Adsorção do glifosato utilizando materiais naturais e resíduos industriais: equilíbrio e cinética

Abstract

Contamination of water bodies by glyphosate, one of the most widely used herbicides in agriculture, and its main metabolite AMPA, represents an environmental and public health concern. In this study, the removal of these compounds by adsorption was investigated using natural materials and modified industrial waste. Different materials were evaluated, including slag, bag filter smoke and sand from the foundry industry, as well as clinoptilolite zeolite and activated carbon of commercial origin. The modification of the materials was performed by immersion in solutions of different reagents such as CuSO₄, SDS, AgNO₃, Fe(NO₃)₃, CTAB and ZnO. The comparative study of materials with and without modification was developed by analyzing the effect of solution pH and chemical modification of the materials on glyphosate removal. The material with the highest removal was selected for dosage (0.625, 1.25, 2.5, 2.5, 5.0, 10, 25 g L-1), kinetics (0.17, 0.5, 1, 2, 4, 8, 16, 24, 36, 54 and 72 h) and isotherm (0.25, 0.5, 1.0, 1.5, 2.5, 5.0 and 7.5 mg L-1) studies. The adsorption studies were carried out in a batch system, volumes of 40 mL and temperature of 25 °C. Transmittance analyses were performed by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) with EDS microprobe, BET analysis and determination of Zeta Potential (ZP). The determination coefficient (r2), correlation coefficient (r) and chi-square (χ2) were used to determine the calibration curve and adjust the kinetic and equilibrium models. In the study of adsorption between different materials with and without treatment, the bag filter smoke in its natural form (without modification) showed the best performance (100% removal). The experiments demonstrated that the removal of glyphosate by smoke was not influenced by pH, reaching 100% removal under the conditions tested (pH 4, 7 and 10), with a quantification limit of the analytical method of 0.025 mg L⁻¹. In the dosage study, using an initial glyphosate solution of 5 mg L⁻¹, removal was total for a smoke dosage of 25 g L⁻¹ and reached 87.91% for a dosage of 1.25 g L⁻¹. This last concentration was considered the most viable, balancing efficiency and lower material consumption, in accordance with water potability standards. Adsorption reached equilibrium after 8 hours of contact, with a maximum capacity of 5.39 mg g⁻¹. The process kinetics followed the Avrami model, while the adsorption isotherm was best represented by the Temkin model. The quantification of glyphosate in the samples was determined by LC-MS after derivatization with FMOC-Cl. The results confirm that tobacco is highly efficient in glyphosate removal, eliminating more than 95% of an initial concentration of 5 mg L⁻¹ without the need for pH adjustment. These findings reinforce the potential of residual materials as sustainable alternatives for contaminant removal, contributing to the improvement of polluted water treatment strategies.