Lower Wham Brake is a cypress, rim-swamp artificially enclosed in 1950 as a 22 km2 industrial reservoir by the International Paper Company (IPC)-Bastrop Mill, for regulating downstream water quality. Sediment cores were examined by XRD to differentiate paper-mill effluent deposition from the underlying detrital sediments and by 210Pb decay spectroscopy to determine sediment accretion rates.

Anatase and kaolin from the IPC paper-mill effluent delineated a well-defined, anthropic, silty-clay, A horizon above a clay, 2Ag horizon. Anatase concentrations were no greater than 1.7% in the A horizon and was absent in the underlying 2Agl horizon. Kaolin deposition was significantly correlated to the A horizon by an average increase of 84% above the kaolinite detrital background. Pyrite was detected in the A horizon as a transformation mineral following sulfur reduction of the paper-mill effluent.

Five of the six sediment cores showed an inflection in the excess 210Pb activity profile consistent with a present-day reduction in sediment supply. The average modern sedimentation rate was 0.05 cm yr−1. Average sedimentation observed during historic accretion was 0.22 cm yr−1, about 4.4 times greater than the modern rate of accretion. Reduction in sediment accretion can be attributed to upstream levees completed in 1934 and loss of organic accumulation following the 1950 reservoir impoundment. However, radiometric dating could not precisely correlate the geochronology of kaolin/anatase introduction due to complex oxidation/reduction cycles concurrent with the modern accretion regime.

While soils formed in tephra are typically dominated by poorly crystalline clay minerals, the occurrence of smectite in E horizons of podzolized soils (Spodosols) has been well-documented. We have observed a well-crystallized smectite mineral dominating the clay fraction of E horizons in tephra-derived soils of northern Idaho. This study was initiated to examine properties and distribution of this mineral along a developmental sequence of high-elevation, forested Spodosols formed in 6800-yr-old Mazama tephra. Three soils exhibiting strong, moderate, and weak E horizon development were sampled along an elevational and climatic gradient. The smectite mineral was identified as beidellite based on expansion and layer charge characteristics. Heated, Li-saturated samples from the most strongly developed E horizon exhibited relatively complete expansion to 1.8 nm with glycerol solvation and mean layer charge was calculated to be 0.44 molc/formula unit using sorption characteristics of alkylammonium ions. Apparent crystallinity and relative abundance of the beidellite in clay fractions decrease with decreasing E horizon development. The more poorly crystalline beidellite is associated with a non-expansive 1.4-nm mineral with considerable Al-hydroxy interlayering. Beidellite was not detected in underlying glacial drift or in a thin layer of 200-yr-old ash that mantles these soils, suggesting it is not inherited from these materials. Rather, our results indicate that beidellite forms in these soils in an environment characterized by low pH and a large flux of organic metal-complexing agents.

The objective of this study was to observe flocculation of montmorillonite in the presence of a glucose polymer (dextran) and to observe the effect of saturating cation and coagulant addition on the flocculation process. Flocculation of montmorillonite was dependent on polymer molecular weight, polymer/clay ratio (w/w), nature of exchangeable cation, and ionic strength of the suspension to which the polymer was added. The T500 dextran (molecular weight = 5 × 105) caused enhanced sedimentation of Ca-montmorillonite suspension at a polymer/clay ratio of ≤0.01. Increasing the polymer concentration above this level stabilized the suspension such that sedimentation was less than or equal to that of the control. The T2000 dextran (molecular weight = 2 × 106) caused a similar increase in the sedimentation of Ca-montmorillonite at polymer/clay ratios of <0.1. The ability of the T2000 polymer to cause flocculation at greater polymer/clay ratios as compared to the T500 polymer was attributed to the lower osmotic pressure between clay particles for equal concentrations of the two polymers. Flocculation of Ca-montmorillonite by dextran was enhanced when the clay had initially been coagulated by the addition of salt. Reduction of the diffuse double layer upon addition of salt permitted the polymer to extend beyond the electrostatic barrier of the clays. Dextran was not able to flocculate Mg-montmorillonite suspensions with or without the presence of coagulant. The displacement of water molecules at the clay surface rather than within the hydration shell of the more highly polarizing Mg cations by polymer segments resulted in a greater polymer collapse on the clay surface leaving fewer and shorter polymer loops and tails available for contacting adjacent clay particles.

Diagenetic clay minerals usually occur as heterogeneous assemblages of submicroscopic layers consisting of different structure types such as illite, smectite and chlorite, with variable composition within a given structure type, and with highly variable concentrations of imperfections. The dimensions of mixed-layering, the semi-coherent to coherent nature of the structures across the layering, and compositional heterogeneity occur at a scale well below that of an individual thermodynamic phase. These relations imply that most clays are not distinct minerals or phases, and that assemblages of clays in shales and mudstones are incompatible with the phase rule. Such relations are better evaluated in terms of the formation of metastable materials with each small unit having unique chemical properties, rather than as a small number of stable homogeneous phases. Consequently, treatment of most clay minerals in terms of equilibrium stability with either a thermodynamic or experimental approach is subject to error.

Chemical reactions involving most clay minerals are best understood with kinetic models. These involve a great variety of parameters such as time, fluid/rock ratio, deformation history, nature of starting materials and transformation mechanisms, as well as the variables, such as temperature, pressure and composition, that are commonly used to define equilibrium. Solubility experiments on the stabilities of clay minerals are unlikely to attain equilibrium at low temperatures. Moreover, the activity of soluble species may be controlled by surface equilibria, or by absorbed or exchangeable cations. Interpretations of available experiments on the solubility of illite vs. other mineral assemblages are in violation of Schreinemakers’ rules and indicate lack of equilibrium.

Predictable sequences of clay minerals as a function of temperature are best understood through the Ostwald step rule, in which clay mineral assemblages undergo reactions in response to kinetic factors that represent reaction progress rather than an approach to equilibrium. Currently used clay mineral thermometers (illite crystallinity, smectite/illite reaction, chlorite composition) are not based on equilibrium reactions. Such systems are not accurate thermometers and therefore have questionable utility.

The nature and number of acid sites per unit weight on a series of materials obtained by interaction of a montmorillonite with zirconium or cerium hydrogenphosphates precipitated in situ by reaction between their precursors have been investigated.

The quantitative determination of the surface acidity has been carried out by three different methods: titration with triethanolamine in aqueous media; TG analysis of the samples after n-butylamine treatment and vacuum desorption; and chemisorption of NH3 at 239.8 K. Additional information about the nature of the surface acid sites has been obtained from the IR spectra of the samples with bases adsorbed.

Results show that the acid site density on the montmorillonite-cerium or zirconium phosphate cross-linked compounds is greater than on the parent montmorillonite and increases as the content in tetravalent metal phosphate rises throughout the different series. Also the number of acid sites for the cerium phosphate-montmorillonite materials is lower than for zirconium ones and the characteristics obtained depend on the bases used for their evaluation.

The presence of two IR adsorption bands at 1400 and 3145 cm−1, assigned to the NH4+ ion, and the absence of the 1170–1361 cm−1 bands, characteristic of the NH3 adsorbed on a Lewis site, strongly suggest the Brönsted character of the acidity of these compounds.

Synthetic aluminum-substituted maghemite samples, γ-(Fe1-xAlx)2O3, have been prepared by thermal decomposition of Al-lepidocrocite (γ-Fe1-xAlxOOH), with × = 0, 0.04, 0.06, 0.14 and 0.18. The particles are needle-shaped and the mean crystallite diameter along the [311] crystallographic direction was found to be between 2.0 and 5.0 nm. Mössbauer spectra were collected at 6 K and from 80 K up to 475 K at steps of 25 K. In a wide range of temperatures the spectra of the non-substituted sample consist of a superposition of a broad sextet and a superparamagnetic doublet, whereas for the Al-maghemites this range is much smaller. From the temperature variation of the fractional doublet area two different parameters were defined: the temperature corresponding to a 50/50 doublet-sextet spectrum (T1/2), and the temperature below which the doublet ceases to exist (T0). These two parameters (T1/2 and T0) decrease from 390 K and 92 K (Al-free sample), to 118 K and 64 K (4 mole % Al) and to 100 K and 48 K (18 mole % Al), respectively. The average hyperfine fields at 6 K undergo a steep drop in going from the Al-free sample (Hhf = 506 kOe) to the sample with 4 mole % Al (Hhf = 498 kOe), but for higher substitutions the effect is much smaller. The A- and B-site quadrupole splittings, obtained from the data between 220 K and 475 K, were found as: ΔEQ,A = 0.86 ± 0.04 mm/s and ΔEQ,B = 0.65 ± 0.04 mm/s for the 4 mole % Al sample. The characteristic Mössbauer temperature, determined from the temperature dependence of the average isomer shift, was found to be in the range of 500–600 K.

Hydrothermal alteration has caused illitization along a 40m vertical profile in the Tsantilis bentonite deposit, Eastern Milos, Greece which consists principally of a Wyoming-type montmorillonite and authigenic K-feldspar. The product K-bentonite which contains illite/smectite, kaolinite, K-feldspar, quartz, sulphates and sulphides exhibits an unusual tendency for increase of expandability with depth.

Mineralogy and I/S textures were determined with X-ray diffraction and SEM and TEM methods respectively and chemistry using X-ray fluorescence. Illitization is characterized by a 5- to 6-fold increase of K and release of Si, Fe, Mg Na, and Ca from the parent rock, indicating a K-influx (K-metasomatism) in the system.

The I/S particle morphology is characterized by both flaky and lath-like particles, the former dominating in the range 100-50% expandable layers (R0 ordering) and the latter in the range 50-10% expandable layers (R1 and R > 1 ordering). Flaky particles are also abundant in samples with R1 ordering and abundant kaolinite, indicating that the latter might affect illitization. The I/S particles are classified in populations with thickness multiples of 10 A, their thickness being probably smaller than the coherent XRD domain. As the reaction proceeds, particles grow thicker and more equant. The distribution of I/S particle dimensions forms steady state profiles showing log-normal distribution; however, sensu stricto Ostwald ripening is unlikely. It seems that the reaction proceeds toward minimization of the surface free energy of I/S, being affected principally by temperature and K-availability. The spatial distribution of expandability implies that the heating source was probably a mineralized vein with T < 200°C, directed away from the bentonite, suggesting that illitization might be used as an exploration guide for mineral deposits.

Adsorption of uranyl to SWy-1 montmorillonite was evaluated experimentally and results were modeled to identify likely surface complexation reactions responsible for removal of uranyl from solution. Uranyl was contacted with SWy-1 montmorillonite in a NaCIO4 electrolyte solution at three ionic strengths (I = 0.001, 0.01, 0.1), at pH 4 to 8.5, in a N2(g) atmosphere. At low ionic strength, adsorption decreased from 95% at pH 4 to 75% at pH 6.8. At higher ionic strength, adsorption increased with pH from initial values less than 75%; adsorption edges for all ionic strengths coalesced above a pH of 7. A site-binding model was applied that treated SWy-1 as an aggregate of fixed-charge sites and edge sites analogous to gibbsite and silica. The concentration of fixed-charge sites was estimated as the cation exchange capacity, and non-preference exchange was assumed in calculating the contribution of fixed-charge sites to total uranyl adsorption. The concentration of edge sites was estimated by image analysis of transmission electron photomicrographs. Adsorption constants for uranyl binding to gibbsite and silica were determined by fitting to experimental data, and these adsorption constants were then used to simulate SWy-1 adsorption results. The best simulations were obtained with an ionization model in which AlOH2+ was the dominant aluminol surface species throughout the experimental range in pH. The pH-dependent aqueous speciation of uranyl was an important factor determining the magnitude of uranyl adsorption. At low ionic strength and low pH, adsorption by fixed-charge sites was predominant. The decrease in adsorption with increasing pH was caused by the formation of monovalent aqueous uranyl species, which were weakly bound to fixed-charge sites. At higher ionic strengths, competition with Na+ decreased the adsorption of UO22+ to fixed-charge sites. At higher pH, the most significant adsorption reactions were the binding of UO22+ to AlOH and of (UO2)3(OH)5+ to SiOH edge sites. Near-saturation of AlOH sites by UO22+ allowed significant contributions of SiOH sites to uranyl adsorption.

IronIII for TiIV substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. Mössbauer- and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated FeIII in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm−1, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H2O/mol Fe. At 600°C structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiO5, was formed.

The uniformity of clay films affects the transport of an anionic electroactive probe through the film. When cations other than Na+ are present in the initial swelling of the film (such as native K+ and Ca2+), or when the native clay is highly charged, internal dislocations of the film, caused by variable stacking domains, enhance the diffusive transport of Fe(CN)63− across the film. This effect is investigated using clay-modified electrodes in which the clays are of variable exchange forms (Na+, Ca2+, or K+) and variable charge. The charge on the clay is determined both by the native form of the clay and by reduction of structural Fe3+. The results suggest that swelling of clays increases in a linear fashion with CEC, at least for minimally charged clays.

The form under which Ti occurs in kaolinitic materials from various environments has been investigated using second derivative diffuse reflectance spectroscopy. The position of the absorption edge may be used as a diagnostic band to determine Ti-phases (anatase, rutile, Ti-gels). Ti-oxides may be detected in kaolins, down to 0.1 wt. % TiO2. Diffuse reflectance spectra show the presence of Ti-gel-like phases occluded in sedimentary kaolinite particles. These phases, which record conditions at the time of kaolinite growth, constitute the first direct evidence of Ti mobility at the scale of mineral assemblages and question the substitution of Ti for Al in kaolinite. The nature of the Ti-oxides associated with kaolinite particles gives some constraints on the temperature conditions of hydrothermal kaolins, the evolution of sedimentary kaolin during basin diagenesis and the source of parental material in soil kaolins.

Single-crystal, X-ray examination of Mg,Fe-rich chlorites that were heated at 650°C for 24 hours in air and have undergone dehydroxylation of the interlayer shows that two product phases result with a topotactic relationship, with the c axis of both phases parallel. One phase (“modified chlorite” or “14-A phase”) has relatively sharp reflections with a 14-A c-axis repeat, indicating that it is well crystallized and maintains the 2:1 layer from the parent. Cell parameters are a = 5.368(1)A, b = 9.297(2)A, c = 14.215(6)A, a = 89.86(3)°, ß = 97.15(3)°, γ = 89.98(2)°, and it crystallizes in CĪ symmetry. A structure refinement, details of which will be reported later, indicates that the interlayer consists of two planes, each containing (M + O), where M is the interlayer cation species. These planes show about ±0.5A positional disorder along the [001] direction. There is no evidence for scattering material at z = 0.5 between the 2:1 layers. The second phase in the topotactic relationship is based on a 27-A unit c axis (“27-A phase”). The diffraction data are limited with about 15 diffuse reflections observed, indicating that it is poorly crystallized. The 27-A spacing suggests that both octahedral sheets in the parent chlorite contribute to the formation of this phase.

Heating Mg,Fe-rich chlorite powder in a closed system to 550°C, under either reducing or oxidizing conditions, prevents the formation of the 27-A phase. Because the 27-A phase forms in an open system, we infer that water fugacity is an important factor in its formation. Heating experiments involving samples with different polytypes and octahedral “type” (dioctahedral vs trioctahedral) of the 2:1 layer suggests that these two variables are important. However, the results are equivocal, and an ill-defined B-rich chlorite from Madagascar breaks the observed trends for both variations in stacking sequence and octahedral type. However, B-content may be a factor in the transformation also for those chlorites that contain B.

The corrensite from a chlorite vein-like rodingite blackwall in serpentinites has been studied. The proper identification of swelling layers in corrensite using heating at 500°C was ambiguous because of the spontaneous rehydration. Even K+-saturated samples heated to 500°C readily rehydrated after being cooled. This can be prevented if XRD patterns are recorded at 300°C, without cooling the sample. A standard heating at 500°C can result in partial decomposition of brucite-like sheet as evidenced by ASN simulation.

The ASN-calculated XRD patterns of contracted corrensite proved that an inhomogeneous distribution of heavy atoms (Fe, Ni, Mn, Cr etc.) between brucite-like sheet and talc-like layers and between two adjacent corrensite units in the interstratified mineral may result in the disappearance of low angle reflections (24 Å and 12 Å), which can lead to miscellaneous interpretation if distribution of heavy cations is not checked.

The corrensite occurred together with regular chlorite. However, it is assumed to be formed due to direct crystallization from late hydrothermal solutions as deduced from comparison of the Mg/(Mg + Fe) ratio in the corrensite, serpentinite and chlorite.