The desorption of methanol and isopropanol by a series of charge-deficient Ca-montmorillonites (prepared by a partial Li-saturation and subsequent heat treatment of Camp-Berteau material) has been monitored gravimetrically and by XRD. The results indicate that about half the total adsorbed molecules do not occur within the interlamellar space of the montmorillonite but are occluded in micropores between particles.

Adsorption isotherms of aniline and p-chloroaniline were determined from very dilute solutions on montmorillonite saturated with different cations (i.e. Na+, K+, Ca2+, Mg2+, Cu2+, Fe3+ and Al3+).

In all cases p-chloroaniline was absorbed to a greater extent than aniline. The shapes of the isotherms depend on the adsorbate and on the exchangeable cation and are interpreted in terms of adsorption mechanisms.

For aniline, the solvation of the adsorbate and the electronegativity of the saturating cation seem to be the main factors, whereas for p-chloroaniline the polarizing power of the exchange cation plays an important part. In the case of the Fe3+ ion the oxidizing power seems also be involved.

The enthalpy changes (ΔH°), calculated from the temperature coefficient of the equilibrium constant are exothermic but less exothermic as the polarizing power of the exchange cation increases. The adsorption of the amines on Na-, K- and Ca-, Mg-montmorillonite gives rise to an entropy loss which is higher for the divalent cations. This result is in good agreement with desorption curves obtained after several washings which indicated for the nature of the organo-clay complexes the decreasing order of stability, viz Mg2+ > Ca2+ > K+ > Na+.

UV-visible light absorption spectra of dilute suspensions of standard and commercial montmorillonites (bentonites) and of nontronite, hectorite and pyrophyllite, were studied.

All montmorillonites exhibit either an absorption band or a shoulder at a wavelength of 245 nm. The absorption peak for nontronite is shifted to 260 nm and absorption intensity is very high. Hectorite exhibits a very slight shoulder whereas pyrophyllite shows almost none. Absorption intensity in the UV range was found to be in direct correlation to structural octahedral Fe(III) contents. Direct evidence for the role of Fe(III) in the specific UV absorption of smectites was obtained by the fact that reduction with hydrazine fumes resulted in the disappearance of the peak and reoxidation with H2O2 caused its reappearance with even stronger intensity than originally. Mössbauer spectra showed that the Fe(III) disappeared almost completely in the reduced clay.

L'eau présente dans les divers types de pores que contiennent des solides divisés a été étudiée par calorimétrie à balayage entre 200 et 270° K et sa chaleur spécifique a été mesurée entre 100 et 260° K. Les solides étudiés sont des argiles de la famille des smectites, l'endellite, des zéolites et une opale.

Les informations obtenues à l'aide de ces techniques sont comparées à celles dérivées d'autres techniques notamment la résonance magnétique nucléaire et la spectroscopie infra-rouge.

Des différences intéressantes sont observées entre des agrégats tri et bidimensionnels de molécules d'eau.

From equilibrium silica concentrations over imogolite and boehmite at 100–155°C, the heat and free energy of the reaction (HO)3Al2O3SiOH + H2O ⇌ 2AlOOH + Si(OH)4 have been obtained: ΔH°r (298·15 K)=38·6 ± 4·1, ΔG°r (298·15 K) = 26.8 ± 1·1 kJ mol−1, and hence the heat and free energy of formation of imogolite: ΔH°f (298·15 K) = −3189·6 ± 4·1, ΔG°f (298·15 K) = − 2926·7 ± 1·1 kJ mol−1 These results are consistent with observations indicating that imogolite, halloysite and gibbsite can co-exist in soils, but that imogolite is metastable relative to either halloysite or gibbsite in the long term. At temperatures above 25°C there is a widening range of silica concentrations in which imogolite is more stable than halloysite, although both are metastable relative to kaolinite.

On a étudié les interactions de différents ligands (cryptands et composés couronne) qui ont la propriété de complexer un grand nombre de cations en solution, avec des montmorillonites saturées par différents cations (Li+, Na+, K+, Ca2+, Cu2+).

Les résultats obtenus montrent qu'il y a bien ‘encagement’ des cations interfoliaires de la montmorillonite dans ces complexants. Ces cations complexés peuvent d'ailleurs s'échanger ultérieurement contre des cations simples.

Suivant la nature du cation complexé on obtient un gonflement à 14·5–15 Å ou à 16–17 Å. Ces ouvertures sont discutées en relation avec les encombrements des cations complexés.

Volume resistivities of various homoionic montmorillonite films and their polyacrylonitrile (PAN) complexes were determined with a high-resistance meter. It was found that: (i) electrical conductivities of the homoionic montmorillonite films decreased in the order: Li- > Na- > K- > Mg- > Ca- > Sr- > Ba-montmorillonite, (ii) conductivities of the PAN-complex films varied with the amount of polymer present in the interlaminar space, and (iii) heating the PAN-complex films for 12 h at 150°C generally resulted in an increase in conductivity due to carbonization of the polymer.

On étudie l'influence des cations compensateurs sur le spectre P.I.R. d'une vermiculite hydratée à deux couches. La définition d'un paramètre IR permet de quantifier cet effet. On conclue que l'énergie d'hydratation du cation est en relation avec la rigidité de la couche interfoliaire.

IR spectroscopy has shown that adsorbed water is almost completely removed from ferrihydrite by evacuation at room temperature. Absorption bands at 3615 and 3430 cm−1 appearing thereafter are interpreted as arising from OH groups located respectively at the surface and deeper in the structure. These groups are readily converted to OD on treatment with D2O vapour and this has allowed the OH deformation vibration to be identified at 800 cm−1. It is proposed that OH groups in ferrihydrite are about half as numerous as those in akaganéite (β-FeOOH) and that they may occur in environments similar to those in this mineral. The formula for ferrihydrite proposed by earlier workers, 5 Fe2O3.9H2O, should thus be amended to Fe2O3. 2 FeOOH.2·6H2O in order to indicate the presence of structural OH groups. A re-appraisal of the ferrihydrite structure appears desirable.

L'étude de la conductivité hydraulique sous de faibles charges de pâtes et de gels d'hectorite-Na, montre que:

• 1. La loi de Darcy peut être appliquée,

• 2. Le rayon hydraulique moyen qui est probablement relié à la distance moyenne entre les particules d'hectorite varie linéairement avec la teneur en eau et est très sensible à la présence d'électrolyte dans la suspension.

Some predominantly kaolinitic tropical soil clays when examined by DTA in a nitrogen atmosphere gave two exothermic reactions (at ∼880°C and ∼950°C) instead of the usual single exotherm. During heating, iron present in the samples is reduced, possibly by organic carbon, and reacts with the metakaolin phase to form hercynite (FeAl2O4). The presence of Fe2+ also causes mullite to form at a lower temperature than normal. These reactions accompany the lower-temperature exotherm. The higher-temperature exotherm is due to formation of γ-alumina. Although this exothermic doublet is an artifact of the experimental conditions, its occurrence may help to elucidate the sequence of reactions involved in the metakaolinite recrystallization process.

The composition of the soil solution of various horizons of Galician soils was studied to gain insight into the direction of the processes of weathering and neoformation by means of stability diagrams of the clay minerals. The soil solution was extracted by compression at various pF values.

The most significant results are as follows. In all the cases studied the mineral in equilibrium with the soil solution is a 1:1 philosilicate. As the pF at which the soil solution is extracted increases, corresponding to smaller pore size, pH increases and silica concentration falls. The stable mineral does not vary significantly between different horizons of the same profile. Each parent material gives rise to a different zonation in the stability diagrams. The predictions of the stability diagrams are in general agreement with the mineralogical data of the clays of the horizons in question.

Finally, weathering processes in Galicia are briefly commented on.

La fixation du potassium par la montmorillonite sous l'effet des cycles d'humectation et de dessiccation est un phénomène bien connu. On ne peut cependant considérer ce dernier comme responsable de la rétrogradation du K dans les sols que si cette fixation peut se produire même en présence d'autres cations. Chaussidon (1963) avait étudié dans ce but l'évolution de la montmorillonite de Camp-Berteaux K-Ca soumise à des cycles d'humectation et de dessiccation, et avait observé aussi, dans ce cas, une fixation du K. Depuis, les auteurs de la présente communication ont pu proposer un mécanisme de fixation du K par la montmorillonite. A la lumière de ces résultats (aussi les résultats de Glaeser & Mering (1954)) l'étude de l'évolution de la montmorillonite biionique K-Ca sous l'effet des cycles d'humectation-dessiccation a pu être reprise et interprétée. Les résultats de Chaussidon sur la montmorillonite de Camp-Berteaux et ceux qui ont été obtenus sur celle du Wyoming permettent d'établir une comparaison entre les deux minéraux. Le mécanisme de fixation du K est identique et une interprétation des différences observées est proposée.

Aluminium substituted goethites (Fe, Al)OOH were synthesized from Fe(III), Al systems (ferrihydrites) in m KOH at room temperature. A linear correlation existed between degree of Al substitution and log[Al] in solution. Incorporation of up to 12 mole % Al was obtained. The rate of conversion of ferrihydrite to goethite decreased as [Al] increased. The goethite consisted of thin elongated plates approximately 0·1 µm long with serrated edges and reduced growth in the crystallographic X-direction. The presence of salts and the nature of the starting material either an Al-ferrihydrite or a ferrihydrite in aluminate solution did not influence the degree of substitution, but only the rate of formation of the goethite.

β-FeOOH (akaganéite) was prepared by slow hydrolysis of an FeCl3 solution. X-ray diffraction measurements gave refined unit-cell parameters of a=10·535 Å, c=3·030 Å.

Two doublets with δ(Fe)=0·39, ΔEQ=0·95, and δ=0·38, ΔEQ=0·55 mm s−1, respectively, can be fitted to the Mössbauer spectrum taken at room temperature.

Magnetically split Mössbauer spectra were registered at 135 and 4°K. These can be resolved into at least three superimposed sextets, corresponding to different Fe3+ sites in the β-FeOOH structure. At 4°K a three sextet model gives parameters of δ=0·36, ΔEQ=0·90, Hi=473; δ=0·35, ΔEQ=0·30, Hi=479; and δ=0·37, ΔEQ=−0·05 mm s−1, Hi=486kOe, respectively.

The complexity of the Mössbauer spectra of β-FeOOH limits the usefulness of this method as a tool for the identification of akaganéite in composite natural samples.

Dans les andosols, les horizons de surface et les horizons profonds sont caractérisés par des propriétés d'hydratation bien distinctes. Pour expliquer cette différence, nous avons supposé que la matière organique des horizons superficiels avait subi des dessiccations qui induisent des transformations moléculaires.

Dans cette communication, nous montrons que la dessiccation d'une suspension d'humates calciques n'est pas un phénomène simple mais qu'elle se fait en trois étapes successives qui correspondraient à différents états physico-chimiques du couple matière organique-eau (agrégats moléculaires et eau libre, associations d'agrégats moléculaires avec eau capillaire et eau d'hydratation). On met également en évidence que ces trois étapes se distinguent d'autant moins que l'indice de polymolécularité est grand.

Poorly crystallized lepidocrocites precipitated from ferriferous spring waters differ from better crystallized samples by differentially broadened X-ray diffraction lines and higher basal spacings. On the basis of high magnification EM, this was explained as due to the fact that the lath-like crystals consist only of 3–15 unit layers with possibly weakened H-bonding between the layers. These properties are analogous to those of the so called ‘pseudoboehmite’ as compared to boehmite. Poorly crystallized lepidocrocites, exhibiting similar features, were synthesized by oxidation of Fe(II) solutions. From these experiments it was suggested that such lepidocrocite forms in nature by a rapid oxidation of Fe2+ in spring water when it emerges at the surface.

IR spectroscopy has been used to study the interaction of alkali metal hydroxides with dioctahedral smectites having iron contents of 0·7% (montmorillonite) to 22% (nontronite), in connection with the alkali-stabilization of soils. The results have shown that the alkalis (LiOH, NaOH, KOH and CsOH) deprotonate hydroxyl groups co-ordinated to octahedral ferric iron, causing distortion of tetrahedral and octahedral layers. This concept of distortion is supported by a striking change in Mössbauer spectra and a large increase in b cell dimensions. The perturbation of the smectite structure, shown by shifts in the Si-O and O-H stretching vibrations, is greater for Na, K and Cs than for Li, suggesting that the larger cations interact with surface oxygens around the hexagonal hole. IR spectra suggest that the effect of NaOH on nontronite is substantially reversed by treating the smectite with CO2 or acetic acid vapour or by washing it with dilute salt solution, although Mössbauer spectroscopy and XRD indicate that the structure of the regenerated smectite is more disordered than that of the original.

An Illite/Montmorillonite mineral found in a porphyritic rock of Alpe di Siusi has an I/M ratio of 80:20. Introducing proper chemical parameters in a Q-Mode program of sixty-six Illites and Illite/Montmorillonite from the literature suggests the possibility of distinguishing Illites from Illite/Montmorillonite.