Precipitation of short-range order hydroxy aluminosilicate (HAS) and hydrous ferric silicate (HFS) at ambient temperature: Insights into mineral formation pathways, crystal chemistry and solubility-stability relationships

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dc.contributor.authorBaldermann, A.
dc.contributor.authorStamm, F.M.
dc.contributor.authorFarkaš, J.
dc.contributor.authorLöhr, S.
dc.contributor.authorRatz, B.
dc.contributor.authorLetofsky-Papst, I.
dc.contributor.authorDietzel, M.
dc.date.issued2024
dc.descriptionAvailable online 25 December 2023
dc.description.abstractChemical weathering of silicates on continents and the subsequent formation of clay minerals are important processes within the Earth’s critical zone, controlling pH, water-holding capacity and ion exchange properties of soils. Short-range ordered (SRO) hydroxy aluminosilicate (HAS) and hydrous ferric silicate (HFS) phases, such as allophane (~Al₂O₃(SiO₂)₁.₃–₂⋅2.5-3H₂O) and hisingerite (~Fe³⁺Si₂O₅(OH)₄•2H₂O), are such common soil clays, but their crystal-chemical properties, solubilities and formation paths remain disputed. In this study, pure HAS and HFS phases were precipitated at molar [Al]ₐq/[Si]ₐq and [Fe]ₐq/[Si]ₐq ratios of 1.0, 1.3, 1.5 and 2.0 and ambient temperature using equilibrium-approaching experiments. The formation of HAS-HFS minerals was studied at [(Al + Fe)]ₐq/[Si]ₐq = 1 using replacement levels of [Fe]ₐq for [Al]ₐq of 10%, 25%, 50%, 75% and 90%. HAS, HFS and HAS-HFS minerals were formed at pH ~3–6 through condensation of silica tetrahedrons onto Al/ Fe-O-OH octahedral templates. The [Al]s/[Si]s, [Fe]s/[Si]s and [(Al + Fe)]s/[Si]s ratios of the precipitated SRO phases ranged from 0.7 for HAS and 0.7–1.0 for HAS-HFS to 1.0–1.3 for HFS minerals, and correlate linearly with the values of the solubility constants (pK) obtained herein and from literature as follows: pKHAS = 2.9⋅[Al]s/[Si]s + 7.9 (r² = 0.96; n = 6) pKHAS-HFS = - 23.2⋅[(Al + Fe)] /[Si]s + 24.8 (r² = 0.94; n = 5) pKHFS = 23.5⋅[Fe]s/[Si]s–26.3 (r² = 0.86; n = 4) The faster formation kinetics and lower solubility of HFS phases (pK = -2.2 to 4.7) and HAS-HFS phases (pK = -1.0 to 6.0) compared to HAS phases (pK = 10.2 ± 0.3) suggests that hisingerite-like and Fe-substituted allophane-like minerals are probably more abundant in the Earth’s critical zone than previously thought, thus hly reactive substrates for the formation of thermodynamically more stable kaolinite and smectite minerals.
dc.description.statementofresponsibilityAndre Baldermann, Franziska M. Stamm, Juraj Farkaš, Stefan Löhr, Bettina Ratz, Ilse Letofsky-Papst, Martin Dietzel
dc.identifier.citationChemical Geology, 2024; 646:121911-1-121911-16
dc.identifier.doi10.1016/j.chemgeo.2023.121911
dc.identifier.issn0009-2541
dc.identifier.issn1872-6836
dc.identifier.orcidLöhr, S. [0000-0002-1242-552X]
dc.identifier.urihttps://hdl.handle.net/2440/140594
dc.language.isoen
dc.publisherElsevier
dc.relation.granthttp://purl.org/au-research/grants/arc/DP210100462
dc.rights© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
dc.source.urihttp://dx.doi.org/10.1016/j.chemgeo.2023.121911
dc.subjectAllophane; Hisingerite; Weathering; Soils; Clay nanoparticles; Aluminosilicate
dc.titlePrecipitation of short-range order hydroxy aluminosilicate (HAS) and hydrous ferric silicate (HFS) at ambient temperature: Insights into mineral formation pathways, crystal chemistry and solubility-stability relationships
dc.typeJournal article
pubs.publication-statusPublished

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