Amount Of CaO Research Articles

Dephosphorization study on hydrogen reduction-melting separation of high-phosphorus oolitic hematite

In order to clarify the dephosphorization mechanism of DRI (Direct Reduced Iron) derived from hydrogen reduced high-phosphorus iron ore during the electric arc furnace melting process, slag was prepared using reagent-grade powder based on the gangue mineral composition of high-phosphorus oolitic hematite. By incorporating varying amounts of CaO, FeOx, and reduced iron powder, experiments simulating the dephosphorization of melting separation slag from DRI with different basicity and metallization rates were conducted at 1873 K. The results show that phosphorus in the iron primarily exists in the form of Fe-P-O spherical slag inclusions and FexP, while in the slag, phosphorus mainly resides within the silicate phases. As the amount of CaO added increases, there is a significant decrease in the phosphorus content within the slag inclusions, and the P-containing compounds in the iron gradually shift from FexP and Fe3(PO4)2 to FeO. As the dephosphorization capacity of the slag increases, the distribution of phosphorus-rich phases in the rapidly cooled slag becomes more extensive. When the basicity increases to 3, the phosphorus-rich phases in the slag transition to 2CaO·SiO2 and 3CaO·SiO2. When the basicity is fixed at 2.5, regulating the metallization rate can control the FeOx content in the melting slag, thereby enhancing the dephosphorization ability of slag. The results show that under conditions of a DRI basicity of 2.5 and a metallization rate of 85%, slag/metal separation can produce low-phosphorus iron with 0.022 wt% P, achieving a dephosphorization rate exceeding 95%.

Hydration process and fluoride solidification mechanism of multi-source solid waste-based phosphogypsum cemented paste backfill under CaO modification

The large-scale, environmentally friendly utilization of phosphogypsum (PG) remains a global challenge. PG cemented paste backfill (PCPB) is a promising method to manage PG, but using ordinary Portland cement as the binder has drawbacks such as high cost, low mechanical strength, and high fluoride leaching risk. This paper presents a multi-source solid waste-based PCPB (MPCPB) material that enhances mechanical properties and reduces fluoride leaching risks. In MPCPB, industrial waste residues like steel slag (SS) and ground granulated blast furnace slag (GBFS) are used as precursors (SS: GBFS = 1:2). Additionally, 4–8 wt% CaO (relative to the dry weight of PG) is used as a neutralizing modifier and alkaline activator. The results indicate that an optimal amount of CaO can neutralize the residual acidity of PG, provide sufficient Ca(OH)2 for MPCPB hydration, and react with PG to produce significant amounts of AFt. Furthermore, CaO promotes the geopolymerization reaction between SS and GBFS, generating more calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrate (C-A-S-H) gels. Fluoride stabilization in MPCPB results from synergistic effects involving hydration reactions, complexation, ionic mobility, rearrangement, and physical adsorption. Notably, CaO enhances the conversion of free fluoride ions into stable compounds like fluorapatite, fluorite (CaF2), [AlF6]3-, and [FeF6]3- complexes. This approach offers a cost-effective, environmentally friendly, and efficient solution to the PG stockpiling challenge.

The effect of carbonate assimilation and nanoheterogeneities on the viscosity of phonotephritic melt from Vesuvius

Interaction between magma and carbonate plays a pivotal role in volcanic systems, yet its impact on magma transport properties remains inadequately explored. This study presents novel viscosity data on a leucite-bearing phonotephritic melt from the 472 CE Pollena eruption (Vesuvius, Italy), doped with varying amounts of CaO and CaO + MgO. The compositions match the chemistry of melt inclusions and interstitial glasses from skarns at Vesuvius, which have been interpreted as related to mixing of magma with different amounts of CaO and MgO derived from the host carbonates (limestone and dolostone). Viscosity measurements were conducted at both high (1150–1400 °C) and low temperatures (640–760 °C) by concentric cylinder viscometry, differential scanning calorimetry, and micropenetration methods. Through an integrated approach which combines Brillouin and Raman spectroscopy with the aforementioned techniques, we accurately predict the viscosity changes induced by magma‑carbonate interaction and identify the formation of nanoheterogeneities during low-temperature viscosity measurements. Notably, viscosity models from the literature fail to accurately reproduce our experimental data set at both high and low temperature. In the high-temperature regime, the addition of CaO induces a remarkable viscosity decrease, surpassing that produced by CaO + MgO addition. Furthermore, our findings reveal a significant viscosity/temperature crossover resulting from the addition of CaO and CaO + MgO to the melt phase. Undoped melt exhibits a higher viscosity compared to doped melts above 750 °C, with an inverse trend observed below this temperature threshold. Such rheological constraints may affect the mobility and mixing capability of melts exposed to different levels of carbonate assimilation.

MINERALOGIA, GEOQUÍMICA, FERTILIDADE E ORIGEM DOS SEDIMENTOS DE PRAIA (BARRA EM PONTAL) DAS BACIAS DOS RIOS PURUS E JURUÁ NOS TERRENOS DO ESTADO DO ACRE

The Acre state is in the southwestern part of the Brazilian Amazon region with an area of 164.123.738 km2 and a low population density (5.52 inhabitants/km2 for 2021). The geological context is mainly related to recent units that outcrop at the Acre basin and associated with the Solimões Formation, besides old alluvial terraces that follow main drainages. The Solimões Formation comprises fossil-bearing clayey siltstones intercalated to fine sandstones. The old alluvial terraces are composed by sand, silt, clay, and occasionally fossil fragments. The area of the Acre state is crossed by two main hydrographic basins: The Purus and Juruá rivers in the eastern and western part, respectively. Both rivers are the so-called “white-water rivers”. They exhibit a typical dendritic drainage pattern and are extremely meandering what give rise to lakes formed after abandoned meanders. During dry season, several beaches (point bars) are exposed on river‘s meanders, frequently used for swimming but also playing a very important role in the small-scale agriculture. These beaches are also used for planting corn (Zea-Mays) and beans (Vigna unguiculata (L) Walp). The main purpose of this work is to investigate the mineralogical and geochemical aspects of those beach sediments to understand their high fertility and to identify their primary source. Fourteen stations were selected for sampling purposes throughout the river valley close to BR-364 highway. Laboratory analyses were carried out as follow: grain sizes, x-ray diffraction, scanning electron microscopy and optical microscopy of heavy minerals concentrates; sediment whole chemistry (major and traces elements analyses including rare-earth elements) by means of ICP-MS; macronutrients (P, Mg, Ca, and K) besides available Na and Al and organic matter. The river sediments are mainly fine-grained, angular sub-angular and selected moderately. Mineralogical assemblage is represented by quartz, clay minerals (smectite, illite and kaolinite) and feldspars (K-feldspars and albite). The heavy minerals contents ranged from 0.5 to 4.6% and are mainly represented by zircon, epidote, kyanite, tourmaline, garnet, rutile, apatite, staurolite, ilmenite and hematite. Chemical results shown that the sediments are mainly composed by SiO2, besides minor amounts of Al2O3, Fe2O3, K2O, CaO and MgO, what is compatible with mineralogical composition. High SiO2 contents are mainly related to quartz and Al2O3 contents reflects the presence of clay minerals. Contents for alkaline and alkali-earths are relatively high for such beach environment related to feldspars and smectites. P2O5 is related to apatite and can also be adsorbed on smectite. Fe2O3 contents are mainly associated to smectite and a minor amount to ilmenite and hematite, the most common opaque minerals found in the beach sediments. Strong correlation coefficients were observed between Al2O3 and most major and trace elements, except for Zr, Hf, Ni and As. On the other hand, strong negative correlation was obtained between SiO2 and major and trace elements what points to the importance of smectites as scavenger of trace elements in such environment. The chemical results were compared with the mean of the Upper Crust and post-Archean Australian Shales (PAAS) and show that they are impoverished in MgO, CaO, Na2O and K2O in comparison with the former and MgO, in comparison with the latter. Such impoverishment is higher in samples enriched on sand fraction. The same comparison was carried out with the Chinese Changliang and Huanghe river sediments, showing impoverishment in CaO and MgO in comparison with the Changjiang River and MgO, CaO, Na2O and Sr, in comparison with the Huanghe River. The small value obtained for the Chemical Index of Alteration (CIA) shows that these sediments have experienced small degree of chemical weathering and consequently, physical weathering has prevailed in the source area. The beach sediments also exhibit high immature index as evidenced by the following very low rations: SiO2 / Al2O3 (11,64) and K2O/ Na2O (2,08). Rare-earth elements were normalized to the Upper Crust and to the PAAS patterns. They show similar patterns of LREE depletion and HREE enrichment. On the other hand, normalized to the chondrites present enrichment in LREE and horizontalization of the HREE, with similar standards of distribution between each other, presenting typical Eu negative anomalies of granitic and intermediary nature rocks. Analytical results for macronutrients exhibited high concentrations for P, Mg, Ca and K, and low contents of available Na and Al. Organic matter contents in below 1%. The sediments show high cation exchange capacity, base saturation over 70% and low Na and Al saturation. Accordingly, those sediments can be interpreted as representing a redistribution of the recent Miocene sediments (Solimões Formation) and the own sediments that were deposited in old alluviums. Chemical and mineralogical characteristics with a silty granulometry indicate that beach sediments are like the eutrophic cambisols.

The Stabilization of Copper and Cadmium in The Hydrated CaO-CuO-SiO2 and CaO-CdO-SiO2 Composites

The stabilization of toxic metals in the stable matrices is quite well-known. Research on copper and cadmium stabilization in the CaO-CuO-SiO2 and CaO-CdO-SiO2 composites was conducted to study the characteristics of CaO-CuO-SiO2 and CaO-CdO-SiO2 composites as well as the Cu and Cd metals stabilization in the hydrated composites. The composites of CaO-CuO-SiO2 and CaO-CdO-SiO2 were synthesized by the solid-state reaction method. A stoichiometric amount of CaO, SiO2, Cu(NO3)2, and CdO were calcined at 1050°C for 4 hours. The synthesized compounds were further hydrated in a soaking time of 30, 60, and 90 days. The hydration produced calcium silicate hydrate that can stabilize metals. The Cu and Cd stability in CaO-CuO-SiO2 and CaO-CdO-SiO2, respectively, were tested using the Toxicity Leaching Procedure (TCLP) method. The hydrated and hydrated composite characterizations were performed using X-ray diffraction (XRD), Fourier Transform Infra-Red Spectrophotometer (FTIR), and Scanning Energy Mocroscopy-Energy Dispersive X-ray analyzer (SEM-EDX) and the Atomic Absorption Spectroscopy (AAS) methods. The composites mainly consist of Ca3SiO5, Ca2SiO4, Ca(OH)2, SiO2, and metal oxide of CuO, Cu2O, and CdO. The composites were able to stabilize ~100% of the heavy metals of Cu and Cd.

CO2 capture by the slag from lignite's chemical looping gasification using carbide slag

Due to its large amount, solid waste used as an oxygen carrier in chemical looping gasification (CLG) is not generally recycled. In order not to turn solid waste into secondary solid waste, re-resourcing research of the slag from CLG is worth consideration. The slag from lignite's CLG mainly consists of CaCO3, CaO, and small amounts of Ca(OH)2. In order to further purify CaCO3 and to achieve reduction in carbon emissions, the present work proposed the use of slag from lignite's CLG to capture CO2 and obtain purer calcium carbonate. The reaction properties and the reaction mechanism of the slag from CLG for CO2 capture were investigated using thermodynamic simulations, tubular furnace experiments, thermogravimetric experiments and characterizations. After analyses, it was suggested that reaction temperature for CO2 capture using slag from CLG lied within the temperature range of 300–800 °C. Reaction mechanism of slag from CLG to capture CO2 was different at different reaction temperatures. When the reaction temperature lied within the range of 300–400 °C, <Ca(OH)2+CO2→CaCO3+H2O> and <CaO+CO2→CaCO3> were the main reactions. When the reaction temperature lied within the range of 400–800 °C, <CaO+CO2→CaCO3> was the main reaction. The present study provides a method to turn waste into treasure without the need of subsequent recycling during lignite's CLG, and promotes the realization of “International Double Carbon Policy".

Accelerated Carbonation of Steel Slag and Their Valorisation in Cement Products: A Review

Mineral carbonation emerges as a promising technology to tackle a contemporary challenge: climate change. This method entails the interaction of carbon dioxide with metal-oxide-bearing materials to produce solid carbonates resembling common substances (chalk, antacids, or baking soda). Given that steelmaking industries contribute to 8% of the global total emissions annually, the repurposing of their by-products holds the potential to mitigate CO2 production. Steel slag is a by-product of the metallurgical industry which is suitable for capturing CO2 due to its chemical composition, containing high CaO (24%–65%) and MgO (3%–20%) amounts, which increases the reactivity with the CO2. Moreover, the carbonation process can improve the hydraulic and mechanical properties of steel slag, making this by-product interesting to be reused in building materials. Different studies have developed in the last years addressing the possibilities of reducing the environmental impact of steel products, by CO2 sequestration. This study is dedicated to reviewing the basics of mineral carbonation applied to steel slag, along with recent advancements in research. Special emphasis is placed on identifying parameters that facilitate the reactions and exploring potential applications for the resulting products. The advantages and disadvantages of steel slag carbonation for the industrialization of the process are also discussed.

Chemical looping reforming with water splitting (CLRWS) for syngas and hydrogen coproduction using the ternary metal-oxides (Ca-Fe-Cu–O) as oxygen carriers

In this work, chemical looping reforming with water splitting (CLRWS) using ternary metal oxides (Ca-Fe-Cu–O) as oxygen carrier (OC) was investigated for syngas and hydrogen coproduction. The introduction of Cu into the Ca-Fe-O system results in the formation of the main crystalline phases, which include Ca2Fe2O5, CuFe2O4, and a small amount of CaO. The presence of Cu enhances the oxygen transfer capacity (OTC) and reduces the reduction temperature of Ca-Fe-O oxides. When the ratio of Ca:Cu:Fe equals 0.5:0.5:2, the Ca0.5Cu0.5Fe2O4 exhibited the highest hydrogen yield and purity of 9.15 mmol/(g OC) and 96.80 %, respectively. The syngas yield, purity and fuel conversion were 66.48 mol/L, 74.76 % and 83.12 %, respectively. It can be attributed to the suitable ratio of brownmillerite Ca2Fe2O5 and the spinel CuFe2O4 in Ca0.5Cu0.5Fe2O4. The crystal phases of Ca2Fe2O5 and CuFe2O4 exhibit a synergistic effect in the Ca-Fe-Cu–O system, the formation of CuFe2O4 enhances the lattice oxygen activity, while the brownmillerite-structured Ca2Fe2O5 inhibits the sintering and agglomeration of CuFe2O4 due to the morphology effect. The Ca0.5Cu0.5Fe2O4 showed almost stable reactivity after 10 cycles.

Optimization mechanisms of density and quality factor of Ba(Mg1/3Ta2/3)O3 ceramics by adding CaO–B2O3–ZnO glass

In this study, Ba(Mg1/3Ta2/3)O3 (BMT) ceramics added with different amounts of CaO–B2O3–ZnO (CBZ) glass were prepared through the solid-state sintering route. The sintering behavior, microstructure, phase composition and dielectric properties of the BMT ceramics added with CBZ glass were investigated. The addition of CBZ glass decreased the sintering temperature of BMT ceramics by over 300 °C, resulting in a highly dense microstructure without interacting with the main BMT phase. The lower sintering temperature led to small ceramic grains and caused a decrease in the Q × f value. Prolonging the sintering time improved the ordering degree of cations on the B-site in BMT ceramic, leading to an enhancement in the Q × f value. The BMT ceramic added with 0.4 wt% CBZ glass exhibited excellent microwave dielectric properties: εr = 24.19, Q × f = 115,100 GHz, τf = 9.84 ppm/°C, after sintering at 1400 °C for 12 h.

Observations and simulations for separation mechanism of vanadium and chromium: Progressive study based on oxides, spinels and vanadium-chromium slag

In this study, V2O3-CaO-Cr2O3 oxides system, Fe2VO4-CaO-FeCr2O4 spinels system and V-Cr slag-CaO system were established progressively to investigate the separation effect of vanadium and chromium components in vanadium-chromium slag (V-Cr slag). Then, the separation mechanism was proposed by XRD, SEM and leaching experiments. The results show that the reaction ability of vanadium with calcium is far stronger than that of chromium. In oxides and spinels systems, as CaO increases, CaV2O6, Ca2V2O7, and Ca3V2O8 are generated sequentially. In V-Cr slag-CaO system, additive CaO, along with manganese, magnesium and iron components in V-Cr slag reacts with vanadium, resulting in the complex composition of vanadate. As to chromium component, Cr2O3 in oxides system will be converted into CaCrO4 as n(CaO)/n(V2O3) is higher than 2. Iron in the spinels system reacts with chromium and form solid solution (FexCr1-x)2O3, resulting in less chromium reacting with calcium to produce CaCrO4. In V-Cr slag-CaO system, SiO2 generated by the decomposition of silicate phase combines with part of calcium expected to react with chromium, making CaCrO4 generation more difficult, promoting the separation of vanadium and chromium further. Consequently, during H2SO4 leaching, chromium leaching ratios are 98.75%, 45.77% and 5.91%, respectively, in oxides, spinels and V-Cr slag system when n(CaO)/n(V2O3) is 5. And when n(CaO)/n(V2O3) is 2, more than 90% of vanadium can be leached, however, the leaching ratios of chromium are 0.22%, 0.17% and 0.094% in these three systems. Furthermore, the variation regularities of chromium leaching ratios with CaO amount are described by regression equations. These findings would provide the theoretical support for the calcification roasting process with V-Cr slag.

FORMING AND PROPERTIES OF GLASSES MADE FROM TWO THAI BOTTOM ASHES

Industrial wastes are often an under-utilized source of raw materials. Bottom ashes resulting from incineration processes can contain various metal oxides, including many commonly used in glass making. This research studied the forming and properties of glasses made from two bottom ashes. Lignite bottom ash (BL) from Lampang, Thailand and a municipal solid waste incinerator bottom ash (BP) from Phuket, Thailand. Both bottom ashes were found to contain significant amounts of SiO2, CaO, Al2O3, and Fe2O3. After ball milling, the ashes were melted without additions, at temperatures from 1300 to 1500°C. The resulting glasses, as confirmed by XRD, were black and fully opaque, a result of the high Fe2O3 content. It was found that the BP glasses were slightly more refractory, had a greater average thermal conductivity of 1.52 W/m·K and a lower coefficient of thermal expansion (CTE) of 6.97x10-6/°C, compared to the BP glasses, which had an average thermal conductivity of 1.39 W/m·K and a CTE of 7.98x10-6/°C. The BL glasses also had a higher average density of 2.88 g/cm3 and a Vickers hardness of 6.29 GPa, compared to the BP glasses, with average values of 2.74 g/cm3 and 6.06 GPa, respectively. The increase of glass melting temperature up to 1450°C tended to improve the observed properties, followed by a decrease at 1500°C. Despite the atypical glass chemistry of the two bottom ashes, they were successfully melted to produce glasses and the measured properties demonstrated suitable potential to warrant further study.

Impact of Limestone Surface Impurities on Quicklime Product Quality

Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s).

Solid-state exchange reactions during sintering of dispersed alumina

In this article, the mechanism of sintering of Al2O3 in the presence of small amounts of Na2O and CaO was investigated. Based on the results of the electron microscopy, the granulometry and morphological features of the particles of the studied alumina were established. The uniform nature of the distribution of sodium-containing phases was revealed, in contrast to silicon-containing ones, and the dislocation of submicron particles from calcium-containing phases was determined mainly on the basal planes of relatively large corundum particles. It was shown that such an arrangement of calcium-containing phases promotes the formation of a dense layered microstructure during sintering, especially in the presence of -alumina. The general pattern of the branched mechanism of the reaction phase formation during the sintering of the compositions in the Na2O–СаО–Al2O3 system was illustrated by a diagram explaining the trend of physicochemical processes and the feasibility of using specific types of dispersed alumina for technologies of corundum products and refractory concretes with different contents of aluminous cements.

Thermal Activation of High-Alumina Coal Gangue Auxiliary Cementitious Admixture: Thermal Transformation, Calcining Product Formation and Mechanical Properties.

In this paper, a new preparation technology is developed to make high-alumina coal gangue (HACG) auxiliary cementitious admixture by calcining HACG-Ca(OH)2 (CH) mixture. HACG powders mixed with 20 wt.% CH were calcined within a temperature range of 600-900 °C, and the thermal transformation and mineral phase formation were analyzed. The hydration reaction between activated HACG-CH mixture and cement was also investigated. The results showed that HACG experienced a conventional transformation from kaolinite to metakaolin at 600 °C and finally to mullite at 900 °C, whereas CH underwent an unexpected transformation process from CH to CaO, then to CaCO3, and finally to CaO again. These substances' states were associated with the dehydroxylation of CH, the chemical reaction between CaO and CO2 generating from the combustion of carbon in HACG, and the decomposition of CaCO3, respectively. It is the formation of a large amount of CaO above 800 °C that favors the formation of hydratable products containing Al2O3 in the calcining process and C-A-H gel in the hydration process. The mechanical properties of HACG-cement mortar specimens were measured, from which the optimal calcination temperature of 850 °C was determined. As compared with pure cement mortar specimens, the maximum 28-d flexural and compressive strengths of HACG-cement mortar specimens increased by 5.4% and 38.2%, respectively.

Studying on mineralogical and petrological characteristics of Gara Djebilet oolitic iron ore, Tindouf (Algeria)

Demand for iron ore worldwide has been steadily increasing which leads to the extraction of iron ore deposits with more complex mineralogies and higher levels of silicon and phosphorus impurities. This is the case in Algeria with the iron ore deposit of Gara Djebilet, Tindouf; where it has recently been exploited to ensure the sufficiency of iron ore required to produce iron and steel products. This deposit has remained unexploited for several decades due to inadequate knowledge of its mineralogy, treatment, and economic assessments. The aim of this study is to find out the microstructure, chemical composition, and mineralogical distribution of valuable minerals and impurities, to understand the efficient processing methods for this specific iron ore. The characterization of representative ironstone samples taken from the studied area was carried out using optical microscopy, X-ray fluorescence spectrometer (XRF), petrographic microscope, X-ray diffractometer (XRD), and scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results of the mineralogical analyses confirmed that it is an oolitic fine-grained ore consisting of gangue minerals principally composed of quartz, apatite, and iron-rich concentric cored structures. Chemical analyses of the ore indicate that it contains 56.58 wt% Fe with 7.98 wt% SiO2, 7.09 wt% Al2O3, and minor amounts of P2O5, CaO, MgO, and TiO2 compounds. The phosphorus associated was present in both ooids and groundmass, indicating that the ore has a complex texture with very rich and diverse mineralogy. For that, two potential scenarios were proposed for processing of the studied iron ore.

Effect of alkaline oxides (CaO and MgO) on the mechanical properties of SiC-based foam ceramics

Fly ash is potentially useful as a sintering additive in the synthesis of SiC-based foam ceramics (SFC). However, the influence of CaO and MgO, the main alkaline oxides in fly ash, on the performance of SFC is not well understood. This study synthesized SFC using SiC and fly ash as the primary raw materials (mass ratio of 7:3), and systematically investigating the effects of CaO and MgO on the properties of SFC, including porosity, density, strength, apparent morphology, and phase composition. The results indicated that addition of CaO and MgO promoted oxidation of SiC at relatively low temperatures. With a CaO content of 1.5 wt% or an MgO content of 2 wt%, SFC with uniformly distributed porous structures and exceptional properties was achieved at sintering temperatures as low as 1150 °C. Additionally, CaO and MgO facilitated formation of crystalline phases such as wollastonite, calcium feldspar, and cordierite, enhancing the thermophysical properties of SFC. However, excessive CaO or MgO led to over-sintering of the SFC samples. With a CaO content of 1.5 wt% and a sintering temperature of 1175 °C, SFC was completely deformed. This was also observed with an MgO content of 3 wt% and a sintering temperature of 1250 °C, indicating that CaO promotes SiC oxidation more effectively than MgO. It is suggested that addition of appropriate amounts of CaO and MgO is conducive to production of high-quality SFC at low sintering temperatures, significantly enhancing their commercial viability.

Effects of CaO addition on the reactivity and reaction kinetics of coke

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.

Effects of CaO additive on sintering behaviour and properties of CaO–B2O3–SiO2 glass-ceramics for LTCC applications

The effects of CaO additive on the phase composition, sintering behaviour, microstructure, and properties of CaO–B2O3–SiO2 (CBS) glass-ceramics were investigated. The results revealed that a small amount of added CaO (0.5 wt%, 1 wt%) facilitated the transformation of α-CaSiO3 to β-CaSiO3 and improved the crystallinity. When the amount was greater than 1 wt%, it weakened this transformation and also decreased the crystallinity. The pure CBS sample needed a sintering temperature of 850 °C for maximum densification, whereas the CaO-added samples achieved densification at a sintering temperature of 750–770 °C. The addition of an appropriate amount of CaO significantly enhanced the densification, dielectric properties, and flexural strength of CBS glass-ceramics. However, the addition of CaO had minimal impact on the coefficient of thermal expansion (CTE), which varied from 7.69 to 8.51 ppm/°C. The sample doped with 1 wt% CaO was sintered at 770 °C for 15 min, and it exhibited fairly ideal performance with a bulk density of 2.64 g/cm3, εr of 6.43, tanδ of 0.9 × 10−3 (15 GHz), and a CTE value of 7.69 ppm/°C.

Combustion synthesis of nanostructured calcium silicates: A new approach to develop bioceramic cements in endodontics

Calcium silicate is widely used in endodontics because its bioactivity precedes tissue regeneration. The synthesis of pure compounds is challenging, especially for the C3S phase (3CaO·SiO2) because, despite the use of pure phases to understand the phenomena involved in the fresh and hardened states, its isolated production requires specific conditions. Synthesis by combustion is an alternative method for obtaining improved endodontic cements. This study presents an alternative method for obtaining C3S-based nanostructured cements with the smallest possible amounts of polymorphs and CaO. To obtain the powders, citric acid was used as the fuel, and tetraethylorthosilicate was used as the silica precursor. In addition, two calcium precursors—calcium carbonate and calcium nitrate—were evaluated as oxidizers. Different parameters were investigated, including combustion temperatures (400 and 600 °C), equivalence ratios (χ) (citrate/nitrate) of 3, 5, and 7, type of oxidizer, and heat treatment temperatures (800, 1000, and 1200 °C). The thermal and structural properties, functional groups, and surface area were evaluated. The results indicate that at the combustion temperature of 600 °C, followed by heat treatment at 1000 °C with an equivalence ratio (χ) of 7, it is possible to obtain a nanostructured cement based on the M3 polymorph of C3S with 23.62 nm. The obtained material shows potential for application in endodontics because of its highly reactive and bioactive behavior.

Simulation of Biogas Upgrading by Sorption-Enhanced Methanation with CaO in a Dual Interconnected Fluidized Bed System

In this work, ASPENplus was used to simulate biogas upgrading by sorption-enhanced methanation in a dual interconnected bubbling fluidized bed configuration using inexpensive, abundant, and eco-friendly CaO to remove H2O from the reaction environment. The chemical looping scheme consisted of two reactors: a methanator/hydrator, where the catalytic reactions occurred on a catalyst with 20% Ni supported on alumina as well as the steam removal by CaO, and a regenerator, where the Ca(OH)2 was dehydrated back to CaO. The simulations were carried out to identify possible reactant compositions (H2 and biogas), CaO amount, and the methanation temperature able to produce an outlet gas matching the specifications for direct grid injection. When considering a stoichiometric gas feed ratio at the methanator inlet, the unwanted CaO carbonation worsened the process performance, subtracting CO2 from the desired methanation reaction. However, optimal conditions were found with hydrogen-lean gas feedings, balancing the limited H2 amount with the capture of CO2 due to the sorbent carbonation. Thermodynamic considerations pointed out the possibility of solid carbon formation induced by sorption-enhanced methanation conditions, especially for H2 sub-stoichiometric feedings.