• Journal of the Korean Ceramic Society
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• v.31 no.2
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• pp.117-128
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• 1994

Hematite particles were obtained by hydrothermal reaction of ferric hydroxide in the presence of small amount of citric acid which is acted as crystal growth controller. The effects of hydrothermal reaction condition son the morphology and crystal structure of powder were investigated using X-ray, TEM and FT-IR. Ellipsoidal or rectangular hematite particles were formed in the range of pH 10.75~11.75 as initial basicity of reactants and 3$\times$10-5 ~9$\times$10-5 mol as citric acid content. Crystallization of hematite was inhibited in the range of pH9. 0~10.5 and above citric acid content of $1.5\times$10-4 mol. Hematite particle length and aspect ratio were decreased gradually with increasing of citric acid content. Hematite particles formed at 14$0^{\circ}C$ exhibited particle properties with the length of 0.7 ${\mu}{\textrm}{m}$ and aspect ratio of 8. Hematite particles having a good acicular-type were not obtained above 22$0^{\circ}C$.

• Advances in environmental research
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• v.5 no.1
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• pp.51-59
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• 2016

In this study, nitrate reduction of real groundwater sample by 2.2%Cu-1.6%Pd-hematite catalyst was evaluated at different nitrate concentrations, catalyst concentrations, and recycling. Results show that the nitrate reduction is improved by increasing the catalyst concentration. Specific nitrate removal by 2.2%Cu-1.6%Pd-hematite increased linearly with the increase of nitrate concentration showing that the catalyst possesses significantly higher reduction capacity. More than 95% nitrate reduction was observed over five recycles by 2.2%Cu-1.6%Pd-hematite with ~56% nitrogen selectivity in all recycling batches. The results from this study indicate that stable reduction of nitrate in groundwater can be achieved by 2.2%Cu-1.6%Pd-hematite over the wide range of initial nitrate inputs.

• Journal of Korea Soil Environment Society
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• v.1 no.2
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• pp.51-60
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• 1996

Removal of Mn-EDTA complex and fluoride by use of hematite and ferrite, which are the by-product to be disposed of as industrial wastes, was investigated. For the comparison of removal rate, Na-bentonite known as excellent absorbent of inorganic contaminants was included in the experiments. As the results of batch mode experiments, for manganese, ferrite-A revealed 48∼65% of removal capacity, ferrite-B 46∼57%, hematite 17∼26%, while Na-bentonite showed 10∼23% of removal, depending on the initial concentration. Meanwhile, in case of fluoride : hematite revealed 53 ∼63% of removal : ferrite-A 54∼63 %, while ferrite-B did 20∼38 %. From the results, it can be postulated that the capacity of hematite and ferrite to attenuate inorganic pollutants, especially when they form complex ions, is superior to that of Na-bentonite. Consequently, the mixing of such oxide minerals with Na-bentonite will reinforce the function of Na-bentonite, especially in the undergroud liner aspect.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.78-82
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• 2003

Development of hematite-coated sand was evaluated for the application of the PRB (permeable reactive barrier) in the arsenic-contaminated subsurface of the metal mining areas. The removal efficiency of As(III) and As(V), the effect of anion competition and the capability of arsenic removal in the flow system were investigated through the experiments of adsorption isotherm, arsenic removal kinetics against anion competition and column removal. Hematite-coated sand followed a linear adsorption isotherm with high adsorption capacity at low level concentrations of arsenic (< 1.0 mg/l). When As(III) and As(V) underwent adsorption reactions in the presence of anions (sulfate, nitrate and bicarbonate), sulfate caused strong inhibition of arsenic removal, and bicarbonate and nitrate caused weak inhibition due to specific and nonspecific adsorption onto hematite, respectively. In the column experiments, high content of hematite-coated sand enhance the arsenic removal, but the amount of the arsenic removal decreased due to the higher affinity of As(V) than As(III) and reduced adsorption kinetics in the flow system, Therefore, the amount of hematite-coated sand, the adsorption affinity of arsenic species and removal kinetics determined the removal efficiency of arsenic in the flow system. arsenic, hematite-coated sand, permeable reactive barrier, anion competition, adsorption.

• Journal of the Korean Ceramic Society
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• v.22 no.6
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• pp.87-93
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• 1985

The hematite the magetite and the maghemite thin film were prepared by oxidation and reductino of the vaccum-evaporated iron thin film. Interre;atoms between film preparation process and the electrical properties were investigated. At room temperature the electrical conductivity of the iron the hematite the magnetite and the maghemite thin film were $1{\times}10^4\Omega^{-1}cm^{-1}$, 2{\times}10^{-5}\Omega^{-1}cm^{-1}$, $3{\times}10^{-5}\Omega^{-1}cm^{-1}$, and $4{\times}10^{-5}\Omega^{-1}cm^{-1}$, resp-ectively. The surface of each thin film was dense and homogeneous. At the temperature that the iron thin film was converted into the hematite thin film the electrical conductivity decreased rapidly and the electrical con-ductivity of the hematite thin film increased as temperature increased. The hematite thin film was reduced to the magnetite thin film in H2 atmosphere. The electrical conductivity decreased rapidly at the temperature that the maghemite thin film is formed by oxidation of the magnetite thin film and the electrical conductivity of the maghemite thin film increased as temperature increased.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.2918-2925
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• 2021

The efficiency of decontamination of model spent ion exchange resins, contaminated with magnetite and hematite, with mineral acid solutions, and using electro-decontamination, was evaluated. It has been shown that effective hematite dissolution occurs in concentrated mineral acid solutions. However, the use of direct current increases the decontamination efficiency of spent ion exchange resins contaminated with hematite. It is determined that with increasing voltage and acid concentration, the dissolution efficiency of hematite deposits increases and can exceed 99%. It has been shown that hematite dissolution is accompanied by secondary adsorption of radionuclides due to ion exchange, which can be removed with sodium nitrate solutions.

• Journal of Sensor Science and Technology
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• v.30 no.4
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• pp.210-217
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• 2021

Gas sensors based on semiconducting metal oxides have attracted considerable attention for various applications owing to their facile, cheap, and small-scale manufacturing processes. Hematite (α-Fe₂O₃) is widely considered as a promising candidate for a gas-sensing material owing to not only its abundance in the earth's crust and low price but also its chemical stability and suitable bandgap energy. However, only a few studies have been performed in this direction because of the low gas response and sluggish response of hematite-based gas sensors. Nanostructures present a representative solution to both overcome these disadvantages and exploit the desirable features to produce high-performance gas sensors. However, several challenges remain for adopting gas sensors based on metal oxide nanostructures, such as improving cost efficiency and facilitating mass production. This review summarizes the recent studies on gas sensors based on hematite nanostructures. It also provides useful insights into various strategies for enhancing the gas-sensing properties of gas sensors based on hematite nanostructures.

• Economic and Environmental Geology
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• v.31 no.4
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• pp.291-296
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• 1998

Pedogenic hematite is a well known agent for sink of pollutants and nutrients and for aggregation of particles in soils. Changes in physical and chemical properties of two sandy loam soils (Anahuac and Crowley soils) from the Southern Coastal Plain, the United States of America, were tested after adding finely ground crystalline hematite prepared for drilling fluid weighting material. There was an increase in hydraulic conductivity (HC) of the soils with addition of up to 3% by weight of hematite but a decrease in HC with addition of more hematite. The aggregate stability (AS) of the soils was not affected by adding hematite. Anahuac soil with higher content of organic matter and lower sodium adsorption ratio (SAR) had higher values of HC and AS than Crowley soil. Adding hematite also resulted in a slight increase in zinc (Zn) adsorption by the soils, but had no influence on the adsorption of phosphate.

• Korean Journal of Materials Research
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• v.27 no.4
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• pp.206-210
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• 2017

In this study, an ${\alpha}-Fe_2O_3$ (hematite) coated porcelain plate was sintered in a temperature range from $1100^{\circ}C$ to $1250^{\circ}C$ using ferrous sulfate. The specimens were investigated by X-ray diffractometer (XRD), scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and UV-visible spectrophotometer. It was confirmed that ${\alpha}-Fe_2O_3$ (hematite) was densely fused to the surface at several tens of ${\mu}m$, the ${\alpha}-Fe_2O_3$ (hematite) was in the form of thin platelet and polyhedra, and no other compounds appeared in the sintering process. In the specimen coated with ${\alpha}-Fe_2O_3$ (hematite), the reflectance spectra show a red absorption band of 560-650 nm. The $L^*$ value decreased from 53.18 to 46.94 with the firing temperature. The values of $a^*$ and $b^*$ were at 19.03 and 15.25 at $1100^{\circ}C$ and gradually decreased with increasing temperature; these values decreased rapidly at $1250^{\circ}C$ to 11.54 and 7.98, respectively. It is considered that the new phases are formed by the phase transition of the porcelain plate (clay), and thus the $a^*$ and $b^*$ values are greatly influenced.

• Journal of the Korean earth science society
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• v.29 no.7
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• pp.523-530
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• 2008

The phase changes and variations of elemental contents in hematite medicinal mineral were investigated by a traditional processing operation including heating and quenching in vinegar. Hematite was processed at $650^{\circ}C$ and $900^{\circ}C$ through at least 5 processing cycles. Metal extraction tests in water were carried out with the processed hematite. Heating and quenching in vinegar could not change the phase of hematite. The effect of this traditional method was not clear because there were no variational trends between extracted elements and the number of processing cycles at $650^{\circ}C$ and $900^{\circ}C$. However, the traditional processing operation of heating and quenching in vinegar was very effective to change the hematite mineral towards soft and easily crushing medicinal material.