Smectite-group Minerals Research Articles

Hydrologic regulation of clay-mineral transformations in a redoximorphic soil of subtropical monsoonal China

Abstract Clay-mineral evolution in supergene environments is commonly a complex process subject to hydrologic influences on clay-mineral transformations, yet these influences remain insufficiently investigated to date. A quaternary red soil profile with evident redoximorphic features in subtropical monsoonal China was investigated with a focus on processes of secondary clay-mineral transformation. Evidence provided by soil physical and chemical descriptions, clay-mineral analysis, spectroscopic characterization, extractions of pedogenic Al and Fe species, and geochemical compositions reveals a complex relationship of clay minerals and iron phases to pedogenic weathering conditions as a function of depth in the studied soil profile. The soil profile can be divided into a homogenous horizon (HH; 0–2.0 m), a redoximorphic horizon (RH; 2.0–6.0 m), and a basal layer (BL; 6.0–7.2 m), and these three horizons are dominated by various intermediate clay phases. The HH is characterized by moderately acidic conditions (mean pH = 5.2) and low total organic content (TOC; TOC ≤2.1 g kg–1). More importantly, compared with the lower horizons, the HH contains significantly more active acid-forming cations, as reflected by a greater abundance of Al phases and higher aluminum saturation levels. We infer that the occurrence of hydroxy-interlayered vermiculite (HIV) in the HH is tightly coupled with the nature of the soil acidic pools, which include both H+ ions (i.e., pH) and active acid-forming cations (e.g., Al3+ and Fe3+). The reaction pathway from primary minerals to final weathering products appears to be highly sensitive to dynamic hydrological processes. HIV is favored in generally oxic, well-drained soil systems with adequate acidic cations to maintain acidic weathering. When soils are more waterlogged and the aqueous solution is dominated by base cations, primary minerals tend to transform to smectite group minerals. Therefore, discrete smectite, interstratified illite-smectite (I-S), and interstratified kaolinite-smectite (K-S) were observed only in the RH and BL. We present a novel framework that links clay-mineral transformation pathways to soil hydrological disturbances, providing new insights into understanding the kinetics of water-mineral interactions in natural soil systems.

Determination of layer charge density in expandable phyllosilicates with alkylammonium ions: A combined experimental and theoretical assessment of the method

Layer charge deficit is a key crystal-chemical parameter for the classification and nomenclature of 2:1 phyllosilicates that also controls some of their fundamental properties such as cation exchange capacity, expandability, water content, or rheology. The clay community has thus devoted significant efforts to determine this parameter either from the smectite/vermiculite chemical composition (the structural formula method) or experimentally using the alkylammonium method, that theoretically allows the determination of the mean layer charge density and of its distribution. In the present study density functional theory (DFT) and molecular dynamics (MD) simulations are compared to experimental X-ray diffraction data for a series of synthetic saponites with layer charge ranging from medium-charge smectite to medium-charge vermiculite. Consistency of computed and measured layer-to-layer distances confirms the ability of computational approaches to accurately predict the organization of alkylammonium cations in smectite interlayers. Thermalization of DFT-optimized structure models through MD simulations allows probing possible alternative interlayer configurations such as the electrostatically-favored location of ammonium heads above/below Al-substituted tetrahedra. X-ray diffraction results showed that layer-to-layer distances intermediate between those corresponding to the stable h1, h2, etc. interlayer configurations described in the literature result from the interstratification of different stable configurations. The overall consistency of computational and experimental results confirms also the ability of the alkylammonium method to accurately determine a mean value of layer charge density consistent with smectite structural formula when using the revised equations proposed by Laird et al. (1989). The validity of the method appears however limited to smectite-group minerals [layer charge density ranging from ~0.5 to ≤1.2 per O20(OH)4] most likely owing to the coexistence of both stable “layered” and paraffin-like interlayer configurations for higher values of layer charge. In addition, this consistency challenges the ability of the method to quantitatively describe distributions of layer charge in expandable phyllosilicates even when using the complete series of alkylammonium cations.

Systematics of smectite hydrogen-isotope composition: Structural hydrogen versus adsorbed water

Atmospheric water adsorbed onto clay mineral surfaces, of smectite group minerals in particular, can contaminate hydrogen released from structural hydroxyl groups during hydrogen-isotope analysis. Interlayer cation composition and cation hydration enthalpy, in particular, can affect the magnitude of this excess hydrogen yield and hence the hydrogen isotope composition (δ2H) of smectites. To evaluate this problem, δ2H of different cation-saturated (Ca2+, Na+, K+), dried forms of six smectite standards from the Clay Minerals Society Source Clays were measured using a modified sample drying and on-line High-Temperature-Conversion-Elemental-Analysis (TCEA) Continuous-Flow-Isotope-Ratio-Mass-Spectrometry (CF-IRMS) protocol. More negative interlayer cation hydration enthalpies (Ca2+ > Na+ > K+) led to higher residual adsorbed water contents, which produced poorer δ2H reproducibility for the determination of smectite hydroxyl hydrogen. The lowest adsorbed water contribution and the most reproducible and possibly accurate δ2H for smectite hydroxyl hydrogen was obtained for K-saturated smectites dried for both 4 and 24 h at 220 °C prior to isotopic analysis and transferred to a “Zero-Blank” autosampler in ≤2.5 min. This approach provided the lowest measurement error for hydroxyl δ2H and facilitated much greater sample throughput than classical methods for smectitic clays. This study proposes a protocol for hydroxyl δ2H determination in smectitic clay minerals, and reveals the effect of H-isotope fractionation of adsorbed water during sample preparation.

Styrene removal by surfactant-modified smectite group minerals: Efficiency and factors affecting adsorption/desorption

In this study the styrene adsorption/desorption efficiency by surfactant-modified smectites was evaluated. The materials showed a remarkable styrene uptake at relative humidity (RH) in the range of 40–50% ± 5%. In most cases the uptake was much higher than observed for commonly used activated carbons. The research indicated the importance of specific surface area (SBET) and cation exchange capacity (CEC) of the host minerals. A high SBET was crucial for the montmorillonite material (STx) which also had a high CEC (~68.9 meq/100 g). However, effective adsorbents were also based on beidellite (BId) which had a lower CEC (~37.8 meq/100 g). In this case a lower charge resulted in lower density of intercalated surfactants. This provided more space for styrene and limited the steric effects. The surfactant to CEC ratio close to 1.0 was optimal to achieve the highest adsorption. This was connected to sufficient hydrophobization of mineral surfaces and expansion of the interlayer space. The highest styrene uptake was observed for smectites intercalated with surfactants having a long alkyl chain. A bulky benzyl head group lowered the adsorption efficiency due to steric hindrance. Raman spectroscopy confirmed styrene polymerization after subsequent adsorption/desorption cycles. This led to a significant swelling of the organosmectites attested by XRD and resulted in an increasing styrene uptake in subsequent cycles. However it also inhibited the styrene desorption and the adsorbent regeneration. The research also indicated the negative impact of high humidity (80% ± 5%) which significantly lowered the adsorption by organosmectites and activated carbon. Thus, the application of adsorbents for styrene removal must be accompanied with strict humidity control.

Effect of activation temperature on surface basicity of natural aluminosilicates

Montmorillonite and nontronite are layered aluminosilicates of smectite group minerals widely demanded in many industries owing to their unique physical-chemical and other properties. By thermal activation of raw clays there are variations in their porosity, surface area and physical-chemical properties, including formation and redistribution of surface active site of acid-base or redox character. The aim of present studies included investigation of the effect of thermal activation on the character of distribution and a number of basic sites on the surface of natural layered aluminosilicates by means of the new method of inverse thermoprogrammed desorption of СО2.
 Samples of natural aluminosilicates rich in montmorillonite (Montmorillonite 67%, illite 5%, quartz 5%, feldspars 21%) and nontronite (nontronite 70%, illite 10%, kaolinite 5%, quartz 10%, feldspars 8%) were characterized by XRD, XRF, BET N2 adsorption techniques. To probe surface basicity and determine the number of basic sites a new iTPD-CO2 was used. Prior the iTPD-CO2 measurement 100 mg of a sample was activated at 200, 300, 400oC, then cooled down and loaded with CO2 (3ml/min flow rate of CO2 for30 min). Next, the reactor was flushed by 5 ml/min N2-flow to desorb weakly sorbed CO2. The iTPD-CO2 profiles were recorded within 20-800oC at a 20oC/min heating rate and treated using ChemStation software.
 The experimental profiles of CO2 desorption for Mt and Nt samples observed two temperature regions. Low temperature peaks evolved around 80-90oC for Mt and between 110-127oC for Nt were most likely related to the weak basic sites, whereas high temperature peaks around 510 and 620oC for Mt and above 320oC for Nt testified to stronger ones. The reasoning of the obtained iTPD-profiles was done considering thermal behavior of layered aluminosilicates.
 The total basicity of Nt and Mt samples was 359.2 and 209.9 mmol/g respectively. The 1.6 times higher basicity of Nt was, obviously, caused by its phase and chemical composition and developed surface area and porosity. At higher activation temperatures the number of weak basic sites related to hydroxyl groups of adsorbed water molecules gradually decreased, namely, by 21 times for Mt and by 2.8 times for Nt.
 Dehydroxylation of structural Al-OH, Fe-OH, Mg-OH above 200oC, which becomes irreversible above 300oC, provided formation of residual oxygen atoms and their contribution to population of stronger basic sites. In accordance with thermal behavior of dioctahedral smectites, is assumed that strong basic sites of Mt are trans- and cis-vacant Al-OH groups dehydroxylating correspondingly at ~550 and 650oC. Fe-rich sample of Nt rapidly lost hydroxyls at rather lower temperatures that resulted in more heterogeneous distribution of strong basic sites of varying strength. At higher activation temperatures the ratio of stronger sites number to weak sites increased from 23 to 200 for Mt, whereas for Nt this ratio varied between 54-67 times. In general, total basicity of Mt and Nt decreased by 2.2-2.3 times as a result of their dehydration and dehydroxylation by thermal activation. The normalized values of basicity per unit surface area (BΣ/S, mmol/m2) were 1,5 times higher for Mt surface, testifying to higher occupancy and density of active sites for Mt than that of Nt.

Comparative Compressibility of Smectite Group under Anhydrous and Hydrous Environments.

High-pressure synchrotron X-ray powder diffraction studies of smectite group minerals (beidellite, montmorillonite, and nontronite) reveal comparative volumetric changes in the presence of different fluids, as pressure transmitting media (PTM) of silicone oil and distilled water for anhydrous and hydrous environments at room temperature. Using silicone oil PTM, all minerals show gradual contraction of unit-cell volumes and atomistic interplane distances. They, however, show abrupt collapse near 1.0 GPa under distilled water conditions due to hydrostatic to quasi-hydrostatic environmental changes of water PTM around samples concomitant with the transition from liquid to ICE-VI and ICE-VII. The degrees of volume contractions of beidellite, montmorillonite, and nontronite up to ca. 3 GPa are ca. 6.6%, 8.9%, and 7.5% with bulk moduli of ca. 38(1) GPa, 31(2) GPa, and 26(1) GPa under silicone oil pressure, whereas 13(1) GPa, 13(2) GPa, and 17(2) GPa, and 17(1) GPa, 20(1) GPa, and 21(1) GPa under hydrostatic and quasi-hydrostatic environments before and after 1.50 GPa, respectively.

Characteristics of an Altered Diabase Dike in a Coal Seam: A Case Study from the Datong Coalfield, Shanxi, China

Carboniferous–Permian coal seams in the Datong coalfield are intruded by Mesozoic magmatic dikes and sills. Our observations indicate that these dikes and sills have been seriously altered and have lost their original characteristics. Although this phenomenon has been mentioned in some studies, there is a lack of detailed research on the alteration mechanism. To fill this research gap, six dike samples were collected in this study to analyze their alteration characteristics and mechanisms. Petrographic analysis, scanning electron microscopy, and X-ray diffraction were used to determine the mineralogy of the altered igneous samples. The results suggest that the mineral alteration is associated with severe carbonation and clavization. The carbonation of mafic minerals is due to the release of CO2 generated from the coking of high volatile bituminous coals that may have occurred during the intrusive event. However, labradorite did not react with CO2. The water activity in the coal seam was enhanced by the dikes, and mafic minerals were converted into mixtures of chlorite and smectite group minerals. The water activity is especially high at the edges of the dike. Albite and clay minerals were formed due to the albitization of labradorite. Based on these effects, the dike can be divided into weak alteration, carbonation, and clavization bands. The alteration processes in the coal seam are described in detail in this work, and potential formation mechanisms are suggested.

Experimental constraints on Mg isotope fractionation during clay formation: Implications for the global biogeochemical cycle of Mg

The direction and magnitude of magnesium (Mg) isotope fractionation attendant to the formation of clay minerals is fundamental to the use of Mg isotopes to decipher the biogeochemical cycling of Mg in the critical zone and for the oceanic Mg budget. This study provides experimental data on the Mg fractionation factor for two smectite-group minerals (stevensite and saponite) at temperatures relevant for Earth surface processes. The resultant solids were characterised by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) to confirm the mineralogy and crystallinity of the product. A series of experiments were performed to asses the impact of temperature and pH on isotope fractionation. Bulk solid samples were treated with ammonium chloride to remove exchangeable Mg in order to distinguish the Mg isotopic fractionation between these sites and octahedral sites.All bulk and residual solids were enriched in 24Mg compared to the initial solution and δ26Mg values of the exchangeable pool were lower than, or within error of, the initial solution. Final solutions were either within error of, or enriched in, 26Mg compared to the initial solution, depending on the fraction of Mg removed from solution (fMg). For experiments with small or negligible fMg, increasing the pH resulted in a higher reaction rate and reduced fractionation from the initial solution. This could point to a kinetic effect, but the composition of the residual solid (Mg/(Li+Mg) ratio) was also dependent on pH. The change in the composition was reflected in the wavenumber of the Mg3-OH stretch in FT-IR data, which is a proxy for bond strength, and suggests an equilibrium control. An equilibrium control is further supported by the observation of reduced fractionation compared to the initial solution with increasing temperature. Rayleigh and batch fractionation models were fitted to the data giving fractionation factors of 0.9991 and 0.9990 respectively.We compare our results with existing field and experimental data and suggest that the apparent contradictions surrounding the direction of Mg isotope fractionation into phyllosilicate minerals could be due to the similarity of Mg bond lengths between clay octahedral sites and dissolved Mg. Thus small changes in mineral structure or initial solution conditions may result in a change in bond length sufficient to alter the direction of fractionation, implying that the magnitude and direction of Mg isotope fractionation into clay minerals could be dependent on local field conditions. Alternatively, if the precipitation of secondary clay minerals in the field preferentially incorporates light Mg, as observed in this experimental study, this implies the contribution of carbonate weathering to dissolved Mg fluxes has been underestimated, with major implications for the global biogeochemical cycle of Mg.

Discontinuity Nomenclature and Its Significance in Geotechnics

The trinity of the water-discontinuity-clay is the main cause behind most geotechnical problems involving rock slopes. The water molecule is unique to have a dipole property and is a common reactant in numerous chemical reactions. Discontinuity controls the slope stability. The planarity, continuity, and clay mineral infill are particularly important in the areas where outslope bedding dominates. The shear strength of clay mineral approaches zero upon saturation. The discontinuity nomenclature reduces the volume of the geomodel (GM) works, which comprise geology, hydrogeology, engineering geology, geoenvironment, and the geotechnics over 80%. The smectite-group clay minerals have a unit cell with net negative charge. Hence the water is readily captured by the electrically unbalanced mineral causing it to swell by more than 10% of its dry volume and then its shear strength approaches zero. The outsloping bedding, layering, or the basically imbricated thrust faults in places are the common examples of large-scale landslides. The discontinuity survey with the proposed nomenclature and approach is especially important in locating and orienting linear engineering structures. Consequently, this approach enhances the researchers and designers considerably in conducting projects conveniently in terms of timing, environment, safety/security and the cost.

A joint study in geomorphology, pedology and sedimentology of a Mesoeuropean landscape in the Meseta and Atlas Foreland (NW Morocco). A function of parent lithology, geodynamics and climate

The origin of the landscape spreading across NW Morocco (Meseta, Atlas Mts. Foreland) is geodynamically controlled by two collisional and one extensional regime, while climate changes had only a minor impact on the shaping the landscape. The existing landscape pertains to the series characterized by highly to partially eroded mountain blocks of Paleozoic and Early Mesozoic age which is represented at its best by the relics of the Variscan orogeny resultant in what is called “Mesoeurope”. The Mesoeuropean landscape in Morocco is described by four morphodynamic units.MD 1 (0.4–1.8 Ma/generation 3) has brought about landforms in a fluvial (-alluvial) depositional environment with a strong aeolian influence at its margins. Its drainage patterns feature a moderate to gentle dip of the palaeo-current with a predominantly meandering depositional regime. The major minerals are quartz, calcite, smectite, and smectite-illite mixed-layers (submature landscape).MD 2 (2.0–3.0 Ma/generation 2) involves coastal-marine processes of a microtidal environment. Only quartz warrants mentioning as major constituent (supermature landscape).MD 3 (Neogene/generation 1) is the core zone with extensive planation and chemical weathering which gave rise to amorphous silica and smectite-group minerals (mature landscape).MD 4 (Quaternary/generation 4) encompasses landforms typical of alluvial-fluvial environments evolving under a moderate to strong palaeo-current in the foothills of the Atlas Mts. Aside of quartz, calcite, chlorite, muscovite, illite, and feldspar, labile heavy minerals are as widespread as the calcitic carbocretes. Modern structural disturbances are accountable for the immature landforms and high preservation potential of labile mineral constituents.A morphodynamic comparison between the reference type of “Mesoeurope” and the current morphodynamic type under study in Morocco results into a binary classification scheme encompassing two phases, an older one called phase of planation and a younger one called phase of dissection, a sequence which reflects quiescence and relative stable geodynamic conditions succeeded by a period of tectonic mobility. There is one striking difference between the Moroccan landscape and the reference type in Mid-Europe; the reference type has no equivalent morphodynamic unit which was triggered by the opening of the Atlantic Ocean denoted by the lack of U/Pb data of supergene alteration minerals in the reference log. The most widespread soil types encountered in the Moroccan study sites are vertisols (MD 1, MD3), luvisols (MD 1, MD 2, MD 4) and cambisols. Second in abundance are planosols, which are confined to MD 2 and, locally, arenosol associated with plinthite (MD 1); kastanozem and chernozem (MD 3) are rare members of the topsoil. While the log activity of SiO2 varies in a narrow range, the pH of the meteoric water is considerable wide, from 4.2 to 9.4. The physical-chemical regime suggests a binary subdivision into a more acidic regime (MD1, MD2) in the N and an alkaline one (MD 3, MD4) in the S which goes along with the change in the redox ratios of organic matter (LER/HER) and the climate-zonation.

Transformation of halloysite and kaolinite into beidellite under hydrothermal condition

AbstractUnderstanding clay mineral transformation is of fundamental importance to unraveling geological and environmental processes and to better understanding the unique structure and property of phyllosilicates. To date, two pathways have been identified, i.e., the transformation among 2:1 type clay minerals (e.g., illitization of smectite) and from 2:1 type to 1:1 type (e.g., kaolinization of smectite). However, the transformation of 1:1 to 2:1 type is less commonly observed. In this study, hydrothermal experiments were conducted to investigate the possibility of the transformation of 1:1 type clay minerals (i.e., halloysite and kaolinite) into 2:1 ones (i.e., beidellite). The obtained products were characterized by XRD, TG, FTIR, 27Al and 29Si MAS NMR, and HRTEM. XRD patterns of the hydrothermal products display characteristic basal spacing of smectite group minerals at 1.2–1.3 nm with dramatic decrease/disappearance of the (001) reflection of halloysite and kaolinite. This is consistent with HRTEM observations, in which clay layers with a thickness of 1.2–1.4 nm are observed in all hydrothermal products and the Si/Al ratio determined by EDS analysis is close to that of beidellite. The basal spacing increases to ~1.70 nm upon ethylene glycolation, displaying swelling ability of the resultant minerals. The consumption of surface OH in precursor minerals during the transformation leads to a dramatic decrease of mass loss of dehydroxylation and merging of the well resolved OH stretching vibrations in precursor minerals into one at ca. 3667 cm−1, which is indicative of beidellite. These results demonstrate that both halloysite and kaolinite can be converted to 2:1 beidellite under hydrothermal condition, and the transformation of halloysite is easier than that of kaolinite. Such transformation of 1:1 clay minerals to 2:1 ones could be a new pathway for the transformation of clay minerals in nature. Meanwhile, the substitution of Al3+ for Si4+ is found in all newly formed beidellite, suggesting the chemical composition of the newly formed Si-O tetrahedral sheet is different from the one inherited from the precursor clay minerals. This can well explain the formation of “polar layer” in mixed-layer phyllosilicates. These findings are of high importance for better understanding the transformation among clay minerals and unique structure of mixed-layer phyllosilicates.

Geochemical characteristics of Kırka (Sarıkaya) borate deposit, northwestern Anatolia, Turkey

The Kırka borate deposit was deposited in a Miocene lacustrine basin which is closely associated with volcanic activity which lasted from Paleogene to the beginning of Quaternary. Borate mineralization alternates with claystone, mudstone, tuff and fine-layered limestone and mostly shows a lenticular structure. The mineral paragenesis is composed of borax, tincalconite, ulexite, kurnakovite, probertite, tunellite, colemanite, dolomite, smectite group minerals, illite and some firstly reported minerals for the Kırka deposit including hydrochloroborite, brianroulstonite, hilgardite-4M and searlesite minerals. In comparison to average values of earth crust, concentrations of Cs, Sr, Li, As and Se were significantly enriched with respective rates of 21, 15, 14, 3 and 188 folds. Regarding KY, KS1 and KS2 locations, there are differences in both element abundances and their geochemical tendencies which are attributed to variations in discharge regime and physico-chemical conditions of the depositional environment. Independent behaviour of B2O3 might indicate that boron is not associated with clays and carbonates and, therefore, most part of boron must be derived from volcanic activity (hydrothermal solutions, gases). REE data indicate that the Kırka borate deposit was formed in a sedimentary environment where highly alkaline (high pH) hydrothermal solutions also took part in borate precipitation process.

Radium distribution in anthropogenic soils as a function of soil physicochemical and mineralogical parameters

We investigated the effects of physicochemical and mineralogical compositions of radioactively contaminated podzolic and soddy–meadow soils on the 226Ra distribution in the soil profile. It was shown that the physicochemical compositions of soils depend on the type of contamination and have different effects on the mobility of the radionuclide. The presence of phosphorus and organic matter was shown to reduce 226Ra mobility. The highest Ra content was observed in the fraction <10 µm. The role of the composition of the fine fraction of the anthropogenic soil was evaluated. Relations between 226Ra and organic matter contents in different size fractions are satisfactorily described by the logarithmic function CRa = a + bln(Corg) (R2 = 0.9, p < 0.05). The concentrations of 226Ra and organic matter show a positive correlation with relative percentages of illite- and smectite-group minerals and a negative correlation with chlorites.

Swelling pressure of natural and modified smectite-bearing clay raw materials

Smectite clays, due to their barrier properties and swelling ability, are often applied for waterproofing purposes. A proper value of swelling pressure is one of the parameters, which must be met by the fillers used in hybrid waterproofing materials. The authors determined the swelling pressure of selected clay raw materials in their natural state and after chemical modification. This parameter was measured by the Komine method, as this procedure is more accurate than the standard edometric method. The authors introduced some changes in the method. The samples represent Krakowiec clays (Miocene) and a Triassic clay, collected in active pits of building clays, which are widely exploited in south Poland. The content of the smectite group minerals, determined from the sorption of methylene blue and copper(II) triethylenetetramine, ranges between 15 and 35%. Further characteristics of the clays were obtained with X-ray diffraction, chemical analyses (calcium carbonate content including) and pH measurements. It has been found that the activation of smectite clays with sodium lowers their swelling pressure as water penetrates easier the interlayer spaces of the smectites modified. This is important from the viewpoint of assessing the quality of bentonite fillers.

Removal of selected anions by raw halloysite and smectite clay

The structure of clay minerals is made up from tetrahedral and octahedral sheets, which can be stacked in different ways, forming 1:1, 2:1 and 2:1:1 layers. Halloysite, which belongs to the kaolin group, is composed of 1:1 layers while smectite group minerals exhibit 2:1 dioctahedral layered structure. The most important feature of these minerals is the presence of numerous active centers on their surface and/or in the interlayer space, which allows them to attract and exchange ions from aqueous solutions. These makes them perfect candidates which could be used for the purification of wastewaters from harmful ions (Bhattacharyya & Gupta 2008; Lee & Tiwari 2012). The aim of this work was to examine the sorption capacity of natural halloysite and smectite clay towards P(V), As(V) and Cr(VI). Two samples used in the research came from Polish deposits. Natural halloysite (H) was obtained from Dunino deposit, while smectite clay (SC) was obtained from Belchatow Lignine Mine where it forms an overburden cover. For the both raw samples the XRD patterns and FTIR spectra were collected. The sorption of P(V), As(V) and Cr(VI) was conducted as a function of anions concentration in the range from 0.05 to 50 mmol/L for initial pH 5 in a single-element system. The suspension of H or SC and an adequate solution (solid/solution ratio: 20 g/L) was shaken for 24 h at 25°C. Afterwards the anions concentration in the supernatant solution was measured using colorimetric methods. The P(V) and As(V) concentration was determined with molybdenum blue method, while Cr(VI) concentration was measured with diphenylcarbazide method. The XRD pattern of the H sample showed a basal peak at 7.20 A, which confirms the presence of dehydrated halloysite-(7 A). In turn, the SC exhibited a peak centered at ~12.5 A with an asymmetric profile starting from ~15.0 A. Such reflection suggests the presence of smectite which has both Na + and Ca 2+ cations in its interlayer space. The peaks at 4.26 A and 3.34 A are associated with quartz. The IR spectra of the H showed bands characteristic for kaolin group minerals related to the OH-stretching region (3700-3620 cm -1 ), vibrations of water molecules (~1630 cm -1 ) and bands assigned to stretching and bending vibrations of aluminosilicate framework (1200-400 cm -1 ). The IR spectrum of SC shows bands characteristic for smectite minerals i.e. 3623 cm -1 band attributed to OH hydroxyl located inside the 2:1 layer and a broad band centered at ~3400 cm -1 due to interlayer water surrounding cations. Also the structural vibrations of the 2:1 layer may be observed in the 1200-400 cm -1 region. The results of the experiment indicated that the sorption capacity of the H sample and the SC sample were relatively high. The amount of removed P(V) was the highest for both materials, where the sorption was respectively equal to: 201 and 256 mmol/kg. The sorption capacity of As(V) for the H was equal to 168 mmol/kg, while it was significantly lower on the SC (96 mmol/kg). In the case of H the Cr(VI) sorption reached only 36 mmol/kg and for the SC it was equal to 104 mmol/kg. In most cases the sorption isotherms were fitted to the Freundlich model. The only exception was for P(V) sorption on the H sample, which was better described by Langmuir model. The specific surface areas (S BET ) of the studied materials do not differ significantly: SC = 69.10 m 2 /g and H = 49.52 m 2 /g. The sorption centers that may attract anions in both, H and SC samples, were limited, because isomorphic substitutions in tetrahedral and/or octahedral sheets generate positively charged sites, which attract cations. It is believed that the mechanism responsible for the adsorption of anions on both materials is mainly surface complexation, which occurs at the crystals edges (Bradl 2004). The sorption capacity of the H and the SC was significantly lower than that reported for hydrotalcite-based anion-exchange materials (HTLc). For comparison, the sorption capacity towards P(V), As(V) and Cr(VI) on uncalcined HTLc was as follows: 498 mmol/kg (Kuzawa et al. 2006), 596 mmol/kg (Wu et al. 2013) and 314 mmol/kg (Alvarez-Ayuso & Nugteren 2005). Nevertheless, the examined mineral samples might be useful as sorbents for industrial wastewater treatment involving the removal of P(V) and As(V).

Expansion Behavior of Octadecylammonium-Exchanged Low- to High-Charge Reference Smectite-Group Minerals as Revealed by High-Resolution Transmission Electron Microscopy on Ultrathin Sections

AbstractUltrathin sections of reference 2:1 layer silicates treated with octadecylammonium cations were examined using high-resolution transmission electron microscopy (HRTEM) to establish the layer structure. Hitherto, few HRTEM ultrathin-section data existed on the expansion behavior of smectite-group minerals with different interlayer-charge values. Without such information, the expansion behavior of both low-charge and high-charge smectite minerals cannot be characterized and the structures observed in HRTEM images of clay-mineral mixtures cannot be interpreted reliably. Reference smectite-group minerals (Upton, Wyoming low-charge montmorillonite; Otay, California high-charge montmorillonite; a synthetic fluorohectorite; and a Jeanne d’Arc Basin offshore Newfoundland clay sample) with a range of layer charge values were examined. To prevent possible intrusion of epoxy resin into interlayers during embedding, the clay samples were first embedded in epoxy, sectioned with an ultra microtome, and then treated with octadecylammonium cations before examination using HRTEM. Lattice-fringe images showed that lower-charge (&lt;0.38 eq/O10(OH)2) 2:1 layers had 13–14 Å spacings, whereas higher-charge (&gt;0.38 eq/O10(OH)2) 2:1 layers had 21 and 45 Å spacings. These differently expanded silicate layers can occur within the same crystal and an alternation of these layer types can generate rectorite-like structures. For comparison, clay samples were also treated with octadecylammonium before epoxy embedding and sectioning and then examined with HRTEM. These samples mostly had highly expanded interlayers due to epoxy intrusion in the interlayer space. The reference clay minerals embedded in epoxy resin, sectioned, and treated with octadecylammonium cations were used to characterize smectite-group minerals in a natural clay sample from the Jeanne d’Arc Basin, Eastern Canada. Smectite-group minerals in this sample revealed similar structures in lattice-fringe images to those observed in the pure reference clay samples. Rectorite-like structures observed in lattice-fringe images were in fact smectite crystals with short, alternating sequences of low-charge and high-charge smectite layers rather than illite-smectite (I-S) phases with expanded smectite layers and non-expanded 10 Å illite layers.

Ecological Binding Material of First Generation

Abstract Bentonite is clay rock, which is created by decomposition of vulcanic glass. It is formed from mixture of clay minerals of smectite group, mainly montmorillonite, beidellite and nontronite. Its typical characteristics is, that when in contact with water, it intensively swells. First who used this term was W.C. Knight in 1887. The rock had been named after town Fort Benton in American state Montana. For its interesting technological properties and whiteness has wide technological use. Bentonite is selectively mined and according to its final use separately modified, which results in high quality product with specific parameters. In the beginning of 21st century belong bentonite moulding mixtures in foundry to always perspective. Mainly increased ratio of ductile cast iron castings production cannot be ensured without the need of quality bentonite. Great area of scope remains to further research of moulding materials, which return also to bentonite producers.

The Interaction Between Bentonite and Water Vapor. I: Examination of Physical and Chemical Properties

AbstractThe influence of water vapor on bentonites or smectites is of interest in many different fields of applied mineralogy such as nuclear-waste sealing or casting in the foundry industry. The water vapor affects the smectite surface and perhaps its structure probably leading to mostly unfavorable changes in its properties. In this first part of the present study, the influence of hot water vapor (200°C) on the physicochemical and mineralogical properties of smectite-group minerals was studied. After the steam treatment, turbidity measurements, methylene-blue sorption, water adsorption, and cation exchange capacity (CEC) were measured on both untreated and treated samples. Mineralogical changes were monitored by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) was used to measure O, Al, and Si. Only a few parameters showed differences between the untreated and vapor-treated samples. Sedimentation volumes (SV) decreased following the treatment. As shown by XRD and XPS, the crystalline structure of smectite remained unaffected by the steam treatment. Equivalent sphere diameters (ESD) were not affected systematically by the steam treatment. Differences in CEC values between untreated and treated samples were observed, but only for smectites with monovalent interlayer cations. From the variety of different measurements the conclusion of the present study was that steam treatment changes the charge properties at or near the smectite particle surface.

Radiocesium interception potential (RIP) of smectite and kaolin reference minerals containing illite (micaceous mineral) as impurity

Cesium-137 (137Cs) is strongly adsorbed on clay minerals, especially on illite. The adsorption of Cs+ on reference clay minerals, however, has not been fully investigated in relation to the presence of illite. The objective of this study was to clarify the effect of impurities (i.e., illite and vermiculite), present in reference smectite group minerals and kaolin minerals, on the retention of Cs+. The clay mineralogy of the reference minerals was characterized by X-ray diffraction (XRD). The radiocesium interception potential (RIP) was measured as an index of the Cs+ retention ability of clays. The content of illite in clay was represented by the total potassium (K) content given that illite is a major source of K in the clay fraction. The content of vermiculite in clay was represented by the Cs fixation capacity induced by Cs saturation followed by heating of samples at 110°C. Metabentonite and beidellite gave extremely high RIP values compared with other smectite group minerals, although a peak for illite (at 1.0 nm) was not observed in XRD analysis. The reference smectite and kaolin minerals showed a range of RIP values, even though their RIP values are theoretically zero. The RIP values had a significant positive correlation with the total K content of all the reference clay minerals (rs = 0.621*). This indicated that the retention ability for 137Cs depended more on the content of illite, as impurity, rather than the type of bulk mineral. Hence, the contribution of illite to the magnitude of the RIP was elucidated by the combination of measurement of total K content and XRD analysis.

The Influence of Oxalate-Promoted Growth of Saponite and Talc Crystals on Rectorite: Testing the Intercalation-Synthesis Hypothesis of 2:1 Layer Silicates

AbstractThe intercalating growth of new silicate layers or metal hydroxide layers in the interlayer space of other clay minerals is known from various mixed-layer clay minerals such as illite-smectite (I-S), chlorite-vermiculite, and mica-vermiculite. In a recent study, the present authors proposed that smectite-group minerals can be synthesized from solution as new 2:1 silicate layers within the low-charge interlayers of rectorite. That study showed how oxalate catalyzes the crystallization of saponite from a silicate gel at low temperatures (60ºC) and ambient pressure. As an extension of this work the aim of the present study was to test the claim that new 2:1 silicate layers can be synthesized as new intercalating layers in the low-charge interlayers of rectorite and whether oxalate could promote such an intercalation synthesis. Two experiments were conducted at 60ºC and atmospheric pressure. First, disodium oxalate solution was added to a suspension of rectorite in order to investigate the effects that oxalate anions have on the structure of rectorite. In a second experiment, silicate gel of saponitic composition (calculated interlayer charge -0.33 eq/O10(OH)2) was mixed with a suspension of rectorite and incubated in disodium oxalate solution. The synthesis products were extracted after 3 months and analyzed by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The treatment of ultrathin sections with octadecylammonium (nC =18) cations revealed the presence of 2:1 layer silicates with different interlayer charges that grew from the silicate gel. The oxalate-promoted nucleation of saponite and talc crystallites on the rectorite led to the alteration and ultimately to the destruction of the rectorite structure. The change was documented in HRTEM lattice-fringe images. The crystallization of new 2:1 layer silicates also occurred within the expandable interlayers of rectorite but not as new 2:1 silicate layers parallel to the previous 2:1 silicate layers. Instead, they grew independently of any orientation predetermined by the rectorite crystal substrate and their crystallization was responsible for the destruction of the rectorite structure.