Ferronickel is vital importance to modern society. It is because ferronickel is main feedstock in stainless steel production. Without stainless steel, we would not be able to enjoy many of the things that we take for granted, such as stainless steel appliances in our home and workplaces and computer.
There are two types of nickel ore on earth: nickel sulfide ore at the subtropical area and nickel oxide ore at the tropical area. Nickel oxide ore is usually called laterite, which represents 61% nickel ore on earth and 40% of world is in the form of laterite.
Laterite ore normally classifide into two groups:
- Limonite, which occur near the surface, easily mined. Limonite layer consists of a mixture of minerals that have a high iron and low MgO content. The general formula of goethite, (Fe,Ni)OOH, is used to represent limonite ores in chemical reactions
- Saprolite, which occur below limonite. The saprolite ores have a low iron and a high MgO content. Because it is further from the surface, it is less weathered or chemically altered, than limonite. The minerals found in this layer are magnesium hydroxysilicates, such as chysotile, Mg3Si2O5(OH)4. The generic formula of garnierite, (Mg[Ni,Co]3Si2O5(OH)4, is used to represent saprolite ores in chemical reactions.
Feed material for ferronickel production is predominantly saprolite, rather than limonite. This is because the iron content of the saprolite ore about 15% Fe, is lower than that of limonite ore. The choice of saprolite ore ensures that the ferronickel product is not excessively diluted by iron.
Production process of ferronickel consists of four main steps.
- Drying: elimination of most or a substantial portion of free moisture content of the nickel ore
- Calcination-reduction: elimination of the remainder of the free ore moisture and its crystalline water, preheating of the ore, and reduction of a substantial portion of the nickel and a controlled portion of the iron
- Electric furnace smelting: completion of reduction of the nickel separation of the product ferronickel
- Refining: elimination of undesirable minor elements from the ferronickel to meet market specitication
- Ronald A. Bergman, 2003, Nickel production from low-iron laterite ores: process description, Metallurgy
- Frank Crundwell et al, 2011, Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals, Elsevier
- JOM: A publication of the minerals, metals, and materials society, April 2006