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Dispersive soil is a widely distributed problematic soil in arid or semiarid areas of the world and can cause pipe erosion, gully damage and other seepage failures. This study analyzed the effect of environmentally friendly enzyme-induced carbonate precipitation (EICP) on the dispersivity of dispersive soils. This methodology was tested for the stabilization of three dispersive soil types (two high-sodium soils, two low-clay-content soils, and two soils with both high sodium and low clay contents) to examine the impact on dispersivity based on the results of pinhole tests and mud ball tests. Physical, chemical, mechanical, and microscopic tests were also conducted to investigate the effects of the components in the EICP reaction solution on dispersive soil modification. The experiments showed that the concentration of the reaction solution and the curing time required to limit the dispersivity decreased with increasing clay content in the soil. Ca2+ limited the dispersivities of dispersive soils via four distinct mechanisms. The first mechanism was ion exchange; Ca2+ decreased the percentage of exchangeable sodium ions to less than 7% while reducing the thickness of the diffuse double layer such that the spacings between soil particles were reduced and the chemical dispersivity was limited. Second, Ca2+ increased the viscosity of the solution by salting out the organic matter present in the soybean urease. Subsequently, the D1-class physically dispersive soil was converted into an ND2-class nondispersive soil. Third, Ca2+ decreased the soil pH by reducing the CO32− content, which could hydrolyze to increase the soil alkalinity. Finally, the presence of Ca2+ led to the generation of cementitious minerals through the precipitation of CaCO3 crystals that continuously generated CO32−, filling and cementing soil particles and thereby limiting their physical dispersivity. These results indicated that a low-concentration EICP reaction solution efficiently controlled the dispersivities of the three dispersive soils. [ABSTRACT FROM AUTHOR]

The municipal wellfield in Collierville, Tennessee, is contaminated with trichloroethylene (TCE) and hexavalent chromium (Cr (VI)) due to industrial operations dating back to the 1970s and 1980s. This study aims to elucidate the aquifer's contaminant transport mechanisms by determining longitudinal and transverse dispersivities through inverse modeling. Utilizing MT3DMS for contaminant transport simulation, based on a well-calibrated groundwater flow model, and leveraging Python's multiprocessing library for efficiency, the study employs a trial-and-error methodology. Key findings reveal that longitudinal dispersivity values range from 5.5 m near the source to 20.5 m further away, with horizontal and vertical transverse dispersivities between 0.28 m and 3.88 m and between 0.03 m and 0.08 m, respectively. These insights into the aquifer's dispersivity coefficients, which reflect the scale-dependent nature of longitudinal dispersivity, are crucial for optimizing remediation strategies and achieving cleanup goals. This study underscores the importance of accurate parameter estimation in contaminant transport modeling and contributes to a better understanding of contaminant dynamics in the Collierville wellfield. [ABSTRACT FROM AUTHOR]

Copyright of New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigated the improvement behaviors on dispersivity, water stability and mechanical properties of dispersive soil by calcined coal gangue (CCG) at 700 °C, and analyzed the modification mechanism. Dispersive soil specimens with different content of CCG (varying from 1 % to 10 %) were prepared and cured for 0–28 days. The dispersivity of the soil was determined by three different dispersivity determination tests. The tensile strength and compressive strength of the dispersive soil were determined by mechanical property tests. SEM, EDS, TG and XRD analytical methods were employed to reveal microstructure and mineral changes during modification. The results of the study show that the admixture of CCG and the prolongation of curing time contributed favorably to suppressing the dispersivity of the soil and enhancing the water stability, the compressive strength and tensile strength of the dispersive soil. With the increasing of CCG content and the prolongation of curing time, the dispersive soil gradually transforms into non-dispersive soil. Microstructural and mineral analysis indicate that CCG has pozzolanic activity, and the production of pozzolanic reaction products significantly increase the friction and cohesion among soil particles. The results show that the utilization of CCG as an admixture to improve the dispersive soil not only solves the disposal problem of waste gangue, but also optimizes the undesirable characteristics of the dispersive soil. And the modification effect of CCG on dispersive soil in practical engineering is confirmed by validation test.

Dispersive soil is a common problem soil in engineering projects, which has the potential risk of causing serious engineering failures. In this paper, calcined waste phosphorus slag (CPS) was chosen to enhance the mechanical properties and reduce soil dispersivity. Dispersive soil samples with 1 % to 10 % CPS content were prepared and cured for 0 to 28 days. The dispersivity identification test was used to assess soil sample dispersivity. The compressive and tensile strength, conductivity, and pH were determined for the soil. Microstructural and mineral composition were analyzed using SEM/EDS, TG/DTG, and XRD analysis. The natural dispersive soil was selected to verify the effect of CPS in improving soil. Experiments show that the CPS inhibits soil dispersivity and converts it into non-dispersive soil. Both compressive and tensile strength increases significantly with the increase in the content of CPS and curing time. The tensile strength of the soil samples cured for 28 days increased by about 76 % and the compressive strength by about 61 % as the mixed content of CPS was increased from 1 % to 10 %. Results show that CPS can improve the strength and modify the dispersivity of soil, its optimal mixing content is 5 %. In addition, using CPS in dispersive soil could also solve the disposal problem of phosphate slag, which is a win-to-win solution.

In situ groundwater remediation technique is a commonly adopted method for the treatment of contaminated groundwater and the porous media associated with it. Engineered Injection and Extraction (EIE) has evolved as an improved methodology for in situ remediation, where sequential injection and extraction of clean water around the treatment area enhances the spreading of treatment reagents by inducing additional flow fields. Conventional EIE studies were based on flow fields in two dimensions. There are only limited experimental and theoretical studies exploring the potential of inducing a three-dimensional flow field using EIE. The present study experimentally and numerically evaluates the effect of a three-dimensional flow field induced by partially screened wells. EIE experiments were conducted on a laboratory-scale aquifer model with laterite soil as the porous medium. Tracer transport in porous medium was studied by measuring the concentration at various observation points and enhanced dilution was observed when EIE was employed with partially screened wells. Experimental observations were also used to calibrate and validate the numerical model developed using Visual MODFLOW Flex. Enhancement in spreading was quantified in terms of concentration mass attenuation and maximum mass attenuation was observed when EIE was employed with partially screened wells. HIGHLIGHTS Experimental investigation of engineered injection extraction (EIE) in three-dimension is carried out in this study using a laboratory-scale aquifer model.; Study experimentally proved the improvement in spreading when EIE is employed with partially screened wells over EIE with fully screened wells.; Calibrated and validated numerical model created using Visual MODFLOW Flex using experimental observations.;

The municipal wellfield in Collierville, Tennessee, is contaminated with trichloroethylene (TCE) and hexavalent chromium (Cr (VI)) due to industrial operations dating back to the 1970s and 1980s. This study aims to elucidate the aquifer’s contaminant transport mechanisms by determining longitudinal and transverse dispersivities through inverse modeling. Utilizing MT3DMS for contaminant transport simulation, based on a well-calibrated groundwater flow model, and leveraging Python’s multiprocessing library for efficiency, the study employs a trial-and-error methodology. Key findings reveal that longitudinal dispersivity values range from 5.5 m near the source to 20.5 m further away, with horizontal and vertical transverse dispersivities between 0.28 m and 3.88 m and between 0.03 m and 0.08 m, respectively. These insights into the aquifer’s dispersivity coefficients, which reflect the scale-dependent nature of longitudinal dispersivity, are crucial for optimizing remediation strategies and achieving cleanup goals. This study underscores the importance of accurate parameter estimation in contaminant transport modeling and contributes to a better understanding of contaminant dynamics in the Collierville wellfield.

Nano-clay has the potential to improve the properties of cement-based materials. However, the effectiveness of this improvement is influenced by the dispersion of the nano-clay. The effects of different nano-clay dispersion techniques on cement-based material properties and pore structure complexity were studied. The samples were prepared using manual and mechanical dispersion methods. The mechanical properties of the specimens were evaluated, and the pore characteristics of the cement-based materials were analysed using mercury intrusion porosimetry. The study investigated the effect of the dispersion method on the nano-clay dispersion. The complexity of the pore structure was evaluated using a fractal model, and the relationship between the fractal dimension, mechanical properties, and pore structure was analysed. The findings indicate that mechanical dispersion results in better dispersion than manual dispersion, and the mechanical properties of mechanical dispersion are superior to those of manual dispersion. Nano-clay particles can improve the internal pore structure of cement materials. Through mathematical calculation, the surface fractal dimension is between 2.90 and 2.95, with good fractal characteristics. There is a good correlation between the surface fractal dimension and the mechanical properties. The addition of nano-clay can reduce the complexity of the pore structure, and the fractal dimension has an excellent linear relationship with the pore structure. [ABSTRACT FROM AUTHOR]

Mixing of solute in sub-surface flows, for example in the leakage of contaminants into groundwater, is quantified by a dispersion coefficient that depends on the dispersivity of the medium and the transport velocity. Many previous models of solute transport data have assumed Fickian behaviour with constant dispersivity, but found that the inferred dispersivity increases with the distance from the point of injection. This approach assumes that the dispersion on either side of the advective front is symmetric and that the concentration there is close to half of the injected value. However, field data show consistent asymmetry about the advective front. Here, motivated by experimental data and a fractal interpretation of porous media, we consider a simplified heterogeneous medium described by a dispersivity with a power-law dependence on the downstream distance from the source and explore the nature of the asymmetry obtained in the solute transport. In a heterogeneous medium of this type, we show that asymmetry in solute transport gradually increases with the increase in heterogeneity or fractal dimension, and the concentration at the advective front becomes increasingly different from 50% of that at the inlet. In particular, for a sufficiently heterogeneous medium, the concentration profiles at late-time approach a non-trivial steady solution and, as a result, the concentration at a downstream location will never reach that at the inlet. By fitting the Fickian solution to our results, we are able to connect the parameters from our model to those found from experimental data, providing a more physically grounded approach for interpreting them. [ABSTRACT FROM AUTHOR]

This study assessed the dispersivity of soils extracted from the northern region of Cartagena de Indias (Colombia) using the pinhole test, crumb test, and chemical–microstructural analyses. Dispersive soils are susceptible to erosive phenomena upon contact with water, yet they have not been adequately characterized in the city. To evaluate the dispersivity degree of different deformed and undisturbed soil samples, soil characterization tests included particle size analysis, chemical composition, Atterberg limits, specific gravity, and compaction. The results showed that the soils are highly plastic clays (i.e., CH) with a slight to moderate dispersivity level (i.e., ND3) according to the pinhole test and a moderate degree of dispersivity confirmed by the crumb test. The extracted soil sample sodium levels ranged from 0.72% to 1.94%, and the soil had an optimal moisture content of 26% and a maximum apparent dry unit weight of 13.87 kN/m3. According to standards and results, Cartagena de Indias's studied marine clays are unsuitable for civil construction due to the degree of uncertainty in their behavior. [ABSTRACT FROM AUTHOR]

A comprehensive investigation of the characteristics of clay from the Gurlan deposit showed that in a chemical formulation Gurlan hydromicaceous clay possesses a relatively high content of iron oxide and alkali oxides as well as fine dispersity and a small amount of finely dispersed free quartz, which make this clay readily fusible. It was also found that the Gurlan clay can be used as a low-temperature fluxing component, instead of cullet, erklez [glass stones], nepheline syenite, etc., in the development of ceramic compositions. [ABSTRACT FROM AUTHOR]

The results of experimental studies of the dispersivity of an aerosol obtained using two injector devices arranged differently mutually are presented. The dependences of the numerical and volume concentrations of droplets in the aerosol formed in the course of variation of the relative angle of attack of jets on the size of droplets are presented. The limiting initial distances between droplets in the aerosol, at which the sizes of the droplets practically do not change during their free fall, are determined. Based on the research results, recommendations were formulated to ensure predictable distributions of the droplets of liquid in a gaseous medium at different distances from the fire zone. [ABSTRACT FROM AUTHOR]

In a comparison of modified nanoscale zero-valent iron (NZVI), bare NZVI used to remediate deep contaminated groundwater source areas has more advantages. However, the influence of injected bare NZVI deposition on the permeability of aquifer remains unclear, together with which are still the key factors of engineering cost and contamination removal. Hence, this study sought to assess a method of measuring hydraulic conductivity with a constant head device and to examine the permeability loss mechanism of NZVI injected into different saturated porous media, using column tests. The results showed that it was feasible to determine hydraulic conductivity by the constant head device. The permeability loss caused by NZVI injection increased with a decrease in the grain size of the porous media, and was determined by the amount and distribution of NZVI deposition. The NZVI distribution area had a good linear correlation with dispersivity of the porous media. Additionally, although surface clogging occurred in all porous media, the amount of NZVI deposition at the injection point was largest in fine sand, so that its permeability loss was the most; this was more likely to cause hydraulic fracturing and expand the area of the contaminant source zone. These results have implications for NZVI field injection for successful groundwater remediation. HIGHLIGHTS The amount and distribution of NZVI deposition determines permeability loss.; NZVI distribution area has a good positive linear correlation with dispersivity of the porous media.; Coarse and medium sand were classified as mix clogging, while fine sand was surface clogging.;

Rare earth luminescent complexes encounter defects such as poor thermal stability, poor dispersibility, and easy quenching of fluorescence emission by water in practical applications. To improve these defects, we innovatively propose using polyhedral oligomeric silsesquioxane (POSS) to enhance the performance of rare earth complexes. We designed and prepared POSS-MAA-EuL composite materials. POSS is modified with long chains containing -COOH functional groups, allowing it to bind with rare earth complexes through coordination interactions. Experimental results have shown that the combination of POSS not only improves the dispersibility of rare earth complexes, but also enhances their thermal stability. It is worth noting that the binding of POSS endows rare earth complexes with the ability of resisting fluorescence emission quenching by water. When the same volume of deionized water is added (2000 μL), the fluorescence of rare earth complex is almost completely quenched, with a quenching efficiency of 99.0 %, while the quenching efficiency of POSS-MAA-EuL is only 39.2 %. There are few reports on improving the water quenching resistance of rare earth luminescent complexes by combining with POSS. Therefore, this work provides a new way to improve the performance of rare earth complexes. [Display omitted] • The EuL complex modified by POSS-MAA exhibits a layered cubic morphology. • The composite of POSS-MAA enhances the dispersibility and thermal stability of EuL complexes. • POSS-MAA-EuL composite material exhibits resistance to water luminescent quenching. [ABSTRACT FROM AUTHOR]

The micro-continuum method is a novel approach to simulate flow and transport in multiscale porous materials. For such materials, the domain can be divided into three sub-domains depending on the local porosity ε : fully resolved solid phase, for which ε = 0, fully resolved pores, for which ε = 1.0, and unresolved pores, for which 0 < ε < 1.0. For such domains, the flow can be solved using the Darcy-Brinkman-Stokes (DBS) equation, which offers a seamless transition between unresolved pores, where flow is described by Darcy's law, and resolved pores, where flow is described by the Stokes equations. Species transport can then be modelled using a volume-averaged equation. In this work, we present a derivation of the closure problem for the micro-continuum approach. Effective dispersivity tensors can then be calculated through a multi-stage process. First, high resolution images are chosen for characterizing the structure of the unresolved pores. Porosity, permeability and effective dispersivity for the unresolved parts are calculated by solving a closure problem based on Direct Numerical Simulation (DNS) in the high-resolution images. The effective dispersivity is then expressed as a function of the Péclet number, which describes the ratio of advective to diffusive transport. This relationship, along with porosity and permeability, is then integrated into the multiscale domain and the effective dispersivity tensor for the full image is calculated. Our novel method is validated by comparison with the numerical solution obtained for a fully-resolved simulation in a multiscale 2D micromodel. It is then applied to obtain an effective dispersivity model in digital twins for two multiscale materials: hierarchical ceramic foams and microporous carbonate rocks. [Display omitted] • We derive a formulation of the closure problem for the micro-continuum approach for calculation of dispersivity. • The model is applied to calculate dispersivity in multiscale porous materials. • We apply our novel model to hierarchical foam with Kelvin cell of type 1 and 2, and to a carbonate rock (Estaillades). • We show that Kelvin cells oftype 1 are more efficient than Kelvin cells of type 1 to transport speciesinside the fibres. • We show that for calculation ona micro-CT image of Estaillades, a segmentation that includes 5 phases wassufficient. [ABSTRACT FROM AUTHOR]

Nano-clay has the potential to improve the properties of cement-based materials. However, the effectiveness of this improvement is influenced by the dispersion of the nano-clay. The effects of different nano-clay dispersion techniques on cement-based material properties and pore structure complexity were studied. The samples were prepared using manual and mechanical dispersion methods. The mechanical properties of the specimens were evaluated, and the pore characteristics of the cement-based materials were analysed using mercury intrusion porosimetry. The study investigated the effect of the dispersion method on the nano-clay dispersion. The complexity of the pore structure was evaluated using a fractal model, and the relationship between the fractal dimension, mechanical properties, and pore structure was analysed. The findings indicate that mechanical dispersion results in better dispersion than manual dispersion, and the mechanical properties of mechanical dispersion are superior to those of manual dispersion. Nano-clay particles can improve the internal pore structure of cement materials. Through mathematical calculation, the surface fractal dimension is between 2.90 and 2.95, with good fractal characteristics. There is a good correlation between the surface fractal dimension and the mechanical properties. The addition of nano-clay can reduce the complexity of the pore structure, and the fractal dimension has an excellent linear relationship with the pore structure.

This research explores the possibility of creating an underground water reservoir by injecting treated wastewater and evaluates the recovery efficiency and water quality under different injection/recovery scenarios. An injection/recovery well was established in the Dammam Formation aquifer in Kuwait. Six observation wells were also drilled nearby to monitor the water levels and quality. A three-dimensional (3D) numerical hydraulic and transport model was set up using the coupled version of MODFLOW and MT3DMS. Four scenarios of cyclic and continuous injection with different injection and pumping rates stretching over 5,400 days were investigated. Two dispersivity values, low (10 m) and high (200 m), were used in each scenario in order to establish the minimum and maximum recovery limits of useful water that can be expected from the site. The combination of injection rate of 650 m3/d and subsequent recovery at 1,000 m3/d proved to be the optimum option for the storage of water, resulting in good recovery efficiency and acceptable water quality. Based on these results, it was concluded that aquifer storage is a feasible strategy for mitigating growing water scarcity in the State of Kuwait and other countries in the larger Middle East. HIGHLIGHTS Aquifer storage is considered as one of the solutions to water scarcity.; The applicability of aquifer storage in the Dammam Formation in Kuwait has been investigated.; The results under various scenarios suggested that artificial aquifer recharge is a viable option.; From operational considerations, the lower rate of recharge (650 m3 d−1) and recovery (1,000 m3 d−1) is recommended.;

The effects of bed roughness on the longitudinal dispersion coefficient (DL) were experimentally and numerically investigated in the present study. The tracer experiments were first carried out in a circular flume with a diameter of 1.6 m over both smooth and rough beds (coarse sand) with four sizes (ks = d65) of 1.04, 2.09, 3.01, and 4.24 mm. In addition, the one-dimensional advection–dispersion equation was numerically solved. The longitudinal dispersion coefficient was calculated by comparing the numerical and experimental breakthrough curves. The results showed that by increasing the bed roughness height (from zero to 4.24 mm), the longitudinal dispersion coefficient increased by 34%. In addition, the longitudinal dispersivity (λ = DL/V) increased with increasing relative roughness (ks/h), so that the range of longitudinal dispersivities in smooth bed experiments were 0.037–0.049 m and for rough bed (ks = 4.24 mm) were 0.07–0.084 m. In other words, with increasing the bed roughness height from zero (smooth bed) to 4.24 mm, the longitudinal dispersivities increased from 0.037 to 0.077 m, indicating an increase of about 108%. Furthermore, a relationship was developed using non-dimensional longitudinal dispersion (DL/(Vh)) as a function of relative roughness (ks/h). It can be concluded that taking into consideration bed roughness as the driving force of shear dispersion would improve predictive equations of the longitudinal dispersion in the rivers. As the bottom of all natural rivers has roughness elements with different sizes, the results of this study will definitely be useful in estimating the longitudinal dispersion coefficient in natural rivers and quantifying the effect of roughness in the longitudinal dispersion coefficient equations. HIGHLIGHTS By increasing the bed roughness height (from zero to 4.24 mm), the longitudinal dispersion coefficient increased significantly.; A relationship was developed using non-dimensional longitudinal dispersion (DL/(Vh)) as a function of relative roughness.; Taking into consideration bed roughness as the driving force of shear dispersion would improve predictive equations of the longitudinal dispersion in the rivers.;

Copyright of Journal of Chinese Institute of Food Science & Technology is the property of Journal of Chinese Institute of Food Science & Technology Periodical Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study assessed the dispersivity of soils extracted from the northern region of Cartagena de Indias (Colombia) using the pinhole test, crumb test, and chemical–microstructural analyses. Dispersive soils are susceptible to erosive phenomena upon contact with water, yet they have not been adequately characterized in the city. To evaluate the dispersivity degree of different deformed and undisturbed soil samples, soil characterization tests included particle size analysis, chemical composition, Atterberg limits, specific gravity, and compaction. The results showed that the soils are highly plastic clays (i.e., CH) with a slight to moderate dispersivity level (i.e., ND3) according to the pinhole test and a moderate degree of dispersivity confirmed by the crumb test. The extracted soil sample sodium levels ranged from 0.72% to 1.94%, and the soil had an optimal moisture content of 26% and a maximum apparent dry unit weight of 13.87 kN/m3. According to standards and results, Cartagena de Indias’s studied marine clays are unsuitable for civil construction due to the degree of uncertainty in their behavior.

The aim of this study was to investigate the long-term effect of magnesium and iron nanoparticles on solute transport and its parameters, which has not been investigated to date. Different concentrations of two types of nanoparticle metal oxides, MgO and Fe3O4, were mixed with a loamy soil and their effects on solute transport and its parameters after three years were investigated. Nanoparticles improved soil structure through increased macro pores compared to the control, by 2.3% in the 3% concentration of MgO to 15.3% in the 3% concentration of Fe3O4. Immobile water content of the soil decreased from 0.42 in the control to 0.05–0.24 cm3 cm−3 in the treatments. The mass transfer coefficient was decreased from 0.48 in the control to 0.005–0.37 in the nanoparticle treatments. Moreover, nanoparticles increased the breakthrough curve peak concentration and decreased discharge time of chloride in the extract from 0.41 and 88.8 min in the control to 0.62–0.76 and 24.7–87.9 min in the treatments, respectively. The results of this study showed that the nanoparticles affected the solute transport and its parameters in the soil. Therefore, nanoparticles could be used to simplify the nutrients transport and leaching of salt and contaminants. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive approach to estimating annual atrazine residues in China's agricultural soils, integrating machine learning algorithms and mechanism-based models. First, machine learning was used to predict essential parameters influencing atrazine's adsorption, degradation, and dispersivity of solute transport. The results demonstrated that soil organic matter was the most important input variable for predicting adsorption and degradation; clay content was the primary variable for predicting dispersivity. The SHapley Additive exPlanations (SHAP) contribution of various soil properties on target variables were also analyzed to reveal whether each input variable has a positive, negative, or complex effect. Subsequently, these parameters inform the construction of a detailed model across 23,692 subregions of China, with a 20 km × 20 km resolution. The model considered regional variations and soil layer heterogeneity, including rainfall, soil depth-specific properties, and parameters for adsorption, degradation, and dispersivity. Utilizing the convection-dispersion equations and the Phydrus, the model simulated atrazine's transport and degradation patterns across diverse soil environments after applying 250 mL of atrazine (40%) per Chinese mu. The outcomes provided a spatially explicit distribution of atrazine residues, specifying that the arid areas have the highest residual risk, followed by the Northeast, Southwest, and Southeast. Atrazine levels may exceed national drinking water standards at 50 cm depth in Inner Mongolia, the Qinghai-Tibet Plateau, and the Jungar Basin. This study's integrative approach may also offer valuable insights and tools for evaluating residues of various pesticides and herbicides in agricultural soils. [Display omitted] • Machine learning effectively predicted adsorption, degradation, and dispersivity. • The annual fate and transport of atrazine was simulated by Phydrus. • Arid areas have the highest residual risk, followed by the Northeast China. • Atrazine levels may exceed 2 μg L−1 at 50 cm depth in some northwest regions. [ABSTRACT FROM AUTHOR]

The work is devoted to study of the high-temperature hydrochemical decomposition of mineral complexes of diaspore-bemite bauxites by the Bayer method with the extraction of macro-components-aluminum and iron in the presence of metal reducing agents. X-ray phase studies were performed to determine the composition and structure of new compounds in magnetized spent red mud. Based on the results of physical and chemical studies of leaching products, optimal parameters for reducing leaching of bauxite are recommended, aimed at extracting aluminum and synthesizing magnetite. The regularities of the influence of the type of metal reducing agent on the morphology, phase composition, and particle size in the red mud are revealed.

Heterogeneity significantly effects the accuracy of flow and contaminant transport prediction in subsurface formations. The spatial correlation structure of hydraulic conductivity (K) is a crucial factor to characterize the heterogeneous architecture. In presented study, the relationship between the spatial correlation structure of K and plume dispersion is analyzed through the integration of experimental and numerical simulation approaches. A detailed description on the sedimentary facies types in a column experiment is obtained to ensure the accuracy of the heterogeneous characterization. The spatial correlation structure of K is analyzed with the components of ln(K) covariance and facies transition probability structures. Lagrangian-based models are developed to estimate solute dispersion in nonreactive tracer injection experiments. The results show that the model can predict plume spreading accurately when the spatial correlation structure is well defined. The dispersivities calculated by the Lagrangian-based model are slightly higher than those obtained from the solute transport experiments. Further, the upscaled dispersivity derived from the transition probability is dominated by the cross-transition probability structure, while the contribution of the auto-transition terms is quite small. The numerical modeling results confirm that the upscaled dispersivity can reproduce the solute breakthrough in the heterogeneous sediment well. The scale dependence of dispersion is strengthened when the flow direction is perpendicular to the bedding plane where the conductivity dramatically changes along the flow path in a layered bedding sediment. [ABSTRACT FROM AUTHOR]

The engineering problems caused by dispersive soil are of worldwide concern. Traditional high carbon emission soil amendments such as cement and lime cause several environmental problems, including pollution and soil alkalization. Inorganic polymers are considered to be an economical, effective, and environmentally friendly soil amendment. Therefore, this paper proposes the use of the polymeric coagulant polyaluminum chloride (PAC) to improve soil dispersivity. PAC was added to the dispersive soils at different dry mass ratios of 0%, 0.5%, 1%, 1.5%, 2.5%, 4%, 5%, 6%, 7%, 8%, and 10%. The soil samples were then cured for 1, 4, 7, 14, and 28 days. Soil dispersivity was determined by crumb tests, pinhole tests, and exchangeable sodium ion percentage tests. Soil mechanical strength was assessed through unconfined compressive strength tests and unconsolidated undrained triaxial tests. Particle size distribution, pH, resistivity, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests were conducted to investigate soil improvement mechanisms. Experimental results indicate that 1.5% PAC can transform highly dispersive soil into non-dispersive soil after 1 day of curing. When the PAC content increases from 0% to 7%, the unconfined compressive strength of the soil increases by 110.1%, and the internal friction angle and cohesion increase by 61.1% and 24.2%, respectively. The changes in the physicochemical properties and microstructure of the soil indicate the high-valence cations produced by PAC hydrolysis can effectively replace Na+ in the soil, while significantly reducing the pH value of the soil. Simultaneously, the coagulation effect generated markedly reduces soil porosity, resulting in a more compact soil structure. In summary, PAC demonstrates excellent potential in improving soil dispersivity and mechanical properties. Compared to traditional high carbon emission amendments such as cement and lime, PAC can effectively reduce soil alkalinity, mitigate environmental issues associated with these materials, and offer new possibilities for improving dispersive soils. • 1.5% polyaluminum chloride transform dispersive soil into non-dispersive soil. • Polyaluminum chloride increase the strength of the soil by up to 113.19%. • 1.5% polyaluminum chloride reduces exchangeable sodium content in soils. • Intergranular cementation is different for different contents. [ABSTRACT FROM AUTHOR]

• An upscaling framework is proposed to predict dispersivity in natural fracture. • Geostatistical analysis of the fracture aperture is implemented. • The upscaling dispersivities of the fracture core samples are predicted. Fluid flow and mass transport parameters are greatly impacted by the fracture surface's heterogeneous properties. By quantifying the spatial correlation patterns of fracture apertures, this study intends to establish an upscaling framework utilizing Lagrangian-based transport models to estimate dispersivities of naturally fractured granite cores. To do this, the surface morphology of the fragmented core sample was photographed using a 3D laser profile scanner with varied degrees of accuracy. Following a geostatistical analysis of the fracture aperture data, common covariance models were fitted to determine the integral scale of log fracture aperture. This information was used to estimate dispersivity using the Lagrangian-based transport models, which only required the collection of fractured geostatistical data. The study also assessed how the dispersivities are affected by fracture lengths and the measurement accuracy of aperture data in this model. The findings showed that the fracture aperture spatial bivariate correlation structures follow the exponential covariance model. Additionally, while the variance of log fracture apertures is significantly influenced by both the data resolutions and the core samples themselves, the integral scale of log fracture apertures primarily depends on the length of the fracture. In terms of the fracture length, the upscaled dispersivities range from 2.35% to 7.21%. The development of upscaling techniques for estimating dispersivities in fractured and heterogenous granitic rocks and scaling them up to the field size for the accurate prediction of solute transport mechanisms can be guided by these findings. [ABSTRACT FROM AUTHOR]

The characterization and modelling of membrane chromatography processes require the axial dispersion coefficient as a relevant and effective intrinsic property of porous media, instead of arbitrary assumptions on pore size distribution. The dispersion coefficient can be easily measured by experiments completely independent of chromatographic tests. The paper presents the prediction of experimentally obtained breakthrough curves using B14-TRZ-Epoxy2 membranes as a test case; the mathematical model implemented is based on the use of the experimentally measured axial dispersion coefficient as an input parameter. Application of the model and its comparison with the data demonstrate that alternative ways of explaining the shape of breakthrough curves, based on unverified assumptions about the membrane pore size distribution, are not feasible and not effectively supported by experimental evidence. In contrast, the axial dispersion coefficient is the only measurable parameter that accounts for all the different contributions to the dispersion phenomenon that occurs in the membrane chromatography process, including the effects due to porous structure and pore size distribution. Therefore, mathematical models that rely on the mere assumption of pore size distribution, regardless of the role of the axial dispersion coefficient, are in fact arbitrary and ultimately misleading.

The relationship between the scale-dependent dispersivity and heterogeneous sedimentary structures is investigated through conducting non-reactive tracer experiments in a three-dimensional heterogeneous sand tank. The heterogeneous porous media consists of three sedimentary facies of silty, fine, and medium sands collected from the west of the Songnen Plain, China. Moreover, several corresponding individual facies soil columns were constructed for comparison. A conservative tracer was continuously injected from an upstream source. The effective parameters were estimated by inverse modeling of a one-dimensional transport model. The results show that the scale dependence of the estimated dispersivities was discovered in the individual facies column (with relatively weaker effect) and the heterogeneous porous media (with more significant effect). With increasing transport distances, the dispersivities of the individual facies tend to reach an asymptotic value, while those of the heterogeneous media increase continuously. Furthermore, the results show that a power function can describe the relationship between effective dispersivities and transport distances. The exponent of the function is greater than one for the heterogeneous media, but less than one for the individual facies. The results also indicate that the dispersion plume is macroscopically dominated by the distribution of facies. The heterogeneity of hydraulic conductivity causes the variations of flow velocity, which further enhances the scale dependence of dispersivities. The tracer experiment in heterogeneous media provides the fundamental insight into the understanding of contaminant transport processes. [ABSTRACT FROM AUTHOR]

The objective of this paper is to evaluate effects of stratified porous formation on solute dispersion using twodimensional laboratory tracer tests. An image analysis technique was used to analyze the solute dispersion processes and quantify the dispersivity and behaviors of forward and backward tails of solute plumes. Longitudinal dispersivity estimates for the stratified porous media increased with travel distance and are in reasonable agreement with previous work. Moreover, in all of the stratified cases the transverse dispersivity exhibited a similar trend which decayed with travel distance. The summary of dispersivities estimated from this study and previous studies suggests that if both degree of heterogeneity and scale for stratified and randomly heterogeneous porous media are similar, the longitudinal dispersivity is larger in stratified media than in randomly heterogeneous media. In order to quantify behaviors of forward and backward tails, we defined the travel distances x05 and x95 corresponding to the 5th and 95th percentiles, respectively, of the cumulative concentrations in the longitudinal direction, and found that the distance between x05 and x95 spread out linearly in the stratified cases. [ABSTRACT FROM AUTHOR]

Calcite dissolution, porosity development are strongly influenced by mixing phenomenon, fluid density and heterogeneity (variability of the hydraulic proprieties). This study presents an approach for calculating porosity change in a heterogeneous porous media during mixing of seawater and freshwater. The proposed approach is based on the Phillip’s analytical solution and is determined by five main steps: (1) Generate a random K-field, (2) Calculate the flow and transport of the heterogeneous porous media, (3) Evaluate the dispersivity coefficient results of the heterogeneity aspect, (4) Evaluate the dissolution capacity of calcite during mixing of two solutions and (5) calculate the porosity change. This approach takes into account the effect of the aquifer heterogeneity on the dispersivity and is applied to simulate the effect of calcite dissolution on the porosity development in a heterogeneous idealized aquifer during seawater intrusion. Results presented in this work are preliminary to assess the effect of heterogeneity on the geochemical reaction during mixing. [ABSTRACT FROM AUTHOR]

Summary: Based on the frame of elastic theory for unsaturated porous medium, considering the influence of thermal effect, the propagation characteristics of Rayleigh wave in unsaturated porous media are studied. Firstly, the thermoelastic wave equations for three‐phase porous media are established, in which the mass balance equations, generalized Darcy law, momentum balance equations, and generalized non‐Fourier heat conduction law are taken into account. Secondly, through theoretical derivation, the dispersion equation of Rayleigh wave for unsaturated porothermoelastic media is given by introducing the potential functions. Finally, the variations of the phase velocity of Rayleigh wave are analyzed with numerical examples. The results show that the thermal conductivity has little effect on the phase velocity of Rayleigh wave. The phase velocity of Rayleigh wave increase with increasing of the thermal expansion coefficient and media temperature. [ABSTRACT FROM AUTHOR]

The main objectives of this study is to model the transport of methylene blue (MB) in homogenous and layered soils which has been studied experimentally by fixed bed column. The effect of soil stratification has been studied through numerical investigation based on the coupled solute transport model in three-layered soil. The effect of some significant parameters such as flow rate, initial concentration of MB, thickness of each layer and the numbers of layers on the breakthrough curves have been undertaken. A finite element analysis model was employed to predict the transport of MB in soils. A two dimensional model based on Richards equation and advection-dispersion equation coupled with adsorption model has been developed and an analytical model has been used to predict the dispersivity. The results shows that the soil heterogeneity has a significant effect on methylene blue (MB) adsorption through unsaturated layered media and the effect of the parameters of the upper layer of the soil is more significant than those of the lower layer but this effect can be controlled with the choice of the thicknesses of each layer. [ABSTRACT FROM AUTHOR]

Continuum‐scale models for two‐phase flow and transport in porous media are based on the empirical constitutive relations that highly depend on the porous medium heterogeneity at multiple scales including the microscale pore‐size correlation length. The pore‐size correlation length determines the representative elementary volume and controls the immiscible two‐phase invasion pattern and fluids occupancy. The fluids occupancy controls not only the shape of relative permeability curves but also the transport zonation under two‐phase flow conditions, which results in the non‐Fickian transport. This study aims to quantify the signature of the pore‐size correlation length on two‐phase flow and solute transport properties such as the capillary pressure‐ and relative permeability‐saturation, dispersivity, stagnant saturation, and mass transfer rate. Given the capability of pore‐scale models in capturing the pore morphology and detailed physics of flow and transport, a novel graphics processing unit (GPU)‐based pore‐network model has been developed. This GPU‐based model allows us to simulate flow and transport in networks with multimillions pores, equivalent to the centimeter length scale. The impact of the pore‐size correlation length on all aforementioned properties was studied and quantified. Moreover, by classification of the pore space to flowing and stagnant regions, a simple semianalytical relation for the mass transfer between the flowing and stagnant regions was derived, which showed a very good agreement with pore‐network simulation results. Results indicate that the characterization of the topology of the stagnant regions as a function of pore‐size correlation length is essential for a better estimation of the two‐phase flow and solute transport properties. Key Points: A novel fully GPU‐based pore‐network model simulates two‐phase flow and transport at the centimeter‐scaleA semianalytical equation for mass transfer across flowing and stagnant regions is validated against simulation resultsPore‐size correlation length controls the constitutive relations for two‐phase flow and transport through porous media [ABSTRACT FROM AUTHOR]

Dispersivity and chemical composition of ash and slag particles at dust combustion of milled peat were investigated in this work. Shapes and sizes of the particles depending on the sampling points in different parts of the boiler system were determined experimentally. The histograms and the particle size distribution functions were obtained.

Chemical composition, dispersivity and optical properties of peat ash particles are investigated in this paper. Calculation of gas phase components is based on thermal characteristics of the original fuel. Methodology and results of the calculation of the thermal radiation of heterogeneous combustion products at peat burning are given.

• Two simplified methods are proposed based on t p and t a to estimate the regional groundwater flow velocity, effective porosity and dispersivity; • Compared with previous methods, the t a method takes the chase phase into account which is important to minimize the impact of well skins and wellbore storage on the shape of BTCs; • Compared with traditional curve-fitting methods, the t p and t a methods require fewer observation data and do not require any optimization algorithms, thus avoiding the problem of falling into local optimum. The single-well push–pull (SWPP) test has been widely used for several applications, including determination of transport parameters such as regional groundwater flux velocity, effective porosity and dispersivity. A complete SWPP test usually includes four phases of injection, chase, rest, and extraction, while previous models mostly ignore the chase phase for the sake of simplification. Actually, the chase phase is important to minimize the impact of well skins and wellbore storage on the shape of the breakthrough curves (BTCs), thus is necessary and should be included in the model. To this end, two simplified methods are proposed in this study based on two different time t p and t a during a four-phase SWPP test to estimate the parameters related to transport, where t p and t a correspond to the time of the peak concentration during the injection phase and the time when the center of tracer mass returns to the wellbore during the extraction phase, respectively. Specifically, the t p method can be used to estimate the regional groundwater flow velocity and dispersivity (transverse and longitudinal), while the t a method is used to estimate the regional groundwater flow velocity and the effective porosity. Finite-element numerical modeling of the SWPP test based on the coupling of two-dimensional transient groundwater flow and solute transport is employed to test the applicability of the proposed methods. Results indicate that both the t p and t a methods proposed in this study perform satisfactorily in estimation of regional groundwater flow velocity, effective porosity and dispersivity, and these two methods require fewer observations than traditional curve fitting methods and do not require any optimization algorithms. We have also compared the proposed two methods with several previous methods, and conclude that these two new methods generally perform better than those of previous studies in terms of parameter estimation reliability. [ABSTRACT FROM AUTHOR]

• Improving test of dispersive soil is conducted by GGBFS in this study. • Dispersive soil can be changed into nondispersive soil by the admixture of GGBFS. • GGBFS could enhance the water stability of dispersive soil. • Mechanical properties of dispersive soil are improved by GGBFS. This paper focused on the influence of ground granulated blast furnace slag (GGBFS) on the dispersivity and mechanical properties of dispersive soil. Different contents of GGBFS, varying from 1% to 10%, were mixed in dispersive soil and curried for 28 days. Eroded soil weight and flow speed during pinhole test under different water heads were recorded. Dispersivity of soil samples was determined by pinhole test and two kinds of crumb test. Unconfined compression test and splitting test were conducted to determine the compressive and tensile strength of soil samples. Electronic conductivity and pH were also measured during curing time for all soil samples. Microstructural and mineral analyses of soil samples were performed by SEM (with EDS), XRD, and TG/DTG tests. A natural dispersive soil sample was selected to validate the improving effectiveness of GGBFS on the dispersivity and mechanical property of dispersive soil. Experiments show that water stability, compressive strength and tensile strength of dispersive soil are significantly improved with the increase in the mixed content of GGBFS in soil. Results indicate that GGBFS is capable of improving both the dispersivity and mechanical properties of dispersive soil, and this effect is more obvious with the increase in curing time. Appropriate curing time is encouraged during the construction process to intensify the improving effect of GGBFS. Enhancing of water stability of dispersivity soil by GGBFS would ensure the safety and normal operation of soil constructions in geotechnical, agricultural, and hydraulic engineering, which could be a win-win application in the future. The use of GGBFS can effectively reduce the environmental problems caused by the use of traditional high carbon emission materials such as cement and lime. [ABSTRACT FROM AUTHOR]