Electrochemical Study of the Oxidation on Ammonia and Cyanide by Cyclic Voltammetry

In the cyclic voltammetry (CV) of ammonia, no oxidation peak was observed before reaching the oxygen evolution potential (OEP) when using two types of dimensionally stable anode, Pt/Ti and IrO 2 /Ti. This suggests that the direct electrochemical removal of ammonia is extremely ineffective. The OEP of Pt/Ti (1.47 V) is higher than that of IrO 2 /Ti (1.25 V), and thus, the current efficiency (CE) of Pt/Ti is better than that of IrO 2 /Ti in removing ammonia, there were 5.18% and 4.79%, respectively. According to the CV curve of cyanide removal, both Pt/Ti and IrO 2 /Ti anodes presented significant oxidation peaks before reaching OEP. Therefore, the CE of direct electrochemical oxidation in removing cyanide is much better than that in removing ammonia, where the CE of Pt/Ti is better than that of IrO 2 /Ti, there were 22.09% and 17.18%, respectively. In the CV of sodium chloride, the chlorine evolution potential (CEP, 1.07 V) of the Pt/Ti anode was much lower than the OEP (1.47 V) of this anode. In contrast, the CEP of the IrO 2 /Ti anode (1.07 V) was similar to the OEP (1.25 V) of this anode. The chlorine evolution efficiency of the Pt/Ti anode was better than that of the IrO 2 /Ti anode, and thus, the indirect oxidation CE of the Pt/Ti anode was better than that of the IrO 2 /Ti anode for the removal of ammonia, there were 59.12 and 22.46, respectively. Similarly, the indirect oxidation CE of the Pt/Ti anode was better than that of the IrO 2 /Ti anode for the removal of cyanide, there were 92.78 and 40.34, respectively. When adding (NH 4 ) 2 SO 4 or NaCN to a NaCl electrolyte solution, the integral of the chlorine evolution/reduction peak concurrently decreased with increases in additive concentrations; the magnitude of this decrease for the Pt/Ti anode was greater than that for the IrO 2 /Ti anode, and the magnitude of the decrease when adding NaCN was greater than that when adding (NH 4 ) 2 SO 4 . Changes in the integral reduction magnitude of reduction peaks imply that the CE of the Pt/Ti anode was higher than that of the IrO 2 /Ti anode for the removal of ammonia and cyanide, where the removal of cyanide was easier than that of ammonia.