Researchers rehabilitate bauxite residue

Researchers from The University of Western Australia (UWA), working with Alcoa of Australia, are breaking new ground on finding ways to transform bauxite residue into healthy soils. Their work has been published in the journal Ecological Engineering.

Bauxite residue - a by-product in the production of alumina - is typically highly alkaline and saline, and contains very little organic matter, nutrients or microorganisms, all of which are vital ingredients for plants to grow. The research team, led by Dr Natasha Banning from the UWA School of Earth and Environment, evaluated amendments with the potential to improve the residue’s rehabilitation potential and its capacity to support plants. The team also investigated how microorganisms behave in bauxite residue sand and their influence on nutrient availability such as nitrogen.

“The effects of textural (carbonated residue mud or soil-derived clay), organic (raw-state or mature compost) or combined textural-organic amendment of the bauxite residue sand fraction on key physical, chemical and microbial properties and growth of annual ryegrass were studied in a glasshouse trial,” the researchers explained. Two watering treatments were used to assess the efficacy of amendments under nutrient- or water-limited growth environments.

“Adding green waste compost to bauxite residue sand improved plant growth, because it increased the amount of water stored in residue sands,” Dr Banning said. “The compost also added nutrients for the plants to use and increased the amount of microorganisms in the residue.”

Alcoa of Australia is a major alumina producer globally, with three facilities in Western Australia that refine bauxite ore into alumina. The company has an active research group working collaboratively with local universities to develop best practice methods to store and remediate bauxite residues.

“This collaborative research will help Alcoa to develop best-practice strategies for rehabilitating these areas,” Senior Research Scientist at Alcoa Dr Ian Phillips said. “Importantly, if we can work out ways to increase the rate of in-situ remediation of our residue deposits, then we can reduce our long-term environmental impact.”

This understanding of rehabilitation performance can be applied globally to other residue storage areas under a wide range of environmental conditions.

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