Rio Tinto has produced the first copper using its Nuton bioleaching technology at the Johnson Camp mine, in Arizona, marking a step in commercialising a process the company says could transform copper production economics and decarbonisation.

The milestone comes after more than 30 years of research and development. The first copper cathode was produced last month through a deployment of Nuton at Gunnison Copper’s Johnson Camp operation, where a dedicated heap-leach pad is targeting about 30 000 t of refined copper over a four-year demonstration period. Rio Tinto is also engaging with prospective US customers as it seeks to support domestic copper supply chains.

Rio Tinto Copper CE Katie Jackson described the achievement as a “breakthrough” for Nuton, highlighting its rapid path from concept to production. “In an industry where projects typically take about 18 years to move from concept to production, Nuton has now proven its ability to do this in just 18 months,” she said.

Nuton uses naturally occurring microorganisms, grown at scale in proprietary bioreactors, to extract copper from primary sulphide ores that are traditionally difficult or uneconomic to process. The microbes accelerate mineral oxidation in stacked ore heaps, allowing copper to dissolve into solution before being processed into 99.99% cathode. The technology, deployed as a modular package, can be tailored to different ore types and offers recoveries of up to 85% from primary sulphides.

The bioleaching route eliminates the need for concentration, smelting and refining, enabling mine-gate production of cathode and shortening supply chains. Rio Tinto says the technology can extend mine life, extract value from material that would otherwise be classified as waste, and deliver significant environmental gains, including up to 80% less water use and up to 60% lower carbon emissions than conventional concentrator flowsheets.

At Johnson Camp, Nuton aims to produce the lowest-carbon copper in the US. Through the purchase of 134 000 Green-e Energy renewable-energy certificates, 100% of site electricity is matched with renewable sources. The project is expected to deliver a mine-to-metal carbon footprint of 0.82 kg CO₂-equivalent per kilogram (CO₂-e/kg) of copper, well below the projected 2026 global average of 3.4 kg CO₂-e/kg. Water intensity is forecast at 71 L/kg, compared with an estimated global industry average of around 130 L/kg.

Gunnison Copper CEO Stephen Twyerould said the first cathode production reflected “exceptional teamwork” between the companies and underscored the potential for Nuton to strengthen US access to cleaner, low-carbon copper.

With first production achieved, the next phase of work will focus on validating long-term technical performance, including multi-year testing, independent third-party verification and internal Rio Tinto review to confirm consistent recoveries and environmental outcomes.