Síntese e caracterização de resina à base de melamina, tioureia e formaldeído para remediação de mercúrio em amostras ambientais

• Main Author: Freire, Emerson dos Santos
• Publication Date: 2019
• Format: Master thesis
• Language: por
• Source: Repositório Institucional da Universidade Federal de Alagoas (UFAL)
• Download full: http://www.repositorio.ufal.br/handle/riufal/6619
• topic: Água – Teor de Elementos traços; Resinas; Polimerização; Água contaminada; Produtos químicos; Mercúrio; Mundaú, Lagoa (AL); Water - Content of trace elements; Resin; Polymerization; Contaminated water; Chemicals; Mercury; Mundaú Lagoon; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

The contamination of aquatic environments by trace elements, such as Hg, has revealed the importance of developing studies that involve the determination and removal of these elements in aquatic environments, highlighting, in this context, the use of resins that act as promising chelating agents for the removal of metals in water, due to the multiadsorbent function of these materials. The objective of this work was to synthesize a resin based on Melamina-Tiourea-Formaldehyde (MTF), characterize and apply in aqueous samples of the Mundaú lagoon, Alagoas - Brazil. The resin was synthesized by a polymerization reaction in a molar ratio of 1:5:1, melamine, formaldehyde and thiourea, respectively. By way of comparison, Melamine-Urea-Formaldehyde (MUF) was also synthesized under the same conditions as MTF. The characterization of the resin was performed by X-ray diffraction (XRD), adsorption-desorption analysis of nitrogen by the BET method, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The application was initially performed with standard of inorganic Hg(II). Resin mass (5 to 50 mg), standard concentration (5 to 8000 μg L-1) adsorption time, pH (5.0, 7.0 and 9.0) and study of adsorption kinetics were evaluated. After optimization, the adsorption profiles of different mercury species by MTF resin (Hg(II); CH3Hg+; C2H5Hg+; PhHg+) were evaluated, initially in standards and then in water samples collected in Mundaú Lagoon, by comparing the concentrations before and after adsorption, which were determined using atomic fluorescence spectrometry with cold vapor (CV AFS). From the DRX analysis, it can be inferred that MTF and MUF resins have characteristics of amorphous material. The BET data revealed information about the pore volume of the MTF resin, the diameter and the surface area with measurements of 0.027 cm3 g-1, 33 Å and 47.7 m2 g-1, respectively. Through TGA characterization, it was observed that MTF and MUF resins have a thermal stability between 75 and 80 °C and their combustion processes are composed of three stages. MTF does not have a hygroscopic profile. The images obtained by SEM showed an irregular structure with microspheres for MTF and a more compact structure, with a rough surface for MUF. Preliminary adsorption tests performed with standard solutions of Hg(II) were promising and thus, the optimization of adsorption conditions were performed with inorganic Hg(II) standards.Applying the results in the pseudo-primary and second order and Weber-Morris kinetics equations, a better linearity of the results was observed when applied to the pseudo-second order equation for adsorption of Hg(II) by MTF. The adsorption of inorganic Hg(II) by MTF was immediate in all pH conditions, reaching 92 % when using mass of 30 mg of resin. With a view to environmental application, the pH condition selected was pH 7.0. The maximum adsorption capacity was not reached for the concentration range used (5 to 8000 μg L-1of Hg(II)), being increasing. The adsorption capacities for each species of mercury used were: 87 % of Hg(II); 85 % of CH3Hg+; 93 % of C2H5Hg+ and 96 % of PhHg+ at pH 7.0. The results demonstrated a promising application of synthesised resin for the removal of Hg(II) species in aquatic environments contaminated with this element.