A new metallurgical process for the clean utilization of chromite ore

•Iron and chromium in chromite ore are both converted into valuable resource.•Pollution-free residue is obtained due to the formation of KFe3O5 particle.•The oxidative kinetics of chromite ore is systematically investigated.•The resistance of oxygen transmission during the reaction process is first studied.

A new metallurgical process for extracting chromium from chromite ore is proposed to overcome the severe chromium (VI) pollution in chromate production industry. When the 60 wt.% KOH solution was used to decompose chromite ore, the chromium and iron ions in chromite ore were oxidized into soluble K2CrO4 crystal and insoluble KFe3O5 particle, respectively. The chromium levels in the new residue meet the emission standard of chromium-containing waste due to the KFe3O5 crystal's compact appearance, hence the pollution problem of chromite ore process residue is thoroughly resolved. The effect of the main variables on this clean metallurgical process was systematically investigated. Under the condition of leaching temperature 200 °C, oxygen partial pressure 2.0 MPa, and particle size 0.045–0.063 mm, the chromium extraction reached up to 99.4% after 5 h reaction. There is no product layer existing during the leaching process, and the reaction rate is controlled by the surface reaction. The resistances of oxygen transport during the leaching process were calculated step by step, and the surface chemical reaction was the main resistance factor that was consistent with the kinetics study.