Top Russian miner says waste rock may absorb millions of tonnes of greenhouse gases

Russian mining giant Nornickel has begun studying how its tailings – the waste rock from ore processing operations – could help reduce the carbon footprint associated with metal production.

Nornickel’s waste rock, which typically looks like sand with a grain size of under 0.4 mm, may potentially absorb several million tonnes of CO2 per year, but a more exact estimate is yet to be calculated.

The use of tailings to absorb carbon dioxide was first explored by diamond miners, as diamond-bearing ore (kimberlite) is able to absorb carbon dioxide when in contact with water and atmospheric air. Diamond giant De Beers, alongside research centres in Australia, Canada and the United States, conducted studies on the absorption capacity of kimberlite rocks from South African and Canadian deposits in 2016–2018. It turned out that the absorption of carbon dioxide depends entirely on the chemical composition of kimberlites and ranges from 47 to 240 kilograms of carbon dioxide per tonne of processed ore, giving an average of 138 kilograms. According to Russian companies, the content of carbonates in ten-year-old kimberlite tailings can reach 150 kilograms per tonne of waste rock.

The Russian miner examined its largest tailing dump in the Arctic, Lebyazhye, and also took samples from the No. 1 storage facility at the Norilsk Concentrator, which was closed back in the 1970s. These samples, according to the miner, are expected to show accumulation of carbonates in both the oldest and the most active tailings. As many as 200 core samples were taken at different points, to the very bottom of the reservoir at a depth of 50 metres. Processing engineers hope to understand how CO2 in the air binds with minerals in the tailings via a process called mineralization in the surface layers and how the mineral composition changes over time.

In addition, samples were taken at the tailings of the Talnakh Concentrator and directly at the factory (incoming raw materials and outgoing effluent). Nornickel said in a press release published on its website that the collection of samples continues at the company’s other sites, the Kola MMC and the Bystrinsky processing factory. Scientists will then analyse the mineral and elemental composition of the samples in order to assess the content of absorbed carbon dioxide.

Why it matters

Polymetallic ore enrichment leaves tailings, which mainly consist of waste rock and are typically unsuitable for further use and difficult to enrich. Nevertheless, they can still be useful.

Mineralization involves the active absorption of carbon dioxide from the atmosphere. Silica and magnesium oxide contained in waste rock can absorb carbon dioxide while being exposed to air. By reacting with water and air, carbon dioxide is bound with minerals and metals, which are present in these types of rock, resulting in the formation of carbonates.

Sergey Vagner, Head of Technologies for Recycling and Utilization of By-Products, Nornickel Technology Innovation Department: “We plan to develop a methodology to estimate and calculate carbon units based on the results we obtain, and to use that as the basis for a standard for taking stock of carbon units. This way we will have a methodology to assess the absorbing capacity of tailings based on the mineral composition per tonne of ore mined. In turn, that will give us an understanding of how many tonnes of ore we have processed and how much CO2 has been absorbed.”

Together with scientists, Nornickel is also developing a technology for the so-called artificial mineralization of tailings, which can be used at the company’s production sites. It will be possible to pass flue gas from thermal power plants or process gas from melting furnaces – which also contain carbon dioxide – through slurry, or waste rock mixed with water. This will significantly increase the potential for absorption of the greenhouse gas.

Nornickel, one of the world’s largest producers of nickel, palladium, platinum and copper, has vowed to bring down its scope 1 and 2 greenhouse gas emissions by 25% to 7.7 million tonnes over the next six years.