.

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