Showing papers in "Clays and Clay Minerals in 1991"
TL;DR: In this article, the authors measured the adsorption of aromatic hydrocarbons from water by organo-clays and found that the planar surfaces of the compounds adsorb directly to the clay surface.
Abstract: The nature of the siloxane surface in smectites was investigated by measuring the adsorption of aromatic hydrocarbons from water by organo-clays. The organo-clays were prepared by replacing the hydrophilic, inorganic exchange cations of a series of smectites with the small, hydrophobic organic cation, trimethylphenylammonium (TMPA). Smectites with a range in charge densities were used that resulted in different TMPA contents in the organo-clays. Adsorption isotherms of benzene, alkylbenzenes, and naphthalene from water by the TMPA-smectites indicated that sorption was inversely related to TMPA content. The Langmuir form of the isotherms suggests that the aromatic compounds adsorb to the clay surface. Possible adsorptive sites in TMPA-smectites are limited to the TMPA cations and the siloxane oxygen surfaces. Because sorption increased as layer charge and TMPA content decreased, the organic compounds must adsorb to the siloxane surfaces. Calculations based on an adsorbed compound monolayer, which was estimated by fitting adsorption data to the Langmuir equation, and the N2 specific surface area of each TMPA-clay, indicate that the surface area occupied by each adsorbed molecule increases as the planar area of the molecule increases. This strongly indicates that the planar surfaces of the compounds adsorb directly to the clay surface. Apparently, the TMPA cations function to keep the smectite interlayers open. Interactions between the phenyl groups of TMPA cations on opposing interlayer clay surfaces may act to increase the size of the adsorptive regions. These results show that the siloxane surfaces of smectites can effectively adsorb aromatic hydrocarbons from water if the hydrophilic, inorganic exchange cations are replaced with small, hydrophobic organic cations. The strong adsorption of hydrophobic organic molecules from water demonstrates the hydrophobicity of the siloxane surfaces in smectites.
340 citations
TL;DR: In this paper, the authors measured the basal spacing of a set of smectites, with layer charges between 0.74 and 1.14 electrons per unit cell, with NaCl solutions having concentrations of 0.25 to 2.5 molal.
Abstract: The basal spacing of a set of smectites, with layer charges between 0.74 and 1.14 electrons per unit cell, have been measured while the smectites were in equilibrium with NaCl solutions having concentrations of 0.25 to 2.5 molal. Except for the most highly charged smectites, an expansion from ~15.5 to ~18.5 A occurred as the NaCl concentrations were reduced. This expansion (or “crystalline swelling”) corresponds to the transition from two to three sheets of water between the silicate layers. A random interstratification of 15.5 and 18.5 A structure units was present during the change and gave rise to broad diffraction peaks for the 001 reflections. A balance between cation hydration forces, interlamellar electrostatic forces, and van der Waals forces was apparently the basis of the relationship between surface charge and swelling. The results can be expressed in terms of the relative vapor pressures at which the transitions were half complete; these pressures increased with surface density of charge, and over the range of surface charge studied, the P/P0 values ranged from 0.943 to 0.974.
155 citations
TL;DR: Weathered perthite and mixed muscovite-kaolinite from a kaolinitic granite at Trial Hill in east Queensland and kaolinized sericitic alteration from a granite from the Ardlethan Tin Mine of New South Wales were examined by optical, scanning electron (SEM), and transmission electron microscopy (TEM) as discussed by the authors.
Abstract: Weathered perthite and mixed muscovite-kaolinite from a kaolinitic granite at Trial Hill in east Queensland and kaolinized sericitic alteration from a granite from the Ardlethan Tin Mine of New South Wales were examined by optical, scanning electron (SEM), and transmission electron microscopy (TEM) to determine the alteration process of muscovite to kaolinite and kaolinite to halloysite (7A). Muscovite was found intimately interleaved with kaolinite in a variety of proportions on a sub-micrometer scale. The contact was generally parallel to the (001) layers of both minerals, and the thickness of the contact layer alternated between 10 and 7 A over short distances. Where the kaolinite to muscovite contact was at an acute angle to the muscovite layers, a small angle existed between the layering of the two phases, consistent with a topotactic alteration of muscovite to kaolinite. One tetrahedral sheet in the muscovite appeared to have been removed over 50–100 A, converting a 10-A layer to a 7-A layer. The mica near the contact with kaolinite was easily damaged in the electron beam and showed Al loss during analytical transmission electron microscopy; thus, H3O+ probably substituted for K+ in this transitional phase.
121 citations
TL;DR: In the Wairakei geothermal field, mixed-layer clays were identified by X-ray diffraction analysis of glycolated and orientated sample fractions at less than 2 um and less than 0.2 um, respectively as mentioned in this paper.
Abstract: Mixed-layer clays of variable composition and structure occur in core samples from two drillholes (WK207 and WK210) drilled into the Te Mihi sector of the Wairakei geothermal field. These were identified by X-ray diffraction analysis of glycolated and orientated sample fractions at less than 2 um and less than 0.2 um. Low permeability lacustrine sediments encountered by drillhole WK207 contain a well-developed sequence of mixed-layered clays. The shallowest downhole appearance of mixed-layered illite/smectite occurs at 146 m depth where temperature is only 100 degrees C. Discrete illite is present only below 297 m (200 degrees C) in the finer size fraction (less than 0.2 um). Chlorite first appears downhole, in association with illite-smectite, at 177 m depth (110 degrees C). Drillhole WK210 encountered predominantly ignibrites and rhyolites, and fluid flow here is mainly in channel. Within these rocks, a sequence of interlayered clays is poorly developed. Discrete illite and chlorite are present in core from only 224 m (180 degrees C), but the measured temperatures where interlayer clays occur ranges from 140 to 209 degrees C. Differences in the identity of clay minerals present in the Wairakei reservoir, where conditions are otherwise the same, demonstrate the strong control that the type of fluid flow has on their formation. In poorly-permeable sediments, where diffuse fluid flow prevails, a clearly-defined sequence of mixed-layer clays occurs. These are absent where channel flow dominates, the discrete chlorite and illite deposit directly from solution.
117 citations
TL;DR: In this paper, a procedure for the determination of cation exchange capacity and the amounts of exchangeable cations adsorbed to montmorillonite is proposed, which consists of a single incubation of the clay in a suspension containing a low concentration of an organic dye of large binding affinity, followed by analysis of the displaced inorganic cations by inductively-coupled plasma emission spectrometry (ICPES).
Abstract: Ahstract--A procedure for the determination of cation exchange capacity (CEC) and the amounts of exchangeable cations adsorbed to montmorillonite is proposed. The method consists of a single incubation of the clay in a suspension containing a low concentration of an organic dye of large binding affinity, followed by analysis of the displaced inorganic cations by inductively-coupled plasma emission spectrometry (ICPES). The CEC is obtained by taking the largest sum of displaced exchangeable cations. Montmorillonite suspensions were incubated with methylene blue (MB) or crystal violet (CV) at dye concentrations below 4 mM, for one, three or fourteen days. For total dye concentrations up to the CEC, all the dye was adsorbed and equivalent amounts of exchangeable cations were released. Both dyes could adsorb to the clay in excess of the CEC. After one day of incubation in the presence of dye concentrations of about 50% in excess of the CEC, the total amounts of cations released were reduced to below the CEC. This reduction was interpreted as due to massive aggregation of the clay particles induced by the dye. With CV the total amounts of cations released after three or fourteen days of incubation increased and became equal to the CEC. The same CEC was found for Na-, Ca- and SWyl crude-montmorillonite, by employing either of the dyes.
112 citations
TL;DR: In this article, a nonionic surfactant of general formula C~z_~4H25_290(CH2CHzO)sH (commercial name, Tergitol 15S-5) was used during the synthesis of the aluminum hydroxide pillaring reagent.
Abstract: New pillared clay-based adsorbents have been prepared by incorporating a nonionic surfactant of general formula C~z_~4H25_290(CH2CHzO)sH (commercial name, Tergitol 15S-5), during the synthesis of the aluminum hydroxide pillaring reagent. Different loadings of surfactant have been examined. The presence of the surfactant enhanced the adsorption capacity of the clay toward 3-monochlorophenol from aqueous solution. On the basis of adsorption results for a series of clays with increasing surfactant loadings, the best adsorbent was obtained at a surfactant loading of 255 mg/g of clay. At this loading, the surfactant occupies the micropores, as well as the mesopores and the external surfaces of the pillared clay. Analysis of the adsorption isotherms for 3-monochlorophenol, 3,5-dichlorophenol, 3,4,5-trichlorophenol and pen- tachlorophenol at different pH shows that the most energetic adsorption sites are the surfactant-occupied micropores between pillars. Additional binding of chlorinated phenols occurs at surfactant sites on external surfaces and mesopores. Upon calcination at 500~ the clay is converted to a conventional alumina- pillared clay with a basal spacing near 16 A. This calcined product can be reused as an adsorbent for chlorinated phenols by readsorbing fresh surfactant. The recycled adsorbent exhibits performance prop- erties comparable to the original adsorbent. These results demonstrate the feasibility of utilizing a sur- factant-modified pillared clay as a recyclable adsorbent and combustion catalyst for environmental pol- lutants.
101 citations
99 citations
TL;DR: Large-pore La-Al-pillared montmorillonite has a basal spacing of about 26 A, surface areas of 300-500 m2/g, and pore volumes in the range 0.2-0.3 cm3/g as discussed by the authors.
Abstract: Large-pore La-Al-pillared montmorillonite was prepared by reacting montmorillonite with hydrothermally treated mixtures of aluminum chlorohydrate and lanthanum chloride. The large-pore La- Al-pillared montmorillonite is characterized by basal spacings of about 26 A, surface areas of 300-500 m2/g, and pore volumes in the range 0.2-0.3 cm3/g. Large-pore pillared montmorillonite products were obtained from solutions refluxed for >72 hr or treated in autoclaves at 120~176 for 12-96 hr. The most favorable pillaring solution for the production of large-pore La-Al-pillared montmorillonite had an OH/AI ratio of 2.5, a La:A1 ratio of 1:5, and was 2.5 M with respect to A1. The elemental composition of large pore La-Al-pillared montmorillonite is similar to that of a conventional Al-pillared montmoril- lonite that has a basal spacing of about 19 ~. The 26-Zk spacing is believed to be associated with the formation of large polymeric La-bearing Al-cations upon hydrothermal treatment of the solutions.
98 citations
TL;DR: In this paper, a thin stratigraphic zone within the contact aureole of the lampro- phyric Walsen dike record changes due to thermal effects that are not influenced by detrital differences.
Abstract: Pierre shale samples from a thin stratigraphic zone within the contact aureole of the lampro- phyric Walsen dike record changes due to thermal effects that are not influenced by detrital differences. Analyses of fixed-NH4, mineralogy, and Rock-Eval pyrolysis indicators of organic matter maturity provide new insights on the fixation process. Fixed-NH4 increases with the quantity of authigenic iUite formed from illite/smectite, but the maximum fixation per unit of illite formed occurs within the "oil window" where thermal breakdown of organic matter is rapid. Extrapolation of these results to the burial diagenetic regime supports the potential use of fixed-NH4 as an indicator of organic maturity and hydrocarbon migration pathways:
79 citations
TL;DR: In this paper, the authors used infrared spectroscopy and X-ray diffraction to characterize the properties of 3:1 and 1:1 Si:A1 solutions to pH 8 with Ca(OH)2 for 8-12 weeks.
Abstract: Solutions containing A1C13 and Si(OH)4 (concentrations <-1.5 mM with molar Si:A1 ratios of 1:2, l:l and 3:l) and FeC12 (0, 0.5 and 1.0 mM) were adjusted to pH 8 with Ca(OH)2, and incubated at 23~ and 890C without exclusion of air in the presence of CaCO3 for 8-12 weeks. The products were characterized by infrared spectroscopy and X-ray diffraction. Systems with 3:1 and 1:1 Si:A1 ratios without Fe gave hydrous feldspathoids at 23 ~ and 890C. Systems with 3:1 Si:A1 ratios containing Fe gave aluminous nontronites at 89~ and noncrystalline, nontronite-like products at 230C. Systems with 1:1 Si:AI ratios with added Fe gave Fe(III)-substituted hydrous feldspathoids at 23"C. At 89~ the system with 1:1 Si: A1 ratios and 0.5 mM Fe produced a "protohalloysite," while that with 1.0 mM Fe gave a poorly ordered nontronite-like layer silicate. In systems with 1:2 Si:AI ratios, the formation of"protoimogolite" at 230C was little affected by additions of Fe. At 89~ the "protoimogolite" decomposed to boehmite and poorly- ordered layer silicate phases. Inclusion of 1 mM MgC12 in the above systems had no effect on the products at 230C, but at 890C produced saponites and a mixed layer saponite-chlorite in the 3:1 Si:A1 systems, and saponite-like layer structures in the 1:1 and 1:2 Si:A1 systems.
70 citations
TL;DR: Aqueous gels of unaltered (oxidized) and chemically reduced ferruginous smectite (SWa-1 from the Source Clays Repository of The Clay Minerals Society) were characterized by transmission electron microscopy, electron diffraction, and energy-dispersive X-ray fluorescence to establish details regarding their texture, inter-layer and interparticle arrangements, and chemical composition as discussed by the authors.
Abstract: Aqueous gels of unaltered (oxidized) and chemically reduced ferruginous smectite (SWa-1 from the Source Clays Repository of The Clay Minerals Society) were characterized by transmission electron microscopy, electron diffraction, and energy-dispersive X-ray fluorescence to establish details regarding their texture, inter-layer and inter-particle arrangements, and chemical composition. Micrographs revealed that the reduction of structural Fe(III) to Fe(II) caused a consolidation of smectite particles from an extensive network of small crystals (1–6 layers thick) to distinct particles of limited size in the a-b direction and about 20–40 layers thick. The interlayer distances in the reduced sample appeared to be more uniform than in the oxidized sample, but both exhibited spacings of about 12.6 A. Chemical analysis showed no qualitative differences as a result of oxidation state. Electron diffraction patterns displayed marked differences. The pattern of the oxidized sample consisted of homogeneous rings, indicating that the stacking order in the a-b plane was turbostratic or disordered, whereas the reduced pattern exhibited much more order as evidenced by distinct spots amid low-intensity rings, suggesting that inter-layer attractive forces were stronger if Fe(II) was present in the clay crystal.
TL;DR: In this paper, the rate of Fe(II) oxidation at a constant rate of oxygen supply in the presence of citrate was measured at pH 6.0 at various citrate/Fe (II) molar ratios at 23.5~ in 0.01 M ferrous perch/orate system.
Abstract: The rate of Fe(II) oxidation at a constant rate of oxygen supply in the presence of citrate was measured at pH 6.0 at various citrate/Fe(II) molar ratios at 23.5~ in 0.01 M ferrous perch/orate system. The kinetics followed a first-order reaction with respect to Fe(II) concentration at constant pH (6.0) and aeration (5 ml/min). The rate constant decreased exponentially from 41.3 x 10 -4 to 7.6 x 10-"/min with an increase in the citrate/Fe(II) molar ratio from 0 to 0.1. The nature of the hydrolytic products formed after 120 min of oxidation was arrived at by X-ray powder diffraction (XRD), infrared spectrometry (IR), and transmission electron microscopic (TEM) analyses. In the absence of citrate, goethite (a-FeOOH) and poorly crystalline lepidocrocite (7-FeOOH) were the oxidation products formed at pH 6.0. The formation of lepidocrocite was promoted at the expense of goethite at citrate/Fe(II) molar ratios of 0.0005 to 0.005. The formation of lepidocrocite was especially pronounced at a citrate/Fe(II) molar ratio of 0.001, as observed from the width at half height (WHH) and the area of the 020 XRD peak of lepidocrocite. At a citrate/Fe(II) molar ratio of 0.01, however, the crystallization was perturbed resulting in the formation of noncrystalline Fe oxides, and no precipitate was observed at a citrate/Fe molar ratio of 0.1. The strong complexation of Fe(II) with citrate retarded the kinetics of Fe(II) oxidation and the formation and hydrolysis of Fe(III). The complexation, electrostatic, and steric effects of the coexisting citrate anions in solution apparently influenced the oxygen coordination and the way by which the double rows of edge-sharing Fe(O,OH)6 octahedra linked during crystallization, resulting in the formation of lepidocrocite.
TL;DR: In this paper, the extent of illite/smectite (I/S) reactions is linked with quantitative measurements of shale fabric in a suite of samples from a lower Frio Formation well.
Abstract: The extent of illite/smectite (I/S) reactions is linked with quantitative measurements of shale fabric in a suite of samples from a lower Frio Formation well. Greater illitization of the I/S clays is found in laminated shales that possess a larger pore surface area/pore volume (SA/V) of 3.21 x 106 cm-~ than the adjacent massive shale lithofacies with a SA/V of 1.97 x 106 cm -~. Mean pore diameter in both shale lithologies is 0.0145 micrometers, though in the laminated shale distributions are skewed towards more smaller-sized pores. While no direct permeability measurements were made, estimates of perme- ability that are based on simple physical models using SA/V suggest that lower permeabilities are associated with laminated shales. The trend of greater illitization at higher SA/V values is contrary to expectations that reaction extent is enhanced by greater permeabilities, such as created by silt laminations in shale. The limitations of estimated permeabilities emphasize that porosimetry measurements of shale fabric are useful for estimating the access of material to all reaction sites, and do not just describe the effect of a few large pores that dominate permeability. Greater reaction extent in the laminated shales is associated with the accessibility of fluids to more pore space than in the massive shales.
TL;DR: In this article, the authors divided the drill core at Searles Lake into three diagenetic zones on the basis of clay-mineral reactions and inferred the pH of the lake and pore water of the lower and upper zones.
Abstract: Core KM-3 at Searles Lake, California, comprises 693.4 m of lacustrine sediments deposited over the past 3.2 m.y. The lake water evolved from moderately saline, slightly alkaline, and dominated by Na, Ca, C1, SO4, and HCO3 + CO3 to a highly alkaline brine dominated by Na and CO3 ions. Sediments are chiefly muds and evaporites. Montmorillonite and illite are the principal detrital clay minerals supplied to Searles Lake at present and probably during the late Pliocene and Pleistocene. The drill core is divided into three diagenetic zones on the basis of clay-mineral reactions. The upper zone (0-291.1 m) contains authigenic Fe-illite, Mg-smectite, K-feldspar, and analcime, which average 60-70% of the <2-tim silicate fraction of mud samples. The principal silicate reactants are detrital montmorillonite and kaolinite, which have been largely consumed. The middle zone (291.1-541.6 m) also contains authigenic Fe-illite, Mg-smectite, K-feldspar, and analcime, but they form only 20 to 30% of the < 2-~m silicate fraction, and considerable detrital montmorillonite and kaolinite remain unaltered. In muds of the lower zone (541.6-693.4 m), a small amount of clinoptilolite is the only authigenic silicate mineral identified, although authigenie montmoriUonite probably coexists here as well. Vitric ash is the silicate reactant, and detrital clay minerals apparently remain unaltered in the lower zone. Diagenetic zoning reflects the pore-water chemistry, in which pH may have been the most important parameter. Sediments of the upper zone were deposited in highly alkaline lakes of variable salinity, and sinking brines with a pH of 9.0-10.0 have saturated all sediments. Sediments of the middle zone were deposited in lakes of moderate to high salinity. The pH was overall lower than in the upper zone, although it probably exceeded 9.0, at least locally, during silicate diagenesis. Moderate salinity and a slightly alkaline pH (-7.5-8.0) are inferred for both the lake and pore water of the lower zone. Oxygen-isotope values of authigenic Fe-illite, Mg-smectite, and K-feldspar, and phillipsite in the upper diagenetic zone reflect a high degree of evaporative concentration and presumably of salinity. Equilibrium water values calculated for 22~ from the oxygen-isotopic composition of authigenic phyllosilicates range from -3.5 to + 1.9~ averaging -1.207o0 (SMOW). Higher salinities are suggested for K-feldspar, for which water values range from + 1.8 to +4.807~, averaging +3.4%o. The water value for phillipsite is +0.307o0. By comparison, rainfall at Searles Lake has an average fi~80 value of about -9.80700, and a brine sample has a value of +4.007o0. Mud samples of the middle and upper diagenetic zones tend to be rich in Fe-illite or Mg-smectite, but not in both, indicating that the two minerals are favored to some extent by different environments. Fe- illite seems to be generally favored by oxidizing conditions and probably by a playa environment, and Mg-smectite seems to be favored by reducing conditions and an open-water environment. One strati- graphic unit of the upper zone does not fit this pattern and contains abundant Fe-illite in sediments of a deep perennial hake.
TL;DR: In this article, the authors used elemental sulfur as an active phase supported on sepiolite and palygorskite fibrous clays to eliminate mercury vapor from gas streams, using condensation, absorption, and adsorption.
Abstract: To eliminate mercury vapor from gas streams, three major methods are used: condensation, absorption, and adsorption. This work deals with adsorption, using elemental sulfur as an active phase supported on sepiolite and palygorskite fibrous clays. Sulfur loads of 5–30% were deposited by catalytic oxidation of hydrogen sulfide at temperatures of 6 nm for the sulfurized silicates. Also, the allotropic state of the deposited sulfur, where Sπ (octo-catena) is better than Sλ (octo-cycle), may also be a contributing factor.
TL;DR: The effect of electrolyte concentration, exchangeable sodium percentage (ESP), sodium ad- sorption ratio (SAR), and pH on the flocculation-dispersion behavior of 50/50 mixtures of reference illite with reference kaolinite or reference montmorillonite was investigated.
Abstract: The effect of electrolyte concentration, exchangeable sodium percentage (ESP), sodium ad- sorption ratio (SAR), and pH on the flocculation-dispersion behavior of 50/50 mixtures of reference illite with reference kaolinite or reference montmorillonite was investigated. The clays were Na- or Ca-saturated and freeze-dried before use. Critical coagulation concentrations (CCCs) were investigated in the range of pH 5.9 to 9.6, percent Na-clay 0, 10, 20, 40, 60, 80, and 100 and SAR 0, 10, 20, 40, 60, 80, and co. CCC values increased with increasing ESP, increasing SAR, and increasing pH. The pH dependence of illite/kaolinite was greater than that ofillite/montmorillonite especially at high ESP and SAR. The presence of illite did not play a dominant role in determining flocculation-dispersion behavior of the 50/50 clay mixtures. The CCCs of illite/kaolinite resembled reference illite more than reference kaolinite for SAR 0 to SAR 60. Illite/montmorillonite exhibited CCCs more similar to reference illite than reference mont- morillonite at SAR 40 and SAR 60. At the agriculturally desirable ESP and SAR values of 0 to 15, all the 2:1 clays and 2:1 clay mixtures demonstrated similar CCC values.
TL;DR: The Kimmeridgian-volgian(-Ryazanian) claystone is the principal oil source rock in the troughs of the North Sea as mentioned in this paper and the proportion of illite layers in I/S increased to 95% d,aring diagenesis in these claystones.
Abstract: The Kimmeridgian-Volgian(-Ryazanian) claystone is the principal oil source rock in the troughs of the North Sea. Randomly (R0) ordered mixed-layer illite/smectite (US) appears to have transformed to RI-(IS) or R3-(ISII) ordered simultaneously with oil generation. The proportion of illite layers in I/S increased to 95% d,aring diagenesis in these claystones. Exceptions are three samples of I/S of probably bentonitic origin; these have apparently changed during diagenesis to R0-0rdered I/S containing 40-50% illite layers. Fine fractions of the claystones dominated by I/S were analyzed by ZTAl and 29Si magic-angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, ~TFe Mrssbauer spectroscopy, and X-ray powder diffraction (XRD), and for total chemical composition. Si/AI ratios determined from MAS- NMR agree closely with those calculated from total chemical analysis; however, tetrahedral and octahedral AI occupancies were most accurately determined by NMR. An increase in the percentage of illite layers and in the ordering of the I/S was accompanied by fixation of K ~ and NH4 + in the I/S, by tetrahedral AI- for-Si substitution, and by octahedral Al-for-(Mg + Fe) substitution, resulting both in an increase of charge in the 2:1 layers and in a migration of charge from octahedral to tetrahedral sheets. The I/S of probably bentonitic origin had a larger tetrahedral and a smaller octahedral charge than expected from its content of illite layers. MAS-NMR showed a significantly higher content of tetrahedral AI (most likely in smectitic sites) than expected from the percentage ofillite layers calculated from XRD. Correspondingly, XRD of K+-saturated and glycolated specimens showed that several smectite layers possessed a significant charge. A constant b-dimension of the I/S and the presence of a significant charge in the smectite layers suggest that a transformation of smectite to illite layers in the I/S by tetrahedral Al-for-Si substitution followed by interlayer cation fixation and interlayer contraction is the most probable genesis for the I/S investigated.
TL;DR: In this paper, the authors performed X-ray diffraction and chemical analyses on clay fractions separated from an acid brown soil (Dystrochrept) by means of size fractionations using high-gradient magnetic separation techniques.
Abstract: X-ray diffraction and chemical analyses were performed on clay fractions separated from an acid brown soil (Dystrochrept) by means of size fractionations using high-gradient magnetic separation techniques. Breakdown of large phyllosilicates preexisting in the saprolite involved physical fragmentation and mineralogical transformations strongly related to chemical weathering. Compared to the C horizon, the proportion of chlorite and vermiculite decreased strongly in the silt and coarse-clay fractions of the Al horizon, but was maintained in the finer clay fraction (< 1 μm). The distribution of mica in the different fractions was quite the opposite. Micas are the major component of the Al, 1–2 μm fractions, and their proportion progressively decreased with decreasing fraction size. Thus, it is concluded that during fragmentation and/or simple transformation of the larger phyllosilicates, clusters of chlorite, mica/vermiculite, and vermiculite layers were preferentially affected. A concentration of mica layers took place in the coarse clay fractions as chlorite and vermiculite residues were accumulated in the fine clays. The process involved the loss of Fe and Mg, leaving, or forming, more aluminous dioctahedral minerals. As the transformation processes occurred, dissolution of preexisting minerals led to the precipitation of amorphous and/or crystalline Fe- and Al-oxides, and possibly of phyllosilicates. The new phyllosilicates appear to be montmorillonitic. The most abundant end products of the weathering processes in either the Al or the Bw horizons appeared to be quite different. In the Al horizon they were identified mainly a hydroxyl-Al (Fe) intergrade smectite (montmorillonite), whereas in the Bw horizon the major component was an intergrade vermiculite originating, at least in part, from chlorite.
TL;DR: In this paper, the rehydration properties and behavior of interlayer cations of Ca-, Mg-, Na-, and K-saturated homoionic saponite and vermiculite heated at various temperatures were examined.
Abstract: The rehydration properties and behavior of interlayer cations of Ca-, Mg-, Na-, and K-saturated homoionic saponite and vermiculite heated at various temperatures were examined and their rehydration mechanisms elucidated. The most notable features of saponite were (1) except for the Mg- saturated specimen, all saponite samples rehydrated until the crystal structure was destroyed by heating; (2) the rehydration rate in air after heating decreased in the order: K + > Na § > Ca 2+ > Mg2+; (3) the interlayer cations apparently migrated into hexagonal holes of the Sit4 network on thermal dehydration; and (4) the b-parameter expanded on thermal dehydration. The rehydration properties and behavior of interlayer cations of vermiculite were: (1) except for the K-saturated specimen, all vermiculite samples rehydrated until the crystal structure was destroyed by heating; (2) the rehydration rate in air after heating decreased in the order: Mg 2+ > Ca ~+ > Na + > K+; (3) the interlayer cations apparently did not migrate into the hexagonal holes, but remained at the center of the interlayer space, even after thermal dehydration; and (4) except for the K-saturated specimen, the b-parameters of the samples contracted on thermal dehydration. The different rehydration properties of saponite and vermiculite were apparently due to the behavior of the interlayer cations during thermal dehydration. For rehydration to occur, the interlayer cations of saponite had to migrate out of the hexagonal holes. Consequently, saponite saturated with a large cation rehydrated rapidly, whereas saponite saturated with a small cation rehydrated slowly. On the other hand, the interlayer cations of vermiculite remained in the interlayer space; therefore, the rehydration properties of vermiculite were strongly affected by the hydration energies of the interlayer cations. Fur- thermore, electron diffraction patterns suggested that the saponite and vermiculite consisted of random stacking and ordered stacking of adjacent 2:1 layers, respectively. The nature of the stacking of the minerals seemed to be the most important factor controlling the behavior of interlayer cations in the thermal dehydration process.
TL;DR: In this article, the chemical composition and the thermal behavior of sodium and hydrogen octosilicate were studied by chemical and thermal analysis, infrared (IR), magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray diffractometry.
Abstract: The chemical composition and the thermal behavior of sodium and hydrogen octosilicate was studied by chemical and thermal analysis, infrared (IR), magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray diffractometry. Both compounds are layer silicates with basal spacings of 11.10 and 7.38 A, respectively. In both forms the ratio of Q4 silicon (connected via oxygen bridges with four silicon atoms) to Q3 silicon (connected with only three other Si atoms) is 1. At least a small part of the Q4 silicon can be substituted by aluminum. Elimination of water coordinated to the cations in sodium octosilicate results in a concomitant structural collapse. Replacement of the sodium ions by protons affects the atomic arrangement in the sheets only to a minor degree, but results in a decrease of the periodicity along the crystallographic c axis. Upon heat treatment an endothermal structural rearrangement occurs at about 360 K as revealed by significant changes of the IR and 29Si MAS-NMR spectra. Reexchange with Na ions largely, but not completely, restores the structure of the parent octosilicate. The X-ray diffraction pattern of sodium octosilicate was indexed in the monoclinic system with a = 7.345 A, b = 12.74 A, c = 11.25 A and β = 99.3°. Based on conclusions drawn from the results of the present study, the X-ray pattern of hydrogen octosilicate was tentatively indexed in the monoclinic system with a = 7.345 A, b = 12.74 A, c = 8.51 A and β = 119.8°.
TL;DR: The International Society of Soil Science (ISSS) recognized these problems and challenges as discussed by the authors and established a provisional working group to focus attention on soil colloids with a view to understanding better the interactions that take place at their surfaces.
Abstract: About 20 years ago the emphasis in soil chemistry research switched from studies of problems related to scarcities of plant nutrients to those arising from soil pollutants. The new problems have come about because of the excessive uses of fertilizers, the inputs from farm and industrial wastes, the widespread applications of anthropogenie xenobiotic chemicals, and the deterioration of soil structure resulting from certain modern agriculture practises. The International Society of Soil Science (ISSS) recognized these problems and challenges. A provisional Working Group was set up in 1978 to focus attention on soil colloids with a view to understanding better the interactions wh ich take place at their surfaces. It was recognized that these interactions are fundamental to problems of soil fertility, as weIl as to those of soil pollution. After the group had received the official support of ISSS at its 12th International Congress in New Delhi in 1982 it set as its priority the assembling and evaluation of information, relevant to the soil and environmental sciences, concerning the composition and structure of soil colloids. Prior to that aseries of Position Papers were published in the Bulletin of the International Society of Soil Science (Vol. 61, 1981) outlining the state of knowledge about the composition and properties of soil colloids.
TL;DR: In this article, the authors measured the heat capacities of DMSO intercalated with kaolinite (20 to 310 K) by adiabatically shielded calorimetry.
Abstract: The heat capacities of kaolinite (7 to 380 K) and of dimethyl sulfoxide (DMSO) intercalated kaolinite (20 to 310 K) were measured by adiabatically shielded calorimetry. The third law entropy of kaolinite, S298, is 200.9 ± 0.5 J½mol−1K−1. The “melting point” of the DMSO in the intercalate, 288.0 ± 0.2 K, is 3.7 K lower than that of pure DMSO, 291.67 K. The heat capacity of DMSO in the intercalate above 290 K is approximately 5.2 J·mol−1·K−1 smaller than that of pure liquid DMSO at the same temperature.
TL;DR: A ternary complex of Ti(III), citrate, and ethylenediaminetetraacetate (EDTA) as reductant and bicarbonate as a proton acceptor has been used to measure the abundance of free Fe oxide phases and associated elements in soils and sediments.
Abstract: A new iron oxide dissolution method designed to measure the abundance of “free” Fe oxide phases and associated elements in soils and sediments has been tested. The method employs a ternary complex of Ti(III), citrate, and ethylenediaminetetraacetate (EDTA) as a reductant and bicarbonate as a proton acceptor. The Ti(III)-citrate-EDTA-HCO3 method dissolved more synthetic amorphous ferric oxide and goethite, but less synthetic hematite, than the dithionite-citrate-HCO3 method of Mehra and Jackson. The production of acidity by the dissolution indicated that Ti(IV) is hydrolyzed to TiO2 during the extractions. The heated dithionite method dissolved 3–6 times more Al from kaolinite and nontronite standard clays than room temperature dithionite, and 4–6 times more Al than the Ti(III)-citrate-EDTA-HCO3 method. Furthermore, the release of Fe from the clay mineral samples consistently and rapidly reached a plateau during multiple extractions by the Ti(III)-citrate-EDTA-HCO3 method, indicating that a well-defined Fe oxide fraction was removed. Fe released by the dithionite method continued to increase with each extraction, suggesting that some release of structural Fe occurred. Tests on two natural sediments and one heavy mineral fraction from the Miocene Cohansey Sand in the New Jersey Coastal Plain suggested that the Ti(III)-citrate-EDTA-HCO3 method removed Fe oxides more effectively and more selectively than the dithionite method. The selectivity of the Ti(III)-citrate-EDTA-HCO3 method is enhanced by rapid extractions at room temperature and low free ligand concentrations.
TL;DR: In this article, the modification of the external surface area and the two types of microporosity of palygorskite (structural and interfiber porosity) were examined as a function of the temperature of a vacuum thermal treatment to 500°C.
Abstract: The modification of the external surface area and the two types of microporosity of palygorskite (structural and interfiber porosity) were examined as a function of the temperature of a vacuum thermal treatment to 500°C. The methods used included: controlled-transformation-rate thermal analysis, N2 and Ar low-temperature adsorption microcalorimetry, conventional and continuous gas-adsorption volumetry (for N2 and Ar) at 77 K and CO2 at 273 and 293 K, water vapor adsorption gravimetry, and immersion microcalorimetry in water. At temperatures 225°C.
TL;DR: In this paper, single crystal X-ray diffraction and electron-optical analysis were used to investigate the weathering of a chromium-bearing muscovite (fuchsite).
Abstract: Single crystal X-ray diffraction and electron-optical analysis were used to investigate the weathering of a chromium-bearing muscovite (fuchsite). The muscovite had mostly altered to kaolinite with minor amounts of halloysite occurring between kaolinite plates. Evidence for both epitactic and topotactic growth of kaolinite from muscovite was obtained and no intermediate poorly-crystalline phases were detected. About half of the Cr in fuchsite was incorporated into kaolinite, whereas most of the Ti, Fe and Mg was lost.
TL;DR: In this paper, Raman and Fourier-transformed infrared spectra of natural trioctahedral chlorites of polytype IIb were obtained for a series of samples characterized by distinct Fe/(Fe + Mg) and Si/Al ratios ranging, respectively, from 0.04 to 0.94 and from 5.18 to 1.86.
Abstract: Raman and Fourier-transformed infrared spectra of natural trioctahedral chlorites of polytype IIb were obtained for a series of samples characterized by distinct Fe/(Fe + Mg) and Si/Al ratios ranging, respectively, from 0.04 to 0.94 and from 5.18 to 1.86. All samples were characterized by X-ray powder diffraction, and quantitative electron microprobe analysis. In the 3683-3610-cm−1 spectral range, the wave number of the OH-stretching band from the 2:1 layer (band I) decreased with an increase of iron content at constant Al(IV) content. The more intense bands II and III at about 3600 cm−1 and 3500 cm−1, were assigned to hydroxyl groups involved in hydrogen bonds: (SiSi)O... HO, with the hydrogen bonds being roughly perpendicular to the basal plane, and (SiAl)O... HO, respectively. At higher tetrahedral Al and octahedral Fe contents, spectra exhibited OH-bands II and III, respectively, at a lower frequency. Band III intensity increased and band II was enlarged for chlorites displaying higher Al(IV) contents.
TL;DR: In this paper, a structural model was proposed for a two-sheet, kaolinite-like structure containing defects (holes in the tetrahedral sheet) is curved into a sphere in which imogolite-like orthosilicate units are anchored into the octahedral sheet and fit into the tetric defects.
Abstract: Examination of two volcanic and two precipitated allophanes by solid-state NMR, thermal analysis and X-ray powder diffraction shows three of the samples to contain structural features similar to both tubular imogolite and defect layer-lattice aluminosilicates such as kaolinite. The fourth allophane, a precipitated sample from New Zealand, had no imogolite-like features and contained tetrahedral as well as octahedral aluminum. The imogolite-like units in allophane are less stable thermally than tubular imogolite. The NMR spectra and their changes on heating can be accounted for by a structural model in which a two-sheet, kaolinite-like structure containing defects (holes in the tetrahedral sheet) is curved into a sphere in which imogolite-like orthosilicate units are anchored into the octahedral sheet and fit into the tetrahedral defects. Computer simulation shows that the model is crystallographically sound, and accounts for all the known facts, including the spherical morphology, the solid-state NMR spectra and the thermal dehydroxylation behavior of all except the New Zealand allophane, which is of a different structural type.