Heidi Vella
8 min read
Sixty-five miles east of the sun-drenched city of Tucson, Arizona, lies the historic copper mine, Johnson Camp. Active on and off since the 1970s, the mine is being resurrected in response to a booming copper market.
As material is extracted at the mine, it will be separated into different piles; oxide copper in one pile and primary sulphide copper in another. The former will be sent to one portion of the heap leach pad for conventional oxide leaching using hydrometallurgy. The sulphides will leach using novel technology developed over three decades by Rio Tinto.
Johnson Camp, now operated by Gunnison, will be the scene of the first industrial-scale trial to prove the technology’s efficacy – a major milestone since Rio Tinto launched a new venture called Nuton to develop it in 2021. After the technology is installed in August, first copper is expected by the end of 2025.
Primary sulphide ore, typically dominated by copper deporting to the mineral chalcopyrite, is the most abundant type of copper ore in the world. It is typically crushed and milled producing a flotation concentrate. This flotation concentrate is then typically smelted using a heat intensive pyrometallurgical process, casting the copper into raw copper anodes, which are then electro-refined to produce a pure copper product.
Nuton’s process, however, uses a unique culture of microorganisms added to the ore. These bacteria multiply, harnessing energy from the oxidation of minerals in the rock to grow and simultaneously assist with leaching of the copper, achieving a recovery rate of up to 85%. Aeration and acidified water support the process with subsequent processing of the leach solutions producing 99% pure copper cathode.
Bioleaching is just one of several novel methods conceived to extract more copper from new and existing mines – including copper previously considered uneconomical because of low grades or small deposits – more sustainably and more quickly to meet the growing demand.
The International Energy Agency predicts a 30% shortfall in supplies of copper, a key component in electricity networks, by 2035 if nothing is done. This is against a wider expectation that to achieve net zero, copper demand will grow from 25 million tonnes (mt) in 2021 to 31.3mt by 2030.
At Johnson Camp, the plan is to optimise Nuton’s technology so it can be adopted at a commercial scale across a portfolio of around ten partnerships Nuton has been brokering.
“It feels like a special moment,” says CEO Adam Burley, who has worked at Rio Tinto for more than 20 years. “With data, analytics and AI there is an enormous ability to rapidly evaluate the performance of the technology and run different scenarios around the operating conditions and how we apply and adjust it – we couldn’t have done that 30 years ago.”
