Although Thermal Analysis is a useful technique in characterizing the clay constituent of a potentially valuable clay deposit, it is, perhaps, even more useful when the type and amount of non-clay impurities are important factors in its commercial appraisal. The effect of impurities on the physical and chemical properties of the clay may determine its potential uses in bulk, or it may be advisable to remove the impurity, either to improve the grade and quality of the clay or to provide a useful by-product. The application of both qualitative and quantitative thermal data, in the analysis and control of laboratory work in this field, is demonstrated by its use in the assessment of materials such as evaporite-rich clays, siliceous clays, and high-alumina clays.

A method is outlined and apparatus described to prepare rapidly and conveniently a reproduceable linear density gradient of any low-to-high value. The apparatus consists of two prismatic connected vessels of triangular shape one of which is inverted and tilted to a pre-calculated degree to account for the density difference of the liquids in the vessels. The liquids emerge, by gravitational levelling, from a common efflux tube connecting the vessels. 30 ml of density gradient can be withdrawn in 5 min. The linearity of the etflux is theoretically derived and shown experimentally using a number of organic liquids.

The weathering of hornblende in the Rehiran profile has been investigated by optical, X-ray, infrared and differential thermal methods. Optical studies of the fresh hornblende show that it contains discrete lamellar intergrowths of another amphibole which, from infrared evidence, is of an iron-rich nature. This minor phase is selectively weathered in the lower horizons and yields a clay mineral which was identified as interstratified swelling chlorite-saponite. The major hornblende component remains relatively unchanged. Single crystal photographs indicate that the formation of the clay mineral is not structurally controlled by the parent hornblende, although there is a tendency towards alignment along cleavage planes. The clay mineral becomes unstable in the upper part of the profile and could not be detected in the A horizon. Comparisons are made with the findings of other workers.

The electron microscope has been used to study the mechanisms of thermal decomposition of kaolinite in the temperature range 800-1350°C. Three main reaction mechanisms appear to be important in this temperature range. At 850°C metakaolinite breaks down to produce an amorphous defect oxide phase which is homogeneous and finely porous. When heated at 900°C the reaction product is a defect spinel with strongly preferred orientation and microporous structure. This defect spinel phase is observed in the temperature range 900-1150°C and shows little change in microstructure throughout this temperature range where the secondary development of muUite also occurs to a limited extent. Above 1150°C mullite develops in quantity and appears to represent the bulk of the reaction product at 1200°C.

Because of increased interest in mineralogical analysis of soils a rapid, generally applicable method to separate clay minerals is needed, and such a method is described here. The technique is a modification of the heavy liquid density gradient centrifugation method which is commonly applied in mineralogical practice. Modifications are:

1. (1) The use of suitable surface active agents to overcome the flocculation problem.

2. (2) The use of the ultra centrifuge at about 33,000 g to hasten sedimentation.

3. (3) The use of a linear density gradient which supplies in addition a quick identification of the mineral composition.

Preliminary experiments, evaluating different variables (e.g. cation form, ultrasonic treatment, influence of surfactant), reveal the scope and limitations of the procedure presented.

Clay minerals of different density can be separated. However, if the clay minerals of a mixture have overlapping densities, or if they contain a series of mixed-layer minerals, only a broad fractionation is possible. This is shown by X-ray diffraction and electron microscope studies of isolated zones (or parts of them) which develop in the centrifuged density gradient columns containing various pre-treated natural clays or clay mixtures.

The weathering of biotite in a sedentary soil profile developed on biotitehornblende- rock near Rehiran, Inverness-shire has been investigated by optical, X-ray, chemical, infrared and differential thermal methods. In the C horizon a direct transformation to hydrobiotite was observed. This involves oxidation of all the ferrous iron present and subsequent movement of ferric ions from the octahedral sheet. In the B horizon weathering proceeds to a fully expanded 14A phase and this was identified as interstratified vermiculite-chlorite in a 1:1 ratio. Chemical analysis indicates that this stage is accompanied by a substantial addition of magnesium, much of which goes to form the brucite-like interlayers. In the more acid surface horizon these interlayers tend to break down thus yielding a more vermiculitic product. The possible general implications of this type of biotite weathering are briefly discussed.

The choice of kaolinite sample for surface chemical studies is examined. An adsorption apparatus, particularly suited for those studies where the adsorbate acts as a deflocculant, is described. Some preliminary results are given for the adsorption of total phosphate from tetrasodium pyrophosphate solutions and of polyacrylate from sodium polyacrylate solutions. The release of aluminium and silicon from the kaolinite was measured; with tetrasodium pyrophosphate, aluminium-phosphate complexes are formed.

Competitive adsorption measurements suggest that the polyacrylate is adsorbed on the positively charged edges of the kaolinite.

Studies were conducted on the feasibility of using the Dupont 900 thermal analyser for quantitative estimation of clay minerals. The results indicate that kaolinite, gibbsite, goethite and calcite can be determined quite accurately and in small concentrations provided there are no serious interferences. Quartz in excess of 5 mg or more can be determined with a reasonable degree of accuracy. Approximate estimates of montmorillonitic contents of soil clays can be made by measuring the areas of the low temperature endotherms of samples which were equilibrated over saturated Mg(NO3)2.

Examination of rock samples from Job's Hill, St Mary, Jamaica, by chemical, X-ray, differential thermal, and infrared analyses showed predominant dickite with associated nacrite and kaolinite. The uniqueness of this deposit makes it possible that selected material could be used as a standard mineral.

The electrical conductivity of synthetic zeolites, types X and Y has been studied to give information about the distribution and possibility of migration of the exchangeable cations, located at various sites. The Na+ samples were exchanged with K+, Cs+, Ag+, Li+, and NH4+. The various cationic forms were pressed into pellets and treated at 430°C under high vacuum for 24 hours. After cooling, the electrical conductivity and capacity was measured as a function of frequency (500–20,000 c/s) at various temperatures from −20°C up to 500°C. For each sample the reversibility was investigated. The experimental results allow the calculation of the specific conductivity, the real (ε′) and imaginary (ε″) part of the complex dielectric constant (ε*) and the loss factor tgδ.

The results show an ionic conductivity: the specific conductivity depends on the nature of the exchangeable cations as follows: Cs+ > K+ > Ag+ > Na+ > Li+. There is a different conductivity mechanism in the high temperature region compared with the low temperature region. At high temperatures (T > 400°K) the activation energy is independent of frequency. At low temperatures, a dielectuc absorption phenomenon occurs. The activation energy, calculated for this process was somewhat higher, but of the same order of magnitude as that of the high temperature region. It is suggested that the migration of the exchangeable cations in the supercage to interstitial positions gives rise to this dipole absorption phenomenon.

A comparison of the decationated Y zeolites with Na+Y and Na+X made it possible to attribute the conductivity to the cations in the supercage only. The exchangeable cations in the cubo-octahedra and in the hexagonal prisms lower the activation energy of the moving cations. Thus the energy of activation of X zeolites is lower than of Y zeolites.

Two types of cells for magnetic separation of clay minerals in aqueous suspension, were designed. The ceils can be used with a standard Franz Isodynamic Separator. The technique reported is effective in separating chlorite from a natural clay mixture.

Poly(ethylene glycols) of molecular weights 200 to 20000 were strongly adsorbed on montmorillonite from aqueous solution. Free energies of adsorption calculated from the adsorption isotherms became more negative with increase in molecular weight and the entropy change became increasingly positive, probably due to a net desorption of water from the clay surface as the organic compound was adsorbed. The adsorption of the higher molecular weight polymers caused an increase in the interlamellar separation. The effect of the exchangeable cation on the adsorption followed the order Cs > Na > Ca > Al, indicating that the cation retained its hydration shell and did not form a direct association with the adsorbed organic molecules. Some evidence was obtained that 'water bridges' were formed between exchangeable calcium an aluminium ions and the ether groups of the polymers.

The fibrous aluminosilicate imogolite has been studied by electronoptical and infrared absorption methods. Electron diffraction patterns are interpreted in terms of repeat units of 8·4 Å parallel and 23 Å perpendicular to the fibre axis. These spacings can not be reconciled with a continuous silicate chain structure and this conclusion is supported by an Si-O vibration near 930 cm−1. A structure is postulated in which distorted chains of Al-O octahedra are cross-linked through isolated Si2O7 groups.

Multiple OH stretching vibrations indicate different types of OH group in the imogolite structure. Absorption bands near 1000, 700 and 600 cm−1 are sensitive to sample orientation. This is attributed to the morphology and dimensions of the imogolite fibres.

Water adsorption by interlamellar complexes of poly(ethylene glycols) and montmorillonite has been determined using a silica spiral spring, and supplementary data obtained by X-ray and infrared techniques. The adsorbed water enters the interlamellar region, where it is associated with the exchangeable cation. The lattice swells to accommodate the intercalated water. Only weak hydrogen bonds are formed between the surface of the clay and the adsorbed water or between adsorbed PEG molecules and adsorbed water. The presence of PEG did not prevent extensive swelling of sodium montmorillonite.

Adsorption isotherms for an homologous series of primary aliphatic alcohols from aqueous solution by montmorillonite and kaolinite saturated with either sodium or calcium ions have been determined. The results show that adsorption is a function of chain length and exchangeable cation in the case of the more insoluble alcohols. Exchangeable cation does not affect the adsorption of the soluble alcohols to any significant extent. Adsorption of the longer chain alcohols occurs in voids in the mineral aggregates.

X-ray analyses indicate that chlorite, illite and mixed-layer chloritesmectite are present in the < 2μ fraction of the Precambrian Gowganda Formation near Bruce Mines, Ontario. The mixed-layer material is restricted to the porous graywacke sandstones and is epigenetic in origin. The chlorite and illite are ubiquitous and may reflect high-grade diagenesis, low-grade metamorphism or a source rich in these minerals.

The usefulness of various techniques for characterizing poorlyordered inorganic gel systems in clays is considered. Many established instrumental techniques are unsuitable, but thermal methods, chemical dissolution techniques, and specific surface reactions are more appropriate. The reaction of fluoride with clays is used as an example of the latter and methods for detection and monitoring of the fluoride uptake are described. Its value is demonstrated for studying gel materials in soils and relating them to synthetic alumina-silica gels.

Clays may be flocculated from suspension by various polymeric flocculating agents. In this study the technique of differential thermal analysis is used to identify the flocculating agent and to study its behaviour when adsorbed on the clay particles. It is shown that the clay particles display normal properties on sedimenting in the presence of sufficient polymer to cause flocculation. The differential thermal analysis trace for clays is only affected when the flocculating agent is present on the surface in quantities in excess of that required for effective sedimentation.