The internal surface area of Na-Wyoming bentonite was determined for linearly swelling pastes, using a physically based equation which describes such swelling. Information required is simply the linear relationship between interplatelet spacing, determined by X-ray powder diffraction, vs total water content determined gravimetrically. However, before the three-unknown parameter equation can be so applied, that portion of external-pore water, which normally increases linearly commensurately as interstitial water increases, must be decreased to zero. This was accomplished by adding dilute quantities of NaCl salt to the clay-paste system to decrease the attractive forces between positive-edge and negative-face sites, and stirring vigorously to further destroy the card-house structure and align the clay platelets.

This paper presents further results concerning the nature of the exothermic reaction of meta-kaolinite near 950°C. In a previous work (Lemaitre et al., 1975), we proposed that the exothermic effect had a double origin: (a) direct formation of mullite, promoted by CaO and (b) formation of a segregated spinel-type phase, i.e. γ-Al2O3, promoted by MgO.

In this paper, we examine the influence of a further parameter on the reaction sequence, namely the crystallinity of the starting kaolinite as defined by Hinckley's index (c.i.; Hinckley, 1963). By combining X-ray and DTA techniques it is shown that the direct mullite formation path (a) occurs readily at 900°C in well-ordered kaolinite, but not in poorly ordered samples, even when fired with CaO. On the other hand, path (b) can be promoted in all samples using MgO as a mineralizer. When the indirect reaction path (b) occurs, a second exothermic effect is observed at approximately 1200°C indicating secondary mullite formation by recombination of segregated silica and alumina phases. This effect occurs in poorly ordered kaolinites even in the presence of CaO [path (a) promotor] indicating that path (b) is the most probable reaction mechanism in very disordered kaolinites.

The adsorption of the cationic oxidized safranine S+ by a Na+, Ni2+ and Fe3+ montmorillonite has been studied with X-ray powder diffraction, u.v., visible and i.r. spectroscopy. In solution S+ may be protonated: S+, SH2+ and SH23+ have characteristic spectra in the 500–600 nm region where the clay structure does not absorb. In the Na+ as well as in the Ni2+ and Fe3+ clays, the adsorption of S+ is a cation exchange process accompanied by the protonation of the adsorbed dye such as variable concentrations of M+ (Na+, Ni2+ or Fe3+), S+ and SH2+ are simultaneously present. Protonation activity decreases from Fe3+ to Ni2+ and Na+, being the protonation site the amine group as shown by i.r. In the interlamellar space it seems that a SH2+.. S+ association exists that could be described as a sandwich structure 6.5 Å thick.

A reliable method, utilizing a fluoride ion-selective electrode, is described for the determination of fluoride in clays and shales. Interference by aluminum and iron is minimal. The reproducibility of the method is about ±5% at different levels of fluoride concentration.

Data are presented for various clay minerals and for the <2-µm fractions of marine and nonmarine clays and shales. Fluoride values range from 44 ppm (0.0044%) for nontronite from Colfax, WA, to 51,800 ppm (5.18%) for hectorite from Hector, CA. In general, clays formed under hydrothermal conditions are relatively high in fluoride content, provided the hydrothermal waters are high in fluoride content. Besides hectorite, dickite from Ouray, CO, was found to contain more than 50 times as much fluoride (6700 ppm) as highly crystalline geode kaolinite (125 ppm). The clay stratum immediately overlying a fluorite mineralized zone in southern Illinois was found to have a higher fluoride content than the same stratum in a nonmineralized zone approximately 1 mile away. Nonmarine shales in contact with Australian coals were found to be lower in fluoride content than were marine shales in contact with Illinois coals.

It is believed that, in certain instances, peak shifts on DTA curves of similar clay minerals are the result of significant differences in their fluoride content.

Organic solvent soluble organosilicate compounds retaining silicate backbone were obtained by the reaction between biotite and trimethylsilylating reagent. The soluble product which was formed at room temperature or at reflux temperature was a viscous liquid and was soluble in a wide range of organic solvents, but insoluble in water. Molecular weights of the soluble products and their thinlayer chromatograms made it clear that the soluble products consisted of several trimethylsilylated derivatives of silicic acids which were mainly the derivatives of mono- and disilicic acid. The influence of reaction temperature for the trimethylsilylation reaction also was discussed.

Hydroxyl orientation has a major influence on the strength of the ionic interlayer bonding in micas because of the strong repulsion between the hydrogen and the interlayer cation (IC). In order to determine if other factors also influence the magnitude of the interlayer bond energy, the effect due to the varying H-IC distance, as one finds, for example, between a dioctahedral and a trioctahedral mica, must be removed. This can be done by calculating the bond energy as a function of the H-IC distance; a plot of which is a smooth curve with a minimum energy for the minimum H-IC distance. If there are no other factors which substantially contribute to the interlayer bonding energy, such curves for all micas should be superimposed. If, however, the curves are not superimposed but fall into groups with common attributes (stacking sequence, ionic substitutions, etc.) the energy separations between groups of curves indicate the influence of these other factors.

The results of such calculations for four dioctahedral micas (2M1 muscovite, 3T muscovite, and two 1M muscovites) and four trioctahedral micas (2M1 biotite, 1M phlogopite, 2M2 lepidolite and a 1M MgIV mica) indicate that these curves are at higher energy for dioctahedral than for trioctahedral micas and this energy increase is due to the filling of the octahedral sites. The dioctahedral micas are arranged in terms of energy as 1M ≥ 3T ≫ 2M1 while the order for the trioctahedral micas is 1M ≥ 2M1 ≅ 2M2. In addition, the calculated energies suggest that the distribution of the layer charge between the octahedral and tetrahedral sheets affects the strength of the interlayer bond such that the greater the charge on the octahedral sheet, the stronger the interlayer bond.

Clay materials separated from estuarine sediments in Louisiana exhibit a selectivity for exchangeable calcium in laboratory experiments. The studies were conducted at 25°C and 60°C in mixed calcium and potassium chloride solutions in which the equivalent fraction of potassium varied from 0.12 to 0.54. Calcium selectivity was observed to increase with an increase in the equivalent fraction of potassium in the external solution and the temperature. The results suggest the possible importance of ion exchange reactions in the regulation of calcium availability during early diagenetic reactions in sediments.

The effect of swelling on the b-dimension of Na-saturated, Upton, Wyoming montmorillonite was re-examined using powdered silicon as an internal standard. After being corrected with reference to the internal standard, the b-dimension did not increase through the entire range of swelling as reported previously. It increased up to a water content of ~3.0g/g montmorillonite and remained constant thereafter. However, the diffraction peak of the internal standard shifted towards lower angles at higher water contents. This shift was attributed to a relaxation of the wetter samples away from the knife edge of the diffractometer. Presumably, a similar relaxation occurred in the earlier study and was responsible for the apparent increase in b-dimension at water contents above ~3.0g/g.

The b-dimension of Upton montmorillonite saturated with different cations was determined using powdered silicon and a colloidal quartz impurity as internal standards. The water content at maximal swelling decreased as the b-dimension increased.

Characteristics and properties of complexes of a smectite (hectorite) with 1,10-phenanthroline (phen) chelates with iron or copper were determined by a variety of physical and chemical measurements. The complex ions showed high selectivity for the hectorite surface. Basal spacings of 17.4 Å were produced by Fe(II) or Cu(II) analogues of M(phen)32+ hectorite. Adsorption of gases and vapors by the M(phen)32+ hectorite complex revealed large surface areas and reflected intrinsic characteristics of the complex ions. Lower surface areas were found for copper phen hectorite than iron phen hectorite probably because of the loss of a ligand from the Cu(II) ion. ESR spectra confirmed that appreciable Cu(II) existed as the bis-phen complex under certain conditions. An increase in the oxidation potential of the Fe(phen)32+-Fe(phen)33+ couple above that in pure solvent was noted when these complexes were supported by the mineral surface.

The ESR spin probe, TEMPAMINE+, was used to study the interlamellar behavior of adsorbed organic cations on hectorites solvated with water, ethanol, and water-ethanol mixtures, and saturated with several monovalent and divalent metallic cations. The mobility and orientation of the probe was affected greatly by the solvent, and to a lesser extent by the predominant exchangeable cation on the silicate surface. Most of the effects could be interpreted in terms of the basal spacings of the hectorite. In all instances, the adsorbed probe was much less mobile than in solution despite the different interlamellar volumes available for molecular motion.

The standard method of assessing the available portion of the nutrient reservoir of a forest soil is to use a neutral salt solution, such as NH4OAc, to extract the exchangeable plus dissolved ions, which are analyzed and considered available. This approach, designed for evaluating nutrients available for the short growth term of agricultural crops, is inadequate for assessing the nutrient pool of forests where tree growth term may reach 100 yr or more.

Soil nutrient reservoirs were evaluated in two forest soils for K, Na, Ca, Mg and Fe, using an approach based on continuous extraction of the elements and kinetic analyses of the extraction rate curves. The analyses of the curves indicate that K, Na, Ca and Fe are each released at four separateconstant rates, and Mg is released at three separate constant rates. By analogy with similar kinetic studies done on monomineralic layer silicate samples, each separate extraction rate is thought to correspond to a single type of bond site in the soil. Higher extraction rates indicate greater ease of removal and are interpreted as indicating a higher degree of availability relative to the extractant.

The available K reserves of the Everett soil evaluated by standard methods, compared with annual net K uptake rates of its forest system, indicates growth limiting K deficiency in 12–17 yr. K availability assessed by kinetic analyses indicates about 100 yr supply of K is available.

From 2 to 28% opal-cristobalite was isolated from the 2–20 µm fraction of rhyolitic and andesitic tuffaceous pyroclastics from the Island of Honshu, Japan, where it had been formed in hydrothermal springs at temperatures of ∼25–170°C as calculated from the oxygen isotopic ratios (18O/16O). Three of the isolates gave X-ray powder diffractograms with strong peaks at 4.07 Å. Two of these also had very weak peaks at 4.32 Å indicative of the presence of traces of tridymite. The fourth isolate had a strong 4.11 Å cristobalite peak and a very weak 4.32 Å peak. The morphology, determined by the scanning electron microscope, varied with the formation temperature indicated by the oxygen isotopic ratio (δ18O), from spheroidal and spongy for the opal-cristobalite formed at ∼25°C (δ18O = 26.0‰) in contrast to angular irregular plates and prisms for that formed at ∼115°C (11.9‰), ∼135°C (7.9 ‰) and ∼170°C (6.8 ‰). The differences in δ18O values are attributed to variation in hydrothermal temperature, but some variability in oxygen isotopic composition of the water is possible. The field-measured temperatures related roughly with the calculated fractionation temperatures except in one site, while the contrast in cristobalite morphology related well to calculated low and high fractionation temperatures. Low-cristobalite of hydrothermal origin in New Zealand (δ18O = 9‰) had characteristic rounded grains with some evidence of platiness. Co-existing quartz grains (δ18O = 10‰) showed more subhedral and irregular prismatic morphology.

Sesquioxidic soil clays from Oxisols in South Africa, Australia and Brazil, and two clays from Andosols in Japan and New Zealand, were investigated by selective dissolution techniques. Acid ammonium oxalate (pH 3) was found to be superior to currently popular alkaline reagents for extracting amorphous aluminosilicates and alumina from these clays. Boiling 0.5 N NaOH dissolved large amounts of finely-divided kaolinite and halloysite, while hot 5% Na2CO3 reaction was too slow (partial dissolution of synthetic amorphous aluminosilicates with one extraction) and insufficiently selective (gibbsite and kaolin of poor crystallinity dissolve to a variable extent). On the other hand, synthetic gels (molar SiO2/Al2O3 ranging from 0.91 to 2.55) dissolved completely after 2 hr shaking in the dark with 0.2 M acid ammonium oxalate (0.2 ml/mg). Specificity of oxalate for natural allophane was indicated by removal of similar quantities of silica and alumina using different clay:solution ratios. Oxalate extraction data indicated that allophane is absent in Oxisol clays. Allophane was determined quantitatively in volcanic-ash soil clays by allocating hydroxyl water content to oxalate-soluble silica plus alumina on the basis of an ignition weight loss-chemical composition function for synthetic amorphous alumino-silicates. Parameters of chemical reactivity and distribution of electric charges following various chemical pretreatments of allophane were found to correspond closely to those predicted on the basis of synthetic gel behaviour. Results for Oxisol clays suggested that the role of amorphous (oxalate-soluble) alumina in governing physicochemical properties is generally less than that of the poorly-crystalline, Al-substituted iron oxide component which is removed by deferration with citrate-dithionite-bicarbonate reagent.

Microprobe analysis of a synthetic large crystal type X zeolite shows that the silica to alumina molar ratio increases from the crystal center to the exterior.

The d(001) spacings for a series of montmorillonite samples containing increasing amounts of Cu(en)32+ were recorded after exposure to 50% humidity, 10% humidity, and air that had been saturated with ethylene glycol. It was found that Cu(en)32+ is too large to fit between the montmorillonite particles and that in those samples with large amounts of ethylenediamine Cu(II) added, the clay platelets are associated with stronger interactions than those with small amounts of Cu(II) complex added.

Infrared spectroscopy and electron spin resonance analysis indicate that the absorbed copper (II) complex is the square planar bis ethylenediamine Cu(II) and that the complex ion is oriented so that the $d_{z^2}$ orbital is perpendicular to the clay surface. The montmorillonite particles may act as ligands and coordinate with Cu(en)22+ ions.

The surface charge density of mica (001) cleavages was determined by counting the number of fission particle tracks in a given area of a 6-mm muscovite disc replica with optical and scanning electron microscopy after saturation of the layer charge by washing with 0.5 M UO2(NO3)2 solution, dilution of the excess salt by washing with 0.01 M UO2(NO3)2 in 0.005 M HNO3 (pH 2.4), blotting off the excess liquid, thermal neutron activation in contact with the muscovite disc, etching the muscovite, and counting the 235U fission tracks/cm2. In initial studies, the uranyl cations were found to hydrolyze from the cleavage surface continuously during the washings with water, ethanol or acetone to remove excess salts, but the uranyl cations in the interlayers near broken edges and crystallographical steps were strongly retained even against washings with 0.5 M CaCl2 solution. The hydrolysis of UO22 + from the smooth portions of the flake surfaces was avoided by the use of three 1-hr final washings with the 0.01 M UO2(NO3)2 in 0.005 M HNO3 solution. Each flake was pressed between filter papers three times to remove the excess solution. A negligible amount of excess salt remained on the cover glass controls. The UO22 + cations retained (mean, 3.6 ± 0.2 × 10−7 mequiv./cm2) on the cleavage surfaces of various micas were nearly equivalent to the theoretical surface charge (cation exchange capacity, 3.5 × 10−7 mequiv./cm2), showing that hydrolysis was prevented. The uranium on the unblemished mica planar surfaces increased with increasing uranyl concentrations in the final washing solution, indicating that the excess salt remaining on the surfaces had become significant. With a given UO22 + salt concentration, the uranium on the surface increased on increasing the solution pH from 2.5 to 3.5, attributable to the formation of polymeric ions such as U2O52 + and U3O82 + with higher uranium retention per unit positive charge equivalent to the fixed negative charge of the mineral surface. Uranyl cations replaced much of the interlayer cations from vermiculites even after K, Rb and Cs presaturation and drying from 110°C were employed. Strong adsorption of uranyl cations (in a form not replaced by washings with a neutral salt solution), which occurred in the defects of micaceous minerals, is important in the interpretation of actinide element retention in soils and sediments wherein these minerals are abundant.

The electrical conductivity of a colloid-water-electrolyte system increases with the frequency of the applied alternating electric current. The phenomenon is referred to as conductivity dispersion. This paper reports on the effects of electrolyte type, electrolyte concentration, and water content on the dispersion characteristics of kaolinite, illite, and silty clay soils, with emphasis on the mechanisms governing the dispersion phenomenon. It was observed that magnitude of conductivity dispersion increases with a reduction in water content, electrolyte concentration, and cation-exchange capacity of the clay. The type of ions influence the electrical dispersion through their size and mobility. Frequency effect increases as the hydrated radius of the counterions associated with the clay surface increases. Conductivity dispersion is explained primarily in terms of counterion/co-ion ratio in the diffuse double layer. Increase in the ratio of counterions to co-ions is an indication of a larger contribution to conduction by counterions than by co-ions, which in turn results in a larger frequency effect. Although diffusion coupling has an important role in the electrical dispersion characteristics of clay—water—electrolyte systems, other coupling phenomena, particularly electro-osmotic coupling, plays a significant part.

The surface charge characteristics of a range of synthetic amorphous aluminosilicates, hydrous alumina, hydrous silica and two allophanic soil clays were determined by the retention of Na+ and Cl− as counter-ions from 0.1 M NaCl solution. In the pH range investigated (3–9), only negative charges could be detected in the hydrous silica and the most siliceous aluminosilicate [Al/(Al + Si) = 0.29], and only positive charges were detected in the hydrous alumina; whereas both positive and negative charges were detected in the more aluminous aluminosilicates and the soil allo-phanes. In all cases, the surface charges were pH-dependent and in the aluminosilicate series negative charge decreased and positive charge increased with Al/(Al + Si). Consequently, the point of zero charge increased with Al/(Al + Si).

The charge characteristics of the amorphous aluminosilicates could be explained by current models of their structure. Negative charge can be attributed to isomorphous substitution of Al for Si in the silicate structure and to the dissociation of silanol groups in structural and adsorbed silicate. Positive charge is attributed to protonation of hydroxy-aluminum species occupying cation exchange sites.

Some dehydroxylated sericites were boiled with solutions of various salts. A rectorite-like regular mixed-layer was formed when 2M sericite was treated with solution containing salts such as NaNO3, Na2SO4, CaSO4, CaCl2, MgCl2 and MgSO4 respectively. A random mica/montmorillonite mixed-layer was formed from 1M sericite. In order to change the 2M sericite into a regularly interstratified mineral, they are heated to the temperature range of dehydroxylation. The formation of a regularly interstratified mineral from 2M sericite can be explained by the change in the (OH) bond direction after the extraction of the potassium ion.