Obtaining high purity silica from rice hulls
José da Silva JúniorCarlo Requião da CunhaFlávio Luiz Silva de CarvalhoUbirajara Pereira Rodrigues FilhoPaulo Renato de OliveiraMarcos Antônio Segatto Silva
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Abstract:
Many routes for extracting silica from rice hulls are based on direct calcining. These methods, though, often produce silica contaminated with inorganic impurities. This work presents the study of a strategy for obtaining silica from rice hulls with a purity level adequate for applications in electronics. The technique is based on two leaching steps, using respectively aqua regia and Piranha solutions, which extract the organic matrix and inorganic impurities. The material was characterized by Fourier-transform infrared spectroscopy (FTIR), powder x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy (SEM), particle size analysis by laser diffraction (LPSA) and thermal analysis.Keywords:
Rice hulls
Powder Diffraction
Powder Diffraction
Anhydrous
Characterization
Crystal habit
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To get CaTiO3catalyst with high photocatalytic properties,the effect of calcination conditions,on the photocatalytic activity of CaTiO3 was investigated.The calcination conditions included heating rate of calcination precursors,calcination temperature,calcination time and cooling rate of calcination products,The catalyst was synthesized by solid-state reaction method with Ca(NO3)2and TiO(OH)2as raw materials and NaOH as mineralizer.The physical properties of the catalyst were characterized using XRD and SEM.The experimental results showed that the activity increased until reached a maximum,and then decreased with the increasing heating rate of calcination precursors;the photocatalytic activity decreased drastically with the fast cooling rate of calcination products.Moreover,the optimal values of calcination temperature and calcination time were obtained.As a result,the CaTiO3catalysts with high photocatalytic activity can be obtained under an optimized calcination conditions after loading CoO(0.2 wt%)co-catalyst.
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X-ray analysis confirmed that in all investigated samples, the active API (acetylsalicylic acid and ascorbic acid) was present. The values of the interplanar distance d hkl for the studied samples are in good accordance with those presented in the ICDD database. The intensities of the diffraction lines depend on the content of the component in the tested preparation. Therefore, different intensities of lines for the APIs were observed in the obtained diffraction patterns. Thermal analysis of the studied substances showed that during the thermal analysis, the following phenomena might occur: dehydration and (or) melting, crystalline transformation. Moreover, it was found that the chemical structure of the studied compounds affects the process of their thermal decomposition. The data obtained during these investigations can be useful in quick tests of physicochemical discrepancies and abnormalities between potential components of pharmaceutical preparations. The evidence for the interaction can be obtained by comparing DSC and TG curves of the drug and the excipient, as well as those of their physical mixtures. For this reason, the study of characteristics of thermal decomposition of drugs and excipients is necessary. Based on the above investigations, it may be stated that a combination of two methods: XRPD and DSC can be used to distinguish the original drugs from counterfeit products, e.g., by checking for the presence of the correct API or by a comparison of the drugs fingerprint.
Powder Diffraction
Excipient
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The aim of this study is to investigate the extraction of molybdenum from the spent HDS catalyst. The experiment was performed by using the pyro-hydrometallurgical process; calcination and leaching. The spent catalyst was calcined at different temperatures in order to investigate the effect of calcination temperature on the recovery of molybdenum in the subsequent process. Leaching of the calcined samples was subsequently performed by using the different concentrations of leaching reagent. The leaching was conducted by varying the concentration of NaCO 3 of 20 g/L, 30 g/L and 40 g/L with a fixed leaching temperature of 90°C, a S/L ratio (weight of calcined sample/volume of leaching reagent) of 100 g/L and leaching time of 1 hrs. under the stirring condition at a speed of 250 rpm. It was found that carbon and sulfur contained in the spent HDS catalyst could be reduced by the calcination process and resulting in enhanced extraction efficiency of molybdenum. The extraction efficiency of molybdenum increased with increasing concentration of leaching reagent. At a certain concentration of leaching reagent, the extraction efficiency of the sample calcined at lower temperatures was higher than the sample which was subjected to calcination at a higher temperature.
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In order to improve the activation effect of deactivation catalysts, calcination of V2O5-WO3-MoO3/TiO2 catalysts were investigated. The experimental results demonstrate that calcination time have an effect for recovering the activity of V2O5-WO3-MoO3/TiO2 catalyst. Calcination not only ensures the better mechanical strength and integrity of the catalyst, but also plays an important role in the denigration activity of the catalyst. However, the particles of the catalyst surface enlarged with the increase of the calcination temperature. The suitable calcination time can improve the denigration efficiency and increase the mechanical strength of the catalyst. In addition, the calcination time mainly affects the formation of MoO3. These findings can provide reference for the activation of SCR-Den Ox catalyst.
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Powder Diffraction
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We calcined six kinds of limestone from various localities up to 900, 1000, 1100, 1200, 1300 and 1400°C with or without NaCl, and observed the growth of CaO crystals in their thin sections. The CaO crystals occurring in the specimens calcined with NaCl are, as usual, better grown than those without NaCl, and it is more evident at lower temperature calcination. In the case of higher temperature calcination, the formers are hardly over-burnt.With regard to the limestones, those of cryptcrystalline make finer CaO crystals. Especially it is evident at higher temperature calcination. This may show to have larger range for optimum calcination, that is easy to work with.
Atmospheric temperature range
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Atmospheric temperature range
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