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Reduction Processes. Another process which involves electron transfer (except in the opposite direction as AOP) is reductive dechlorination. An example is the reduction of halogenated hydrocarbons. . Reductive dehalogenation with zero valent iron:. - PowerPoint PPT Presentation
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Reduction Processes
Another process which involves electron transfer (except in the opposite direction as AOP) is reductive dechlorination. An example is the reductionof halogenated hydrocarbons.
o 2
o 2
RX H 2e RH X
Fe Fe 2e____________________________
RX H Fe Fe RH X
Reductive dehalogenation with zero valent iron:
Hydrogen gas is usually inert but in the presence of Pd, Ni, Pt and possibly Feo hydrodehalogenation is possible.
M2H RX RH H X
It is also possible that Feo can react with H+ to form H2.
o 22Fe 2H Fe H
03 2 2 3 210Fe 6NO 3H O Fe O 6OH 3N
Other chemical species can be reduced by the iron.For example nitrate can be reduced to nitrogen gas:
Potential long term problem:
As the dehalogenation process proceeds pH will rise as H+ is used. This could result in precipitation of CaCO3 or FeCO3 which will ultimately reduce porosity of the permeable barrier.
Typical Design Results:
First order decay rate approx.
0.03 per hour ( half life = 20 hours)
With a Feo barrier of 1.2 m thickness and a flow rate through the barrier equal to 0.4 m/day get approx. 90% reduction in RX.