Unsteady transport of divalent salt through a mineral membrane of ultrafiltration: Numerical estimation of physical parameters

This work focuses on the study of adsorption phenomena of magnesium chloride upon an ultrafiltration mineral membrane. Two experimental protocols are studied: first, filtration tests are carried out immediately after filling the pilot plant tank and secondly after contact during 12 h with the magnesium chloride solution. The operating performances are very different: a steady-state operation is reached in the second protocol (filtration tests are carried out immediately after the 12 h of contact) while it is reached after more than 5 days in the first one. To understand this difference of behaviour, an unsteady investigation (theoretical) is made to estimate the difference between the two protocols at the beginning of the experimental tests. A knowledge model (Donnan-Steric Pore Model) was used to estimate the physical parameters governing electric and dielectric exclusion. These simulated results are compared with the experimental estimation (qualitative and quantitative) of the membrane charge. It seems that, at the beginning, the membrane is highly positively charged and becomes slowly neutral and even negatively charged. The comparison between experimental and numerical investigations allows a semi-quantitative estimation of dielectric effect. These approaches (experimental, theoretical and simulated) show that depending on the protocol equilibrium is reached according to different thermodynamic pathways. (C) 2010 Elsevier B.V. All rights reserved.