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Abstract: In this paper, a knowledge model is used to describe the rejection of ionic solutions: pure monovalent salt–water solutions and four halide ions–water mixture. This model is based on a description of the transport within the pores via the extended Nernst–Planck equation. Electric and dielectric contributions on the separation selectivity are investigated from experimental results. The first version of the numerical model, based on Donnan Steric Pore Model, cannot be used to simulate the experimental curves obtained with the mixture of halide monovalent salts. Then, the introduction of ion energy hydrations in the model to describe the dielectric contribution of each ion, which are proportional to the polarizability of ions, is necessary to adapt the model. This result confirms the contribution of Van der Waals forces in the rejection process observed. [Copyright &y& Elsevier]

Abstract: 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 12h 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 12h of contact) while it is reached after more than 5days 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. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a knowledge model is used to describe the rejection of ionic components in various proportions obtained by mixing two salts (NaCl and Na2SO4 or NaCl and MgCl2). This model is based on a description of the transport within the pores via the extended Nernst–Planck equation and the steric, electric and dielectric exclusion phenomena at the membrane/solution interfaces. Electric and dielectric contributions on the separation selectivity are investigated from experimental results by estimating, respectively, the membrane charge density X d and the solvation energy through the dielectric constant within the pores ɛ p . A new way of numerical identification is presented in this paper, which consists in identifying simultaneously this couple of parameters (ɛ p , X d ) from mixture experiments. This method appears to be particularly convenient, as it does not require additional assumption to decouple their influences on rejection. The obtained values are discussed with respect to the mixture type and its composition. It was found that the values of both ɛ p and X d are physically consistent and show monotonous behaviors with the proportions of ions. In particular, ɛ p decreases linearly when the proportion of divalent ions increases. [Copyright &y& Elsevier]