2553 Figure 1: Batch kinetic test. (1) Heating plate; (2) Resins; (3) 1 mol·L⁻¹ LiOH solution; (4) Beaker; (5) Magnetic stirrer; (6) Thermometer. Source: Authors. The fixed-bed column system operating under continuous flow conditions is schematically presented in Figure 2. The experimental procedure consisted of percolating a lithium hydroxide (LiOH) solution, at a concentration of 1 mol·L⁻¹, through the polymeric bed. To ensure operational stability and hydrodynamic precision, a high-precision peristaltic pump (Masterflex L/S®) was employed to promote the controlled displacement of the liquid phase through the column, maintaining a constant flow rate throughout the experiment. Following the saturation of the bed by the LiOH solution, a washing step with deionized water is performed to remove the excess interstitial solution and recover the unadsorbed lithium. Subsequently, the elution of the retained divalent contaminants (Ca2+ and Mg2+) is promoted through the passage of a hydrochloric acid (HCl) solution at concentrations of 1 to 2 N. This regeneration process promotes the desorption of metallic ions from the chelating matrix, which enables the reuse of the resins in subsequent cycles and the recovery of the original ion-exchange capacity of the system. After passing through the adsorbent bed, the effluent was directed to a collection reservoir, from which aliquots were withdrawn at regular 15-minute intervals for analytical monitoring. The adoption of a continuous flow regime is a fundamental aspect of the kinetic evaluation of the process, as it enables the maintenance of a nearly constant concentration gradient at the solid-liquid interface. Under these conditions, the resin remains continuously exposed to the initial electrolyte concentration (C0), preserving a high driving force for mass transfer throughout the assay. Such conditions mitigate effects associated with diffusional resistances and favor the progressive occupation of the active sites available in the polymeric matrix, allowing the system to approach its maximum adsorption capacity under equilibrium conditions. Figure 2: Continuous flow column test. Legend: (1) 1 mol·L⁻¹ LiOH solution; (2) Beaker; (3) Tubing; (4) Peristaltic pump; (5) Valves; (6) Resin column; (7) Purified solution; (8) Reservoir. Source:: Authors. 3.RESULT AND DISCUSSION 3.1 Ion exchange capacity of the resins Figure 3 illustrates the adsorption behavior of the investigated resins throughout the experimental assay. For the IRC747 resin, an increase in lithium retention capacity was observed, rising from 49.30 mg·g⁻¹ to 66.04 mg·g⁻¹ during the experiment, indicating a progressive evolution of the active site occupation process. In contrast, the rapid saturation of calcium in both resins reinforces that, under conditions of low ion concentration in solution, the limited availability of ionic species prevents the development of significant concentration gradients within the solid phase. Consequently, the IRC747 resin exhibits superior kinetic performance in relation to lithium during extended operations, demonstrating a gradual increase in adsorption
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