Saponite Clay Research Articles

Back-reacted saponite in Jurassic mudstones and limestones intruded by a Tertiary sill, Isle of Skye

AbstractThe Lòn Ostatoin stream section, Trotternish Peninsula, Isle of Skye, exposes a sequence of Middle Jurassic mudstones and limestones which have been locally metasomatized by a transgressive sill of Tertiary age. Limestones in the sequence, including some previously reported as bentonite, have been altered to an unusual assemblage of grossular garnet and saponite clay. The mudstones also contain large proportions of saponite together with pyroxene and zeolites. Saponite also occurs within the basalt intrusion. Grossular and pyroxene represent artifacts of relatively high-temperature assemblages that formed during an early phase of alteration. As the intrusion and adjacent altered country rocks cooled, lower-temperature fluids flowed through a late set of contraction (micro)fractures. Back-reacted saponite, analcime and clinoptilolite were formed, possibly as alteration products of the unstable higher-temperature minerals. The lower-temperature mineral assemblage eventually sealed the late fracture system.This paper highlights an important concept for the study of analogue sites used to investigate thermal effects on engineered liners or barrier host rocks for the landfill and radioactive-waste industries. This is that the original thermally altered mineral assemblage may be overprinted by later, lower-temperature back-reactions. A detailed understanding of both processes is necessary in order to construct a sensible model for the thermal and mineralogical evolution of the site.

Synthesis and characterization of saponite clays

A new procedure has been developed for a fast preparation of saponite clays under the non-hydrothermal synthesis conditions of 90 degrees Celsius and 1 atmosphere. Saponites were synthesised from a stoichiometric mixture containing Si/Al3+ gel, M2+-nitrate (M2+ = Mg, Zn, Ni, Co, or Cu), urea and water within a few hours. The synthesis products were characterised with XRD, IR, TEM, XRF, N2-physisorption, Al-EXAFS, and 27Al- and 29Si-MASNMR Incorporation of Mg, Zn, Co, Ni, or a combination of these cations in the octahedral sheet, as well as controlling the Si/Al ratio in the tetrahedral sheet in the range between 5.67 and 39.0 could easily be established. Pure Cu-saponite could not be synthesised due to the preferred formation of chrysocolla, but a combination of Mg2+ and Cu2+ resulted in saponite formation. The chemical composition strongly influences the textural properties of the saponites. It is possible to prepare saponite samples of a specific surface area and pore volume of 100 to 750 m2/g and 0.15 to 1.05 ml/g, respectively. The lateral size and the amount of stacking of the saponite platelets could be influenced by the composition, synthesis duration and amount of urea. The new synthesis procedure provides an easy way to prepare high quantities of saponites with far-reaching control on the texture as well as the composition.

Synthesis and characterization of saponite clays: Part 2. Thermal stability

Synthetic saponites prepared at atmospheric pressure and at 90°C within 20 hours with Mg2+, Zn2+, Ni2+, Cu2+, and/or Co2+ in the octahedral sheets have been thermally treated under reducing and non-reducing conditions with or without the presence of steam. The thermal stability of saponite in air is investigated at temperatures up to 900 degrees Celsius. The nature of the octahedral cation largely determines the thermal stability of the saponite, which increases in the order Zn2+, Co2+, Mg2+, to Ni2+ from 450 to 800 degrees Celsius. The stability against reduction of the octahedral cations increases in the order Cu2+, Ni2+, to Co2+ from 150 to 600 degrees Celsius. The recrystallization of saponite at high temperatures is usually topotactic resulting in the formation of either pyroxene or olivine types of minerals. The reduction of saponites depends also on the nature of the octahedral cation. Cu2+ containing saponites are most easily reduced, followed by Ni2+ containing saponites. The difficult reduction of Co-saponites is possibly related to the thermal breakdown of the saponite structure. Mg- and Zn-saponites do not show any reduction up to 800 degrees Celsius. Incorporation of Mg2+ in Co2+ or Ni2+ containing saponites enhances the resistance against reduction. A fully reduced Ni-saponite shows a high dispersion of small Ni particles (10 nm) throughout the sample, whereas a fully reduced NiMg-saponite consists of large Ni particles (up to 60 nm), clustered together. The influence of steam on Mg-saponite is small, though incorporation of Zn2+ corresponding to an Mg/Zn ratio of 2 into the octahedral sheets results in a decrease of the hydrothermal stability. The drop in the stability is evidenced by a decrease in crystallinity and in a movement of aluminium from sites within the saponite structure to non-framework positions

Catalytic activity of synthetic saponite clays: effects of tetrahedral and octahedral composition

This paper describes the catalytic characteristics of synthetic saponites with well-known chemical composition, thermal stability, and acidity in three catalytic reactions: (1) catalytic cracking of n-dodecane, (2) hydro-isomerisation of n-heptane, and (3) Friedel–Crafts alkylation of benzene. Saponites with Mg in the octahedral position were by far the best catalysts for the catalytic cracking of n-dodecane, which can be explained by the higher surface area of these saponites compared with saponites with other compositions. All saponites performed better in the hydro-isomerisation reaction of n-heptane and Friedel–Crafts alkylation compared with commercially available catalysts such as HZSM-5 and ASA. The shape selectivity in the Friedel–Crafts alkylation of benzene for p- and o-DIOPB was remarkably high for the synthetic saponites.

Synthesis and characterisation of boron and gallium substituted saponite clays below 100 °C at one atmosphere

This paper describes a simple procedure for the synthesis of saponites with isomorphous substitution of Si 4+ by B 3+ and Ga 3+ below 100 °C and at 1 atmosphere. The XRD pattern of the Ga- and B-substituted saponites are similar to Al-substituted saponites. The 71Ga MAS-NMR spectra of Ga 3+ containing Mg- and Zn-saponite show two broad peaks at approximately 25 and 180–195 ppm, attributed to Ga 6 and Ga 4, respectively. the dimensions of Mg-saponite particles are considerably smaller than those of Zn-saponites. The lateral dimensions of the platelets of B 3+ containing Mg-saponites range between 40 and 100 nm, exhibiting hardly any stacking after 20 h of synthesis, while the platelets of the Zn-saponites are 200–350 nm in length with some degree of stacking. B 3+ containing Mg-saponite exhibits a broad double signal at 12.6 and 9.0 ppm of a low intensity, together with a sharp peak at −0.8 ppm, presumably corresponding to BO 3 and BO 4, respectively. 29Si MAS-NMR on the B 3+ containing saponites reveals two signals at approximately −85 due to Q 2 Si(OB) and −96 ppm corresponding to Q 3 Si(OB).

Infrared reflection absorption spectroscopy study of smectite clay monolayers

Infrared reflection absorption spectroscopy (IRRAS), also called infrared external reflection spectroscopy, is used for studying ultrathin hybrid clay films prepared by the Langmuir–Blodgett (LB) method. Infrared spectra of the hybrid films have been obtained at the air–water and air–solid (gold) interface. The presence of a smectite monolayer is observed when cationic surfactants are spread over the surface of a dilute aqueous smectite clay suspension. The in-plane ν(Si–O) band of saponite is observed in IRRAS spectra of saponite clay monolayers at the air–water interface. In contrast, the out-of-plane ν(Si–O) band at 1063 cm −1 is the dominant band in the p-polarized IRRAS spectra of a saponite monolayer deposited on a gold surface. These data correspond to the first-reported infrared spectra of clay minerals showing the enhancement of the out-of-plane vibrational modes and the nearly complete suppression of the in-plane vibrational modes. The results provide direct spectroscopic evidence confirming the orientation of the smectite particles parallel to the substrate.

マグネタイト粒子の析出によるサポナイトの複合化と構造評価

Saponite clays with fine magnetite particles were synthesized by adding solution containing Fe2+ and Fe3+ ions and 10N-NaOH to 1wt%-clay suspension in order to expand the application of clay as an absorbent. The products were analyzed by X-ray powder diffraction (XRD) and thermal analysis. Their microstructure was observed by transmission electron microscopy (TEM). The properties of absorption were evaluated by nitrogen gas and by methylene blue adsorption measurement. The results of XRD showed that products indicated only two phases, clay and magnetite crystal structure, and saponite with fine magnetite particles. Furthermore, from the results of methylene blue adsorption measurement, the usage of saponite clays with fine magnetite particles could result in the removal of methylene blue as an absorbent.

Induction of Circular Dichroism by Coadsorption of Chiral and Achiral Metal Complexes on a Colloidal Clay

Two kinds of metal complexes, an achiral metal complex, [Fe(terpy)]2+ (terpy = 2,2‘,2‘ ‘-terpyridyl), and a chiral metal complex, Δ-[Ni(phen)3]2+ (phen = 1,10-phenanthroline), were coadsorbed by colloidally dispersed sodium saponite clay. Interaction between these molecules on a clay surface was investigated by electric dichroism and circular dichroism measurements. The molecular orientation of an adsorbed [Fe(terpy)]2+ ion was determined in the absence or presence of Δ-[Ni(phen)3]2+ by electric dichroism measurements. The angle of the C2 axis of [Fe(terpy)]2+ with respect to a clay surface changed from 35.4° to 44.4° when the complex was coadsorbed with Δ-[Ni(phen)3]2+. The circular dichroism spectrum of a clay dispersion containing [Fe(terpy)]Cl2 and Δ-[Ni(phen)3]Cl2 was measured in the wavelength region of 350−600 nm. Δ-[Ni(phen)3]2+ had no electronic absorption in this region. Circular dichroism due to adsorbed [Fe(terpy)]2+ appeared when Δ-[Ni(phen)3]Cl2 was added to the ratio of [Fe(terpy)]Cl2/Δ-[Ni...

Aluminated Derivatives of Porous Clay Heterostructures (PCH) Assembled from Synthetic Saponite Clay: Properties as Supermicroporous to Small Mesoporous Acid Catalysts

Mesostructured aluminosilicate intercalates belonging to the new class of solid acids known as porous clay heterostructures (PCH) have been prepared by the postsynthesis grafting of aluminum into the mesostructured intragallery silica framework of a PCH precursor derived from a synthetic saponite clay. Elemental analyses, powder X-ray diffraction, N2 adsorption, and 27Al MAS NMR spectroscopy were used to characterize the reaction products, which we designate Al−SAP/PCH. Depending on the choice of aluminum reagent (AlCl3 or NaAlO2), the Al−SAP/PCH derivatives exhibited basal spacings of 32−34.8 A, BET surface areas of 623−906 m2/g, pore volumes of 0.32−0.45 cm3/g, and pore sizes in the large micropore to small mesopore range (14−25 A). The aluminum content was strongly correlated with the Si/Al stoichiometry of the postsynthesis reaction mixture. Nearly all of the grafted aluminum was incorporated into tetrahedral sites in the intragallery silica framework. In comparison to the initial silica-intercalated ...

Microscopic Structure and Microscopic Environment of a Polyfluorinated Surfactant/Clay Hybrid Compound: Photochemical Studies of Rose Bengal

The microenvironments of a series ofpolyfluorinated surfactants [C n F 2 n + 1 CONH(CH 2 ) 2 N + (CH3) 2 C 1 6 H 3 3 Br - ; designated as CnF-S, where n = 1-3]/clay (saponite) hybrid compounds dispersed in water-saturated benzenewere investigated based on the photochemical behavior of Rose Bengal (RB) as a probe molecule. A small-angle X-ray scattering study showed that the interlayer distance (clearance space) of the C3F-S/clay hybrid compounds was expanded up to 3.8 nm by the dispersion in water-saturated benzene from the original distance of 3.0 nm for the dried hybrid compound, indicating expansion of the hybrid compound upon swelling with the solvent benzene. The RB molecules are proposed to form ion-association complexes with the CnF-S surfactant, most likely existing in the vicinity of the ammonium group of the surfactant intercalated in the cation-exchangeable clay saponite. The absorption and fluorescence maxima of RB intercalated in the hybrid compounds were significantly red-shifted from those in aqueous solution. The hybrid compounds provide an environment with polarity between that of ethyl acetate and 1-butanol. The microscopic polarity of the hybrid compounds depends on the fluorocarbon chain length (n) of the surfactant, and the polarities increase with increasing fluorocarbon chain length. On the basis of the observed photochemical behavior of RB, including the relative decomposition rates, excited triplet lifetimes, and relative excited triplet quantum yields, the microscopic concentration of water in the hybrid layer was estimated to decrease in the order C3F-S > C2F-S > C1F-S. These differences are discussed in relation to differences in the microscopic orientational structure of the polyfluorinated surfactant within the clay layer.

27Al MQ-MAS NMR as a Tool for Structure Determination in Nanocomposite Materials: The Nature of Al Pillars in “Al13−heidi” Pillared Clays

27Al 3QMAS 2D NMR was used to study the molecular-level organization of a clay pillared with the “Al13(heidi)63+” polycation, whose unusual structure is stabilized by hydroxyethyliminodiacetate (heidi) ligands. The quadrupolar line shape and the isotropic chemical shifts were first unambiguously determined on a solid salt of the polycation. This compound was then used to identify the fingerprint of the Al13(heidi)x3+ polycation in a sample of saponite clay that had been intercalated with a solution containing Al(III) and heidi ligands, showing that the basic structure of the Al polymer had been preserved upon intercalation. A more detailed analysis of 3QMAS 2D NMR line shapes indicated, however, that a selective partial hydrolysis reaction had occurred, most probably leading to Al13(heidi)33+ polycations (loss of three heidi ligands). Thus, 3QMAS NMR allowed to choose one structural model for these nanocomposites from the several compatible with previously published characterizations.

Biogenic Saponite From an Active Submarine Hot Spring, Iceland

AbstractA study of the mineralogy, chemical composition and structure of poorly-crystalline saponite precipitated from a submarine hot spring in Eyjafjordur, northern Iceland is reported. Special emphasis was placed on the microstructures of the minerals and a possible connection with biological activity during their precipitation. The microstructures of the minerals were found to be very similar to specific clay minerals precipitated from geothermal vents in oceanic rift zones. The composition of the minerals was, however, found to be similar to magnesium silicate scales formed in geothermal installations in Iceland where geothermal waters were mixed with cold fresh waters. High contents of organic substances were found in the clay mineral samples as compared to geothermal precipitates from other localities. Microstructural features of the layer silicates in one of the samples suggest that a gelatinous substance was a precursor of the saponite clay. The organic matter content appears to be greater when the precipitates are more crystalline.

Atacamite Inclusions in Rock-Forming Feldspars and Copper-Bearing Smectites from the Radomiro Tomic Mine, Chile: Copper-Insoluble Mineral Occurrences

Recovery of copper from the Radomiro Tomic deposit in Chile employs innovative large-scale hydrometallurgical extraction methods, with sulfuric acid used for heap leaching. Here, we report on improvements in understanding mineral components of copper oxide ores, which are insoluble in acid leach solutions, in order to advance leaching technology. Using optical, electron microprobe, X-ray diffraction, energy dispersive spectroscopy, and least squares inversion methods, two different occluded mineral occurrences were discovered in oxide ores, which present two distinct metallurgical challenges for heap leaching but offer important new opportunities in process mineralogy. First, in a high chloride to sulfate ratio, feldspar-stable portion of the orebody at Radomiro Tomic, disseminated atacamite (Cu4Cl2(OH)6) inclusions, 1 to 8 μ m in diameter, occur in microfractured feldspars and biotites. These account for the acid-insoluble fraction, often as high as 30 percent of the total contained copper. About 70 percent of the total copper occurs generally as atacamite in cracks, which upon crushing is exposed along surfaces of the rock fragments and is hence soluble. In contrast, in more intensely hydrothermally altered, feldspar destructive, weak argillic alteration zones, insoluble copper exists more probably within the crystal structure of well-crystallized saponitic smectite clays in nonexchangeable, octahedral crystallographic sites. The two different forms of applied acid-insoluble components are products of contrasting microchemical environments, one in a reactive potassic alteration gangue and the second in a nonreactive gangue. In both cases, however, the nature of hydrothermal alteration, though pervasive, was relatively weak and left intact rock mineral buffers capable of neutralizing acidic and reducing fluids. Hence, the insoluble components with respect to the applied sulfuric acid reflect strong wall-rock mineral assemblage control on the behavior of copper on all scales: the macrofield zonal scale, the microscale of individual crystals in cracks, and the atomic scale of octahedral sites in the clay structure. The metallurgical implications of these atacamite microinclusions in rock-forming minerals and structurally bound copper in smectites are different. In the former case, exposing ore inclusions on fragment surfaces would require extremely costly grinding to a grain size well below 400 mesh. Secondly, chemical extraction of microinclusion copper from feldspar host phases would entail high acid consumption, as hydrolysis of feldspars by chemical reaction with applied acid would occur causing neutralization. In the case of Cu smectites, since the copper occurs in structurally bound, nonexchangeable sites, processes to remove the copper via ion exchange or acidic leach cannot work. Alternatives to ion exchange could involve destroying the smectite host mineral, perhaps by its conversion to kaolinite that may only incorporate copper or other divalent cations in negligible amounts.

Acidic Porous Clay Heterostructures (PCH): Intragallery Assembly of Mesoporous Silica in Synthetic Saponite Clays

Mesostructured intercalates belonging to the class of solid acids known as porous clay heterostructures (PCH) have been prepared through the surfactant-directed assembly of mesoporous silica within the galleries of synthetic saponite clays with targeted layer charge densities in the range x = 1.2−1.7 e- units per Q+x[Mg6](Si8-xAlx)O20(OH)4 unit cell. The removal of the intragallery mixture of neutral alkylamine and quaternary ammonium ion surfactant (Q+) by calcination afforded PCH intercalates with basal spacings of 33−35 A, BET specific surface areas of 800−920 m2 g-1, and pore volumes of 0.38−0.44 cm3 g-1. The framework pore sizes were in the supermicropore to small mesopore region ∼15−23 A. Temperature-programmed desorption of chemisorbed cyclohexylamine (CHA) indicated the presence of both weak and strong acid sites, corresponding to desorption temperatures near 220 and 410 °C, respectively. The total acidity (0.64−0.77 mmol CHA g-1) increased with the saponite layer charge density (x), indicating th...

Continuously Changing the Conformational Dependence of Saponite Hybrid Materials on the Intercalation Degree: Electric Linear Dichroism of Stilbazolium Derivatives Intercalated in Saponite Clay

Abstract The molecular alignmet of 2- and 4-[4-(dimethylamino)styryl]-1-ethylpyridinium cations (2- and 4-DASEP, respectively) adsorbed on saponite clay and suspended in N,N-dimethylformamide (DMF) has been investigated by the electric linear dichroism (ELD) method. An ELD analysis of the saponite clay complex involving 4-DASEP molecules in DMF indicated that although the tilt angle of the 4-DASEP molecular plane increased considerably from 14.1 to 32.1°, the roll angle remained constant at ca. 31°, with a coverage of 10 to 100% of 4-DASEP molecular in saponite. In contrast, the tilt and roll angles of the corresponding positional isomer, 2-DASEP, on the clay surfaces slightly increased with the same coverage degrees. The change in tilt and roll angles in the 2- and 4-DASEP molecules may be significantly influenced by the structural variation of the guest molecules, especially the steric hindrance around the pyridinium N+ atoms. The conformational structure of the adsorbed stilbazolium cations in saponite is discussed based on these results.

Field-cycling NMR relaxometry of water in synthetic saponites: Lévy walks on finite planar surfaces

Aqueous suspensions of synthetic saponite clays have been studied using field-cycling NMR relaxometry. The saponite platelets form planar surfaces on which water molecules are adsorbed. As the strong-adsorption limit applies, “bulk mediated surface diffusion” as originally suggested by Bychuk and O’Shaughnessy is expected to occur. That is, within the so-called retention time, adsorbate molecules tend to perform Lévy walks along the surfaces. A corresponding formalism (the “pancake model”) is derived and compared with the experimental data. The low-frequency spin-lattice relaxation dispersion can perfectly be described on this basis. The platelet diameter can be estimated from the peculiar adsorbate dynamics on the surfaces in accordance with literature data.

Synthesis and spectroscopy of clay intercalated Cu(II) bio-monomer complexes: coordination of Cu(II) with purines and nucleotides

The spectroscopic properties of Cu(bio-monomer)nm+ complexes [BM=bio-monomer (purine, adenine, guanine, hypoxanthine, 5′-ADP and 5′-GMP)] in saponite clays have been investigated by diffuse reflectance spectroscopy (DRS) in the UV-Vis-NIR region and electron paramagnetic resonance (EPR) at X-band. Mono- and/or bis complexes of Cu(purine), Cu(adenine), Cu(5′-ADP) and Cu(5′-GMP) have been intercalated between the layers of saponite by a simple cation exchange procedure from aqueous solutions of pre-formed Cu(BM)nm+ complexes. Successful immobilisation was obtained with a BM:Cu2+ ratio of 5, but the exact coordination geometry of the intercalated complexes was determined by the overall Cu-loading, the pH of the initial exchange solution and the type of BM. Mono Cu(adenine) and Cu(purine) complexes with a NNOO coordination dominate at low Cu-loadings, or at an exchange solution pH between 3 and 4, whereas bis Cu(adenine)22+ and Cu(purine)22+ complexes with a NNNN coordination are exclusively present at higher Cu-loadingswithanexchangesolutionpHbetween5and8.Ontheotherhand, clay-intercalated Cu(5′-ADP)+ and Cu(5′-GMP)+ are always present as mono-complexes, most probably in a NOOO coordination.

Contribution of shape resonance and Pt–H EXAFS in the Pt L2,3 X-ray absorption edges of supported Pt particles: Application and consequences for catalyst characterization

The electronic and geometric effects induced by hydrogen chemisorption on small platinum particles supported on high surface-area saponite clay and zeolite LTL were studied by near edge X-ray absorption fine structure (XAFS) spectroscopy. A new subtraction procedure was developed to separate the electronic from geometric effects. A significant Pt–H extended X-ray absorption fine structure (EXAFS) scattering (structural effect) was found for energy values between 0 and 20 eV. In addition, the Pt–H antibonding state (electronic effect) was found to produce a shape-resonance and was isolated from the near edge of the L3 X-ray absorption spectrum. Moreover, for Pt/LTL the shape and energy of the shape-resonance was found to strongly depend on the acidity/alkalinity of the support material, implying a direct influence of the support on the electronic properties of the platinum particles. The results of the study of the resonance state and the Pt–H EXAFS scattering demonstrate the potential of these techniques for characterization of hydrogen chemisorption, metal-promoter, and metal-support effects in catalysis research.

Kinetic approach to the mineral reaction processes during hydrothermal treatment of a saponitic clay

AbstractIn the course of hydrothermal experiments with a saponitic clay, evidence for the dissolution of the accessory sepiolite and the formation of smectite has been detected above 120°C Hydrothermal reactions with a clay to water ratio of 1:3 were performed at temperatures of 60, 90, 120, 175 and 200°C with time intervals of one month to one year.The BET surface area and cation exchange capacity (CEC) are correlated with the sepiolite and the smectite content determined from XRD data. These relations have been used to recalculate the time dependence of the mineral contents in the time/temperature conditions of the experiments. The Ea values obtained for sepiolite dissolution (7-18 kcal/mol) or smectite formation (4.8-5 kcal/mol) indicate that sepiolite dissolution controls the rate of the process. Both results fit an apparent firstorder reaction and the system seems to evolve to a stable mineral composition in a short time period, ranging from one to 10 years as temperature decreases.

Al and Zr pillared acid-activated saponite clays: characterization and properties

An acid-activated saponite has been used in the preparation of Al and Zr pillared acid-activated clays. The properties of this new family of pillared clays (pillared acid-activated saponites, PAASs) have been compared to those of conventional pillared (non-activated) saponites (PILSs). It is found that the acid treated materials incorporate less Al or Zr than the parent saponite, with the most likely cause being the reduced cation exchange capacity of the matrix following acid-activation. Powder X-ray diffraction suggests that Al PAASs are thermally more stable than the corresponding Zr PAASs. The acidity of the pillared materials (as monitored by cyclohexylamine adsorption–desorption thermogravimetry studies) is related to the nature and to the amount of the metal oxides incorporated between the sheets of the host clays. Catalytic data for the Bronsted catalysed dehydration ofpentan-1-ol is reported.