Insight into the oxidation mechanisms of vanadium slag and its application in the separation of V and Cr

Abstract

Vanadium slag contains valuable element vanadium and heavy metal element chromium. V and Cr in the traditional oxidation roasting process were simultaneously oxidized by oxidant O2 in the air, which made the separation of V and Cr difficult, and produced highly toxic Cr6+ that polluted seriously the environment. The valence states of Fe, Cr and V in vanadium slag increased during oxidation roasting. In order to reveal the oxidation mechanisms, the oxidative roasting of Na2CO3–Cr2O3, Na2CO3–FeCr2O4 and Na2CO3–V2O3 was investigated. The results showed that Cr2O3 could be oxidized by O2 and the presence of Fe2+ reduced the oxidation ratio of Cr3+. Moreover, it was found for the first time that the V3+ could be oxidized by CO2. The calculation of FactSage 8.0 showed that V2O3 could be oxidized by Na2CO3. However, V2O3 could not be directly oxidized to VO2 or V2O5 by CO2. Due to the lack of NaVO2 data in the thermodynamic database, the reaction of NaVO2 and CO2 was firstly simulated by Vienna ab initio simulation package (VASP). The results indicated that NaVO2 could be oxidized by CO2. On the basis of revealing the oxidation mechanisms of V, Cr, and Fe, an innovative method for selective oxidation of vanadium by oxidant CO2 was proposed. The extraction ratio of vanadium could reach 90.5% at 800 °C, in which the mass ratio of V/Cr was 32,400. Mass ratio of V/Cr in this work was 1448 to 20,250 times larger than that in the literatures. Based on the high vanadium extraction ratio, the problems of separation of V and Cr and the presence of Cr6+ were solved from the source. This novel discovery may provide an inspiration for the vanadium metallurgical revolutionary.