Sedimentation and water electrolysis effects in electrofiltration of kaolin suspension



Filtration combined with an electric field (electrofiltration) enhances the filtration kinetics of aqueous suspensions. Although electrophoresis and electroosmosis largely contribute to electrofiltration behavior, side effects such as water electrolysis, heat production, and gravitational sedimentation of particles may be influential. A mathematical model was developed to include gravitational sedimentation of particles and electrolytic gas in electrofiltration theory. The model successfully represented electrofiltration data obtained from kaolin suspensions with a laboratory horizontal filter. Electrolytic gas contributed to an increase of 13% in electrofiltration rate. Settling particles increased cake resistance to downward electrofiltration flow and could substantially offset electrokinetic effects at high settling velocities. Because of electrolysis ionic products, a decrease of pH occurred in the filter during electrofiltration, causing the coagulation of kaolin particles and an increase in hydraulic cake permeability. Subsequent filtration could then take place rapidly without any electric field. The overall processing time was decreased by half when an electric field is applied only for 37% of the processing time. This coagulation phenomenon seems to be a promising means to accelerate the filtration kinetics without the need for full-time electrofiltration. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3120–3133, 2004