Chile’s miners turning to seawater amid falling grades

The Chilean mining sector is increasingly turning to seawater as it grapples with declining ore grades amid a decade-long drought.

During the last 13 years rainfall has decreased by 20-40% in the southern and central regions and the country is facing a future scenario of water scarcity, environment minister Maisa Rojas told a recent water seminar hosted by Universidad de Chile.

Meanwhile, the declining ore grades in the local mining sector will require a new business model with more technology, efficiency and circular economy, state copper commission Cochilco said in a report. As ore grades decline, the volume of water needed to obtain fine copper increases, since a larger amount of mineral needs to be processed.

"The Chilean mining sector has been called upon to use water that does not compete with human consumption and all the companies are working towards this," Camila Montes, a public policy analyst at Cochilco, tells BNamericas.

By 2032, around 68% of the water consumed by the local mining industry will come from the sea and about 32% from continental water, according to the Cochilco report that analyzed water use at 56 copper operations.

One of Chile's mining policy goals is to have continental water account for only 10% of the water used by the sector by 2025, and 5% by 2040.  

As a result of the record drought, the sector has deployed desalination plants and new water systems. Its desalination capacity is being expanded from around 4,400l/s in 2020 to about 7,500l/s by 2030, according to the mining ministry.

Treated wastewater could become an option in the future but needs a legal framework, especially for the benefit of investors, said Montes.

Mining companies’ consumption of continental water is estimated to reach 6.7m3/s in 2032, a decrease of 45% from 2020, while the consumption of seawater is expected to jump 165% to 14.2m3/s in the same comparison, the Cochilco report shows. 

In 2020, 73% of the water used by copper mines came from reused water (70% continental water; 30% seawater or desalination).

Cochilco’s report also shows that the concentrates in the mining process will increase in the coming years, which will lead to greater use of water, tailings waste and the need for more land for disposal.  

There are currently 11 mining firms in Chile using seawater in their operations, including: 

• BHP's Spence mine in Antofagasta region, which has a throughput of 95,000t/d to produce copper concentrate and molybdenum. It has a desalination plant with capacity of 86,400m3/d. Spence currently operates only with desalinated seawater.
• BHP also has a desalination facility to supply water at the Escondida copper mine in the Atacama desert in Antofagasta. Its production in 2021 was 1.1Mt. Seawater represents over 93% of the mine’s water withdrawal volumes, according to the company’s annual report.
• The Sierra Gorda copper mine in Antofagasta, which had a production last year of 198,000t. To move the seawater it employs a 144km aqueduct that carries it to a storage pool with 750,000m3 capacity.

There are also other projects involving aqueduct replacements and capacity expansions at existing plants. 

Through 2025, 10 projects are expected to come into operations, including three replacement/expansion projects, says Cochilco’s Montes.

• Los Pelambres desalination plant will begin using seawater in 2H22 when the construction of the first 400l/s stage is completed. Capacity will be increased to 800l/s by 2025, allowing Pelambres to reduce its use of continental water. Desalinated and reused water will then account for more than 90% of its operational usage, according to the company’s 2021 sustainability report.
• Codelco northern district desalination plant in Antofagasta region. It will supply water to the Radomiro Tomic mine (326,456t in 2021), Chuquicamata (319,280t) and Ministro Hales (181,704t) through a 160km aqueduct. The plant will have capacity of 250,000m3 with a flow of 840l/s in the first stage and 1.956 l/s in the second stage.
• Quebrada Blanca phase 2 (QB2) desalination plant for Teck’s copper mine. It will have a 165km aqueduct and construction progress has surpassed 82%. The project will also see the construction of a new deposit that is expected to become fully operational in 2H22 with production estimated at 300,000t/y for the first five years of the 25-mine life.
• Collahuasi desalination plant in Tarapacá region, which will produce a maximum seawater flow of 788l/s in the first phase and 1,050l/s in the second phase. It is expected to come into operation this year to ensure the continuity of the Collahuasi mine’s operations for an estimated 20 years. In 2021, it produced 630,000t of fine copper.
• At Antofagasta Minerals, water optimization last year through seawater accounted for 45% of its operations, led by the Antucoya (96%) and Centinela (86%) mines. The target is for seawater and reused water to account for more than 90% by 2025, according to the company’s annual report.

Several projects that are at the environmental permit application stage are expected for 2027-28, including the Enapac distribution plant in Atacama region, which will transport seawater through a 166km aqueduct to industrial clients.

“Our vision is that many users can access a sustainable water source in such a way that inland water and water from the region's basins, which are under severe stress, are no longer used”, said the project manager Rafael Bustos in a press release.

CHALLENGES

There are two main challenges for the expansion of desalination in the mining sector, according to Montes. 

At the national level, she sees a need for increased multisectoral coordination that includes ministries to address issues such as the legal framework, shared infrastructure, analysis of treated water and integrated management for water optimization.

At the local and more technical level, adopting a common methodology for the reporting of water information is key to generating trust among stakeholders.

“The water shortage is evident and there is the case of Los Bronces, which had to reduce its production due to the lack of water. But considering the projects in the pipeline, it is expected that these will be allowed to continue producing and avoid an imbalance between available water and production,” says Montes.