Copper bugs in Chile

Corporacion Nacional del Cobre de Chile (Codelco), the state-owned king of copper producers, could be the first major mining company to build an industrial-scale copper plant that employs heat-loving bacteria as processing agents.

Codelco and Melbourne-based mining titan BHP Billiton have invested roughly US$60 million over the past four years in a pilot bioleaching project at the Mansa Mina deposit, near Codelco’s Chuquicamata mine in northern Chile.

The bioleaching plant, still in its pilot phase, is producing about 20,000 tonnes of copper a year. The project is slated to end in November, at which time Codelco and BHP Billiton will decide its fate.

The pilot plant has had some success. For instance, engineers have shortened the leaching process to between two and five days, whereas previous experiments with other bacteria have taken weeks to recover less copper.

Bioleaching processes material that has been dug out of the earth and ground up for processing. Bacteria are added to a solution containing the ground ore, and the microbes dissolve copper and other metals into a solution that is recovered in a separate plant.

Bioleaching is the result of experiments in gold mining practices, and the process has been used on an industrial scale since the early 1990s. In recent years, heat-loving bacteria known as thermophiles (often found in geysers) have been used to extract base metals such as copper.

Copper is key to Chile’s economy, but the country’s existing high-grade reserves will be mostly depleted in a decade, so miners like Codelco need to find a cheap way to process low-grade ore from slag heaps and mines that have been in production for 100 years, such as the El Teniente mine. Codelco’s copper reserves are based on a cutoff of 0.3 gram copper per tonne, a relatively low-grade threshold.

Codelco is involved in another bioleaching project, called BioSigma; it is a joint venture with Japan-based Nippon Mining & Metals, which has invested US$5 million since 2001. BioSigma is examining new bioleaching processes that could be used to extract copper from sulphide minerals, which require a different refining process from the oxide minerals at the Codelco-BHP Billiton pilot project. BioSigma aims to start a prototype plant in 2005.

Codelco hopes eventually to map the genetic code of bacteria, isolate the gene that is doing the work, and create new “super” bacteria that would be more efficient.