A Cr~(6+)-Free Extraction of Chromium Oxide from Chromite Ores Using Carbothermic Reduction in the Presence of Alkali

摘要

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 Cr_2O_3 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 ℃. Under these conditions, the iron oxides present in the ore body are reduced to metallic iron and the resulting separation of chromium occurs by forming sodium chromite (NaCrO_2). The reduced samples are magnetically separated for the recovery of an iron-rich fraction, and a non-magnetic fraction containing NaCrO_2, MgO and other impurities. The further treatment of the non-magnetic fraction by leaching yields a Cr_2O_3-rich product of approximately 85% purity, with remaining alumina, alkali and magnesia. The main advantage of the process is that, under reducing atmosphere 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.