A cleaner and efficient process for extraction of vanadium from high chromium vanadium slag: Leaching in (NH4)2SO4-H2SO4 synergistic system and NH4+ recycle

A cleaner and novelty leaching medium, (NH4)(2)SO4-H2SO4 synergistic system was introduced into the leaching process for extracting vanadium efficiently after calcification roasting with high chromium vanadium slag (HCVS), and then V2O5 was prepared after precipitation and roasting. The effects of leaching and precipitation conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 93.45% vanadium and 0.24% chromium were leached when the calcification roasted sample was leached in the (NH4)(2)SO4-H2SO4 synergistic system at 20 degrees C for 60 min with a liquid-solid ratio (L/S) of 10, achieving the efficient separation of vanadium and chromium in HCVS. The optimal (NH4)(2)SO4-H2SO4 synergistic system was composed with 250 g/L (NH4)(2)SO4 and 3.75 mol/L H2SO4, the amount of H2SO4 was 1 mL in every 30 mL leaching system. The introduction of (NH4)(2)SO4 provided much NH4+, which could promote the acid leaching reaction. 99.75% vanadium was precipitated further from vanadium-containing leaching liquid when heating the liquid at 60 degrees C for 60 min after adjusting the system pH at 8.0, and the deposit was ammonium polyvanadate (NH4)(2)V6O16. Then, V2O5 with a purity of 95.71% was prepared after roasting, and recovery rate of vanadium from HCVS was higher than 93%. After precipitation, the supernatant containing a large amount of NH4+ could be recycled as the new leaching medium with some (NH4)(2)SO4 adding according to NH4+ loss after vanadium precipitation. This process achieved the efficient extraction of vanadium from HCVS and provided a new thinking for the leaching process based on the (NH4)(2)SO4-H2SO4 synergistic system.