Improved bioleaching

Billions of years before man even dreamed of the golden riches hidden beneath the earth’s surface, naturally occurring microorganisms had been leaching valuable metals out of heaps of mineralized rubble.

Now researchers from three continents are collaborating to examine how to harness the leaching power of these microbes to bring about greater efficiency in the metals extraction process.

As part of that push, a new project has been launched in order to develop methods to understand what occurs within ore heaps when the microbes are at work.

“There’s not a lot of information about what happens inside heaps, and so we’re trying to understand the processes and represent that knowledge mathematically in a model,” explains Helen Watling, principal research scientist at the Commonwealth Scientific and Industrial Research Organization (CSIRO), based in Melbourne, Australia.

The development of various novel methods, including the mathematical model, should lead to a lesser need for testing and monitoring of ore heaps prior to processing and enable a faster response to any changes that do occur within operating heaps.

“So instead of doing a huge experiment at great cost, we can say to the model, ‘Well what happens if the microbes only perform at half their normal rate?’ or ‘What happens if the temperature rises by ten degrees?'” says Watling.

Launched in May, the project involves researchers from CSIRO Minerals and CSIRO Land and Water as well as the University of British Columbia and the University of Cape Town.

Run under the auspices of AMIRA, an industry association Down Under, the 6-month project is being sponsored by seven companies: Rio Tinto, BHP Billiton, Placer Dome, Kumba Resources, Anglo American, Phelps Dodge and WMC Resources. If successful, the project will likely be expanded into a full 4-year international research program.

It is just one part of a broader push within CSIRO and the Parker Centre towards better harnessing of the natural process by which microorganisms extract metals.

Although mining industries in certain parts of the world have been using bioleaching for 30 years (in the oxidation of gold, for example, in South Africa, and in the extraction of copper from secondary sulphides in the Andes of South America), it is hoped the process can be refined and extended to extract metals from a broader range of ores, such as chalcopyrite or zinc and nickel sulphides, and low-grade or difficult-to-process ores.

“By building a more robust scientific foundation, we believe we can actually make bioleaching a much more efficient process,” says Watling. She explains that use of the bioleaching process could deliver significant benefits to a mining company’s bottom line.

“Cost savings are likely to come from reducing the inventory of copper that you have sitting around in piles of rubble. If you can leach in one year instead of three years, then the amount of copper that’s potentially yours is greatly increased.”

While bioleaching generally requires a low capital cost to establish, extracting metals using the process is generally slower than using traditional technologies.

“Currently heap bioleaching is used mainly as a secondary operation to recover metal from low-grade ores that can’t be concentrated or ores which would be uneconomic to process by other means,” explains Watling. “However, I see bioleaching as playing an increasing role in companies’ metal-recovery operations as improved heap management practices lead to increased heap leach efficiency.”

Watling adds that the process can also deliver significant benefits to the environment, allowing for more efficient processing (because the ore is processed in situ) and through the reduction of waste, emissions, chemical use, water use and landscape impact.

— The preceding is an excerpt from Process Magazine, a monthly publication of the Commonwealth Scientific and Industrial Research Organization.