MgAl-LDH@Fe3O4 based heterogeneous electro-Fenton process for the concentrated liquor of gas field wastewater treatment: Optimization, mechanism, and stability

Abstract The concentrated liquor of gas field wastewater (CL-GFW) obtained by cryogenic multi-effect distillation is high-concentration organic wastewater. The MgAl-LDH@Fe3O4 particles were successfully synthesized as the catalysts of the heterogeneous electro-Fenton (EF) system to effectively degrade refractory organic pollutants in the CL-GFW. The particles broadened the pH range of the EF process under optimal conditions. The highest COD removal efficiency could achieve 88.18% after 4 h with pH of 5. The mesoporous particles were systematically studied via a series of characterization techniques. The heterogeneous degradation mechanisms were explored by radical quenching experiments, variation of H2O2 and Fe ion concentrations, and X-ray photoelectron spectroscopy (XPS) analysis. The results indicated that the synergistic effects of the active free radical oxidation, enhanced catalysis, and surface complexation contributed to the degradation of recalcitrant organics in the heterogeneous EF process. Electrocatalysis and homogeneous EF trials exhibited lower COD degradation rates of 45.68% and 62.86% comparing with the heterogeneous EF. The representative refractory organics before and after the heterogeneous EF reaction were identified by GC-MS and HPLC-MS methods. The excellent stability and reusability of the particles in the heterogeneous EF system were verified through five cyclic experiments with low sludge production and metal leaching rate.