Effect of an Electrical Field on the Motion of Uncharged Impurities in Concentrated Fine Disperse Systems

The diffusion of o-chlorotoluene (OCT), a hydrophobic organic compound, solubilized by means of the Triton X-100 surfactant from the region of local contamination into adjacent pure layers has been experimentally studied in a model kaolin based dispersion. The study is aimed at clarifying the factors influencing the motion of impurities in a dispersion medium with and without an electrical field. The theoretical analysis of obtained experimental data makes it possible to establish the effective diffusion coefficients of formed OCT/surfactant complexes in the pore space, which demonstrate the acceleration of the spread of contamination due to the influence of an electrical field. It has been shown that the diffusion coefficients of these complexes grow due to electroosmosis and hydrodynamic flows induced by it. Electroosmosis along negatively charged kaolin particles promotes the transport of impurities towards the cathode. At the same time, local narrowing of pores with a closed experimental cell leads to the pore solution hydrodynamic flows, which transport the impurities in the direction opposite to electroosmosis. Hence, due to a complicated interparticle space configuration, the electrical field actually results in pore solution mixing, which affects the character of the diffusion flows of impurities. Mixing may also be additionally intensified due to the heterogeneous charge of kaolin particles, which causes local changes in the direction of electroosmosis. At the same time, not only the fact of mixing as such is important, but also its specific features caused by different characters of electroosmotic and hydrodynamic flows and, correspondingly, by an sharp change in the direction of liquid flow near the surface of kaolin particles. As a consequence, the desorption of OCT/surfactant complexes from the surface of particles into the pore solution should be intensified and, correspondingly, the efficiency of their removal from the disperse systems should increase.