A novel pyro-hydrometallurgy process for efficient recovery of tungsten, vanadium, and titanium from spent SCR catalysts

The spent selective catalytic reduction (SCR) catalysts are a hazardous solid waste, but they are also a highquality secondary resource, consisting of a matrix of TiO2 at 80 % or more, an additive WO3 at 5-10 %, and an active ingredient V2O5 at 0.5-1.5 %. However, high recoveries of the key rare metals V and W require highpressure leaching at 300 degrees C or high-temperature roasting at more than 1000 degrees C. The high-pressure or hightemperature processes have the drawbacks of safety risks, environmental risks, and excessive costs. A novel pyro-hydrometallurgy process for efficient recovery of Ti, V and W from spent SCR catalysts was proposed. The spent SCR catalysts was firstly roasted with concentrated sulfuric acid, and then leached by water to obtain the leach solution containing Ti, V and W. The leaching efficiency of Ti, V and W reached 96.52 %, 97.5 % and 97.7 %, respectively, under optimal conditions. In addition, the reaction mechanism of WO3 was studied. Furthermore, a novel solvent extraction process was developed to completely separate Ti, V and W in the leaching solutions. Firstly, Ti and W were co-extracted by N1923 in the form of polymeric ions TiO(SO4)2- 2 and TiW12O4-40, respectively, while V remained in the raffinate. Then, TiO(SO4)2-2 was stripped by HSO-4 and H2O2 in the form of TiO(H2O2)2+. Finally, TiW12O4-40 was stripped by OH-. The organic phase can be recycled after H2SO4 regeneration. The closed-loop strategy shows great promise for the efficient recovery of valuable metals on an industrial scale to promote circular economy and environmental protection.