Utilização da concha de sururu (Mytella falcata) na remoção de corantes de solução aquosa

Abstract

Dyes are substances widely used in industries, whether for dyeing textile fibers, coloring food, cosmetics, automobiles and other applications. When in contact with water resources, some dyes can cause serious damage to fauna and flora, also offering risk to humans. As a way to reduce the amount of these substances in the effluents, the present work uses the sururu shells (Mytella falcata), for the removal of five dyes (acid fuchsin, auramine o, basic fuchsin, malachite green and crystal violet) in aqueous solution. Initially, affinity tests of these dyes were carried out with the raw materials and heat treated (pyrolysate and calcined), then the best adsorbate and the best adsorbent material were defined and chosen, continuing the studies. The natural adsorbent agent was characterized via thermogravimetric analysis (TG/DTG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDS). In the adsorption tests in finite bath, removal percentages above 90% were obtained. The maximum adsorption capacity of the Mytella falcata shell reached a value of 539.24 mg.g-1 at 60o C, which is higher than that obtained by several similar materials, applied for the removal of dyes from aqueous solution. The results of the kinetic study indicated that the process follows the pseudo-second order model and that the adsorption mechanism is based on multiple stages, bulk diffusion, intraparticle diffusion and, finally, microporous diffusion. The balance data were better adjusted to the Sips model, with higher values of R2 and lower values of relative average error (ARE) for all temperatures studied (30, 40, 50 and 60oC). The regeneration/reuse test by ultraviolet photo-regeneration indicated that the adsorbent agent maintained removal percentage values above 85% for the 5 cycles evaluated. Thermodynamic studies suggested that the adsorption is endothermic, governed by a process of chemisorption and that there were structural changes on the surface of the solid. In short, the sururu shells have been successfully applied to remove the malachite green dye from the water, proving to be a promising alternative biosorbent.