Rio Tinto's Utah Copper Mine Builds a 30-Megawatt Solar Plant From Its Own Waste Tellurium

What happened

Rio Tinto's Kennecott copper operation near Salt Lake City, Utah, has spent the past several years building a supply chain that turns leftover sludge from copper refining into solar power for its own site. The company began recovering tellurium, a rare metalloid, from anode slime — the residue left behind after copper is electrorefined — in May 2022, through a $2.9 million recovery circuit built at its Magna, Utah refinery. That made Kennecott one of only two tellurium producers in the United States. The roughly 20 tons of tellurium the site recovers each year is shipped to Canada's 5N Plus, which refines it into cadmium telluride semiconductor material, which First Solar then turns into thin-film photovoltaic panels. In December 2025, Kennecott energized a new 25-megawatt solar plant built with those panels, completed about two months ahead of schedule in partnership with Bechtel. Combined with a 5-megawatt array finished in 2023, the mine's onsite solar capacity now stands at 30 megawatts across more than 71,000 panels — built in part from tellurium the mine produced itself.

The details

Copper anode slime is the dark, metal-rich sludge that settles at the bottom of the tanks used to electrorefine copper into the near-pure form industry needs. For most of the last century, smelters treated it mainly as a source of gold and silver, the two metals slime is best known for. Tellurium sat further down the value chain — present in small enough quantities, and demanded in small enough volumes, that separating it out rarely paid for itself.

That calculus started to change once thin-film solar technology created sustained demand for the metalloid. Cadmium telluride, or CdTe, panels use tellurium as their light-absorbing layer instead of the silicon wafers found in most rooftop solar installations, and First Solar has built its US manufacturing base around that chemistry. Rio Tinto's Kennecott team first tested pulling tellurium out of the site's slime as early as 1990, shelved the idea, then revived it around 2012 as renewable-energy demand for the metal grew. Construction of a dedicated recovery circuit at the Magna, Utah refinery followed, and the site began commercial tellurium production in May 2022 on a $2.9 million investment — making Kennecott one of only two tellurium producers anywhere in the United States.

What makes the Kennecott case notable is not just that it recovers a byproduct — plenty of copper refiners do that for gold and silver — but that this particular byproduct closes a loop back onto the mine itself. The roughly 20 tons of tellurium Kennecott produces each year is shipped to 5N Plus in Canada, which converts it into cadmium telluride semiconductor material, and on to First Solar, which builds it into finished panels. Some of those panels came back to Kennecott: a 25-megawatt array built with construction partner Bechtel was energized in December 2025, about two months ahead of schedule, adding to a smaller 5-megawatt plant from 2023 for 30 megawatts of onsite solar capacity spread across more than 71,000 panels.

For a copper mine, the emissions math is modest but real — Rio Tinto estimates the buildout cuts Kennecott's Scope 2 emissions by around 6%, about 20,000 tonnes of carbon dioxide equivalent a year, similar to taking 4,400 cars off the road. The larger significance is structural. Tellurium has no dedicated mines of its own; global supply rides almost entirely on copper refiners choosing to build recovery circuits rather than on tellurium-specific exploration. Kennecott's project demonstrates a fully North American supply chain, from anode slime to finished panel, for a metal that has historically depended on byproduct volumes recovered wherever copper happens to be refined. As demand for CdTe panels grows alongside the broader US push to build domestic solar manufacturing capacity, other refiners already processing copper slime for gold and silver now have a working template for adding tellurium recovery without opening a new mine — the metal was already coming out of the ground, just left in the waste stream.

Why it matters

Tellurium has no primary mines of its own — global supply comes almost entirely as a byproduct of copper, and to a lesser extent lead and zinc, refining. That means new tellurium supply grows or shrinks with copper refining capacity and refiners' own investment decisions, not a separate tellurium demand cycle. As more copper refiners weigh recovering tellurium from anode slime the way Kennecott does, the economics of that choice ride on copper throughput and refining margins rather than a standalone tellurium market. For India, which imports the bulk of its solar panel components and has its own ambitions to build thin-film manufacturing capacity, a North American, vertically integrated supply chain for CdTe inputs is one more data point on how concentrated — and how byproduct-dependent — the materials behind next-generation solar technology remain.