Aggregation Of Clay Particles Research Articles

Microstructure of kaolinite sediments made with unaged FeCl3

Fine kaolinite suspensions were prepared with unaged FeCl3 to perform sedimentation tests in this study. The microstructure of kaolinite sediments was examined by scanning electron microscopy after CO2 supercritical drying. The interaction between clay particles and FeCl3 in an aqueous medium was investigated by means of electrophoresis and analytical transmission electron microscopy. Clay particles were connected in three basic modes — edge to edge (EE), edge to face (EF) and face to face (FF). Clay particles with different connection modes formed aggregates or flocs in sediments. The flocs not only exhibited a fractal structure themselves, but also formed sediments with fractal characteristics. This study determined the formation conditions of different clay particle connection modes, aggregates or fractal flocs in the presence of unaged FeCl3 in an aqueous medium.

Aggregation of clay in the hydrometer test

Recent studies have compared particle-size analysis methods for soils containing fine clay particles. The results showed significant differences between the techniques. This study consisted of a series of hydrometer experiments designed to give greater understanding of the behavior of kaolinite clay during the ASTM 422-63 hydrometer test. The results were consistent with the aggregation of fine clay particles, possibly due to the known hydrolysis behavior of the sodium polyphosphate dispersants used in the experiment. To avoid a serious underestimation of the fraction of submicron clay particles in soils, dispersants that do not suffer from time-dependent hydrolysis should be evaluated for the hydrometer test.

MODIFICATIONS INDUCED IN SOIL PHYSICO-CHEMICAL PARAMETERS BY EXPERIMENTAL FIRES AT DIFFERENT INTENSITIES

Field studies on the effects of heating soil are rare. Studies in which the temperature was varied and measured are even rarer. To cover this lack of knowledge, we conducted some experimental fires in which the fuel was controlled to obtain different fire intensities. Induced temperatures were measured by k-type thermocouples placed at various soil depths. These induced temperatures were highly variable at the soil surface, whereas below 2.5-cm depth, the temperature rise was negligible. Modifications of various soil physico-chemical parameters caused by fire were related to increasing temperatures at the soil surface. The passage of fire promoted the aggregation of clay particles into sand-sized particles, which become even more resistant to the disrupting action of water. The soil pH decreased at temperatures up to 395°C, followed by a clear increase at higher temperatures; however, both the cation exchange capacity and the organic matter content decreased continuously with increasing soil temperature. Total nitrogen content remained surprisingly constant as the soil surface temperature increased, whereas ammonium nitrogen peaked at 184°C. The organic phosphorus decreased continuously, and the available fractions increased. These results are in agreement with the results of our previous research on the effects of the artificial heating on soil properties and confirm that the processes occurring in soil are related to the temperature reached during the fire. The ashes, at least immediately after fire, do not affect these processes.

An AEM-TEM study of nanometer-scale mineral associations in an aquifer sand: Implications for colloid mobilization

Analytical and transmission electron microscopy (AEM-TEM) techniques were used to identify mineral juxtapositions at the nanometer-scale in the interstitial matrix of a shallow, Southeastern Coastal plain aquifer sand (Georgetown, South Carolina, USA). In doing so, we sought to infer particle-particle interaction mechanisms holding the matrix intact. The aquifer is a fine-to-medium quartz sand with approximately 12% by weight <63 μm size fraction composing the interstitial matrix. The clay-size fraction contains kaolinite, goethite, gibbsite, and vermiculite. The arrangement of the clay minerals is that of a framework of face-associated domains. Selective extraction revealed that goethite constituted 95% by weight of the free iron oxyhydroxides in the <63 μm size fraction, but AEM-TEM and high resolution TEM (HRTEM) indicated that the goethite occurred only in discrete aggregates among the clays. Conversely, the remaining 5% of the free iron oxyhydroxides comprised an amorphous iron phase which was found to be distributed throughout the matrix and directly associated with the clay particles. This evidence suggests that the amorphous iron oxyhydroxide phase could act as an effective binding intermediary among the clay-clay associations, possibly electrostatically or through bond linkages with the clay surfaces. In addition, HRTEM indicated the presence of another amorphous phase which appeared to hold the clay particle aggregates in a cementitious web. AEM suggested that this amorphous phase was silicon enriched, probably biogenic opal. This evidence suggests that instigating dissolution of the opaline silica phase may be necessary to induce substantial colloid mobilization in this aquifer sediment.

Stabilization of aqueous clay suspensions with AOT vesicular solutions

Greatly extended stability of clay aqueous suspensions of particles of size about 10–100 nm is achieved by the incorporation of Aerosol OT (AOT) vesicular solutions. Direct images of the interactions between clay particles with AOT vesicles and liposomes in aqueous suspensions, with and without added NaCl, have been obtained for the first time by artifact free (no drying and no staining) cryogenic transmission electron microscopy (cryo-TEM). Combined centrifugation and cryo-TEM results indicate that the heightened stability of the clay-AOT suspension is due mainly to strictly limited mobility and separation of clay particle aggregates in the presence of large multi-bilayers, and to a lesser extent by the encapsulation of clay particles. Greatly reduced rigidity of bilayers and shrinking of vesicles, with the added NaCl, lead to a lowered effect of stabilization with AOT vesicular solutions.

Slow vapor‐phase desorption of toluene from several ion‐exchanged montmorillonites

Abstract The sorption and desorption of volatile compounds from soils and clays exhibit a wide range of kinetics. While much of the sorptive interaction is very rapid, a certain fraction of volatile compounds that enter soil and clays are only slowly desorbed. It is generally believed that the formation of this recalcitrant or slowly desorbing fraction of volatile organic compounds (VOCs) in soils is due to the diffusion of compounds to poorly accessible sorption sites. However, the exact nature of these sites is in doubt. In montmorillonite, there are two likely possibilities for formation of the recalcitrant fraction: sites between the clay lamella and sites within clay particle aggregates. Because montmorillonite may be an important fraction of many soils, we have explored the formation of slowly desorbing toluene on a montmorillonite clay that was ion exchanged with five different ions (K+, Na+, Ca2+, Mg2+, and Fe3+) to form mineralogically similar clays with varying interlamellar spacing. The recalcitrant fraction was quantified for varying sorption and desorption times. The type of ion exchanged into the clay appears to have an important influence on the formation of a recalcitrant fraction.

Kinetics of colloidal particle deposition on pulp fibers 2. Deposition of clay on fibers in the presence of poly(ethylenimine)

The rate of deposition of clay particles on fibers dispersed in water was determined as a function of the amount and the sequence of poly(ethylenimine) addition. The polymer was introduced either to a mixture of fibers and clay or to only one of the components prior to addition of the second one. The primary role of the positively charged polymer was to adsorb onto the negatively charged components, thus modifying their surfaces and consequently promoting their interaction. It has been established that the extent and rate of particle deposition result from an interplay of several kinetic factors, namely the rate of polymer adsorption on fibers and on clay, the rate of collision between clay particles and fibers, and the rate of clay particle aggregation. Under the conditions of low shear rate, the polymer adsorption on fibers is a rather slow process and is comparable to the rate of deposition of dispersed clay particles on fibers. In contrast, polymer adsorption on clay particles proceeds at a faster rate, causing aggregation of the particles. The deposition of aggregates is considerably faster than that of dispersed clay particles.

Characterization of organic matter in particle-size fractions of Vertisols

The nature of organic matter (OM) of five Vertisols was investigated by means of Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFT) on whole soil samples and on stable aggregates of different size, separated by water dispersion. This method allows the IR spectra of soil OM to be obtained in its original state, unaltered by chemical treatments and with part of the functional groups bound to the mineral components. Further information on the nature of OM was obtained by electrofocusing (EF) analyses of the 0.1 M Na 4P 20 7-NaOH extracts of soils and of water stable soil aggregates. The relationship of OM with soil fabric was investigated by determining the organic carbon distribution in the different waterstable fractions. Our results show that OM is concentrated in the silt size aggregates and its nature appears rather uniform in the five Vertisols. In particular, DRIFT analyses reveal the existence of very strong hydrogen bonds between the OM and the soil mineral fraction and the presence, in the natural soils, of compounds, such as cyclic anhydrides. Moreover, aromatic substances appear concentrated in the water-stable, silt-size aggregates, while relatively simple aliphatic compounds seem to prevail in clay fractions. In the “apparent”silt fraction EF analyses show the presence of considerable amounts of organo-metal complexes, probably responsible for the aggregation of fine clay particles.

A model for clay filter cake properties

Clay filter cake properties, such as porosity, compressibility and permeability, have been studied by means of a structural network model. The electric double layer repulsion and Van der Waals attraction forces together with the equilibrium conditions of the network structure are shown to be fundamental in simulating the properties of filter cakes. The factors which affect the properties of filter cakes, such as clay particle size, salt concentration, and surface charge density have also been investigated. Results from the model show that the porosity, compressibility and permeability are predictable functions of compression pressure. The porosity of a filter cake is very sensitive to the degree of aggregation of clay particles. The compressibility of filter cakes is most sensitive to the size of clay particles and to the salt concentration. Salt concentration is also a sensitive factor influencing the permeability of filter cakes and its dependence on applied pressure. The porosity, compressibility and permeability are obtained as a function of compression pressure and can be used in static or dynamic filtration calculations.

Stability of polymer—clay suspensions. The polyacrylamide—sodium kaolinite system

Kaolinite is characterized by three exposed surfaces of different chemical composition. Adsorption measurements in dilute suspensions of radioactively labelled polyacrylamide as a function of surface area on several well-fractionated kaolinite samples, indicate that polyacrylamide is preferentially adsorbed on the platelet edge. The effect of polymer addition on the stability of the clay suspension was determined in concentrated medium. The stability and/or destabilisation behavior of the suspension in presence of polymer reflects the edge face—polymer association. The nature of adsorption forces and the mode of clay particle aggregation are discussed.

Stability of polymer—clay suspensions. The polyacrylamide—sodium kaolinite system

Kaolinite is characterized by three exposed surfaces of different chemical composition. Adsorption measurements in dilute suspensions of radioactively labelled polyacrylamide as a function of surface area on several well-fractionated kaolinite samples, indicate that polyacrylamide is preferentially adsorbed on the platelet edge. The effect of polymer addition on the stability of the clay suspension was determined in concentrated medium. The stability and/or destabilisation behavior of the suspension in presence of polymer reflects the edge face—polymer association. The nature of adsorption forces and the mode of clay particle aggregation are discussed.

TEM analysis of pillared and delaminated hectorite catalysts

When a dispersion of clay particles flocculates in water, the plates may associate as face-to-face (FF), edge-to-edge (EE), or edge-to-face (EF). The FF association forms thicker particles whereas EF and EE interactions generate large three-dimensional aggregates which was described as having a house-of-card structure. These two modes of particle association can be observed also in solids. In fact, by ion-exchanging the charge compensating cations in layer-lattice clay minerals such as montmorillonite or hectorite with large organic or inorganic cations, multilayered FF aggregates are formed called pillared clays. Clay particle aggregates containing EF and EE linkages are called delaminated clays. Delaminated clays are a new family of catalysts first prepared by reacting a synthetic hectorite with polyoxocations of aluminum. In these materials, 001 X-ray reflections are absent due to a lack of long range FF stacking of the clay silicate layers. Short range FF layer ordering is believed to be responsible for the zeolite-like selectivity in cracking gas oil. Delaminated clays are characterized by EE and EF connections which form a macrospace of the type found in amorphous alumino-silicate supports. In contrast, pillared clays, are characterized by regularly spaced FF layers of clay platelets propped apart by inorganic oxide clusters. Tokarzmore » and Shabtai have shown transmission electron micrographs (TEM) of Ce/sup +3/-montmorillonite before and after pillaring. It is the purpose of this note to present TEM and electron diffraction data that will further characterize the structure of delaminated clay catalysts.« less

Viscosities of dilute aqueous suspensions of montmorillonite and kaolinite clays

We have measured viscosities and densities of dilute aqueous suspensions of Na-kaolinite (25 °C), of Na-montmorillonite (25–55 °C), and of mixtures of Na-kaolinite/Na-montmorillonite (25 °C). Results of the measurements at 25 °C have been analyzed in terms of the Einstein equation with conclusions that are consistent with previous knowledge that colloidal particles of these clays are non-spherical and that montmorillonite is a swelling clay. Viscosities of mixed clay systems are nearly consistent with a simple additivity model; the small non-additivities are in accord with previous evidence that relatively small montmorillonite particles are adsorbed on the surface of relatively large kaolinite particles. The effect of temperature on the viscosities of suspensions of montmorillonite is consistent with the idea that aggregation of clay particles diminishes with increasing temperature.

Indirect Evaluation on Frost Susceptibility on Clay Roofing Tiles

Thirty one kinds of clay roofing tiles were prepared under different fabrication conditions, such as deairing pressure in extrusion, grain size of clay particle aggregates, raw clay and firing temperature. Fundamental data set of frost damage for indirect evaluation of frost susceptibility were obtained by direct freezing-thawing method which has been developed by Hudec for natural aggregates in concrete. Water absorption, saturation coefficient, apparent porosity, water adsorption, bending strength, capillary water saturation and several characteristic values from pore size distribution were employed as indirect evaluation factors for frost susceptibility. Indirect evaluation procedures were undertaken as follows. First, the multi-regression equation to achieve the maximum value of a poly-nominal multi-correlation coefficient among weight loss after 130 cycles of freezing-thawing (FT130) and several characteristic variables is derived. Second, the indirect evaluation values, “Frost Index” (“FINDX”) calculated from the multi-regression equation were compared. Considering the analysed results from the time and cost saving point of view, the following reliable equation for indirect evaluation of frost susceptibility for clay roofing tiles was suggested.“FINDX”=0.762×Ln(ADS45)+21.387×Ln(WABSB)-24.154×Ln(APPRS)+27.575 Moreover, the critical range of pore radius for frost damage of a clay roofing tile was suggested as 100-400nm from the correlation analysis between FT130 value and specific pore volume within a respective range of pore size.

Aggregation of clay particles as indicated by indirect transforms of small-angle scattering data

Clays prepared by sedimentation from aqueous suspension were shown to contain aggregates much larger than individual clay particles. Small-angle X-ray scattering data were obtained with an automated Bonse–Hart instrument. The distance distribution functions for the clay aggregates were obtained using the Glatter indirect Fourier transform method. The distance distribution function extended to over 200000 Å, and the average radius of gyration was over 50000 Å in the most extreme cases.

Loess from the Pleistocene of the Wirral Peninsula, Merseyside

A pale coloured silt from the cliffs at Dawpool has many of the distinctive characteristics of loess. It occurs as a thin, irregular bed in a complex sequence between two thick Pleistocene tills. A sample underwent rapid collapse when flooded under load and was clearly metastable. Grain size analysis revealed a poorly sorted silt with a clay tail. However, scanning electron microscopy showed silt-sized aggregates of clay grade quartz particles. X-ray diffraction indicated the presence of quartz, feldspar, mica, dolomite, calcite and chlorite but no other clay minerals. Parallels are drawn with other loess deposits and with other sediments. The identification of the loess deposit implies a definite order of events and conflicts with the view that there was a single ice advance or that the overlying till was a lacustrine clay. It is suggested that there are two types of loess deposit in Britain: distinct, unweathered, localised beds and thin, weathered, superficial sheets. The former have been recognised only occasionally while the latter occur mainly in the east and south of England and mainly on limestone bedrock. In view of the porous, friable, metastable, homogeneous nature of the sediment at Dawpool it is considered to be a true eolian loess of the first type, hitherto unrecorded from this area.

Freeze-drying of soil clays

The crystallization of ice during preparation of soil clays for freeze-drying can cause aggregation of clay particles. This often results in sample loss by the ejection of material in the water vapour stream during sublimation. These undesirable effects are overcome with many soil clays by the addition of ethanol to a concentration of approximately 4% in the suspension before freezing. The structure of the clay body obtained by freeze-drying appears to depend mainly on the particle-size distribution of the clay; a more coherent structure being obtained from finer clays.

Mechanism of stabilizing action of PMSya sulfonate additive

In an investigation of the mechanism of stabilizing action of the calcium sulfonate additive PMSya, the following have been demonstrated: 1. With increasing concentration of PMSya in a suspension of kaolin in naphtha, the size of the clay-particle aggregates becomes smaller, and peptization sets in. 2. The adsorption of PMSya on the surface of kaolin particles takes place in two stages, i.e., chemisorption and reversible adsorption. 3. The optimum condition for formation of the stiffest precipitate from the suspension, with a maximum volumetric solids content, is the presence of hydrophobic and hydrophilic sections on the kaolin particle surface in a certain ratio that is achieved by incomplete adsorption of the PMSya by the kaolin, equivalent to approximately 50% of the maximum possible adsorption. 4. Smaller quantities of active ingredient and the presence of “mechanical, admixtures” in the additive will reduce its stabilizing action, so that greater consumption of additive is required for hydrophobization of the clay particles.

Coagulation, Cake Filtration, and Filtrability

Results of this study indicate that the aggregation of clay particles can occur either by coagulation, or by flocculation, or by both, depending upon various factors. Two systems consisting of two different clay minerals and aluminum sulfate have been used to demonstrate the effect of the combined phenomena on cake‐forming filtration.

Aeolian Deposits of Clay Sand

ABSTRACT Wind erosion of granular clay soils in fallow fields occurs during the winter months in southern Manitoba. The eroded clay grains first accumulate in and on snowdrifts and are later left as elongate low ridges of sandsized aggregates of clay particles. Although these clay aggregates may eventually break down and form a uniform clay deposit, they remained as distinct aggregates throughout the summer following deposition. Such deposits may be formed in the glacial or periglacial environment or adjacent to areas such as floodplains, dry lagoons, or dry lake plains where clay-rich materials are subjected to fragmentation but are not stabilized by vegetation.