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 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.