Talvivaara mining company – From a project to a mine

• Bioheapleaching of Talvivaara black schist ore works in subarctic conditions.
• Nickel and zinc recoveries are over 95%.
• Description of the Talvivaara bioheapleaching plant.

The latest commercial application of bioleaching, and the first in Europe, is the Talvivaara Sotkamo Mine in North-Eastern Finland. The ore is low grade black schist, and contains pentlandite, pyrrhotite, chalcopyrite, sphalerite and pyrite as the main sulphide minerals. The ore and the possible utilization of the deposits have been extensively studied for over 20 years. Bioheapleaching technology was chosen for the extraction of nickel from the ore based on its favourable capital and operational costs and the good performance data obtained in a large on-site pilot trial. Mining was started in Sotkamo in April 2008 and building of the industrial scale bioheap in August 2008. The first shipment of nickel sulphide product was delivered to the customer in February 2009.The mining method at Talvivaara is open pit mining, after which the ore is crushed and screened, agglomerated and finally stacked on the primary heap pad. Air is supplied to the stacked ore with low pressure fans through aeration piping inside the heap. The heap is irrigated from the top with acidic leaching solution, and the solution is collected from the bottom of the heap. A 10% side flow is taken for metals recovery and the rest of the solution is recycled back to the irrigation of the heap. After approximately 13–14 months of bioleaching on the primary pad, anticipated recoveries are about 70% for nickel and 60% for zinc. The leached ore is then reclaimed and re-stacked onto the secondary heap pad. In secondary leaching the rest of nickel and zinc and part of cobalt and copper will be leached. The anticipated total recoveries after both primary and secondary leaching are 85% for nickel, 80% for zinc, and 50% for both copper and cobalt. In the metals recovery process, the metals are precipitated from the pregnant leaching solution using gaseous hydrogen sulphide. The resulting products are intermediates which are transported for further processing in refineries operated by the company’s customers.