A nanoscale study of the formation of Fe-(hydr)oxides in a volcanic regolith: Implications for the understanding of soil forming processes on Earth and Mars

The role of organic colloids in the sequestration and mobilization of copper in smelter-impacted soils

“…62 Depending on its chemical composition, the composition of the pore uids, pH, temperature and water activity, ferrihydrite NPs aggregate and transform over time into hematite or goethite via rearrangement, dissolution-re-precipitation and aggregationbased crystal growth. 60,63,64 Schwertmann et al 65 suggested that the latter crystal growth process was essential to induce crystallization of ferrihydrite to hematite and Schindler et al 66 showed that the aggregation of ferrihydrite nanoparticles promoted their transformation into hematite within pore spaces of altered volcanic glass. Aggregation-based crystal growth of hematite may have occurred in the colloid depicted in Fig.…”

Deciphering the Distribution and Crystal-Chemical Environment of Arsenic, Lead, Silica, Phosphorus, Tin, and Zinc in a Porous Ferrihydrite Grain Using Transmission Electron Microscopy and Atom Probe Tomography

“…The Fe-(hydr)­oxide matrix is composed of nanodomains with diameters varying between 4 and 20 nm (Figure e), which are larger than those observed in previous studies (<5 m). , The domains depict lattice fringes with d = 2.0 Å in similar orientations, which is also apparent in a Fast Fourier Transformation pattern (Figure e). Selected area diffraction (SAED) pattern (Figure S3) indicate sharp diffraction spots with d = 2.0 Å and diffuse diffraction ring (with very weak diffraction spots) at d = 2.5 Å and d = 1.47 Å.…”

“…Iron-(hydr)­oxides such as hematite, maghemite, magnetite, goethite, akaganeite, lepidocrocite, feroxyhyte, ferrihydrite, and hydrohematite play fundamental roles in biogeochemical processes at the Earth’s surface due to their wide occurrence and high reactivity. , An important member of this mineral group is ferrihydrite, ∼(Fe 3+ 10 O 14 (OH) 2 ), a reddish-brown, poorly ordered Fe-(hydr)­oxide with variable and nonstoichiometric composition. − It is a nanocrystalline phase composed of individual particles or domains in the lower nanometer range. , The mineral has a high surface-area and surface-reactivity and plays a significant role as a scavenger of trace metals and metalloids in various near-surface environments. − , Two competing structural models exist for ferrihydrite: one in which Fe is exclusively octahedrally coordinated, and one in which 20% of the Fe atoms are tetrahedrally coordinated [so-called akdalite model]. , …”

Effects of Geochemical and Environmental Parameters on Abiotic Organic Chemistry Driven by Iron Hydroxide Minerals

“…As one example, iron precipitation in an aqueous environment can form iron hydroxide minerals similar to the precipitates formed in our experiments, but can also form iron‐silica gels as precursors to hydrothermal/sedimentary precipitates (Grenne & Slack, 2003; Hopkinson et al., 1988; Oehler, 1976; Tosca et al., 2016; Zheng et al., 2016); these silica/iron‐silica gels can form lower water activity environments that might be beneficial for facilitating abiotic/prebiotic organic reactions (Gorrell et al., 2017; Pierre, 2020; Quinson et al., 1988; Trevors & Pollack, 2005; Westall et al., 2018). Hydrated silica‐rich materials are present on Mars, and these may represent hydrothermal or other aqueous alteration environments that could also contain iron oxyhydroxides (Pineau et al., 2020; Schindler et al., 2019; Sun & Milliken, 2018; Tosca et al., 2018); in the case of potential Martian hot spring environments (e.g., Ruff et al., 2020; Sun & Milliken, 2020), it is especially possible that variations in temperature or water activity over time could have facilitated both aqueous reactions as well as those dependent on wet‐dry cycles. It is also possible that complex abiotic/prebiotic chemistry on planets could be facilitated by multiple, interconnected environmental settings with varying conditions over space and time (Stüeken et al., 2013).…”