Reduction in water usage is a key concern for miners globally. Image: Pixabay
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Mining without water

Reducing water usage is a key sustainability challenge for mining operations around the globe. Anglo American is leading the charge with its vision for fully waterless mines. Carly Leonida looks at the company's efforts

On March 22, a date declared by the United Nations (UN) to be World Water Day 2019, Anglo American reaffirmed its commitment to developing waterless mines; a powerful stance given the number, and scale, of tailings-related disasters the industry has seen in recent years.

“It’s our duty to serve the communities we impact in a positive way,” the company said in a press release. “Our ambition is to operate waterless mines in water-scarce areas. We hope to eliminate freshwater usage from mining processes and to eventually achieve a near-waterless mine.”

The group has been working on the concept for some time, and has even written the pledge into its Sustainable Mining Plan that was developed to reflect the UN’s Sustainable Development Goals. As part of the plan, Anglo has committed to reducing its abstraction of freshwater in water-scarce regions by 20% and increasing its water-recycling levels to 75% by 2020. By 2030, it aims to reduce its abstraction of freshwater in water-scarce regions by 50%.

A reduction in water use is one, very positive step, but how do you go about eliminating water from a mine altogether? Aside from its use in the actual mining process (drilling, haul road management, in-situ mining etc), water is a crucial part of mineral processing operations, forming the backbone for many industry-standard processes such as flotation. Zero-discharge concentrators already exist in water-scarce areas, but these still require a certain level of abstraction…

“With around three-quarters of our portfolio located in water-scarce regions, water conservation is critical,” Anglo chief executive, Mark Cutifani, said in the company’s 2018 Sustainability Report. “Our ambition to eliminate freshwater usage from mining processes – and to eventually achieve a near-waterless mine – is focused on innovative ways to separate and transport waste, evaporation measurement, dry-tailings disposal and non-aqueous processing.”

A number of miners are looking into eliminating tailings storage facilities from their operations using techniques such as preconcentration, paste backfill and then dry stacking of waste. And some are investigating reprocessing their existing tailings, not just for the environmental benefits but also to create a very lucrative source of income. However, in order to remove water entirely from mineral/metal production stream, the entire process will need to be reconsidered.

Rethinking mineral processing

Anglo has name checked its FutureSmart Mining programme as a key enabler of its ‘waterless mine’ vision and, after a bit of digging, I found a 2018 article on the FutureSmart web page entitled ‘Picture this: the waterless mine’. On closer inspection, it appears that the first step in Anglo’s plan is a closed-loop system that will initially still involve water as part of mineral processing.

“We are already making inroads into our water challenge through our ambitious closed loop approach to water dependency,” stated Anglo in the article. “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.”

Evaporation measurement and dry tailings disposal will be key to this approach.

“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,” the company said.

Anglo already employs an innovative evaporation measurement system developed by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) at its Drayton mine in Queensland Australia. This calculates over a period of 3-6 months the relationship between local meteorological conditions and evaporation from the mine’s tailings pond.

“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,” Anglo said.

It also explained that this technology has the potential to feed into others such as pervasive monitoring which uses fibre optics to measure water flows to support conservation and process control.

“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 trialling this technology in our open-pit platinum mine in South Africa,” the company said.

Reducing tailings

In terms of limiting the amount of water that is sent to tailings ponds in the first place, Anglo is looking to use a combination of coarse particle flotation and dry stacking technologies to dewater mine waste.

“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 additives that separate interstitial water from fine metal particles – not only making them easier to recover but also resulting in dry, stackable tailings,” the company said.

More targeted comminution methods will help to get rid of waste material earlier in the process, and Anglo said that dry separation could create a 30-40% reduction in water used per unit of mineral production.

“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,” the company concluded.

“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.”

Non-aqueous solvents are already used in the mining industry to extract oil from oil sands and reduce the amount of fine tailings sent to storage facilities. The concept of solvometallurgy (as opposed to hydrometallurgy) is championed by companies such as SOLVOMET and it will be interesting to see if Anglo goes down this type of route, or with something entirely different.

Personally, I can’t wait to see the results. Nice work Anglo.

I’d be interested to know if other miners/consultants/engineers are looking into waterless methods for mineral processing. Please comment below if you know of any projects

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