Simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process

Sodium and calcification roasting processes are traditional technologies to recover vanadium from vanadium slag. However, these processes are associated with many drawbacks, including high energy consumption, serious environment pollution, and the inability to simultaneously extract associated titanium resources. In this paper, a novel technology for simultaneous extraction of vanadium and titanium from vanadium slag was proposed, in which the vanadium slag was roasted with recyclable (NH4)2SO4 (AS) at moderately high temperatures followed by dilute H2SO4 leaching. To enhance the extraction, an activation pretreatment of the vanadium slag through high-temperature water quenching was employed. The results demonstrated that the activation significantly accelerated the extraction, with the vanadium and titanium extraction increasing by 16% and 12%, respectively, compared with the raw vanadium slag. The extraction of vanadium and titanium were 91% and 77%, respectively, after roasting at an AS-to-vanadium slag mass ratio of 4:1 and 370 °C followed by leaching in a 6% H2SO4 solution. X-ray diffraction analysis indicated that the spinel phases in the vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, began to transform into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4 at 320 °C and a nearly complete conversion could be achieved at 370 °C. The mass ratio of AS to vanadium slag significantly affected the extraction of both vanadium and titanium, which increased with the increasing mass ratio until an 8:1 ratio was achieved, after which, the extraction decreased. A stratification phenomenon of the vanadium slag and ammonium bisulfate at high AS/slag mass ratios was observed, which could be responsible for the decreasing extraction.