The process of producing chromium oxide from chromium salts. Commercially speaking, chromium oxide refers to Cr2O3. Chromium oxide is mainly used as raw materials of chromium metal calorimetry, also for the production of paints, coatings and catalysts. The production methods of chromium oxide mainly include a sodium dichromate method, a chromium anhydride method, and a chromium hydroxide method.
Sodium dichromate method: a process of reducing sodium dichromate crystals to chromium oxide with solid ammonium chloride at elevated temperatures. The response is:
Na 2 Cr 2 O 7 •2H 2 O+2NH 4 Cl=2NaCl+C 2 O 3 +N 2 +6H 2 O
After reduction, the material is washed, NaCl is removed, filtered, and dried to obtain chromium oxide. It is also a method of reducing carbon, sulfur or other reducing agents. The production process of sodium dichromate is long, the corrosion of equipment factory and environmental pollution are serious, and the quality and color of chromium oxide produced are not good. China used this method before the 1970s, and the former Soviet Union and Japan also used this method.
Chromic anhydride method: chromium oxide is decomposed by heating to obtain chromium oxide. The sodium dichromate melting method used is relatively backward, and the operating environment is harsh due to the large amount of acid used. The response is:
Na 2 Cr 2 O 7 •2H 2 O+2H 2 SO 4 =2CrO 3 +2NaHSO 4 +3H 2 O
Since the operation of separating NaHSO 4 is difficult, the obtained CrO 3 is unstable in sulfur, which affects the quality of the produced chromium oxide. In China, some factories in the 1960s produced this method, and the chrome oxide produced was very bright.
Chromium hydroxide method: Under the condition of heating the sodium chromate solution, a reducing agent sodium sulfide solution (or sulfur) is added to obtain a chromium hydroxide precipitate. The response is:
8Na 2 CrO 4 +6Na 2 S+23H 2 O=3Cr(OH) 3 +3Na 2 S 2 O 3 +22NaOH
The precipitate is washed, dried, and calcined to obtain chromium oxide. This is a chromium oxide production methods currently widely used around the world, China Hunan Iron Alloy Factory since the mid-1960s to develop their own research organization, 70 years junior owned several factories for industrial production, low production of chromium impurities (FeO <0.1%, S<0.01%, SiO 2 <0.3%), for the production of high quality metal chromium. The chromium hydroxide process has a short process, high recovery rate, good quality and less pollution, but the color of chromium oxide is not good.
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