A Cr6+-Free Extraction of Chromium Oxide from Chromite Ores Using Carbothermic Reduction in the Presence of Alkali

Abstract

Oxidative alkali roasting of chromite is the state-of-the-art process for manufacturing chromium-containing chemicals, which involves dealing with serious environmental problems arising from handling Cr 6+ -containing wastes generated in this process. In this article a new method for the extraction of Cr2O3 from chromite ores is explained, based on the carbothermic reduction of concentrates in the presence of alkali investigated in the temperature range of 950-1050 o C. Under these conditions, the iron oxides present in the ore body are reduced to metallic iron and the resulting separation of chromium complex occurs by forming sodium chromite (NaCrO2). The reduced samples are magnetically separated for the recovery of an iron-rich fraction, and a non-magnetic fraction containing NaCrO2, MgO and other impurities. The further treatment of the non-magnetic fraction by leaching yields a Cr2O3-rich product of approximately 85% purity, with remaining alumina, alkali and magnesia. The main advantage of the process is that, under reducing and subsequent leaching conditions, the oxidation of Cr 3+ to Cr 6+ is completely avoided; thereby decreasing the risk of land, air and water pollution.

Effect of Quartz on the Preparation of Sodium Stannate from Cassiterite Concentrates by Soda Roasting Process

“…Sodium salt roasting was one of the effective methods to treat minerals [28][29][30][31]. The roasting tests were performed in the high-temperature zone of a horizontal electric resistance furnace.…”