In pH-swing mineral carbonation, several acid/base systems has been investigated. Currently the main acid/base systems employed are HCl/NaOH and NH 4 HSO 4 /NH 4 OH. However, the use of a HCl/NH 4 OH system was not yet elucidated. This study proposes to evaluate the feasibility of a pH-swing mineral carbonation based on HCl/ NH 4 OH system at atmospheric pressure and moderate temperatures using mining waste from asbestos production from Goiás State, Brazil (S-GO) for two conditions (i.e. stoichiometric conditions (T2E) and acid excess (T2)). Results indicated that the Fe 3+ content in S-GO acted as a catalyst, due to FeCl 3 hydrolysis in aqueous solutions. Thus, high Mg and Fe extraction efficiency (95 ± 2%), were achieved in the leaching stage for both conditions. The S 1 solid residue was mainly SiO 2 with 90 ± 1% purity content. In the purification stage 91.7 ± 1.9% of Fe t were removed, however, a loss of Mg of 13.6 ± 2.3% was also detected. On the carbonation stage, high purity hydromagnesite was formed in T2E; this stage had a 85% efficiency, thus, 36.7% of CO 2 was fixed. On T2, excess H 2 O and CO 2 promoted dypingite formation and reduced hydromagnesite formation. After carbonation, the formation of crystals was observed in the NH 4 Cl aqueous solution at 25°C, indicating NH 4 Cl supersaturation. The results of mass balance indicate that 4 ton of mineral waste will be employed for each ton of captured CO 2 , as well as 2.6 ton of HCl, and 4.5 ton of NH 4 OH. However, 1.7 ton of SiO 2 , 0.55 ton of iron oxides, and 2.7 ton of hydromagnesite could be produced.

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In this work are presented analyzes from calcination and sintering of zinc niobate ceramics by microwave processing. In order to obtain minimum processing parameters, the behavior of the material was first studied for the calcination at different temperatures in the range of 450 to 1150°C, with duration time of 10 minutes. The sintering was carried out between 950 and 1050°C. The results showed that the crystalline structure of the calcined and sintered samples was influenced by the temperature, because, according to the increase in temperature, the evolution of the formed crystalline phases was observed and only the Zn3Nb2O8 and ZnNb2O6 phases prevailed in the final microstructure. The densification of the sintered ceramics was influenced by the time and temperature of the heat treatment, with lower residual porosity and grain growth with the increase of the sintering temperature in the microwave oven.

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The propane oxidative dehydrogenation (ODH) reaction has been considered as an alternative method for propene production owing to its exothermic nature, which renders it environmentally friendly. The use of alkaline promoters for supported V catalysts can increase propene selectivity and partially inhibit the formation of CO and CO2. Our goal was to evaluate the promoting effect of K and Na and the support effect using gibbsite as precursor for the propane ODH reaction. Catalysts were prepared via co-impregnation of V and alkali metals on a previously prepared alumina support and were characterized using N2 adsorption-desorption, X-ray diffraction, temperature-programmed reduction, and isopropanol decomposition tests to evaluate their acid-base properties. The activity of the synthesized catalysts for the propane ODH reaction was evaluated at the O2:C3H8:He molar ratios of 5:2:4, 6:1:4, and 4:3:4. The addition of alkali metals to the V catalysts increased propane conversion and propene selectivity; moreover, both parameters increased with increasing molar fraction of O2 in the reactants. K doping increased the propene selectivity of the doped catalysts, because it inhibited a large fraction of catalytic surface acidic sites. A high molar fraction of O2 in the reactants facilitated the regeneration of the catalyst, whereas a high reoxidation rate improved catalytic activity and propene selectivity.

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RESUMO-O trabalho visa realizar um estudo exploratório das sínteses que formam hexaaluminato de bário para utilização como suporte na impregnação de CoO-Mn2O3 avaliando sua eficiência e durabilidade na decomposição de propelentes verdes (H2O2 e N2O) de sistemas propulsivos a monopropelentes. As sínteses foram realizadas pelo método de coprecipitação que conduziu ao precursor da formação de hexaaluminato de bário, o qual possui as propriedades necessárias para suportar as condições de reação. Os resultados obtidos pelas análises por termogravimetria, difratometria de raios X e fisissorção de nitrogênio definiram o GBa como a melhor síntese para posterior impregnação de CoO-Mn2O3 e realizar a decomposição catalítica dos H2O2 e N2O.