Reduction of Contaminants in Soil and Water By Direct Electric Current - Electrokinetics for Petroleum and Environmental Engineers - page 61

concentrations of ammonia were found in the anode cham-
ber in both tests, where pH was at 4. At this pH, the ammonia
in the anode chamber would be in the form of ammonium
ion. In the cathode chamber where the pH was well above
9.3, the ammonium would readily convert to uncharged
ammonia (NH 3 ). The solubility of ammonia is fairly low in
water (Henry's constant, K H = 57.6 mol/L.atm). Therefore
the ammonia removed to the cathode could have converted
to vapor phase and escape into the head space of the cham-
ber. Strong ammonia smell was detected when the trapped
gasses were released at intervals from the cathode reservoir.
The portion of ammonia that was collected in the anode
chamber was due to colloidally enhanced transport whereby
the positive ion NH 4 + was expected to collect at the posi-
tive electrode by electro-migrating colloids (i.e., bacterial,
organic or inorganic). The colloidal transport was observed
visually as the anolyte clouded with suspended particles dur-
ing the treatment. Charged colloids are known to strongly
adsorb ions of opposite charge and enhance transport of
these substances in porous media (Grolimund et al., 1996).
D. Simultaneous Extraction of Cyanide, CN- and Fluoride F- :
Spent pot-lining sludge from Columbia Falls Aluminum
Company was tested to determine the efficacy of electroki-
netics in removing cyanide and fluoride metals prior to its
disposal. The sludge contained 0.2% cyanide and 9% fluoride
by mass, initially. At the end of the 7 days of electrokinetic
treatment, about 8% of the cyanide and 2% of the fluoride
by mass was removed from 118 g of a sample of the sludge.
In these tests 15V of constant potential was applied across
the electrodes, and the anolyte and catholyte solutions were
replenished with fresh solutions at 29 hrs of this constant
potential. As shown in figure 2.18, the electrical potential
measured within the sample was small and changed with
current when the electrolytes in the electrode chambers
were replaced with fresh ones. The current remained high
in the range of 15-20 mA in the first stage and dropped to
about 7 mA in the second stage. The removal of metals over
time, as shown in figure 2.19, demonstrated that preferen-
tial removal of CN - towards anode was prevalent, as the Fl -
transport picked up only after the 4th day against the control
value of diffusion to the cathode.