Navegando por Palavras-chave "Reciclagem de alumínio"

Agora exibindo 1 - 1 de 1
  • Imagem de Miniatura
    Item
    Acesso aberto (Open Access)
    Uso de zeólitas na remoção de amônio de efluentes da indústria de reciclagem de alumínio
    (Universidade Federal de São Paulo, 2013-10-15) Wu, Luis Fernando [UNIFESP]; Shinzato, Mirian Chieko [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Brazil is the world's largest recycler of aluminium. However, this activity produces ammonia/ammonium-rich liquid effluents, which may cause eutrophication and intoxication of some aquatic species when discharged into local water bodies. With this issue in mind, the aim of this study was to analyze the use of natural zeolites in the treatment of this effluent for the removal of ammonium ions and for the reuse of saturated minerals as slow-release fertilizers. Two samples of rock containing zeolites were studied, one from Cuba (ZC) and other from the Northeastern Brazil (ZB). These samples, which are sandstones with zeolitic cement, show different mineralogical composition. ZC sample is composed of the following zeolite minerals: clinoptilolite (98%) and modernite (2%), whereas ZB sample is composed of quartz (72%), stilbite (15%) and smectite (13%). However, the chemical composition of both samples is similar (SiO2, Al2O3, CaO, Fe2O3, Na2O, K2O and MgO), although the percentages of chemical compounds are different. Additionally, ZC sample has larger specific superficial area and greater cation exchange capacity when compared with ZB sample. Before using zeolites as adsorbents of ammonium ions from the effluent, batch tests for removing ammonium ion (NH4+) from synthetic solutions using zeolites were carried out aiming to evaluate the effect of the contact time, temperature, pH, NH4+ initial concentration, and ion competition. It was observed that after 30 min the adsorption equilibrium was achieved and that the temperature does not effectively affect the removal of NH4+. However, pH is a determining factor in the removal of NH4+ ions, and the optimum pH range is from 4 to 8, since ionized ammonia (NH4+) predominates. After tests with synthetic solutions were performed, ZC zeolite (which achieved the best results in removing NH4+) was tested for the treatment of effluents from the aluminium recycling industry. During 1 year, this effluent was sampled and analyzed in order to define some of its main parameters, such as pH, electrical conductivity and inorganic species concentrations (N-NH3, Na+ and K+). The data recorded during the monitoring period showed pH values and N-NH3 concentrations above those established by the CONAMA (Brazilian National Environment Council) N°430/2011 for the discharge of effluents into water bodies (N-NH3 concentration up to 20 mg.L-1 and pH between 5 and 9), as well as high concentrations of dissolved salts (Na+ and K+). Removal of NH4+ present in industrial effluent was carried out in fixed-bed column filled with zeolites. In this system, the effluent of the aluminium recycling industry was percolated under constant-flow conditions until NH4+ saturation was reached. The test results showed that the N-NH3 removal capacity of zeolites is high (14.38 mg.g-1), when the effluent pH is kept below 9 for 4.5 hours at the constant-flow rate of 14 mL.min-1, i.e., within the limits established by the CONAMA N°430/2011. On the other hand, this study also showed that the efficiency of zeolite in removing NH4+ is reduced in up to 45% when other ions, such as potassium, are present in the solution. When sodium is present, the efficiency is reduced in up to 21%. This behavior shows that the zeolite exchange sites adsorb preferentially cations with lower hydration energy. After zeolites were saturated with NH4+, their use as slow-release fertilizers was tested with two different methods: leaching with water and acid solution (acetic acid, pH = 4.9), and soil incubation. The tests indicated that NH4+ is less susceptible to loss by leaching, since water extraction released only 3% of the N-NH3 retained in the zeolite pores, and acid solution extraction released 12%. The NH4+ zeolites, in turn, also prevent nitrification of NH4+ by bacteria, and medium acidulation. Overall, it was observed that the use of natural zeolites in the treatment of industrial effluents, such as effluents from the aluminium recycling industry, may reduce N-NH3 concentration and pH of the medium. It also allows minerals saturated with NH4 to be reused as slow-release fertilizers.