Movement of water in compacted bentonite and its relation with swelling pressure

A testing procedure was proposed to study water movement in compacted bentonite and the development of swelling pressure (ps) when compacted bentonite specimens were wetted. In this procedure, a multi-ring mold was introduced for ps measurements, after which the specimen was sliced for X-ray diffraction to find movement of water in the interlayer space of montmorillonite. Results revealed a relation between four phases of ps development and evolution of four states of interlayer water molecule arrangement of montmorillonite (L): when ps reached its first peak in phase I, L moved from 1 row water arrangement (1w) to at least 2w; when ps decreased and re-increased in phases II or III, L moved from 2w to at least 3w; and when ps reached a steady state in phase IV, L = 3w. The w distribution in the compacted bentonite was also measured as water absorption time increased. Based on those results, the global water movement was estimated in terms of diffusivity (D) following a method employing Boltzmann transform. Results of comparisons implied that D calculated using this method matched experimental data well and the method was rather easily handled.

Crystalline Swelling Process of Mg-Exchanged Montmorillonite: Effect of External Environmental Solicitation

This work reports characterization of the possible effects that might distress the hydration properties of Mg-exchanged low-charge montmorillonite (SWy-2) when it undergoes external environmental solicitation. This perturbation was created by an alteration of relative humidity rates (i.e., RH%) over two hydration-dehydration cycles with different sequence orientations. Structural characterization is mainly based on the X-ray diffraction (XRD) profile-modeling approach achieved by comparing the “in situ” obtained experimental 00l reflections with other ones calculated from theoretical models. This method allows assessing the evolution of the interlayer water retention mechanism and the progress of diverse hydration state’s contributions versus external strain. Obtained results prove that the hydration behavior of the studied materials is strongly dependent on the RH sequence orientation which varied over cycles. The interlayer organization of Mg-exchanged montmorillonite (i.e., SWy-2-Mg) is characterized by a heterogeneous hydration behavior, which is systematically observed at different stages of both cycles. By comparing the interlayer water process evolution of Mg-exchanged montmorillonite with the observed SWy-2-Ni sample hydration behaviors, a same hysteresis thickness characterized by obvious fluctuations of interlayer water molecule abundances is observed. Nevertheless, in the case of Hg and Ba-saturated montmorillonite, the retention water process versus the applied cycles was steadier comparing with Mg ions.

Crystal chemistry of zinc incorporation in strunzite-group minerals containing zeolitic water

A comparative study is presented of the chemistry and crystallography of zinc-bearing strunzites from Hagendorf Süd, Bavaria, Germany and the Sitio do Castelo mine, Folgosinho, Portugal. Electron microprobe analyses of samples from the two localities show quite different cation substitutions. The Hagendorf Süd mineral is a Zn-bearing ferristrunzite, with compositional zoning due to Zn2+ replacing predominantly Fe3+ as well as minor Mn2+, whereas the Portugese mineral is a Zn-bearing strunzite, in which Zn2+ replaces Mn2+, with minor replacement of Fe3+ by Mn3+. Zincostrunzite, with dominant Zn in the interlayer octahedrally coordinated site, is a new strunzite-group mineral that has been characterized at both locations. Analysis of single-crystal synchrotron data for zinc-bearing ferristrunzite and zincostrunzite crystals from Hagendorf Süd show that the structures of both minerals contain zeolitic water in the interlayer region. The formula for strunzite-group minerals containing the zeolitic water is MFe23+(PO4)2(OH)2·6.5H2O, M=Fe, Mn, Zn. This formulation agrees with that found for zincostrunzite from the Sitio do Castelo mine, but differs from that reported previously for strunzite, MFe2+(PO4)2(OH)2·6H2O, which has no interlayer water. Interestingly, the zincostrunzites from the two localities differ in the location of the interlayer water molecule, with a corresponding difference in the H bonding.

Structural characterization of the clay mineral illite-1M

This work reports the structural characterization of illite-1M from northern Hungary, with the first attempt to refine the structure model and locate the interlayer water molecule. Structural characterization was accomplished using state-of-the-art analytical methods available for clays. The results illustrate the status of techniques for clay structure determination, as well as providing a structural model for illite. The chemical formula for the illite-1M under investigation can be written as K0.78Ca0.02Na0.02(Mg0.34Al1.69FeIII0.02)[Si3.35Al0.65]O10(OH)2·nH2O. Structure simulations withWILDFIREyielded a model with 30% ofcis-vacant layers and an expandability percentage of 10%. The value of the percentage of expandability was confirmed withNEWMOD, with which the best simulation was obtained with 90% of di-octahedral mica with K (80% site population) in the interlayer region and 10% of expandable layers. The best structure simulation obtained withDIFFaXwas also obtained with a population of K atoms of 80%, six cells alongc(in agreement with the results of a transmission electron microscopy study) and an average dimension of the particles in theabplane of 300 nm. Besides the determination of the basic structure unit (the results are consistent with those obtained with the local information provided by a fit of the pair distribution function data) and the model of disorder, refinement withDIFFaX+allowed the calculation of a possible position for the interlayer water molecule. Although physically sound, both the observed tetrahedral layer corrugation and the location of the water molecule need further experimental evidence, because the final fit of the observed pattern is still imperfect. The reasons for this misfit are discussed.