Estudo da utilização de biomassas lignocelulósicas como adsorventes para a remoção de Rodamina B

Abstract

Rhodamine B is a cationic dye widely used in dyeing processes because of its intense and stable color but is a carcinogenic, genotoxic and neurotoxic chemical. Its removal of wastewater is a difficult process due to its slow degradation and complex composition. In order to find a treatment for efficient removal, the present work has as objective to study four lignocellulosic biomasses (sugarcane bagasse, sugarcane straw, banana pseudocaule and eucalyptus sawdust) as adsorbents for the removal of the Rhodamine B dye of aqueous solutions. The lignocellulosic biomasses were used in natura and characterized by zero charge point determination (), Fourier transform infrared spectroscopy (FTIR) and scanning microscopy (SEM). For the optimization of the adsorption process of Rhodamine B, an experimental design of the type Rotational Central Compound Design for each biomass. The effects of biomass granulometry, pH of the dye solution and biomass dosage (g of dye solution / mL of dye solution) were analyzed, and according to the results only the biomass dosage showed statistically significant effects for the process of adsorption of Rhodamine B for the four biomasses studied. Through of analysis of ANOVA variance, the models obtained by the statistical analyzes were significant and predictive, since they presented a high correlation coefficient and p-value lower than the level of significance adopted (p <0.05), allowing to generate the contour curves for analysis of the regions. For the four biomasses studied the best biomass dosage was 0.49%, as it presented satisfactory values of adsorption capacity and percentage of removal of Rhodamine B. Among the four biomasses studied, eucalyptus sawdust had the highest values of adsorption capacity and percentage of removal of Rhodamine B. This biomass was selected for the kinetic study, the construction of the isotherms and the thermodynamic study. According to the kinetic study, the process equilibrates after 420 minutes and the data conforms to the kinetic model of Pseudo-second order. By the construction of the isotherms, the maximum adsorption capacity of 37.88 mg.g-1 was obtained by adjusting to the Sips model, which presented the best fit. From the thermodynamic study it was possible to obtain Gibbs Energy variation values which indicated that the adsorption process of Rhodamine B using eucalyptus sawdust is spontaneous and that as the temperature of the process increases, Gibbs energy decreases, indicating that the increase in temperature favors the adsorption process. The Enthalpy variation obtained (38,32 kJ.mol-1) indicates that the process is endothermic and chemisorising.