Aggregation Of Clay Particles Research Articles

Goethite affects phytolith dissolution through clay particle aggregation and pH regulation

Formed in plant tissues as fine silica particles, phytoliths are deposited within plant debris in soils where they can dissolve and feed silicon (Si) fluxes to the biosphere and hydrosphere. Yet, soil phytoliths can be protected from dissolution by entrapment in aggregates, and thus be withdrawn from the global silica cycle. Among clay-sized minerals interacting in stable aggregates, goethite and kaolinite are ubiquitous in soils. We analyzed the impact of goethite-mediated aggregation on the release of aqueous Si from phytoliths entrapped in microaggregates containing organic matter and kaolinite, with quartz and goethite at variable concentrations, simulating a soil sequence with increasing contents of clay and iron oxide, as it can commonly occur in terrestrial ecosystems. The microaggregates stored sizable amount of organic carbon, the release of which decreased with increasing goethite concentration. Aqueous Si was assessed through a kinetic extraction with dilute CaCl2, while pH, aluminum (Al) and germanium (Ge) concentrations were measured in the CaCl2 extracts. Our experimental data showed that phytoliths were the source of aqueous Si. They also showed that the process of phytolith dissolution prevailed over Si adsorption on goethite. As mediated by goethite, aggregation protected phytoliths from dissolution at goethite concentrations above 20 g kg−1. Increasing goethite concentration enhanced aggregation on the one hand, but increased pH from 5.5 to 7.5 on the other. Thus, while aggregation significantly reduced the release of aqueous Si by 1.7- to 3-fold at a given pH, the increase in pH enhanced it. Overall, at common soil solution pH (5–6), aggregation reduced Si release by 2–3 times. Thus, preservation of phytoliths in aggregates can be widespread in well-aerated soils and more effective than Si adsorption on secondary oxides in retaining Si.

Sand modification with a saponite clay suspension as a waste of the diamond mining industry

The results of the laboratory water permeability tests of a sand modified by a saponite clay fraction from the diamond mining industry waste are presented. The filtration of clay suspension through a landfill ground bed as a method of the additive enrichment is approved. The experimental apparatus consisted of the triaxial test chambers and semi-automatic devices for water and suspension supplying. The chambers excluded a sidewall leakage in the samples and provided required values of the vertical and horizontal stresses when measuring permeability. The samples of an alluvial fine sand and a sand mixed with 3 and 5 % a chalk and a dolomite were investigated. After preliminary saturation the rate of distilled water flow through the samples were determined at four values of hydraulic gradient. Then the filtration of a suspension containing up to 0.58-0.63 % clay particles was conducted. After that, the pore disks at the top of samples were washed by circulating water flow. At the last step of experiments the velocity of water flow was measured again at four values of hydraulic gradient. The experiments indicated that the modification of the sand by clogging the pores by the saponite clay fraction from a suspension flow is possible if a sand comprises the additives causing the aggregation of clay particles. The hydraulic conductivity of a sand with 3 % chalk decreased by 15-31 times, with 5 % - by 15-39 times at different values of relative compaction. The effect of a dolomite addition was not significant, the hydraulic conductivity decreased by a maximum of 14.3 times. To achieve the maximum depth of clogging, it is recommended to filtrate the suspension through a loose sand at a hydraulic gradient that provides a flow rate more than 3.5 m/day, after that, the sand layer should be compacted.

Organic matter deposition and preservation in ancient deep‐sea levée sediments: Implications for Neoproterozoic trends in carbon burial

AbstractDeep‐marine levées are areally extensive features that experience high rates of sedimentation, making them ideal sites for significant carbon burial and preservation. Although modern deep‐marine levées have been shown to sequester a large proportion of the world's total buried organic carbon, few studies have attempted to assess carbon deposition and preservation in ancient deep‐marine levée deposits. Observations of well‐exposed levée deposits of the Neoproterozoic Windermere Supergroup in British Columbia, Canada, have shown that depositional processes in levées can result in the concentration and enrichment of sedimentary marine organic matter. In contrast to many previous studies where organic‐rich strata occur as black shales formed in anoxic conditions, organic matter in this study occurs mostly in banded, mud‐rich sandstones deposited under oxic conditions. Scanning electron microscopy shows that this organic carbon occurs primarily as nano‐scale coatings on clay particles, but also as uncommon sand‐sized organomineralic aggregates and discrete sand‐sized amorphous grains. As flows overspilled the channel margins, the rapid collapse of the turbulent suspension resulted in elevated rates of sediment fallout that promoted aggregation of organic matter and clay particles, increasing cohesive forces in the flow, and ultimately en masse deposition. Rapid burial plus association with clay mineral surfaces prevented organic matter degradation, thereby effectively sequestering significant amounts of carbon in the sediment and therefore a net sink for atmospheric CO2. However, the mechanisms and efficiency by which organic matter is buried and preserved on geological timescales is influenced by many factors, including glacial, sea‐level and tectonic cycles. This work elucidates the fundamental physical and chemical processes that control organic matter accumulation and preservation in deep‐marine levées, and how these processes have evolved throughout geological time.

Aggregation of microplastics and clay particles in the nearshore environment: Characteristics, influencing factors, and implications

Since nearly half of the world's population lives near the coast, coastal areas have become hotspots for microplastic (MP) pollution due to human activity. The ubiquity of natural colloids in coastal waters plays a critical role in the potential fate of, and risks posed by, MPs. Nevertheless, far less has been known regarding the aggregation of MPs with inorganic natural clay colloids, especially in the complicated nearshore environment. In this study, the aggregation behavior of MPs as well as the interaction between MPs and clay particles were investigated under different nearshore environmental conditions (MP-to-clay ratio, salinity gradient, humic acid concentration, and wave energy). The aggregation behavior was subjected by the repulsive energy barrier between particles and external energy transferred to the system. The low energy associated with mild wave conditions was favorable for the occurrence of aggregation, whereas sustained high energy under intense wave conditions was found to be detrimental to the aggregation behavior, and the aggregates were prone to fragmentation even if particles coalesced into large clusters. The analysis for the environmental fate of MPs demonstrated that the shoreline was likely to be the sink for most MPs ultimately.

Features of granulometric and material composition of road dust, bottom sediments and soils in the Rostov region

An expedition was carried out to take samples of road dust, soils, sediments at the water’s edge and bottom sediments of watercourses and reservoirs of Eastern Donbass and other districts of the Rostov region. The goal was to study the granulometric composition of the selected material. In all samples, particles with a dimension of less than 0.01 mm were dominant, while particles with a diameter of <0.002 played a subordinate role. Particles with a diameter of <0.01 prevailed in the composition of the studied samples, regardless of the place of their selection. It was found that the content of the sum of fractions with particle sizes < 0.01 mm and <0.002 are in the selected samples in the following sequence: bottom sediments > sediments at the water’s edge > soil > road dust. The composition of natural formations includes soil particles, aggregates of clay particles, fine sand-siltstone quartz grains, calcite, feldspar, gypsum, single grains of magnetite and titanomagnetite. Technogenic impurities in the dust were represented by aluminosilicate microspheres, metal particles of varying degrees of corrosion, carbon particles.

Long-Range Ionic and Short-Range Hydration Effects Govern Strongly Anisotropic Clay Nanoparticle Interactions.

The aggregation of clay particles in aqueous solution is a ubiquitous everyday process of broad environmental and technological importance. However, it is poorly understood at the all-important atomistic level since it depends on a complex and dynamic interplay of solvent-mediated electrostatic, hydrogen bonding, and dispersion interactions. With this in mind, we have performed an extensive set of classical molecular dynamics simulations (included enhanced sampling simulations) on the interactions between model kaolinite nanoparticles in pure and salty water. Our simulations reveal highly anisotropic behavior, in which the interaction between the nanoparticles varies from attractive to repulsive depending on the relative orientation of the nanoparticles. Detailed analysis reveals that at large separation (>1.5 nm), this interaction is dominated by electrostatic effects, whereas at smaller separations, the nature of the water hydration structure becomes critical. This study highlights an incredible richness in how clay nanoparticles interact, which should be accounted for in, for example, coarse-grained models of clay nanoparticle aggregation.

Effect of Sulfate on the Aggregation of Clay Particles in Loess

The type and structure of clay minerals are among the main factors affecting the physical and mechanical properties of loess, and the salt content plays a dominant role in many factors affecting aggregation. In this study, the grain size analysis, Atterberg limits tests, scanning electron microscopy (SEM), and energy spectrum analysis (EDS) were used to explore the microstructure and physicochemical mechanisms of the aggregation of clay particles. Finally, the unconfined compressive test, direct shear test, and elastic wave velocity test were conducted to explore the effect of sulfate agglomeration on loess properties. The results show that the salt-washing process leads to the loss of the original soluble salt, dispersion of the original aggregates, and increase of fine particles, such as fine silt and clay. With the increase of sulfate content, the content of fine silt and clay decreases, the liquid limit and plasticity index decrease, the plasticity limit remains unchanged, the aggregate content of fine silt and clay increases, the adsorption capacity weakens, and the diffusion layer compresses and thins. The mechanical test results show that when the sulfate content is less than 3%, the sulfate is almost completely dissolved and the aggregate is less, which increases compressive strength and the cohesion; when the sulfate content is more than 3%, too much sulfate cannot be dissolved and precipitated; hence, the aggregate increases. However, the existence of large volume mirabilite crystals reduces the cementation, which reduces the compressive strength, increases the internal friction angle, and weakens the cohesion.

Risk of colloidal and pseudo-colloidal transport of actinides in nitrate contaminated groundwater near a radioactive waste repository after bioremediation

The possible role of biogeochemical processes in the transport of colloidal and pseudo-colloidal U, Np, and Pu during bioremediation of radionuclide- and nitrate-contaminated groundwater was investigated. In two laboratory experiments with water samples taken from contaminated aquifers before and post bioremediation, we found that microbial processes could cause clayed, ferruginous, and actinide colloids to coagulate. The main mechanisms are biogenic insoluble ferrous iron species formations (goethite, pyrrhotite, siderite, troilite, and ferrihydrite), the aggregation of clay particles by microbial metabolites, and the immobilization of actinides in the bacterial cells, large polymers, and iron and clayed sediments. This process decreases the risk of colloidal and pseudo-colloidal transport of actinides.

Geotechnical properties of oil-polluted soil: a review.

Soil polluted by oil and its derivatives is a critical environmental issue worldwide that jeopardizes ecological systems and causes geotechnical problems. This review paper focuses on the previous studies concerning the impacts of oil pollution on soil geotechnical properties. To this end, related academic literature on this topic was investigated and discussed. The findings of this study demonstrated that the addition of oil pollution in coarse-grained soils significantly reduces particle surface roughness. On the other hand, in fine-grained soils, it results in flocculation and secondary aggregation of clay particles, less aggregated and loose packing in the soil matrix, the formation of isometric pores, the formation of fissure-like pores, and an increase in mesoporosity. In general, it was found that the geotechnical properties of oil-polluted soils are mostly determined by the physicochemical and/or physical interactions between the soil and contaminant. Additionally, previous research has demonstrated that oil pollutants alter the geotechnical propertiesof cohesive and non-cohesive soils significantly, including the Atterberg limits, particle-size distribution, compaction behavior, unconfined compressive strength, friction angle, cohesion, hydraulic conductivity, and consolidation characteristics. However, no general pattern could be established for the majority of them. Besides, it was found that the degree of geotechnical property alteration of oil-polluted soil is strongly influenced by the soil type and features, as well as the quantity, type, and chemical composition of oil pollutants.

Drying Shrinkage Reduction of Korean Loess Using Cations

The loess produced in South Korea is an eco-friendly material with high gas adsorption performance. Korean loess, however, cannot be used as a structural material because it has a very low compressive strength compared to cement. However, even if it is recommended as an interior material, its large drying shrinkage during drying disturbs wet construction. Therefore, this study aimed to develop a method to reduce the amount of water added while maintaining the consistency required for the plastering work of Korean loess. The experimental results showed that the dispersion of clay particles was improved when Na+ and K+, which are monovalent cations, were added to the loess colloid; the reverse occurred, i.e., aggregation of clay particles, when Ca2+ and Mg2+, which are divalent cations, were added. In addition, the dispersion and aggregation of clay particles affect the consistency of loess. The dispersion allows the loess paste to obtain the required consistency using less water, but the aggregation may exhibit the opposite effect. Accordingly, based on the same consistency, the specimens with less water exhibited less drying shrinkage. The drying shrinkage decreased by 9.23% for the specimen fabricated with the 0.01 M Na2SiO3 aqueous solution.

Kaolinite and illite colloid transport in saturated porous media

Understanding the transport of naturally abundant clay colloids is critical in colloid associated contaminant transport in porous media. This study was focused on the impact of the median size of sand grains and the ionic strength of solution on the transport and retention behavior of clay colloids. Two clay samples of kaolinite and illite colloids were selected to represent clay samples containing 1:1 and 2:1 clay minerals, respectively. The observed retention profiles and breakthrough curves demonstrated that the impact of ionic strength on the retention behavior of clay was consistent with other colloidal colloids such as latex colloids or graphene oxide. The quantity of the retained clay increased as the median sizes of sand decreased, and the ionic strength increased from 0 to 0.1 M. However, a similar quantity of retained illite at the ionic strength of 0.01 M and 0.1 M indicates the presence of threshold ionic strength in clay colloid retention. The exponential relationship between sand-to-clay size ratio and first-order retention coefficient at given ionic strength implies the chance in long-term prediction of clay colloid transport from the observed retention profiles. • Transport of kaolinite and illite was investigated in saturated sand column. • Quantity of retained clay does not increase for ionic strength greater than 0.01 M. • Porosity of sand can be a critical factor in clay particle transport. • Impact of aggregation and aspect ratio of clay particles should be considered.

Quantitative evaluation of thixotropy-governed microfabric evolution in soft clays

Thixotropy-governed temporal microfabric evolution, in a naturally occurring illitic marine clay and a manufactured kaolinitic clay at their respective liquid limits, was probed quantitatively by both one-dimensional X-ray diffraction (1DXRD) and 2DXRD via orientation index (OI) and texture index (TI) respectively. Results showed that the two fabric indexes, OI and TI, continuously evolved nonmonotonically but consistently during the thixotropic hardening periods of up to 125 days. Due to the initial remolding-induced large-strain shearing, both clays started with a fabric consisting of highly parallel-oriented clay particles. With increasing time, the OI varied from 23.1 to 36.6 and from 3.8 to 4.5, while their TI ranged from1.004 to 1.008 and 1.010 to 1.029 for the kaolinitic and illitic clays, respectively. Moreover, the same trend of changes between the OI and TI for both clays indicated that the two XRD-based techniques are applicable to characterizing the temporal microfabric changes in soft clays undergoing thixotropic hardening. The fabric evolution may result from various microscale particle rearrangements, likely including clay particle reorientation, aggregation, and flocculation, which in turn are controlled by interparticle forces. The two XRD-based techniques are also discussed in terms of their advantages and can expectedly shed light on similar studies of time-dependent behavior of soft clays.

Effects of crude oil contamination on geotechnical properties of sand-kaolinite mixtures

Abstract In this study, a series of laboratory tests were performed to investigate the interaction between crude oil, clay minerals, and sand particles in contaminated soils and the effect of crude oil on the engineering properties of sand-kaolinite mixtures with different weight ratios of clay to sand was evaluated. Mixtures with a weight ratio of 10%, 30% and 50% kaolinite to sand contaminated with different contents of crude oil (including 0%, 4%, 6% and 8% by dry weight of soil) have been considered. Standard compaction, unconsolidated undrained triaxial, permeability, pH, and water holding capacity (WHC) tests have been conducted on the clean and contaminated specimens at the same dry density. In addition, Scanning Electron Microscope (SEM) has been used to identify the microscopic interactions between crude oil, kaolinite and sand particles. The results show that due to an increase in contamination, the maximum dry density, optimum water content, permeability and pH values were decreased. Different ratios of clay/sand had a significant effect on WHC value and soil shear strength parameters in the presence of the crude oil. While in the sandy specimens with low clay quantity, the addition of crude oil decreased the internal friction angle, in the specimens with high clay quantity, the angle of friction increased. SEM images showed that crude oil contamination caused aggregation of clay particles and a flocculated structure with more macropores. The findings of this paper can clarify the hydro-chemo-mechanical properties of a wide range of soils and help in geotechnical designs of contaminated soils.

Early plant organics increased global terrestrial mud deposition through enhanced flocculation.

An irreversible increase in alluvial mudrock occurred with the Ordovician-Silurian evolution of bryophytes, challenging a paradigm that deep-rooted plants were responsible for this landscape shift. We tested the idea that increased primary production and plant organics promoted aggregation of clay into flocs in rivers and facilitated mud deposition on floodplains. In experiments, we observed that clay readily flocculated for organic and clay concentrations common to modern rivers, yielding settling velocities three orders of magnitude larger than those without organics. Using a transport model, we found that flocculation substantially increased mud deposition, resulting in muddier floodplains. Thus, organic-induced flocculation may have been more critical than deep-rooted plants in the proliferation of muddy floodplains.

What matters for mudrocks

Geology Rock such as slate and shale, which form from mud, suddenly start appearing in the geologic record around 450 million years ago. Their appearance at about the same time as certain plants seems to implicate plant roots in the formation of these ubiquitous rocks. Zeichner et al. found a different route for creating the flocculation required for mudrock. Using analog experiments, the authors found that organic matter from plants alone was sufficient for the formation of flocs—aggregates of small silt and clay particles—which are required to deposit mudrock. This observation could explain the appearance of these rocks in places where the plants did not have deep roots. Science , this issue p. [526][1] [1]: /lookup/doi/10.1126/science.abd0379

Investigating the mechanism of pH effect on saturated permeability of remolded loess

The pollution of remolded loess caused by acids and bases greatly affects its engineering performance, and thereby seriously threaten the service life of loess buildings or structures. To explore the changes in saturated permeability of the remolded loess polluted by hydrochloric acid or sodium hydroxide solutions, a series of the saturated seepage tests were designed in presence of different pH values. In addition, the hydrochemical components in the leachate along with the zeta potentials in water-soil solutions under different pH were measured. The changes in mineralogical, chemical, and microstructural properties of the loess samples before and after the seepage were also investigated. The results demonstrate gradual increase in the permeability of the loess samples with the decrease of pH of the solution. When acid enters the loess, the dissolution of carbonate cement and chemical cement (Al 2 O 3 and Fe 2 O 3 ) lays the foundation for the enlargement of pores. The decrease in thickness of the diffuse double layer results in aggregation of clay particles and enlarges the space of gravity water moving in the free layer. Hence, the significant increase in the permeability takes place over time during the seepage at pH = 3. The change in permeability at pH = 7 shows similar behavior to the acidic condition, and this is mainly responsible for the leaching of carbonate. However, the alkaline (pH = 11) condition inhibits the dissolution of carbonate minerals, and calcite is precipitated due to the incongruous dissolution of dolomite and dedolomitization. Al(OH) 3 , Fe(OH) 3 , and H 2 SiO 3 colloids are formed and attached to the particles. These processes plug the pores during the seepage. Moreover, the development of the diffuse double layer results in wide distribution of the clay particles with highly cementation, which greatly reduces the effective connectivity of the pores. Therefore, its permeability decreases with the seepage time. These findings will offer reference for the practice of geological engineering in the loess areas. • The change laws of saturated permeability of remolded loess are investigated at different pH. • The geochemical process, chemical behavior, and electrokinetic property are explored during the seepage. • The similarities and differences of physicochemical interactions between soil and water are revealed at different pH. • The mechanisms of pH effect on saturated permeability of remolded loess are disclosed.

Cyclic swell–shrink behaviour of an expansive soil treated with a sulfonated oil

The effects of a sulfonated oil (SO) stabiliser on the swell–shrink properties of an expansive soil were investigated through cyclic wetting–drying tests. The cyclic wetting–drying action led to the reconstruction of the soil microstructure by inducing clay particle aggregation. Accordingly, the greater the number of applied cycles, the lower the swell–shrink potential up to the fourth cycle, beyond which the swelling and shrinkage strains attained elastic equilibrium. At any given cycle, the tendency for swell–shrink reduction was in favour of the SO concentration up to 0·75%, beyond which the excess SO molecules self-associated in the form of aggregates, thereby acting as a ‘lubricant’ rather than a clay-stabilising agent. As a result of SO treatment, the accumulated axial strain progressively transitioned towards a desirable, ‘neutral’ state, with 0·75% SO exhibiting the highest resistance against cyclic wetting–drying. For any given SO concentration, the equalised void ratio–moisture content curves for wetting and drying followed the same S-shaped path, further corroborating that the swelling and shrinkage processes, on achieving elastic equilibrium, become reversible. The shrinkage and liquid limits indicated a progressive transition towards a desirable, aggregated fabric, with 0·75% SO identified as the optimum concentration.

Effect of Sodium Chloride Concentration on Saturated Permeability of Remolded Loess

Loess contains many sodium and chloride ions that can easily be leached when seepage occurs, thus affecting the mechanical properties of loess. This study investigated a series of sodium chloride solution concentrations to explore their influence on the permeability of remolded loess, as well as the underlying mechanism of such. The results indicated that the saturated hydraulic conductivity of remolded loess increases with time in response to different sodium chloride concentrations, and the sample was more permeable with increasing concentration. Moreover, the salt effect promoted the dissolution of calcite and dolomite, and the cation exchange stimulated the leaching of other cations, thus leading to further structural loosening. Furthermore, the aggregation of clay particles increased, thus forming a larger pore space among aggregates and providing effective channels for permeation. These findings provide a theoretical basis for an improved understanding of channel degradation in the loess area of Northwest China.

Effect of compaction time delay on compaction and strength behavior of lime-treated expansive soil contacted with sulfate

Application of lime as an additive for controlling the volume change behavior and improving the strength of expansive soils has been in use over several decades. However, the contamination of lime-treated expansive soil with sulfate always results in the deterioration of treated expansive soil. Therefore, this paper highlights the effect of sodium sulfate solution on compaction and strength behavior of lime-treated expansive soil. Further, the effect of compaction time delay and contact period of sulfate solution with lime-treated soil is also brought out in this paper. To bring out the above effects, the lime contents corresponding to the initial consumption of lime (ICL) and ICL ± 1% were used along with sulfate solutions of 5000, 10,000 and 20,000 ppm. The experimental study showed that upon mixing the lime-treated expansive soil with sulfate solutions, the maximum dry unit weight decreased and optimum moisture content increased with increase in concentration of sulfate solutions when compacted without any compaction delay. With compaction time delay, the lime-stabilized soils mixed with distilled water led to the formation of flocs and aggregation of clay particles and decreased the maximum dry unit weight and optimum moisture content. However, the effect of compaction time delay was negligible on maximum dry unit weight as the formation of flocs and aggregation of clay particles were inhibited in lime-treated soil mixed with sulfate solutions. These changes in dry unit weights and soil structure were reflected on the strength of lime-treated expansive soil as well.

A triple porosity hydro-mechanical model for MX-80 bentonite pellet mixtures

This paper describes the application of a triple porosity model to characterise the hydro-mechanical behaviour of MX-80 bentonite pellet mixtures. The macroscopic behaviour of the system was assumed to be fundamentally controlled by three functional levels, the microstructure (associated with the pores existing inside the clay particle aggregates), the Macrostructure 1 (which integrates the space between the aggregates inside the pellets) and the Macrostructure 2 (related to the void space between the pellets). The role played by each functional level in the overall behaviour of the system was modelled by means of an overlapping continua approach. The usual framework in the simulation of the behaviour of compacted bentonite blocks has been adapted to describe the behaviour of the microstructure and the Macrostructure 1. To model the behaviour of the Macrostructure 2, a simplified formulation of granular materials was adopted.To illustrate the capacity of the proposed approach, two hydration tests were simulated in which significantly different pellet mixtures were used: an open mixture with a dry density of 953kg/m3, and a closed mixture with 1520kg/m3 of dry density. Despite the difference between the two mixtures, the model allowed very satisfactory fits to be obtained using in both cases the same material parameters. This shows the consistency of the proposed conceptual framework.Since the response of the two Macrostructural levels is differentiated, the model provides a richer description of the mixture behaviour than that obtained using a double porosity model. However, the interest of the model lies not only in its descriptive richness. The differentiation of the effect of both Macrostructural levels improves the description of the time evolution of the system compared with that obtained when using a double porosity model. However, if the Macrostructure 2 is small (as occurs in the second of the two tests analysed), or there is sufficient confinement for the inter-pellet void space to be considerably reduced when the microstructure swells, double porosity models can satisfactorily characterise the performance of the bentonite pellet mixture.