Iron-rich Spinel Research Articles

Oxidized pellets production from stainless steel solid wastes: induration characteristics and harmful elements migration behavior

Stainless steel solid wastes (SSSW) treatment and recycling has attracted wide attention in recent years because of more stringent environment laws and regulations. Recycling of SSSW through carbothermal reduction of chromite (SRC)-electric furnace (EF) process is favorable to the effective treatment of SSSW and recovery of valuable elements. In this paper, SSSW are used to manufacture sufficiently strong oxidized pellets with the coexistence of chromite concentrates for ferrochrome production based on the SRC-EF process. The induration characteristics and harmful element migration behavior during oxidation of pellets are investigated and revealed. It is found that the oxidized pellets made from 100% SSSW possess low mechanical strength. Increasing the ratio of chromite concentrate from 0% to 80% can significantly improve the pellet strength from 460 N/pellet to 1868 N/pellet when preheating at 1000 °C for 12min and roasting at 1275 °C for 15min. Oxidized pellets made from SSSW and chromite are mainly dominated by the solid-phase consolidation due to the recrystallization of iron-rich spinel phases and sesquioxide derived from oxidation of ferrous oxides. In addition, slag bonding of CaO–CaF2–SiO2–FeO system also plays an important role in the consolidation of oxidized pellets. As for pellets made from 32% SSSW and 68% chromite concentrate, 39.96% F, 91.06% S, 66.73% Cl can be removed from the pellets when preheating at 1000 °C for 12 min and roasting at 1275 °C for 15 min.

Understanding reactions between water and steelmaking slags: Iron distribution, hydrogen generation, and phase transformations

Environmentally friendly energy harvesting can be achieved by the H2O thermochemical treatment of steelmaking slags. Hot slag from steel manufacturing is used as a sacrificial material to produce H2 in a stream of steam. In parallel, this process enhances the magnetic properties of the slag, benefitting the Fe recovery. In this work, the occurrence states of different iron species in slags, as well as their reactivity and phase transformations in H2O, were investigated. The results showed that Fe2+ was mainly distributed in olivine (Ca, Fe, Mg, Mn)2SiO4 when the basicity was low. As the basicity increased, a gradual enrichment of Fe2+ in RO phase (divalent oxides solid solution, R = Fe, Mg, Mn etc.) was observed. In addition to steelmaking slags, the H2O splitting reactions of synthetic model iron compounds, RO phase (Mg1–xFexO, x = 0.36, 0.63, 0.77) and kirschsteinite (CaFeSiO4) were also tested. RO phase exhibited fast kinetics, with its activity proportional to the FeO content. Oxidation of the magnesia-rich RO phase resulted in the phase segregation of iron-depleted magnesiowüstite (Mg,Fedepleted)O and iron-rich spinel (Mg,Ferich)3O4. The H2O splitting of CaFeSiO4 suffered from extremely low kinetics below 900 °C, which could be enhanced by raising the temperature. The H2 production capacity of steelmaking slags was strongly affected by the basicity, which improved when more Fe2+ existed as RO phase rather than CaFeSiO4. After oxidation in steam at 850 °C, the slag sample with a basicity of 1.83 produced 29.3 cm3⋅g−1material hydrogen at 850 °C for 60 min, with a conversion ratio of 80.1%.

Effect of zinc injection on the electrochemical behavior and crack growth rate of a 316 L stainless steel in simulated primary coolant of pressurized water reactors

Zinc was added to high-temperature borated and lithiated water and its effect on the oxide film formation, electrochemical behavior and crack growth rate of 316 L stainless steel was investigated. The actual concentrations of zinc in the coolant solution at 300 °C and 350 °C were determined by ICP-Mass spectrometry. Zinc improved the electrochemical corrosion parameters of steel and reduced the crack growth rate of the sample by more than 13 times. Zinc also reduced the thickness of the formed oxide layers on steel and modified the chemical composition of the oxides to a mainly zinc and iron rich spinel.

Influence of Carbothermal Reduction Process on the Microscopic Properties of Lime-Free Roasting Chromite Ore Processing Residue (COPR)

The lime-free roasting chromite ore processing residue (COPR) was more environmentally friendly than the lime-based COPR. And its components in lime-free COPR should be reused as secondary resource. The process of carbothermal reduction associated with magnetic separation was adopted in this study to reclaim the iron oxide in lime free roasting COPR. The microscopic properties of COPR samples treated by carbonthermal reduction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), etc. The effects of process parameters on iron recovery rate were studied by single-factor experiments. The results indicated that the carbothermal reduction roasting process was beneficial to the destruction of the iron-rich spinel in the original lime-free roasting COPR and the enrichment of iron metal in lime-free roasting COPR. The optimal conditions were obtained as follows: reduction calcination temperature of 1100 °C, reduction time of 2 hours, coke ration of 3.5 times of theoretical content. The main components of the separated fraction were iron particles and some magnesium aluminum spinel.

Effect of Cyclic Reaction on Corrosion Behavior of Chromium-Containing Alloys in CO2 Gas at 650 °C

In this work, seven commercial alloys (602CA, 310SS, 253MA, F321, F316L, 800H and 304SS) were investigated in Ar–20% CO2 gas at 650 °C under a cyclic condition (1-h reaction and 0.25-h cooling in each cycle) for up to 310 cycles. The corrosion behavior of these alloys in isothermal reaction condition was also carried out for a purpose of comparison. The results showed that nickel-based 602CA alloy stayed protective in both isothermal and cyclic reaction conditions by forming a thin protective alumina scale. However, alloys F321, F316L, 800H and 304SS all formed thick multilayered oxides with external iron-rich oxides and internal spinel oxides in all reaction conditions. Alloys 310SS and 253MA behaved protective in isothermal reaction condition but formed pitting corrosion in cyclic reaction condition. The high corrosion resistance of 310SS and 253MA was attributed to the high Cr content and the effect of other alloying elements, e.g., Si and Mn, forming additional oxide layers to enhance chromia protection. Cyclic reaction created stress on oxide scale during cooling and heating which accelerated the initiation of breakaway corrosion of these alloys. Carburization due to CO2 reaction was identified for F321, F316L and 304SS, but not for other alloys because of the formation of highly protective alumina or chromia scales.

Fe2O3–MgAl2O4 for CO Production from CO2: Mössbauer Spectroscopy and in Situ X-ray Diffraction

Fe2O3/MgFeAlOx materials are promising oxygen storage candidates for chemical looping CO2 conversion. In this work, the cyclic stability of a 50Fe(2)O(3)/MgFeAlOx (containing 50 wt % Fe2O3 and 50 wt % MgAl2O4) oxygen storage material is investigated. The evolution of its bulk properties over the course of 1000 H-2/CO2 redox cycles has been studied by means of( 57)Fe Mossbauer spectroscopy and in situ X-ray diffraction. As expected, all iron in the as-prepared oxygen storage material was present as Fe3+, 64% of which in iron-rich phases alpha-Fe2O3 and alpha-FeOOH and 36% in the form of a MgFeAlOx spinel. In contrast, after 1000 redox cycles, only 19% of iron was present in an iron-rich spinel such as Fe3O4, gamma-Fe2O3, and MgFe2O4. The remaining 81% was present in the form of Mg-Fe-Al-O, including Mg-x Fe1-xO. ILEEMS measurements showed surface enrichment of Fe3+ in 50Fe(2)O(3)/MgFeAlOx after 1000 redox cycles, with 36% of all surface Fe present as Fe3+ in iron-rich spinel phases such as gamma-Fe2O3 and/or MgFe2O4.

High Performance Iron-Rich Magnesia-Spinel Composite for Burning Zone of Cement Rotary Kiln

The structure and properties of iron-rich magnesia-spinel composite prepared using sintered iron-rich magnesia and MgO-rich spinel for burning zone of cement rotary kiln were analyzed. The results show that fine-grained magnesioferrite precipitation and magnesiowustite improved the flexibility of magnesia. The formation of Mg (Al,Fe)2O4 reaction rim between iron-rich magnesia and MgO-rich spinel by inter-diffusion reaction of Fe3+ and Al3+ improved the direct-bonded degree and high temperature strength. At high temperature, Fe3+ diffused into the grain of periclase of MgO-rich spinel and was precipitated in the from of magnesioferrite during cooling, which strengthened the structure flexibility of MgO-rich spinel. Iron-rich magnesia-spinel composite had a good adhesion property to clinker because of the uniform distribution of FeOn. Under the same content of Al2O3 and Fe2O3, the iron-rich magnesia-spinel composite had higher hot modulus of rupture, better thermal shock resistance and adhesion property to clinker compared to MgO-spinel composite and MgO-hercynite composite.

Oxide Scales Grown on Stainless Steels during Simulated Reheat

including, external oxide layers, internal grain boundary oxidation structures as well as many other forms of internal oxidation. During the present study, needle like grains of hematite have been observed within the top layers of a number of external oxide scales formed during simulated reheat of 316L stainless steel. It is believed that these needles are caused by the decomposition of an iron rich spinel (approximated to magnetite) along a preferred crystal direction within the spinel grains. The needles have been studied using optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD).

Óxidos de ferro magnéticos de um tufito da região do Alto Paranaíba, MG

The Mossbauer analysis along with the structural Rietveld refinement based on powder X-ray data for the magnetic fraction (saturation magnetization, s = 19 J T-1 kg-1) separated from a tuffite material from Alto Paranaiba, state of Minas Gerais, Brazil, reveal that a (Ti, Mg)-rich maghemite (deduced s = 17 J T-1 kg-1) and, for the first time observed in this lithodomain, magnesioferrite (characteristic s = 21 J T-1 kg-1) respond for the magnetization of the rock material. Consistent models for the ionic distribution in these iron-rich spinel structures are proposed.

Iron-rich spinel phases from sand fraction of three Chilean soils developing on volcanic materials

The magnetic separates from the sand fraction of three Chilean soils forming on volcanic materials were studied by powder XRD, RT and 80 K Mössbauer spectroscopy, saturation magnetization measurements, and scanning electron microprobe analysis. Soil samples were collected from the B-horizon of pedons from native and cultivated areas. Results, particularly from powder x-ray diffractometry, Mössbauer spectroscopy, and chemical analysis, reveal relatively complex magnetic mineral assemblages in all samples. Fe (>70 mass% Fe2O3), Ti (ranging from ~2 to ~26 mass% TiO2), Al (from 1 to ~6 mass% Al2O3) and Mg (from 1 to ~6 mass% MgO) are the main elements found in the iron oxide-spinel structures. In at least one sample, namely the magnetically separated portion from the sand fraction of the fertilized Collipulli soil, the 80 K Mössbauer spectrum indicates that magnetite undergoes the Verwey transition. This sample, with saturation magnetization being of order of 40 J T−1 kg−1, is also the most magnetic of all magnetic separates. Results on the iron oxide spinels, from electron microprobe data, reveal a large variability not only of chemical composition, but also of crystalline structure and magnetic properties of these magnetic minerals. The effect of agricultural practices, particularly the continuous chemical fertilization and soil acidity correction over several years, on the iron oxide mineralogy could not be unequivocally established, but the present data provide a relatively detailed description of the magnetic iron oxide assemblages of these Chilean volcanic soils.

Magnetita e sua transformação para hematita em um solo derivado de esteatito

O presente trabalho objetivou caracterizar o mineral magnético e identificar suas rotas pedogenéticas de transformação em um solo formado sobre esteatito, de Minas Gerais, Brasil. O óxido de ferro isoestrutural ao espinélio foi identificado e caracterizado por análises químicas, difração de raios X, espectroscopia Mössbauer e medidas de magnetização de saturação. Na rocha fresca, foi encontrada magnetita estequiométrica e bem cristalizada, com parâmetro da rede cúbica, a o = 0.8407(5) nm. Nas frações areia e silte, foram detectadas magnetita parcialmente alterada e hematita estequiométrica e bem cristalizada, com parâmetros da rede hexagonal, a = 0.5036(3) nm e c = 1.375(4) nm. A ocorrência dessas hematitas deveu-se principalmente à oxidação do Fe2+ a Fe3+, no sítio octaédrico da magnetita, durante a pedogênese. Esse processo foi caracterizado pelo aparecimento de pequena quantidade de Fe3+ eletronicamente desacoplada, encontrada nas magnetitas parcialmente oxidadas, cujas fórmulas para as diferentes estequiometrias foram propostas. Verificou-se também pequena quantidade de ilmenita nas amostras de rocha e de solo.

Multiple Iron-Rich Spinel Phases and Hematite in a Magnetic Soil Developing on Tuffite

A dusky red Latosol developing on tuffite was examined in detail in order to characterize its iron oxide mineralogy. Magnetic separation and selective chemical treatment were employed. The mineralogical analyses were carried out by powder X-ray diffraction and Mossbauer spectroscopy, with the electron microprobe technique being used to assess the chemical composition of selected grains. Results reveal that iron-rich spinel-structure phases from this pedosystem are rather variable in chemical composition and lattice parameters, and can be grouped in at least three major populations: the first group consisting of the iron-richest phase, with very low Ti and Cr and virtually no Mg content and high Al; the second group presenting Ti>Mg>>Al>Mn contents but no Cr and the third group related to the Mg-richest phase with Mg>Ti>>Al>Mn. Two major populations of hematite were also identified: one with ∼15 mol% Al and other practically Al-free. The first group is thought to be a product of neoformation in an Al-rich pedogenic medium whereas the second is likely to be transformed directly from maghemite. Though chemical treatment along with physical techniques provide a powerful way to characterize iron oxides of tropical soils, some methodological difficulties still remain, particularly those concerned with (i) the characterization and quantification of maghemite in presence of relatively large amount of hematite in the soil mixture, particularly by Mossbauer spectroscopy, and (ii) the allocation of the isomorphous substituents for iron in the cation sites of the spinel structure. Possible mechanisms of alteration of iron-rich phases in this pedosystem are discussed.

Retrograde pressure-temperature path for spinel-bearing metapelites in Rayagada, Eastern Ghats, India

Two assemblages have been identified in spinel-bearing metapelites from Rayagada, in the Eastern Ghats Belt, India: the first, an iron-rich assemblage, is characterized by iron-rich spinel and garnet; the second, iron-poor assemblage, by iron-poor spinel and garnet, together with cordierite and hematite. Garnet and sillimanite coronas around spinel show elongation parallel to the dominant fabric in the iron-rich assemblage but not in the iron-poor one. Both textures suggest the corona forming retrograde reaction spl + qtz = grt + sil. The P-T conditions for these corona-forming reactions are estimated at ∼950°C and 8.7-9.0 kbar for the iron-rich, and ∼800°C and 8 kbar for the iron-poor assemblage. Thermobarometric results and observed phase relations, using the model system FeO-MgO-Al2O3-SiO2 (FMAS) indicate near-isobaric cooling from ∼950° to ∼800°C and subsequent decompression from ∼8 to ∼6.5 kbar. The corona-forming event in the iron-rich assemblage has been correlated with the dominant second phase of deformation (D2), but that in the iron-poor assemblage apparently postdates D2.

Mg-rich iron oxide spinels from tuffite

Powdered crystals of an iron-rich spinel separated from tuffite were examined by chemical analysis, X-ray diffractometry (XRD), magnetometry, scanning electron microscopy and Mossbauer spectroscopy. They are found to contain mainly 48 mass% Fe2O3; 16.9% FeO; 14.3% TiO2; 9% MgO and 3% Al2O3. The magnetization is 29 J T-1 kg-1 at B0 ~ 0.9 T. XRD pattern reveals two cubic phases with α0 = 0.8382(5) and 0.8412(5) nm, respectively. Mossbauer spectra are very complex, but the hyperfine field distribution patterns can be decomposed in two relatively well-resolved Gaussian distributions for the Fe3+ block (averaged isomer shift relative to α-Fe, δ = 0.27 mm s-1) with Bhf = 43.6 T (14.6% of the whole spectral area, WSA) and Bhf = 47.3 (27.7% WSA). A second less resolved distribution block (δ = 0.63 mm s-1) shows two main maxima in the P(Bhf) curve at 35.3 T (25.7% WSA) and 45.2 T (19.7% WSA), respectively. The Mg-rich maghemite (lower α0) appears to be a direct alteration product of a Mg-rich magnetite (higher α0), via an oxidation process of structural Fe2+ to Fe3+ proceeding from the outer to the inner part of the crystal.

Temporary phase segregation processes during the oxidation of (Fe 0.7Mn 0.3) 0.99O in N 2H 2O atmosphere

A two-step thermochemical cycle with the ternary metal oxide system (Fe 1 − xMn x) 3O 4 (Fe 1 − xMn x) 1 − yO is applied to convert solar energy to chemical energy. Experimental investigations on the water splitting reaction of (Fe 1 − x Mn x ) 1 − y O revealed temporary formation of a manganese rich rock salt phase and an iron rich spinel phase due to phase segregation processes.

Microstructural evolution during high energy ball milling of Fe2O3-SiO2 powders

Abstract The reaction of a 25 mol% Fe2O3-SiO2 (hematite-amorphous silica) powder mixture during high energy ball milling in both closed and open containers has been studied by x-ray diffraction and Mossbauer spectroscopy. After around 21 h of milling, the α-Fe2O3 powders with an average particle size of 15 nm have formed and no reaction between α-Fe2O3 and SiO2 is found in the two types of milling containers. This demonstrates that the high energy mechanical milling technique is able to prepare a dispersion of ultrafine α-Fe2O3 particles. After extended milling in the open container all iron atoms are found in a hematite phase. In the closed container the hematite phase transforms into an iron-rich spinel phase and some of the iron atoms react with the amorphous SiO2, forming a new Fe(II)-containing silicate compound.

Anhydrous partial melting of an iron-rich mantle I: subsolidus phase assemblages and partial melting phase relations at 10 to 30 kbar

Anhydrous partial melting experiments, at 10 to 30 kbar from solidus to near liquidus temperature, have been performed on an iron-rich martian mantle composition, DW. The DW subsolidus assemblage from ≤5 kbar to at least 24 kbar is a spinel lherzolite. At 25 kbar garnet is stable at the solidus along with spinel. The clinopyroxene stable on the DW solidus at and above 10 kbar is a pigeonitic clinopyroxene. Pigeonitic clinopyroxene is the first phase to melt out of the spinel lherzolite assemblage at less than 20°C above the solidus. Spinel melts out of the assemblage about 50°C above the solidus followed by a 150° to 200°C temperature interval where melts are in equilibrium with orthopyroxene and olivine. The temperature interval over which pigeonitic clinopyroxene melts out of an iron-rich spinel lherzolite assemblage is smaller than the temperature interval over which augite melts out of an iron-poor spinel lherzolite assemblage. The dominant solidus assemblage in the source regions of the Tharsis plateau, and for a large percentage of the martian mantle, is a spinel lherzolite.

Grain size distribution of the matrix in the Allende chondrite

HRTEM, ATEM and SEM studies of the Allende chondrite reveal that the matrix is composed of very fine-grained iron-rich olivine, Ca-poor and iron-rich clinopyroxene, iron-rich spinel, and Ni-bearing troilite. There are two types of very fine-grained aggregates: one is not sintered and the other is slightly sintered. Most (1–10 μm) olivine aggregates show the sintered microstructure but ultrafine-grained aggregates (1–10 nm) display little evidence of sintering. This means that coarse-grained olivine aggregates experienced a heating event but ultrafine-grained aggregates underwent no heating event. The size distribution of matrix grains were measured by SEM and TEM at magnifications of 570, 000 to 2000 corresponding to grain sizes ranging from 1 nm to 10 μm. The frequency distribution shows a log-normal pattern having a peak at 5 nm in the range from 1 to 10 nm, and it has a long-term tail with power law. This distribution means that the fine-grained matrix seems to be formed at conditions far from equilibrium in the protosolar cloud.

The characterization by raman spectroscopy of oxide scales formed on a 20Cr25NiNb stabilized stainless steel

Laser Raman spectroscopy (LRS) has been used to examine the composition of 0.3–2 μm thick scales formed on the 20Cr25NiNb stabilized stainless steel during oxidation, at 600–950°C, in CO 2 and in CO 2 + 4%CO + 350 vpm CH 4 + 300 vpm H 2O + 400 vpm H 2. All the scales contained iron rich spinel oxides, except in carbon dioxide at 600°C, where Fe 2O 3 predominated. This difference was responsible for the greater attack of the stainless steel at 600°C in carbon dioxide than in the mixed gas environment. Increasingly at ≥800°C the spinel composition was modified by manganese incorporation and Cr 2O 3 was also a major component of the scales formed in both environments. The principal scale constituents identified by LRS accord both with thermodynamic predictions and current understanding of scale development on the 20/25/Nb stainless steel.

ChemInform Abstract: KINETIC STUDIES ON THE PRECIPITATION OF HEMATITE FROM IRON‐RICH SPINEL SOLID SOLUTIONS

AbstractDie kinetischen Untersuchungen werden mit besonderem Augenmerk auf den Einfluß 2wertiger Kationen und der Fe‐oxid‐Konzentration durchgeführt.