Why are chromite ores with more than 46 percent chromium oxide preferred for ferrochromium production?

For the production of ferrochromium, chromite ores containing more than 46 percent chromium oxide (${\text{Cr}}_2{\text{O}}_3$) are preferred because they are considered rich enough to be used directly in the smelting process. Additionally, these preferred ores typically possess a chromium-to-iron ratio greater than 2:1.1

While ores with lower chromium-iron ratios and as little as 40 percent ${\text{Cr}}_2{\text{O}}_3$ are also utilized in ferrochromium production, higher-grade ores are favored for their efficiency in the electric furnace environment. In contrast, ores that are high in alumina are specifically preferred for refractory applications rather than metallurgical ones.1