Variations in the peptization resistance of selected samples of clay mineralogical materials toward alkaline dispersing agents are discussed from a quantitative point of view.

Clay samples, collected from South Carolina, Wyoming, Illinois, New Mexico, South Wales, Great Britain and Cornwall, England were subjected to the action of solutions of Calgon (“sodium hexametaphosphate”), ammonia, sodium hydroxide, sodium carbonate, sodium pyrophosphate, and “sodium lignosulfonate.” The resulting apparent dispersion, in each case, was expressed as a function of the employed concentration and chemical nature of the dispersing agent. Pipette analysis and Oden balance techniques at constant temperature were used to measure the degree of dispersion. All clay samples employed were identified as to type by X-ray diffraction, chemical analysis, thermal analysis, and electron microscopy.

All samples examined exhibited a maximum in apparent dispersion (suspension stability) at a specific concentration of dispersing agent. Such maximum was followed by a sudden decrease in apparent dispersion, i.e., flocculation, at higher concentrations of dispersing agent. Concentrations of dispersing agent were varied in steps of one part per thousand. One hundred and twenty experimental runs were made on each type of material examined. Differences in the degree of apparent dispersion attained by use of different dispersing agents were expressed in terms of a threshold concentration which altered “equivalent diameter” one tenth of a phi unit. Among dispersing agents employed, “sodium lignosulfonate” was found to be least selective of clay mineral type in its peptizing action.

An equation for the calculation of a “peptization resistance factor” is presented. Results obtained by application of this equation indicate that differences in the response of the same clay material to different alkaline dispersing agents may be attributed, in part, to differences in degree of peptization achieved by “threshold mechanisms” of peptization and by “adjustment mechanisms” along the peptization path. Such equation may have future value in the differentiation of marine and terrestrial clay deposits.

Acid clays prepared by electrodialysis or by treatement with dilute (< about 0.1N) mineral acid solutions were largely Al-saturated, and had little catalytic effect on ester hydrolysis and sucrose inversion. On the other hand, clays exhaustively treated with cold 1N HCl were largely H-saturated, and served as effective H-ion catalysts. When various quantities of clay were used as catalysts, reaction rates were proportional to the concentration of H-ions in the system.

H-montmorillonites prepared from Plymouth, Utah bentonite and from Volclay bentonite were from 50 to 200 percent more effective catalysts for ethyl acetate hydrolysis than was HCl. For sucrose inversion, <2 μ H-clays had a somewhat greater catalytic effect than did HCl, while clay aggregates were much less effective catalysts. For ester hydrolysis, the degree of dispersion of the clay made little difference in its catalytic activity.

The thermodynamic activities of ion pairs were measured electrometrically in a series of aqueous mixtures of monoionic bentonite and the corresponding chlorides. Ion exchange membranes and Ag-AgCl electrodes were used. The lyotropic order for the various cation species varied somewhat for two different preparations. The apparent relative escaping tendencies of the various cations did not correspond to that usually assumed on the basis of related phenomena: ion exchange selectivity, electromigration velocities, flocculation values or rates, etc.

Some divergent experimental data have been reported on the swelling behavior of sodium montmorillonite. At water contents above 50 percent (based on the weight of dry clay) the basal reflection of sodium montmorillonite at 19.2 Å becomes weak and very diffuse; some workers have stated that it disappears altogether while others report a persistent weak line even at very high water content. The pronounced differences in physical properties of sodium and calcium montmorillonite suggest that their lattice expansions should also be dissimilar. This paper describes some X-ray diffraction experiments using purified lithium, sodium, and potassium montmorillonites dispersed in water and in salt solutions which were conducted for the purpose of resolving some of these disputed points. The X-ray diffraction instrument employed was a General Electric geiger counter spectrometer unit with a copper tube and nickel filters. The knowledge thus gained has provided some insight into other properties of these clays, such as their rheological behavior.

A recording Couette-type viscometer designed to provide a wide spectrum of shear rates and shearing stresses has been used to examine the rheological transformations which occur in passing from states of maximum dispersion to states of varying degrees of agglomeration as a result of interactions between LiCl, NaCl, KCl, and CaCl2, and the Li, Na, K, and Ca salts of montmorillonite in terms of certain ideal rheological models. Filtration characteristics of these systems have also been explored using a standard technique.

The constant consideration, punctuated by periods of almost frantic concentration of effort and by periods of dull lassitude, given to chemically bonding soil particles into structural materials has yielded some useful products, some laboratory curiosities, and some ideas as to how current and future efforts may be more meaningfully evaluated. Current work indicates that attempts to evaluate chemicals for bonding clay soils are significantly clouded by: (1) lack of knowledge of the soil-chemical bond; (2) lack of knowledge of the type of soil surface susceptible to bonding; (3) lack of knowledge of the inhibitors to chemical reactions present in soil systems; (4) lack of a correlation of the differences in response to treatment between readily indentifiable clays and soil fractions apparently composed of these clays; and (5) lack of satisfactory laboratory techniques by which rapidly reacting chemicals can be properly incorporated with soils.

A program is proposed whereby standards of response to treatment are established for different categories of known bonding agents when used with fractionated silica, kaolin and kaolinitic soils, montmorillonite and montmorillonitic soils. A device suitable for laboratory use in this program is suggested.

Examination of the silt and clay fractions of two northern Wisconsin soils, Omega loamy sand of the Brown Podzolic group and Ahmeek loam of the Brown Forest group, revealed considerable quantities of interstratified layer silicates. The two soils contained montmorin, vermiculite, chlorite, and illite both as discrete and interstratified components. Regularly alternating montmorin-illite structures, which registered a 28 Å first order diffraction peak, and vermiculite-illite structures, which yielded a 24 Å first order peak, were observed in the fine silt fractions of the Ahmeek loam A3 and B22 horizons, respectively. Weak diffraction peaks in general and lack of binary mixture average spacings was suggestive of ternary or quarternary interstratification of illite, chlorite, vermiculite, and montmorin in the medium and fine clay fractions of the Ahmeek loam horizons. Randomly interstratified vermiculite-chlorite and vermiculite-montmorin, as revealed by comparative basal diffraction peaks before and after heating potassium saturated samples, were evidenced in the fine silt and clay fractions of the Omega profile.

Mixed layer components in the Omega and Ahmeek soils originated from illite and chlorite in the? horizons with a progressive increase in proportions of first vermiculite and finally montmorin with proximity to the soil surface. The observed weathering transitions within the mixed layer structures illustrates the effects of accelerated leaching which has taken place in these coarse textured soil profiles, even though these soils are relatively young (late Pleistocene).

At the 4th International Soil Science Congress held in Amsterdam (1950) a special meeting discussed the nomenclature of clay minerals and suggested “hydrous mica” as a general term for those clay minerals that are neither well crystallised micas nor pure expanding minerals.

In the past various names have been used for the hydrous micas. As early as 1912, Galpin, and later, in 1920, Bayley, introduced the terms “hydro-mica” and “hydrous mica” respectively, to designate a micaceous clay mineral. Since then, reports have been made of the presence in soils of a potash-bearing clay mineral (Wherry et al., 1929), and in clays of a mica-like clay mineral (glimmerartige Tonmineralien) (Endell et al., 1935), and a sericite-like mineral (Grim, 1935). In 1937 Grim et al., for the first time proposed the term “illite” as a “general term for the clay mineral constitutents of argillaceous sediments belonging to the mica group.” Other names include bravaisite (Ross and Hendricks) and sarospatite (Maegdefrau and Hofmann, 1937), but the validity of these as specific minerals is questionable since they have been found to exist as mixtures of hydrous micas and montmorillonoids (Bradley, 1945; Brindley, 1951).

Clay mineral analyses were made of three groups of soil profiles — one developed from Peorian loess overlying Illinoian till — one associated with glacial till of Wisconsin age — one developed on deep to thin loess overlying Wisconsin till. These groups were investigated to determine the influence of parent material and intensity of weathering upon the soil profile development and clay mineral composition.

Montmorillonite, illite, and chlorite are the dominant clay minerals in all the samples studied. In known loess samples, montmorillonite is invariably the most abundant clay mineral component. In the samples of unweathered till of Wisconsin age, illite and chlorite are the abundant clay minerals.

Mineralogical studies for the <2 μ fractions are presented for seventeen soil profiles and two surface horizon samples, which represent eight soil types and five geological regions in the state. There was no evidence of clay mineral formation in the upper 6 feet or more of soil. X-ray diffraction data from the Lufkin, Ruston and Katy soils suggested some decomposition of montmorillonite and kaolinite in the upper horizon. However, the overall picture is one of little change in clay mineral composition between the soils and parent sediments.

The soils of the lower Mississippi Delta are derived from the Mississippi or Red River depositions or some combination of these two.

Profiles of the Iberia, Baldwin, Buxin, Sharkey, and Mhoon were selected for the study. The comparative results indicate that the Sharkey was highest in cation exchange capacity and exchangeable calcium and magnesium. Base saturation was highest in the Iberia and lowest in the Baldwin. The variation in cation exchange capacity was possibly due, in general, to the differences in texture, except for the Iberia. The clay fraction of the Iberia contained slightly larger quantities of high cation exchange capacity minerals than the other soil series of the study.

Silica was highest in the Baldwin while the oxides of aluminum, iron, magnesium, and potassium were highest in the Buxin. Iberia was highest in calcium oxide. Silica-sesquioxide and silica-ferric oxide ratios were highest in the Sharkey and lowest in the Buxin. The silica-alumina ratio was highest in the Baldwin and lowest in the Buxin. The comparison of the Buxin with soils of the Mississippi River deposition indicates that the Red River depositions were generally lower in silica-sesquioxide ratios and total calcium oxide and higher in total magnesia and potash.

The X-ray patterns indicate that montmorillonite and illite were the dominant clay minerals present. The greatest quantities of montmorillonite were generally found in the Iberia profiles, although this was not always true. Also, in general, the content of montmorillonite increased and illite decreased with profile depth. Secondary minerals were halloysite, kaolinite, vermiculite, and chlorite. The cation exchange capacity of the clay fraction also indicated the higher content of montmorillonite or associated minerals in the Iberia than in the Buxin, Baldwin, Sharkey or Mhoon soils.

The apparent porosity of flint, boehmite and diaspore clays bears no direct, consistent relation to the permeability of the same type of clay or to the alumina content of each type. The coefficient of permeability varies with the type and the structure of each flint clay. Diaspore clays have high permeability compared to flint clays, and the boehmite clays measured generally have a permeability intermediate between that of diaspore and that of flint clays. The apparent increase in permeability with increase in alumina content suggests that permeability has increased as silica was removed from flint clay to form boehmite and diaspore clays.

A vertical pipe of diaspore clay 1½ inches in diameter was collected by Fred Mertens of the Laclede Christy Company at the Shockley-Thompson diaspore pit at Belle, Missouri. The pipe contains 69.16 percent alumina compared with 55.30 percent alumina for the average of the walls a few inches from the pipe. Diaspore in the pipe has vertical banding indicating it was deposited along a vertical crack. The formation of cracks in brittle flint clay is an important process in increasing the permeability and providing openings along which ground water can migrate.

A restudy of boehmite and diaspore clays emphasizes not only a replacement of the colloform and oolitic structures of flint clays by diaspore and boehmite, a gradual alteration of flint clay to diaspore clay along fractures, and second-generation diaspore cutting early diaspore, but also the importance of secondary processes in the origin of diaspore and boehmite clays.

H-montmorillonite, -beidellite, and -nontronite were found to change spontaneously into Al-clays. Rates of conversion of H- to Al-clay were slow at 0°C, but at temperatures of around 100°C, moist H-montmorillonite changed to Al-saturated montmorillonite within 24 hours. It appeared that Al-ions moved from lattice positions to exchange positions, with octahedral Al moving more rapidly than tetrahedral Al.

Treatment of montmorillonoids with HCl solutions at 80°C resulted in the removal of large quantities of Fe, Mg, and Al. The residue after hot acid treatment appeared to be a mixture of essentially unaltered montmorillonoid and SiO2, rather than a new mineral.

On heat treatment, H- and Al-montmorillonites became largely non-expanding of 300°C, and lost the bulk of the CEC which could be attributed to permanent lattice charge, H- and Al-nontronite and -beidellite, on the other hand, did not suffer irreversible dehydration and loss of CEC until heated to sufficiently high temperatures to cause the expulsion of lattice OH. Montmorillonites with largely octahedral charge had smaller CEC’s after heating to 500°C than did montmorillonites with appreciable tetrahedral charge.

The transfer of ions during the weathering of a Medford diabase, a granite from British Guiana, and of the Cheto Arizona tuff is traced by recasting the analyses of the fresh rocks and their altered counterparts into 160-oxygen rock cells, and by comparing algebraically the products of the weathering reaction with the original reactants.

Hydrolysis and hydration are the first steps in the reaction. H ions were added in the weathering environment of the diabase and granite, but Mg ions were added in the change of tuff to bentonite.

Silica and alkali metal ions are dissolved and removed during weathering of the diabase and granite, presumably under acid conditions, but it appears that the Cheto tuff was formed under a non-acid environment where Mg was added. During the hydrolysis of silicate rocks, H ions are concentrated temporarily in the clay minerals on land, while OH ions go to the ocean.

More examples of ion transfer during weathering than the three given herein are needed to define the reactions occurring in the many environments of alteration which rocks encounter.

Oriented slides of twelve different mixtures of kaolinitic and illitic underclays were studied with the X-ray spectrometer and the resulting curves were evaluated on the basis of the area of the 001 peaks. Although the areas from the unmixed components varied greatly, within any given mixture the two clays were quantitatively comparable on the basis of a 1/1 001 peak area ratio. The considerable peak area variations from slide to slide are the result of different degrees of preferred orientation and are not due to any appreciable differences in crystallinity. Mixed-layering of expandable material with the illitic component does not affect the quantitative comparisons significantly.

Studies of Recent marine sediments from the North Atlantic Ocean were made in order to understand better the effects of diagenesis on the clay minerals. Samples from the continental shelf, the continental slope and the floor of the northwestern basin, north of Bermuda, were made available through the courtesy of the Lamont Geological Observatory of Columbia University.

Most of the argillaceous material in these sediments is a poorly crystalline, complex mixture of chlorite and illite. The samples contain a small amount of kaolinite and montmorillonite. Some of the problems involved in the identification of these complex mixtures are discussed. Studies of the clay minerals reveal that a slight diagenetic change takes place, as indicated by the increasing crystallinity of chlorite and illite, with increasing depth below the clay-water interface and with increasing water depth. Some of the cores contain zones of red clay and the clay minerals contained therein are relatively well crystallized materials in contrast to the clay minerals in the greenish-gray clays. An hypothesis based on the oxidation state of the iron is advanced to explain the differences between the crystallinity of the three layer clay minerals in the red and greenish-gray clays.

A few days after Dr. RudoIf Wegscheider of the University of Vienna celebrated his sixtieth birthday in October, 1919, he began his next class with the following words:

Essentially all interactions between atoms, molecules and ions spring from the electrical charges borne by the nuclei and electrons of which they are constituted. Two broad classes of interaction are distinguished by the terms “chemical” and “physical,” the former referring to those cases wherein some of the electrons of the two participants have become shared, with the consequent formation of a chemical bond. Such chemical forces have the property of saturation, are of very short range, and are usually associated with the comparatively large binding energies of a few electron volts. Some of the more important types of physical interactions, listed more or less in order of decreasing energy, are: ion-ion, ion-dipole, dipole-dipole, ion-induced dipole, induced dipole-induced dipole, etc. Those not involving ions are often grouped together under the term “van der Waals forces,” and generally have energies of only a fraction of an electron volt. The (long-range) ion-ion interactions (“ionic bonds”) are mainly responsible for the stability of ionic crystals, and thus may have energies comparable with those of chemical bonds.

An adsorbed molecule interacts very nearly additively with all the constituent atoms and ions of the adsorbent surface, and with other adsorbed molecules as well. The collective effect may be described through the “energy of adsorption,” which will generally be a function of the amount adsorbed. In physical adsorption, multilayer films and capillary condensation may occur at gas pressures approaching saturation.

The small size and high dipole moment of the water molecule make it strongly adsorbed on ionic substrates. The lamilar structure of the clay minerals furnishes enormous surface areas for adsorption. Investigation of these interactions at the molecular level provides a fundamental basis for a more complete understanding of clay-water systems.

This paper discusses some of the factors affecting the density vs. stability relationships of compacted clays and some of the limitations of the concept that the stability of a compacted soil increases with an increase in density.

A series of tests performed on silty clay, in which stability was measured by triaxial compression tests, are described. It is shown that the relationship between density and stability of a soil depends on the criterion used to define stability; the greater the permissible strain before a sample is considered unstable, the greater is the possibility that an increase in density will cause an increase in stability. For the silty clay, when the stability is defined as the load required to cause 10 percent strain or less, an increase in density at a given water content caused an increase or decrease in stability depending upon the water content and the range of densities involved; at constant degrees of saturation, however, an increase in density always caused an increase in stability.

The effect of compaction method on the density vs. stability relationship is illustrated. Test data are presented for two soils, a silty clay and a sandy clay, comparing the stabilities, at various water contents and densities, of partially saturated samples compacted by impact methods, static pressure and kneading action. It is shown that, at equal water contents and densities, samples compacted by static pressures exhibit higher stabilities than samples compacted by impact or kneading methods; also, that the stabilities of samples at equal densities and water contents, compacted by impact and kneading methods, are very similar, with kneading compaction producing somewhat higher stabilities at lower degrees of saturation, and impact compaction producing slightly higher stabilities at higher degrees of saturation. For static compaction, both soils showed an increase of stability with increase in density at all water contents, while for samples compacted by impact and kneading methods, an increase in density at a given water content did not necessarily lead to an increase in stability.

The effect of saturation on the stability of compacted clays is shown and the influence of water content at compaction on the stability of saturated samples having the same density and water content is illustrated.

Finally, a comparison is made of the stability and swell pressures developed at various densities of samples of the sandy clay compacted by kneading action and static pressure and subsequently saturated by exudation of moisture from the samples under static loads. It is shown that very much higher swell pressures and stabilities are exhibited by the statically compacted samples than by the samples prepared by kneading action.