Sedimentation Behavior Research Articles

Phosphorus immobilization/release behavior of lanthanum-modified bentonite amended sediment under the dual effects of pH and dissolved organic carbon

Lanthanum modified bentonite (LMB) is typical P-inactivating agent that has been applied in over 200 lakes. Dissolved organic carbon (DOC) and high pH restrict the phosphorus (P) immobilization performance of LMB. However, the P immobilization/release behaviors of LMB-amended sediment when suspended to overlying water with high pH and DOC have not yet been studied. In the present work, batch adsorption and long-term incubation experiments were performed to study the combined effects of pH and DOC on the P control by LMB. The results showed that the coexistence of low concentration of DOC or preloading with some DOC had a negligible effect on P binding by LMB. In the presence of DOC, the P adsorption was more pronounced at pH 7.5 and was measurably less at pH 9.5. Additionally, the pH value was the key factor that decided the P removal at low DOC concentration. The increase in pH and DOC could significantly promote the release of sediment P with a higher EPC0. Under such condition, a higher LMB dosage was needed to effectively control the P releasing from sediment. In sediment/water system with intermittent resuspension, the alkaline conditions greatly facilitated the release of sediment P and DOC, which increased from 0.087 to 0.581 mg/L, and from 11.05 to 26.56 mg/L, respectively. Under the dual effect of pH and DOC, the P-immobilization performance of LMB was weakened, and a tailor-made scheme became essential for determining the optimum dosage. The desorption experiments verified that the previously loaded phosphorus on LMB was hard to be released even under high pH and DOC conditions, with an accumulative desorption rate of less than 2%. Accordingly, to achieve the best P controlling efficiency, the application strategies depending on LMB should avoid the high DOC loading period such as the rainy season and algal blooms.

A hydrate reservoir renovation device and its application in nitrogen bubble fracturing

Abstract. Natural gas hydrate (GH) is a significant potential energy source due to its large reserves, wide distribution, high energy density, and low pollution. However, the gas production rate of past gas hydrate production tests is much lower than the requirement of commercial gas production. Reservoir stimulation technologies like hydraulic fractures provide one potential approach to enhance gas production from GH. The reservoir reformation behavior of the hydrate-bearing sediments (HBSs), particularly sediments with a high clay content, is a complex process during a hydraulic fracturing operation which has been poorly understood and thus hardly predictable. This paper presents an experimental facility that was developed to analyze the hydraulic fracture mechanism in synthesized HBSs. This facility can be used to form GH in sediments, conduct visual observation of hydraulic fracturing experiments, and measure the permeability of HBSs under high-pressure (up to 30 MPa) and low-temperature conditions (from 253.15 to 323.15 K). It is mainly composed of a pressure control and injection unit, a low temperature and cooling unit, a cavitation unit, a visual sapphire reactor, and a data acquisition and measurement unit. The hydraulic fracture module consists of a gas cylinder, fracturing pump, hopper, proppant warehouse, and valves. The sapphire reservoir chamber is applied to observe and measure the fracture of HBSs during hydraulic fracturing. The permeability test module is composed of a constant-flux pump and pressure sensors, which can evaluate the permeability performance before and after the hydraulic fracture in HBSs. The fundamental principles of this apparatus are discussed. Some tests were performed to verify hydraulic fracture tests, and permeability tests could be practically applied in the HBS exploitation.

Sustainable Coating Materials: Exploring the Influence of Adjuvants on Kaolinite Suspension with Insights from Five Local Mining Clays.

Herein, we presented a comprehensive case study on the kaolin suspension derived from mining powder, with a specific emphasis on its mineral constituents within the size range of 2-5 μm and its suitability in spray applications. We have systematically investigated the influence of adjuvants, existing in both organic molecules and polymers, on the sedimentation behavior of clay suspensions. The investigations included the analysis of turbidity, dispersion weight, pH, and surface charge as key parameters. Our findings revealed that the specific presence of PEG-PPG-PEG, PAA, and PSAMA had a notable effect on delaying the suspension of sedimentation by the actual sediment weight as well as enhancing the uniformity of clay coating by the reflection efficiency of coating materials in PPFD units. To enhance sustainability in coating materials, it was essential to elucidate the optimal amounts of adjuvants and the pH levels as they are closely related to the efficacy of tree-coated spraying and soil conditions.

Effects of tire-road wear particles on the adsorption of tetracycline by aquatic sediments.

Tire-road wear particles (TRWPs) are formed by friction between the tire and the road. TRWPs are ubiquitous across the globe, especially in sediments. However, the possible effects of TRWPs on tetracycline (TC) in aquatic sediments are unknown. To investigate the potential role of TRWPs as carriers of co-pollutants, this study investigated the pore surface properties and TC adsorption behavior of TRWP-contaminated sediments and explored the TC behavior in water sediments, as well as the role of aging processes and TRWPs abundance. The results showed that the surface morphology of TRWP-contaminated sediments changed and the adsorption capacity of sediments to TC increased. The TC adsorption capacity of sediments contaminated by 2% TRWPs increased from 3.15 to 3.48mg/g. Moreover, the surface physical and chemical properties of TRWPs after UV aging changed, which further increased the TC adsorption capacity. The TC adsorption capacity of the sediments contaminated by aged TRWPs increased from 3.48 to 3.65mg/g. Changing the proportion of aged TRWPs, we found that the adsorption capacity of sediments contaminated by different proportions of TRWPs for TC was 2% > 1% > 0.5% > 4% > blank sediment. These results may contribute to predicting the potential environmental risks of TRWPs in aquatic sediments.

An analytical study for predicting incipient motion velocity of sediments in ecological open channel flows

Sediment movements on the riverbeds are crucial in fluvial processes. Therefore, studying incipient sediment motion is valuable for predicting changes in sediment behavior. In this study, the influence of aquatic vegetation is introduced into the momentum balance equation under the condition of a bare bed. The presented model for incipient sediment motion in open channels covered by vegetation is derived, in consideration of vegetation density and relative submergence. This study simplifies the model format. The model and its coefficients demonstrate good applicability to various working conditions without requiring numerous changes. The predicted velocity determined by the proposed model is validated against experimental data. Results show excellent agreement between the two in various scenarios, including combinations of rigid or flexible conditions and submerged or emergent states. Additionally, the velocity for incipient sediment motion is observed to decrease with increasing vegetation density. However, a further increase in vegetation density may amplify vegetation resistance, hindering incipient sediment motion. Meanwhile, sediment movement becomes challenging as water depth increases, assuming that flow discharge and vegetation conditions remain constant.

Sedimentation kinetics of kaolinitic and illitic clay: Impact of cation valence, ionic concentration, and water content

Investigating the sedimentation of clay in saline water was extensively studied because of its wide applications in engineering. This study investigated the impact of cation valence, ionic concentration, and water content on sedimentation behavior of kaolinitic and illitic clays through batch sedimentation tests for the comprehensive understanding of clay particle association and elapsed time for the transition of settling regimes from initial hindered settling to zone settling. The quantitative representation of observed settling curves was achieved using four fitted parameters in batch sedimentation model, which represented the shape of settling curves and the boundary of the initial hindered, zone, and consolidation settling regimes. In addition, the obtained settling velocity from the settling curves provided the fraction of clay particles and the size of clay flocs. The observed settling curves, trends of fitted parameters, and the estimated size of clay flocs shown in this study implied that the type of clay particle association (face-to-face aggregation or edge-to-face flocculation), settling velocity, final interface height, and boundary between initial hindered and zone settling are function of clay mineralogy, water content, cation valence, and ionic concentration.

Mechanical Behavior of Hydrate-Bearing Clayey-Silty Sediments in the South China Sea: Strain-Rate Dependency

Mechanical Behavior of Hydrate-Bearing Clayey-Silty Sediments in the South China Sea: Strain-Rate Dependency

Incorporation of snail meat particles in gellan gum fluid gels: Stability against sedimentation and rheological behavior

Snail meat, despite its nutritional value and popularity in some countries, is still underutilized due to its slimy texture. Snail meat powder could be an alternative way to exploit this source of protein. In the present study, the effect of incorporating snail meat powder without the mucus (SMWM) into the matrix of a fluid gel of gellan gum (GG) was studied in terms of SMWM particles stability against sedimentation and gels rheological features, at pH 4.5 and 7.8. All gels were stable against sedimentation after storage, except those with SMWM at pH 7.8 in the presence of NaCl, attributed to deacetylation of GG during gel formation. Τhe particles were larger at pH 7.8 than those at pH 4.5, whilst the presence of NaCl resulted in smaller particles. The presence of SMWM increased the final viscosity of the GG gel at pH 4.5 upon cooling. The transition temperature at pH 4.5 was higher in that case compared to GG gel. The presence of NaCl had a profound effect on the GG rheological behavior when SMWM particles were present regardless the pH or the concentration. A 3D network was developed according to G′ predominating values over the G″, but the narrow differences indicated its delicate nature. All gels, except that at pH 7.8 with SMWM, demonstrated a typical shear thinning behavior of a non-Newtonian fluid. Overall, the stabilization of SMWM particles in the network of GG fluid gel is promising, especially at pH 4.5 and in the presence of 0.25% NaCl.

The Influence of Current Magnitudes and Profiles on the Sedimentation of Magnetorheological Fluids: An Experimental Work

Magnetorheological fluids (MRFs) are widely used for various kinds of controllable devices since their properties can be controlled by an external magnetic field. Despite many benefits of MRFs, such as fast response time, the sedimentation arisen due to the density mismatch of the compositions between iron particles and carrier oil is still one of bottlenecks to be resolved. Many studies on the sedimentation problem of MR fluids have been carried out considering appropriate additives, nanoparticles, and several carrier oils with different densities. However, a study on the effect of current magnitudes and profiles on the sedimentation is considerably rare. Therefore, this study experimentally investigates sedimentation behaviors due to different current magnitudes and different magnitude profiles such as square and sine waves in different diameters. The evaluation was performed by visual observation to obtain the sedimentation rate. It was found that the average sedimentation rate of the square type of current is slower compared to the sinusoidal type. It has also been identified that the higher intensity of the applied current results in a stronger electromagnetic field, which could slow down the sedimentation. The results achieved in this work can be effectively used to reduce particle sedimentation in the controller design of various application systems utilizing MRFs in which the controller generates a different magnitude and different profile of the external magnetic field.

Intrinsic correlation between the generalized phase equilibrium condition and mechanical behaviors in hydrate-bearing sediments

The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs. In heating closed systems, the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate, reflecting the porous media effect in phase equilibrium. A generalized phase equilibrium equation was established for hydrate-bearing sediments, which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane. In contrast to bulk hydrate, hydrate-bearing sediment always contains a certain amount of unhydrated water, which keeps phase equilibrium with the hydrate within the hydrate stability field. With changes in temperature and pressure, a portion of pore hydrate and unhydrated water may transform into each other, affecting the shear strength of hydrate-bearing sediment. A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment. The model is validated by experimental data with various hydrate saturation, temperature and pressure conditions. The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress. The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation. The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.

Dimensional analysis for sedimentation behavior of magnetorheological fluids

Magnetorheological fluids (MRFs) are primarily composed of magnetic particles suspended in carrier liquids, exhibiting a remarkable capacity to respond dynamically to external magnetic fields. However, the phenomenon of solid–liquid phase separation, attributable to particle sedimentation, represents a formidable barrier to the real-world application of MRFs in engineering contexts. As a result, it becomes critically imperative to conduct a thorough investigation into the sedimentation behavior of MRFs under static conditions, to significantly enhance their practical utility. In the study, computational analysis through COMSOL was utilized to elucidate the sedimentation dynamics of MRFs. The findings indicated that particle sedimentation harbored the potential to induce localized turbulence within the flow field, thereby significantly impacting the sedimentation dynamics of MRFs. The motion of particles consistently followed a pattern where sedimentation rates decreased as the viscosity of the carrier liquids increased. Moreover, the elucidation of the settling behavior of MRFs was facilitated by the introduction of two dimensionless numbers. These dimensionless numbers were employed to systematically characterize the temporal evolution of the supernatant height throughout the settling process. This investigation further explored the intricate interdependence between these dimensionless parameters via a comprehensive series of settling experiments. The outcomes of this research uncovered a unique pattern in the solid–liquid separation process of MRFs, marked by a phase of gradual initiation, followed by acceleration, and culminating in deceleration. However, as the viscosity of the carrier liquids increased, this pattern became less pronounced, gradually shifting toward a more uniform settling trajectory.

An experimental and numerical study investigating sediment transport position in the bed of sewer pipes in Karbala

Abstract The complex phenomenon of sedimentation in urban areas is well studied using numerical models. Because they may be used to mimic sediment flow, obstructions, and drainage system optimization, the simulations are useful in urban planning and design. By merging ANSYS Fluent with Rocky, researchers were able to track the motion of sediment particles of various sizes and speeds. The sizes of the sediment particles were measured using a sieve after being collected from the streets of Karbala. The particle sizes established by the sieve analysis were used in both the computational and experimental procedures. Varied particle sizes and velocities, including 0.1, 0.2, 0.3, 0.35, 0.4, and 0.49 m/s, as well as varied particle sizes, including 0.4, 0.6, 0.8, 0.1, and 1.2 mm, were investigated. Numerical analysis showed that 1.2 mm-sized particles sedimented between 10 and 148 cm from the input pipe’s X coordinate at a rate of 0.49 m/s. A maximum sedimentation distance of 380 cm was also observed for particles with a diameter of 1 mm. Sediment did not include 0.4 mm-sized objects flowing at the same speed. The findings demonstrated that particle size and velocity significantly impacted the quantity of drag and lift forces acting on the particles. As the particle size increased, the drag force increased, which led to more sedimentation. The particle positions along the X coordinate (pipe bed) showed a declining trend. Overall, this work offers crucial insights for understanding sediment transport in urban drainage systems by illuminating the connection between velocity, particle size, and sedimentation behaviour.

Insights on trace metal enrichments in tourists beaches of Santa Elena Province, Ecuador

Metal concentrations in beaches of major coastal cities is directly identified based on the enrichment pattern of bioavailable metals in sediments. The main objective of the study is to know the present level of metal enrichments in beach sediments of Santa Elena Province in Ecuador. Sediment beach quality was assessed in five tourist beach zones (n = 52) by analyzing the bioavailable trace metal concentration. Distribution pattern of trace metals indicates Cd, Co, Pb is on higher side exceeding the UCC. Geochemical indices calculations (Geoaccumulation index, Enrichment factor, Degree of contamination) and ecological risk indices (Hazard quotient, potential risk index, pollution load index) indicates that Cd has the high degree of enrichment level (Cd ≥ 32) followed by Co, Pb and As posing adverse ecological risk (RI > 600). Sediment quality assessment results reveals that the sediments were very unsafe in nature with a probability level of 11–21% being toxic. Statistical correlation suggests that carbonates vs Cu, Ni, Co, Pb, Cd (r2 = 0.51–0.98) were the main controlling factor for the metal behavior in sediments. Overall results reveals that the toxic elements were derived locally accompanied by anthropogenic influences enriching the geochemical elements affecting the beach quality in the Santa Elena coast region and for future coastal management programs.

Plasma pretreatment to enhance the sedimentation of ultrafine kaolinite particles: Experiments and mechanisms

Coal-slime water treatment not only has a direct impact on the reuse of water as well as the recovery of coal-slime, but also has an essential significance for the sustainable development of a green ecology and carbon neutrality. In this study, the sedimentation behavior of ultrafine kaolinite particles (the main component of high-ash fine slime) using plasma pretreatment was investigated via sedimentation tests, turbidity detections and high-speed camera observations. The results showed that with plasma pretreatment, the arrival time of the maximum (final) thickness of the thickening layer considerably shortens, the final thickness of the thickening layer slightly decreases, and the turbidity of the supernatant significantly reduces. The mechanism of the plasma pretreatment method for the enhanced sedimentation of ultrafine kaolinite particles was elaborated via laser particle size analysis, microscopic observations, zeta potential determinations, and particle interaction energy calculations. The results showed that with plasma pretreatment, the zeta potential of kaolinite particles lowers, and the decrease in repulsive electrostatic force strengthens the coagulation of kaolinite particles, therefore making kaolinite flocs more compact and enhancing the sedimentation process of ultrafine kaolinite particles. And the enhanced sedimentation mechanism of ultrafine kaolinite particles via plasma pretreatment was drawn.

Viscosity of Cohesive Sediment‐Laden Flows: Experimental and Empirical Methods

AbstractThe rheological behaviors of suspended sediments are crucial for investigating near‐bed particle dynamics; for these investigations, the viscosity of a highly concentrated suspension is primarily focused on quantifying its resistance to deformation. By using a rotational viscometer, the relationships between relative viscosities (ηr) for different sediment types and their volumetric concentrations (ϕ) are studied for low‐to high‐concentration slurries. The results show that the conventional Einstein formula for diluted sand severely underestimates ηr. In the case of pure silts and non‐cohesive quartz, ηr demonstrates a gradual linear increase, reaching values around order of 101 as ϕ increases within the range of 0.2–0.4. Meanwhile, the ηr values of clays exhibit an exponential rise before leveling off at a plateau. Specifically, the ηr values of kaolinite, montmorillonite, and bentonite rise with ϕ lower than 0.3 and reach to plateau of values of thousands, which rise more rapidly than chlorite and illite. The modified viscosity model based on Costa (2005, https://doi.org/10.1029/2005GL024303) agrees reasonably well with observations and produces similar ηr ∼ ϕ relationships. In addition, the model is coupled with a hydrodynamic model to simulate the deposition of a thickened tailings slurry and a one‐dimensional dam break. The proposed model performs well in predicting the quasi‐equilibrium profiles of the non‐Newtonian fluid, which are validated by available analytical solutions. The results suggest that future models should be focused on the effects of flow properties, especially for non‐Newtonian fluids, and on large‐scale modeling applications, which can increase the accuracy of predictions of the transport characteristics of sediments and pollutants in rivers, lakes, and coastal areas.

Investigating Sedimentation Behavior of Montmorillonite Flocs between Flat Plates in a 2D System Using Image Analysis

The sedimentation of flocs in aquatic environments is a fundamental phenomenon that has not yet been fully elucidated. This study quantitatively examines sedimentation behavior, particularly focusing on sedimentation turbulence, in a two-dimensional system between flat plates, utilizing image analysis. Experiments were conducted in a rectangular container with montmorillonite suspensions coagulated in a sodium chloride solution. The settling motion of flocs was visualized using a green laser from above and captured horizontally with a digital camera. The study employed Particle Image Velocimetry (PIV) to analyze the velocity field in floc sedimentation, using the flocs as tracers to calculate the mean velocity at the sediment–supernatant interface. The results showed that the mean PIV value is affected by rising particles caused by sedimentation turbulence, indicating that PIV analysis of flow fields using flocs as tracers is reliable. The maximum settling velocity was found to increase with the initial interface height and the thickness of the container. The study further notes that flow velocity fluctuations increase during rapid sedimentation, marked by repeated collisions, separation, and the flocculation of variably sized flocs, offering a clear explanation of sedimentation turbulence. Additionally, Fourier analysis of vertical spectra in the container reflects the formation and collapse of flocs.

Effect of Hydrate Saturation and Pore Pressure on the Safe Exploitation of Natural Gas Hydrate Resources

A comprehensive study of the mechanical behaviors of hydrate-bearing sediments (HBSs) is the key to safely exploiting hydrate resources. The mechanical behaviors of HBSs are related to many variables, among which hydrate saturation (Sh) and pore pressure (PP) are vital factors. In addition, Sh and PP are related to the location of hydrates in the subsea layer, so it is of positive significance to investigate their comprehensive influence on the mechanical behavior of HBSs. In this work, a series of triaxial tests were conducted on the HBSs synthesized in the laboratory to explore the influence of Sh and PP on the mechanical properties of the HBSs. The results show that the strength of HBSs increases with increasing PP and Sh. With increased PP and Sh, the stress-strain behaviors will shift from strain-hardening to strain-softening. Moreover, under different Sh conditions, a critical PP point of strain-hardening and softening transition exists in numerical perspective. The critical PP point will develop towards low pressure with increased Sh.

Experimental evidences of bio-chemo-mechanical processes in contaminated sediments

The research shows the results of a micro to macro testing programme carried out on contaminated marine sediments from a natural deposit to assess the effects of bio-chemo-mechanical coupled processes which may act in complex natural environments and affect the geotechnical properties of the clays. The research has been triggered by the emblematic case of the contaminated Mar Piccolo (MP) basin in Taranto (Southern Italy), where the high degree of pollution recorded in the clayey sediments at the sea bottom, has been found to worsen water quality and promote bioaccumulation of pollutants in several species. Several samples of sediments collected in the basin from the top layer exhibited peculiar geotechnical properties, in terms of plasticity and activity indexes, compressibility and hydraulic permeability. The results of the geotechnical testing were interpreted taking into account the XRD mineralogical results and the chemical composition of the soil matrix. Furthermore, thermogravimetry tests results were examined to explore the nature of the sediment skeleton and of its organic matter content, based on the main thermal reactions occurring within different temperature ranges. Lastly, scanning electron microscopy and mercury intrusion porosimetry were performed to assess the sediment pore size distribution as well as their content in microfossils and diatoms. The original multiscale analysis carried out on some selected sediment samples showed that the biogeochemical degradation of organic matter and the presence of microfossils and diatoms significantly affect the micro to macro behaviour of marine sediments.

Mechanical behaviour and microstructure of methane hydrate-bearing sandy sediment observed at various spatial scales

Methane hydrates (MHs) are considered an alternative energy resource but also a potential source of geo-hazards and climate change. The physical/mechanical properties of gas hydrate-bearing sandy sediments are strongly dependent on the distribution of hydrates within the pore space. The purpose of this study is to investigate morphologies and pore-habits of MHs formed in sandy sediments by means of experiments that probe a wide range of scales, from the pore scale – using Synchrotron X-Ray Computed Tomography (SXRCT) and optical microscopy – to the core scale, through mechanical property measurements. The same synthetic sands are used, in which MHs are generated successively under excess gas and excess water conditions. At the macroscopic (core) scale, MH pore habits are inferred by comparing the measured sonic wave velocities to velocities calculated from rock physics models and further assessed via triaxial compression tests. Furthermore, Magnetic Resonance Imaging is used to investigate the kinetics of MH formation and distribution along the core height. The pore habits and MH morphologies are directly visualized at the pore (grain) scale by SXRCT and, with still better spatial and temporal resolution, by transmission optical microscopy, revealing some more complex morphologies than in the hydrate pore habits commonly admitted.

Stress-strain response and deformation behavior of hydrate-bearing sands under different grain sizes: A particle-scale study using DEM

Natural gas hydrates are crystalline solids found in sediments beneath the seabed and permafrost, which significantly affect the mechanical behavior of sediments. The effect of hydrates often varies for different sediments, which has been captured in some laboratory studies. But the particle-scale information involved is obscure and the underlying mechanisms often rely on assumptions. In this study, discrete element method (DEM) was used to improve understanding of the hydrate effect on the mechanical behavior of different sands. Triaxial compression tests were carried out using DEM on the digital hydrate-bearing sands (HBS) with different grain sizes. Simulation results shows that the large-grain samples often yield earlier and tend to strain-hardening behavior, while hydrate occurrence induces strain-softening behavior. In terms of stress-strain response and porosity changes, the hydrate strengthening on the small-grain samples is much greater than the large-grain samples. Particle-scale observations indicate that particle rotation usually occurs in regions with small particle displacement and is more intense on shear slip surfaces. Hydrate bonds are mainly subjected to tensile failure, and large grain size may hinder bond shear failure. Hydrates restrict the development of radial fabrics and enhance the stress-induced anisotropy, rendering a more stable framework for sediments.