An Arizona copper mine bets on microbes to stretch its ore

Copper is rarely lying on the ground waiting to be scooped up. It is locked inside rock that also holds iron and sulfur, and getting it out takes a chain of chemical steps. At the Carlota mine in Arizona, owned by KGHM Polska Miedz, those steps are applied to rock piles larger than ten sports stadiums. The mine has been running for a long time, which means less copper is left in the ore, and the cost of extracting what remains keeps rising.

The conventional method already relies on sulfuric acid, which is spread over the ore to dissolve the metal. The new step is biological. According to Bloomberg, the startup Endolith supplies acid-loving microbes that are mixed into that acid and distributed by a sprinkler system dripping over the ore. The microbes digest the iron and sulfur compounds surrounding the copper, which sets off biochemical reactions that release it. This is the process called bio-leaching.

The pressure behind the experiment is demand. Copper is essential to renewable energy and electric transport, and a report published in January by the research firm S&P Global projects a worldwide shortfall of 10 million metric tons by 2040, or 25 percent less than the projected demand. Carlota today produces only about a third of the copper it once did. Its manager, Brock Johnston, told Bloomberg that any improvement is welcome, and Endolith is keeping its methods and results private. Without a better yield, the mine may have to close by the end of this decade.

The mine is not alone in looking for gains. Jetti Resources, another Colorado startup, develops chemical catalysts to break down sulfide ore. Emerson Electric, in Missouri, adds smart sensors and automation to conventional leaching systems. Nuton, a subsidiary of Rio Tinto, is building its own microbial solution. Buz Barstow, an associate professor at Cornell University, judges that next-generation bio-leaching may be a partial solution, but that it still has a long way to go before it becomes commercially viable.

For the Carlota mine, the gain would be concrete: more metal from the same rock, and fewer chemicals per tonne if the hopes voiced by its manager hold. For the wider copper market, the question is whether methods like this can add supply fast enough to narrow a gap that could otherwise appear by 2040. The answer will come from published yields at Carlota and from whether competitors' trials move from the lab into working mines before the decade is out.