Electro-osmosis in kaolinite with pH-dependent surface charge modelling by homogenization

Abstract

A new three-scale model to describe the coupling between p H -dependent flows and transient ion transport, including adsorption phenomena in kaolinite clays, is proposed. The kaolinite is characterized by three separate nano/micro and macroscopic length scales. The pore (micro)-scale is characterized by micro-pores saturated by an aqueous solution containing four monovalent ions and charged solid particles surrounded by thin electrical double layers. The movement of the ions is governed by the Nernst-Planck equations, and the influence of the double layers upon the flow is dictated by the Helmholtz-Smoluchowski slip boundary condition on the tangential velocity. In addition, an adsorption interface condition for the N a + transport is postulated to capture its retention in the electrical double layer. The two-scale nano/micro model including salt adsorption and slip boundary condition is homogenized to the Darcy scale and leads to the derivation of macroscopic governing equations. One of the notable features of the three-scale model is the reconstruction of the constitutive law of effective partition coefficient that governs the sodium adsorption in the double layer. To illustrate the feasibility of the three-scale model in simulating soil decontamination by electrokinetics, the macroscopic model is discretized by the finite volume method and the desalination of a kaolinite sample by electrokinetics is simulated.

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

“…8,9 Kaolinite (Al 2 Si 2 O 5 (OH) 4 ), the most abundant phyllosilicate group clays, comprises mainly silicate sheets (Si 2 O 5 ) bound to aluminum oxide/hydroxide layers (Al 2 (OH) 4 ), which is vital in ceramics and agriculture. 10,11 However, its sedimentation behavior in water limits its effectiveness, causing the rapid precipitation of inorganic particles. 12 The primary factors influencing sedimentation are the self-weight of coarsegrain particles and the electrostatic force acting on fine-grain particles.…”

A Two-Scale Computational Model of pH-Sensitive Expansive Porous Media

“…A first attempt at incorporating pH-effects in the homogenization-based approach has been pursued by Lemaire et al [33]. Subsequently, in a series of papers (Lima et al [34][35][36][37]) have extended the homogenization based approach of Moyne and Murad [30] to incorporate pH effects in a nondeforming kaolinite clay and applied the theory to numerically simulate an electro-osmosis experiment. The results obtained highlighted the paramount role of the acidification/alkalinization phenomena on the effectiveness of the electrokinetic remediation processes (see Ref.…”