Water being poured into tank. Photo: Arne Hoel/The World Bank
Environment

Getting creative with mine water management

Water management is one of the biggest, if not the biggest, operational and social challenge that mining companies currently face. So how do we make sure there is enough for everyone?

“Everybody should have access to sanitation and clean water, so it’s very important that mines manage their water use carefully,” Jim Spenceley, told me as we settled down to talk about water and its role in the mining industry’s future.

Water management in this context is a vast topic. So, in a bid to get a handle on the issues we are facing and some potential solutions, I turned to EPC firm, Black & Veatch.

Spenceley, who is senior vice president of the company’s mining division, put the matter into perspective. “Effective water management and use of that resource is critical, because often a mine’s impact on communities is directly related to how it manages water,” he said.

“If a mine manages its water well, its relationships with local communities are typically good. But a lot of disruptions around social licence to operate are centred around the relationship between local communities and mine water use, because it’s a shared resource.

“It does vary geographically, depending on whether it’s a water surplus or water negative area, the number of local inhabitants, the presence of agriculture… There are a lot of variables, but water is always a top priority issue for miners at any site.”

Victoria Gosteva, senior marketing manager, and Corné Pretorius, director of mine water management at Black & Veatch Mining, also joined us for the debate.

“The criticality is absolutely there,” Gosteva emphasised. “The World Economic Forum named climate change and weather-related risks as the top five biggest threats in its 2020 World Risk report. It’s the first time in history that all of the top five spots went to environmental risks.”

Gosteva got to the crux of the matter quite quickly; water availability is intrinsically linked to the greatest risk the human race faces going forward: climate change.

A warming climate will disrupt meteorological patterns, and while we can make predictions as to average rainfall certain regions will receive in 1, 2, or 5 degree temperature rise scenarios, we will also see an increase in anomalous rainfall events. And there will be knock on impacts to water scarcity/surplus like the devastating bushfires we saw in Australia in January, and flooding in previous years.

Top 10 risks to society over the next 10 years, taken from the World Economic Forum's 2020 Risk Report
Top 10 risks to society over the next 10 years, taken from the World Economic Forum’s 2020 Risk Report

How can we adapt extraction processes and operations that have taken decades, in some cases, centuries to optimise, to cope with these changes, and minimise our contribution to the cause and effect? And that’s before we even get started on business models and practices.

How much water?

First things first, how much water does the mining industry actually use? How big an impact can we have?

“A lot of people think that mining is a massive consumer of water relative to everything else, but when you compare its usage to that of agriculture, there’s really no comparison,” Spenceley said.

“Agriculture can dwarf mine water consumption by an order of magnitude or more, but there’s a relationship between agriculture and communities that’s different than with mining. Agriculture is often seen as part of the community, whereas mining isn’t.”

The US Geological Survey states that, in 2015, water abstraction in the US from mining was 1% of the total water abstraction.

That’s a regional number but, to give it some perspective, the World Bank estimates that, at present, 70% of freshwater consumption globally can be attributed to agriculture. Feeding 9 billion people by 2050 will require a 60% increase in agricultural production and a 15% increase in water withdrawals.

The UN also states that, between 2000-2050, global water demand for manufacturing is predicted to increase by 400%; more than any other industrial sector.

With greater pressure on resources comes greater competition so it’s clear that all industries (mining included) will need to get creative with their water management strategies to ensure there is enough to go around.

I wondered how that 1% figure will change in the coming years as more preconcentration technologies and waterless mineral processing methods come into play?

“That’s an interesting point,” said Spenceley. “Because average ore grades are declining, and the amount of water required to produce the equivalent amount of metal is increasing, even though our efficiency in water use is rising.

“Are we going to see a decrease in water use as these technologies grow in popularity? I hope so. We need to offset the extra water we’re using through decreasing grades with increasing efficiency.”

Agriculture is the biggest consumer of freshwater water globally, accounting for around 70% of consumption. Photo: Jutta Benzenberg/World Bank
Agriculture is the biggest consumer of freshwater water globally, accounting for around 70% of consumption. Photo: Jutta Benzenberg/World Bank

The water-energy trade-off

Energy is, of course, the other big issue that mines face.

It’s all very well using technology to create alternative sources of water for mining processes e.g. to recover water from mine tailings or desalinate sea water, but we must also consider the amount of energy required to do so and, at what point that becomes/stops being cost effective in contrast to traditional sources.

We must also consider where that energy comes from and whether it is sustainable or renewable.

“The energy-water cost curve ramps up quite significantly once the easy to reach sources have been exhausted,” explained Pretorius. “That’s something that we, as an industry, need to develop good models for so that we can understand what it will take to get to that ‘waterless mine’, or as close to it as possible.”

Against the backdrop of increased metal demand, particularly for copper which is vital to the production of green energy technologies like electric vehicles and wind turbines, the water-energy cost-use curve will also impact the mining industry’s ability to create carbon-neutral mine sites; something which many major miners are working towards.

Is it even possible to create a carbon-free mine given that context?

“It will be possible if commodities are priced correctly in the market,” stated Pretorius. “With current prices, I would say no. Metal prices needs to reflect the value of water and our climate.”

Spenceley agreed: “It’s definitely doable,” he said. “Companies like BHP and Rio Tinto are looking at their supply chains holistically, so part of the solution could come from offsetting or sinking carbon elsewhere.

“My view is that eventually we’ll see carbon pricing factored into commodity pricing in some way.  Certainly, the financial institutions that hold large amounts of mining stocks are going to be pushing for that. Some miners are already incorporating carbon pricing into their investment modelling as well, so it’s going to come. It’s just a question of the pace of change.

“The challenge around the waterless mine is actually harder, because the carbon-free mine is a question of price. But with water, there are other factors such as evaporation, and you can’t ever really hit 100% on dewatering tailings. You also get more impurities in process water as you recirculate it…

“We’re on a journey where the market is going to have to pay for these improvements, inclusive of energy costs, capital investment and the fact the ore grades are declining. It poses a huge challenge, but I think it’s all doable.”

Finding new sources of water

The advantage that mining has over industries like agriculture when it comes to sourcing water, is that mines can use water of much lower quality; it does not need to be potable.

Conventional sources of freshwater include groundwater, surface water collection or underground aquifers. But what happens once those are no longer viable?

The first port of call for many miners, particularly those in water-scarce regions like northern Chile, is desalination.

“Although it’s expensive, desalination can be done very efficiently with negligible impact to the ecosystem,” said Spenceley. “But there are other places we can go for water. We can decrease water loss to evaporation. A novel example of that is Anglo American has put floating solar panels on one of its storage reservoirs as a pilot to produce green energy and also reduce evaporation.

Anglo American has installed 256 floating photovoltaic panels on the Las Tórtolas tailings pond at its Los Bronces copper mine to help cut evaporation. Image: Anglo American
Anglo American has installed 256 floating photovoltaic panels on the Las Tórtolas tailings pond at its Los Bronces copper mine to help cut evaporation. Image: Anglo American

“Another source is the water that’s trapped in tailings; that’s one of the largest untapped sources of water that miners have access to, so finding a way through technology to access that is important.

“Then there is water seepage from impoundments; often, water storage reservoirs aren’t lined, so a lot of the water seeps back into the ground. Collecting that seepage is another source.”

Pretorius added: “Those are the most relevant sources within the boundaries of the mine water circuit but if we look outside of the mine, then reuse of domestic wastewater is also an option in some areas. Rather than treating the water and discharging it back to the environment, some of it could potentially be used within mine water circuits.

“I’ve also seen water that was stored in underground mines in South Africa reused in the mine water circuit, and some upgraded to become part of the municipal supply.

“In another case, a petrochemical facility was taking water from underground mines and upgrading it to boiler feedwater quality to produce steam. This not only saved a fair volume of water that would otherwise have been abstracted from a local river, it also cleaned up pollution that was lying dormant in that mine.

“It’s important to look for integration opportunities between the mining industry and domestic water utilities or, indeed, other industries.”

To filter or not to filter?

Let’s look at one of these options in more depth. One that is being touted, by many, as the answer to our tailings-related problems: dewatering.

The technology that is likely to have the greatest impact in this space are filter presses, and some smaller mines, such as Pumpkin Hollow in Nevada, are already in production using filters to dewater tailings. However, the technology is yet to be proven at a large-scale copper operation.

“In the future, we’re going to move away from large conventional tailings impoundments, and ultimately it’s going to be a question of cost,” said Spenceley. “I think we’re going to see an incremental approach to filtered tailings, with percentages of tailings streams being filtered while miners learn to incorporate these systems into their operations. Their ability to scale up is going to be a question, but there’s no doubt that this is the way of the future, especially when we look at the number of tailings dam failures the industry has been plagued with.”

There are other technologies such as cyclones and centrifuges that can be used to dewater tailings to a degree, but these do not deliver the same capabilities as filters.

Pretorius jumped in: “This is where that cost curve I was referring to earlier comes into play. At what point does it become cost effective to implement filters for dewatering? Maybe we could use other, less energy-intensive technologies to get that first, say, 10% of the water out that you would not get out from conventional thickening and settling.

“Then, as we ramp up that curve, higher percentages of recovery would require more capital and more energy, because it’s also a function of the particle size, and the mineralogy of the fine particles that determines how difficult it is to squeeze that water out; for example the clay content present in the tailings stream.”

Pretorius is right; eventually, once high-capacity filtration solutions are proven at scale, it will not be a question of whether it’s technically feasible to dewater tailings using this method, but at what point it is economic in contrast to other water sourcing methods, like desalination.

Socially and ethically, it’s always preferable to have dry tailings, but let’s not forget that mining is a business, one that needs to turn a profit. If getting the last 10% of that water out requires 60% of the total energy input, does it make financial sense to chase that last 10%? Maybe not.

These functions can ramp up significantly at the latter end of the cost curve, and that’s why many miners are still grappling with the financial reality of filtered tailings.

Many miners in highly water stressed regions such as northern Chile are turning to desalination to secure their mine supply in the long term. Image: Pixabay
Many miners in highly water stressed regions such as northern Chile are turning to desalination to secure their water supply in the long term. Image: Pixabay

Pumped hydro with energy storage

Pumped hydro with storage is another option, one that ticks multiple sustainability boxes.

Spenceley explained: “For pumped hydro storage, you need an upper and a lower reservoir. You have your renewable energy supply, which could be wind or solar, and you take some of the energy when the sun is shining or wind blowing to pump water from the lower reservoir to the upper reservoir.

“Then when the renewable resource is not available, e.g. at night or when the wind stops blowing, the water is released from the upper reservoir through a hydroelectric turbine to produce a stable level of renewable energy. It’s basically an energy storage system, more cost effective for grid scale than a battery system would be.

“In a water stressed area like northern Chile or southern Peru, the ocean can serve as the lower reservoir, and the Andes provide elevation for the upper reservoir. Then you add a renewable energy source, like solar, to power the whole system and a desalination plant.

“The desal plant requires high-pressured water to drive the salt out of the seawater through a reverse osmosis membrane. Having this upper storage reservoir that can provide water under gravitational pressure to the desal plant saves a lot of energy and money.”

Again, the technology exists and there are multiple studies underway to explore the cost of such a system, but Spenceley isn’t aware of a full-scale operation as of yet.

Of course, off takers are required for the water and power, mines need the right developer and community support… the business dynamics are complex but, where the circumstances are right this could prove a secure and sustainable water option for mines in water-stressed regions.

Rising to the challenge

As all of these concepts demonstrate, the mining industry is at a point where most of the easy to implement technologies and solutions for water management have been exhausted.

To tackle the more difficult challenges that we face going forward will require ‘thinking outside of the box’ and a willingness to look to other industries for help in developing new solutions.

And while this in itself presents a challenge for some engineers and consultants, it is also reinvigorating the profession to a degree. For some, the new opportunities presented by these challenges are an enjoyable part of the job.

Two thirds of the world’s population (4 billion people) currently live without sufficient access to fresh water for at least one month of the year, so responsible water management is key to good mine-community relations. Photo: Arne Hoel / World Bank
Two thirds of the world’s population (4 billion people) currently live without sufficient access to fresh water for at least one month of the year, so responsible water management is key to good mine-community relations. Photo: Arne Hoel / World Bank

“To me, it’s absolutely fascinating,” Gosteva enthused. “Mining companies have been working on finding solutions for water use for decades. “So, what’s next? What are the next engineering innovations?”

Pretorius agreed: “It’s really exciting to see what’s happening. We are helping some clients with shaping their innovation and technology development approaches in complex mining operations, and to see these technologies evolving is really interesting. There’s a very healthy innovation drive happening in mining right now.

“It’s also interesting to see how technologies developed in industries not directly related to mining are now finding potential applications in the mining space.”

“Collaboration is the key,” added Spenceley. “In my opinion, the big solutions are going to come with improved partnering with communities, regulators, the mining industry and service providers all working together to unlock value.

“All the easy solutions have been implemented, just like all the easy orebodies have been developed. Now, we have to move on to the next level of challenge and it’s going to require us to work differently together, for sure.”

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