124
mercury
contaminalion
a}
b)
leaching
~sou rce
electrolytic
leachate
preparation
water add itive
J
f
preparation
electrokinetic
M. Hempel and I. Thoeming
concen trate
containing
mercury
process -
mercury
-.
.....
contamination
Fig. 5 a Principle of the e1ectroleaching process; b principle of the electrokinetic technique
Sanstede and Kohling (1993a) propose the use of electrodes dipping into a
suspension as was described earlier by Scheiner et al. (1972). In contrast to the
latter, they assume an oxidation of elemental mercury directly at the anode, a
reaction which seems unlikely to happen. The dissolved mercury should be
reduced at the cathode. Besides, they propose an addition of an oxidant and also of
a dissolved tenside (Sanstede et al. 1993b). Unfortunately, it is not explained how
redissolution of the reduced mercury can be avoided. Redissolution can be
assumed because of the suspended soil particles which lead to an abrasion not only
of the electrodes but also of the layer of reduced mercury sticking on the cathode.
Foust (1994) focused on the use of iodine as an oxidant dissolved in potassium
iodide solution. The removal efficiency for a soil artificially polluted with nine
different species with an average Hg-concentration level of about 1000 mg/kg
varied between 80 and 100%. It should be taken into account that artificially
polluted probes usually lead to better results than probes from the field which are
"matured" (diffusion of Hg into matrices, complexation by organic matter). To
run a process as a whole, Foust suggests a preparation of the leachate with
electrolysis for regeneration of the iodine and separation of the dissolved
mercury
contaminalion
a}
b)
leaching
~sou rce
electrolytic
leachate
preparation
water add itive
J
f
preparation
electrokinetic
M. Hempel and I. Thoeming
concen trate
containing
mercury
process -
mercury
-.
.....
contamination
Fig. 5 a Principle of the e1ectroleaching process; b principle of the electrokinetic technique
Sanstede and Kohling (1993a) propose the use of electrodes dipping into a
suspension as was described earlier by Scheiner et al. (1972). In contrast to the
latter, they assume an oxidation of elemental mercury directly at the anode, a
reaction which seems unlikely to happen. The dissolved mercury should be
reduced at the cathode. Besides, they propose an addition of an oxidant and also of
a dissolved tenside (Sanstede et al. 1993b). Unfortunately, it is not explained how
redissolution of the reduced mercury can be avoided. Redissolution can be
assumed because of the suspended soil particles which lead to an abrasion not only
of the electrodes but also of the layer of reduced mercury sticking on the cathode.
Foust (1994) focused on the use of iodine as an oxidant dissolved in potassium
iodide solution. The removal efficiency for a soil artificially polluted with nine
different species with an average Hg-concentration level of about 1000 mg/kg
varied between 80 and 100%. It should be taken into account that artificially
polluted probes usually lead to better results than probes from the field which are
"matured" (diffusion of Hg into matrices, complexation by organic matter). To
run a process as a whole, Foust suggests a preparation of the leachate with
electrolysis for regeneration of the iodine and separation of the dissolved