EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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5 resultados
Resultados da Pesquisa
Item Precipitation of a layered double hydroxide comprising Mg2+ and Al3+ to remove sulphate ions from aqueous solutions.(2018) Guimarães, Damaris; Rocha, Natasha Cristina Machado da; Morais, Rafaela Aparecida Pedro de; Resende, Andréia De-Lazarri Bicalho Peixoto; Lima, Rosa Malena Fernandes; Costa, Geraldo Magela da; Leão, Versiane AlbisThis work presents an alternative route to remove sulphate ions from aqueous solutions, which is simple and fast, and its efficiency of sulphate removal is slightly influenced by temperature (26 °C–70 °C) and pH (4–12). The lowest residual sulphate concentration was about 60 mg L−1, which was observed in continuous experiments using wastewater (26 °C, pH 6 and initial sulphate concentration of 630 mg L−1). All these outcomes together have not been observed in the current most used processes of sulphate precipitation, i.e. gypsum and ettringite precipitation. Sulphate removal experiments were carried out in the batch and continuous systems using synthetic solutions. In these conditions, about 75% of sulphate ions were removed for an initial ion concentration of 1800 mg L−1. A continuous test was also performed using a wastewater sample in addition to a synthetic solution. The system reached steady-state conditions after four residence times (40 min) in the experiment with synthetic solutions, whereas three residence times (30 min) were necessary for the tests with the wastewater (initial sulphate concentration of 630 mg L−1). In the latter case, the sulphate removal efficiency was approximately 90%. The characterisation of the experimentally precipitated solids was carried out by DRX, FTIR, SEMEDS, elemental analysis and thermal analysis. These techniques showed that, except in pH 4, the sulphate removal process occurred due to the precipitation of a layered double hydroxide, comprising Mg2+ and Al3+ as its metallic ions and nitrate (due to the salts used for precipitation) and sulphate anions occupying its interlayer space.Item Kinetic and thermal decomposition of ettringite synthesized from aqueous solutions.(2016) Guimarães, Damaris; Oliveira, Víctor de Andrade Alvarenga; Leão, Versiane AlbisThe kinetics of the thermal decomposition of a synthetic ettringite sample was studied between 298 and 820 K in an inert atmosphere for the present work. The ettringite and its thermal decomposition products were characterized using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Four endothermic events were observed with thermogravimetry curves, the maxima of which occurred at 366, 397, 537, and 641 K. All events were associated with the loss of water molecules with different degrees of interaction within the ettringite structure. Chemical equations for each decomposition step were proposed based on the percentages of mass loss observed. In addition, for the first time, the activation energies of each ettringite decomposition events were determined by the isoconversional methods of Ozawa–Flynn–Wall, Friedman, and Kissinger–Akahira– Sunose. The modeling revealed that the activation energy varied from *50 kJ mol-1, characteristic of mass transfer control steps, to *150 kJ mol-1, which is typical of chemical control, as the temperature increased and the ettringite structure lost water. A total of 32 mol of water was released equivalent to 43.1 % of the initial sample mass.Item Batch and fixed-bed assessment of sulphate removal by the weak base ion exchange resin Amberlyst A21.(2014) Guimarães, Damaris; Leão, Versiane AlbisThis paper investigated sulphate removal from aqueous solutions by Amberlyst A21, a polystyrene weakbase ion exchange resin. Both the pH and initial sulphate concentration were observed to stronglyaffect sorption yields, which were largest in acidic environments. Working under optimum opera-tional conditions, sulphate sorption by Amberlyst A21 was relatively fast and reached equilibrium after45 min of contact between the solid and liquid phases. Sorption kinetics could be described by eitherthe pseudo-first order (k1= 3.05 × 10−5s−1) or pseudo-second order model (k2= 1.67 × 10−4s−1), andboth the Freundlich and Langmuir models successfully fitted the equilibrium data. Sulphate uptake byAmberlyst A21 was a physisorption process ( H = −25.06 kJ mol−1) that occurred with entropy reduction(deltaS = −0.042 kJ mol−1K−1). Elution experiments showed that sulphate is easily desorbed (∼100%) fromthe resin by sodium hydroxide solutions at pH 10 or pH 12. Fixed-bed experiments assessed the effects ofthe initial sulphate concentration, bed height and flow rate on the breakthrough curves and the efficiencyof the Amberlyst A21 in the treatment of a real effluent. In all studied conditions, the maximum sulphateloading resin varied between 8 and 40 mg (SO42−) mL (resin)−1.Item Fundamental aspects related to batch and fixed-bed sulfate sorption by the macroporous type 1 strong base ion exchange resin Purolite A500.(2014) Guimarães, Damaris; Leão, Versiane AlbisAcid mine drainage is a natural process occurring when sulfide minerals such as pyrite are exposed to water and oxygen. The bacterially catalyzed oxidation of pyrite is particularly common in coal mining operations and usually results in a low-pH water polluted with toxic metals and sulfate. Although high sulfate concentrations can be reduced by gypsum precipitation, removing lower concentrations (below 1200 mg/L) remains a challenge. Therefore, this work sought to investigate the application of ion Exchange resins for sulfate sorption. The macroporous type 1 strong base IX resin Purolite A500 was selected for bath and fixed-bed sorption experiments using synthetic sulfate solutions. Equilibrium experiments showed that sulfate loading on the resin can be described by the Langmuir isotherm with a maximum uptake of 59 mg mL-resin 1. The enthalpy of sorption was determined as þ2.83 kJ mol^-1, implying an endothermic physisorption process that occurred with decreasing entropy (-15.5 J mol^-1.K^-1). Fixed-bed experiments were performed at different bed depths, flow rates, and initial sulfate concentrations. The Miura and Hashimoto model predicted a maximum bed loading of 25 e 30 g L-bed-1 and indicated that both film diffusion (3.2 x 10^-3 cm s-1 to 22.6 x 10^-3 cm s^-1) and surface diffusion (1.46 x 10^-7 cm2 s^-1 to 5.64 x 10^-7 cm2 s^-1) resistances control the sorption process. It was shown that IX resins are an alternative for the removal of sulfate from mine waters; they ensure very low residual concentrations, particularly in effluents where the sulfate concentration is below the gypsum solubility threshold.Item High-temperature bioleaching of nickel sulfides : thermodynamic and kinetic implications.(2010) Cruz, Flávio Luciano dos Santos; Oliveira, Víctor de Andrade Alvarenga; Guimarães, Damaris; Souza, Adelson Dias de; Leão, Versiane AlbisThe effect of temperature on nickel sulfide bioleaching was studied in the presence of mesophile (Acidithiobacillus ferrooxidans) and moderate thermophile (Sulfobacillus thermosulfidooxidans) strains and the results were discussed in terms of sulfide dissolution thermodynamics (Eh–pH diagrams) and kinetics (cyclic voltammetry). It was observed that in the pH range 1.8–2.0 the highest nickel dissolution was achieved which reached 50% for mesophiles and over 80% for moderate thermophiles. External ferrous iron addition had no effect on the metal dissolution at 34 °C, but adversely affected nickel leaching at higher temperatures. The best outcomes were accomplished with low FeSO4 additions (2.5 g/L) at 50 °C. Pyrrhotite dissolution avoided the need for external iron addition, providing Fe2+ concentrations as high as 7 g/L during bioleaching, which supports bacterial growth. Eh–pH diagrams for pentlandite and pyrrhotite show a negligible effect of temperature on the stability field of each sulfide whilst cyclic voltammetry indicated that temperature has the strongest influence on pyrrhotite oxidation. The latter along with a rapid increase in solution potential (Eh) explains the higher and faster extraction observed with S. thermosulfidooxidans.