I am trying to chalk out a plan for the remediation of soil contaminated with Cr(VI). Contamination levels are as high as 5000 mg/kg of soil. In situ remediation will be preferable.
Biochar addition to the contaminated soil could be helpful. How large is the scale could also be a problem given the amount of biochar needed.
Go for cultivating high biomass crop like Maize or plant trees preferably Bamboo, Casuarina which are hyperaccumulators that will remove maximum from the soil. Poultry wastes compost is another option.
The method/ experimental details are noted from two references given at the end for your perusal and authentication.
[A]It can be removed by Electrokinetic remediation[applied in situ] by applying 50-150V depending upon the nature of soil having moisture[ but not having saturated condition], low salinity, low conduction.
[B]It is applied in situ, with electrodes on both sides of the contaminated soi/slurry with the electrode placed directly on the ground to the depth of 3-5 meters.
[C]The Cr(VI) cotaminants will concentrate around the anode in aquous phase. The anode reservoir cotained a column packed adsorbent (immobilized tannin chemically incorporated into cellulose). Cr(VI) gets adsorbed to this adsorbent .
[D] The pH of the aqueous solution in the anodic reservoir is decreased by the electrolysis of water but is kept around 6 ( by the proper addition of an aqueous alkaline solution ).
[E]The advantage of pH control is that it promotes the release of Cr(VI) from the soil by electromigration, thus permitting the maximum adsorption of Cr(VI) on the immobilized tannin. Simultaneous collection of Cr(VI) from the anodic reservoir leads to the protection from secondary contamination with Cr(VI).
TWO REFERENCES.
[A] Chromium(VI) Handbook[page-296]
edited by Jacques Guertin, James A. Jacobs, Cynthia P. Avakian
[B]Waste Management
Volume 24, Issue 5, 2004, Pages 483–490.
To Dr.Manohar, My doubt is what happens to the tannin in the soil then?
you will be needing easily oxidizable organic amendments (low mw) to get a quick result (and you do because Cr VI is very soluble). I suspect that biochar would not do the job quickly. Anyway 5g/kg of Cr, either III or VI is way too much. Consider ex-situ intervention where leaching would be effective
Sir
Such a high concentration of Cr(VI) in soil would have definitely polluted the ground water in phreatic aquifer and it is very difficult practically to remove Cr (VI) from ground water system insitu at present.Has the leaching of Cr (VI) has been noticed in the polluted soil has ever been noticed?
The similar situation has been observed in Kanpur Industrial area, where soil contaminated with Cr (VI) has caused ground water pollution
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