A B S T R A C T: The adsorption of cerium(IV) by both natural and Na-exchanged kaolinite from aqueous solutions of ceric ammonium nitrate was studied in equilibrium systems. Cerium may be adsorbed either as a monomeric species or as a polymeric hydroxy cation. The species adsorbed depends on the concentration of cerium in the stock solution, the age of this solution prior to the preparation of the equilibrium system and on the equilibration period. Adsorbed cations undergo polymerization on the surface of the kaolinite; the resulting polymeric species forms strong bonds with the clay surface--it is not desorbed by sulphuric acid--and may be considered fixed. Adsorption of cerium reaches a maximum in solutions containing 0.15 M sulphuric acid. Very little is known about the adsorption of lanthanides by clay minerals, although this process seems to be important in the geochemical cycle of these elements. Recently, the adsorption of a few lanthanides by montmorillonite was investigated by Bruque et al. (1980) and Miller et al. (1982, 1983). The present communication deals with the mechanism of adsorption of cerium by kaolinite.

The Adsorption of Quadrivalent Cerium by Kaolinite

Cation exchange capacity methodology III: Correct exchangeable calcium determination of calcareous clays using a new silver–thiourea method

Lithium sorption to Yucca Mountain tuffs

The adsorption of the large cationic alkaloid berberine by montmorillonite in aqueous suspensions was investigated. An adsorption isotherm of berberine and desorption isotherms of exchangeable Na + , K + , Mg 2+ and Ca 2+ were determined by chemical analysis of the non-adsorbed berberine and the released cations in the supernatants. The isotherms suggest that the adsorption of berberine takes place in two different types of reaction mechanism: (1) cation exchange, and (2) a secondary organophyllic adsorption. The cation exchange occurring first is followed by the secondary adsorption which is accompanied by Cl − adsorption. Monovalent cations are exchanged before the divalent cations. Samples loaded with increasing amounts of berberine were examined by X-ray diffraction at room temperature, and after gradual heating up to 420°C. The basal spacing of the loaded samples after the thermal treatment became 1.28 nm, indicating the formation of carbon in the interlayer, thus proving that the adsorbed berberine was located in the interlayer space. At room temperature the basal spacing of samples loaded with 8 and 15 mmol of berberine per 100 g of clay was 1.28–1.30 nm indicating that in the interlayer space berberine cations were lying parallel to the alumino-silicate layers. The basal spacing of a sample with 36 mmol of berberine per 100 g of clay was 1.48 nm. This spacing does not give conclusive information on the arrangement of berberine in the interlayer. The spacing of samples with 57–147 mmol of berberine per 100 g of clay was 1.59 nm, suggesting the presence of bilayers of berberine in the interlayers. During thermal dehydration, the spacing of samples with 36–73 mmol of berberine per 100 g of clay decreased, but that of samples with 105–147 mmol of berberine per 100 g of clay increased to 1.66 nm. These samples contain organophilic adsorbed berberine and it is suggested that due to the thermal treatment berberine was tilted relative to the TOT lamellae, with anhydrous Cl − between the berberine cations.

The adsorption of berberine by montmorillonite and thermo-XRD analysis of the organo-clay complex

Titanium determination with disodium 4,5-dihydroxybenzene-m-disulfonate (Tiron) in oxalic acid solution

The amount of cations displaced by LiCl—LiOAc from standard clay minerals and soil clays was dependent on the concentration and pH of the replacing solution. Lithium was more effective in replacing monovalent ions than ammonium. Appreciable quantities of Li were adsorbed by replacement on the broken bonds of the clay surfaces, especially in the amorphous clays. Certain montmorillonite clays fixed some of the sorbed Li. In general, the cation exchange behaviour was highly dependent on the structure of the clay mineral and the nature of its surface. The sum of displaced cations can be taken as representing the exchange capacity of the clay at the experimental conditions, while the amount of retained Li provides supplemental information on the nature of the bonds.

The Effect of Lithium on the Cation Exchange Behaviour of Crystalline and Amorphous Clays

The effect of varying concentrations of neutral salts on the initial pH of maximum color in the colorimetric determination of Ti by tiron was studied. A direct method was developed for the determination of Ti in the presence of great amounts of Ca and Fe. The various reducing or masking agents used for the prevention of the interference of iron were discussed. Many ions were found not to interfere, and the limiting tolerance of others was given. The method may find application in the determination of Ti in rocks and alloys.

The Determination of Titanium by Tiron in the Presence of Large Amounts of Calcium and Iron. II

A pH-spectrophotometric study of the Ti-tiron complex in the presence of Ca ions revealed the existence of mixed compounds of Ca-Ti-tiron. These could account for the interference of Ca in the determination of Ti by tiron. The formation of these mixed compounds under varying concentrations of components and at varying pH is discussed. The absorbance of the Ti-tiron was likewise studied in the presence of many colorless salt solutions, but the behavior of Ca was found to be unique. Use was made of the color of the mixed compounds of Ca-Ti-tiron to develop a method for the identification of small amounts of Ca in the presence of large quantities of many common salts.

The Mixed Compounds of Calcium and Titanium With Tiron. I

The amounts of exchangeable K displaced by NH4, Na, and Li using methods adopted in cation exchange determinations were compared. Besides differences due to the effect of the geometric factor of the replacing ion, related to its size and hydration characteristics, the behaviour of clays of two groups of soils was consistently and significantly different. A critical assessment of the data suggests that there is a considerable diversity in the distribution and bonding energy of the K adsorption sites on the various clays.

Displacing Exchangeable Potassium in Cation Exchange Determinations

A method is presented for the direct determination of iron in the HCl soluble fraction of carbonate rocks. Use is made of the absorbance-difference technique as developed by Glasner and Avinur, whereby the chloroferrate absorbance of the solution is measured at two wavelengths and the difference of absorbance between them is made the basis of the determination. Determination of iron by the chloroferrate absorbance when measured at only one wavelength was found to be impeded by the variation of the absorbance with the following factors: the ratio of chloride salt to free HCl; the nature of the chloride salt (Ca or Mg); slight changes in the total chloride concentration; and temperature. All these difficulties were largely overcome by the application of the absorbance-difference technique.

D. H. Yaalon

Papers

The Effect of Lithium on the Cation Exchange Behaviour of Crystalline and Amorphous Clays

The Determination of Titanium by Tiron in the Presence of Large Amounts of Calcium and Iron. II

The Mixed Compounds of Calcium and Titanium With Tiron. I

Displacing Exchangeable Potassium in Cation Exchange Determinations

Direct Spectrophotometric Determination of Iron in the HCl Soluble Fraction of Carbonate Rocks