Improvements in the treatment of chrome-iron ores

摘要

Chrome iron ore is melted in the presence of a reducing agent, and an added base, under such conditions as to form an underlying molten layer of metal high in iron and low in chromium, with an overlying molten layer of ore containing the greater part of the chromic oxide of the original ore, the molten metal being then separated from the ore melt. In an example, 100 lbs. of ore is mixed with 164 lbs. of lime and 50 lbs. of coke, all of which are ground to pass a 1 1/2 inch mesh screen, and the mixture is charged into an electric furnace of the three phase submerged arc type and heated to about 1600 DEG C. At time intervals of about an hour, a metal containing 3,8 per cent chromium, 0,54 per cent carbon and 95,66 per cent iron, and an ore melt containing 43 per cent Cr2O3, 17,2 per cent CaO, and 10,4 per cent silica are tapped off into separate receptacles. Iron oxide present in the original ore as ferrous chromite is replaced by lime, forming calcium chromite. The concentrated ore, when reduced by ferrosilicon, yields ferrochromium containing 71 per cent chromium and with a carbon content of 0,04 per cent. The ferrosilicon employed for this reduction may be obtained by reduction of the iron chromium alloy of low chromium content from the underlying layer. The percentage of chromium in the ferrochromium obtained varies from 70 to 99, and is dependent upon the ferrosilicon content of the reducing agent. The reduced iron may be removed as a phosphide or sulphide by the addition of a phosphate or a sulphur compound to the furnace charge, for example phosphate rock on iron pyrites. Metallic chromium may be obtained by reducing the ore melt with silicon. The amount of reducing agent added is preferably sufficient to reduce to metal all the iron in the ore, but only about 3 to 10 per cent of the chromium. In a modification, the chrome ore concentrate may be made by first producing high carbon ferrochromium from the natural ore, and then oxidizing the ferrochromium with iron ore in the presence of a lime-silica slag bath, the products being a basic ore melt high in chromium, and a metallic layer of a low carbon iron alloy low in chromium.