Tailings are a conspicuous part of the mining industry's global footprint.
Created as by-product from the processing and extraction of valuable minerals and metals from mined ore, tailings form a liquid slurry of fine mineral particles that is pumped to vast tailings storage facilities (TSFs) where it accumulates for years or even decades.
But such stockpiles are inherently unstable if poorly managed.
Every TSF has its own innate problems caused by local climate, topography, hydrology and the physical and chemical properties of the tailings themselves.
Although tailings management has improved significantly over the last few decades, the recent 2019 tragedy of Brumadinho dam in Brazil was a bleak and urgent reminder to the mining industry of their environmental, social, and corporate governance (ESG) responsibilities.
The Brazilian disaster resulted in 259 deaths and 11 missing persons, caused when a catastrophic failure of the tailings storage facility released more than 11.7 million cubic meters of tailings, which surged from the mine site, through the countryside to the local town, resulting in over 8 km of environmental destruction.
Resetting the agenda
In 2020, impelled by such devastating tragedies, the 'Global Industry Standard on Tailings Management' was established, seeking to achieve the ultimate goal of zero harm to people and the environment, with zero tolerance for human fatality. It aims to prevent catastrophic failure and enhance the safety of TSFs across the globe.
Solving the many problems that comes with tailings goes well beyond simply better management of TSFs.
Innovative solutions are needed that challenge traditional practises, looking at the entire mining chain to develop and trial new technologies and processes.
Team Leader Phil Fawell from CSIRO Mineral Resources stresses, "There is an emerging philosophy that storing tailings long term should be the last possible choice.
The grand vision is we should also be looking at other solutions, such as elimination of tailings, further processing, and minimising emissions from these facilities."
CSIRO has been working on tailings for decades.
Fawell has spent more than 25 years investigating gravity thickening during ore processing, trying to achieve better flocculation and dewatering of tailings then sent off to TSFs.
"We've also had CSIRO researchers working on many other aspects, from pumping and transportation of tailings, to their bacterial treatment to destroy any residual acid mine-drainage activity," says Fawell.
"But the difference today is the shift in focus from storage to what can we do differently."
Amira Global is addressing the global tailings challenge through a holistic and interconnected work program — the 'Amira Collaboration on Tailings'.
Through its eclectic membership of major, mid-tier and small-cap mining companies, service suppliers and consultants, Amira is responding to the industry’s mega challenges in three-priority areas:
- Avoiding catastrophic failure through monitoring and containment
- Tailings repurposing that results in a step-change in existing tailings volumes
- Step-changes in the characterization, extraction and processing of material in the production of tailings volume.
Dr Jacqui Coombes, CEO and MD of Amira Global explains there is an urgency by the mining industry to deal with tailings, which is a response to their social license to operate within an ESG framework, and a readiness in society to really take responsibility.
"It's a maturing of the industry, where it's the right thing to do, not because somebody is telling us to do it," says Dr Coombes.
"Amira has been involved in 70 projects over the last two to three decades, so although there is an urgency, it's important to recognize that the mining industry has actually been investing in preparing for these hard responses to tailings issue for many years through investing and collaborating with researchers," says Dr Coombes.
CSIRO has a long history of working with Amira on many of these projects.
"In the past it wasn't framed as an ESG issue, but certainly the intent behind it was to improve productivity, to use less water, to use less energy.
"So, although it clearly is an ESG issue today, there is also a real financial cost of maintaining tailings.
"If you can reduce that cost, then it just makes good business sense," she says.
Amira's current projects range from how to manage large-scale TSFs; developing technologies to recycle the water from these facilities and reduce mine-water consumption; and how to change tailings makeup so that liquefaction and water consumption can be reduced.
A new approach for tailings management
Although tailings come with a range of problems, they can be a good source for an emerging market of valuable products.
CSIRO has several projects investigating the reuse and reprocessing of tailings.
Work by Philip Ofori, Senior Research Engineer at CSIRO’s Sustainable Mining Technologies Program has looked at repurposing coal industry tailings into geopolymer concrete.
The potential benefits are a drastic reduction in tailings volumes and additional revenue for miners.
Other researchers are investigating ways to recover higher value by-products, such as forming zeolites from clay-rich lithium tailings.
However, as Fawell argues one of the dangers about primarily focussing on reuse and reprocessing of tailings is that we're essentially treating it as a legacy issue — now we have these tailings, what are we're going to do with them?
"What we should be thinking is how do we change what we do upstream to make the whole process better," says Fawell.
‘’We should be developing entire ‘snout-to-tail’ flowsheet for future mining operations and identifying upfront what products we can ultimately produce or recover from the tailings, and thereby minimise mining waste."
To support this, Fawell and his team are currently working towards a totally new approach to mathematical modelling flocculation and dewatering on these upstream solutions to better predict and optimize tailings suspension properties that are delivered to TSFs.
Such modelling has previously been unable to capture broad particle-size distributions or distinguish between large particles and flocculated aggregates of similar size that have very different properties.
‘’Taking advantage of very specific small-scale laboratory tests, the model stores a wealth of information about every particle and aggregate. We can then predict how the flocculated state shifts when tailings properties change,” says Fawell.
"We're hoping to deliver new measurement protocols and a new modelling interface for people to better design process flowsheets.
"You're also able to evaluate alternative processing and hydrometallurgy options that delivers better downstream solutions.’’
Ultimately, such innovation aims to reduce the quantities of both tailings and water delivered to TSFs.
‘’Deliver too much material and you risk vast quantities of very fluid tailings,” warned Fawell.
He is currently working with Amira Global on a major project proposal to further advance this modelling.
The most precious commodity is water
In many mining operations, fresh, reusable water is one of the most valuable components recovered from tailings, especially in Australia where aridity, high evaporation and poor-quality groundwater conditions are often encountered.
As Dr Coombes explains, the water issue is particularly important as we move into a world that is facing climate uncertainty.
"In that uncertainty, if you have a tailings facility with half of it made up of water, then you're locking away a valuable resource that the community is entitled to and could access," says Dr Coombes.
"This is an important part of the evolving circular economy that the world now operates within."
Principal Research Scientist Dr Ramesh Thiruvenkatachari from CSIRO’s Centre for Advanced Technologies heads a water treatment research team that is recovering freshwater from mine wastewater using forward osmosis – reverse osmosis (FO–RO) technology.
Forward osmosis – reverse osmosis technology
CSIRO and mining companies have partnered in the development stages of this FO–RO technology for over 12 years.
Maximising water recovery from tailings not only reduces freshwater usage, but also minimises the TSF footprint and reduces reliance on chemical and mechanical dewatering methods.
"By combining forward and reverse osmosis processes, we can minimise the conventional pre-treatment requirements of reverse osmosis for mine wastewater treatment," says Dr Thiruvenkatachari.
"At our trial site we were able to recover 90–95% reusable water from highly turbid coal-mine impacted water, minimising the pre-treatment train and reducing the volume of waste.
"Treating mine-impacted water then enables mining companies to safely discharge it into the environment.
"We're also looking at it from a water resource point of view, recovering some of that water to reuse in the mining operation or for irrigation and livestock, thereby relieving dependence on the freshwater resource," he says.
Thiruvenkatachari stresses that minimising mine water use and recovering it before it reaches TSFs and is lost to evaporation is where new technologies need to be applied.
"By dewatering tailings, we are also able to concentrate those remaining valuable elements and potentially make them viable for recovery."
"Within each mining operation, we're looking at the characteristics of the mine-impacted water, where the recovered water is going to be used and what facilities are available at the mine site. It's a combination of these aspects and trying to develop technologies around them," says Thiruvenkatachari.
The water treatment research team is also now looking at legacy mine sites where water can be recovered from disused mine pits and TSFs.
This is a particularly important remediation application as many sites have saline and acid mine-drainage problems that require suitable treatment, preferably with minimum chemical usage and maximizing energy efficiency.
Thiruvenkatachari is quietly philosophical about the crucial role that CSIRO and the mining industry have in dealing with mine-impacted water and tailings.
"There is a need out there to deal with them in a sustainable way. That's what drives us. We need to look further and try to solve those problem gaps. This is our role."