Experimental data and theoretical predictions for the rate of electrophoretic clarification of colloidal suspensions

An experimental and theoretical investigation of the electrophoretic clarif ication rate of colloidal suspensions was conducted. The suspensions includ ed a coal-washing effluent and a model system of TiO2 particles. A parametr ic study of TiO2 suspensions was performed to validate an analysis of the e lectrophoretic motion of the clarification front formed between a clear zon e and the suspension. To measure the electric field strength needed in the prediction of the location of the front, a moveable probe and salt bridge w ere connected to a reference electrode. Using the measured electric field s trengths, it was found that the numerical solution to the unit cell electro phoresis model agrees with the measured clarification rates. For suspension s with moderately thick electric double layers (kappa a > 15) and high part icle volume fractions (alpha = 0.3% or 1.2 wt %) the deviations from classi cal Smoluchowski theory are substantial, and the numerical analysis is in s omewhat better agreement with the data than a prior solution of the problem . The numerical model reduces to the predictions of previous theories as th e thickness of the electric double layer decreases, and it is in good agree ment with the clarification rate measured for a coal-washing effluent suspe nsion (alpha = 0.411% or 0.493 wt %) with thin electric double layers (kapp a a = 144).