Integrated process of flocculation-UF- membrane absorption for the treatment of Rare Earth Refining Wastewater and recovery of NH4Cl

During the rare earth refining process, high concentrations of ammonia nitrogen generated from the ammoniation reaction are significant pollutants in wastewater. The low cost and energy efficiency of membrane absorption technology have garnered widespread attention. This study optimized the key operating parameters of the membrane absorption process. A pretreatment (alkaline adjustment and ultrafiltration (UF))- membrane absorption integrated process was used to successfully remove and recover ammonia nitrogen from actual rare earth smelting wastewater. The pre-treatment process effectively removed large particulate matter from the water, reducing turbidity from 1.60 NTU to 0.60 NTU. Additionally, the removal rates for metal ions such as Fe, and Mg exceeded 98%. Under the optimized membrane absorption parameter conditions (when the pH of the feed solution is between 11.50 and 12.00, and the absorbent solution is between 1.00 and 1.30, maintaining efficient absorption conditions with a feed solution flow rate of 1.13   L/h and an absorbent flow rate of 0.75   L/h), the purification/removal of ammonia nitrogen from the wastewater was carried out. The ammonia concentration in the treated water was reduced to just 0.02   mg/L, achieving a removal efficiency of 99.99%, fully meeting the discharge standards for ammonia nitrogen in water. The chemical oxygen demand (COD) also decreased to 134   mg/L, with a removal efficiency of 61.71%. Furthermore, an ammonium chloride solution (1850 mg/L) was obtained from the absorption side, with the ammonium chloride content in the solute reaching 86.52%. This integrated treatment process offers an efficient method for the selective separation and recovery of ammonia nitrogen resources from rare earth refining wastewater.