Showing papers in "Clays and Clay Minerals in 1980"

Physico-chemical properties of synthetic hydrotalcites in relation to composition

Abstract: Ahstraet--Hydrotalcite solid solutions were prepared by coprecipitation followed by hydrothermal treatment between 150 ~ and 250~C. Based on the structural formula [Mgl_xAlx(OH)~lX+l(COz)x/2 �9 mH20] x-, pure solid solutions were formed in the range Al/(Al + Mg) = 0.2 to 0.33, where m = (1 - 3x/2). Maximum crystallite size was achieved by hydrothermal treatment between 180 ~ and 200~ with x = 0.337 to 0.429. Crystal strain was also minimized at these values of x. The adsorption c~pacity for Naphthol Yellow S increased as x increased and reached a maximum (1.56 x 10 6 moles/m 2) when x = 0.287, a value eight times larger than that of Mg(OH)~. A weak endothermic DTA peak at about 350~ is probably due to the loss of structural water in the main layer of the structure. On calcination between 400 ~ and 700~ only periclase was detected, probably containing A1 in solid solution. Hydration of the calcined product resulted in the reconstruction of the original hydrotalcite structure.

Precise identification of illite/smectite interstratifications by X-ray powder diffraction

Abstract: The thickness of the two-layer ethylene glycol complex of dioctahedral smectites varies under room conditions between 17.3 and 16.5 A because of such factors as layer charge density, type of interlayer cation, and relative humidity. Neglecting this variability can give up to 30% error in the X-ray powder diffraction estimation of the smectite:illite ratio of the mixed-layer structures. Three methods have been developed for the interpretation of X-ray powder diffraction patterns of glycolated mixed-layer illite/smectite which take layer-spacing variability into account. The methods include a technique for quantifying the degree of layer ordering. In addition, the proposed techniques minimize the error due to the influence of domain size on positions of reflections. The experimental error can be kept below 5% or below 1% smectite layers, depending on the method applied, provided that the peak positions are measured with the accuracy of ± 0.02°2θ.

Crystal chemistry of boehmite

Abstract: Thirty two boehmites, synthesized at temperatures ranging from room temperature to 300~ were examined by scanning electron microscopy, transmission electron microscopy, electron diffraction, X-ray powder diffraction, differential thermal analysis, and infrared spectroscopy. The results show that boehmite exhibits a continuous gradation in crystallite size ranging from single octahedral layers or a few unit cells to about 65 unit cells in the y-direction. This conclusion suggests that the term pseudoboehmite is inappropriate for finely crystalline boehmite. Finely crystalline boehmite contains more sorbed water than coarsely crystalline boehmite; this water is commonly intercalated between octahedral layers, usually randomly but sometimes regularly. The regularly interstratified boehmite gives rise to a diffuse "long spac- ing" X-ray diffraction reflection. Calculated 020 X-ray diffraction peaks approximate closely those ob- served experimentally when a range of crystallite sizes is taken into account.

Structure of some allophanes from New Zealand

Abstract: Allophane samples from soils, pumice, and stream beds have been studied by electron optical, infrared absorption, X-ray fluorescence, gas chromatography, and phosphate adsorption methods. The allophane particles were hollow spherules or polyhedra 35 and 50 Angstrom in diameter with molar Al/Si ratios close to 2.0. The thickness of the wall of the spherules was estimated to be 7 Angstrom. For the pumice allophanes, the wall was largely composed of imogolite structural units (OH) 3 Al 2 O 3 SiOH. Defects or pores were present in the wall and probably were the sites where phosphate was adsorbed. It is suggested that these allophanes with molar Al/Si ratios close to 2.0 should be called "proto-imogolite" allophane. Two soil allophanes had a similar structure to the allophane from Stratford pumice, but small amounts of layer silicates, including halloysite, were also present in the soil samples, as indicated by infrared bands at 470, 1030, and 1100 per cm. The allophane from the stream bed at Silica Springs had an infrared spectrum similar to feldspathoids, and it did not have the imogolite structure

Alkali cation selectivity and fixation by clay minerals

Abstract: Two variables must be considered when calculating exchange free energies (ΔG°ex) for 2:1 clays: (1) anionic field strength, as expressed by equivalent anionic radius (ra), and (2) interlayer water content, as expressed by interlayer molality. For smectites that are in a state of high hydration, interlayer molality is determined by the cations undergoing exchange. Thus ΔG°ex for an exchanging cation pair can be calculated solely from measurements of ra. ra is related to layer charge per half unit cell (C) and ab unit cell area (A) by: ra = (-A/8πC)1/2. The layer charge necessary for cation fixation can be predicted by calculating the ra at which cation exchange with an illite structure expresses a AG°ex equal to that of exchange with a smectite structure. The theory can also be applied qualitatively to understand the high selectivity of illite for Cs+, the fixation of K+ rather than Na+ in shales during diagenesis, the stability of illite over muscovite in the weathering environment, and cation segregation in smectite.

Thermal behavior of hydrotalcite and of anion-exchanged forms of hydrotalcite

Abstract: Chloride-, sulfate-, and perchlorate-exchanged forms of hydrotalcite have been prepared and their layer spacings determined after equilibration in hydrous atmospheres and after heat-treatments up to the temperature of decomposition in the range 300–400°C. The initial carbonate form of hydrotalcite and also brucite, for purposes of comparison, have been similarly studied. Only chloride-hydrotalcite and brucke exhibit a single phase stable to the decomposition temperature. The other anionic forms exhibit various phases with different layer spacings which are interpreted in terms of the size, orientation, and stability of the anions and, in some cases, the presence of additional water. A regularly interstratified form of sulfate-hydrotalcite (layer spacing = 19.80 A) is obtained at room temperature and relative humidity <50%; at higher humidities, a fully hydrated phase is obtained, and at 50°C a collapsed form is obtained. In the preparation of perchlorate-hydrotalcite, an interstratified phase (layer spacing = 17.0 A) was recognized with alternating carbonate and Perchlorate layers, although the evidence is less certain.

Identification and structure of two types of allophane from volcanic ash soils and tephra

Abstract: Samples containing allophane with molar Al/Si ratios from 1.0 to 2.0 have been examined by infrared spectroscopy, X-ray fluorescence, and phosphate adsorption methods. The infrared spectra of allophane with Al/Si ratios close to 2.0 showed that the wall of the allophane spherules is made up of imogolite structural units similar to "proto-imogolite". X-ray fluorescence gave no clear evidence of Al in tetrahedral sites (Al(t)), while pyridine adsorption results suggested that a small number of Bronsted acid sites (Al(t)OH) are present in silica-rich allophanes. Lewis acid sites (AlH 2 O) are present in both silica-rich and alumina-rich allophanes. The results suggest that the framework for the allophane structure is an Al octahedral sheet. Allophanes with Al/Si ratios close to 1.0 contain condensed silicate units either on the outside surface of the Al octahedral sheet, giving rise to a halloysite-like structure, or bonded on the inside surface of an imogolite-like structure. Allophanes with Al/Si ratios between 1.0 and 2.0 appear to be mixtures of the "proto-imogolite" structure and the allophane (Al/Si = 1.0) structure

Dehydroxylation of Dioctahedral Phyllosilicates

Abstract: Mossbauer spectroscopy of dioctahedral phyllosilicates showed that on dehydroxylation iron which originally occupied M(2) and M(l) sites became, respectively, 5- and 6-coordinated. The 6-coordinated sites are very distorted. No migration of cations occurs in the course of heating the specimens for 1–3 hr at 600°–700°C. By using a combination of several physicochemical methods, different successive stages of the dehydroxylation process could be distinguished: (1) migration of protons; (2) localized dehydroxylation of individual associations without significant change in the overall configuration of the octahedral sheets; and (3) loss of most of the hydroxyl groups with concomitant changes in the cell dimensions. Penetration of Li into the octahedral sheets does not affect the course of the reaction, but reduces the dehydroxylation temperature and the stability of the products. Dehydroxylation was preceded by or associated with the oxidation of any divalent iron present. Fe3+ derived from Fe2+ was indistinguishable by Mossbauer spectroscopy from iron initially present in the trivalent form. High concentrations of Fe lower the dehydroxylation temperature and reduce the stability of the dehydroxylate to the extent that partial disintegration may precede complete dehydroxylation.

Interfacial Water Structure in Montmorillonite from Neutron Diffraction Experiments

Abstract: Neutron diffraction measurements for a preferentially oriented aggregate slab sample of deu- terated Na-montmorillonite from Upton, Wyoming, are described for a series of clay-water contents rang- ing from 0 to 500 mg/g. A neutron wavelength of 2.39 A was used with extended detectors to collect much of the "out of plane" component of the diffraction peak intensities. The diffraction pattern intensities from the 00~ e planes of the clay, corresponding to a reflection geometry, are a strong function of sample water content and show a variation in basal spacing from 9.8 to 19.0/~. The hk reflections from transmission geometry measurements show, however, that the lattice a and b axes are constant within experimental uncertainty (0.02/~) over the range in water content and their intensities vary only by a few percent. In this geometry, a broad, water-like diffraction pattern was noted as a background under the usual hk peak intensity series. This underlying water-like pattern varies in proportion to the sample water content. Data reduction steps included consideration of background removal, multiple scattering, flux normali- zation, and attenuation of scattering due to sample thickness. Analysis of the reduced data revealed that the clay-water has a "liquid-like" ordering, with a density increase of approximately 5% over bulk water. An association between a few interlayer water molecules and the silicate superstructure is indicated by the slight change in the hk band intensities, but this change seems to be complete at water contents below 100 mg/g. Fourier analysis of the basal peak series from the dry clay shows that the hydrogens of the lattice hydroxyl groups lie in the same basal plane as their associated oxygen atoms.

Influence of pH, concentration, and chelating power of organic anions on the synthesis of aluminum hydroxides and oxyhydroxides

Abstract: Chelating organic acids hampered the hydrolytic reactions of Al and affected the nature of the crystalline aluminum hydroxides. Chemical composition, structure, size, nature of functional groups, and concentration of each organic anion, as well as the pH of the system, controlled the rate of Al(OH)3 crystallization. The order of effectiveness of the various acids was: glutaric < succinic = phthalic < glycine < malonic < glutamic < aspartic < oxalic < salicylic = malic < citric < tartaric. An increase in the stability of complexes formed between the organic ligands and Al decreased the rate of crystallization and changed the final aluminous products from bayerite to nordstrandite and/or gibbsite and then to pseudoboehmite and/or amorphous material. In the presence of anions with a great affinity for Al, particularly at pH equal to or less than 9.0, the reaction products were commonly poorly crystalline or structurally distorted. In the range of pH 8.0 to 10.0 moderately or strongly chelating anions acted to retard or prevent olation and facilitated the formation of stable pseudoboehmite or X-ray-amorphous products. The stronger the chelating power or the higher the concentration of organic anions, the easier was the formation of pseudoboehmite or amorphous material.

Natural Occurrence of Feroxyhite (δ'-FeOOH)

Abstract: Feroxyhite (δ′-FeOOH) in association with goethite and lepidocrocite was found as a dominant mineral in some rusty precipitates from Finland. These precipitates formed in the interstices of sand grains from rapidly flowing, Fe(II)-containing water which was very quickly oxidized as it flowed through the sediment. The mineral is distinguished from other FeOOH forms and from ferrihydrite mainly by its X-ray powder diffractogram. Further characteristics are an acicular morphology (possibly thin, rolled plates), an internal magnetic field at 4°K of ∼510 kOe, Fe-OH stretching bands at ∼2900 cm−1 and Fe-OH bending bands at 1110, 920, 790, and 670 cm−1, and an oxalate solubility between ferrihydrite and goethite or lepidocrocite. Feroxyhites with very similar properties were synthesized by oxidation of an Fe(II) solution with H2O2 at a pH between 5 and 8.

High resolution electron microscopy of feldspar weathering

Abstract: High resolution imaging by transmission electron microscopy has revealed a mechanism for the weathering of intermediate microcline in a humid, temperate climate. Dissolution of the feldspar begins at the boundary of twinned and untwinned domains and produces circular holes which enlarge to form negative crystals. Amorphous, ring-shaped structures develop, about 25 A in diameter, within the larger holes. These rings, in turn, crystallize to an arcuate phase having a 10-A basal spacing and then to crinkled sheets of illite or dehydrated montmorillonite. The 10-A layer silicate shows an irregular stacking sequence, including 10-,-20-, and 30-A sequences. Included plagioclase crystals show a similar mechanism of weathering and, moreover, are more intensely weathered.

Intercalation of silica in smectite

Abstract: Silica has been intercalated in swelling clays by hydrolysis and/or oxidation of tris(acetylacetonato)siIicon(IV) cations, Si(acac)3+, and polychlorosiloxanes, (-SiOCl2-)n, in the interla-mellar regions of the minerals. The Si(acac)3+ ions have been placed on the interlamellar surfaces by ion exchange and by in situ reaction of the acetylacetone-solvated clays with SiCl4. The (-SiOCl2-)n polymers were formed in the interlayers by reaction of adsorbed benzaldehyde with SiCl4. The optimum (001) spacing observed after firing the clays in air at 500°C (12.6 A) corresponds to the presence of a monolayer of siloxane chains. Nitrogen BET surface areas range from 40 to 240 m2/g, depending on the amount of internal surface covered by the intercalated silica. In some cases, highly ordered products were formed which exhibit four orders of (00l) reflection. Interstratifled products with d(001) values between 9.6 and 12.6 A exhibit surface areas consistent with the presence of a random mixture of totally collapsed interlayers and interlayers containing siloxane monolayers. Attempts to achieve silica intercalation by hydrolysis of SiCl4 in the clay interlayers were not productive.

Syntheses of glauconite at surface temperatures

Abstract: Ahstraet--Glauconite has been synthesized at low temperature by precipitation of Fe-hydroxides from Si-, Fe-, Al-, and K-containing solutions under reducing conditions. The compositions favorable for the synthesis at 20~ and pH 8.5 are 1 ppm Fe, 0.15 ppm Al, 13 ppm SiO2, 1000 ppm KC1, and 1000 ppm dithionite. The K-content of the solutions must be sufficiently high to fix K in the precipitate. Under special early diagenetic conditions glauconite is formed in marine sediments, probably at the interface between reducing and oxidizing zones in the muddy sediments. The silica content of pore waters seems to control the formation of glauconite or chamosite rather than depth or temperatures of the bottom waters.

pH-Independent and pH-Dependent Surface Charges on Kaolinite

Abstract: Model cation-exchange curves are presented for an idealized kaolinite surface where the charge on the surface (1) has its origin in cation substitution in the structure, and hence, is pH independent; and (2) is produced by protonation/deprotonation reactions of oxide-like sites, and hence, depends on the acid and base strengths of the surface sites, as welt as the ionic strength. Two pH-independent situations are considered: one where the exchanging ions have no selectivity for the surface and are all in the diffuse layer; and one where selectivity exists for one ion and where that ion is partly in a Langmuir-Stern layer and partly in the diffuse layer. If one of the exchanging ions is a proton, the shape of the curves and their position on the pH scale depend on ionic strength and ionic selectivity. The model curves are compared with data for actual kaolinites. Under most conditions exchangeable AI is released from the structure, and the shape of the charging curves becomes similar to that of an oxide- like surface. However, if titration is carried out rapidly, or account is taken of the presence of AI, the proton binding curves are similar in shape to those expected for sites resulting from cation substitution in the structure of kaolinite, either near the surface or at the edge of the crystal.

Formation and characterization of clay complexes with bitumen from athabasca oil sand

Abstract: Montmorillonite, kaolinite, illite, and chlorite were found to adsorb bitumen and its pentane- soluble and pentane-insoluble fractions. The formation of clay-bitumen complexes is influenced by the nature of the exchangeable cation on the clay and by the solvent carrier which stabilizes the bituminous compounds. Ca-clays adsorb organic compounds more strongly than sodium forms except in the presence of nitrobenzene. Solvents of high dielectric constant, such as nitrobenzene, promote ionization so that the ion-exchange mechanism of adsorption is favored, whereas solvents of lower dielectric constant, such as chloroform, tend to solvate rather than to dissociate bitumens. The behavior of the montmorillonite-bi- tumen complex in variable relative humidity indicates that organic molecules adsorb primarily on external surfaces and cause the clay to become less hydrophilic than prior to treatment. Clay-organic complexes are sufficiently stable to resist powerful organic solvents. The clay-organic complex separated from the Athabasca oil sand behaves similarly during chemical treatment to complexes formed between bitumen and the four reference clay minerals.

Kaolins: sources of differences in cation-exchange capacities and cesium retention

Abstract: Seven kaolins from Georgia (southeastern U.S.A.), ranging from high to low commercial grade, were characterized by X-ray powder diffraction and chemical techniques to establish that the variation in quality was caused by impurities. The Ca and Cs cation-exchange capacities (CEC) varied from 2.67 to 8.17 and from 3.29 to 8.77 meq/100 g, respectively. Selective dissolution and correlation analyses strongly indicated that expandable 2:1 minerals, particularly smectite (1.2-5.9%), Were responsible for most of the observed variations in Ca CEC (r = 0.85*). The external surface CEC of kaolinite ranged from 0 to 1 meq/ 100 g. The positive significant correlation (r = 0.90**) between the Ca CEC and the K-mica content (0- 3.9%) suggested that Ca CEC may be related to the degree of mica weathering through an expandable mineral stage. The Cs-retention capacity (0.19-1.14 meq/100 g) was closely related to Cs-measured vermiculite content (r = 0.80"), and this content plus specific surface (R = 0.93**) or mica content (R = 0.86*). The Cs reten- tion appeared to be primarily related to the presence of interlayer wedges at mica/vermiculite XY interfaces.

Manganese minerals in clays; a review

Abstract: Vernadite (MnO2·nH2O) is a mineral with a poorly ordered structure. Its synthetic analogue is designated δ-MnO2. Birnessite and vernadite are independent mineral species and cannot be described further under the same name. They have similar hexagonal unit-cell parameters, a0, but different c0 parameters. Rancieite has a structure similar to that of birnessite. Calcium bearing, 14-A birnessite occurring in nature was first described by the authors. In addition to the todorokite having the parameters a0 = 9.75 A, b0 = 2.84 A, and c0 = 9.59 A, other species of natural todorokite are known having a0 parameters that are multiples of 4.88 A equal to 14.6 and 24.40 A, the b0 and c0 parameters being the same.

The influence of aluminum on iron oxides. VI. The formation of Fe(II)-Al(III) hydroxy-chlorides, -sulfates, and -carbonates as new members of the pyroaurite group and their significance in soils.

Abstract: In the absence of oxygen, Fe(II) chloride, sulfate, and carbonate solutions react at pH 6.5 to 7 with aluminum hydroxide suspensions to form new Fe(II)-Al(III) hydroxy anion compounds of the pyroaurite group. The Fe(II)-Al(III) hydroxy-chloride and -sulfate compounds are isostructural with Fe(II)- Fe(III) “green rust” compounds with A1 essentially substituting for Fe(III). Where CO,2 is the only anion in the system, an Fe(II)-Al(III) compound isostructural with hydrotalcite is formed. Either in the dried or wet state, these compounds are unstable in air due to oxidation of Fe(II). Oxidation of the dried sample in air yields akaganeite or aluminous ferrihydrite, whereas, if the sample is maintained in a moist condition and oxidized by air under water, lepidocrocite or aluminous goethite is produced along with small amounts of ferrihydrite. On X-ray powder diffraction, the lepidocrocite so formed commonly shows no diagnostic (020) basal reflection, or one with a markedly reduced intensity. The products of oxidation, and the rapidity of their formation, appear to be dependent on the composition of the initial double hydroxy compound and the conditions under which the oxidation is carried out.

Kaolinite, smectite, and K-rectorite in bentonites; relation to coal rank at Tulameen, British Columbia

Abstract: The Tulameen coal field is part of an Eocene nonmarine basin which received extensive vol- caniclastic sediments due to its location within an active magmatic arc. Bentonite partings in the coal originally consisted of glassy rhyolitic tephra with phenocrysts of sanidine, biotite, and quartz. During the initial alteration, which took place within the swamp or shortly after burial, glass was transformed to either smectite-cristobalite-clinoptilolite or to smectite-kaolinite. The formation of kaolinite depended on the de- gree of leaching of silica and alkalies in the swamp environment. Some beds are nearly 100% kaolinite and can be designated as tonsteins. The smectite shows no evidence of interlayering; the kaolinite is well or- dered. During alteration, sodium, originally a component of the glass, was lost from the system, A later thermal event, which affected only the southern part of the basin, metamorphosed the smectite to a regularly interstratifled illite/smectite with 55% illite layers and rectorite-type superlattice (IS-type). The sour~:e of potassium was dissolution of sanidine. Vitrinite reflectance measurements of the coal suggest that the smectite was stable to 145-160~ at which temperature it transformed to K-rectorite. The absence of randomly interstratified intermediates, even in beds rich in potassium, suggests that the transformation of smectite to K-rectorite was controlled by a steep thermal gradient possibly resulting from local magmatism or circulating geothermal fluids.

Adsorption of Cadmium and Cobalt on Montmorillonite as a Function of Solution Composition

Abstract: Adsorption of Co 2+ and Cd ~+ on Wyoming montmorillonite was studied by the batch equilibra- tion technique, as a function of salt concentration (0.01-4 M NaC1 and NaNO3), pH (5.0-6.5), adsorbate concentration (trace-10 -2 moles/liter), and presence of complexing ions. Comparison was made with the adsorbability of Sr 2+, known to follow simple ion-exchange equations. The distribution coefficients for Co and Cd in noncomplexing media varied with salt concentration (from -500 liters/kg in 0.01 M Na § to -10 liters/kg in 1 M Na+; pH = 5), but to a lesser extent than that of St. Adsorbability varied also with pH (- 1 order of magnitude/pH unit), especially at high ionic strength, compared to a negligible pH effect on Sr. The distribution coefficients of Cd and Co decreased with increasing loading on the clay at a very low percentage (0.2%) of the ion-exchange capacity compared to Sr (20%). These data suggest two classes of sites participating in the adsorption of Cd and Co. The adsorbability of Cd in highly concentrated chloride solution (>1 M) was less than 1 liter/kg, pre- sumably because of the chloride complex formation. This effect increased with increasing pH. The low adsorbability of Cd on montmorillonite from concentrated NaCI solution is promising with respect to its use as a tracer for monitoring flow through formations containing montmorillonite.

Adsorbed Cr(III) on chlorite, illite, and kaolinite; an X-ray photoelectron spectroscopic study

Abstract: The adsorption of Cr(IH) 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. Изучалась адсорбция Сг(Ш) хлоритом и каолинитом при рН 1, 2, 3, 4, 6, 8, и 10 и иллитом при рН 1, 2, 3, и 6. Количество хрома, адсорбированного хлоритом, изменяется от 3.1 × 10} моль/г при рН 1 до 16,6× 10} моль/г при рН 4, и иллитом от 4,9× 10} моль/г ло× 10} моль/г при рН 1 и 3 соответственно. Каолинит адсорбировал 3,7× 10−5 моль Сг/г при рН 1, 2, и 3 и 5,5× 10−5 моль Сг/г при рН 4. Измерения связывающих энергий Сг на ядерном уровне 2р показывают, что хром, вероятно адсорбируется как водный ион Сг(Ш) при величинах рН меныше 4. Связывающие энергии для Сг на уровне 2р для образцов, приготовленных при рН выше 4, сильнее по сравнению с величиной, найденной для гидроокиси хрома, из чего следует, что соединение хрома, присутствующее при рН 6, 8, и 10 является гидроокисью. [N. R.]

Interaction of Clay Minerals with Adenosine-5-Phosphates1

Abstract: Adenosine-5-phosphates (ATP, ADP, AMP) are adsorbed by clay minerals at very low concen- trations (~<2 mg/liter). In contrast to quartz, the clay minerals exhibit a strong preference for ATP over AMP. The experimental data are expressed as recovery rates (adenosine-phosphate in solution to total nucleotide added). For example, the recovery rates of ATP, ADP, and AMP in the presence of sodium montmorillonite are 0, 17, and 100%; in the presence of quartz 95,100, and 99%. The recovery rate of AMP on clays is markedly decreased by the presence of ATP, that is, ATP increases the adsorption of AMP by cooperative interactions. A part of ATP not recovered in the equilibrium solution is dephosphorylated to ADP. For example, 45% of ATP not recovered in equilibrium solution with calcium montmorillonite is recovered as ADP; with sodium montmorillonite only ADP can be recovered in solution.

Fe2+-Fe3+ Transformations in Clay and Resin Ion-Exchange Systems

Abstract: The pH, Eh, electrical conductivity (EC), and the amounts and valency of replaceable iron were measured periodically on Fe2+- and Fe3+-saturated montmorillonite and cation-exchange resin at three temperatures. Differences in the pattern of change of pH, Eh, and EC with time appear to be related more to the histories and modes of preparation of the systems than to intrinsic differences in the hydrolysis of the iron in them. Electron transfer reactions involving crystal components of the clay can cause oxidation of adsorbed Fe2+ ions; the activation energy (Ea) for oxidation on the clay’s surface was 6 kcal/mole, less than a third of the activation energy reported for Fe2+ oxidation in solution. In the Fe2+-resin, where Ea = 10.7 kcal/mole, perturbed surface-water molecules may act as electron acceptors enhancing Fe2+ oxidation. Polymerization and precipitation of the adsorbed iron is affected by the necessity to maintain electro-neutrality, the ability of the iron-hydroxy ions and small polymers to move about in the voids of the ion exchanger, and the steric hindrance posed by the matrix of the ion exchanger to the formation of large polymers. In resin, little or no iron precipitates, probably due both to steric hindrance and the inability of the resin to release ionic components to maintain electroneutrality. In clays, steric hindrance is small, and Al and Mg are released from the crystal to maintain electroneutrality, thus the precipitation of iron is abundant and is controlled by the rate of release of Al and Mg from the crystal.

Formation, Compositions, and Properties of Hydroxy-Al- and Hydroxy-Mg-Montmorillonite

Abstract: Hydroxy-Al- and hydroxy-Mg-montmorillonite were prepared by treating dispersed Na-montmorillonite with aluminum and magnesium nitrate solutions and titrating with NaOH solutions so that the OH/A1 ratio varied from zero to 3.0 and the OH/Mg ratio from zero to 2.0. External precipitation of Al and Mg hydroxides was observed when the OH/M ratios (M = metal) approached 3 and 2, respectively. From chemical analyses of the initial Na-montmorillonite and the hydroxy-metal montmorillonites, structural formulae were derived by assuming that the silicate layer compositions remained unchanged. Prior to the addition of NaOH, the average interlayer material approximated in composition to [Al(OH)2]+ and [Mg(OH)]+. With additions of NaOH the interlayer compositions moved progressively towards Al(OH)3 and Mg(OH)2. When the hydroxy interlayers approached completion, external precipitation was observed. X-ray powder diffraction data showed that the hydroxy-Mg products have less tendency to swell in ethylene glycol and water, and greater thermal stability than the hydroxy-Al products. Initially, when the average interlayer compositions were near Al(OH)2 and Mg(OH), swelling followed more nearly the normal behavior.

Interpretation of the variability of selectivity coefficients for exchange between ions of unequal charge on smectites

Abstract: Ion-exchange experiments in expanding clay minerals conducted over a wide range of surface ionic compositions and ionic strength produce variable mass-action selectivity coefficients. When the ex- changing ions are of unequal charge, tactoid structure appears to influence selectivity, although configu- rational entropy of adsorbed ions may also generate variable selectivity. The degree of deviation from ideal mass-action exchange is related to the dissimilarity of the ions undergoing exchange. Data involving tri- valent ion adsorption on smectites suggest that mass-action is a poor approximation when the adsorbing and desorbing ions have different hydration energies and charge. No form of exchange equation is suc- cessful in describing ion exchange for a wide range of experimental conditions, although the fluctuation of the selectivity coefficient follows consistent trends with changing experimental conditions. The strong ad- sorption of high-charge ions on clays is not exothermic, but must be driven by the increasing disorder of ions and/or water.

Determination of noncrystalline soil components by weight difference after selective dissolution

Abstract: Abstraet--A procedure based on loss of weight after selective dissolution analysis (SDA) and washing with (NH4)zCO3 was developed for estimating the noncrystalline material content of soils derived from widely different parent materials. After extracting with 0.2 N ammonium-oxalate or boiling 0.5 N NaOH solutions, samples were washed with 1 N (NH,)2CO3 to remove excess dissolution agents and to prevent sample dispersion. The amount of noncrystalline material removed from the sample by the extracting solution was estimated by weighing the leached products dried to constant weight at 110~ The results match closely with those obtained by chemical analyses of the dissolution product and assignment of the appropriate water. The proposed weight-loss method is less time-consuming than the chemical method, and no assumptions need be made concerning sample homogeneity or water content of the noncrystalline material. Extractions of whole soil and dispersed clay fractions indicated that noncrystalline material determinations on the clay fractions underestimated the noncrystalline material content for whole soils from 0 to 34%. Acid ammonium oxalate was found to be a much more selective extractant for noncrystalline materials than NaOH.