Modeling calcium dissolution from oil shale ash: Part 1. Ca dissolution during ash washing in a batch reactor

Batch dissolution experiments were carried out to investigate Ca leachability from oil shale ashes formed in boilers operating with different combustion technologies. The main characteristics of Ca dissolution equilibrium and dynamics, including Ca internal mass transfer through effective diffusion coefficients inside the ash particle were evaluated. Based on the collected data, models allowing simulation of the Ca dissolution process from oil shale ashes during ash washing in a batch reactor were developed. The models are a set of differential equations that describe the changes in Ca content in the solid and liquid phase of the ash-water suspension.     

NMR studies of equilibriums in electrolytes: Ionic pairing in glymes

In this article, the formation constants of ionic pairs in salt-low molecular weight analogs of PEO (glyme, diglyme, triglyme) systems are estimated using NMR spectroscopy. The results from ⁷Li, ¹¹B and ¹⁹F NMR titration are compared and the role of the nuclei studied is discussed. It is shown that even in the solvents of very similar coordination (in terms of the donor and acceptor number values) and dielectric properties, the ionic pair formation constant depends on solvent used. The role of the solvent is discussed in terms of effects related to ion agglomerate formation, non-covalent interactions between ions and liquid matrix as well as the number of interacting centers present in the molecules of the solvent. The discrepancies between the results obtained using various nuclei NMR as well as discrepancies between ion pair formation constant calculated for different experimental regimes are also analyzed.     

CO2 supercritical fluid extraction of Jordanian oil shale utilizing different co-solvents

In this study, extracting shale oil from Jordanian oil shale using supercritical fluid extraction has been investigated. Experimental data indicates that by using supercritical extraction with carbon dioxide, using co-solvents can be viable. A relatively high yield can be obtained at relatively moderate pressure. At the highest temperature and pressure of 450 °C and 3200 psi, respectively, and with hexane as a co-solvent, the highest yield obtained was 100 kg/ton of oil shale, which was at the highest temperature and pressure of 450 °C and 3200 psi, respectively, and with hexane as a co-solvent. Increasing both the operating pressure and temperature increases the oil yield. In the supercritical state, carbon dioxide along with other co-solvents, such as hexane and acetone, interact with the kerogen leading to the dissolution of fragments due to an increase in solubility and mass transfer.Increasing the particle size of oil shale for extraction decreases the oil yield. Most of the extracted oil obtained is saturated hydrocarbons, olefinic and a portion of aromatic hydrocarbons. As the extraction temperature increases, the production of low-molecular weight compounds increases.     

Cement composition and sulfate attack: Part I

Four cements were used to address the effect of tricalcium silicate content of cement on external sulfate attack in sodium sulfate solution. The selected cements had similar fineness and Bogue-calculated tricalcium aluminate content but variable tricalcium silicates. Durability was assessed using linear expansion and compressive strength. Phases associated with deterioration were examined using scanning electron microscopy and X-ray diffraction. Mineralogical phase content of the as-received cements was studied by X-ray diffraction using two methods: internal standard and Rietveld analysis.The results indicate that phase content of cements determined by X-ray mineralogical analysis correlates better with the mortar performance in sulfate environment than Bogue content. Additionally, it was found that in cements containing triclacium aluminate only in the cubic form, the observed deterioration is affected by tricalcium silicate content. Morphological similarities between hydration products of high tricalcium aluminate and high tricalcium silicate cements exposed to sodium sulfate environment were also observed.     

Solubility and diffusivity of CO2 in poly(l-lactide)-hydroxyapatite and poly(d,l-lactide-co-glycolide)-hydroxyapatite composite biomaterials

Solubility and diffusivity of supercritical CO₂ in poly(l-lactide)-hydroxyapatite (PLLA-HA) and poly(d,l-lactide-co-glycolide)-hydroxyapatite (PLGA-HA) composite materials were measured using a magnetic suspension balance at a temperature of 313 K and a pressures range of 10-30 MPa. The effect of the HA concentration on the solubility and diffusivity was investigated by varying filler content in the range of 0-50 wt%. For the PLLA-HA composites the solubility decreases with the increase of filler concentration. Diffusivity of the gas in the substrate is also lower as the HA content increases. In the case of PLGA-HA composites, small filler content favors the solubility and diffusivity of CO₂ due to incomplete wetting of the solid particles by the polymer. As the amount of HA increases solubility decreases. The results suggest that dense CO₂ could be used as a ‘green’ processing agent for composite biomaterials when organic solvents or high temperatures should be avoided.     

Supercritical CO2 extraction of Plumula nelumbinis oil: Experiments and modeling

Supercritical CO₂ extraction of Plumula nelumbinis oil was investigated at temperatures of 308–338 K and pressures of 15–45 MPa. The yield of the extracted oil was 0.128 g/g material at optimal conditions, in which gamma-sitosterol, unsaturated fatty acids and gamma-tocopherol had higher relative concentrations as determined by GC–MS. The broken and intact cell (BIC) model, with reduced adjustable parameters, was utilized to simulate the SFE process. The values of average absolute relative deviation (AARD) were in the range 2.34–10.9%, indicating that the improved method had a similar effect to the BIC model when three parameters were adjusted. The parameters obtained during the modeling had clear physical meanings and were used to gain an in-depth understanding of the SFE process theoretically.     

Equilibrium,kinetic, and thermodynamic studies of the Ca2+ and Mg2+ ions removal from water by Duolite C206A

The uptake of Ca²⁺ and Mg²⁺ ions from synthetic aqueous solutions by Duolite C206A was studied in static-batch mode. Results revealed that there is no need of pH adjustment. The equilibrium is reached after 30 min with 0.5 g of resin at 25°C. Equilibrium data were well fitted by Langmuir isotherm model. Maximum uptake capacities Q_max were about 23.04 mg Mg²⁺/g and 64.10 mg Ca²⁺/g. The pseudo-second-order model was found as the best to explain the ions exchange kinetics effectively. The uptake of Ca²⁺ and Mg²⁺ ions by Duolite C206A is exothermic and the process is spontaneous.     

Luminescent properties of a novel afterglow phosphor Sr3Al2O5Cl2:Eu,Ce

A series of Eu²⁺ and Ce³⁺ doped/co-doped Sr₃Al₂O₅Cl₂ afterglow phosphors that presented various bright colors were successfully synthesized via high temperature solid state reaction. The structure and luminescence properties of the obtained samples were characterized by X-ray powder diffraction (XRD), photoluminescence (PL) spectra and decay curves as well as the thermoluminescence (TL) glow curves. The XRD results showed that all the phase could be indexed to the orthorhombic structure with the space group P2₁2₁2₁. After being exposed to a 254 nm or 365 nm mercury lamp, blue/yellow-orange afterglow emissions with broad bands peaking around 620 nm/435 nm, which were ascribed to the characteristic 4f⁶5d–4f⁷/5d¹–4f¹ transitions of Eu²⁺/Ce³⁺, could be observed in phosphors of Sr₃Al₂O₅Cl₂:Eu²⁺/Sr₃Al₂O₅Cl₂:Ce³⁺, respectively. Because of the overlap spectral range between the Sr₃Al₂O₅Cl₂:Eu²⁺ and Sr₃Al₂O₅Cl₂:Ce³⁺ phosphors, the energy transfer (ET) from Ce³⁺ to Eu²⁺ occurred. The related ET process was discussed in detail. Moreover, the incorporation of Ce³⁺ could significantly prolong the afterglow duration of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor, which was due to the increase of trap concentration. Consequently, 6 h of the afterglow duration could be observed in Sr₃Al₂O₅Cl₂:1.0%Eu²⁺, 0.5%Ce³⁺ sample, exhibiting much longer than that of Sr₃Al₂O₅Cl₂: 1.0%Eu²⁺ (3 h). From the afterglow decay curves and the fitting results, the optimal concentration of Ce³⁺ for the enhanced afterglow property was experimentally determined to be 0.5%.     

A comparative study of ordinary and mineralised Portland cement clinker from two different production units Part II: Characteristics of the calcium silicates

Portland cement clinkers from two production units were investigated in order to determine the effects of mineralisation on alite and belite; Plant 1: ordinary clinker (P1) and clinker mineralised with CaF₂₊CaSO₄ (P1m); Plant 2: ordinary clinker (P2) and two clinkers mineralised with CaF₂₊CaSO₄ (P2m, P2m′).The polymorphism of alite was studied using synchrotron X-ray powder diffraction (XRD), wavelength 1.5227 Å, and electron diffraction (ED) in a transmission electron microscope. The substitutions of minor elements in alite and belite were determined using electron microprobe analysis. Clinkers P1 and P1m both contained apparent rhombohedral alite (XRD) with an incommensurately modulated structure (ED), while clinkers P2, P2m, and P2m′ all contained monoclinic alite (XRD). The addition of mineralisers in the process caused increased content of fluoride in alite and increased substitution of Si(4+) by Al(3+) and S(6+) in both calcium silicates. The latter effect was most pronounced in clinker P1m due to its high molar SO₃ to alkali oxide ratio (R=2.18).The improved hydraulic activity of P1m compared to P1 was caused by substitutions rather than a change in symmetry. The decreased hydraulic activity of P2m and P2m′ compared to P2 was explained by the high levels of fluorine, which had a retarding effect on the hydration.     

The effect of foreign ions on the reactivity of the CaO-SiO2-Al2O3-Fe2O3 system: Part II: Cations

The subject of this paper is the effect of foreign cations on the reactivity of the CaO-SiO₂-Al₂O₃-Fe₂O₃ system. One reference mixture and eighteen modified mixtures, prepared by mixing the reference sample with 1% w/w of chemical grade MnO₂, CuO, V₂O₅, PbO, CdO, ZrO₂, Li₂O, MoO₃, Co₂O₃, NiO, WO₃, ZnO, Nb₂O₅, CrO₃, Ta₂O₅, TiO₂, BaO₂ and H₃BO₃ were studied. The effect on the reactivity is evaluated on the basis of the free lime content in samples sintered at 1200 and 1450 °C. At 1200 °C, the reactivity of the mixture is greatly increased in the presence of Cu and Li oxides. Based on their effect at 1450 °C, the added elements can be divided into three groups. W, Ta, Cu, Ti and Mo show the most positive effect, decreasing the free CaO (fCaO) content by 30-60%, compared with the pure sample. Cr and B cause an increase of fCaO content, while the rest of the elements exhibit a marginal positive effect. According to their volatility at 1450 °C, the added compounds can be subdivided into three groups of low (Ti⁴⁺, Cu²⁺, Mo⁶⁺, W⁺⁶, V⁵⁺, Zn²⁺, Zr⁴⁺), moderate (Cr⁶⁺, Co³⁺, Ni²⁺, Mn⁴⁺) and high volatility (Cd²⁺, Pb²⁺). All burned samples, analyzed by means of X-ray diffraction, have a final mineralogical composition, which corresponds to the structure of a typical clinker.     

Signaling Pathways Used by the Specialized Pro-Resolving Mediator Maresin 2 Regulate Goblet Cell Function: Comparison with Maresin 1

Specialized pro-resolving mediators (SPMs), including Maresins (MaR)-1 and 2, contribute to tear film homeostasis and resolve conjunctival inflammation. We investigated MaR2′s signaling pathways in goblet cells (GC) from rat conjunctiva. Agonist-induced [Ca²⁺]_i and high-molecular weight glycoconjugate secretion were measured. MaR2 increased [Ca²⁺]_i and stimulated secretion. MaR2 and MaR1 stimulate conjunctival goblet cell function, especially secretion, by activating different but overlapping GPCR and signaling pathways, and furthermore counter-regulate histamine stimulated increase in [Ca²⁺]_i. Thus, MaR2 and MaR1 play a role in maintaining the ocular surface and tear film homeostasis in health and disease. As MaR2 and MaR1 modulate conjunctival goblet cell function, they each may have potential as novel, but differing, options for the treatment of ocular surface inflammatory diseases including allergic conjunctivitis and dry eye disease. We conclude that in conjunctival GC MaR2 and MaR1, both increase the [Ca²⁺]_i and stimulate secretion to maintain homeostasis by using one set of different, but overlapping, signaling pathways to increase [Ca²⁺]_i and another set to stimulate secretion. MaR2 also resolves ocular allergy.     

Enhanced photoluminescence property of Dy co-doped BaAl2O4:Eu green phosphors

Eu²⁺-doped BaAl₂O₄ green phosphors were prepared by a conventional solid-state reaction and the effects of Dy³⁺ co-doping on the photoluminescence property were investigated. The phosphors were characterized by X-ray powder diffraction (XRD), fluorescence spectroscopy, field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD showed that all prepared samples exhibited a hexagonal BaAl₂O₄ phase. Fluorescence spectroscopy showed that the photoluminescence efficiency increased with increasing Eu²⁺ concentration until 3 mol% then decreased at higher concentrations due to concentration quenching effect. Moreover, Dy³⁺ co-doping increased the photoluminescence efficiency of the Eu²⁺-doped BaAl₂O₄ phosphor.     

The effect of surface chemistry and nanoclay loading on the microcellular structure of porous poly(d,l lactic acid) nanocomposites

Three series of polymer nanocomposites, based on poly(d,l lactic acid) (PDLLA) and organically modified montmorillonite, were prepared by the melt and the solution intercalation technique. The first series was prepared by extrusion using different clay loadings. The second series of nanohybrids was obtained using montmorillonite modified with different types of alkylammonium surfactants in terms of carbon-chain lengths (i.e., 4, 8, 12, 16 and 18). In the third series of nanocomposites, the organic cation concentration of the surfactant was varying. Microcellular porous materials were, afterwards, fabricated from these three series of nanocomposites. The porous structures of pure and nanocomposite PDLLA were prepared by isothermal pressure quench using supercritical CO₂ as foaming agent. The morphology of the produced porous materials was investigated by scanning electron microscopy (SEM). Image processing of the samples revealed that the final cellular structure is strongly related to clay loading and, both, the type and the organic cation concentration of the alkylammonium used for the modification of the clay. The results suggest that the size of the pores decreases and the cell density and bulk foam density increase with the increase of clay loading or the surfactant's carbon chain length or the cation concentration in clay. Clay dispersion seems to be enhanced by the supercritical treatment upon foaming.     

Fluorescence improvement of Ba1.3Ca0.7SiO4:Eu,Mn phosphors via Dy addition and their color-tunable properties

A series of novel single-phase white phosphors Ba_1.3Ca_0.69−x−ySiO₄:0.01Eu²⁺,xMn²⁺, yDy³⁺ were synthesized by the solid-state method. The excitation spectra of these phosphors exhibit a broad band in the range of 260–410 nm, which can meet the application requirements for near-UV LED chips (excited at 350–410 nm). The emission spectra consist of two broad bands positioned around 455 nm and 596 nm, which are assigned to 5d→4f transition of Eu²⁺, and ⁴T₁→⁶A₁ transition of Mn²⁺, respectively. The luminescence intensity of phosphors enhances obviously by doping Dy³⁺ ions, and the intensity of two bands reaches an optimum when Dy³⁺ amounts to 2 mol%. In addition, thermoluminescence investigation of phosphor was conducted, getting two shallow trap defects with activation energy of 0.43 eV and 0.45 eV, which demonstrates the energy transfer mechanism of Dy–Eu through the process of hole and electron traps. By precisely tuning the Mn²⁺ content, an optimized white light with color rendering index (CRI) of R_a=84.3%, correlated color temperature (CCT) of T_c=8416 K and CIE chromaticity coordinates of (0.2941, 0.2937) is generated. The phosphor could be a potential white phosphors for near-UV light emitting diodes.     

Non-destructive characterisation of alumina/aluminium titanate composites using a micromechanical model and ultrasonic determinations: Part II. Evaluation of microcracking

A method for non-destructive detection of microcracks in ceramic composites is described. The method involves the combination of ultrasound characterisation with the application of a three-phase micromechanical model, which considers cracks and pores as void constituents. Four alumina-aluminium titanate materials with different levels of microcracking, from no cracks (monophase alumina) to severely cracked (alumina + 40 vol.% of aluminium titanate) including an alumina + 10 vol.% aluminium titanate material with incipient microcracking have been developed to test the validity of the method. Specimens have been fabricated by colloidal processing and the longitudinal and transverse ultrasound velocities have been determined by the ultrasonic pulse-echo and transmission ultrasound-immersion techniques, employing a digital signal processing. It has been demonstrated that it is possible to differentiate between pores and microcracks, both modelled as void constituents, in terms of the aspect ratio.     

Autogenous deformations of cement pastes: Part II. W/C effects, micro-macro correlations, and threshold values

A broad experimental study has been performed, from the end of mixing up to 2 years, on a set of plain cement pastes prepared with the same type I ordinary portland cement (OPC) and various water-to-cement ratios (W/C), and cured at various constant temperatures. Several parameters have been measured on the hydrating materials, such as chemical shrinkage, volumetric and one-dimensional autogenous deformations, degree of hydration of the cement, Ca(OH)₂ content and Vicat setting times. Drying shrinkage has also been measured on the mature materials. In this part II of the paper, the effects of W/C within the range 0.25-0.60 have in particular been analysed in relation to the microstructural characteristics of the materials. This micro-macro analysis has highlighted a W/C threshold value (located around 0.40) both at the macro-level (on autogenous, but also on drying deformations and durability-related properties) and at the micro-level (characteristics of the hydration products, MIP porosity and pore size distribution, etc.).In addition, volumetric and one-dimensional autogenous shrinkage deformations have been compared in the case of W/C=0.25 and T=20 °C. Finally, a critical twofold (chemical and structural) effect of calcium hydroxide has been found. When significant structural effects, generated by the formation and the growth of large-size Ca(OH)₂ crystals, take place, swelling can become prominent, as observed for one-dimensional autogenous deformations in the case of medium and high W/C, and deviations are recorded on linear relationships.     

Clay minerals in nonaqueous extraction of bitumen from Alberta oil sands: Part 1. Nonaqueous extraction procedure

A non-aqueous bitumen extraction process was studied where only toluene and heptane, with no water additions, were used to extract bitumen from two Alberta oil sands ore samples. One sample had a high bitumen (13.5 wt.%) and low fines (5.3 wt.% < 45 μm) contents, while the other sample had an intermediate bitumen (10.5 wt.%) and high fines (23.3 wt.%) contents. Bitumen recovery and product quality were measured under different process conditions such as the ratio of toluene to heptane and settling time. The Dean Stark procedure was used to determine the solids, bitumen and water contents of the extraction products. In addition, the water content was determined by the Karl Fischer titration method. High bitumen recovery was obtained for both oil sands ore samples although the high fines ore sample was more sensitive to the extraction conditions, especially the toluene to heptane ratio. A product with high purity, containing more than 99.5 wt.% bitumen on a solvent-free basis, was produced at room temperature under the optimum extraction conditions tested. The optimum settling time to achieve a pure product was less than 10 min, based on solids and water contents in the supernatant.     

Phase separation induced by hydration of the mixed Ca/Sr aluminates Ca3−xSrxAl2O6: A crystallographic study

The compounds formed by the hydration of single-phase samples of the mixed, solid solution, Ca/Sr aluminates, Ca_3−xSr_xAl₂O₆, 3≤x≤0 have been studied using high-resolution synchrotron powder diffraction. Hydration of these mixed metal aluminates generally resulted in the formation of at least two hydrogarnet phases, one Ca-rich and the other Sr-rich. The structures of these hydrogarnets have been refined from neutron or synchrotron powder X-ray diffraction (XRD) data. A simple solubility model to explain the phase separation is presented.     

Room temperature transesterification of soybean oil to biodiesel catalyzed by rod-like CaxSiOx + 2 solid base

Rod-like Ca_xSiO_x + 2 catalysts were synthesized by using one-pot hydrothermal method. Catalysts calcined at 550 °C were used in the transesterification reaction of soybean oil with methanol. Under methanol reflux condition, FAME yields of 82% and 95% were achieved on Ca₄SiO₆ in a reaction time of 1 and 2 h, separately. Also, the FAME yields on different Ca_xSiO_x + 2 catalysts were correlated with their basic properties. Besides, a FAME yield of ca. 80% can be achieved under room temperature over Ca₄SiO₆ catalyst.     

Polymorphism of tricalcium silicate, the major compound of Portland cement clinker: 2. Modelling alite for Rietveld analysis, an industrial challenge

A comprehensive quantification of the various phases of clinkers by X-ray diffraction with a Rietveld-like analysis is an important industrial challenge. Various available structural models are used for the most frequent M1 and M3 polymorphs of alite usually found in industrial clinkers, referred to as M1- or M3-based clinkers. In this paper, the effect of C₃S structural model is investigated. Four models are tested and compared using either synthetic M1 and M3 alites or M1- and M3-based clinkers. The comparison validates the available models for M1 and M3 alites and an average model, given here, derived from our recently proposed M1 structure as a catch-all model when the nature of the clinker is unknown. The latter model is meant to be used for industrial on-line quantification.