How Kennecott’s Utah copper mine may be key to our solar future

Utah refinery to produce tellurium — which is rarer than gold and vital in solar panels — loosening China’s grip on the market.

(Trent Nelson | The Salt Lake Tribune) Gov. Spencer Cox activates machinery at an event announcing that Rio Tinto has started producing tellurium at its Kennecott copper operation, on Wednesday, May 11, 2022.

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Gov. Spencer Cox pushed the switch Wednesday to dump copper bits into large tanks as a ceremonial start to Utah’s new role as a major domestic supplier of tellurium, most of which will go to the U.S. production of photovoltaic solar panels.

“What we’re talking about today is national security,” Cox said. “I think what we’re doing today is just as important as the F-35s at Hill Air Force Base for national security.”

(Trent Nelson | The Salt Lake Tribune) Gov. Spencer Cox speaks at an event announcing that Rio Tinto has started producing tellurium at its Kennecott copper operation, on Wednesday, May 11, 2022.

Most tellurium is produced in China, as are 90% of solar panels. But the United States is second only to China in the amount of tellurium reserves.

That has made domestic production a priority for the nation. Kathleen Hogan, deputy undersecretary for infrastructure at the U.S. Department of Energy, said in a recorded statement that the plant “will really help the United States grow the reserve of a very important material used to manufacture clean energy technologies.”

(Trent Nelson | The Salt Lake Tribune) Pure tellurium, shown here, is used to produce high-efficiency solar panels.

Gaby Poirier, managing director for Rio Tinto’s Kennecott, said tellurium is eight times rarer than gold, and only 580 tons of it is produced each year. If Kennecott reaches its target of 20 tons per year, it will be more than 3% of world production. Most tellurium is found in copper ores, and Kennecott’s mine produces 15% of U.S. copper. Poirier thanked his employees, most of whom are unionized, for their critical role.

Wednesday’s event also included executives from 5N Plus and First Solar. 5N Plus is a metals processor that will take the copper telluride Kennecott produces and turn it into pure tellurium at its Montreal plant. Some also will go to 5N Plus’ St. George manufacturing facility, where it will be used in space and defense applications.

The pure tellurium will go to First Solar, the largest U.S. manufacturer of solar panels and the only U.S. company among the top 10 solar panel producers. The other nine are in China. First Solar CEO Mark Widmar said the U.S. solar industry has faced headwinds because of China’s unfair trade practices that have squeezed out other U.S. manufacturers.

“The more tellurium you can extract,” Widmar told Kennecott’s workers, “the more competitive we can be.”

(Trent Nelson | The Salt Lake Tribune) Copper telluride, shown here, is produced in a new process at Rio Tinto's Kennecott copper operation. It will be sent to Canada to be refined into pure tellurium.

Saskia Duyvesteyn, chief adviser for research and development for copper at Rio Tinto, said Kennecott’s smelter produces 99% pure copper that goes to its refinery to be further refined to 99.99% purity. That process, in which the company pulls out small amounts of gold, silver and selenium, produces “anode slime.” That slime, which contains tellurium, was previously sent to waste piles. Now it is being put in a solution with the copper bits to produce the copper telluride that is sent to 5N Plus.

No. 52 on the periodic table, tellurium is a silver white metalloid that has been used in copper and steel alloys for a long time. It is chemically related to selenium, which has also been used in making the thin films in solar panels. It is combined with cadmium to make cadmium telluride, which is then used to make panels that are more efficient than selenium solar panels.

Tim Fitzpatrick is The Salt Lake Tribune’s renewable energy reporter, a position funded by a grant from Rocky Mountain Power. The Tribune retains all control over editorial decisions independent of Rocky Mountain Power.