Green and Efficient Process for Extracting Chromium from Vanadium Slag by an Innovative Three-Phase Roasting Reaction

The traditional industrial practice for extracting vanadium from vanadium slag involves a Na2CO3 Na2SO4 NaCIadded pellet roasting at 800 degrees C followed by water leaching. About 5% of chromium and 85% of vanadium can be extracted in this case. The disposal of this leaching residue containing high contents of chromium and vanadium is still an unsolved problem and has seriously impeded the sustainable production of vanadium in China. A complete extraction of chromium and vanadium from vanadium slag might be a solution. To extract efficiently chromium from vanadium slag, some NaOH-added pellets were used to replace traditional pellets here. It was found that the volume of a NaOH-added pellet increased by 144% and many cavities were formed spontaneously throughout the pellet during roasting and a three-phase reaction of solid (slag)-liquid (NaOH)-gas (O-2) occurred in the porous pellet. The Cr extraction was thus increased by 43% when a NaOH-added pellet sample was used to replace the corresponding powder sample. The Cr extraction increased with increasing temperature and reached up to 97.5% and 99.1% at 700 and 800 degrees C, respectively, with a molar ratio of NaOH to V of 18.5. This process avoids the emission of toxic gases such as chlorine and hydrogen chloride.