The literature on the complexes of n-alkylammonium ions with layer silicates is characterized by marked divergences, not only in the deductions and conclusions of the different investigators but also in their experimental results. An attempt is made to reconcile and rationalize the differences, and to form a self-consistent picture of these systems.

Given a saturating solution of sufficient concentration, the complexes tend during their formation to adopt an arrangement in which silicate layers are separated by double layers of ions oriented so that the alkyl chains are extended away from the silicate surfaces at a high angle. Water molecules, salt and free alkylamine may also be present in the interlayer spaces. When the excess material is removed by washing and the complexes dried, ideally the alkyl chains from opposing surfaces move over one another and interpenetrate so as to form a single layer of ions. During the contraction, however, the chains interact with one another and tend to stick at some point short of complete interpenetration. Weak attractive forces acting to bring the silicate layers together, and consisting mainly of electrostatic forces originating in the mineral layers and van der Waals interactions arising from increasing association of opposing alkyl chains with increasing interpenetration, are insufficient to overcome this tendency fully. As a result, an alkyl chain of given length can give rise to a series of complexes differing in their XRD characteristics.

Previous workers have noted the difficulty of achieving reproducible results and some have recommended grinding the complexes, but it appears that this treatment significantly alters the nature of the end-product.

The adsorption of various alkylammonium cations from aqueous solution by sodium and calcium montmorillonite has been studied. Adsorption occurred through an exchange reaction between the inorganic cations on the clay and the alkylammonium ions in solution. The affinity of the clay for these cations was linearly related to molecular weight, with the exception of the smaller methyl-ammonium and the larger quaternary ammonium ions. Comparison of primary, secondary and tertiary amines containing the same alkyl groups showed that the affinity of the clay was greatest for the primary amine and least for the tertiary. This behaviour has been interpreted in terms of the size and shape of the cations. X-ray diffraction analysis showed that no more than a single layer of adsorbed cations was present in the inter-lamellar space at maximum adsorption. Comparison between Δ-values and the thickness of the adsorbed ions showed that there was a contraction in the apparent contact distance of these cations. The amount of contraction could be accounted for by ‘keying’ of the adsorbed ions into the montmorillonite surface.

Infrared absorption by a mineral arises from the vibrations of its constituent atoms, and the frequencies of these vibrations are dependent on the mass of the atoms, the restraining forces of the bonds, and the geometry of the structure. The resultant spectrum of absorption frequencies is a characteristic property of the mineral which can not only serve as a fingerprint for its identification, but also give, in favourable cases, unique information on features of the structure, including the nature of isomorphic substituents, the differentiation of molecular water from constitutional hydroxyl, the degree of regularity of the structure and an indication of the family of minerals to which an unknown mineral is related.

The dissolution of hectorite suspensions in M/20 CaCl2 has been studied under conditions of low acidity. The reaction was almost completed within 2 weeks but very slow changes continued. There was an initial preferential release of Mg which corresponded approximately to the number of Mg atoms exposed at the clay edges but thereafter Mg and Si were released into solution in nearly equimolar amounts until most of the clay was decomposed. The release of octahedral cations was equivalent to the amounts of H+ ions added. Some earlier views on the acid attack of 2:1 clays were supported. With increasing amounts of acid added, the Si released into solution as monosilicic acid become supersaturated before final precipitation as amorphous silica of high surface area.

The molar proportion of Si/Mg released into solution was less than that of the original sample yet there was no chemical or X-ray evidence of the development of significant siliceous ‘fringes’. The residues of the tetrahedral layer probably separate continually, thus maintaining the same kind of reaction surface throughout the reaction, without passing into solution or forming a stable sol. Acid attack in the presence of excess silicic acid did not result in any appreciable selective dissolution of octahedral layer.

The chemisorption of methylene blue by kaolinite crystals increased as the aqueous suspensions changed from acid to alkaline because, at high pH values, not only the basal pinacoids but the edge-faces were negatively charged. The inability to calculate acceptable specific surfaces or cation exchange capacities from the chemisorption data is discussed, with special reference to the orientation of adsorbed dye cations, the covering of more than one exchange site by a monomer or polymer, the different concentrations of exchange sites on the basal pinacoids and edge-faces respectively, the possibility that such sites occur on the tetrahedral rather than on the octahedral basal pinacoid, and the incomplete replacement of inorganic cations.

The oxidation of benzidine to benzidine-blue on silicate minerals is shown to occur at aluminium atoms exposed at crystal edges and at transition metal atoms in the higher valency state present in the silicate lattices. The transition metals in the silicate lattice undergo chemical oxidation-reduction reactions.

Changes in the colour of the benzidine-blue radical cation with the conditions of reaction are discussed in terms of the solvent used for the reaction and its influence on the pH of the mineral surface.

A pyridine-vermiculite complex has been investigated by three dimensional X-ray diffraction techniques. The preparation of the complex was carried out at a pH ∼ 4 using a solution of pyridinium hydrochloride. Exsolved magnesium from the octahedral positions satisfied approximately one-half of the cation exchange capacity. The rest of the exchange capacity is satisfied by hydrogen ions and pyridinium ions which are statistically distributed over crystallographic sites so that less than three electrons per Å3 are present at any given point. Three dimensional difference electron density maps did not locate the carbon atoms except to indicate that the organic molecule occupies positions in the true and in the two pseudo mirror planes in the unit cell. Water molecules were present in the interlayer in octahedral arrangement around the cation as in the natural mineral.

The chemical equilibrium of a purified sample of hectorite was studied over a range of pH, silicic acid, and magnesium chloride concentrations. The quasi-equilibrium reached by about 6 weeks was reversible with respect to added magnesium ions but only partially so for added silicic acid. The free energy of formation of hectorite at 25° C was calculated at −2680 kcal/unit cell, using the derived equilibrium constant and the stoichiometry of the reaction as previously established.

Using the adiabatic calorimeter which has been developed by Nagasaki & Takagi (1948) and manufactured by the Rigaku Denki Company, the energy changes associated with the dehydration and dehydroxylation processes of clay minerals were measured at room pressure. The samples studied were mont-morillonite, chlorite (trioctahedral type), and three kinds of interstratified minerals with component layers such as mica, dioctahedral chlorite, and montmorillonite. ΔH-values due to the dehydration of the interlayer region were 9·8 kcal/H2O mole for montmorillonite and 12·4–13·4 kcal/H2O mole for interstratified minerals mica-montmoriIlonite and dioctahedral chlorite-montmorillonite. The values due to dehydroxylation of the silicate layer were 17·7 kcal/H2O mole for montmorillonite, 16·8–17·5 kcal/H2O mole for the interstratified mica- montmorillonite, and 19·3 kcal/H2O mole for chlorite. The value for the dehydroxylation of the hydroxyl layer of chlorite was 19·3 kcal/H2O mole. For the sake of comparison, the heat of transition α↔β of quartz was found to be 140 cal/mole. The reproducibility of these values was in the range of ±5%.

The mechanism of colour reactions of clay minerals with amines, diphenylpicrylhydrazyl, tetracyanoethylene, and leuco bases are elucidated, and the results used as a guide to the reaction mechanism of polymerization reactions catalysed by clay surfaces.

Quantitative gas chromatographic analyses supplemented by X-ray diffraction studies of the adsorption of ethanol and acetone (as model polar organic compounds) on homoionic montmorillonite revealed marked variation in the number of molecules associated with each exchange cation. The results show increasing association in the order K+ <Na+<Ba2+<Ca2+. K+ and Na+ associate with two and three molecules, respectively, of either ethanol or acetone, and the resulting complexes expand to form a monolayer (∼13 Å). Ba2+ and Ca2+ form both monolayer complexes as well as double layer complexes. In the single layer complexes Ba2+ associates with either four molecules of ethanol or four molecules of acetone, Ca2+ associates with five molecules of ethanol or four molecules of acetone. In the double-layer complexes the observed cation-molecule ratios are 1 : 8 for both Ba2+-ethanol and Ba2+-acetone, 1 : 10 for Ca2+-ethanol, and 1 : 8 for Ca2+-acetone.

The striking dependence of ethanol and acetone adsorption on the nature of the exchangeable cation suggests that cation-dipole interactions play an important role in the adsorption process. Structural models of the organic complexes are presented.

A study has been made of the influence of adsorbed alkylammonium ions on the water sorption and swelling of Na+ and Ca++ montmorillonite, under controlled conditions of temperature and suction. The water uptake and extensive crystalline swelling of Na+ montmorillonite decrease as the proportion of exchangeable alkylammonium/ammonium ions increases. This decrease is more associated with the degree of surface coverage than with the degree of saturation of the exchange sites by the alkylammonium ions. These observations are explained in terms of binding of the organic cation by the clay surface and the collapse of diffuse double layers on interlamellar surfaces. Differences in water uptake betwen complexes saturated with different alkylammonium ions are attributed to differences in the structural arrangement of the clay crystals in the swollen state. Similarly, there is a continual slight decrease in the water uptake and swelling of Ca++ montmorillonite as the amount of alkylammonium ions present increases. However, for alkylammonium ions containing less than five carbon atoms and when only about half of the exchangeable Ca++ ions have been replaced by the organic ions, extensive crystalline swelling sometimes takes place. When this occurs, it is suggested that the alkylammonium ions disrupt the regularity of the water network initially associated with the Ca++ ions, enabling these to participate in the formation of diffuse double layers in the interlamellar space.

Clays from the Ae and C horizons of five Podzol soil series in New Brunswick were examined by X-ray, chemical and infrared absorption methods. All the experimental evidence indicated that the Ae horizons contained predominantly a dioctahedral randomly interstratified mica-vermiculite-smectite clay, whereas the C horizons contained abundant dioctahedral mica (illite) and trioctahedral chlorite. Since no trace of chlorite as a separate phase or as one component of the interstratified structure was found in the Ae horizons, it was concluded that, while the inherited chlorite was decomposed in all of the Ae horizons, mica was differentially hydrated giving an interstratified structure. Fourier transforms of the three-component interstratified clay revealed different ratios of hydrated layers (vermiculite and smectite) to non-hydrated layers and different stacking sequences. The proportion of hydrated layers and randomness of stacking was related to the degree of weathering as measured by the accumulation of TiO2 in the Ae horizon and it was suggested that they may be related to the degree of podzolization.

The heavy metal cations studied were adsorbed by hectorite suspended in 0.05 M calcium chloride as a pH-dependent reaction in the order, Cu > Zn > (Co, Mn) > Ni. The adsorption of heavy metal cations was accompanied by the removal from solution of silicic acid released by clay dissolution. It is proposed that the reaction takes place on edge surfaces such that the clay lattice is effectively extended. This result complements other work in which it has been shown that the adsorption of silicic acid by other silicate clays results in an increased adsorption of zinc, cobalt and nickel. The present study did not provide evidence of the exchange of zinc and other cations for lattice magnesium.

The solubility of hectorite was decreased in the presence of heavy metal cations in the same order that favoured their adsorption. It is proposed that they limit the dissolution of hectorite in weakly acidic solutions by adsorption on or near the sites most prone to proton attack, that is, the magnesium ions of the octahedral layer exposed at edges and defects.

Sorption of an acidic, amphoteric, sulphur containing and basic α-amino-acid (glutamic acid, glycine, methionine and lysine) by copper montmorillonite was studied by chemical and X-ray methods. With glutamic acid complex formation occurs only in solution but increasing basicity of the aminoacid favours complex formation in the clay interlayers.

A 2–20 µ fraction of phlogopite has been converted to the sodium form by use of sodium tetraphenylboron-NaCl solutions. The cation exchange capacity of the treated material increases to a maximum of about 212 m-eq/100 g, which agrees well with the K2O + Na2O content of the initial mineral. Li-, Na-, Ca-, and Mg-saturated forms have been prepared and examined by X-ray diffraction and by thernogravimetric measurements in air, in vacuo, and at progressively elevated temperatures. Hydration states corresponding to double water layers are observed for the Mg- and Ca- forms, and to single water layers for the Mg-, Ca-, Na-, and Li- forms. The numbers of water molecules per unit cell and per interlayer cation are considered for the various hydration states.

Thin green clay layers and lenses in the lower part of the Lower Oligocene Kerkom Sand near Aardebrug, east of Louvain in Belgium, were found to consist of glauconitic illite. This mineral contains about equal amounts of iron and aluminium oxides (14%) and is therefore intermediate in chemical composition between most illites and glauconites.

Comparison with the results of five published investigations of similar green clays in France and the United States shows that the green clays, which all have an intermediate glauconite-illite composition, are formed, unlike pelletoidal glauconite, in a non-marine environment. It is assumed that they developed in a lagoonal or hypersaline-lacustrine environment, probably as a result of the alteration of detrital illite-montmorillonite clay.

The evidence is reviewed for the various hypotheses put forward to explain the origin of the Chalk montmorillonite.

Recent X-ray investigation of the mineralogy of the acid-insoluble clay fractions (buffered 2 N acetic acid at pH 3; <2 µ e.s.d.) of the Lower Chalk of England sheds light on the origin of the montmorillonite. The relations between the qualitative and semi-quantitative mineralogy of the clay fractions and the facies and stratigraphy in this formation have been studied in detail. Montmorillonite, illite, kaolinite, chlorite, vermiculite, pyrophyllite, mixed-layer minerals, quartz, low-temperature cristobalite and apatite have been identified; their semi-quantitative distribution reveals that two main antipathetic assemblages are present, between which all gradations occur. The first is characterized by montmorillonite, illite, quartz and by montmorillonite/illite (M/I) values of 0·7 and above; and the second by illite, kaolinite, chlorite, vermiculite and by M/I values of below 0·2. The distribution of these assemblages or of any particular mineral does not show obvious relations to the facies or stratigraphy.

There is strong evidence that the second of these assemblages is of detrital origin, introduced into the Lower Chalk seas by currents flowing mainly from areas to the east and south-east of England. There is no evidence to suggest that the montmorillonite and the illite of the first assemblage are of detrital or volcanic origin, and their distribution in the Lower Chalk is best explained by their neoformation in the sediment on the sea floor by precipitation from the porewaters. By extrapolation it is thought that most of the Chalk montmorillonite of clay-grade is of neoformational origin. Some from the Campanian and younger Chalks may be detrital. Locally in N.W. Germany and possibly Poland minor amounts may have been derived from the decomposition of volcanic glass in the Chalk seas.

The OH-OD exchange of kaolin minerals through contact with D2O introduced into interlayer space via intersalation resulted in a partial shift of the OH absorption bands. The total decrease in OH absorbance upon deuteralion was 52, 56, and 47% for the kaolinite, dickite-nacrite, and halloysite respectively, but the percentage decrease differed for the different absorption maxima of any one mineral. A secondary OH—OD exchange in the deuterated specimens was also observed upon heating to 350 and 400° C. These data together with the lack of deuteration in montmorillonite, and available orientation data on the kaolin OH groups by infrared spectroscopy, suggest that only two-thirds of the inner-surface OH groups form the interlayer OH—O bonds.

The materials formed by dialysis of the precipitates formed by the reaction of NaOH with mixed Mg-Al solutions are described. In addition to aluminium and magnesium hydroxides, two hydrocarbonates having Mg/Al ratios of about 5 : 1 and 2 : 1 are formed, essentially pure, from solutions with Mg/Mg + Al molar ratios of 0.8 and 0.7, respectively. X-ray powder data shows that they have partially ordered hexagonal layer structures with unit layer dimensions a = 3.048 Å, layer thickness 7.60 Å for the Al-rich compound and a = 3.072 Å, layer thickness 7.92 Å for the Al-poor compound. X-ray and chemical data show that the new compounds resemble the minerals hydrotalcite and manasseite and also the compounds described as Mg-Al hydroxides by Feitknecht.