| Abstract
| - Nanoscale Fe0 particles are a promising technology for insitu remediation of trichloroethene (TCE) plumes and TCE-DNAPL source areas, but the physical and chemical propertiescontrolling their reactivity are not yet understood. Here,the TCE reaction rates, pathways, and efficiency of twonanoscale Fe0 particles are measured in batch reactors: particles synthesized from sodium borohydride reduction offerrous iron (Fe/B) and commercially available particles(RNIP). Reactivity was determined under iron-limited (high[TCE]) and excess iron (low [TCE]) conditions and withand without added H2. Particle efficiency, defined as thefraction of the Fe0 in the particles that is used to dechlorinateTCE, was determined under iron-limited conditions. Bothparticles had a core/shell structure and similar specific surfaceareas (∼30 m2/g). Using excess iron, Fe/B transformedTCE into ethane (80%) and C3−C6 coupling products (20%).The measured surface area normalized pseudo-first-order rate constant for Fe/B (1.4 × 10-2 L·h-1·m-2) is∼4-fold higher than for RNIP (3.1 × 10-3 L·h-1·m-2). Allthe Fe0 in Fe/B was accessible for TCE dechlorination, and92 ± 0.7% of the Fe0 was used to reduce TCE. For Fe/B,H2 evolved from reduction of water (H+) was subsequentlyused for TCE dechlorination, and adding H2 to the reactorincreased both the dechlorination rate and the mass ofTCE reduced, indicating that a catalytic pathway exists. RNIPyielded unsaturated products (acetylene and ethene).Nearly half (46%) of the Fe0 in RNIP was unavailable forTCE dechlorination over the course of the experiment andremained in the particles. Adding H2 did not change thereaction rate or efficiency of RNIP. Despite this, the massof TCE dechlorinated per mass of Fe0 added was similarfor both particles due to the less saturated products formedfrom RNIP. The oxide shell composition and the boroncontent are the most likely causes for the differencesbetween the particle types.
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