Technical noteApplication of lime in two-stage purification of leaching solution of spent vanadium catalysts for sulfuric acid production

•The flow sheet of reprocessing of spent vanadium catalysts is proposed.•Two-stage hydrolytic purification of acidic leaching solution from arsenic and iron impurities has been investigated.•On the first stage the precipitate of iron and arsenic impurities is obtained, with which 2-4% of vanadium are lost.•On the second stage deep purification of vanadium solution occurs.•Neutralization of oxidized leaching solution with lime allows to avoid changes in composition of promoter salts.

Two-stage hydrolytic purification of acidic solution of reductive leaching of spent vanadium catalysts for sulfuric acid production from arsenic and iron impurities has been investigated. After oxidation of Fe(II) and As(III) with hydrogen peroxide and neutralization of vanadium (IV) solution with lime to рН 2.8 at 25 °С, the concentration of iron and arsenic has been reduced from 4.5 to 1.6 g·L− 1 and from 1.0 to 0.6 g·L− 1, correspondingly. After neutralizing excessive acidity to рН 8.5 at 60 °С and oxidation of vanadium, the concentration of iron and arsenic in obtained solutions of sulfates and vanadates of alkali metals does not exceed 0.1 mg·L− 1. Lime's calcium ions are bound with excessive sulfate ions to form gypsum, which allows to preserve the composition of promoter salts and to return them into production of catalysts after vanadium separation. Washing of the second stage precipitation with initial leaching solutions allows to avoid vanadium losses, guarantees return of impurities to the first stage and their extraction in a convenient form for arsenic burial. The kinetic equation for an oxidation of vanadium (IV) solutions with atmospheric oxygen during their neutralization with lime in presence of ferric compounds has been acquired.