TCE dechlorination rates, pathways, and efficiency of nanoscale iron particles with different properties

Nanoscale Fe-0 particles are a promising technology for in situ remediation of trichloroethene (TCE) plumes and TCEDNAPLsource areas, but the physical and chemical properties controlling their reactivity are not yet understood. Here, the TCE reaction rates, pathways, and efficiency of two nanoscale Fe-0 particles are measured in batch reactors: particles synthesized from sodium borohydricle reduction of ferrous iron (Fe/B) and commercially available particles (RNIP). Reactivity was determined under iron-limited (high [TCED and excess iron (low [TCED conditions and with and without added H-2. Particle efficiency, defined as the fraction of the Fe-0 in the particles that is used to dechlorinate TCE, was determined under iron-limited conditions. Both particles had a core/shell structure and similar specific surface areas (similar to30 m(2)/g). Using excess iron, Fe/B transformed TCE into ethane (80%) and C3-C6 coupling products (20%). The measured surface area normalized pseudo-firstorder rate constant for Fe/B (1.4 x 10(-2) L(.)h(-1.)m(-2)) is similar to4-fold higher than for RNIP (3.1 X 10(-3) L(.)h(-1.)m(-2)). All the Fe-0 in Fe/B was accessible for TICE dechlorination, and 92 0.7% of the FeO was used to reduce TCE. For Fe/B, H2 evolved from reduction of water (H+) was subsequently used for TCE dechlorination, and adding H2 to the reactor increased both the dechlorination rate and the mass of TICE reduced, inclicatingthata catalytic pathway exists. RNIP yielded unsaturated products (acetylene and ethene). Nearly half (46%) of the Fe-0 in RNIP was unavailable for TCE dechlorination over the course of the experiment and remained in the particles. Adding H2 did not change the reaction rate or efficiency of RNIP. Despite this, the mass of TCE dechlorinated per mass of Fe-0 added was similar for both particles due to the less saturated products formed from RNIP. The oxide shell composition and the boron content are the most likely causes for the differences between the particle types.