Metal concentrations in river water and bed sediments of the Lower Litani River Bassin, Lebanon

The distribution of pollutants in the Litani River is almost severe. It resulted from domestic, sewage, agricultural and industrial sources. In this study, the distribution of metals (Cu, Fe, Cd, Mg, Zn, Pb , Al, Ba, Ni, Mn, Ag and Cr) were measured in river water and the bed sediments of the Lower Litani River Basin (LLRB). The impacts of metals on the water quality were monitored during the rainy, mid rainy and dry season in the year 2012. The objectives of this study were first to identify possible sources of metals (i.e. geological and/or anthropogenic) and then to characterize the chemical behavior of these metals in water and bed sediments. Water and bed load sediments were sampled at six sites along the LLRB main watercourse, The metal concentrations in the river sediments were remarkably high, but varied between different sampling sites, and the concentrations in water were mainly within the permissible limits. The metal contents in bed sediment were highest during closure of summer period. By applying the principal component analysis applied to total and extractable metal contents as a tool for studying metal pollution in the LLRB, it was useful to distinguish between anthropogenic and natural sources

Synthesis of a red iron oxide/montmorillonite pigment in a CO2-rich brine solution

International audienceThe homoionic calcium-montmorillonite was used to synthesize a red iron oxide/clay pigment in a CO2-rich brine solution (0.5 M of NaCl) by using an agitated batch-reactor (engineer autoclave). The operating conditions were 15 days of reaction, 200 bars of pressure and 150 °C of temperature. SEM/EDS, STEM/EDS, XRD and Infrared Spectrometry were performed to characterize before and after reaction the solid phase. The results showed the precipitation of spherical nanoparticles (50–500 nm) of iron oxide (Fe2O3) dispersed and/or coagulated in the clay-matrix. Evidently, this oxide produced red coloration in the final product. For this case, the Fe3+ cation was provided to the aqueous solution by the dissolution of Ca-montmorillonite, particularly, the dissolution of most fine particles contained in the starting clay material. The cation exchange process and precipitation of polymorph silica were also observed

Sur la possibilité d’observer les vibrations de valence OD aux dilutions naturelles : Apport de la spectroscopie IRTF en réflexion diffuse

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Sur la possibilité d’observer les vibrations de valence OD aux dilutions naturelles : Apport de la spectroscopie IRTF en réflexion diffuse

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A coupled XRD-TEM comparative study of kaolinites morphological aspects

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Mineralogy and geochemical behaviour during weathering of greenstone belt under tropical dry conditions in the extreme North Cameroon (Central Africa)

International audienceMineralogy, major, trace and rare earth elements of a weathering profile developed on tertiary greenstone belt in the extreme North Cameroon are reported. The aim of which was to investigate mineralogical evolution and element mobilization and redistribution during weathering under dry tropical climate. The weathering profile consists of four main horizons: (1) a spheroidal weathering zone constituted by a corestone shell complex, (2) a C horizon, (3) a Bw horizon and an Ah horizon. The results indicate that nontronite, a Fe-rich smectite, is the exclusive clay mineral formed in the exfoliated shells and the C horizon. It is associated with kaolinite in the upper horizons. The coexistence of these two clay minerals induced a decrease of CEC and pH which becomes neutral. The weathering index (WI) values reveal that weathering becomes more and more intensive from the corestone up to Bw horizon, which is the most weathered horizon in the weathering profile. Mass balance calculations, using Th as immobile element, indicate that Ti is quite mobile and that Al and Fe are relatively enriched at the bottom and strongly leached at the top of the profile. Alkalis and alkaline earth elements are strong leached through out the profile, except Ca which displays similar trend as Al and Fe. The same goes for LILE (Cs, Sr),TTE (Cr, Co, Ni) and HSFE (Y, Nb, Hf). In opposite, REE are depleted at the bottom and enriched in the upper horizons, with more enrichment for LREE than for HREE. It appears that weathering of greenstone belt causes a fractionation of HREE and induces a concentration of LREEs. Ce and Eu anomalies display opposite behaviour. (C) 2013 Elsevier GmbH. All rights reserved

Transport of HPAM Solutions in low Permeability Porous Media: Impacts of Salinity and Clay Content

International audienceChemical EOR is now considered as an attractive option for low permeability reservoirs, in particular wherelack of gas supply does not allow gas injection processes. However, its application can be challenging forpermeabilities below 100 mD, as poor injectivity and high chemical retention are frequently observed inthese cases. This work aimed at investigating the impact of both chemical and mineralogical parameters onthe transport of polymer solutions in well-controlled low permeability porous media.The intrinsic viscosity and hydrodynamic size of partially hydrolyzed polyacrylamide (HPAM)solubilized in brines of variable ionic strengths and hardnesses were firstly investigated. Polymer injectioncorefloods were then conducted using granular packs (sand and clays mixtures) with similar petrophysicalcharacteristics (permeability 60-80 mD) but having several controlled mineralogical compositions. Thegranular packs were especially characterized in terms of structure (SEM) and specific surface area (BET)before and after polymer injections. The main observables from the coreflood tests were the resistanceand residual resistance factors generated by the polymer, the polymer inaccessible pore volume and itsirreversible retention.Homogenous and reproducible granular packs were successfully prepared thanks to a dedicatedmethodology and using different ratios of quartz and clays (kaolinite and illite separately).Results from the viscometric analysis showed that the intrinsic viscosity of the HPAM solutions decreasedwith increasing total salinity, as expected from charge screening, and that it decreased sharply in presenceof divalent cations, even at low ionic strength, which was less expected.Coreflood experiments showed that polymer retentions, resistance factors and irreversible resistancefactors increased significantly:– with increasing ionic strength and hardness for porous media of a given mineralogicalcomposition. This appeared consistent with the outcomes of the viscometric study andconfirmed the major impact of hardness;– in presence of kaolinite and illite, even at low ionic strength and hardness.The polymer inaccessible pore volume was significantly impacted by the presence of clays, but not bythe ionic strength and hardness. Analysis of the results indicated that these effects could not be attributedonly to polymer adsorption linked to the increase of specific surface area, but that more complex polymeradsorption/retention mechanisms occur depending on the clay type (layer charge and expandability).This systematic study allows dissociating the impacts of salinity, hardness and clay contents/types on thetransport of polymer solutions in low permeability porous media. The results obtained should be of interestto the chemical EOR industry as they provide guides to help tuning the injection brine composition andpolymer concentration to the reservoir properties

STUDY OF LOW-PRESSURE ARGON ADSORPTION ON SYNTHETIC NONTRONITE: IMPLICATIONS FOR SMECTITE CRYSTAL GROWTH

International audienceBecause relatively little information about the crystal-growth process of smectite is available, the process was assessed here by studying the size and shape of nontronite particles synthesized at six different temperatures from 75 to 150 degrees C over a period of 4 weeks.The morphology of nontronites was studied using low-pressure isotherms of argon adsorption at 77 K, a method which enables the measurement of the basal and edge surface areas of the nontronite particles and of their mean diameter and thickness. During the crystal growth of nontronite, the mean particle length increased whereas their thickness (and the number of stacked layers) did not vary significantly.A specific two-dimensional crysial-growth process Was observed for smectite via the lateral extension of the layers. This process also appears to occur during the growth of neoformed natural smectite

Effect of chemical modification on surface free energy components of Aerosil silica powders determined with capillary rise technique

International audienceThe knowledge about interfacial energy interactions and surface free energy is necessary for understanding and modeling many surface and interface processes. The aim of this paper is to study the effect of the chemical modification on the surface free energy components of Aerosil OX50. This fumed silica is chemically modified using the hydrophobic organosilane hexadecyltrichlorosilane (HTS). The modification process is studied by Fourier transform infrared spectroscopy (FTIR) and total carbon mass measurements performed on solid silica samples. The combination of these two techniques allows the determination of the adsorption isotherm of HTS onto silica showing the formation of a plateau for an initial concentration of 3 mM. The quantity adsorbed of HTS at maximum coverage is 2.14 mu mol/m(2). However, the chemical modification does not elaborate a compact layer. The HTS density is approximately 1.2 molecules/nm(2) which is close to the density of hydroxyl groups on the surface. A recent method, developed by Chibowski and Perea-Carpio, based on imbibition of probe liquids into a thin porous layer (capillary rise), is used for the determination of the surface free energy components. The surface free energy decreases continuously from 54.2 mJ/m(2) for bare silica to 46.7 mJ/m(2) for silica treated at an initial concentration of 4 mM following a linear diminution of gamma(s) with the HTS adsorbed amount. The apolar Lifshitz-van der Waals component gamma(LW)(s) is reduced from 41.1 mJ/m(2) to 35.8 mJ/m(2). The electron-donor parameter gamma(-)(s) drops from 53.9 mJ/m(2) to 27.5 mJ/m(2) while the electron-acceptor parameter gamma(+)(s) remains roughly constant (1 mJ/m(2)). Trends in the surface free energy components are notably linked to observations in infrared spectra and give additional information about the structure of the HTS layer

The synthesis of MCM-41 nanomaterial from Algerian Bentonite: The effect of the mineral phase contents of clay on the structure properties of MCM-41

International audienceThis study focuses on the MCM-41 material (Mobil Composition of Matter). The MCM-41 nanomaterial presents higher physical properties such as pore sizes, surface areas and pore volumes. This material is usually synthesized by using laboratory reagents as silicate sources and aluminium source. These laboratory reagents are still expensive and toxic for large scale production. The main aim of this work is to resolve this problem and to replace these expensive laboratory reagents by more cost effective ones. The volclay and Algerian bentonite low-cost mass clay materials are used as silicate and acuminate sources separately by adopting an alkaline fusion process to extract both silicon and aluminium (1 kg of silicium and aluminium from volclay and Algerian bentonite cost around 0.03 and 0.01 (sic) whereas the same amount of silicon from ludox and aluminium from sodium aluminates cost around 350 (sic)). The synthesis of MCM-41 from bentonite was carried out by the hydrothermal method using the supernatants of bentonite (in the form of sodium silicate and sodium aluminate). On the basis of the data obtained from powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and N-2 adsorption and desorption, the results revealed that the properties of MCM-41 synthesized from Algerian bentonite and volclay separately depend on both elemental composition and mineral phase contents of the used bentonite. Pure and highly ordered hexagonal mesoporous MCM-41 with uniform pore sizes and a high specific surface area have been successfully synthesized without any phases which exist in natural bentonite. The Algerian bentonite was chosen because of its low cost compared to volclay, another commercial clay source. (C) 2013 Published by Elsevier Masson SAS on behalf of Academie des sciences