The role of mine waste in global climate change

Associate Professor Anita Parbhakar-Fox, Sustainable Minerals Institute, The University of Queensland

As 2021 draws to a close, the global community is reflecting on COP26. The overarching theme - reduction of carbon dioxide emissions to slow global climate change. However, one very sobering statement was made by the Secretary-General of the United Nations Antonio Guterres: "enough of brutalising biodiversity, killing ourselves with carbon, treating nature like a toilet, burning and drilling and mining our way deeper".

Whilst we can all agree with much of this, the high-level summary interpreted by the media has been ‘no more mining’. Whilst there are obvious links between coal mining and carbon dioxide emissions, the links between metalliferous mining and the low-carbon future are far more complex as we move through this required energy transition.

As a child, I was always terrified by the inescapable doom faced by our solar system. I would torture myself looking at encyclopedia illustrations of our sun running out of hydrogen, entering its red giant phase, and engulfing planet Earth five billion years into the future. Though the time scale was unfathomable, I was distraught thinking humanity would be wiped out. As a teenager, this fascination with the end of time continued, but this time poring over the Intergovernmental Panel for Climate Change (IPCC) reports. The graphs were compelling, due to industrialisation and societies moving upwards through Rostow's Stages of Economic Growth, dangerous quantities of greenhouse gases (GHG) were being produced. The result, doom for humanity, but this time on a conceivable timescale. No longer billions of years or even millions, but now centuries or less until utter devastation.

Fast-forward 25 years, there has been a great deal of talk about designing industry practices and indeed encouraging consumers to make different choices to reduce our GHG emissions to slow climate change. But ask yourself, how much action has been taken? How much more is needed? What has really changed since the IPCC started documenting our impacts?

Indeed, the Kyoto Protocol, Sustainable Development Goals and the Paris Agreement were significant in encouraging countries to set, and commit, to GHG reduction targets and transition towards a lowcarbon future. The requirements for this brave new world, which our governments have arguably been reluctant to embrace, include significant increases in the manufacturing of electrical vehicles and renewable energy technologies. But what does this mean for mining, and more importantly mine waste?

To meet the green demands of Earth 2050 we will need to mine at least nine times more copper, meaning many more billions of tonnes of waste. Currently, mine waste is managed by placing them into purpose-built facilities or dumps. However, there are potential geotechnical and geoenvironmental risks associated with these. These risks will be exacerbated as the climate evolves towards more extreme weather conditions. Drastic management changes are required, or else more Brumadinho-scale tailings disasters will occur, not to mention continued acid and metalliferous drainage formation and spontaneous combustion risks.

To support the development of greener technologies, the world requires resources of critical metals or, as the Queensland Government terms it, ‘new economy minerals’. These include cobalt, tungsten, indium, gallium, germanium, vanadium and a whole range of rare earth elements.

Traditionally, these metals were considered unwanted by-products of base metal and precious metal mining operations, and consequently are concentrated in mine waste. But, in the climate of 2021 where the Ernst & Young ‘Risks in Mining’ cite ‘environmental and social’ as the number one risk for the coming year - it pays to ask the question: what is waste?

In the past decade alone, there has been a considerable shift in the value attached to waste. No longer are tailings storage facilities, waste rock dumps, fly ash, red muds or slag heaps considered problem children affecting the triple bottom line, but instead potential assets waiting to be snapped up with strong support from ESG funds.

In November 2021, Rio Tinto announcing their support for the new venture ‘Regeneration’, a Washington-based start-up aiming to extract valuable minerals and metals from mine tailings, waste rock and water. The mining industry notoriously has a ‘fast-follower’ culture, which ultimately in the short-term could be a big win for both mine operators looking to reduce long-term closure liability costs as well as for the environment.

So, what does this mean for Queensland? Mine waste reprocessing is by no means a new business venture; indeed, it has been the lifeblood for mines including New Century (zinc), Mount Carbine (tungsten) and soon Mount Morgan (gold) and Tick Hill (gold). It is noteworthy that these operations have focused on recovery of typically sought commodities (i.e., base and precious metals).

The Queensland State Government have recognised this and, aligning with the Federal Government's Australian critical metals strategy, they have invested over $1 million in a four-year program looking to uncover new value from mine waste. Specifically, teams at the University of Queensland are working on developing new characterisation workflows and optimising analytical instruments to identify these new commodities in mine wastes as well as metallurgical recovery methods to unlock the value.

To date, 16 sites have been characterised in detail, with a focus on cobalt, indium and rare earth elements in the North West and North East provinces. The waste sampled has ranged from tailings though to phosphogypsum slimes.

Research results indicate that cobalt is hosted primarily in pyrite (and other sulfides) around the Mount Isa-Osborne mine region. Geologically, cobalt is associated with iron oxide copper gold and sediment hosted deposits. Back-of-the-envelope calculations indicate there could be millions of tonnes of cobalt if, on average, copper mining has produced 998 million tonnes of waste rock and 640 Mt of tailings, assuming average cobalt grades in pyrite are around 0.2%.

To recover this value, ongoing research is focused on recovery using conventional methods, for example roasting, (bio) leaching and novel methods such as in-situ electrokinetic recovery. However, there is a further opportunity to grow the Mining Equipment and Technology Sector (METS) in Queensland through companies such as NSW-based Cobalt Blue collaborating with the Queensland State Government and the University of Queensland in this program.

Indeed, international investors are already taking note with the Japanese Oil, Gas and Metals National Corporation co-funding a detailed study for cobalt recovery from tailings at the Rocklands mine. Looking to the future, continued evaluation of mine waste as sources to supplement the demand for critical, or new economy, metals necessary to meet our future metals needs is vital.

Many new opportunities exist for Queensland, such as evaluating coal mine waste and bauxite residues as future resources of rare earth elements, selenium, gallium and germanium; rhenium extraction from tungsten mine waste or even indium from metallurgical slags. The real message that should have been delivered at COP26 was not to imply a future where mining shouldn’t exist. It should have been to deliver policies to mandate smarter mining with a systems thinking approach.

Identifying how existing and future mine waste could support the transition to a low-carbon future and benefit future societies is perhaps what the global community needs to put it on the pathway to pushing back the Doomsday clock a minute or two. 