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Fe(II)-Catalyzed Recrystallization of Goethite Revisited

Lookup NU author(s): Dr Anke Neumann

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Abstract

Results from enriched ⁵⁷Fe isotope tracer experiments have shown that atom exchange can occur between structural Fe in Fe(III) oxides and aqueous Fe(II) with no formation of secondary minerals or change in particle size or shape. Here we derive a mass balance model to quantify the extent of Fe atom exchange between goethite and aqueous Fe(II) that accounts for different Fe pool sizes. We use this model to reinterpret our previous work and to quantify the influence of particle size and pH on extent of goethite exchange with aqueous Fe(II). Consistent with our previous interpretation, substantial exchange of goethite occurred at pH 7.5 (≈ 90%) and we observed little effect of particle size between nanogoethite (average size of 81 × 11 nm; ≈ 110 m2/g) and microgoethite (average size of 590 × 42 nm; ≈ 40 m2/g). Despite ≈90% of the bulk goethite exchanging at pH 7.5, we found no change in mineral phase, average particle size, crystallinity, or reactivity after reaction with aqueous Fe(II). At a lower pH of 5.0, no net sorption of Fe(II) was observed and significantly less exchange occurred accounting for less than the estimated proportion of surface Fe atoms in the particles. Particle size appears to influence the amount of exchange at pH 5.0 and we suggest that aggregation and surface area may play a role. Results from sequential chemical extractions indicate that 57Fe accumulates in extracted Fe(III) goethite components. Isotopic compositions of the extracts indicate that a gradient of 57Fe develops within the goethite with more accumulation of 57Fe occurring in the more easily extracted Fe(III) that may be nearer to the surface.

Publication metadata

Author(s): Handler RM, Frierdich AJ, Johnson CM, Rosso KM, Beard BL, Wang C, Latta DE, Neumann A, Pasakarnis T, Premaratne WAPJ, Scherer MM

Publication type: Article

Publication status: Published

Journal: Environmental Science & Technology

Year: 2014

Volume: 48

Issue: 19

Pages: 11302-1131

Print publication date: 07/10/2014

Online publication date: 23/09/2014

Acceptance date: 08/09/2014

ISSN (print): 0013-936X

ISSN (electronic): 1520-5851

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/es503084u

DOI: 10.1021/es503084u

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