Characterization of the catalytic films formed on stainless steel anodes employed for the electrochemical treatment of cuprocyanide wastewaters

Surface composition changes at stainless steel anodes in an electrochemical reactor applied for the electrochemical treatment of cuprocyanide-containing wastewaters operating under different hydrodynamic conditions were investigated. Under highly alkaline conditions in situ generation of a surface film on the anode with catalytic properties towards cyanide electrolysis was observed. X-ray photoelectron spectroscopy (XPS) results demonstrated that only copper oxi-hydroxide compounds constitute the surface film developed on the stainless steel anodes, as no traces of N- and C-containing compounds were observed. The collected XPS spectra revealed relevant details concerning the oxidation states of copper in the film, and the products Cu2O, CuO and Cu(OH)2 were identified on the surface of the anodes. However, the quantitative proportions of the individual products differ and depend on the type of mixing employed during reactor operation.