Showing papers on "Calcium oxide published in 2014"

Influence of Calcium Sources on Microbially Induced Calcium Carbonate Precipitation by Bacillus sp. CR2

Abstract: Stimulation of microbially induced calcium carbonate precipitation (MICCP) is likely to be influenced by calcium sources. In order to study such influences, we performed MICCP using Bacillus sp. CR2 in nutrient broth containing urea, supplemented with different calcium sources (calcium chloride, calcium oxide, calcium acetate and calcium nitrate). The experiment lasted 7 days, during which bacterial growth, urease activity, calcite production and pH were measured. Our results showed that calcium chloride is the better calcium source for MICCP process, since it provides higher urease activity and more calcite production. The influences of calcium sources on MICCP were further studied using Fourier transform-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. These analyses confirmed that the precipitate formed was CaCO3 and composed of predominantly calcite crystals with a little amount of aragonite and vaterite crystals. The maximum yield of calcite precipitation was achievable with calcium chloride followed by calcium nitrate as a calcium source. The results of present study may be applicable to media preparation during efficient MICCP process.

Stabilising a clay using tyre buffings and lime

Abstract: The objective of this study was to evaluate the influences of both tyre buffings and lime in clay. California Bearing Ratio (CBR) and Unconfined Compression (UC) tests were conducted on the mixtures prepared with tyre buffings and lime. Tyre buffings and lime contents in the mixtures were 0%, 5%, 10%, and 15%, and 0%, 2%, 4%, and 6% by dry weight of the specimens, respectively. The response of the specimens was investigated with the inclusion of tyre buffings only, lime only, and tyre buffings and lime together. Test results revealed that addition of tyre buffings only reduces the CBR value of clay, while addition of lime only increases the CBR value of clay. Addition of a small amount of lime to the clay with tyre buffings increases the CBR values of the specimens, and thereby may cause a substantial decrease in design thickness of a highway pavement. Similar results were also obtained by the UC tests. Consequently, this research suggests to use both tyre buffings and lime as an alternative method to imp...

Effect of calcium–silicon ratio on microstructure and nanostructure of calcium silicate hydrate synthesized by reaction of fumed silica and calcium oxide at room temperature

Abstract: A C–S–H series with calcium–silicon ratio 0.6–3.0 was synthesized by pozzolanic reaction. Phase composition, nanostructural and morphological characteristics were determined using XRD, XRF, SEM and 29Si NMR. Most of the samples were phase-pure, poorly crystalline C–S–H. Significant changes in the nanostructure of the C–S–H samples were observed when the calcium–silicon ratio reached values of 0.8, 1.0 and 1.5. At calcium–silicon ratio 0.8 the basal XRD peak began to develop, crosslinking between layers was seen below this ratio but not above, and there was a substantial decrease in mean silica chain length at this ratio. At calcium–silicon ratio 1.0 there was a pronounced microstructural change from granular to reticular and another substantial decrease in mean chain length (indicated by an abrupt increase in the Q1 peak intensity and decrease in the Q2 peak intensity). At calcium–silicon ratio 1.5 the basal XRD peak began to diminish again, the mean silica chain length decreased further, and isolated tetrahedra (Q0) were observed.

Fast detection of low concentration carbon monoxide using calcium-loaded tin oxide sensors

Abstract: Solid state sensors with noble metal-loaded tin oxide as sensing elements are widely used for the detection of flammable and toxic gases and volatile organic compounds (VOCs). Apart from rendering high cost, incorporation of noble metals often increases the preconditioning time and introduces a drift in baseline properties of the sensors. Herein, we report on the development of stable and economically viable sensor modules for fast and efficient detection of carbon monoxide (CO) in air. The sensing layer comprises sonochemically synthesized calcium-loaded tin oxide (Ca-SnO 2 ) nanocrystals, in which calcium primarily gets segregated at the SnO 2 grain boundaries as calcium oxide (CaO) and thereby restricts the growth of SnO 2 particles. Due to larger ionic radius of Ca 2+ as compared to that of Sn 4+ , a minute quantity of calcium can be doped as well into the SnO 2 lattice. The variation of calcium concentration in SnO 2 has a prominent effect on the sensor performance, where 5 wt% calcium loading shows the highest sensor response. The sensors exhibit a lower detection limit of 1 ppm CO in air. The response time (10–12 s) and recovery time (30–45 s) of our sensors, for different concentrations of CO, are equivalent or less compared to those of commercially available metal-oxide sensors. Additionally, a highly stable baseline with minimal drift even after being operational for over 1.5 years is observed.

Pyrolysis behavior of biomass with different Ca-based additives

Abstract: CaO is an important catalyst in biomass gasification and pyrolysis. However, CaO can stem from many precursors. And, the effect between different precursors has still not been studied. Calcined natural limestone, natural dolomite, calcium oxide, calcium carbonate, calcium acetate, and calcium propionate were used to investigate their pyrolysis reactivity of biomass (peanut shells and pine sawdust) at high temperature (>800 °C). Experiments were conducted using a thermogravimetric apparatus and a fixed-bed pyrolysis system. Pine sawdust displayed higher pyrolysis reactivity than peanut shells. During pyrolysis, Ca-based additives fixed carbon dioxide mainly in the temperature range of 300–700 °C. By addition of Ca-based additives, the concentrations of hydrogen and carbon monoxide were increased and the concentrations of methane and carbon dioxide (over 18 vol%) were decreased. De-carbonation started around 700 °C. The emission of CO2 by de-carbonation promoted the reduction of char by the Boudouard reaction and methane by the dry reforming reaction. The total pyrolysis conversion decreased as PI-Dol > PI-CaA > PI-Lime > PI-Ca > PI-CaP > PI Raw > PI-CaC. The excellent pyrolysis reactivity of biomass in the presence of calcined calcium acetate can be ascribed to its preeminent physical structure. Addition of Ca-based additives increased the activation energy of the main devolatilization region. The activation energy of biomass with calcined natural dolomite, about 110 kJ mol−1, was much lower than that of other Ca-based additives studied at high temperatures. Pyrolysis of the pure biomass sample can be simply hypothesized as a first order reaction, but it varied significantly with the addition of additives.

Synthesis of nitrogen‐containing porous carbon using calcium oxide nanoparticles

Abstract: Nitrogen-containing porous carbon has been produced by acetonitrile vapor deposition at 700 and 800 °C on the products of thermolysis of calcium tartrate doped by iron. The template was removed by dilute HCl acid treatment, and the samples obtained were comparatively studied using transmission electron microscopy, N2 adsorption measurements, thermogravimetric analysis (TGA), X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. It was found that increase in the synthesis temperature results in an extension of the specific surface area from ∼640 to ∼670 m2/g, enlargement in the average pore size from ∼9 to ∼13 nm, and a decrease in the nitrogen content from ∼4.4 to 2.7 at%. TGA revealed that the samples differ by ∼80 °C in the temperature of nitrogen loss, which was desorbed as the NO species mainly. Scheme of nitrogen-doped porous carbon synthesis.

Enhancing the sorption performance of surfactant-assisted CaO nanoparticles

Abstract: Microsized calcium oxide prepared via precipitation and thermal decomposition of calcium carbonates has been widely used in industrial hydrogen production and biomass gasification processes to remove CO2 from the reactors. One of the most interesting perspectives in catalysis is the development of nano-sized, high performance, low cost catalysts. However, due to the high cost of nano-sized calcium oxide (CaO), it is critically important to develop new techniques that overcome this challenge. The main goal of this study was to prepare zwitterionic surfactant (BS-12) modified nano calcium oxide sorbents. Ctenocardia fornicata shell was used as the precursor for nano CaO, as it is cheap and easily available. The effect of BS-12 on the physico-chemical properties and the performance of the nano CaO sorbent for CO2 capture were investigated. Thermo gravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), X-ray fluorescence (XRF), N2 adsorption–desorption (BET) measurements, transmission electron microscopy (TEM), zeta potential and temperature programmed desorption (TPD-CO2) studies were used for the characterization of the prepared nano-sized CaO particles. The results showed that BS-12 modified nano CaO exhibited the best performance for CO2 capture. The particle size and morphology of CaO varied from rod shape (45–33 nm) to cubic (13–23 nm) by changing the operating variables. A suggested mechanism for nanoparticle formation in the presence of BS-12 is also discussed.

Behavior of Clayey Soil Stabilized with Rice Husk Ash & Lime

Abstract: In India the soil mostly present is Clay, in which the construction of sub grade is problematic. In recent times the demands for sub grade materials has increased due to increased constructional activities in the road sector and due to paucity of available nearby lands to allow excavate fill materials for making sub grade. In this situation, a means to overcome this problem is to utilize the different alternative generated waste materials, which cause not only environmental hazards and also the depositional problems. Keeping this in view stabilization of weak soil in situ may be done with suitable admixtures to save the construction cost considerably. The present investigation has therefore been carried out with agricultural waste materials like Rice Husk Ash (RHA) which was mixed with soil to study improvement of weak sub grade in terms of compaction and strength characteristics. Silica produced from rice husk ashes have investigated successfully as a pozzolanic material in soil stabilization. However, rice husk ash cannot be used solely since the materials lack in calcium element. As a result, rice husk ash shall be mixed with other cementitious materials such as lime and cement to have a solid chemical reaction in stabilization process. Lime is calcium oxide or calcium hydroxide. It is the name of the natural mineral (native lime) CaO occurs as a product of coal seam fires and in altered lime stone xenoliths in volcanic ejection. In this study RHA and Lime is mixed in different percentage like (RHA as 5%, 10%, and 15%) and (Lime as 3%, 6%, 9%) and laboratory test CBR is done with a curing period of 4, 7 and 14 days with different percentages of RHA & Lime

Simultaneous decontamination of cross-polluted soils with heavy metals and PCBs using a nano-metallic Ca/CaO dispersion mixture.

Abstract: In the present work, we investigated the use of nano-metallic calcium (Ca) and calcium oxide (CaO) dispersion mixture for the simultaneous remediation of contaminated soils with both heavy metals (As, Cd, Cr, and Pb) and polychlorinated biphenyls (PCBs). Regardless of soil moisture content, nano-metallic Ca/CaO dispersion mixture achieved about 95–99 % of heavy metal immobilization by a simple grinding process. During the same treatment, reasonable PCB hydrodechlorination efficiencies were obtained (up to 97 %), though higher hydrodechlorination efficiency by preliminary drying of soil was observed.

Effect of calcination temperatures of CaO/Nb2O5 mixed oxides catalysts on biodiesel production.

Abstract: Calcination temperature greatly influences the total basicity and surface area of catalysts. Investigations were conducted on calcium and niobium (CaO-Nb2O5) mixed oxides catalysts prepared via conventional solid state method (oxides were mixed and ground in agate mortar) and calcined at different temperatures ranging from 300-800oC for 5 h. The catalysts were then characterized by using X-ray diffraction (XRD), CO2 temperature-programmed desorption (TPD-CO2), Brunauer-Emmett-Teller (BET) surface area analyzer and scanning electron microscope (SEM). The formation of Ca(OH)2 and CaCO3 at lower calcination temperatures ( 600oC), due to sintering of the fine crystals, which promotes cluster agglomeration. Thus, the optimum calcination temperature for CaO/Nb2O5 mixed oxides was 600oC, which produced the largest surface area (7 m2/g) and total basicity (1301 μmol/g). The biodiesel was produced via transesterification of palm oil, methanol and the catalysts calcined at various temperatures. CaO/Nb2O5 mixed oxide calcined at 600oC showed the highest biodiesel conversion (98%) with methanol/oil molar ratio of 12, 3 wt.% of catalyst, a reaction temperature of 65oC and reaction time of 2 h.

Modifier for acidic soil

Abstract: The invention relates to a modifier for acidic soil. The modifier comprises the following components in percentage by weight: 10-30% of yellow phosphorus slag, 5-20% of acidic soil modifier, 5-10% of artificially synthesized high-molecular compound, and the balance of mineral substances, wherein the yellow phosphorus slag mainly comprises CaSiO3; the acidic soil modifier refers to lime substances such as calcium carbonate, calcium oxide, lime nitrogen and the like; the artificially synthesized high-molecular compound refers to one or a mixture of more of polyacrylic acid, vinyl acetate maleic acid and polyvinyl alcohol type high-molecular compounds; mineral substances refer to peat, lignite, decomposed coal, vermiculite, bentonite, zeolite, perlite, sepiolite and the like. The modifier can effectively improve the yield reduction phenomenon of crops caused by an acidic hardened land, and has the advantages of being low in cost, fast, and simple to operate and the like.

The mechanism of vapor phase hydration of calcium oxide: implications for CO2 capture.

Abstract: Lime-based sorbents are used for fuel- and flue-gas capture, thereby representing an economic and effective way to reduce CO2 emissions. Their use involves cyclic carbonation/calcination which results in a significant conversion reduction with increasing number of cycles. To reactivate spent CaO, vapor phase hydration is typically performed. However, little is known about the ultimate mechanism of such a hydration process. Here, we show that the vapor phase hydration of CaO formed after calcination of calcite (CaCO3) single crystals is a pseudomorphic, topotactic process, which progresses via an intermediate disordered phase prior to the final formation of oriented Ca(OH)2 nanocrystals. The strong structural control during this solid-state phase transition implies that the microstructural features of the CaO parent phase predetermine the final structural and physicochemical (reactivity and attrition) features of the product hydroxide. The higher molar volume of the product can create an impervious shell a...

Hardening accelerator composition

Abstract: The invention relates to a process for the preparation of a hardening accelerator composition by reacting a calcium source selected from calcium hydroxide, calcium oxide with a water-soluble silicate compound in the presence of at least one water-soluble polymeric dispersing agent and the hardening accelerator composition obtainable by said process. The composition has a low content of anions and of alkali cations and is therefore broadly applicable in building material mixtures.

Synthesis and mechanism of tetracalcium phosphate from nanocrystalline precursor

Abstract: Tetracalcium phosphate (TTCP, Ca4(PO4)2O) was prepared by the calcination of coprecipitated mixture of nanoscale hydroxyapatite (HA, Ca10(PO4)6(OH)2) and calcium carbonate crystal (CaCO3), followed by cooling in the air or furnace. The effect of calcination temperature on crystal structure and phase composition of the coprecipitation mixture was characterized by transmission electron microscope (TEM), thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and Raman spectroscopy (RS). The obtained results indicated that the synthesized mixture consisted of nanoscale HA and CaCO3 with uniform distribution throughout the composite. TTCP was observed in the air quenching samples when the calcination temperature was above 1185°C. With the increase of the calcination temperature, the amount of the intermediate products in the air quenching samples decreased and cannot be detected when calcination temperature reached 1450°C. Unexpectedly, the mixture of HA and calcium oxide was observed in the furnace cooling samples. Clearly, the calcination temperature and cooling methods are critical for the synthesis of high-purity TTCP. The results indicate that the nanosize of precursors can decrease the calcination temperature, and TTCP can be calcinated by low temperature.