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

The concentrated liquor of gas field wastewater (CL-GFW) obtained by cryogenic multi-effect distillation is high-concentration organic wastewater. The MgAl-LDH@Fe 3 O 4 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 H 2 O 2 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.