Chromium Is A Brittle Metal.

Chromium is a brittle metal can not be used as a metal material alone, but after alloy with iron, nickel, cobalt, titanium, aluminum, copper, etc., it becomes an engineering material with heat resistance, thermal strength, wear resistance and special properties. Chromium metal is used as an alloying agent in the production of various nickel or cobalt based superalloys, titanium alloys, aluminum-based alloys, resistance alloys and copper alloys. Some are used to produce stainless steel and heat-resistant steel. These materials are widely used in aviation, aerospace, nuclear reactors, automobiles, shipbuilding, chemical, military and other industries.

Chromite is the main natural chromium resource in thermite smelting. The production of chromium metal by thermit is made of chromium oxide as chromium raw material, so the whole process is divided into two steps. Chromite is first used as raw material to produce chromium oxide. Chromium metal is then smelted with aluminum reduction of chromium oxide (i.e., thermit process). Chromium oxide production with chromite is first alkali roasting, the insoluble Cr3+ chromium salt into water soluble Cr6+ chromium salt, that is, Na2CrO4, by water immersion to obtain sodium chromate (Na2CrO4) aqueous solution. There are three industrial methods for preparing chromium oxide from sodium chromate aqueous solution: (1) ammonium chloride reduction method. By adding sulfuric acid: Na2CrO4 becomes sodium bichromate (Na2Cr2O7) solution. Na2SO4 crystals were precipitated after concentration.

Then the mother liquor was cooled to 25℃ to obtain sodium dichromate crystals. Sodium dichromate crystals were mixed with ammonium chloride and reduced to Cr2O3 and NaCl at 700-800 ℃. Chromium oxide was obtained by washing to remove NaCl, and then obtained by oxidation calcination desulfurization at about 1200℃. (2) Thermal decomposition of chromium anhydride. Chromic anhydride (CrO3) is formed by the reaction of sodium dichromate crystals with concentrated sulfuric acid, and the chromic anhydride is decomposed into chromic oxide in a high-temperature calcination furnace. (3) chromium oxide thermal decomposition method. Add sulfur powder or sodium sulfide solution to sodium chromate solution to reduce Cr6+ to Cr3+, that is, Cr(0H)3 precipitation. Chromium oxide is then calcined at high temperature.

The process of chromic oxide preparation by chromic hydroxide process is short. High chromium recovery; Does not produce corrosive gas, is beneficial to plant and equipment maintenance; Save a lot of sulfuric acid and chemical raw materials; The by-product Haibo (Na2S2O3) can be recycled. Cost reduction and other advantages. Figure 1 is the process flow chart of chromium oxide production and metal chromium smelting by chromium hydroxide method.

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