Mine waste is, essentially, a design flaw. A rather big one when you consider the level of risk involved in its management and that the industry generates over 100 billion tonnes of it every year.
Do we like design flaws in this industry? No. Do we tolerate them…? I think you know the answer.
But, what if we had the chance to redesign mining processes and turn some, if not all, of that waste into saleable products? What if, rather than dumping the material, it could be repurposed and used elsewhere? Maybe even provide a rather profitable source of critical minerals or rare earth elements…
Now we’re talking, right?
More than just tailings
Dr Anita Parbhakar-Fox and her team at the Sustainable Minerals Institute (SMI) at the University of Queensland are developing new ways to characterise mine waste – identifying the mineralogical composition of both historical and fresh waste streams generated by mining operations to better understand their potential value.
“It’s great that we want to move towards low-carbon energy technologies and electric vehicles,” she told me. “But the consequence of that is that the mining industry is going to produce more waste as it tries to keep up with metals demand.”
“When we talk about mine waste, what types of materials are we referring to?” I asked.
“There’s a distinct difference between mining waste and metallurgical waste,” Parbhakar-Fox replied. “In terms of mine waste, we’re talking about overburden and waste-rock material. But metallurgical waste includes a whole gamut of different things…
“Tailings is the big one, but there’s also spent heap-leach material and slag. Some people consider impacted mine water and dusts as waste streams too, but the first three are the main ones in terms of volume.”
The Global Tailings Review, which was instigated following the Brumadinho tailings dam collapse in Brazil in 2019, estimates that there are around 8,500 active, inactive and closed tailings facilities globally. Collectively, these contain 282.5 billion tonnes or 217km3 of waste material.
Parbhakar-Fox recently gave an online seminar entitled The War on Mine Waste. In it, she showed an illustration which put these figures into perspective; a cube 6km high (roughly the equivalent of 217km3 of waste) dwarfs New York city. It is a stark representation but without it, those numbers would be hard for many to grasp.
“In solving one environmental problem [climate change], we’re contributing to another, so we need to be more strategic and circular in how we deal with mine waste,” said Parbhakar-Fox.
“Events like Brumadinho and Samarco are creating more awareness about the immediate geotechnical risks surrounding the storage of mine waste, but things like acid mine drainage (AMD) and exposure to heavy metals over a long period of time can have a chronic impact on local communities and the environment long after waste materials are dumped.”
Mineralogy for mine waste
Parbhakar-Fox has a background in environmental geochemistry. She studied at the Royal School of Mines in London, UK, before moving to Tasmania with her husband.
At the time, the AMIRA GeM project was just kicking off. The team was examining the geometallurgical properties of various mineral deposits, and Parbhakar-Fox was tasked with applying the data in an environmental context, looking at how acid rock drainage (ARD) was predicted in the mining industry. She began her PhD and the rest, as they say, is history.
“With ARD, the traditional sampling methods used are really poor for environmental characterisation,” she told me. “In a new project, I want you to imagine a mineral deposit the size of a mountain. 35% of this deposit was hyperspectrally scanned (to understand the geology and mineralisation), 10% metallurgically tested and less than 1% of the whole deposit was subjected to environmental characterisation.
“Which, when considering the majority of the material is waste, seems a bit short sighted. So, my research focused on ways to make environmental characterisation better and cheaper. I wanted to introduce more mineralogy into the process to understand how certain minerals evolve under certain conditions.”
Following some consultancy work and post-docs, Parbhakar-Fox joined the team at the SMI in Brisbane as a Senior Researcher. She now leads the Mine Waste Transformation through Characterisation (MiWaTCH) project.
What can we do with this data?
“Is the characterisation of fresh waste a standard practice for mines today?” I asked.
“It is but, fundamentally, we undersample and undertest,” Parbhakar-Fox replied. “And we also use static testing methods that were developed in the 1970s. They were great for their purpose, which was to approximate the maximum potential acidity of coal mine waste, but they’re not entirely appropriate for metalliferous mine waste.”
Today, given the widespread availability of low-cost, portable mineralogy tools like handheld X-Ray diffraction (XRD) and, importantly, their reasonably high level of accuracy, there really are no excuses for mines not knowing what’s in their waste dumps. It’s as easy as walking into the field and spending a few minutes taking analyses. This would then inform the need for more in-depth tests in the lab.
Characterising mine wastes can reveal a lot about the minerals in a deposit and how they will behave over time under specific environmental conditions. Having this information can help mines to optimise their processes both up and downstream from the point of waste generation.
Today, many of the conversations around secondary prospectivity are based on existing wastes. That’s good because it offers the potential to treat AMD that’s already generated but, of course, there is also an opportunity to better understand and widen the spectrum of minerals recovered through primary processing too.
This is where the University of Queensland has an edge: as well as being home to MiWaTCH, the SMI also houses the Julius Kruttschnitt Mineral Research Centre (JKMRC), an institute world renowned for its expertise in mineral processing.
“At UQ, we have the chance to work collaboratively with other disciplines,” Parbhakar-Fox told me. “There’s a huge opportunity to look at waste management as a more holistic part of mineral extraction.”
Waste valorisation
Downstream, characterisation enables waste generated through mining to be managed in an appropriate and responsible manner – there will be no surprise AMD streams popping up in 10, 20 or 30 years-time.
Secondary prospectivity also offers the chance to recover valuable metals that were previously uneconomic to extract, and markets can potentially be found for some, if not all, of the residual materials.
“Now that we’re seeing this big drive towards the circular economy, certainly the conversation around secondary prospectivity is increasing,” Parbhakar-Fox told me.
“The first five years of my post-PhD life involved knocking on people’s doors and trying to get them interested in new testing characterisation methods. Most weren’t but, now we’re talking about applying these techniques to secondary prospectivity, doors are opening.”
One project that the MiWaTCH team has been working on is looking at metallurgical waste from smelting to see if extra zinc, lead or silver could be recovered from the material. If the material isn’t leaching toxic metals beyond acceptance levels for that particular country, then it could also potentially be used in construction applications.
“Even bauxite (aluminium) operations that produce red muds… red muds could potentially contain rare-earth elements which could be recovered, and the rest of the materials used as geopolymers,” Parbhakar-Fox explained.
“We could even harness the material for its alkaline properties and, if you’ve got a sulphidic dump at a mine site, build it into a cover for the waste material. Knowing the geo-environmental and mineralogical characteristics of the material means that you can make better decisions about what you’re doing with it, and ultimately reduce your waste footprint.”
The chance to design mines differently
“Would you say that waste characterisation has moved up the industry’s agenda over the past five years following events like Brumadinho and Samarco?” I asked.
“Definitely,” Parbhakar-Fox’s response was swift. “We’ve got a couple of million-dollar projects now looking at mining waste that probably wouldn’t have come about if Brumadinho hadn’t happened.
“Smaller mining companies and mid-tiers seem a bit more agile in their thinking. I’m not saying that larger ones aren’t, but they have the opportunity when they develop new mines, to design them better.
“Some companies are still taking traditional approaches to dealing with their waste. Which is a missed opportunity, because they’ve got a whole new understanding of their deposit enabled by technologies like hyperspectral scanning.
“We’ve still got a way to go in terms of highlighting to people the opportunity they have to do things differently for future mine wastes.”
Optimising for secondary prospectivity
While secondary prospectivity and waste valorisation have sparked the interest of many mines, it’s important to note that the mineral processing technologies used by operations today are not necessarily designed or configured to handle materials that have sat oxidising for a long time, or that have undergone special processes.
“Processes will need optimisation, that’s something that mining companies do need to understand if they’re getting into waste valorisation,” cautioned Parbhakar-Fox. “Yes, you can dig tailings out and chuck them back through the mill. But you may not necessarily get the recovery that you’re hoping for.
“Once you’ve characterised the material in a waste facility, you know exactly what the mineral hosts are. You can then start thinking about the processes and technologies that best suit their recovery.”
It’s a fair point: orebodies aren’t homogeneous, so why on earth would the waste material be?
“Do you envisage a time when fresh waste, and maybe historic, too, is a thing of the past at mine sites?” I asked.
“Yes, we can achieve zero-waste mining,” said Parbhakar-Fox with passion. “It all starts with characterisation. If we know what’s there, and we’ve got modelling tools that can help us understand how the minerals are going to behave, then there’s no reason why we need to create waste.
“There are ways to use everything if we put our minds to it. Continuing to do things, just because it’s the way we’ve always done them… Does it speak to us being a bit complacent? A bit lazy? Maybe.
“Certainly 40 or 50 years ago, it was okay, but there’s no excuse today with the technologies that are available.”
From risk to opportunity
Parbhakar-Fox believes that pressure from communities and consumers, as their awareness of mine waste and the risks associated with it grows, could prove to be a turning point for the industry.
“As a consumer, we’re all responsible for mine waste,” she said. “Our lives are underpinned by mining, so it’s everyone’s problem. And I think more people are becoming more cognisant of that fact.”
There are challenges associated with waste valorisation but, mainly, it’s a massive opportunity.
An opportunity to reduce the footprint of mining, create new revenue streams, diversify business models… even connect with people who previously may have been unaware of the role that mining plays in their day-to-day lives.
Take the beauty industry, for instance. It’s a multi-billion-dollar global industry and a huge consumer of minerals, many of which are used to produce makeup. Minerals like micas, that are sometimes sourced through opaque pathways, could potentially be sourced responsibly and transparently from mine waste.
That’s not only an opportunity for waste valorisation, it’s also a chance to connect mining with a whole new generation of consumers.
If mining companies want to diversify their workforces and attract young talent from different backgrounds and walks of life, then here’s a massive opportunity to speak to and educate them through a much-loved consumer product.
“There are big opportunities in that space,” said Parbhakar-Fox. “Paint is another. Take the metalliferous drainage that we see at many mines in Western Tasmania; when you’ve got those piles of sludge, one potential way to use them is to produce art pigments. They can be used in ceramics too.
“There’s a company called WASP which, through the Tecla project, is 3D printing houses using local clays to help communities. Mine waste is often full of clays, why not use it as a source of material? And then, there are quartz and feldspars. Quartz could potentially be used in the production of TVs which require high-purity silica…
“In these cases, it’s not necessarily about pulling out a critical metal, or a secondary metal that was missed, it’s just thinking differently about waste.
“Going forward, if we’re going to achieve zero-waste mining, it does mean more collaboration. Not necessarily with mineral processors, but cross-scientific collaboration with material scientists.”
As the saying goes: one person’s trash can be another’s treasure.
Excellent Dr Anita