Abstract
Removal of heavy metal ions from soils by electrokinetic treatment has several advantages. The extent of removal, however, is both soil specific and ion specific. The conditions to be maintained have to be established based on laboratory studies. With a view to maximize the removal of metal ions the trends of removal of heavy metal ions such as iron, nickel and cadmium form a natural Indian kaolinitic red earth during different conditions maintained in the electrokinetic extraction process are studied. A laboratory electrokinetic extraction apparatus was assembled for this purpose. Attempts are also made to elucidate the mechanism of removal of the metal ions from soil. The composition of the flushing fluid, voltage and duration of extraction are varied. While dilute acetic acid has been used to neutralize the alkalinity that develops at the cathode, EDTA solution has been used to desorb heavy metals from clay surface. Generally the extent of removal was proportional to the osmotic flow. Nickel and Cadmium are more effectively removed than iron. The percentage removal of Ni is generally proportional to the osmotic flow but shows sensitivity to the pH of the system. There is an optimum voltage for removal of metal ions from soil. The removal of iron was negligible under different conditions studied.
Highlights
Heavy metal toxicity occurs far more often and people are exposed to toxic metals on a day-today basis in our environment
The oven dried soil samples were mixed with required amount of water so as to bring it to 110 % of optimum moisture content (OMC) which is about 17.93 %
Attempt has been made to understand the utility of passing acetic acid to control pH and the role of EDTA to desorb and remove contaminant has been studied
Summary
Heavy metal toxicity occurs far more often and people are exposed to toxic metals on a day-today basis in our environment. These include: (i) It is an in-situ process that is 50-90% less expensive than the currently available metals remediation technologies, such as soil washing, pump and treat, and excavation, which are ex-situ methods; (ii) It is extremely effective in finegrained low permeability soils where other techniques, such as pump and treat, are not feasible This is due to the fact that the contaminants are transported under charged electrical fields and not hydraulic gradients. As the coefficient of electro-osmotic conductivity is insensitive to soil type, the electro-osmotic fluid volume flow rates in different soil layers will be very similar Complete removal of those metals that possess complex aqueous and electrochemistry and tendency for speciation and forming hydroxide complexes is difficult under variable pH and redox conditions. It is necessary to understand the relative influences of various mechanisms such as osmotic flow induced and the applicability of various enhancement schemes and conditions to be maintained during extraction
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