the superior affinity of the chelating resin for divalent cations compared to monovalent ones. The maintenance of reduced levels for both interferents, even under constant feed, confirms that the system operates efficiently in solution purification, with the retention mechanism predominantly associated with chemisorption at sites containing iminodiacetic groups. The analysis of the elution profile for the IRC 747 resin at a flow rate of 30 mL·s⁻¹ (Figure 3, Plots E and F) reveals a particular kinetic behavior regarding the removal of interfering species. For the Li+ ion, the breakthrough curve presents a profile similar to that obtained at 10 mL·s⁻¹, suggesting that the increase in the fluid superficial velocity does not promote significant changes in the early saturation of the bed against the high concentration of the majority electrolyte. However, the elution profile of sodium (Na+) exhibits a sharp increase within the first 10 minutes of the assay, reaching concentrations above 35 mg·L⁻¹. This behavior can be attributed to the leaching of residual sodium remaining from the resin synthesis or conditioning process, which contaminates the solution during the initial stages of percolation. Despite the initial concentration peak, the system demonstrates purification efficiency over time, as the Na+ concentration in the effluent progressively decreases, reaching approximately 10 mg·L⁻¹ at 60 minutes. This final value is substantially lower than the influent concentration of the interferent (25 mg·L⁻¹), evidencing the selective retention capacity of the resin even under more severe hydrodynamic conditions. Calcium (Ca2+), in turn, maintains residual concentrations below 5 mg·L⁻¹ after the initial transient, corroborating the high selectivity of the chelating functional groups for divalent cations over monovalent ones, according to the affinity series principles for iminodiacetic acid-type resins. (A) (B) 111
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