Numerical Approach in Determination of Thermophysical Material Properties in Decomposition of Lumpy Dolomite Particles (original) (raw)
Related papers
Journal of Materials Science, 2005
Many workers [1–9] studied the kinetics of dolomite decomposition to study the effects of different parameters like, gas (CO2, N2 etc.) pressures, water vapor, presence of other impurities, particle size and grain size of the dolomite samples, crystallinity etc. on the decomposition kinetics of dolomite using different tools like, thermal analysis, thermo-gravimetric analyses, XRD technique etc. and different values of the activation energies for the decomposition reaction, order of reactions have been reported. It has been observed that pure dolomite decomposed in only two steps. The first stage of the thermal decomposition of dolomite resulted in the formation of Mg-calcite [(CaMg)CO3] and periclase (MgO), with the liberation of CO2. It was further observed that under CO2, dolomite decomposed directly to CaCO3, accompanied by the formation of MgO between 550 and 765∘C. Calcite decomposed to CaO between 900 and 960∘C and under air, simultaneous formation of CaCO3, CaO and MgO accompanied dolomite decomposition between 700 and 740–750∘C. At the latter temperature, the calcite began to decompose even though a significant amount of dolomite was still present and simultaneous decomposition of the two carbonates was terminated at 780∘C. Also, changes in decomposition rates of the various phases correlated with changes in the rate of weight loss determined by derivative thermo-gravimetric analysis.
2001
The effects of procedural variables on dolomite decomposition in carbon dioxide were investigated. The partial pressure of carbon dioxide causes dolomite decomposition to split into a two-stage process. It was observed that the first stage of dolomite decomposition is progressively displaced to higher temperatures with an increase in heating rate. However, the second stage is not affected significantly by changes in the heating rate. These studies also indicate that decrepitation analysis on dolomite in CO 2 provides better information as compared to experiments in other atmospheres. The flow rate of the purge gas does not influence the thermal behavior of dolomite.
Thermal decomposition of dolomite and the extraction of its constituents
Minerals Engineering, 1997
Several analytical techniques were used to identify and optimize the main variables affecting Jthe separation of magnesium and calcium carbonates from dolomite using partial thermal decomposition followed by hydration and recarbonation processes. It is shown that by careful control of these variables, the MgO content in the calcium carbonate residue can be reduced to less than 3.3% in a single processing cycle, resulting in a suitable raw material for the production of portland cement. High purity hydromagnesite, having less than 1% total impurities, was obtained from the aqueous residue.
The Effect Of Composition On The Decomposition Behaviour Of Dolomite Nuggets
Composition affects the calcination behaviour of Dolomite. This effect has been studied by varying the relative amounts of MgCO 3 and CaCO 3 .The Abrasion index and Shatter index are found to deteriorate slightly with increasing CaCO 3. The rate of Calcination gradually reduces with time. Interfacial chemical reaction is identified as the rate controlling step. The Activation energy is calculated from the slope of the plot 1-(1-f) 0.5 vs time, where f is the extent of Calcination. At high temperatures (1473 K), a greater contribution from diffusion is felt due to a little deviation from linearity. Depending on the composition, the Activation energies vary between 169.49 and 225.77 kJ/mol. CaCO 3 is found to raise the apparent activation energy, E. The average increase in the activation energy is found to be 1.309 kJ/mol per unit mass % increase in CaCO 3 .
Thermochimica Acta, 2003
Natural dolomite powders have been decomposed in high CO 2 partial pressure regime with H 2 O (g) flowing and in the temperature range 913-973 K. All kinetics and microstructure data concerning the first half decomposition step have been compared with equivalent data obtained from the same dolomite powders decomposed under the same conditions with no H 2 O fluxing. The water vapor reduced the value of the total apparent enthalpy of the reaction from 440 ± 10 to 345 ± 10 kJ mol −1 , but the rate-limiting step of the half decomposition process is not changed, consisting in each case in the transport of the CO 2 from the reacting interface. It has been showed that this possibility is plausible because H 2 O (g) can enhance the sintering of the formed MgO crystallites with subsequent changes of the CO 2 mode of adsorption on the MgO surfaces from a strong bonded regime to a weaker one. In presence of H 2 O (g) and high CO 2 (g) pressure, the rate-limiting step of the first half decomposition of dolomite is still the transport of CO 2 across the reacting interface, as it has been proved for the decompositions in CO 2 environment. In the temperature range explored, H 2 O (g) does not change the nature of the solid products which are formed by MgO, CaCO 3 and a solid solution of MgO into CaCO 3 . The microstructure of the solid products is still formed through a shear-transformation mechanism, but H 2 O (g) enhances the rate at which this step is occurring. Critical analysis of the microstructure data, allow to conclude that the stress level inside the decomposing particles is increasing and enhancing the cracking rate because H 2 O (g) can increase the MgO grain growth rate. These findings might explain the technical procedure used to decompose the dolomite stone in the ancient ovens.
The decomposition of dolomite monitored by neutron thermodiffractometry
2013
Dolomite powder from Coín (Spain) was heated in air at a constant rate of 2°C/min to 1000°C, while neutron diffraction patterns were collected every 150 s. Rietveld refinement was applied and raw intensity data were used to monitor decomposition. The full process happened in two stages: dolomite decomposition to give calcite and periclase, and calcite breakup. The first stage activation energy was 47 kcal�mol �1 from fitting to a contracting sphere model. The dolomite mean thermal expansion coefficients were (6.7 � 0.4) � 10 �6 and (2.7 � 0.2) � 10 �5 K �1 along the a and c axes, respectively. Changes in the Ca–O and Mg–O bond distances were also measured. I.
Decomposition of Dolomite Monitored by Neutron Thermodiffractometry
2002
Dolomite powder from Coín (Spain) was heated in air at a constant rate of 2°C/min to 1000°C, while neutron diffraction patterns were collected every 150 s. Rietveld refinement was applied and raw intensity data were used to monitor decomposition. The full process happened in two stages: dolomite decomposition to give calcite and periclase, and calcite breakup. The first stage activation energy was 47 kcal⅐mol ؊1 from fitting to a contracting sphere model. The dolomite mean thermal expansion coefficients were (6.7 ؎ 0.4) ؋ 10 ؊6 and (2.7 ؎ 0.2) ؋ 10 ؊5 K ؊1 along the a and c axes, respectively. Changes in the Ca-O and Mg-O bond distances were also measured.
Conventional and controlled rate thermal analysis of nesquehonite Mg(HCO3)(OH)·2(H2O)
Journal of Thermal Analysis and Calorimetry, 2008
The understanding of the thermal stability of magnesium carbonates and the relative metastability of hydrous carbonates including hydromagnesite, artinite, nesquehonite, barringtonite and lansfordite is extremely important to the sequestration process for the removal of atmospheric CO 2. The conventional thermal analysis of synthetic nesquehonite proves that dehydration takes place in two steps at 157, 179°C and decarbonation at 416°C and 487°C. Controlled rate thermal analysis shows the first dehydration step is isothermal and the second quasi-isothermal at 108 and 145°C. In the CRTA experiment carbon dioxide is evolved at 376°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of magnesium carbonates such as nesquehonite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal partial collapse of the nesquehonite structure
Non-isothermal, in situ XRD analysis of dolomite decomposition
Thermochimica Acta, 1989
In situ X-ray diffraction (XRD) was used to elucidate the thermal decomposition of dolomite. As opposed to previous efforts that required samples be heated to a specific temperature and held for the duration of an X-ray scan, data was collected at 4O C intervals while continuously heating the sample at 3O C min -l. Under CO,, dolomite decomposed directly to CaCO,, accompanied by the formation of MgO between 550 and 765" C. No evidence was offered for the formation of either CaO or MgCO, during this first stage. Calcite decomposed to CaO between 900 and 960 o C. Under air, simultaneous formation of CaCO,, CaO and MgO accompanied dolomite decomposition between 700 and 740-750 o C. At the latter temperature, the calcite began to decompose even though a significant amount of dolomite was still present. Simultaneous decomposition of the two carbonates terminated at 780 o C. Also, changes in decomposition rates of the various phases correlated with changes in the rate of weight loss determined by derivative thermogravimetric analysis.