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Release of colloids in saturated porous media under transient hydro-chemical conditions: A pore-scale study
Colloids and Surfaces A: Physicochemical and Engineering Aspects ( IF 5.2 ) Pub Date : 2021-01-22 , DOI: 10.1016/j.colsurfa.2021.126188
Safna Nishad , Riyadh I. Al-Raoush , Motasem Y.D. Alazaiza

The deposition and consequent release of colloids pose a significant challenge to the environment, groundwater quality and human health. Subsurface soil contains numerous types of colloids that exhibit a diverse range of interaction favorability with the soil grains and their impact on release behavior remains unclear. The objective of this study was to investigate, at the pore-scale, the impact of colloid interaction favorability on colloid deposition and subsequent release in response to perturbations of flow rate and solution chemistry in saturated porous media. Pore-scale experiments were conducted using a micromodel that is geometrically representative of a real sand-stone rock. Favorable, medium-favorable and unfavorable colloids (i.e., repulsion absent, repulsion at long-range of separation distances and attraction absent with the micromodel surface, respectively) were deposited in the micromodel and then a series of colloid release experiments were conducted at different conditions including increasing the flow rate, decreasing the ionic strength and increasing the solution pH. Favorable colloids exhibited extensive deposition on the collector center where the flow streamlines are parallel to the collector surface, as adhesion forces overcome hydrodynamic forces. However, at medium and high ionic strength, deposition in Forward Flow Stagnation Zone (FFSZ) was dominant for unfavorable colloids as the hydrodynamic forces are negligible. Pore-scale images showed that, upon perturbations in flow rate and solution chemistry, colloids that were initially deposited on collector centers were more susceptible to release as compared to colloids that were initially deposited in FFSZs. The negligible hydrodynamic drag forces in FFSZ and deep primary minimum interaction at short separation distances were the major factors that hindered the release of colloids in FFSZ under transient hydro-chemical conditions. The intensity of colloid deposition and release decreases as the favorability of colloids decreases and as the ionic strength decrease for unfavorable colloids. This study provides a clear insight to the pore-scale colloid deposition and release mechanisms during transient hydro-chemical conditions that help in the modeling of environmental and engineering applications including managed aquifer recharge, groundwater contamination and wastewater treatment processes.



中文翻译:

瞬态水化学条件下饱和多孔介质中胶体的释放:孔尺度研究

胶体的沉积和随后的释放对环境,地下水质量和人类健康构成了重大挑战。地下土壤包含多种类型的胶体,这些胶体与土壤颗粒之间相互作用的适应性范围各不相同,它们对释放行为的影响尚不清楚。这项研究的目的是在孔隙尺度上研究胶体相互作用的适宜性对胶体沉积和随后释放的影响,这些响应是对饱和多孔介质中流速和溶液化学性质的扰动。使用在几何上代表真实砂岩岩石的微模型进行了孔隙度实验。有利,中等和不利的胶体(即不存在排斥力,分别在远距离上排斥和在微模型表面上不存在吸附),然后在增加流速,降低离子强度和增加溶液的不同条件下进行了一系列胶体释放实验pH值 当粘附力克服流体动力时,有利的胶体在集流器中心(流动流线平行于集流器表面)上显示出大量沉积。但是,在中等强度和高离子强度下,不利的胶体在顺流停滞区(FFSZ)中的沉积占优势,因为流体动力可以忽略不计。孔径图像显示,在流速和溶液化学性质受到干扰后,与最初沉积在FFSZ中的胶体相比,最初沉积在收集器中心的胶体更易于释放。在瞬态水化学条件下,FFSZ中可忽略的流体动力阻力和短距离内的深层主要最小相互作用是阻碍FFSZ中胶体释放的主要因素。胶体沉积和释放的强度随着胶体的亲和性降低以及离子强度的降低而降低。这项研究为瞬态水化学条件下的孔垢胶体沉积和释放机理提供了清晰的见识,有助于对环境和工程应用(包括受控的含水层补给,地下水污染和废水处理过程)进行建模。

更新日期:2021-02-01
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