A clean technology to separate and recover vanadium and chromium from chromate solutions

In this work, a clean technology is introduced to separate and recover vanadium and chromium from vanadium-containing chromate solution. It was found that vanadium can be precipitated from vanadium-containing chromate solution by hydrolysis. The hydrolysate is the mixture of polyvanadic acid and sodium polyvanadate. The concentration of V in the solution can be decreased to 0.76 g/L under pH 2.0 at 95 °C. The Na in the mixture can be effectively removed by washing with (NH4)2SO4 solution as the bind of NH4-VO3 is stronger than that of Na-VO3. The V2O5 with purity 98.6% was acquired by calcining the washed mixture. The vanadium residue in precipitated solution can be completely removed by adding Fe2+ or Fe3+ to form iron vanadate under pH 3.8-4.5. The chromium in the V free solution was reduced from Cr(VI) to Cr(III) with Na2SO3, and then the precipitate of Cr2O3∙xH2O was formed under pH above 8.5 at 90 °C. At last, the Cr2O3 with purity 98.7% was obtained by the treatment of the chromic oxide hydrate. Using the process above, the generation of V-Cr-bearing reducing slag and the mixture of Na2SO4 and (NH4)2SO4 can be avoided in vanadium pentoxide production from vanadium-containing chromate solution.