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(a) XRD shows goethite formation under different experimental conditions. Major goethite peak intensities increase with NaOH concentration. Dotted lines indicate the characteristic line for maghemite; (b) enlargement of the 20À40º2y region showing maghemite peaks shift from magnetite.
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Magnetite is a redox active Fe oxide common in most soil and sedimentary environments. In this study, we investigated magnetite transformations under extreme alkaline conditions (0.1−2 mol l−1 NaOH) similar to those found under high-level radioactive waste storage tanks at the Hanford site in the State of Washington, USA. X-ray diffraction (XRD) an...
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Citations
... It involves the integration of complementary investigation techniques to perform multiscale and multimodal experiments, all focused on the same area of interest [1][2][3][4] . This approach is particularly valuable when studying metals and their alloys, which exhibit significant heterogeneity, including the coexistence of multiple phases and the formation of various polymorphs [5][6][7][8] . ...
... In this specific case, the formation of clusters was not the main issue. On the other side, in Fig. 2 (a1), goethite ( -FeOOH) intermediates appear as anisotropic crystals (needle-shaped) and magnetite as isotropic and topotactic structures [30]. Most micrographs exposed different particle sizes ranging from 5 to 50 nm. ...
This study presents the preparation of magnetic carbon nanocomposites (MCNCs) through a two-step procedure: (i) in situ co-precipitation of magnetite (Fe 3 O 4) nanoparticles into four different carbonaceous matrixes and (ii) post-pyrolysis treatment to coat the magnetic core. Four post-pyrolysis MCNCs were obtained: MACP (post-pyrolyzed magnetic activated carbon), MCCP (post-pyrolyzed magnetic charcoal), MHCP OR (post-pyrolyzed magnetic hydrochar from orange residue), and MBCP SFH (post-pyrolyzed magnetic biochar from sunflower husk). These four samples were compared with the starting MCNCs prepared without post-pyrolysis treatment: MAC, MCC, MHC OR , and MBC SFH , respectively. After post-pyrolysis treatment, a thin carbon layer surrounding some of the magnetite nanoparticles was identified by transmission electron microscopy. Post-pyrolysis modified the porous structure and chemical composition of MCNCs. Furthermore, a leaching test with acid sulfuric solution at 90 °C was carried out. The results suggested that the MHCP OR and MBCP SFH were more stable in an acidic medium than MACP and MCCP, indicating that the coat generated during post-pyrolysis of hydrochar and biochar could partially protect the magnetic core by reducing Fe leaching into the aqueous solution. Biochar and the hydrochar-based MCNCs before and after post-pyrolysis treatment exhibit superparamagnetic properties; however, their saturation magnetization (M s) decreased considerably. These results open the potential application fields of MCNCs obtained by post-pyrolysis of biochar and hydrochar-based materials in acidic mediums.
... The possible reaction pathways were investigated in Eqs. 8-20 (Grundl and Delwiche, 1993;Li et al., 2018;Prazeres et al., 2019;Hu et al., 2020;He and Traina, 2018;Gilbert et al., 2008). The predominant iron species in the raw-phosphoric acid is ferric, and ferrous ion is a rare species. ...
In the present work, the combination of experimental investigation and statistical analysis has been used for the first time to study iron precipitation from wet-process phosphoric acid. Firstly, eight types of additives including different carbonate and hydroxide salts were studied in the chemical precipitation reaction in order to decrease the iron content in wet-process phosphoric acid. From different studied reagents, calcium carbonate and calcium hydroxide showed the best to remove ferric ions from crude wet-phosphoric acid. Under the optimum conditions, about 80% and 83% of the iron can be removed at 70 ℃ after the addition of calcium carbonate and calcium hydroxide, respectively. The maximum P2O5 losses from crude phosphoric acid was less than 4% after the addition of calcium hydroxide. Based on the Arrhenius behavior, the activation energy of iron precipitation was calculated about 47.43 and 51.55 kJ/mol for calcium carbonate and calcium hydroxide addition, respectively. The iron state studies showed that the pretreatment process was unnecessary to reduce iron state from ferric to ferrous form before precipitation. Furthermore, the kinetics parameters showed that the iron precipitation process was an endothermic reaction. The XRD analysis of the precipitates produced confirmed the formation of Fe(OH)3, α-Fe2O3, α-FeOOH and FeCO3 through the reaction of iron with carbonate and hydroxide ions. Possible pathways of iron precipitation were proposed. Both calcium carbonate and calcium hydroxide showed good efficiency to remove iron from wet-process phosphoric acid accompanied by moderate P2O5 losses. The Taguchi technique was applied to optimize the parameters using signal-to-noise ratio analysis as well as ANOVA. The analysis showed a greater susceptibility of the response against changes in the value of calcium carbonate, more than calcium hydroxide.
... Indeed, the main phase observed at the interface between the metal and the rust layer is goethite. The formation of the TM, in red, could be explained by the dissolution of iron and reprecipitation of iron corrosion/oxidation products over the surface of the object, perhaps over the original surface 27,[30][31][32][33] . ...
The best strategy to tackle complexity when analyzing corrosion in iron artefacts is to combine different analytical methods. Traditional techniques provide effective means to identify the chemistry and mineralogy of corrosion products. Nevertheless, a further step is necessary to upgrade the understanding of the corrosion evolution in three dimensions. In this regard, Multiscale X-ray Microscopy (XRM) enables multi-length scale visualization of the whole object and provides the spatial distribution of corrosion phases. Herein, we propose an integrated workflow to explore corrosion mechanisms in an iron-nail from Motya (Italy) through destructive and non-destructive techniques, which permit the extraction of the maximum information with the minimum sampling. The results reveal the internal structure of the artefact and the structural discontinuities which lead the corrosion, highlighting the compositional differences between the tip and the head of the iron nail.
... On the other hand, Figure 4e shows the presence of maghemite because broad Raman characteristic features around 369, 499, and 720 cm À1 have been detected (Chamritski and Burns 2005;Slavov et al. 2010). These results are consistent as it is known that magnetite and goethite can be obtained by oxidation of green rust and that magnetite can be also oxidized to maghemite (He and Traina 2007;Usman et al. 2018). The peak at 982 cm À1 may be due to sulphate ions. ...
Mackinawite was biologically synthetized by immersing carbon steel coupons in artificial seawater containing Sulphate-Reducing Bacteria (SRB) for 6 months. These coupons were removed from the culture medium solution and some were stored in air while others were placed in SRB-free culture medium solution. In operando Raman spectroscopy was used to analyse all these coupons immediately after extraction from the incubation medium and nanocrystalline, well-crystallized and partially oxidized mackinawite was detected. The evolution of these corrosion products was also monitored as a function of ageing time with this technique. Nanocrystalline and well-crystallised mackinawite transformed into partially oxidised mackinawite, greigite and sulphate green rust for an ageing time between 4 and 72 h. After 120 h, maghemite, magnetite, lepidocrocite, goethite appeared on the coupons placed in SRB-free culture medium solution as opposed to those stored in air atmosphere. Greigite and sulphate green rust were not observed for Raman measurements performed in air.
... 72 Interestingly, this suggests that partial incorporation of Tc(IV) within Fe (oxyhydr)oxides may occur during reoxidation of hydrous TcO 2 associated with magnetite in these elevated pH systems. The exact phase into which Tc(IV) is incorporated is unclear, however, goethite is known to form during the oxidation of magnetite 73 and as discussed, the Tc−Fe distances are consistent with those reported for Tc incorporated into goethite. 72 For the nitrate reoxidation experiments with no added Fe(III), the pH remained elevated (pH 9.5−10.5) ...
... Goethite is an oxidation product of iron oxide minerals such as magnetite favored by pH and temperature (He and Traina, 2007). Smectile group clay formation are inherited from the breakdown of primary silicates, such as olivine and pyroxene of the parent carbonates or from weathering of host granitic gneiss (Churchman et al., 2012). ...
The diversity and complexity of basement rocks at Eppawala are accompanied by complicated matrices of phosphate deposits. Detailed field, geochemical and mineralogical studies were carried out on phosphatic weathering crusts developed on carbonatite occurrences to elucidate the weathering process and to explore mineralization of possible economic minerals. The presence of markedly distinguished weathering horizons at the Eppawala southern quarry (ES) site provided an advantage for studying the sequence of alteration and weathering processes occurred on the parent bodies. Leaching of carbonate minerals in the early stages had resulted in the alteration of primary apatite. Under diverse conditions, several generations of supergene phosphate minerals have formed. All major and trace elements in the profile are mobile and displaced due to weathering of the principal minerals, with the exception of Mg, Sr, Na and Ba. The lower leached zone and higher-saprolitic layers are enriched with Rare Earth Elements (REEs) due to the presence of a high amount of secondary phosphates, such as crandallite, gorceixite, florencite and goyazite. Anomalies of REEs in upper lateritic layers are inherited by the presence of smectite group clay minerals. The presence of a high amount of silicate minerals and high SiO2 content indicates the interactions between carbonatites and surrounding granitic rocks during the weathering process. Moreover, geochemical results confirm that the several phosphate matrices are highly enriched with Fe2O3. Therefore, iron bearing phases must be removed during the production of phosphate fertilizer. Understanding of detailed mineralogical and geochemical variations of exposed phosphate orebodies along with the weathering profiles at Eppawala is critical to mining processes and beneficial for the production of phosphate fertilizer and REEs.
... Formation of shrinkage cracks that develop at higher degree of LTO (Petersen & Vali, 1987) allows moisture and oxygen to penetrate into the interior of particles, thereby enlarging the effective crystal surface exposed to alteration. Strongly maghemitized magnetite can finally transform into hematite (Sidhu, 1988;Torrent et al., 2006) or goethite (He & Traina, 2007). ...
Magnetic records in sedimentary sequences are often used as paleoclimate proxies. Climate‐specific alteration of magnetite during rock weathering in the catchment might contribute to proxy variations in sediment sinks. In an actualistic study, we investigated the effects of magnetite alteration using weathered pebble material on basaltic parent rock. We collected samples from the Deccan basalts (India) across a large difference of mean annual precipitation (MAP; ∼800–3,200 mm), and also from the Emeishan basalts (SW‐China) to compare alteration effects at similar MAP (∼1,100 mm) but ∼12°C–15°C lower mean annual temperature (MAT). We used rocks with lamellar magnetite‐ilmenite texture to ensure the best possible uniform parent rock magnetic mineralogy. We separated the weathered material into five groups by grain size, assuming that alteration increases in finer pebbles. Only magnetic susceptibility (χ) shows a systematic change, with an increase that is weakly stronger for higher MAP. Consistent with a simplified model, the χ‐increase may represent progressive maghemitization. For the Emeishan basalts, we found a significantly stronger degree of alteration, including loss of magnetite. We explain this effect, which is surprising regarding the clearly lower MAT, by frost‐induced micro‐cracks due to physical weathering that opens pathways for oxygen and humidity into particle interiors. Based on these findings, we conclude that climate‐related alteration effects of magnetite during rock weathering are in most cases outweighed by parent rock heterogeneity, and magnetic proxy records in derived sediment archives are unlikely to record climate‐related magnetite alteration acquired during rock weathering, at least for catchment with basalts.
... The X-ray diffraction revealed that the nanoparticles obtained were characterized by a cubic spinel crystal structure (JCPDS Card Number 19-0629 [50]) ( Fig. 1). Also, the diffraction patterns of samples Fe3, Fe4, and Fe5 showed an additional phase of goethite FeOOH [50]. As can be estimated from the results of the TEM study ( Fig. 1), synthesized nanoparticles are nanosized and characterized by weak agglomeration. ...
Currently, the fight against cancer diseases and the development of the noninvasive and less harmless methods of its treatment are among the most pressing issues. In this context, magnetic hyperthermia (MHT) is one of the promising and safe methods with the local effect and is gradually being introduced into world medical practice. This chapter presents various ideas and approaches to self-controlled MHT based on the use of complex magnetic oxide nanoparticles. To begin with, we expose the methods and conditions of synthesis of magnetic nanoparticles with the spinel and perovskite structures, such as cryochemical method, precipitation in microemulsions and nonaqueous solutions, hydroxide precipitation, and solgel method. We then turn to the research outcome for the materials requiring external temperature control as well as for those with its automatic preset when used in MHT on the example of nanoparticles of ferrimagnetic spinel and lanthanum–strontium manganites. Experimental aspects are reviewed in the next sections, constructed according to material and sample types, explaining the special role played by the characteristic parameters of magnetic nanoparticles (saturation magnetization, the effective magnetic anisotropy constant, the coercivity, the volume of the magnetic nanoparticle (MNP) and the relaxation time of the MNPs system) and external parameters (the frequency of the external magnetic field and temperature) in the processes of nanoparticles remagnetization and thus in their behavior as heat mediators of magnetic hyperthermia. Also there considered in vitro and in vivo biomedical studies of the magnetic fluids based on the lanthanum–strontium manganite nanoparticles which have been investigated only episodically by this time. The authors try to provide a unified view of the vast research on the subject and the basic unresolved issues together with the remaining challenges in the way of wide MHT application.
... ( Fig. 1 f) samples is related to the spontaneous passivation that uniquely arises from 219 the etching reagent chemistry (Nital is solution of nitric acid and ethanol). The reagent 220 forms a reaction with the steel surface layer that preferentially induces goethite to form 221 due to the alkaline nature of the nitride enriched surface [52]. The effect is also 222 visualized optically by the green coloration of the surface layer, as seen in Fig. 1 ...
The improvement of corrosion lifetime of commonly used steels is an important characteristic that is required for development of steel products for usage in non-traditional corrosion environments and specialized applications such as oil and gas industry. In order to achieve the required enhancements in a versatile manner, a combination of material and surface processing schemes can be used. In this research, the effect of surface finishing (original, polished, etched and immersed in LN2) on corrosion behavior of steel AISI M35 is investigated. Furthermore, the change of corrosion properties with the application of deep cryogenic treatment (DCT) is researched and compared with the effect of conventional heat treatment (CHT). The various surface finishing induce modified corrosion product development and degradation of material. The surface finishing with contributing nitrogen presence (etching and immersion in LN2) display significant suppression in development of corrosion products related to the formation of green rust. On the other hand, DCT induces microstructural and mechanical changes, which also influence the corrosion dynamics. DCT is confirmed to reduce exfoliation of the corrosion product layer due to reduced surface cracking induced by residual stress-of the microstructure. Additionally, DCT reduces pitting formation and growth, resulting from the changed alloying element concentration and microstructure. The cross-effect of both nitrogen-introducing surface finishing and DCT have the most positive influence on corrosion properties of steel AISI M35. The modifications lead to improved self-corrosion protection and stability of the surface resulting in increased durability of AISI M35 in saline corrosive media.
