The present study investigated the anisotropy in the orientation of particles in synthetic swelling clay media prepared from the sedimentation of particle-sized fractions of vermiculite. The different size fractions (<0.1, 0.1–0.2, 1–2, and 10–20 μm) were chosen because they represent the wide range of particle sizes of swelling clay minerals encountered in natural environments. Small-angle neutron scattering (SANS) and neutron diffraction measurements allowed the characteristic scattering/diffraction features to be derived and the quantitative information about the particle orientation distributions along two directions with respect to the sedimentation plane to be extracted. The results obtained confirmed that the increase in particle size was associated with the development of a random orientation for the particles, whereas the hydration state had a negligible impact on the organization of the porous media. For finer vermiculite particles, the rocking curves demonstrated an anisotropy of the systems that is similar to those reported previously on natural montmorillonite minerals. This result suggests that the location of the layer charge has little or no impact on the anisotropy features of particle orientation. For the coarsest fraction (10–20 μm), quantitative information about the particle orientation revealed that the relative proportion of the isotropic contribution represents up to 85% of the material. The anisotropy in the 2D SANS patterns revealed a pore-network anisotropy that was consistent with the particle size.

Creating an environmentally friendly precursor to form a kaolinite intercalation compound is important for promoting the applications of nanohybrid kaolinite in electrochemical sensors, low- or zero-toxicity drug carriers, and clay-polymer nanocompounds. In the present study, a stable hydrated kaolinite pre-cursor with d001= 0.84 nm was prepared successfully by heating the transition phase, the as-prepared kaolinite-hydrazine intercalate, at temperatures between 40 and 70ºC. The structure of the hydrated kaolinite was characterized by X-ray diffraction and infrared spectroscopy. The morphology was examined using scanning electron microscopy. The results showed that the hydrated hydrazine of the transition phase was easy to decompose to hydrazines and water molecules in the interlayer at 40-70ºC. Hydrazine molecules de-intercalated gradually, and water molecules remained in the ditrigonal holes of the silicate layer with sufficient stability, finally forming the stable 0.84 nm hydrated kaolinite in the system with a success rate of 80–90%. The 0.84 nm hydrated kaolinite may become an excellent precursor for the preparation of other kaolinite intercalates. A degree of intercalation of ~100% was obtained for the kaolinite-ethylene glycol intercalate, and a degree of intercalation of ~80% was obtained for the kaolinite-glycine intercalate from the 0.84 nm hydrated kaolinite precursor.

Syntheses of Fe-, Co-, and Ni-containing Mg-Al-layered double hydroxides (LDHs) are described here because Fe, Co, and Ni represent the major constituents in steel containers used for storing spent nuclear fuel. Much evidence exists for the formation of LDHs during the corrosion of such containers under repository-relevant conditions. Because of their anion-exchange properties, LDHs can be considered as materials with the potential to retain and immobilize anionic radionuclides. Evaluation of the thermodynamic properties of LDHs is essential for reliable prediction of their behavior (solubility, anion exchange properties) in geochemical environments. The impact on the thermodynamic properties of the isostructural incorporation of divalent cations into the LDH was the main focus of the present study.

Mg-Al-Cl-LDH and the Fe-, Co-, and Ni-doped LDHs were synthesized by the co-precipitation method and then characterized (using powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), and thermogravimetric analyses (TGA)).

The PXRD and EXAFS analyses indicated that all synthesized samples were pure LDHs where Co, Ni, and Fe were incorporated isostructurally. The EXAFS and XANES results demonstrated that Ni and Co were incorporated as divalent cations and Fe as a trivalent cation. Thermodynamic calculations were performed assuming an equilibrium state between aqueous solutions and corresponding precipitates after synthesis. The first estimates of the molar Gibbs free energies for Fe-, Co-, and Ni-containing LDHs at 70ºC were provided. The calculated Gibbs free energy of the pure Mg-Al-LDH (-3629 kJ/mol) was slightly less than those for Fe-, Co-, and Ni-containing compositions (-3612±50, -3604±50, -3593±50kJ/mol).

In situ thermal recovery methods such as cyclic steam stimulation (CSS) are required to extract highly viscous bitumen from the Clearwater Formation oil sands of Alberta, Canada. The injection of hot fluids during CSS has altered the mineralogy of the sands, resulting in the loss of some minerals (e.g. disseminated siderite, volcanic glass) and precipitation of others (e.g. zeolites and abundant hydroxy-interlayered smectite). The high temperatures and high water—rock ratios associated with CSS might also alter the oxygen and hydrogen isotopic compositions of pre-existing clay minerals even in the absence of mineralogical changes. The present study exploits this fact to track the movement of injected hot fluids during CSS. Berthierine, a common diagenetic clay mineral in the Clearwater sands, survived CSS but acquired substantially lower δ18O and δ2H values in cores located ≤ 10 m from the injection well. In contrast, the oxygen and hydrogen isotopic compositions of berthierine in cores located further from the injection well were generally unaffected, except at the depth of steam injection where horizontal fractures facilitate greater lateral penetration of hot fluids. Smectitic clays in near-injector cores also acquired lower δ18O values during CSS, but a systematic shift in δ2H values was not observed. While hydrogen-isotope exchange undoubtedly occurred, the particular combination of temperature and H isotopic composition of the injected fluid used during CSS appears to have yielded post-steam δ2H values that are indistinguishable from pre-steam values. Only samples from near-injector core G-OB3 that contain hydroxy-interlayered smectite have lower δ2H values as a result of CSS.

A compositional gap between sepiolite and palygorskite has long been accepted even though they have similar structures, but recent studies found that such a gap does not exist and that the compositional series is continuous between them. If this is true, intergrowths between these two minerals should exist. The purpose of the present study was to demonstrate the existence of sepiolite-palygorskite intergrowths in all possible proportions, in order to establish the compositional links between ideal sepiolite and ideal palygorskite and to define the compositional limits of these two minerals. Sepiolite and palygorskite have similar structures but different chemical compositions: sepiolite is the most trioctahedral and magnesic extreme, while palygorskite is dioctahedral with Al and Mg in its octahedral sheet. The existence of all intermediate compositions between these two pure extremes has led to the definition of the intermediate minerals, Al-sepiolite and Mg-palygorskite, which can have similar chemical composition. The structural relations between the different minerals of the palygorskite—sepiolite series were studied here by powder X-ray diffraction (XRD), and continuous variation in the chemical composition is explained by the existence of intergrowths of sepiolite and palygorskite polysomes forming a continuous polysomatic series. The existence of intergrowths by mixtures of polysomes in modulated structures can be considered in the same way that the mixed-layer minerals in layered structures are considered. The continuous polysomatic series of sepiolite-palygorskite can be expressed by the general formula: [Si12Mg8O30(OH)4(OH2)4]y∙[Si8O20(Mg2Fe2)x(Mg2Al2)(1-x)(OH)2(OH2)4](1-y)·nH2O, where sepiolite and palygorskite are the end-members. They and xvalues can be calculated using a ternary plot with the oxide contents of the main octahedral cations (Al2O3, Fe2O3, and MgO). The proposed model, which is based on the intergrowth of sepiolite and palygorskite polysomes, explains both the variability in the chemical composition and the compositional limit for the identification of these minerals by X-ray diffraction.