Calcined Dolomite Research Articles

Exploring dolomite as a promising support for Ni catalysts in CO2 methanation

Ni catalysts supported on Al-modified calcined dolomite were developed, using a natural mineral as the precursor. Treatment with 3% w/w Al improved thermal stability and increased the surface area. The variation in Ni loading (5–30% w/w) was studied to characterize the structural, morphological, and chemical properties. The CO2 capture capacity of the solids, evaluated by Thermogravimetric Analysis at 400 °C (100–800 μmol∙g−1), decreased with increasing Ni loading due to the reduction of basic sites. CO2-TPD analyses revealed the presence of captured CO2 in various basic sites, especially in the strong ones, with efficient formation of thermally stable carbonates. In catalytic tests at 400 °C, conversions exceeding 50% were achieved for higher Ni loadings and around 50% for lower loadings, with 100% selectivity towards CH4. The application of in situ and operando Diffuse reflectance infrared Fourier transform spectroscopy techniques provided insights into the formation of carbonates and their transformation into formate, methoxy, and formyl species, explaining the total selectivity towards CH4 and the absence of CO in the products. This comprehensive approach significantly contributes to the understanding of the reaction dynamics and opens new perspectives for the utilization of Ni catalysts supported on modified dolomite.

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.

Research on dolomite-based shape-stabilized phase change materials for thermal energy storage: Feasibility study of raw and calcined dolomite as skeleton support materials

Mid and high-temperature inorganic salts have limited applications due to their corrosiveness and low thermal conductivity. Shape-stabilized phase change materials (SSPCMs) can ease these issues. This study explored using dolomite, an affordable and abundant mineral with good thermal properties, in SSPCMs. We developed SSPCMs using raw and calcined dolomite at 700 °C, 750 °C, and 800 °C (700Do, 750Do and 800Do) as skeletal support materials (SSMs) and NaNO3-KNO3 as the phase change materials (PCMs). Calcined dolomites had a porous structure compared to raw dolomite (RawDo). 700Do, 750Do and 800Do require a minimum of 50 wt%, 40 wt% and 30 wt% to stabilize the shape of the sintered material by 100 cycles. RawDo was unsuitable for SSM during cycling. XRD confirmed chemical compatibility between components, and SEM showed an even distribution of SSMs within the PCMs. The thermal conductivity of SSPCMs ranged from 1.09 to 1.27 W/(m·K), compared to 0.52 W/(m·K) for NaNO3-KNO3. The NaNO3-KNO3 has a latent heat of about 110.60 J/g and a supercooling degree of 5.84 °C. The latent heat of SSPCMs depends on the proportion of SSMs, slightly lower than the theoretical value by 0.01 %–2.37 %, and the supercooling degree of SSPCMs varies between 4.75 °C and 6.25 °C. The SSPCMs were chemically stable with little latent heat change after 100 cycles, showing excellent cycling stability. The thermal decomposition temperature of SSPCMs containing 700Do was about 580 °C, while SSPCMs containing 750Do and 800Do exhibited a minor decomposition onset at around 380 °C, attributed to Ca(OH)2 decomposition. The best-performing SSPCM contained 30 wt% 800Do, offering a thermal conductivity of 1.27 W/(m·K) and thermal energy storage density of 359 kJ/kg in the 100–320 °C range. In general, calcined dolomite-based SSPCMs offer excellent thermal energy storage performance at a low cost compared to many SSPCMs.

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.

Immobilization of Pb and Zn leached from mining residue materials in Kabwe, Zambia: Performance of calcined dolomite in column experiments

Legacy Pb-Zn mine in Kabwe, Zambia, has left massive stockpiles of mining residue materials (MRM) that contain potentially toxic elements, such as lead (Pb) and zinc (Zn), which pollute the environment. In situ remediation of the contaminated area is an attractive technique for immobilizing hazardous metals. In this study, the efficacy of modified dolomite, i.e., calcined dolomite (CD), was evaluated by mixing with the MRM at 1, 5, and 10 % ratios (CD1, CD5, and CD10, respectively). The leaching of hazardous metals, Pb and Zn, from the MRM was assessed by four-column experiments. Measurements of mineralogical and chemical constituents of the MRM, sequential extraction, and thermodynamic modeling of the leachates were carried out to determine the attenuation mechanisms. Sequential extraction results indicated that the leachable Pb and Zn in the MRM were mainly from the exchangeable and carbonate fractions. Furthermore, the results showed that the effluents from the column with MRM (CD0) exceeded the Zambian effluent regulatory values throughout 30 weeks of the experimental period. The introduction of the CD into the MRM increased effluent pH and decreased the leaching concentrations of Pb and Zn. The CD5 was enough to decrease the leaching concentrations of both hazardous metals below the Zambian effluent standard by prohibiting the release of Pb and Zn via the dissolution of carbonate minerals and retaining them in the carbonate fraction. The saturation indices of Pb and Zn suggest that the retention mechanisms by the CD accredit to precipitation, co-precipitation, and adsorption reactions. These results present an effective and inexpensive immobilization technology for hazardous wastes in abandoned mines.

Accelerated carbonation of one-part sodium carbonate-activated slag cements modified by calcined dolomite

One-part or ‘just add water’ alkali-activated material is one promising option of the clinker-free cementitious material being actively researched as the alternative to traditional Portland cements for lowering the energy consumption and CO2 emission involved in the clinker production. The one-part sodium carbonate (Na2CO3)-calcined dolomite (CD)-activated slag cements were developed in this work. The CD additions were effective in shortening the setting times and meanwhile enhancing the compressive strengths of the binders. The carbonation resistance was investigated under accelerated carbonation protocols at 3.0 ± 0.2% CO2. The CD additions slowed down the kinetics of carbonation. Although the binders still underwent the pore structure degradation, the reactive CaO and MgO supplied by CD promoted the formation of calcium hemi-carboaluminate and hydrotalcite-like phase, which had the layered double hydroxide structure with the anion exchange capacity for binding the ingressive CO32− ions. Therefore, the CD addition should be recognized as a novel approach for improving the carbonation resistance of such one-part Na2CO3-activated slag material.

Hydrogen sulfide removal from simulated synthesis gas using a hot gas cleaning system

This study investigated the removal, adsorption, and regeneration performances of simulated H2S produced from rice straw gasification in a hot gas cleaning system with combination of three types of adsorbents including zeolite, calcined dolomite and activated carbon. These experiments were conducted at 250 ℃ hot gas cleaning system and simulated synthesis gas containing hydrogen sulfide (H2S) concentration at 200 ppm. The experimental results indicated that the tested H2S removal efficiency and adsorbed capacity were observed to be adsorbed in decreasing order: activated carbon > calcined dolomite > zeolite. The adsorption capacities of zeolite, calcined dolomite, and activated carbon are 2.22, 3.16, 5.88 mg S/g adsorbents, respectively. In this research, the calcined dolomite shows poor adsorption-regeneration ability due to its deactivation by H2S. However, the tested zeolite and activated carbon could be fully regenerated at 350 °C with a stable sulfur adsorption capacity during four adsorption-regeneration cycles. These results gained from this study could significantly support researchers obtaining more information about the synthesis gas contaminants removal during hot gas temperature operation process.

Novel SCMs produced by the calcination of secondary aluminium dross with dolomite and their potential usage in cemented paste backfill

In this study, novel supplementary cementitious materials (SCMs) were produced by the mixed calcination of secondary aluminium dross and dolomite. The thermal activation effect on calcined mixes, hydration properties of pastes with the novel SCMs and workability of cemented paste backfill (CPB) were experimentally investigated. The results demonstrated that high-temperature calcination evidently increased the activity of SCM, and the improvement by thermal activation was positively correlated with calcination temperature. Pastes with calcined SCMs hydrated to form more CsbndSsbndH, ettringite and Ht but less portlandite because of the accelerated pozzolanic reaction of SCMs. Moreover, CPB samples with novel SCM had an imporved transportation performance and mechanical strength with denser pore structure. Furthermore, heavy metals (Cu, Pb, Zn and Cr) were well-immobilised/stabilised by CPB with novel SCMs calcined at 900 °C and 1,000 °C, which can make secondary aluminium dross be used without environmental risks.

The steam-assisted calcination of limestone and dolomite for energy savings and to foster solar calcination processes

CaO and MgO are important industrial raw materials commonly produced by either the decomposition of calcium carbonate at about 900 °C, or the calcination of dolomite, a mixed calcium and magnesium carbonate, calcined either to MgO.CaCO 3 at about 750 °C, or to MgO.CaO at 900 °C. ln this research, the decomposition reaction of 104–147 μm dolomite and limestone particles was investigated, both without and with steam added to the reaction. A series of experiments was performed in terms of relevant parameters such as time, temperature and amount of H 2 O added. Reactants and reaction products were fully characterized and demonstrate the different morphology and specific surface area of the raw carbonate ores and the calcined oxides. Adding H 2 O during calcination has a significant positive effect. The calcination shows that steam can significantly accelerate the reaction rate, and reduce the decomposition temperature by ∼100 °C, thus reducing the cost of the decomposition by increasing the yield for a given reaction time, while also reducing the required sensible heat of the feedstock and combustion air . This ultimately reduces the amount of fossil fuel or alternative energy carriers, thus reducing the CO 2 footprint of the system. The improved operating conditions foster the use of concentrated solar calcination. The CO 2 footprint of the carbonate decomposition can be reduced by ∼4% in traditional kilns , and by as much as 20% if concentrated solar kilns are used. Both applications are currently investigated in pilot-scale operations. • Calcination of dolomite and limestone particles was studied, without and with adding steam. • Steam accelerates the reaction rate and reduces the calcination temperature by ∼100 °C. • Adding steam reduces the energy requirement, thus reducing the CO 2 footprint of the system. • CO 2 emissions are reduced by ∼4% in conventional kilns, and by ∼20% in solar kilns applications.

Ni-modified dolomite for the catalytic deoxygenation of pyrolyzed softwood and non-wood to produce bio-oil

This study investigated the effect of process conditions during the catalytic pyrolysis of softwood and non-wood on the pyrolysis product. Ni modified on calcined dolomite (Ni-DM) was used to determine the effectiveness of the catalytic activity and the effect of doping non-noble metals on the product distribution of both pyrolyzed biomasses. The lignocellulosic biomass components showed different effects on the decomposition characteristics of the pyrolysis vapor and its devolatilization, while Ni-DM showed a catalytic effect to enhance the decarbonylation, decarboxylation, and secondary reaction of tar cracking affecting CO2 and CO removal; additionally, the catalytic activity also promoted the formation of aliphatic and olefin hydrocarbon compounds and facilitated C–C cleavage and scission to smaller hydrocarbon compounds. With increased Ni loading, the yield of noncondensable gas increased. Furthermore, gas chromatography analysis indicated that the composition of gas mainly consisted of hydrogen gas, which increased significantly due to a water-gas shift during the catalytic pyrolysis of biomass at high temperature with 10% Ni-dispersed calcined dolomite acting as the catalyst. Meanwhile, the pore structure and the modified-Ni on calcined dolomite enhance decrease acids and sugars in bio-oil yield and favor the formation of alkane gases of liquid hydrocarbon fuels including the dramatically increased in alkane gases.

The effects of reductant and additive on the magnesium extraction from calcined dolomite via metallothermic reduction under vacuum condition

The extraction of magnesium from calcined dolomite via vacuum metallothermic reduction process has been evaluated thermodynamically and investigated experimentally. The equilibrium phases formed during the metallothermic reduction as a function of pressure, reductant, temperature, and additive combination were thermodynamically analyzed. The experimental work consisted of calcination of dolomite – (Ca,Mg)CO3 and metallothermic reduction of the calcined dolomite/dolime – (Ca,Mg)O. The metallothermic reductions of the dolime with different reductants and additives were carried out in a laboratory scale vertical retort at a final holding temperature of 1200 °C and pressure lower than 10−4 atm using different reductant types (ferrosilicon or aluminum) and different additive combinations (CaF2 and B2O3). Magnesium metal was extracted from the dolime through metallothermic reduction by either ferrosilicon or aluminum. The residue from reduction with ferrosilicon disintegrated into fine powder, while the residue from reduction with aluminum remained as briquette. The physical degradation of the residue from reduction with ferrosilicon was found to be minimized by the B2O3 addition. The CaF2 addition increased the magnesium extraction, while the B2O3 addition decreased the magnesium extraction.

Development of a New Dolomite-Based Adsorbent with Phosphorus and the Adsorption Characteristics of Arsenic (III) in an Aqueous Solution

In recent decades, the removal of hazardous chemicals that have entered wastewater and groundwater as a result of industrial and consumer activities has become an issue of concern. Specifically, removing arsenic (III) from groundwater is critical and equally crucial in the use of low-cost, efficient adsorbent materials. One purpose of this study was to develop a low-cost hydroxyapatite adsorbent (Ca5(PO4)3OH) by reacting the Ca component of calcined dolomite with phosphorus, and another was to apply the developed adsorbent to remove arsenic (III) from well water in developing countries. In this study, phosphorus adsorption was performed on thermally calcined dolomite, and the adsorption isotherm of the phosphorus study was investigated on selected calcined dolomite. The maximum amount of phosphorus on the selected calcined dolomite was 194.03 mg-P/g, and the Langmuir isotherm model was fitted. Arsenic (III) adsorption was investigated in a wide pH range (pH 2~12) using the new adsorbent. The amount of arsenic (III) adsorbed was 4.3 mg/g. The new absorbent could be effective in removing arsenic (III) and become an affordable material.

Dolomite-based binders manufactured using concentrated solar energy in a fluidised bed reactor

Dolomite-based binders are characterised by interesting technical and environmental features. For their synthesis, sources of both CaO and MgO are required. The idea developed in this work is to couple the synthesis of dolomite-based binders, starting from a natural dolomite, through the concept of concentrated solar energy (needed to drive the endothermal dolomite calcination process) in fluidised bed reactors. To this end, a fluidised bed system, where the concentrated solar radiation is mimicked by the use of Xe-lamps (short-arc), has been set up and operated. Natural dolomite (sieved in the 420–590 μm size range) was calcined at a nominal temperature of 850 °C, and bed temperature profiles during solar-driven calcination were investigated. Then, four binders were prepared by mixing slaked dolomite (obtained from the hydration of solar calcined dolomite) with either blast furnace slag or coal fly ash as supplementary cementitious materials. The binders were hydrated for curing times ranging from 7 to 56 days. X-ray fluorescence, X-ray diffraction and combined differential thermal and thermogravimetric analyses were employed as characterisation techniques both to analyse the chemical composition of starting materials and to investigate the evolution of the hydration in the four systems.

Effect of calcium-based sorbents on the reduction of chlorinated contaminants during municipal solid waste thermal treatment.

Chlorinated contaminants are a cause of significant concern in the development of municipal solid waste (MSW) thermal treatment techniques. This study investigates the efficacy of two calcium (Ca)-based in-furnace additives, calcium oxide (CaO), and calcined dolomite (CD), at reducing the levels of chlorinated contaminants during MSW thermal treatment. The results reveal that Ca-based additives could effectively reduce the chlorine (Cl) content by more than 76.8% and 37.3% in the gas and tar phases, respectively. The total concentration and the international total equivalent (I-TEQ) value of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-p-furans (PCDD/Fs) were significantly higher under the incineration condition than pyrolysis and gasification conditions. Adding CaO could reduce the total concentration and the I-TEQ value of PCDD/Fs by more than 43.4% and 36.7%, respectively. The reduction effect on PCDD/Fs was more significant in the gaseous phase and the tar phase than the solid phase. CD was more effective than CaO at reducing the chlorinated contaminants, including hydrogen chloride, Cl in the tar phase, and PCDD/Fs. Thus, adding Ca-based sorbents in the furnace during MSW pyrolysis and gasification can effectively reduce PCDD/Fs generation. Based on the experimental results, the mechanism of Ca-based sorbents on the high-temperature homogeneous reaction of PCDD/Fs formation was analysed.

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.

Production Biofuels from Palm Empty Fruit Bunch by Catalytic Pyrolysis Using Calcined Dolomite

In this study, Palm Empty Fruit Bunch (PEFB) was utilized to produce bio-oil through non-catalytic and catalytic pyrolysis process. A fixed-bed reactor was applied to conduct pyrolysis experiments at atmospheric pressure. Comparison of bio-oils obtained from non-catalytic and catalytic pyrolysis wih different pyrolysis temperature was studied in terms product yield. The maximum bio-oil yield of 52.4% was obtained at pyrolysis temperature of 600 °C. Furthermore, based on Gas Chromatography-Mass Spectrophotoscopy (GC-MS) analysis, the percentage of phenolic compounds in bio-oil products from catalyzed pyrolysis showed more higher compared with the non-catalyzed pyrolysis.

Reaction mechanisms for H2O-enhanced dolomite calcination at high pressure

Despite extensive research, our understanding of the dolomite calcination mechanism remains unclear, especially concerning how dolomite calcination is influenced by a change in H2O and CO2 partial pressure under high-pressure conditions. In this study, dolomite calcination behaviors and mechanisms at different H2O and CO2 partial pressures were investigated using thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. Under dry thermal conditions, CO2 has a delaying effect on dolomite calcination; however, this effect is independent of CO2 partial pressure, indicating that the calcination could be controlled by the CO2 adsorption capacity on dolomite active sites. In an H2O atmosphere, calcination might begin at a low temperature due to the adsorption of H2O on active sites and then be controlled by the dissociation of HCO3−. A delaying effect of H2O was also observed, with the H2O partial pressure being lower than the CO2 partial pressure in an H2O and CO2 mixture. This could be attributed to the formation of CO32− via 2OH− + CO2 = CO32− + H2O. A model was developed to predict the dolomite conversion time under isothermal conditions. A process window considering the effect of operating variables on the conversion time at 550–1000 °C and H2O partial pressures of 1–20 bar is presented.

A Comparative Study on the Calcination and Hydration of Dolomite Using Microwave and Electric Furnaces

A Comparative Study on the Calcination and Hydration of Dolomite Using Microwave and Electric Furnaces

Phosphate removal from aqueous solutions using natural and thermic treated dolomites: equilibrium, kinetic, and thermodynamic

This study aims to evaluate the effect of natural and calcined dolomites on phosphate removal in aqueous solution. The solids were characterized and the effects of pH, contact time, and solid concentration on the removal process were analyzed. Dolomite showed an enhanced surface property induced by the thermal treatment at 800 °C, which increased the surface area from 2.350 to 6.229 m2 g−1, calcium and magnesium carbonates were converted to their respective oxides, and the material showed better sorption proprieties for phosphate removal. The adsorption process showed 70–90% of phosphate removal using natural and calcined dolomites, respectively, under the experimental conditions of pH 11, 60 min contact time, and 10 mg L−1 initial phosphate concentration. Pseudo-second-order and Langmuir/Redlich–Peterson were the mathematical models that best described the kinetic and equilibrium mechanisms for phosphate removal. The thermodynamic parameters suggest a spontaneous, endothermic, and random process at the solid/solution interface, confirming a favorable adsorption system. The removal process was controlled by chemisorption phenomena. In that context, natural dolomite can be modified to enhance the surface property induced by the thermal treatment making it a more promising material for use in immobilization of anion pollutants such as phosphate.

A preliminary investigation on gamma-rayattenuation of alkali-activated concrete waste based-geopolymer modified with pozzocrete-fly ash

In the current investigation, pozzocrete fly ash (PFA) was employed to assess its effects on physical, mechanical and radiation shielding properties of alkali-activated geopolymer mixtures prepared using calcined concrete waste-based dolomite aggregate (DCW). Two series of geopolymer samples comprising 6% and 10% sodium hydroxide as alkaline activator were designed. Concrete waste was partially substituted by PFA at levels of 0%, 10%, 15%, 20% and 30%, by weight. Bulk density, compressive strength, attenuation coefficients (μ & μm) as well gamma transmission factors (half-value layer, HVL; tenth-value layer, TVL and mean free path, MFP) of studied samples were determined at different hydration times. The gamma attenuation coefficients of the blend were experimentally conducted with NaI (Tl) scintillation detector utilizing radiation sources namely Cs-137 with photon energy of 0.662 MeV and Co-60 with photon energies of 1.173 and 1.333 MeV. The inclusion of 15% PFA in DCW-geopolymer system alkali-activated with 10% NH has resulted in the enhancement of both physical and mechanical properties. In a similar fashion, this geopolymer composite demonstrated superior performance in terms of attenuation of gamma rays through a 5 cm thickness shield over the corresponding mixtures.