Talvivaara black schist bioheapleaching demonstration plant

Talvivaara complex multi-metal black schist deposit in Sotkamo, Finland, is the largest known sulfide nickel deposit in Europe with 340 million ton of classified resources. The mine can be operated for a minimum of 25 years with an annual nickel output of over 30 000 ton, which is about 2,5 % of the global production of primary nickel. Significant amounts of zinc, copper and cobalt can also be produced. In summer 2005, a 50 000 ton demonstration plant was constructed to the mine site. A representative ore sample was mined, crushed to 80 % -8 mm, agglomerated and built to a two-part heap (8 m high, 50m times 80 m). Irrigation of the heap was 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 ones. The start-up of the solution flow resulted soon in elevated temperatures of over 50 0C in the pregnant leaching 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. At the end of the year 2006 94 % of Ni, 83 % of Zn, 3 % of Cu and 14 % of Co have been recovered. The demonstration plant is still running. The study has proven that Talvivaara black schist ore is well suited for bioheapleaching. Building of the mine will start in spring 2007, bioheapleaching in summer 2008 and the metal recovery plant in autumn 2008, if everything proceeds according to the plans.