Identification and Quantification of Mineral Precipitation in Fe 0 Filings From a Column Study
Quantifying precipitates and determining corrosion rates of zero-valent iron (Fe 0 ) during groundwater treatment were pursued in two field columns by analyzing column core samples using thermo-gravimetric analysis (TGA) combined with x-ray diffraction (XRD) and scanning electron microscopy (SEM). The core precipitates included goethite, magnetite, aragonite, and calcite as major phases with lesser amounts of Fe?(OH)?CO?, and green rust, similar to other studies [1-5]. Corrosion rates derived from TGA-MS analysis of core samples ranged in 0.5 ? 6.1 mmol kg -1 d -1 , higher than a previous report [6] but not unreasonable considering that the influent contained up to 13.5 mM NO? - . At the inlet sand-Fe 0 interface, corrosion rates were similar (4.09 and 4.86 mmol kg -1 d -1 ) for both columns. Corrosion rates derived from pore water chemistry showed a decreasing trend over time. The time-weighted average corrosion rates for both columns of different throughput fell in the range based on TGA-MS results, suggesting that the aqueous mass balance calculation could provide an alternative to estimating corrosion rates in the absence of core analyses. The porosity reduction based on water chemistry was confirmed by TGA-MS results (7?77%), where the high porosity reduction occurred at reactive regions and the low at regions near the effluent. Normalized with the treatment volume, porosity reduction values agree with other studies that used high levels of SO? ?- and HCO? - [2,7,8]. The near 80% porosity reduction in more corroded regions, subjected to high throughput of an equivalent of 17-yr operation, is significant to be considered for long-term performance of permeable reactive barriers.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15020717
- Report Number(s):
- PNNL-SA-40171; 2559; KP1301030; TRN: US200521%%238
- Journal Information:
- Environmental Science and Technology, Vol. 38, Issue 21
- Country of Publication:
- United States
- Language:
- English
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