| Although the zero-valent iron (Fe0)-based reactive barrier has been introduced as a cost-effective remediation technology for groundwaters contaminated by chlorinated organic compounds and reducible metals, the current approach of the technology has been criticized for its low process efficiency (reaction rate) and the effective life of the medium (longevity). The objectives of this study are to (1) develop and evaluate electro-enhanced technology using Fe0 for mobile radionuclides and trichloroethene in groundwater, (2) develop and evaluate an iron-oxide-based electroremediation for TCE-contaminated groundwater, (3) perform mineralogical characterization of the precipitates formed during contaminated groundwater treatment, and (4) understand the mechanisms of the chemical processes involved in Fe0 oxidation and the effect of cations and anions on the initial precipitation and subsequent phase transformation of the precipitates.; Application of direct current on the Fe0 medium column results in a significant enhancement of the dechlorination rate of TCE and the longevity of Fe0 as a reductive medium for radionuclides. Several factors affect the removal of radionuclides and TCE, including (1) electrode configuration, (2) applied voltage and current, (3) distance between cathode and anode, (4) material used as electrodes, and (5) influent concentration and water chemistry. Direct current applied to palladized multiphasic iron oxide minerals not only increases the efficiency and effective life of the medium by controlling iron oxidation but also increases the dechlorination rate of solvents by providing an external supply of electrons. The mineralogical characterization of the precipitates in reactive Fe0 columns shows that the principal corrosion products are magnetite, intermediate products (green rusts), and hydrated forms of ferric oxides, such as akaganeite (β-FeOOH), goethite (α-FeOOH), or lepidocrocite (γ-FeOOH), depending on the degree of oxidation and the chemical environment. These amorphous and crystalline minerals formed on the reactive medium and reduced the effectiveness and porosity of the Fe0 medium. A pyroaurite-type mineral was synthesized as a host iron mineral for the radionuclides through anodic corrosion of iron from Fe0 foam. The electrochemical synthesis of a crystalline pyroaurite-type mineral could be an effective and economical approach to remediating groundwaters contaminated by uranium, technetium, and other reducible heavy metals. |
