In Situ Synchrotron Powder Diffraction Studies of Reduction–Oxidation (Redox) Behavior of Iron Ores and Ilmenite (original) (raw)
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Mining, metallurgy & exploration, 2021
The present work aims to investigate the link between the oxidation and reduction of a weathered ilmenite concentrate in terms of phase transitions, microstructural changes, and element distribution. An ilmenite concentrate sample was pelletized and fired at 1000°C in air, and as a result, the pellets were oxidized. The oxidized pellets were reduced by hydrogen gas at 1000°C, which yielded almost complete metallization of the iron content of the pellets. The ore and the pellets were characterized in each step by XRD and SEM techniques, and distribution of elements and phases were investigated. Ilmenite, pseudorutile, and rutile were the main phases detected in the ilmenite concentrate sample, and depending on the weathering degree of the particles, different fractions of the phases were identified in their microstructure. It was found that irregular rutile grains dispersed in a pseudobrookite matrix is the morphology of the oxidized ilmenite phase. However, increasing microcracks and porosities were the only microstructural changes in the pseudorutile phase after oxidation in air. Studying the specific types of the ore particles and their oxidized and reduced forms indicated that the phase distribution in the ilmenite ore particles dictates the phase distribution in the oxidized and reduced ones. Results show that the morphology of the reduced particles includes a titanium (III) oxide matrix in which reduced iron globules are dispersed.
Investigations on reduction of ilmenite ore with different sources of carbon
It is crucial to understand the relative impact of different reductants on ilmenite ore from the same source, since different reductants may have different levels of impact on the reduction of the ore. Such a study will throw light on the nature and mechanism of reduction and help in devising suitable industrial processes for the production of TiO 2 and titanium metal. Reduction of ilmenite with graphite and coke has been investigated in the temperature range 1273-1423 K. Iron was the only phase produced in the ore after reduction at 1173 K, when coke was used as the reducing agent. Significant reduction occurred at 1273 K and above. At 1273 K, Fe 3 C and rutile were formed by reduction. At higher temperatures, lower oxides of titanium were also formed by reduction. The process was controlled by diffusion at 1373 K and by reaction at the phase boundary at 1423 K, when coke was used as the reducing agent. The reduction process was controlled by nucleation at 1373 K and by reaction at the phase boundary at 1423 K, when graphite was used as the reducing agent. The rate of reduction decreased at 1423 K compared to that at 1373 K in the case of both reductants. Graphite was less effective as a reducing agent at 1273 K but more effective compared to coke at 1423 K. Whereas reduction of TiO 2 to lower oxides occurred at shorter time intervals when graphite was used as the reductant, this reaction occurred only after longer reduction periods when coke was used for reduction.
Physicochemical Problems of Mineral Processing, 2021
An upgrade of Malaysian ilmenite (FeTiO3) concentrate to synthetic rutile (TiO2) using aeration leaching was investigated in this study. Carbothermal reduction using Sarawak Mukah-Balingan coal and compressed National Gas (CNG) as a reductant was used to produce reduced ilmenite (RI) as an intermediate phase consisting of titanium oxide matrix with metallic iron prior to aeration leaching. Metallic iron was dissolved in ammonium chloride solution after the reduction process, separating synthetic rutile in the leaching residue. This study aims to evaluate the leaching parameters, such as concentration, temperature, and leaching time. The optimum conditions established by the design of the experiment (DOE) and the analysis of variance (ANOVA) has indicated that leaching temperature was the most significant parameter for iron dissolution. It was found that iron dissolution at a maximum value of 97.0% was achieved at an optimum condition of 0.5 M NH4Cl at 90°C for 7 hours. With an initial weight of 46 wt.%TiO2 and 37 wt.% Fe2O3, ilmenite was successfully upgraded to 80 wt.% and 8 wt.%, respectively. In conclusion, Malaysian ilmenite has a high potential value to be upgraded to synthetic rutile by aeration leaching with ammonium chloride via Becher process.
Fe(II) reduction of pyrolusite (β-MnO2) and secondary mineral evolution
Geochemical transactions, 2017
Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth's crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids. We used Fe isotopes (56 and 57) in conjunction with 57Fe Mössbauer spectroscopy to isolate oxidation of Fe(II) by Fe(III) precipitates or pyrolusite. Using these complementary techniques, we determined that Fe(II) is initially oxidized by pyrolusite and that lepidocrocite is the dominant Fe oxidation product. Additional Fe(II) exposures result in an increasing proportion of magnetite on t...
International Journal of Mineral Processing, 2008
57 Fe-Mössbauer spectroscopy is demonstrated to be a sensitive phase analysis tool for control of the ilmenite reduction process in a commercial rotary kiln. Knowledge of recoil-free fractions for each of the key Fe-bearing phases would further reduce the error of quantitative determination. In this case, the feed material is predominantly pseudorutile and rutile and the key phases are confirmed to evolve in two stages, namely the formation of ilmenite from pseudorutile (Fe 3+ → Fe 2+) followed by the reduction of ilmenite into metallic iron and rutile (Fe 2+ → Fe) via ferrous pseudobrookite.
Geochimica et Cosmochimica Acta, 2017
23 In pedogenic and diagenetic processes, clay minerals transform from pre-existing 24 phases to other clay minerals via intermediate interstratified clays. Temperature, pressure, 25 chemical composition of fluids, and time are traditionally considered to be the important 26 geological variables for clay mineral transformations. Nearly ten years ago, the role of 27 microbes was recognized for the first time, where microbial reduction of structural Fe(III) 28 in smectite resulted in formation of illite under ambient conditions within two weeks. 29 However, the opposite process, the oxidation of structural Fe(II) in illite has not been 30 studied and it remains unclear whether or not this process would result in the back 31 reaction, e.g., from illite to smectite. The overall objective of this study was to investigate 32 biological oxidation of structural Fe(II) in illite coupled with nitrate reduction and the 33 effect of this process on clay mineral transformation. Laboratory incubations were set up, 34 where structural Fe(II) in illite served as electron donor, nitrate as electron acceptor, and 35 Pseudogulbenkiania sp. strain 2002 as mediator. Solution chemistry and gas composition 36 were monitored over time. Mineralogical transformation resulting from bioreduction was 37 characterized with X-ray diffraction and scanning and transmission electron microscopy. 38 Our results demonstrated that strain 2002 was able to couple oxidation of structural Fe(II) 39 in illite with reduction of nitrate to N 2 with nitrite as a transient intermediate. This 40 oxidation reaction resulted in transformation of illite to smectite and ultimately to 41 kaolinite (illite→smectite→kaolinite transformations). This study illustrates the 42 importance of Fe redox process in mediating the smectite-illite mineral cycle with 43 important implications for Fe redox cycling and mineral evolution in surficial earth 44 environments. 45 3
Clay Minerals, 2004
The alteration and transformation behaviour of montmorillonite (Wyoming bentonite) was studied experimentally to simulate the mineralogical and chemical reaction of clays in contact with steel in a nuclear waste repository. Batch experiments were conducted at 80 and 300ºC, in low-salinity solutions (NaCl, CaCl 2) and in the presence or otherwise of magnetite and hematite, over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, transmission Mössbauer spectroscopy and EDS-TEM. Experimental solutions were characterized by ICP-AES and ICP-MS. The main results are that no significant change in the crystal chemistry of the montmorillonite occurred at 80ºC, while at 300ºC, the presence of Fe oxides leads to a partial replacement of montmorillonite by high-charge trioctahedral Fe 2+-rich smectite (saponite-like) together with the formation of feldspars, quartz and zeolites.
Experimental study of the transformation of smectite at 80 and 300°C in the presence of Fe oxides
Clay Minerals, 2004
A B S T R A C T : The alteration and transformation behaviour of montmorillonite (Wyoming bentonite) was studied experimentally to simulate the mineralogical and chemical reaction of clays in contact with steel in a nuclear waste repository. Batch experiments were conducted at 80 and 300ºC, in low-salinity solutions (NaCl, CaCl 2 ) and in the presence or otherwise of magnetite and hematite, over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, transmission Mössbauer spectroscopy and EDS-TEM. Experimental solutions were characterized by ICP-AES and ICP-MS. The main results are that no significant change in the crystal chemistry of the montmorillonite occurred at 80ºC, while at 300ºC, the presence of Fe oxides leads to a partial replacement of montmorillonite by high-charge trioctahedral Fe 2+ -rich smectite (saponite-like) together with the formation of feldspars, quartz and zeolites.
Electrochemistry and dissolution kinetics of magnetite and ilmenite
Geochimica et Cosmochimica Acta, 1994
Natural samples of magnetite and ilmenite were experimentally weathered in pH 1-7 anoxic solutions at temperatures of 2-65°C. Reaction of magnetite is described as [Fe*+Fe:+lO,(,,,.,,,,,, + 2H+ + ~[Fe~+lO~~mag~emite~ + Fe'+ + H20. Dynamic polarization experiments using magnetite electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3 [Fe2+Fe:+104(magnetife) -, 4y[Fe:+103(maghem,te) + Fe*+ + 2eand