(C) (D) Figure 04: A) Resin IRC747 to Li e Na; B) Resin IRC747 to Ca e Mg, C) Resin IRC748 to Li e Na; e D) Resin IRC748 to Ca e Mg. Source: Authors 3.3. IRC747 resin column under continuous flow conditions In fixed-bed column assays operated under continuous flow conditions using IRC 747 resin (Figure 4A–F), removal rate analysis evidenced the significant influence of volumetric flow rate on system performance. The applied flow rates directly impacted the contact time between the liquid phase and the resin, resulting in distinct concentration profiles over time. As presented in Figure 4, experiments conducted at flow rates of 10 mL·s⁻¹ (A and B), 20 mL·s⁻¹ (C and D), and 30 mL·s⁻¹ (E and F) exhibited differentiated kinetic behaviors, reflecting the influence of hydrodynamic conditions on ion exchange efficiency. At the lowest evaluated flow rate (10 mL·s⁻¹), no significant variations in Li+ concentration were observed over time, indicating a regime close to equilibrium between adsorption and desorption processes. Under these operational conditions, effective ion exchange for this element was not evidenced. For calcium and sodium ions, the lowest concentrations were recorded at 10 and 50 minutes, respectively, suggesting more efficient initial removal followed by potential partial saturation of the active resin sites. At the intermediate flow rate of 20 mL·s⁻¹ (Figure 4C–D), Li+ ion behavior remained relatively stable throughout the experimental interval, with a discrete decrease observed at 40 minutes, followed by a return to stability in the subsequent point. This behavior indicates a more uniform interaction regime between the solute and the fixed bed, suggesting operational stability of the system under this flow condition. For sodium and calcium ions, the best removal results occurred at 60 minutes, indicating that this operational condition favored the ion exchange process performance. The concentration profiles of sodium (Na+) and calcium (Ca2+) evidence the high selectivity of the polymeric matrix for metallic impurity retention. Sodium concentration shows an initial stability trend around 7.5 mg·L⁻¹, followed by a slight increment to approximately 9 mg·L⁻¹ at 40 minutes, and a subsequent decrease to 5 mg·L⁻¹ at the end of the 60-minute cycle, a behavior suggesting a dynamic ionic displacement process. In parallel, calcium presented significantly lower residual concentrations, varying between 1.5 and 4 mg·L⁻¹, which confirms 110
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