Taking water back to the environment

Contaminated wastewater in a copper project being treated with the Virtual Curtain technology.

Virtual Curtain proves that cleaning up contaminated mining wastewater can be cost-effective, in contradiction to popular beliefs about responsible mining. Vanessa Zhou writes.

CSIRO senior principal research scientist Grant Douglas has brought a double-edged sword to wastewater treatment – a critical part of every mining operation.

He invented a technology called Virtual Curtain, which demonstrated its worth by successfully treating 56 million litres of acidic, contaminant-laden mine pit water in a Queensland copper mine within just two weeks.

The technology not only extracted water safely, but also returned a better water quality to the environment.

The miner then recovered around $1 million worth of ore back from the bottom of the mine pit, with over 90 per cent of the treated solute being discharged to the environment. The material produced by the Virtual Curtain process contained an ore grade that is substantially higher than what was mined – eight per cent copper and four per cent zinc – with potential for reprocessing.

“Virtual Curtain has absolute technological advantage over current technologies in that you do have that opportunity now to produce an even greater ore grade that was originally mined. You can get that out of the wastewater by concentrating up the contaminants into a solid,” Douglas tells Safe to Work.

“That’s really why Virtual Curtain is at the forefront with advantages over a lot of existing techniques.”

Queensland copper pit prior to treatment.

 

What’s more, Virtual Curtain allowed copper mining to commence about six weeks after the treatment. This is only one of Douglas’ success stories in completing the full cycle of processing contaminated, acid pit water back to re-mining.

Douglas, who developed the invention in 2008, has 25 years of experience in surface, groundwater and sediment geochemistry.

In the Beverley uranium mine in South Australia, Virtual Curtain removed a suite of radionuclides while evaluating the treatment of its effluent in a benchtop study.

“We were able to take out any remaining uranium following processing, and take out a lot of the radioactivity. So you have the opportunity, if required, to release a higher quality water,” Douglas says.

Virtual Curtain demonstrates that wastewater processing can go to another level, often far beyond current industry capability.

The technology can be applied to copper and zinc, as well as other hard rock mining in Australia and internationally.

Not only can Virtual Curtain be implemented from the initial mining stage, acid wastewater treatment, metallurgical processes through to improving the performance of other technologies, it can also be used to clean up the water after commodity extraction. 

In China, the Virtual Curtain technology was used to treat seven billion litres of coal to chemicals wastewater a year – ‘a big drink’ according to Douglas – producing reductions of 60 per cent in total hardness, 66 per cent in silica and 85 per cent in turbidity.

The result was a 50 per cent increase in reverse osmosis output at a fraction of the comparable infrastructure costs.

Wastewater treatment with Virtual Curtain requires only a couple of tanks, while recovering much less solid and more water (up to 90 per cent) compared to the traditional lime method (often around 60 per cent).

Contaminated wastewater in a copper project being treated with the Virtual Curtain technology.

 

“A lot of the time, the use of lime is the default in mine wastewater treatment. It is the traditional method that has been used since the Roman times. But lime is imperfect and involves quite an intensive process and considerable infrastructure costs,” Douglas says.

While Virtual Curtain is mostly retrofitted, its subsidiary Virtual Curtain China is building the first ever sites dedicated to the technology at China’s biggest copper operation and in a chemical plant north of Beijing.

Both plants are designed to treat a couple of gigalitres of water a year to a standard in line with China’s ‘water 10 plan’ – a rigorous action plan to control the country’s pollution discharge.

That policy is the reason behind Douglas’ 11 trips to China in the past three years. Given the sheer scale of mining operations in China entail a significant volume of water, what the companies need is an efficient solution and now.

“It’s the 21st century and there is universal acknowledgment among mining companies and legislators that there’s a need to operate more efficiently,” Douglas says.

“Everyone is reasonably open-minded in that aspect. And there is certainly a drive to improve operational and environmental efficiency among mining companies. There’s no doubt about that.”

An emptied mining pit in Queensland following wastewater treatment.

 

On the push side, environmental legislations challenge mining companies to operate to a higher standard. On the pull side, mining companies are taking up the mantle in being more efficient with water use and reuse. The push and pull drives the search for more efficient technologies, according to Douglas.

Not many technologies are currently available to remove contaminants rapidly, leaving only a small volume of material and producing water of sufficient quality at the end. But Virtual Curtain allows mining operation to treat its wastewater often to a much higher standard.

This article also appears in the July–September edition of Safe to Work.