Shewanella putrefaciens CN32 reduces Fe(III) within two illites which have different properties: the Fithian bulk fraction and the <0.2 µm fraction of Muloorina. The Fithian illite contained 4.6% (w/w) total Fe, 81% of which was Fe(III). It was dominated by illite with some jarosite (∼32% of the total Fe(III)) and goethite (11% of the total Fe(III)). The Muloorina illite was pure and contained 9.2% Fe, 93% of which was Fe(III). Illite suspensions were buffered at pH 7 and were inoculated with CN32 cells with lactate as the electron donor. Select treatments included anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. Bioproduction of Fe(II) was determined by ferrozine analysis. The unreduced and bioreduced solids were characterized by Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. The extent of Fe(III) reduction in the bulk Fithian illite was enhanced by the presence of AQDS (73%) with complete reduction of jarosite and goethite and partial reduction of illite. Mössbauer spectroscopy and chemical extraction determined that 21–25% of illite-associated Fe(III) was bioreduced. The extent of bioreduction was less in the absence of AQDS (63%) and only jarosite was completely reduced with partial reduction of goethite and illite. The XRD and TEM data revealed no significant illite dissolution or biogenic minerals, suggesting that illite was reduced in the solid state and biogenic Fe(II) from jarosite and goethite was either released to aqueous solution or adsorbed onto residual solid surfaces. In contrast, only 1% of the structural Fe(III) in Muloorina illite was bioreduced. The difference in the extent and rate of bioreduction between the two illites was probably due to the difference in layer charge and the total structural Fe content between the Fithian illite (0.56 per formula) and Muloorina illite (0.87). There may be other factors contributing to the observed differences, such as expandability, surface area and the arrangements of Fe in the octahedral sheets. The results of this study have important implications for predicting microbe-induced physical and chemical changes of clay minerals in soils and sediments.

To eliminate mercury vapor from gas streams, three major methods are used: condensation, absorption, and adsorption. This work deals with adsorption, using elemental sulfur as an active phase supported on sepiolite and palygorskite fibrous clays. Sulfur loads of 5–30% were deposited by catalytic oxidation of hydrogen sulfide at temperatures of <200°C, the clays acting first as a catalyst of the reaction and then as a carrier of the obtained sulfur. The ability of the sulfurized clay adsorbents to retain mercury was studied at 45°C and 1 mm Hg pressure. The high values found, about 4 g Hg/g S supported on clays, compared with 1.69 g Hg/g S on activated carbon under the same conditions are related to a more appropriate pore size distribution, with more of the pore widths >6 nm for the sulfurized silicates. Also, the allotropic state of the deposited sulfur, where Sπ (octo-catena) is better than Sλ (octo-cycle), may also be a contributing factor.

A reliable method, utilizing a fluoride ion-selective electrode, is described for the determination of fluoride in clays and shales. Interference by aluminum and iron is minimal. The reproducibility of the method is about ±5% at different levels of fluoride concentration.

Data are presented for various clay minerals and for the <2-µm fractions of marine and nonmarine clays and shales. Fluoride values range from 44 ppm (0.0044%) for nontronite from Colfax, WA, to 51,800 ppm (5.18%) for hectorite from Hector, CA. In general, clays formed under hydrothermal conditions are relatively high in fluoride content, provided the hydrothermal waters are high in fluoride content. Besides hectorite, dickite from Ouray, CO, was found to contain more than 50 times as much fluoride (6700 ppm) as highly crystalline geode kaolinite (125 ppm). The clay stratum immediately overlying a fluorite mineralized zone in southern Illinois was found to have a higher fluoride content than the same stratum in a nonmineralized zone approximately 1 mile away. Nonmarine shales in contact with Australian coals were found to be lower in fluoride content than were marine shales in contact with Illinois coals.

It is believed that, in certain instances, peak shifts on DTA curves of similar clay minerals are the result of significant differences in their fluoride content.

Clay particle aggregation affects a number of environmental processes, such as contaminant sorption/desorption, particle movement/deposition, and sediment structure and stability, yet factors that control clay aggregation are not well understood. This study was designed to investigate how microbial reduction of Fe(III) in clay structure, a common process in soils and sediments, affects clay-particle aggregation. Microbial Fe(III) reduction experiments were conducted with Shewanella putrefaciens CN32 in bicarbonate buffer with structural Fe (III) in nontronite as the sole electron acceptor, lactate as the sole electron donor, and AQDS as an electron shuttle. Four size fractions of nontronite (D5–D95 of 0.12–0.22 µm, 0.41–0.69 µm, 0.73–0.96 µm and 1.42–1.78 µm) were used to evaluate size-dependent aggregation kinetics. The extent of Fe(III) bioreduction and the amount of exopolysaccharide (EPS), a major biopolymer secreted by CN32 cells during Fe(III) bioreduction, were measured with chemical methods. Nontronite particle aggregation was determined by photon correlation spectroscopy and scanning electron microscopy. The maximum extent of Fe(III) bioreduction reached 36% and 24% for the smallest and the largest size fractions, respectively. Within the same time duration, the effective diameter, measured at 95% percentile (D95), increased by a factor of 43.7 and 7.7 for these two fractions, respectively. Because there was production of EPS by CN32 cells during Fe(III) reduction, it was difficult to assess the relative role of Fe(III) bioreduction and EPS bridging in particle aggregation. Thus, additional experiments were performed. Reduction of Fe(III) by dithionite was designed to examine the effect of Fe(III) reduction, and pure EPS isolated from CN32 cells was used to examine the effect of EPS. The data showed that both Fe(III) reduction and EPS were important in promoting clay mineral aggregation. In natural environments, the relative importance of these two factors may be dependent on local conditions. These results have important implications for understanding factors in controlling clay particle aggregation in natural environments.

Fabric refers to the spacial arrangement of clay particles in a sample relative to a reference plane. X-ray diffraction data yield an ‘amount of orientation’ (AO) that varies from zero for ideal random to 100 for ideally oriented fabric. The AO has been related to the average angle of inclination of clay particles to the reference plane.

Fabric data from 50 samples involving 2000 determinations are presented on the effects of: the method of sample preparation prior to one-dimensional consolidation; the magnitude of consolidation stress from 0·1 to over 1000 kg/cm2; changes in direction of consolidation stress; isotropic consolidation; and disturbance during removal of samples from oedometer cells. The single most important variable was the method of sample preparation, as illustrated by the following data on samples consolidated one-dimensionally to 1·5 kg/cm2:clay initially moist, AO = 27 per cent; air-dry clay, AO = 44 per cent; clay slurries, AO = 76–95 per cent. The change in fabric with increasing consolidation stress was most pronounced with samples at very low stresses, the changes in fabric were small for consolidation stress increments usually encountered in engineering practice.

Fabric data provide a very sensitive measure of sample disturbance. Extrusion causes significant disturbance at the center of a 24cm dia, sample cylinder.

The adsorption of Cr(III) was studied at pH 1, 2, 3, 4, 6, 8, and 10 on chlorite and kaolinite and at pH 1, 2, 3, and 6 on illite. The amount of chromium adsorbed on chlorite varied from 3.1 × 10–5 mole/ g at pH 1 to 16.6 × 10–5 mole/g at pH 4, and on illite from 4.9 × 10–5 mole/g to 9.2 × 10–5 mole/g at pH 1 and 3, respectively. Kaolinite adsorbed 3.7 × 10–5 mole Cr/g at pH 1, 2, and 3 and 5.5 × 10–5 mole Cr/g at pH 4. Measurements of the Cr 2p core-level binding energies indicate that chromium is probably adsorbed as a Cr(III) aqua ion at pH values below 4. The binding energies for the Cr 2p level for samples prepared above pH 4 compare favorably with the value determined for chromium hydroxide and lead to the conclusion that the chromium species present at pH 6, 8, and 10 is chromium hydroxide.

A comparison is made of the ion exchange behavior, towards the cobalt ion, of five sodium montmorillonite clays. The selectivity for the bivalent ion at low cobalt loading is correlated with the average dimensions of the particles in the various clays, as characterized by several methods. The data are interpreted in terms of a higher selectivity of the bivalent ions for the broken bonds located at the edges of the clay crystals. Using a model comprising two areas of different charge densities, the experimental differences in behavior can be predicted reasonably well.

In a lateritic pallid zone ilmenite crystals alter via pseudorutile to porous leucoxene grains composed of randomly oriented aggregates of ~0.06 μm anatase crystals. This style of alteration differs from that in beach sands where parallel oriented rutile crystals develop from pseudorutile. Increased Si and Al in the altered grains is due to the crystallization from soil solution of halloysite, kaolinite and gibbsite within pores rather than to the incorporation of these elements into anatase crystals. Manganese was a significant constituent (3.2% Mn2O3) of the original ilmenite but was not retained by the leucoxene grains. The minor constituents Ni, Zn, Cu, Mg, Co and Ca were also lost, but Cr and V were retained.

Along the inner Coastal Plain, kaolinite-metahalloysite-rich, neritic muds of Cretaceous-Eocene age have undergone intense postdepositional alteration in the recharge area of the regional groundwater system. Weathering processes have had the following profound effects on the original sediments: 1) strong compositional and textural modification of both clay and non-clay minerals; 2) whitening of the originally darker sediments by partial removal of organic matter, Fe and Mn; and 3) recrystallization of kaolinite and metahalloysite, most conspicuous where there are coarse stacks and vermiforms. Where the combination of initial sediment composition and alteration intensity was most favorable, these changes have produced important deposits of commercial quality, which now sustain the world's largest kaolin production district. The earliest change was partial sequestration of iron as sulfide and concurrent destruction of some organic matter, mediated by sulfate-reducing bacteria. Subsequent weathering resulted in gradual leaching of alkalies, alkaline earths, iron and silica, and attendant nucleation and growth of minerals compatible with the compositional changes. The existence of several closely spaced erosional unconformities, separated by neritic sediments, is proof that weathering conditions commonly changed at a given site, in response to changes in thickness or lithology of the overlying rocks. Dsyoxic → ← oxic reversals modified both the rate and kind of alteration. (“Dysoxic” refers to molecular oxygen concentration too low to be toxic to anaerobes or cause abiotic oxidation; less extreme than “anoxic”.) Kaolins were produced partly by slower dysoxic weathering in saturated groundwater zones but mainly by more rapid oxic weathering in unsaturated zones, where bauxites also locally formed. Gradual transformation of some sediments to kaolin rarely began and ended in the same epoch. At several places most of the kaolinization (see “Definitions”) took place during Recent time, tens of millions of years after deposition of the sediments. Since the kaolins resulted from postdepositional alteration rather than sedimentary processes, they are better referred to as “Coastal Plain” rather than “sedimentary” kaolins.

This paper describes the calculation of the diffracted intensity for models of powdered minerals with lamellar structure, in order to compare experimental and theoretical X-ray diagrams. The calculation takes into account at the same time (i) the possibility of coexistence of different kinds of layers in the stackings, (ii) the possibility of stacking faults between the layers (translative or rotative ones) and (iii) the unavoidable orientation of particles in the powder sample (the method of determination of the orientation is described).

At pH 12 Co-ferrihydrite transformed to either Co-goethite or Co-magnetite, the latter compound appearing at Co additions of > 18 mole %. Although Co was readily taken up by the magnetite structure, chemical analysis showed that no more than 7 mole % substitution of Co in goethite was achieved. Hematite formation was not strongly promoted by the presence of Co; with 9 mole % Co in the system, the amount of hematite relative to goethite in the product increased slightly. Co-substituted goethites grew as long, thin crystals. The presence of Co promoted some dendritic twinning of goethite. Cobalt retarded the transformation of ferrihydrite to more crystalline oxides mainly by stabilizing ferrihydrite against dissolution. A comparison of Co with divalent ions previously studied showed that their stabilizing ability decreases in the order Cu > Co > Mn, i.e., they follow the Irving-Williams series for the stability of metal complexes.

Smectite close to the pure Fe end member of the nontronite-beidellite series was found in the fine clay separated from a 354-cm deep sediment core in the southwestern Pacific Basin. The mineral has a b-axis of 9.09 Å and an unusually low dehydroxylation temperature of 454°C and is composed of sheaves of fibers less than 50 Å wide. Its charge density is 5.09 × 10~4 esu/cm2. The charge originates mainly from the presence of 18% of the total Fe in tetrahedral positions, as determined by Mössbauer analysis. Slight deviations of the infrared spectra from those reported for nontronites are probably due to the presence of more octahedral Mg. The presence of authigenic quartz in the same sample permits some speculation on the concentration of dissolved silicon during nontronite genesis. A δ18O value of 26 ± 0.3‰ indicates a temperature of formation of about 22°C. The Sr isotope ratio suggests that the nontronite formed at least 12 million years ago.

The expandabilities of kaolin-group minerals in different horizons in 10 soils from New Zealand and Fiji were measured immediately after the application of formamide and after the sequential application of hydrazine, water, and glycerol (HWG treatment). The expandabilities of these minerals in some of the soil samples with dimethylsulphoxide (DMSO) and after long-term (4-day) formamide treatments were also measured. The abundance of characteristic halloysite shapes was determined from electron micrographs of selected samples. The expandabilities of several non-soil kaolinite samples with the DMSO and HWG treatments were also measured.

The expansion of kaolin-group minerals showed the same trends within almost all profiles, whether determined using formamide (by the immediate-formamide treatment) or glycerol (by the HWG treatment). Except where both treatments led to complete intercalation, the HWG treatment always caused more expansion of kaolin-group minerals than obtained immediately after formamide application. The HWG treatment expanded some non-soil kaolinite samples, but well-crystallized kaolinite was not affected by this treatment. The DMSO treatment expanded kaolin-group minerals in the soils to a similar extent as the HWG treatment and also expanded well-crystallized kaolinite. The degree of expansion resulting from the immediate-formamide treatment matched abundance of typical halloysite particle shapes more closely than the degree of expansion given by the other intercalation treatments. The degree of expansion immediately following formamide application could be diminished, if the samples were heated at 40 ± 5°C.

The influence of added sodium and calcium nitrate electrolyte on the particle aggregates in the colloid fraction of natural bentonite and kaolin was studied. Clays were flocculated in distilled water and various electrolyte concentrations. Aggregate size was studied by sedimentation analysis; the mean radius of the aggregates was plotted against the concentrations of Na+ and Ca2+. For bentonite, the mean radii decreased with an increase of Na+ and Ca2+ concentration, reaching a minimum; and further increases in concentration led to an increase of the mean radii of the aggregates. For kaolin, an increase in Na+ and Ca2+ concentration gave rise to an increase in the mean radii of aggregates.

Scanning electron micrographs showed different types of aggregates, depending on the physico-chemical conditions of a sedimentation process. In bentonite and kaolin sediments formed from a distilled water slurry, the dominant aggregate was an edge-face type. The small addition of salts to a bentonite slurry led to the formation of edge-edge-type aggregates; for kaolin edge-face-type aggregates formed, although within the microaggregate face-face associations were observed. The highest concentrations of electrolytes for sediments of both clays led to formation of compact, face-face-type aggregates.

The basic outlines of most of the hydrous layer silicate structures were determined during the 1930’s. Present escalating interest in obtaining additional detail is indicated by (a) publication of over twenty structural refinements (2-D or 3-D) during 1954-64, (b) publication of at least nine structures in 1965 or early 1966, and (c) personal communication that at least fifteen additional refinements are in progress. Points of especial interest in these recent studies follow.

1. 1. Octahedral cation order is common, but tetrahedral cation order is confirmed in only three cases. Because ordering of Si, Al does not significantly affect the statistical tests for centrosymmetry, centrosymmetric space groups that do not permit order should be avoided during refinement.

2. 2. Oversize tetrahedral sheets articulate with smaller octahedral sheets by tetrahedral rotation and, for dioctahedral species, by tetrahedral tilting around vacant octahedra. The latter mechanism influences the type and regularity of layer sequences. Undersize tetrahedral sheets articulate with larger octahedral sheets by tilting plus octahedral contraction or by inversion of some tetrahedra.

3. 3. The amount and direction of tetrahedral rotation and tilt, length of T—O, M—O, and O—O bonds, sheet thicknesses, and relation of cell dimensions to composition can now be predicted with some confidence.

4. 4. Variation in layer stacking (polytypism) is common. In some cases the stabilities of different polytypes can be explained by the relative amounts of repulsion and attraction between the ions in the structures. The stabilities can be correlated with the energy available in the environment of crystallization.

The low-temperature alteration of a rhyolitic rock from Kimolos Island, Aegean, Greece, yielded an alteration profile characterized by gradual transition from fresh glass to bentonite containing homogeneous Chambers-type montmorillonite and then to a mordenite-bearing bentonite. Both mordenite and smectite were formed from poorly crystalline precursors, which probably had compositions comparable to that of the crystalline end-product. However, their composition may have been modified to some degree after reaction with the fluid phase. Particle length and width measurements of smectite crystals yielded lognormal profiles, which suggest supply-controlled crystal growth in an open system or random ripening in a closed system. The former mechanism is in accordance with the observed sustained supply of Mg and Fe by the fluid phase throughout the alteration profile and is believed to be the dominant formation mechanism of smectites in bentonites in general. In the mordenite-bearing zone, random ripening is expected in domains with low permeability, in which the system was essentially closed, favoring the formation of mordenite. The level of supersaturation with respect to smectite was probably lower in the mordenite-bearing zone. Smectite probably affected pore-fluid chemistry either through ion exchange or via dissolution of initially formed K-bearing smectite. The latter process raised the K+/(Na+ + Ca2+) activity ratio of the pore-fluid favoring K-bearing mordenite.

The infrared absorption spectra of a palygorskite sample from Cáceres, Spain, showed two previously unreported bands in the OH-stretching region at 3420–3440 and 3220–3230 cm−1 after evacuation at 90°–230°C. These bands, which reached maximum intensity after the sample was heated at 150°C, were assigned to OH in the

$$\begin{array}{*{20}{c}} H \\: \\ {Si - O - Si\,and\,} \\ \end{array}\begin{array}{*{20}{c}} H \\: \\ {Si - O - A1} \\ \end{array}$$

Inverse gas chromatography at infinite dilution, employing alkanes and alkenes as probes, has been used to characterize the surface properties of a series of smectites of varying chemical composition. The results of this study show that the acidic centers and the interlayer distances have a great influence on the specific interaction of the smectite surface with π-bonds of alkenes. High values of the specific interaction parameter, ɛπ, are caused by the existence of strong acidic centers that are connected with interlayer cations as well as with the chemical structure of the mineral sheets. On the other hand, alkanes, whose interaction with the smectites is predominantly dispersive, are unaffected by changes in the clays’ composition and/or structure.

A series of mixed iron and titanium oxide coprecipitates ranging in composition between 0 < Ti/Ti + Fe < 1 was synthesized and aged under varying conditions of pH, temperature and time in order to establish a working model for pedogenic titanium and titano-ferric oxides. X-ray powder diffraction (XRD), selective chemical dissolution, magnetic susceptibility, charge distribution and electron optical data indicate that the freshly prepared Fe-Ti oxides consist of an Fe-rich (Ti-ferrihydrite) phase (Ti/Ti + Fe ⩽ 0.70) having pH-dependent positive charge and a Ti-rich phase (Ti/Ti + Fe ⩾ 0.7) with permanent and pH dependent negative charge.

Synthetic Ti-ferrihydrite and amorphous TiO2 were completely soluble in acid ammonium oxalate (2 hr extraction in the dark) whereas poorly crystalline anatase (width at half height, WHH > 2.0°2θ) was partly oxalate soluble. NH4-oxalate soluble Ti was particularly high in soils developed under a cool montane climate (afro-alpine) and lower in soils of warmer subtropical climate, which contain anatase and rutile.

Several mixed Fe-Ti crystalline phases were identified after aging NH3 coprecipitates of Fe and Ti nitrate at 70°C and pH 5.5 for 70 days:

1. (1) goethite and hematite in the composition range 0 < Ti/Ti + Fe ⩽ 0.20; at low Ti concentrations (<5 mole %) goethite was favored and/or hematite inhibited

2. (2) microcrystalline pseudorutile in the composition range 0.20 ⩽ Ti/Ti + Fe ⩽ 0.70

3. (3) anatase and ferriferous anatase in the range 0.70 ⩽ Ti/Ti + Fe < 1.0; with decreasing proportion of Ti the crystal-Unity of anatase decreased.

The results suggest that secondary or pedogenic Ti-Fe oxides can form by coprecipitation and crystallization in the weathering solution, and emphasize the essential role of water (as opposed to dry oxidation) in the alteration of primary titaniferous minerals.