Oxidation of CH3SH by in situ generation of ferrate(VI) in aqueous alkaline solution for odour treatment

This study demonstrated a new approach of odorous gas treatment in a wet scrubbing-oxidation system with in situ generation of ferrate(VI), in which gaseous CH3SH can be quickly absorbed by aqueous alkaline solution and rapidly oxidized by liquid ferrate(VI) generated through electrochemical synthesis in situ. In this study, the electrochemical generation of ferrate(VI) in aqueous NaOH solution was studied and the experiments demonstrated that a maximum current efficiency to generate ferrate(VI) occurred at 14 M NaOH concentration, while an applied current density of 14.06 mA cm−2 was applied. Then the self-decomposition of ferrate(VI) in such strong alkaline solutions was studied, and the results showed that ferrate(VI) behaved more stable in the stronger alkaline solution. Furthermore, the reactivity of ferrate(VI) with CH3SH in this highly-concentrated NaOH solution was investigated under different reaction conditions as the first time. The experimental results confirmed that CH3SH can be fully oxidized by ferrate(VI) to sulphate ion as a final product. The second-order reaction model is suitable to describe the kinetics of CH3SH reaction with ferrate(VI) in the strong alkaline solution. Meanwhile, stoichiometry of ferrate(VI) reaction with CH3SH in aqueous solution was determined with a minimum molar ratio of 2.20:1 (Fe(VI):CH3SH) to destruct CH3SH effectively and a higher molar ratio of 4.53:1 to convert CH3SH to sulphate ion completely. The experiments also demonstrated that the NaOH concentration in aqueous solution would be a key parameter and the best performance of CH3SH removal was achieved at the optimum NaOH concentration of 6 M under our experimental conditions due to an optimum balance between the oxidation potential of ferrate(VI) and its generation rate in this wet scrubbing-oxidation system.

► A new approach to treat gaseous odours with in situ generation of ferrate(VI).
► The electrochemical production of ferrate(VI) achieved a maximum current efficiency of 90.4%.
► Methyl mercaptan (CH3SH) can be fully oxidized by ferrate(VI) to sulphate ion.
► We determined a minimum dosage of [Fe(VI)]/[CH3SH] = 2.20 to destruct CH3SH.
► We determined a sufficient dosage of 4.53 to convert CH3SH to sulphate ions completely.