Flux decline during cross flow membrane filtration of electrolytic solution in presence of charged nano-colloids: A simple electrokinetic model

An electrokinetic transport based approach for quantification of reversible flux decline due to the concentration polarization of an electrolyte solution in presence of charged colloids is presented. The model envisions the electrolyte transport across a charged cake or gel layer as transport of ions through charged cylindrical capillaries. This model is coupled with the standard theory of concentration polarization during cross flow membrane filtration. The analysis is carried out entirely in terms of generalized, non-dimensional variables. A dimensionless group termed as the scaled gel layer resistance evolves from the analysis, which accounts for the electrical properties of the charged nano-colloids and the electrolyte solution. A parametric study is performed to elucidate the coupled influence of mass transfer, membrane resistance, gel resistance, and electrical properties of the gel-electrolyte polarized layer. The effects of these parameters are examined on the filtration performance through the model equations.

An electrokinetic model for cake enhanced concentration polarization in a nanostructured gel formed during membrane filtration of a colloid-electrolyte system.Figure optionsDownload high-quality image (65 K)Download as PowerPoint slideResearch highlights
► A simple electrokinetic model for enhancement of electrolyte concentration polarization in a charged colloidal cake or gel is developed.
► The electroviscous retardation of the solvent flow through the charged cake or gel layer causes additional flux decline.
► The influence of this electroviscous retardation is typically small for aqueous systems and large colloids.
► The electroviscous retardation may be significant in polyelectrolyte gels or low dielectric constant media.