When processing sulphide ores to extract copper, zinc or lead, the focus is on ensuring that the mill is always operating at full capacity. The challenge is to optimise the process by eliminating waste in the early stages and maintain a high recovery rate, TOMRA Mining says.

This means that less barren or low-content rock will be processed, consequently increasing the metal content in the input of the mill. The result: significant cost savings and reduced environmental impact per produced tonne of metal.

In the case of copper, the mineralogy and lithology of the ore will affect how effective sorting can be at removing waste. When sorting copper sulphides with a non-disseminated texture, the focus is on waste removal to maximise recovery. However, three quarters of global copper production come from porphyry deposits, where very small grains of the metal are disseminated, making detection particularly challenging. Zinc and lead sulphides present similar sorting challenges to non-disseminated copper, although the metal content in the mineral is typically higher, so the focus will be on waste removal while maintaining the recovery levels.

The technology to sort copper, zinc and lead sulphides effectively to optimise the process is available from TOMRA Mining, it says. Its X-ray Transmission (XRT) sensor-based sorting technology can effectively detect sulphides in mineralised run of mine materials as they carry elements with higher atomic densities than non-mineralised waste rocks. After crushing, the ore in a size range from +8 mm to 80 mm is fed into the sorters and the barren and low content rocks are eliminated, resulting in a higher head grade of the mill feed. In addition, the eliminated waste can be replaced in the mill with more upgraded sulphides, increasing the efficiency of the mineral process.

However, in order to maintain the capacity of the mill, it is necessary to increase the amount fed to the crusher. This will have an impact on the mine and extraction planning. Due to the lower processing costs of sensor-based sorting, it is also possible to bring this in the calculation of the resource evaluation and the final pit design, according to TOMRA Mining.

TOMRA’s XRT sorters scan the individual rocks fed into the machine on a conveyor belt with overhead X-ray sources. At the same time, detectors located inside the belt collect data from the ore. The position of sensors, close to the rocks, combined with the strong X-ray power sources result in extra high-resolution images. This enables TOMRA’s XRT sorters to effectively process even most of the challenging porphyry copper disseminated deposits. Waste rocks are ejected by high-precision, fast pneumatic module, which adds to the sorter’s efficiency.

In copper sulphides with disseminated texture, a TOMRA XRT sorter can achieve an upgrade ratio of copper content in the mill feed ranging from 20% to 100%, while separating 20%-45% of mass as the waste material. With porphyry copper, the cut-off grade is typically 0.5%, but in view of the surging demand, it is now often as low as 0.2-0.3%. With TOMRA’s XRT technology, it is possible to achieve high recovery rates even at the lower grade, as shown by the tests conducted on run-of-mine samples from at OZ Minerals’ Antas Norte mine, in Brazil, the company says. The sorter demonstrated its ability to achieve recovery rates of at least 90% or reduce the waste grade down to 0.3% copper.

Heitor Mesquita Carmelo, Plant Manager at OZ Minerals Brazil, explains: “A bulk test was conducted to evaluate TOMRA’s XRT technology, and subsequently, the company decided to test it continuously in a pilot installation at the Antas Norte site. The results were consistent in both tests, demonstrating that the technology is effective for industrial application. TOMRA’s technology holds significant potential for OZ Minerals Brazil’s strategic plan, with the possibility of making deposits with lower ore grades viable, reducing operational costs, enhancing transportation safety for pre-concentrated ore, as well as decreasing the CO2 emission resulting from this activity.”

In lead and zinc sulphides, tests conducted by TOMRA have shown that it is possible to achieve an upgrade ratio of two to three times lead or zinc in the output of the sorter. Here the mineralisation plays an important role and can dramatically affect the upgrade ratio, TOMRA Mining says.

TOMRA’s XRT sorter delivers multiple benefits for copper, zinc and lead mining operations, beginning with its uniquely high capacity, which can be as high as 150-200 t/h per sorting width meter – a differentiator of TOMRA’s which also meets the requirements for medium- and large-size operations, it says. The sorter’s operational efficiency can be further improved with TOMRA Insight, a cloud-based subscription service that turns the sorter into a connected device that generates process data. It enables mining operations to monitor and measure performance in real time and optimise the process as well as tracking faults to improve maintenance and keep the plant always operating at its best.

Another important benefit of the sorter is the capacity to lower operating costs through its efficiency and energy saving features such as its ejection module that uses compressed air to eject the particles – up to 80% less compared to other ejection systems – dramatically reducing energy consumption compared to conventional sorting machines.

Optimising the process also reduces its impact on the environment. In addition, TOMRA’s XRT technology is a dry process, so that the overall use of water and chemicals is also reduced.