Reaction Of Lime Research Articles

Influence of using rice husk ash in soil stabilization method with lime

In clayey lands, swelling problem causes vertical displacements on road subbase, and finally, failure in pavement occurs due to lack of appropriate drainage systems. One popular and inexpensive method of soil stabilization is using lime. Investigations indicate that based on environmental and atmospheric conditions, the chemical reaction of lime and clayey soil is not accomplished well, owning to low temperature and high humidity. This paper aims to investigate the influence of adding rice husk ash on the reaction between soil and lime and lime reaction and determine soil physical and mechanical characteristics. Therefore, sufficient laboratory soil tests, such as Atterberg limits, compaction, California bearing ratio (CBR), and direct shear test are carried out, and the results are analyzed. The results generally indicate that adding lime and rice husk ash (RHA) causes a decrease in dry density and an increase in optimum water content. Increasing lime and RHA causes a decreasing rate in soil liquid limit and plastic limit. Adding lime and RHA to the soil causes a decrease in deformability of soil samples and gives more brittle materials. Also, this action causes an increase in shear strength. Moreover, increasing in CBR amount under the influence of increasing RHA is one of the main results of this paper.

Role of Gypsum in the Strength Development of Fly Ashes with Lime

The strength of fly ash mixture often needs to be enhanced for its better utilization in geotechnical and environmental applications. Many fly ashes often improve their strength with lime but may not meet the requirements. Gypsum, which reduces the lime leachability, further improves the strength. An attempt is made in this paper to study the effect of gypsum on the strength development of two Class F fly ashes with different lime contents after curing them for different periods. The sustainability of improved strength has been examined after soaking the cured specimens in water and with different leachates containing heavy-metal ions. The strength of both the fly ashes investigated improved markedly up to a particular amount of the lime content, which can be taken as optimum lime content, and thereafter the improvement is gradual. The improvement in strength at higher lime contents continues for a longer period (even up to 180 days). Gypsum accelerates the gain in strength for lime-stabilized fly ashes, particularly in the initial curing periods at about optimum lime content. At high lime contents gypsum attributes very high strength after curing for long periods mainly due to the alteration of fly ash lime reaction compounds. Gypsum not only improves the reduction in the loss of strength due to soaking even at low curing periods but also improves the durability of stabilized fly ashes due to repeated cycles of wetting and drying.

Dissolution of Lime in Synthetic ‘FeO’‐SiO2 and CaO‐‘FeO’‐SiO2 Slags

AbstractDissolution of different CaO samples into molten synthetic ‘FeO’‐SiO2 and ‘FeO’‐SiO2‐CaO slags was carried out in a closed tube furnace at 1873 K. The slag was kept stagnant. It was found that the dissolution rate was very fast when CaO rod was dipped into ‘FeO’‐SiO2 slag. In the case of ‘FeO’‐SiO2‐CaO slag, the dissolution of CaO rod in the stagnant slag was retarded after the initial period (2 minutes). Only less than 16 percent CaO reacted with the slag, irrespective of the type of lime. Three phase‐regions were identified in the reacted part of the lime rod by SEM‐EDS analysis. The formation of these regions was explained thermodynamically. A dense layer of 2CaO · SiO2 was found to be responsible for the total stop of the dissolution. It could be concluded that constant removal of the 2CaO · SiO2 layer would be of essence to obtain a high dissolution rate of lime. In this connection, it was found necessary to study the dissolution of lime in moving slag to reach a reliable conclusion regarding the relevance of the reactivity obtained by water ATSM test to the real reactivity of lime in high temperature slag.

The influence of sucrose on the crystallization behaviour in the system CaO–SiO 2–C 12H 22O 11–H 2O under hydrothermal conditions

Hydrothermal synthesis in the presence of sucrose has been carried out at 200 °C and autogeneous pressure in the system CaO–SiO 2–C 12H 22O 11–H 2O to investigate the influence of C 12H 22O 11 on phase formation and the crystal habit of calcium silicate hydrates (CSH-phases). A sucrose/lime ratio of 0.5 was utilized in all experiments and the reactivity of the SiO 2 source was varied using educts of different grain size of ∼40 mesh and >230 mesh. CaO/SiO 2 concentration ratios of 0.5 and 0.8 have been selected, the latter with respect to the composition of the important CSH-phase 11 Å tobermorite. The results were compared with experiments under similar but sucrose-free conditions. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX-analysis) as well as Fourier transform infrared spectroscopy (FTIR-spectroscopy) have been applied for analyses. A retarding effect of sucrose on CSH-phase formation has been observed. Only minor amount of CSH without regular morphology was observed instead of typically fibrous 11 Å tobermorite formed in the sucrose-free system. Sucrose altered the reaction mechanism in the CSH-system and hydrothermal process started with rapid reaction of sucrose and lime. The further course of crystallization was dominated by an extended precipitation of calcium carbonate and small amounts of calcium oxalate hydrate. Formation of these stable hydrothermal decomposition products of saccharated lime is strongly suppressing the CSH-crystallization.

Precipitation of calcium carbonate from hydrated lime of variable reactivity, granulation and optical properties

Different sources of lime for the production of precipitated calcium carbonate were studied. The reactivity of lime, its optical properties and those of the final products are reported and discussed, and a comparison made between lime from different sources. The influence of the temperature of hydration water on the optical properties and particle sizes after hydration and precipitation was also studied. It was found that coarser granulations of lime have better optical properties than finer granulations. The hydration temperature does not have an appreciable impact on the optical properties, but influences the intermediate, i.e. the calcium hydroxide particle sizes and subsequently the particle sizes of the precipitated calcium carbonate. Furthermore, the maximum temperatures of lime hydration from different European sources do not vary significantly, but they differ in the kinetics of the hydration process.

Hydrothermal solidification of zeolite/tobermorite composites

Novel zeolite/tobermorite composites were prepared by hydrothermal treatment of a powder-compact consisting of mordenite and slaked lime. Tobermorite formed after the hydrothermal process due to the reaction of mordenite and slaked lime. The bending strength after the hydrothermal process was more than 7 MPa. X-ray diffraction analysis results showed that mordenite remained after the hydrothermal treatment, resulting in the existence of inherent micropores of mordenite in the composites. The composites exhibited a broad mesopore size distribution of more than 6 nm. The improvement in strength, mesopore formation, and specific surface area of the composites depended on the amount and size of the tobermorite that was formed.

Monitoring and selection of optimum production parameters for metallurgical-grade lime to be used in ferrous metallurgy

We describe the specifications for production of ISO and EN-compliant metallurgical-grade lime; present analysis results and requirements regarding the chemical composition of lime; present the results of tests to determine the reactivity of lime; and propose an explanation for the essential kinetics of the dissociation process in lump lime.

Roman ceramics of hydraulic mortars used to build the Mithraeum house of Mérida (Spain)

Roman ceramics of two hydraulic mortars used to build the pond and water channel of Mithraeum house from Merida (Spain) have been studied. The sizes of the ceramic fragments found were different in both of the samples studied, showing different behaviour in the reactions with the lime. The X-ray diffraction of the ceramic shows the presence of quartz, mica (biotite), anorthite and hematite accompanied by amorphous phase, being observed scarce vitrification. The presence of mica confirms a firing temperature for manufacturing the ceramic below 900°C. In one of the ceramics studied, X-ray diffraction did not show calcite. However, in the FTIR appear bands that could be assigned to carbonates absorptions and likewise, carbonates were identified in the DTA-TG curves. Ca and small quantities of Si and Al were also identified by SEM-EDX on the surface of the pores that could be due to an amorphous phase formed in the reaction of lime with the Si and Al of the ceramic. On the other hand, in other ceramic samples carbonates (about 10%) were detected. The carbonates have been found filling the pores, sometimes accompanied by a new calcium-aluminium-silicate phase produced by the reaction between the lime and the amorphous phase of the ceramic. The carbonates and the new phases formed inside the pores are responsible for the decrease of the porosity and for the formation of new phases during the heating of the ceramics.

Mobilidade de cátions e correção da acidez de um Cambissolo em função da aplicação superficial de calcário combinado com sais de potássio

A menor reatividade do calcário abaixo dos locais de aplicação deve-se principalmente à sua baixa solubilidade, ao aumento das cargas negativas nas camadas aplicadas devido ao aumento do pH e à pequena permanência dos ânions adicionados na solução do solo. O presente trabalho teve por objetivo avaliar o efeito da adição de ânions a partir de sais de K sobre a superfície do solo, no incremento da reatividade do calcário e na mobilidade de seus cátions em um Cambissolo Húmico. O experimento foi realizado em 2005, em solo com 360 g kg-1 de argila, 60 g kg-1 de matéria orgânica e pH 4,1. Foram utilizadas três doses de calcário dolomítico (0, 0,74 e 1,48 kg m-2), combinadas com 40 g m-2 de K, na forma de KCl ou de KNO3, e com uma testemunha sem K, todos incorporados no primeiro centímetro da coluna do solo. As unidades experimentais (colunas de PVC com 10 x 30 cm, contendo 1,5 kg de solo) foram percoladas 21 vezes, a cada sete dias, com 300 mL de água destilada por semana, totalizando o equivalente a 800 mm de chuva. Os sais potássicos lixiviaram muito mais Ca e Mg do que o calcário. Na média dos três tratamentos de calagem, a adição dos sais aumentou a lixiviação total de Ca, Mg e K, respectivamente de 36 para 132 mg, de 5,8 para 26 mg e de 25 para 51 mg/coluna, relativamente ao tratamento sem adição de sal. Na ausência dos sais, a aplicação da maior dose de calcário dolomítico lixiviou apenas 5 mg de Ca e 1,2 mg/coluna de Mg, em relação ao tratamento sem calcário. A calagem superficial afetou o pH do solo e a concentração de Ca, Mg e Al trocável até a profundidade máxima de 5,0 cm, cujas alterações foram quase sempre proporcionais à dose aplicada, porém não foram influenciadas pela adição dos sais. A aplicação dos fertilizantes potássicos não influenciou a capacidade reativa do calcário aplicado na superfície do solo.

Methodology for Rapid Determination of Pozzolanic Activity of Materials

Abstract Determination of pozzolanic activity, and in particular lime reactivity, of various materials such as fly ash, cenospheres, blast furnace slag, etc., is quite essential for their efficient application in cement and concrete. It also plays an important role in the selection of the material as a stabilizer in various environmental cleanup projects, such as heavy metal retention and waste immobilization strategies. Though ASTM C 311, ASTM C 593, and IS 1727 are being followed to determine pozzolanic activity of different materials, they are quite time consuming. This necessitates development of a methodology that can be employed for determining the pozzolanic activity of different materials, quite rapidly and easily. With this in view, a methodology that indirectly estimates pozzolanic activity of different materials, by measuring electrical conductivity of their mixture in partially saturated lime solution, has been developed and its details are presented in this paper.

Protocol to Quantify the Reactivity of Carbonate Limestone for Horticultural Substrates

The current method for comparing the reactivity of different limestones used to correct pH in horticultural substrates is based on batch trials, where the limestones are incorporated into the substrate and the pH is measured over time (typically up to 28 days). The objective was to test a laboratory approach to provide a rapid analytical test on reactivity of various limestone sources. To a lime sample, 4M hydrochloric acid (HCl) was added, and the volume of carbon dioxide (CO2) released into a burette was measured over time. Reagent‐grade calcium carbonate (CaCO3) and two commercially available pulverized dolomitic limestones were tested. In addition, six particle‐size fractions derived from each of the limestone samples were also evaluated for reaction rate and the corresponding pH responses. In less than 1 min after acid addition, 100% of CaCO3 reacted, whereas it took 3.9 and 11.5 min, respectively, for 50% of the limestone samples to react, and 14 and 52 min, respectively, for 90% neutralization. Reaction rate increased as the particle size decreased; however, a similar reaction rate was observed for the particle sizes larger than 150 µm (>100 U.S. mesh). Time to 90% reaction was negatively correlated with pH response when 6 g of each lime was incorporated per L of peat substrate. It may be possible to establish a lime reactivity index, for example based on the time required for 50% or 90% reaction, and thereby provide a rapid screening of different limestone sources.

Origin of cementing calcite in “carbonatite” tuffs

Many tuffs contain crystal, glass, and rock fragments that are supported by calcite cement, and some of these have recently been classified as carbonatites, i.e., igneous rocks dominated by magmatic carbonate minerals. In samples studied here, the cementing calcite has lower Sr and higher Mg concentrations, and higher 18O/16O but lower 13C/12C, than magmatic calcite. These chemical data, together with textural evidence, indicate that the cementing calcite in these tuffs was precipitated as coatings on the pyroclastic fragments by meteoric water. A single thin section of a calcite-cemented tuff (whether it holds carbonatite or silicate lapilli) can contain as many as five texturally and chemically distinct kinds of carbonate, precipitated sequentially, and never in equilibrium with each other. The secondary calcite in some occurrences may have formed by reaction of lime calcined by hot silicate magma from limestone wall rocks. Pyroclastic deposits that contain calcite only in pore-filling cement or replacing silicates should not be called carbonatites.

Effect of calcination temperature and heating rate on the optical properties and reactivity of rice husk ash

Rice husk is an agricultural waste and its conversion to value added products makes it a secondary resource material. On heating, rice husk gives ash with >90% by weight of silica with some carbon and other nonmetallic and metallic impurities. Silica of high purity, chemical reactivity and white color can be produced from rice husk by controlling the heating conditions and this material finds wide industrial applications. Properties of the ash depend upon various pretreatments and calcination conditions. The present work deals with the investigation on a rice husk sample from the state of Andhra Pradesh in India. The raw husk and its acid treated form were calcined at different conditions such as temperatures, soaking periods and heating rates. Lime reactivity, surface area, brightness and color values of the ash samples were measured. The high potassium content in the husk has been found to inhibit the carbon removal during ashing which affected the color as well as reactivity of the ash. Properties of the ash samples from the untreated and acid treated husk have been compared and correlated with the formation conditions.

MODELING LIME REACTION IN PEAT-BASED SUBSTRATES

Limestone is incorporated into peat-based substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual” lime. In horticulture, lime reactivity is currently measured empirically in batch tests whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the nonlimed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

(66) Modeling Lime Reaction in Horticultural Substrates

Limestone is incorporated into horticultural substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual”? lime. In horticulture, lime reactivity is currently measured empirically in batch tests, whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the non-limed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

Optimum Dose Of Lime And Fly Ash For Treatment Of Hexavalent Chromium–Contaminated Soil

The presence of hexavalent chromium, Cr(VI), in soil is an environmental concern due to its effect on human health. The concern arises from the leaching and the seepage of Cr(VI) from soil to groundwater. In this paper, a stabilization technology to prevent this problem was simulated on an artificial soil contaminated with hexavalent chromium. The process is a physico-chemical treatment in which the toxic pollutant is physically entrapped within a solid matrix formed by the pozzolanic reactions of lime and fly ash to reduce its leachability and, therefore, its toxicity. This paper presents the optimum ratio of fly ash and lime in order to stabilize artificial soils contaminated with 0.4 wt.% of Cr (VI) in a brief term process. The degree of chromium released from the soil was evaluated using a modified Toxicity Characteristic Leaching Procedure (TCLP) by US Environmental Protection Agency (EPA). Overall, experimental results showed reduced leachability of total and hexavalent chromium from soils treated with both fly ash and quicklime, and that leachability reduction was more effective with increasing amount of fly ash and quicklime. Stabilization percentages between 97.3% and 99.7% of the initial chromium content were achieved, with Cr(VI) concentration in the TCLP leachates below the US EPA limit for chromium of 5 mg/l. Adequate treatment was obtained after 1 day of curing with just 25% fly ash and 10% quicklime.

Effect of sulphate on the shear strength of lime-treated kaolinitic soil

Lime has been extensively used to improve the strength of fine-grained soils. It has recently been reported that the presence of sulphate in soils causes abnormal volume changes in lime stabilised soil. This paper presents the strength behaviour of lime-treated kaolinitic natural red earth in the presence of varying sulphate contents, up to 3%, after curing for periods of up to 365 days. Alteration of soil–lime reactions in the presence of sulphate leads to the formation of ettringite after curing for longer periods. The formation of these compounds affects strength development by cementation. However, after curing for short periods, the strength of lime-treated soil is improved in the presence of sulphate. It is only after curing for longer periods that the strength is decreased. Consequently the stress–strain behaviour and effective stress paths of treated soil cured for long periods show the behaviour of a normally consolidated soil rather than of cemented soils. The reduction in strength is due primarily to a reduction in the effective cohesion intercept. The effective friction angle has not been affected significantly. La chaux est largement utilisée pour améliorer la résistance des sols à grains fins. On a noté récemment que la présence de sulfate dans les sols cause des changements de volume anormaux dans les sols stabilisés à la chaux. Cet exposé montre le comportement de résistance d'une terre kaolinique naturelle traitée à la chaux en présence de diverses teneurs en sulfate, allant jusqu'à 3%, et après cuisson pendant des périodes allant jusqu'à 365 jours. Le changement de la réaction sol-chaux en présence de sulfate conduit à la formation d'ettringite après les périodes de cuisson les plus longues. La formation de ces composés affecte le développement de la résistance par cimentation. Cependant, après cuissons plus courtes, la résistance du sol traité à la chaux est améliorée par la présence de sulfate. Ce n'est qu'après la cuisson pendant des périodes plus longues que la résistance diminue. En conséquence, le comportement contrainte-déformation et les chemins de contrainte effective du sol traité et cuit pendant de longues périodes reflètent le comportement d'un sol consolidé de manière normale plutôt que celui de sols cimentés. La baisse de résistance est due principalement à une réduc-tion de l'interception de cohésion effective. L'ange de friction effectif n'est pas affecté de manière significative.

Study of the Reaction of Lime with HCl under Simulated Flue Gas Conditions Using X-ray Diffraction Characterization and Thermodynamic Prediction

Hydrochloric acid (HCl) is commonly removed from flue gases using hydrated lime (Ca(OH)2) as a sorbent in the dry scrubbing process. Although this method is relatively easy to operate and the lime sorbent is cheap, this process is highly inefficient, as only ∼25% of the lime used is converted, due to the short contact time and the lack of understanding of the reaction chemistry of lime in a complex flue gas system. A comprehensive X-ray diffraction (XRD) characterization was carried out on the product of a hydrated lime reaction with HCl in a simulated flue gas system containing SO2, CO2, O2, and moisture. Together with thermodynamic calculations, the chemical nature of the multiple reactions that happened in this system was investigated. It was confirmed that the products of hydrated lime with HCl under the simulated flue gas conditions were chiefly Ca(OH)Cl, CaCl2, CaCO3, CaSO3·1/2H2O, CaSO4·2H2O, and anhydrous CaSO4. Previous results suggested that the presence of CO2 and SO2 in the system formed products with a high product diffusion resistance, leading to pore blockage and the premature termination of the reaction. However, in this study, experimental proofs showed that HCl was able to break down the CaCO3 and CaSO3·1/2H2O layer, allowing the reaction to continue. In the presence of excess O2 (and moisture), part of the CaSO3·1/2H2O was oxidized to CaSO4·2H2O and CaSO4. The presence of O2 is, therefore, counterproductive to the full utilization of hydrated lime, as sulfur in its S(VI) form is more stable and resistant to HCl attack, thereby preventing blocked pores from being cleared.

A Protocol to Quantify the Reactivity of Carbonate Lime for Horticultural Substrates

Lime sources vary in their reactivity depending on particle size, surface area and crystalline structure, and chemical composition. Current horticultural practice for testing lime reactivity and the appropriate lime rate is through batch trials where lime is incorporated into growing media. Our objective was to test a laboratory approach that would provide a rapid analytical test on reactivity of lime sources, and could eventually be applied to measuring unreacted (residual) lime in container media. Four moles HCl was added to a lime sample, and the volume of CO2 released over time was measured in a burette. Three lime types were tested, including reagent grade CaCO3, and two pulverized dolomitic limestones used in horticultural media. 100% of CaCO3 reacted in less than a minute after acid addition, whereas only 79.8% and 49.5% of the two commercial lime samples had reacted after 10 minutes. The time required for 50% of the two commercial lime samples to react was 5 and 10 minutes, respectively, whereas it took 20 and 60 minutes, respectively, for 95% neutralization. Reaction rates in the laboratory test correlated with the time required to achieve a stable pH level when limes were incorporated into a peat substrate. The reagent-grade CaCO3 raised pH more rapidly (within 7 days) and to a higher level (maximum pH 7.5 at 9 g of lime per liter of peat) compared with the dolomitic lime sources. It may be possible to establish a lime reactivity index, for example, based on CO2 release after 10 minutes, and thereby provide a rapid screening of limes. Further gasometric analysis of lime types used in horticultural substrates is therefore needed.

Hydrated Lime Reaction with HCl under Simulated Flue Gas Conditions

Hydrochloric acid (HCl) is a common acidic pollutant present in the flue gas of most municipal and hazardous waste incinerators. Hydrated lime [Ca(OH)2] is often used as a sorbent to remove HCl through the dry and semidry scrubbing process. However, this process provides a very short residence time for the lime and HCl to react, causing the lime conversion efficiency to be low and generating a large amount of fly ash. Following our previous studies on the kinetics of the HCl−lime reaction, the current paper is aimed at the investigation of the effects of other species present in the flue gas, namely, CO2, SO2, and moisture, on the HCl−lime reaction. The reaction was carried out in a thermogravimetric analyzer at a temperature of 200 °C under 9% of O2, and the products of the reaction were identified and quantified using X-ray diffraction. The sequential reactions of lime with CO2 (or SO2)−HCl−CO2 (or SO2) were also conducted to compare the different effects of these species on the formation of product lay...