China Nonferrous Metallurgy

Oxalic acid was used as a leaching agent to extract vanadium from spent FCC catalysts. The impacts of the main leaching conditions on extraction rates of vanadium, silicon and aluminum were examined. With a leaching time of 240min, a leaching temperature of 95℃, and an oxalic acid concentration of 2.0mol/L, the vanadium extraction rate exceeded 70%. The residue of the spent FCC catalysts after leaching and the steel slag were coupled as raw materials to prepare geopolymers, and the leaching concentration of vanadium toxicity was tested. The results showed that the leaching concentration of vanadium toxicity increased after the residue of the spent FCC catalysts was used to prepare the geopolymers, and the fixation rate decreased. The existence form of vanadium in the spent FCC catalysts and its changes during the reaction process were analyzed by XPS. During the geopolymer preparation process, V₂O₅ in the spent FCC catalysts was transformed into NaVO₃, causing the vanadium in the geopolymers to exist mainly in the form of VO^-₃ anions. Therefore, the vanadium in the spent FCC catalysts can only be immobilized by the geopolymers through physical encapsulation, and the immobilization rate is positively correlated with compressive strength of the geopolymers. The leaching of silicon and aluminum should be controlled simultaneously during the leaching process, so that the geopolymer products prepared have better mechanical properties, thus improving the fixation rate of residual vanadium and meeting the standard of vanadium toxicity leaching.