Granular Magnetite Research Articles

Genesis of submarine volcanic iron deposits in the Central Asian Orogenic Belt: Insights from the texture and chemical composition of magnetite from the Langwashan iron deposit in the Beishan orogenic belt, NW China

Carboniferous submarine volcanic rocks hosting iron deposits are widely distributed in the Tianshan and Beishan orogenic belts. However, the genesis of these deposits remains unresolved, with contrasting magmatic and magmatic-hydrothermal models being proposed. The Langwashan iron deposit (83.18 Mt @ 37% Fe) is one of the largest iron deposits in the Beishan orogenic belt. In this paper, we present detailed textural and trace-elemental properties of magnetite from the Langwashan iron deposit to elucidate the genesis and evolution of iron mineralization hosted in Lower Carboniferous submarine volcanic rocks. The Langwashan iron deposit has various types of iron ore that are closely associated with skarn minerals, including garnet and epidote. Magnetite in these samples can be classified into two distinct types, early-stage mushketovite (Mag1) and late-stage granular magnetite (Mag2), both of which show oscillatory zoning, with low Ti (mean of 0.03–0.07 wt%) and V (mean of 0.03–0.04 wt%) contents, and variable Si contents (mean of 0.74–6.50 wt%). These textural and compositional data classify the Langwashan deposit as a typical Fe-skarn deposit. Results also reveal that iron oxides in the Langwashan deposit underwent a complex evolution comprising three episodes: (1) early-stage influx of low-oxygen-fugacity, calcium-rich hydrothermal fluids, causing the transformation of original hematite to mushketovite (Mag1-1) and the formation of scheelite inclusions; (2) subsequent dissolution–reprecipitation between high-temperature magmatic-hydrothermal fluids and Mag1-1, generating trace-element-rich mushketovite (Mag1-2) and the precipitation of trace-element-rich granular magnetite (Mag2-1) from magmatic-hydrothermal fluids; and (3) final multiple fluid metasomatism under the influence of trace-element-poor hydrothermal fluids, involving dissolution–reprecipitation that produced trace-element-deficient Mag1-3, Mag2-2, and Mag2-3. Results also highlight that the submarine volcanic iron deposits from both the Tianshan and the Beishan orogenic belts were probably formed in a similar geological setting, with similar timing of formation, mechanism of mineralization, and evolution, and they are likely Fe-skarn deposits.

Precipitation Behavior of Magnetite Phase during Modified Nickel Slag Treated by Molten Oxidation

Nickel slag is a kind of solid waste with a high yield and low utilization rate. However, there is a large amount of Fe in nickel slag, which mainly exists in the form of fayalite. In this study, nickel slag is used as raw material. The addition of CaO can destroy the network structure of fayalite, and the iron-rich phase can be oxidized to magnetite under oxidation condition. It is beneficial to the recovery of iron resources. The effect of basicity on structural reconstruction of molten slag and precipitation of magnetite is investigated. The results show that when the basicity is 0.38–1.50, the degree of polymerization of silicate structure decreases with the increase of basicity. When the temperature is 1450–1500°C, viscosity of slag decreases first and then increases with the increase of basicity. The viscosity is the lowest with the basicity of 0.90, and the granular magnetite begins to precipitate during the non-equilibrium solidification at 1455°C. The growth rate of the magnetite is 1.20 µm/s at 0–10 s, which is significantly higher than the magnetite growth rate of 0.16 µm/s at 10–22 s, and the grain size of the magnetite remains unchanged after 22 s.

Magnetite texture and trace element evolution in the Shaquanzi Fe-Cu deposit, Eastern Tianshan, NW China

The Shaquanzi deposit is an important Fe-Cu deposit in the Yamansu Fe mineralization belt, Eastern Tianshan. Three types of magnetite were distinguished based on the textural and mineral assemblages, including the platy mushketovite (TA), granular magnetite coexisting with K-feldspar and epidote (TB), and granular magnetite intergrown with pyrite (TC). TA magnetite consists of three generations, including a bright core (TA-1), a dark-gray inner rim (TA-2), and a light-gray outer rim (TA-3), under BSE observations. TA-1 magnetite was transformed from the primary hematite due to a sharply reduced oxygen fugacity and retains its platy pseudomorph. With the changing temperature (increase or decrease), TA-1 magnetite underwent dissolution and re-precipitation (DRP) processes to form TA-2 and TA-3 magnetite. TB magnetite consists of two generations (TB-1 and TB-2). TB-1 magnetite contains abundant mineral inclusions and microporosity. With the decrease of fO2 and temperature, TB-1 magnetite underwent a fluid-assisted recrystallization process to form TB-2 magnetite with foam texture. TC magnetite consists of four different generations (TC-1, TC-2, TC-3, and TC-4). TC-1 magnetite with densely-distributed oscillatory zonings (generally smaller than 1 μm) is surrounded by the darker TC-2 magnetite. TC-2 magnetite with foam texture may be formed by recrystallization of TC-1 magnetite. TC-3 magnetite replaced or cut TC-2 magnetite, indicating that it was formed by the DRP process of TC-2 magnetite. Following periodic changes of fO2 and temperature, TC-4 magnetite with oscillatory zones formed around TC-3 magnetite.This study proposes a new Fe/(Mg + Al + Mn) vs Ti discrimination diagram to distinguish hydrothermal and magmatic magnetite. Magnetite compositions of the Shaquanzi deposit are quite different from those of magmatic magnetite, but very similar to those observed in the hydrothermal system such as IOCG and skarn deposit, indicating that magnetite of the Shaquanzi deposit was formed by hydrothermal process rather than magmatic differentiation.

Frequency Dependence of Initial Heat Generation in Granular Magnetite Nanoparticles

The frequency dependence of heat generation in granular magnetite nanoparticles was studied using vibrating sample magnetometry and the nanoTherics Magnetherm™ hyperthermia testing system. First, the particle size and its distribution were obtained by fitting the M-H curve to the classical Langevin function weight-averaged with a modified log-normal size distribution function. Next, the ac power dissipation model for monodispersed nanoparticles was extended to the polydispersed case, and the volumetric heating rate was predicted as a function of the frequency of the applied field under the assumption of the Neel relaxation mechanism. Finally, the temperature increase caused by the application of an ac magnetic field was measured experimentally at frequencies of 50, 112, 261, 335, 474 and 523 kHz, with the root-mean-squared field fixed to 250 Oe, and the results were compared with those from theoretical calculation. The frequency dependence of the initial heating rates was found to be in good agreement with the results predicted by using the polydispersed power dissipation model.

Texture and composition of magnetite in the Duotoushan deposit, NW China: implications for ore genesis of Fe–Cu deposits

AbstractThe Duotoushan deposit is an important Fe–Cu deposit in the Aqishan–Yamansu metallogenic belt of eastern Tianshan, NW China. Magnetite occurs in two main habits which are common in many Fe–Cu deposits, i.e. platy (TD1 Mag) and granular magnetite (TD2 Mag) have been identified at Duotoushan. Platy magnetite shows two different zones (bright and dark) based on the observations by scanning electron microscopy. The bright part (TD1-L) is the main part of TD1 magnetite and lacks inclusions. The dark part (TD1-D) is very porous and has abundant tiny silicate inclusions. Granular magnetite is usually anhedral with obvious oscillatory zoning in back-scattered electron images. In general, the dark zones of magnetite are characterised by greater Si, Ca, Al and lesser Fe contents than the bright zones. In situ X-ray diffraction (XRD) analysis shows that the lattice parameter of TD1 magnetite is approximately equal to that of standard magnetite and slightly higher than that of TD2 magnetite, indicating that some cations with ionic radii smaller than those of Fe2+ or Fe3+ entered the magnetite lattice by simple or coupled substitution mechanisms in TD2 magnetite.The results in the present study show that the effects of temperature and $f_{{\rm O}_ 2}$ on platy magnetite are very limited and the changing fluid composition might be the major controlling factor for the formation of Duotoushan platy magnetite. Although the possibility that mushketovite transformed from hematite cannot be excluded entirely, evidence from in situ XRD data, pore-volume ratio calculation and the growth habit of intergrown minerals indicates that platy magnetite (TD1) coexisting with amphibole was more likely to have been precipitated originally from hydrothermal fluid. This was then affected by changes in the fluid composition which consequently led to dissolution of primary magnetite (TD1-L) and re-precipitation of TD1-D magnetite (with abundant porosity and mineral inclusions). Meanwhile, granular magnetite (TD2) with oscillatory zoning, and coexisting with epidote and quartz, was precipitated from fluid with periodic variation in temperature. These oscillatory zones are characterised by bands enriched in Si, Al and Ca alternating with bands depleted in these elements. The present investigation revealed a complex evolutionary process for magnetite formation in the Duotoushan deposit. The importance of combined investigation of texture and compositional characterisation of magnetite for study of the ore genesis and evolution of Fe–Cu deposits is highlighted.

Rapid small scale column tests for Cr(VI) removal by granular magnetite

Rapid small scale column tests for Cr(VI) removal by granular magnetite

Rapid small-scale column tests for Cr(VI) removal by granular magnetite

This study evaluates the possibility of using magnetite as an adsorbent for the removal of Cr(VI) in a bed column setup under continuous flow conditions. For this purpose, granular magnetite was synthesized on a large scale and tested in both batch and rapid small-scale column experiments using reliable conditions of drinking water treatment. Column tests, which were designed to scale-down larger adsorption systems in terms of size, time and water flow, indicate a higher removal capacity compared to that observed during batch experiments with magnetite powder, reaching 9.2 mg/g at pH 6.4 before residual Cr(VI) exceeds 10 μg/L. The main parameters of this process, including pH, contact time and granular size, were also examined under similar column tests suggesting the improvement of the overall effectiveness and operation time at lower water pH, higher empty bed contact times and larger particle dimensions.

Enhanced recovery of nickel from chromite overburden (COB) using dissimilatory Fe (III) reducers: A novel Bio-Reduction Acid Leaching (BRAL) approach

The nickeliferous chromite overburden (COB) awaits a suitable technology to extract the obstinate nickel ingrained in its goethite matrix. In the present study, a novel Bio-Reduction Acid Leaching (BRAL) approach has been proposed using dissimilatory iron reducing bacteria (DIRB) which is inherently capable of transforming iron mineral phases via bio-reduction (BR). Mineralogical characterization of the bio-reduced COB using XRD and FTIR confirmed the phase transformation of goethite to hematite and magnetite with exposure of the nickel oxide peaks. Further, morphological characterization using FESEM vividly highlighted the changes of acicular goethite to granular magnetite deposits on the extra polymeric substance (a scaffold for electron transfer) secreted by DIRB consortium over the surface of COB. Further, enhanced nickel extraction was achieved with a reductive acid leaching (AL) approach with 6N sulfuric acid and 2% glucose (reducing agent) at 65°C for 6h. A cumulative of 83.6% nickel was achieved through this BRAL approach. The pregnant leach solution (PLS) generated as a result of the AL approach was subjected to a hydrometallurgical route to recover metallic nickel. Solvent extraction (SX) of the PLS was performed using 0.5M NaD2EHPA as extractant. The pregnant nickel-loaded electrolyte was subjected to electrowinning (EW) to recover metallic nickel of 99.6% purity. The process flow-sheet is believed to provide a suitable eco-friendly, potential method to efficiently extract nickel from low grade nickel laterites to meet the ever growing demands caused by depletion of high grade nickel sulfidic ores.

Magnetization and susceptibility of ion-irradiated granular magnetite films

Porous granular films of magnetite (Fe${}_{3}$O${}_{4}$) with grains of \ensuremath{\sim}3 nm in size were prepared using a state-of-the-art nanocluster deposition system. The films are initially superparamagnetic but become magnetized following Si${}^{2+}$ ion irradiation. A significant increase in the grain size and a dramatic change in the microstructure are observed. There are dipolar interactions between the nanoparticles in both the unirradiated and irradiated films. The in-phase alternating current magnetic susceptibility of the unirradiated film shows a blocking temperature of \ensuremath{\sim}150 K, depending on frequency. A broadened Verwey transition for the irradiated film occurs at \ensuremath{\sim}75 K, above which the susceptibility exhibits unusual behavior: a nearly linear decrease with decreasing temperature. There are irreversible domain rotations in the irradiated film during zero-field cooling and warming cycles between 10 and 300 K. The observed behavior of the irradiated granular films is quite distinct from that of metallic nanostructures after irradiation, and is due to the dramatic change in microstructures.

Interface scattering and spin-dependent transport in granular magnetite

We have prepared nearly monodisperse Fe 3O 4 of ∼50 nm by a chemical route and investigated the electrical and magnetic transports of the composite granular system. A Verwey transition is observed in the vicinity of 113 K. Above and below the Verwey transition, the electrical transport is dominated by electron hopping behavior showing a good linear relation between resistance and T −1/2. The magnetoresistance (MR) increases with the applied field and does not follow the magnetization to reach the saturation at 10 KOe field. This indicates that the MR is mainly arising from the spin-dependent scattering of electrons through the grain boundaries. The temperature dependence of MR shows it has the highest MR value near the Verwey transition.

Electrodeposited magnetite with large magnetoresistive response at room temperature and low magnetic fields

Iron oxide layers were obtained by electrodeposition method on Cu substrates. The electrolyte containing Fe2(SO4)3, NaOH, and Triethanolamine was stirred at a temperature of 65 °C and the depositions were performed potentiostatically in a conventional three electrode cell at a potential of −1.1 V vs SCE. Parallel magnetoresistance values of −6.2% at 3 kOe were obtained for measurements at room temperature. The magnetoresistive curves showed reduced hysteresis loop, temporal stability, and no saturation for the maximum applied magnetic field. Our results show that for the case of the granular magnetite that we grow, the AMR has opposite sign of that of 3d magnetic alloys. Allied to high values of resistivity, these properties are potentially adequate for the development of magnetic devices such as field sensors. Additional characterization was obtained by using scanning electron microscopy and vibrating sample magnetometry.

Effect of interface passivation on the magnetoresistance of granular magnetite Fe3(1−δ)O4

The reductive passivation of granular interface was proposed to enhance the tunneling magnetoresistance of bulk granular magnetite. For this, an annealing in paraffin wax has been applied. As a result, the low-field magnetoresistance response was increased up to 8% at 300K and 32% at 130K. The effect is attributed to the passivation-induced depletion of density of the tunneling-active spin-depolarized interface states. The obtained results indicate the important role of interface states in tunneling contacts with magnetite electrodes and suggest a way to control these states.

Sintering conditions for simulating the formation of mineral phases in industrial iron ore sinter.

In industrial iron ore sintering, the raw material is heated in a reducing atmosphere and cooled in an oxidizing atmosphere. In order to study the effects of gas atmosphere in industrial sintering, small tablet specimens containing powdered commercial iron ore, limestone, quartz and kaolin were heated in controlled gas atmospheres to examine the effects of gaseous atmosphere, heating temperature and cooling condition on the formation of minerals in sinter. The results obtained are summarized as follows.In the heating stage of laboratory sintering, with a decrease of partial pressure of oxygen, the magnetite content increases and hematite content decreases. The calcium ferrite content is found also to decrease at the low sintering temperature (1 210°C). However, at a higher sintering temperature (1 255°C), a medium oxygen potential (5×10-3 atm) produces the most calcium ferrite. In the air cooling stage, magnetite may react with the silicate melt and oxygen to generate a large amount of columnar calcium ferrite.A typical microstructure of the bond composed of columnar calcium ferrite, granular magnetite grain and glassy silicate in a normal industrial sinter can be simulated reasonably by heating a specimen to 1 255°C for 4 min in the gaseous mixture CO=1%, CO2=24% and N2=75% and then cooling it slowly in air.

Petrologia do Maciço alcalino de Itapirapuã, SP

The alkaline rock complex of Itapirapua covers an area of approximately 4 km², with irregular shape, and elongated NW-SE. It was intruded in a large body of granitic rocks. The alkaline intrusion consists exclusively of undersatured rocks, predominantly nepheline syenites with variable amounts of titaniferous garnet (melanite). Basic alkaline varieties are less abundant and are represented by biotite melteigite and melanite malignite. Wollastonite-melanite-nepheline syenite, pulaskite and cancrinite mariupolite were also formed and correspond to petrographie varieties enriched, respectively, in calcium, potassium and sodium. Tinguaites, which probably occur in small vertical dikes, cut the alkaline as well as the surrounding granitic rocks. Irregular carbonatite veins clearly intersect the nepheline syenites in the central part of the complex. In the southern part of the alkaline body a magmatic breccia forms an outcrop of only a few square meters, consisting mainly of nepheline syenites. A funnel shaped ore body composed of idiomorphic granular magnetite is being exploited near the southern margin of the alkaline complex. The main felsic mineral constituents of the alkaline rocks are nepheline, with its alteration products cancrinite, sodalite and a mineral aggregate, and perthitic orthoclase. The ferromagnesian minerals are represented principally by pyroxenes (soda-augite, aegirine-augite and aegirine) as well as melanite. The crystallization sequence of the pyroxenes, as suggested by optical and chemical data, was: soda-augite → aegirine-augite → aegirine. The more common accessories are magnetite, titanite and apatite. Accidental minerals are biotite, wollastonite, pectolite, fluorite, eucolite, pyrite, pyrrhotite, calcite, and minerals A and B. Calcite and zeolites occur as alteration products. The chemical composition of the alkaline rocks from Itapirapua is characterized by the lack of silica and magnesium, high content of calcium, alkalies and volatile constituents, as well as notable concentrations of V, Nb, Y, Cu and Ba. An analysis of the different variation diagrams seems to indicate that fractional crystallization was the prevailing rock forming process at Itapirapua. In a general way the curves show a trend that would be expected to correspond to the fractionation of a basaltic magma. However, assimilation of limestone and sialic crustal material, as well as metasomatic processes and the action of volatiles also may have taken place. Mineralogical and chemical evidences indicate that the contact zone of the enclosing granitic rocks was subjected to fenitization processes. The alkaline rock intrusion of Itapirapua shows similarities to the Brazilian occurrences of Jacupiranga, Serrote and Anitapolis. Iron Hill and Magnet Cove in the USA and Ivaara, Finland, also have many mineralogical and petrographical features in common with Itapirapua.

Rodingite in nickeliferous serpentinite, near Beaconsfield, Northern Tasmania

Abstract Rodingite (gametised gabbro) with associated hydrous lime silicates (vesu‐vianite, prehnite, zoisite, etc.). occurring in the ultrabasic‐basic igneous complex of the Anderson's Creek district, west of Beaconsfield, Northern Tasmania, has been developed from hornblende gabbro by a process of lime metasomatism which antedated the intrusion of serpentinite. Xenoliths, rafts and/or roof pendants of rodingite, hornblende gabbro, pyroxenites and metamorphosed older sediments, occur in the serpentinite which is cut by later veins of gamierite, chrysotile, opaline silica, and fibrous and granular magnetite.