Electrodialyzed suspensions of clay minerals are viewed generally as insoluble silicates in which the exchange complex is saturated with hydrogen. An investigation of the relative activities of different exchangeable ions on beidellite clay brought to light the fact that a freshly prepared hydrogen clay containing a trace of the non-adsorbed chloride ion, when filtered, yielded a solution containing the chloride ion in association with silica rather than with hydrogen.

The filtrate from the freshly prepared suspension was clear and had a pH value of 5.5. After standing 24 hours the filtrate became cloudy and the pH value dropped to 3.5 corresponding to the concentration of acid produced by the chlorides in association with hydrogen. Analysis of the clear filtrate revealed that the chlorides were associated with silica. The amount of soluble silica in the filtrate from the clay suspension was related directly to the amount of exchangeable hydrogen in the clay. No soluble silica was present in the filtrate from clay which had been neutralized with either potassium or calcium hydroxide.

Results of the study of the kaolinite-sodium hydroxide interaction showed extensive dissolution of the kaolinite structure at particle edges, with some production of “silicate relicts” as a secondary effect. The method of specimen preparation for electron micro-scopy precluded electron-diffraction study of soluble reaction products. The study of the kaolinite-calcium hydroxide interaction revealed a similar attack on particle edges and formation of “silicate relics” and, in addition, formation of an insoluble reaction product that was tentatively identified by electron diffraction as prehnite, Ca2Al2Si3O10(OH)2. Both studies showed an ephemeral phase that, by selected area elec- tron diffraction, appeared to be a layer lattice silicate in (001) orientation. In the calcium hydroxide-treated kaolinite, formation of the reaction product was followed from nucleation along particle edges, after 24 hr, to growth of particles about 0.5 to 1 μ in size after 15 days. The combination of electron microscopy of surface replicas to detect changes in morphology with selected area electron diffraction of parallel pseudoreplicas for identification shows promise as a tool for study of the early stages in mineral- chemical interaction.

Analytical electron microscopy was used to confirm the location of pillars of zirconia in pillared montmorillonite. Data show that the pillared clay is of “high” quality, with surface areas ranging from 200 to 250 m2/g and (001) spacings in the 17–18 Å range. The zirconia-rich pillars were observed using bright-field imaging, annular dark-field imaging, and energy-filtered imaging. The composition of the pillars was confirmed by performing nano-analysis using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy. The pillars apparently have an irregular shape <50 Å in size. The shape and relatively large size of the pillars suggest that zirconia dispersion is not ideally distributed in this sample. This study is apparently the first report of electron microscopy observation of pillaring material in clays.

The electron microprobe has been used to analyse mixtures of fine-grained silicates such as clay minerals in order to determine directly how cations distribute themselves between mixtures of two fine-grained ion-exchanging materials in pure water and in dilute solutions.

Cation distributions have been determined for mixtures of:

1. (a) a zeolite, faujasite, and the clay mineral in an Arizona bentonite

2. (b) the clay mineral in an Arizona bentonite and hectorite; and

3. (c) three synthetic beidellites of varying charge density.

Distributions have been found for varying ratios of Ca to K ions in the suspensions. The results for the faujasite-bentonite mixture show complex behavior and exhibit curves with maxima and minima. For the system bentonite-hectorite most of the Ca goes to the montmorillonite in the bentonite. For the mixture of synthetic beidellites, the results are rather confusing but it appears that the calcium is more associated with the beidellite with the highest exchange capacity. In all these systems, hydrolysis takes place and the hydronium ion plays a part in determining the equilibrium.

The cation exchange capacity of a series of commercially available vermiculite-biotite minerals (Traveler’s Best, South Carolina; Libby, Montana; and Polobora, South Africa) was measured by a column method using various cations. The selectivity of the clay mineral for various ion pairs was determined with particular attention given to the adsorption from a sodium chloride-cesium chloride mixed electrolyte solution. The mineral was found to be highly selective for cesium ion, a large part of the amount adsorbed probably replacing potassium ions in the biotite layers. This replacement in the biotite is a much slower process than normal ion exchange and greatly lengthened the time required to come to equilibrium in the column.

The cesium ion cannot be removed easily from cesium-saturated vermiculite. The fixation of cesium ion was close to 100 percent at room temperature in contact with a cesium chloride solution. An isotopic exchange, Cs 133 for Cs 134, removed only very small quantities of the fixed cesium. Boiling with sodium chloride was only slightly more effective. All the results are in general agreement with the theory explaining ion fixation on the basis of collapse of the vermiculite structure to that of biotite.

Crystal truncation rod (CTR) X-ray diffraction is an invaluable tool for measuring mineral surface and adsorbate structures, and has been applied to several environmentally and geochemically important systems. Traditionally, the method has been restricted to single crystals with lateral dimensions >3 mm. Minerals that meet this size criterion represent a minute fraction of those that are relevant to interfacial geochemistry questions, however. Crystal screening, data collection, and CTR measurement methods have been developed for crystals of <0.3 mm in lateral size using the manganese oxide mineral chalcophanite (ZnMn3O7·3H2O) as a case study. This work demonstrates the feasibility of applying the CTR technique to previously inaccessible surfaces, opening up a large suite of candidate substrates for future study.

One Tertiary and two Cretaceous gray kaolin sites in Georgia were examined using X-ray radiography of core sections to determine the processes of formation of the deposits. The Tertiary kaolin was oxidized in the upper 3 m of the deposit and reduced below that point. The two Cretaceous kaolins were reduced from the top of the deposit to an abrupt boundary with oxidized red kaolin below. Radiography of the first Cretaceous core revealed thin laminar bedding in the gray kaolin and in the underlying red kaolin. The laminae continue without interruption across the gray kaolin/red kaolin boundary. The laminae were not visible in the gray kaolin except in radiographs. Sedimentary bedding was not observed visually or radiographically at the Tertiary site nor in sections of the core from the second Cretaceous site where kaolinite was recrystallized to large vermiforms. The original sedimentary structure in the first Cretaceous kaolin was preserved possibly due to the inhibition of kaolinite recrystallization by a higher organic matter content. Recrystallization of kaolinite and iron compounds may have destroyed sedimentary structures in part or all of the other two kaolin cores. It is hypothesized that the first Cretaceous physical and biological mixing. The same hypothesis may apply to the other two kaolins but recrystallization after deposition has destroyed sedimentary structures.

The hydraulic conductivity of geosynthetic clay liners (GCLs) is not fully understood and certain gaps in knowledge are still present, such as the effect of coupled mechanical and chemical processes. The current study aimed to develop a simplified mathematical model to predict the hydraulic conductivity of GCLs, particularly regarding the coupled effects of mechanical and chemical processes. Based on Darcy's Law and Poiseuille’s Law, the method combines diffuse double layer (DDL) theory and fractal theory. External factors such as confining pressure and the concentration of the permeating solution, and inherent properties such as exchangeable cations, ionic radius, montmorillonite surface fractal dimension, the distance between two montmorillonite layers (m) after swelling at the exchangeable cation i (i denotes the primary exchangeable cations, such as Na+, Ca2+, K+, and Mg2+ in bentonite), density, and coefficient of viscosity of interlayer water between two montmorillonite layers, were considered. The proposed theoretical model gave relatively accurate predictions. A practical estimate of GCL hydraulic conductivity was also derived. The predictions were compared with experimental results and good qualitative agreement was found. From the experimental results, the proposed prediction model has a maximum deviation of ~1:10–10:1, and the empirical model has a mean deviation of ~1:15–15:1.

Bentonite is often proposed as an engineered-buffer material in high-level radionuclide waste-management systems. For effective design of the barrier that will provide protection over the long time periods required, the physical/thermal/chemical processes taking place in the barrier material must be understood thoroughly. These processes, which interact, include the flow of water and gas, the flow of heat, and the transport and reaction of chemical constituents. The purpose of this study was to better understand the processes that occurred in a small-scale experiment within a confined bentonite space. A conceptual and mathematical model (FADES-CHEM) was built in order to simulate the results of an experiment conducted in 2000, and thereby to gain a better understanding of the controlling processes. In that experiment, a block of compacted bentonite was placed in an air-tight cell and subjected, for 6 months, to simultaneous heating and hydration from opposite sides. The bentonite block was then sliced into five sections each of which was then analyzed in order to obtain a series of physicochemical parameters illustrating the changes that had occurred. Before modeling, the chemical composition of the bentonite pore waters was restored in order to account for different processes such as gas outgassing and cell cooling. Modeling indicated that gas-pressure build up was a relevant process when computing the saturation of bentonite, and the computations in the present study suggested that evaporation/condensation processes played a crucial role in the final distribution of the water content. Gas pressure and evaporation/ condensation also affected the geochemical system, and the numerical model developed gives results that were consistent with the experimental values and trends observed. The model reproduced the results obtained and enable use at the repository scale and over longer time frames, provided that adequate data are available.

In order to remove impurities, natural illite is often subjected to chemical pretreatments before analysis, the assumption being that such pretreatments have little or no effect on the composition of illite. Bulk analyses are sometimes reported before and after pretreatment (Aja et al. 1991) but, because the contribution of the impurities to the bulk composition is unknown, the possible effects of chemical pretreatments on the composition of illite cannot be assessed. Recently, Rosenberg and Hooper (1996) have shown that analytical transmission electron microscopy (ATEM) techniques, which exclude impurities, can be used to determine the bulk compositions of relatively pure illite by averaging the analyses of at least 50 crystals per sample. This approach can be applied to impure illite in order to determine the effect of chemical pretreatments on the composition of natural illite.

The effects of heat on the behavior of sodium and calcium bentonite in bonding foundry sands were studied.

Tests such as differential thermal analysis, viscosity, and melting or vitrification temperatures do not indicate the suitability of a bentonite for foundry use.

The deterioration temperatures of sodium and calcium bentonite are 1180° and 600°F respectively.

Reactivities of bentonites with cereal as affected by temperature and mulling were also studied. Flowability of sands, defined as mold densification in this paper, is better with heated calcium than sodium bentonite.

Heating bentonites alone does not simulate the conditions encountered in heating bentonite-sand mixtures in a mold.

Landfill leachate is one of the most difficult effluents with which to deal from an environmental perspective because of its concentration and complex composition, including refractory and toxic components such as heavy metals or xenobiotic organic compounds. The objective of the present study was to use organically modified bentonite (OMB) to dispose of landfill leachate >10 y old. The OMB was synthesized using a new method, which removed four steps (filtering, washing, drying, and grinding) from the traditional process. After treatment using OMB, the chemical oxygen demand concentration (COD concentration, an index of the organic pollutants in the landfill leachate, was determined using the potassium dichromate method) of the landfill leachate sample decreased from 2400 to 245 mg/L in 5 h, i.e. the organic pollutants reduction efficiency was as high as 90%. Gas chromatography-mass spectrometry results indicated that most of the organic compounds were removed during the process. The modified and unmodified bentonite contained in the OMB deal with the hydrophobic and hydrophilic organic pollutants, respectively, resulting in significant degradation of the leachate. The study results have provided a new cost-effective method for treatment of landfill leachate.

On the Helen claim in Homansville Canyon, East Tintic district, a small deposit of kaolinic clay typical of argillic alteration, together with hematite and manganese, occurs at the intersection of a minor north-south fissure with a steep east-trending contact of Tertiary quartz latite lava and dolomitized Cambrian Herkimer limestone. The fissure ends at a small, completely argillized monzonite plug about 100 yd north.

Argillic alteration and other types of hydrothermal alteration are common near the ore deposits and many of the intrusive bodies that are scattered through the roots of the Eocene volcanic field in which the East Tintic and Tintic districts lie. In most areas of argillic alteration abundant pyrite or alunite and barite suggest that the alteration was caused largely or in part by sulfur acids, but in the Helen claim these minerals are virtually lacking and in contrast fluorite, hematite, and manganese and aluminum oxides are abundant.

A mineral zonation parallel to the lava-dolomite contact is conspicuous. The zones in the lava outward from the contact are: (L 1) a silicic zone 1–5 in. wide with some kaolinic clays, mixed-layer clay and micaceous minerals; (L 2) a strongly argillized zone about 3 ft wide having much montmorillonite and a moderate amount of kaolinic and micaceous minerals, but in which the kaolinic minerals decrease away from zone L 1; (L 3) transition zone 2–5 ft wide in which montmorillonite diminishes, micaceous minerals increase, and kaolinic minerals disappear as altered rock grades into normal country rock. The bulk density of the rock decreases with the intensity of argillic alteration and nearly all chemical constituents decrease in amount per unit volume; magnesium, water, manganese, and fluorine, however, increase conspicuously.

The zones in the altered dolomite away from the lava contact are (D 1) a hematite-quartz zone 5–8 ft wide, which contains some minor sericite and manganese oxides; (D 2) a manganiferous zone 1–2 ft thick containing abundant manganese oxides and hematite, and minor clay, quartz, and kaolinic minerals; (D 3) a discontinuous zone about 8 in. thick of halloysite and kaolinite; (D 4) a fluorite–kaolin zone with minor diaspore about 1 ft thick; (D 5) a diaspor-fluorite zone about 41/2 ft wide in which the kaolin minerals diminish away from zone D 4; (D 6) a diaspore–kaolinite zone about I ft wide with minor fluorite and mixed-layer clays; (D 5) a kaolin and mixed-layer clay zone about 3 in. thick with very minor manganese oxide, fluorite, and diaspore; (D 8) a “sanded dolomite” zone about 10 ft wide, consisting chiefly of weakly bonded granular dolomite with some kaolinite and mica; (D 9) hard fresh hydrothermal dolomite extending outward for several hundred feet. Zone D 8 grades imperceptibly into D 9.

The mineral zones suggest reaction of dolomite with hot halogen-rich acid emanations carrying halides of iron, aluminum, and silicon; the precipitation of the oxides of iron, manganese, silicon, and aluminum, and of fluorite, is appropriate to zonation responsive to the increasing pH caused by reaction with the carbonate wall rock.