Nikiforova A. Obtaining of vanadium compounds from spent catalysts of sulfuric acid production

The dissertation is devoted to research of processes of complex processing of the spent vanadium catalysts (SVC) of sulfuric acid production. Physicochemical regularities of vanadium leaching processes with H2SO4 solutions from SVC with addition of H2O2, SO2 and without introduction of additional reagents are considered. It is shown that reductive leaching with SO2 allows to achieve quantitative extraction of vanadium and reduction of the arsenic impurities content in the catalyst base to the MPC levels at S:L≥1:3. In the range of pH=0,70–1,75, the leaching rate is determined by the diffusion of hydrogen and vanadyl ions, according to the kinetic model kτ = 1/5(1-α)−5/3−1/4(1-α)−4/3+1/20. The processes of precipitation of arsenic and iron impurities in a mixture of sparingly soluble FeAsO4 and Fe(OH)3 have been studied. It is shown that neutralization of vanadium(V) sulfate solutions to pH=8–9 in the presence of alkali metal sulfates by lime does not lead to precipitation of calcium vanadates. The kinetic parameters of oxidation of vanadium(IV) by oxygen in leaching solutions were determined. When maintaining the pH=8–10 with lime, the residual content of arsenic and iron in the solutions does not exceed 0,1 mg/l. From purified solutions of KVO3 and K2SO4, vanadium products were precipitated in the form of sparingly soluble calcium vanadate, ammonium vanadate, hydrated vanadium pentoxide compounds. Calcium vanadate concentrates were used to produce ferrovanadium (50ФВд0,3) on a semi-industrial scale. On the basis of the researches the basic technological scheme of complex processing of SVC of SO2 conversion with obtaining of diatomite, calcium vanadate and potassium sulfate is developed, impurity of arsenic is concentrated in suitable for waste disposal FeAsO4.