GB573117A - Compositions and methods or processes suitable for use in producing metallic chromium-bearing materials - Google Patents

Abstract

573,117. Chromic oxide ; chromium compounds and alloys. UDY, M. J. Nov. 3, 1942, No. 15488. [A Specification was laid open to inspection under Sect. 91 of the Acts, Oct. 21, 1943] [Class 1 (iii)] [Also in Group II] Chromite ore, its concentrates, and similar chromite-containing materials are oxidized in the presence of an alkali metal compound, e.g., sodium carbonate, hydroxide or sulphate, alkali metal chromate recovered from the product, and reduced, directly or after conversion to dichromate, as with a solid carbonaceous reducing material such as charcoal, coal or coke, to produce chromic oxide which is ultiLized in the preparation of a reduction charge or reacting mixture for the production of metallic chromium-bearing products, and alkali metal compound which is used in the oxidation of additional ore. The reduction product on extraction with water gives a solution of sodium hydroxide, mixed with sodium carbonate in the case of chromate reduction, and a residue of chromic hydroxide. This residue contains some alkali, probably combined as sodium chromite, and may be roasted in air at above 500‹C. and leached with water to extract sodium chromate from the residual chromic oxide. The reduction of the chromate or dichromate may be effected with carbon, and calcium oxide or carbonate when calcium chromite and sodium carbonate are produced. Solutions of sodium hydroxide obtained in the process may be used to wash flue gases and are thereby carbonated. In an example, sodium chromate is ignited with an excess of charcoal, and the cooled product ground in water to extract sodium hydroxide and carbonate. The residue of chromic hydroxide is roasted at 1,000‹C. to give chromic oxide which is leached to remove sodium chromate having the pure oxide. Ferrochromium of high chromium content may be produced from low grade ore by treatment according to the invention to give an iron free product in the form of chromic oxide as such or combined, for example, as calcium chromite or chromate, which is smelted with a further amount of the ore. High grade, low carbon ferrochromium or ferrochrome silicon can be made by producing a high carbon alloy from low grade ore, incorporting silicon to eliminate carbon, and then eliminating silicon wholly or in part by the use of iron-free chromic oxide products produced according to the invention, with sodium nitrate or other oxidizing material if necessary. Lowsilicon ferrochrome silicon thus produced may be refined with iron-free products of the invention in an electric furnace or with such products, and oxidizing material if necessary, added to form a mixture reacting exothermically on ignition to give ferrochrome very low in silicon which may be incorporated at the same time in molten steel. Specification 558,986 is referred to. The Specification as open to inspection under Sect. 91 comprises also production of calcium chromate by roasting di- or tri-calcium chromite, mono-calcium chromite and calcium oxide. or chromic oxide, or hydroxide and calcium oxide, the products being utilized in exothermic reaction mixtures for chromiumbearing metal. This subject-matter does not appear in the Specification as accepted.