Deposition Characteristics of Polydisperse Particles in Saturated Porous Media under Different Ionic Strengths

doi:10.11988/ckyyb.20240389

Abstract

Abstract:

[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.

Key words: polydisperse particles, deposition characteristics, ionic strength, numerical simulation, energy barrier, attachment efficiency, hyper-exponential distribution

CLC Number:

TV139.16模型试验

ZOU Zhi-ke, YU Lei, LI Ya-long, NIU Shu-yao, QIAO Wei, BIAN Jiu. Deposition Characteristics of Polydisperse Particles in Saturated Porous Media under Different Ionic Strengths[J]. Journal of Changjiang River Scientific Research Institute, 2025, 42(6): 71-77.

Figures/Tables 8

Fig.1 Microscopic morphology and gradation of polydisperse particles

Table 1 Potentials of particle and medium surface under different ionic strengths

材料	不同离子强度下颗粒和介质表面的电位/mV
材料	1 mM	6 mM	20 mM	200 mM
介质表面	-95.4	-69.7	-55.3	16.30
颗粒	-78.2	-27.7	-15.5	-0.69

Fig.2 Illustration of sand column experiment setup

Fig.3 DLVO energy profiles of particle-medium surfaces under different ionic strengths

Fig.4 Attachment efficiencies and capture probabilities of polydisperse particles under different ionic strengths

Fig.5 Breakthrough curves (BTCs) of polydisperse particles under different ionic strengths

Fig.6 Final deposition profiles of particles under different ionic strengths

Table 2 Mass balances of final deposition profiles under different ionic strengths

离子强度/ mM	颗粒沉积量百分比/%																沉积总量/ mg
	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
	(0.5)	(3)	(5.5)	(8)	(10.5)	(13)	(15.5)	(18)	(22)	(26)	(30)	(34)	(38)	(42)	(46)	(50)
1	2.7	12.0	10.0	8.5	7.4	6.5	5.8	5.3	7.5	6.6	5.8	5.2	4.8	4.3	4.0	3.7	94.163±1.15
6	2.1	9.5	8.3	7.5	6.8	6.2	5.7	5.3	7.9	7.2	6.6	6.1	5.7	5.3	5.0	4.7	94.729 ±1.37
20	2.0	9.2	8.2	7.5	6.8	6.3	5.8	5.4	8.0	7.3	6.7	6.1	5.7	5.3	5.0	4.7	98.615 ±2.32
200	1.6	7.8	7.3	6.8	6.4	6.1	5.7	5.4	8.2	7.6	7.1	6.7	6.3	5.9	5.6	5.4	105.807 ±1.95

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