Efficient removal of the residual ammonium from weathered crust elution-deposited rare earth tailings by a ternary compound eluent

The development of low-cost compound eluent for the efficient removal of the residual ammonium from the weathered crust elution-deposited rare earth tailings, is highly attractive to meet the growing demands for green metallurgy. Herein, a ternary compound eluent composed of K+, Mg2+, and Na+ was prepared for the first time, and its elution behavior and mechanism for the residual ammonium were investigated in detail. Results showed that the maximum ammonium elution amounts of 1702.9 mg/kg was achieved at a K/Mg/Na molar ratio of 5:6:4, which was much higher than the single eluents of K+ (1264.9 mg/kg), and Mg2+ (1105.6 mg/kg), and Na+ (925.9 mg/kg). In addition, higher eluent concentration and faster flow rate would help to improve the elution efficiency. Besides, the dynamic kinetic study revealed that the residual ammonium elution was controlled by internal diffusion. Moreover, XPS analysis demonstrated that K+, Mg2+, and Na+ ions were all involved in and promoted the residual ammonium elution. The novel ternary compound eluent had great potential application in the residual ammonium removal from the rare earth tailings.