bluuebunny/crossref_metadata_2025 huggingface dataset:
A Golden-Colored, Ferri-Nickel Chloritic Mineral from Morro do Niquel, Minas Gerais, Brazil
Authors: Brindley G. W. , de Souza Jefferson Vieira
Published: September 2006

A golden-colored, flaky mineral from Morro do Niquel, Minas Gerais, Brazil, gives an X-ray diffraction pattern of a IIb chlorite polytype, with basal spacing 14·21 ± 0·02 Å and b = 9·23 Å. Thermogravimetric analysis shows a progressive weight (water) loss up to 500°C, followed by a rapid weight loss corresponding to dehydroxylation of the interlayer material and a slower weight loss due to dehydroxylation of the 2:1 layer. The structural formula derived from the chemical analysis on the basis of O10 (OH)8, or total cation valence of +28, shows 5·3 total octahedral cations, i.e. probably 2·3 in the interlayers where normally 3 cations are found. This deficiency together with the appreciable loss of water below 500°C suggests a partially vermiculitized interlayer. A new method for deriving the interlayer composition gives R1·67(OH)4·08(H2O)0·59, and a ratio (OH + H2O)/R = 2·80, which approaches that of a dioctahedral interlayer and is consistent with a predominance of R3+ ions. The mineral may resemble the golden, vermiculitized biotite described by Walker and others.
Fabric of Consolidated Kaolinite
Authors: Martin R. Torrence , Ladd Charles C.
Published: September 2006

Fabric refers to the spacial arrangement of clay particles in a sample relative to a reference plane. X-ray diffraction data yield an ‘amount of orientation’ (AO) that varies from zero for ideal random to 100 for ideally oriented fabric. The AO has been related to the average angle of inclination of clay particles to the reference plane.

Fabric data from 50 samples involving 2000 determinations are presented on the effects of: the method of sample preparation prior to one-dimensional consolidation; the magnitude of consolidation stress from 0·1 to over 1000 kg/cm2; changes in direction of consolidation stress; isotropic consolidation; and disturbance during removal of samples from oedometer cells. The single most important variable was the method of sample preparation, as illustrated by the following data on samples consolidated one-dimensionally to 1·5 kg/cm2:clay initially moist, AO = 27 per cent; air-dry clay, AO = 44 per cent; clay slurries, AO = 76–95 per cent. The change in fabric with increasing consolidation stress was most pronounced with samples at very low stresses, the changes in fabric were small for consolidation stress increments usually encountered in engineering practice.

Fabric data provide a very sensitive measure of sample disturbance. Extrusion causes significant disturbance at the center of a 24cm dia, sample cylinder.
The Formation of Hematite from Amorphous Iron(III)Hydroxide
Authors: Fischer W. R. , Schwertmann U.
Published: September 2006

The formation of hematite from amorphous Fe(III)hydroxide in aqueous systems at pH 6 and 70°C, both with and without oxalate, was followed by kinetic measurements, electron microscopy, i.r. spectroscopy and thermal analysis.

In the absence of oxalate, small amorphous particles coalesce into aggregates which eventually become single crystals of hematite. When oxalate is present, crystal growth is much faster and does not proceed through the intermediate stage of aggregation. Aggregates, when formed, consist of groups of single crystals. It is suggested that oxalate accelerates the nucleation of hematite crystals by acting as a template, the Fe-Fe distance in Fe-oxalate ions being similar to that in hematite.
Clay Distributions in Recent Estuarine Sediments
Authors: Edzwald James K. , O’Melia Charles R.
Published: September 2006

The distribution of clay minerals in Recent sediments can be explained by the relative stability of the clays. The rates of particle aggregation for three clays were determined in the laboratory in synthetic estuarine solutions; from the kinetic studies stability values were calculated. The results indicate that illite is more stable than kaolinite which is more stable than montmorillonite. The distribution of the clays in the Pamlico River Estuary can be explained on the basis of relative clay stability where kaolinite which aggregates rapidly (relatively unstable clay) is found upstream of illite.
Adsorption of Ethylenediamine (EDA) on Montmorillonite Saturated with Different Cations—III. Na-, K- and Li-Montmorillonite: Ion-Exchange, Protonation, Co-Ordination and Hydrogen-Bonding
Authors: Laura R. D. , Cloos P.
Published: September 2006

Ethylenediamine (EDA) is adsorbed from aqueous solution on Na-, K- and Li-montmorillonite as the monoprotonated cation (EDAH+) through an ion-exchange process. On washing with distilled water the second amine function is protonated—probably through dissociation of water near the clay surface—and simultaneously formed alkali hydroxide is removed.

In air-dried clay films, prepared from unwashed suspensions, EDA is retained mainly through hydrogen-bonding with water co-ordinated to the exchangeable cation.

EDA adsorbed from the vapour phase is retained through co-ordination, either direct or indirect (i.e. through a ‘water-bridge’), depending on the hydration properties of the exchangeable cation. Indirect coordination increases the stability of the amino-clay complex against atmospheric humidity and heating in vacuum in the order K+ < Na+ < Li+.

Upon heating co-ordinated EDA is almost completely desorbed, whereas EDAH+ and EDAH22+ decompose above 160°C to form NH4+.
Nickel Containing Regularly Interstratified Chlorite-Saponite from Szklary, Lower Silesia, Poland
Authors: Wiewióra Andrzej , Szpila Kazimierz
Published: September 2006

The present paper describes a new mineral species, namely a regularly interstratified chlorite —trioctahedral smectite bearing as much as 24% NiO. The high Ni content proves it to be nickel mineral.

On the diffractogram of the raw sample, an integral series of reflections with l.d(001) = 30·1 Å was obtained. To study the nature of the component layers, X-ray examinations of glycerol saturated samples and also dehydrated by heating were accomplished. Thermal and chemical analyses were performed in the usual way.

The crystallochemical formula can be presented as follows: saponite layer—(Mg,Ni)3·00 (Si3·75Al0·25) O10(OH)2, charge −0·25; Ca0·06 (Mg,Ni)0·06 K0·01, 4·07 H2O, charge +0·25; chlorite layer—(Mg, Ni)2·02(Al,Fe*)0·65(Si3·76Al0·24) O10(OH)2, charge −0·25; (Mg,Ni)2·75 (Al,Fe3+)0.25 (OH)6, charge +0.25.

The full mineral and chemical characteristics lead to precise conclusions concerning the composition and structure not only of the nonexpanding chlorite layers, but especially of the expanding layers. The latter show the chemical composition of saponite but the interlayer material is composed partly of exchange cations and molecular water and partly of “brucite-like pillows”.
Perturbation of Structural Fe3+ in Smectites by Exchange Ions
Authors: McBride M. B. , Pinnavaia T. J. , Mortland M. M.
Published: September 2006

The electron spin resonance of some structural Fe3+ for montmorillonites having low Fe3+ content, is perturbed by electrostatic interaction between exchange cations and structural charge sites. The position of charge centers of organic and inorganic cations in the interlayer can thus be determined at various levels of solvation. Dielectric media between the silicate layers lower the electrostatic attraction between the silicate and the exchange cations. The silicate charge appears to be partially delocalized on structural oxygen atoms as shown by electron spin resonance and i.r. spectroscopy. There is also evidence that divalent exchange cations on dehydrated montmorillonites cause hydrolysis of water; the protons so produced migrate to structural charge sites.
Halloysite-Kaolinite Transformation at Room Temperature
Authors: La Iglesia A. , Galan E.
Published: September 2006

Halloysite (metahalloysite) of various particle sizes has been altered with oxalic and EDTA acids, at room temperature and during different periods of time (5–90 days). The oxalic acid attack at first achieved only a recrystallization of halloysite. The recrystallization is much more significant the smaller the size of the treated halloysite particles. Later the material is destroyed. The EDTA treatment also has provoked during the first days a recrystallization of the halloysitic material which is destroyed again after about 20–25 days. Later kaolinite is formed. The kinetic curve of kaolinite formation is symmetrical with respect to that corresponding to the diminution of amorphous material in the sample. The influence of the halloysite particle size and the complexing effect of the acids in relation to the resulting products are discussed.
Structural Hydroxyls in Sepiolites
Authors: Ahlrichs J. L. , Serna C. , Serratosa J. M.
Published: September 2006

Three sepiolite clays studied showed evidence for the presence of structural hydroxyl groups in three to five different environments depending on the composition of the clay. A 3720 cm−1 i.r. frequency is shown to be characteristic of SiOH at crystal edges which are very abundant in sepiolites. This band has not been seen by most workers because the Nujol, fluorolube or KBr used in sample preparation perturb it sufficiently to obscure it under other OH stretching bands. The 3680 cm−1 band is confirmed as being from the (Mg)3OH and evidence of a very small band near 3640 cm−1 is suggested to arise from limited trioctahedral substitution. The very crystalline Ampandrandava sepiolite shows only the above three bands. The intermediately crystalline Vallecas shows a 3620 cm−1 band in addition which is characteristic of dioctahedral systems and is due to either some vacancy sites or to the presence of attapulgite. This dioctahedral band is greater in the less crystalline Salinelles sepiolite; in addition, it has a smaller 3585 cm−1 band. Mg-Al-vacancy and Mg-Fe‴-vacancy are suggested as the source of the 3620 cm−1 and 3585 cm−1 bands.
Electrical Conductivity of Na—Montmorillonite Suspensions
Authors: Shainberg I. , Levy Rachel
Published: September 2006

The electrical conductivity of Na-montmorillonite suspensions in various salt and clay concentrations was measured. The weight conductance of the clay suspension was found to decrease with increase in clay concentration between 0 and approximately 0·5 g clay/100 ml, then rose to a plateau at 6–10 g clay/100 ml. The weight conductance of the clay suspensions also increased with an increase in the salt solution concentration. If the model of two resistors in parallel is used in interpreting the experimental data, these changes can be attributed to an increase in the mobility of the adsorbed Na ions. It is proposed that the two resistors in series model is more realistic in describing the conductivity of the suspensions. This model predicts the observed weight conductance changes of the suspensions, while the mobility of the adsorbed ions remains constant. A constant mobility of the adsorbed Na ions in clay-water systems of low to medium salt and clay concentrations also is predicted by the diffuse double layer.
Od-Interpretation of Kaolinite-Type Structures—I: Symmetry of Kaolinite Packets and Their Stacking Possibilities
Authors: Dornberger-Schiff K. , Ďurovič S.
Published: September 2006

The idealized symmetry of kaolinite-type minerals (1:1 phyllosilicates) is analysed in detail. They can be considered as OD-structures consisting of three kinds of OD-layers. Each of them, taken separately, possesses higher symmetry than their combination. This explains the well-known tendency of kaolinite-type minerals to form a wide variety of ordered and disordered polytypes as well as twins. The possible stacking sequences result from the different kinds of pairs of kaolinite layers which are derived for dioctahedral, trioctahedral as well as ‘monoctahedral’ kaolinite-type minerals, the latter being defined as those in which the three octahedral positions are occupied by three different cations or two different cations and a void. The analysis makes use of a simple symbolism and a simplified pictorial representation.

A brief summary of the most important terms and definitions of the theory of OD-structures is given in an Appendix.
Natural Alteration of Mica and Reactions between Released Ions in Mineral Deposits
Authors: Rimsaite J.
Published: September 2006

Chemical changes during the natural alteration of micas were studied by electron microprobe and classical chemical analyses of fresh and altered portions of mica flakes from 10 Canadian mineral deposits. Results of 50 new analyses are discussed in five examples, starting from simple changes in the interlayer followed by exsolution of titania and ending with complex replacements of anions and cations in all layers of the mica structure. Alteration of micas starts along 001 cleavage planes and fractures and gradually extends into the entire flake leaving some or no remnants of the host mica. The removal of ions from the mica structure and from the flake takes place by gradual depletion, by exsolution of oxides, and/or by alternating removal and redeposition of a newly-formed oxide, illustrated in the following example of the removal of Ti;

(1)

removal of Ti from the mica structure and exsolution of rutile in the parent mica

(2)

destruction of rutile and recrystallization as anatase on the surface of the mica; and

(3)

destruction of anatase, removal of Ti from the surface of the host and crystallization of anatase away from the parent mica.

Residual minerals replacing the original micas are secondary and recrystallized micas, chlorite, vermiculite, serpentine, talc and depleted, optically amorphous flakes. Newly-formed minerals which may incorporate the released ions into their structures are rutile, anatase, sericite, hydronepheline, chlorite-serpentine aggregates, goethite and jarosite. The following partly-altered micas are indicative of sulphide mineralization;

(a)

bright-green, partly altered phlogopite from ultrabasic rocks and from Co-Cu-Fe-Ni sulphide assemblages. The green phlogopite formed by replacement of K, Al and Ti by Fe, Mg and OH

(b)

depleted mica coated with jarosite and Ni-goethite in the oxidation zone of a nickel deposit.

The jarosite formed from released S and Fe from decomposed Fe-Ni sulphides and K released from the host mica; and

(c)

chlorite-sericite-biotite alteration zones adjacent to Pb-Zn-Cu-Fe deposits.
Dielectric Properties of Montmorillonites Saturated by Bivalent Cations
Authors: Calvet R.
Published: September 2006

This study deals with the analysis of dielectric measurements made on montmorillonites saturated by bivalent cations. These measurements are performed between — 150°C and +30°C at frequencies ranging from 300 to 10,000 Hz. Their interpretation is based on a numerical analysis allowing determination of the dielectric losses due to free charge carriers conductivity phenomena and losses due to relaxation phenomena. The free charge carriers conductivity is due to the movement of protons. It depends very much on the nature of compensating cations and on the water content and seems to be closely related to the characteristics of the swelling.

Two types of relaxation phenomenon are described: a Debye relaxation due to electric dipole rotations and a Maxwell-Wagner relaxation due to heterogeneity effects. The analysis of the first phenomenon leads to the examination of the values of the relaxation time. It appears that the rotations of water molecules are difficult with bivalent cations. This essentially is shown by the high activation energy of the phenomenon. The discussion of these parameters shows that the state of adsorbed water molecules are certainly different as compared to the state of water molecules in ice or in liquid water. The characteristics of the second relaxation phenomenon are closely dependent on the free carriers charge conductivity.
Closed form Equations for X-Ray Diffraction by Interstratified Clay Systems —I: Randomly Occurring Interlamellar Species
Authors: Wright A. C.
Published: September 2006

A closed form equation is derived for the calculation of the oriented diffraction pattern given by single particle size layer silicates having randomly interstratified interlamellar species. A general method for treating any particle size distribution is indicated and closed form results are presented for the Poisson, normal, gamma and binomial distributions. No restriction is placed on the number of interlayer types. The structure factors for these types are explicitly introduced. Graphs of two of the variables appearing in the equations applicable to particle size distributions provide a means of visualizing the effects of both interstratification and particle size on observed X-ray patterns.
Kaolinite Synthesis: The Role Of The Si/Al And (Alkali)/(H+) Ratio In Hydrothermal Systems
Authors: Eberl Dennis , Hower John
Published: September 2006

The Si/Al ratio of an hydrothermal system plays an important role in kaolinite synthesis. If the atomic Si/Al ratio of a system is greater than 2-0, kaolinite will disappear at 345 + 5°C and 2 kbars water pressure according to the reaction kaolinite + 2 quartz → pyrophyllite + H2O. If the atomic Si/Al ratio is less than 2-0, however, kaolinite will persist until 405°C where it will react according to the equation 2 kaolinite → pyrophyllite + 2 boehmite + 2 H2O. The Si/Al ratio of the system and temperature are also factors in determining whether b-axis ordered or disordered kaolinite will crystallize. The ordered variety is favored by a lower Si/Al ratio and a higher temperature than is the disordered form.

Hydrothermal experiments also show that kaolinite can be synthesized at 150°C and 5 bars pressure in distilled water from amorphous starting materials. Previous investigators were unsuccessful in forming kaolinite under these conditions because their systems were contaminated with alkalis.

Attempts to synthesize halloysite and dickite failed, but halloysite was converted to kaolinite at 150°C, suggesting that halloysite can be synthesized only at low temperatures.
Electron-Microscopic and Mössbauer Spectroscopic Studies of Iron-Stained Kaolinite Minerals
Authors: Jefferson D. A. , Tricker M. J. , Winterbottom A. P.
Published: September 2006

An electron-microscopic and Mössbauer spectroscopic study of a range of kaolinites has revealed three distinct types of iron contamination within these minerals: a) Ferric ion may substitute for aluminium and be evenly distributed throughout the lattice, b) Ferric ion may be present as a crystalline coating of goethite, as indicated by lattice-imaging studies, or c) as an amorphous coating. The distribution of the iron in the groups b and c is non-uniform and is highest at the flake surfaces. Ferrous ion, when detected, is thought to be evenly distributed throughout the lattice. The size of the contaminating goethite crystallites and the observed Mössbauer spectra of these samples suggest that such particles are super-paramagnetic. All kaolinites can be cleaned by acid treatment except those having iron substituting for Al3+.
The Definition and Nomenclature of Halloysites
Authors: Churchman G. J. , Carr R. M.
Published: September 2006

This review of the literature shows that there have been many attempts to modify or revise the original definition of halloysites as distinguished from kaolinites, which was based on the greater water content of the halloysites. In general, these various attempts have arrived at definitions of halloysites as distinguished from kaolinites that are based on one or more particular instrumental or chemical techniques. Further investigations with almost all of these techniques have shown the apparently clear distinctions of this kind to be misleading. All such instrumentally—or chemically—based definitions were shown to either complicate and confuse the distinction between halloysites and kaolinites or to provide only empirical and subtle distinctions. It is concluded that only the original definition, with slight adaptations, enables clear and unambiguous distinctions to be made between halloysites and kaolinites. It is noted, however, that a distinctive structure for halloysite has been postulated as a result of electron diffraction studies. Further studies of this kind could well establish such a structure as being definitive of the mineral species.

The literature also reveals a long-standing disagreement over the nomenclature of different forms of halloysite and particularly over the nomenclature of and distinction between the two forms of halloysite at the extreme ends of the hydration series. An analysis of experimental studies of the relationship between these two and other hydration states of halloysite reveals that forms of halloysite with all possible interlayer water contents between 0 and 2 molecules H2O per Al2Si2O5(OH)4 unit cell may exist and that the two end members of the hydration series may not be seen as distinct phases. The fully dehydrated halloysite is the only thermodynamically stable form of the mineral. A nomenclature system which was proposed by MacEwan in 1947 is consistent with these results. This system, amended only by the exclusion of the unnecessary term ‘metahalloysite’ should therefore be adopted in all studies of halloysites.
Nickeliferous Nontronite, A 15Å Garnierite, at Niquelandia, Goiás, Brazil
Authors: Bosio Nivaldo J. , Hurst Vernon J. , Smith Robert L.
Published: September 2006

Garnierite from the Tocantins Complex at Niquelandia, Brazil, is a 15Å, dioctahedral clay mineral, nickeliferous nontronite. The principal octahedral cations are Fe3+, Al and Ni. The ferric state of the iron has been verified by ESCA. Ni occupies both the octahedral site and an exchange site. The garnierite formed (and is still forming) by the weathering of nickeliferous pyroxenite. Although the garnierite is a secondary product of weathering, it undergoes further change as weathering progresses: Ni and silica decrease, Fe3+ and Al increase, and the color changes from bright yellow green to red brown. Eventual breakdown of the garnierite leaves mainly hydrated oxides of iron and aluminum.
The Effect of Heating In Vacuo on the Microporosity of Sepiolite
Authors: Dandy A. J. , Nadiye-Tabbiruka M. S.
Published: September 2006

The t-plot method has been applied to the results of nitrogen adsorption at 76°K on sepiolite first heated in vacuo at various temperatures. Heating sepiolite samples in vacuo at 427°K results in a large decrease in surface area compared with samples outgassed at 373°K. A change in structure and a consequent collapse of micropores is postulated. However, the t-plots indicate that some microporosity remains. Outgassing at 623°K appears to destroy completely the micropores.
Anatase and Rutile Determination in Kaolinite Deposits
Authors: Sayin Mahmut , Jackson M. L.
Published: September 2006

Hexafluorotitanic acid (H2TiF6) selectively dissolves kaolinite and most other phyllosilicate minerals of soils and sediments, concentrating free crystalline (Ti,Fe)O2 minerals (partially substituted anatase and rutile) in the residue. A series of H2TiF6 reagents was standardized by analysis of the Ti content and by tests with pure anatase and commercial kaolinites. The Ti in the H2TiF6 solution selected (made from 49% HF + reagent TiO2) was 16·5% by weight as analyzed by the Tiron method. Treatment of pure anatase with the reagent H2TiF6 resulted in a 98% by weight recovery of TiO2 in the residue. The fraction of TiO2 recovered in the residue of commercial Georgia kaolinites was 88–101% after treatment with the selected H2TiF6 reagent. Isolates from nine Georgia kaolinite samples with varying amounts of TiO2 and Fe2O3 were examined by X-ray powder diffraction, scanning electron microscopy and elemental analysis. The main constituent of the (Ti,Fe)O2 isolates was anatase for all samples, with minor amounts of coarser rutile and mica from coarser kaolinite. The anatase and rutile isolates contained 74–93% (Ti,Fe)O2 with 0·5–3·1% Fe. The other constituents of the isolates were muscovite of mica (0·3–7%), quartz (0–9%) and amorphous relics of vermiculite and/or kaolinite (6–19%). Rutile, muscovite and quartz appear to be detrital but the anatase and relics are probably authigenic. Fine anatase appears to stick on the muscovite flakes as revealed by scanning electron microscopy and heavy liquid data for separation of these two minerals. The (Ti,Fe)O2 isolates from kaolinites which passed with the first magnetic concentrate of anatase were coarse, on the order of a few microns dia., as revealed by the scanning electron microscopy. Those passed with subsequent extensive magnetic concentrates from the same samples were finer. The anatase isolated from kaolinite purified by removal of as much of the impurities as possible by magnetic means was extremely fine, most of the particles being on the order of 0·1 µm dia. More than one third of the total Fe2O3 in kaolinites magnetically separated in the first pass was extracted by the citrate-bicarbonate-dithionite treatment after hot NaOH dissolution of 52–74% of the kaolinite, showing that the Fe2O3 had been mainly associated within the kaolinite. Only 2–6% of the total Fe2O3 was extracted from magnetically purified kaolinite after 40–50% of this kaolinite had been dissolved, indicating that most of the Fe is in the anatase and rutile fraction.
Stabilization of Clay Soils Against Erosion Loss
Authors: Kawamura Mitsunori , Diamond Sidney
Published: September 2006

Accelerated soil erosion from construction sites and the resulting increase in downstream sediment load constitute a significant environmental problem. Laboratory studies indicate that small percentages of hydrated lime or of Portland cement will stabilize clay soils against rainstorm erosion by preventing particle detachment. Coordinated measurements of the size distribution of water-stable aggregates, of pore size distribution by mercury porosimetry and of microstructure by scanning electron microscopy and energy dispersive X-ray spectrometry were used to clarify aspects of the mechanisms responsible for the development of erosion resistance. Attainment of such resistance was marked by aggregation of a significant part of the clay into water stable aggregations of the order of several mm in size and of minimal change in porosity and pore size distribution on exposure to the test rainstorms. At least some of the clay particles in the aggregations appeared to be partly converted to calcium-bearing reaction products and formation of the “reticulated network” variety of calcium silicate hydrate gel linking adjacent particles was demonstrated.
Adsorption of Xylene by Organoclays
Authors: Slabaugh W. H. , Vasofsky R. W.
Published: September 2006

Based on X-ray powder diffraction measurements of swelling, thermodynamic analysis of adsorption and kinetics, a mechanism of interaction between xylene isomers and two organoclay complexes was derived. The work is intended to resolve the factors which make possible the chromatographic separation of the xylene isomers with organoclays. Significant differences between the behavior of fresh organoclays and xylene vapor-conditioned organoclays were noted. Only small differences were apparent between the montmorillonite and the hectorite organoclays. Force constants, enthalpy changes, entropy changes, free energy changes and two specific rate constants were derived from the information obtained from this study.
The Separation of Alunite in Alunitic Kaolin by Selective Flocculation
Authors: Ustaer C. , Gürgey I.
Published: September 2006

This work describes the separation of alunite from natural alunitic kaolins by applying a selective flocculation procedure. In order to determine the most efficient separating procedure preliminary experiments were performed with artificial mixtures of alunite and kaolin. The same procedure was then applied to natural alunitic kaolin which enabled the preparation of kaolin of considerable purity.
Interaction of Clay Minerals with Adenosine-5-Phosphates
Authors: Graf G. , Lagaly G.
Published: September 2006

Adenosine-5-phosphates (ATP, ADP, AMP) are adsorbed by clay minerals at very low concentrations (≤2 mg/liter). In contrast to quartz, the clay minerals exhibit a strong preference for ATP over AMP. The experimental data are expressed as recovery rates (adenosine-phosphate in solution to total nucleotide added). For example, the recovery rates of ATP, ADP, and AMP in the presence of sodium montmorillonite are 0,17, and 100%; in the presence of quartz 95, 100, and 99%. The recovery rate of AMP on clays is markedly decreased by the presence of ATP, that is, ATP increases the adsorption of AMP by cooperative interactions.

A part of ATP not recovered in the equilibrium solution is dephosphorylated to ADP. For example, 45% of ATP not recovered in equilibrium solution with calcium montmorillonite is recovered as ADP; with sodium montmorillonite only ADP can be recovered in solution.
Interfacial Water Structure in Montmorillonite from Neutron Diffraction Experiments
Authors: Hawkins R. K. , Egelstaff P. A.
Published: September 2006

Neutron diffraction measurements for a preferentially oriented aggregate slab sample of deuterated Na-montmorillonite from Upton, Wyoming, are described for a series of clay-water contents ranging from 0 to 500 mg/g. A neutron wavelength of 2.39 Å was used with extended detectors to collect much of the “out of plane” component of the diffraction peak intensities.

The diffraction pattern intensities from the 00ℓ planes of the clay, corresponding to a reflection geometry, are a strong function of sample water content and show a variation in basal spacing from 9.8 to 19.0 Å. The hk reflections from transmission geometry measurements show, however, that the lattice a and b axes are constant within experimental uncertainty (0.02 Å) over the range in water content and their intensities vary only by a few percent. In this geometry, a broad, water-like diffraction pattern was noted as a background under the usual hk peak intensity series. This underlying water-like pattern varies in proportion to the sample water content.

Data reduction steps included consideration of background removal, multiple scattering, flux normalization, and attenuation of scattering due to sample thickness. Analysis of the reduced data revealed that the clay-water has a “liquid-like” ordering, with a density increase of approximately 5% over bulk water. An association between a few interlayer water molecules and the silicate superstructure is indicated by the slight change in the hk band intensities, but this change seems to be complete at water contents below 100 mg/g. Fourier analysis of the basal peak series from the dry clay shows that the hydrogens of the lattice hydroxyl groups lie in the same basal plane as their associated oxygen atoms.
Scanning Electron Microscope Morphology of Deeply Weathered Granite
Authors: Gilkes R. J. , Suddhiprakarn Anchalee , Armitage T. M.
Published: September 2006

Laterite profiles developed from granite in southwestern Australia were studied by scanning electron microscopy. The morphology of soil materials reflects the mineralogy of secondary minerals formed from feldspar. In the saprolite, etched feldspar surfaces are coated with kaolinite or radiating, spherical aggregates of tubular halloysite. In the lower pallid zone these minerals have replaced most of the feldspar. In the upper pallid zone a porous framework has developed consisting mainly of quartz and gibbsite with 5-/μm euhedral gibbsite crystals in voids. Halloysite crystals in the upper pallid zone are partly unrolled and have splayed ends. Differences in mineralogy and morphology between profiles are thought to be due to variations in the intensity of leaching.
Determination of Noncrystalline Soil Components by Weight Difference after Selective Dissolution
Authors: Hodges Steven C. , Zelazny L. W.
Published: September 2006

A procedure based on loss of weight after selective dissolution analysis (SDA) and washing with (NH4)2CO3 was developed for estimating the noncrystalline material content of soils derived from widely different parent materials. After extracting with 0.2 N ammonium-oxalate or boiling 0.5 N NaOH solutions, samples were washed with 1 N (NH4)2CO3 to remove excess dissolution agents and to prevent sample dispersion. The amount of noncrystalline material removed from the sample by the extracting solution was estimated by weighing the leached products dried to constant weight at 110°C. The results match closely with those obtained by chemical analyses of the dissolution product and assignment of the appropriate water. The proposed weight-loss method is less time-consuming than the chemical method, and no assumptions need be made concerning sample homogeneity or water content of the noncrystalline material.

Extractions of whole soil and dispersed clay fractions indicated that noncrystalline material determinations on the clay fractions underestimated the noncrystalline material content for whole soils from 0 to 34%. Acid ammonium oxalate was found to be a much more selective extractant for noncrystalline materials than NaOH.
Mössbauer Study of the Attenuation of Iron in an Irrigated Greensand Lysimeter
Authors: Ross C. A. M. , Longworth G.
Published: September 2006

Fe57 Mössbauer spectroscopy has been used to determine the nature of iron-containing minerals in Lower Greensand samples from an experimental lysimeter at Uffington, Oxfordshire, both before and after a three-year irrigation with a synthetic heavy metal leachate. Analysis of the spectra measured at 300°, 77°, and 4.2°K and at 4.2°K in an applied field of 45 kOe shows that iron is present in the uncontaminated sandstone in fine-grained goethite (α-FeOOH) and glauconite. In the irrigated samples iron is precipitated as a fine-grained ferric hydroxide gel having values for the hyperfine field at 4.2°K of 435 and 470 kOe. The stability of the gel over the three-year period of irrigation may be explained by surface energy considerations.
Physico-Chemical Properties of Synthetic Hydrotalcites in Relation to Composition
Authors: Miyata Shigeo
Published: September 2006

Hydrotalcite solid solutions were prepared by coprecipitation followed by hydrothermal treatment between 150° and 250°C. Based on the structural formula [Mg1−xAlx(OH)2]x+[(CO3)x/2 • mH2O]x−, pure solid solutions were formed in the range A1/(A1 + Mg) = 0.2 to 0.33, where m = (1 − 3x/2). Maximum crystallite size was achieved by hydrothermal treatment between 180° and 200°C, with x = 0.337 to 0.429. Crystal strain was also minimized at these values of x. The adsorption capacity for Naphthol Yellow S increased as x increased and reached a maximum (1.56 × 10−6 moles/m2) when x = 0.287, a value eight times larger than that of Mg(OH)2. A weak endothermic DTA peak at about 350°C is probably due to the loss of structural water in the main layer of the structure. On calcination between 400° and 700°C, only periclase was detected, probably containing Al in solid solution. Hydration of the calcined product resulted in the reconstruction of the original hydrotalcite structure.
Thermal Behavior of Hydrotalcite and of Anion-Exchanged Forms of Hydrotalcite
Authors: Brindley G. W. , Kikkawa S.
Published: September 2006

Chloride-, sulfate-, and perchlorate-exchanged forms of hydrotalcite have been prepared and their layer spacings determined after equilibration in hydrous atmospheres and after heat-treatments up to the temperature of decomposition in the range 300–400°C. The initial carbonate form of hydrotalcite and also brucite, for purposes of comparison, have been similarly studied. Only chloride-hydrotalcite and brucite exhibit a single phase stable to the decomposition temperature. The other anionic forms exhibit various phases with different layer spacings which are interpreted in terms of the size, orientation, and stability of the anions and, in some cases, the presence of additional water. A regularly interstratified form of sulfate-hydrotalcite (layer spacing = 19.80 Å) is obtained at room temperature and relative humidity <50%; at higher humidities, a fully hydrated phase is obtained, and at 50°C a collapsed form is obtained. In the preparation of perchlorate-hydrotalcite, an interstratified phase (layer spacing = 17.0 Å) was recognized with alternating carbonate and Perchlorate layers, although the evidence is less certain.
Effect of SiO2/Al2O3 Ratio on the Thermal Reactions of Allophane
Authors: Henmi Teruo
Published: September 2006

Differences were found in the differential thermal analysis curves and in the temperatures of new-phase development between allophanes of high (1.91–1.99) and low (1.47–1.53) SiO2/Al2O3 ratios. The endothermic peak due to continuous dehydration and dehydroxylation was at higher temperatures (153°-185°C) for allophanes with high SiO2/Al2O3 ratios and at lower temperatures (148°–165°C) for those with low SiO2/Al2O3 ratios. The temperature of the exothermic peak was lower and the height affected more by the exchangeable cation content for allophanes with high ratios than for those with low ratios. New phases did not develop in allophanes having high Si02/Al2O3 ratios even after they were heated to 1000°C, above the temperature of the exothermic peak. In contrast, a symptomatic development of new phases was noted in allophanes with low SiO2/Al2O3 ratios at 900°C, below the temperature of the exothermic peak. The effect of SiO2/Al2O3 ratio in the thermal behavior of allophane strongly suggests that differences in the structure are closely associated with the chemical composition of this material.
Adsorbed Cr(III) on Chlorite, Illite, and Kaolinite: An X-Ray Photoelectron Spectroscopic Study
Authors: Koppelman M. H. , Emerson A. B. , Dillard J. G.
Published: September 2006

The adsorption of Cr(III) was studied at pH 1, 2, 3, 4, 6, 8, and 10 on chlorite and kaolinite and at pH 1, 2, 3, and 6 on illite. The amount of chromium adsorbed on chlorite varied from 3.1 × 10–5 mole/ g at pH 1 to 16.6 × 10–5 mole/g at pH 4, and on illite from 4.9 × 10–5 mole/g to 9.2 × 10–5 mole/g at pH 1 and 3, respectively. Kaolinite adsorbed 3.7 × 10–5 mole Cr/g at pH 1, 2, and 3 and 5.5 × 10–5 mole Cr/g at pH 4. Measurements of the Cr 2p core-level binding energies indicate that chromium is probably adsorbed as a Cr(III) aqua ion at pH values below 4. The binding energies for the Cr 2p level for samples prepared above pH 4 compare favorably with the value determined for chromium hydroxide and lead to the conclusion that the chromium species present at pH 6, 8, and 10 is chromium hydroxide.
Metallation-Demetallation Reaction of Tin Tetra(4-Pyridyl) Porphyrin in Na-Hectorite
Authors: Abdo S. , Cruz M. I. , Fripiat J. J.
Published: September 2006

The adsorption of Sn(IV)TPyP (mesotetrapyridylporphyrin) in sodium hectorite was studied using ultraviolet-visible and luminescence spectroscopy. The adsorbed complex was found to demetallate forming the TPyP dication as the clay is dehydrated. This process was found to be reversible indicating that the Sn4+ ion remains in the vicinity of the porphyrin upon demetallation. The luminescence spectrum of the adsorbed complex was found to be a composite of the Sn(IV)TPyP and the dication spectra. The presence of a band at 750 nm in the luminescence spectrum of the adsorbed species suggested an enhanced interaction between the π-systems of the pyridyl substituents and the porphin nucleus. This is believed to result from a decrease in the dihedral angle between the nucleus and the substituents when they are squeezed between the clay sheets.
Thermal Decomposition of a Kaolinite:Dimethyl Sulfoxide Intercalate
Authors: Adams J. M. , Waltl G.
Published: September 2006

The thermal decomposition of a kaolinite:dimethyl sulfoxide intercalate has been studied by thermogravimetry. The decomposition is complete by 175°C and has a ΔH of 58 ± 5 kJ/mole of dimethyl sulfoxide. For the first 70–80% of the reaction a plot of log(l — α) vs. time is linear, where α is the reaction fraction complete. A two-dimensional, contracting-circle type of mechanism is consistent with this linearity, provided that the nucleation process is considered to be exponential rather than instantaneous. An activation energy of 105 ± 8 kJ/mole of dimethyl sulfoxide has been derived. This value is inconsistent with the simple assumption that the rate-determining step is the freeing of single organic molecules from their bonding to the clay layers. The mechanism of this decomposition is different from that found for kaolinite: N-methyl formamide, and the activation energy is considerably greater than that found for that material (30 ± 3 kJ/mole).
Adsorption of 1,10-Phenanthroline by Some Clays and Oxides
Authors: de Bussetti S. G. , Ferreiro E. A. , Helmy A. K.
Published: September 2006

The adsorption of 1,10-phenanthroline (OP) onto some clays and oxides was studied as a function of concentration, pH, and time. The adsorption was found to be irreversible and the isotherms, except for silica gel, were hyperbolic and gave rise to plots similar to that of Langmuir. Kinetic and light scattering studies show that OP is adsorbed as a micellar unit composed on the average of 3.5 molecules/micelle. This fact explains the overestimation observed in the surface areas of some sorbents since no true monomolecular layer of OP is formed on the surfaces. The adsorption was also found to be pH dependent, attaining a maximum, independent of the sorbent, at about pH 6. This maximum was approximately at the same pH in which only the molecular form of OP began to be present. The partial desorption of OP as the pH increased beyond 6 is possibly associated with the aggregation of micelles on the surfaces.
Alkali Cation Selectivity and Fixation by Clay Minerals
Authors: Eberl Dennis D.
Published: September 2006

Two variables must be considered when calculating exchange free energies (ΔG°ex) for 2:1 clays: (1) anionic field strength, as expressed by equivalent anionic radius (ra), and (2) interlayer water content, as expressed by interlayer molality. For smectites that are in a state of high hydration, interlayer molality is determined by the cations undergoing exchange. Thus ΔG°ex for an exchanging cation pair can be calculated solely from measurements of ra. ra is related to layer charge per half unit cell (C) and ab unit cell area (A) by: ra = (-A/8πC)1/2. The layer charge necessary for cation fixation can be predicted by calculating the ra at which cation exchange with an illite structure expresses a AG°ex equal to that of exchange with a smectite structure. The theory can also be applied qualitatively to understand the high selectivity of illite for Cs+, the fixation of K+ rather than Na+ in shales during diagenesis, the stability of illite over muscovite in the weathering environment, and cation segregation in smectite.
High Resolution Electron Microscopy of Feldspar Weathering
Authors: Eggleton Richard A. , Buseck Peter R.
Published: September 2006

High resolution imaging by transmission electron microscopy has revealed a mechanism for the weathering of intermediate microcline in a humid, temperate climate. Dissolution of the feldspar begins at the boundary of twinned and untwinned domains and produces circular holes which enlarge to form negative crystals. Amorphous, ring-shaped structures develop, about 25 Å in diameter, within the larger holes. These rings, in turn, crystallize to an arcuate phase having a 10-Å basal spacing and then to crinkled sheets of illite or dehydrated montmorillonite. The 10-Å layer silicate shows an irregular stacking sequence, including 10-,-20-, and 30-Å sequences. Included plagioclase crystals show a similar mechanism of weathering and, moreover, are more intensely weathered.
Mössbauer, Thermomagnetic, and X-Ray Study of Cation Ordering and High-Temperature Decomposition in Biotite
Authors: Bagin V. I. , Gendler T. S. , Dainyak L. G. , Kuz'min R. N.
Published: September 2006

To explain the large values of the quadrupole splittings and line widths in the Mössbauer spectrum of oxybiotite, a formalized analysis of the distribution of effective charges in the anion network was conducted using an idealized model of the biotite octahedral layer. Based on this analysis, a qualitative physical model has been proposed, according to which the Mössbauer spectrum consists of a superposition of six quadrupole doublets. The proposed model explains the appearance of residual magnetization well below the biotite decomposition temperature. Annealing the biotite at 1070°K leads to the formation of nuclei of the magnetic phase in chains consisting of R3+ and vacancies. This phase is the decomposition product of biotite at 1370°K, i.e., a ferrispinel having Fe2−xMgAlxO4 (x = 0.5–0.6) composition.
Adsorption of Cr(NH3)63+ and Cr(en)33+ on Clay Minerals and the Characterization of Chromium by X-Ray Photoelectron Spectroscopy
Authors: Koppelman M. H. , Dillard J. G.
Published: September 2006

The nature of Cr(NH3)63+ and Cr(en)33+ (en = ethylenediamine) adsorbed on chlorite, illite, and kaolinite has been studied by X-ray photoelectron spectroscopy (XPS). The interaction of the chromium complexes with the clays began at pH 3. During the 7-day interaction time the pH of the complex-clay suspension increased to 8 for illite and chlorite. For kaolinite the pH increased to about 3.6 with Cr(NH3)63+ and to 6.4 with Cr(en)33+. These pH changes appear to be associated with a clay-catalyzed hydrolysis of the chromium-amine complexes. XPS binding-energy data for adsorbed chromium indicate that the dominant species are chromium aqua complexes. Nitrogen/chromium atom ratios, calculated from the XPS photopeak intensities, are less than 6:1 for complexes adsorbed on the clays, suggesting that chromium complexes are initially adsorbed but subsequently hydrolyze to produce aqua-chromium surface species.
Syntheses of Glauconite at Surface Temperatures
Authors: Harder Hermann
Published: September 2006

Glauconite has been synthesized at low temperature by precipitation of Fe-hydroxides from Si-, Fe-, Al-, and K-containing solutions under reducing conditions. The compositions favorable for the synthesis at 20°C and pH 8.5 are 1 ppm Fe, 0.15 ppm Al, 13 ppm Si02, 1000 ppm KC1, and 1000 ppm dithionite. The K-content of the solutions must be sufficiently high to fix K in the precipitate.

Under special early diagenetic conditions glauconite is formed in marine sediments, probably at the interface between reducing and oxidizing zones in the muddy sediments. The silica content of pore waters seems to control the formation of glauconite or chamosite rather than depth or temperatures of the bottom waters.
Interpretation of the Variability of Selectivity Coefficients for Exchange Between Ions of Unequal Charge on Smectites
Authors: McBride M. B.
Published: September 2006

Ion-exchange experiments in expanding clay minerals conducted over a wide range of surface ionic compositions and ionic strength produce variable mass-action selectivity coefficients. When the exchanging ions are of unequal charge, tactoid structure appears to influence selectivity, although configurational entropy of adsorbed ions may also generate variable selectivity. The degree of deviation from ideal mass-action exchange is related to the dissimilarity of the ions undergoing exchange. Data involving trivalent ion adsorption on smectites suggest that mass-action is a poor approximation when the adsorbing and desorbing ions have different hydration energies and charge. No form of exchange equation is successful in describing ion exchange for a wide range of experimental conditions, although the fluctuation of the selectivity coefficient follows consistent trends with changing experimental conditions. The strong adsorption of high-charge ions on clays is not exothermic, but must be driven by the increasing disorder of ions and/or water.