Iron dynamics: Transformation of Fe(II)/Fe(III) during injection of natural organic matter in a sandy aquifer
- Oak Ridge National Lab., TN (United States)
- Clemson Univ., Georgetown, SC (United States)
The dynamics of dissolved, colloidal, and deposited iron phases were examined during a forced-gradient field experiment. The experiment involved the injection of oxygenated water containing high levels of natural organic matter (NOM) into a sandy aquifer. The initial redox potential of the aquifer favored Fe(II) in the groundwater. The changes in the concentrations of Fe(II) and Fe(III) were observed in sampling wells. Under the increased dissolved oxygen (DO) conditions, Fe(II) oxygenation was rapid, resulting in the formation of Fe(III) (hydr)oxide colloids. The oxidation follows the rate law as given in Stumm and Morgan (1981). For an averaged pH and DO of the groundwater, the half time of Fe(II) oxidation is 49 h. The NOM was postulated to stabilize the newly formed colloids, thereby increasing the turbidity in the groundwater. The additional increase in the colloidal fraction of Fe(III) oxide suggested that transport of the colloidal particles was occurring. At those locations where DO remained constantly low, the turbidity increase was moderate, and up to 80% of Fe(III) was in the dissolved phase (<3000 mol. wt.). The latter observation was attributed to the presence of NOM, forming Fe(III)-organic complexes. In addition, NOM may play a role in the oxygen consumption through a Fe(II)/Fe(III) catalyzed oxidation of organic matter as outlined by Stumm and Morgan (1981, p. 469). In this mechanism, Fe(II) oxidation is slow, maintaining a near constant Fe(II) concentration, in agreement with field data. The overall increase in Fe(III) under low DO conditions was postulated to be a combination of (1) slow oxidation, (2) ligand-promoted and catalytic dissolution of deposited iron phases, and (3) the transport of newly formed iron oxide colloids along flow paths. 47 refs., 7 figs., 6 tabs.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 6114617
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 57:9; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AQUIFERS
CHEMICAL REACTIONS
IRON
OXIDATION
ORGANIC MATTER
INJECTION
CHEMICAL REACTION KINETICS
IRON OXIDES
CHALCOGENIDES
ELEMENTS
INTAKE
IRON COMPOUNDS
KINETICS
MATTER
METALS
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
540210* - Environment
Terrestrial- Basic Studies- (1990-)