Could microbes make barren ore waste productive?

The billions of tonnes of red mud produced as a by-product of refining alumina from bauxite ores might one day become fertile soil, thanks to a microbe-driven remediation system developed by researchers from the University of Queensland’s Sustainable Minerals Institute (SMI).

Australia is currently the second largest producer of alumina, the precursor to aluminium, which becomes part of mobile phones, drink cans, household appliances, cars, power lines, buildings and aircraft. The waste output generated by the extraction of metals like aluminium for use in renewable energy products also represents one of the biggest hidden problems in sustainable development.

For every tonne of useful alumina produced from raw bauxite ore, refineries generate up to two tonnes of highly alkaline and saline ‘red mud’ waste, which is hostile to almost anything that might try to grow on or in it. This effect persists for a long time and is extremely difficult to neutralize in real-world conditions.

The remediation of red mud has become a major problem globally and there is yet to be an effective solution. “Worldwide, there are about five billion tonnes of red mud in storage facilities and dams, and this increases by 125 million tonnes or more each year,” explains SMI’s Longbin Huang. “Such red mud deposits contain large amounts of caustic soda and alkaline minerals that aren’t easily dissolved or washed away, resulting in extremely alkaline and salty conditions that are difficult for normal living soil microorganisms and plants to overcome.”

Huang’s breakthrough was to develop a ‘bioweathering’ approach to break down these alkaline materials. Working with industry partners Rio Tinto and Queensland Alumina Limited, he turned to one of the only forms of life found in red mud – naturally occurring extremophile microbes that thrive in highly alkaline environments.

“While I can’t speak in detail about our approach, which is in the process of being patented, broadly it employs the activated power of a number of indigenous extremophile microbes proliferating in mine wastes like red mud,” says Huang. “The process of geochemical stabilization that follows results in the more rapid development of soil with physical, chemical and biological properties suitable for sustaining plant growth over very large areas.”

SMI’s remediation system has been in field trials for the last two years on a half-hectare site in central Queensland where the bio-engineered soil is already starting to support native vegetation growth.

Huang’s team has also just begun a larger four-year trial on five hectares across two sites in central Queensland and one in the Northern Territory. The aim is to see if the remediation system can create a soil environment that supports native vegetation in a variety of environmental conditions. In a few years, Huang hopes to set up a spin-off company to commercialize the system and help the alumina refinery industry worldwide.

Because implementation is relatively simple on a landscape scale, the system could be quickly rolled out using labour from local communities, adds Huang. This should work out to be 60−70% cheaper than current remediation technologies.

“After some news media attention, I have been receiving interest from companies in India, Brazil and Saudi Arabia, among others. We have the technology, using molecular DNA markers, to identify indigenous microbes that will work in different areas, so there’s no reason we couldn’t take our system to all of those places,” he says.

It’s not just aluminium tailing dams that could benefit. Sulfuric acid drainage site remediation is also in Huang’s sights, as well as marginal land soil enrichment. “I started looking into bioweathering about 15 years ago, but it’s pretty exciting now. It looks like we might now be able to make a big difference to the world really quickly.”