2551 lithium cobalt oxide (LiCoO2). The production chain frequently utilizes lithium carbonate (Li2CO3) or lithium chloride (LiCl) as initial feedstocks for the crystallization of lithium hydroxide monohydrate (LiOH·H2O). The present study aims to investigate the dynamic performance of IRC 747 and IRC 748 resins to identify operational conditions that favor maximum selectivity for divalent contaminants over minimum retention of monovalent cations. Preliminary results indicate that the IRC 747 resin exhibits high efficacy, removing up to 76% of Ca2+ and 92% of Mg2+, thus consolidating its position as a robust alternative for the production of high-purity lithium solutions. Considering the requirement to refine lithium hydroxide (LiOH) solutions to battery-grade standards, this work aims to investigate the operational conditions that promote maximum selectivity of AmberSep™ IRC 747 and IRC 748 resins toward divalent calcium (Ca2+) and magnesium (Mg2+) ions. The research is based on the analysis of the dynamic behavior of the fixed-bed system, aiming to identify the equilibrium point at which the polymeric matrix exhibits minimum affinity for monovalent cations, such as lithium (Li+) and sodium (Na+). This differentiation in affinity is crucial to mitigate the undesirable retention of the analyte of interest, ensuring that the final polishing process results in a high-purity solution with the lowest possible mass loss. Specifically, the study evaluates the influence of flow rate variations (10 to 30 mL·min⁻¹) and ion exchange capacity on the mass transfer zone. Therefore, it seeks to establish a methodological protocol that utilizes selective chemisorption to remove contaminants that compromise the lifespan and safety of lithium-ion battery cathodes, such as LiFePO4 and LiCoO2. The ultimate goal is to validate the effectiveness of these chelating resins in consecutive sorption-desorption cycles, ensuring the technical and economic viability of producing purified precursors (TADESSE et al., 2019). The attainment of lithium hydroxide (LiOH) solutions meeting battery-grade specifications necessitates the elimination of metallic cations such as Mg2+, Ca2+, and Na+, a task for which ion exchange technology demonstrates technical superiority over conventional chemical precipitation. While precipitation processes are constrained by the thermodynamic equilibrium of the solubility product (Ksp), which precludes reaching ultra-high purity levels, chelating resins enable the polishing of solutions to concentrations in the parts per billion (ppb) range without the requirement for additional chemical reagents. The efficacy of this separation arises from the specific interaction between the functional groups of the polymeric matrix and the contaminants, although the economic viability of the system demands rigorous control of the competitive adsorption of the analyte of interest, lithium (Li+), to prevent significant mass losses during purification (BING et al., 2020). The objective of this study was to evaluate the efficiency of IRC 747 and IRC 748 ion-exchange resins in the purification of lithium hydroxide ($LiOH$) solutions intended for crystallization and subsequent lithium-ion battery manufacturing, as an innovative technique to replace chemical precipitation. Although ion exchange is a consolidated method for obtaining lithium compounds from brines, its application in the refining of $LiOH$ derived from spodumene ore still lacks extensive scientific and industrial exploration. To substantiate such feasibility, the work investigated the ion-exchange capacity of the resins, the adsorption kinetics in batch systems, and the dynamic behavior of the system under continuous flow in a fixed-bed regime. 2. METHODS AND MATERIALS The Amberlite™ IRC747 and IRC748 cation exchange resins, manufactured by DuPont®, were evaluated regarding their efficiency in purifying lithium-containing solutions, a precursor stage in the crystallization process aimed at obtaining battery-grade LiOH. The IRC747 resin is applied for the separation of ions such as zinc and lead, as well as for brine purification (Abusultan et al., 2023). Similarly, the IRC748 resin is utilized for brines, notably in the removal of trace metals and metal recovery. Table 1 presents the primary characteristics and technical specifications for each resin.
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