Mineralization of cyanides via a novel Electro-Fenton system generating •OH and •O2−

• The traditional mineralization path of CN − was overturned in a novel Electro-Fenton system. • CN − could be converted into NO 3 − but not CNO − by the synergy of •OH and •O 2 − . • The Electro-Fenton system shows the feasibility of practical application for the actual cyanide residue eluent. Traditional methods of cyanides’ (CN − ) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO − ) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O 2 − . The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, • OH and • O 2 − were simultaneously generated and 92.9% of free cyanides were transformed into NO 3 - within 120 min. No low-toxic CNO − intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN − was activated into electron-deficient cyanide radical ( • CN) by • OH, and then the • CN intermediates reacted with • O 2 − via nucleophilic addition to quickly form NO 3 - , preventing the formation of CNO − and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater. .