Electrokinetic extrapolation

The method was extended for the materials whose PZC falls at very low pH values, where classical electrokinetic methods fail, and the CIP cannot be observed. For such material a linear relationship between tKL+ and pH over the pH range s4-7 was observed. Extrapolation of this straight line to k+ =0.5 gives the PZC. The data points obtained for low pH values show substantial deviations from linearity and they are not used in this extrapolation. 

Davis et al. [54] designed a graphical extrapolation procedure to calculate parameters of TLM from surface charging data. Similar graphical procedure was used to estimate the ApKa from electrokinetic data [55]. Bousse and Meind [56] postulate combination of potentiometric titration data with surface potential data... 

In the triple layer model, values of the capacitance, Ci, can be obtained experimentally from the slopes of plots used in linear (Davis et al., 1978), double (James et al., 1978), or electrokinetic (Sprycha, 1984) extrapolations as described... 

A hysteresis in the electrokinetic behavior of alumina and hematite was found in [288] the absolute value of the potential at constant pH increased with T, but no return to lower potential on cooling was observed. An increase in the absolute value of the potential at constant pH with T was reported in [2370], Uptake of cations from a 1-1 electrolyte by silica and alumina at constant Gp was rather insensitive to temperature [1842], The surface potential of alumina was studied in [3057] as a function of temperature (ISFET response). The temperature effect on tlie streaming potential is reviewed in [3058], The PZCs at very high temperatures reported in [3047] were obtained by extrapolation of experimental results obtained at moderate temperatures. 

The importance of these geochemical processes cannot be overemphasized. More importantly, they are contaminant specihc, soil specific, dynamic, reversible, and pH dependent. Therefore, it may be dangerous to generalize the implications of these processes and to extrapolate previous experimental results to other cases without a detailed study. However, the complex nature of these processes may lead to new avenues for innovative apphcations of electrokinetics in geotechnical and geoenvironmental engineering, in particular electrochemical remediation of contaminated soils. 

Some review articles cited above present cost estimates for full-scale systems based on pilot trial extrapolation with little or no full-scale site data. However, these estimates appear to be fairly accurate, considering inflation, and fall within the range of current costs outlined in Table 27.1. Table 27.1 summarizes the present costs of commercial, full-scale electrokinetic remediation for typical installations to treat organic and inorganic contamination. These data are based on information from Holland Environment BV/RL and Terran Corporation. There may be other... 

Transverse ICEP motion of metallo-dielectric Janus particles in a uniform AC field has recently been observed by Gangwal et al. [10]. Consistent with theoretical predictions in Fig. 3, the particles align and translate perpendicular to the field in the direction of the less polarizable (light) end, as shown in Fig. 4. Larger particles move faster than smaller ones, as expected from Eq. 2, and the velocity scales like the field squared in dilute NaCl solutions. The ICEP velocity decays at higher concentrations, extrapolating to zero around 10 mM. The same concentration dependence is also observed in AC electroosmotic flow and other nonlinear electrokinetic phenomena, which, although poorly understood, further reinforces that the motion is indeed due to ICEP. 

While the electrokinetic surface, or -potentials, originate from the surface or interfacial properties of solid materials, they are actually situated about 0.3 to 0.5 nm outside a material s surface and have to be extrapolated inward to the (i/>o) potential at the actual surface, using Eq. 5.54. The electrostatic free energy of interaction, AG, between two surfaces, 1, reaches a value of about -M.O mJ/m at V o 75 mV, in an aqueous medium with a 100 mM salt content of a mono-mono-salt see Table 5.1. Now various clay and other mineral particles can have V o-potentials that are between 50 and 90 mV, in which case AG, while not dominant, is no longer negligible. For instance for a contact between two platey clay particle surfaces over about 100 nm (= 10 ° cm ) an attraction of 1 mJ/m still corresponds to w 2,500 kT. Thus, it is always wise to measure -potentials, from which the actual surface, or V o-potential can be derived. 

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