Crystallization Pathway of Magnetic NaA Zeolite from Bayan Obo Tailings and Coal Gangue for Selective Ion Uptake from NdFeB Electroplating Effluents

Abstract Industrial residues containing aluminosilicate and iron-bearing phases provide an opportunity to prepare functional zeolites, but the crystallization pathway of zeolites formed from multicomponent solid wastes remains insufficiently understood. Herein, Bayan Obo tailings and coal gangue were used as complementary precursors to synthesize magnetic NaA zeolite through alkali fusion followed by low-temperature hydrothermal crystallization. The time-dependent phase evolution and framework assembly were investigated by X-ray diffraction, Raman spectroscopy, and solid-state 29Si/27Al MAS NMR. The 6-h product was selected because it balanced LTA crystallinity, cubic morphology, and magnetic separability. Rietveld refinement of the 6-h product gave reliable fitting parameters, with Rwp = 1.92%, Rp = 1.34%, Rexp = 1.23%, and GOF = 1.56; VSM analysis showed a saturation magnetization of 4.38 emu g–1. Spectroscopic results suggest the progressive ordering of Si/Al = 1 aluminosilicate units and the development of β-cage- and α-cage-related LTA framework environments during NaA crystallization. The obtained magnetic zeolite was evaluated for the adsorption of Ni2+, Cu2+, and Zn2+ and for selective ion uptake from simulated and real NdFeB electroplating wastewater. Adsorption equilibrium was reached within 60 min, and Cu2+ showed the highest uptake among the tested divalent metals. In simulated Ni-rich systems, Nd3+ and Pr3+ showed preferential uptake over Ni2+, and the apparent distribution-coefficient order was Pr3+ > Nd3+ > Ni2+. This selectivity was further verified using real NdFeB nickel-plating wastewater containing 10.87 mg L–1 Pr, 131.57 mg L–1 Nd, and 959.44 mg L–1 Ni. At an adsorbent dosage of 15 g L–1, the removal efficiencies of Pr and Nd reached approximately 99% and 94%, respectively, while Ni co-removal remained low. Regeneration tests showed acceptable reusability after three adsorption-desorption cycles, and toxicity leaching tests indicated low release levels of hazardous elements. This work provides a dual-solid-waste route for preparing magnetic NaA zeolite and demonstrates its potential for selective rare-earth enrichment from Ni-rich NdFeB electroplating wastewater.