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.”