Oxidation of sulfide with the CuO catalyst assisted oxygen microbubbles in alkaline wastewater: Efficiency, sulfur conversion, and mechanisms

Abstract

Alkaline sulfide wastewater is toxic, corrosive, and malodorous, detoxification of which usually be realized by oxidizing S2− to corresponding sulfate salts. Due to complex reaction pathway and sluggish reaction kinetics, complete oxidation of S2− to SO42− usually can only be realized under extreme reaction condition. In this study, MgO-supported CuO catalyst assisted oxygen microbubble oxidation of S2− in NaOH solution has been investigated. It was concluded that the oxidation efficiency of S2− reached 99.98% at 90 °C and ambient pressure in 180 min, with 98.70% being converted to SO42−. This coupled process exhibits the same oxidation effect as the wet catalytic oxidation method operating under high temperature and high pressure. Mechanism study suggested that SO3− and SO4− were primary reactive oxygen species responsible for S2− deep oxidation. Furthermore, the microbubbles could inhibit the S poisoning of the CuO catalyst to ensure the continuation of the catalytic reaction. The generation of reactive oxygen species under mild conditions was achieved under physicochemical action in this process. The proposed novel oxidation method featuring CuO catalyst assisted microbubble oxidation therefore can be considered an attractive alternative approach for alkaline sulfide wastewater treatment.

Keywords

• Microbubble
• Sulfide oxidation
• Catalytic oxidation
• Copper oxide
• Sulfur-containing free radicals