Ore Sorting Bad For The Environment?

I'm fortunate to be exposed to many new technologies being developed out there for the mining industry and am continually trying to wrap my head around the potential application of these into an entire system. That means not just looking at the technology itself and its unit operation, but also understanding the impacts on the entire system (upstream, downstream, economics, social, environment etc.) like a good engineer should. The topic of how recent engineers have been hyper-specialized and resulting in very narrow thinking is an entirely different discussion I'm going to park for now.

Ore sorting has been touted as a massively positive game-changer in terms of economics and environmental impacts. A few links for these claims... ThermoFisher, Published Journal Paper. Through this article, I hope I'll demonstrate why systems thinking in mining is so important and how ore sorting is potentially a very bad thing from an environmental point of view. There are many variants of ore sorting but fundamentally they all do the same thing, reject waste from an ore stream. I'll focus on optical ore sorting in this article but the broader concepts should wholly apply to ore sorting in general.

The concept of optical ore sorting has been around for a fair amount of time but it appears that the system impacts, and the technology itself, are still not well understood. We only have to look as far as the recent news article published about Vital Metals to see how they have fundamentally changed their application of the technology away from what they previously set out to do once they really started to understand how the technology worked. (Vital Metals Article at Mining.com). I'll explain a little about what I can infer from this article and how this applies to the broader application.

The go-to concept for ore sorting is that you crush your typical 'ore' from the mine and then feed this into the optical ore sorter which then identifies waste and rejects this from the stream. The implied benefit is that you now have a much smaller volume of material that you have to treat through the process plant and store in tailings which then results in less processing and tailings which translates into capex and opex cost savings, less power consumption and a smaller tailings footprint. Vital Metals, looks to have set out on this same path initially as evidenced in their publication in the Canadian Mining Journal. They too were touting the environmental benefits of ore sorting at this point. See the two graphics below for a depiction of how this is usually presented.

If you put together the economic model for the ore-sorting scenario above, you'll discover the reality of this arrangement and will typically find that the economic benefits are marginal. This is because the cost savings of not processing and storing waste material has to offset the added costs of the ore-sorting equipment which is relatively expensive. You'll also see that you're not really reducing the environmental footprint because you're really just storing more waste rock that would've made its way to a tailings facility previously. This is why we haven't seen ore-sorting live up to its potential of being an absolute game-changer for mining.

If you go and start to flex that ore sorting model, you'll find a phenomenon that somehow is eluding a large portion of the mining industry that is looking into using this technology, as Vital Metals recently discovered for themselves. The graph below shows how the overall economic value of ore-sorting (NPV) changes with varying feed-grade and recovery. You can see that the reality of ore-sorting from an economics perspective is that the NPV impact increases with reductions in grade.

This phenomenon is very important to understand and it is something that Vital Metals have obviously discovered for themselves. It means that ore-sorting high-grade feed material has much less economic impact than applying this to low-grade material that may be close to being considered as waste. If you apply this logic, you can then imagine that you would rather take material that was previously considered as waste material, upgrade that using ore-sorting and blend that with the existing stream that was previously classified as ore.

If you zoom out even further and contemplate what this means for the system as a whole, it means that you are effectively lowering your economic cut-off grade to include an even bigger volume of material in the classification of 'economic ore' (i.e. make the yellow volume in the mine cross-section even bigger). That will increase the volume of commodity that will be recovered and will likely increase the life-of-mine if the process plant capacity remains the same. The economic benefits of doing so should be quite apparent.

If you read the Vital Metals article, you will see this logic reflected as follows:

“The 58 000 t of ore mined contains approximately 11 500 t of ore previously identified within our pit design with the remaining 47 500 t previously classified as waste. This includes ore which was in the top 5 m from surface and hence excluded from the original resource and hence mine inventory, the high-grade zone in the ‘dragon’s tail’ and material which was below the resource cut-off which, during commissioning of the ore sorter, we found could be successfully sorted and is now regarded as ore which is suitable for processing. This presents a significant opportunity for increasing the quantity of rare earths to be processed from the North T deposit. “Because we have identified all this additional material which we are now able to process, we made the decision to amend our mining campaign, so that we can redesign the pit to ensure we maximise this additional quantity of rare earths which we will mine at North T in subsequent campaigns,” Atkins said.

Vital Metals have stumbled onto this logic through on-site testing are on the right track to applying these principles for economic benefits. But what does this mean for the widely touted 'environmental benefits of ore sorting then? If we apply this logic to the overall mine concept, we can see the following:

1. The overall reported reserve and mine plan footprint get much bigger to access low-grade material that lies deeper in the ore body and in the extremities.
2. The amount of waste rock produced increases substantially because of the increased mine plan footprint.
3. The volume of tailings produced increases because the originally contemplated ore mass is still being processed but an additional stream of sorted waste is being added to this for processing.

Therefore, it should be obvious to see that ore-sorting is going to have a hugely negative impact on the environment because it incentivizes the extraction of larger volumes of low-grade material and the associated waste that comes along with accessing that.

If you now read through the most recent press release published by Vital Metals, the improved economic benefits are the singular focus but the greater impact on the environment is now not mentioned at all. Clearly, this is a company that is putting economics ahead of the environment. When it suited them, the environment was a critical consideration but when it didn't, it fell off the bus. It's a perfect example of greenwashing that we're seeing in the industry right now.

If you think about this logic further, it has even greater implications... where improvements in technology create more efficiencies, the cost savings will likely translate into increased reserve and will similarly be translated into bigger mine plans and larger environmental impacts. This serves to prove the point that if the mining industry truly wants to reduce environmental impacts, it should move away from chasing efficiencies in doing effectively the same thing as yesterday and start implementing technologies that are targeted at extracting less ore out of the ground. Period.

Lastly, we need more systems thinkers in the mining industry that can expand thinking beyond the realms of unit operations and can understand the broader impacts in terms of technical systems, social and environmental impacts. I would encourage more engineers to start to learn more about the entire ecosystem into which their designs will be deployed and to start questioning how these designs will have impacts beyond the scope of their unit operation.

Ken Murray?is CEO of Captrics Consulting which he founded to increase the effectiveness and efficiency of the mining industry through the use of improved management techniques and new technologies.

He is a professional mechanical engineer and professional project manager with a 20-year background in capital projects, management consulting, innovation and technology. His passion is to improve our lives by continually learning and trying to conceptualize new ways of working. His background allows him to adopt a systems-based approach to tackle most problems and to create an integrated world where the system is better than the sum of the parts.