Reversing the trend of failed mine remediation

Kakadu National Park in Australia’s Northern Territory has dual World Heritage listings for its ecological and cultural value. Its escarpment country, rainforests, wetlands, and mudflats are home to cascading waterfalls, indigenous communities, and a diverse range of species, including crocodiles lurking in billabongs and creeks.

Perhaps only in Australia – a country where the mining industry has poignantly been described as “disaster and triumph entwined” – would such a unique reserve surround one of the world’s biggest and longest-operating uranium mines.

Located 260km southeast of Darwin, Ranger Mine started producing uranium oxide in 1981. The mining lease, which is owned and operated by Energy Resources of Australia (ERA), a subsidiary of mining giant Rio Tinto, was approved at around the same time as Kakadu was formed.

After 40 years of operation, including several expansion projects, and more than 120,000 tonnes of uranium oxide produced, commercial work at Ranger ceased in January 2021. The 79km² site – which includes a power station, retention ponds, open-mined pits, and tailing dams – will now be rehabilitated for around A$744m (£400m). The government wants it restored to a standard “similar to the adjacent areas of Kakadu National Park” so it could eventually be incorporated into the heritage site.

The task is “unprecedented”, says Gavin Mudd, a groundwater expert and a professor at RMIT University in Melbourne. “It’s a huge experiment, because no other mine globally has this sort of context.”

Australia’s 150-year-old mining industry is one of the largest mineral exporters globally. Despite its scale, poor governance has meant successful mine restoration is relatively uncommon. In Western Australia alone there are currently around 10,000 abandoned mines.

Professor Kingsley Dixon of Curtin University, who is also the director of the Australian Research Council (ARC) Centre for Mining Restoration, says that despite company promises, mining restoration globally is often poorly executed. “Only a fraction of one per cent of mines close with a representative native ecosystem reinstated,” he says. “Ninety-nine per cent of mines do not have the technology or the capacity to deliver effective post-mining restoration.” This is because investment in R&D and regulation are both lacking, he elaborates.

The Rio Tinto-operated Rum Jungle, the country’s first uranium mine, is an example. The mine was closed 47 years ago but never rehabilitated properly. Ever since, acid and metals from the site have leached into parts of the nearby Finniss River, causing environmental devastation. It will now be cleaned up at a cost of more than A$300m (£160m) to the taxpayer.

In the context of climate change, emphasis on land rehabilitation and rewilding is growing. Restoring the soils of degraded ecosystems has the potential to store up to three billion tons of carbon annually, according to the United Nations Convention to Combat Desertification.

The restoration of Ranger, therefore, is an opportunity to develop the tools and knowledge and to prove that successful rehabilitation of mine sites at scale is possible – something that will be pivotal for Rio Tinto, and the industry at large, to win the social licence to operate in the future. This licence is particularly important as, having extracted all the low-​hanging fruit, companies look to mine in more complex ecosystems, such as the Amazon.

Mining at Ranger was conducted using a conventional open-cut process. This involves removing everything that covers the ground and then drilling and blasting out the earth to extract the oxide. The low-grade ore and non-mineralised rock are stockpiled. As part of the remediation process at Ranger, this ore will be returned as backfill to the mined-out pits and contoured to create the final landform.

ERA started this rehabilitation process, as outlined in its Ranger Mine Closure Plan, in the late 1990s, and has been progressively removing infrastructure, backfilling Pit 1 with 13 million tonnes of bulk material and plugging the vent shaft access. The next step will be readying the area for revegetation.

Backfilling and re-engineering of the landform is the most well understood process in mine remediation, says Dixon. However, reinstating native ecosystems is much more challenging.

“Often there is not access to what was taken away, and seeds and soils need to be sourced. People confuse engineering for biology, but the biological part puts back the ecosystem,” he explains. Dixon and colleagues at the Society for Ecological Restoration are currently developing mine restoration standards.

Water management is also a known difficulty. At Ranger, ERA must ensure tailings are isolated from the environment and that any contaminants arising from them don’t create detrimental environmental impacts for at least 10,000 years.

At the Tailings Dam – a ‘ring dyke’ with sides of about 1km in length – Pit 1 and Pit 3 have been approved for the storage of tailings and process water. Drainage from these areas, if done incorrectly, could create huge legacy problems for Ranger, as it has done at other sites.

At Rum Jungle, Mudd says, acid drainage occurred because the company tried to save money and used the wrong type of soil. It then didn’t layer it thickly enough over the top of the wastewater bank and so it failed to limit water and oxygen seeping down.

At Mary Kathleen, another Rio Tinto uranium mine site, rehabilitation in the 1980s led to tailings repository seepage into evaporation ponds and local drainage, causing widespread death of native vegetation.

In 2009, it was confirmed that at least 100,000 litres of contaminants were leaking each day from the tailings dam at Ranger. This has caused a contaminated plume of groundwater of at least 1GL (1 billion litres) beneath the dam.

Experts are concerned that a lack of remediation planning and the de-prioritisation of rehabilitating the tailings plume, as well as a proposal to leave the floor of the tailings dam in place, risk contaminants entering Kakadu.

ERA and the Supervising Scientist Branch (SSB), the government office overseeing the project impacts, acknowledge there are gaps in knowledge relating to the tailings dam. Experts says these need to be addressed urgently, especially in the context of climate change, which has been designated a ‘critical risk’.

“The impact of climate change could be profound,” says Dave Sweeney, the national nuclear campaigner for the Australian Conservation Foundation, who co-wrote a report with Mudd and others critiquing the Ranger rehabilitation plans. “Increased rain, for example, will mean extra pressure on water storage and processing, which can impact the success rate of revegetation impacts on key contaminant pathways, with effects on surface and groundwater movement.”

Another issue highlighted is the project deadline. Under an act of parliament ERA has just five years, until 2026, to finish its work. After this, responsibility falls to the national government. ERA, which was contacted for comment but declined, has said it will monitor the site for 25 years but not to what extent.

Dixon believes five years is too short to understand, for example, whether the savanna seedlings planted now will be on a trajectory to make a savanna woodland in 50-100 years’ time.

“Not many mines operate in savanna woodlands, in an arid-wet tropic environment, so there is no transferable template – that’s one of the most critical issues,” he explains.

As the rehabilitation project gets under way, despite the concerns and challenges raised, many of its watchers agree Rio Tinto has shown a deep commitment to the project. Hopes are high for a positive outcome.

“Five years ago, I thought the company had limited ability, but it has turned a corner,” says Dixon. “There’s been an extraordinary commitment to full reinstatement of the native ecosystem.”

Only time will tell if Ranger bucks a trend of failed rehabilitation. But there’s little doubt successful mining restoration will be imperative to the future of the industry, with Ranger hopefully leading the way.