Direct Observation of Nanoparticulate Goethite Recrystallization by Atom Probe Analysis of Isotopic Tracers
MetadataShow full item record
Funding and Sponsorship
© 2019 American Chemical Society. Goethite (α-FeOOH) is dispersed throughout the earth's surface, and its propensity to recrystallize in aqueous solutions determines whether this mineral is a source or sink for critical trace elements in the environment. Under reducing conditions, goethite commonly coexists with aqueous Fe(II) (Fe(II)aq), which accelerates recrystallization by coupled electron transfer and atom exchange. Quantifying the amount of the mineral phase that exchanges its structural Fe(III) atoms with Fe(II)aq is complicated by recrystallization models with untested assumptions of whether, and to what extent, the recrystallized portion of the mineral continues to interact with the solution. Here, we reacted nanoparticulate goethite with 57Fe-enriched Fe(II)aq and used atom probe tomography (APT) to resolve the three-dimensional distribution of Fe isotopes in goethite at the sub nm scale. We found that the 57Fe tracer isotope is enriched in the bulk structure (tens of nanometers deep), with some samples having 57Fe penetration throughout at a level that is similar to the isotopic composition of Fe(II)aq. This suggests that some particles undergo near-complete recrystallization. In other cases, however, the distribution of 57Fe is more heterogeneous and generally concentrates near the particle periphery. Nanoparticle encapsulation and subsequent APT can hence capture hidden recrystallization mechanisms which are critical to predicting mineral reactivity in aqueous solutions.
Showing items related by title, author, creator and subject.
Deformation-enhanced recrystallization of titanite drives decoupling between U-Pb and trace elementsGordon, S.M.; Kirkland, Chris ; Reddy, Steven ; Blatchford, H.J.; Whitney, D.L.; Teyssier, C.; Evans, Noreen ; McDonald, B.J. (2021)Titanite is a common accessory mineral that is useful in determining both age (U-Pb isotopes) and pressure-temperature (P–T) conditions (trace-element composition: Zr, rare earth elements (REE)). However, titanite has a ...
Fougerouse, Denis; Reddy, Steven; Kirkland, Chris; Saxey, David; Rickard, William; Hough, R. (2018)© 2018 China University of Geosciences (Beijing) and Peking University The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In ...
Iron oxide formation from FeCl2 solutions in the presence of uranyl (UO22+) cations and carbonate rich mediaDoornbusch, B.; Bunney, K.; Gan, B.; Jones, Franca; Gräfe, M. (2015)The mineral goethite (a-FeOOH) has previously been investigated as a thermodynamically stable repository for many potentially toxic metals (e.g., Cd, Pb, Cu). The substitution of uranium (U as uranyl, UO22+) for Fe, ...