Joëlle Duplay

Influence of interlayer cations on the water sorption and swelling-shrinkage of MX80 bentonite

Abstract The potential of water sorption and swelling–shrinkage in the expansive clays is practically defined by the nature of interlayer cations. The purpose of this paper is to estimate the effects of the cation saturation (Mg+, Ca+, Li+, Na+, and K+) on the swelling–shrinkage behaviour of the MX80 bentonite. The MX80 bentonite (a “commercial clay”) was treated with concentrated solutions (1 N) of sodium, calcium, magnesium, potassium, and lithium chlorides. This treatment was made three times with constant agitation for 1 h. Then, the clay was washed three times with distilled water. The scanning transmission electron microscopy (STEM) and inductively coupled plasma atomic emission microscopy (ICP-AES) analyses were used to verify the efficiency of the cation saturation. Finally, two techniques were employed to estimate the effect of the cation saturation on the swelling–shrinkage behaviour of the bentonite: the first one uses an isothermal system of water adsorption, where the water activity is controlled by a supersaturated salt solution. In the second, environmental scanning electron microscopy (ESEM), coupled with a digital image analysis (DIA) program, was used to estimate the swelling–shrinkage potential at different water activities. The swelling–shrinkage isotherms were always estimated on isolated aggregates. The isotherms of water adsorption and swelling–shrinkage of the bentonite MX80 show that the amount of adsorbed water and the swelling–shrinkage potential depend directly on the interlayer cation. For example, the sodium bentonite presents an excellent capacity to swell while the lithium bentonite does not swell significantly at the aggregate scale. In addition, other textural properties may be modified by the cation saturation, such as the specific surface, the particle size, porosity, etc.

Swelling-shrinkage kinetics of MX80 bentonite

The swelling–shrinkage kinetic of an industrial Bentonite (MX80) was investigated using a new technique of environmental scanning electron microscopy (ESEM) coupled with a digital image analysis (DIA) program (Visilog). This expansive clay was characterized by several analytic tools (ICP-AES, SEM, STEM, XRD, etc.), before applying the new ESEM technique. The swelling–shrinkage was directly observed at high magnification and at different relative humidity states in an ESEM. Nine wetting/drying cycles were performed on the sample. Each cycle was performed at different relative humidities (55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%). A DIA program was used to determine swelling–shrinkage. This method consists of estimating the percent augmentation of the surface as a function of time. Finally, a swelling–shrinkage kinetic model was tested, based on a first-order linear kinetic equation. The results show that the coupled ESEM and DIA can be a powerful method of estimating the swelling/shrinkage potential of expansive clays. The exponential model fits well with the experimental data. D 2003 Elsevier Science B.V. All rights reserved.

Kaolinite to halloysite-7 Å transformation in the kaolin deposit of São Vicente de Pereira, Portugal

The transformation of kaolinite to halloysite-7 Å was identified in the kaolin deposit of São Vicente de Pereira (SVP), using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Both the 02, 1̄ and 13̄, 13 reflections show changes in the XRD patterns along the kaolinite to halloysite-7 Å transition, and the FTIR spectra show changes corresponding to both OH− and Si-O-stretching bands and Al-O-Si-bending vibrations. The interlayer water content in the kaolinite structure increases during transition. The two-layer periodicity of well-ordered kaolinite and rolling up of kaolinite plates are observed using high-resolution transmission electron microscopy (HRTEM). Long and short tubes exhibit halloysite-7 Å. No structural Fe was found in the kaolinite samples. Analytical electron microscopy (AEM) indicates no substitution of Al3+ for Si4+. The Si/Al ratio shows values of ∼1 for the kaolinite and rolled kaolinite plates. The 27Al magic angle spinning neutron magnetic resonance (MAS-NMR) spectra display a resonance centered at ∼1 ppm, assigned to six-coordinated aluminum. The transformation of kaolinite to halloysite-7 Å is controlled by surface reaction.

A method of estimateng the Gibbs free energies of formation of hydrated and dehydrated clay minerals

Clay minerals are commonly hydrated, and water molecules are attached in two different interlayer and interparticle hydration sites. Both sites contribute to the hydration energy involved when a dry clay aggregate is placed in contact with water or when a wet and swollen aggregate is placed in a dry atmosphere. The amounts of adsorbed water, and the hydration energy as well, vary as functions of the activity of water in which particle aggregates are placed. Integration of dehydration isotherms, established for different samples of various compositions of clay minerals, was used to evaluate the Gibbs free energies of hydration at different hydration stages, i.e., from the water-saturated phases to the dry states. The proposed model of estimating Gibbs free energies is based on the following steps and assumptions: 1. (1) Hydrated and dehydrated clay minerals are ideal solid solutions, as presented by Tardy and Fritz (1981) 2. (2) In each of the series of phyllosilicates (talc, mica, and celadonites), hydrated, dehydrated, and wellcrystallized Gibbs free energies of formation from the oxides are linearly dependent on the parameters ΔOMz+2− related to the electronegativity of the cation Mz+ in the octahedral position 3. (3) In each of the mineral series, hydration energies are proportional to the layer charge; and 4. (4) In each of the mineral series of the same charge and same interlayer cation, the hydration energy is also proportional to ΔOMz+2−. The principal results of the model are 1. (1) poorly crystallized but hydrated clay minerals of a given chemical composition 2. (2) poorly crystallized, dehydrated clay minerals 3. (3) dry, largely sized, wellcrystallized phyllosilicates of the same chemical composition, all of which differ largely in their Gibbs free energies of formation and in their stability fields in natural conditions. Furthermore, the solubility products and the corresponding cation exchange constants of these minerals are dependent on the activity of water in which the equilibrium reactions take place. These parameters also depend on the tetrahedral, octahedral, or total interlayer charge, and finally on the nature of the cation located in the octahedral layer (i.e., Mg2+, Fe2+, A13+, or Fe3+). It is also proposed that for a given interlayer cation (Li+, Na+, K+, Mg2+, or Ca2+) and for a given octahedral composition (Mg2+, Fe2+, A13+, or Fe3+), the hydration energy generally increases with the layer charge so that most of the minerals of high charge are hydrophylic and should hydrate spontaneously in water. However, the hydration energy of K+-exchanged nontronites (Fe3+) and beidellites (A13+), both dioctahedral, decreases with the layer charge so that illite and glauconite, muscovite, and ferrimuscovite presumably appear as hydrophobic and should not hydrate spontaneously when placed in contact with water.

TEXTURAL TRANSITION AND GENETIC RELATIONSHIP BETWEEN PRECURSOR STEVENSITE AND SEPIOLITE IN LACUSTRINE SEDIMENTS (JBEL RHASSOUL, MOROCCO)

In the Tertiary lacustrine sediments of the Jbel Rhassoul (Morocco), stevensite and sepiolite, confined to the dolomitic facies, are commonly mixed at lower parts of the so-called “Formation Intermédiate”. Transmission electron microscopy (TEM) observations reveal a relation between these 2 magnesian clay minerals. One can observe the different transition steps, from the initial folded layers of stevensite to the fibers emerging from the layers, and finally to the complete replacement of stevensite by sepiolite. That transition can also be observed by scanning electron microscopy (SEM), where the fibers seem to grow at the expense of stevensite. Thermodynamic calculations have been applied to provide geochemical conditions for the formation of sepiolite after stevensite. Early deposition of the “Formation Intermédiaire” occurred under climatic conditions varying between dry and wet. During dry periods, the relative silica enrichment and the pH decrease in the lake water should destabilize stevensite, leading to the formation of sepiolite. Subsequently, a perennial wet climate would lead to the formation of pure stevensite without any trace of sepiolite.

THERMAL DIAGENESIS OF CLAY MINERALS WITHIN VOLCANOGENIC MATERIAL FROM THE TONGA CONVERGENT MARGIN

Abstract Clay minerals are examined in detail in the sediment from the Tonga Trench margin at Site 841 (Leg 135 ODP). The changes in amount and nature of secondary clays with depth provide an alternative explanation for the intensive alteration of volcanogenic material at convergent margins. A characteristic distribution of clay minerals with depth shows four distinct zones unexplainable by simple burial diagenesis processes. These are named the upper, reactive, lower and rhyolitic zones. The reactive zone is intercalated with numerous sills and is characterized by the dominant iron-rich clays such as saponite, corrensite and chlorite associated with analcime. The occurrence of such iron-rich clays, mostly associated with a large amount of analcime, yields chemical and mineralogical evidence for thermal diagenesis. The required heat for the diagenetic process was transferred from recently intruded basaltic andesite sills. In the vicinity of these intrusions, the iron-rich clay minerals may have formed at temperatures up to 200°C. A zoning with respect to clay and zeolite minerals indicates that the influence of the palaeoheat flow decreased with the distance from the intrusion. The formation of interlayered I/S, illite, kaolinite and aluminous chlorite, which are recognized as major secondary minerals within the rhyolitic complex, was mainly controlled by both early diagenesis at moderately elevated temperatures, and since the Eocene by burial diagenesis at low temperatures. The occurrence of a steam zone in an early stage of the intrusion is restricted to Miocene tuffs and has overprinted the early alteration of the volcanogenic material within the tuffs and has changed the originally pristine composition of the pore fluids.

Late Cretaceous and Palaeocene clays of the northern Tunisia: potential use for manufacturing clay products

Late Cretaceous and Palaeocene clay deposits of the northern Tunisia were studied for potential valorization in clay product manufacturing. To achieve this goal, physicochemical characterization based on multidisciplinary approaches including mineralogy, geochemistry and thermal analyses was carried out. Clay samples collected from the Bir M’Cherga and Tajerouine study sites have undergone chemical analysis by using atomic absorption spectroscopy. The obtained results showed that the studied samples were mainly composed of silica, alumina, calcium and iron oxide. Mineralogical analysis confirmed the results of chemical analysis; it showed the main peaks of quartz, calcite, kaolinite, smectite and illite. Those clay samples were used as natural resources for manufacturing earthenware tiles. Mixtures of clays and dolomites were prepared from the Late Cretaceous and Palaeocene clays and then heated to the desired temperature to obtain different earthenware products. Finally, the prepared clay products were tested via different geotechnical analyses. It was found that the clay percentage needed to be decreased in the starting mixture to enhance the properties of the final products. Those results also indicated that industrial application of both Late Cretaceous and Palaeocene clays of the northern Tunisia could be done, especially for manufacturing clay products.

Geochemical background and contamination level assessment in Tunisian and Moroccan Mediterranean coastal lagoon sediments

The calculation of enrichment factors (EF) enables estimating contamination levels of trace elements in lagoon sediments. It is based on normalization to a conservative element and to a reference material. This reference can be from the literature or from analyses of local sediments or rocks which have to be representative of the studied site. Calculations of enrichment factors were applied to Cu, Pb, Zn, Sc and Al measured in three semi-arid coastal lagoons, El Kelbia and El Meleh in Tunisia, and Nador in Morocco. For El Meleh and El Kelbia lagoons, EF calculations were done using the post-Archean Australian shale as global reference material, and deep sediments as local reference material. For Nador Lagoon (Morocco), the chosen global and local reference materials are the continental crust and the Gourougou volcanic body, respectively. The comparison between results of both methods of EF calculations shows that using a global reference from the literature induces an underestimation of the contamination level. The use of a local reference allows a more reliable estimation of contamination levels in the studied lagoon. It appears that El Meleh Lagoon is moderately enriched in Pb, especially at the mouth of Oued and near agriculture activities. The Lagoon of Nador is severely contaminated with Zn, Pb and Cu near mine dumps and in the vicinity of cities. El Kelbia Lagoon shows a high enrichment in Pb near garbage dumps and main roads and an overall low to medium enrichment in Zn.

Thermodynamique des hydrates

Abstract The thermodynamic properties of the hydration water of hydrated minerals contribute to the variations of the solubility products and cation selectivity constants. This is illustrated here as an example taken from series of hydrated magnesium and strontium chlorides. Such variations are a function of temperature, pressure, or activity of water. The proposed method, applicable to clay minerals, allows hydration processes to be taken into account for calculating solubility products when only the thermodynamic properties either of the dehydrated or hydrated mineral phase, the hydration isotherm of the mineral and the thermodynamic properties of the hydration water are established.

Reconstruction of the Late Cretaceous-Paleocene paleoenvironment (northern Tunisia) from biostratigraphy, geochemistry and clay mineralogy

A multidisciplinary approach was adopted for the reconstitution of the depositional environments based on clay minerals distribution, biostratigraphy and geochemical properties of the Late Cretaceous-Paleocene deposits. Evolution of the mineralogical compositions (i.e. clay minerals contents) was ascertained in two cross sections from the Late Cretaceous and Paleocene belonging to different paleogeographic domains: the Bir M’Cherga (Tunisian Dorsal) and Tajerouine (Northern West of Tunisia) study sites. Chemical analysis of the original clay samples, collected in both sites (i.e. Late Cretaceous and Paleocene clays), showed significant amounts of oxides including calcium, silica, alumina and iron. Three distinct mineralogical zones were identified. Clay mineral assemblages of the Late Cretaceous showed the predominance of kaolinite, subordinated by variable proportions of illite and smectite. In contrast, those of Paleocene clearly showed the predominance of smectite to the detriment of kaolinite and illite. The predominance of kaolinite in the Late Cretaceous clay deposits indicated a calm and shallow depositional environment influenced by hot and wet climate, especially in northeastern Tunisia (Bir M’Cherga study site). Kaolinite typically forms under lacustrine environment where appreciable movement of water would be expected, leading to the development of kaolinite. During Paleocene, the smectite-enriched mineralogical sequence suggested similar climatic conditions with further deepening of the depositional environment in salt lakes. The regional geodynamic context of both sections showed an important Maastrichtian unconformity with a Paleocene major hiatus extending from the East to the West.