Pore fluid electrolyte

Effect of Electrolyte In electrokinetic processes, electrolyte is frequently employed to induce the electrical current to pass through the pore fluid. Electrolyte concentration is associated with electrical potential and power consumption, and affects the zeta potential of soil, thus also influences electroosmotic flow. In general, the presence of an electrolyte reduces the CMC of a surfactant because of a solution-depolarizing effect, so greater micellLzation and less surfactant adsorption can be expected (Saichek and Reddy, 2003a). 

Pore fluid electrolyte NaCl. Dielectric constant of fluid taken as ew = 19. 

Model parameters for different clay-water aggregates [12] Pore fluid electrolyte NaCl. ew taken as 79. 

Summarizing, during aging the pore structure, surface area and stiffness of the gel network are changed and controlled by the following parameters time, temperature, pH, added electrolyte and pore fluid.25... 

Pamukcu and Wittle [133] investigated the feasibility of electrokinetic treatment at 30 V of different clay mixtures containing a number of heavy metals including Cd, Co, Ni, and Sr. The metal removal success ranged between 85-95% and appeared to depend on the soil matrix, the metal, and the pore fluid composition. At low initial metal concentrations, electroosmosis appeared to be the dominant mechanism for metal removal. At higher concentrations, electrolytic migration of the ionic species played a more dominant role. Of the three soil types tested, kaolinite had the highest electroosmotic efficiency. 

The electrical resistivity of water-saturated sediments depends on the resistivity of its solid and fluid constituents. However, as the sediment grains are poor conductors an electrical current mainly propagates in the pore fluid. The dominant transport mechanism is an electrolytic conduction by ions and molecules with an excess or deficiency of electrons. Hence, current propagation in water-saturated sediments actually transports material through the pore space, so that the resistivity depends on both the conductivity of the pore water and the micro structure of the sediment. The conductivity of pore water varies with its salinity, and mobility and concentration of dissolved ions and molecules. The microstructure of the sediment is controlled by the amount and distribution of pore space and its capillarity and tortuosity. Thus, the electrical resistivity cannot be considered as a bulk parameter which strictly only depends on the relative amount of solid and fluid components, but as shown below, it can be used to derive porosity and wet bulk density as bulk parameters after calibration to a typical sediment composition of a local sedimentation environment. 

Soil has long been considered as a chemical system due to its semipermeability to chemicals, bioactivity, interactions with chemicals, and so on. As a result, soil has been idealized as a leaky semipermeable membrane in chemical osmosis to explain various abnormal transport phenomena of water and chemicals in soil (Hanshaw, 1972 Marine and Fritz, 1981 Fritz and Marine, 1983 Yeung, 1990 Keijzer, Kleingeld, and Loch, 1999) as a Donnan membrane (Donnan, 1924) to examine the influences of soil type, water content, electrolyte concentration, and the cation and anion distribution in pore fluid on electroosmotic flow of fluid in soil (Gray and Mitchell, 1967) as a bioreactor to evaluate the impact of oxygen transfer on efficiency of bioremediation (Woo and Park, 1997) and so on. 

As discussed before, EOF is proportional to the zeta potential and porosity of the soil and the dielectric constant of the pore fluid. It has been reported that the zeta potential of the soil became more positive in the presence of cationic surfactants. However, anionic surfactants decreased the zeta potential, and nonionic surfactants caused slight increase (Kaya and Yukselen, 2(X)5). The influence of surfactants on zeta potential is closely related to the sorption of surfactants in sods. The sorption of surfactants onto the solid phase is affected by various factors, including solid and surfactant types and environmental conditions such as pH, temperature, and electrolytes (Rosen, 1989). 

In case of dispersed shale, the shale conductivity is added to the pore fluid conductivity. With this idea, Waxman and Smits (1967, 1968) and Waxman and Thomas (1974) developed the dispersed shaly sand model They implemented the fundamental mechanisms of the shale conductivity based on cation exchange processes at the clay mineral-electrolyte (water) interface. 

Figure 7 illustrates the dynamics of fluid migration through porous carbon electrodes to obey the Hagen-Poiseuille equation that is normally used to describe the transport through membranes having the pores of cylinder-like shape. Therefore, this method can probably be used for express analysis of the electrolyte dynamics in different porous carbon materials. 

Concentration Polarization As a reactant is consumed at the electrode by electrochemical reaction, there is a loss of potential due to the inability of the surrounding material to maintain the initial concentration of the bulk fluid. That is, a concentration gradient is formed. Several processes may contribute to concentration polarization slow diffusion in the gas phase in the electrode pores, solution/dissolution of reactants/products into/out of the electrolyte, or diffusion of reactants/products through the electrolyte to/from the electrochemical reaction site. At practical current densities, slow transport of reactants/products to/from the electrochemical reaction site is a major contributor to concentration polarization ... 

Hemofiltration (HF) is a similar modaUty whereby solute is removed by convection. The hemofiltration apparatus differs from HD in that no dialysate circuit is present. Rather, blood within the cartridge is subject to pressure across a high-flux (large pore) membrane creahng an ultrafiltrate of solutes and water while cells and large solutes remain in the blood and return to the circulation. Hemofiltration typically requires replacement of fluid and electrolytes lost in the ultrafiltrate. 

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