Wasting water on dust control

While water shortages are generally felt in every community across Australia, the impacts are certainly felt hardest in arid, regional areas.

For the mining operations located in such areas, dust control is one of the principal uses of water.

According to a report by Western Australia’s Water Corporation in May this year, 70% of the Pilbara region’s water was used in mining activities.

Furthermore, around 50% of the water in Harding Dam, the principal reservoir for Karratha and Port Hedland, is used for dust suppression on the stockpiles of iron ore in the ports.

The towns’ fresh drinking water must be used, because salt water or brine water can contaminate the ore.

According to Mason Trouchet, a technical manager at dust control services provider Rainstorm, the lack of available water is hindering the State Government’s efforts to develop and grow these regional centres.

“Something of a political water war has broken out in the Pilbara,” he told Australian Mining.

“Regional Development Minister Brendon Grylls has said the Government cannot actually develop any more subdivisions in the area because the water infrastructure is so far behind.

“The region desperately needs more houses to accommodate growth, but there is not enough water to accommodate all of these expansion projects.”

Wasted on roads

The amount of water used in traditional dust control techniques is staggering, especially when you consider that much of this water cannot be recycled. 

“If an operation in a dry region like the Pilbara has an unsealed haul road, they would need to apply about four litres of water on every square metre, every day in order to effectively suppress the dust,” Trouchet said.

“If you multiply that across a five kilometre haul-run, there is obviously an enormous amount of water being used.

“Let say this five kilometre road has a width of 25 m; the mine would be using 500,000 L every single day just to keep the dust under control.”

The miners cannot simply alleviate this by reducing the amount of water used, because the four litres is necessary to ensure the ground will actually retain the moisture.

“If they only sprayed one or two litres, they would end up with nothing, because the water would evaporate as soon as it hit the ground,” Trouchet said.

According to Trouchet, many miners are now forced to exceed their water allocations, leading to penalty charges and added expenses.

“A typical miner’s water allocation is primarily used up in their processing plant,” he said. 

“A reasonable amount of that water, somewhere between 40% and 60%, can actually be recycled.

“But the water used on the roads is lost, so it is just adding to the costs of running the operation.”

Rainstorm uses a magnesium chloride product called DustMag as an alternative measure.

According to Trouchet, this chemical compound is regarded around the world as the most effective dust control product.

“DustMag actually draws in moisture from the atmosphere, overnight dew for instance, and retains it,” he said.

“We come in within our own trucks and spray only two litres of the chemical for every square metre, so there is already a net saving there.

“But because it traps the ambient moisture, the miner would not need to rewater the road for another 90 days.”

“So the choice is between four litres per square metre per day

“So while there is the actual physical water saving, it also means the miner can use its water allocation more effectively.”

Stockpile protection

Of course, haul road watering is but one of the many dust control processes necessary in mining.

The enormous ore stockpiles found on minesites and ports have also traditionally required massive amounts of water to ensure the dust is kept under control.

There can be a range of serious consequences if some of the material escapes, including health problems in the nearby communities, environmental damage and added expenses.

For the last five years, Rainstorm has been trialling an alternative procedure for stockpiles using both a polymer emulsion product and a weather prediction service.

Trouchet described the Gluon polymer emulsion as a plastic, spray-on film similar to cling wrap.

“The film is like a tiny fly-screen; the water will still pass through it but it cannot escape,” he said.

The company was recently recognised the Earth Award from the Civil Contractor Federation for a particularly innovative application of this emulsion.

The contractor used helicopters to deliver the Gluon to stabilise re-seeded portions of the Dampier to Perth gas pipeline in Western Australia.

“The film will create a bit of a hot-house effect underneath the topsoil, so you can still get seed germination,” Trouchet said.

“The dunes have become alive with growth over the last three years.”

The product can be used to cover open rail cars, tailings dams and in environmental rehabilitation programs.

The polymer is designed to act as veneer on the surface of the stockpiles and has a chemical composition that will not contaminate any downstream processes.

“Because it is a thin film, it is designed for surfaces that do not have any heavy equipment or vehicle traffic,” Trouchet said.

“You do not need much of it to cover the surface area, which is a bonus when the time comes for the stockpile to be moved.

“The processing plant engineers do not need to worry about the polymer either, because it is not mixed in with the ore.”

The company also uses a weather prediction service from Sinclair Knight Merz called the Proactive Management System (PAMS), to watch for wind events approaching the stockpiles.

“PAMS gives us a outline of weather patterns down to a square kilometre two days in advance,” Trouchet said.

“We have carried out wind-tunnel tests to determine the ‘dust lift-off’ for each ore type, so if a particularly strong wind event is about to occur we can proactively apply the most appropriate Gluon polymer to protect the stockpile. 

“We can tailor-make the polymer coating according to the ore type, the wind speed and the duration of stockpiling.”

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