Modelling two-sided electrofiltration of quartz suspensions: Importance of electrochemical reactions

A new phenomenological model is proposed for two-sided electrofiltration of incompressible micron-sized particles with infinite electric resistance and negligible surface conductivity under application of a constant pressure and voltage. The model includes pressure-driven filtrate generation, electroosmosis and electrophoresis effects. Corrections are also discussed for varying electric fields and suspension concentration changes during the electrofiltration run due to a changing particle zeta potential as a consequence of the different electrochemical reactions occurring at the cathode and anode. The model, with the particle zeta potential as the sole adjustable parameter at each electrode side, appeared to fit very well to the experimental data, yielding physically sound zeta potential values. Electrofiltration experiments using both buffered and unbuffered quartz suspensions revealed the importance of electrochemical effects and the migration of hydroxide ions and especially protons into the filter chamber, altering the cake surface properties and even influencing the suspension particle flocculation state and as such the cake resistance and porosity. These effects may have biased modelling attempts and discussions regarding the beneficial effect of electrofiltration in some cases in the available literature.