Lithium adsorption performance of Co-doped manganese-based lithium-ion sieves prepared via solid-phase synthesis

With the rapid development of 5G/6G communications, new energy vehicles, and lithium battery industries, the demand for lithium compounds (especially Li₂CO₃) has dramatically increased in recent years. Many countries have regarded lithium as a strategic mineral resource. Lithium is mainly found in liquid mineral resources around the world, and the extraction of lithium from the mother liquor of lithium precipitates has thus garnered significant attention. The main methods for recovering lithium from solutions include membrane separation, solvent extraction, electrochemistry, and adsorption. Among them, the adsorption method is one of the most promising. The key to successful adsorption technology is the construction of high-performance adsorbents with high adsorption capacity, high ionic selectivity, and high structural stability. The manganese-ion sieve named as LMO, is a promising adsorbent that has been widely studied because of its good chemical stability, excellent adsorption properties, and outstanding ion selectivity for lithium extraction. However, its inherent dissolution loss greatly restricts its practical application. To reduce the dissolution loss of manganese-ion sieves, several strategies, such as adjusting the synthesis process, composition optimization, ion doping, and surface modification, were adopted. This study introduces Co³⁺ doping to mitigate manganese loss in LMO, resulting in the preparation of cobalt-doped manganese-based ion sieves (LCMO). LCMOs prepared at various calcination temperatures and times were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). The XRD characterization results indicate that Co doping has no effect on the spinel structure of LMO. The SEM results confirmed the successful doping and uniform Co distribution in LCMO-5%. The XPS results show that a Co doping molar fraction of 5% can reduce the content of Mn³⁺ from 9.67% in the undoped precursor to 3.63%, which may be because the partial substitution of Mn³⁺ by Co³⁺ reduces the proportion of Mn³⁺. The lithium adsorption capacity increased from 39.299 to 41.708 mg·g⁻¹, and the manganese dissolution significantly decreased from 1.288% to 0.84%. The performance improvement of the LCMO greatly promotes the practical application of manganese-based ion sieves. The prepared 5% molar fraction of the Co-doped ion sieve (LCMO-5%) exhibited excellent cycling performance, and the adsorption efficiency of Li⁺ remained above 81% after five cycles. In the simulated lithium precipitation mother liquor, the separation coefficients of Li/Na and Li/K were 74.655 and 64.547, respectively, indicating that LCMO-5% effectively adsorbed Li⁺ from solutions containing high concentrations of Na⁺ and K⁺. Therefore, the LCMO-5% ion sieve exhibits outstanding application prospects for Li⁺ extraction from liquid lithium resources.