Rio Tinto is to construct a new plant that will recover tellurium, a critical mineral used in solar panels, from copper refining at its Kennecott mine near Salt Lake City, Utah.

The company is investing $2.9 million to set up the plant, which will recover tellurium as a by-product of copper smelting, extracting a valuable mineral from waste streams. The plant will have a capacity to produce around 20 t/y of tellurium, the miner said.

Rio expects to begin production of tellurium in the December quarter of 2021, creating a new North American supply chain for the critical mineral.

Tellurium is an essential component of cadmium telluride, a semiconductor used to manufacture thin film photovoltaic solar panels. Thin films made of this compound can efficiently convert sunlight into electricity, according to the miner. Tellurium can also be used as an additive to steel and copper to improve machinability, making these metals easier to cut. It can also be added to lead to increase resistance to sulphuric acid, vibration and fatigue.

Rio Tinto Kennecott Managing Director, Gaby Poirier, said: “The minerals and metals we produce are essential to accelerate the transition to renewable energy. Adding tellurium to our product portfolio provides customers in North America with a secure and reliable source of tellurium produced at the highest environmental and labour standards with renewable energy. Rio Tinto is committed to using innovation to reduce waste in our production process and extract as much value as possible from the material that we mine and process.”

Utah Governor, Spencer Cox, said: “With abundant natural resources, Utah is ideally positioned to help supply the critical minerals essential to maintain American manufacturing competitiveness. Rio Tinto’s smelter at Kennecott is one of only two that is capable of producing copper and other critical minerals. The new tellurium plant is another valuable contribution to critical mineral independence and energy security in the US”

Along with producing almost 20% of US copper, Kennecott’s smelting process also recovers gold, silver, lead carbonate, platinum, palladium and selenium, while molybdenum is recovered from the Copperton concentrator. In total, nine products are currently recovered from the ore extracted at Kennecott.

Rio Tinto is a partner with the US Department of Energy’s Critical Materials Institute (CMI) and works closely with CMI experts to discover further ways to economically recover critical mineral by-products such as rhenium, tellurium and lithium. The company is also investing in new facilities to extract battery-grade lithium from waste rock at its Boron, California mine site and high quality scandium oxide from waste streams at its metallurgical complex in Sorel-Tracy, Quebec.