Iron hydroxy carbonate formation in zerovalent iron permeable reactive barriers: Characterization and evaluation of phase stability

Journal Article · Fri Oct 22 04:00:00 EDT 2010 · J. Contam. Hydrol.

DOI:https://doi.org/10.1016/j.jconhyd.2010.05.009· OSTI ID:1002609

Wilkin, Richard T; Lee, T R ^[1]

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1. U.S. EPA

Predicting the long-term potential of permeable reactive barriers for treating contaminated groundwater relies on understanding the endpoints of biogeochemical reactions between influent groundwater and the reactive medium. Iron hydroxy carbonate (chukanovite) is frequently observed as a secondary mineral precipitate in granular iron PRBs. Mineralogical characterization was carried out using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray absorption spectroscopy on materials collected from three field-based PRBs in the US (East Helena, MT; Elizabeth City, NC; Denver Federal Center, CO). These PRBs were installed to treat a range of contaminants, including chlorinated organics, hexavalent chromium, and arsenic. Results obtained indicate that chukanovite is a prevalent secondary precipitate in the PRBs. Laboratory experiments on high-purity chukanovite separates were carried out to constrain the room-temperature solubility for this mineral. An estimated Gibbs energy of formation ({Delta}{sub f}G{sup o}) for chukanovite is - 1174.4 {+-} 6 kJ/mol. A mineral stability diagram is consistent with observations from the field. Water chemistry from the three reactive barriers falls inside the predicted stability field for chukanovite, at inorganic carbon concentrations intermediate to the stability fields of siderite and ferrous hydroxide. These new data will aid in developing better predictive models of mineral accumulation in zerovalent iron PRBs.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE
• OSTI ID: 1002609
• Journal Information: J. Contam. Hydrol., Journal Name: J. Contam. Hydrol. Journal Issue: (1-4) ; 07, 2010 Vol. 116; ISSN JCOHE6; ISSN 0169-7722
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
BIOGEOCHEMISTRY
CARBONATES
CONTAINMENT SYSTEMS
FORMATION HEAT
GROUND WATER
HYDROXY COMPOUNDS
IRON COMPOUNDS
MINERALOGY
PRECIPITATION
REMEDIAL ACTION
SOLUBILITY
STABILITY