Removing Sulfide in Gas Field Produced Water by Electrooxidation

Certain amounts of sulfide are present in gas field produced water, which brings negative effects on the environment and human health. Since the electrochemical oxidation method has the advantages of high efficiency without secondary pollution, we introduce it into the sulfide removal process under the conditions of high salinity and hardness. Based on the cyclic voltammetry characteristics, sulfide removal efficiency, and economic analysis, Ti/RuO₂-SnO₂-IrO₂ was selected as the anode. The removal of sulfide by two-dimensional electrochemical oxidation followed zero-order kinetics, which was namely that residual sulfide concentration in solution had a linear relationship with time in all reaction stages. Sulfide existed in the form of HS⁻ in the solution. For the reason that H⁺ would be released when HS⁻ was oxidized, it was necessary to select a suitable initial pH and control the reaction time. The sulfide removal ratio and corresponding energy consumption of simulated gas field produced water with 300 mg/L sulfide and 2.50% (mass fraction) NaCl were above 99.2% and 55.2 kW·h (calculated by S²⁻ of per kilogram), respectively, with the electrode distance of 5 cm, current density of 200 A/m², aeration rate of 1 L/min, the initial pH of 9−10, and running time of 35 min. Moreover, reversing cathode and anode was found to effectively solve the problem of scaling on cathode caused by high Ca²⁺ and Mg²⁺ concentration.