Síntese, caracterização e aplicação de zeólita para adsorção dos íons Mn e Zn em solução aquosa

Abstract

There is significant attention given to the pollution of water resources by inorganic contaminants, particularly those related to industrial activity, and in this context, the interest in developing treatment methodologies to promote the removal of these substances from aqueous media is growing. Adsorption is a promising alternative for the decontamination of effluents containing metal ions, and zeolites, in turn, have demonstrated good performance in this role. In this work, an attempt was made to synthesize zeolites using the sol-gel method, followed by hydrothermal treatment under microwave radiation, and subsequently evaluate the adsorption capacity of Mn²⁺ and Zn²⁺ metal ions by the synthesized material. The synthesis attempts involved variations in process parameters but did not result in the formation of zeolites, as confirmed by the absence of crystalline peaks in the XRD results. Therefore, commercial LTA-type zeolite was used, which was characterized and applied in the adsorption of Mn²⁺ and Zn²⁺ metal ions in an aqueous solution. The analysis results revealed that the studied commercial zeolite has a well-defined crystalline structure, confirmed by XRD. Scanning electron microscopy showed cubic-shaped particles with an average size of 5 µm. The FTIR results revealed the presence of Si-O bonds typical of aluminosilicates. Furthermore, the nitrogen adsorption isotherm demonstrated a Type II profile, indicative of a mesoporous to macroporous structure. The measured zeta potential was -45.0 mV, suggesting a highly negative surface charge in an aqueous medium, which is favorable for the adsorption of metal cations. To carry out the adsorption experiments, a study of the pH of the zeolite suspensions was conducted to avoid the precipitation of cations as hydroxides. Then, kinetic tests were performed by varying the contact time between the zeolite particles and the ion solutions at 10 mg.L⁻¹ and 50 mg.L⁻¹. The results indicated that the adsorption of Mn²⁺ and Zn²⁺ reached high percentages at all contact times. The adsorption tests were promising, demonstrating the high adsorption capacity of LTA zeolite, showing that the equilibrium time was achieved in just 1 minute, and the adsorption rate followed first-order kinetics. The adsorption isotherm tests showed that LTA zeolite demonstrated significant removal capacity for Mn²⁺ and Zn²⁺ ions, even at higher concentrations. The model that best fit both Zn²⁺ and Mn²⁺ was the Langmuir model. Thus, it was found that the adsorbent surface has good adsorption capacity for the ions, confirming the higher efficiency of the adsorbent for Zn²⁺ compared to Mn²⁺.