Showing papers on "Kaolinite published in 1988"
TL;DR: The relationship between the composition and the crystallization temperature of chlorites and illites has been investigated in different geothermal fields and in particular the Los Azufres system in Mexico, considered to be a natural analogue to experimental laboratories.
Abstract: A B S T RA C T : The relationships between the composition and the crystallization temperature of chlorites and illites have been investigated in different geothermal fields and in particular the Los Azufres system in Mexico, considered to be a natural analogue to experimental laboratories, as the main changes in physical and chemical conditions and mineralogy are related to progressively increasing temperature with depth. Temperature was estimated from combined geothermometric approaches, and especially from fluid inclusion studies on quartz coexisting with clays. The Al(lv) content in the tetrahedral site of chlorites, and the K content and total interlayer occupancy of illites increase with temperature. These chemical changes are mainly related to the marked decrease in the molar fraction of the Si(lv)-rich end-members (kaolinite for chlorites, and pyrophyllite for illites) which become negligible at ~ 300~ Other chemical changes, such as the variation in Fe and Mg contents, are partly influenced by temperature, but are strongly dependent on the geological environment, and consequently on the solution composition. The empirical relationships between chemical variables and temperature were calibrated from 150-300~ but extrapolations at lower and higher temperatures seem possible for chlorites. Such geothermometers provide tools for estimating the crystallization temperature of the clays, and are important for the study of diagenetic, hydrothermal and low-T metamorphic processes. Clay minerals are the most abundant minerals in most of the geological environments submitted to temperatures from 50 ~ to 350~ where estimation of the crystallization temperature of the clay minerals may be difficult. Most of the classical geothermometers cannot be applied, fluid inclusions may be absent, and experimental data are scarce. Nevertheless, such temperature estimations are of critical importance for geological studies related to oil field exploration, as well as for diagenetic and low-T metamorphic processes. 1"here are three types of chemical or crystallographic change occurring in the clay fraction of rocks which may indicate temperature of crystallization. (1) The changes in the clay mineral assemblages described in studies of the burial metamorphism of sediments (Weaver, 1959; Dunoyer de Segonzac, 1970; Perry & Hower, 1970; Velde, 1977) and the thermal metamorphism of rocks in geothermal fields (Schoen & White, 1966; Steiner, 1968; Tomason & Kristmannsdottir , 1972; Cathelineau & Izquierdo, 1988). However, only the boundaries between two mineral assemblages may yield a temperature estimate, largely restricting their use.
823 citations
TL;DR: In this paper, the authors show that the dissolution rate of slightly soluble oxide and silicate minerals is controlled by the adsorption of H+ and OH− ions to specific metal cation surface reaction sites.
295 citations
TL;DR: The 27Al and 29Si NMR signal analysis of samples heated above 400°C demonstrates that the tetrahedral sheet of kaolinite begins to break down near 600°C and continues to do so to 900°C as discussed by the authors.
Abstract: The 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS-NMR) study of the kaolinite-mullite transformation has shown the presence of Al in tetra- and pentacoordination in dehydroxylated kaolinite. The 29Si NMR signal analysis of samples heated above 400°C demonstrates that the tetrahedral sheet of kaolinite begins to break down near 600°C and continues to do so to 900°C. From the 27Al NMR signal evolution, it can be deduced that the exothermic peak at 980°C in DTA curves is associated with the modification of the coordination of Al, which changes from the tetra- or pentacoordination to the more stable octahedral coordination. Heating the sample at 880°C for 36 h produces the same transformation in the coordination of Al ions and the elimination of the exothermic peak at 980°C in the DTA diagram. After this transformation, all spectra show two tetrahedral lines characteristic of mullite, indicating that nuclei of mullite with low crystallinity are generated during the exothermic process which are not detected by XRD. At higher temperatures tetrahedral NMR peaks increase in intensity, yielding, at 1200°C, the 3:2 mullite NMR spectrum.
216 citations
TL;DR: In this article, a site-binding model of the kaolinite edge was proposed, in which the edge was viewed as composite layers of AI and Si oxide, and the adsorption of both chromate and sulfate can be described in terms of a sitebinding model.
Abstract: Chromate (CrO4 2-) adsorption was investigated on kaolinite (0.2-2 ~m) saturated with NaC104 over a range of pH. Adsorption increased with decreasing pH because of protonation of chromate and/ or variable charge sites on kaolinite. Chemical pretreatment to remove noncrystalline and crystalline oxide contaminants affected the magnitude ofCrO42- adsorption, but not the pH range over which CrO42- adsorbed. Chromate adsorption at different sorbate and sorbent concentrations increased below the pHz~ for the kaolinite edge, suggesting the formation of weak surface complexes. If frO4 2- and SO42- were present at equal concentration (5.0 x 10 -7 M), the two solutes sorbed independently, suggesting binding to separate sites. The presence of excess SO42- (5.0 x 10 -4 M), however, unexplainably enhanced CrO42- adsorption. The adsorption of both chromate and sulfate can be described in terms of a site-binding model of the kaolinite edge, in which the edge is viewed as composite layers of AI and Si oxide. Surface complexation constants for CrO4 2- on kaolinite were similar to those for alumina, pointing to the im- portance of A1-OH edge sites in chromate adsorption.
154 citations
138 citations
TL;DR: The authors showed that the coexistence of authigenic K-feldspar and kaolinite may indicate that this narrow range of conditions did prevail and that the system behaved as a closed system.
Abstract: Although thermodynamic calculations indicate a narrow range of conditions for coprecipitation of kaolinite and K-feldspar, coexistence of authigenic kaolinite and K-feldspar is common in Jurassic sandstones of the North Sea. This paper shows that the coexistence of authigenic K-feldspar and kaolinite may indicate that this narrow range of conditions did prevail and that the system behaved as a closed system. These conditions are presence of muscovite in the sediment, pore waters supersaturated with respect to quartz, and temperatures lower than 50°C. At higher temperatures, the authigenic kaolinite and (authigenic) K-feldspar may react and form authigenic illite ("muscovite") and quartz cement. The direction of the isochemical reaction is thermodynamically determined by the degree of supersaturation with respect to quartz in the formation water. Published data on the degree of supersaturation with respect to quartz in formation waters suggest that the illitization of kaolinite may take place at temperatures as low as 50°C--much lower than previously believed.
128 citations
TL;DR: In this article, the authors investigated the competition of several agents, reported as root exudates, with P on adsorption sites on kaolinite and montmorillonite, and the agents studied were acetate, bicarbonate, citrate and oxalate, and amino acids phenylalanine and alpha-amino isobutyric acid.
Abstract: The mechanisms by which roots affect the release of phosphate from soil surfaces into the solution is not clear. This study was undertaken to investigate the competition of several agents, reported as root exudates, with P on adsorption sites on kaolinite and montmorillonite. The agents studied were acetate, bicarbonate, citrate and oxalate, and the amino acids phenylalanine and alpha-amino isobutyric acid. The adsorption or desorption of P on the clays in the presence of the noted agents at various fixed pHs and known ionic strength, and the effect of slurry density on P adsorption, were determined
110 citations
TL;DR: In this article, the authors used NIR reflectance spectra for mixtures of ordered kaolinite and ordered dickite to estimate the octahedral vacancy disorder in nine disordered kolinite samples by comparing the sample spectra to the spectra of reference mixtures.
Abstract: Near-infrared (NIR) reflectance spectra for mixtures of ordered kaolinite and ordered dickite have been found to simulate the spectral response of disordered kaolinite. The amount of octahedral vacancy disorder in nine disordered kaolinite samples was estimated by comparing the sample spectra to the spectra of reference mixtures. The resulting estimates are consistent with previously published estimates of vacancy disorder for similar kaolin minerals that were modeled from calculated X-ray diffraction patterns. The ordered kaolinite and dickite samples used in the reference mixtures were carefully selected to avoid undesirable particle size effects that could bias the spectral results. NIR spectra were also recorded for laboratory mixtures of ordered kaolinite and halloysite to assess whether the spectra could be potentially useful for determining mineral proportions in natural physical mixtures of these two clays. Although the kaolinite-halloysite proportions could only be roughly estimated from the mixture spectra, the halloysite component was evident even when halloysite was present in only minor amounts. A similar approach using NIR spectra for laboratory mixtures may have applications in other studies of natural clay mixtures.
103 citations
TL;DR: In this paper, the authors obtained depleted δ18O- and δD-values of +6.1 to +9.4 and −107 to −94, respectively, from kaolinite samples of early Permian (Sakmarian-Artinskian) age from the Gunnedah Basin, eastern Australia.
Abstract: Depleted δ18O- and δD-values of +6.1 to +9.4‰ and −107 to −94‰, respectively, have been obtained from kaolinite samples of early Permian (Sakmarian-Artinskian) age from the Gunnedah Basin, eastern Australia. The samples come from kaolinite clayrocks representing both in situ kaolinitic weathering profiles and the eroded and re-deposited products of this weathering developed in the Quirindi-Wingen and Boggabri-Gunnedah areas of New South Wales, Australia. The clayrocks were produced by the intense surficial weathering of an underlying volcanic sequence, with subsequent erosion and re-deposition in basins flanking the volcanic pile. The calculated isotopic composition of meteoric water in equilibrium with kaolinite from the clayrocks had δ18O of ⩽ −17‰ and δD of ⩽ −125‰, indicating polar or sub-polar temperatures of condensation. As kaolinite formation cannot occur below the freezing point of water, the highly depleted isotopic results obtained from the samples suggest equilibrium with waters partly derived from deglaciation of the Gondwanan landmass, an event which consequently must have been well underway in eastern Australia by the Sakmarian-Artinskian. The climate prevailing at the time of kaolinite formation is unlikely to have been warmer than cool temperate, a conclusion which is difficult to reconcile with the classical interpretation of kaolinitic weathering as a tropical or subtropical phenomenon. This suggests that high rates of infiltration, efficient leaching of soluble cations, and good drainage are of more importance to kaolinite formation than the temperature at which the process operates. Oxygen-isotope exchange in the kaolinite samples since formation is thought to have been negligible, however, marked post-formational hydrogen-isotope exchange is demonstrable at temperatures not exceeding ∼ 80°C and probably considerably lower in some cases.
94 citations
TL;DR: In this paper, specific effects of total P concentration, pH, ionic strength, and equilibration time on P partitioning between solid and solution phases of Ca- and K-kaolinite and -montmorillonite suspensions as model systems of soils containing these minerals were studied.
Abstract: The objective of this work was to study specific effects of total P concentration, pH, ionic strength, and equilibration time on P partitioning between solid and solution phases of Ca- and K-kaolinite and -montmorillonite suspensions as model systems of soils containing these minerals. Phosphorus concentration in the solution phase (C p ) stabilized within 24 to 48 h after introducing P into the system
88 citations
TL;DR: In this article, two types of aluminosilicate gels have been synthesized by using different precursors and by varying pH and water content during the gelification process.
Abstract: Earlier works of mullitization through the gel route have been reviewed and the results show 980°C DTA and crystalline phases. Some Al2O3-SiO2 gels have been synthesized by using different precursors and by varying pH and water content during the gelification process. Thermal changes of these coherent gels were studied by DTA and X-ray powder diffractometry. The results demonstrate that two types of aluminosilicate gels form. The first type produces orthorhombic mullite directly on heating at 980°C, whereas the second type forms cubic mullite first at 980°C and then transforms to the orthorhombic variety on further heating. Lastly, the cause of the 980°C exotherm is explained with reference to kaolinite.
Journal Article•
TL;DR: In this article, the optimum lime additive for maximum increase of the plastic limit of the soil is referred to as the lime fixation point, and lime added in excess of the fixation point is used in the cementation process and gives rise to an increase in soil strength.
Abstract: Clay soil can be stabilised by the addition of a small percentage, by weight, of lime. This produces an improved construction material. Generally the amount of lime needed to modify a clay soil varies from 1 to 3 per cent, whilst that required for cementation varies from 2 to 8 per cent. Montmorillonitic clay soils respond more rapidly to lime treatment than do those in which kaolinite is the dominant clay mineral. When lime is added to clay soils, calcium ions are combined initially with or adsorbed by clay minerals which leads to an improvement in soil workability, that is, to an increase in the plastic limit of the clay and generally to a decrease in its liquid limit. The optimum lime additive for maximum increase of the plastic limit of the soil is referred to as the lime fixation point. Lime added in excess of the fixation point is utilised in the cementation process and gives rise to an increase in soil strength. The initial increase in strength has been attributed to the formation of poorly ordered reaction products which surround the clay materials. However, the development of long-term strength appears to be due to the gradual crystallisation of structurally-ordered new minerals from the initial disordered reaction products. The principle uses of the additions of lime to clay soils is for, firstly, stabilisation of subbases and subgrades in pavement construction and, secondly, to dry out wet soils. Lime treatment also has been used to stabilise embankments and canal linings, and to improve foundation soils. In the latter instance soil is stabilised beneath strip or raft foundations, or lime piles or columns are formed. (TRRL)
TL;DR: Sorption characteristics of Cs and S r + + on montmoril lonite and kaolinite type clays and soil fractions f rom various regions of Turkey were studied using the batch method.
Abstract: Sorption characteristics of Cs and S r + + on montmoril lonite and kaolinite type clays and soil fractions f rom various regions of Turkey were studied using the batch method. 1 3 7 C s and , 0 S r were used as tracers. Concentrations of Cs and S r + + ions ranged from 1 0 \" ' to 10\" 2 mol/1; natural groundwater was used and the grain size of the solid particles was < 20 /am. Equilibrium was reached in 4 7 days for Cs and 7 1 1 days for S r + + . The distribution coefficient, R D , increased with decreasing grain size, suggesting mainly a surface phenomenon. The sorption isotherms were non-linear suggesting at least two different sorption processes. The sorption was found to be predominantly reversible. Cs was sorbed much stronger than S r T T in all samples.
TL;DR: In this article, the dispersion component of surface free energy of these solids was calculated from the equation which was derived on the basis of an equilibrium state of the system solid-water drop-hycrocarbon for two different hydrocarbons.
Abstract: The wetting contact angle was measured for water drops settled on the surface of pressed discs of kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite immersed in hexane, octane, dodecane, cis-decalin, and air. Minimum and maximum values of the contact angle were obtained for the given systems of solid-water drop-hydrocarbon, depending on the manner of disc preparation. Using both minimum (θmin) and maximum (θmax) values of the contact angle, values of the dispersion component (γsd) of surface free energy of these solids were calculated from the equation which was derived on the basis of an equilibrium state of the system solid-water drop-hycrocarbon for two different hydrocarbons. The values of γsd for kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite obtained from θmin are 83.5, 98.1, 98.9, 80.2, 95.9, and 89.7 mJ/m2, and from θmax are 73.1, 85.0, 84.4, 75.8, 85.5, and 75.5 mJ/m2. These values for marble and quartzite are similar to those in the literature (marble = 67.7 mJ/m2; quartzite = 71.3 and 76.0 mJ/m2). The values of the dispersion components of surface free energy for marble and quartzite covered with a water film (γsfd) were found to be: 41.8, 36.9; 49.2, 42.5; 49.6, 42.2; 40.2, 38.1; 48.1, 42.8; and 44.9, 38.0 mJ/m2, respectively. Values of γsfd for kaolinite, bentonite, and montmorillonite agreed well with those obtained from hydrocarbon adsorption isotherms determined by differential thermal analysis (35.5, 36.5, and 37.4 mJ/m2). Using values of γsfd and contact angles measured in the system solid-water drop-air, the nondispersion component of the surface free energy of solids with adsorbed water film (γsfn) was calculated from the modified Young equation. The values of γsfn for kaolinite and quartzite are as follows: 55.8, 69.0; 85.6, 94.0; 52.1, 75.0; 64.7, 68.9; 54.9,71.3; and 59.2,74.4 mJ/m2. The values of the nondispersion components determined for kaolinite, bentonite, and montmorillonite agreed well with those obtained by differential thermal analysis (67.6, 78.3, and 65.5 mJ/m2, respectively). Further, based on the assumption that the adsorbed water film decreased the surface free energy of these solids by the value of the work of spreading wetting, the nondispersion component (γsn) of the surface free energy of the solids was calculated to be: 86.9,129.6; 169.5, 187.7; 67.1, 144.8; 117.5, 129.3; 83.0, 135.7 and 100.2, 143.4 mJ/m2. These calculated values of the nondispersion component of marble and quartzite surface free energy agree with those obtained from adsorption isotherms determined by chromatographic and differential thermal analysis (marble = 103.8, 106.4; quartzite = 112, 115, 153.6 mJ/m2).
01 Jan 1988
TL;DR: Aluminum is the most abundant metallic element of minerals in soils and the associated environments and occurs in a series of Al-bearing minerals (e.g., feldspars, micas, chlorites, vermiculites, smectites, kaolinite, halloysite, and gibbsite) as discussed by the authors.
Abstract: Aluminum is the most abundant metallic element of minerals in soils and the associated environments. It occurs in a series of Al-bearing minerals (e.g., feldspars, micas, chlorites, vermiculites, smectites, kaolinite, halloysite, and gibbsite). It makes up 81, 82, 25, and 4 g kg-1 of igneous, shale, sandstone, and limestone rocks, respectively (Jackson, 1964; Brady, 1974; McLean, 1976).
TL;DR: In this paper, X-ray diffraction and thermal analysis of tetradecylammonium exchanged clays and structural formulae calculations indicated all hydroxyinterlayered minerals, except for one HISM, to have high layer charge deficiencies (X > 0.5 equivalents per 0.8 unit cell).
Abstract: Coarse clay fractions (2-0.2 ) of selected soil samples containing variable quantities (10-52%) of Al-hydroxyinterlayered smectite (HISM) or vermiculite (HIV) were investigated by XRD, thermal, elemental and solution composition analyses. The HISM vs. HIV nature of the sample was determined from the smectitic or vermiculitic origin of the sample and by alkylammonium ion exchange, expansion with glycerol and resistance to collapse after K-saturation and heating at 300° and 550 °C. X-ray diffraction and thermal analysis of tetradecylammonium exchanged clays and structural formulae calculations indicated all hydroxyinterlayered minerals, except for one HISM, to have high layer charge deficiencies (X > 0.5 equivalents per 0.5 unit cell). A greater portion of the total charge deficiency was satisfied by [Al(OH)x] in HIV minerals which resulted in generally higher free energies of formation . Hydroxyinterlayered smectites on the other hand, exhibited higher cation exchange capacities and higher OH/Al ratios in the hydroxyinterlayer material. Compositions of soil solutions in contact with these minerals supported a metastable HISM region in relatively Si-enriched solutions and a metastable or stable HIV region in somewhat Si-deficient solutions comparable to those supporting the stability of kaolinite. Structural formulaeand soil solutioncompositions of the studied samples appeared to be consistent with the dynamic nature of these minerals in soil environments in terms of mineralogical distribution, physicochemical behavior, and stability. View complete article To view this complete article, insert Disc 5 then click button8
TL;DR: In this article, the adsorption kinetics of Al 3+ by montmorillonite, kaolinite, and vermiculite were investigated as a function of the initial Al concentration, the surface area of the clay, and H + concentration, at 25°, 18°, and 10°C.
TL;DR: In this paper, the adsorption of n-octane and water vapor on natural kaolinite was measured and the dispersion and non-dispersion components of the surface free energy were calculated.
Abstract: The adsorption of n-octane and water vapor on natural kaolinite was measured. From ad- sorption isotherms film pressures were determined which were then used to calculate the dispersion and nondispersion components of the kaolinite surface free energy. In addition, thermodesorption of water from the kaolinite surface was determined. These results suggest that physically adsorbed water remained on the kaolinite surface, even at temperatures as great as 125"(2. Therefore, experimentally determined dispersion and nondispersion components appear to relate to the surface precovered with a film of water. These values are: ~gw) = 34.4 mJ/m 2 for dispersion interactions and ~gw) = 60.2 mJ/m 2 for nondispersion interactions. Assuming a kaolinite surface precovered with a film of water, which decreased the free energy by the work of spreading, the following components of the energy for the bare surface were calculated: ~s = 67.6 mJ/m 2 and 3'~ = 103.4 mJ/m 2, for dispersion and nondispersion components, respectively.
TL;DR: In this article, the composition and distribution of clay minerals in the continental shelf between Visakhapatnam and the Ganges were analysed by X-ray diffraction for the composition of clay.
Journal Article•
TL;DR: In this article, the authors performed DT, IR and X-ray diffraction of sediments from the Central Indian Ocean Basin and found that there are two smectite minerals (montmorillonite and Fe-rich montmorillonites).
Abstract: DT, IR and X-ray diffraction < 1,1 -2 and 2-4 /μm) of sediments from the Central Indian Ocean Basin. Results indicate that there are 2 smectite minerals (montmorillonite and Fe-rich montmorillonite). Montmorillonite is present in all size fractions of sediments, whereas Fe-rich montmorillonite is present onlyin < 1 and 1-2 μm fractions of siliceous and < lμm fractions of pelagic clays. Distribution of clay minerals suggests that illite, chlorite and kaolmite are the detrital products from Ganges and Brahmaputra and montmorillonite is derived from the weathering of the ridge rocks.Fe-rich montmorillonite in siliceous and pelagic clays is a result of early diagenetic processes. Size fraction studies suggest that montmorillonite tends to crystallise in <2μm size range.
TL;DR: In this article, the effect of polymer addition on the stability of the clay suspension was determined in concentrated medium and the stability and/or destabilisation behavior of the suspension in presence of polymer reflected the edge face polymer association.
TL;DR: In this article, the chemistry and mineralogy of seven pedons developed in Quaternary volcanic ashes under different moisture regimes in northern Tanzania have been studied and high contents of clays in soil samples (410-860 g/kg) are believed to indicate advanced stages of weathering.
TL;DR: In this article, microcalorimetric measurements were carried out to explain reactions of H+>OH− on the surface of three different groups of minerals: oxides, salt-type minerals, and kaolinite and feldspar.
01 Jan 1988
TL;DR: TEM investigations on goethite and hematite associated with kaolinite in lateritic weathering profiles (Cameroon) have shown : (I) the variability of Goethite habit, in contrast to Hematite, according to sampling locality, (II) the occurrence of intermediate phases, primary or resulting from a topotactic transformation of hematites into goethites, and (III) intergrowths of Hematites and Goethites as discussed by the authors.
Abstract: TEM investigations on goethite and hematite associated with kaolinite in lateritic weathering profiles (Cameroon) have shown : (I) the variability of goethite habit, in contrast to hematite, according to sampling locality, (2) the occurrence of intermediate phases, primary or resulting from a topotactic transformation of hematite into goethite, (3) intergrowths of hematite and goethite, and (4) epitaxy of goethite upon kaolinite. These data are discussed in terms of growth and genetic relationships between minerals (mineral development and relative stability). Petrological implications are considered.
TL;DR: In this paper, the authors used the σ = f(t) curve associated to congruent dissolution in dilute hydrofluoric acid at 25°C to estimate the chemical reactivity of transitory phases (TACK synthetic pozzolanic binders).
TL;DR: In this paper, the authors used the Grand Rapids reservoir in northern Alberta, Canada, to determine the potential for hydrothermal reactions between clays and carbonate minerals in a natural reservoir sand.
TL;DR: In this article, the effect of ESP on infiltration was found also to depend on the clay mineralogy of the soil, and it was suggested that kaolinitic and illitic soils are less dispersive than smectitic soils.
Abstract: Crust formation and infiltration rates and their dependence on the exchangeable sodium percentage (ESP) of South African (SA) soils, with kaolinite and illite as the dominant clay minerals, were studied by subjecting them to simulated rain. The final infiltration rate (FIR) values of these soils at ESP ca. 2,5 were compared to values reported for Israeli soils having similar clay content but with smectite as the dominant clay mineral. The SA soils have higher FIR values, which indicates that they were less affected by raindrop impact than the smectitic (Israeli) soils. It is therefore suggested that kaolinitic and illitic soils are less dispersive than smectitic soils. The effect of ESP on infiltration was found also to depend on the clay mineralogy of the soil. The FIR values of the kaolinitic soil with no smectite were only slightly affected by ESP. When smectite was present in kaolinitic soil, the susceptibility of the soil to sodicity, as reflected by crust formation, increased. The illitic soil was f...
TL;DR: In this paper, the authors studied the clay fraction of soils from a toposequence developed on a sandy clay Tertiary sediment in the Brazilian Amazonia and found that the clays (kaolinite and gibbsite) have been weathered by acido-complexolysis (podzolization) which involves complexing organic acids both in the weathering of the clay fractions and in the removal of A1 from the soil profile.
Abstract: The clay fraction of soils from a toposequence developed on a sandy clay Tertiary sediment in the Brazilian Amazonia was studied. Clayey Acrorthox located at the upper part of the sequence have transformed progressively into sandy Tropohumods down the slope. Along the slope important chemical and mineralogical changes linked to modifications in the weathering conditions were observed. In the Acrorthox the hydrolysis process largely prevails and the clay fraction is composed mainly of Fe-rich kaolinite. Fe and AI amorphous compounds become increasingly abundant along the slope. In the Spodosols, hydrolysis and acidocomplexo- lysis processes have both been effective, and the clay fractions contain not only more gibbsite, but also amorphous materials which are particularly abundant in the Bh horizons. In the area near Manaus (Brazil), Acrorthox (sols ferrallitiques), Paleudult (sols ferrallitiques A diff6renciation texturale) and Tropohumod (podzols) are associated in soil toposequences. According to Klinge (1965), the podzols have developed from sandy materials covering the valley bottoms, and the Acrorthox from a more clayey sediment which has settled on the plateau surfaces. Chauvel et al. (1987) and Lucas et al. (1987) demonstrated that the whole toposequence was derived from the same parent material, known as the Barreiras sediment. From the upper to the lower part of the sequence, Acrorthox was progressively transformed into podzols through destruction of the clays leaving quartzose residual material. According to Chauvel et al. (1987) the clays (kaolinite and gibbsite) have been weathered by acido- complexolysis (podzolization) which involves complexing organic acids both in the weathering of the clay fraction and in the removal of A1 from the soil profile. However, Lucas et al. (1987) considered that a previous clay impoverishment of the ferrallitic material was necessary before podzolization. The purpose of this paper is the geochemical and mineralogical characterization of the clay fractions (< 2/zm) in order to obtain more information about the weathering conditions, and particularly the respective roles of the podzolization and hydrolysis processes in the development of the soil toposequence.
TL;DR: In this article, the authors studied the flocculation properties of polyacrylamides on sodium kaolinite under controlled conditions of ionic strength, temperature and agitation, and examined the mechanisms of floccuration as a function of the charge of the polymer and clay.