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05 January 2018

As part of our FutureSmart MiningTM approach to innovation and sustainability, we have developed four aspirational concepts that we are working to achieve. In this article, we take a look at the Waterless Mine…

Mining has always been heavily dependent on water. Without water, the extraction of copper, platinum group metals, diamonds and other valuable products would be practically impossible. But water is becoming increasingly scarce: with a predicted shortfall of 40% by 2030, the shortage of clean fresh water represents the greatest global societal and economic risk over the next decade [source: World Economic Forum]. And with approximately three quarters of our operations across the world in water-stressed areas water conservation is a critical concern for Anglo American.

Our ambition is, where possible, to eliminate fresh water from our mining processes, especially in the separation and transportation of ore and waste (tailings).

We are already making inroads into our water challenge through our ambitious closed loop approach to water dependency. This sealed system approach aims to deliver greater water efficiencies through direct water recycle and reuse. Most mines operate some sort of recycling system to minimise the draw on new water but the concept behind “closed loop” is to absolutely minimise water losses by using the same water again and again. Today, we meet two thirds of our total operational water requirements in this way.

To implement this closed loop strategy, our operations employ number of existing and new technologies.

We are focusing our innovation efforts in two areas: evaporation measurement and dry tailings (waste) disposal.

Evaporation

For most mining operations, water is stored in dams to ensure a reliable water supply and to enable the recycling of water. Evaporation losses in our own dams account for 10% to 25% of total water lost at a mine. Not only are we wasting a very scarce and precious resource, this water costs approximately US$200 million annually to replace.

At our Drayton Mine, in Queensland Australia, we have installed a new technology developed by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) that supports the more accurate measurement of evaporation rates. Consisting of two floating buoys, the technology quickly calculates (over 3-6 months) the relationship between local meteorological conditions and actual evaporation – producing much more accurate evaporation data. Having accurate evaporation data drives a better understanding of the water balance at the mine site, focusing efficiency efforts in areas where impact can be greatest.

The potential for this technology to feed into other data-rich technologies is exciting. For example, it supports “pervasive sensing”, another innovation that uses fibre optics to measure water flows, not only to conserve water but to support process control and, ultimately, metal recovery. Our mine sites are large and complex so delivering accuracy, automation and real-time monitoring of all mine-wide water and process flows provides the type of control needed to deliver real water savings. Following a successful proof of concept we are now trialing this technology in our open-pit platinum mine in South Africa.

(Low-cost) Dry tailings disposal

Water sent to tailings disposal often represents the largest water loss at a mine.
Fine particle slurries in particular are difficult to dewater and current dry disposal options have prohibitive capital and operating costs. As part of our pioneering Concentrate the MineTM concept we are exploring low cost methods to minimize the amount of water sent to the tailings pond in the first place.

Our approach combines course particle flotation to concentrate the mineral, and dry stacking technologies to dewater the residual waste, producing dry, stackable tailings. Essentially, it allows us to float particles at sizes two to three times larger than normal making it easier to extract water from the process and leaving a waste stream that is dry and stackable.
But there will always be a portion of ultra-fine particles that also require processing. In partnership with major chemical companies we have done some promising lab work on copper tailings using [Soane] additives that separate interstitial water from fine metal particles – not only making them easier to recover but also resulting in dry, stackable tailings.

Dry separation

In addition to dry processing, we are also exploring innovative methods for dry separation. Dry separation involves finding innovative methods for dry comminution (the crushing and grinding, usually sequentially, of ore to the required particle size.

More targeted comminution creates a pre-concentrate of the ore, rejecting and dewatering waste far earlier in the process. Early estimates indicate the potential for a 30-40% reduction in water used per unit of mineral production, as well as the other benefits including increased production.

Non-aqueous processing

In parallel with our dry separation technologies, we are also laboratory testing a non-aqueous processing technique, again in partnership with a global leader in science innovation, using a bespoke polymer instead of water to separate the valuable ore from the remaining waste rock particles.

Applicable across most of our core assets, we are confident that these dry processing techniques will allow us to reuse 80% of process water, moving us closer to our goal of a waterless mine – while delivering on our sustainability goals.

Picture this: The Modern Mine

Picture this: The Concentrated Mine

Picture This: The Intelligent Mine

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