|80 % of entire nickel is extracted by sulphide deposits processing by concentration through a froth flotation process. Sulfidic ores, which contain 0.5-2% nickel, can with concentration treatment be processed into concentrates with a (Ni-Cu) content varying from 6% to 20%. The aim is to eliminate Iron and Sulphur by selective oxidation and fluxing.|
Modern technology uses electric smelting or flash smelting. Flash smelting is the most common process but electric smelting is used for more complex raw materials when increased flexibility is needed. Both processes use dried concentrates. Electric smelting requires a roasting step ahead of the smelter to reduce Sulphur content and volatiles. Older nickel smelting processes, such as blast or reverberatory furnaces, are no longer acceptable because of low energy efficiencies and because of environmental concerns.
In flash smelting, dry sulfide ore containing less than 1% moisture, is fed to the furnace along with pre-heated air, oxygen-enriched air (30-40% Oxygen), or pure oxygen. Iron and Sulphur are oxidized, and the heat that results from exothermic reactions is adequate to smelt concentrate to produce a liquid matte (up to 45% nickel) and a fluid slag. Furnace matte still contains Iron and Sulphur that are oxidized in the converting step to sulfur dioxide and iron oxide by injecting air or Oxygen into the molten bath. Oxides form a slag which is skimmed off. Slags are processed in an electric furnace prior to discard to recover nickel. Process gases are cooled followed by removal of particulates by gas cleaning devices. After concentration Copper, nickel and pyrrhotine concentrates are separated.
The nickel furnace charge is melted in electric or reverberatory furnaces for obtaining the molten metal sulfide (matte) formed during smelting of nickel. Iron, Cobalt and, almost entirely, Copper noble metals also get into the matte. In the case of nickel, the primary end product is a nickel matte with a low (0.5-3%) iron content, and in the case of copper it is blister copper. Metallic copper can be produced by oxidizing Cu2S at relatively low temperatures, 1.200-1.300°C., whereas the production of metallic nickel requires temperatures over 1.600°C. After extracting Iron fusion of Copper and Nickel - NIS material is obtained. After cooling and disintegration the NIS material is provided for Copper and Nickel flotation separation. Nickel concentrate is heated in fluidized bed until NiO. After that nickel oxide is reduced until pure Nickel in arc-type furnaces. As a result crude Nickel is yielded from which anodes are made for electrical refining.
Carbonyl process based on reversible reaction is also used for Nickel-Copper separation. Carbonyl is obtained under 100-200 atm at 200-250°C after which it is decomposed under 1 atm and at 200°C. Ni(CO)4 decomposition is used for nickel coating and various products manufacturing.
Nickel matte may be obtained also from silica ores by adding gypsum or pyrites into the flash smelting charge. The flash smelting is processed in shaft furnaces, the matte consists of 16-20% Nickel, 16-18% Sulphur, the rest is Iron.