The State Of The Art In Nickel Smelting: Direct Outokumpu Nickel Technology

In 1959 Outokumpu started up an integrated nickel smelter and refinery at Harjavalta. The flash smelting ? Peirce-Smith converting route was applied, and the high-grade converter matte was further refined to nickel cathodes by leaching and electrowinning. In 1995 the production capacity was increased from 17 000 mtpa to 52 000 mtpa, based on the Direct Outokumpu Nickel Smelting Process. The additional refinery capacity is based on hydrogen pressure reduction, producing nickel powder and briquettes. The smelting operation is currently part of Boliden Group and the nickel refinery part of OM Group. In the DON technology, high-grade nickel matte with low iron content is produced in the flash smelting furnace directly without subsequent converting. The metal values in the smelting slag are recovered in an electric furnace as an iron containing Ni-matte. The mattes produced differ from the conventional nickel mattes in many respects, and therefore focused R&D efforts have been made in order to cope with their melting points, fluidities and settling properties. When developing and operating metallurgical processes it is crucial to manage and control the characteristics of the products as well as by-products generated in different steps of the process chain. The low melting points of the high-grade nickel mattes produced in the DON furnace, particularly those low in copper, have pointed out challenges in the furnace design, in particular in the hearth and its thermal engineering. Also key issues of the DON technology are smelting of high-magnesia concentrates, the recoveries of nickel and copper, as well as those of PGM`s and cobalt. These factors can be affected by a proper selection of the process concept, and the operational conditions in the processing vessels. This paper deals with the experience of the DON technology gained over the first ten years of operation, including the significant environmental impacts. Selected results of the thermo-dynamic modelling of DON and EF mattes and high-magnesia slags are reviewed, with the reference to the mattes produced. Also the design principles of the FSF and EF will be discussed.