Reduction of Contaminants in Soil and Water By Direct Electric Current - Electrokinetics for Petroleum and Environmental Engineers - page 41

Through laboratory experiments K has been shown to be a constant,
independent of the electric field and soil mineralogy for similar major ion
concentrations of the bulk fluid (Pamukcu and Wittle, 1992; Wittle and
Pamukcu, 1993). In these studies, the volume of electroosmotic flow (V,
cc) per electric charge (either in Coulombs or moles of electrons) referred
to as the electroosmotic efficiency coefficient, K ef (cc/C) were determined
from numerous electroosmotic tests of different clay and solute combi-
nations. The relation between the cumulative electrical charge versus the
cumulative volume of electroosmotic flow was found to be linear for a
given clay type (e.g., kaolinite, montmorillonite, and sand-clay mixtures),
at given initial concentration of different ion species (As, Cd, Co, Cr, Cs,
Hg, Ni, Pb, Sr, U and Zn), all applied separately in the pore fluid. In these
series of experiments (Wittle and Pamukcu, 1993), the clay matrixes used
were pure kaolinite (KS), montmorillonite (MS), kaolinite with simulated
groundwater electrolytes (KG), kaolinite with humic substances (KH), and
a mixture of fine sand and 10% by weight montmorillonite (SS). In all cases
the transport experiments were conducted over 48 hours with a constant
electric field of 4 V/cm applied across the electrodes. The clay specimens
were sandwiched between two electrode chambers housing a set of graph-
ite electrodes in tap water as shown in Figure 2.1.
he K ef was demonstrated to be a constant factor for the soil type, but
changed with the initial concentration of the major ion. Figure 2.2 shows
this variation for Cd +2 as the major metal ion in clay pores. Also shown
on the graph is data from a reference soil matrix (Synthetic Soil Reference
Soil Matrix, SSRM), which represented a typical well-graded reference
soil matrix (USEPA). The behavior of K ef shown in figure 2.2 is typical of
all the other major contributing ions tested in these series of experiments
(Pamukcu and Wittle, 1992, 1993).
The constancy of K ef with soil type or clay mineral demonstrates that
the assumptions made in developing equation 2.8 are valid. The following

auxiliary electrode

teflon
adaptors

Water
connection

anode

Cathode

Soil

porous stone

power
connection

electrode

Figure 2.1 Schematic and photo of the Lehigh EK test cell assembly