Features of formation and neutralization of environmentally hazardous CrO₃ in chromium pyrometallurgy

This paper examines the behavior of environmentally hazardous hexavalent chromium (Cr(VI)) during the production of chromium-containing ferroalloys. Based on the evaluation of changes in Gibbs free energy, the oxidation of trivalent chromium in ore at the top of the smelting furnace to hexavalent chromium is shown to be possible due to interaction with atmospheric oxygen in the workshop and lime added during the process. It is hypothesized that the likelihood of Cr(VI) formation inside the furnace itself is low, due to the strictly reducing nature of the ferrochrome production process. The presence of Cr(VI) in slags is believed to result from the interaction of relic ore minerals containing trivalent chromium, such as Cr₂FeO₄ and Cr₂MgO₄, with atmospheric oxygen during slag tapping and transportation in ladles to waste disposal areas. Comprehensive thermodynamic modeling involving industrial slags and carbonaceous reducers has demonstrated the feasibility of converting all chromium and iron oxides into a metal phase consisting of chromium and iron carbides, similar to carbon-rich ferrochrome. It is recommended to agglomerate slag wastes containing Cr(VI) with bitumen prior to smelting. Bitumen serves not only as a binder but also as a reducing agent. Experiments conducted in a high-temperature furnace have confirmed the feasibility of implementing this technology in industrial conditions.