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Siderite ore is difficult to treat using conventional processing methods such as gravity, magnetic separation, and froth flotation owing to its low iron grade, complex mineral composition, and easy sliming in the grinding process. In this study, magnetization roasting in a low-oxygen atmosphere without carbon additives has been carried out for the treatment of siderite ore. An iron concentrate with an iron grade of 60.12% and a recovery of 80.06% was obtained with a raw ore assaying 22.99% iron. The samples were characterized by X-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometry, and scanning electron microscopy. The results indicated that the siderite (FeCO3) and hematite (α-Fe2O3) were primarily transformed into magnetite (Fe3O4) and maghemite (γ-Fe2O3) at a roasting temperature of 650°C with an O2 concentration of 1.0%. The saturation magnetization of the raw ore increased from 2.04 to 20.89 A m2/kg after magnetization roasting owing to the formation of ferrimagnetic magnetite and maghemite. This study is conducive to exploiting siderite ore resources using low-carbon magnetization roasting technology. [ABSTRACT FROM AUTHOR]

Nonisothermal and isothermal kinetic studies were carried out to determine the decarbonization mechanism for fluidized roasting of vanadium-bearing carbonaceous shale. The nonisothermal kinetics were calculated with the Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Kingssger, and Šatava-Šesták methods based on thermogravimetric analyses performed with five heating rates (8, 10, 13, 15, and 20 K min−1). The decarbonization rates of the roasted products were used for the isothermal kinetic studies. The results showed that the decarbonization process followed second-order reaction kinetics (F2) with E = 224.84 kJ mol−1. The isothermal kinetics showed that the early stage of decarbonization was controlled by both chemical reactions and diffusion. The shrinking core model (R2) with cylindrical symmetry was the most appropriate function (E = 139.54 kJ mol−1, A = 9.36 × 105 min−1). Then, control of the late roasting stage was changed to diffusion alone because three-dimensional diffusion (D6) was selected (E = 220.43 kJ mol−1, A = 9.92 × 109 min−1). Furthermore, a sufficient oxygen supply and a fine particle feed provided decarbonization efficiency, especially during the first 30 min of carbonaceous shale decarbonization. [ABSTRACT FROM AUTHOR]

In order to develop limonite and decrease CO2 emissions, siderite is proposed as a clean reductant for suspension magnetization roasting (SMR) of limonite. An iron concentrate (iron grade: 65.92wt%, iron recovery: 98.54wt%) was obtained by magnetic separation under the optimum SMR conditions: siderite dosage 40wt%, roasting temperature 700°C, roasting time 10 min. According to the magnetic analysis, SMR achieved the conversion of weak magnetic minerals to strong magnetic minerals, thus enabling the recovery of iron via magnetic separation. Based on the phase transformation analysis, during the SMR process, limonite was first dehydrated and converted to hematite, and then siderite decomposed to generate magnetite and CO, where CO reduced the freshly formed hematite to magnetite. The microstructure evolution analysis indicated that the magnetite particles were loose and porous with a destroyed structure, making them easier to be ground. The non-isothermal kinetic results show that the main reaction between limonite and siderite conformed to the two-dimension diffusion mechanism, suggesting that the diffusion of CO controlled the reaction. These results encourage the application of siderite as a reductant in SMR. [ABSTRACT FROM AUTHOR]

The application of coal-based reduction in the efficient recovery of iron from refractory iron-bearing resources is comprehensively reviewed. Currently, the development and beneficiation of refractory iron-bearing resources have attracted increasing attention. However, the effect of iron recovery by traditional beneficiation methods is unacceptable. Coal-based reduction followed by magnetic separation is proposed, which adopts coal as the reductant to reduce iron oxides to metallic iron below the melting temperature. The metallic iron particles aggregate and grow, and the particle size continuously increases to be suitable for magnetic separation. The optimization and application of coal-based reduction have been abundantly researched. A detailed literature study on coal-based reduction is performed from the perspectives of thermodynamics, reduction kinetics, growth of metallic iron particles, additives, and application. The coal-based reduction industrial equipment can be developed based on the existing pyrometallurgical equipments, rotary hearth furnace and rotary kiln, which are introduced briefly. However, coal-based reduction currently mainly adopts coal as a reductant and fuel, which may result in high levels of carbon dioxide emissions, energy consumption, and pollution. Technological innovation aiming at decreasing carbon dioxide emissions is a new trend of green and sustainable development of the steel industry. Therefore, the substitution of coal with clean energy (hydrogen, biomass, etc.) for iron oxide reduction shows promise in the future. [ABSTRACT FROM AUTHOR]

Iron ore tailings are industrial solid wastes generated from mineral processing. The disposal of iron ore tailings leads to environmental threat and serious security because of their tiny particle size and large storage. In this paper, suspension magnetization roasting and magnetic separation technology were utilized to recover iron tailings. The results showed that iron concentrates with iron grade of 65.01% and recovery of 89.07% could be obtained under conditions of CO concentration 30%, roasting temperature 520 °C, roasting time 20 min, grinding particle size of roasted products with 94% mass fraction of − 38 μm and magnetic field strength 1800 Oe. The vibration sample magnetometer, X-ray diffraction, specific surface area detector, scanning electron microscope and energy-dispersive spectrometer showed that unit mass magnetic moment, specific magnetization coefficient and saturation value of magnetization intensity of magnetic concentrate were all significantly improved. Weak magnetic iron ore was selectively transformed into strong magnetic magnetite. Compared with raw ore, there was porous and cracked structure on the surface of roasted ore and magnetic concentrate, which was conducive to magnetization reaction, magnetism and phase transformation of iron ore. [ABSTRACT FROM AUTHOR]

A new surfactant butane-3-heptyloxy-1,2-diamine [CH3(CH2)6OCH(CH3)CH(NH2)CH2NH2; BHLD] was synthesized. It has been innovatively used as a collector in the flotation of quartz. In this present study, the flotation behaviors of quartz with BHLD were investigated by micro-flotation of quartz. It was found that the recovery of the quartz reaches 98.9%. Furthermore, the hydrogen bond lengths were measured, calculated and simulated in a molecular dynamics (MD) model, and the interaction energy between the four species of BHLD and the quartz surface were determined under vacuum and aqueous conditions. Based on the results of the zeta potential measurements, the FT-IR measurements and the MD simulation in this paper, it is revealed that the BHLD collector adsorbs onto the quartz surface through electrostatic adsorption and hydrogen bond adsorption. Furthermore, micro-flotations were studied by the radial distribution function (RDF) and the relative concentrations. The results show that the hydrogen bond adsorption between the O atom on the quartz surface and the H atom in BHLD are the main interactive forces causing BHLD to adsorb onto the quartz surface. The BHLD cations adsorb significantly more strongly than the BHLD molecules, which agrees well with the results of the micro-flotation tests. [ABSTRACT FROM AUTHOR]

An innovative process of coal-based reduction followed by magnetic separation and dephosphorization was developed to simultaneously recover iron and phosphorus from one typical high-phosphorus refractory iron ore. The experimental results showed that the iron minerals in iron ore were reduced to metallic iron during the coal-based reduction and the phosphorus was enriched in the metallic iron phase. The CaO-SiO-FeO-AlO slag system was used in the dephosphorization of metallic iron. A hot metal of 99.17% Fe and 0.10% P was produced with Fe recovery of 84.41%. Meanwhile, a dephosphorization slag of 5.72% P was obtained with P recovery of 67.23%. The contents of impurities in hot metal were very low, and it could be used as feedstock for steelmaking after a secondary refining. Phosphorus in the dephosphorization slag mainly existed in the form of a 5CaO·PO·SiO solid solution where the PO content is 13.10%. At a slag particle size of 20.7 μm (90% passing), 94.54% of the PO could be solubilized in citric acid, indicating the slag met the feedstock requirements in phosphate fertilizer production. Consequently, the proposed process achieved simultaneous Fe and P recovery, paving the way to comprehensive utilization of high-phosphorus refractory iron ore. [ABSTRACT FROM AUTHOR]

Ag/AgCl/TiO nanotubes have been synthesized through a simple method. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electronmicroscopy, Raman spectra, photoluminescence spectroscopy, X-ray photoelectron spectroscopy and UV-Vis diffuse reflectance spectroscopy, were used to characterize the as-synthesized photocatalyst. The as-prepared Ag/AgCl@TiO photocatalyst show excellent visible-light photocatalytic performance and good reusability for decomposing organic pollutant of Rhodamine B dyes in water. Additionally, the recycling experiment of Ag/AgCl/TiO has been done, demonstrating that Ag/AgCl/TiO have high efficiency and stability. This study may provide a new insight into the design and preparation of advanced visible-light photocatalytic materials. [ABSTRACT FROM AUTHOR]

Mixtures of oolitic iron ore and coal with different C/O molar ratios (1.5, 2.0, 2.5, and 3.0) were heated from 600 to 1300 °C at four heating rates (5, 10, 15, and 20 °C min). The degree of reduction and reduction rate were calculated from the measurements of weight loss and off-gas composition using thermogravimetry technique and NDIR gas analyzer. The kinetic parameters (the activation energy, pre-exponential factor, and reduction model) were determined by Ozawa-Flynn-Wall kinetic method and by Šatava-Šesták method. It was found that, as temperature increased, the degree of reduction increased, while the reduction rate rapidly increased first, subsequently stabilized, and then decreased. The non-isothermal reduction of oolitic iron ore with coal was significantly influenced by both heating rate and C/O molar ratio, although the impact of the latter was much less. The values of activation energy estimated by Ozawa-Flynn-Wall method ranged from 159.2 to 169.6 kJ mol. The mechanism function for the non-isothermal coal-based reduction of oolitic iron ore was D reaction model. The non-isothermal kinetic models for coal-based reduction of oolitic iron ore were proposed based on the obtained kinetic parameters. The iron oxide in the oolitic ore was reduced to metallic iron in the sequence of FeO → FeO → FeO (FeAlO, FeSiO) → Fe. Phase change and reduction mechanism shift were observed during the reduction. [ABSTRACT FROM AUTHOR]