Technology

Talvivaara's application of the bioheapleaching technology has its origins at the Outokumpu Research Centre, where it has been developed using the Talvivaara ore since 1987 under the leadership of Marja Riekkola-Vanhanen who is now employed by Talvivaara. Talvivaara is continuing the development at a laboratory scale with financing from the National Technology Agency of Finland, Tekes.

A pilot scale leaching trial with 110 tonnes of ore has also been carried out as part of the European Union sponsored Bioshale project, which studies the properties of black schist ores. This trial, run in a log column in Outokumpu, Finland, was successfully started in    -20°C conditions in March 2005, thereby providing a strong indication of the applicability of the process in sub-arctic environmental conditions.

During summer 2005, a 17 000 tonne demonstration plant was constructed at the mine site. A representative ore sample was mined, crushed to 80 % -8 mm, agglomerated and built to an 8 m high heap. Irrigation of the heap started in August 2005.  The pilot heap was inoculated with indigenous bacteria collected from the site. The amount of bacteria in the pregnant leaching solution has been in the range of 106 - 108 cells/ml. The bacteria involved are mesophilic and thermophilic. The start-up of the solution flow resulted soon in elevated temperatures of over 50 0C in the pregnant leach solution. The rise is due to the oxidation of the large quantity of pyrrhotite and pyrite in the ore. The elevated temperatures have also been maintained over the boreal winter conditions. Metal recovery was started in November 2005. In winter 2007 the heap was reclaimed and the secondary leaching phase begun.

Combined trials with the bioheapleaching technology have provided Talvivaara with understanding on the key parameters of the process.  One of the most important determinants of leaching rate is the particle size of ore.  Other key factors include pH, temperature and rate of aeration.