Since the beginnings of mining some 40,000-odd years ago, there has been a need to separate the valuable minerals and metals from the waste – to sort the wheat from the chaff, as it were. Today, we use ore-sorting technologies to identify and remove waste and below-grade ore to pre-concentrate the process plant feed, ensuring only economic ore is processed, reducing costs and improving efficiency.

However, as with any technology, ore sorting is a process that is undergoing continual refinement, as mining operators look to optimise their processes and boost their bottom line. For the companies responsible for developing and selling ore-sorting solutions, their systems can always be that much faster, the particles they process can always be that much finer and their operational costs can always be that much lower. One such company has developed a new ejection module for one of its leading ore sorters, specifically designed for sorting small particle sizes.

Mighty oaks from little acorns grow

TOMRA was founded in 1972 by two brothers, Petter and Tore Planke, from Asker, Norway, who invented the world’s first automated reverse vending machine. From these humble beginnings, TOMRA Mining now designs and manufactures sensor-based sorting technologies for the global mineral processing and mining industries. As a global leader in sensor-based ore sorting, TOMRA is responsible for developing and engineering cutting-edge technology designed to withstand harsh mining environments.

In February 2023, TOMRA Mining launched a new ejection module for its COM Tertiary XRT Fines ore sorter. This new TS100C module, alongside the sorter’s recently introduced image processing unit, is capable of sorting particle sizes down to 4mm in high-capacity applications with much higher energy efficiency, delivering a high-quality product at low operating costs.

“If you look at sensor-based ore sorting in general, they analyse every single particle separately and, after that, they take a decision if [the particle] should be ejected or not – that’s the main principle,” explains Ines Hartwing, director product management at TOMRA Mining. Fine particle sorting boasts one big advantage in the market as, typically, ore sorting depends on good liberation – the separation of waste and product from each other. The smaller the particles used in a sorter, the more effective the liberation of product from waste.

However, crushing material to fine particles also presents a number of challenges for particle sorters – the main one being that if you reduce the particle size, the resulting tonnage goes down in tandem. At the same time, the amount of particles that need to be analysed rises – and with more particles to be analysed, the ejection rate of the sorter goes up too. “The more you need to eject, typically means that air consumption goes up as well, because we use air in the ejection process,” says Hartwig. “And this is a big driver on the operational costs.”

As she says, energy for compressed air is indeed one of the main drivers of costs in sensor-based sorting. “In general, if you look at the energy consumption of the sorter, the main product consumes around 10–15kW – but for the compressor to create the compressed air required, we need around 75–100kW. So, it requires a much higher amount of energy to create air needed to eject the particles than to run the sorter itself.”

With energy prices on the rise, this can be a big operational cost for mining operators, so being able to bring this cost down can be a huge benefit. This is where the new ejection module comes in. Field tests have shown that TS100C module can deliver a 70% reduction in energy use on a production scale. “That’s a real difference,” Hartwig adds. “For the customer to just have that money back in their pocket, to not have to pay it.”

With this in mind, mining and mineral companies select the ejectors for their sorters depending on the intended application and particle size. Bigger particles require more power, as they require a higher airflow to be successfully ejected. Smaller particles, on the other hand, require a lower airflow and therefore less power – however, they also require that the ejectors operate at a very high speed as the throughput goes much faster. TOMRA Mining’s new high-resolution TS100C ejection module features a new type of ejector that is four times faster than the version it replaces, making it ideal for use with small particles.

At the same time, pairing the ejection module with the new image processing unit was another big step in enhancing the efficiency of TOMRA Mining sorting solutions. “If you look at the perfect sorting performance, which we always do, that’s always a combination of mechanics, electronics, software, image processing, [and so on],” says Hartwig. “So, if you just have one perfect part, then that does not mean that your ore sorting is working in perfect condition and performance. We need to look at how all these needs fit together.

“If you want to sort very small particulates, the fast ejectors are one thing, but you also need a very high resolution of the sensor and your image processing due to the number of particles you need to analyse – it must be much more powerful,” she explains. The new image processing unit is a PC-based solution, Hartwig adds, which provides more freedom for the user to make changes to the system, while also enabling them to run different processing units in parallel to provide more options for particle analysis. The two new elements, when used in combination with some mechanical changes, provide peak performance and higher precision when sorting small particles at high throughputs.

Similarly, the mechanical design of the sorter has also been improved with the introduction of a new splitter plate and more precise calibration equipment, all helping to ensure greater precision in the alignment between detection and ejection systems required for fine particle sorting.

Waste not, want not

Being able to process even smaller particles is a huge boon to TOMRA Mining’s ore sorter offerings, Hartwig says. As things currently stand, she notes, typical mining processes generate a lot of fines, which either results in a lot of waste material being processed or else the creation of stockpiles until a suitable sorting solution is brought in to process this material properly.

“I recall a site visit with a customer and standing in front of a really huge pile of material,” Hartwig notes. “And they were not able to use that properly because processing this material was much too expensive to get the product out of it – so they just put that aside and waited for a solution.” The benefits of TOMRA Mining’s ore sorters, then, is that they can use all the material that a mining operator gets out of a mine in a much more efficient way, creating higher-value products while reducing product loss.

While developing the new ejection module, extensive test work was conducted at the TOMRA Test Center, using both artificial material mixtures and real-world sample material. The tests showed a spectacular reduction in air consumption compared to industry standards, as well as an improvement in product purity of around 15%. “After that, we were quite confident with what this module can really achieve in the market,” notes Hartwig.

From there, TOMRA Mining looked for a specific customer that could gain the maximum benefit out of this new ejection module and found one in Turkey, which had already been running a COM Tertiary XRT sorter to produce high-grade magnesite for over two years. This was an opportunity to test the TS100C module in the field, so TOMRA Mining went to that customer with the numbers from the test study and laid out the benefits that they could expect if changes were made to his current setup. At the time, the customer’s sorter was removing up to 50% low-grade and waste material from the raw magnesite feed, with particle sizes ranging from 10–35mm at about 20t/h. “So, a really high ejection rate,” Hartwig summarises.

The customer completed several trials, carefully taking note of the energy savings and sorting efficiencies. Just by changing the ejection module, the customer was able to reduce the amount of air consumption by about 70%, with an increase in product recovery with a lower mass-pull-to-waste by producing the same product quality. At the same time, they achieved higher throughputs of about 50% – up from 20t/h to around 30t/h with comparable results. “It was a real win-win for us,” says Hartwig. “To get the information from the field, not just on a smaller sample – to really run it on a daily basis on two or three shifts per day, and really prove the experience, as we had done in the test centre.”

Every resource counts

Of course, improving ore-sorting solutions isn’t only about generating valuable material and reducing costs – it helps reduce mining’s environmental footprint, which is a key focus for TOMRA Mining. Being able to preconcentrate valuable ore through sorting reduces the industry’s reliance on other solutions, which typically involve dense media separation and the use of a lot of water and chemicals

“‘Greener mining’ sounds a little bit strange because you are digging into the dirt,” says Hartwig. “But I think sensor-based ore sorting in general is a big step into a greener and more environmentally friendly solution.” TOMRA Mining’s customers are well aware, however, of the benefits of integrating greener solutions into their operations. After all, a European Corporate Governance Institute study from September 2022 found that 72% of the mining companies surveyed link ESG metrics to executive pay.

The development of the TS100C ejection module came about in response to customer demand, Hartwig notes. Many of the company’s customers were already running sorters on a bigger size fraction, ending up with a lot of material they were unable to adequately sort through. The need to make TOMRA’s sorting capabilities usable for even smaller particles was out there – just waiting to be addressed.

“At the moment, we get more and more inquiries. I think that’s due to the market trends that we’re seeing – using the material that is already there, which is mined in the best and optimal way,” Hartwig adds. “And that actually fits with the TOMRA mission quite well. If you look at our slogan, ‘TOMRA creates sensor solutions for optimal resource productivity’ – that’s exactly what we as TOMRA want to do.”

Across TOMRA’s various divisions, from mining to recycling, food and collection, another variation of this motto is commonly expressed – ‘Every resource counts’. The company is happy to put this into practice for its clients, and to demonstrate this it has installed a COM Tertiary XRT Fines sorter featuring the new TS100C ejection module and the new image processing unit at the TOMRA Test Centre in Wedel, Germany. There, customers and potential customers alike have the opportunity to run tests on material samples from their mines, to see if they too could benefit from this solution. After all, every customer counts too.

This article first appeared in World Mining Frontiers magazine.