Microstructure Of Clay Research Articles

Mathematical Modeling of Sorptive Extraction of Lithium Chloride from Lithium-containing Brine of the Aral Sea Region

Introduction The article presents the results of chemical and physicochemical analysis of initial lithium-containing hydromineral raw materials and sorbent based on bentonite clay with titanium oxide addition. Methods It is established that the mineral is montmorillonite group and kaolinite according to the results of the analysis of the microstructure and elemental composition of bentonitic clay of the Darbazinsky deposit. Brine is characterized by the change of lithium chloride content in the range of 403- 1001 mg/l. Physical and mechanical characteristics of the obtained sorbents based on bentonite clay and titanium oxide additive are characterized by a high mechanical strength of 5.31 MPa, density of up to 2,6 g/cm3, and specific surface area of 1572 cm2/g. The technological parameters of sorption extraction of lithium chloride from lithium-containing hydromineral raw materials were optimized using the system analysis “STATISTICA” developed by StatSoft company. It is established that to increase the rate of lithium chloride extraction from brine, it is necessary to maintain the rate of brine flow within 8 l/min at maximum humidity of solution output up to 43g/m3 on the basis of the obtained volumetric graphical dependencies. Results The microstructure of the used sorbents with titanium oxide addition up to 20% is characterized by the predominance of lithium chlorides, which are represented by heap-shaped, prismatic crystals. Conclusion The maximum amount of lithium chloride in the form of clusters of light-white crystals of tabular shape on the surface of the sorbent is observed at increasing the content of titanium oxide up to 40%.

Micro to macro investigation of clays advising their constitutive modelling - part II

This paper reports the second part of the keynote lecture, whose part I has been already published in this journal, presenting extensive experimental research on the investigation of clay microstructure and its evolution upon loading. Whether the first part focused on the micro to macro behaviour of different reconstituted clays, this part instead concerns the microscale features of the corresponding natural clays, their changes under different loading paths and the ensuing constitutive modelling implications. The experimental investigation is carried out according to the methodology outlined in the part I-paper, hence micro-scale analyses are presented on natural clays subjected to macro-scale mechanical testing, with the purpose to provide experimental evidence of the processes at the micro-scale which underlie the clay response at the macroscale. As for the reconstituted clays in the part I-paper, original results on stiff Pappadai and Lucera clay, this time in their natural state, are compared to literature results on clays of different classes, either soft or stiff. The results presented in this paper, together with those discussed in the part I, allow for a conceptual modelling of the microstructure evolution under compression of natural versus reconstituted multi-mineral clays, providing microstructural insights into the macro-behaviour described by constitutive laws and advising their mathematical formalization in the framework of either continuum mechanics or micro-mechanics.

HTO and selenate diffusion through compacted Na-, Na–Ca-, and Ca-montmorillonite

Radionuclide transport in smectite clay barrier systems used for nuclear waste disposal is controlled by diffusion, with adsorption significantly retarding transport rates. While a relatively minor component of spent nuclear fuel, 79Se is a major driver of the safety case for spent fuel disposal due to its long half-life (3.3 × 105 yr) and its low adsorption to clay (KD < 10 L/kg), thus a thorough understanding of Se diffusion through clay is critical for understanding the long-term safety of spent fuel disposal systems. Through-diffusion experiments with tritiated water (HTO, conservative tracer) and Se(VI) were conducted with a well-characterized, purified montmorillonite source clay (SWy-2) under a constant ionic strength (0.1 M) and three different electrolyte compositions: Na+, Ca2+, and a Na + -Ca2+ mixture at pH 6.5 in order to probe the effects of electrolyte composition and interlayer cation composition on clay microstructure, Se(VI) aqueous speciation, and ultimately diffusion. The results were modeled using a reactive transport modeling approach to determine values of porosity (ε), De (effective diffusion coefficient), and KD (distribution coefficient for adsorption). HTO diffusive flux was higher in Ca-montmorillonite (De = 1.68 × 10−10 m2 s−1) compared to Na-montmorillonite (De = 7.83 × 10−11 m2 s−1). This increase in flux is likely due to a greater degree of clay layer stacking in the presence of Ca2+ compared to Na+, which leads to larger inter-particle pores. Overall, the Se(VI) flux was much lower than the HTO flux due to anion exclusion, with Se(VI) flux following the order Ca (De = 1.03 × 10−11 m2 s−1) > Na–Ca (De = 2.12 × 10−12 m2 s−1) > Na (De = 1.28 × 10−12 m2 s−1). These differences in Se(VI) flux are due to a combination of factors, including (1) larger accessible porosity in Ca-montmorillonite due to clay layer stacking and smaller electrostatic effects compared to Na-montmorillonite, (2) larger accessible porosity for neutral-charge CaSeO4 species which makes up 32% of aqueous Se(VI) in the pure Ca system, and (3) possibly higher Se(VI) adsorption for Ca-montmorillonite. Through a combination of experimental and modeling work, this study highlights the compounding effects that electrolyte and counterion compositions can have on radionuclide transport through clay. Diffusion models that neglect these effects are not transferable from laboratory experimental conditions to in situ repository conditions.

Characterization of pore water microdynamics and microstructure of clays: The effect of pore fluid chemistry and temperature

It is crucial to figure out the microdynamics of pore water and the microstructure of clays under various thermal and chemical environments when characterizing the physical properties of clays. In this study water microdynamics in clay was investigated via the nuclear magnetic resonance (NMR) technique. The NMR measurements were performed on three clays saturated with distilled water and three salt solutions from 25 to 75°C. The saline and thermal effect on soil-water interaction, water microdynamics and microstructure of clays has been investigated through relaxation times by invoking the DDL theory and the ionic hydration mechanism. Number of jumps (τS/τm) for water molecule is 82 for soils A or C and 520 for soil B when saturated with distilled water, implying the larger surface molecular affinity of soil B. Salt solutions increase the values of τS/τm in the sequence of K+>Ca2+>Na+. Effective activation energy of pore waterΔE= 2.33 kcal/mol, 1.49 kcal/mol and 1.19 kcal/mol for soils A, B and C when saturated with distilled water are obtained. The effect of salt solution on ΔE depends on cation exchange capacity (CEC) and specific surface area (SSA), the larger the CEC and SSA, the smaller the saline effect. In addition, it is found that the pore size distribution of the compacted clay is bimodal, and inter-aggregate pores are greatly influenced by pore fluid chemistry, due to clay aggregation.

Preliminary study on the mechanical behavior of clay in one-dimensional compression with DEM simulations

The mechanical behavior and physical properties of clay are closely associated with its microstructure. Current research on the macroscopic mechanics and physical properties of clay is comprehensive and systematic. However, the microstructural variations underlying these characteristics have been predominantly examined under mercury intrusion porosimetry and scanning electron microscopy, while quantitative and systematic studies are notably limited. This research employs the discrete element method (DEM) simulation to investigate the microscopic responses of clay, simulating one-dimensional compression tests on two clay types: card-house and book-house structures. The analysis of pore size and morphology was conducted using virtual mercury intrusion porosimetry and the pore segmentation method. The clay microstructure was quantitatively characterized by parameters such as pore aspect ratio, orientation distribution, and cumulative pore volume curve. The findings demonstrate that DEM effectively replicates the fundamental mechanical behavior of clay, revealing and explaining the evolution pattern of clay pore structure during one-dimensional compression in terms of platelet alignment adjustment. This macroscopic compression is characterized by variations in pore size distribution, orientation, and aspect ratio.

Dynamic characteristics and microstructure of clay reinforced by the splitting grouting method under subway dynamic loading

The splitting grouting reinforcement method is typically used to improve the stability of surrounding rock when constructing subways in water-rich and weak strata. However, in contrast to normal soil, the dynamic characteristics and microstructure of reinforced soil under cyclic loading of a subway necessitates further clarification to obtain a technical basis for controlling the deformation and settlement of the reinforced soil during later stages. Based on field-reinforced soft clay samples, this study analyzed the dynamic characteristics and microstructure of reinforced soft clay under cyclic loading through stress-controlled undrained cyclic triaxial and scanning electron microscope tests. The results showed that the lower the frequency or the larger the cyclic dynamic stress amplitude, the faster the residual strain development of the reinforced soft clay. There were three cyclic creep characteristic curves of reinforced soft clay: peak, base, and valley creep curves, and the development of base creep represented the overall trend of cyclic creep in reinforced soft clay. In addition, calcium silicate hydrate and ettringite were produced in the reinforced soft clay, which improved the connectivity between the soil particles.

Effect of freeze-thaw cycles on the mechanical performance of wheat straw biomass ash modified soil

In cold regions, freeze-thaw cycles (FTCs) can alter the properties of soil used as a foundation filler, leading to failures in foundation engineering. The increase in biomass power plants has resulted in a significant amount of waste biomass ash, causing negative environmental impacts. To address these issues, waste wheat straw biomass ash (WSBA) is harnessed to enhance the properties of silty clays. This study examines how WSBA affects the mechanical properties and microstructure of silty clay after FTCs through FTCs tests, Triaxial tests, and Scanning Electron Microscopy (SEM) tests. The findings reveal that incorporating WSBA significantly enhances the mechanical properties and microstructure of the soil by filling internal pores and strengthening its structure. The mechanical properties of all soil samples exhibit significant deterioration after 1 FTC, with gradual stabilization ensuing after 6 FTCs. Notably, WSBA-modified samples show better resistance to freeze-thaw weathering compared to unmodified samples, particularly at a WSBA content of 10%. Furthermore, the study establishes empirical formulas linking mechanical parameters, freeze-thaw cycles, and WSBA content using binary quadratic equations. The investigation results could serve as a valuable reference for projects involving roadway subgrade backfill materials in regions with seasonal frozen soil.

Investigation of the effect of additives on the microstructure of clay

In civil engineering, some soils cause many problems in terms of geotechnical engineering. Especially high plasticity clayey soils cause serious problems in road, airport, pavement and highway construction. Such soils can be stabilized using the chemical stabilization method. Additives such as lime, cement, fly ash and blast furnace slag are generally used in chemical stabilization. In addition, in recent years, there have been many studies on the use of natural and artificial fibers in ground stabilization. In this study, the effects of basalt fiber and mineral additives on the microstructure of clay soil were examined. Microstructures of pure and additively mixed clayey soil specimens were investigated for this purpose. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed on compacted soil specimens. In sum, it has been shown that the addition of lime, fly ash, and silica fume is effective in improving the compactivity properties. Pore sizes in SEM images vary depending on additive addition. SEM images showed that the soil particles adhered to the basalt fiber surface, which contributed to the force and friction between the soil particles and the basalt fiber.

Micro to macro investigation of clays advising their constitutive modelling - part I

This keynote lecture discusses the results of a long lasting experimental research, devoted to the investigation of clay microstructure and its evolution upon loading. Micro-scale analyses, involving scanning electron microscopy, image processing, mercury intrusion porosimetry and swelling paths to test the clay bonding, are presented on clays subjected to different loading paths, with the purpose of providing experimental evidence of the processes at the micro-scale which underlie the clay response at the macro-scale. Data from the literature on clays of different classes, either soft or stiff, are compared to original results on two stiff clays, Pappadai and Lucera clay, both in their natural state and after reconstitution in the laboratory. The results presented herein allow building a conceptual model of the evolution of clay microstructure upon different loading paths, providing microstructural insights into the macro-behaviour described by constitutive laws and advising their mathematical formalization in the framework of either continuum mechanics or micro-mechanics. For editorial purposes, the research results are presented in two parts. The first part, presented in this paper, concerns the results for reconstituted clays, whereas a second part, concerning the corresponding natural clays, is discussed in a second companion paper.

Study on water migration and the microstructure of unsaturated expansive clays

Because of the characteristics of water swelling and drying shrinkage, the mechanical performance of expansive clays in semi-arid areas deteriorates with changes in humidity and temperature. Hence, investigating the moisture migration in expansive clays is of great significance. Herein, scanning electron microscopy and water migration tests of unsaturated soil were carried out to address the water variation law and microscopic mechanisms in unsaturated expansive clays. It was found that small- and medium-sized pores (2–10 μ m) are dominant, and these pores are conducive to an increase in the water content in the soil. Soil with a high water content exhibits a flocculent structure, characterized by a small fractal dimension and a high relative hydraulic conductivity. Conversely, soil with a low water content displays a dispersed structure, featuring a large fractal dimension and a low relative hydraulic conductivity. The water migration tests, which were carried out at constant temperatures (5, 20 and 40°C) and variable temperatures (15–25°C), show that the amount of migration at 5 and 20°C was about 25–40 and 40–60% of that at 40°C, respectively. The amount of water migration at a constant temperature was obviously lower than that recorded at variable temperatures. The research results have provided technical support for the effective control of soil change.

Compressibility and microstructure of compacted lateritic clay at different suction levels

Compressibility and microstructure of compacted lateritic clay at different suction levels

Elevated temperature effects (T > 100 °C) on the interfacial water and microstructure swelling of Na-montmorillonite

Montmorillonite-based barriers are key elements of the engineered barrier systems (EBS) in geological disposal facilities (GDF). Their performance at temperatures above 100 °C is not sufficiently understood to assess the possibility of raising the temperature limits in GDF designs that could reduce construction costs and CO2 footprint. The present work provides new fundamental insights through molecular dynamics (MD) simulations of Na-montmorillonite's water-clay interactions and swelling pressure at temperatures 298–500 K and basal spacings of 1.5–3.5 nm. At temperatures above 100 °C, the swelling behaviour is governed by the attractive van der Waals force and the repulsive hydration force instead of the repulsive electrostatic (double layer) force. The swelling pressure reduction with increasing temperature is related to the weakened hydration repulsion and electric double layer repulsion, which result from the deterioration of the interlayer water layer structure and the shrinkage of the electric double layer. The applicability and breakdown of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory at elevated temperatures are examined. By excluding the osmotic contribution in the DLVO theory, the summation of the van der Waals interaction in DLVO and an additional non-DLVO hydration interaction can predict our MD system's swelling under high temperatures. The findings of this study provide a fundamental understanding of the swelling behaviour and the underlying molecular-level mechanisms of the clay microstructure under extreme conditions.

The sensitivity of Prazeres clay – some results on reconstituted samples

Soil’s structure is defined as the issue responsible for the differences observed in the mechanical response of natural soil samples compared to the intrinsic behaviour of reconstituted samples. The parameter that incorporates the differences in microstructure of intact and reconstituted clays is designated by stress sensitivity. The influence of microstructure and fabric on the behaviour of soils has been evaluated by comparing strength and compressibility characteristics of intact and reconstituted samples of the same material. Included on a broad characterization study of Lisbon Miocene Prazeres clay held at Porto University, some oedometer and triaxial tests were undertaken on intact and reconstituted samples. In this paper, the process of preparing reconstituted samples and consolidating them in a large oedometer to the in-situ stress is thoroughly described. The results of oedometer and triaxial tests on reconstituted samples are presented and compared with results for intact samples from the same site. A proposal for parameterisation of the intrinsic characteristics of this clay is established on the basis of test results. Concerning compressibility, oedometer test results show good adjustment to the isotropic compression line (ICL). Triaxial test results for intact samples in the light of critical states soil mechanics are similar to those obtained in s’-t space for the reconstituted samples. The intrinsic parameters show good agreement with those described in the literature for soils of the same nature.

Investigation of the microscopic properties of natural structured clay

Conducting quantitative research on the microstructure of soft clay can reveal the essence of its soil mechanical behavior, which is of important practical significance for geological disaster risk assessment and prevention. To quantitatively investigate the microscopic properties of natural structured clay, soft clay soils from various sedimentary environments in the Hangzhou Estuarine Bay area were chosen as the research subject in this study. Subsequently, a comprehensive investigation into the microstructure of clay was conducted, involving X-ray phase analysis and SEM imaging analysis. The results revealed the following: (1) In comparison to the deep clay deposited in fluvial-lacustrine environments, the shallow mucky clay in marine sediments had a higher clay mineral content, accounting for 48%. Illite makes up the majority of it, with minor levels of kaolinite and montmorillonite being present. (2) The shallow mucky clay in the Hangzhou Estuarine Bay area had a typical agglomerate-flocculated structure. In contrast, the deeper clay showed a flocculated structure with less uniform particle sizes, strong stacking randomness, poor directional alignment of soil pores, and tends to form arrangements where edges are adjacent to faces or edges are adjacent to other edges. (3) Compared to the deep clay deposited in fluvial-lacustrine environments, the marine-deposited shallow mucky clay displayed orderly pore arrangements, strong directional alignment, significant pore shape variability, and minimal pore size changes between adjacent pores. The microstructure of soil plays a crucial role in determining the physical, mechanical, and other engineering properties of the soil. This study provides insightful information about the relationship between clay microstructure and geotechnical characteristics in Hangzhou and the surrounding areas.

Stochastic dynamics construction of a three-dimensional microstructure of red clay

Constructing a microstructure of red clay is an important part of studying the physical and mechanical properties of red clay. The study of red clay microstructure is generalized. The red clay matrix and pores are regarded as two types of randomly moving particles, and the microstructure model of three-dimensional red clay random porous media is established from the Langevin equation of the phase separation process in stochastic dynamics, using the separation and aggregation of the two particles. The model controls the evolution process of the porous medium by artificially controlling the particle placement. Here, the trends of porosity, average pore length, Euler’s number, and the fractal dimension of the porous medium during the evolution process under different parameter conditions (smooth length Δ and rise and fall term η) are calculated, and a feasible method for surviving the microstructure of red clay is summarized. Due to the consideration of the interaction forces between the solid- and void-phase particles, the porous media generated by this model are more similar to the real porous media in nature, with connected and unconnected pore structures and tortuous pore channels. Finally, the red clay of Bijie, Guizhou, is modeled as an example to prove the feasibility of the method.

Microstructural observations of clay-hosted pores in black shales: implications for porosity preservation and petrophysical variability

AbstractTypical unconventional gas/liquid plays of China were studied using field-emission/focused ion beam scanning electron microscopy (SEM) for clay mineralogy and microstructural development. The SEM microstructural investigations of clay-rich shale and mudstone reservoirs provided significant information about clay mineral type, size, distribution and aggregates, which allows for interpretations regarding porosity preservation and petrophysical variability. The major clay-hosted porosity types are interparticle clay pores, intraparticle clay pores and aggregate pores. Interparticle clay pores occur in open spaces of the clay aggregates and include four subtypes: (1) elongated pores, (2) packed pores, (3) jagged pores and (4) card-house pores. Intraparticle clay pores are present within clay particles and have mostly secondary origin. These pores are diagenesis dependent and are restricted to secondary illite particles during the transformation of clay minerals from smectite to illite. Intraparticle clay pores constitute only isolated porosity and could not contribute to hydrocarbon molecule storage and migration. Aggregate pores were predominantly encountered in association with organic–clay and pyrite–clay aggregates. In places, organic–pyrite–clay aggregates can also display polymerization, but they do not contribute significantly to overall porosity and permeability. Combining SEM morphological analyses with the software ImageJ is critical in clay microstructure and porosity analyses via semi-quantitative characterization of the 3D pore surface, 2D pore profile, pore quantity, pore size, areal porosity, etc. These visual and semi-quantitative results highlight the significance of jagged pores and pyrite–clay aggregate pores in shale gas/liquid reservoirs because they may be important facilitators of gas storage and transmission.

Quantitative examination of microstructural transformations of clay-rich sediments in river-dominated deltas under the influence of polluted pore water

Coastal water pollution has a significant impact on sedimentary environments, altering the microstructure of clay-rich sediments and further destabilizing river-dominated delta strata. However, the understanding of the microstructure of clay sediment, influenced by burial depth and pore water chemistry, remains limited due to challenges in quantitatively analyzing clay texture at varying depths. The perturbable of clay microstructures, and the cost of deep sampling have hindered such efforts. To address this issue, this study aims to quantitatively analyze the clay anisotropy at different depths and pore water chemistry through laboratory-simulated sediment samples by using centrifugal modeling and 2DXRD technology. The results suggest that 1DXRD (Orientation index) is prone to generating incorrect conclusions, whereas 2DXRD (pole density) yields more precise and reliable results. Specifically, the results indicated that the introduction of salt ions promoted clay precipitation and stabilized the oriented microstructure at shallower depths. In acidic solutions, clay sediment still contained a certain proportion of edge to face (EF) microstructure at depths less than 6 m, suggesting higher soil thixotropy and lower strength than that of clay sediments in other types of solutions. Overall, our findings provide valuable insights into the relationship between water pollution, delta disappearance, and ocean acidification, highlighting the urgent need for effective environmental management strategies to prevent further damage to fragile coastal ecosystems.

Microstructure and Mechanical Properties of Expansive Clay under Drying–Wetting Cycle

Expansive clay is one of the most widely distributed soils in the world. Due to its rich content of strongly hydrophilic minerals—such as montmorillonite—expansive clay exhibits substantial swelling and shrinkage properties, and overconsolidation. The formation process of undisturbed expansive clay has a long and complicated geological history and innumerable drying–wetting cycles, resulting in the formation of special internal structures. In this study, the mud-to-natural-consolidation deposition process was simulated using a saturated mud-remolded sample preparation device, and then, mud-remolded soil under a certain consolidation pressure was prepared. Subsequently, the effects of the stress history and drying–wetting cycle on its mechanical properties and microstructure were examined through uniaxial consolidation compression experiments, K0 consolidation experiments, and pressure plate experiments of undisturbed soil, mud-remolded soil, and a drying–wetting cycle sample. The results showed that the mud-remolded soil completely broke the natural structure of the undisturbed soil, with the structural characteristics of the remolded soil being restored to a certain extent after the drying–wetting cycle. This not only reduced the void ratio of the soil sample, but also changed its compressibility and water retention characteristics, revealing the role of atmospheric drying–wetting cycles in the natural overconsolidation state of expansive clay and providing a theoretical basis for understanding their overconsolidation characteristics.

Effects of freeze–thaw actions on mechanical properties and constitutive model for diesel-contaminated soil

Oil pollution is widespread in frozen regions around the world, and the mechanical properties of clay are highly susceptible to prolonged freeze–thaw cycles and diesel pollution. In order to study the properties of diesel-contaminated clay at the influence of freeze–thaw cycles, the laboratory tests are performed here, based on which the mechanical properties of diesel-contaminated soil under freeze–thaw cycles are studied. Additionally, the effects of freeze–thaw cycles and contents of diesel on the microstructure of clay are studied by scanning electron microscopy. The results show that the shear strength and strength parameters of soil samples decrease with the increase of diesel content and freeze–thaw cycles. Moreover, the scanning electron microscopy (SEM) results show that the freeze–thaw cycle and the increase in diesel content increase the number of large pores and decrease the number of small pores. The soil particles coagulate and form larger pores after the soil sample undergoes freeze–thaw and diesel pollution. The appearance of macropores leads to soil compaction worse and soil strength decrease. Based on the poromechanics, the diesel-contaminated soil is considered as porous material, and a constitutive model with consideration of the influence of freeze–thaw cycles and diesel content is established. The model can model the test results and the main features of diesel-contaminated soil can be duplicated relatively well. Therefore, the study can provide some help in understanding diesel-contaminated engineering under freeze–thaw cycles in cold regions.

Microstructure Investigations of Natural Clay From Pattallassang District, Takalar Regency, South Sulawesi Province, Indonesia

The study aimed to investigate the microstructure of natural clay from Pattallassang District, Takalar Regency, South Sulawesi Province. The clay was characterized using X-ray diffractometer (XRD), surface area analyzer (SAA), and scanning electron microscope (SEM). The XRD analysis showed that the main mineral composition of the clay was kaolinite, quartz, hematite, geothite, magnetite, and anatase phases. The SAA using BET analysis shows the large surface area of 59.26 m2/g and BJH analysis for pore distribution of 32.77 nm. SEM observations revealed that the clay consists of plate-like kaolinite particles arranged randomly. The results indicate that the natural clay from Pattallassang District has good potential for use in various industrial applications due to its high kaolinite content and favorable microstructure.Keywords: kaolinite, microstructure, mineral, clay.