Degradation of thiocyanate by electrochemical oxidation process in coke oven wastewater: Role of operative parameters and mechanistic study

This study presents the removal of thiocyanate (SCN-) from coke oven wastewater by the electrooxidation (EO) process. Initially, the performances boron-doped diamond (BDD) and different DSA (Dimensionally stable anode) electrodes including Ti/IrO2, Ti/IrO2-RuO2, and Ti/IrO2-RuO2-TiO2 in SCN- removal were compared. BDD anode outperformed the Ti-based mixed metal oxide (MMO) anodes achieving 96.51% SCN- removal efficiency. The most favorable conditions for the removal of SCN- using BDD anode were determined as follows: pH = 9, current density = 43.10 A m(-2), and the electrolyte concentration (Na2SO4) = 2.5 g L-1. The strong role of (OH)-O-center dot in the removal of SCN- was confirmed by the addition of radical quenching agents. The evolution of the intermediates as a result of the EO of SCN- was determined. Under the determined conditions, the EO process could remove 84.13% of SCN- and 94.67% of phenol from a real coke oven wastewater, which was comparable to that of the simulated solution. The electrical energy consumption cost of the process to remove 1 kg of SCN- was calculated as 0.208 US $. Overall, the study showed the EO using BDD anode is a cost-effective method for the removal of SCN- from a coke oven wastewater. (C) 2020 Elsevier Ltd. All rights reserved.