observed in sodium values over time indicates that the rate-limiting step occurs predominantly in the initial moments of contact between the solution and the adsorbent material, with a regime close to system equilibrium subsequently established. The work of Foureaux (2021) found similar behaviors for Amberlite IRC 747 resin in the removal of cobalt, nickel, and copper ions. This corroborates that, in this context, the distribution of species within and on the surface of the resins exerts a direct influence on the performance of the ion exchange process, such that the adsorption capacity tends to increase according to the quantity of active sites available on the surface. Figure 03: Ion exchange capacity of IRC747 and IRC748 resins for Li and Na. Source: Authors. 3.2. Batch removal of contaminants The experimental data presented in Figure 4A-B demonstrates significant differences in the resin's exchange capacity regarding the various cations present in the solution. A higher affinity for monovalent ions (Figure 4A and C) is observed, particularly for sodium and lithium, compared to the divalent calcium and magnesium ions (Figure 4B and D). This trend is corroborated by the loading capacity values at time (qt), which, after 60 minutes of contact, reach 139.26 mg·g⁻¹ for sodium and 66.04 mg·g⁻¹ for lithium, evidencing higher retention efficiency for monovalent cations under the evaluated experimental conditions. The removal kinetics for sodium and lithium ions exhibit a profile of continuous decrease in solution concentrations over the 60-minute interval, indicating that the thermodynamic equilibrium of the system was not fully established during the monitored period. The high initial concentration of these ions establishes a significant driving force, favoring the diffusion of analytes from the solution to the active sites of the resin. 108
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