Navegando por Assunto "Argilas aniônicas"

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Acesso aberto (Open Access)
Síntese de hidróxidos duplos lamelares do sistema Cu, Zn, Al-Co2: propriedades morfológicas, estruturais e comportamento térmico
(Universidade Federal do Pará, 2009-09-05) SANTOS, Sheila Silva dos; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
Hydrotalcites are anionic clays, also known as layered double hydroxides (LDH), which have structure formed by stacking layers of mixed hydroxides of divalent and trivalent cations with hydrated anions in the spaces between those layers. Your structure is similar to brucite mineral. This compounds can be represented by general formula: M2+ 1- x M3+ x (OH)-1 2 Anx/ n yH2O, where M2+ represents the bivalent cation, M3+ represents a trivalent one and An- an anion with n- charge. The LDHs of system Cu, Zn, Al – CO3 were synthesized in the laboratory under conditions that favor the formation of small crystals of high surface area. The characterization was made by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy and scanning electron microscopy (SEM). The syntheses were based on co-precipitation method, under different synthesis conditions (hydrothermal bath; tritation time), using copper and zinc sulphate, aluminum and sodium hydroxide solutions, all with analytical grade. The compounds synthesized have high crystallinity, the intensity of its peaks prove that the materials have been well organized and stacked with the lamellae. The objective of this work was to synthesize and characterize layered double hydroxides with Cu, Zn, Al – CO3 system, analyzing morphological and structural properties and your thermal behavior through variable synthesis conditions.
Acesso aberto (Open Access)
Síntese de hidróxidos duplos lamelares do sistema Cu, Zn, Al-CO3: propriedades morfológicas, estruturais e comportamento térmico
(2011-09) SANTOS, Sheila Silva dos; CORRÊA, José Augusto Martins
Hydrotalcite-like compounds are anionic clays, also known as layered double hydroxides (LDH), which have structure similar to brucite mineral. The LDHs of the system Cu, Zn, Al-CO3 were synthesized under conditions to promote the formation of small crystals with high surface area. The characterization was done by X-ray diffraction, thermogravimetric analysis, FTIR spectroscopy, and scanning electron microscopy. The synthesis were based on the co-precipitation method, under different conditions (hydrothermal bath, titration time) using copper and zinc sulfate, aluminum and sodium hydroxide solutions. The X-ray diffraction patterns show that synthesized compounds have high crystallinity, the peak intensities show that they are well organized and stacked with the lamellae. The infrared spectrum shows bands associated with carbonate anion in the interlayer region.
Acesso aberto (Open Access)
Síntese e caracterização da piroaurita e hidroalcita a partir do horizonte laterítico da mina de bauxita de Juruti (PA).
(Universidade Federal do Pará, 2024-10-01) ARAÚJO, Bruno Eduardo Oliveira de; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
Anionic clays, also known as LDH, are nanomaterials with diverse technological applications, as well as versatile nanocomposites with properties such as ion exchangers, adsorbents, catalysers, and the ability to simulate cations and anions in their lamellar structure, which expands their applications as environmental remediators. Mining activities in the Amazon are growing exponentially, so it is necessary to find sustainable and practical ways to minimize environmental charges. Another possibility is the reuse of mining waste with specific applications in the recovery of chemical elements through concentration processes in tailings piles or treatment of acid mining drainage. Bauxite deposits have been explored for 15 years in the Juruti city, Pará state, and are part of the world's largest reserves, with high levels of aluminium oxide (Al2O3). The exploration and processing of aluminium mining leave large lakes where the disposal of tailings occurs. There are several studies that aim to use bauxite dispersion as a starting material for the synthesis of LDH, however this work focuses on the synthesis of LDH from the lateritic horizon, which makes up one of the six horizons of the lateritic-bauxitic profile of Juruti mines. The high levels of Fe3+ and Al3+ observed in the lateritic horizon allow its use as a starting material, together with magnesium chloride and sodium hydroxide to create optimized conditions for the synthesis of LDH by the coprecipitation method at variable pH. X-ray diffraction (XRD), scanning electron microscopy (SEM), spectrometry (FTIR), thermal analysis (TG-DSC) and surface area analysis (BET) techniques were used to characterize the synthesized LDH. The crystalline phases include pyroaurite (Mg2Fe(OH)16CO3.4H2O) and hydrotalcite (Mg6Al2(OH)16CO3.4H2O), in addition to brucite, spinel (mixed oxide) and hematite as secondary phases. Scanning electron microscopy (SEM) showed characteristic LDH morphologies, with small crystals with hexagonal habits, rougher structures and plate-like shapes that resemble honeycombs, when grouped, Infrared spectra (FTIR) indicated the presence of carbonate ions in the interlayer space in both types of LDH, through the characteristic weak absorption bands around 1373.51 –1394.67 cm-1. The conjugate TG/DSC curves indicated three endothermic events for the pyroaurite-type LDH, in addition to an exothermic event at a higher temperature, forming spinel, while the hydrotalcite-type LDH presented four endothermic events. The total mass loss of hydrotalcites is 15%, while that of pyroaurites reaches approximately 50%. Regarding the surface and porosity analysis (BET), a specific surface area (ASEBET) of 74.397 m2/g and a pore volume (VPBJH) of 0.173 cm3g-1 were obtained, and the average pore diameter was 18.64 Å. The ASEBET values of the hydrotalcite-type LDH are considerably higher, with similar VPBJH and pore radius values. The physisorption isotherm is type IV with hysteresis curve H3 that is associated with mesoporous structures as some clays and particle aggregates, such as plates with narrow slit-type pores. Thus, from the defined synthetic routes and having the lateritic horizon as a low-cost starting material, it is possible to continue adsorption tests using pyroaurite and hydrotalcite, synthesized and characterized in this work, with efficient potential to mitigate metal contamination in water resources.