Calcination Of Calcium Carbonate Research Articles

Silica extraction from sodium silicate for wollastonite synthesis at low temperatures

In this study, ceramic wollastonite was prepared at low temperatures by using amorphous silica and calcium oxide powders. The amorphous silica was extracted from sodium silicate, while calcium oxide (CaO) was obtained through the calcination of calcium carbonate (CaCO3) particles. The effect of reaction temperature on the formation of wollastonite was systematically investigated. The synthesized powders were analyzed using various characterization techniques, including X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results indicate that the synthesized silica nanopowders exhibit a notable surface area, with specific surface area (SSA) values reaching 148 m²/g for samples subjected to calcination at 600°C. Furthermore, based on XRD and differential scanning calorimetry (DSC) analyses, it is evident that β-CaSiO3 forms at approximately 780°C and subsequently undergoes complete transformation into α-CaSiO3 at 1200°C. Notably, this study underscores that the utilization of amorphous silica expedites wollastonite formation at lower temperatures compared to those reported in existing literature.

Decarbonising the Portland and other Cements-Via Simultaneous Feedstock Recycling and Carbon Conversions Sans External Catalysts.

The current overarching global environmental crisis relates to high carbon footprint in cement production, waste plastic accumulation, and growing future energy demands. A simultaneous solution to the above crises was examined in this work. The present study focused on decarbonizing the calcination process of the cement making using waste plastics and biowastes as the reactants or the feedstock, to reduce the carbon footprint and to simultaneously convert it into clean energy, which were never reported before. Other studies reported the use of waste plastics and biowastes as fuel in cement kilns, applicable to the entire cement making process. Calcination of calcium carbonate and magnesium carbonate is the most emission intensive process in cement making in Portland cements and Novacem-like cements. In the Novacem process, which is based on magnesium oxide and magnesium carbonates systems, the carbon dioxide generated is recycled to carbonate magnesium silicates at elevated temperatures and pressures. The present study examined the Novacem-like cement system but in the presence of waste plastics and biomass during the calcination. The carbon dioxide and the methane produced during calcination were converted into syngas or hydrogen in Novacem-like cements. It was established that carbon dioxide and methane emissions were reduced by approximately 99% when plastics and biowastes were added as additives or feedstock during the calcination, which were converted into syngas and/or hydrogen. The reaction intermediates of calcination reactions (calcium carbonate–calcium oxide or magnesium carbonate–magnesium oxide systems) can facilitate the endothermic carbon conversion reactions to syngas or hydrogen acting as non-soot forming catalysts. The conventional catalysts used in carbon conversion reactions are expensive and susceptible to carbon fouling. Two criteria were established in this study: first, to reduce the carbon dioxide/methane emissions during calcination; second, to simultaneously convert the carbon dioxide and methane to hydrogen. Reduction and conversion of carbon dioxide and methane emissions were facilitated by co-gasification of plastics and bio-wastes.

Correlation between Uniaxial Compression Test and Ultrasonic Pulse Rate in Cement with Different Pozzolanic Additions

This work aims to study the relationship between the compression resistance and velocity from ultrasonic pulses in samples of mortars with 25% of pozzolanic content. Pozzolanic cement is a low-priced sustainable material that can reduce costs and CO2 emissions that are produced in the manufacturing of cement from the calcination of calcium carbonate. Using ultrasonic pulse velocity (UPV) to estimate the compressive resistance of mortars with pozzolanic content reduces costs when evaluating the quality of structures built with this material since it is not required to perform an unconfined compression test. The objective of this study is to establish a correlation in order to estimate the compression resistance of this material from its ultrasonic pulse velocity. For this purpose, we studied a total of 16 cement samples, including those with additions of pozzolanic content with different compositions and a sample without any additions. The results obtained show the mentioned correlation, which establishes a basis for research with a higher number of samples to ascertain if it holds true at greater curing ages.

Green Preparation of Few‐Layer Graphene Sheet Materials Using Naturally Occurring Calcium Carbonate and Plant Leaves

AbstractGraphene sheets were prepared by calcination of calcium carbonate with plant leaves under the protection of an argon gas atmosphere. This is an environmentally friendly approach to produce graphene. Calcium carbonate decomposes with the evolution of carbon dioxide at high temperature, which is reduced into graphene by the magnesium from plant leaves. The formation mechanism of graphene is discussed in detail. The synthesized graphene sheets were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Raman spectroscopy. Calcium carbonate and plant leaves are readily available and inexpensive natural resources, and this new methodology can be applied for large‐scale graphene production in industry.

Co-Pyrolysis of Beet Pulp and Defecation Lime in TG-MS System

The process of pyrolysis of beet pulp, a by-product after the extraction of raw sugar from sugar beet, with the addition of defecation lime was studied in a thermobalance coupled with a mass spectrometer. The beet pulp pyrolysis process took place completely at 600 °C, and the resulting char, tar and gas were characterized by higher heating values of 23.9, 21.6 and 7.77 MJ/kg, respectively. The addition of the defecation lime to beet pulp caused both an increase in the char production yield and a decrease in the tar production yield. At the same time, the higher heating value of char and tar decreased along with the increase of defecation lime added to the sample. The deconvolution of derivative thermogravimetric (DTG) curves allowed us to identify the basic components of beet pulp, for which the activation energy by isoconversion method was calculated. The 20 wt.% addition of defecation lime caused an increase of the activation energy by about 18%. Further increase in the defecation lime content resulted in a reduction of activation energy. At the temperature above 600 °C, calcination of calcium carbonate contained in defecation lime occurred. The CO2 produced during calcination process did not cause auto-gasification of char.

Probing the Influence of Thermally Induced Structural Changes on the Microstructural Evolution in Shale using Multiscale X-ray Scattering Measurements

Various pathways to accelerate the recovery of hydrocarbons from unconventional subsurface environments have been proposed, including the use of high-temperature fluids. However, the influence of temperature on the structural and microstructural changes in complex subsurface materials characterized by compositional and morphological heterogeneity are not very well understood. In this study, in operando ultrasmall angle, small angle, and wide-angle X-ray scattering (USAXS/SAXS/WAXS) measurements were performed to link the structural and morphological changes in shale when heated from 30 to 1150 °C. The structural changes observed from the wide-angle X-ray scattering measurements were complemented by the changes in the porosity, particle size, and surface morphology. Overall, the combined USAXS/SAXS measurements showed enhanced smoothness in the pore–solid interface on heating. The dehydroxylation of illite and calcination of calcium carbonate were noted prior to the formation of denser and sintered silicat...

Power cycles integration in concentrated solar power plants with energy storage based on calcium looping

Efficient, low-cost and environmentally friendly storage of thermal energy stands as a main challenge for large scale deployment of solar energy. This work explores the integration into concentrated solar power plants of the calcium looping process based upon the reversible carbonation/calcination of calcium oxide for thermochemical energy storage. An efficient concentrated solar power-calcium looping integration would allow storing energy in the long term by calcination of calcium carbonate thus overcoming the hurdle of variable power generation from solar. After calcination, the stored products of the reaction (calcium oxide and carbon dioxide) are brought together in a carbonator reactor whereby the high temperature exothermic reaction releases the stored energy for efficient power production when needed. This work analyses several power cycle configurations with the main goal of optimizing the performance of the overall system integration. Possible integration schemes are proposed in which power production is carried out directly (using a closed carbon dioxide Brayton power cycle) or indirectly (by means of a steam reheat Rankine cycle or a supercritical carbon dioxide Brayton cycle). The results obtained show that the highest plant efficiencies (up to 45–46%) are achievable using a closed carbon dioxide Brayton power cycle.

An approach for synthesizing graphene with calcium carbonate and magnesium

Graphene sheets were prepared by the calcination of calcium carbonate with magnesium powder under the protection of argon gas flow. CaO, MgO and graphene sheets were achieved by the reaction of CaCO3 with Mg, which is an environmentally friendly way for producing graphene. The graphene sheets were characterized by transmission and scanning electron microscopy, X-ray diffraction, atomic force microscopy and Raman spectroscopy. Few-layer graphene was prepared, with the number of layers ranging from 4 to 10.

Carbon dioxide capture from combustion flue gases with a calcium oxide chemical loop. Experimental results and process development

Post-combustion carbonate looping processes are based on the capture of carbon dioxide from the flue gases of an existing power plant in a circulating fluidized bed reactor (CFB) of calcium oxide (the carbonator) particles. The calcination of calcium carbonate in a new oxy-fired CFBC power plant regenerates the sorbent (calcium oxide particles) and obtains high purity carbon dioxide. This communication presents experimental results from a small test facility (30 kWt) operated in continuous mode using two interconnected CFB reactors as carbonator and calciner. Capture efficiencies between 70 and 97% have been obtained under realistic flue gas conditions in the carbonator reactor (temperatures around 650 °C). The similarity between process conditions and those existing in CFBC power plants should allow a rapid scaling up of this technology. The next steps for this process development are also outlined.

Investigation of Phase Evolution During the Thermochemical Synthesis of Tricalcium Phosphate

The formation of tricalcium phosphate (TCP) from dicalcium phosphate and calcium carbonate was investigated using differential thermal analysis (DTA), thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD). DTA showed three distinct thermal events attributed to dehydration of dicalcium phosphate dihydrate (brushite, DCPD) to dicalcium phosphate anhydrous (monetite, DCPA), the formation of beta-calcium pyrophosphate (β-Ca2P2O7), and the calcination of calcium carbonate. TGA showed three weight losses corresponding to the three thermal events, respectively. XRD analysis showed that β-TCP formed, beginning at about 900°C, by the reaction of β-Ca2P2O7 with CaO and β-TCP changed to α-TCP above 1200°C. Further examination of the formation of TCP from calcium hydroxide (Ca(OH)2) and DCPA showed that β-TCP would form only after the decomposition of Ca(OH)2 to CaO and from the reaction of CaO with β-Ca2P2O7 at a fairly low temperature of 800°C. In addition, by naturally cooling α-TCP, formed at 1300°C within the heating furnace, to room temperature, it was difficult to obtain a pure phase of β-TCP. The proposed mechanism of the reaction to form TCP may include the dehydration of brushite to monetite, dehydration of monetite to beta-calcium pyrophosphate, decomposition of calcium carbonate, the formation of β-TCP, and phase transition.

Phase Evolution during the Formation of α‐Tricalcium Phosphate

The formation of α‐tricalcium phosphate from monobasic ammonium phosphate and calcium carbonate was investigated using a number of complementary techniques. Differential thermal analysis showed five distinct thermal events attributed to melting of the ammonium phosphate, decomposition of acidic calcium orthophosphate into an amorphous calcium metaphosphate, crystallization of β‐calcium metaphosphate, crystallization of β‐calcium pyrophosphate, and calcination of calcium carbonate. X‐ray diffraction analyses as a function of temperature supported the evolution of these events and phases and also showed the formation of other intermediates, including an amorphous phase, apatite, lime, and β‐tricalcium phosphate. Thermal gravimetric analysis (TGA) showed a large weight loss occurring between 150° and 250°C due to reaction between the acidic phosphate liquid and the calcium carbonate. This resulted in an amorphous intermediate with a Ca/P ratio between 0.5 and 1.0 from which both β‐calcium metaphosphate and β‐calcium pyrophosphate crystallized. Mass spectroscopy indicated that the ammonia and carbon dioxide were evolved in four different steps, while water was evolved in at least five steps. These decomposition steps correlated with those observed by TGA. Scanning electron microscopy indicated the formation of an intermediate phase that coated the calcium carbonate by 250°C. The proposed mechanistic reaction path to alpha‐tricalcium phosphate involves the formation and consumption of the following sequence of intermediates: an acidic amorphous condensed phosphate; β‐calcium metaphosphate and β‐calcium pyrophosphate; lime, apatite, and β‐tricalcium phosphate.

Hydrothermal synthesis of xonotlite whiskers by ion diffusion

Xonotlite, a calcium silicate hydrate, has been industrially produced as a main constituent for heat insulating material [1, 2], building material [1, 3] and artificial wood [1, 4], because of its high stability at high temperature and fibrous crystal form. It is usually prepared from a suspension of silica and calcium hydroxide by hydrothermal treatment [5– 10]. Formation mechanism of xonotlite crystals from the suspension is complicated, because various intermediate reaction products are formed in the reaction processes. For example, calcium hydroxide reacts with low-quartz particles to form calcium-rich CSH (low crystalline calcium silicate hydrates) in the first stage of the reaction. Compositional change in CSH to equivalent Ca=Si ratio leads to crystallization of tobermorite which transforms to xonotlite by further hydrothermal treatment [5]. The size of the xonotlite crystals thus prepared is limited because of formation from these intermediate products. Kunugida et al. [11] pointed out that direct preparation of xonotlite, not through intermediate products such as CSH and tobermorite, was important for preparation of long fibre xonotlite. They obtained long fibre xonotlite crystals with maximum length 2 mm at 350 8C in the continuoustype autoclave by the two processes, in-situ mixing and rapid heating of raw materials. They reported that recrystallization of xonotlite also lengthened the crystals. We consider that continuous crystal growth provides elongation of xonotlite crystals under conditions where xonotlite is stable. We report here the preparation of xonotlite whiskers at 250 8C using a continuous supply of calcium and silicate ions in a multichamber autoclave where silica and calcium hydroxide are separately placed. The multichamber autoclave used in this study is shown in Fig. 1. It was made of stainless steel with total inner volume 50 cm3 and had two separate chambers each with volume 12.5 cm3. Two kinds of silica sources were used; silica gel (Wakogel C-300, Wako Pure Chem. Ind., Japan, 200–300 mesh) and low-quartz powder (SiO2 99.5 wt %, Al2O3 0.2 wt %) consisting of coarse grains from 20–150 im in diameter, produced by crushing silica stone (from Fukushima Prefecture, Japan) and classifying from the water suspension by gravitational sedimentation. Calcium source was a pellet of calcium oxide produced by calcination of calcium carbonate (reagent grade, Wako Pure Chem. Ind., Japan) at 1100 8C for 3 h. After placing the silica and calcium source (0.5 g each) at the bottom of each chamber, decarbonated distilled water (30 cm3) was poured slowly into the autoclave so not to suspend the raw materials. The silica source was brought into contact with the calcium source via the water; thus, ion species dissolved from the two sources diffuse to each other in the autoclave to produce calcium silicate hydrates. Platinum plates were placed in the autoclave (Fig. 1) to collect the reaction products formed by ion diffusion. These operations were performed in a glove box purged of carbon dioxide with nitrogen gas. The autoclave was heated at 250 8C for 2 to 72 h in an electric oven without temperature gradient; it took about 1 h to heat the autoclave to 250 8C. At the conclusion of the hydrothermal treatment, the autoclave was cooled down to room temperature by a cold air blow, and dried in vacuum after removal of the water. The reaction products, precipitated on the platinum plates, were observed by scanning and transmission electron microscope equipped with an energy dispersive X-ray spectrometer and identified by X-ray powder diffraction. When silica gel was used as a silica source, a large quantity of ribbon-like crystals were obtained after 2 h at 250 8C (Fig. 2a). X-ray diffraction showed that they were low crystalline tobermorite

The Potential Use of Catalysts in the Cement Industry

Abstract The calcination of calcium carbonate in a cement or a lime kiln requires approximately two to four times the theoretical quantity of energy predicted from thermodynamic analysis depending upon the type of cement kiln used. The potential for using catalysts to reduce the total energy requirements was explored. It is, of course, impossible to reduce the theoretical energy requirement for the calcination process. Two possible ways considered to reduce this total requirement were (1) to either increase the rate of calcination at a specific temperature or (2) to decrease the temperature of calcination. Several classes of catalysts show promise of doubling the calcination rate (or decreasing the energy requirement by ½).