Estudo adsortivo da casca da Castanha-do-Brasil (Bertholletia excelsa) no tratamento de água contaminada com corante.

Abstract

The industrial sector is responsible for a variety of environmental impacts, notably the contamination of water bodies due to inadequate waste disposal. Among the most significant pollutants originating in the textile industry are dyes, used to impart colors to manufactured products, thus expanding the range of shades available. Conventional water treatment is not suitable for removing dyes, requiring specific tertiary treatment methods. Without this adequate treatment, contaminated water returns to water bodies with high concentrations of dyes. A viable option for removal is adsorption, a mass transfer process that uses an adsorbent material to remove substances present in fluids. Bioadsorbents, such as Brazil nut shell, appear as promising alternatives, reducing waste generation, costs with synthetic adsorbents and enabling the reuse of discarded materials. In the present study, the characterization of the bioadsorbent from the Brazil nut shell was carried out and its potential in removing the dye Safranin from contaminated water was investigated. Spectroscopy analysis in the Fourier Transform Infrared (FTIR) region identified characteristics such as OH stretches, C-H bonds, and C=O and C-O groups, typical of holocellulose and lignin, while X-ray Diffraction (XRD) confirmed the noncrystallinity of the material and characteristics of the Brazil nut shell. According to the affinity test studies, it presented satisfactory results for removing the safranin dye. Kinetic models were evaluated to understand the adsorption mechanism, with the pseudo-second order model being the one that best fitted the data, corroborated by the coefficient of determination (R²) values close to 1 and low mean relative error (ARE). Furthermore, the equilibration time was determined to be 300 minutes. The adsorption isotherms were studied to understand the influence of the adsorbate concentration in the liquid phase, with the Sips model being the one that best represented the adsorptive process. Thermodynamic studies showed that the adsorptive process is endothermic due to the positive value of the enthalpy change, due to the negative value of the Gibbs free energy change, it can be seen that the process occurs spontaneously and the entropy change presented a positive value resulting from the disorder of molecules after the adsorption process. Therefore, the respective characterized and presented a sustainable alternative for treating water contaminated with the dye Safranin through the reuse of Brazil nut waste.