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Producing metals with the help of microbes

Talvivaara Mining produced its first metal sulphides in northern Finland in October 2008, using its proprietary bioheap leaching technology. Designed for extracting metals such as nickel, copper, cobalt, and zinc from low-grade ore, the technology is cost-effective and environmentally friendly.
Talvivaara Mining Company Plc

What makes microbes exciting for the mining and mineral processing industries is their 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. Talvivaara Mining has developed a bioheap leaching process to create and maintain the ideal environment for this type of bacterial activity, based on careful heap design and the efficient management of internal parameters, such as temperature, aeration, water, nutrients, and acid balance.

The metals recovery plant at the new mine is expected to produce 33,000 t/a of nickel and 60,000 t/a of zinc by 2010 from one of Europe’s largest known sulphide nickel deposits.

The Talvivaara method addresses the need to maintain a variety of microbial populations, manage their growth rates, and guarantee 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 for early heat generation needs to be 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 understand what can inhibit or retard microbial growth.

In addition to attractive cost benefits, Talvivaara’s bioheap leaching technology offers valuable environmental advantages, as bacteria consume carbon dioxide and convert it into organic material that can be returned to the carbon cycle and no noxious gases are generated, and all the sulphides are converted into water-soluble sulphates.

From theory
to practice

The technology was proved at a small, on-site demonstration plant, using a heap inoculated with indigenous mesophilic and thermophilic bacteria collected from the site – and enabled full-scale bioheap leaching to begin, as planned, in July 2008. Heap temperatures reached 80° C and bacterial counts rose well within a month. 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, and expects to produce around 60% of its planned output in 2009 and full output in 2010.

Multiple benefits

  • Ore can be upgraded at the mine
  • Simple process 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.
  • Low capital costs compared to a smelter
  • Suitable for both small and large operations
  • Zero SO2 emissions
  • Can handle ores not amenable to conventional treatment.
> Marja Riekkola-Vanhanen
(Published in HighTech Finland 2009)