In contrast to South African operations, ores from Kazakhstan, for example, have very high Cr/Fe ratios (∼3.8), resulting in metal products of higher grades (>70% Cr, 20% Fe, 8% C, <1% Si).

The metal composition is relatively fixed, but the slag composition varies based on the fluxing regime employed by the specific operation. High-carbon ferrochromium contains roughly 50–52% Cr, 6–8% C, 0.5–1.5% Si, with the balance being Fe and some minor impurities (including some P). Ores are often mixed to achieve a blend that can be processed economically. In typical South African operations, where ores have Cr/Fe ratios of 1.3–1.7, the product produced will be high-carbon ferrochromium. Ferrochromium is sold according to its Cr content, and there is usually no payment given for other elements present, such as Fe, Si, and C. A selection of typical ore compositions is shown in Table 1.Īn important parameter in chromite smelting is the Cr/Fe ratio, as this ratio largely determines, for a given furnace type, the grade (% Cr) of the product. Most of the reduction occurs as the reductant interacts with the slag.Ĭhromite ores vary considerably in composition. Fluxes are added to the furnace in order to decrease the melting temperature of the oxide melt where the reactions take place. This material has the primary spinel at its core, with an outer layer of secondary spinel (essentially MgAl 2O 4 from which Cr and Fe was removed). As this reacts with carbon, some small quantity of “partially altered chromite” remains. (Cr,Al) 2O 3, that is very stable even at high temperatures.The chromite ore has a spinel crystalline structure, represented by (Fe,Mg)O (1) shows a highly simplified version of the principal reaction that takes place. The production of ferrochromium takes place at very high temperatures, by reacting chromite ore, together with fluxes such as lime and silica, with a carbonaceous reducing agent. Since then, the size of these furnaces has expanded, and the power has increased from 12 MW to 72 MW, and this technology has been applied to the production of numerous other commodities in furnaces up to 80 MW. It has been over thirty years since DC arc furnace smelting technology was first implemented industrially, in 1984, for the smelting of fine chromite ores to produce ferrochromium.

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