Geochemical assessment of metal transport in glacial till during electrokinetic remediation |
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Authors: | Ashraf Z Al-Hamdan Krishna R Reddy |
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Institution: | (1) Department of Civil and Environmental Engineering, University of Alabama in Huntsville, 301 Sparkman Drive, Huntsville, AL 35899, USA;(2) Department of Civil and Materials Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, IL 60607, USA |
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Abstract: | This paper presents the chemical speciation and retention behavior of chromium (Cr), nickel (Ni), and cadmium (Cd) prior to
and after the electrokinetic remediation in glacial till soil. The speciation of the metals was predicted using the chemical
speciation program MINEQL+. The simulations were performed for single-contaminant with only Cr(VI) or Ni, and multi-contaminants consisting of: (1)
Cr(VI), Ni, and Cd; (2) Cr(III), Ni and Cd; (3) Cr(VI), Cr(III), Ni and Cd; (4) Cr(VI), Ni, and Cd with reducing agents; and
(5) Cr(III), Ni, and Cd with oxidizing agent (Mn). The results showed that the speciation and distribution of cationic metals
Ni, Cd, and Cr(III)] in glacial till soil remain unaffected or slightly affected during electrokinetics. This is attributed
to the high pH buffering capacity of the glacial till, leading the metals to precipitate in the soil prior to and after electrokinetics.
This study showed that during electrokinetics, Cr(VI) existed as anionic complex and migrated towards the anode and the migration
is maximum in case of a single-contaminant system. The study also showed that near the anode in the absence of any reducing
and oxidizing agent, Cr(VI) mostly adsorbed, and some of Cr(VI) reduced to Cr(III) and migrated towards the cathode and finally
precipitated due to high pH conditions. Ni and Cd remain adsorbed or precipitated due to the high pH conditions throughout
the soil. Among the reducing agents, the sulfide had significant effect on the migration of metals compared to ferrous ions.
While in the presence of oxidizing agent (Mn), no noticeable Cr(VI) was found in the soil sample indicating the reduction
of Cr(VI) to Cr(III) and the predominance of reducing conditions due to the presence of naturally occurring iron in the glacial
till soil. Overall, this study provides a reasonable explanation of the speciation and distribution of chromium, nickel and
cadmium during the electrokinetic remediation of glacial till soil. |
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Keywords: | Soil Clay Heavy metals Adsorption Remediation Electrokinetics Electromigration Electroosmosis Speciation |
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