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It’s all in the microbes

Talvivaara Mining Company Plc
Talvivaara Mining’s proprietary bioheapleaching technology offers a highly cost-effective and environmentally friendly method for extracting metals such as nickel, copper, cobalt, and zinc from low-grade sulphide ore.

Microbe-based technology represents an exciting development for the mining and mineral processing industries because of microbes’ ability to oxidise ferrous iron to ferric iron, and sulphur to sulphates, enabling the target metals to be dissolved out into a solution and recovered using conventional methods.

Leveraging this opportunity, Talvivaara Mining has developed a bioheapleaching process to create and maintain the ideal environment for this type of bacterial activity – based on careful heap design and the efficient management of parameters, such as temperature, aeration, water, nutrients, and acid balance.

The Talvivaara method is capable of maintaining a variety of microbial populations, managing their growth rates, and guaranteeing the temperatures required for enhanced primary sulphide mineral leaching. As these temperatures need to be in excess of 50 °C for successful bioleaching, the mesophile population required during the initial stage is replaced by a thermophile population for sustained heat generation at the appropriate point.

Factors such as micro-organism dynamics, adaptation and succession rates, as well as ore energy-generating capacity, have also been addressed, as has the need to optimise the rate of leaching and minimise factors that might inhibit or slow microbial growth.

The bacteria in Talvivaara’s bioheapleaching technology consume carbon dioxide and convert it into organic material that can be returned to the carbon cycle. No noxious gases are generated and all the sulphides are converted into watersoluble sulphates.

Full output expected in 2012

The technology was proved at a small demonstration plant at Talvivaara’s site in northern Finland, which produced excellent leaching results and enabled work to start, as planned, on a full-scale bioheapleaching plant.

Combined with the successful ramp-up of materials handling and crushing, the mine was able to produce its first metal sulphides at the beginning of October 2008. Full output is expected to be reached in 2012, when the mine’s metal recovery should total approximately 50,000 t/a of nickel, 90,000 t/a of zinc, 15,000 t/a of copper, and 1,800 t/a of cobalt.

Talvivaara produced its first metal sulphides from one of Europe’s largest sulphide nickel deposits in 2008 and is now ramping up full-scale output there. Its proprietary process precipitates the metals in the ore as sulphides, producing first copper, followed by zinc and then nickel and cobalt.

Talvivaara bioheapleaching

  • Ore can be upgraded on-site
  • Substantially lower capital and operating costs than conventional smelting and refining technologies
  • Suitable for both small and large operations
  • Can handle ores not amenable to conventional treatment
  • Produces metal ions, acid, and inert rock. Metals can be removed by electrolysis and/or precipitation, and any acid generated is circulated back to the bioleaching process
  • Zero SO2 emissions.
> Marja Riekkola-Vanhanen
(Published in HighTech Finland 2011)