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Deposition Characteristics of Polydisperse Particles in Saturated Porous Media under Different Ionic Strengths
ZOU Zhi-ke, YU Lei, LI Ya-long, NIU Shu-yao, QIAO Wei, BIAN Jiu
Journal of Changjiang River Scientific Research Institute ›› 2025, Vol. 42 ›› Issue (6) : 71-77.
PDF(5891 KB)
PDF(5891 KB)
Deposition Characteristics of Polydisperse Particles in Saturated Porous Media under Different Ionic Strengths
[Objectives] Polydisperse particles are widely present in natural environments. Accurately predicting the transport and deposition of polydisperse particles in saturated media under unfavorable conditions (where repulsive forces exist between particle and medium surfaces) is crucial. [Methods] A series of constant-flow one-dimensional sand column experiments with artificial recharge were conducted using polydisperse particles (0.375-18.863 μm) under different ionic strength conditions (1, 6, 20, and 200 mM). Deposition characteristics of polydisperse particles under different ionic strengths (unfavorable and favorable conditions) were investigated. By coupling the colloid attachment efficiency model under unfavorable conditions with the polydisperse particle deposition model, a deposition model for polydisperse particles under unfavorable conditions was established, and corresponding numerical simulations were performed. [Results] Both physical experiments and numerical simulations showed that under favorable conditions, the capture probability of polydisperse particles exhibited a non-monotonic V-shaped characteristic of first decreasing and then increasing with particle size due to uneven micro-force distribution. Compared with favorable conditions, the repulsive double-layer force between polydisperse particles and the medium surface under unfavorable conditions formed an energy barrier, leading to an 8.5%-67.6% reduction in capture probability. The smaller the particle size, the greater the reduction in particle capture probability. Under favorable conditions, the final deposition profile curve of particles exhibited a hyper-exponential distribution with “upper-steep, lower-gentle”. The total deposition amount increased with increasing ionic strength, with 16.7%-24.6% of the total deposition occurring in the upper part of the sand column. A decrease in ionic strength exacerbated the uneven “upper-steep, lower-gentle” distribution of the deposition profile. [Conclusions] The research results not only further reveal the transport and deposition characteristics of polydisperse particles under natural unfavorable conditions, but also provide a scientific basis for effective watershed water quality management.
polydisperse particles / deposition characteristics / ionic strength / numerical simulation / energy barrier / attachment efficiency / hyper-exponential distribution
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A series of one-dimensional column experiments were conducted to investigate the transport and retention of micron-sized plastic spheres (MPs) with diameters of 0.1-2.0 μm in seawater-saturated sand. In seawater with salinity of 35 PSU (practical salinity units), the mass percentages recovered from the effluent (M) of the larger MPs increased from 13.6% to 41.3%, as MP size decreased from 2.0 μm to 0.8 μm. This occurred because of the gradual reduction of physical straining effect of MPs in the pores between sands. The smaller MPs (0.6, 0.4, and 0.1 μm) showed the stronger inhibition of MPs mobility, with M values of 11.5%, 11.9%, and 9.8%, respectively. This was due to the lower energy barriers (from 108 kT to 16 kT) between the smaller MPs and the sand surface, when compared with the larger MPs (from 296 kT to 161 kT). In particular, the aggregation of MPs (0.6 or 0.4 μm) triggered a progressive decrease in MP concentration in the effluent. Retention experiments showed that the vertical migration distance of most MP colloids was 0-4 cm at the inlet of column. For 0.6 or 0.4 μm MPs, the particles were concentrated over a 0-2 cm vertical distance. Moreover, the salinity (35-3.5 PSU) did not affect the transport of the larger MPs (2.0-0.8 μm). However, as seawater salinity decreased from 35 PSU to 17.5 or 3.5 PSU, the aggregation of the smaller MPs (0.6-0.1 μm) was dramatically inhibited or completely prevented. Meanwhile, ripening of the sand surface by the MPs (0.6 and 0.4 μm) no longer occurred. By contrast, all MPs in deionized water (0 PSU) achieved complete column breakthroughs because of the strong repulsive energy barrier (from 218 kT to 4192 kT) between the MPs and the sand surface. Consequently, we find that the transport and retention of MPs in sandy marine environment strongly relies on both the MP size and the salinity levels.Copyright © 2018 Elsevier Ltd. All rights reserved.
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Nanotechnology, an emerging technology, has witnessed rapid development in production and application. Engineered nanomaterials revolutionize the industry due to their unique structure and superior performance. The release of engineered nanoparticles (ENPs) into the environment, however, may pose risks to the environment and public health. To advance current understanding of environmental behaviors of ENPs, this work provides an introductory overview of ENP fate and transport in porous media. It systematically reviews the key factors controlling their fate and transport in porous media. It first provides a brief overview of common ENPs in the environment and their sources. The key factors that govern ENP transport in porous media are then categorized into three groups: (1) nature of ENPs affecting their transport in porous media, (2) nature of porous media affecting ENP transport, and (3) nature of flow affecting ENP transport in porous media. In each group, findings in recent literature on the specific governing factors of ENP transport in porous media are discussed in details. Finally, this work concludes with remarks on the importance of ENP transport in porous media and directions for future research. Copyright © 2016 Elsevier B.V. All rights reserved.
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Despite several decades of research there currently exists no mechanistic theory to predict colloid attachment in porous media under environmental conditions where colloid-collector repulsion exists (unfavorable conditions for attachment). It has long been inferred that nano- to microscale surface heterogeneity (herein called discrete heterogeneity) drives colloid attachment under unfavorable conditions. Incorporating discrete heterogeneity into colloid-collector interaction calculations in particle trajectory simulations predicts colloid attachment under unfavorable conditions. As yet, discrete heterogeneity cannot be independently measured by spectroscopic or other approaches in ways directly relevant to colloid-surface interaction. This, combined with the fact that a given discrete heterogeneity representation will interact differently with differently sized colloids as well as different ionic strengths for a given sized colloid, suggests a strategy to back out representative discrete heterogeneity by a comparison of simulations to experiments performed across a range of colloid size, solution IS, and fluid velocity. This has recently been performed for interaction of carboxylate-modified polystyrene latex (CML) microsphere attachment to soda lime glass at pH 6.7 with NaCl electrolyte. However, extension to other surfaces, pH values, and electrolytes is needed. For this reason, the attachment of CML (0.25, 1.1, and 2.0 μm diameters) from aqueous suspension onto a variety of unfavorable mineral surfaces (soda lime glass, muscovite, and albite) was examined for pH values of 6.7 and 8.0), fluid velocities (1.71 × 10(-3) and 5.94 × 10(-3) m s(-1)), IS (6.0 and 20 mM), and electrolytes (NaCl, CaSO4, and multivalent mixtures). The resulting representative heterogeneities (heterodomain size and surface coverage, where heterodomain refers to nano- to microscale attractive domains) yielded colloid attachment predictions that were compared to predictions from existing applicable semiempirical expressions in order to examine the strengths and weaknesses of the discrete heterogeneity approach and opportunities for improvement.
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Transport and deposition of nanoparticles in porous media is a multi-scale problem governed by several pore-scale processes, and hence, it is critical to link the processes at pore scale to the Darcy-scale behavior. In this study, using pore network modeling, we develop correlation equations for deposition rate coefficients for nanoparticle transport under unfavorable conditions at the Darcy scale based on pore-scale mechanisms. The upscaling tool is a multi-directional pore-network model consisting of an interconnected network of pores with variable connectivities. Correlation equations describing the pore-averaged deposition rate coefficients under unfavorable conditions in a cylindrical pore, developed in our earlier studies, are employed for each pore element. Pore-network simulations are performed for a wide range of parameter values to obtain the breakthrough curves of nanoparticle concentration. The latter is fitted with macroscopic 1-D advection-dispersion equation with a two-site linear reversible deposition accounting for both equilibrium and kinetic sorption. This leads to the estimation of three Darcy-scale deposition coefficients: distribution coefficient, kinetic rate constant, and the fraction of equilibrium sites. The correlation equations for the Darcy-scale deposition coefficients, under unfavorable conditions, are provided as a function of measurable Darcy-scale parameters, including: porosity, mean pore throat radius, mean pore water velocity, nanoparticle radius, ionic strength, dielectric constant, viscosity, temperature, and surface potentials of the particle and grain surfaces. The correlation equations are found to be consistent with the available experimental results, and in qualitative agreement with Colloid Filtration Theory for all parameters, except for the mean pore water velocity and nanoparticle radius.Copyright © 2017. Published by Elsevier B.V.
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邹志科, 李亚龙, 余蕾, 等. 雨洪水回灌中多分散颗粒运移-沉积特征及数值模拟[J]. raybet体育在线
院报, 2021, 38(10): 126-132.
雨洪水回灌过程中多分散颗粒造成的堵塞问题实质上是多孔介质中颗粒的运移和沉积。为了揭示饱和多孔介质中多分散颗粒的沉积特性,开展了5种不同浓度条件下多分散雨洪颗粒(0.375~55.82 μm)人工回灌一维砂柱定流量试验,基于胶体过滤理论,建立多分散颗粒运移-沉积的改进模型并进行相应的数值模拟。物理试验和数值模拟结果表明:不同浓度条件下多分散颗粒的沉积剖面都符合“上陡峭,下平缓”的超指数分布,而不是常规模型预测的指数分布。超指数分布是多分散颗粒的非均等沉积造成的,常规模型均化了沉积颗粒的空间分布,Kozeny-Carman模型可以模拟颗粒的非均等沉积造成介质不同位置渗透性能降低,介质的堵塞程度与颗粒大小直接相关,介质渗透性能最大降低为原来的52%,雨洪水中粒径>2.26 μm颗粒的沉积是造成堵塞的主要原因。
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The blockage caused by polydisperse particles in the process of stormwater recharge is in essence the transport and deposition of particles in porous media. To find deposition feature of polydisperse particles, a one-dimensional sand column test for artificial recharge is carried out to observe the outflow and inflow concentration of polydisperse particles ranging from 0.375 to 55.82 μm at five injection concentrations. A modified model in consideration of the particle polydispersity is theoretically derived based on the colloid filtration theory (CFT). Both the experimental and simulation results show the retention profiles of five concentrations compile with the hyper-exponential law, rather than the exponential retention predicted by the conventional model. The highly hyper-exponential retention profiles are caused by non-uniform deposition of polydisperse particles; and, the conventional model is found to homogenize the spatial distribution of retention of polydisperse particles. Local and overall permeability reductions are assessed by the Kozeny-Carman model. The blockage degree of media is directly relevant to particle size. The permeability of the medium is reduced to 52%, and the deposition of particles larger than 2.26 μm in the stormwater is the main cause of blockage.
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A time-distance-dependent deposition model is built to investigate the effects of hydrodynamic forces on the transport and deposition of polydispersed particles and the evolution of deposition rates with time and distance. Straining and the heterogeneity of the particle population are considered to play important roles in the decreasing distribution of deposition rates. Numerical simulations were applied in a series of sand column experiments at different fluid velocities for three different porous media. The effects of hydrodynamics forces are elaborated with the systematic variations of deposition dynamic parameters of the proposed model. With retention distributions with particle size as well as temporal and spatial evolutions of deposition rates, the transport and deposition mechanisms of polydispersed particles will be elucidated through the interplay of the variation of the particle size distribution of mobile particle populations and the geometrical change of the porous medium due to retention (straining and blocking).Copyright © 2017 Elsevier Ltd. All rights reserved.
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