Identificação dos mecanismos de sorção em diferentes sólidos

• Autor(a) principal: Fagnani, Hélida Monique Cordasso
• Data de Publicação: 2014
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Estadual de Maringá (RI-UEM)
• Texto Completo: http://repositorio.uem.br:8080/jspui/handle/1/3769
• topic: Mecanismos de sorção; Zeólita NaY.; Sílica gel; Adsorção; Troca iônica; Brasil.; Engenharias; Engenharia Química

The existence of metals in wastewater can cause damage to both human health as industry, because metals like calcium and magnesium are responsible for water hardness. Therefore, it is essential to remove these contaminants. The processes of adsorption and ion exchange are methods that are efficient and low operating cost. However, are similar phenomena and may occur simultaneously, providing difficulties related to the design of equipment for the treatment of waste. Parameter such as the pH of the effluent may become a favorable process in an unfavorable. In this context, the aim of this study was to evaluate the mechanism of sorption of metal ions, in different solids. The study was conducted with an exclusively adsorbent material (silica gel) and one with high capacity ion exchange (zeolite NaY). Silica gel is an amorphous inorganic polymer, formed by tetrahedral units of SiO2 randomly distributed. The zeolite NaY is a crystalline material formed by tetrahedrons of SiO4 and AlO4-, which originate from a microporous structure. These adsorbents were characterized by zero point of charge (PZC), adsorption/desorption of N2, Fourier transform infrared (FTIR), X-ray diffraction (XDR). Kinetic and equilibrium investigation were conducted for the sorption of ions Ca2+ and Mg2+, in addition to measuring the pH of the solution after each test. These studies, together with the characterizations of the adsorbents, allowed identification of the mechanism of sorption of silica gel and zeolite NaY. The kinetic models of pseudo-first-order, pseudo-second-order and intraparticle diffusion were adjusted to the experimental data obtained. To equilibrium tests, models of Langmuir, Freundlich and Langmuir-Freundlich were adjusted. For zeolite NaY, the ion exchange mechanism is performed between the Na+ ion that is released with the ion Ca2+ or Mg2+ is sorbed. Thus, the difference that exists between the amounts sorbed by the released is the adsorption mechanism. Therefore, the mechanism that prevails in zeolite NaY is ion exchange. The PZC of zeolite NaY is 6.3 and the highest sorption capacity was at pH 4.3. When the adsorbent is submitted to a solution of pH different of PCZ, charges are generated on the surface of this material. In this case, the pH 4.3 of solution generates positive charges, these ions attract the chlorides that are present in the solution, therefore, attract metal ions from solution. Simultaneously, the ion exchange of Na+ ions from zeolite NaY with Ca2+ or Mg2+ ions that are in solution occurs. At pH 8.3, the zeolite NaY performs the ion exchange of Na+ ions with Ca2+ or Mg2+ ions of the solution, and due to the adsorbent surface is negatively charged, occurs also the attraction of metal ions Ca2+ or Mg2+ from solution. At pH 6.3, occurs only ion exchange of Na+ ion with Ca2+ or Mg2+ ion and adsorption, but this less intense. Silica gel, attractions between the surface and ions in solution occurs, but the mechanism is that adsorption takes prevail. At pH 4.7 only the adsorption occurs, at pH 6.7 the negative charges generated on the surface of the adsorbent attract Ca2+ or Mg2+ ions, and pH 2.7 the positive charges generated on the surface repel Ca2+ or Mg2+ ions. For zeolite NaY, the most representative model sorption data obtained was the pseudo-first-order, indicating that the sorption was preceded by diffusion through a boundary layer. For silica gel, the model pseudo-second-order better adjusted, assuming that strong adsorption is the stage that control the speed of the adsorption. In addition, the isotherm model best fit for zeolite NaY and silica gel was the Langmuir-Freundlich model. This model showed that the force of attraction adsorbent-adsorbate is stronger in PZC for both adsorbents. Concluding that in zeolite NaY the ion exchange has great power of attraction adsorbent-adsorbate and, other attractions that occur between adsorbent-adsorbate are weak forces. Similarly, has been observed in silica gel, theadsorption has great power of attraction adsorbent-adsorbate and other attractions are weak.