ALKALINE ROASTING OF LOW-GRADE CHROMITE

A low-temperature soda-roasting and water-leaching method. was investi gated to extract chromium from a low-grade chromite concentrate. The s oda roasting was performed in a temperature range of 450 to 650 degree s C and chromium was solubilized by water leaching at room temperature . It was found that high extraction yields of chromium were primarily dependent on the conversion of Cr3+ to Cr6+ during the roasting step, and this was enhanced significantly by simple attrition of chromite pa rticles during this step. It was also found that gangue impurities (ma inly silicon) were more detrimental to chromium extraction than lattic e impurities, such as aluminium or magnesium. Characterization by scan ning-electron microscopic methods suggests that oxidation occurs direc tionally along the crystallographic (111) plane, which contains the ch romium ions. The effects of roasting time, temperature, soda to chromi te ratio and particle size on the extraction of chromium are presented .