Produção e caracterização de carvão ativado a partir de escamas de peixe para remoção de 2,4-D de meios aquosos

Abstract

The growing use of pesticides has generated a number of serious health and environmental problems in the long term, as they are commonly applied incorrectly on agricultural plantations and in excessive doses. Thus, given their persistent feature, such compounds end up affecting water resources and accumulating in the environment. In general, the available treatments for water treatment plants are not effective enough to remove or degrade such compounds and consequently to mitigate their effects. In this context, currently, there is a great need for the development of efficient and low-cost technologies for the treatment of this type of compound. Amongst the treatment techniques, adsorption processes have high potential, due to the possibility of application to pollutants in low concentrations, which are commonly presented by such compounds in water bodies. With regard to the adsorption technique, most of the costs associated with the process involve the adsorbent material, hence the production of low-cost and effective adsorbent materials for a given purpose is a critical step in the process. In view of this, the objective of this research was to use fish scales as a precursor material for the production of activated carbon in order to apply in the removal of the 2,4-D herbicide from aqueous media. After the production of two activated carbons (pre-carbonized active carbon: PCAC and fish scale in natura activated carbon: CAIN), preliminary tests were performed to evaluate the adsorption capacity as a function of pH (2; 4; 6.5; and 10). Subsequently, for the best activated carbon at the optimal pH condition, adsorption kinetic studies were performed in different initial concentrations (5, 10, 20, 30 and 50 mg/L), in order to obtain equilibrium data; and in different temperatures (30, 40 and 50°C), in order to obtain thermodynamic data, to support the understanding of the mechanisms involved in the process. In addition, the activated carbons were characterized in terms of thermogravimetric analysis (TGA), point of zero charge (pHpcz), infrared spectroscopy with Fourier Transform (FTIR). It was verified that the CAPC at pH 6.5 presented higher adsorption capacity, although it presented adsorption potential in a wide pH range. From the kinetic study, it was observed an equilibrium time of approximately 6 h for the temperature of 30°C and 12 h for 40 and 50°C, and the maximum adsorption capacity (q = 11.49 mg/g) occurred at 30°C. In addition, the equilibrium data were better described by the BET model, which is associated with multilayer adsorption and also with adsorption enthalpy (ΔHads = -39.6 kJ/mol) characteristic of exothermic and physisorption adsorption. In general, the activated carbon produced showed efficiency in removing the herbicide, and desirable characteristics such as versatility over a wide range of pH and mild temperature conditions, which brings practical advantages for use in treatment systems. Thus, based on the results obtained in this work, as well as the residual character and abundance, the activated carbon from the fish scale presents potential for application in the treatment of water and even of industrial effluents containing the 2,4-D.