Precipitation in the Mg-carbonate system—effects of temperature and CO2 pressure

The precipitation of different forms of magnesium carbonate has been studied at temperatures between 25 and and at a partial pressure of CO₂ between 1 and 100 bar. These conditions are relevant for mineral carbonation applications. Precipitation was triggered by the supersaturation created by mixing Na₂CO₃ solutions in equilibrium with a CO₂ atmosphere with MgCl₂ solutions. Experiments were monitored using attenuated total reflection Fourier transform infrared (ATR-FTIR) and Raman spectroscopy as well as a focused beam reflectance measurement (FBRM) probe and a turbidimeter. Solubility and supersaturation were calculated using the software package EQ3/6. Solids were identified using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. At and , only the hydrated carbonate nesquehonite (MgCO₃·3H₂O) precipitates, as it has previously been observed. Solutions undersaturated with respect to nesquehonite did not form any precipitates in experiments lasting 16 h. Induction times increased with decreasing supersaturation with respect to nesquehonite. At and , hydromagnesite ((MgCO₃)₄·Mg(OH)₂·4H₂O) was formed which transformed within 5-15 h into magnesite (MgCO₃). Solutions undersaturated with respect to brucite (Mg(OH)₂) did not form any precipitates in experiments lasting 19 h. At and , direct formation of magnesite and, at elevated levels of supersaturation, the co-precipitation of magnesite and hydromagnesite has been observed. In the latter case, hydromagnesite transformed within a few hours into magnesite. Solutions undersaturated with respect to hydromagnesite did not form any precipitates in experiments lasting 20 h.     

Investigations on the synthesis of KVO3 and Cl2 from KCl and V2O5 in the presence of oxygen

Investigation was carried out on the optimal conditions of the synthesis of KVO₃ and Cl₂ from KCl and V₂O₅ in the presence of atmospheric oxygen. The research was performed for the temperature range 673- for 1-. The influence of the air flux rate on the reaction yield was investigated.     

Reduction and oxidation kinetics of Mn3O4/Mg-ZrO2 oxygen carrier particles for chemical-looping combustion

The kinetics of reduction with methane and oxidation with oxygen of Mn₃O₄ supported on Mg-ZrO₂ prepared by freeze granulation has been investigated. The reactivity experiments were performed in a thermogravimetric analyzer (TGA) using different reacting gas concentrations and temperatures in the range of 1073-1223 K. The oxygen carrier particles showed high reactivity during both reduction and oxidation at all investigated temperatures. An empirical reaction model, which assumes a linear relation between time and conversion, was used to determine the kinetic parameters for reduction and oxidation, with chemical reaction being the main resistance to the reaction. The order of reaction found was 1 with respect to CH₄ and 0.65 with respect to O₂. The activation energy for the reduction reaction was 119 and for the oxidation reaction. The reactivity data and kinetic parameters were used to estimate the solid inventory in the air and fuel reactor of a CLC system. The optimum solid inventory obtained was at a value of ΔX_s=0.4. At these conditions, the recirculation rate of oxygen carrier between air and fuel reactor was per MW of fuel, which could be accomplished in an industrial reactor. The high reactivity of the Mn₃O₄/Mg-ZrO₂ with both methane and oxygen showed that this is a very promising oxygen carrier for CLC.