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.

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.

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.

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.

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.

Se estudia la interacción del isocianato de butilo y del isocianato de fenilo con sepiolita, utilizando las técnicas de espectroscopía IR y anáilisis químico. En determinadas condiciones experimentales se produce un injerto de grupos orgánicos sobre la superficie mineral por formación de enlaces tipo uretano ≡ Si-O-CO-NH-R. Se ha puesto de manifiesto que el agua adsorbida sobre la superficie mineral, tiende a formar ureas simétricamente disustituídas como sub-producto de la reacción.

The adsorption of aniline (ANL) and p-chloroaniline (PCA) from 0·02 M methanol and chloroform solution on air-dried montmorillonite is determined by the conjunction of several factors: (i) basicity of the solute, (ii) complexing ability, Brönsted and Lewis acidity of the exchangeable cation, (iii) polarity and Lewis basicity of the solvent. The principal adsorption mechanisms, inferred from infrared data, are direct or indirect coordination and protonation of the adsorbate. They take place simultaneously and to a relative extent depending mainly on the exchange cation.

On Fe-, Al- and H(Al)-montmorillonite ANL and PCA give rise to type II complexes, characterised by an intense charge-transfer band in the infrared region and by the formation of radical cations, evidenced by ESR spectroscopy. This oxidation process occurs on heating in air, but with Fe3+ in vacuo also and even at ambient temperature in methanol solution. On Cu-montmorillonite ANL, contrary to PCA, does not give a type II complex; however, radical species are produced in air and in vacuo and their production is enhanced by heating.

Fe substitution for Al in kaolinite (from Venezuelan laterites) is proved by infrared spectroscopy and chemical techniques. The location of Fe in the octahedral sheet is characterized by two absorption bands, at 865–875 and 3607 cm−1, assigned as δ Al-OH-Fe and v OH respectively. The detection of the 865 cm−1 band requires the use of CsCl for the preparation of the disks heated to 270°C so that the clay delaminates as a result of a kaolinite-CsCl-H2O complex formation. The 3607 cm−1 absorption is detected when KI disks are prepared. These two characteristic frequencies persist after either thermal decomposition or selective chemical dissolution of free iron and aluminium hydroxides.

Selective chemical dissolutions by consecutive treatments for; (1) the removal of free iron oxides, (2) gibbsite removal and (3) extractions of Fe and Al from kaolinite, give additional evidence about the occurrence of this solid solution.