Crystallization Of Clay Minerals Research Articles

Swelling of compacted bentonite in organic solvents: Correlation of rate and extent of swelling with solvent properties

The swelling of clay minerals within shale formations during oil and gas exploration, and within compacted bentonite barriers for radioactive waste containment, presents a number of challenges to operators. Whilst much work has been devoted to understanding the interlayer swelling properties of clay mineral crystals, significantly less has been devoted to understanding coupled pore and interlayer swelling in reactive shale/compacted clay minerals. Here we study the swelling of compacted clay mineral tablets on exposure to a range of organic solvents, selected so that the effect of key solvent properties such as dielectric constant, density, octanol-water partition coefficient, viscosity and surface tension can be correlated with the swelling observed. We use a novel non-contact swelling meter to carry out the swelling tests, allowing us to access information on rate of swelling. Short-term swelling rate showed the strongest correlation to the solvent octanol-water partition coefficient. In long term swelling, good correlation was found between total linear swelling and viscosity, and the octanol-water partition coefficient.

A double structure model for hydro-mechano-chemical behavior of expansive soils based on the surface phenomena of mineral crystals

It is well known that the typical swelling behavior of expansive soils is mainly caused by the nanoscale electrochemical phenomena on the surface of their main constituent mineral (i.e., smectite). In this study, the hydro-mechano-chemical (HMC) model for unsaturated expansive soils, which combines the macroscale soil skeleton behavior and the nanoscale interlaminar behavior of mineral crystals based on the surface phenomena is proposed within a double structure framework. The soil skeleton behavior is modeled using the Cam clay type model based on Bishop's effective stress, which considers the degree of saturation-induced hardening. Thus, it is capable of describing hydraulic collapse. Furthermore, the interlaminar behavior is demonstrated through the interlaminar force equilibrium of clay mineral crystals. To describe the swelling process during wetting, namely the crystalline and osmotic swellings, the hydration and osmotic forces acting on the mineral crystals are related to the degree of saturation. Through simulations of a series of the suction-controlled oedometer tests and the swelling pressure tests with various solutions for FEBEX bentonite, it is indicated that the proposed model demonstrates that it can comprehensively describe the typical HMC behavior of expansive soils.

Effect of the surface hydration of clay minerals on the adsorption of cesium and strontium from dilute solutions

The use of clay minerals for the decontamination of liquid radioactive waste generated during the work of nuclear energy enterprises remains currently relevant. The effect of the surface hydration of a montmorillonite nanocrystal on the adsorption of cesium and strontium ions from dilute solutions was studied. As opposed to the generally accepted mechanism of the adsorption of cesium and strontium ions on active sites of clay mineral crystals, we considered the adsorption of radiocesium and radiostrontium by montmorillonite taking into account its colloidal chemical properties. When montmorillonite nanocrystals interact with water, a double electric layer with a mobile diffuse ionic atmosphere forms on the surface of the solid phase. The adsorption of cesium and strontium ions from dilute aqueous solutions confines itself to ion-exchange reactions of cesium and strontium ions of a dispersion medium with exchange cations of the diffuse ionic atmosphere of montmorillonite. Enhanced adsorption of cesium ions compared with strontium ions was explained by low charge density on the outer shell of cesium ions and the ability of cesium ions to overcome the diffuse ionic atmosphere easily and to be fixed firmly on the outer surface of the montmorillonite nanocrystal.

A method for extending a general constitutive model to consider the electro‐chemo‐mechanical phenomena of mineral crystals in expansive soils

SummaryThe mechanical behavior of expansive soils varies according to the chemical composition of the pore fluid. It is well known that electrochemical phenomena on the surface of clay mineral crystals considerably affect their macrostructural behavior. In particular, a change in the pore fluid composition causes osmotic consolidation or swelling. In this study, a model is constructed to describe the characteristic behavior of expansive soils by coupling the interlaminar behavior of clay mineral crystals and the soil skeleton behavior. The interlaminar behavior is derived from the electro‐chemo‐mechanical coupling equilibrium of mineral crystals, and the soil skeleton behavior is given by a general elastoplastic constitutive model for soils. This modeling approach extends a general model to consider the electro‐chemo‐mechanical phenomena of mineral crystals. Oedometer tests with the replacement of the cell fluid and the swelling pressure and deformation tests on expansive clays are simulated with the proposed model. The simulation results indicate that the proposed method can reasonably represent the typical behavior of expansive soils.

Swelling Curve in Terms of Effective Stress for Expansive Clays

Expansive soils can present an unsaturated state where the soil exhibits volume changes due to both moisture variations that change the state of stresses and moisture variations that interact with its mineralogical characteristics. These special kinds of soils are normally clay type soils that had suffered isomorphous substitution creating a charge imbalance of the clay mineral crystals. This imbalance promotes the trapping of water molecules by the clay particles. It is commonly assumed that a high plasticity index can be an indication of a clay´s high swell potential. However, in arid regions, it is possible to have clays with very high swell potential and low plasticity indexes due primarily to a decrease in the state of effective stress, which will produce expansion of the material. It is common practice to study the swelling characteristics of these soils by performing free-swell tests that can be used for designing removal and replacement backfills or drilled shafts. However, the expansion percentage obtained from this type of test is actually in terms of total stresses and not in terms of effective stress, as it is commonly assumed. Moreover, it is highly dependent on the magnitude of the preload used. This paper presents some efforts made to obtain the swelling part of the curve in terms of effective stresses from the traditional free-swell test. It was hypothesized that the shape of this curve could either have the shape of the rebound curve from a saturated consolidation test or a shape similar to the soil-water characteristic curve.

The degradation of organic compounds impacts the crystallization of clay minerals and vice versa

Expanding our capabilities to unambiguously identify ancient traces of life in ancient rocks requires laboratory experiments to better constrain the evolution of biomolecules during advanced fossilization processes. Here, we submitted RNA to hydrothermal conditions in the presence of a gel of Al-smectite stoichiometry at 200 °C for 20 days. NMR and STXM-XANES investigations revealed that the organic fraction of the residues is no longer RNA, nor the quite homogeneous aromatic-rich residue obtained in the absence of clays, but rather consists of particles of various chemical composition including amide-rich compounds. Rather than the pure clays obtained in the absence of RNA, electron microscopy (SEM and TEM) and diffraction (XRD) data showed that the mineralogy of the experimental residues includes amorphous silica and aluminosilicates mixed together with nanoscales phosphates and clay minerals. In addition to the influence of clay minerals on the degradation of organic compounds, these results evidence the influence of the presence of organic compounds on the nature of the mineral assemblage, highlighting the importance of fine-scale mineralogical investigations when discussing the nature/origin of organo-mineral microstructures found in ancient rocks.

Experimental and analytical investigations of volume change behaviour of saturated expansive soils in oedometer test

The chemical and mechanical behaviours of saturated bentonite were experimentally and analytically investigated. A series of oedometer tests on saturated bentonite was conducted. By replacing the cell fluid during the oedometer test, one-dimensional osmotic consolidation and swelling behaviour were observed. The experimental results were simulated numerically using a constitutive model by considering the influence of electrochemical phenomena of clay mineral crystals on the macrostructural behaviour. It was concluded that the typical mechanical swellability of water-saturated bentonite in oedometer test is affected by a positive dilatancy behaviour due to the lower shear strength. After the osmotic consolidation test, a lateral contraction of the specimen in the oedometer was observed; this affected the compressibility during the subsequent mechanical consolidation. It was also concluded that the concentration of Na+ in the pore fluid affects the specific mechanical properties of bentonite.

The Lanthanide Tetrad Effect in Argillic Alteration: An Example from the Jizvan District, Northern Iran

AbstractIntrusion of quartz‐monzodioritic igneous bodies of Oligocene age into Eocene lithic crystal tuffs and trachy‐basalts resulted in the occurrence of a widespread argillic alteration zone in the Jizvan district (northern Iran). Mineralogically, the argillic alteration zone includes minerals such as kaolinite, quartz, smectite, pyrophyllite, muscovite‐illite, alunite, rutile, calcite, feldspar, chlorite, hematite and goethite. Therefore, the non‐CHARAC behaviour for trace elements in the argillic samples is reflected in the non‐chondritic Y/Ho and Zr/Hf ratios and the irregular REE patterns, which appear related to the tetrad effect phenomenon. The chondrite‐normalized REE distribution patterns indicate both concave (W‐shaped) and convex (M‐shaped) tetrad effects in the argillic samples. Based on the field evidence and the results from geochemical studies, it can be concluded that the samples from the argillic alteration zone having high fourth tetrad effect values (>0.30) were developed in the fault and breccia zones. The results indicate that factors such as preferential scavenging by Mn‐oxides, crystallization of clay minerals, fluid‐rock interaction, overprint of hypogene mineral assemblage by supergene ones, and the structural control, have all played an important role in the occurrence of tetrad effects in samples of the argillic zone in the Jizvan district.

Shale reservoir characterization and control factors on gas accumulation of the Lower Cambrian Niutitang shale, Sichuan Basin, South China

The Lower Cambrian Niutitang shale is reported to be the oldest strata for large‐scale shale gas reserves. Based on outcrop observations and laboratory analyses, this study used a comprehensive approach that integrated sedimentology, mineralogy, petrology, organic geochemistry, and reservoir geology to estimate the prospects for exploring for shale gas in the Lower Cambrian Niutitang Formation, southern China. Whole rock and clay mineral X‐ray diffraction, scanning electron microscope (SEM) observations, and petro‐physical property measurements indicate that the Niutitang shale is dominated by quartz and clay minerals with minor amounts of plagioclase, potassium feldspar, calcite, dolomite, and pyrite. The organic matter in the Niutitang shale is dominated by type‐1 kerogen, with TOC levels ranging from 1.35% to 14.3% (average 4.46%) and Ro values ranging from 1.86% to 4.18% (average 2.79%). The three primary types of pores in the shale are organic pores, microfractures, and micropores. The micropores are primarily found in the clay mineral crystals and pyrite, and the microfractures are found along the boundaries of quartz grains. Most of the pore diameters are less than 20 nm, mainly concentrate at about 10 nm, which is consistent with that the organic pores act as the main storage space. The pore volume and gas content are strongly controlled by the mineral composition and lithofacies, and TOC content. The factors favouring shale gas accumulation of the Niutitang shale in the study area include (1) an effective thickness and widespread distribution, (2) a high organic carbon content and appropriate organic matter maturity, and (3) a favourable depositional environment.

Characterizing fluids associated with the McArthur River U deposit, Canada, based on tourmaline trace element and stable (B, H) isotope compositions

The origin and nature of fluids responsible for U deposits of the Athabasca Basin have been in debate. This study presents the trace element abundances and stable isotope ratios (D/H and 11B/10B) of well characterized tourmaline samples determined by in situ analytical techniques, in order to evaluate the nature of fluids during the mineralization of the McArthur River U deposit, the world's largest high-grade U deposit. Magnesio-foitite, an alkali-deficient Mg-rich tourmaline, is abundant along the 13-km long P2 fault, a reverse structure that controls the location of the McArthur River deposit. Magnesio-foitite contains variable concentrations of rare earth elements (REEs, up to 46ppm in total) and Y (up to 35ppm). Chondrite normalized patterns indicate low light REEs (LREEs) relative to heavy REEs (HREEs) (CeN<YN, Y as a proxy for HREEs) and slight negative Eu anomalies, similar to those of uraninite from the deposit. The data combined with textural evidence suggest that magnesio-foitite and uraninite co-crystallized with LREE-rich aluminum phosphate sulfate minerals. Relatively high REE contents of magnesio-foitite in the ore zone indicates the incursion of a REE-rich basement fluid. Low values of δD (−98 to −41‰) for magnesio-foitite suggests that the mineralizing fluid originated from groundwater. Variably high values of δ11B (+13.1 to +23.2‰) are explained by the dissolution of B from carbonate or evaporitic rocks and preferential removal of 10B by the crystallization of illite and kaolinite. The results of this study support the ascent of a REE-rich basement fluid during mineralization and extensive modification of basinal fluids through the crystallization of clay minerals.

Catalyzed Synthesis of Zinc Clays by Prebiotic Central Metabolites

How primordial metabolic networks such as the reverse tricarboxylic acid (rTCA) cycle and clay mineral catalysts coevolved remains a mystery in the puzzle to understand the origin of life. While prebiotic reactions from the rTCA cycle were accomplished via photochemistry on semiconductor minerals, the synthesis of clays was demonstrated at low temperature and ambient pressure catalyzed by oxalate. Herein, the crystallization of clay minerals is catalyzed by succinate, an example of a photoproduced intermediate from central metabolism. The experiments connect the synthesis of sauconite, a model for clay minerals, to prebiotic photochemistry. We report the temperature, pH, and concentration dependence on succinate for the synthesis of sauconite identifying new mechanisms of clay formation in surface environments of rocky planets. The work demonstrates that seeding induces nucleation at low temperatures accelerating the crystallization process. Cryogenic and conventional transmission electron microscopies, X-ray diffraction, diffuse reflectance Fourier transformed infrared spectroscopy, and measurements of total surface area are used to build a three-dimensional representation of the clay. These results suggest the coevolution of clay minerals and early metabolites in our planet could have been facilitated by sunlight photochemistry, which played a significant role in the complex interplay between rocks and life over geological time.

Formation of Replicating Saponite from a Gel in the Presence of Oxalate: Implications for the Formation of Clay Minerals in Carbonaceous Chondrites and the Origin of Life

The potential role of clay minerals in the abiotic origin of life has been the subject of ongoing debate for the past several decades. At issue are the clay minerals found in a class of meteorites known as carbonaceous chondrites. These clay minerals are the product of aqueous alteration of anhydrous mineral phases, such as olivine and orthopyroxene, that are often present in the chondrules. Moreover, there is a strong correlation in the occurrence of clay minerals and the presence of polar organic molecules. It has been shown in laboratory experiments at low temperature and ambient pressure that polar organic molecules, such as the oxalate found in meteorites, can catalyze the crystallization of clay minerals. In this study, we show that oxalate is a robust catalyst in the crystallization of saponite, an Al- and Mg-rich, trioctahedral 2:1 layer silicate, from a silicate gel at 60°C and ambient pressure. High-resolution transmission electron microscopy analysis of the saponite treated with octadecylammonium (n(C)=18) cations revealed the presence of 2:1 layer structures that have variable interlayer charge. The crystallization of these differently charged 2:1 layer silicates most likely occurred independently. The fact that 2:1 layer silicates with variable charge formed in the same gel has implications for our understanding of the origin of life, as these 2:1 clay minerals most likely replicate by a mechanism of template-catalyzed polymerization and transmit the charge distribution from layer to layer. If polar organic molecules like oxalate can catalyze the formation of clay-mineral crystals, which in turn promote clay microenvironments and provide abundant adsorption sites for other organic molecules present in solution, the interaction among these adsorbed molecules could lead to the polymerization of more complex organic molecules like RNA from nucleotides on early Earth.

Minerological and O-isotope studies of diagenesis and porewater evolution in continental sandstones, Cretaceous Belly River Group, Alberta, Canada

The mineralogy and O-isotope geochemistry of diagenetic phases from continental sandstones of the Upper Cretaceous Belly River Group, west-central and south-western Alberta, have been determined. Diagenesis of the continental sandstones is dominated by crystallization of clay minerals, including Fe-rich chlorite (δ 18O = +3.3 to +9.3‰), I/S, C/S and illite (δ 18O= +9.5 to + 10.7‰), kaolinite (δ 18O = +5.9 to +12.7‰), S/I and smectite (δ 18O = +11.0 to 14.0‰). Other diagenetic phases include quartz overgrowths (δ 18O = +12.0 to +21.0‰) and calcite (δ 18O = +8.5 to +12.9‰; δ 13C = #x02212;14.3 to −2.0‰). Chlorite generally crystallized first in the paragenetic sequence, followed by quartz, I/S, calcite and kaolinite, and then S/I and smectite. Interpretation of these data suggests that early diagenesis occurred in the presence of low- 18O meteoric water whose δ 18O value rose moderately during subsequent burial. Highest burial temperatures (≈110°C) were probably achieved in the south-western portion of the study area, and are reflected by the appearance of R1-ordered I/S in this locality. Post-Laramide influx of meteoric water subsequently resulted in a substantially lower porewater δ 18O value. Values of δ 18O for diagenetic minerals from the continental sandstones and immediately underlying deltaic and shoreline, basal sandstones are systematically lower (by +1 to +6‰) than equivalent phases from the Lower Cretaceous marine sandstones of the Viking Formation. Relative differences in the oxygen isotopic compositions of connate waters (freshwater vs sea water) have been preserved, surviving δ 18O-enrichment during burial and δ 18O-depletion during post-Laramide influx of meteoric water. While substantial meteoric dilution of the porewater has occurred, flushing of (evolved) connate waters has not been complete.

Subplasticity in Australian soils. V. Factors involved and techniques of dispersion

The subplastic soils studied were two from the Riverina area of New South Wales, two montmorillonite rich clays formed on basalt, from South Australia and Queensland, and a krasnozem from New South Wales. To assess the effectiveness of physical and chemical methods of dispersion, theoretical clay contents were calculated from the ratio of the CEC of the soil to that of separated clay. The composition of the clay from the soils showed little or no change with degree of dispersion. To disperse the soils without chemical pretreatment, a method of disaggregation was devised that involved vigorous shaking of a soil paste. Following this technique the Riverina soils and the krasnozem yielded almost all their clay. Lithium saturation was the only chemical treatment that aided dispersion of the montmorillonite clays, and this, together with the high tetrahedral lattice charge, suggests that aggregate stability is mainly due to a large electrostatic interaction between clay sheets. Any pretreatments involving the use of sodium hydroxide improved clay yields for the Riverina soils. The data indicated that the loss of subplasticity was accompanied by the solution of clay, suggesting that aggregate stability was due to non-ionic bonds between clay particles, possibly as the result of intergrowth of clay mineral crystals. Organic matter and/or free iron oxide was responsible for cementation of the krasnozem.

Crystallochemistry of clay minerals and their properties

Experimental studies on a series of three-layer minerals (pyrophyllite, montmorillonite, hydromica, biotite) have shown the dependence of intercrystalline swelling in these minerals on the degree and localization of isomorphic substitutions in the crystals. With the increase of the magnitude of isomorphic substitutions, the degree of intercrystalline swelling will at first rise and then decline. It has also been shown that the increase of isomorphic substitutions in the tetrahedral layer raises the non-exchangeable K+ ion content in these minerals and lowers their swelling capacity. Measurements of clay particle orientation in electrostatic field at different pH values of the medium indicate that the edges of clay mineral crystals have a positive charge in the acid medium and a negative charge in the alkaline medium, which confirms the views previously expressed by Van Olphen, Schofield and Samson. The data obtained suggest that in the acid medium the basal surfaces and the edges of clay mineral particles have an opposite double electric layer. These observations make it possible to explain a number of structural-mechanical features of clays and thus to get a more comprehensive understanding of the nature of their strength.

Chemical Weathering of Biotite-Plagioclase Gneiss

AbstractThe weathering of biotite-plagioclase gneiss was studied in a warm humid climate under good drainage conditions, in De Kalb County, Georgia. A series of samples ranging from completely weathered to fresh rock were studied. The degree of weathering was determined by bulk specific gravity and abrasion pH of samples in various stages of decomposition. Quantitative determination of clay minerals was done by DTA. Results show that the stable products of andesine weathering are kaolinite and endellite, and that biotite weathers to a mixture of amesite and kaolinite. There is no volume change in the gneiss as it weathers from fresh rock with a bulk specific gravity of 2.78 to a completely friable saprolite with a bulk specific gravity of 1.4. The weathering is accompanied by an increase in kaolin minerals from zero to about 35 per cent. The process involves the solution of plagioclase and biotite with approximately simultaneous crystallization of clay minerals and hydrated oxides of aluminum and iron.

Decomposition of clays and the fate of aluminum

Processes that may be important during the weathering of clay minerals in soils or other geologic materials occur under laboratory conditions. These are: 1) the movement of Al ions from clay lattice positions to ion-exchange sites; 2) the hydrolysis of Al ions in clay systems with the deposition of Al(OH) 3 , or the sorption of hydroxy-aluminum ions. The first reaction proceeds under conditions of acid weathering when metal ions such as Ca, Mg, or K are displaced by H ions. Its rate is much accelerated by increase in temperature. The hydrolysis of Al ions, which may occur either in solution or on change sites, produces H ions that can cause further clay decomposition. It is suggested that the 2 processes operating together can provide a reaction mechanism that removes Al from coordination positions in clay mineral crystals and deposits it as a hydrous oxide. Under conditions where silica is removed by leaching or crystallization as secondary quartz such a reaction could lead to the conversion of alumino-silicate clay into aluminum oxides.

Diffraction intensities from bent crystals

Simple expressions are derived for the diffraction intensities given by coherently diffracting regions of a crystal in which the lattice is elastically bent, on the assumption that the amount of bending within such a region is small. Evidence is provided that under normal experimental conditions the geometric coherence of the incident radiation is usually such that coherent diffraction cannot take place between atoms more than a few hundred ~ngstrSm units apart, and the assumption of small amounts of bending in the coherently diffracting region gives a good approximation even for highly bent clay-mineral crystals. The profiles of the broad hit bands observed in X-ray powder patterns of metahalloysite were calculated. The assumption that the crystallites are bent about a single axis improved the agreement with the measurements of Brindley & Robinson (1948). I t is shown that some results obtained in electron-diffraction structure analyses of single crystals may be explained on the assumption of very small amounts of bending and that such an assumption may provide an explanation for the apparent discrepancy between theoretical prediction and experimental evidence on the range of application of electron-diffraction structure-analysis methods for both polycrystalline and single-crystal samples.