Thermal Decomposition Of Dolomite Research Articles

High-temperature dolomite decomposition: An integrated experimental and computational fluid dynamics analysis for calcium looping and industrial applications

The thermal decomposition of dolomite was investigated as a potential low-cost and high-performance precursor to CaO in the calcium looping process, which shows great promise when integrated with carbon capture and storage and thermochemical energy storage technologies. Experimental thermogravimetric analysis (TGA) and computational fluid dynamics (CFD) modelling were used to study the isothermal calcination process of dolomite considering industrially relevant conditions, focusing on high temperatures (800–1200 °C), sample sizes (12–18 mm), different calcination atmospheres (air and CO2) and gas velocities (0.2–3 m·s−1). Based on experimental findings, optimal calcination conditions for industrial applications require a minimum temperature of 1000 °C to achieve complete conversion within 25 min and smaller particles for faster conversion rates. Calcination atmosphere is flexible as CO2 concentration shows minimal impact on conversion rates. Laminar flow gas velocity is not a limiting factor and its value should be considered based on other aspects (i.e., costs). Higher particle initial porosity is seen to increase reactivity and thermal efficiency. The CFD model was validated with experimental data, resulting in determination coefficients (R2) higher than 0.9 for all simulated cases. Model predictions revealed insights into particle level phenomena during calcination, such as increased rates at higher temperatures with proportional self-cooling effects, wake formation enhancing fluid mixing and the presence of a thermal boundary layer reducing heat transfer. The findings presented in this paper can be used in future work to determine reaction mechanisms and optimize kinetic parameters for decomposition, as well as further optimize other aspects of the process at industrially relevant operating conditions.

Gas-solid carbonation of lime produced by thermal decomposition of dolomite

Gas-solid carbonation of lime produced by thermal decomposition of dolomite

Influence of dolomite particle size on the kinetics of its thermal decomposition process

The results of an experimental study of the thermal decomposition of natural dolomite, carried out on laboratory equipment at constant temperatures of 650 °C, 700, 750, 800 and 850 °C, are discussed. Particles of Belarusian dolomite weighing 0.58 g, 0.88, 2.3, 2.7, 7.6 and 16.3 g were used as the test samples. An integral equation describing the kinetics of thermal decomposition of natural dolomites of Belarus is presented. It is shown that the reaction rate of thermal decomposition of dolomite depends not only on the temperature regime in the reaction zone, but is also largely determined by the mass of the samples under study. It has been established that the rate constant of thermal decomposition of dolomite in the studied range of sample masses can be determined by the empirical expression identified in the course of this study. The rate constants of thermal decomposition of dolomite particles of various masses have been determined. The values of the rate constants obtained empirically and those calculated taking into account the mass of the samples are compared. It is noted that the developed model is physically justified, and the dependence proposed in the work can be incorporated into existing engineering methods for calculating generator gas purification systems using dolomite as a catalyst and sorbent.

Effect of Thermal Treatment on Natural Dolomite

Dolomite is a mineral material that is formed from limestone which is mostly contains the calcite (CaCO3) and magnesite (MgCO3). This paper aimed to study on thermal decomposition of dolomite under air atmosphere. Calcination of dolomite was carried out by using furnace with heating rate of 10 °C/minute in an air atmosphere. The different temperature of calcination was varied at 400 °C, 600 °C, 800 °C, and 1000 °C within 6 hours. Phase analysis (XRD) and functional group analysis (FTIR) were carried out to analysis the dolomite after calcination. Microstructural (SEM) and Energy Dispersive X-ray (EDX) analysis showed that the main constituents of pure dolomite include CaCO3 (calcite), MgCO3 (magnesite), CaO, and MgO. From the results, XRD showed that the high intensity of CaO and MgO at 800 - 1000 °C was much stronger than that of dolomite at 400 - 600 °C. In addition, FTIR presents strong and intense bands are observed at 3632.23 and 3690.98 cm−1 (800 °C), and also 3694.03 and 3633.60 cm−1 (1000 °C) due to the calcium oxide.

Development of the Method for Forecasting and Calculating the Operation of Sorption Systems for Purifying the Generator Gas Based on Dolomite Use. Part I

A trend towards energy diversification creates the expansion of small energy facilities that involve the production of solid fuel generator gas, rather than its direct combustion. The economic indicators of such facilities significantly depend on the efficiency of the generator gas purification. A promising sorbent for the purification of the generator gas is dolomite. When working as a sorbent, dolomite particles usually form a layer, through which the generator gas that is heating them is filtered. The objective of the study is to determine kinetic parameters of the thermal decomposition of dolomite, depending on the size of the sample. It was achieved using the thermogravimetric study of the thermal decomposition of single dolomite particles under static conditions at various temperatures. The most significant scientific result was that a dependence of the kinetic parameters of the gross reaction on the size of the initial particle is revealed, and a regression equation was proposed for its quantitative assessment. In addition, since the heat treatment process of the material was fairly long lasting, and the sizes of the particles allowed them to be referred to thermally thin bodies, it was inferred that the effect of a grain size on the reaction kinetics should be explained through the description of the evacuation process of gaseous reaction products from the material. The significance of the results of the study lies in the fact that a particle size must be considered as a factor that affects the progress of the technological process, which increases the reliability of the calculation of sorption-catalytic systems based on the use of dolomite.

Macrokinetic Models of Thermal Decomposition of Dolomite for Engineering Calculations

Macrokinetic Models of Thermal Decomposition of Dolomite for Engineering Calculations

Physico-mechanical properties and microstructure of multi-phase ceramic composites based on zircon and dolomite mixtures

Four composites containing zircon and dolomite were designed by adding dolomite from 5wt% to 35wt% at the expense of zircon content. Densification parameters in terms of bulk density, apparent porosity and linear change were determined at different firing temperatures (1200°C–1400°C). Cold crushing strength of sintered composites, phase composition and microstructure were investigated. Samples contain 35wt% of dolomite and fired at 1200°C for 2 hours exhibited higher porosity (AP ∼ 51.25%) than other samples and can be used as porous ceramics. This is due to CO2 evaporation through the thermal decomposition of dolomite. Dense ceramics can be obtained by adding 5wt% of dolomite and fired at 1400°C for 2 hours (bulk density ∼3.67 g/cm3 and apparent porosity ∼4.5%). Only zirconia and diopside crystalline phases were detected at composite containing 35wt% of dolomite and fired at 1400°C. Due to the liquid phase sintering process, the densification parameters of the sintered samples have been enhanced by increasing the temperature. The mechanical properties of the sintered samples were improved due to the transformation toughening mechanism of tetragonal zirconia. Microstructure and EDAX analysis of the sintered composites show the presence of sub-prismatic zircon and rounded zirconia crystals as well as irregularly dark diopside crystals.

Investigation of decomposition of dolomite and distribution of iodine migration during the calcination-digestion process of phosphate ore

In this work, the thermal decomposition and digestion of dolomite during the calcination of medium and low grade phosphate ore were investigated. Moreover, the migration distribution of co-associated iodine in gas, liquid and solid phases was also examined. The effects of calcination temperature and time, digestion temperature and time, and liquid-solid ratio on the P2O5 grade, MgO removal rate and iodine migration distribution of phosphate ore were systematically studied. The results showed that the main phase Ca5(PO4)3F remained almost no change during calcination-digestion process of phosphate ore. The impurity dolomite was decomposed into magnesium and calcium oxides, and carbon dioxide was precipitated. With the thermal decomposition of dolomite, most of the accompanying iodine adsorbed in phosphate ore was oxidized to iodine and sublimated to the gas phase. A small amount of iodine continued to exist as an isomorph in the fluoroapatite lattice. Increasing the temperature and prolonging the time accelerated the decomposition rate of dolomite in phosphate ore. However, excessively, high calcination temperature and prolonged calcination time affected the decomposition reaction and led to the reduction of effective CaO and MgO content. This was not conducive to the removal of calcium and magnesium, or to the improvement of phosphate grade. Appropriate digestion temperature, time and water volume facilitated the digestion reaction and increased the MgO removal rate. During calcination and digestion progress, 80%~90% of the associated iodine migrated to the gas phase in the form of elemental I2. Under the optimized calcination conditions, the removal rate of MgO reached (85.0 ± 0.1)%, the grade of phosphate concentrate increased up to (32.5 ± 0.1)%, and the content of MgO was (1.02 ± 0.1)%.

Superheated steam, hot CO2 and dynamic recrystallization from frictional heat jointly lubricated a giant landslide: Field and experimental evidence

We used thermogravimetry to determine that the frictionally heated sliding surface reached ∼850°C at the base of the 1.16×109 m3 Daguangbao landslide, triggered during the 2008 Ms8.2 Wenchuan earthquake. Optical and electron microscope images reveal evidence of dolomite thermal decomposition, hot fluid penetrating fine cracks and dynamic recrystallization of minerals. A high-speed rotary shear apparatus simulated the rapid sliding and provided data on very low frictional resistance (friction coefficient, μ≈0.05) during shearing above 1 m/s. Electron-probe analysis of samples from the experiments showed lime and magnesia from thermal decomposition of dolomite. Some of the sheared minerals formed a dynamically recrystallized layer ∼0.1 mm thick, and its viscous resistance would have contributed to the low apparent friction during high-speed sliding. A further explanation, however, was very high pore-fluid pressure from hot supercritical CO2 (and superheated steam at a partial pressure of >10 MPa in the field situation with groundwater). These friction-reducing mechanisms are not mutually exclusive and both were present simultaneously at the landslide base.

Разработка модели термического разложения доломита в кипящем слое для обеспечения сорбционных систем газогенераторных установок

Разработка модели термического разложения доломита в кипящем слое для обеспечения сорбционных систем газогенераторных установок

Thermal decomposition of dolomite under CO2: insights from TGA and in situ XRD analysis.

Thermal decomposition of dolomite in the presence of CO2 in a calcination environment is investigated by means of in situ X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The in situ XRD results suggest that dolomite decomposes directly at a temperature around 700 °C into MgO and CaO. Immediate carbonation of nascent CaO crystals leads to the formation of calcite as an intermediate product of decomposition. Subsequently, decarbonation of this poorly crystalline calcite occurs when the reaction is thermodynamically favorable and sufficiently fast at a temperature depending on the CO2 partial pressure in the calcination atmosphere. Decarbonation of this dolomitic calcite occurs at a lower temperature than limestone decarbonation due to the relatively low crystallinity of the former. Full decomposition of dolomite leads also to a relatively low crystalline CaO, which exhibits a high reactivity as compared to limestone derived CaO. Under CO2 capture conditions in the Calcium-Looping (CaL) process, MgO grains remain inert yet favor the carbonation reactivity of dolomitic CaO especially in the solid-state diffusion controlled phase. The fundamental mechanism that drives the crystallographic transformation of dolomite in the presence of CO2 is thus responsible for its fast calcination kinetics and the high carbonation reactivity of dolomitic CaO, which makes natural dolomite a potentially advantageous alternative to limestone for CO2 capture in the CaL technology as well as SO2in situ removal in oxy-combustion fluidized bed reactors.

Thermal Decomposition of Dolomite Containing Phosphorus

In this paper,DTA-TG and TEM are used to investigate dolomite containing phosphorus. The investigations suggest that the thermal decomposition of dolomite containing a little bit of phosphorus powder has only one reaction while that of dolomite has two reactions, and the final temperature of the reaction reduces by about 18°C. The oxidation reaction of the phosphorus in dolomite begins at about 500°C, which is 140°C higher than that of the oxidation reaction of phosphorus in standard atmosphere condition. Round-bubble-shape structure gradually appears on the surface of the dolomite sample when observed using TEM. Furthermore, the number and size of this structure increased with the rising of the temperature. Finally, the round-bubble-shape structure breaks to small hollows, showing as teared-shape, and forms a series of protruding and intensive larger hollows and spherical shape. Therefore, the temperature of thermal decomposition of thermal decomposition of dolomite is decreased and the components of thermal decomposition products of dolomite containing phosphorus are almost the same as that of dolomite.

Thermal Decomposition of Dolomite

Thermal decomposition of dolomite was investigated using DTA-TG and TEM. There have two obvious endothermic valley and the first one is narrow and sharp, the second endothermic valley is wide and flat. Between the two valley there is a temperature difference about 15-20°C and no decomposition in this region. Before the decomposition of dolomite some spherical particles formed on the surface of mineral grain. The first endothermic valley formed when these particles started to decompose, and the remaining material decomposed into the second endothermic valley.

Antibacterial characteristics of CaCO3–MgO composites

Dentifrices, such as tooth-paste, are pastes containing insoluble abrasives that aid in the removal of plaque from the teeth and help to polish them. Composite powders contributing to oral hygiene application, i.e., nano-scale MgO crystallite dispersed in CaCO 3 grain, were fabricated by the thermal decomposition of dolomite. The composite obtained by heating at 800 °C consisted of CaCO 3 grains including 20 nm MgO fine crystallite, being the purpose powder in this study. The antibacterial activity of these powders related to gram-positive and gram-negative bacteria was evaluated in vitro . The thermal decomposition above 800 °C resulted in the mixture of CaO and MgO. Antibacterial activity of the composite enhanced with increasing powder concentration. Though antibacterial action toward Staphylococcus aureus was greater than towards Escherichia coli , the death rate constant was identical in both bacteria. It can be concluded that the obtained composite possesses two functions able to improve the oral hygiene: as a tooth abrasive and as an antibacterial agent.

Kinetic analysis of non-isothermal decomposition of dolomite in nitrogen atmosphere

In the present paper, a comparative study of five different non-isothermal kinetic analysis methods for the determination of the mechanism of the thermal decomposition of dolomite from thermogravimetric experiments, is presented. The experiments were carried out in a thermogravimetric analyser under a nitrogen atmosphere from 50 to 1100°C under non-isothermal conditions at five different heating rates, i.e. 5, 10, 20, 30 and 40 K min-1. By applying each of these methods, the kinetic parameters of the reaction were evaluated and the discrimination of the conversion function (kinetic model) that best verifies the experimental data was attempted. From a comparative study of the results of the above methods, it was concluded that the heating rate affects the activation energy values. For the model free methods, the activation energy was calculated at 242˙5 kJ mol-1 and the pre-exponential factor ln ( A, s-1 ) at 20˙6. The phase boundary reaction model of zero order was found to best represent dolomite decomposition.

The heat treatment and particle size effects in the thermal decomposition of dolomite for separation of constituents

The effect of particle size and heat treatment on partial decomposition of dolomite for the extraction of calcite has been investigated. Isothermal firing trials varying the soaking period were performed for dolomite at temperatures between 1013–1033 K according to schedules derived from thermogravimetric analysis (TGA). Samples of dolomite representing three size fractions were used. It is shown that, the optimum heat treatment for reducing the residual MgO in extracted CaCO3 and maximising the yield of CaCO3 is accomplished at 1013 K. A soaking time of 160 min seems adequate. The highest degree of partial decomposition was obtained for the 150 μm size fraction of dolomite. A single processing cycle performed under the optimised conditions coupled with relatively short periods of hydration and re-carbonation (24 h, 15 min) yielded CaCO3 with 7˙5% MgO from a dolomite containing 23˙6% MgO.

Carbon calabashes in a shock-produced carbon melt

Carbon calabashes similar to those reported during decomposition of CH 4 between 900 and 1050 °C also formed after thermal decomposition of dolomite, CaMg(CO 3) 2 in a low-angle impact experiment that produced a carbon melt and complex gas phase between 2700 and 3700 °C. The interrelationships among various carbon forms in this experiment support that the calabashes are quenched carbon-melt bubbles at high gas to liquid ratios. Carbyne forms of carbon that crystallized within the quenched-liquid shell of the bubbles did not require a spiral growth mechanism. Carbon calabashes are an oddity but not a new form of elemental carbon.

The influence of preparation conditions on adsorption properties and porosity of dolomite-based sorbents

Abstract In this paper the porosity and adsorption properties of dolomitic sorbents, prepared via thermal decomposition of dolomite, are presented. Thermal decomposition of carbonates, as a result of heating, is governed by a number of factors, e.g. temperature, heating time, atmosphere over a heated sample and sample weight and each of these has its role in the creation of new solid phase. It has been experimentally stated that the heating of dolomite at 800 °C leads to the partial decomposition (magnesium carbonate dissociation) and the creation of a new solid—a mixture of calcite and magnesium oxide. The increase of heating time and a sample weight result in the decrease of new sorbents porosity. Of the sorbents prepared in various atmospheres, the most developed porous structure is achieved by the sample heated in the inert one. Adsorption properties of new sorbents have been estimated by means of gas chromatography (GC) method. Some information about the energetic heterogeneity of the examined sorbents may be obtained from the adsorption energy distribution function χ(e).

Removal of exhausted oils by adsorption on mixed Ca and Mg oxides

Adsorption tests were performed on two different exhausted oils to reduce their polluting and health hazard potential: a “water-insoluble oil”, utilised for automotive engine lubrication, and an “emulsified” oil, used as coolant for metal-cutting tools. Dolomite, a low-cost recovery material, was used to prepare two effective adsorbents: (a) a mixed Ca and Mg oxide obtained by thermal decomposition of dolomite at 1800°C, and (b) an activated material obtained by submitting this product to chemical treatment with HCl. Preliminary tests carried out with an excess of the former material showed that the insoluble oil was adsorbed with lower yield ( Y=0.40) than the soluble (emulsified) oil ( Y=0.60). The material activation with HCl remarkably improved the adsorption of soluble oil organic fraction ( Y>0.90), while only a little increase in the removal yield was observed for the insoluble oil ( Y=0.44). The results presented and discussed in this work pointed out that the products of dolomite calcination can successfully replace the conventional adsorbing materials in the removal of organic pollutants, with particular concern to exhausted soluble oils, which cannot usually be recycled, thus reducing the operational costs of their treatment.

Thermal Decomposition of Dolomite in an Atmosphere of Carbon Dioxide: The effect of procedural variables in thermal analysis

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 CO2 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.