Sustainable water management in the mining industry

Water shortages, vast distances and increasing water costs have mining companies, particularly in Australia, seeking cost-efficient and environmentally friendly ways to manage water supply on-site. Issues surrounding water storage, transport, recycling and identifying underground sources all make for a significant challenge. However, by engaging in water recycling initiatives, companies can move towards a zero water discharge mine, while satisfying stakeholders who are increasingly demanding greener practices and an improvement on the bottom line.

Much of the water at mine sites exists in the form of slurries, used to transport the product and waste materials such as tailings. A large component of mine water is retained within the tailings storage. Therefore, understanding rheology and slurry behaviour of tailings, in order to optimise the water needed for transport, is critical to water sustainability.

Australia is leading the world’s rheology and slurry engineering practices with cutting-edge new technology and assessment techniques. Heading up the rheology and slurry engineering group at ATC Williams, I see the water sustainability issues facing mining companies every day.

The industry accounted for 4% of water consumption in Australia in 2009-10, with 489 gigalitres of water used* - this equates to more than quarter of a million Olympic swimming pools. These numbers will only have increased over the past four years in line with the resources boom.

Optimising slurry pumping has become increasingly important to mining companies as water becomes more valuable, mine and plant sites become more remote, and economic and environmental pressures force companies to cut costs and increase efficiencies.

New technology is entering the rheology and slurry market, meaning mining companies have access to more targeted assessment, strategy and execution to help lower the water required for slurry transport.

Generating solutions isn’t easy. Transporting liquid and semi-liquid matter is complex, unique to each situation and involves significant cost and environmental considerations.

The issues we see vary - we have areas in Western Australia where companies may pump slurries hundreds of kilometres, and want to do this at low water content with higher solids concentration to reduce overall water demand and therefore costs of make-up water. In contrast, in some wetter areas in Queensland, a risk exists of temporary mine closure due to excess water and flooding to the environment, in which case there is less imperative for high-concentration slurries.

The tailings stream from any mining operation is a slurry - a mixture of solids and water - and is pumped from the processing plant to the tailings disposal area. Essentially the challenges lie in predicting the effect of the solid particles in the mixture as it flows through the pipe.

A good example of sustainable water management is the Paulsen’s Gold Mine near Paraburdoo. The Tailings Storage Facility (TSF) is a sidehill-type facility with a crescent-shaped earth embankment approximately 1 km long at the base of a low hill. ATC Williams has been involved in the design and construction of five successive raises of the TSF since 2006.

The TSF is rated a category 2 facility of Significant Consequence in accordance with DMP and ANCOLD guidelines. Sandy silt tailings are discharged at approximately 450,000 tpa with a typical solids concentration of 50 to 55%, forming a non-segregating beach deposit with a slope of approximately 1%. The tailings dry and gain strength rapidly, allowing the beach to be used for the upstream method of embankment raise construction. This significantly saves on heavy earthworks and associated diesel and CO₂ emissions.

Evaporation is the dominant process in the water balance, and this is one driver to adopt thickeners in order to recycle water and minimise evaporation losses. This has resulted in only a very small decant pond forming, reducing the opportunity for evaporation, particularly since the onset of drought conditions in early 2009. The minimal pond size also means that rehabilitation will occur much faster.

With a falling Australian dollar, rising environmental impacts and a recently uncertain political period, our current environmental and economic climate presents a fitting opportunity for mining companies to assess and improve their water consumption practices. Companies are ardent about finding solutions, and our rheology and slurry team are resolute in providing them.

*Australian Bureau of Statistics - Yearbook of Australia - 2012

*Dr Paul Slatter heads up ATC Williams’ Rheology and Slurry Engineering Group. He has written over 400 published technical papers, presented 16 invited international keynote addresses and is cited in 15 design textbooks on mining and mineral processing plant design. His previous involvement in the hydrodynamic contexts of pipe flow, fittings losses, pump de-rating and free surface flows has produced pragmatic design tools for industry.  He has served on a number of international technical committees in rheology, slurry flow and pump and pipeline design.