Mine tailings: Waste not, want not

Traditionally considered ‘waste’, tailings are just one of a number of by-products generated by the mining industry which are now being assessed for their economic value.

For the uninitiated, tailings are created as ore is crushed, ground and treated to extract the valuable metals or minerals within. They usually take the form of a liquid slurry comprising fine rock particles suspended in water which must be stored and managed forever.

For this reason, tailings storage represents a significant cost as well as an ongoing environmental and social liability for mining companies. And, as calls for more responsible management practices increase, so too will the resources required to store tailings safely.

But there is another option.

A growing number of companies are investigating ways in which tailings storage requirements can be minimised, and the material held within legacy operations exploited to pay for current management costs and technologies as well as environmental remediation and restoration.

Making rehabilitation economic

Today, mineral processing techniques are more efficient than in the past. As metal recovery rates are higher, the percentage of residual metals contained within tailings is generally much lower.

However, the grade of metals residing in some legacy tailings is significant enough to make re-mining and reprocessing them economically attractive today when metal prices are right.

To put the opportunity into perspective, the Global Tailings Review has calculated that 12.7 billion metric tonnes of tailings are produced every year.

There are around 8,500 active, inactive and closed tailings storage facilities worldwide whose collective footprint exceeds 280 billion metric tonnes, and the estimated value of precious, critical and strategic metals contained within those sites is thought to exceed US$3.4 trillion.

That number doesn’t take into account the value of industrial minerals such as silica and micas that make up a larger percentage of tailings and could potentially be used in industrial or consumer applications.

Economic rehabilitation provides an opportunity to harness this value. It involves using the remanent value within tailings to rehabilitate mining operations and improve their social and environmental outcomes.

Patrick Walta is Managing Director of Australia-based New Century Resources. The company is focused not only on mining, but tailings management and economic rehabilitation too.

“We established New Century Resources to produce metals for the future through economic rehabilitation,” he told me. “We are focused on sustainably producing metals from globally significant assets, acquired on highly attractive terms, while rehabilitating legacy impacts to the environment.”

In 2017, New Century Resources acquired the Century Zinc mine in north-west Queensland. The operation boasts a large zinc reserve as well as historic workings that have left behind tailings rich in zinc and lead, plus infrastructure with an estimated replacement value of AU$2 billion. However, there was also a requirement to rehabilitate the mine’s environmental footprint.

“We established the largest hydraulic mine in Australia, restarting operations by 2018, mining, reprocessing and marketing metal while rehabilitating the historical environmental impact,” said Walta.

“New Century Resources is now a global top-15 zinc producer and the largest tailings retreatment management company in Australia. Since restarting operations, we have produced over 750,000t of zinc concentrate from tailings at Century.

“In 2021, we secured our second project, acquiring the option to restart green copper production at the Mt Lyell mine in Tasmania using 100% renewable energy to power the underground operations.”

Tailings as a business

It’s a fascinating business model. One which harnesses the company’s expertise and intellectual property (IP) to collectively improve the environmental, social and economic outcomes of mining.

This is waste valorisation for the 21st Century.

New Century Resources has two business objectives. Firstly, acquiring assets where mining of residual mineralisation, tailings retreatment and the existing sunk capital provides a base for long-term sustainable metal production while reducing the environmental impact of past and present operations.

And, secondly, partnering with existing mining companies to provide low-cost holistic tailings management solutions.

Through these pillars, it aims to deliver net environmental benefits and shareholder value while actively contributing to the circular economy.

Walta explained: “We are pursuing opportunities with industry peers to reprocess and rehabilitate contemporary and historical mineralised waste assets at operational and legacy mine sites. Under this model, we could employ our expertise in economic rehabilitation with partners allowing our clients to focus on core mining operations while simultaneously benefitting our shareholders and the environment.

“On a valuation model, mining companies are incentivised to delay rehabilitation for as long as possible to maximise the remaining apparent value of assets. At the end of a mine’s life, the significant task to rehabilitate the mine then becomes a cost burden. Consequently, ‘closure’ is one of the fastest growing divisions in mining, due to a significant number of large mines coming to the end of their mine life.”

Indeed, the requirement to improve environmental, social governance (ESG) metrics in mining is increasing pressure on miners to consider progressive rehabilitation strategies.

However, the skillset within mining companies, as well as the main profit centres are associated with the discovery and operation of primary mining operations. This presents a significant opportunity for New Century Resources to utilise its track record at the Century mine, IP and expertise to establish a client-focused tailings management division.

“The focus will be to secure long-term tailings service contracts with existing mining operations,” said Walta. “The aim is to provide value-add by delivering a net environmental benefit in the reprocessing and rehabilitation of tailings, and in doing so provide innovative and holistic solutions.

“This will allow our clients to focus on their core operations, with these ‘non-core’ activities competently outsourced. Our value proposition is the integration and management of tailings, waste-rock management and storage, tailings retreatment, water management and treatment, and progressive closure planning.”

Using analytics to identify value

Canada-headquartered EnviroGold Global is another company with an interesting business model. It claims to be “a clean technology company accelerating the world’s transition to a circular-resource economy through the production of metals without mining”.

It plans to do this through producing gold, silver, copper lead and zinc from mine waste at its Hellyer and Buchans tailings reprocessing projects. These are expected to show a 96% reduction in greenhouse gas intensity per gold-ounce equivalent produced, and over an 80% reduction in energy intensity relative to industry averages for conventional mining.

The company is using an analytics-driven approach to project origination and development. This leverages mine production and mill data as well as geological records to identify tailings sites that could contain significant quantities of residual metals due to refractory mineralogy and/or to the inefficiency of outdated technology used during legacy mining operations.

Initially, EnviroGold is targeting tailings sites with at least six million metric tonnes of tailings and a gross recoverable metal value of US$124/tonne of tailings.

The company has reviewed over 325 sites to date and now has eight major projects in its global project pipeline. This includes two major projects under definitive contracts (Hellyer and Buchans) and six additional projects at various stages of commercial negotiation and detailed technical/economic review.

In addition to recovering precious, critical and strategic metals, EnviroGold remediates the tailings in line with environmental best practices to reduce the environmental footprint of legacy mining. By eliminating the extractive phase of metal production, the company expects to reduce the energy intensity of metal production by over 80%.

In a recent press release, EnviroGold said it expects to commence commercial metal production later this year at the Hellyer Tailings Reprocessing Project in Tasmania and is aiming to have seven major projects in commercial production by 2025.

A growing opportunity

Economic rehabilitation offers a win-win solution for both mining stakeholders and the environment. It demonstrates responsibility and could prove a valuable tool in helping to build trust with local communities.

As such, it’s not just junior and mid-tier miners that are looking to incorporate it into their portfolios.

In November 2021, Rio Tinto announced it’s partnering with Washington-based non-profit organisation, RESOLVE, to launch a start-up company called Regeneration. This will re-mine and reprocess waste from legacy mine sites to support rehabilitation activities and restore natural environments.

Regeneration will extract valuable minerals and metals from mine tailings, waste rock and water. Earnings from the sale of the responsibly sourced materials will be reinvested to help fund habitat restoration and closure activities (i.e., economic rehabilitation), including at legacy and former mine sites.

Regeneration will also seek to create and trade biodiversity and carbon credits through the rehabilitation of land and the generation of environmental offsets.

RESOLVE has significant expertise in supply chain leadership for minerals and metals and is involved with the Salmon Gold restoration projects in Canada, the FPIC Solutions Dialogue and the Climate Smart Mine Emissions Widget. It has much to bring to the venture, as does Rio Tinto.

In addition to sinking US$2 million into Regeneration, the miner said it would analyse its portfolio to identify potential opportunities for the first Regeneration project, and site review and selection is now underway.

In the press release, Stephen D’Esposito, Chief Executive Officer and Chair of Regeneration, said: “We see mine waste as an untapped resource and an opportunity to create a double win for the climate and communities. We will produce minerals for the energy transition and supply sustainable brands while restoring legacy mine sites. As a result, Regeneration will deliver positive community and product impacts.”

Challenging the tailings status quo

OZ Minerals’ Think & Act Differently (TAD) innovation incubator has also turned its attention to tailings recently.

The company has an aspiration to consume and produce in a way that generates zero net waste and creates value for stakeholders, and it believes that the potential flow-on benefits of producing less waste and finding value in wastes could change the way future mines are designed.

In November 2021, TAD launched a crowd challenge inviting innovators from around the world to propose an approach that reimagines mining and processing to minimise, eliminate and find value in waste.

The challenge recently closed, and the TAD team is currently reviewing submissions from 36 teams. Submissions cover themes across the mining value chain including selective mining, in-situ recovery, ore sorting, new grinding and flotation technology, recovery of metals from tailings, making products from tailings and waste-water treatment.

Transformation Entrepreneur and TAD Intrapreneur, Burkhard Seifert, explained: “We knew that there were quite a lot of people working on solutions, particularly in relation to tailings management. But we also knew that many of these studies were fairly long dated. Our challenge is complementary but quite different.

“We are looking for ideas that could be unlocked or partially investigated through short experiments. We also felt there was an opportunity to look outside of mining to understand technologies that could be applied to our industry and support a new way to operate.

“We wanted to create an opportunity for innovators to test their thinking or technologies and get feedback from the industry and other innovators in this space. From the previous crowd challenges we have run, we know that this exposure helps innovators accelerate their thinking and decisions about which ideas to pursue.”

Importantly, the team has approached this challenge as a collaboration and OZ Minerals has partnered with industry research body, AMIRA, and the International Copper Association (ICA) Australia who are also looking at strategies to approach waste and water.

Rethinking the mine-waste system

The Waste to Value Challenge is about exploring new approaches to managing waste across the mining process to create better value from ‘waste’ and reduce the footprint of mining operations.

This includes processes and practices to minimise the production of waste and strategies to think differently about wastes that have already been produced to understand the value that may lie within them.

OZ Minerals believes that the benefits of reducing waste could be game-changing, as a reduction of waste in one area of the value chain will impact other areas of the mining and processing system.

For example, developments in selective mining methods would mean less waste material would flow through the whole supply chain, leading to opportunities to develop more compact haulage and processing equipment and a reduced requirement for tailings facilities. This would have other flow-on benefits such as lower energy requirements and a reduced environmental impact generally.

“Our aim is to understand how different people are looking at different pieces of the puzzle and build up a picture of the whole system,” said Seifert. “Once we layer enough of these innovations across the supply chain, we can start to think about designing new ways to extract and process metals and a new blueprint for mining.”

Over the next month, in partnership with AMIRA and ICA, the TAD team will work with a group of challenge finalists to understand more about their potential experiments and willingness to collaborate as a cohort, before selecting teams to accelerate and fund.

Katie Hulmes, Head of Transformation and TAD, expanded: “What we’re essentially doing is building up a portfolio of ideas and technologies that we understand quite a lot about. If we only asked for very specific solutions, we could miss out on learning about opportunities that may unlock significant future value.

“The benefit of this approach is that more choices are available, in addition to the suite of proven technologies, when you get to a decision point in assessing a new project or expansion of a current operation. We are working directly with innovators to conduct trials and experiments help test how and if their technologies can be considered in that list of options.”

Seifert added: “As part of the Waste to Value Challenge selection process we are talking to people who are trying to further develop technologies that relate to in-situ leaching, flotation, biomining, ore sorting, acid mine drainage and hydrometallurgy. This breadth is an acknowledgment that a whole-of-system approach is needed to really move the dial.”

To try and get as many experiments funded as possible, OZ Minerals, AMIRA and ICA are keen to talk to other like-minded mining companies who may be interested in co-sponsoring experiments.

Proposed experiment duration ranges from 3-12 months and innovators maintain ownership of their IP. Innovators benefit as they get funding and support, including access to a mentor and subject matter experts and, of course, they get to progress their ideas.

The industry will also benefit in the long term, as challenges and opportunities move closer to being unlocked, providing optionality.

These are just a selection of the projects going on around the globe to better harness the value of mine tailings. If you know of any other interesting examples or would like to add to the conversation, drop us a line below in the comments