Showing papers on "Goethite published in 2016"
TL;DR: In this article, the binding capacity of clay minerals may be close to or even higher than that of Fe/Al oxides, depending on the specific surface area of these soil constituents.
346 citations
TL;DR: It is confirmed that the double bond equivalence and the number of oxygen atoms are valuable parameters indicating the selective fractionation of DOM at mineral and water interfaces.
Abstract: Adsorption by minerals is a common geochemical process of dissolved organic matter (DOM) which may induce fractionation of DOM at the mineral-water interface. Here, we examine the molecular fractionation of DOM induced by adsorption onto three common iron oxyhydroxides using electrospray ionization coupled with Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Ferrihydrite exhibited higher affinity to DOM and induced more pronounced molecular fractionation of DOM than did goethite or lepidocrocite. High molecular weight (>500 Da) compounds and compounds high in unsaturation or rich in oxygen including polycyclic aromatics, polyphenols and carboxylic compounds had higher affinity to iron oxyhydroxides and especially to ferrihydrite. Low molecular weight compounds and compounds low in unsaturation or containing few oxygenated groups (mainly alcohols and ethers) were preferentially maintained in solution. This study confirms that the double bond equivalence and the number of oxygen...
294 citations
TL;DR: This process provides an alternative interpretation for the origin of seismic and geochemical anomalies in the deep lower mantle, as well as a sporadic O2 source for the Great Oxidation Event over two billion years ago that created the present oxygen-rich atmosphere.
Abstract: First-principles calculations and experiments are used to identify a stable, pyrite-structured iron oxide at 76 gigapascals and 1,800 kelvin that holds an excessive amount of oxygen and to show that goethite (rust) decomposes under these deep lower-mantle conditions to form an iron oxide and release hydrogen; this process provides another way to interpret the origin of seismic and geochemical anomalies in the deep lower mantle of Earth. First-principles calculations and direct experiments are used to identify a highly stable, pyrite-structured iron oxide at pressures and temperatures relevant to Earth's deep lower mantle. Ho-Kwang Mao and colleagues show that the mineral goethite (FeOOH), ubiquitous in nature as 'rust' and found in large quantities as bog iron ore, decomposes under such conditions to form FeO2 and release H2. The reaction could cause accumulation of the heavy FeO2-bearing patches in the deep lower mantle, upward migration of hydrogen and separation of the oxygen and hydrogen cycles. The authors conclude that the process provides an alternative interpretation for the origin of seismic and geochemical anomalies in the deep lower mantle, as well as a sporadic oxygen source for the Great Oxidation Event over 2 billion years ago that created the present-day oxygen-rich atmosphere The distribution, accumulation and circulation of oxygen and hydrogen in Earth’s interior dictate the geochemical evolution of the hydrosphere, atmosphere and biosphere1. The oxygen-rich atmosphere and iron-rich core represent two end-members of the oxygen–iron (O–Fe) system, overlapping with the entire pressure–temperature–composition range of the planet. The extreme pressure and temperature conditions of the deep interior alter the oxidation states1, spin states2 and phase stabilities3,4 of iron oxides, creating new stoichiometries, such as Fe4O5 (ref. 5) and Fe5O6 (ref. 6). Such interactions between O and Fe dictate Earth’s formation, the separation of the core and mantle, and the evolution of the atmosphere. Iron, in its multiple oxidation states, controls the oxygen fugacity and oxygen budget, with hydrogen having a key role in the reaction of Fe and O (causing iron to rust in humid air). Here we use first-principles calculations and experiments to identify a highly stable, pyrite-structured iron oxide (FeO2) at 76 gigapascals and 1,800 kelvin that holds an excessive amount of oxygen. We show that the mineral goethite, FeOOH, which exists ubiquitously as ‘rust’ and is concentrated in bog iron ore, decomposes under the deep lower-mantle conditions to form FeO2 and release H2. The reaction could cause accumulation of the heavy FeO2-bearing patches in the deep lower mantle, upward migration of hydrogen, and separation of the oxygen and hydrogen cycles. This process provides an alternative interpretation for the origin of seismic and geochemical anomalies in the deep lower mantle, as well as a sporadic O2 source for the Great Oxidation Event over two billion years ago that created the present oxygen-rich atmosphere.
227 citations
TL;DR: Co-precipitation of As with ferrihydrite and schwertmannite was the most effective As sequestration mechanism in the removal of As(V) from acid mine drainage.
113 citations
TL;DR: In this article, the authors reported the enhanced removal of tylosin (TYL) from water by a novel goethite biochar (BCF) composite, which was constructed by well-crystallized cubic phase Goethite nanoparticles as examined by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).
79 citations
TL;DR: The hydrophobic character of the anhydrous hematite surface is confirmed by MDS which also reveals that after hydrolysis the hematites surface can be wetted by water, similar to the goethite (001) surface.
75 citations
TL;DR: In this paper, the authors obtained iron oxides (goethite phase, α-FeOOH) to be used as Fenton catalysts in the catalytic oxidation of methylene blue (MB).
Abstract: The aim of this study was to obtain iron oxides (goethite phase, α-FeOOH) to be used as Fenton catalysts in the catalytic oxidation of methylene blue (MB). Moreover surface modifications were attempted by treating the oxides with boric acid in order to improve the materials’ catalytic properties through the generation of more active groups on the surface of goethite. The types of structures formed on the surface were investigated through the following characterization techniques: vibrational infrared spectroscopy, Mossbauer spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and BET surface area measurements. The results of these characterization analyses the showed complexation of boric acid on the surface of goethites and the partial reduction of some Fe(III) to Fe(II) species, resulting of a hybrid material containing both goethite and magnetite phases. When tested in the oxidation of organic compounds, the new class of iron oxide showed high capacity for degradation of organic compounds present in the solution. The Gt-B catalyst exhibited enhanced catalytic activity in degradation of methylene blue compared with the pure goethite, especially Gt-B1 × 4 which, after 240 min of reaction, was able to degrade about 80% of the MB in solution. The increase in the catalytic activity was assigned to the role of boron as a promoter in the transfer of electrons from iron to hydrogen peroxide, the increasing of surface area and the presence of Fe(II) species, which are kinetically more favourable for the Fenton’s reaction. In addition, theoretical calculations were carried out at the density functional theory (DFT) level in order to investigate the interaction between goethite and boric acid. The theoretical findings showed that the treatment with the H3BO3 significantly modifies the electron density of goethite (100).
73 citations
TL;DR: In this article, the authors investigated the molecular mechanisms of desorption kinetics of phosphate from ferrihydrite and goethite nanoparticles in the absence of competing ligands.
65 citations
TL;DR: In this article, the first application of Fe-citrate-based photo-Fenton chemistry for the inactivation of Escherichia coil was reported, while using low iron concentration and avoiding precipitation of ferric hydroxides.
Abstract: This study reports the first application of Fe-citrate-based photo-Fenton chemistry for the inactivation of Escherichia coil. Promising results of bacterial inactivation at near-neutral and alkaline pH conditions were obtained, while using low iron concentration (Fe-citrate concentration: 0.6 mg/L, relative to the Fe content) and avoiding precipitation of ferric hydroxides. The effects of the solution pH and Fe-citrate complex concentration on E. coil inactivation during the photo-Fenton reaction were investigated. The efficiency of the homogeneous photo-Fenton process using Fe-citrate complex as a source of iron strongly improved bacterial inactivation as compared with the heterogeneous photo-Fenton treatment (FeSO4 and goethite as sources of iron) at near-neutral pH. The bacterial inactivation rate increased in the order of goethite< FeSO4 < Fe-citrate, which agreed well with the trend for the HO center dot radical formation, monitored by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples from Lake Geneva (Switzerland) at pH 8.5, since no bacterial reactivation and/or growth were observed after photo-Fenton treatment. This type of application is promising, considering the simplicity of the installations and procedures, the ability to use the Sun as the light source, and the safety of all of the chemicals in this system. (C) 2015 Elsevier B.V. All rights reserved.
65 citations
TL;DR: In this article, a sample processing protocol for δ56Fe analysis was developed to study Fe phase-specific fractionation related to dissimilatory iron reduction in a modern marine sediment.
64 citations
TL;DR: P pH revealed that the adsorption process in all mineral systems was exothermic, and pH altered the heat effect of EPS-mineral reactions, and ITC results revealed that proteins were predominantly distributed on the montmorillonite and kaolinite surfaces, while nucleic acids were mainly on the goethite surface.
TL;DR: In this article, the goethite nanoparticle was used as a multifunctional additive to fabricate antifouling polyethersulfone (PES) nanofiltration membranes.
Abstract: The goethite nanoparticle was used as a multifunctional additive to fabricate antifouling polyethersulfone (PES) nanofiltration membranes. The goethite/PES membranes were synthesized via the phase inversion method. The scanning electron microscopy (SEM) photographs showed an increase in pore size and porosity of the prepared membranes with blending of the goethite. The static water contact angle measurements confirmed a hydrophilic modification of the prepared membranes. With increase in the goethite content from 0 to 0.1 wt %, the pure water flux increased up to 12.7 kg/m2 h. However, the water permeability decreased using high amount of this nanoparticle. Evaluation of the nanofiltration performance was performed using the retention of Direct Red 16. It was observed that the goethite/PES membranes have higher dye removal capacity (99% rejection) than those obtained from the unfilled PES (89%) and the commercial CSM NE 4040 NF membrane (92%). In addition, the goethite/PES blend membranes showed good selectivity and antifouling properties during long-term nanofiltration experiments with a protein solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43592.
TL;DR: It is concluded that decomposition of organic matter present in dark and grey sections promote the redox conditions and trigger mobilization of As into groundwater.
TL;DR: In this article, the effects of Fe(II) on the sorption and precipitation of Sb(V) on soils and goethite were investigated using batch experiments and X-ray photoelectron spectroscopy (XPS).
TL;DR: Correlations between eight characteristics and 4-ClNB degradation rate constants were observed, and improved predictions of the reactivity of Fe(II)-goethite with pollutants based on properties of the humic substances are possible.
Abstract: Natural organic matter (NOM) is ubiquitous in surface water and groundwater and interacts strongly with mineral surfaces. The details of these interactions, as well as their impacts on mineral surface reactivity, are not well understood. In this work, both the reactivity and aggregation of goethite (α-FeOOH) nanoparticles were quantified in the presence of well-characterized humic substances. Results from monitoring the kinetics of reductive degradation of 4-chloronitrobenzene (4-ClNB) by Fe(II) adsorbed onto the goethite nanoparticles with and without added humic substances demonstrates that, in all cases, humic substances suppressed Fe(II)–goethite reactivity. The ranking of the standards from the least to most inhibitive was Pahokee Peat humic acid, Elliot Soil humic acid, Suwannee River humic acid, Suwannee River NOM, Suwannee River fulvic acid I, Suwannee River fulvic acid II, and Pahokee Peat fulvic acid. Correlations between eight characteristics (molecular weight, carboxyl concentration, and carbo...
TL;DR: It is demonstrated that the morphology of goethite nanoparticles does change during recrystallization, which is an important step toward identifying the driving force(s) of recystallization.
Abstract: When goethite is exposed to aqueous Fe2+, rapid and extensive Fe atom exchange can occur between solid-phase Fe3+ and aqueous Fe2+ in a process referred to as Fe2+-catalyzed recrystallization. This process can lead to the structural incorporation or release of trace elements, which has important implications for contaminant remediation and nutrient biogeochemical cycling. Prior work found that the process did not cause major changes to the goethite structure or morphology. Here, we further investigated if and how goethite morphology and aggregation behavior changed temporally during Fe2+-catalyzed recrystallization. On the basis of existing literature, we hypothesized that Fe2+-catalyzed recrystallization of goethite would not result in changes to individual particle morphology or interparticle interactions. To test this, we reacted nanoparticulate goethite with aqueous Fe2+ at pH 7.5 over 30 days and used transmission electron microscopy (TEM), cryogenic TEM, and 55Fe as an isotope tracer to observe chan...
TL;DR: In this paper, Magnesite tailings were used to remediate acid mine drainage (AMD) which is the byproduct of gold mining, and the results showed that MAGNITE tailings can neutralize and attenuate elevated concentrations of chemical species in AMD.
Abstract: The present study was developed with the aim of beneficiating two waste materials by converting them into a resource. Magnesite tailings, which is the byproduct of magnesite mining, was used to remediate acid mine drainage (AMD) which is the byproduct of gold mining. This will go a long way in minimizing the use of virgin resources and thus fostering the process of sustainable development. AMD was reacted with magnesite tailings at an optimum equilibration time of 30 min and 1 g of magnesite tailings dosage. Contact of AMD with magnesite tailings led to an increase in pH (pH > 10) and a drastic reduction in inorganic contaminants (>99%), except for sulphate that achieved >80% for sulphate removal efficiency. Kinetic studies showed that ·adsorption of chemical species by magnesite tailings fitted well to pseudo-second-order adsorption kinetics hence confirming chemisorption. Pore diffusion was also determined to be one of the principal mechanisms acting as a major rate governing step. pH Redox Equilibria (PHREEQC, in C language) geochemical modelling predicted that Fe removed as Fe(OH) 3 , goethite (FeOOH), and jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ), Al as basaluminite (Al 4 (SO 4 )(OH) 10 ·5(H 2 O)), boehmite (γ-AlO(OH)), jurbanite (AlSO 4 (OH)·5H 2 O, and Al(OH) 3 as gibbsite and diaspore. Al and Fe also precipitated as iron (oxy)-hydroxides and aluminium (oxy)-hydroxides. Mn precipitated as rhodochrosite (MnCO 3 ) and manganite (MnOOH). Ca was removed as gypsum (CaSO 4 ·2H 2 O) and dolomite (CaMg(CO 3 ) 2 ). Sulphate was removed as gypsum and Fe, Al hydroxyl sulphate minerals. Mg was removed as brucite (Mg(OH) 2 ) and dolomite (CaMg(CO 3 ) 2 ). This would explain the reduction in the chemical species contents in the treated water. Based on the above, it was concluded that magnesite tailings can neutralize and attenuate elevated concentrations of chemical species in AMD to within prescribed legal frameworks for water use in agricultural and industrial sectors in South Africa.
TL;DR: This specific adsorption of the Sr (as SrOH(+)) explains why it was still adsorbed to the minerals under very high ionic strength conditions and was not out-competed by Na.
Abstract: Strontium is an important contaminant radionuclide at many former nuclear sites. This paper investigates the effect of changing pH and ionic strength on the sorption of Sr to a range of common soil minerals. Specifically it focuses on the sorption of Sr onto illite, chlorite, goethite, and a mixed sediment. The interplay between ionic strength and pH was determined by varying the background ionic strength of the system using both NaCl (for a constant pH) and NaOH (to also vary pH). Under conditions of moderate pH, Sr sorption decreased with increasing ionic strength, due to competition between the Na and Sr atoms for the outer-sphere complexes. However, where increasing ionic strength was accompanied by increasing pH, Sr sorption remained high. This suggested that Sr was sorbed to the minerals without competition from background Na ions. Extended X-ray absorption fine structure (EXAFS) spectra confirmed that at highly alkaline pH (>12.5) Sr was forming inner-sphere complexes on the surfaces of all mineral...
TL;DR: In this paper, the authors studied the mineralogy of the tailings of a former Ag-Pb mine (Auzelles district, France) and the contribution of the waste materials to the heavy metal dissemination in the environment.
TL;DR: In this paper, the photodegradation of paracetamol in the α-FeOOH (Goethite) used as a catalyst was studied in aqueous suspension up on irradiation at 365 nm and by solar light.
Abstract: Heterogeneous photodegradation of paracetamol (PC) in the α-FeOOH (Goethite) used as a catalyst was studied in aqueous suspension up on irradiation at 365 nm and by solar light. The mechanism involves PC-Goethite system operate electron–hole pairs. The rate of photocatalytic degradation of PC is slow and follows pseudo-first order kinetics. The addition of H 2 O 2 in the previous solution leads to OH radicals formation via the Fenton system. Goethite in the presence of oxalic acid can form Goethite–oxalate complex on the surface. So under irradiation the photo-reduction of Goethite–oxalate complexes yields Fe(II) and oxalate radicals (C 2 O 4 ) − , which induces the formation of active species ( OOH\O 2 − ) leading to the Fenton reaction. The effect of catalyst loading, initial concentration of PC, hydrogen peroxide (H 2 O 2 ) and oxalic acid concentrations were determined. The optimal initial concentration of hydrogen peroxide and oxalic acid for the PC degradation with Goethite under the experimental conditions was found to be 5 × 10 −3 and 5 × 10 −4 mol L −1 respectively. The photodegradation of PC in the mixtures PC–Goethite, PC–Goethite–H 2 O 2 and PC–Goethite–oxalic acid under solar light was significantly accelerated in comparison with artificial irradiation at 365 nm.
TL;DR: In this article, the authors investigated the mechanisms of phosphate adsorption on oxides and found that oxides are often associated with organic matter and form mineral-organic complexes, which is of particular importance in regulating the transport and bioavailability of phosphates in environmental system.
Abstract: Purpose
The phosphate adsorption on natural adsorbents is of particular importance in regulating the transport and bioavailability of phosphates in environmental system. In soils, oxides are often associated with organic matter and form mineral-organic complexes. The aim of the present paper was to investigate the mechanisms of phosphate adsorption on these complexes.
TL;DR: Ferric oxides and hydroxides are assumed to be principal mineral phases for arsenic and antimony attenuation by adsorption/co-precipitation processes to determine their distribution model in water-sediment system and its compatibility with the existing theoretical model.
TL;DR: By resolving the bulk and surface thermal decomposition of FeOOH polymorphs, this work provides clearer insight into the fate of these materials in natural and technological settings where important thermal gradients are commonplace.
Abstract: In this study, bulk and surface thermal decomposition of synthetic iron oxyhydroxides to iron oxides was followed using the temperature-programmed desorption (TPD) technique. Submicron-sized akaganeite (β-FeOOH), rod- and lath-shaped lepidocrocite (γ-FeOOH), and goethite (α-FeOOH) particles were heated in vacuo in the 30–400 °C range, and their OH vibrational modes were monitored by Fourier transform infrared (FTIR) spectroscopy while H2O(g) release was monitored by quadrupole mass spectrometry. Peak thermal dehydroxylation temperatures were larger in the order of lath lepidocrocite (200 °C) < akaganeite (200/260 °C) < rod lepidocrocite (268 °C) < goethite (293 °C). Pre-equilibration of these particles to aqueous solutions of HCl increased dehydroxylation temperatures of all minerals except goethite by 13–40 °C. These shifts were explained by (1) the dissolution of particles or regions of particles of lower degree of crystallinity by HCl, as well as (2) the strengthening of the hydrogen bond environment i...
01 Nov 2016
TL;DR: In this paper, the physical, electronic and photocatalytic properties of four different polymorphs of nanostructured iron oxyhydroxides, namely, goethite, akaganeite, lepidocrocite, and feroxyhyte, were compared.
Abstract: Four different polymorphs of nanostructured iron oxyhydroxides, namely; goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (ɣ-FeOOH), and feroxyhyte (δ-FeOOH) were synthesized and fully characterized by X-ray diffraction, electron microscopy, UV-Visible spectrophotometry, BET measurements and X-ray photoemission spectroscopy. The relationship between these iron oxyhydroxide polymorphs and their photocatalytic properties was explored by examining the extent of methylene blue (MB) degradation by each polymorph under visible light irradiation. Feroxyhyte exhibited the best photocatalytic properties and degraded 85% of the MB dye in five hours. In comparison, goethite, akaganeite and lepidocrocite degraded only 40%, 35% and 30% of the MB in five hours, respectively. In order to understand this trend, the surface area, particle size and shape, and electronic band properties were systematically studied and discussed. It was found that the rate of MB degradation relates mainly to the surface area of the FeOOH polymorphs more than any other factor. This is the first report of a comparative study of the physical, electronic and photocatalytic properties of all four polymorphs of nanostructured iron oxyhydroxides.
TL;DR: The geochronology of 33 goethite grains from in situ ferruginous duricrusts overlying the Parana flood basalt in the Guarapuava region, Parana, Brazil, reveals ages ranging from 3.6 ± 0.4 to 0.1 Ma as discussed by the authors.
TL;DR: Pu(IV) and Pu(V) sorption to goethite was investigated and it suggested that Pu surface redox transformations are sufficiently rapid to achieve an equilibrium state within 1 week, regardless of the initial Pu oxidation state.
Abstract: Pu(IV) and Pu(V) sorption to goethite was investigated over a concentration range of 10–15–10–5 M at pH 8. Experiments with initial Pu concentrations of 10–15 – 10–8 M produced linear Pu sorption isotherms, demonstrating that Pu sorption to goethite is not concentration-dependent across this concentration range. Equivalent Pu(IV) and Pu(V) sorption Kd values obtained at 1 and 2-week sampling time points indicated that Pu(V) is rapidly reduced to Pu(IV) on the goethite surface. Further, it suggested that Pu surface redox transformations are sufficiently rapid to achieve an equilibrium state within 1 week, regardless of the initial Pu oxidation state. At initial concentrations >10–8 M, both Pu oxidation states exhibited deviations from linear sorption behavior and less Pu was adsorbed than at lower concentrations. NanoSIMS and HRTEM analysis of samples with initial Pu concentrations of 10–8 – 10–6 M indicated that Pu surface and/or bulk precipitation was likely responsible for this deviation. In 10–6 M Pu(I...
TL;DR: Characterization results demonstrated that increasing Al content in goethite led to a reduction in crystallinity, increase in specific surface area (SSA), and morphology change from needle-like to granular, and better understanding of the effect of Al substitution on the structure and properties ofGoethite and the cycling of phosphate in the environment is facilitated.
Abstract: Al substitution in goethite is common in soils, and has strong influence on the structure and physicochemical properties of goethite. In this research, a series of Al-doped goethites were synthesized, and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The adsorption behavior of these samples towards PO43 − was also investigated. Characterization results demonstrated that increasing Al content in goethite led to a reduction in crystallinity, increase in specific surface area (SSA), and morphology change from needle-like to granular. Rietveld structure refinement revealed that the lattice parameter a remained almost constant and b slightly decreased, but c was significantly reduced, and the calculated crystal density increased. EXAFS analysis demonstrated that the Fe(Al)–O distance in the structure of the doped goethites was almost the same, but the Fe–Fe(Al) distance decreased with increasing Al content. Surface analysis showed that, with increasing Al content, the content of OH groups on the mineral surface increased. The adsorption of phosphate per unit mass of Al-doped goethite increased, while adsorption per unit area decreased owing to the decrease of the relative proportion of (110) facets in the total surface area of the minerals. The results of this research facilitate better understanding of the effect of Al substitution on the structure and properties of goethite and the cycling of phosphate in the environment.
TL;DR: In this paper, the processes occurring during roasting of bog iron ores were characterized using TG-DTG-DTA-QMS, XRD, FTIR and specific surface analysis.
Abstract: The processes occurring during roasting of bog iron ores were characterized using TG–DTG–DTA–QMS, XRD, FTIR and specific surface analysis. Removal of physically adsorbed water is followed by dehydroxylation of iron oxyhydroxides and oxidation of organic matter at 200–600 °C. The main product of the transformations is disordered nanocrystalline (proto)hematite or hematite/maghemite mixture, depending on organic matter content and heating conditions. The conversion of iron oxyhydroxides to hematite occurs at temperatures different than those reported for pure compounds. At higher temperatures, protohematite undergoes recrystallization to the stoichiometric hematite, and manganese oxides are partially reduced. At 1000 °C, the roasting products consist of hematite and cristobalite together with Mn–Fe spinels if the initial ore contained Mn oxides. The admixtures of various secondary silicates were encountered as well. Low- to moderate-temperature roasting slightly affects the specific surface area and lowers volume of micropores. The high-temperature transformations lead to decrease in the specific surface area and to the destruction of porous texture of the bog iron ores. Although the general course of the processes during roasting was similar in all the samples, some of their details as well as mineralogy and properties of the products are highly dependent on the composition of the initial material.
TL;DR: In order to improve the understanding of factors influencing weathering in hydromorphic soils, the clay mineral and chemical compositions, iron (hydr)oxides, organic compounds, and 87Sr/86Sr and 143Nd/144Nd isotopic compositions were investigated in this paper.
TL;DR: Insight is provided about the composition and potential preservation of microfossils that could have formed in Fe- and Si-rich Precambrian oceans and the effects of Si on the preservation of microbial cells during the whole process.
Abstract: The reconstruction of the history of microbial life since its emergence on early Earth is impaired by the difficulty to prove the biogenicity of putative microfossils in the rock record. While most of the oldest rocks on Earth have been exposed to different grades of diagenetic alterations, little is known about how the remains of micro-organisms evolve when exposed to pressure (P) and temperature (T) conditions typical of diagenesis. Using spectroscopy and microscopy, we compared morphological, mineralogical, and chemical biosignatures exhibited by Fe mineral-encrusted cells of the bacterium Acidovorax sp. BoFeN1 after long-term incubation under ambient conditions and after experimental diagenesis. We also evaluated the effects of Si on the preservation of microbial cells during the whole process. At ambient conditions, Si affected the morphology but not the identity (goethite) of Fe minerals that formed around cells. Fe-encrusted cells were morphologically well preserved after 1 week at 250 °C-140 MPa and after 16 weeks at 170 °C-120 MPa in the presence or in the absence of Si. Some goethite transformed to hematite and magnetite at 250 °C-140 MPa, but in the presence of Si more goethite was preserved. Proteins-the most abundant cellular components-were preserved over several months at ambient conditions but disappeared after incubations at high temperature and pressure conditions, both in the presence and in the absence of Si. Other organic compounds, such as lipids and extracellular polysaccharides seemed well preserved after exposure to diagenetic conditions. This study provides insights about the composition and potential preservation of microfossils that could have formed in Fe- and Si-rich Precambrian oceans.