SOIL, SEDIMENT AND SLUDGE: IN-SITU CHEMICAL/PHYSICAL TREATMENT
Electo-Kinetic Seperation
Electrokinetic Remediation (ER) System
Process
Note:
Two approaches during electrokinetic remediation:
1) "Enhanced Removal":
(AKA electro-migration: charged particles are transported through the substrate)
Used for remediation of soils contaminated with metals.
2) "Treatment without Removal":
(AKA electroosmosis: the movement of an aqueous liquid relative to a stationary charged surface).
Used for in-situ remediation of soils contaminated with organic species.
Limitations:
Cost:
The cost varies dependent on the amount of soil to be treated, the conductivity of the soil, the type of contaminant & the spacing of electrodes.
- ER is an in situ soil processing technology using electro-chemical and electro-kinetic processes to desorb (separate), and then remove metals & polar organic contaminants from low permeability soils.
- A low-intensity direct current is applied through the soil between ceramic electrodes (divided into both a cathode and anode array).
- The current creates an acid front at the anode (+ve) and a base front at the cathode (-ve).
- This mobilises charged species so ions and water move towards the electrodes:
Note:
- -Metal ions, ammonium ions & positively charged organic compounds move toward the cathode (+ve).
- -Anions (e.g. chloride, cyanide, fluoride, nitrate) & negatively charged organic compounds move towards the anode.
- The direction and rate of movement of ions depend on their charge & magnitude of the electro-osmosis-induced flow.
- Non-ionic species (organic & inorganic) will also be transported along with the electro-osmosis induced water flow.
Two approaches during electrokinetic remediation:
1) "Enhanced Removal":
(AKA electro-migration: charged particles are transported through the substrate)
Used for remediation of soils contaminated with metals.
- It uses electro-kinetic transport of contaminants towards the polarised electrodes to concentrate the contaminants for removal and ex-situ treatment
2) "Treatment without Removal":
(AKA electroosmosis: the movement of an aqueous liquid relative to a stationary charged surface).
Used for in-situ remediation of soils contaminated with organic species.
- It uses electro-osmotic transport of contaminants (back and forth) through treatment zones between electrodes
Limitations:
- in-effective if the moisture content<10% / if the soil includes deposits with high electrical conductivity (ore deposits).
- Inert electrodes (carbon/graphite or platinum) must be used so no residue is introduced into the treated soil mass.
- Electrolysis may dissolve metallic electrodes & introduce corrosive products into the soil.
- Most effective in clays (due to surface charge of clay particles) but the clay surface charge can be altered by the pH of the pore fluid & the adsorption of contaminants.
- Oxidation/reduction reactions can form undesirable products (e.g., chlorine gas).
Cost:
The cost varies dependent on the amount of soil to be treated, the conductivity of the soil, the type of contaminant & the spacing of electrodes.