Magnetic NaA Zeolites Synthesized from Dual Solid Wastes Enables Selective Efficient Recovery of Rare Earth Ions from Neodymium Iron Boron Electroplating Wastewater

This research leverages the minor iron oxides and carbon contained in Bayan Obo tailings (BOT) and coal gangue for the synthesis of magnetic zeolite NaA, which was subsequently applied to recover and separate rare earth elements (REEs) from Nd-Fe-B passivation solutions. To control the synthesis conditions of the magnetic zeolite, the effects of different raw material ratios, silicon/aluminum ratios, alkali fusion temperature, and hydrothermal reaction time on the phase composition, microstructure, and adsorption properties were investigated. The results show that magnetic NaA zeolite with a complete crystal structure can be synthesized when roasting is performed at 750 °C for 120 min, followed by a hydrothermal treatment at 75 °C for 6 h. Adsorption of Nd³⁺ and Pr³⁺ from aqueous solutions by the BOT-coal gangue-based magnetic zeolite conforms to the Langmuir isotherm model and the pseudo-first-order kinetic equation. The adsorption rate is controlled by the adsorption resistance between particles. The saturated adsorption capacities of the zeolite for Nd³⁺ and Pr³⁺ reached 350 mg/g and 156 mg/g, respectively. After 5 cycles, the adsorption efficiency remains above 89.2%, confirming its excellent regeneration capability. When RE³⁺ and Cr³⁺ coexist, rare earth ions are preferentially adsorbed. This characteristic enables the separation of RE³⁺ and Cr³⁺ in Nd-Fe-B electroplating wastewater. Dynamic adsorption experiments demonstrated that under conditions of 4 g of magnetic zeolite, an initial RE³⁺ concentration of 100 mg/L, and a flow rate of 8 mL/min, nearly all rare earth ions were completely adsorbed within the first 4 h.