Síntese e caracterização de zeólitas nanoestruturadas para adsorção de íons Mn2+ em meio aquoso

Abstract

An Increasing attention has been paid to water resources pollution by heavy metals. One of the main environmental issues involved in industry and mining activities is the treatment of effluents generated by them. In mining, acid mine drainage is a quite common problem. In this context, there is a growing interest in the development of methodologies for the treatment of water which efficiently promote the removal of these substances, such as the adsorption process. This work’s main interest was the obtaining of zeolite nanoparticles and the evaluation of their adsorption capacity for Mn2+ ions dispersed in aqueous solutions. The zeolite particles were synthesized in the powder form by the sol-gel method, followed by a hydrothermal aging under microwave radiation and several syntheses were performed. The proportion of reactants, the reaction medium temperature, the hydrothermal aging time and the source of silica were varied during the syntheses, in order to establish the influence of these parameters on the structural and morphological particles’ characteristics. The first tests aimed at the obtaining of a new zeolites formation route, using crystalline silicon dioxide as reagent and did not prove efficient in the formation of the zeolite structure. Most of the crystalline silica remained unreacted and some zeolite particles appeared as a minor impurity. The values of surface area and pore volume founded for the synthesized material were very low compared to the commercial zeolite. In the following syntheses, conducted with pyrogenic amorphous silica, the GIS zeolite structure was formed when the temperature adopted was 140ºC and the hydrothermal treatment time was one hour. Adsorption tests were conducted to evaluate the Mn2+ ions removal using this zeolite as adsorbent. The ion adsorption was highly favorable for the Na-P1 zeolite, with the highest removal percentage obtained at pH 8, with a particle concentration of 1g/L, and the process was controlled by the pseudo-second order kinetic model. The adsorption isotherm of the processes fitted to the Langmuir model, with the maximum adsorption capacity calculated by the method of 44,05mg of Mn2+ per gram of zeolite.