Mining is changing. On the one hand the threats are clear – climate change, declining ore reserves, concerns over carbon footprint, water scarcity and demands for use of clean energy. On the horizon though, is a revolution in renewables which will be built and sustained by metals and materials of the future. Many companies in the sector have responded by pledging to make sustainability the foundation of their licence to operate.
The search for sustainable solutions begins with technology and change agents in the sector are looking to solve the challenges of today with the technologies of tomorrow. At Axora, we’ve been working hard to help solve these challenges with solutions to make mining sustainable.
One big area is tailings dams. On 25 January 2019, one of the mining industry’s worst disasters unfolded in a small Brazilian village called Brumadinho. A decommissioned tailings dam failed and killed over 250 people and wrecked the local environment. The cost of Brumadinho will reach billions of dollars.
In Samarco, a similar disaster occurred just three years earlier in the same region of Brazil and is currently subject to the world’s largest litigation case. The failure of these two dams, so close together, has undermined confidence in the industry’s commitment towards better ESG practices.
In a nutshell:
(All data was collated from a Reuter’s report published in January 2020)
There are many who consider tailings dams ticking time bombs. A failure or collapse can lead to fatalities, environmental damage and a loss of credibility for the industry.
“Many mining companies have placed minimal attention on tailings management, expecting a solution by the time of closure, but now tailings management can’t be ignored,” says Dr Priscilla Nelson at the Department of Mining Engineering, Colorado School of Mines.
Tailings has traditionally been seen by the mining industry as a bottom-line cost - the mindset has often been around doing this as cheaply as possible to focus on production from the mine. Tailings is often an afterthought.
Incidents like the Brumadinho dam disaster have brought tailings management into sharp focus. Recently the International Council on Mining and Metals (ICMM) - jointly with the UN Environmental Program (UNEP) and the Principles for Responsible Investment (PRI) - published standardsthat companies will need to follow. There is a need for bold ideas that can transform our understanding of and approach to tailings management.
So what exactly are tailings? Expertsdefine tailings as “a by-product of separating valuable minerals from uneconomic material, and comprise ground-up rock, process water, and chemical reagents.” Tailings dams are engineered structures that are built to hold tailings. There are three main types of tailings dams – upstream, centreline, and downstream – based on how they are constructed. Many dams across the world are decommissioned. That means no new tailings materials are being added to these dams (which doesn’t automatically ensure that they are safer). Also, many dams are old - having closed long ago - and some no longer have owners due to the original companies having gone out of business. These dams often fall into the remit of the government who are underprepared for the task of managing them effectivity.
The other major issue with TSFs is that there have been no global standards in their design, construction or running. Many countries have differing rules regarding dams, and these are rarely updated. The result is that companies have dams designed to differing standards which vary wildly across jurisdictions, with the mine (not the mining company) often having ownership of these key structures.
The mining industry is on the lookout for solutions that will prevent dams from failing.
Potential Solution 1: Focus on the water
The biggest factors affecting a TSF (tailings storage facility) are water pressure and seismic factors. In almost all dams the only major factor you can control is the water pressure within the dam - so it’s almost always a major focus.
“In many cases, the challenge isn’t with the dam construction, it is with the pore water pressures. If you can find a solution that drives dissipation of any excess pore water pressure, dam stability can be ensured,” says Dr Nelson. The current approach involves studying the dam is detail. "Dam instrumentation investments have been escalating, providing point measurements of water pressure, strength or displacement. But the focus has to be on the water, and all too often it is not.”
It is easy to assume that tailings dams behave like engineered water retention structures. “They aren’t like engineered water retention dams and won’t behave like them,” explains Dr Nelson. Often, upstream dams are considered riskier than downstream. But as Dr Nelson says, regardless of the type of dam, the focus needs to be on using technology to accurately measure the pore water pressure in a dam, and to implement a system capable of servo-controlling the pressures. She believes that there are technology solutions available to do this, but these aren’t being used.
Local factors also have a significant impact on dam stability. For example, new upstream dams in the outback of Australia where it is dry, flat and empty represent a very different risk profile to an old upstream dam in the tropics - despite being the same dam design.
Potential Solution 2: Dry stacking
The industry has tried another solution – no dams. The water from the tailings is removed and the dry stack is stored securely. Especially popular in areas with water scarcity, Dry Stack Tailings (DST) has some limitations and the process isn’t entirely free from risks.
“Some people think Dry Stack is the silver bullet. Well, DST requires care and maintenance. There are dry stacks that have failed, and there is also the risk of acidic drainage. The material could become saturated. There are lots of risks,” says Dr Nelson. Experts agree that DST is simply unviable for mines with larger throughputs.
There’s also issues with dry stacking of existing TSFs. It is accepted that these are unable to be reprocessed and dry stacked. The economics make it unviable - so even if we were to move fulling to DST tomorrow, we would still be left with a huge number of legacy dams to manage going forward.
Potential solution 3: Tailings utilisation
“New uses for tailings is something I am very interested in,” says Dr Nelson. “But before you can think of tailings in that way it is important to consider the variability of the mineralogy, chemistry and grain size of the tailings feed. This is a period of discovery. As we know more about tailings, we may push back on processing to ensure we have better quality tailings which may actually produce a profit,” says Dr Nelson.
The Weir groupsuggests, that thinking of tailings as “a resource” could lead to using it for the manufacture of “everything from commercial shotcrete and concrete products for self-sustaining uses such as mine roads, brick and tile manufacture, insulation, or even foamed products.”
According to Dr Nelson, there are many exciting possibilities. “We can melt the tailings and produce fibres that can be used to manufacture rebars. These can be put back in the mine for ground support. Or used to reinforce concrete,” She explains.
“Can you imagine, if we didn’t use steel in concrete and replace it with a material that’s as strong as steel and doesn’t corrode?” Dr Nelson says that some Russian companies have been making basalt fibres from basalt rock for years and this is an exciting possibility.
Solution 4: Microwave radiation
You can also look upstream, as experts in Toronto, Newcastle and Australia are doing. We are talking about microwave technology. Microwaves can be applied at the beginning of the comminution circuit. “If you use microwave, you actually grow grain boundary cracks in the rock. You can then disaggregate it with less energy, and much of the ore is at the grain boundaries. You could decrease crushing and grinding as a result of this technology,” says Dr Nelson. A lot of power is consumed during the crushing and grinding stage. Use of microwave technology could significantly reduce consumption of power. It would produce tailings that are coarser, drain more easily and are easier to handle. Microwave technology isn’t popular just yet, but Dr Nelson believes that this could be a game changer.
Solution 5: A new mindset
Dr Nelson believes that we are at the edge of a major transformation in the mining industry workforce, and this transformation needs to extend into professional education. “We have been graduating students who can run the mines of today, but we need to be educating those who can run the mines of tomorrow.” People who manage mining companies seem to favour those who can run the mines of today – and that attitude must change. “When you talk about Mining Engineering you are talking about the core function of grinding, crushing and making metals from the ore,” says Dr Nelson. She says a blinkered view of the mining industry is reductive. “We’ve got to think of mining engineers as stewards of the Earth’s resources. Mining education has to be recast into Earth resource stewardship.” But doing that isn’t easy as many in the industry just aren’t ready for the change yet.
But for tailings management change is on its way. As ore grades decline, tailings dams will become bigger and concerns around their failure will need to be dealt with.
At the Colorado School of minesunder the leadership of Dr Nelson, a tailings management programme is being developed. They are developing a six-course series for professional development towards fundamentals of tailings management. They are looking to develop a graduate programme and a PhD programme in the fall next year.