Electrochemical oxidation of cyanide on 3D Ti-RuO₂ anode using a filter-press electrolyzer

The novelty of this communication lies in the use of a Ti-RuO₂ anode which has not been tested for the oxidation of free cyanide in alkaline media at concentrations similar to those found in wastewater from the Merrill Crowe process (100 mg L^-1 KCN and pH 11), which is typically used for the recovery of gold and silver. The anode was prepared by the Pechini method and characterized by SEM. Linear sweep voltammetries on a Ti-RuO₂ rotating disk electrode (RDE) confirmed that cyanide is oxidized at 0.45 < E < 1.0 V vs SHE, while significant oxygen evolution reaction (OER) occurred. Bulk oxidation of free cyanide was investigated on Ti-RuO₂ meshes fitted into a filter-press electrolyzer. Bulk electrolyzes were performed at constant potentials of 0.85 V and 0.95 V and at different mean linear flow rates ranging between 1.2 and 4.9 cm s^-1. The bulk anodic oxidation of cyanide at 0.85 V and 3.7 cm s^-1 achieved a degradation of 94%, with current efficiencies of 38% and an energy consumption of 24.6 kWh m^-3. Moreover, the degradation sequence of cyanide was also examined by HPLC.