Electrokinetic phenomena electro-osmosis

Electrokinetic Phenomena Electro-osmosis, Electrophoresis and Streaming... 

An innovative technology called the "lasagna" process is based on the electrokinetic phenomenon called electro osmosis. The lasagna process was created to treat difficult wastes in low permeabiUty, sdt- and clay-laden soils (40). The lasagna process is so named because it consists of a number of layered subsurface electrodes and treatment zones. These layers can be constmcted either horizontally where contaminants are forced to more upward or in vertical position where lateral contaminant movement is desired. 

Electrokinetic phenomena are generally characterized by the tangential motion of liquid with respect to an adjacent charged surface. In the above example the surface was that of a negatively charged clay particle the particle moved with respect to the stationary liquid. The surface may also be that of a droplet as in emulsions. Alternatively, the particles may be stationary with the liquid moving, as for Instance in electro-osmosis. For sand this phenomenon was also discovered by Reuss I... 

Electro-osmosis is another electrokinetic phenomenon-in which an electric field is applied across a charged porous membrane or a slit of two charged nonporous membranes (see figure IV - 31). Due to the applied potential difference an electric current will flow and water molecules will flow with the ions (electro-osmotic flow) generating a pressure difference. As can be derived from nonequilibrium thermodynamics (sec chapter V) the following equation can be obtained indicating that both phenomena, electro-osmose and streaming potential, are similar... 

AC electro-osmosis (ACEO) is a nonlinear electrokinetic phenomenon of induced-charge electro-osmotic flow around electrodes applying an alternating voltage. 

The four possible types of electrokinetic phenomena are streaming (current) potential (electric potential generated by fluid movement relative to another phase), sedimentation potential or Dorn phenomenon or Dom effect (due to dispersed particles motion relative to the fluid caused by sedimentation) and electrophoresis and electro-osmosis (movement of two phases is caused by an external potential difference). 

In Equation 19.12, Cq = 8.854 x j-i qi -1 jg jjjg dielectric constant in vacuum, e is the relative dielectric permittivity of the solvent (e = 78.5 for water at room temperature 298 K), and are the electrokinetic zeta potential defined at the shear plane (see Figure 19.3), r is the dynamic viscosity of the solvent (q = 8.91 x 10 kgm" s for water at room temperature 298 K), and E is the externally applied electric field. The first equation in Equation 19.12 represents the fluid motion in a stationary channel under the action of an externally appUed electric field. The motion is called electro-osmosis and the velocity is v. The second equation in Equation 19.12 gives the velocity v, of charged suspended colloidal particle (or a dissolved molecule) driven by the same electric field. This phenomenon is called electrophoresis. The EDL thickness 1/k depends on the concentration of background electrolyte [18,19,25,26]. 

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