Mechanism of saponite crystallization from a rapidly formed amorphous intermediate
Rogier BesselinkTomasz M. StawskiHelen M. FreemanJoern HoevelmannDominique J. ToblerLiane G. Benning
0
Citation
0
Reference
10
Related Paper
Abstract:
Although clays are crucial mineral phases in Earth's weathering engine, it is unclear how they form in surface environments under (near-)ambient pressures and temperature. Most synthesis routes, attempting to give insights into the plausible mechanisms, rely on hydrothermal conditions, yet many geological studies showed that clays may actually form at moderate temperatures (< 100 deg. C) in most terrestrial settings. Here, we present the mechanism of the low-temperature (25-95 deg. C) crystallization of a synthetic Mg-clay, saponite. We describe the pathway at the various sub-stages of the reaction, as we derived from high-energy X-ray diffraction, infrared spectroscopy and transmission electron microscopy data. Our results reveal that saponite crystallizes via a two stage process: 1) a rapid (several minutes) co-precipitation where ~20% of the available magnesium becomes incorporated into an aluminosilicate network followed by 2) a much slower crystallization mechanism (many hours to days) where the remaining magnesium becomes gradually incorporated into the growing saponite sheet structure.Keywords:
Saponite
The adsorption of two pharmaceuticals, carbamazepine and paracetamol, onto the expandable clay mineral saponite has been studied through the combination of kinetic experiments, X-ray diffraction, and theoretical modeling. Kinetic experiments indicate low adsorption for carbamazepine and paracetamol on expandable smectite clay. Accordingly, X-ray diffraction experiments show that neither compound enters smectite interlayer space. Molecular dynamics simulations were carried out to understand the interactions between the two pharmaceuticals and the saponite basal surface in the presence of Na+ cations. Calculations reveal that paracetamol almost does not coordinate solution cations, whereas a rather low coordination to cation is observed for carbamazepine. As a result, the adsorption onto the clay surface results mainly from van der Waals interactions for both pharmaceuticals. Carbamazepine does adsorb the surface via two configurations, one involving cation coordination, which corresponds to a rather stable adsorption compared to paracetamol. This is confirmed by structural analyses completed with desorption free energy profile.
Saponite
Powder Diffraction
Cite
Citations (18)
Talc
Saponite
Brucite
Cite
Citations (25)
A new successful short time synthesis route for the preparation of FSM is developed using the leached natural aluminosilicate saponite, in combination with a low concentration of cetyltrimethylammoniumbromide [C16H33N+(CH3)3Br- or CTMA] as surfactant. The leaching of the smectite increases with higher acid concentrations (5−10 M HCl) and temperature (25 °C and 100 °C). The leached saponite generated by these acid treatments allows the formation of mesoporous aluminosilicate hexagonal structures (FSM-16) with high porosity (max. 0.6 cm3/g), high specific surface area (max. 900 m2/g), thick pore wall, and uniform pore structure.
Saponite
Cite
Citations (29)
Kaolinite and dioctahedral and trioctahedral smectite were hydrothermally synthesized using silicate gels with variable Al/Fe/Mg ratios (0.9/0.05/0.05 to 0.05/0.05/0.9) at temperatures of 175 degrees , 200 degrees , and 225 degrees C and time periods of 192, 360, 720, and 1440 hrs. The solids were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis and thermogravimetry (DTA-TG), scanning electron microscopy coupled with an energy dispersive spectrometer (SEM-EDS), and transmission and analytical electron microscopy (TEM-AEM). Kaolinite and smectite were the only mineral phases found in the products. EDS and AEM analyses of individual smectite particles show that many of them have compositions intermediate between dioctahedral and trioctahedral smectite. Nevertheless, XRD and FTIR results show that the two structures are segregated from each other. We interpreted those particles of intermediate composition to be due to topotactic growth of dioctahedral smectite on trioctahedral smectite lamellae. Kaolinite and trioctahedral smectite seem to grow readily from the starting amorphous materials with compositions moderately similar to these minerals. In some of the experiments, kaolinite started to dissolve after approx 15 days, seemingly favoring the formation of dioctahedral smectite. Trioctahedral smectite formation seems to have been enhanced by the presence of brucite domains in the original gel. Dioctahedral smectite always coexisted with kaolinite (Al-rich gels) or trioctahedral smectite (intermediate Al/Mg gels), seemingly needing an appropriate substrate to nucleate (kaolinite or trioctahedral smectite in this study) and/or a specific gel composition to grow at a sufficient rate. The formation rates of the three phases were modeled assuming that kaolinite formed from the gel and that dioctahedral and trioctahedral smectite formation occurred through an intermediate phase.
Saponite
Differential thermal analysis
Thermogravimetry
Illite
Structural formula
Cite
Citations (31)
Saponite
Sepiolite
Nontronite
Brucite
Structural formula
Cite
Citations (45)
A qualitative chemical analysis of three reference clay minerals, Mikawa montmorillonite, synthetic saponite and Nabeyama illite, was performed using a recently developed TEM-EDS set-up built around a microcalorimeter device that has a very high energy resolution. The spectrum obtained by the microcalorimeter EDS showed the small peaks of minor elements present in these clay minerals. It was also used to detect the SKβ peak in saponite and the SiKβ' peak in montmorillonite and saponite whereas by conventional Si(Li) EDS, these peaks disappeared or overlapped. Microcalorimeter EDS with TEM provided us with valuable elemen- tal data of clay minerals in this study, and will considerably contribute to the progress of the study of clay minerals.
Saponite
Illite
Cite
Citations (0)
Hydrothermal experiments were conducted to explore the effects of changing chemistry, temperature, and pressure on the reaction of smectite, run I : I with pure water, to mixed-layer clay. At high temperatures trioctahedral smectites are more stable than dioctahedral smectites' For dioctahedral smectites, hydrothermal stabil ity is enhanced by saturation with interlayer cations of greater hydration energy than potassium, and by increased water pressute. Introduction Many of the unusual physical and chemical properties of the smectite group of clay minerals are related to the expandable interlayer region. These properties, which include swell ing, cation exchange capacity, catalytic activity, and thixotropy, are sometimes diminished or lost during hydrothermal treatment as the smectite reacts to form mixed-layer clay. It is of interest, therefore, from both a geologic and an industrial point of view, to determine the conditions under which smectites are least l ikely to react. Our experiments explore the effects of chemical composition, temperature, and pressure on the hydrothermal alteration of smectite to mixed-layer clay. Experimental techniques A direct comparison between the reactivity of dioctahedral and trioctahedral smectites was made by saturating each type of clay with various interlayer cations and then subjecting them to identical hydrothermal conditions. Trioctahedral starting materials included a natural saponite from Karolihof, Switzerland (<2 micron size fraction) saturated with K, Na, Ca, or Mg; u natural saponite from the Amargosa Valley, Nevada ((2 micron fraction); and gels of potassium and magnesium saponi te composi t ion, Mg.Sir..rAlo3aOr0(OH)rxilrr, where X+ is the exchangeable cation. Dioctahedral starting materials were the Wyoming bentonite ((2 micron fraction, Mol l e l a l . , 1975) saturated wi th K, Na, Ca, or Mg, and a gel of potassium montmor i l lon i te composi t ion, Alrsia 6?4.10 $Oro(OH)rKo.re. Gels were prepared by the method of Hami l ton and Henderson (1968). oo03-004x/78/0304-0401$02 00 401 Hydrothermal runs were prepared by introducing 30 mg of clay or gel and 30 pl of pure water into gold tubes (20 mm long, 2.5 mm I.D.) which were then welded shut. These charges were heated in large hotseal autoclave reaction vessels or in small cold-seal reaction vessels. The former generated maximum pressures of approximately 0.3 kbar, and the latter were maintained at 0.5 or 2 kbar by equil ibration with a large reservoir (see Eberl and Hower, 1976). All vessels were heated in resistance furnaces, and temperatures were controlled by on-off regulators attached to thermocouples located in wells near or in the base of the vessels. Run products were oriented on glass slides, glycolated, and X-rayed with a Norelco diffractometer, using Ni-fi l tered CuKa radiation. The expandabil ity of mixed-layer i l l i te/smectite was determined by comparison with the calculated patterns of Reynolds and Hower (1970). Experimental results The difference in reactivity between dioctahedral and trioctahedral smectite is clearly shown in Tables I and 2 and in F igures 1,2, and 3. At 400'C and autoclave pressure, the K-montmoril lonite gel (run I ) and the natural montmoril lonites saturated with K, Na, Ca, and Mg (runs 2-5) reacted extensively to lbrm regularly interstratif ied mixed-layer clay. The sraponites run under equivalent conditions did not react (runs l0-18). The effect of interlayer chemistry on the reaction of dioctahedral clays is also shown in Table l. Montmoril lonite with interlayer potassium (run 6) reacted at a lower temDerature than did mont402 EBERL ET AL.' REACTIVITY OF SMECTITE Table I Montmor i l loni te autoclave runs Run n o . Start ing mater i .a l Ternp. ( oc ) Time (days ) Run produc ts
Saponite
Bentonite
Structural formula
Cite
Citations (82)
Saponite
Cite
Citations (2)
Saponite
Bentonite
Illite
Expansive clay
Silicate minerals
Cite
Citations (22)
Saponite
Bentonite
Palygorskite
Distilled water
Cite
Citations (55)