Today, it is impossible to talk of mine tailings – the unfortunate but unavoidable legacy of mining – and not think of the Brumadinho dam disaster in Brazil, which, in 2019, claimed 259 lives. Aidan Davy, co-COO of the International Council on Mining and Metals (ICMM) called it a “stark wake-up call”, adding that it “marked the beginning of a vital journey to make these facilities safer for people and the environment”.

That journey should not only focus on strong governance but also the implementation of “good engineering practices” for tailings management across the life cycle, the ICMM noted in its  latest updated guidance, published in February.

Kim Morrison, an environmental, social and governance consultant with 30 years’ experience and former senior director for global tailings management and technical services at Newmont, couldn’t agree more.  

“Technological approaches and innovative solutions are the best way the industry can achieve impactful and positive change in how it manages tailings,” says Morrison, who was also managing editor of the Tailings Management Handbook: A LifeCycle Approach and is a committee founding chair and fellow of the Society of Mining, Metallurgy & Exploration.

Fortunately, in reaction to the Brumadinho tragedy, innovation in tailings is springing up ─ and despite the industry being notoriously cautious about adopting new technologies, pilots are tentatively under way.

Trialling new tailings techniques

Anglo American is trialling a patented Hydraulic Dewatered Stacking technology, which it developed with partners including WSP at a 150,000m³ capacity tailings facility at the El Soldado copper mine in Chile.

This technology was developed after the company successfully implemented coarse particle recovery (CPR) technology. CPR recovers particles much larger than those traditionally targeted in the mill flotation process, resulting in particle sizes that are easier for tailings engineers to manage.

Erick Vlot, global manager for tailings and backfill at engineering solutions provider Weir, says these new processes requires less energy to grind rock, making them an attractive prospect for miners. Weir is working with mineral processing equipment provider Eriez on developing coarse particle flotation systems.

Vlot says that Anglo American realised it could use the coarse tailings to make “a float of layers” and then discharge the fine tailings in-between those layers to make more solid and dry, and thus stable, tailings.

“This is why this collaboration is so important,” he adds. “The finer the tailings, the more problematic it becomes to dewater them. The coarser they are, the easier it is to dewater them, but also there [are] energy savings at the beginning and at the end of the circuit.”

The process essentially allows Anglo American to reclaim and reuse tailings water in the mining process and create stable, dry land post-mining. The company says early results measured water recovery at more than 80%, and the extensive instrumentation is confirming that the tailings remain unsaturated.

Vlot says the technology is now proven, and more and more mining companies are open to using it, including several he is working with in North and South America, and Australia.

Increasing filtering rates

Historically, filtered tailings applications, which increase the amount of water returned to the plant for reuse, as well as decreasing the amount of water lost to evaporation and seepage, have been under 20,000 tonnes per day (tpd), says Morrison. However, she adds that now the largest filtered tailings plant, at Karara Mining Australia, has capacity of around 35,000tpd. 

“Because grades of ore are reducing, the throughput of the processing mills are increasing in order to achieve the same sort of quantities of valuable commodity,” explains Morrison, who will be joining Australia-based consulting engineering company ATC Williams as CTO in July. “So we need to look at increasing filter capacity and a faster rate.”

She cautions, however, that while these methods do produce tailings that have a reduced moisture content and hence should be easier to manage and more stable, they still require proper design, construction, instrumentation and monitoring. She points to a failure late last year of a filter tailing stack at Jaguar Mining’s Turmalina mine in Brazil.

“This demonstrates that you can’t think that if you filter your tailings, you don’t need to do anything further,” she says.

Commingling of tailings

Another technological method being explored is commingling. This is where tailings are combined with waste rock to improve both the geotechnical and geochemical behaviour.

This is the opposite to a process known as ‘stream separations’, which involves separating out the coarse fractions and filtering them, while placing the fine fractions inside a pit to reduce metal leaching risk and potentially eliminate requirements for a dam. However, managing two waste streams [strip rock and tailings] separately requires a much larger footprint than combining them, explains Morrison.

The GeoStable Tailings Consortium, for which Morrison was previously a chair of the Steering Committee, is focused on developing geotechnical and geochemically stable facilities with commingling.

Consortium member the Antamina Mine in Peru, a large copper and zinc operation in the Andes mountains, is currently working to advance GeoStable tailings technology for future expansion.

Emerging technological innovation

The new focus on improving tailings management, as well as the wider political rush to recover critical minerals, has also spurred start-ups to develop and push alternative solutions.

One is Canadian clean-tech company Tersa Earth. It uses patented microbial fuel cell technology, in a self-powering process, to extract metals such as copper, nickel, zinc, cobalt and gold from tailings – and to neutralise acidic water, which can then be reused in the mining process.

“We are, as far as we are aware, one of the only solutions that generates revenue while the company is fulfilling their remediation obligations. Our unit also does not impede on current processes,” says Barinder Rasode, company CEO and co-founder.

Tersa Earth, which is currently running a financial raise, won the BHP Global Water Challenge and will trial the technology with BHP over the next 18 months.

In addition, CoTec Holdings is developing technology that can concentrate and extract minerals from very fine tailings. The company has 31 iron ore mining claims in Lac Jeannine, Quebec, Canada. Pending positive testing results and permitting, CoTec plans to recover and produce low-cost and low-carbon iron ore pellets from the waste at these sites.

“The end result [at Lac Jeannine] will be a much smaller footprint of the waste and much more beautiful and pure and natural environment, plus the rehabilitation liability will be significantly reduced,” says company president, CEO and director Julian Treger, who was formerly the CEO of Anglo Pacific Group. 

Treger believes waste presents big, low risk-high reward opportunities. His wider ambition is to have 20–30 projects like Lac Jeannine.

BAIE Minerals is also developing novel and proprietary fluid-based technologies for cleaning up abandoned mine tailings and extracting saleable minerals and metals. It plans to pilot the technology at an old asbestos mine in Baie Verte, Newfoundland.

Trina Barrett, managing director of regulatory and environmental affairs at BAIE, says the planned path towards commercialisation is largely driven by customer demand for extracted minerals in the large global cement, construction material and fertiliser markets. Once proven, the company hopes to license the technology.

Innovation vs uptake of new tailings technology

Morrison says technology that can extract metals and minerals from waste is very important but faces challenges such as understanding what the resources are, which can be difficult as resource models aren’t built for tailings but geology, and how to safely remove those tailings and process them.

Similarly, Vlot agrees that some of the emerging early-stage technologies are “quite promising”, including those that bioengineer tailings or offer carbon sequestration.

“Technologies that handle tailings and enable them to be cemented when they are deposited are really promising,” Vlot says. However, he cautions that most are in the early stages of development and it could be at least a decade before adoption.

“We should promote [these initiatives] and drive for change,” he adds.

This can be challenging for an industry that is characterised as being a ‘fast follower’ rather than an ‘early adopter’, characteristically leaning towards caution – or as Treger puts it, “always leaving the waste for another day”. 

Changing attitudes towards tailings innovation

Ultimately, adoption of new or improved tech comes down to cost ─ and it is typically more expensive to adopt, at least initially, than existing methods.

However, Morrison says they are only more costly if viewed through the lens of “net present value”.

“This is extremely flawed because you are managing your tailings in perpetuity, so should be looking at it on a 20–30 year mine-life basis,” she says.

The Global Tailings Review estimates that the cost of mine tailings management can be around 15% of mine development, with ongoing operational costs generally less than 5% of the total cost of production.

Morrison believes attitude change must start “at the top” by educating mining executives on the financial benefits of investing in advanced tailings technologies that can reduce later liabilities and ongoing management costs.

“We need to, as an industry, highlight more case studies and continue to emphasise the impact tailings have on company reputation and social licence to operate,” adds Morrison. “A bold and courageous approach to technology is necessary.”