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Rehabilitating red mud

Renewing bauxite residue while reducing our environmental impact

Last updated: 8 November 2023


Aluminium is a vital, versatile metal. But while it’s easily recyclable, we need to produce more to meet global demand.

To make aluminium, bauxite is refined into alumina and then processed into aluminium. The alumina refining process produces a residue slurry, often called “red mud”, which plants can’t grow in when it’s untreated.

And there’s a lot of it. Globally, around 4 billion tonnes of red mud sit in ponds or dams, with more added every year.

Red mud
Globally, around 4 billion tonnes of bauxite waste, known as 'red mud', sits in containment ponds or dams, with more added every year.

Usually, red mud is rehabilitated with traditional engineering methods like containment ponds and liners, topped with a metre or so of topsoil. These require careful maintenance to help plants establish in the shallow soil of the capping layer.

Rehabilitating red mud is a huge, ongoing challenge for the mining industry – one we’re still working on after decades of research.

But we’re making progress. Seawater is sometimes used to treat red mud before it’s stored, neutralising its alkalinity, but increasing its salinity. And we’ve been working to rehabilitate some remote sites like Mt Rosser in Jamaica, and Gove in the Northern Territory, Australia with a topsoil-free solution.

A new eco-engineering solution we’re working on with researchers from The University of Queensland (UQ) in Australia processes red mud into a soil-like material that can be replanted faster and with less impact on the environment than other methods.

And field trials have shown it’s possible to rehabilitate extremely alkaline or saline bauxite residues this way within 2–3 years.

Professor Longbin Huang from The University of Queensland's Sustainable Minerals Institute is working on a new ecoengineering solution to rehabilitate red mud

Responsible closure

We're committed to careful maintenance when our operations close to ensure the lands we operate on are safe, stable and non-polluting.

Since 2015, we’ve been working on this new approach with the Bauxite Residue Research Team in the Sustainable Minerals Institute at UQ, led by Professor Longbin Huang.

Working at alumina refineries in Queensland and the Northern Territory, the research and project teams have refined a robust process that we're now working to scale up in larger trials.

University of Queensland
Professor Longbin Huang with Rio Tinto's principal environmental advisor David and a member of the Bauxite Residue Research Team in the lab at UQ's Sustainable Minerals Institute

Translating research to the "real world”

The team initially ran a lab study at UQ in Brisbane and a small field trial at Gove in the Northern Territory, before setting up a larger field trial at Queensland Alumina Limited in Gladstone. This time, they were working with a bigger sample, with residues treated by seawater. This partially neutralises the red mud, but leaves it with high saline levels that local plant species don’t grow in.

There were other challenges too.

"In the field, you’re dealing with many more variables, which you can’t control like you can in a laboratory – like operators with differing levels of training and experience, environmental issues across a much bigger sample area, and bad weather,” said Longbin.

“We needed to make sure any treatment we developed was robust enough that even if any part of it went ‘wrong’, it would still work.”

Despite these challenges, the team successfully treated the red mud with their patent-pending microbial treatment, sowing a pilot species – hardy plants that can grow in difficult conditions – that helped to spread the treatment deep into the red mud itself through the roots and organic matter as the plants grew.

Within 2 years, local plant species also started to naturally blow in and grow around the pilot species, showing that the treated red mud had become viable to regrow local plants in.

The process also reduces our impact on the environment. Upcycling the red mud in situ means we don’t have to disturb a second location for pond-capping topsoil, or use heavy machinery to dig, deliver and distribute the topsoil at both ends.

“By embracing research expertise and translating those findings to our operations, we’ve been fortunate to yield exceptional results,” said David, our partnership manager and principal environmental advisor for the project.

Rehabilitation site
Longbin collects samples from matured pioneer plants at Queensland Alumina Limited's Gladstone field trial site

Scaling up a field trial

We’re now running a large-scale pilot trial at Gove, due to finish in 2025. We’ll create a field operational guide as we go, incorporating it into the rehabilitation strategy as we close the rest of Gove’s bauxite residue areas.

Eventually, the team forecasts that the same process will translate not just to other alumina refineries, but to any site with similar materials – creating opportunities for local communities to farm, supply plant biomass, and work in field operations and land management.

How the ecoengineering process works

Soil treatment

Step 1: Soil treatment

First, the team treats the red mud with a patent-pending mineral and biological process, which reduces its alkalinity and begins the process of restoring vital soil microbes, soil structure and nutrients.

Plant crop

Step 2: Pioneer plant crop

Then the treated red mud can sustain a range of pioneer plants, such as grasses and shrubs. As they grow, their roots help to spread the treatment further into the ground, restoring organic material, nutrients and soil structure.

Re-introducing local species

Step 3: Re-introducing local species

As the pioneer crop does its work, the pH level lowers until we can safely replant the area with species that are more suited to the surrounding area’s existing ecosystem.

Then, as these establish and thrive, they continue to develop the soil and attract local animals and more diverse plant species to the area as well.

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