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New mining wastewater treatment from CSIRO

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CSIRO has come up with a new, sustainable treatment for removing contaminants from mining wastewater.

The treatment solution uses hydrotalcites to overcome complexities of lime-based methods and offers a more water smart process.

CSIRO senior principal research scientist Dr Grant Douglas said the team found hydrotalcites, which are layered minerals that have aluminium, and magnesium-rich layers, can simultaneously remove contaminants in wastewater in a single step.

“We realised that hydrotalcites begin to form when aluminium and magnesium are present at an ideal ratio and under conditions during neutralisation of acidic waters. As hydrotalcites form, the contaminants become trapped and are easily removed from the wastewater as a solid,” he said.

“Mining wastewater often contains substantial magnesium and aluminium concentrations. This means that we can create hydrotalcites utilising common contaminants that are already present in the wastewater, by simply adjusting their concentrations and adding alkaline compounds to rapidly increase the pH level.”

The process initially focused on treating wastewater from mining and extraction of uranium. It has removed contaminants such as uranium, rare earth elements, transition metals, metalloids and anions (negatively charged molecules such as arsenate).

“This process purifies the wastewater from mines in a faster, more effective way that does not require large amounts of infrastructure or difficult chemistry to achieve it,” Douglas said.

Centrifugation is used to remove the hydrotalcites, leaving behind a cleaner sludge and a lot less of it. Initial tests revealed the treatment produces around 80 to 90 per cent less sludge than lime-based treatments – so it does not have the same level of handling and final disposal problems.

Water consumption can also be lowered through this process. Douglas said the hydrotalcites-treated water can be recycled back into the plant to reduce water cost used in mining operations.

This also means less water will be drawn from the environment such as from the groundwater near the mine.

“Around the world the minerals industry is keen to find more efficient ways to treat their wastewater and reduce their environmental footprint. With the inherent technical advantages and added benefits of using hydrotalcites, there’s a high likelihood of the mining industry adopting this technology globally,” Dr Douglas said.

Commercialisation of the technology is under way with Australian company Virtual Curtain.

The treatment can also reprocess and recover commodities and produce ore-grade material out of the contaminants. The material can be fed back into the recovery process to recover more metals.

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