Leaching characteristics and solidification mechanism of vanadium in preparation of titanium-containing pellets using spent SCR catalyst

Abstract

The spent SCR catalysts produced from flue gas denitrification are hazardous to the environment and human health. This study proposed a harmless strategy for utilizing the spent catalysts for manufacturing magnetite pellets, in which the mechanical properties of the spent catalyst pellets and the distribution of vanadium during heating were studied. The leaching characteristics and solidification mechanism of vanadium in magnetite pellets were investigated. The results confirmed that the pellets with 10 wt% spent catalysts have mechanical properties satisfactory for application as an ironmaking feedstock. After preheating and roasting the pellets, 91.2 wt% vanadium in spent catalysts was solidified. The leaching ratio of vanadium in spent catalyst pellets was less than 1 % under different pH, liquid-to-solid ratio, and leaching time conditions. Raman, XPS, XRD, and SEM analyses confirmed that the V2O5 started to liquefy at 700 °C, and 8.8 wt% of V2O5 was volatilized into the flue gas at 700–950 °C. The remaining vanadium oxides reacted with iron oxides to form FeVO4, Fe2VO4, and FeV2O4 at 700–1250 °C, leading to its consolidation in the pellets. The treatment of spent catalysts by the pelletizing process is a new technology with the advantages of low investment cost and controllable environmental risk. This new technology could not only solve the problem of spent catalysts utilization in the iron and steel industry but also provide a reference for the treatment of spent catalysts generated from flue gas denitrification in thermal power generation, waste incineration, and other industries.