{"type": "FeatureCollection", "features": [{"id": "10.1016/j.geoderma.2022.116217", "type": "Feature", "geometry": null, "properties": {"license": "Open Access", "updated": "2026-07-26T16:16:13Z", "type": "Journal Article", "created": "2022-10-23", "title": "Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils", "description": "Open AccessISSN:0016-7061", "keywords": ["13. Climate action", "Wetlands", "Iceland", "0401 agriculture", " forestry", " and fisheries", "Colloids", "04 agricultural and veterinary sciences", "15. Life on land", "01 natural sciences", "Iron biogeochemistry", "Organic carbon", "0105 earth and related environmental sciences"]}, "links": [{"href": "https://doi.org/10.1016/j.geoderma.2022.116217"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Geoderma", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.1016/j.geoderma.2022.116217", "name": "item", "description": "10.1016/j.geoderma.2022.116217", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.1016/j.geoderma.2022.116217"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2022-12-01T00:00:00Z"}}, {"id": "10.3929/ethz-b-000663192", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:21:10Z", "type": "Journal Article", "title": "Vivianite formation and transformation processes in intertidal sediments and the influence of isomorphic substitution", "description": "unspecifiedPhosphor (P) ist ein wesentlicher N\u00e4hrstoff f\u00fcr die Prim\u00e4rproduktion in aqautischen \u00d6kosystemen, aber \u00fcberm\u00e4\u00dfiger P Eintrag kann zur Eutrophierung dieser \u00d6kosysteme f\u00fchren. Wie P in Sedimenten gebunden ist, wirkt sich auf dessen Bioverf\u00fcgbarkeit aus. Unter reduzierenden, sulfid-freien Bedingungen kann das eisenhaltige Phosphatmineral Vivianit eine wesentliche Rolle bei der P-Bindung in K\u00fcstensedimenten spielen und somit die Wasserqualit\u00e4t positiv beeinflussen. Trotz der Bedeutung von Vivianit f\u00fcr die Regulierung der P-Verf\u00fcgbarkeit in K\u00fcstensedimenten sind die in-situ Bildung, Zusammensetzung und Stabilit\u00e4t von Vivianit nur unzureichend untersucht. In dieser Doktorarbeit wurden Feldexperimente mit einer Laborstudie kombiniert, um die Bildungs- und Umwandlungsprozesse von Vivianit in gezeitenbeeinflussten Sedimenten und den Einfluss der isomorphen Substitution auf diese Prozesse aufzudecken. Diese Erkenntnisse bieten wertvolle Einblicke in die Prozesse des P-Kreislaufs in K\u00fcstensedimenten und sind bedeutend f\u00fcr die Entwicklung industrieller Anwendungen, die darauf abzielen, den anthropogenen P-Kreislauf zu schlie\u00dfen.   Im ersten Teil der Arbeit wurde eine Methode entwickelt, bei der isotopisch 57Fe-markiertes Ferrihydrit mit dem Sediment vermischt wurde, um die Vivianitbildung in-situ in gezeitenbeeinflussten Sedimenten zu verfolgen. Mit dieser Methode konnte gezeigt werden, dass sich Vivianit innerhalb von sieben Wochen in gezeitenbeeinflussten Sedimenten mit g\u00fcnstigen geochemischen Bedingungen bilden kann. Die Adsorption von Phosphat an Ferrihydrit war ein wesentlicher Vorl\u00e4ufer f\u00fcr die Bildung von Vivianit. Die reduktive Aufl\u00f6sung des Ferrihydrits bildete wahrscheinlich lokale Bedingen, welche n\u00f6tig waren, um die Vivianitbildung auszul\u00f6sen. W\u00e4hrend das gebildete Vivianit nur ein kleiner Teil des Eisen (Fe)-Pools war (bis zu 15%), machte es bis zu 72% des P-Pools aus basierend auf st\u00f6chiometrischen Berechnungen. Diese Ergebnisse zeigen, dass Vivianit eine entscheidende Rolle bei der Regulierung der P-Retention in K\u00fcstensedimenten spielen kann.   In der Umwelt enth\u00e4lt Vivianit h\u00e4ufig andere zweiwertige Kationen, wie Mangan (Mn) und Magnesium (Mg), die in der Kristallstruktur Fe ersetzen. Im zweiten Experiment wurde untersucht, ob Mn oder Mg bei unterschiedlichen Salzgehalten bevorzugt eingebaut wird und wie die isomorphe Substitution die Kristallstruktur und Morphologie ver\u00e4ndert. Die Synthese von neunzehn Vivianiten mit unterschiedlichen Mn- und/oder Mg-Konzentrationen bei verschiedenen Salzgehalten ergab, dass bei niedriger Ionenst\u00e4rke sowohl Mn als auch Mg Fe in der Kristallstruktur gleichwertig ersetzen k\u00f6nnen, wobei Mn bei h\u00f6herer Ionenst\u00e4rke bevorzugt wurde. Vivianit weist zwei unterschiedliche Fe-Atompositionen auf. Die Substitution von Fe durch Mn und/oder Mg fand vorzugsweise an der Atomposition statt, welche Elektronentransfer ausf\u00fchren kann, wodurch Vivianit gegen Oxidation stabilisiert wird. Somit kann sich die isomorphe Substitution wahrscheinlich direkt auf das Oxidationsverhalten von Vivianit auswirken. Au\u00dferdem f\u00fchrte die isomorphe Substitution zu kleineren, raueren Kristallen mit geringerer Kristallinit\u00e4t. Diese beobachteten Ver\u00e4nderungen k\u00f6nnten sich auf die Reaktivit\u00e4t von Vivianit in der Umwelt auswirken, weshalb die isomorphe Substitution bei der Untersuchung der Reaktivit\u00e4t von Vivianit ber\u00fccksichtigt werden sollte.   Umweltver\u00e4nderungen, einschlie\u00dflich des Anstiegs des Meeresspiegels, k\u00f6nnten die Bildung von Sulfid in derzeit nicht sulfidischen Sedimenten, die Vivianit enthalten, verst\u00e4rken und zu thermodynamisch instabilen Bedingungen f\u00fcr Vivianit f\u00fchren. Das letzte Experiment untersuchte die in-situ Stabilit\u00e4t von unsubstituiertem und Mn-Mg-substituiertem Vivianit, gemischt mit Meeressand und mit oder ohne die Zugabe von Kalziumkarbonat. Die Mischungen wurden 56 Tage lang in zwei Gezeitenzonen inkubiert, von denen ein Standort eine niedrige und der andere eine hohe Sulfidkonzentration aufwies. Die Inkubation von unsubstituiertem und Mn-Mg-substituiertem Vivianit bei unterschiedlichen Sulfidkonzentrationen ergab eine teilweise Aufl\u00f6sung von Vivianit, die durch die isomorphe Substitution deutlich verst\u00e4rkt wurde. Der gr\u00f6\u00dfte Teil der verbleibenden Mineralphase wurde weiterhin als Vivianit charakterisiert, was darauf hindeutet, dass ein Teil des Vivianits \u00fcber die Versuchsdauer erhalten blieb. Bei niedrigen Sulfidkonzentrationen war Gr\u00fcner Rost das Hauptumwandlungsprodukt, das wahrscheinlich einen Teil des freigesetzten Phosphats adsorbierte. Bei hohem Sulfidgehalt dominierte die Bildung von Fe-Sulfidmineralen, welche aufgrund der geringen Sorptionskapazit\u00e4t f\u00fcr Phosphat zu einem erh\u00f6hten P-Verlust f\u00fchrte. Ein erh\u00f6htes Sorptionspotenzial f\u00fcr Phosphat durch die Zugabe von Kalziumkarbonat k\u00f6nnte den Phosphatverlust geringf\u00fcgig verringern. Diese Ergebnisse zeigen, dass vivianithaltige Sedimente als Quelle f\u00fcr bioverf\u00fcgbares Phosphat dienen k\u00f6nnen, wenn sich die geochemischen Bedingungen \u00e4ndern.   Diese Arbeit liefert neue experimentelle Ans\u00e4tze zur Untersuchung und Quantifizierung von Umwandlungs- und Bildungsprozessen von Vivianit. Die Ergebnisse zeigen eine schnelle in-situ Bildungskinetik, w\u00e4hrend die Aufl\u00f6sung von Vivianit unter den untersuchten Bedingungen langsam verl\u00e4uft. Die schnelle in-situ Bildungskinetik deutet darauf hin, dass die Vivianitbildung die P-Retention in Umgebungen mit sowohl schwankenden als auch stabilen geochemischen Bedingungen regulieren kann. Die Ver\u00e4nderungen der Kristallstruktur und -morphologie durch isomorphe Substitution erh\u00f6hten das Ausma\u00df der Aufl\u00f6sung und Umwandlung des Vivianits. Aufgrund der langsamen in-situ Aufl\u00f6sung k\u00f6nnte Vivianit bei kurzfristigen Umweltst\u00f6rungen eine stabile P-Retentionsphase darstellen. Langfristig destabilisierende Bedingungen k\u00f6nnten jedoch zu einer vollst\u00e4ndigen Aufl\u00f6sung f\u00fchren und die P-Retentionskapazit\u00e4t des Sediments schw\u00e4chen. Die Ergebnisse unterstreichen die Bedeutung von Vivianit als P-Retentionsphase in salzarmen K\u00fcstensedimenten, k\u00f6nnten aber auch f\u00fcr das Verst\u00e4ndnis von Bildungs- und Umwandlungsprozessen von Vivianit in anderen Umweltsystemen, wie limnischen Sedimenten und B\u00f6den in Feuchtgebieten, von Bedeutung sein. Dar\u00fcber hinaus haben diese Ergebnisse Auswirkungen auf andere Forschungsbereiche, wie die Gew\u00e4ssersanierung und die industrielle P-R\u00fcckgewinnung.", "keywords": ["iron biogeochemistry", "info:eu-repo/classification/ddc/550", "Phosphorus cycling", "Coastal biogeochemistry", "X-ray absorption spectroscopy", "Laboratory experiments", "VIVIANITE (MINERALOGY)", "Field experiments", "6. Clean water", "M\u00f6ssbauer Spectroscopy", "Earth sciences", "X-Ray Diffraction", "13. Climate action", "IRON PHOSPHATES (INORGANIC CHEMISTRY)", "14. Life underwater", "iron minerals", "mineral transformation", "Redox geochemistry"], "contacts": [{"organization": "Kubeneck, Luisa Jo\u00eblle", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.3929/ethz-b-000663192"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Thesis/Dissertation", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.3929/ethz-b-000663192", "name": "item", "description": "10.3929/ethz-b-000663192", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.3929/ethz-b-000663192"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2024-01-01T00:00:00Z"}}, {"id": "10.3929/ethz-b-000648810", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:21:10Z", "type": "Journal Article", "title": "Transformation of jarosite and iron oxyhydroxides in acid sulfate paddy soils", "description": "Open AccessMinerals containing Fe are ubiquitous in soils. By providing an abundance of sites for the sorption and incorporation of major and trace elements, Fe minerals can govern the fate and behaviour of numerous pollutants and nutrients in soils. Furthermore, the reactivity of Fe in redox-dynamic soils produces a web of Fe mineral transformation processes with broad consequences for element cycling. The importance of Fe cycling is no exception in acid sulfate soils, although the high sulfur and low pH conditions produce unique Fe mineral transformation processes and compositions. In acid sulfate soils, jarosite, an Fe-K hydroxysulfate mineral, and ferrihydrite, a common short-range-ordered Fe oxyhydroxide mineral, play a central role in the pedological development of active and post-active acid sulfate soils. Soil pH and the dynamics of metals, such as aluminium, are key to understanding the toxicity of acid sulfate soils and can be directly influenced by jarosite and ferrihydrite transformation processes.   Although the transformation of Fe minerals is a key component of biogeochemical processes in redox-active soils, the variables that control the rates and pathways of Fe mineral transformations in soil remain uncertain. The uncertainty arises from the difficulty of tracing molecular processes within a matrix of diverse soil components. Iron minerals are regularly characterised in soils, but the processes that explain the Fe mineral composition of soils cannot be easily resolved. An alternative approach is to perform simplified experiments, such as mixed mineral suspension experiments, under controlled laboratory conditions, to test the effect of individual variables. These systems often use synthetic minerals, although relatively pure jarosite may also be isolated from soils and tested in mixed suspension experiments. While useful to derive mechanistic understanding, the measured outcomes of mixed suspension experiments may not represent the rates and products of transformations that occur in soils.  Therefore, the objective of this thesis was to gain new understanding of the stability and transformation of jarosite and ferrihydrite in acid sulfate soils by developing novel experimental techniques to follow the transformation of synthetic jarosite and ferrihydrite directly in soils. The central theme of the thesis is the comparison of jarosite and aluminium-substituted jarosite transformation in experimental media of increasing complexity. The experiments are performed under conditions that are relevant to rice paddy soils because of the importance of rice in global food production, and the unique management of rice paddies whereby regular flooding during the growing season produces distinct redox cycles. In Thailand, large areas of the Chao Phraya River delta are cultivated as rice paddies despite being acid sulfate soils, providing a suitable site to observe the effects of regular redox cycling on the biogeochemistry of Fe minerals in acid sulfate soils.  The thesis begins with characterisation of synthetic and natural jarosite mineral composition and reactivity. Spectroscopic techniques (Raman spectroscopy, M\u00f6ssbauer spectroscopy and Energy-dispersive X-ray spectrometry) and X-ray diffraction (XRD) were used to assess the element substitution of mineral samples from two jarosite-alunite synthetic solid solution series. The same characterisation techniques were then applied to a sample of jarosite from an acid sulfate soil in Thailand has a natural Al-for-Fe substitution. The mineral characterisation was followed by a transformation experiment in a mixed-suspension system, similar to experimental designs that have been previously used to study mineral transformation processes. The experiment followed the transformation of the natural jarosite sample from an acid sulfate soil in Thailand and three jarosite samples with variable amounts of Al substitution. The reaction solution mimicked the pH (circumneutral) and Fe(II) content (up to 1:1 ratio of Fe(II) in solution to Fe(III) in solids) of flooded acid sulfate soils. Furthermore, using a 57Fe tracer, the simultaneous transformation processes that explained the distribution of mineral products could be resolved from one another. The transformation experiment revealed the relative reactivity of the minerals in the presence of Fe(II), and created a baseline that could be used to compare traditional mixed-suspension experiments with transformations in complex media such as soil.   To advance mineral transformation experiments towards studies in which transformation processes may be followed within a soil matrix, several novel techniques were developed. In a first step, ferrihydrite was incubated for up to twelve weeks in microcosms, each containing 300 g of 5 mM CaCl2 solution and 250 g of one of five paddy soils. The ferrihydrite was buried in the soil within a mesh bag (polyethel terephthalate, 51 \u03bcm pores, 30 mm x 12 mm x 3 mm) that allowed free contact between the synthetic minerals and the pore water, but separated the minerals from direct contact with the soil matrix. The mineral products of the transformation were identified and quantified by Rietveld fitting of XRD patterns. Further, the spatial arrangements of the ferrihydrite and transformation products were measured after two weeks by Raman spectroscopy, which could be used to assess the effects of pore water chemistry and diffusion processes on mineral transformation in the mesh bags. The second step involved measuring jarosite and Al-substituted jarosite transformation in flooded topsoil and subsoils from a rice paddy located on the Bangkok Plain in Central Thailand using an adaptation of the mesh bag method. To test the effect of pore water on the transformation of jarosite in soil, mesh bags were filled with synthetic jarosite and aluminium-jarosite and incubated in topsoils and subsoils, both in laboratory mesocosms and directly in the field. Then, the effect of the soil matrix was tested by completing a parallel experiment using mesh bags containing soil that was pre-enriched with synthetic 57Fe-labelled jarosite and aluminium-substituted jarosite. To facilitate the deployment and collection of small mesh bags in large soil volumes, the mesh bags were inserted into soils using custom-designed 3D-printed sample holders. At three timepoints within twelve weeks, one set of mesh bags were removed from the soil. Transformation products were identified and quantified in the pure jarosite and aluminium-jarosite mesh bags using Rietveld fitting of XRD patterns, while the fate of the 57Fe in enriched soil mesh bags was traced using 57Fe M\u00f6ssbauer spectroscopy.   Performing experiments in increasingly complex media provides an insight into the effect of experimental design on the observation of Fe mineral transformations and provides new information regarding the transformation rates and pathways of jarosite and ferrihydrite within full complexity of soil media. Indeed, this thesis demonstrates that the complex chemistry, biological activity, and physical arrangement of components in the soil have strong effects on the rate and products of jarosite and ferrihydrite transformation processes. The transformation of jarosite and Al-substituted jarosite in mixed-suspension experiments presented in this thesis, in agreement with previous mixed-suspension experiments on both jarosite and ferrihydrite, occurred within a matter of hours. By contrast, the rate of ferrihydrite, jarosite and Al-jarosite transformation in soil pore and in direct contact with the soil matrix occurred over the course of several weeks or months. In the ferrihydrite mesh bags, slow ferrihydrite transformation kinetics on the outer rim of the mesh bag, and deep in the core of the mesh bag, indicated that the sorption of chemical components of soil pore water and diffusion limitations of Fe(II) in pore water could be reasons for the slower rates of transformation in soil. In addition, both Al-for-Fe substitution and Fe(II) concentration in solution were important factors that altered the rate of mineral transformation.  The different incubation conditions for jarosite and Al-jarosite also altered the products of the transformation. Whereas the hydrolysis of jarosite in the absence of Fe(II) resulted primarily in the formation of ferrihydrite, jarosite transformation in the presence of Fe(II) led to ferrihydrite, goethite and lepidocrocite formation. The Fe oxyhydroxide products were consistent with Fe(II)-catalysed transformation, and Fe(II)-catalysed recrystallisation of jarosite may have occurred concurrently. Aluminium-for-iron substitution hindered the formation of lepidocrocite formation in favour of ferrihydrite and goethite. Similar product phases occurred when jarosite and Al-jarosite were reacted with pore water from acid sulfate soils, indicating that similar transformation pathways may define the mineral products of jarosite transformations when the jarosite occurs as accumulations of pure mineral in soil. However, non- or poorly crystalline phases predominated in the transformation products when jarosite or Al-jarosite were incubated in direct contact with the soil matrix, indicating that the transformation of jarosite under these circumstances was governed by different pathways and processes.  The new insights into the transformation of ferrihydrite, jarosite and Al-jarosite in acid sulfate soils demonstrate that phases previously considered meta-stable may participate in the biogeochemistry of soil over period of several months. In the context of rice cultivation, the transformation processes may affect the biogeochemistry of the soils throughout the growing season. The formation of poorly crystalline minerals following the transformation in flooded soils may have positive consequences on the sequestration of other trace and major elements that were associated with the ferrihydrite, jarosite or Al-jarosite prior to the transformation. However, the stabilisation of reduced Fe in the soil matrix may have the opposite effect, promoting the mobility of other ions in solution. The methods used to incubate jarosite and ferrihydrite in soils are easily adaptable to new experimental questions involving the behaviour of Fe-bearing minerals in soil. Therefore, the findings open up a new class of experiments within environmental mineralogy and biogeochemistry, that can help to uncover the processes that occur in the environment and explain the natural variation in the composition of Fe phases in soil.", "keywords": ["jarosite", "iron biogeochemistry", "soil chemistry", "acid sulfate soil", "laboratory study", "ferrihydrite", "soil", "soil incubation", "redox chemistry", "goethite", "iron minerals", "2. Zero hunger", "soil biogeochemistry", "info:eu-repo/classification/ddc/550", "M\u00f6ssbauer spectroscopy", "rice paddy soil", "15. Life on land", "6. Clean water", "Earth sciences", "lepidocrocite", "field study", "13. Climate action", "Raman spectroscopy", "iron oxyhydroxide", "mineral transformation", "iron minerals; mineral transformation; soil; soil chemistry; soil mineralogy; soil biogeochemistry; redox chemistry; iron biogeochemistry; acid sulfate soil; rice paddy soil; jarosite; ferrihydrite; goethite; lepidocrocite; iron oxyhydroxide; M\u00f6ssbauer spectroscopy; Raman spectroscopy; field study; laboratory study; soil incubation", "soil mineralogy"], "contacts": [{"organization": "Grigg, Andrew R.C.", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.3929/ethz-b-000648810"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Thesis/Dissertation", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.3929/ethz-b-000648810", "name": "item", "description": "10.3929/ethz-b-000648810", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.3929/ethz-b-000648810"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2023-01-01T00:00:00Z"}}, {"id": "10.3929/ethz-b-000582238", "type": "Feature", "geometry": null, "properties": {"license": "Open Access", "updated": "2026-07-26T16:21:09Z", "type": "Journal Article", "created": "2022-10-23", "title": "Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils", "description": "Open AccessISSN:0016-7061", "keywords": ["13. Climate action", "Wetlands", "Iceland", "0401 agriculture", " forestry", " and fisheries", "Colloids", "04 agricultural and veterinary sciences", "15. Life on land", "01 natural sciences", "Iron biogeochemistry", "Organic carbon", "0105 earth and related environmental sciences"]}, "links": [{"href": "https://doi.org/10.3929/ethz-b-000582238"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Geoderma", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.3929/ethz-b-000582238", "name": "item", "description": "10.3929/ethz-b-000582238", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.3929/ethz-b-000582238"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2022-12-01T00:00:00Z"}}, {"id": "20.500.11850/582238", "type": "Feature", "geometry": null, "properties": {"license": "Open Access", "updated": "2026-07-26T16:25:23Z", "type": "Report", "title": "Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils", "description": "Open AccessISSN:0016-7061", "keywords": ["Iceland; Iron biogeochemistry; Organic carbon; Colloids; Wetlands"], "contacts": [{"organization": "Thomas Arrigo, Laurel K., Kretzschmar, Ruben; id_orcid0000-0003-2587-2430,", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/20.500.11850/582238"}, {"rel": "self", "type": "application/geo+json", "title": "20.500.11850/582238", "name": "item", "description": "20.500.11850/582238", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/20.500.11850/582238"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2022-12-15T00:00:00Z"}}, {"id": "20.500.11850/663192", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:25:24Z", "type": "Report", "title": "Vivianite formation and transformation processes in intertidal sediments and the influence of isomorphic substitution", "keywords": ["Earth sciences", "info:eu-repo/classification/ddc/550", "iron minerals; VIVIANITE (MINERALOGY); IRON PHOSPHATES (INORGANIC CHEMISTRY); Coastal biogeochemistry; mineral transformation; Redox geochemistry; M\u00f6ssbauer Spectroscopy; X-ray absorption spectroscopy; Field experiments; Laboratory experiments; iron biogeochemistry; Phosphorus cycling; X-Ray Diffraction"], "contacts": [{"organization": "Kubeneck, Luisa Jo\u00eblle; id_orcid0000-0003-1894-6809", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/20.500.11850/663192"}, {"rel": "self", "type": "application/geo+json", "title": "20.500.11850/663192", "name": "item", "description": "20.500.11850/663192", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/20.500.11850/663192"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2024-01-01T00:00:00Z"}}, {"id": "20.500.11850/648810", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:25:24Z", "type": "Journal Article", "title": "Transformation of jarosite and iron oxyhydroxides in acid sulfate paddy soils", "description": "Open AccessMinerals containing Fe are ubiquitous in soils. By providing an abundance of sites for the sorption and incorporation of major and trace elements, Fe minerals can govern the fate and behaviour of numerous pollutants and nutrients in soils. Furthermore, the reactivity of Fe in redox-dynamic soils produces a web of Fe mineral transformation processes with broad consequences for element cycling. The importance of Fe cycling is no exception in acid sulfate soils, although the high sulfur and low pH conditions produce unique Fe mineral transformation processes and compositions. In acid sulfate soils, jarosite, an Fe-K hydroxysulfate mineral, and ferrihydrite, a common short-range-ordered Fe oxyhydroxide mineral, play a central role in the pedological development of active and post-active acid sulfate soils. Soil pH and the dynamics of metals, such as aluminium, are key to understanding the toxicity of acid sulfate soils and can be directly influenced by jarosite and ferrihydrite transformation processes.   Although the transformation of Fe minerals is a key component of biogeochemical processes in redox-active soils, the variables that control the rates and pathways of Fe mineral transformations in soil remain uncertain. The uncertainty arises from the difficulty of tracing molecular processes within a matrix of diverse soil components. Iron minerals are regularly characterised in soils, but the processes that explain the Fe mineral composition of soils cannot be easily resolved. An alternative approach is to perform simplified experiments, such as mixed mineral suspension experiments, under controlled laboratory conditions, to test the effect of individual variables. These systems often use synthetic minerals, although relatively pure jarosite may also be isolated from soils and tested in mixed suspension experiments. While useful to derive mechanistic understanding, the measured outcomes of mixed suspension experiments may not represent the rates and products of transformations that occur in soils.  Therefore, the objective of this thesis was to gain new understanding of the stability and transformation of jarosite and ferrihydrite in acid sulfate soils by developing novel experimental techniques to follow the transformation of synthetic jarosite and ferrihydrite directly in soils. The central theme of the thesis is the comparison of jarosite and aluminium-substituted jarosite transformation in experimental media of increasing complexity. The experiments are performed under conditions that are relevant to rice paddy soils because of the importance of rice in global food production, and the unique management of rice paddies whereby regular flooding during the growing season produces distinct redox cycles. In Thailand, large areas of the Chao Phraya River delta are cultivated as rice paddies despite being acid sulfate soils, providing a suitable site to observe the effects of regular redox cycling on the biogeochemistry of Fe minerals in acid sulfate soils.  The thesis begins with characterisation of synthetic and natural jarosite mineral composition and reactivity. Spectroscopic techniques (Raman spectroscopy, M\u00f6ssbauer spectroscopy and Energy-dispersive X-ray spectrometry) and X-ray diffraction (XRD) were used to assess the element substitution of mineral samples from two jarosite-alunite synthetic solid solution series. The same characterisation techniques were then applied to a sample of jarosite from an acid sulfate soil in Thailand has a natural Al-for-Fe substitution. The mineral characterisation was followed by a transformation experiment in a mixed-suspension system, similar to experimental designs that have been previously used to study mineral transformation processes. The experiment followed the transformation of the natural jarosite sample from an acid sulfate soil in Thailand and three jarosite samples with variable amounts of Al substitution. The reaction solution mimicked the pH (circumneutral) and Fe(II) content (up to 1:1 ratio of Fe(II) in solution to Fe(III) in solids) of flooded acid sulfate soils. Furthermore, using a 57Fe tracer, the simultaneous transformation processes that explained the distribution of mineral products could be resolved from one another. The transformation experiment revealed the relative reactivity of the minerals in the presence of Fe(II), and created a baseline that could be used to compare traditional mixed-suspension experiments with transformations in complex media such as soil.   To advance mineral transformation experiments towards studies in which transformation processes may be followed within a soil matrix, several novel techniques were developed. In a first step, ferrihydrite was incubated for up to twelve weeks in microcosms, each containing 300 g of 5 mM CaCl2 solution and 250 g of one of five paddy soils. The ferrihydrite was buried in the soil within a mesh bag (polyethel terephthalate, 51 \u03bcm pores, 30 mm x 12 mm x 3 mm) that allowed free contact between the synthetic minerals and the pore water, but separated the minerals from direct contact with the soil matrix. The mineral products of the transformation were identified and quantified by Rietveld fitting of XRD patterns. Further, the spatial arrangements of the ferrihydrite and transformation products were measured after two weeks by Raman spectroscopy, which could be used to assess the effects of pore water chemistry and diffusion processes on mineral transformation in the mesh bags. The second step involved measuring jarosite and Al-substituted jarosite transformation in flooded topsoil and subsoils from a rice paddy located on the Bangkok Plain in Central Thailand using an adaptation of the mesh bag method. To test the effect of pore water on the transformation of jarosite in soil, mesh bags were filled with synthetic jarosite and aluminium-jarosite and incubated in topsoils and subsoils, both in laboratory mesocosms and directly in the field. Then, the effect of the soil matrix was tested by completing a parallel experiment using mesh bags containing soil that was pre-enriched with synthetic 57Fe-labelled jarosite and aluminium-substituted jarosite. To facilitate the deployment and collection of small mesh bags in large soil volumes, the mesh bags were inserted into soils using custom-designed 3D-printed sample holders. At three timepoints within twelve weeks, one set of mesh bags were removed from the soil. Transformation products were identified and quantified in the pure jarosite and aluminium-jarosite mesh bags using Rietveld fitting of XRD patterns, while the fate of the 57Fe in enriched soil mesh bags was traced using 57Fe M\u00f6ssbauer spectroscopy.   Performing experiments in increasingly complex media provides an insight into the effect of experimental design on the observation of Fe mineral transformations and provides new information regarding the transformation rates and pathways of jarosite and ferrihydrite within full complexity of soil media. Indeed, this thesis demonstrates that the complex chemistry, biological activity, and physical arrangement of components in the soil have strong effects on the rate and products of jarosite and ferrihydrite transformation processes. The transformation of jarosite and Al-substituted jarosite in mixed-suspension experiments presented in this thesis, in agreement with previous mixed-suspension experiments on both jarosite and ferrihydrite, occurred within a matter of hours. By contrast, the rate of ferrihydrite, jarosite and Al-jarosite transformation in soil pore and in direct contact with the soil matrix occurred over the course of several weeks or months. In the ferrihydrite mesh bags, slow ferrihydrite transformation kinetics on the outer rim of the mesh bag, and deep in the core of the mesh bag, indicated that the sorption of chemical components of soil pore water and diffusion limitations of Fe(II) in pore water could be reasons for the slower rates of transformation in soil. In addition, both Al-for-Fe substitution and Fe(II) concentration in solution were important factors that altered the rate of mineral transformation.  The different incubation conditions for jarosite and Al-jarosite also altered the products of the transformation. Whereas the hydrolysis of jarosite in the absence of Fe(II) resulted primarily in the formation of ferrihydrite, jarosite transformation in the presence of Fe(II) led to ferrihydrite, goethite and lepidocrocite formation. The Fe oxyhydroxide products were consistent with Fe(II)-catalysed transformation, and Fe(II)-catalysed recrystallisation of jarosite may have occurred concurrently. Aluminium-for-iron substitution hindered the formation of lepidocrocite formation in favour of ferrihydrite and goethite. Similar product phases occurred when jarosite and Al-jarosite were reacted with pore water from acid sulfate soils, indicating that similar transformation pathways may define the mineral products of jarosite transformations when the jarosite occurs as accumulations of pure mineral in soil. However, non- or poorly crystalline phases predominated in the transformation products when jarosite or Al-jarosite were incubated in direct contact with the soil matrix, indicating that the transformation of jarosite under these circumstances was governed by different pathways and processes.  The new insights into the transformation of ferrihydrite, jarosite and Al-jarosite in acid sulfate soils demonstrate that phases previously considered meta-stable may participate in the biogeochemistry of soil over period of several months. In the context of rice cultivation, the transformation processes may affect the biogeochemistry of the soils throughout the growing season. The formation of poorly crystalline minerals following the transformation in flooded soils may have positive consequences on the sequestration of other trace and major elements that were associated with the ferrihydrite, jarosite or Al-jarosite prior to the transformation. However, the stabilisation of reduced Fe in the soil matrix may have the opposite effect, promoting the mobility of other ions in solution. The methods used to incubate jarosite and ferrihydrite in soils are easily adaptable to new experimental questions involving the behaviour of Fe-bearing minerals in soil. Therefore, the findings open up a new class of experiments within environmental mineralogy and biogeochemistry, that can help to uncover the processes that occur in the environment and explain the natural variation in the composition of Fe phases in soil.", "keywords": ["jarosite", "iron biogeochemistry", "soil chemistry", "acid sulfate soil", "laboratory study", "ferrihydrite", "soil", "soil incubation", "redox chemistry", "goethite", "iron minerals", "2. Zero hunger", "soil biogeochemistry", "info:eu-repo/classification/ddc/550", "M\u00f6ssbauer spectroscopy", "rice paddy soil", "15. Life on land", "6. Clean water", "Earth sciences", "lepidocrocite", "field study", "13. Climate action", "Raman spectroscopy", "iron oxyhydroxide", "mineral transformation", "iron minerals; mineral transformation; soil; soil chemistry; soil mineralogy; soil biogeochemistry; redox chemistry; iron biogeochemistry; acid sulfate soil; rice paddy soil; jarosite; ferrihydrite; goethite; lepidocrocite; iron oxyhydroxide; M\u00f6ssbauer spectroscopy; Raman spectroscopy; field study; laboratory study; soil incubation", "soil mineralogy"], "contacts": [{"organization": "Grigg, Andrew R.C.", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/20.500.11850/648810"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Thesis/Dissertation", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "20.500.11850/648810", "name": "item", "description": "20.500.11850/648810", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/20.500.11850/648810"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2023-01-01T00:00:00Z"}}, {"id": "50|od_______150::4478eab9d4635d38047c68affb52ff8c", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:26:51Z", "type": "Report", "title": "Vivianite formation and transformation processes in intertidal sediments and the influence of isomorphic substitution", "keywords": ["Earth sciences", "info:eu-repo/classification/ddc/550", "iron minerals; VIVIANITE (MINERALOGY); IRON PHOSPHATES (INORGANIC CHEMISTRY); Coastal biogeochemistry; mineral transformation; Redox geochemistry; M\u00f6ssbauer Spectroscopy; X-ray absorption spectroscopy; Field experiments; Laboratory experiments; iron biogeochemistry; Phosphorus cycling; X-Ray Diffraction"], "contacts": [{"organization": "Kubeneck, Luisa Jo\u00eblle; id_orcid0000-0003-1894-6809", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/50|od_______150::4478eab9d4635d38047c68affb52ff8c"}, {"rel": "self", "type": "application/geo+json", "title": "50|od_______150::4478eab9d4635d38047c68affb52ff8c", "name": "item", "description": "50|od_______150::4478eab9d4635d38047c68affb52ff8c", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/50|od_______150::4478eab9d4635d38047c68affb52ff8c"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2024-01-01T00:00:00Z"}}, {"id": "oai:www.research-collection.ethz.ch:20.500.11850/582238", "type": "Feature", "geometry": null, "properties": {"license": "Open Access", "updated": "2026-07-26T16:33:05Z", "type": "Report", "title": "Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils", "description": "Open AccessISSN:0016-7061", "keywords": ["Iceland; 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