HR: 09:45h
AN: H21G-07    [Abstracts]
TI: Effects of Precipitation and Particle Size on Low Frequency Electrical Properties of Zero Valent Iron
AU: * Wu, Y
EM: yuxinwu@pegasus.rutgers.edu
AF: Rutgers University, Department of Earth and Environmental Sciences, 195 University Ave RM 407, Newark, NJ 07102 United States
AU: Slater, L
EM: lslater@andromeda.rutgers.edu
AF: Rutgers University, Department of Earth and Environmental Sciences, 195 University Ave RM 407, Newark, NJ 07102 United States
AB: Observational methods are required to monitor the long-term efficiency of permeable reactive barrier (PRB) installations used to remediate hydrocarbon and heavy metal contaminated groundwater. Our previous studies investigated the relationship between induced polarization (IP) and zero valent iron (Fe0) surface area and electrolyte activity. In this continuous research, we performed experiments on mixtures of Fe0 and Ottawa sand to study (1) the relationship between IP and zero valent iron particle size, and (2) the impact of precipitation induced on the Fe0 surface. The latter experiment addresses the issue of whether reduction in PRB performance can be inferred from electrical measurements. The effect of iron particle size on IP was studied by running background solutions (0.01 ­C 0.1M NaCl) through samples of the mixture of sand with 5% of different sizes of iron (diameter 1-0.2 mm). Precipitation experiments were conducted by running samples with different solutions to induce precipitation on the iron surface. This involved: (1) long term execution (about 1 year) of four identical samples (5% Fe0 mixture with sand) continuously flushed with four different solutions (0.1 M NaHCO3, 0.1 M Na2SO4, 0.1 M Na2HPO4 and pure water); (2) a short term experiment (in days) with high percentage of Fe0 (30%, 70%) run with high highly basic solutions (0.1M NaOH and 0.1 M Na2CO3). The results show that the IP response is correlated with iron particle size: First, the IP magnitude is inversely proportional to iron particle diameter principally due to the inverse relation between particle diameter and specific surface area. Second, the dominant relaxation time of the polarization is inversely proportional to the particle diameter. The short term precipitation experiment revealed two significant observations: (1) the IP magnitude increased after induced precipitation on Fe0 surface which we tentatively attribute to an increase in the surface area due to an irregular coating of metallic precipitants (FeCO3, Fe(OH)2, FeOOH, Fe(OH)3) on the Fe0 (2) a clear increase in the time constant, which we attribute to an increase in the effective particle size due to the precipitation. Our results to date suggest that IP may be a viable method for long-term monitoring of reactive iron barriers.
DE: 3914 Electrical properties
DE: 1829 Groundwater hydrology
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting