Electrokinetic concentration processes

Heterogeneities or anomalies in the soil will reduce removal efficiencies. Extreme pHs at the electrodes may inhibit the system s effectiveness. The electrokinetic remediation process is limited by the solubility of the contaminant, the desorption of the contaminants from the soil matrix, and reduction-oxidation changes induced by the electrode reactors. Electrokinetic remediation requires sufficient pore water to transmit the electrical charge. Contaminant and noncontaminant concentrations effect the efficiency of the process. 

Figure 3. Microfluidic Device. (A) Time lapse illustrating repulsion the ejection of 1.9 pm fluorescent polystyrene microsphere particles from an electroactive microwell. After dissolution of the membrane, the fluorescent particles can be seen in the well. White hnes outline the gold electrodes features. Images are taken every 2 s (total of 10 s). (B) Schematic of the electroactive microwell drug delivery system developed here. Scale bar represents 2 mm. (C) Micro fluidic device with electrical leads connected to thin copper wires. Inset Magnified view of microchip from above looking at the region near the membrane. (D) To illustrate the electrokinetic transport processes involved in the ejection stage, a finite element analysis of time-dependent species transport of the system is shown. Images show cut view of species concentration every 60 s up to 300 s after the ejection process.

A field demonstration of electrokinetic remediation was conducted by the USAEC and the ERDC at the Naval Air Weapons Station (NAWS), Point Mugu, California, in 2000 (USAEC, 2000). Major contaminants in this area were chromium and cadmium, and the system was developed with the aim to reduce the contaminant concentrations below the regulatory action levels for metal concentration and toxicity criteria. The developed system was basically the same as other existing electrokinetic remediation processes. It involved the use of citric acid as an amendment to control the formation of the pH front in the treatment area. The design included a system for the recovery of the electrolyte after separating the metal contaminants. 

As the electrokinetic remediation process proceeds, the heavy metals are depleted from the soil and concentrated around the electrodes, where they are collected in the processing liquid, and the heavy metals can subsequently be removed from the site. 

It also follows from what was said that a zeta potential will be displayed only in dilute electrolyte solutions. This potential is very small in concentrated solutions where the diffuse edl part has collapsed against the metal surface. This is the explanation why electrokinetic processes develop only in dilute electrolyte solutions. 

Electrokinetic remediation is limited by the type of contaminant, heterogeneities or anomalies in the soil, extreme pHs, pore water chemistry, lack of pore water, contaminant and noncontaminant ion concentrations, metals precipitation, and reduction-oxidation changes induced by the process electrode reactions. It may be difficult to estimate the time that will be required to remediate a site using this technology. Laboratory treatability testing may provide a false indication of the applicability of electrokinetic remediation at a specific site. Further research is required to determine the technology s limitations and ramifications. 

Initial and target contaminant concentrations, concentration of nontarget ions, soil characteristics and moisture content, quantity of waste, depth to contamination, residual waste handling and processing, site preparation requirements, and electricity and labor rates have a significant effect on the unit price of electrokinetic remediation technologies (D19938G, pp. 16, 17). 

In addition to the foregoing, it is customary to include under electrochemistry (I) processes for which the net reaction is physical transfer, e g., concentration cells (2) electrokinetic phenomena, e.g.. electrophoresis. eleclroosmnsis, and streaming potential (3) properties ot electrolytic solutions, if they are determined by electrochemical or other means, e g.. activity coefficients and hydrogen ion concentration (4) processes in which electrical energy is first converted to heal, which in turn causes a chemical reaction that would not occur spontaneously at ordinary temperature. The... 

It can be summarized that ellipsometric measurements proved the formation of a surfactant adsorption layer on the photoresist surface. At ceg- it is assumed to form a monolayer. To get more information about the adsorption layer and its influence on the surface properties of the photoresist, an electrokinetic characterization of unexposed and processed photoresist in solutions of the cationic surfactant was carried out. The zeta potential of the photoresist layers is given in Fig. 8 as a function of the surfactant concentration. The measurement was performed at pH = 6 in a background electrolyte (KC1) concentration of 10-5 M to ensure the minimum conductivity of the solution necessary for the measurement. 

In this paper we investigate the process of alternate adsorption of cationic polyelectrolyte and anionic surfactant, structure and properties of adsorbed layers depending on different factors (molecular weight of PE, concentration of polyelectrolyte and surfactant, adsorbed layer formation time, the flow rate of the solution) by measuring potential and streaming current using the capillary electrokinetic method. 

Figure 4.12. Apparent electrokinetic potential as a function of the outer Helmholtz plane potential, when the slip process Is determined by the viscoelectrlc effect. J = 10.2 X 10 V m c Is the concentration of the (1-1) electrolyte In M. (Redrawn from J. Lyklema. Colloids Surf. A92 (1994) 41.)...

Principally, zeta potential measurements with kaolin present no problems at salt concentration > 0.001 M. But electrokinetic studies of kaolin require that the surface of the clay be prepared in a manner that generates a reproducible surface. That means, substances in the material derived from the conditioning process had to be removed. 

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