Reaction Of Lime Research Articles

Optimization of a lime-based sorbent for carbonation at low temperature enhanced by water vapor

Carbonation reaction of lime modified by small amounts of MgO was studied by submitting pelletized samples to the exhaust gas of a petrol engine at about 100°C. The results showed that either the kinetic or the diffusion behavior is non-linearly dependent with the addition of MgO. Moreover, there is an optimum MgO percentage that enhances diffusion and ultimate sample conversions. Samples with 10% and 5% of additive showed faster initial kinetic and greater conversion, respectively. These results demonstrate that a small addition of MgO can increase the reactivity, sorption capacity and gas diffusion. Finally, the studied experiments revealed an intense interaction between CO2 and magnesium oxide. Theoretical analysis of the final conversion parameters suggests an optimized MgO concentration of about 7%.

Improvement of Lime Reactivity towards Desulfurization by Hydration Agents

Three hydration agents namely calcium acetate, ammonium acetate and citric acid were used to augment lime's reactivity through hydration. The performance of these agents was compared with pure distilled water. The produced sorbents were tested in a pH-stat facility and a fixed bed apparatus which simulate wet and dry flue gas desulfurization respectively. It was observed that all agents improved lime's reactivity by a higher percentage than water and that calcium acetate was the best agent, followed by ammonium acetate. Dissolution and hydrolysis of the calcium and acetate ions were thought to be the cause of these results while for acidic agents, high concentration of the hydrogen ion was the cause of the improved performance. BET surface area analysis, XRD and SEM imaging were used to explain the results.

Optimization of synthesis and characterization of nanosilica produced from rice husk (a common waste material)

Rice husk (RH), an inexpensive waste material, was used to produce nanosilica. Acid treatment of RH followed by thermal combustion under controlled conditions gave 22.50% ash of which 90.469% was silica. Various chemical treatments in varied conditions for controlled combustion were investigated in order to produce highly purified nanosilica. The structural properties (such as X-ray diffraction, Brunauer-Emmett-Teller, Fourier transform infrared spectroscopy, and transmission electron microscopy) of the silica were studied. The method was optimized, and the chemical composition of the product was determined by X-ray fluorescence and carbon, hydrogen, and nitrogen analysis. Lime reactivity of the ashes was determined. At optimized conditions, a nanosized, highly purified silica (98.8 mass percentage) was produced with a high surface area, high reactivity, and 99.9% amorphous in form. Strength and number of acidic sites were measured by potentiometric titration. This nanosilica showed strong and a large number of acidic sites in comparison with commercial silica, making it as a good support for catalysts. This economic technology, as applied to waste material, also provides many benefits to the local agro-industry.

Calcium looping in solar power generation plants

The use of a calcium looping based process as a thermal storage and transportation system for concentrated solar power plants is proposed in this work. This system exploits the reversible calcination–carbonation reaction of limestone and lime. Concentrated solar heat is used to calcine CaCO3, which is then released as required by carbonating the resulting CaO. The CaO/CaCO3 system has a high energy density and its high temperature operation allows the use of a gas turbine for power production. This paper presents a first order evaluation of the potential of this application of calcium looping, with particular consideration given to carbonation activity of the sorbent. A model including a solar calciner and a pressurised fluidised bed carbonator feeding a gas turbine in an open Brayton cycle has been developed. Results from the model indicate that electric efficiencies of 40–50% could be achieved with sorbent carbonation activities between 15% and 40%. Higher sorbent activity levels do not affect efficiency but would lead to lower capital costs. According to the model, CaO activity levels above 17% lead to significant reductions in the required storage volume over existing systems, such as molten salts. In principle, high efficiency and smaller footprint solar thermal power plants are possible with calcium looping. Such plants would have no process use of water and could be used as baseload, variable demand load or microgrid systems.

Clinkering Reactions During Firing of Recyclable Concrete

Thermal transformations occurring during firing of recyclable concrete and hydrated Portland cement paste were monitored quantitatively by in situ and ex situ X‐ray diffraction, thermal analysis, and clinker microscopy. Reactions below 1150°C were dominated by either the decarbonation of calcium carbonates of the limestone aggregate fraction in the recyclable concrete or the low temperature decomposition of cement hydrates of the cement paste. Continued heating of the cement paste showed a rapid and extensive reaction of the free lime to form intermediate calcium silicate and aluminate phases such as belite, gehlenite, mayenite, and ye'elimite. The combination of free lime was less rapid in the dominantly limestone‐rich recyclable concrete. Similarly, subsequent melt and clinker phase formation (1250°C and higher) occurred more rapidly in the hydrated cement paste, indicating a positive contribution of cement hydrates to raw meal burnability. Reactions below typical cement clinkering temperatures were enhanced (1) by the intimate mixing of lime, silicate, and aluminate components in the hydrated cement and (2) by the elevated sulfate content that acted as flux and belite mineralizer. Lime formed in the thermal decomposition of portlandite (±450°C) was partially carbonated to calcite at temperatures below the onset of calcite decarbonation (±650°C).

Activation of Fly Ash–Lime Reactions: Kinetic Approach

Lime–fly ash reactions play a key role in improving the mechanical strength and tailoring the permeability characteristics of compacted fly ash. Activation of fly ash–lime pozzolanic reactions should accelerate the rate of strength development and possibly mobilize higher compressive strengths, facilitating improved engineering performance of fly ash amended materials. This paper makes an assessment of activation of lime–fly ash reactions by curing compacted fly ash–lime specimens at ambient (25°C) and at elevated temperature (80°C). The kinetics of fly ash–lime reactions are examined by monitoring the reacted lime as a function of curing period and temperature. The influence of variations in fly ash/lime content and dry density on the compressive strength developed by specimens at both temperatures is evaluated. The thermodynamic parameters for the fly ash–lime reactions have also been examined. Experimental results showed that curing at 80°C for 24 h accelerated fly ash–lime reactions such that it caused the steam cured (SC) specimens to evelop 1.21–2.44 fold larger strengths than room-temperature cured (RTC) specimens cured at 25°C for 28 days. Analysis of thermodynamic parameters indicated that the fly ash–lime reactions are thermodynamically favored at fly ash contents of 50–70% and lime additions of 16–20%, and the reactions are endothermic in nature. DOI: 10.1061/(ASCE)MT.1943-5533.0000482. © 2012 American Society of Civil Engineers.

The Kinetic Analysis of Carbide Lime Reaction Based on Multi-Heating Rate Method

In this paper, research was focused on the carbide lime decomposition mechanism in pure N2 atmosphere by using thermo-gravimetric analysis with multi-heating rate method. Appling equal conversion rate method, activity energy E was calculated which was equal to 84.79 kJ/mol without proposing decomposition mechanism. A more accurate and reliable method based on multi-heating rate methods was put forward to deduce the mechanism function of above reaction, which was called “master plot methods”. Comparison was done between the theoretical master plots drawn by assuming various kinetic models and the experimental master plot, which allows us to select the probably appropriate kinetic model of the process under investigation. And the further detailed kinetic analysis was achieved as the knowledge of the kinetic model. The results are as follows: the reaction mechanism function f(α)=2.95(1-α)0.661 or G(α)=1-(1-α)0.339, the pre-exponential factor lnA=15.95. And the decomposition mechanism of carbide lime turned out to be the phase boundary shrinking sphere reaction.

Use of fly ash, bottom ash and zeolite as additives for enhancing lime reactivity towards flue gas desulfurization

Lime reactivity toward desulfurization was examined by blending lime with pozzolanic additives namely fly ash, bottom ash, and zeolite. The reactivity was tested in a pH-stat apparatus. Apart from lime to additive ratio, other important operating conditions, namely, temperature, solid to liquid ratio, and stirring speed, were varied accordingly using the design expert's design of experiments. Central cubic design was used to investigate linear, quadratic, cubic, and cross-product effect of these operatives. Sorbents made from lime-zeolite blends were found to have the highest reactivity followed by fly ash then bottom ash. These results were confirmed through sorption capacities of the best sorbents using a fixed bed reactor. BET surface area analysis of the best sorbents indicated that surface area improvement is the root cause of improvements in reactivity and sorption capacities. Temperature had the largest effect on reactivity. The other operative's effect varied from one additive to the other. © 2011 American Institute of Chemical Engineers Environ Prog, 32: 75–83, 2013.

Characterisation of Fly Ash and Relevance of Pozzolanic Reactivity

ABSTRACT It is a very well known fact that the use of fly ash in masonry and concrete make the structures durable. Properties of Fly Ash depend upon coal source. For acceptability of fly ash in cement, mortar and concrete various specifications and standards are available. The Indian standard IS 3812: 2003(Part I and Part II) expects some physical and chemical properties similar to world standards, while differs in some, like lime reactivity test. As a part of research activity the authors have collected 23 different fly ash samples from various hoppers of three power stations near Nagpur. The samples were tested as per most of the provisions of IS 3812 and tests specified in IS 1727. Test results are compared with major world standards and specifications. Gain of strength is the most important character of fly ash, especially from the usage in cement and concrete. The paper discusses comparison of various standard specifications and interpretation of pozzolanic reactivity.

Preparation of Porous Mordenite/Calcium Silicate Hydrate Composites for Indoor Environment Control

A micro/mesoporous composite was prepared by a hydrothermal reaction using mordenite and slaked lime to create a comfortable and safe indoor environment. After the hydrothermal reaction, calcium silicate hydrates formed due to the reaction of slaked lime, mordenite, and quartz, led to the generation of mesopores with a broad pore size distribution of more than 3 nm.In this experiment, the microporous structure of mordenite partially collapsed due to dissolution. As compared with mordenite, the composites exhibited higher water-vapor adsorption/desorption properties using their mesopores. The amount of adsorbed harmful gases at 70% relative humidity was larger for the composites than for mordenite.

Physico-chemical Properties of Different Carbonate Rocks: Are They Highly Enough to Control Lime Reactivity?

We have examined 5 different carbonate rocks in order to study their behavior during calcination at different temperatures (900, 1050 and 12000C for 30 min) and hydration properties of quick limes and the final interconnection of the primary material with the reactivity of the slaked lime. Quick limes calcined at 9000C show the lower reactivity values. This could be related to the low calcination temperature or to the short calcination time of 30 min which was insufficient to produce enough lime. The samples calcined at temperatures of 12000C are less reactive compared to those calcined at 10500C, indicated by parameters such as the (CaO+MgO)Lime, the time required to reach the temperature maximum and the reactivity rate. This, probably could be due to annealing effects such as crystal coarsening and reduction of porosity at relatively high temperatures.

Enhancement of lime reactivity by addition of diatomite

Diatomite was used as a Pozzolan to augment lime reactivity. This was confirmed through laboratory wet and dry flue gas desulfurization (FGD) experiments using pH-stat apparatus (representing wet FGD) and fixed bed reactors (representing dry FGD). BET surface area analysis and SEM imaging were used in characterization and to aid in understanding the behavior of the sorbent. After affirming that diatomite improves lime's reactivity, optimization tests were conducted to maximize the reactivity output. The effect of various variables namely; temperature, lime to diatomite ratio, solid to liquid ratio and stirring speed, were maximized linearly, quadratically and interactively. The design of optimization experiments was done through design expert software. Central cubic design was used for regression analysis. As expected, temperature had the highest effect towards reactivity. Some effect showed a mini-max behavior while others had a sinusoidal trend.

Thermal microstructural changes of grain-supported limestones

The microstructure of grainstone, grain-supported limestone, samples representing different geographic and stratigraphic intervals in Egypt were examined before and after calcination at 950°C for 0.25, 0.5, 1 and 2 h. The examination utilized are X-ray diffraction (XRD), X-ray fluorescence (XRF), transmitted light microscopy (TLM), scanning electron microscopy (SEM) and X-ray micro tomography (μ-CT). Both the free lime content and reactivity of the produced quicklime were measured. The quicklime produced at 950°C for 0.25 and 0.5 h is un-reactive (RDIN 30) with variable reactivity due to the differences in the lime microfabric. The grainstones enriched in nummulites resulted in quicklime of higher reactivity than those dominated by foraminifera, peloids and miliolids. This is mainly attributed to the preservation of the intraparticle pores of the original limestone and the development of pinhole and fracture micropores. The shape of pores and not their amount is the main controlling variable in the quicklime reactivity. The grainstones enriched in fracture pores showed more reactive lime, whereas those with compact structures are less reactive post calcination.

Investigating Effects of Zeolites As an Agent to Improve Limestone Reactivity toward Flue Gas Desulfurization

Natural zeolite was utilized as an agent to increase the reactivity of lime for desulfurization. Due to the presence of hydrous silica−aluminates in zeolite, a pozzolanic reaction ensued which ended up with an increase in the surface area of lime thus making it more reactive. Tests were done in a pH-stat apparatus and a fixed bed reactor, representing wet and dry flue gas desulfurization (FGD), respectively, to check if lime reactivity was augmented by the addition of zeolite. It was found that zeolite amplifies reactivity of lime with the highest reactivity being achieved with a lime to zeolite ratio of 1:1 (by mass). This was confirmed by Brunauer−Emmett−Teller (BET) surface area analysis (surface area increment with the reactivity) and scanning electron microscopy (SEM) imaging (rough morphology being formed). Further optimization tests were conducted in the pH-stat apparatus with the aid of design expert software to quantify linear, quadratic, and interactive effects of four variables (temperature, lime to zeolite ratio, liquid to solid ratio, and stirring speed). Temperature as a variable had the highest effect, followed by lime to zeolite ratio. Stirring speed had the least effect on the reactivity.

Effect of particle size of limestone on Ca, Mg and K contents in soil and in sward plants

Liming increases crop production through improved soil conditions in acidic soils. Among the effects of liming, increased availabilities of alkaline and alkaline-earth cations are worth mention. These availabilities may be affected by the particle size of applied limestone, which influences lime reactivity. The effects of particle size and application schedule of magnesium limestone were investigated on extractable Ca, Mg and K in soil, their concentrations in sward plants and dry-matter yield. Magnesium limestone of various particle sizes was applied to experimental plots at a rate of 3 t ha-1, a grass-clover sward was sown, and the plots were monitored during three years. The finest limestone (< 0.25 mm) in a single application yielded the highest soil Ca and Mg concentrations extracted by Mehlich-3 and NH4Cl. The same limestone split in three annual doses was less effective. Plots treated with the coarsest limestone (2-4 mm) did not differ from control plots. Liming had no effect on potassium, either in soil or plants. Soil concentrations of Ca, Mg and K extracted by Mehlich-3 and NH4Cl were correlated with each other (r = 0.76, 0.75 and 0.67, respectively). NH4Cl extracted more Ca than Mehlich-3, while the latter extracted more Mg and K than NH4Cl. Soil Ca, Mg and K extracted by NH4Cl were also correlated to water extractions. Mg concentration in plants correlated to soil Mg extracted by NH4Cl or by water. Neither the concentrations nor the total contents of Ca and K in plants correlated with extractable soil Ca and K. The total dry matter yield was not affected by liming. The yield of sown species was higher in plots treated with the finest limestone than in plots limed with the coarsest limestone. Cations extracted by water or NH4Cl explained the variance of dry matter yield.

Recycling of Ornamental Stones Hazardous Wastes

Sawing and polishing of the ornamental stones always generate large amount of solid and wet hazardous wastes, which pollute the environment. In Shak Al-Thoaban area, East Cairo, Egypt, huge amounts of these wastes were accumulated, during the last years, as rejects “Solid” and wet “Sahala” wastes, representing one of the main sources of environmental pollution. The aim of this work is to characterize and evaluate these wastes for recycling in quicklime production. Hence, samples of both wastes were investigated for their chemical and mineral composition applying XRF, XRD, DTA and TGA methods. Free lime content and reactivity (RDIN) of both samples were also determined after calcination for differnt soaking times (0.25 - 2.0 hrs) at 1000℃. The results were interpreted in relation to composition and microstructure of the fired samples as revealed by TLM and SEM methods. The RDIN reactivity of the resulted lime is changeable along soaking time at 1000℃because of the microfabric of its crystallites. The lime of the “Solid” sample is preserving the original limestone microstructure that contributes in its higher RDIN reactivity values at all soaking times. The relatively higher degree of grain growth of lime crystallites in the “Sahala” sample leads to its lower reactivity. The optimum soaking times for the highest lime reactivity are 0.25 and 1 hr. for the “Solid” and “Sahala” samples, respectively. On increasing soaking time up to 2 hrs, both samples show minimum RDIN values. The “Solid” sample also gives higher free lime content than the “Sahala” one at all soaking times. It is gradually increased in the former sample up to a maximum (96% - 97%) on increasing soaking time up to 1-2hrs. On the other side, a maximum free lime (~95%) is detected in “Sahala” sample at 0.25hr soaking time and gradually decreased to (87%) up to 2hrs.

Possibility of Lime as a Stabilizer in Compressed Earth Brick (CEB)

This paper highlights the production of lime, chemical reaction during the production process, lime reaction with the soil and the prospective use of lime in the future. The research works that has been carried out showed lime has superior properties than cement in enhancing soil structure and also exhibits less embodied energy than cement. The lime through its chemical composition, calcium hydroxide, able to reacts with the pozzolanic materials that presents in the clay soil. This pozzolanic reaction resulted to the formation C-S-H cementitious gel that will further stabilize the soil. The application of lime will also promote healthier environment since carbonation process that occur during carbonation period absorb carbon dioxide in the air. The production of compressed stabilized earth brick using lime will also contributes to greener environment as compared to normal brick production method which consumed extensive energy.

Competition between Hydration and Carbonation in Hydraulic Lime and Lime-Pozzolana Mortars

A combined reaction of hydration and carbonation takes place in hydraulic lime and lime-pozzolana mortars. Hydration reactions are the first reaction and carbonation of lime is the complementary reaction in the strength gain. Competition between these two reactions can occur in lime-pozzolana mortars if the pozzolanic material has low reactivity with lime, leading to the consumption of lime by carbonation reaction. The degree and the order of these reactions are strongly influenced by the moisture content. Hydration reactions are enhanced under moist conditions while carbonation is delayed. Curing under dry conditions does not sufficiently increase their strength because the hydration reactions are slowed down or even terminated by the full carbonation of lime in lime-pozzolana mortars. The consequence of this on the mechanical properties of the mortars is remarkable while the same impact is not observed in their porosity. Such mortars require moist conditions to ensure sufficient strength development.

Gypsum treated fly ash as a liner for waste disposal facilities

Fly ash has potential application in the construction of base liners for waste containment facilities. While most of the fly ashes improve in the strength with curing, the ranges of permeabilities they attain may often not meet the basic requirement of a liner material. An attempt has been made in the present context to reduce the hydraulic conductivity by adding lime content up to 10% to two selected samples of class F fly ashes. The use of gypsum, which is known to accelerate the unconfined compressive strength by increasing the lime reactivity, has been investigated in further improving the hydraulic conductivity. Hydraulic conductivities of the compacted specimens have been determined in the laboratory using the falling head method. It has been observed that the addition of gypsum reduces the hydraulic conductivity of the lime treated fly ashes. The reduction in the hydraulic conductivity of the samples containing gypsum is significantly more for samples with high amounts of lime contents (as high as 1000 times) than those fly ashes with lower amounts of lime. However there is a relatively more increase in the strengths of the samples with the inclusion of gypsum to the fly ashes at lower lime contents. This is due to the fact that excess lime added to fly ash is not effectively converted into pozzolanic compounds. Even the presence of gypsum is observed not to activate these reactions with excess lime. On the other hand the higher amount of lime in the presence of sulphate is observed to produce more cementitious compounds which block the pores in the fly ash. The consequent reduction in the hydraulic conductivity of fly ash would be beneficial in reducing the leachability of trace elements present in the fly ash when used as a base liner.

Use of steel slag as a granular material: Volume expansion prediction and usability criteria

The theoretical equation for predicting volume expansion of steel slag is deduced based on both chemical reaction and physical changes of free lime in steel slag during the hydration process. Laboratory volume expansion testing is conducted to compare the results with the theoretical volume expansion. It is proved that they correlated well. It is furthermore experimentally proved that certain volume expansion of steel slag can be absorbed internally by the void volume in bulk steel slag under external surcharge weight making the apparent volume expansion equal zero. The minimum (lowest) absorbable void volume is approximately 7.5%, which is unrelated to the free lime content. A usability criterion is then developed based on the volume expansion of steel slag (%) and the minimum percentage of the volume that can take the volume expansion of steel slag (%). Eventually the criterion (relationship) is established based on the free lime content, the specific gravity and bulk relative gravity of a specific steel slag sample. The criteria can be used as guidance and specification for the use of steel slag and other expansion-prone nonferrous slags, copper, nickel for instance as a granular material in highway construction.