Hydration Of CaO Research Articles

Properties of hydraulic paste of basic oxygen furnace slag

Basic Oxygen Furnace (BOF) slags are by-products of the conversion of pig iron to steel. They mainly contain C2S, C2F, Fe1−xO, CaO, Ca(OH)2 and CaCO3. According to their chemical composition they are a valuable mineral resource as additions in certain hydraulic binders. This paper presents a hydration study of the BOF slag pastes preserved at different temperatures and in different environments. Pastes are characterized by X-ray diffraction and scanning electron microscopy. The compressive strengths of hydrated pastes are given at 7, 28, 90 and 190days. Results show that – BOF slags containing 40% of C2S – have attractive mechanical properties. Hydration tests under water showed a pastes swelling due to the hydration of CaO contained in BOF slags. A lime extinction procedure was proposed as alternative to standard PR NF EN 13282-2. This approach is more effective for these materials: the volume expansion of pastes cured in water is avoided and the compressive strengths are thus significantly improved.

Effect of CaO hydration and carbonation on the hydrogen production from sorption enhanced water gas shift reaction

Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO2 capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO2, and the solid product is CaCO3, and the Ca(OH)2 may be formed from the reaction of CaO with H2O with the presence of steam in gas phase. The effect of Ca(OH)2 and CaCO3 on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO3 did not show any catalytic reactivity toward WGS reaction at 400 °C. When the temperature was increased to 500 °C and 600 °C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)2 may be the reason of catalytic reactivity recovery. CaCO3 can catalyze the WGS reaction at the high-temperature (>600 °C), this may due to the CaCO3 decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed.

CO2 capture by carbide slag from chlor-alkali plant in calcination/carbonation cycles

The CO2 capture behavior of carbide slag as industrial waste dumped from a chlor-alkali plant in calcination/carbonation cycles was investigated in a fixed-bed reactor and a thermogravimetric analyzer, which was furthermore compared with that of hydration of CaO (Hy-CaO) and limestone. The main component of the carbide slag was the same as that of Hy-CaO which was Ca(OH)2. The effects of reaction temperature, particle size and cycle number on CO2 capture of the carbide slag were discussed. The carbide slag exhibited greater ultimate carbonation conversion than Hy-CaO and the limestone for the same number of cycles. For the same number of cycles, the calcined carbide slag had a smaller volume of pores <155nm in diameter than calcined Hy-CaO and the calcined limestone, but possessed a greater volume of pores >155nm in diameter than the two other calcined sorbents. This was maybe a reason why the carbide slag exhibits a higher ultimate carbonation conversion than the Hy-CaO and the limestone. The cyclic carbonation conversion of the carbide slag was lower than that of the limestone before a certain time (called transition time); however, the converse result was observed after that time. It was attributed to the difference in the volume of pores <220nm in diameter in the calcined sorbents during the cycles.

Reuse of steel slag in bituminous paving mixtures

This paper presents a comprehensive study to evaluate the mechanical properties and environmental suitability of electric arc furnace (EAF) steel slag in bituminous paving mixtures. A variety of tests were executed on samples of EAF slag to characterize the physical, geometrical, mechanical and chemical properties as required by UNI EN specifications, focusing additionally on the volumetric expansion associated with hydration of free CaO and MgO. Five bituminous mixtures of aggregates for flexible road pavement were designed containing up to 40% of EAF slag and were tested to determine Marshall stability and indirect tensile strength. The leaching behaviour of slag samples and bituminous mixtures was evaluated according to the UNI EN leaching test. The tested slag showed satisfactory physical and mechanical properties and a release of pollutants generally below the limits set by the Italian code. Tests on volume stability of fresh materials confirmed that a period of 2–3 months is necessary to reduce effects of oxides hydration. The results of tests performed on bituminous mixtures with EAF slag were comparable with the performance of mixtures containing natural aggregates and the leaching tests provided satisfactory results.

A chemo-mechanical model of lime hydration in concrete structures

A size-effect theory is herein introduced to investigate the average expansion of concrete containing free lime (CaO) and impurities. By drawing an analogy with the structural size-effect, the phenomenon of CaO hydration shows a characteristic length, whose dimension remains constant at all scales. If a grain of free lime is assumed to be a sphere, only a thin layer on the external surface hydrates and doubles the volume, as confirmed by the results of 2D finite element analyses and by some experimental observations. For practical applications, a simplified chemo-mechanical model of CaO hydration is eventually proposed, to predict the consequences of uncombined lime in concrete structures.

Lime Brust of Sintering Bricks of Purple Sandy Shale: the Effect of Limestone Particle Size

Simulating current sintering process in local brickkilns, Hengyang region, Hunan Province, China, at 800°C, througt indoor sintering experiment on a series of brick samples of purple sandy shale, in which particle sizes of limestone are &gt;-1Φ, &gt;0Φ, &gt;1Φ, &gt;2Φ, &gt;3Φ and &gt;4Φ, respectively, it is concluded that the following: (1) Limestone granularity is a crucial factor affecting the quality of sintering bricks of purple sandy shale. Under different particle sizes, the critical content of limestone causing lime brust of sintering bricks is distinct, and lowers with the increasing in limestone granularity. (2) When limestone granularity is different, its impact way on the quality of sintering bricks is also distinct. The more coarse limestone granularity is, the more concentrative the swelling stress produced by the hydration of free CaO is, the more easily lime brust occurs. On the contrary, the more fine limestone granularity is, the more dispersive the swelling stress is, there is the more help to reduce or eliminate the occurrence of lime brust. (3) In view of the relationship between limestone granularity and the critical content of limestone giving rise to lime brust of sintering bricks, the production practice can be effectively guided.

Removal of trichloroethylene from soil using the hydration of calcium oxide

Quicklime addition to soil at a remediation site was observed to sufficiently reduce TCE levels, but the cause of the removal could not be confirmed with the field data collected. Potential mechanisms for CaO treatment of trichloroethylene (TCE) in soil include degradation and volatilization. Since earlier studies found TCE degradation to occur during the hydration of CaO under conditions where volatilization was limited, research was conducted on mechanisms of TCE removal from soil by CaO application under conditions where volatilization was allowed to occur. TCE volatilization in soil treated with 0%, 5%, 10%, and 20% CaO doses was measured in experiments where the degree of volatilization could be tracked. The total TCE removal from soil spiked with TCE at CaO doses from 5% to 20% ranged from 97% to 99% of the initial TCE mass. Volatilization accounted for 64.4–92.5% of the TCE removal, with unrecovered TCE and TCE degradation accounting for the remaining fraction. The greater heat encountered with higher CaO doses helped minimize obstacles to TCE volatilization, such as high soil organic and clay content. Treatment with a 20% CaO dose, however, led to the formation of byproducts such as dichloroacetylene. TCE degradation to dichloroacetylene at the 20% CaO dose ranged from 2.7% to 6.4% of the initial TCE. Volatilization was concluded to be the dominant process for TCE removal from soil during CaO treatment.

Modification of CaO Refractory for Melting Titanium Alloys and its Hydration Resistance

CaO is a promising refractory for melting TiNi shape memory alloys, the carbon contamination can be avoid by using CaO crucible instead of carbon crucible. However, its industrial application is limited by the easy hydration of CaO in the air. In this study, the hydration resistance of CaO is modified by the addition of ZrO2, the powder of CaO adding 6.0 to 15.0mol% ZrO2 and 2.0mol% TiO2 is ball- milled, the mixture is shaped into the chip by the isostatic pressing method (IP), then the samples are sintered at 1750°C. The X-ray diffraction analysis reveals that the sintered samples consist of CaO dissolved with ZrO2 and CaZrO3. The anti-hydration property is described by the weight addition of samples, which are stored at the room temperature and atmosphere. It is shown that the sample with 12% ZrO2 of additive possesses the good hydration resistance, its weight addition stored after 56-days is less than 0.6wt%. Therefore, the powder of CaO with 12.0% ZrO2 additive are used to prepare the crucible by IP, the green crucible is sintered at 1750°C. This home-made crucible is used for melting TiNi alloy by means of the induction method at 1500~1800°C temperature and the vacuum environment, it is found that, the internal and external surface of crucible were almost kept unchanged after melting, this refractory did not obviously react with titanium melts, this result may provide a support for searching a new refractory with the good hydration resistance for melting of titanium alloys.

Approaching Sustainable H2Production: Sorption Enhanced Steam Reforming of Ethanol

Sorption enhanced steam reforming of ethanol (SESRE), featured by yielding high purity of H(2) from one single reaction unit, is a new reaction process with a great potential for realizing sustainable H(2) production. The potential of such process with a CaO-based acceptor has been assessed by thermodynamic analysis and experimental demonstration. As predicted, ethanol can be reformed at relatively low temperatures (500-600 degrees C), still yielding high-quality H(2). Another major advantage of coupling CO(2) capture to the reforming process is predicted to be low risk in carbon formation. The SESRE reaction was carried out over a mixture of hydrotalcite-like material derived Co-Ni catalysts (Co-Ni/HTls) and calcined dolomite with a steam to carbon (S/C) ratio of 3 and temperatures ranging from 500 to 650 degrees C. The chosen reaction system was able to yield H(2) with purity fairly close to the theoretical prediction. Particularly, the best result was obtained over 40Ni and 20Co-20Ni/HTls at 550 degrees C, where the product gas had composition of more than 99 mol % H(2), ca. 0.4 mol % CH(4), 0.1 mol % CO, and 0.2 mol % CO(2). Special emphasis was put on the effect of steam on the stability of the CO(2) acceptor during the SESRE reaction. Hydration of CaO in the acceptor did not cause appreciable induction period, even at the low operating temperatures. However, different from a test under dry atmosphere (CO(2)/argon), the acceptor showed rapid deactivation in a multicycle operation of SESRE. A similar deactivation tend was given by a comparative test in a steam/CO(2)/Ar atmosphere.

Destruction of trichloroethylene during hydration of calcium oxide

Quicklime (calcium oxide, CaO) is often used as part of soil cleanup operations to remove contaminants or to create more favorable physical soil conditions for treatment. The extent to which quicklime chemically reacts with trichloroethylene (TCE) was evaluated by reacting CaO with a TCE–water mixture in test vessels designed to minimize volatilization loss. The impact of excess water and the presence of air were evaluated. During the hydration of CaO, a fraction of the spiked TCE was destroyed, and several different byproducts were detected (chloride and several organic chemicals). The primary organic byproduct was dichloroacetylene (DCA). In the presence of air, the degradation of DCA resulted in the formation of perchloroethylene (PCE), hexachloro-1,3-butadiene (HCDE), and chloroacetylene (CA). The maximum amount of TCE degradation occurred with a CaO/H 2O ratio of 1:1 in the presence of air. The formation of DCA was hindered by the presence of excess water. In the presence of excess water (a CaO/H 2O ratio of 1:2) the detected byproducts accounted for less than 4% of the total chlorine originally spiked as TCE.

High-Temperature CaO Hydration/Ca(OH)2 Decomposition over a Multitude of Cycles

CaO hydration and Ca(OH)2 decomposition cycles can be used to supply or transport energy (heat). The reaction rates and properties of these materials are important parameters for the design of a reactor. In this work, the rates of CaO hydration and Ca(OH)2 decomposition were measured continuously over 20 hydration/decomposition cycles by means of a high-pressure thermogravimetric apparatus. CaO was completely converted to Ca(OH)2 in all cycles, but the CaO hydration rate decreased with increasing number of cycles. Ca(OH)2 was decomposed to CaO completely in all cycles. The extent and rate of conversion for Ca(OH)2 decomposition were not influenced by increasing cycle number. Eutectic melting of CaO and Ca(OH)2 was not observed on the particles after CaO hydration or after Ca(OH)2 decomposition. The compressive strength of CaO particles decreased with increasing cycle number, and the average compressive strength of CaO particles after 20 cycles was about 16.5 kg/cm2.

Effect of rice husk ash addition on CO 2 capture behavior of calcium-based sorbent during calcium looping cycle

Rice husk ash/CaO was proposed as a CO 2 sorbent which was prepared by rice husk ash and CaO hydration together. The CO 2 capture behavior of rice husk ash/CaO sorbent was investigated in a twin fixed bed reactor system, and its apparent morphology, pore structure characteristics and phase variation during cyclic carbonation/calcination reactions were examined by SEM-EDX, N 2 adsorption and XRD, respectively. The optimum preparation conditions for rice husk ash/CaO sorbent are hydration temperature of 75 °C, hydration time of 8 h, and mole ratio of SiO 2 in rice husk ash to CaO of 1.0. The cyclic carbonation performances of rice husk ash/CaO at these preparation conditions were compared with those of hydrated CaO and original CaO. The temperature at 660 °C–710 °C is beneficial to CO 2 absorption of rice husk ash/CaO, and it exhibits higher carbonation conversions than hydrated CaO and original CaO during multiple cycles at the same reaction conditions. Rice husk ash/CaO possesses better anti-sintering behavior than the other sorbents. Rice husk ash exhibits better effect on improving cyclic carbonation conversion of CaO than pure SiO 2 and diatomite. Rice husk ash/CaO maintains higher surface area and more abundant pores after calcination during the multiple cycles; however, the other sorbents show a sharp decay at the same reaction conditions. Ca 2SiO 4 found by XRD detection after calcination of rice husk ash/CaO is possibly a key factor in determining the cyclic CO 2 capture behavior of rice husk ash/CaO.

Preparation and second harmonic generation of Ba 2TiSi 2O 8 films

The synthesis and characterization of the Ba 2TiSi 2O 8 films are described. The Ba 2TiSi 2O 8 crystal was obtained after heat treatment at above 630 °C of a sol–gel derived glassy material which has a chemical composition (mole ratio) 2BaO, TiO 2, 2SiO 2, and then the Ba 2TiSi 2O 8 films were formed from the hydration of CaO–P 2O 5 glass powders. Heat treatment conditions and crystallization of the synthesized materials were studied by DSC-TG, XRD, and FT-IR. Second order nonlinear optical property has been verified by second harmonic generation test at 1064 nm. These results showed that the hydration process has a potential in rendering shape-comfortable optical materials.

Effect of CaO content on hydration rates of Ca-based sorbents at high temperature

The CaO hydration behavior of four Ca-based sorbents (Deyang, Yangguan, Dawa, and Kuzuu) with different CaO contents was examined. A high-pressure thermogravimetric apparatus was used to measure the hydration rates at high temperatures (773–923 K) and high steam pressures (1.3–2.3 MPa). CaO hydration occurred at high temperatures up to 923 K at high steam pressure. The hydration rates and the final CaO conversion values varied substantially among the different sorbents. Hydration rate and CaO conversion decreased with increasing CaO content. The order of CaO hydration rate with respect to the difference between the reactant steam pressure and the equilibrium steam pressure (PH2O−P⁎H2O) varied with CaO content. The apparent activation energy for rate constant k also varied with CaO content.

Study of Limestone Calcination with CO2Capture: Decomposition Behavior in a CO2Atmosphere

In the present work, the effects of temperature (up to 1293 K) and residence time on the decomposition behaviors of limestone particles (0.25−0.5 mm) in a CO2 atmosphere were investigated using a continuously operating fluidized bed reactor for CO2 capture. The results show that the rate of limestone decomposition was strongly dependent upon the pressure difference between the equilibrium CO2 pressure and CO2 partial pressure in experiments (P* − PCO2) with temperature. Decomposition conversions (CaCO3 → CaO) were 73% at 1193 K and 95% at 1293 K, with a 70 min average residence time of particles in the bed. A model was proposed to describe the distribution of limestone particles in the fluidized bed reactor with residence time. The hydration and carbonation reactivities of CaO produced by the limestone decomposition were also tested. The results show that CaO hydration [CaO to Ca(OH)2] can be completed within 11 min; however, the conversion of CaO to CaCO3 in the CaO carbonation test was below 60%.

Using a new composite expansive material to decrease deformation and fracture of concrete

Using minerals of dolomite, serpentine and magnesite produce a new composite material which provides an expansive stress to decrease deformation and fracture of hydraulic concrete. The compositions of the expansive material are mainly MgO, CaO and C 2S by X-ray techniques. Adding the expansive material to concrete, the shrinkage of concrete may be compensated by the hydration of CaO to Ca(OH) 2 in early ages and the hydration of MgO to Mg(OH) 2 in later ages respectively, so decrease deformation and fracture of concrete.

Production of MgO-type expansive agent in dam concrete by use of industrial by-products

A novel MgO-type expansive agent in a designed formula has been prepared with industrial by-products—magnesite, serpentine and dolomite calcined at 1150 °C for 1 h. The compositions of expansive agent were studied by X-ray diffractometry (XRD), DSC and scanning electron microscopy (SEM), and the results showed that the main phases were MgO, CaO and C 2S. The hydration of CaO to Ca(OH) 2 is quick and can be completed in 3 days in water at 20 °C, and MgO to Mg(OH) 2 is slow and about 57% MgO hydrates into Mg(OH) 2 in 180 days under the same condition, which is quicker than in water. The hydrations of CaO and MgO generate expansions in early and later age, respectively. The shrinkage of roller compacted concrete will be compensated by adding the expansive agent. The utilization of these industrial by-products in the construction of hydraulic dams not only compensates the shrinkage of dam, but also reduces the environmental pollution.

CaO Hydration Rate at High Temperature (∼1023 K)

CaO hydration is an exothermic reaction that can be used to supply heat. The amount of heat released by the reaction is dependent on the operating steam pressure. In this work, the rate of CaO hydration was measured with a high-pressure thermogravimetric apparatus under steam pressures in the range of 0.67−3.8 MPa. At these pressures, CaO hydration occurred at high temperatures up to 1023 K. The CaO hydration rate varied by the power of 2, with respect to the difference between the reactant steam pressure and the equilibrium steam pressure (PH2O − ). The apparent activation energy for reaction constant k was determined to be 8.4 kJ/mol. The particle size (dp) slightly affected the CaO hydration rate. The hydration rate (R) is given by R = 1/dp0.11 × 0.0069 exp[−8400/(RT)] × (PH2O − )2.

Continuous experiment regarding hydrogen production by Coal/CaO reaction with steam (II) solid formation

Integration of coal gasification and CO 2 separation reactions in one reactor may produce a high concentration of hydrogen. To design a reactor for this new reaction system, it is necessary to know all reaction behaviors in the integrated reaction system. In our previous study, we performed a continuous reaction experiment of coal/CaO under high steam pressure and confirmed that H 2 concentration higher than 80 vol% with little CH 4 was produced; and that almost all CO 2 was fixed by adding CaO. In this study, the behaviors of solid products during the continuous experiment were investigated. It was found that, CaO first reacted with high-pressure steam to form Ca(OH) 2 (hydration), then the Ca(OH) 2 absorbed the CO 2 generated by coal gasification to form CaCO 3. The hydration of CaO restored sorbent reactivity. Eutectic melting of Ca(OH) 2/CaCO 3 was found to occur in the experiment at 973 K, and this eutectic melting led to the growth of large particles of solid materials. However, at the relatively low temperature of 923 K, eutectic melting could be avoided. Carbon conversion of the coal in the continuous reaction of the coal/CaO mixture with steam was high as 60–80%, even at the lower temperature of 923 K.

Aspects of generation of destructive crystal growth pressure

Growth of some salt crystals, e.g. Na 2SO 4·10H 2O, Na 2S 2O 3·5H 2O, etc., from their supersaturated solutions is often, though not invariably, associated with crumbling of porous materials. Usually, both crystal growth and development of damage-causing pressure are treated using isothermal, equilibrium thermodynamics. The implicit assumption is that crystals have their equilibrium habits. However, experimental and natural crumbling have been associated with the formation of acicular crystals, e.g. Na 2S 2O 3·5H 2O from its melt, Ca(OH) 2 in the hydration of CaO, etc. Slow formation of large crystals, in conditions approaching equilibrium and isothermal requirements, has not been associated with any damage. To resolve the above contradiction, the literature on crystal growth has been critically examined. This examination shows that in most studies the following has not been properly considered: (1) a growing crystal is neither in equilibrium nor in equi-thermal state with the supersaturated solution, (2) supersaturated solutions contain ion agglomerates of larger sizes, (3) different crystallographic faces have different solubility. A similar non-uniform material deposition also occurs in the vapour deposition of metals on irregular particles. More metal accrues on the tips or heights than on planes and sides. A mechanism has been proposed to explain the crumbling of porous materials.