NEWMOD®, developed by R.C. Reynolds, Jr., has been an important tool for evaluating quantitatively X-ray diffraction (XRD) patterns from interstratified clay minerals for more than 20 years. However, a significant drawback to the NEWMOD® approach is that analyses are done by forward simulation, making results sensitive to user input and starting-model assumptions. In the present study, a reverse-fitting procedure was implemented in a new program, FITMOD, which automatically minimizes the differences between experimental and simulated XRD patterns. The differences are minimized by varying model parameters (such as Reichweite, crystal-size distribution, cation content, type of disorder, etc.) using the downhill simplex method. The downhill simplex method is a non-linear optimization technique for determining minima of functions. This method does not require calculation of the derivatives of the functions being minimized, an important consideration with many of the parameters in NEWMOD- type simulations. Instead, the downhill simplex method calculates pseudo-derivatives by evaluating sufficient points to define a derivative for each independent variable. The performance of FITMOD was evaluated by fitting a series of synthetic XRD patterns generated by NEWMOD+, yielding agreement factors, Rwp, of <0.3%. As long as the correct interstratified system was specified (e.g. illite-smectite), excellent fits were obtained irrespective of the starting parameters for the simulations. FITMOD was also tested using experimental XRD patterns, which gave very good fits, in agreement with previously published results. The optimization routine yields good fits for both synthetic and experimental XRD profiles in a reasonable time, with the possibility of varying all important structural parameters. FITMOD automatically provides optimum fits to experimental XRD data without operator bias, and fitting efficiency and accuracy were, therefore, significantly improved.

Maghemite (γ-Fe2O3) is a ferrimagnetic Fe oxide commonly found in tropical and subtropical soils, especially in the topsoil where it is usually a product of burning. Isomorphic substitution (IS) of the Fe in maghemite by different metals (mainly Al3+) can modify its mineralogical and chemical attributes, and these modifications may be important to understanding the formation and properties of this mineral in soils and sediments. The objective of this work was to evaluate the crystallochemical alterations of synthetic, Al-substituted maghemites prepared by the precipitation of magnetites from alkaline aqueous media containing FeSO4·7H2O with increasing amounts of Al2(SO4)3·7H2O to obtain hypothetical Al3+ for Fe3+ substitutions ranging from 0.0 to 40.0 mol %. The Al-substituted magnetites were washed and dried, and then heated to 250ºC for 4 h to form yellowish red maghemites that were characterized by total chemical analysis, X-ray diffraction, specific surface area (SSA), mass-specific magnetic susceptibility, infrared spectroscopy, transmission electronic microscopy, and color. Increasing Al3+ substitution to an experimental maximum of 15.9 mol % decreased both the a0 dimension of the cubic unit cell (a0 = 0.8339 − 396.157 × 10−16 Al, r2 = 0.99) and the mean crystallite dimension (MCD = 76.4–3.15Al, r2 = 0.79) of the maghemites. With the decrease in MCD came a more yellowish color, an increase in SSA, and a decrease in crystallinity as measured through extraction of the samples with acid ammonium oxalate. The mass-specific magnetic susceptibility of the maghemites increased with Al3+ substitution up to 5.3 mol % and then decreased with further replacement of Fe by Al. Solid-phase aluminum in excess of 16 mol % substitution appeared to occur as a separate, poorly crystalline phase that was X-ray amorphous.

A magnetic composite was prepared by wet-impregnating a powder of a natural zeolite with a magnetic Fe oxide-containing synthetic material. Both starting materials were first characterized with X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, and by isoelectric-point using vibrating-sample magnetometry. The synthetic Fe oxide-containing material was characterized as a mixture of magnetite (Fe3O4) and goethite (α-FeOOH). From the Fe Mössbauer analysis, the relative subspectral area for magnetite corresponds to 93(2)%; the remaining spectrum is assignable to goethite. After the impregnation process, magnetite was still identified in the composite material as a magnetic layer surrounding the zeolite particles; no magnetically ordered goethite could be detected. The Mössbauer pattern for this sample indicates a much more complex structure than for the precursor material, based on Fe oxides, with some more altered magnetite and an intense central doublet of (super)paramagnetic Fe3+, probably due to small Fe (hydr)oxides and/or to a residual contribution of Fe-bearing species from the starting zeolite material. The composite preparation procedure also promoted the change of the characteristic A-type zeolite to mordenite. The resulting magnetic composite presented a magnetic coercivity of as much as 0.140 A m−1, at 77 K. The final composite is now being evaluated as an adsorbent: results to date confirm that this novel magnetic material may have applications in the remediation of contaminated water bodies.

Many studies of the chemical composition of sepiolite and palygorskite have been carried out using analytical electron microscopy (AEM). According to the literature, a compositional gap exists between sepiolites and palygorskites, but the results presented here show that they may all be intermediate compositions between two extremes. The results of >1000 AEM analyses and structural formulae have been obtained for the samples studied (22 samples of sepiolite and 21 samples of palygorskite) and indicate that no compositional gap exists between sepiolite and palygorskite. Sepiolite occupies the most magnesic and trioctahedral extreme and palygorskite the most aluminic-magnesic and dioctahedral extreme. Sepiolite and palygorskite with intermediate compositions exist between the two pure extremes: (1) sepiolite with a small proportion of octahedral substitution; (2) palygorskite with a very wide range of substitution (the pure dioctahedral extreme is unusual); and (3) intermediate forms, Al-sepiolite and Mg-palygorskite with similar or the same chemical composition. The chemical compositions of the intermediate forms can be so similar that a certain degree of polymorphism exists between Al-sepiolite and Mg-palygorskite.

The most common means of reducing the particle size of solids is by grinding, a process which can affect the surface properties and the behavior of the solid in later stages (granulation, compaction, etc.), and which can influence the end-use properties of the final product. Inverse gas chromatography (IGC) measurements were used here to evaluate the influence of grinding, in a ball mill, on attapulgite. The milling experiments were performed in dry media for various periods. After 30 min of grinding, significant decreases in the particle size and specific surface areas were observed when calculated using different probes. No noticeable variation in the surface properties was observed by IGC either at infinite dilution or at finite concentration, however. In particular, the distribution functions of the adsorption energies (DFAE), giving information about the surface heterogeneity for both an apolar probe (octane) and a polar probe (isopropanol), remained unchanged, regardless of the grinding time. The stability of the surface energy with respect to the grinding process was seen to be related to the particular fibrous structure of the attapulgite clay.

Electro-osmotic chemical treatment is an innovative method to improve the strength of soft clays for geotechnical engineering purposes; the effectiveness of the treatment may be related to treatment time, the concentration of the solutions injected, and to variation of pH in the clay. The objective of this study was to investigate the relationship between the above-mentioned factors and the improvement in strength when calcium chloride solution was used as an injection material. A series of tests was carried out by injecting different concentrations of calcium chloride solution into a kaolin suspension, for different treatment times, during electro-osmosis. After the tests, the pH, cone resistance, water content, and concentration of Ca2+ in the kaolin at different locations were measured and analyzed. The results show that the concentration of Ca2+ in the kaolin, the pH, and the strength were increased near the cathode with increases in concentration of CaCl2 and treatment time. An insignificant increase in strength, due to ion exchange over the entire specimen, for short treatment times of 2 to 24 h, was observed because of a small increase in concentration of Ca2+ and in pH. During long-term treatment (120 h), a considerable increase in concentration of Ca2+ (137.0 mg/g) and pH (pH = 10) was observed near the cathode. This led to a pozzolanic reaction, which in turn caused a significant increase in the mechanical strength of the kaolin.

Layered double hydroxides (LDHs) are layered ion exchangers, with a large surface-charge density, which react easily with organic anions. Various types of organics are rapidly substituted in the interlayer space of inorganic precursor LDHs. ZnAl-LDHs were intercalated with 1- to 19-carbon monocarboxylic acid anions by anion exchange of NO3-saturated LDH precursor phases in order to study the dependence of exchange reactions on synthesis parameters (temperature, pH, and interlayer anion). The carboxylic acid anion-LDHs synthesized were characterized using X-ray diffraction, infrared spectroscopy, thermal analysis, scanning electron microscopy, chemical analysis, and N2 adsorption. Carboxylic anion quantities in excess of the LDH anion exchange capacity easily replaced exchangeable nitrate anions at moderate pH. The intercalated LDH interlayer space depended on the alkyl chain length and orientation (inclination angle) of thecarboxylic-acid anion. Thelatticeparameter c0 ranged from 3.4 to 13.5 nm, but the a0 lattice parameter remained constant at 0.31 nm. Crystallographic analyses indicated a monomolecular arrangement of intercalated short-chain fatty-acid anions. At pH < 7, intercalated long-chain carboxylates showed a preferred bimolecular interlayer orientation. Carboxylic-acid anion exchange with LDHs at pH 7 resulted in the formation of two different sets of basal spacings, which indicated the coexistence of LDHs intercalated with monomolecular and bimolecular arrangements of interlayer carboxylic compounds.

Thermal treatment of the carboxylic acid anion-intercalated LDHs indicated stability up to ~140ºC. The release of interlayer water led to distortion of the crystallographic units and resulted in smaller basal spacings without collapse of the layered structure. Heat treatment re-oriented alkyl-chain carbon carboxylates (with >10 carbons) to a more upright interlayer position.

The Pleistocene Olorgesailie Formation in the southern Kenya Rift has yielded a remarkable assemblage of Acheulean artifacts and vertebrate fossils, including hominin specimen KNM-OG 45500. Members 1 and 7 both contain clay-rich deposits that have been pedogenically modified into paleosols (UM1p and UM7p, respectively). This study provides the first detailed mineralogical and geochemical analyses of the clays of this important Pleistocene basin. The smectitic clays, which show abundant evidence for pedogenesis, were apparently originally deposited under lacustrine conditions. They have an average structural formula of (Ca0.01Na0.32K0.26)(Si3.76Al0.24)(Al0.86Ti0.04Fe0.68Mg0.42)O10(OH)2. The high layer charge clays indicate diagenetic alteration of detrital clay derived from the volcanic drainage basin, probably involving alkaline waters of variable salinity. Despite overall lower salinity compared to other Plio–Pleistocene basins of the region (e.g. Olduvai Gorge), the basin still shows evidence for authigenic clay mineral precipitation. Clay chemistry and bulk geochemical indicators of pedogenesis imply that UM1p clays more closely reflect depositional paleo-waters, whereas UM7p clays have been more pedogenically altered due to subaerial exposure. UM1p smectites show some Mg enrichment near the western Lava Hump locality, consistent with discharge of Mg-bearing paleo-waters from a volcanic aquifer into a siliceous and alkaline (though not highly saline) paleo-lake. UM7p smectites were deposited in a more saline paleo-lake, but have lost substantial amounts of Mg due to post-depositional weathering. Locally abundant artifacts and vertebrate fossils found in these deposits accumulated at times following deposition of the lacustrine clay, probably concurrent with pedogenesis. The limnological conditions associated with initial clay deposition, therefore, preceded hominin occupation of the exposed surfaces.

The purpose of this study was to investigate the structural and chemical modifications of phyllosilicates that occur under natural conditions, using the progressive deformation of chlorite (sudoite) present in quartz-rich veins from the Internal Zone of the Rif range (Morocco) as the model system. Signs of chlorite deformation include kinks, chevron-like folds, and fractures. The samples also contain later, undeformed grains, which sealed the fractures or grew with (001) perpendicular to the compressive stress. Deformation-induced structural changes consist mainly of basal cleavages associated with ordered replacement of brucite sheets by hydrated layers, thus leading to irregular microdomains of mixed-layer chlorite-vermiculite and sudoite. Such structural modifications represent a mechanism for accommodating the compressive stress. Structural changes were accompanied by minor chemical ones, which lead from di,tri-chlorite (sudoite) to phases with a more trioctahedral character (mixed-layer chlorite-vermiculite). The hydration reaction occurred throughout a topotactic replacement of the pre-existing sudoite grains. Later, undeformed grains consist of mixed-layer chlorite-vermiculite intergrown with retrogressive kaolinite and minor Fe oxide, and are interpreted as having formed through a dissolution-precipitation process, during deformation. Retrogression of sudoite probably occurred during the latest stage of exhumation, in low-temperature conditions.

The incorporation of boron (B) and nitrogen (N) into illite is the key demand-side process responsible for the diagenetic budget of these elements in sedimentary basins, with important implications for pore-water chemistry, natural-gas composition, and borehole geophysics. The purpose of the present study was to take advantage of recent advances in quantitative mineral analysis of sedimentary rocks which have opened new possibilities for investigating this particular process. In order to avoid complications with recycled (detrital) N and B, clays from pyroclastic horizons of sedimentary rocks (bentonites) were used. The B and N contents in illite-smectite were measured in samples from different sedimentary basins, representing a complete range of diagenetic alteration. The bulk-rock chemical measurements, performed on raw rock samples in order to avoid any loss of exchangeable B and N, were referred to the contents of illite-smectite clays and to the content of illite alone, both measured by a combination of XRD and chemistry-based techniques.

Both B and N (as NH4) are present in illite, so their contents in illite-smectite clay increase in a more or less linear manner with progressing illitization. Thus, during diagenesis, the illite-smectite clay is a net consumer of B and N from the pore water. The amount of N in individual illite layers decreases during diagenesis and the amount of B either decreases or remains stable. Bentonitic illite must acquire both B and N from outside of the bentonite bed. In one diagenetic cycle, bentonitic illite fixes up to 800–1000 ppm B and up to >1% N expressed as (NH4)2O, corresponding to >20% of the fixed cation sites.

Due to swelling, smectite minerals are capable of intercalating many organic molecules in their interlayer space. Tetracycline (TC) is a group of antibiotics used extensively in human and veterinary medicine. The great aqueous solubility and long environmental half life of TC mean that the study of interactions between swelling clay minerals and TC are of great importance in TC transport and retention in subsurface soils. In the present study, the intercalation of TC molecules at different levels into smectites was investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The shift of the FTIR bands of amide I and II in comparison to crystalline TC suggested a strong interaction between the amide groups and the clay surfaces. The band at 1455 cm−1 remained the same after TC intercalation into SAz-1, SWy-2, and SYn-1, suggesting that complexation was not a dominant mechanism of TC uptake by these minerals. With cation exchange as the major mechanism of TC intercalation into these minerals, simultaneous removal of H+ from solution protonated the TC molecules and provided a positive charge to interact with negatively charged mineral surfaces even in neutral to slightly alkaline conditions. The increase in interlayer distance after intercalation by TC, as revealed by XRD, suggested a tilted orientation of the intercalated TC molecules in both twisted conformation in acidic condition and extended conformation in alkaline condition.

The present study compares the water-vapor adsorption capacity of bentonites (natural cation population) with the Enslin-Neff method. Water-vapor adsorption at 50% r.h. (relative humidity) or 70% r.h. is known to depend heavily on the amount of permanent charge and on the type of exchangeable cation. At ~80% r.h. Na+- and Ca2+/Mg2+-dominated bentonites take up equal amounts of water. Comparing the water-uptake capacity at 80% r.h. with the cation exchange capacity (CEC) revealed a close correlation between these two variables. Appreciable scatter apparent from this plot, however, suggests that additional factors influence the water-uptake capacity.Water adsorption at external surfaces was considered to be one of these factors and was, in fact, implicated by N2-adsorption data. The ratio of external/internal water ranged from 0 to 1, which suggests that water-adsorption values cannot be applied in the calculation of the internal surface area without correction for external water.

The Enslin-Neff water-uptake capacity, on the other hand, is unaffected by microstructural features (e.g. specific surface area and porosity). The amount of exchangeable Na+ is themost important factor. However, the relationship between the Na+ content and the Enslin value is not linear but may be explained by percolation theory.

Glycerol is a byproduct of biodiesel synthesis by transesterification of triglycerides with short-chain alcohols in the presence of solid base catalysts. Because hydrotalcite is a potentially useful basic catalyst for the transesterification reaction, the interaction of glycerol with hydrotalcite is the focus of this work. Glycerol was intercalated into Mg-Al hydrotalcite with a Mg/Al molar ratio of 4 under elevated temperatures of 4432/503 K in the absence and presence of NaOH. The resulting materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and N2 adsorption. The amount of glycerol incorporated into hydrotalcite increased with increasing temperature of intercalation. However, the brucite-like sheets of hydrotalcite partially decomposed during the intercalation process at the highest temperature. The presence of NaOH stabilized the hydrotalcite layers against decomposition under high temperature (503 K). The intercalated materials exposed large surface areas ranging from 142 to 663 m2 g−1, depending on the preparation conditions. The glycerol-intercalated hydrotalcites were less catalytically active than hydrotalcite with OH− counterions for the transesterification of tributyrin with methanol. The lower reactivity of glycerol-intercalated hydrotalcite was probably the result of a strong interaction between the intercalated glycerolate (HOCH2-CHOH-CH2O−) and the partially decomposed brucite-like sheets.

Acid-activated bentonites are utilized in many applications, including those that depend on their rheological properties and behavior, but little information is available regarding the rheological characteristics of this important industrial material. The purpose of this study was to investigate the effects of solids concentration, salt concentration, and pH value on the shear rate, shear stress, and other flow parameters of acid-activated bentonite suspensions. Activated Na-bentonite was prepared using sulfuric acid. Flow curves of the suspensions were modeled using the Herschel-Bulkley equation, which performed well for this system. The Herschel-Bulkley yield stress increased with the solids concentration and showed a maximum and minimum at the NaCl concentrations of 0.001 M and 0.01 M, respectively, and increased again slightly with further increases in NaCl concentration. The yield stress was at a maximum and a minimum at pH values of ≈5 and ≈7, respectively, followed by a slight increase with pH under alkaline conditions. The variations in dispersion rheological properties can be attributed to the change in the particle-association modes under different conditions.

Guanidine and imidazole are important functional molecules that constitute the side chain of basic amino acids (arginine and histidine); these molecules are capable of interacting with mineral surfaces. However, little information is available about the effect of these molecules on mineral dissolution, including amorphous silica. In this study, to evaluate the effect of these organic molecules on the dissolution rates of amorphous silica, dissolution experiments were performed in solutions containing these molecules and other related heterocyclic compounds. The dissolution experiments were conducted by the batch method using 0.1 g of amorphous silica and 100 mL of 0.1 mM NaCl solution with 0.0, 0.1, 1.0, and 10.0 mM of guanidine, imidazole, pyrazole, or pyrrole at pH values of 4, 5, and 6. The results demonstrated that these compounds can enhance the dissolution rate of amorphous silica, depending on their ionic speciation in the following order: guanidine = imidazole > pyrazole > pyrrole. When 10.0 mM solutions were used, both guanidine and imidazole greatly increased the dissolution rate with an enhancement factor of 5.5—6.5, pyrazole exhibited a smaller change in the dissolution rate with an enhancement factor of 1.5—2.4, and pyrrole exhibited no significant enhancement. ChemEQL calculations confirmed that guanidine (pK = 13.6) and imidazole (pK = 6.99) are fully protonated and mostly present as cationic species in a pH range of 4—6; therefore, these compounds are capable of interacting with the >SiO- sites of amorphous silica. Pyrazole (pK= 2.61) and pyrrole (pK = 0.4), however, existed mostly as neutral forms. The concentrations of cationic species of pyrazole and pyrrole were at least one and three orders of magnitude lower than those of fully protonated compounds, respectively; therefore, pyrazole and pyrrole were less reactive than the fully protonated compounds on the surfaces of amorphous silica.

Shales and claystones in the Permian Irati Formation consist of Al-rich or Fe-Mg clay minerals in its southern/central and northern parts, respectively. The constrasting compositions indicate particular geological and paleo-environmental conditions. The purpose of this study was to determine the conditions of formation by characterizing the black shales and claystones from different sections of the northern edge of the basin, some of which reveal the presence of intruded diabase sills.

Black shales consist of saponite or saponite-talc mixed layers, talc, lizardite, nontronite, and quartz. Green claystones are nontronite-rich but also contain lizardite, talc, and quartz. The chemical compositions of the black shale and claystones, except for one sample (POR-56), exhibit a positive correlation of the TiO2, Cr, and P2O5 contents with Al2O3, which typically results from weathering processes. The presence of saponite, nontronite, and some accessory minerals (spinel, pyroxene, native silver) suggests altered basic-ultrabasic rocks as sediment sources, consistent with the rare earth element (REE) composition being less than the Post-Archean Average Shale (PAAS) or North American Shale Composite (NASC) levels and with negative Ce and Eu anomalies. Sample POR-56 consists largely of nontronite and is anomalously rich in zircon, monazite, and apatite. Chemically, sample POR-56 is different from the black shales and claystones, being richer in Al2O3-Fe2O3, MgO-poor, and having greater REE contents than the PAAS or NASC standards. The POR-56 bed is probably a bentonite resulting from the alteration of volcanic ash in sea water (strong, negative Ce anomaly). The Zr/TiO2vs. Nb/Y relation indicates that the magmatism was andesitic. During the Upper Permian, intermediate to basic volcanic activity was recorded in the Mitu Group of the Central Andes.

Close to the diabase sill, the black shales and claystones contain saponite, talc, and lizardite but nontronite is absent. Saponite and talc crystals, however, exhibit a larger coherent scattering domain size (CSDS) and are randomly oriented with respect to the sedimentary bedding. The thermal metamorphism effect is confirmed by the presence of secondary enstatite-augite and albite crystals.

The placement of metal oxide pillars between clay mineral layers modifies their physical-chemical properties, including surface area, acidity, and catalytic activity. Aluminum is the most commonly used pillar cation, but the use of Fe offers a distinct opportunity to expand the range of catalytic behavior. The purpose of this study was to prepare Fe-pillared Laponite and montmorillonite and to characterize the resulting Fe phase(s). Laponite or montmorillonite suspension was mixed with different pillaring solutions containing Al oligomer and/or Fe oligomer with Fe:(Al+Fe) percent ratios ranging from 0 to 100%. The Al oligomer was obtained by hydrolysis of A1C13·6H2O with NaOH at pH 4.4 and the Fe oligomer was prepared by FeCl3 hydrolysis with Na2CO3 at pH 2.2. The pillared clay was obtained by adding the oligomer to the clay suspension, then heating to 300°C for 3 h. The Fe oligomer and the pillared clay minerals were characterized by variable-temperature Mössbauer spectroscopy, X-ray powder diffraction, and chemical analysis. The unheated Fe oligomer was akaganeite, an Fe oxyhydroxide phase. Heating the Fe oligomer to 300°C transformed the akaganeite to hematite, but heating it in the presence of the clay protected it, at least partially, from this transformation, creating instead a phase which resembled a more poorly ordered akaganeite or a mixture of akaganeite and poorly ordered hematite. Mixing of Al and Fe oligomers in the pillaring solution had no effect on the magnetic hyperfine field of the Fe pillars, indicating that Al forms separate pillars rather than substituting for Fe in the pillar. A small fraction (4%) of the Fe pillar resisted reductive dissolution by citrate-bicarbonate-dithionite.

In spite of many studies of kaolinite synthesis, questions remain as to the transformation of gel into kaolinite, the kinetics of the reaction, and the influence of solution chemistry. The purpose of the present study was to perform a hydrothermal synthesis in order to understand better the transformation from boehmite to kaolinite. Kaolinite was synthesized from amorphous SiO2 and Al(OH)3·xH2O at fixed temperature (250°C) and pressure (30 bar). The initial pH of the solution was 2. The reaction time for the synthesis was varied from 2 to 36 h. The physical properties of synthesized kaolinite were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, field-emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive spectrometry (EDS).

The early stage of kaolinite synthesis followed activation of amorphous Al(OH)3·xH2O to initiate the reactions, i.e. ionization and subsequent crystallization of boehmite. The boehmite reacted continuously with Si4+ dissolved in solution and gradually transformed to disordered, lath-shaped boehmite. In XRD and IR patterns, the typical peaks of boehmite were weakened or disappeared following the reaction.

Structural transformation from boehmite to kaolinite occurred when the Al/Si ratio of the aluminosilicate was 1.0. The kaolinite formed was in the form of curved flakes and its crystallinity increased with reaction time. In the final stage of reaction the morphology of kaolinite changed from flaky to polygonal. The hexagonal, platy kaolinite was therefore developed to allow the gradual variation of the chemical composition, crystal structure, and morphology.

Bentonite is often proposed as an engineered-buffer material in high-level radionuclide waste-management systems. For effective design of the barrier that will provide protection over the long time periods required, the physical/thermal/chemical processes taking place in the barrier material must be understood thoroughly. These processes, which interact, include the flow of water and gas, the flow of heat, and the transport and reaction of chemical constituents. The purpose of this study was to better understand the processes that occurred in a small-scale experiment within a confined bentonite space. A conceptual and mathematical model (FADES-CHEM) was built in order to simulate the results of an experiment conducted in 2000, and thereby to gain a better understanding of the controlling processes. In that experiment, a block of compacted bentonite was placed in an air-tight cell and subjected, for 6 months, to simultaneous heating and hydration from opposite sides. The bentonite block was then sliced into five sections each of which was then analyzed in order to obtain a series of physicochemical parameters illustrating the changes that had occurred. Before modeling, the chemical composition of the bentonite pore waters was restored in order to account for different processes such as gas outgassing and cell cooling. Modeling indicated that gas-pressure build up was a relevant process when computing the saturation of bentonite, and the computations in the present study suggested that evaporation/condensation processes played a crucial role in the final distribution of the water content. Gas pressure and evaporation/ condensation also affected the geochemical system, and the numerical model developed gives results that were consistent with the experimental values and trends observed. The model reproduced the results obtained and enable use at the repository scale and over longer time frames, provided that adequate data are available.