The mineralogy of the clay fractions (<2 µm) of the major soils of England and Wales is reviewed, and the data presented in terms of the 1:250 000 National Soil Map. Most soils developed in pre-Rhaetic sediments are dominated by mica with lesser amounts of chlorite and kaolin. Exceptions are soils developed in calcareous Coal Measure shales which have significant smectite contents, and freely drained soils in Keuper Marl which contain swelling chlorite, sepiolite and palygorskite. Soils developed in post-Triassic sediments are dominated generally by expansible minerals, except for those developed in Lower Lias and Estuarine Series rocks (Jurassic) which are dominated by mica and kaolin respectively. The presence of loess in soils seems to be associated with the occurrence of a complex interstratified mineral with X-ray diffraction properties akin to vermiculite. Weathering of soil clays is most marked in the wetter uplands, but over most of lowland England is detectable only by slight changes in non-exchangeable potassium content and cation-exchange capacity towards the soil surface. Applications of soil clay mineralogy in the fields of plant nutrition and soil mechanics are discussed, in particular the production of maps showing mineralogical provinces.

The soils of Scotland are relatively young, being developed mainly on glacial drift deposited some 10 000 years ago. Only a small number of genetic soil types are represented, but this is more than compensated for by the wide variety of parent materials from which the drift ultimately derives. The major parent materials include granite and granitic gneiss, gabbro, basalt/andesite, mica-schist and related metamorphic rock types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments, fluvioglacial sands and gravels, and estuarine silts and clays. The clay mineralogy of the soil associations developed on these parent materials is described and the origin of the clay minerals is interpreted. It is concluded that the influence of inheritance is predominant, but that the effects of pre-glacial weathering and Holocene pedogenesis can also be discerned. Inheritance has contributed a wide variety of clay minerals to the soils, including illite, kaolinite, chlorite, smectite and a number of interstratified minerals, pre-glacial weathering has resulted in the widespread formation of kaolinite and halloysite, irrespective of soil parent material or drainage class, and recent pedogenesis has brought about the transformation of inherited layer silicates by vermiculitization processes, with concomitant interlayer alumination, particularly in surface horizons.

Mixed SiO2-Al2O3-Fe2O3 gel systems are a feature of many Scottish soils. They are usually associated with the surface of primary soil particles and consequently when present even in small amounts can have an effect on soil properties incommensurate with the proportion present. Currently, chemical dissolution methods provide the most satisfactory means of assessment. A range of chemical techniques, including dissolution by alkali, dithionite, acid oxalate and pyrophosphate, trimethylsilylation and fluoride exchange, have been used to examine the inorganic gel in a Scottish brown forest soil developed on glacial till derived from epidiorite. The reactivity of the gel, as determined by fluoride exchange, is similar to that reported for Japanese and New Zealand allophanic soils.

Synthetic ferrihydrites with Si added at mass ratios of Si/Fe = 0, 10, 20, 40, 80, and 160 × 10−3 have been studied to examine the effect of Si on the properties of ferrihydrite. The Si proportionally reduces the point of zero charge but influences surface area, loss of weight to 800°C and solubility in acid oxalate solution to varying degrees. At a critical concentration of Si (when Si/Fe = 20 × 10−3) these measured properties indicate a greater particle size and a more ordered structure. The relationship between synthetic ferrihydrite and the surface of kaolinite has been studied by a combination of surface area and charge determinations and TEM. An attraction predicted at pH 3 between ferrihydrite particles and the basal surface of kaolinite has been confirmed, and resulted in a stable coating. However, at pH 6 any attraction between the minerals appears to be too weak to produce a coating of the kaolinite surfaces.

A new conceptual model for interstratified clays is proposed, based on complementary use of the transmission electron microscope (TEM) and X-ray diffraction (XRD). Clays yielding interstratified XRD patterns are shown to be composed of aggregates of fundamental particles (here defined as an individual or free particle which yields a single crystal pattern by electron diffraction) whose interfaces are capable of adsorbing water and organic molecules. In these circumstances, the interstratified XRD character results from an interparticle diffraction phenomenon. Smectites are shown to be primarily composed of particles 10 Å thick corresponding to elementary 2:1 silicate layers. Nearest-neighbour regularly interstratified illitesmectite (K-rectorite) is composed of particles of elementary ‘illite’ 20 Å. thick, corresponding to two silicate layers coordinated by a single plane of potassium ions. Regularly interstratified chlorite-smectite (corrensite) consists of particles 24 Å thick corresponding to two silicate layers coordinated by a single brucitic sheet. The layer sequence examined by XRD is determined by the types and proportions of particles present within the clay material. Thus a sedimented aggregate of 20 Å elementary ‘illite’ particles appears to be a regularly alternating sequence of illite and smectite layers by XRD. Randomly interstratified itlite-smectite and chlorite-smectite can be synthesised by making mixed suspensions of the <0·1 µm fractions of smectite with those of K-rectorite and corrensite respectively, providing experimental confirmation of the proposed model. Unusual associations, such as three-component illite-chlorite-smectite interstratified systems can be synthesised by making mixed suspensions of K-rectorite and corrensite. Long range regularly interstratified illite-smectite of the IIS and IIIS types are composed primarily of fundamental ‘illite’ particles 20–50 Å thick. Conventional illite is composed primarily of particles > 50 Å thick. This conceptual model has implications for the chemistry, behaviour and genesis of interstratified clays which are common constituents of soils and sediments.

A modified HGMS system is described in which the inclusion of a peristaltic pump to continuously circulate a suspension of a soil clay through the magnetic trap greatly facilitates the operation of the technique. Application of this purely physical method of mineral separation to a variety of soil clays—using IR spectroscopy to monitor the progress of the separation—illustrates the ease with which magnetic fractions comprising different iron-containing clay minerals may be separated from a single soil clay, thereby making these minerals more accessible for further study by other techniques.

The thermal decomposition of stearic acid in the presence of various clay minerals was studied in an open, inert system under isothermal (250°C) conditions. The distribution of hydrocarbons and the amount of CO2 evolved were determined. The degree of decarboxylation depended on the composition of the octahedral sheets of the clays. It was greater with trioctahedral than with dioctahedral minerals. The presence of dioctahedral minerals tended to reduce the amount of CO2 produced below that obtained with the neat acid. The nature of the hydrocarbons formed depended on the structure of the minerals. Different products were obtained with minerals that have accessible interlayers and channels (smectites, palygorskitesepiolite) than with the 1:1 clays and pyrophyllite or talc. Some minerals caused cracking to light-weight hydrocarbons. Higher surface acidity of the clay interlayers enhanced this process but was not the only decisive factor. In the systems studied, evolution of CO2 did not necessarily precede the formation of light- or medium-weight hydrocarbons from the parent acid.

The data obtained on zeolites, kaolins, alunites, hydrated sulphates and soils by DTA-TG-EGA carried out under various experimental conditions are discussed. Among the main subjects dealt with are chabazite and phillipsite identification and their quantification by TG, clay mineral distribution in size fractions of kaolins, significance and use of thermoanalytical data from alunitic rocks, the influence of calcite and calcined kaolinite on the sulphate DTA curves, rates of decomposition of hydrated sulphates, and thermal analysis of soils in forensic studies.

Emphasis is placed on the advantages of combining simultaneous thermal analysis methods (TG-DTA-DTG) with other complementary physico-chemical techniques for investigating synthesis and various properties of zeolites belonging to the pentasil family. TG and DTA give quantitative information on the dehydration and decomposition of organic guest molecules that interact with intermediate phases obtained during hydrothermal transformation of amorphous aluminosilicate gels into crystalline zeolites. In particular, weight losses (TG) and heat effects (DTA) due to the oxidative decomposition of tetrapropylammonium ions occluded in an intermediate phase have been related to the amount of zeolite ZSM-5 present. As a result, very small particles of this zeolite, amorphous to X-rays, could be detected in the early stages of the crystallization process. Isothermal sorption of small hydrocarbon molecules (n-hexane, 3-methyl-pentane) is used to probe the intracrystalline pore volume of zeolite ZSM-5. The total hydrocarbon uptake (TG) and the shape of the corresponding DTA peak are sensitive to steric modifications of the ZSM-5 channel system by various chemicals, while the sorption rates are better correlated to the extent of zeolite surface poisoning by boron or carbon. TG-DTA data provide an easy means of describing the filling and packing of n-hexane in ZSM-5 pore structure. Various steps characterizing isothermal competitive sorptions (nitrogen, ethylene, water) or catalytic conversions at high temperature (ethylene, methanol) over H-ZSM-5 are described. Finally, the progressive formation (removal) of carbonaceous residues resulting from these transformations are related to the actual rate of de-activation (re-activation) of a zeolitic material. In this respect, three different synthetic zeolites, namely mordenite, offretite and H-ZSM-5, which differ by their shape-selective properties and structure of their channel network, are investigated by TG.

Reactions undergone by leadhillite from the type locality on heating to 1000°C have been followed by DTA, TG, DSC, evolved gas analysis, continuous-heating XRD and IR, and hot-stage microscopy. Intermediate decomposition products were identified by X-ray powder photography. At 80°C, biaxial leadhillite inverts to a uniaxial phase with properties similar to those of susannite, a naturally occurring polymorph of leadhillite, but this higher-temperature modification only partially reverts to the original structure on cooling (up to 24 hours at room temperature is required for complete reversion). Between 250 and 600°C the mineral undergoes two decomposition reactions: PbO.PbCO3 and PbO.PbSO4 form during the first reaction (PbCO3 may form in the initial stages) and 4PbO.PbSO4 during the second. α-2PbO.PbSO4 appears at 650°C due to solid-state reaction between the other lead oxysulphate products. Melting occurs above 850°C. The reaction products are discussed in relation to the phase diagrams for the systems PbO-CO2 and PbO-PbSO4.

Two iron ore samples from Nigeria have been examined using TG, DTA, EGA, XRD, and optical and electron microscopy. Itakpe iron ore is hematite-rich, this mineral being intergrown with magnetite, and silica is the major impurity. Agbaja ore is an acidic oölite ore consisting of goethite and magnetite, with alumina, silica and phosphorus as major impurities. Itakpe is typical of a rich ore formed by magmatic segregation whilst Agbaja is a lean ore of sedimentary origin. Isothermal mass-change measurements in hydrogen and carbon monoxide in the range 800–1100°C show Agbaja to be less reducible than Itakpe; in particular, Agbaja is very irreducible at 1100°C because of sintering of the ore. Characterization and reducibility experiments were also carried out on Corby (Northamptonshire, UK) iron ore for comparison.

Hydrating high-alumina cement will react with calcium carbonate to form the complex mineral calcium carboaluminate hydrate, 3CaO.Al2O3.CaCO3.12H2O. This mineral is reported to be capable of providing strength in concrete and so may provide an alternative to the minerals normally found in the hydration of high-alumina cement, which may under certain conditions convert to other minerals with a loss in strength. Some doubt has been cast on the stability of calcium carboaluminate hydrate and it has been found that in hydrated high-alumina cement, calcium carboaluminate hydrate decomposes at temperatures in excess of 60°C. Cube compressive strength tests on high-alumina cement and high-alumina cement-calcium carbonate pastes have shown that the latter have a lower strength than pastes made with high-alumina cement alone. When cured at 50°C the high-alumina cement-calcium carbonate pastes show a loss in strength with curing time. Cements made with the high-alumina cement-calcium carbonate mixture always have a lower strength than those made with high-alumina cement alone and so no advantage is gained from their use.

The process developed in the UK to produce magnesium hydroxide from seawater is described, together with the heat treatment that the hydroxide receives to produce the active oxide. Some of the characteristics required of the dolomite used in the process are also discussed. Impurities introduced by the seawater are noted and the means by which they can be reduced explained.