KROMINCO, INC
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Mining practice for chromite follows that of most other minerals in that both surface and underground methods are employed. In general, the size, shape, depth and regularity of the deposit determines the mining method. Most podiform deposits are mined by surface methods, while stratiform deposits are mined by underground methods.
Chromite is generally cleaned by hand sorting, washing and screening, or gravity concentration. Concentrates are prepared from fines or size - reduced lower grade ore using such concentrating equipment as jigs, tables, spirals or magnetic separators. Although flotation separations have been used, gravity separation methods predominate.
In the metallurgical industry, chromite is converted to chromium alloys or chromium additives by pyro-metallurgical processes. Chromite, ore, fluxes and reducing agents are smelted in a three- phase electric furnace and by adjusting charge mixes and processes variables, various types of ferrochromium products are produced.
Chromium metal is made by either electromechanical or pyrometallurgical processes. The electromechanical process involves the deposition of chromium metal by electrolysis of a purified chromium-alum solution derives, from chemical solution of ferrochromium. The pyrometallurgical process is alumino-thermic reduction, which involves the reduction of pure chromium oxide by finely divided aluminum metal.
The chemical industry industry treats chromite by a hydro-metallurgical process involving roasting chromite with sodium carbonate, lime and sulfuric acid followed by leaching to remove sodium dichromate and sodium sulfate. After the leach solution is purified, sodium sulfate is removed by an evaporation process and the resulting purified sodium dichromate solution is sent to a crystallizer where crystal of sodium dichromate are obtained. This base material is either used directly or used to produce a wide range of chromium chemicals.
Technology
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