Pollution solutions

Written by Sarah Kellett

Humans produce a lot of waste, from flushing toilets to mining metals, like the copper in electrical wires that power computers, phones and tablets. To clean up our act, a new way to purify contaminated wastewater from mines has been developed by CSIRO scientists.

At a copper mining site in Queensland, the first demonstration of the new ‘Virtual Curtain’ water purification treatment turned 50 million litres of acidic waste into rainwater quality water, which was safely discharged into a river.

An ancient technique

“Since Roman times, lime has been the material of choice for neutralising acid waste,” says Grant Douglas from CSIRO. “This is a new technique to make a mineral from the contamination in solution. We can remove a wide range of contaminants in a single step.”

The Virtual Curtain treatment separates contaminated wastewater into two products – cleaner water and a fine sludge. This is not unique: sludge-producing lime treatments are used in mines around the world. The big advantage of the Virtual Curtain treatment is that it removes more contaminants. It also produces a much more concentrated sludge. So each litre of Virtual Curtain sludge contains much more metal and other contaminants than a litre of lime sludge.

A modern twist

“The concentration of contaminants in the material is so rich, it can form an ore and can be re-mined,” says Grant. Companies can turn their waste into wealth, money back for the cost of environmental treatment.

The Virtual Curtain treatment works by carefully balancing the conditions of the water. Scientists analyse the waste, and then add one or two chemicals and neutralise the acid, raising the pH to around 10. Once the conditions are just right, minerals in the water form hydrotalcites. Hydrotalcites are crystals that can incorporate a wide range of contaminants. Plus, they’re solid, so they drop out of the water and fall to the bottom, taking the trapped contaminants with them.

Grant says mining companies in Australia, Europe and the USA have contacted him and are interested in using the technique. It’s Australian research, made commercial by an Australian company, and taken to the world.