An electrooptic birefringence technique was employed to study the effect of particle size, saturating cation, and clay type on the rotational diffusion coefficient (a measure of the rate at which the particles rotate or relax within the solution) from a preferred orientation. These studies help elucidate the nature of the cation—water environment near the clay particles.

Previous work has shown that some clay particles orient at both low and high voltages due to a permanent dipole and an induced dipole, respectively, whereas other clays under similar short-duration pulses orient only at high voltages. The permanent dipole was attributed to the iron in the octahedral layer of the clay mineral, whereas the induced dipole was probably due to a redistribution of the diffuse double-layer cations. This study shows that smaller clay particles orient more readily at low voltages and have greater rotational diffusion coefficients at high voltages. The higher the rotational diffusion coefficient, the faster the particles move in their surrounding water-cation environment. The effect of the saturating cation on the rotational diffusion coefficients was Na > Li > K for the permanent dipole and K > Li > Na > Ca > Mg for the induced dipole orientation. Previous results (Schepers and Miller, 1974) are interpreted to mean that a particle in dilute suspension can rotate independently of its environment only when the salt concentration in the surrounding medium approaches zero. At higher salt concentrations, or if the particle environment is perturbed by an electric field, the particle rotates with a water shell. As the concentration of salt or strength of the electric field increases further, either the viscosity of the surrounding solution increases or the size of the rotating shell is greatly increased. Thus, the water around clay particles appears to be structurally different than normal, and this condition is probably caused by the nature of the clay—cation interaction.

The present paper presents the mineralogical composition of sediments from the Spanish Wealdian facies, selected from four stratigraphic sections of several regions in the Southern Cordillera Iberica.

Three of these sections show an irregular alternation of kaolinite rich sandy and silty-clay beds. The fourth section which contains calcareous layers, is very important from a geological point of view, because it is located where the structures of two ranges, the Iberian and the Betics, converge.

The clays of about 80 samples from these sections always consist of illite, kaolinite and interstratified clay minerals. The sandy layers also contain quartz, as well as potash and calcic-sodic felspars. The fine fraction (< 2 µm) is composed of kaolinte, between pM and T types, swelling illite and randomly interstratified clay minerals of the type (10I-14M), richer in 10 Å layers.

From the mineralogical and crystalchemical data and field observations, it is deduced that these sediments are mainly detrital. This and the layer alternation suggest, for the Upper Jurasic and Lower Cretaceous (Wealdian facies), a climate alternating from biostatic to rhexistatic. Alternating laterization and erosion might supply the materials to the Wealdian sedimentary basin.

The crystallite sizes in the particles from four fractions of a kaolinite-clay were determined from the broadening of the X-ray diffraction lines. Measurements were made of the <002> and <111> planes whose crystallographic directions correspond to the clay plate thickness and diagonal, respectively. The extent of crystal imperfection was determined by comparing the calculated crystallite size with the mean size based on measurements from electron micrographs. The crystal imperfections were found to be more extensive in the plate diagonal, <111>, than in the plate face, <002>, directions. Electron micrographs of hydrofluoric acid-etched samples revealed plate-edge and plate-face imperfections. The latter show a regularity suggesting a mosaic-like texture in the plate surface. Surface imperfections probably have significant influence on the dispersion and flocculation behavior of kaolinite.

Kaolin floc structures of commercial utility are produced by adsorption of hexamethylenediamine. These flocs are largely face-to-face structures with small diameter platelets of colloidal kaolinite aggregated on larger platelets of kaolinite and muscovite. Because of its higher charge density, muscovite is more effective than kaolinite in scavenging colloidal particles.

Although earlier workers have been at odds as to where amines adsorb on kaolinite, the present work indicates that both edge and basal surfaces are involved. Evidence for this contention is two-fold: (1) Face-to-face and edge-to-face flocculation of hexamethylenediamine kaolins has been observed. (2) Polyesters have been observed adsorbed on basal and edge surfaces of ethylenediamine-treated kaolins.

The mechanism by which kaolinite particles are bonded together into floc structures is unclear. Bridging by hexamethylenediammonium ions is a probable mechanism up to satisfaction of the cation-exchange capacity; further amine addition continues to promote flocculation. From this observation it is inferred that, in addition to bridging, hydrogen bonding and, perhaps, van der Waals forces are instrumental in floc formation. Although rheologically inferior to the untreated equivalent, these chemically induced flocs of kaolinite provide loosely packed, randomly oriented structures in paper coatings. Improved brightness, opacity, and printability of paper coatings arise from this structure.

Cacoxenite having the composition (Al4.0Fe22.5O7.1(OH)14.3(PO4)17(H2O)23.7)·50.3H2O was identified in a bed of mature quartz sand in the Miocene Calvert Formation near Popes Creek, Maryland. This is the first reported occurrence of this mineral in Atlantic Coastal Plain sediments north of Florida. The cacoxenite occurs as silt-size to sand-size grains, both as irregularly shaped aggregates and as radiating arrays of delicate acicular crystals. The presence of discrete cores and overgrowths in some grains indicates at least two generations of crystal growth. Electron microprobe analyses reveal excess Si and Al (relative to the ideal composition), which is believed to reflect ultra-fine clay particles within the cacoxenite grains. Admixed clays probably served as a substrate for the formation of ferric oxyhydroxides, which were subsequently converted to cacoxenite through the addition of dissolved phosphorus.

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.

The stable carbon isotope composition of CO2 occluded in the gibbsite structure is proposed as a potential atmospheric paleo-PCO2 proxy. Analysis of pedogenic gibbsite from a modern Ultisol in the Piedmont of Georgia, USA, was conducted to test the basis for this concept and to help constrain the parameters used to describe physical and biological processes affecting such factors as the respiration rate of CO2. Co-variation of the δ13C and δ18O values with depth along a gradient parallel to the mixing line between the atmosphere and the soil organic material implies that diffusion is the process that determines the stable isotope composition of soil CO2. In the upper 40 cm, the measured δ13C values are not consistent with the expected diffusive depth profile assumed in paleo-PCO2 models. The isotope signature is reset downward in the depth profile with a concentration of the most atmosphere-like δ13C and δ18O values occurring at the top of the Bt horizon by some as-yet-unknown process. Bioturbation, recrystallization, and physical translocation are potential explanations for this observation. Regardless of the process at work, the net effect is an apparent two-component mixing curve between the top of the Bt horizon and deep within the saprolite. In cases where the A horizon is eroded but the Bt horizon is preserved it is possible that δ13C values of gibbsite-occluded CO2 can serve as a proxy for atmospheric paleo-PCO2. Careful textural study of all paleosols is therefore essential to match stable carbon isotope signatures with the horizons preserved. Understanding of modern dynamics and preservation of these isotopic signatures may also be important for those that employ other carbonate proxies.

A method using a finite, first-order Markov chain is presented to estimate rate constants for zeolite formation from experimental nuclear magnetic resonance (NMR) data on the abundance of different silica oligomers. An experimental design is suggested by which this method can be implemented. The method uses weighted least squares to estimate transition probabilities from aggregate NMR data. Rate constants, equilibrium constants, and free energies of elementary zeolite-forming reactions can be estimated. Hypothetical zeolite-forming reactions can also be modeled. An example of modeling, using hypothetical data, shows how zeolite formation can result from reactions involving mainly silica cyclic tetramers.

The clay-mineral composition of 142 samples of Upper Pennsylvania fluvial, deltaic, and marine clays and shales from north Texas was determined by X-ray diffraction. Deltaic lithotypes are of moderate illite, subordinate kaolinite, minor vermiculite and mixed layer composition. Nonmarine (red bed, coaly shales) lithotypes range from this composition to highly (+90 per cent) kaolinitic types, and generally lack vermiculite or chlorite. The marine shales contain a clay-mineral suite which is very similar to that of deltaic beds, but usually contain poorly- to well-crystallized chlorite. These variations are interpreted as results of two opposing mechanisms of clay-mineral genesis: degradation and desilication of detrital clay-micas, and formation of kaolinite, in nonmarine milieux; and regrading of detrital vermiculite to better-crystalline chloritic minerals by magnesium adsorption in marine waters.

The study reveals three pertinent points about clay-mineral environmental relationships:

1. 1. The potential effects of nonmarine clay-mineral alteration processes are of much greater consequence than are those in marine environments. In this case, they led to the formation of beds in which the clay-mineral suite is almost all kaolinite, whereas the gross qualitative detrital clay-mineral suite was little changed in marine waters.

2. 2. The actual extent and effect of the clay-mineral formation processes is quite variable, so that there is considerable overlap in clay-mineral composition between nonmarine and deltaic deposits.

3. (3) “Trace” clay-mineral constituents may be more sensitive environmental indicators than the gross clay-mineral composition, in this case presence or absence and crystal-Unity of the chlorite-vermiculite component was the most diagnostic parameter.

An association between clay minerals and rock type is recognized in the rocks of an interlayered sequence of fossiliferous shaly, sandy bioclastic, and cherty limestone, dolomitic limestone, calcareous and dolomitic quartzite, and quartzite that form a portion of the lower part (Pennsylvanian age) of the Oquirrh formation in the northern Oquirrh Range, Utah. These sedimentary rocks are largely of clastic origin and range from fine- to coarse-grained. In part they are cross-bedded, and fossils are locally abundant. Calcite-rich rocks predominate (78 percent) over dolomite- and quartz-rich rocks (17 and 5 percent, respectively). Clay minerals constitute less than one percent in quartzite and range from one to five percent in some limestones.

Clay minerals and rock types are commonly observed in the following associations: Illite and chlorite occur in limestone; illite, chlorite, and mixed-layer clay occur in cherty, bioclastic, and sandy limestone and in calcareous quartzite; chlorite and illite commonly are present in dolomitic quartzite; chlorite, illite, and mixed-layer clay are found in dolomitic limestone; and kaolinite, illite and chlorite are typically present in quartzite. The mixed-layer clay has a lattice spacing of 29.4 Å that expands to 31.0 Å when glycolated and contracts irregularly to 13.2 Å when heated to 500 °C; the clay is assumed to consist of 14 Å chloritic and 15 Å montmorillonitic material. Chlorite or mixed-layer clay, or both, generally are associated with rocks containing dolomite.

Hydrotalcite minerals are layered double hydroxides (LDH) which play an important role in immobilizing hazardous compounds to decontaminate industrial wastewaters. The stability of an LDH is mostly evaluated in terms of its low solubility in water. However, the solubility of divalent trace metals immobilized by Mg-Al-type LDHs is not well known. Hydrotalcites containing Zn in solid solution, (Mg+Zn)3-Al-LDH, were synthesized by alkaline co-precipitation. A series of eleven LDH phases with Zn mole fractions XZn = Zn/(Mg+Zn) of 0–1 were characterized by powder X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry (TGA), scanning and transmission electron microscopy (SEM/TEM), Brunauer-Emmett-Teller (BET) surface area analysis, and inductively coupled plasma mass (ICP-MS) spectrometry. The XRD analysis provided sharp characteristic spacings for d003 and d006 which occurred for all samples, confirming a layered LDH structure. Cell parameters (a, c) obeyed Vegard’s law and confirmed the formation of a regular solid-solution series without a mixing gap. An aqueous equilibrium time was determined by kinetic dissolution experiments. Steady-state solubility occurred after 120 days, but the experiments continued up to 240 days. The XRD and SEM/TEM analyses indicated no phase changes during the long-term dissolution experiments; neither were phase impurities detected after 240 days. The solubility products of the Mg- and Zn-bearing endmember compositions were calculated from experimentally determined total cation and anion concentrations using the Visual Minteq code for considering element speciation and ion pairing. The solubility product decreased as the Zn mole fraction increased, suggesting that the Zn-bearing LDH phases were more stable than the pure Mg3-Al-LDHs. Solid-solution aqueous-solution thermodynamic equilibrium modeling using the Lippmann “total solubility product” approach and applying Lippmann diagrams with logarithmic x-axes revealed a log-linear decrease in aqueous Zn solubility. The results are promising for remediation of metal-bearing liquid wastes because the metals that co-precipitated with the LDH were more strongly retained and, therefore, less soluble than the hydroxides or carbonates of the trace metal.

Attention is called to the value to be derived from application of diffraction analysis of modern grade to specific, familiar, approximately known crystallizations. Features consequent to ordering of coordination polyhedra of differing sizes in layer structures are discussed, and their bearing upon relations between lattice parameters and chemical compositions are outlined.