Estudo da adsorção da espécie metálica zn2+ em resinas de troca iônica para a remoção de poluentes de efluentes aquosos

Abstract

This study aimed to investigate the removal of Zn2+ ions from aqueous effluents using an ion exchange resin, with emphasis on optimizing adsorption parameters, validating the analytical method, and applying it to real samples from reverse iron ore flotation. Initially, the samples were subjected to acid digestion according to the EPA 3005A method, involving acidification with HNO3, overnight digestion, addition of HCl, and controlled heating, ensuring complete solubilization of the metals present. Quantification was performed by flame atomic absorption spectrometry (F AAS), with optimized instrumental parameters and validation based on figures of merit, showing high linearity (R2 = 0,9998), a detection limit of 0,02 mg L-1, and a quantification limit of 0,06 mg L-1. The adsorption studies evaluated the influence of parameters such as pH, resin mass, contact time, and initial metal ion concentration. pH was found to be a determining factor, with maximum efficiency at pH 2,0, where competition with H+ ions is minimized without Zn2+ precipitation, achieving removal efficiencies above 97%. The adsorbent mass also directly influenced the process, with 0,6 g identified as the optimal condition, providing removals of up to 95% for more concentrated solutions. Adsorption kinetics revealed a rapid process, with equilibrium reached in aproximately 20 minutes and removal efficiencies above 93%. Kinetic modeling showed better agreement with the pseudo-second-order model (R2 = 0,9999), suggesting that the predominant mechanism is chemical in nature, associated with ion exchange between Zn2+ ions and sulfonate groups in the resin. Adsorption isotherm analysis showed a typical saturation behavior, with data well described by the Langmuir and Freundlich models. The Langmuir model exhibited an excellent fit (R2 = 0,9992), indicating monolayer formation and a maximum adsorption capacity of approximately 21,66 mg g-1. The Freundlich model also showed a food fit (R2 = 0,9558), with an n value of 5,70, indicating high affinity between adsorbent and favorable adsorption on a heterogeneous surface. Desorption experiments demonstrated that the use of a 10% (v v-1) HCl solution was highly efficient, achieving nearly 100% recovery of Zn2+ ions within approximately 40 minutes, whereas the 5% solution showed lower efficiency (68%). These results confirm the feasibility of resin regeneration and reuse, contributing to the sustainability of the process. Application of the method to a real effluent sample showed that Zn2+ was initially below the detection limit, requiring a spiking step with a known concentration of the metal to evaluate process efficiency. After spiking, adsorption experiments conducted under optimize conditions demonstrated high removal efficiency, with values close to 99% and low experimental variability (RSD = 0,12%), confirming the method’s high reproducibility. These results indicate that the resin performs effectively even in complex matrices, efficiently removing Zn2+ under realistic conditions, thereby reinforcing its potential application in wastewater treatment and selective metal recovery.