The Engineer

Bacteria species clean up aluminium production

News

Previously unknown species of bacteria are helping to reduce the environmental impacts of alumina and aluminium production thanks to the work of a researcher at the University of Western Australia (UWA).

UWA microbiologist Naomi McSweeney discovered that naturally occurring bacteria break down and remove sodium oxalate, an organic impurity produced during the refining of low-grade bauxite into alumina. Her collaborative project involved UWA, Alcoa of Australia and CSIRO.

At a typical refinery, sodium oxalate forms by the tonne during the production of alumina. It can affect the colour and the quality of the final product.

’Oxalate can be removed by combustion, but this process releases carbon dioxide. The impurity may also be stored but this represents a major cost to refineries so treatment is a preferred option,’ said McSweeney.

’Using bacteria to break down and remove oxalate is a better, more sustainable alternative. The bacterial process breaks down the sodium oxalate and produces significantly less carbon dioxide while avoiding the need to store the impurity,’ she added.

McSweeney worked with researchers from Alcoa’s Global Technology Delivery Group and the CSIRO’s Light Metals Flagship to identify the main bacteria involved in degrading the oxalate within the bioreactor. They used DNA fingerprinting techniques to pick out the key players. What they found was a potentially new genus of Proteobacteria and a new species of the known genus Halomonas that are able to use the carbon in the oxalate to grow.

Now, engineers at Alcoa have designed and installed a large-scale bioreactor with the capability to remove about 40 tonnes a day of sodium oxalate produced at the company’s Kwinana refinery using the bacteria.

To enhance the efficiency of the bioremoval process, the researchers are now determining the best conditions for growing the bacteria. Alcoa is seeking to apply the process to other refineries around the world and hopes it will be able to use it to treat previously stockpiled oxalate.