June/July 2013

High and dry

With water in short supply, some are looking to the ocean for answers

By Pierrick Blin and Antoine Dion-Ortega

In Chile's Atacama Desert, the Escondida mine has been desalinating sea water since 2006 | Nataliya Hora/Shutterstock

KRW 2014Chile’s copper-rich Atacama desert is an acute example of the global water supply problem, but it is certainly not the only one. Around the world, miners are facing costly fresh water shortages, often in regions that are well-endowed with attractive deposits. And because only 2.5 per cent of the Earth’s water is fresh, interest in tapping into the sea is growing.

The water shortage has become so dire in Chile that authorities declared a state of emergency in the Copiapó River watershed in March 2012. “In Chile, in the First (Tarapacá), Second (Antofagasta) and Third (Atacama) regions, water solutions which propose supply from the aquifers for our projects are both unacceptable and near impossible,” says Bernie Loyer, vice-president of South American projects for Goldcorp. His purview includes the El Morro project, which is owned by Goldcorp (70 per cent) and New Gold (30 per cent) and is located around 150 kilometres southeast from Copiapó. Initial production for the project was expected in 2017, but the Chilean Supreme Court halted construction in the spring of 2012 after it identified deficiencies in the consultation process with a local farming community.

Even though the court’s decision resulted from litigation with a community, its underlying cause is the scarcity of water resources, according to Hubert Fleming, who was global director for Hatch Water before becoming an independent water consultant. “Of all the mining projects in the world that have either stopped or slowed down in the past year, it has been, in almost 100 per cent of cases, a result of water, either directly or indirectly,” he says. “It is not so much because of the shortage of water to the mine, but of the secondary effect of competition for water resources from the local communities in water basins.”

Today’s mining conditions exacerbate this competition. As Fleming points out, “There is more water required today per ton of ore than there has ever been, because ore bodies are not as rich.” Deposits are also being found in remote areas that were deemed uneconomical before, mostly in arid or high-altitude regions. Additionally, as national regulations in many countries have been mounting in recent years, there are now more restrictions on the use of aquifers or surface streams. And, as Jerry Rowe, global director of water resources management at Hatch, mentioned in a 2012 study, modern mines are higher tonnage but have shorter lifespans, which can result in steep increases in water demand with more dramatic effects on water resources than if they were spread over a longer period.

According to a Global Water Intelligence report, Australia leads the world in mine water-related spending – which can be broken down into general infrastructure, pumps, and water and wastewater treatment equipment. Australian mining accounts for 20 per cent of global totals, but the top 10 users include Chile, Canada, Brazil and Peru. All-in, the top 10 represent nearly 80 per cent of the world’s mine water costs. The global capital expenditure on mining-related water infrastructure amounted to $7.7 billion in 2011, and, because of the urgent need to solve shortages, could well reach as much as $13 or $14 billion by 2014. The bulk of these expenses account for designing and building water infrastructure, including civil engineering work and pipelines and, in 2011, $1 billion was spent on pumps alone.

Alaskan and northern Canadian struggles over water consumption highlight growing public concern that is also driving up the price of water use. “In Northern Canada, communities are worried about water going to the mine, and the mines potentially polluting their source water through their discharges,” says Fleming.

Is the sea worth its salt?

In order to avoid competing with other users for fresh water, mining companies have been working with engineering firms over the last decade to evaluate the feasibility of using lower-quality waters in their mineral processing. With saline and hyper-saline water in abundance, either from the sea or from the ground, the critical question has been whether to desalinate or not. The decision is often a trade off between operating and capital expenditures, according to Raymond Philippe, water business manager at WorleyParsons. Determining which way to go will depend mostly on the water quality a mine requires. “That is a part of the trade off study, which includes an evaluation of the metallurgy, the concentration process, and what to do with the tailings pond, from which water might filter to the sub-surface,” explains Philippe.

Desalination has proven much more expensive initially than using saline water in processing. “Desalination plants and the associated pumping and pipeline systems are a major mine development and operating cost and can easily have CAPEX costs exceeding $500 million,” Rowe’s study reported.

“Frankly, I don’t think that mining companies are going to prefer desalination, and the reason is they are very much in a financial crunch right now,” says Fleming. “So here is the trade off: If they can do sea water or hyper-saline water, yes, it kills their equipment, yes, their metallurgy dies in five years versus 10 years, but they are just trying to survive for five years at this point, versus spending all of this money upfront.”

However, as Fleming notes, this rationale could be offset by restrictive national regulations: “Many countries are struggling giving permits for sea water or for hyper-saline water because it puts salt on land at the mine site, which is a pollutant […] so you would have no other choice than desalination.”

Besides its metallurgical impacts, sea water has higher density and viscosity than fresh water, meaning it requires more energy to pump it via pipelines to the mine site. As for environmental risks, tailings ponds containing a lot of salt need particular care. “You are risking chloride contamination,” warns Philippe. “Tailings with fresh water may have one gram per litre maximum of chloride. If you are working with sea water, you are very close to 20 grams per litre. Any drop of water draining from the pond will immediately contaminate any aquifer that you may have around. The same holds true for pipelines carrying sea water.”

The managing team at El Morro considered all of these factors before deciding to go with desalination. “There are two reasons for that,” explains Walter Bergholz, engineering manager at the mine. “One is environmental. In the area where we are, there is agriculture, there are a lot of goats and small animals, so it was a requirement we had to fulfill that in case of a break in the water pipeline, there would be no sea water that could contaminate the area. Additionally, we have a better recovery rate with potable water than with sea water.”

The Escondida mine, also located in the Atacama Desert, has been desalinating sea water since 2006, while Freeport MacMoRan has nearly completed a desalinating plant and pipeline to feed its Candelaria project, located south of Copiapó. Other major mines have made similar choices in Australia, such as Newmont’s Boddington, which has contracted Osmoflo to process the brackish water coming out of its dam. According to Fleming, there are about 20 to 30 mines globally that use desalinated water right now, 10 of which are located in Australia or Chile alone. About 15 more desalination projects have already been commissioned, and several dozen are under evaluation.

For her part, Emily Moore, global director of water at Hatch, says there is still some misunderstanding in the mining industry of what desalinating means. The most common mistake, she argues, is considering desalination as an equipment package. Mining companies should understand that desalination above all involves a processing plant that needs to be integrated early in the project design rather than treated as separate. Also, companies should get more involved in the choice of water that they need; there are many different possible water qualities that must be defined early in a project.

Finally, the timeframe needed when planning to use desalination must be well understood. “When you look at the lifetime of a new mine, construction is fairly short compared to the time of designing and commissioning the infrastructure, particularly if you have to do a pipeline,” states Fleming. “You depend on access to communities, a permitting process that can take two, three, even four years. That is much longer than the timeline of starting a mine.”

Direct saline water use

The use of sea water, which contains around 3.5 per cent dissolved salt, for mineral processing has obvious benefits in terms of capital costs, but the processing itself is often complex and introduces a degree of uncertainty. “If you plan to do electrowinning, you will need water with a very low rate of total dissolved solids, so you will almost certainly desalinate,” says Fleming. “If you plan to use a flotation process or a concentrator, it won’t be so important, so you can use sea water.” In the case of copper, the largest current and potential use for saltwater processing, the flotation process often works better when using saline water rather than desalinated water, says Philippe. But saline processes are harder to control, he adds: “If you have a process that requires sudden changes in pH or in chemical conditions, sea water works as a buffer, and so it is very difficult to control.” Conversely, in the case of molybdenum, flotation has proven much more difficult in sea water and has thus required innovative methods of controlling pH. Nevertheless, a number of companies are working hard on technologies to reap the benefits of abundant sea water.

Minera Esperanza, a joint venture between Antofagasta Minerals and Marubeni Corporation located in the Atacama Desert, was the first large-scale project to use raw sea water in its copper flotation process. In operation since 2011, its concentrator plant requires the largest portion of the mine’s water supply. The project was designed after a series of studies determined optimum operating conditions for the primary flotation process.

The main challenge in the flotation of copper–molybdenum sulphide ores in saline water is the flotation of molybdenite. According to Janusz Laskowski, a specialist in flotation processes and professor emeritus at the University of British Columbia, minerals that are hydrophobic by nature (e.g. molybdenite) generally float even better in salty waters. However, these ores also commonly contain pyrite and its depression requires a high pH.

To control the pH, the mining industry usually uses lime, which works well in fresh water. In sea water, however, lime tends to have a detrimental effect on the molybdenite flotation. “Basically, the recovery of molybdenum in the range of 70 per cent would go down to 30 or 35 per cent, and that is not acceptable from an economical point of view,” Laskowski says. “When molybdenite is present in a sulphide ore, it is recommended that lime be replaced by another pyrite depressant. In a process worked out at the University of Concepción, in which Laskowski is involved, sea water is treated prior to its use in flotation. The treatment reduces the content of the components of sea water, which depress flotation of molybdenite in an alkaline environment.

Barrick Gold has recently found a way to tackle the problem of the negative impacts of salt water on the metallurgical process of copper and gold ores: an air-metabisulfite treatment (AMBS). “The advantage of this process is that you don’t need lime, and you can maintain flotation at the natural pH of the ore body,” says Barun Gorain, senior manager of mineral processing at Barrick Gold and inventor of the treatment. “With the AMBS process, you can use sea water or brackish water with minimal metallurgical impact compared to desalinated water and, even better, we have found that this process actually improves the metallurgy significantly, compared to what you can get with the conventional lime-based process.”

The AMBS treatment has also resolved the issue of molybdenum flotation, Gorain says: “With this new Barrick technology, what we have seen is that the molybdenum recovery is not a problem, the metallurgy impact is actually minimal.”

The AMBS treatment was initially developed for the Reko Diq copper-gold project in Pakistan, using brackish water, but it was also tested with sea water, in both cases successfully. “We have now implemented this process in our Jabal Sayid operation in Saudi Arabia and another key copper-gold project in South America is currently implementing it,” says Gorain. “We have also completed piloting for another project in Chile, successfully using sea water.”

Decision time

For a mining company, the choice of desalination or direct sea water use “has to be evaluated on a case-by-case basis,” says Philippe.

And, according to Fleming, “Mining companies don’t want to desalinate, since it’s a huge capital cost. If they can find anything else, they will.” Research and development in new technologies may allow some companies to trim these costs, particularly those using a flotation process. “It doesn’t make sense to desalinate water if you have a technology that can handle the metallurgical issue quite well,” points out Gorain. “From that point of view, we just pump the sea water and use it as long as we can handle the other aspects of it, including any environmental or health and safety concerns, which are immensely important.”

It is difficult to foresee which path mining companies will prefer in the future. Two things, though, are certain: freshwater is a finite resource, and miners are just starting to get their sea legs.

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