METHOD OF ALUMINO-THERMIC PRODUCTION OF LOW-CARBON FERRO-CHROMIUM Russian patent published in 2007 - IPC C22C33/04 

FIELD: metallurgy; production of low-carbon ferro-chromium at nitrogen content not exceeding 0.04 mass-%.

SUBSTANCE: used as chromium raw material is calcined chromium ore at carbon content up to 0.05 mass-% and lime at carbon content not exceeding 0.6 mass-%; aluminum is introduced into ignition part of burden at ratio of 0.75-0.95 relative to amount stoichiometrically required for reduction of oxides of burden; amount of aluminum for heat is introduced at ratio of 1.10-1.20 relative to amount stoichiometrically required for reduction of chromium ore oxides. For production of low-carbon ferro-chromium at nitrogen content not exceeding 0.04 mass-% in ignition part of burden chromic anhydride and sodium or potassium bichromate is used at ratio of 1: (0.25-0.40) at addition of common salt in the amount of 15-25 mass-% relative to mass of aluminum in this part of burden. At reduction of oxides of melt by aluminum, sodium or potassium bichromate, calcium hydroxide and common salt are additionally introduced at ratio of (0.08-0.12): (0.07-0.10): (0.03-0.06) :1 to mass of aluminum per heat; then, part of slag is poured into ingot for skull and fluorite concentrate is charged into hearth on remaining slag at ratio of (0.02-0.04): 1 relative to mass of aluminum per heat as a whole; after its dissolving, remaining slag and metal are poured out. Proposed method excludes stages of enrichment including forming of solid technogenious waste in form of dump chromium-containing sludge increasing through extraction of chromium from ore.

EFFECT: increased through extraction of chromium from ore; possibility of making use of secondary grade aluminum; reduced amount of carbon and nitrogen in ferro-chromium.

4 cl, 1 tbl, 5 ex