ARGILAS ENRIQUECIDAS COM ÍONS FÉRRICOS PARA REMOÇÃO DE CORANTES ANIÔNICOS E SEU REUSO COMO PIGMENTOS HÍBRIDOS

Abstract

In this work, smectite clays (Argel and Volclay) were modified with ferric ions (Argel-Fe and Volclay-Fe) by replacing exchangeable cations with Fe (III). The purpose was to modify the surface charge of the clays, from negative to positive, and use them as sorbents in the removal of seven anionic dyes (canary yellow, gold yellow, turquoise blue, pink, black, flag green and strawberry red) in aqueous medium, in mono and multicomponent systems. The unmodified, modified clays and after sorption of the dye mixture (MC) were characterized by measures of zeta (ζ) potential, X-ray fluorescence (XRF), X-ray diffraction (XRD), Spectroscopy in the infrared (FT-IR) and visible (UV/VIS) and Colorimetry. The change in the net surface charge of the clay minerals was confirmed by the ζ potential measurements, while the combined analysis of the other techniques indicates an intercalation of Fe (III) without changes in the crystalline structure of the clay minerals. The sorption kinetics and isotherm were studied for mono and multicomponent systems; the applicability of the Pseudo-First and Pseudo-Second order kinetic models and the Langmuir, Freundlich and dual-site Langmuir-Freundlich (LF) isotherm models were tested for the systems. The sorption capacity of Argel-Fe and Volclay-Fe in mono and multicomponent studies was higher than the capacity exhibited by other sorbents for anionic dyes. The sorption kinetics indicates that equilibrium is reached quickly, in approximately 5 min. The sorption mechanism of the anionic molecules of the dyes occurs by electrostatic attraction between the Fe (III) ion and the sulfonic groups, and by Lewis acid-base interaction between Fe (III) and the free electrons of the nitrogen atom present in the dye molecules. The enrichment of the clays with Fe (III) added functionality to the clays and generated a new material, with high sorption capacity of dye molecules with anionic nature in aqueous medium. The material after sorption was used as an organic-inorganic hybrid pigment for colorless paint, presenting good coverage, adhesion, color fixation and quick drying in addition to being non-toxic and odorless.