Abstract:A large amount of ammonium salt remains after leaching the weathered crust elution-deposited rare earth ore. Denitrification of leachate from rare earth tailings is an effective method to solve ammonia nitrogen pollution. The ammonia nitrogen was removed from the leachate of rare earth ore tailings by chemical precipitation method and effects of precipitation conditions on ammonia nitrogen removal rate were studied. The response surface method was used to optimize the precipitation process parameters, and the chemical precipitation denitrification process and mechanism were analyzed by solution chemical calculation, XRD and SEM. The results show that under the conditions of pH=7.0, n(N)/n(P)=1.0/1.1, 25 ℃, reaction time of 240 s, the ammonia nitrogen removal rate could reach 86.87%. The results of response surface fitting show that the sequence of influence of each factor on ammonia removal rate is NaOH dosage (pH), n(N)/n(P), and reaction time. Under the optimized conditions, the ammonia removal rate is up to 98.02%, and the ammonia concentration of leachate after chemical precipitation is less than 15 mg/L, which meets the requirement of national emission standard. The precipitated products are mainly MgNH4PO4?6H2O and a small amount of MgHPO4?3H2O, Mg(OH)2 and Mg3(PO4)2 solids with rough surface and hollow rod-like structure.