A Clean Production Process of Chromic Oxide

Chromic oxide is an important basic chemical and finds many applications including metallurgical materials, green pigments, construction materials, refractory materials and catalysts. Presently, the industrial production of chromic oxide generally employs two processes (Ding, 2003): one is the reduction of sodium dichromate with ammonia sulfate; the other is the thermal decomposition of chromic anhydride. Both of the processes employ hexavalent chromium as the raw materials. However, the industrial production of hexavalent chromium compounds, including sodium dichromate and chromic anhydride, leads to serious environmental problem and low resource utilization. Fig. 1 illustrated the traditional production process for hexavalent chromium compounds, as well as chromic oxide. It produces useful products of sodium dichromate and chromium anhydride, as well as several kinds of toxic residues, including chromium-containing residue, aluminum-enriched residue and chromium-containing Glauber’s salt (Na2SO4·10H2O) and sodium bisulfate.