A catalytic ozonation process using MgO/persulfate for degradation of cyanide in industrial wastewater: mechanistic interpretation, kinetics and by-products

Abstract

Cyanide-laden wastewaters generated from mining and electroplating industries are extremely toxic and it is of vital importance to treat them prior to discharge to receiving water resources. The present study aims to oxidize cyanide using an ozonation process catalyzed by MgO and persulfate (PS). A MgO nanocatalyst was synthesized using the sol–gel method and characterized. The results show that the synthesized catalyst had a BET surface area of 198.3 m² g⁻¹ with a nanocrystalline particle size of 7.42 nm. In the present study, the effects of different operational parameters were investigated, and it was found that the MgO/O₃/PS process is able to oxidize 100 mg L⁻¹ of cyanide after 30 min under optimum operational conditions. Cyanide degradation mechanisms in the MgO/O₃/PS process were completely investigated and the main radical species were identified using scavenging experiments. It was found that sulfate and hydroxyl radicals both contributed to the cyanide degradation in the MgO/O₃/PS process. Cyanide degradation by-products were also tracked and it was found that cyanate and ammonium species are primarily generated during the oxidation, but increase of reaction time allowed their conversion to much less toxic compounds such as nitrate and bicarbonate. Cyanide degradation was also conducted in real industrial wastewater containing 173 mg L⁻¹ of cyanide. Although there was a reduction in cyanide removal rate, the MgO/O₃/PS process was able to completely oxidize cyanide within 70 min. Finally, it can be concluded that the ozonation process catalyzed by MgO and persulfate is an efficient and reliable advanced oxidation process for removal of cyanide from industrial wastewater.