Massive mine tailings dams designed to last forever “aren’t a problem” for engineers such as Louise McNab. But she’s among those working to limit the future of conventional tailings storage facilities (TSFs).
A new world view of exponential growth in mine waste could create a burning platform within a decade to change industry process and circularity paradigms, the 2023 Advancing Net Zero Mining WA conference heard.
McNab, a senior tailings engineer in gold major Gold Fields’ global technical leadership group, said at the Perth event she and her sometimes maligned peers designed mine waste storage dams to last 10,000 years.
“When you go to a mine site you won’t see these things [but] they’re the biggest earth-made structures on the planet,” she said.
“There is just as much engineering that goes into a tailings dam as goes into a skyscraper.”
McNab is part of efforts led by the International Council on Mining and Metals (ICMM) and its member companies to find ways to shrink the estimated 285 billion tonnes of tailings “available globally today”, and curtail future production.
Not because the industry can’t build bigger tailings dams.
But because costs – in all forms, including catastrophic failure fallout – could spiral.
And, the conference heard from speakers such as VTT Research Centre of Finland principal scientist, Paivi Kinnunen, because industries such as mining are coming under increasing pressure from governments and communities to account more holistically for one-way resource and water use.
“As demand for minerals for renewable energy and electric cars increases over time so does the demand for the capacity of our tailings storage facilities,” McNab said.
“The more metal we pull out of the ground the more waste residue we produce and we’ve got to put that somewhere.
“It’s not a big problem; we do that today. That’s fine.
“But as we move forward it’s going to incur a lot more cost because we’re going to be bigger. They’re now turning into really big engineering structures. More mines will be required as we expand and continue to grow.”
The scale of modern mine tailings dams has become evident to people outside mining through images of recent disasters in Brazil, Canada, South Africa and other locations. Yet, as McNab indicated, the rarity of such incidents spoke to the calibre of engineering that generally went into TSF design – “a very integrated discipline that you’ve never heard of, and you’ve never seen” – and most tailings dams were virtually invisible despite the volume of material in them (285 billion tonnes) being the “same as a 6km-wide cube being dropped on Manhattan”.
She showed a Gold Fields tailings dam in Peru with a 150m-high retaining wall.
“If you took the Rio Tinto building in the [Perth] CBD, we could drop it in and you wouldn’t even see the top.
“And just because we love a challenge we’ve actually constructed it 4300m above sea level.
“So that’s like Mount Kilimanjaro with a dam on top with Rio Tinto inside.”
The Mineral Research Institute of Western Australia-hosted conference heard society was likely to be less tolerant of waste in all its forms in future.
“[That includes] water losses,” McNab said.
“Tailings are pumped [into dams] as a slurry and when we pump it as a slurry we can’t recover that water, so we need to come up with better ways of doing things.”
Kinnunen said: “We should not only consider water as a cost factor that we need to treat, but actually as an asset.”
The ICMM’s short (34 pages) 2022 Tailings Reduction Roadmap suggested various established, and some new, technologies could impact tailings production at levels ranging from incremental (up to 30% reduction) to “disruptive” (more than 90%). The latter included insitu mining, which McNab said, “I love because it will put me out of a job completely”.
Barriers to rapid change included cost, geology/geometallurgy, technology and, ironically, regulations (existing waste permits dictating long-term use of incumbent methods).
Similarly, long-term project and capital cycles made big changes to existing infrastructure unlikely, without sufficient motivation.
A “lack of drive” or “clear vision of tailings reduction” meant it was “not a current burning platform”, the roadmap report said.
The biggest hurdle for game-changing innovation? “Mainly the mindset,” McNab said. “[The view that] it’s the way things have always been done.”
McNab and Kinnunen said the scale of waste reduction and circularity challenges demanded multi-disciplinary responses.
“This isn’t a tailings challenge, it’s a mine-wide industry challenge,” the former said.
“It’s a huge puzzle that needs to be solved,” Kinnunen said. “That’s why multi-disciplinarity is needed so much.
“It would be nice to say we are there already, but the fact is we are on the right path.
“We still stick to the linear way of doing things and [that means] we are wasting the resources.
“But this is what we want to change and to do that we need to look holistically at metal production streams – not just major metals produced, but by-product metals and even negative-value elements. We must look at how we can recycle the water back into the process, and how we can valorise the residues.
“When we are doing things in a more clever way it is clear that we can also avoid [generating] waste.”