Catalytic oxidation of aqueous sulfide in the presence of ferrites (MFe2O4, M = Fe, Cu, Co)

• Ferrites MFe3O4 (M = Cu2+ and Co2+) are new active catalysts for sulfide oxidation.
• Co2+ and especially Cu2+ have remarkable effect on the catalytic activity.
• Reaction dependent on: redox behavior and electron conductivity of ferrites.
• Redox pairs Cu2+/Cu+, Co3+/Co2+, Fe3+/Fe2+ might be involved in the reaction.
• Surface interaction of S2−aq with Cu2+surf might play important role.

In this work, the spinel structured iron oxides, MFe2O4 (M = Cu2+ and Co2+), magnetite (Fe3O4) and maghemite (γ-Fe2O3) were investigated as catalyst for the sulfide oxidation in aqueous medium. XRD, Mössbauer, BET, TPR, SEM/EDS and XPS analyses suggest the formation of the spinel phase with surface areas varying from 75 to 105 m2 g−1 and the metal ions Cu2+ and Co2+ located in the octahedral and tetrahedral sites. It was observed that the presence of Co and especially Cu strongly increased the catalytic activity for the oxidation of sulfide to polysulfides, i.e. Sx2− (x = 1–4) and other SO species. The strong effect of Cu2+ is discussed in terms of thermodynamically favorable processes comprising a strong surface interaction of S2−–Cu2+, an electron transfer from sulfide to produce Cu1+ followed by an electron transfer from Cu1+ to Fe3+bulk.

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