Enhanced Ammonia Nitrogen Removal From Actual Rare Earth Element Tailings Wastewater by Electrocatalytic Oxidation Technology

The treatment of rare earth element tailings (REEs) wastewater, a problematic byproduct of rare earth mining processes, presents substantial environmental challenges owing to its characteristic combination of high ammonia nitrogen (NH 4 + -N) concentrations, low organic matter content, and strong acidic conditions. Conventional biological and physicochemical treatment methods exhibit limited efficacy in addressing this complex matrix. To overcome these limitations, this study developed an advanced electrocatalytic oxidation system for NH 4 + -N removal from REEs wastewater pretreated by coagulation-sedimentation. The experimental configuration of system employed a small reactor featuring titanium (Ti) plates coated with thin film layer of high-valent metal oxides. Through systematic parameter optimization, the optimal treatment envelope was established: pH range of 8.5~9.5, electrolysis duration of 35~40 minutes, and catalyst loading ≥ 100 mg/L. Under optimized conditions, the system demonstrated exceptional performance with sustained NH 4 + -N removal efficiency > 99%. Notably, process robustness was confirmed through sensitivity analysis showing minimal performance variation across temperature fluctuations (10~40°C) and initial NH 4 + -N concentration (83.47~368.25 mg/L). Scale-up validation at pilot scale (100 m 3 /d) achieved further comprehensive removal of contaminants including chemical oxygen demand, total phosphorus, NH 4 + -N, and total nitrogen. Full-scale implementation at a REE processing facility in Wuping County, Fujian Province (200 m 3 /d capacity) demonstrated consistent performance over 12-month operation, maintaining NH 4 + -N effluent concentrations below 2 mg/L (99% removal). Techno-economic analysis revealed competitive operational costs of 0.8178 $/m 3 , with energy consumption accounting for 25.8% of total expenditure. These findings suggested that electrocatalytic oxidation technology holds significant potential for full-scale implementation in the treatment of REEs wastewater, providing an effective and sustainable solution for managing NH 4 + -N contamination. Graphical