Biossorventes – biomassa de aguapé e esferas de alginato/goma do cajueiro – para adsorção de azul de metileno.

Abstract

In this work was carried out an extensive investigation of the adsorption properties of synthetic dyes on different parts (rhizome, root, stolon and petiole) of Eichhornia crassipes (water hyacinth) and a comparison with the adsorption capacity of the biopolymer alginate beads doped with water hyacinth biomass. The biomasses and spheres were structurally characterized by infrared spectroscopy, scanning electron microscopy - SEM and thermal analysis (thermogravimetric analysis - TGA and Differential Scanning Calorimetry - DSC). The kinetics of adsorption processes were monitored by UV and visible spectroscopy - UV / VIS and the data applied to the models of Freundlich and Languimir. Synthetic anionic dyes (methyl orange), cationic (methylene blue) and azo (indigo carmine) were used in the investigation. Adsorption studies was obtained, under controlled agitation of 70 rpm and temperature ranging between 25°C and 45°C at concentrations of dye in the range 10-250 mg/L and pH 2-12. The best results were achieved with a dye initial concentration of 100 mg/g, an initial quantity of 60 mg biosorbent, at temperature of 45 °C and at basic pH. Among the tested dyes, methylene blue exhibited the best adsorption capacity. The study of adsorption kinetics showed a better fit to the model of pseudo-second order and intraparticle diffusion is involved in the mechanism of adsorption. In the study of the isotherms, the result shows best fit to data by the Langmuir and Freundlich equations, with a maximum capacity of adsorption of methylene blue dye from 819.7 mg/g at 25 °C, to the root. A temperature increase caused an increase in system adsorption capacity and also led to an increase in time to the system reach equilibrium. The values of the rate constant for pseudo-second order increased with increasing temperature. An increase in initial dye concentration caused an increase in the amount of dye adsorbed. The activation energy for all biosorbents are in the range 20-40 kJ.mol-1 demonstrated that the adsorption processes are physical. The thermodynamic parameters ∆H°, ∆S° and ΔG°, for most biosorbents indicate that the process is exothermic in nature, spontaneous and favorable, except for the sphere of ALG/GC/Biomass where values obtained showed endothermic nature. The desorption study showed that the biosorbents can be reused.