Water in Mining

WATER is essential to mineral processing, and is used at various steps in the process to recover valuable metals from ore.

The water use is quite high – for example, around 1600 litres of water is used to obtain about 19kg of copper – about the same as is needed for manufacturing a medium-sized family car.

However the mining sector is a relatively small water user, accounting for less than 3.7 per cent of national water consumption in 2014-15.

By comparison, agriculture (including forestry and fishing) consumed 60 per cent and households consumed a further 12 per cent.

According to the Minerals Council of Australia, the mining sector is one of the highest value water users in Australia.

In 2016-17, the gross value add per gigalitre (GL) of water used by mining ranged between $111m/GL and $127m/GL, compared to $4m/ GL for agriculture.

Valuing Water

Water availability and security of supply is critical for the minerals industry.

Miners face a wide variety of water management challenges, including limited water supply, use and treatment of poor quality water, mine dewatering and the management of excess water.

Operations are required to install, operate and maintain the infrastructure when necessary for their water supply, and in some circumstances the water infrastructure provided and maintained by industry can be shared with other stakeholders, including neighbouring communities, farmers and pastoralists.

Many mining operations are based in remote locations, where water may not be readily available.

This can represent a significant potential constraint on further investment and expansion.

Even environments where it is accessible, processes for making the water suitable for use in the refining process (such as desalinisation) can add significant costs through increased energy use.

As ore grades decline, the amount of water used increases and more intensive processing is required.

Studies conducted by the CSIRO suggest mining lower grade ore is becoming more prevalent in Australia, and the research group has responded by looking at ways to estimate water footprints for major mineral commodities such as nickel, copper and gold.

“By investigating methods of valuing water in mining, mineral processing and metal production, and comparing these with other industrial processes and water users, we will be able to better manage water and reduce the risk of water scarcity,” the CSIRO stated.

The method is a technique called life cycle assessment.

“Using our method, industry can measure and analyse its water footprint from the point where ore is extracted through the production process, and on to its end use and disposal.

“Operators can identify and calculate the direct water use of various processes such as milling and flotation as well as indirect water use.

“Water use ‘hotspots’ can be detected and opportunities for water savings – and the associated cost benefits – highlighted.

“It is leading to more sustainable minerals processing operations.”

Collaborations between industry and scientists, such as the Pilbara Water Resource Assessment project, have examined water ecosystems and how they change during wet and dry periods.

The $3.5 million partnership between the CSIRO, BHP Billiton and the WA Government, was aimed to aid water managers and local

Water scarcity can represent additional costs for businesses, which makes ongoing studies on how we access, use and re-use it in industries – such as mining – invaluable.

industry plan for future water use in an area rich in resources and environmental assets.

The study revealed some of the mechanisms responsible for filling the Pilbara’s groundwater stores.

It found that between 8mm and 30mm of rainfall is required before runoff starts in most catchments, which leaks through streambeds to provide the main source of aquifer replenishment.

Water from these shallow alluvial aquifers then recharges deeper dolomite aquifers, which can store large quantities of water in inland areas.

“Knowing how the water systems operate right across the region, such as how groundwater is affected by rainfall and storm events, helps with the planning and management of local water use,” CSIRO project leader Dr Don McFarlane said.

PROJECT SNAPSHOT Nolans: Groundwater Assessment

In early January, the NT Environmental Protection Agency (EPA) approved Arafura Resources’ $900m Nolans rare earths project, 135km northwest of Alice Springs.

As part of its study, the EPA identified a risk to the stability of groundwater levels, citing that the project would use 2.7 gigalitres of groundwater each year over a lengthy mine life of between 35 and 55 years – but found that it could be managed.

In Arafura’s Environmental Impact Statement (EIS) submission to the EPA, the groundwater model presented indicated that the open pit would become a permanent groundwater sink with estimated inflows of eight litres a second.

“This would result in a continuous drawdown of groundwater surrounding the pit,” the EPA said.

“At the end of mine life the open pit would contain a pit lake that would reach equilibrium where evaporation matches inflows, at a level 80m below the original aquifer depth.”

The EPA projected that the pit lake that would be left behind after the end of Nolans’ mine life would not harm the surrounding geology.

“The groundwater sink from the pit is not predicted to have any significant impact on the high quality aquifers of the Ti Tree Basin and Southern Basins after closure of the project because the rock basement connecting these aquifers has very low transmissivity.”

However, it noted there would be uncertainties surrounding the behaviour of the pit lake post-closure.

“The NT EPA considers further studies are required on the final void water quality including the surrounding groundwater level and expected quality of water held in the void prior to final acceptance of the mine closure plan.”

It recommended that aquifer levels and water usage be monitored in real-time with data made available to the public on a regular basis.

The EPA also recommended that Arafura conduct risk-based assessments of the impacts of on stygofauna in the remaining groundwater.

Arafura said it was happy with the EPA’s recommendations and looked forward to further mine planning, with a view to start construction in 2019.

“Our sustainability team has worked diligently alongside our environmental consultants GHD to produce comprehensive, quality documentation to support the passage of the Nolans project through the Northern Territory environmental approvals process,” Arafura managing director Gavin Lockyer said.

“This should go some way to securing final government approval for the project, enabling construction to move forward, subject to financing and FID.”