As the mining sector faces growing pressure to extract critical minerals more sustainably, the focus on comminution – still the most energy-intensive stage of mineral processing – is growing.
In this Q&A, Bjorn Dierx, director of HPGR and process engineering at Weir, outlines the key challenges and how grinding technologies, AI-based tools and revised flowsheet designs can collectively help reduce energy use, material consumption and greenhouse gas (GHG) emissions.
Ed Pearcey (EP): What are the main challenges facing the mining industry when it comes to crushing and grinding?
Bjorn Dierx (BD): The world needs more transition metals to achieve net zero, but the mining industry needs to extract these using significantly less energy and water, as well as generating less waste.
Because comminution is typically the single-biggest user of energy on a mine site – it uses up 1% of total final energy consumption globally – it makes sense to target energy savings opportunities that can have the largest impact in the short to medium-term.
If the mining industry is going to reduce its emissions in line with the targets outlined in the Paris Agreement, it needs to adopt new technologies and make the switch to alternative methods to begin to reduce the effects comminution has on our planet. [Meeting] this challenge will require collaboration between METS [mining equipment, technology and services] companies and miners.
In response to these challenges, Weir has developed flowsheet solutions whereby traditional tumbling mills are replaced with more energy-efficient grinding technologies like high pressure grinding rolls (HPGRs) and stirred mills.
Where possible, coarse particle flotation (CPF) technology can be utilised to recover ore at a coarser fraction, further reducing energy consumption and generating a safer, more manageable waste stream.
While HPGRs were first utilised in the minerals processing industry more than 30 years ago, most concentrators still use tumbling mills for grinding duties. However, over that same period, the operating environment has changed significantly.
Two of the most notable operational changes are reduced ore grades and increased ore hardness, and the increased cost of milling consumables, such as power and steel grinding media.
Typically, reduced ore grades result in an increased volume of ore being processed for concentration, which, in turn, increases the overall energy input. Additionally, processing harder ores requires higher grinding energies, which, when achieved with tumbling mills, typically consumes more steel media, resulting in significantly higher milling costs.
Therefore, to reduce their milling costs, miners can implement more energy-efficient grinding technologies like HPGRs and stirred mills. Given that grinding power demand is inversely correlated to the final grind size, the ability to recover target metals at a coarser grind size may also significantly reduce operating costs.
EP: Is AI the best way to enhance the efficiency of crushing and grinding in the mining industry?
BD: AI is one way to enhance the efficiency of crushing and grinding. As the mining industry embraces these technologies, OEMs – who understand the equipment better than anyone and have vast amounts of design, manufacturing, operating and maintenance data to leverage when building AI models – have an important role to play.
With that in mind, Weir’s NEXT Intelligent Solutions harness AI-driven technology to optimise the process and maximise efficiency. The platform acts as an AI-based Intelligent Assistant for HPGRs – it offers automated advice and recommendations.
For example, [the platform supports] adapting to changes in ore feed characteristics. These adjustments are made based on the process data and our AI models, which are built to maximise throughput, while maintaining consistent product size.
[The solution] can adjust the equipment [autonomously] or alert the operator when there are relevant drifts from the expected operational parameters so that corrective action can be taken.
EP: Are there any other technical advances that will enhance the efficiency of crushing and grinding?
BD: Historically, operators have tended to look at equipment in isolation when assessing its performance, often without considering what is happening upstream and downstream.
In contrast, Weir takes a more holistic approach. We are continuing to develop innovative flowsheets, and our process engineers are working with miners to test and develop solutions tailored to their specific challenges and operating conditions.
We are also deploying existing technologies in new ways. For instance, when the mineralogy allows it, we are using an air classifier like an ‘ore sorter’. Since multiple material streams can be generated, this can be combined with pre-concentration – like magnetic separation or CPF – and gangue rejection in a single classification system.
Or, alternatively, it can create a stream of sellable byproduct alongside the main targeted minerals without additional pre-concentration. We have had a lot of miners visit our testing facilities and these solutions have been generating a lot of attention, so I don’t think it will be long before we see them being deployed in the field.
EP: Are there any other ways crushing and grinding techniques can be made more efficient and less energy intensive?
BD: Quantifying the environmental benefits of projects is increasingly important to stakeholders, shareholders and regulators, and scope 4 emissions provide a framework for doing this.
Scope 4 emissions, commonly referred to as ‘avoided emissions’, are defined as the reductions in GHG emissions that occur outside of a product’s life cycle or value chain but as a direct result of using that product.
In March 2023, the World Business Council for Sustainable Development (WBCSD) released Guidance on Avoided Emissions to evaluate mining processes and help ensure credible accounting of avoided emissions, including clear separation from a company’s GHG emissions.
Utilising this guidance, in December 2023, Weir released a study, independently assured by SLR Consulting, that highlighted an opportunity to reduce energy use and emissions in comminution by leveraging three alternative technology combinations.
Three technology combinations were evaluated against a conventional comminution circuit design for an archetypal mine processing 15 million tonnes of copper ore per year in Chile. Each circuit was based on a ‘rock-to-recovery’ system boundary; that is, reducing rock direct from the mine to a size that enables the mineral to be recovered.
The four configurations evaluated were: conventional comminution circuit based on a semi-autogenous grinding (SAG) mill and ball mill; Weir’s ENDURON® HPGR replacing the SAG mill at the initial grinding stage; ENDURON® HPGR, plus stirred mill replacing the ball mill; and the addition of Eriez’s HydroFloat CPF unit.
The study demonstrated that replacing conventional technology with innovative new solutions can cut energy use by 40%, while also avoiding 50% of CO2 emissions.
The sustainability benefits also extend beyond scope 4 emissions. For instance, studies have indicated that the same amount of steel required to construct the milling circuit structure is consumed by the circuit’s grinding media in just six weeks of operation. In contrast, HPGRs don’t need any additional grinding media to reduce the size of rocks.
