Leaching of vanadium from chromium residue

A chromium residue containing 4.8% V2O5 and 30.2% Cr was obtained from a wastewater treatment plant. The leaching of vanadium from this residue using H2SO4, NaOH or Na2CO3 was trialled. Different pretreatments including rinse, direct roasting and rinse followed by roasting were studied for their effects on vanadium extraction. It was found that a water rinse enhanced alkaline leaching of vanadium but not acidic leaching. The leaching efficiency of V2O5 was satisfactory when roasted residue was leached by H2SO4, but some gaseous pollutants such as Cl2, HCl, and SO2, were produced when the residue was roasted at 800 °C. Leaching by NaOH extracted more vanadium than by Na2CO3. Vanadium extraction was adversely affected by oxidation of excess H2O2, while using KClO3 improved the extent of V2O5 leaching by NaOH. After being rinsed and oxidized by 2% KClO3, the residue was leached by 30% NaOH with a liquid–solid ratio of 2:1 in a stirred flask for 1 h at 95 °C, and the V2O5 leaching efficiency could reach up to 85%.