Investigation into the impact of nickel ions during the preparation of sodium bicarbonate from by-product sodium sulfate of the ternary lithium battery industry

The high-value utilization of sodium sulfate (Na 2 SO 4 ), a by-product from the lithium-ion battery cathode industry, into high-value sodium bicarbonate (NaHCO 3 ) is crucial for the sustainable development of the battery industry. This study investigated the concentration-dependent effects of nickel ions (Ni 2+ ) impurities on the crystallization, purity, and morphology of NaHCO 3 synthesized from battery-derived Na 2 SO 4 via metathesis reaction with ammonium bicarbonate (NH 4 HCO 3 ). Under optimized conditions, the as-prepared NaHCO 3 achieved a purity of 99.8%, meeting the requirement of the Chinese National Standard GB/T 1606-2008. Characterization by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy revealed that Ni 2+ concentrations below 100 ppm had a negligible impact on NaHCO 3 crystallization. However, at levels exceeding 200 ppm, lattice distortions were observed, including expanded unit cell parameters, reduced particle size, and the formation of irregular nodular morphologies. These effects were ascribed to the adsorption of Ni 2+ at crystal growth sites, which altered surface energy and impeded ion incorporation kinetics. XPS analysis confirmed that Ni 2+ impurities above a critical concentration disrupt NaHCO 3 crystallization through dual incorporation pathways: direct lattice bonding (Ni–O) and immobilized Ni(NH 3 ) n 2+ complexes (Ni–N), leading to lattice strain and consequently growth inhibition. This work elucidates the mechanistic role of Ni 2+ in crystallization pathways, providing critical guidance for optimizing by-product Na 2 SO 4 valorization processes and underscoring the importance of trace metal control in advancing circular economy practices. • Preparation technology of NaHCO 3 derived from byproduct Na 2 SO 4 has been studied. • The purity of NaHCO 3 prepared under the optimized conditions was 99.8%. • The influence of nickel ions on crystallization of NaHCO 3 has been studied. • High Ni 2+ concentration (>200 ppm) affects the appearance and particle size of NaHCO 3 . • Declaration of generative AI in scientific writing