Talvivaara Sotkamo Mine – Bioleaching of a polymetallic nickel ore in subarctic climate

The main activity of the Talvivaara Mining Company Plc. is the development and exploitation of the Talvivaara deposits in Sotkamo, Finland using bioheapleaching. The Talvivaara deposits comprise one of the largest known sulphide nickel resources in Europe with 1004 million tonnes of ore, sufficient to support anticipated production for a minimum of 45 years. The mine started in late 2008 and will have an annual nickel output of approximately 50,000 tons when it reaches full production. In addition, the mine will also produce zinc (approximately 90,000 tpa), copper (approximately 15,000 tpa) and cobalt (approximately 1,800 tpa) as by-products of the process. The viability of bioheapleaching technology for the extraction of nickel has been demonstrated in a large on-site pilot trial using Talvivaara ore. The three year pilot has shown that the leaching process also works well in the subarctic climatic conditions of Eastern Finland. The Talvivaara deposits are located in the southern part of the Kainuu belt in Eastern Finland. They comprise two different polymetallic orebodies, which are located approximately three kilometres apart. The deposits are outcropping and relatively easy to mine. The mineral resources have been classified by Australian JORC code with 0.07% Ni cut-off at 1004 million tons, containing 0.23% of nickel, 0.51% of zinc, 0.13% of copper and 0.02% of cobalt. The black schist ore and the possible utilization of the deposits have been extensively studied for over 20 years. It was quickly apparent from the ore dressing tests that a usable nickel concentrate was not achievable due to the high graphite content of the ore. Chemical and biological leaching options had to be considered as potential options (RIEKKOLA-VANHANEN, 1999). Talvivaara black schist ore contains pyrrhotite, pyrite, sphalerite, pentlandite, violarite, chalcopyrite and graphite. The main silica containing phases are quartz, mica, anorthite and microcline. In addition to nickel, zinc, copper and cobalt the ore contains about 0.3 % of manganese, 10 % of iron, 9 % of sulphur, 8 % of carbon and 50 % of SiO2. The distribution of nickel in different sulphides is pentlandite 71 %, pyrrhotite 21 % and pyrite 8 %. The distribution of cobalt is pentlandite 11 %, pyrrhotite 26 % and pyrite 63 %. All copper is in chalcopyrite and zinc in sphalerite. 2. Production process Overview. The mining method at Talvivaara is large scale open pit mining. Materials handling covers all physical ore processing steps from the primary crusher to