ELECTROCHEMICAL INVESTIGATION OF THE CATALYTICAL PROCESSES IN SULFURIC-ACID PRODUCTION

The electrochemical behavior of molten K2S2O7 and its mixtures with V2 O5 [2-20 mole percent (m/o) V2O5] was studied at 440 degrees C in argo n, by using cyclic voltammetry on a gold electrode. The effect of the addition of sulfate and lithium ions on the electrochemical processes in the molten potassium pyrosulfate was also investigated. The potenti al window for pure K2S2O7 was estimated as 2.1 V, being limited by the S2O72- oxidation and reduction. The oxidation of SO42- to oxygen is r eversible in the basic melt. It is found that V(V) electroreduction pr oceeds in two steps. The first reduction stage [V(V) --> V(IV)], start ing at 0.7-0.8 V vs. Ag+/Ag, is reversible for V2O5 concentrations low er than 5 m/o and at potential scan rates less than 200 mV/s. For all studied compositions, the first reduction stage is a one-electron reac tion. The second reduction stage [V(IV) --> V(III)], starting at 0.1-0 .2 V, is irreversible and under ohmic control at all studied V2O5 conc entrations. The presence of Li2SO4 causes a noticeable depolarization effect on the V(V) reduction and the V(IV) oxidation.