Showing papers on "Clay minerals published in 2003"
TL;DR: In this paper, the authors used FTIR techniques to distinguish between different types of clay minerals and to derive information concerning their structure, composition and structural changes upon chemical modification, and the selection of the sampling technique used depended on the purpose of the study and on the physical state of the sample.
1,497 citations
TL;DR: In this paper, the authors measured arsenic concentrations up to a few milligrams per litre in natural waters and found that in aqueous environment the inorganic arsenic species arsenite (As) and arsenate (As(V)) are the most abundant species.
Abstract: In natural waters arsenic concentrations up to a few milligrams per litre were measured. The natural content of arsenic found in soils varies between 0.01 mg/kg and a few hundred milligrams per kilogram. Anthropogenic sources of arsenic in the environment are the smelting of ores, the burning of coal, and the use of arsenic compounds in many products and production processes in the past. A lot of arsenic compounds are toxic and cause acute and chronic poisoning. In aqueous environment the inorganic arsenic species arsenite (As(III)) and arsenate (As(V)) are the most abundant species. The mobility of these species is influenced by the pH value, the redox potential, and the presence of adsorbents such as oxides and hydroxides of Fe(III), Al(III), Mn(III/IV), humic substances, and clay minerals.
817 citations
TL;DR: In this article, a negative correlation between 14C activity and carbon release after dissolution of the mineral matrix by HF indicates a strong association of stabilised carbon compounds with the mineral phase.
389 citations
01 Jan 2003
TL;DR: The RockJock program as mentioned in this paper is a computer program that determines quantitative mineralogy in powdered samples by comparing the integrated X-ray diffraction (XRD) intensities of individual minerals in complex mixtures to the intensity of an internal standard.
Abstract: RockJock is a computer program that determines quantitative mineralogy in powdered samples by comparing the integrated X-ray diffraction (XRD) intensities of individual minerals in complex mixtures to the intensities of an internal standard. This manual discusses how to prepare and X-ray samples and standards for this type of analysis and describes the operation of the program. Carefully weighed samples containing an internal standard (zincite) are ground in a McCrone mill. Randomly oriented preparations then are X-rayed, and the X-ray data are entered into the RockJock program. Minerals likely to be present in the sample are chosen from a list of standards, and the calculation is begun. The program then automatically fits the sum of stored XRD patterns of standard, pure minerals (the calculated pattern) to the measured pattern by varying the fraction of each standard pattern, using the Solver function in Microsoft Excel to minimize the degree of fit parameter between the calculated and measured pattern. The calculation normally analyses the full pattern (usually 20 to 65 degrees two-theta) to find integrated intensities for the minerals, but it also has the option to carry out an extended clay analysis, in which a smaller region of the XRD pattern (usually 58 to 65 degrees two-theta) is analyzed to find intensities for the clay minerals. Integrated intensities for each mineral then are determined from the proportion of each standard pattern required to give the best fit. These integrated intensities then are compared to the integrated intensity of the internal standard, and the weight percentages of the minerals are calculated. The results are presented as a list of minerals with their corresponding weight percent. To some extent, the quality of the analysis can be checked because each mineral is analyzed independently, and, therefore, the sum of the analysis should approach 100 percent. Also, the method has been shown to give good results with artificial mixtures. The program is easy to use, but does require an understanding of mineralogy, of X-ray diffraction practice, and an elementary knowledge of the Excel program.
381 citations
TL;DR: In this paper, the authors conducted a study to identify the geochemical processes and their relation to groundwater quality in the Palar and Cheyyar River Basin in Tamil Nadu state of Southern India.
Abstract: The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.
374 citations
TL;DR: In this paper, a comprehensive understanding of lithium-isotope fractionation during terrestrial weathering is needed in order to use lithium isotopes to trace chemical cycles, climatic changes and igneous processes.
357 citations
TL;DR: In this paper, the authors measured the elastic properties of clay minerals using independent experimental methods to measure the elastic moduli of the clay minerals as functions of pressure and saturation, and made a comparison between the accuracy of velocity prediction in shaley sandstones and claywater and clay-sand mixtures using the values measured in this study and those from theoretical models.
Abstract: The presence of clay minerals can alter the elastic behaviour of rocks significantly. Although clay minerals are common in sedimentary formations and seismic measurements are our main tools for studying subsurface lithologies, measurements of elastic properties of clay minerals have proven difficult. Theoretical values for the bulk modulus of clay are reported between 20 and 50 GPa. The only published experimental measurement of Young's modulus in a clay mineral using atomic force acoustic microscopy (AFAM) gave a much lower value of 6.2 GPa. This study has concentrated on using independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. First, ultrasonic P- and S-wave velocities were measured as functions of hydrostatic pressure in cold-pressed clay aggregates with porosity and grain density ranging from 4 to 43 per cent and 2.13 to 2.83 g cm - 3 , respectively. In the second experiment, P- and S-wave velocities in clay powders were measured under uniaxial stresses compaction. In the third experiment, P-wave velocity and attenuation in a kaolinite-water suspension with clay concentrations between 0 and 60 per cent were measured at ambient conditions. Our elastic moduli measurements of kaolinite, montmorillonite and smectite are consistent for all experiments and with reported AFAM measurements on a nanometre scale. The bulk modulus values of the solid clay phase (K s ) lie between 6 and 12 GPa and shear (μ s ) modulus values vary between 4 and 6 GPa. A comparison is made between the accuracy of velocity prediction in shaley sandstones and clay-water and clay-sand mixtures using the values measured in this study and those from theoretical models. Using K s = 12 GPa and μ s = 6 GPa from this study, the models give a much better prediction both of experimental velocity reduction due to increase in clay content in sandstones and velocity measurements in a kaolinite-water suspension.
276 citations
TL;DR: Reactive Fe(II) species originating from the reduction of structural Fe(III) in clays may contribute significantly to the biogeochemical cycling of electrons in the subsurface since it is not subject to depletion by reductive dissolution.
Abstract: Mineral-bound Fe(II) species represent important natural reductants of pollutants in the anaerobic subsurface. At clay minerals, three types of Fe(II) species in fundamentally different chemical environments may be present simultaneously, i.e., structural Fe(II), Fe(II) complexed by surface hydroxyl groups, and Fe(II) bound by ion exchange. We investigated the accessibility and reactivity of these three types of Fe(II) species in suspensions of two different clay minerals containing either ferrous iron-bearing nontronite or iron-free hectorite. Nitroaromatic compounds (NACs) exhibiting different sorption behavior on clays were used to probe the reactivity of the various types of reduced iron species. The clay treatment allowed for a preparation of nontronite and hectorite surfaces with Fe(II) adsorbed by surface hydroxyl groups at the edge surfaces. Furthermore, hectorite suspensions with additional Fe(II) bound to the ion exchange sites at the basal siloxane surfaces were set up. We found that both structural Fe(II) and Fe(II) complexed by surface hydroxyl groups of nontronite reduced the NACs to anilines. An electron balance revealed that more than 10% of the total iron in nontronite was reactive Fe(II). Fe(II) bound by ion exchange did not contribute to the observed reduction of NACs. Reversible adsorption of the NACs at the basal siloxane surface of the clays strongly retarded NAC reduction, even in the presence of high concentrations of Fe(II) bound by ion exchange to the basal siloxane surfaces. Our work shows that in natural systems a fraction of the total Fe(II) present on clays may contribute to the pool of highly reactive Fe(II) species in the subsurface. Furthermore, this work may help to distinguish between Fe(II) species of different reactivity regarding pollutant reduction. Although structural iron in clays represents only a small fraction of the total iron pool in soils and aquifers, reactive Fe(II) species originating from the reduction of structural Fe(III) in clays may contribute significantly to the biogeochemical cycling of electrons in the subsurface since it is not subject to depletion by reductive dissolution.
224 citations
TL;DR: In this paper, the sorption and desorption properties of 4,6-dinitro-o-cresol and dichlobenil were investigated using batch-equilibrations and x-ray diffraction (XRD).
Abstract: In soils, organic matter and minerals are often associated such that it is unclear how the presence of the former component influences the sorptive properties of the latter one. In this study, sorption and desorption of the herbicides 4,6-dinitro-o-cresol (C 7 H 6 N 2 O 5 ) and dichlobenil (C 7 H 3 Cl 2 N) by Ca 2+ -, K + -smectites, and humic acid-smectite complexes, was investigated using batch-equilibrations and x-ray diffraction (XRD). Greater sorption of 4,6-dinitro-o-cresol compared with dichlobenil was observed for both smectites and humic acid-smectite complexes. For both pesticides, K + smectites were more effective sorbents than Ca 2+ smectites, with the lower charge-density day (SWy-2) displaying a greater sorption capacity than the higher charge-density day (SAz-1). The presence of humic add did not impact pesticide sorption by K + clays, but could enhance or suppress pesticide sorption by Ca 2+ -clays. A composite model for estimating pesticide sorption, which assumes mineral and organic matter function individually as sorbent phases, predicted sorption within a factor of 0.8 to 1.5 times the measured values. Humic add did not contribute to pesticide desorption hysteresis in K + -humic add-day complexes, but was a source of hysteresis in the corresponding Ca 2+ complexes. The basal spacings of K-SWy-2 and humic add-modified K-SWy-2 increased gradually from approximately 10.4 to 12.2 A with increasing 4,6-dinitro-o-cresol loadings. Also, XRD patterns of humic acid-modified and unmodified K-SWy-2 smectite days were found identical. These results demonstrate the Intercalation of 4,6-dinitro-o-cresol and suggest that humic adds are restricted to the external surfaces of day tactoids. Together, these results indicate that clay mineral fractions in soils, including those with organic coatings, may play an important role in the retention of certain pesticides.
164 citations
TL;DR: Observations indicate that cations take part directly in the formation of nucleic acid-clay complexes, acting as a `bridge' between the negative charges on the mineral surface and those of the phosphate groups of the genetic polymer.
Abstract: Monovalent ([Na+] > 10 mM) and divalent ([Ca2+], [Mg2+] > 10 mM) cations induced the precipitationof nucleic acid molecules In the presence of clay minerals (montmorillonite and kaolinite), there was adsorption instead of precipitation The cation concentration needed for adsorption depended on both the valence of the cations and the chemical nature of the nucleic acid molecules Double-stranded nucleic acids needed higher cation concentrations than single-stranded ones to be adsorbed to the same extent on clay Divalent cations were more efficient than monovalent ones in mediating adsorption Adsorption to the clay occurred only when both nucleic acids and cations were present However, once the complexes were formed, the cations could not be removed from the system by washing, indicating that they are directly involved in the association between nucleic acids and mineral surfacesThese observations indicate that cations take part directly in the formation of nucleic acid-clay complexes, acting as a `bridge' between the negative charges on the mineral surface and those of the phosphate groups of the genetic polymer The relatively low cation concentrations needed for adsorption and the ubiquitous presence of clay minerals in the environment suggest that the adsorption of nucleic acids on mineral surfaces could have taken place in prebiotic habitats This may have played an important role in the formation and preservation of nucleic acids and/or their precursor polymers
163 citations
TL;DR: In this paper, the major impurities in the clay are quartz and siderite, which can be removed at room temperature by using 0.4 M oxalic acid solution, and the iron content of the clay may be reduced further by treating with wet high intensity magnetic separator (WHIMS) or leaching with organic acids.
TL;DR: In this paper, the authors investigated the role of soil-available moisture in the distribution of palygorskite and smectite in the arid and semi-arid areas of southern Iran.
Abstract: The clay mineralogy of soils and of the main calcareous sedimentary parent rocks of southern Iran were investigated to determine their origin and factors controlling their distribution pattern in soils. The results revealed that the soil-available moisture plays the major role in the distribution pattern of palygorskite and smectite clay minerals in the arid and semi-arid areas studied. There is an inverse correlation between palygorskite and smectite with regard to the soil-available moisture as expressed by P/ET° (ratio of mean annual precipitation to mean annual reference crop evapotranspiration). At P/ET° values >0.4 palygorskite transforms to smectite. Smectite is thought to be mainly of ‘transformed’ origin. It is detected in trace amounts in soils of more arid areas and increases in soils having greater available moisture. The general decrease in illite content with depth is related mainly to its transformation to smectite under favourable moisture conditions of the deeper horizons. Palygorskite is considered to be inherited in plateau soils of the arid regions whereas in saline and alkaline soils and soils with high gypsum, it is mainly of authigenic origin. The P/ET° and gypsum content show a significant correlation with the palygorskite content. The occurrence of kaolinite in some soils is due to its inheritance from the surrounding kaolinite-bearing Cretaceous rocks. Illite and chlorite abundance in soils is also largely related to their presence in parent rocks. The rare occurrence of vermiculite in the studied calcareous soils is mainly related to its lower stability under high pH, low Al activity and the presence of large amounts of Si and Mg in soils.
TL;DR: This paper analyzed experimental thermodynamic and X-ray powder diffraction data for smectite and the most common terrestrial zeolite, clinoptilolite to evaluate the state of hydration of these minerals under martian surface conditions.
TL;DR: The results indicate the complex interactive effects adsorption of enzymes to clay particles can have on the availability and capability of hydrolysis, reduction of enzyme reactivity, storage attached to clay particle with changes in transport and distribution, and protection from photodegradation.
Abstract: Enzymes released extracellularly by micro-organisms have major functions in nutrient acquisition and organic matter degradation. Clay particles, common in many surface waters, can modify enzyme activity. Clay minerals are known to form aggregates with organic molecules, and the formation of enzyme-clay complexes could alter the level of activity. Montmorillonite clay and clay extracted from Elledge Lake (Tuscaloosa, Alabama) basin soil were combined with alkaline phosphatase, glucosidase, protease, and xylosidase solutions to assess adsorption and the effect of this adsorption on enzyme activity. Adsorption to Elledge Lake basin clay decreased alkaline phosphatase activity, and adsorption to montmorillonite was observed for all four enzymes with reductions in enzyme activities. Adsorption of substrate onto clay surfaces resulted in a concentration effect and increased enzyme activity associated with the particles. When enzyme-clay complexes were exposed to natural sunlight there was a decrease in enzyme activity, but this decrease was usually not significantly different from the adsorption only treatment. The formation of enzyme-clay complexes may serve to protect the enzymes from natural in situ photodegradation. The results indicate the complex interactive effects adsorption of enzymes to clay particles can have on the availability and capability of hydrolysis – reduction of enzyme reactivity, storage attached to clay particles with changes in transport and distribution, and protection from photodegradation.
TL;DR: In this article, a soil sequence in northern Italy along an elevational gradient ranging from moderate (950 m a.s.l.) to high alpine (2440 m a s.l.).
TL;DR: In this article, X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectroscopy were used in combination to characterize organic carbon structures in a series of wetland soils in Saskatchewan.
TL;DR: In this article, the authors present a dataset including clay mineralogy, gamma-ray spectrometry, organic matter content and magnetic susceptibility of the Hettangian to lowest Sinemurian successions of Dorset and Somerset, southern UK (Blue Lias Formation, Bristol Channel and Wessex basins).
Abstract: We present a dataset including clay mineralogy, gamma-ray spectrometry, organic matter content and magnetic susceptibility of the Hettangian to lowest Sinemurian successions of Dorset and Somerset, southern UK (Blue Lias Formation, Bristol Channel and Wessex basins). In both areas, the clay assemblages comprise predominantly detrital illite, kaolinite and illite/smectite mixed layers. Clays probably originated from the erosion of the Hercynian massifs, the relative proportions of kaolinite and illite being modulated by arid–humid climatic fluctuations. The organic matter (OM) content (types II to IV) ranges up to 12% in both areas. A clear stratigraphical trend in clay mineral assemblages is apparent in Somerset, whereas in Dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long-term evolution. Correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata Zone of the Dorset succession. As expected, the kaolinite/illite ratio correlates with the Th/K ratio deduced from gamma-ray spectrometry. However, significant departures from the correlation occur in OM-rich intervals, suggesting that Th may be partly adsorbed on to OM particles. Surprisingly, high magnetic susceptibility correlates with abundant kaolinite, not with Fe-rich clays, indicating either that kaolinite is accompanied by a soil-inherited magnetisable phase (possibly iron oxide) or that illite-rich rocks are more strongly diluted by carbonate than are kaolinite-rich strata.
TL;DR: In this article, a framework that combines physico-chemical processes with pore scale geometrical, hydrostatic, and hydrodynamic considerations toward prediction of constitutive hydraulic relationships for swelling porous media is proposed.
TL;DR: Sorption of the endocrine-disrupting chemical 17 β -estradiol (E 2 ) from aqueous solutions to goethite, an iron oxide, and the clay minerals kaolinite, illite, and montmorillonite (K and Ca) was measured at 25°C as discussed by the authors.
TL;DR: In this article, a multispecimen simulation of experimental X-ray diffraction (XRD) patterns from mixed-layer minerals, with account taken of layer-thickness fluctuations of the second type and possible difference between structures of outer and core layers, is presented.
Abstract: Different forms of structural and chemical heterogeneity are considered including mixed-layer minerals, disordered layer structures containing rotational and translational stacking faults, interstratification of trans -vacant ( tv ) and cis -vacant ( cv ) layers in true micas, illites and illite-smectite (I-S), short-range order in isomorphous cation distribution etc. Because determination of various structural and chemical imperfections requires elaboration of new diffraction and spectroscopic methodologies, special attention is paid to recent achievements in the development of new methodological approaches such as a multispecimen simulation of experimental X-ray diffraction (XRD) patterns from mixed-layer minerals, with account taken of layer-thickness fluctuations of the second type and possible difference between structures of outer and core layers; experimental determination of thickness distribution of illite crystals by HRTEM and the modified Bertaut-Warren-Averbach technique; XRD and thermal methods for determination of cv and tv layers in true micas, illites and I-S; generalization of Mering’s rules to account for the behaviour of non-basal reflections for any defective structure in which two translations are irregularly interstratified; various ab initio calculations devoted to modelling infrared OH vibrations, octahedral cation distribution in dioctahedral 2:1 layer silicates, etc. It is shown that these recently-developed methodologies have revealed new diversity in the structural and chemical heterogeneity of phyllosilicates and clay minerals, provided new insight into the structural mechanisms of their transformation in different geological environments, and discovered new natural processes.
TL;DR: In this paper, the genesis of weathering products in serpentinitic soils along a moisture regime gradient using conventional x-ray diffraction (XRD) methods and high-resolution transmission electron microscopy (HRTEM) was determined.
Abstract: The origin of secondary phyllosilicates in serpentinitic soils of differing moisture regimes is incompletely understood. The objective of this study was to determine the genesis of weathering products in serpentinitic soils along a moisture regime gradient using conventional x-ray diffraction (XRD) methods and high-resolution transmission electron microscopy (HRTEM), The samples studied were obtained from an Aquic Argixeroll and a Cumulic Endoaquoll on the Trinity ophiolite, in the Klamath Mountains, California. The soils are from backslope and toeslope landscape positions associated with a 3,2-ha wetland on a stabilized landslide bench. Chlorite and serpentine are the major primary minerals in the soils. Chlorite is relatively stable and was found in the clay fraction of all horizons studied. Serpentine was observed in all horizons except the Aquic Argixeroll Cr2 horizon. The soil mineral assemblages indicate that chlorite transforms to vermiculite and both randomly and regularly interstratified chlorite/vermiculite by loss of the hydroxide-interlayer Sheet. The vermiculite then alters to a high-charge smectite that was found only in the lower horizons of the backslope landscape position. Smectite is the predominant secondary mineral in all horizons, Serpentine transformation products could not be directly identified, but the prevalence of a low-charge smectite in the Cumulic Endoaquoll is interpreted as a precipitate from serpentine dissolution products. Thus, the abundant smectite in these serpentinitic soils is of two origins: (i) a high-charge phase derived from chlorite transformation that is found in the backslope landscape positions, and (ii) a low-charge phase neoformed by precipitation of elements released by serpentine weathering.
TL;DR: A study of authigenic clay minerals in sediments from representative depositional environments in the basin (pyroclastic fan, fluvial plain, wetland, lake margin and lake basin) was undertaken to determine whether clay compositions and textures could provide unique geochemical fingerprints characteristic of source area (Plio-Pleistocene trachytic volcanics vs. Precambrian quartzose-feldspathic basement) or paleoenvironmental conditions.
Abstract: Olduvai Gorge, Tanzania (East African Rift) exposes a 100 m thick Plio-Pleistocene sequence of dominantly volcaniclastic sediments deposited in a 50 km wide closed basin containing a playa lake. A scanning transmission electron and analytical electron microscopy (STEM/AEM) study of authigenic clay minerals in sediments from representative depositional environments in the basin (pyroclastic fan, fluvial plain, wetland, lake margin and lake basin) was undertaken to determine whether clay compositions and textures could provide unique geochemical fingerprints characteristic of source area (Plio-Pleistocene trachytic volcanics vs. Precambrian quartzose-feldspathic basement) or paleoenvironmental conditions. Our study shows that compositional signatures obtained by clay minerals during early pedogenesis are inherited from their parent source rocks. Sediments sourced from volcanics contain highly disordered, dioctahedral smectite. Those sourced from Precambrian basement are similar, but are more Al-rich. Subsequent neoformation in the pedogenic (soil) or diagenetic (lake-margin, lake) environments results in the modification of original clay mineralogy, compositions, and textures, and unique paleoenvironmental fingerprints are acquired. Soils developed on the distal pyroclastic fan contain smectite with more Fe(III) and Mg than smectite from the proximal pyroclastic fan sediments. A trend of decreasing Al and increasing Mg content occurs in smectite compositions in samples from the fluvial to lake-margin and lake environments as a result of partial replacement of original dioctahedral Al-rich smectite by neoformed trioctahedral Mg-rich smectite (stevensite). Neoformed celadonite replaces smectite in the most saline lake sediments. The STEM/AEM data collectively indicate that diagenesis in the saline-alkaline lake results in the replacement of Al-rich dioctahedral smectite by Mg-rich trioctahedral smectite (stevensite) and Mg- and Al-rich celadonite. Thus, determination of clay mineral compositions at a basin-wide scale provides a useful tool for interpreting the spatial distribution of depositional and diagenetic environments.
TL;DR: In this article, the adsorption/precipitation properties of a sedimentary humic acid under different conditions of pH and ionic strength in presence of the clay mineral vermiculite were investigated.
TL;DR: In this article, the authors studied the composition and the charge properties of the clays extracted from the weathered B horizon of a perhydrated Andosol developed in andesitic ash in Guadeloupe, French West Indies, by selective dissolution, X-ray diffraction (XRD), thermal analysis and characterization of ion exchange properties.
TL;DR: None of the other clay minerals present in the soils (illite, smectite, kaolinite, hydroxy interlayered clay minerals, chlorite, quartz, microcline, plagioclase) were significant in explaining the Cd distribution coefficient.
Abstract: Cadmium (Cd) distribution between the soil solid phase and the soil solution is a key issue in assessing the environmental effect of Cd in the terrestrial environmental. Previous studies have shown that many individual minerals and other components found in soils can bind Cd, but most studies on whole soil samples have shown that pH is the main parameter controlling the distribution. To identify further the components that are important for Cd binding in soil we measured Cd distribution coefficients (K d ) at two fixed pH values and at low Cd loadings for 49 soils sampled in Denmark. The K d values for Cd ranged from 5 to 3000 L kg -1 . The soils were described pedologically and characterized in detail (22 parameters) including determination of contents of the various minerals in the clay fraction. Correlating parameters were grouped and step-wise regression analysis revealed that the organic carbon content was a significant variable at both pH values. Cation exchange capacity (CEC) and gibbsite were important at the low pH (53) while iron oxides also were important at the high pH (6.7). None of the other clay minerals present in the soils (illite, smectite, kaolinite, hydroxy interlayered clay minerals [HIM], chlorite, quartz, microcline, plagioclase) were significant in explaining the Cd distribution coefficient.
TL;DR: The basement rocks of southern Sweden were deeply weathered in Late Triassic through Cretaceous times, and possibly even earlier as mentioned in this paper, and they showed high detrital smectite and/or kaolinite contents, moderate illite contents, and low chlorite contents.
TL;DR: In this article, a new method for calculation of layer charge and charge distribution of smectites is proposed based on comparisons between X-ray diffraction (XRD) patterns of K-saturated, ethylene glycol-solvated, oriented samples and calculated XRD patterns for three-component, mixed-layer systems for the calculated patterns can be modeled as random interstratifications of fully expanding 171 A layers, partially expanding 135 A layers and nonexpanding 998 A layers.
Abstract: A new method for calculation of layer charge and charge distribution of smectites is proposed The method is based on comparisons between X-ray diffraction (XRD) patterns of K-saturated, ethylene glycol-solvated, oriented samples and calculated XRD patterns for three-component, mixed-layer systems For the calculated patterns it is assumed that the measured patterns can be modeled as random interstratifications of fully expanding 171 A layers, partially expanding 135 A layers and non-expanding 998 A layers The technique was tested using 29 well characterized smectites According to their XRD patterns, smectites were classified as group 1 (low-charge smectites) and group 2 (high-charge smectites) The boundary between the two groups is at a layer charge of −046 equivalents per half unit-cell Low-charge smectites are dominated by 171 A layers, whereas high-charge smectites contain only 20% fully expandable layers on average Smectite properties and industrial applications may be dictated by the proportion of 171 A layers present Non-expanding layers may control the behavior of smectites during weathering, facilitating the formation of illite layers after subsequent cycles of wetting and drying The precision of the method is better than 35% at a layer charge of −050; therefore the method should be useful for basic research and for industrial purposes
TL;DR: In this article, the red smectite clays of Boa-Vista, Paraiba (Brazil) were characterized in their natural form, and after chemical, thermal and acid treatments by X-ray fluorescence, differential thermal analysis, dynamic Xray diffraction, classic X-Ray diffraction analysis, scanning electron microscopy, nitrogen adsorption and model reaction.
Abstract: The original crystalline structure of clay minerals can be altered in a controlled way, through acid or thermal treatments, resulting then in suitable products to be used as catalysts. This paper aims to characterize the red smectite clays of Boa-Vista, Paraiba (Brazil) in their natural form, and after chemical, thermal and acid treatments by X-ray fluorescence, differential thermal analysis, dynamic X-ray diffraction, classic X-ray diffraction analysis, scanning electron microscopy, nitrogen adsorption and model reaction. The results show that acid treatment partially altered the structure of the montimorillonite. An important increase in the surface area of the solid obtained was observed. The obtained reaction for the treated material showed that the clay was more acid than the natural one, yielding a better catalytic activity.
TL;DR: In this paper, the changes in the chemical and mineralogical properties of three acid soils resulting from the application of three industrial by-products (phosphogypsum, red gypsum and sugar foam) were examined.
Abstract: Summary
Lime, mined gypsum and some gypsum-like by-products have been frequently applied to soil to counter acidity We have examined the changes in the chemical and mineralogical properties of three acid soils resulting from the application of three industrial by-products (phosphogypsum, red gypsum and sugar foam) We did so in laboratory experiments on suspensions of soil in saturated solutions of the by-products A sizeable fraction of the Al released by exchange with Ca of the amendments remained on the mineral surfaces as Al polymers, as suggested by changes in the CuCl2-, oxalic–oxalate- and DTPA-extractable Al contents Polymerization of Al was promoted by corresponding neutral and basic pH of red gypsum and sugar foam saturated solutions, respectively Sorption of these Al polymers was particularly favourable in those horizons with more clay fraction and variable-charge clay minerals On the other hand, in most cases there was little or no detectable sorption of sulphate, thus excluding precipitation of crystalline or amorphous basic Al sulphates to alleviate Al toxicity Based on the reduction of the Al saturation of the exchange complex in the soils, as well as on the small contents of heavy metals and natural radionuclides of the three by-products, these can be considered effective alternatives to mined gypsum and lime for alleviating soil acidity and reducing toxic concentrations of Al in agricultural, acid soils
TL;DR: In this paper, chemical reactions between arsenic and several iron hydroxides (goethite, lepidocrocite and green rust) were studied, and it was shown that arsenic was more strongly bound by the iron hydrides than clays.