Chemical and physical analysis of sandstone and relationship with weathering damage of Madâin Sâlih monuments

The present work aims to study the effect of weathering - produced sands across the area in the weathering damage of sandstones in Madâin Sâlih (Saudi Arabia). Our approach is to investigate some chemical and physical properties of sand samples from the study area. The weathered point in this arid area is Qsar al Bint or Place of the daughter monument in which five different samples have been collected. The analysis of scanning electron microscope images reveals that sand surfaces have different roughness and some surface areas were broken except for the rock samples. According to energy dispersive spectroscopy analysis, the rock samples reveal the presence of Ca, Mg, Na, K, Al and Fe at the surface. Mineralogy study using X-ray diffraction revealed that sandstones are clay-cemented sandstone. Fourier Transform Infrared spectroscopy analysis confirmed that the inorganic binding agent of silica grains is essentially Kaolonite (Al2Si2O5(OH)4)

Cristallisation de ZnSO4,7H2O sous ultrasons (Étude expérimentale et étude microscopique)

La cristallisation assistée par ultrasons permet de diminuer le temps d'induction et la largeur de la zone métastable, de modifier la distribution de tailles, de modifier le faciès des cristaux et d'augmenter le nombre des cristaux formés. L'origine microscopique de cet effet reste à ce jour non élucidée. Les ultrasons de puissance engendrent dans un liquide la naissance et l'oscillation très violente de milliards de petites bulles de gaz, phénomène appelé cavitation. Le cycle d'une de ces bulles sur une période acoustique consiste en une phase explosive suivie d'une implosion violente. A la fin de l'implosion, la pression peut atteindre 1 GPa. Plusieurs hypothèses sur les mécanismes mis en jeu sont proposées dans la littérature : refroidissement de la solution et augmentation de la pression au voisinage de l'interface, évaporation du solvant dans la bulle, et ségrégation des molécules ou des ions du soluté au voisinage de la bulle lors de la phase implosive. Afin d'examiner l'influence de la pression, des expériences de cristallisation du sulfate de zinc heptahydraté ont été menées (mesure de temps d'induction). Ce sel présente une solubilité indépendante de la pression entre 0 et 10 000 bars. Nos expériences ont montré que le temps d'induction est fortement diminué en présence d'ultrasons. Ce résultat nous permet d'affirmer que la pression au voisinage de la bulle n'entre pas en jeu dans le mécanisme de la nucléation primaire du ZnSO4,7H2O en présence d'ultrasons. Après l'étude de l'effet de la sursaturation, nous avons essayé d'exploré l'effet de la puissance ultrasonore, du gaz dissous et de la hauteur du liquide dans la cuve sur le temps d'induction. Il a été constaté que les ultrasons permettent de diminuer le temps d'induction. Il a été observé que la courbe du temps d'induction en fonction de la hauteur de la solution présente un minimum. Un autre volet de cette thèse réservé à la modélisation et la simulation. Dans un premier temps, la concentration en clusters ou agrégats moléculaires au voisinage de la bulle été calculée dans le cas du ZnSO4,7H2O grâce à la théorie de la ségrégation en fonction de la pression acoustique. La simulation montre qu'il y a une sur-concentration des clusters (jusqu'à 25 fois supérieure à la concentration stationnaire) augmentant ainsi la probabilité de contact des clusters, durant un temps très court, pouvant ainsi modifier le processus global de nucléation. Dans un deuxième temps, la modélisation/simulation de l'acoustique par COMSOL est réalisée en vue de déterminer les résonances de notre système (liquide + parois de la cuve). Les résonances observées sont cohérentes avec les mesures de temps d'induction.Power ultrasound is known to enhance crystals nucleation, and nucleation times can be reduced by oneup to three orders of magnitude for several organic or inorganic crystals. The precise physics involved in this phenomenon still remains unclear, and various mechanisms involving the action of inertial cavitation bubbles have been proposed. In this paper, two of these mechanisms, pressure and ségrégation effects, are examined. The first one concerns the variations of supersaturation induced by the high pressures appearing in the neighbourhood of a collapsing bubble, and the second one results from the modification of clusters distribution in the vicinity of bubble. Crystallisation experiments were performed on zinc sulphate heptahydrate ZnSO4. 7H2O, which has been chosen for its pressure-independent solubility, so that pressure variations have no effect on supersaturation. As observed in past studies on other species, induction times were found lower under insonification than under silent conditions at low supersaturations, which casts some doubts on a pure pressure effect. The interfacial energy between the solid and the solution was estimated from induction times obtained in silent conditions, and, using classical nucléation theory, the steady-state distribution of the clusters was calculated. Segregation theory was then applied to calculate the over-concentrations of n-sized clusters at the end of the collapse of a 4 lmbubble driven at 20 kHz by different acoustic pressures. The over-concentration of clusters close to the critical size near a collapsing bubble was found to reach more than one order of magnitude, which may favour the direct attachment process between such clusters, and enhance the global nucleation kinetics. The effects of acoustic cavitation on crystallization of ZnSO4. 7H2O was observed in a sono-reactor build-up from a large emitting area transducer located at the bottom of the vessel. The experimental results have shown that the dissipated acoustic power passes through a maximum at about 15+-1 cm, and that the induction-time passes through a minimum for the same liquid-level. The dissipated-power and the induction-time are found to be well correlated as the liquid height was varied. The acoustics of the sono-reactor was studied with linear acoustics, accounting for the wall vibrations by using the COMSOL software. Theoretical dissipated acoustic powers were compared to the experimental ones.TOULOUSE-INP (315552154) / SudocSudocFranceF

Role des chlorocomplexes et des ecarts a l'idealite sur des proprietes d'equilibre de solution de Pb(II) en milieu chlorure

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Effet microscopique des ultrasons sur la cristallisation de ZnSO4,7H2O

National audienceLa cristallisation assistée par ultrasons permet de diminuer le temps d'induction et la largeur de zone métastable, de modifier la distribution de tailles, de modifier le faciès des cristaux et d'augmenter le nombre des cristaux formés. L'origine microscopique de cet effet reste à ce jour non élucidée. En effet, les ultrasons de puissance engendrent dans un liquide la naissance et l'oscillation très violente de milliards de petites bulles de gaz, phénomène appelé cavitation. Le cycle d'une de ces bulles sur une période acoustique consiste en une phase explosive suivie d'une implosion violente. A la fin de l'implosion, la pression peut atteindre 1000 atm. Plusieurs hypothèses sur les mécanismes mis en jeu peuvent êtres émises et sont proposées dans la littérature : refroidissement de la solution et augmentation de pression au voisinage de l'interface (Virone et al., 2006, Ruecroft et al., 2005), évaporation du solvant dans la bulle et ségrégation des molécules ou des ions du soluté au voisinage de la bulle, lors de la phase implosive (Louisnard et al., 2007). Les trois premiers phénomènes peuvent jouer sur la sursaturation locale, en modifiant soit la concentration d'équilibre sous l'effet de la température et/ou de la pression, soit la concentration du soluté C pour l'évaporation, influant ainsi la vitesse de nucléation. Quant à la ségrégation moléculaire, elle pourrait accélérer le mécanisme d'agrégation des ions ou des molécules du soluté bouleversant ainsi le mécanisme de nucléation primaire et donc la vitesse de nucléation. Afin d'examiner l'influence de la pression, des expériences de cristallisation du sulfate de zinc hepta-hydraté ont été menées (mesure de temps d'induction). Ce sel présente une solubilité indépendante de la pression entre 0 et 10 000 bars (Karapétiantz, 1978). Nos expériences ont montré que le temps d'induction est fortement diminué en présence d'ultrasons. Ce résultat nous permet d'affirmer que la pression au voisinage de la bulle n'entre pas en jeu dans le mécanisme de la nucléation primaire en présence d'ultrasons

Encapsulation of bioactive compounds in nanoemulsion-based delivery systems

Encapsulation into nanoemulsion-based delivery systems of bioactive compounds characterized by low solubility in aqueous phase, represents an effective approach to improve the dispersion of the bioactives into food products, to protect them against degradation or interaction with other ingredients, to reduce the impact on organoleptic properties of the food and to improve their bioavailability. The aim of the present work is the fabrication of nanoemulsions, based on natural food ingredients, to be used as delivery systems of two different bioactive compounds, resveratrol and curcumin, with the ultimate goal of improving the antioxidant and/or antimicrobial activities of the encapsulated compounds. A preliminary screening study of the optimal emulsion ingredients was carried out through the construction of a pseudo-ternary phase diagram of kinetic stability. The formation of very fine emulsions in the nanometric range (< 200 nm) was achieved by high pressure homogenization treatment, choosing those formulations containing small amounts of emulsifier, in order to minimize the impact on the organoleptic properties. Resveratrol (0.01% wt) was encapsulated in peanuts oil-based nanoemulsions, using different emulsifiers, such as soy lecithin and sugar esters. Curcumin was encapsulated in stable solid fat nanoemulsions, using stearic acid as lipid phase, up to 0.1% wt concentration. The nanoemulsions were characterized in terms of physical stability of the mean droplet size (dynamic light scattering) and chemical stability of the encapsulated bioactive compounds (HPLC and UV-Vis spectra analysis) upon accelerated ageing conditions. The effectiveness of the delivery systems was evaluated in terms of antioxidant activity of the encapsulated compounds

Adsorption thermodynamics of cationic dyes (methylene blue and crystal violet) to a natural clay mineral from aqueous solution between 293.15 and 323.15 K

Wastewater from dyestuff production is one of the main water pollutants. Several methods have been applied for the remediation of contaminated water. Currently, adsorption using a cheap, abundant, and environmental-friendly adsorbent such as natural clay is the simplest and most useful method. This study aimed to determine the enthalpies of adsorption of the organic cationic dyes, methylene blue (MB) and crystal violet (CV), from polluted water onto a natural clay mineral. Early on, we performed mineralogical and textural analyses of a clay sample using various techniques, namely X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller analysis, Fourier-transform infrared spectroscopy, and differential scanning calorimetry, before and after adsorption. The experimental results showed that this adsorbent is a mesoporous and non-swelling clay with illite and kaolinite as the major components. The effects of various parameters such as contact time, pH, and temperature were examined. The experimental data were analyzed using the linear forms of the Langmuir and Freundlich isotherm models and showed a good fit with the Langmuir equation for MB adsorption. Thermodynamic parameters such as the changes in Gibbs free energy, enthalpy, and entropy were determined from batch experiments. Results revealed that the adsorption of MB onto illitic clay was endothermic, while that of CV was an exothermic and spontaneous process. Keywords: Adsorption, Cationic dyes, Illitic clay, Temperature effect, Enthalpies of adsorptio

An organified mixture of illite-kaolinite for the removal of Congo red from wastewater

Congo red (CR), an anionic dye, is very harmful to the environment and should be removed via an easy and inexpensive technique. The adsorption of CR from an aqueous solution onto a mixture of illite-kaolinite clay minerals and surfactant-modified illite-kaolinite was investigated at different temperatures. The characterization of the raw clay mixture and the organified sample was confirmed with X-ray diffraction, FTIR spectroscopy, nitrogen gas adsorption at 77 K and transmission electronic microscopy techniques. Factors influencing the adsorption such as pH, adsorbent dosage and temperature were tested. The thermodynamic parameters ΔG°, ΔH° and ΔS° have been calculated, and it was found that the adsorption is exothermic in nature. The isotherm data were fitted by the linear form of the Langmuir and Freundlich models and showed a good fit with the Langmuir approach. The maximum adsorption capacity of surfactant-modified clay (83 mg/g) was found to be around 14 times higher than that of unmodified clay. Kinetic studies of CR on illite-kaolinite and organified illite-kaolinite were evaluated by pseudo-first-order and pseudo-second-order models

Adsorption thermodynamics of cationic dyes (methylene blue and crystal violet) to a natural clay mineral from aqueous solution between 293.15 and 323.15 K

Wastewater from dyestuff production is one of the main water pollutants. Several methods have been applied for the remediation of contaminated water. Currently, adsorption using a cheap, abundant, and environmental-friendly adsorbent such as natural clay is the simplest and most useful method. This study aimed to determine the enthalpies of adsorption of the organic cationic dyes, methylene blue (MB) and crystal violet (CV), from polluted water onto a natural clay mineral. Early on, we performed mineralogical and textural analyses of a clay sample using various techniques, namely X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller analysis, Fourier-transform infrared spectroscopy, and differential scanning calorimetry, before and after adsorption. The experimental results showed that this adsorbent is a mesoporous and non-swelling clay with illite and kaolinite as the major components. The effects of various parameters such as contact time, pH, and temperature were examined. The experimental data were analyzed using the linear forms of the Langmuir and Freundlich isotherm models and showed a good fit with the Langmuir equation for MB adsorption. Thermodynamic parameters such as the changes in Gibbs free energy, enthalpy, and entropy were determined from batch experiments. Results revealed that the adsorption of MB onto illitic clay was endothermic, while that of CV was an exothermic and spontaneous process. Keywords: Adsorption, Cationic dyes, Illitic clay, Temperature effect, Enthalpies of adsorptio