This interview by International Mining was first published in their March 2021 issue.

International Mining (IM) caught up with Golder’s Director, Water Strategy and Sustainability, Dr Hu Fleming, who has extensive experience with major desalination projects working for consultancies and industry alike, including as former Global Head of Water at Anglo American. He told IM: “In general desal, the cost per cubic metre delivered has come down significantly which is why we are seeing desal take a much larger role in the global water supply mix, not just in mining. The current delivered at desal plant price broke the $1 per cubic metre level about three years ago and there are commercial operations already running at $0.60 per cubic metre. This has been achieved mainly through various operational and technical improvements. But in mining it’s not that simple – this is probably the smallest part of the cost.

First off, few mines are at the coast so the cost of a desal project in mining is the desalination plant itself, then the intakes and outfall structure, and the pipeline to the mine site, and the associated power/pumping stations to make conveyance happen. Taking Escondida as an example, the desal plant was, approximately $250 million but the pipeline was $300-400 million, and the power boost stations another $50 million plus. This is not unique to Escondida, it holds true for many mining desalination projects – it’s necessary to think about all in cost.”

Fleming added that the other major factor in mining desalination is the management of the brine. Municipal desalination plants may allow brine concentrate to return to the sea, but most governments will not allow miners to do this as there is no direct public benefit to the desalinated water. So, brine management can be another significant cost and has stopped a lot of mining desalination projects early on. You can spend $10- 12 per cubic metre just on brine issues alone.

Mines generally don’t need the quality of desalinated water – taking Chile as an example, everyone focuses on the big desal projects, but for every desal plant there have been 2 or 3 conventional seawater pipelines supplying mines as an alternative approach. Generally, it’s the smaller and medium sized miners that have gone down this route, which comes with its own issues such as corrosion of pipelines and potential cracking plus, depending on the commodity, losses in flotation recovery.

What about mines collaborating to share water from a single large plant? Fleming said this is already happening. In Chile, Teck is building a large-scale desalination plant on the coast for mining in the Tarapacá Region where the desalinated water will be pumped by five booster stations up 4,300 m to the QB2 concentrator plant. But Collahuasi (Glencore and Anglo) have been considering teaming projects, including building an aqueduct to transport desalinated water left over from QB2 to its site as a back-up resource, or, to share in a desalination plant, for example. Similar deals have been and are being, considered elsewhere – such as potentially sharing of a desalination plant between Newmont’s El Morro and Teck’s Relincho copper/ moly project in Chile. Several regional developers are planning building desalination plants for power stations, where miners are considering becoming off-takers to the water, as in the Santiago region with Codelco and Anglo American.

There are also new ways of looking at desalination. Miners are looking at investing in desalination plants that will supply water to populated areas up to 100 km inland, but in exchange those communities could allow the mines to use inland groundwater. These plans are being called virtual water swaps and are being developed not only in Chile but also in Australia, South Africa and elsewhere. The stumbling block here can be legal complexities to allow for it.

Mining desalination is not all about Chile – it may have the biggest and most costly projects – but Fleming said looking at a world map, most mining desalination plants are smaller and outside of Chile. These range from a desalination plant in the Port of Durban with much of the water used to wash the conveyors, pipelines and railcars at the port and recover any remaining fines, to Areva’s port desalination plant in Namibia, to desalination systems for copper and gold recovery in electrolytic reduction and electrowinning operations in Australia and Africa.

Desalination isn’t just about arid regions either. Many of the original desalination plants in mining were built to serve solvent extraction/electrowinning plants where the electrolytic cells need ultrapure water. And in mine waste management there is also a push to remove water from tailings and recover that water along with reuse of process plant water. “Ultimately as the reuse and recycle technology in water advances, in many cases you will also eliminate any need for desal in the first place. For new mining projects, recycling and reuse is now normally top of the list with desal further down the decision tree as a last resort. Golder and others are actively developing process technologies to make water reuse more efficient.”

As a last note on water treatment in mining Fleming cautioned that unlike other industries that also utilise desalination, no two mining projects are exactly the same. Even for the same commodity in the same country the variations in mineralogy means the approach to water can never just be replicated between sites.