High-purity Magnetite Research Articles

Preparation of high-purity magnetite from iron ore concentrate

In pursuit of environmental protection and green, low-carbon economic development, China has proposed the dual-carbon strategies of carbon peak and carbon neutrality. To achieve the dual-carbon goals, traditional steel metallurgical production processes are gradually shifting towards green and low-carbon hydrogen metallurgical processes. However, hydrogen metallurgical processes have strict requirements for raw materials and typically require the utilization of high-grade iron concentrates. The scarcity of high-grade iron ore in China severely constrains the development of hydrogen metallurgical processes. Therefore, this study proposes the utilization of ordinary magnetite concentrate to produce high-grade magnetite. Comprehensive analytical methods, including chemical analysis, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) analysis, laser particle size testing, optical microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and mineral liberation analysis, were employed to elucidate the mineralogical characteristics of the iron concentrate. The analysis revealed that the iron concentrate had a total iron (TFe) grade of 65.56 %, with SiO2 and Al2O3 contents of 8.28 % and 0.38 %, respectively. Subsequently, a combined beneficiation process involving magnetic separation, flotation, and chemical leaching was conducted. Experimental results showed that a single magnetic separation obtained an iron concentrate grade of 67.52 % with an overall recovery of 86.18 %. Following magnetic separation, flotation was conducted to increase the concentrate grade. With one roughing and four cleaning flotation stages, a concentrate grade of 72.19 % and a 36.36 % overall recovery were achieved. A subsequent leaching operation after flotation yielded high-purity magnetite with a Fe grade of 72.30 % and an overall recovery of 35.68 %. The high-purity magnetite was confirmed to have a purity of up to 99.9 % based on chemical titration, XRD analysis, magnetic susceptibility measurement, and SEM analysis. Furthermore, detailed kinetics studies on leaching were conducted to elucidate the reaction mechanism, revealing an apparent activation energy of 25.70 kJ/mol. The successful implementation of this process will provide a benchmark for producing similar high-purity magnetite concentrates and contribute to China’s dual-carbon goals.

Extraction of high purity magnetite from bauxite residue

Bauxite residue is a byproduct of the alumina industry and is characterized by high alkalinity and very fine particle size. Currently, there is a low volume utilization of bauxite residue as an additive in the construction industries, and only 3–4 % of the total volume produced annually (160 million tons) is utilized effectively. Bauxite residue is mainly composed of iron oxide along with oxides of aluminum, calcium, sodium, silicon, and titanium. A high fraction of iron in bauxite residue makes it a potential alternative source. However, recovery of high purity iron products with high recovery is technically challenging. The present work is focused on the recovery of iron from bauxite residue in the form of high purity magnetite through a hydrometallurgical approach. Bauxite residue is first neutralized after leaching with mild hydrochloric acid, followed by the leaching of iron with oxalic acid and photochemical reduction of leach liquor to obtain ferrous oxalate precipitate, which is further converted to high purity magnetite. Three different bauxite residue samples with different mineralogical compositions were used, and a comparative study is presented to illustrate the flexibility of the process toward different grades of bauxite residue.

Development of a three-step approach to repurpose nickel-laterite mining waste into magnetite adsorbents for As(III) and As(V) removal: Synthesis, characterization and adsorption studies

Nickel (Ni)-laterite mining is a major industry in the Philippines but is generating large amounts of Ni-laterite mining waste (NMW) that threatens surrounding water bodies due to siltation. To repurpose this waste as magnetic iron (Fe)-based adsorbent, a three-step extraction-reduction-coprecipitation approach was developed, and the adsorption properties of synthesized product for arsenate (As(V)) and arsenite (As(III)) were investigated. The three-step approach extracted > 90% Fe from NMW and produced fine (<4 µm), high-purity magnetite based on XPS, XRD, FTIR and SEM-EDS. NMW-derived magnetite also exhibited a positively charged surface between pH 5 and 8 (i.e., IEP of 8.5), which could be attributed to the incorporation of impurities like Mg, Al and Cr. The kinetic and isotherm adsorption results at pH 5 showed that NMW-derived magnetite had high maximum adsorption capacities (qmax) for As(V) and As(III) estimated at 714 mg/g and 435 mg/g, respectively. The good fit of pseudo-second-order rate law to the kinetic results implied that chemisorption was a dominant removal mechanism for both As(V) and As(III), which likely occurred via inner sphere complexation based on the XPS results. NMW-derived magnetite could also act as an oxidant or reductant depending on the dominant As species in solution. When As(V) species dominated, they were reduced to As(III) via Fe(II)-surface species. Meanwhile, Fe(III)-surface species on the adsorbent oxidized As(III) to As(V) that improved As(III) removal from solutions. These results demonstrate the potential of NMW as raw material for magnetic adsorbent synthesis for environmental applications.

Comprehensive utilization of bauxite residue for simultaneous recovery of base metals and critical elements

The growing stockpiles of bauxite residue and associated environmental hazards require a sophisticated recycling system for complete utilization and value recovery. The current application is limited as a raw material for building and construction applications. Considering the association of multiple elements (Fe, Al, Si, Ca, Ti, V, Sc) within bauxite residue, metal extraction is of prime interest with respect to the economic value of the final product. The following study presents a hydrometallurgy-based process flowsheet for the sustainable recovery of base metals and critical elements within bauxite residue. Major elements present in bauxite residue are recovered as materials for industrial application, including high purity magnetite, alumina, titania, silica, and calcium carbonate. Trace elements are recovered in the liquid stream generated after the recovery of base metals.

Preparation of reduced iron powder for powder metallurgy from magnetite concentrate by direct reduction and wet magnetic separation

The Höganäs method is considered the most effective method for producing reduced iron powder (RIP). However, this method does not remove impurities; therefore, high-purity magnetite must be used as raw materials. In this study, when RIP was produced using magnetite concentrate (TFe = 64.86%), a strong raw material flexibility was observed. The influence of various parameters on the preparation of RIP was studied. The results showed that pyrite was the optimal additive, and when used under optimized conditions, it produced RIP with a high iron grade of 99.65%, which meets the standard for powder metallurgy. Analysis revealed that the pyrite additive formed a molten iron sulfide (FeS) phase. Spheroidal metallic iron particles were more easily encapsulated by the FeS phase; consequently, the symbiotic relationship between iron and gangue was minimized, which was more conducive to the separation of metallic iron and oxides impurities. Thus, a high-purity RIP was produced.

High Purity Magnetite Microparticles Directly Derived from Mill Scale via Hydrogen-Reduction Method

This study develops a fast and simple way to produce high purity magnetite (Fe3O4) microparticles from mill scale by using hydrogen reduction with the addition of vapour as a retarding agent. By optimising the reduction temperature and gas flow rate, the characterisations by X-ray diffractometry technique shown that the Fe3O4 fraction of over 93 wt.-% is shown at the reduction temperature of 550 – 650 oC with the flow rate of the 4.5-5.5 mol%H2 + Ar gas + H2O gas mixture from 100 – 200 ml/min. The highest Fe3O4 fraction of over 99 wt.-% can be achieved from the reduction with the mixed gas at 650 oC and the flow rate of 200 ml/min for 4 hour.

Magnetic iron oxide particles (Fe3O4) fabricated by ball milling for improving the environmental quality

Nowadays magnetic iron oxide particles (Fe3O4) have been extensively used as nanomaterials due to their broad range of applications. One of their applications is to improve the environmental quality by elimination of harmful pollutants in wastewater. Therefore, preparation method of magnetite (Fe3O4) nanoparticles is one of the most important keys to its adsorption efficiency. This study aims to prepare magnetite nanoparticles from natural iron sand of Arta Beach, Pariaman, West Sumatera using ball milling technique. This technique is simple and easy to carry out. The balls used in this milling are the iron balls with the diameter of 1.5 cm. The phase composition, elemental composition, microstructure and magnetic properties of milled powder of magnetic particles were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) respectively. The results showed that the milling time is a key parameter of the magnetite nanoparticles preparation. By increasing the milling time, then high purity magnetite samples can be obtained. Moreover, the magnetic particle size of the sample decreases as the milling time increases. The SEM micrographs showed that the sample has a broad distribution of particle diameters, ranging from around 1 up to 107 μm and 0.5 to 36 μm after 30 and 90 hours of milling respectively.

Novel monopolar arrangement of multiple iron electrodes for the large-scale production of magnetite nanoparticles for electrochemical reactors

High-purity magnetite nanoparticles with a mixed quasi-spherical and cubic morphology have been successfully synthesized using a new alternating monopolar arrangement of multiple iron electrodes in water. The magnetite nanoparticles have a narrow size distribution with a mean size ranging from 20 to 30 nm, depending on the applied voltage and pH. The formation of magnetite nanoparticles is favored only in the pH range of 7–10; outside this range, magnetite nanoparticles cannot be produced. The magnetite nanoparticles exhibit ferromagnetic properties with saturation magnetization ranging from 16 to 75 emu/g. They demonstrated to be a promising electrocatalyst for oxygen reduction reactions in basic media. This facile method is a promising production route for magnetite nanoparticles and can be easily scaled up for large production.

A stable novel nanostructure of ZnFe2O4 based nanocomposite for improved photoelectrocatalytic and photocatalytic activities

A nonagon ZnO–ZnFe2O4 nanocomposite was synthesized using high-energy ball milling followed by post-annealing with an initial mixture of high purity magnetite (Fe3O4) and zincite (ZnO) powders. The effects of the process parameters on the structural, optical, photocatalytic, and photoelectrocatalytic activities were investigated. X-ray diffraction analysis was used to confirm the presence cubic spinel ZnFe2O4 and hexagonal ZnO crystal phases. The lowest optical bandgap observed was 1.83 eV, which decreased due to post-annealing. The photocatalytic activity of the 800 °C post-annealed nanocomposite exhibited the highest degradation percentage of 96% over 180 min under visible light, with a degradation rate constant of 1.5 min−1. Furthermore, the optimized sample showed no substantial decrease in photocatalytic activity after five cycles of the repeated catalysis experiment. In electrochemical studies, when compared to the other post-annealed samples, the 800 °C post-annealed nanocomposite showed the highest water splitting activity with the lowest charge-transfer resistance of 75 Ω, photocurrent density of 4.3 × 10−5 Acm−2, exchange current density of 4.19 log JA−1 cm−2, and Tafel slopes of 74.1 mVdec−1. In dual activities, the performance of the 800 °C post-annealed nanocomposite was noticed to be enhanced. This nanocomposite has potential industrial applications as a cost-effective catalyst.

On the ‘centre of gravity’ method for measuring the composition of magnetite/maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via 57Fe Mössbauer spectroscopy

We evaluate the application of 57Fe Mössbauer spectroscopy to the determination of the composition of magnetite (Fe3O4)/maghemite (γ-Fe2O3) mixtures and the stoichiometry of magnetite-maghemite solid solutions. In particular, we consider a recently proposed model-independent method which does not rely on a priori assumptions regarding the nature of the sample, other than that it is free of other Fe-containing phases. In it a single parameter, —the ‘centre of gravity’, or area weighted mean isomer shift at room temperature, T = 295 ± 5 K—is extracted by curve-fitting a sample’s Mössbauer spectrum, and is correlated to the sample’s composition or stoichiometry. We present data on high-purity magnetite and maghemite powders, and mixtures thereof, as well as comparison literature data from nanoparticulate mixtures and solid solutions, to show that a linear correlation exists between and the numerical proportion of Fe atoms in the magnetite environment: = Femagnetite/Fetotal , where = 0.3206 ± 0.0022 mm s−1 and = 0.2135 ± 0.0076 mm s−1. We also present equations to relate to the weight percentage w of magnetite in mixed phases, and the magnetite stoichiometry x = Fe2+/Fe3+ in solid solutions. The analytical method is generally applicable, but is most accurate when the absorption profiles are sharp; in some samples this may require spectra to be recorded at reduced temperatures. We consider such cases and provide equations to relate to the corresponding α value.

Production of High-purity Magnetite Nanoparticles from a Low-grade Iron Ore via Solvent Extraction

We produced magnetite nanoparticles (MNPs) and a Mg-rich solution as a nano-adsorbent and a coagulant for water treatment, respectively, using a low-grade iron ore. The ore was leached with aqueous hydrochloric acid and its impurities were removed by solvent extraction of the leachate using tri-n-butyl phosphate as an extractant. The content of Si and Mg, which inhibit the formation of MNPs, was reduced from 10.3 wt% and 15.5 wt% to 28.1 mg/L and < 1.4 mg/L, respectively. Consequently, the Fe content increased from 68.6 wt% to 99.8 wt%. The high-purity <TEX>$Fe^{3+}$</TEX> solution recovered was used to prepare 5-15-nm MNPs by coprecipitation. The wastewater produced contained a large amount of <TEX>$Mg^{2+}$</TEX> and can be used to precipitate struvite in sewage treatment. This process helps reduce the cost of both sewage and iron-orewastewater treatments, as well as in the economic production of the nano-adsorbent.

Synthesis of magnetite nanoparticles by high energy ball milling

We report on the preparation of magnetite nanoparticles, with size ranging from 12nm to 20nm, by high energy ball milling. The synthesis is made using stoichiometric amounts of distilled water and metallic iron powder. The milled powder samples were analyzed by Mossbauer spectroscopy (MS), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Our results indicate that the milling time is a key parameter of the synthesis. By increasing the milling time one achieves high purity magnetite samples. Also, the particle size decreases with the milling time. The sample milled during 10h contained a fraction of 56nm metallic Fe particles and 20nm magnetite particles. By increasing the milling time to 96h we have obtained a sample that is mainly composed of 12nm magnetite particles. MS performed at room temperature showed a spectrum consisting of two sextets with hyperfine parameters related to iron ions occupying octahedral (A) and tetrahedral (B) sites. We have used a self-consistent method to investigate the impact of the dipolar interaction to drive the system to a magnetically blocked regime.

State analysis and relationship between lattice constants and compositions including minor elements of synthetic magnetite and maghemite

Chemical formulae were constructed after the determination of the composition including the minor elements in commercially available synthetic magnetite and maghemite, which gave similar x-ray diffraction patterns with close diffraction lines. The contents of FeO in reagent grade magnetite and high-purity magnetite powders were about 8 mol% less and that in a needle-shaled magnetite powder was about 24 mol% less than the 50 mol% in the expected composition (FeO · Fe2O4) of magnetite. They were solid solutions of magnetite-maghemite (γ-Fe2O3) including minor elements in the lattice. A linear relationship was found between the total mole percentage if divalent iron, manganese and zinc oxides and their lattice constants ac corrected by increments of the lattice constant based on the replacement of divalent iron with manganese and zinc atoms. The possibility of a non-destructive total analysis of the same iron oxide samples by an x-ray method is discussed. It was found that magnetite was considerably oxidized in air even at 110°C to form a solid solution, but not to form any separated compound.

Ferrimagnetic resonance and low temperature transition in Ni- and Co-substituted powder magnetite

The effects of nickel and cobalt substitution on ferrimagnetic resonance in high-purity magnetite powder have been investigated. The low-temperature transition temperature and damping parameter, α, are found to decrease with increasing solute additions. The linewidth, ΔH, varies in proportion to the anisotropy field of the ferrites, narrowing with increasing nickel content but broadening with increasing cobalt content. Theg factor increases with the dopant concentration, passing through a maximum around room temperature. Decreasing the deviation from stoichiometry by appropriate annealing decreases the transition temperature shift but slightly increases ΔH, g and α.

An experimental study of a direct route from iron oxide superconcentrate to strip

AbstractA direct route from commercially available high-purity magnetite superconcentrate to thin steel strip has been investigated on a laboratory scale. The experimental procedure was first to produce an oxide strip prepared from a thick aqueous slurry of the superconcentrate and an organic binder. After drying, the strip was reduced and sintered in hydrogen or a hydrogen-carbon monoxide mixture to produce a coherent strip of iron sponge. The sponge was then hot and cold rolled to give fully dense strip. In some cases a thin layer of iron powder was bonded to one side of the iron oxide strip in order to increase its coherence during processing. On a microscale the product is characterized by a fine grain size and a large number of uniformly distributed fine inclusions. The inclusions vary from 25 μm down to submicron size and are derived from the residual impurities in the concentrate, most of which were originally in the magnetite lattice. After suitable working and heat treatment, strength and ductili...

Cobalt Impurity, Cation Vacancies and the Magnetic Relaxation of Magnetite

Disaccommodation spectrum of magnetite found by Braginski were investigated experimentally and theoretically. Peak II is caused by the presense of extremely small concentration of cobalt impurity and it disappears for the high purity magnetite. Peak III is caused by the preferential occupation of cation vacancies and the accurate expression of the relaxation time is 1/τ=8 I 0 =6.0×10 13 exp (- Q / k T ), where Q =0.94 eV and I 0 is the jumping frequency of an iron ion into the nearest neighbor cation vacancy. A suggestion is made for the low temperature line width anomaly of Li 0.5 Fe 2.5 O 4 that it is due to ppm cobalt impurity.

Magnetocrystalline anisotropy in cobalt-substituted magnetite single crystals

The growth of single crystals corresponding to x=0 (high-purity magnetite), x = 0.01 and x = 0.04 in the composition series CoxFe3-xO4 is described. First- and second-order anisotropy constants of these crystals are determined by the torque method over the temperature range 120–450°K. The substitution of small amounts of cobalt for iron is found to add a positive contribution to K1 and a negative contribution to K2. At low cobalt concentrations the magnitude of this contribution is a linear function of the amount of cobalt added. It is suggested that the effect of cobalt on the anisotropy is enhanced by the presence of divalent iron in magnetite, and it is concluded that the change in sign of K in magnetite at about 130°K is not caused by the presence of cobalt or any other foreign impurity.