Decomposition Of Dolomite Research Articles

Properties of CaO-MgO-SiO2 insulating refractories prepared from phosphorus tailings

CaO-MgO-SiO2 insulating refractories were prepared using phosphorus tailings through in-situ pore-forming technology in this work, aiming to achieve the efficient utilization of solid waste phosphorus tailings. microsilica was used to react with free CaO generated by the decomposition of dolomite from phosphorus tailings during the calcination in order to prevent the hydration of CaO in the materials. The influence of microsilica addition and heating temperature on the properties of insulating refractories prepared from phosphorus tailings was investigated. The results showed that CaO-MgO-SiO2 insulating refractories with 8.8 wt% microsilica addition exhibited excellent comprehensive performance after heating at 1300 °C for 3 h. The insulation refractories prepared from phosphorus tailings were anti-hydration, had lower thermal conductivity, and could be used as insulation refractories for high-temperature kilns.

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.

Exploring in-situ combustion effects on reservoir properties of heavy oil carbonate reservoir

Laboratory modeling of in-situ combustion is crucial for understanding the potential success of field trials in thermal enhanced oil recovery (EOR) and is a vital precursor to scaling the technology for field applications. The high combustion temperatures, reaching up to 480 °C, induce significant petrophysical alterations of the rock, an often overlooked aspect in thermal EOR projects. Quantifying these changes is essential for potentially repurposing thermally treated, depleted reservoirs for CO2 storage.In this study, we depart from conventional combustion experiments that use crushed core, opting instead to analyze the thermal effects on reservoir properties of carbonate rocks using consolidated samples. This technique maintains the intrinsic porosity and permeability, revealing combustion's impact on porosity and mineralogical alterations, with a comparative analysis of these properties pre- and post-combustion. We characterize porosity and pore geometry evolution using low-field nuclear magnetic resonance, X-ray micro-computed tomography, and low-temperature nitrogen adsorption. Mineral composition of the rock and grain-pore scale alterations are analyzed by scanning electron microscopy and X-ray diffraction.The analysis shows a significant increase in carbonate rocks’ porosity, pore size and mineral alterations, and a transition from mixed-wet to a strongly water-wet state. Total porosity of rock samples increased in average for 15%–20%, and formation of new pores is registered at the scale of 1–30 μm size. High-temperature exposure results in the calcite and dolomite decomposition, calcite dissolution and formation of new minerals—anhydrite and fluorite. Increased microporosity and the shift to strongly water-wet rock state improve the prospects for capillary and residual CO2 trapping with greater capacity. Consequently, these findings highlight the importance of laboratory in-situ combustion modeling on consolidated rock over tests that use crushed core, and indicate that depleted combustion stimulated reservoirs may prove to be viable candidates for CO2 storage.

Pore Structure Evolution and Failure Mechanism of Limestone in the Taiyuan Formation of the Ordos Basin under High Temperature.

The study on the destruction of the limestone microstructure after high-temperature treatment has a significant value in the airtightness and safety of underground high-temperature geotechnical engineering. In order to truly simulate the influence of the underground high-temperature environment on limestone, taking seven groups of limestones of the Taiyuan Formation in the Ordos Basin as examples, we carried out a high-temperature (25-1200 °C) heating experiment of limestone in an argon atmosphere. The pore structure of limestone after the high temperature is studied based on scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), porosity, and permeability, and the change in the fractal dimension of the limestone pore structure was discussed based on the thermodynamic fractal theory, combined with X-ray diffraction (XRD) and thermogravimetry differential scanning calorimetry (TG-DSC), the variation of mineral composition with temperature is characterized, and the evolution mechanism of the limestone microstructure under high temperature is discussed. The results show that the evaporation of pore water does not destroy the lattice structure of limestone minerals; however, with the increase of temperature, the complete decomposition of dolomite and calcite occurs, along with the tensile fracture of calcite crystals under the effect of swelling stress. Moreover, the new minerals generated by the decomposition products under the effect of temperature severely damage the crystal structure, leading to the rapid increase of porosity and permeability. The comprehensive results show that the decomposition, expansion, and recrystallization of calcite and dolomite minerals after 800 °C led to the development of limestone macropores and fissures, increased the pore throat radius, enhanced the pore connectivity, simplified the pore structure, and sharply increased the permeability; thus, 800 °C can be used as the critical temperature to change the limestone pores and fractures. The research results can provide data support for subsurface high-temperature geotechnical engineering.

Decomposition mechanism of lumpy dolomite particles

Cylindrical cm-sized dolomite particles were decomposed using the two steps decomposition scheme. Several studies on dolomite decomposition have been done using µm- to mm-sized samples over the years. However, these sizes are too small for industrial kiln application and ignore the influence of important parameters, e.g. thermal conductivity, on the decomposition process. In this work, the decomposition behavior of lumpy dolomite particles in each step was investigated. Experimentally measured sample temperature and conversion profiles in steps 1 and 2 are respectively similar to those obtained for the decomposition of pure magnesite and limestone. To measure the core temperature and conversion is to essentially analyze the decomposition behavior. The thermophysical material properties of the decomposition product in each step as a function of temperature was estimated using the shrinking core model. Finite difference method was employed in solving the 1D heat equation describing the process. The reaction rate coefficient in step 1 is shown to have a weak temperature dependence, the thermal conductivity of the product, MgO∙CaCO3, slightly increases with temperature but the permeability is not dependent. In step 2, the reaction coefficient and MgO∙CaO thermal conductivity and pore diffusivity do not show a clear temperature dependence. Finally, the sensitivity of the material and transport properties on the decomposition process was studied under shaft kiln condition. Thermal conductivity is observed to have the highest influence on decomposition with a value of up to 60 % at 1400 °C and for 120 mm particles.

Preparation of diatomite-based porous ceramics containing interlayer porous MgO by low-temperature sintering for integration of high strength and low thermal conductivity

In this work, hierarchical porous ceramics based on diatomite with both high strength and low thermal conductivity were prepared by low-temperature sintering using modified diatomite and dolomite as the main raw materials. In particular, dolomite served both as a pore-forming agent to produce CO2 gas and as a ceramic component to produce porous MgO in situ. The prepared porous ceramics exhibited a hierarchical pore structure, retaining 2–300 nm nano-pores of the diatomite itself while using dolomite decomposition to produce 1–10 µm macro-pores and porous MgO with inter-layer pore sizes of 50–300 nm. The main phases of porous ceramics were cristobalite phase, pyroxene phase, wollastonite phase and MgO phase with special structure. The effect of dolomite addition on the mechanical properties and thermal insulation of porous ceramics was investigated. It was found that the addition of 30% dolomite resulted in a porous ceramic with a porosity of 59.8% and the most favorable pore size distribution. At this time, the presence of wollastonite and pyroxene-like products in the porous ceramics contributed to the highest compressive and bending strengths of 29.66 MPa and 7.22 MPa, respectively. The lowest thermal conductivity of the porous ceramics reached 0.094 W·m−1K−1, which can be attributed to the synergistic effect of the hierarchical pores and the increasing interfacial thermal resistance. Overall, the prepared hierarchical porous ceramics exhibited great potential as an alternative material to ceramic fiber insulation in high-temperature kilns.

Half-decomposition of salt-bearing dolomite.

Half-calcined dolomites (HCDs) have been widely used in environmental remediation, medicine, and construction. However, advanced calcination technologies are required to modify their microstructure and thus improve their working performance. Herein, we investigated the effects of a variety of inorganic salts on the decomposition of dolomite based on thermogravimetric, compositional, and morphological analysis. The thermogravimetric data showed that certain salts significantly lowered the half-decomposition temperature of dolomite, which included LiCl, CaCl2, MgCl2, AlCl3, LiNO3, KNO3, K2CO3, Li2CO3, Li2SO4, Na3PO4, and K3PO4. Compositional analysis demonstrated that only half-decomposition occurred when salt-bearing dolomite was calcined at a temperature of 723-923 K, leading to the formation of CaO-free HCDs composed of periclase and Mg-calcite having a Mg level of 2.0-10.5 mol%. Morphological analysis showed that porous HCDs were feasibly obtained by calcining salt-bearing dolomite at 723-923 K. MgO coarsening occurred at a temperature above 873 K, but it could be avoided by controlling the calcination time. The mechanism of salts may be related to the heterovalent doping effect, which may lead to an increase in the concentration of vacancies in the dolomite lattice.

A rapid and environment-friendly process for dolomite pellets calcination with Joule-heating

Dolomite is an important industrial raw material for the production of metal magnesium. However, the calcination of dolomite is a typical pollution-intensive industry and is one of the major contributors to CO2 emissions in China. The requirements of energy conservation and environmental protection are driving the development of new calcination technologies. Herein, we developed a rapid and environment-friendly strategy for the calcination of dolomite used in subsequent magnesium production through carbothermal reduction, in which the pellets containing dolomite and carbon additive are calcined with in-situ Joule-heating in a vacuum. The effect of input volumetric specific power, heating time, vacuum conditions, carbon additive, and the size of the pellets on the decomposition process has been systematically studied. The dolomite in the pellets can be completely decomposed within tens of seconds. And the kinetic analysis shows that the activation energy of the decomposition of dolomite with the Joule-heating method is 108.4 kJ mol−1, which is much lower than the previous reports. Note that, the novel strategy shows a reduction of calcination time by 70 times, a reduction of energy consumption by 6.22% and a reduction of direct carbon emissions by 56.77% compared to the traditional methods. Combining the results of finite element simulations and density functional theory calculations, we revealed the mechanism of Joule-heating to enhance the decomposition of dolomite. The results show that the Joule-heating method can offer a distinct heating mechanism and deteriorate the structure stability of CaMg(CO3)2.

Thermal Decomposition Analysis of Indonesian Natural Dolomite in Air

Dolomite is widely used in the construction, glass ceramics, iron and steel, pharmaceutical industries, as a source of CaO and MgO and as thermal energy storage material. Thermal decomposition analysis of natural dolomite of the so-called Jeddih limestone has been carried out. A thermogravimetry analysis (TGA) in the air evaluates the thermal decomposition of dolomite. The natural dolomite has been analyzed by x-ray flourescence (XRF) and x-ray diffraction (XRD) to test crystal structure and decomposition phase, fourier transform infra-red (FTIR) was utilized to identify the presence of functional groups. The particle morphology was observed by scanning electron microscopy. TGA curve shows that the thermal decomposition of dolomite occurs in two stages. The first stage is in temperature range of 600 - 779°C and the second one is at the temperature 779°C. The results are in line with the XRD and FTIR measurements. Which shows that calcite begins to grow at a temperature of 600°C and MgO phase is observed at 700 - 900°C. Moreover, CaO phase starts to be found at 800°C.

Effect of trisodium phosphate on the decomposition of dolomite

Dolomite calcination is of important industrial significance in versatile scenarios. This paper reports the effect of trisodium phosphate on dolomite decomposition. The thermogravimetric tests showed that the dolomite with 1.0 wt. % Na3PO4 (Na3PO4-dolomite) partially decomposed into MgO and magnesian calcite (Mg-CaCO3) and the formed Mg-CaCO3 then decomposed subsequently. The Na3PO4 lowered the temperature and significantly enhanced the rate of partial decomposition of dolomite. The change in the apparent activation energy (178.5-104.0 kJ/mol) versus the conversion indicated that multiple steps were involved in the partial decomposition of Na3PO4-dolomite. In the partial decomposition, Mg-CaCO3 with different Mg contents and MgO formed as final products. The Mg content of the Mg-CaCO3 was dependent on the calcination conditions. High-magnesian calcite (>10 mol% Mg) was obtained by calcining Na3PO4-dolomite at 873 K within 60 min.

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

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

A novel route for the fabrication of melilite-spinel porous ceramics with ultralow thermal conductivity and sufficient strength

Melilite-spinel porous ceramics with high apparent porosity, sufficient strength and ultralow thermal conductivity were successfully prepared via a direct-thermal decomposition route using the solid waste of phosphorus tailings and coal gangue as raw materials. The micropores are derived from the in situ decomposition of dolomite and kaolinite, whose morphology, distribution form and quantity determine the thermal insulation performance and physical properties of porous ceramics. Melilite-spinel porous ceramics with an ultralow thermal conductivity of 0.036 W/(m·K) (tested at 200 °C), an apparent porosity of 61.3% and a compressive strength of 2.95 MPa, exhibited promising application prospects in thermal insulation materials used for high-temperature fields.

Sorption-enhanced chemical looping steam reforming of glycerol with CO2 in-situ capture and utilization

Hydrogen production from chemical looping steam reforming using an oxygen transport catalyst is definitely enhanced by CO2 in-situ capture, which shifts the chemical equilibrium and reduces the energy demands. The utilization of CO2 from this process as a reactant for chemicals and fuels could help to improve economic reasons and mitigate its impact on climate. In this study, we proposed a sorption-enhanced chemical looping steam reforming of glycerol to realize the synergetic capture and conversion of CO2 in one integrated chemical looping hydrogen production process. The process is characterized to usethe oxidized NiO/NiAl2O4 as a steam reforming catalyst, the reduced NiO/NiAl2O4 as a CO2-CH4 dry reforming catalyst, and the inexpensive dolomite as a CO2 sorbent. The surface carbon that would deactivate the catalyst is combusted by air after CO2-CH4 dry reforming and the Ni on the catalyst is re-oxidized. The coupling of these different processes of chemical looping steam reforming, CO2 in-situ capture, dolomite decomposition and CO2 in-situ utilization, results in simultaneous generation of high purity hydrogen and syngas. The results demonstrated that hydrogen of above 92.5% was one-step generated and CO2 was decreased to zero in the pre-CO2 breakthrough periods. The reduced NiO/NiAl2O4 catalysts favored the CO2-CH4 dry reforming at 850 °C. The syngas of H2-to-CO molar ratios of 0.8–1.1 through the conversion of CO2 from in-situ extraction of the absorbed CO2 dolomite, was produced. The NiO/Al2O4 with 15 wt% NiO gave the highest hydrogen and syngas yields, and maintained high performance for the proposed system. The catalysts and dolomite exhibited good stability with no obvious loss of activity in 10 cycles.

Phase evolution and lightweight application of dolomite@Al2O3 spherical particle with core–shell structure

AbstractDolomite@Al2O3 spherical particles with core–shell structure were fabricated by using the dolomite powders as the core and wrapping corundum powders on their surface. The phase evolution and microstructure of the dolomite@Al2O3 spherical particles with different firing temperatures were studied. As the spherical particles fired at different temperatures, the dolomite in the spherical core decomposed into MgO and CaO. Due to the Kirkendall effect, MgO and CaO diffused into the shell of the spherical particle and left Kirkendall holes in the core. The holes produced by the Kirkendall effect and the decomposition of dolomite act together to form a hollow structure in the center. And during the diffusion process, MgO and CaO reacted with corundum to generate spinel and calcium hexaaluminate. A small amount of spinel and calcium hexaaluminate can form a ternary compound Ca2Mg2Al28O46. Moreover, simulation software Factsage and Abaqus were used separately to help prove the phase evolution and the introduction of spherical particles to the properties of refractories. To test the lightweight effect of dolomite@Al2O3 spherical particles on refractories, it was introduced into spinel–corundum refractories as medium particles in different content and fired at different temperatures. The results show that after firing at 1650°C for 3 h with introducing 30% dolomite@Al2O3 spherical particles, the samples can reach a high compressive strength (128 MPa), high refractoriness under load (1683°C), and low thermal conductivity (1.79 W (m K)−1).

Reservoir Properties Alteration in Carbonate Rocks after In-Situ Combustion

Summary This study summarizes the work conducted as a part of laboratory modeling of in-situ combustion (ISC) experiments on cores from carbonate heavy oil fields. Porosity, permeability, fluid saturation, thermal, and geochemical properties are crucial characteristics of the target field defining the performance of the combustion technology. Here, we report the changes in reservoir properties, porous structure, and mineral composition of the rock samples induced by the thermal exposure and registered by a set of standard and advanced experimental techniques. Most combustion tests are conducted on the crushed core pack, which does not accurately represent the reservoir properties. In this paper, we present the results of three combustion tube tests (classic ISC and consecutive hot-water treatment ISC) involving actual field core samples. Gas porosimetry, nuclear magnetic resonance (NMR), and microcomputed tomography (μCT) revealed an increase in total porosity and pore size distribution and enabled visualizing the changes in the porous core structure at nano- and microlevels. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated the change in mineral composition and lithological texture as a result of dolomite decomposition; Rock-Eval pyrolysis and elemental analysis were utilized to confirm the changes in the rock matrix. Optical scanning registered the changes in thermal conductivity (TC) of samples, which is important for numerical modeling of the combustion process. The proposed core analysis has proved its efficiency in providing a complete petrophysical description of the core of a heavy oil carbonate reservoir in the framework of evaluation of the ISC application for dolomite-rich carbonates and demonstrated the different responses of rock to the ISC technology.

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.

Calcination Condition of Dolomite‐Based Materials Influencing Static Dissolution in Synthetic Electric Arc Furnace Slag

The addition of basic additives in steelmaking processes is essential because these lead to slag adaptation and enable refining reactions. In calcination treatment, the process parameters temperature and dwell time influence the decomposition of dolomite as a magnesium‐containing lime substitute. It results in specific properties such as varying residual fractions of carbonates CaCO3·MgCO3 and porosity. The properties affect the dissolution kinetics, and the fast and complete dissolution is of interest. Hence, the static high‐temperature dissolution tests using dolomite‐based samples in diverse conditions (raw, modified, soft‐burnt, and hard‐burnt) are executed to determine the impact of the calcination state. The specimens are immersed in synthetic electric arc furnace slag, including 10 wt% Al2O3, 25 wt% SiO2, 25 wt% CaO, 8 wt% MnO, and 32 wt% FeO. The dolomite or dolime dissolves in the stagnant oxidic melt within the reaction time of 10 min at 1450 °C. The resulting chemistries of quenched slags, representing the current dissolution status, are examined by scanning electron microscopy using energy‐dispersive X‐ray spectroscopy analysis on metallographically prepared cross‐sections and via X‐ray fluorescence analysis of mechanically extracted slag fractions. The dissolution performance is characterized and compared for the different additive materials.

Dissolution and sedimentation patterns of typical minerals in artificial reservoirs under different environments

Injection of circulating fluids (usually water) is the predominant means of heat extraction in enhanced geothermal systems (EGS), but the additional injection of circulating fluids can cause a water-rock reaction with the dry-thermal rock mass, resulting in the generation of a large number of secondary minerals. These secondary minerals cause fracture closure in artificial reservoirs and severely impede the sustainable use of geothermal systems. So, this paper combines the laboratory test with PHREEQC hydrogeochemical simulation. Firstly, the changes and mechanisms of mineral and aqueous chemical fractions in the artificial reservoir fractures were analysed after using groundwater from the sandstone aquifer at the FORGE site, as a heat transfer fluid, in the FORGE project of USA. Secondly, The patterns of dissolution and precipitation of minerals commonly found in artificial fractures in four different environments were then simulated with the aid of Phreeqc after completion of the transconversion. Finally, the effect of different unblocking fluids on the unblocking of these typical minerals is evaluated. The results show that groundwater as a heat transfer fluid causes dissolution of K-feldspar, albite, illite and partial decomposition of kaolinite and proto-silicate, and is also accompanied by rapid production of anorthite, decomposition of dolomite, sodization of Ca-montmorillonite and dolomitization of black mica. Mud acid will be more effective in unblocking fissure closures caused by anorthite, chlorite and kaolinite. NaOH will be more effective in unblocking fissure closures caused by illite and Ca-montmorillonite. Groundwater is not suitable as a blocking remover and can produce secondary mineral blockages(calcite, aragonite)easily. The effect of ultrapure water is relatively stable, it can be used as a heat exchange fluid or blocking remover, but when used as a blocking remover, it is mainly a physical-mechanical action process.

Thermal decomposition of ferroan dolomite: A comparative study in nitrogen, carbon dioxide, air and oxygen

The mechanism and kinetics of the process of thermal decomposition of low-manganese ferroan dolomite were investigated by non-isothermal derivative thermogravimetric analysis in this work. The study of the effect of the composition of gaseous phase on the mechanism and kinetics of thermal decomposition process includes the kinetics experiments performed in nitrogen, carbon dioxide, air and oxygen. While the process of endothermic decomposition takes place in one-step in a carbon dioxide-free atmosphere or in air, three separate reactions take place in carbon dioxide. The activation energy of these three reactions is also significantly higher than that of the thermal decomposition of ferroan dolomite in nitrogen, oxygen or air.

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.