Iron-based degradative solidification/stabilization (Fe(II)-DS/S) is a treatment
method that could be economically applied to smaller DNAPL-contaminated sites and to
those sites with impermeable soils. Reductive dechlorination is achieved by compounds
that are formed by reaction of ferrous iron with components of Portland cement or with
defined chemicals (FeCl3 + Ca(OH)2). These dechlorinating agents can effectively
degrade chlorinated hydrocarbons (PCE, TCE, and 1,1,1-TCA) that are dissolved in
aqueous solution. This research investigated the application of Fe(II)-DS/S to remove
chlorinated hydrocarbons that are present as DNAPLs in source zones and to compared
the reactivity of ferrous iron in different mixtures, including the conventional mixture
with cement (Fe(II)+C) and an iron-solid mixture (ISM) that was synthesized without
the addition of cement.
The modified first-order model, which the rate was proportional to the
concentration of target in the aqueous phase and it was also nearly constant when
DNAPL was present, was developed to describe dechlorination kinetics. The modified
second-order model assumed that the rate was proportional to the product of the concentration of target in the aqueous phase and the concentration of reductive capacity
of the solid reductant. The modified first-order model was used to describe degradation
of target compounds with ISM, and the modified second-order model was used to
describe removals for TCE and 1,1,1-TCA with Fe(II)+C. Results of experiments on
PCE dechlorination with ISM indicated that the increase of Fe(II) in ISM increased rate
constants and decreased the solubility of targets. The half-life was increased with
increasing total PCE concentration. The product analysis implied that degradation of
PCE with ISM was via a combination of the hydrogenolysis and β-elimination pathways.
A comparison of the types of targets and reductants indicated that Fe(II)+C had better
reactivity for chlorinated ethenes (PCE and TCE) than ISM. However, ISM could
dechlorinate a chlorinated ethane (1,1,1-TCA) as rapidly as Fe(II)+10%C. The ratio of
[RC]o/[Fe(II)]o implied that Fe(II) in Fe(II)+C was more involved in reducing
chlorinated ethenes than was Fe(II) in ISM. Dechlorination of a DNAPL mixture
followed the same order of reactivity as with individual DNAPLs with both reductants.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2470 |
| Date | 15 May 2009 |
| Creators | Do, Si Hyun |
| Contributors | Batchelor, Bill |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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