MICROWAVE-ASSISTED CARBOTHERMIC REDUCTION OF ILMENITE

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Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate

Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate(VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reduction product, the order of the metallization rate of reduction product being CaCO3 > no additive > CaSO4 > CaCl2, which indicated that the addition of CaCO3 was more conducive to promoting the reduction of iron than other calcium compounds. Gas analysis showed that there were mainly two processes in the carbothermic reduction of VTC, a solid–solid and a solid–gas reaction. The concentrations of CO and CO2 were highest when CaCO3 was added, while that in a roasting system decreased the most when CaCl2 was added. X-ray diffraction(XRD) analysis showed that calcium compounds could change the reduction process of ilmenite in VTC. The phase compositions of the reduction products were changed from metallic iron(Fe) and anosovite(FeTi2O5) to metallic iron(Fe) and perovekite(CaTiO3) when calcium compounds were added. Additionally, CaSO4 and CaCl2 could significantly promote the growth of metallic iron particles, though the existence of Fe-bearing Mg2TiO4 in reduction products was not conducive to the reduction of iron. The formation of FeS would further hinder the reduction of iron after adding CaSO4.

Carbothermic reduction of vanadium titanomagnetite with the assistance of sodium carbonate

The carbothermic reduction of vanadium titanomagnetite concentrate(VTC)with the assistance of Na_(2)CO_(3)was conducted in an argon atmosphere between 1073 and 1473 K.X-ray diffraction and scanning electron microscopy were used to investigate the phase transformations during the reaction.By investigating the reaction between VTC and Na_(2)CO_(3),it was concluded that molten Na_(2)CO_(3)broke the structure of titanomagnetite by combining with the acidic oxides(Fe_(2)O_(3),TiO_(2),Al_(2)O_(3),and SiO_(2))to form a Na-rich melt and release FeO and MgO.Therefore,Na_(2)CO_(3)accelerated the reduction rate.In addition,adding Na_(2)CO_(3)also benefited the agglomeration of iron particles and the slag–metal separation by decreasing the viscosity of the slag.Thus,Na_(2)CO_(3)assisted carbothermic reduction is a promising method for treating VTC at low temperatures.

Analysis of the behavior of magnesium and CO vapor in the carbothermic reduction of magnesia in a vacuum

The aim of this paper is to experimentally investigate the behavior of magnesium and carbon monoxide vapor in the carbothermic reduction of magnesia at condensing zone temperatures ranging from 923 K to 1223 K.The phase,surface morphology,and composition of the condensates obtained were examined by means of scanning electron microscopy and energy-dispersive X-ray spectroscopy.The main findings of this paper include:the reverse reaction products,carbon and magnesium oxide,were formed following the process of magnesium vapor condensation,preventing two metal clusters from mutually combining.Moreover,the nearer the temperature of the condensation zone approached the liquid transformation temperature(810-910 K),the lower the rate of the reverse reaction between carbon monoxide and magnesium vapor.Decrease in the rate of the reverse reaction of magnesium was possible by controlling the condensation temperature.

Formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate by adding CaCO3

The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate(VTC)by adding CaCO3 was investigated.Thermodynamic analysis was employed to show the feasibility of calcium titanate formation by the reaction of ilmenite and Ca CO3 in a reductive atmosphere,where ilmenite is more easily reduced by CO or carbon in the presence of CaCO3.The effects of CaCO3 dosage and reduction temperature on the phase transformation and metallization degree were also investigated in an actual roasting test.Appropriate increase of CaCO3 dosages and reduction temperatures were found to be conducive to the formation of calcium titanate,and the optimum conditions were a CaCO3 dosage of 18 wt%and a reduction temperature of 1400°C.Additionally,scanning electron microscopy–energy dispersive spectrometry(SEM–EDS)analysis shows that calcium titanate produced via the carbothermic reduction of VTC by CaCO3 addition was of higher purity with particle size approximately 50μm.Hence,the separation of calcium titanate and metallic iron will be the focus in the future study.

Carbothermic reduction characteristics of ludwigite and boron–iron magnetic separation

Ludwigite is a kind of complex iron ore containing boron, iron, and magnesium, and it is the most promising boron resource in China. Selective reduction of iron oxide is the key step for the comprehensive utilization of ludwigite. In the present work, the reduction mechanism of ludwigite was investigated. The thermogravimetry and differential scanning calorimetry analysis and isothermal reduction of ludwigite/coal composite pellet were performed. Ludwigite yielded a lower reduction starting temperature and a higher final reduction degree compared with the traditional iron concentrates. Higher specific surface area and more fine cracks might be the main reasons for the better reducibility of ludwigite. Reducing temperature highly affected the reaction fraction and microstructure of the reduced pellets, which are closely related to the separation degree of boron and iron. Increasing reducing temperature benefited the boron and iron magnetic separation. Optimum magnetic separation results could be obtained when the pellet was reduced at 1300°C. The separated boron-rich non-magnetic concentrate presented poor crystalline structure, and its extraction efficiency for boron reached 64.3%. The obtained experimental results can provide reference for the determination of the comprehensive utilization flow sheet of ludwigite.

Magnesium production by carbothermic reduction in vacuum

In present work,we investigate production of magnesium by carbothermic reduction under vacuum conditions.The process was divided into two parts,one is reduction process,and the other one is condensation process.The experimental results revealed that during reduction process,the gas-solid reaction between MgO and CO was not occurred at a temperature and pressure of 1723 K and 30-100 Pa respectively.So the main reduction reaction was MgO(_(s))+C(_(s))=Mg(_(g))+CO(_(g))(under vacuum)and reaction type belonged to solid-solid reaction.In Condensation Process,according to a contrast and analysis,the condensation quality of magnesium is associated with CO concentration.The resultant product C was formed and it followed magnesium vapor condensation which prevents mutual combination of two metal droplets to forms the compact condensation produces.Therefore,in order to compact morphological forms of magnesium crystal whiskers,we must control the technical conditions and find the method to separate the magnesium vapor and carbon monoxide.That's the key factor to get better crystalline structure.

Preparation of Mg and Ca metal by carbothermic reduction method–A thermodynamics approach

The Gibbs free energy and critical reaction conditions of preparing Mg and Ca metal by carbothermic reducing calcined dolomite were calculated and analyzed.New thermodynamic criterion for reduction reaction,including the critical temperature and vacuum degree,was studied.The results show that:when T/P^(0.0449)<1199.2,neither MgO nor CaO can be reduced by carbon;when T/P^(0.0449)≥1199.2 and T/P^(0.0462)<1350.9,MgO can be reduced while CaO can not be;when T/P^(0.0462)≥1350.9,both MgO and CaO can be reduced.According to the requirements,we can obtain only Mg,Mg first then Ca,Mg and Ca simultaneously by controlling temperature,vacuum degree or both of them properly,by carbothermic reducing calcined dolomite.

Use of Solid State Carbothermic Reduction in Production of Transition Metals and Their Carbides

Many transition metals are produced by pyrometallurgical procedures which require very considerable amounts of energy, commonly electrical. On the other hand, some transition metals are obtained by employing very complex hydrometallurgical process routes. Solid state carbothermic reduction offers an alternative route for the production of both the metals and their carbides for energy saving and process step elimination. Consequently, it seemed worth to review the work carried out in this area The metals covered in this brief review are chromium, tungsten, titanium, manganese, niobium and molybdenum. Silicon is also mentioned although it is not a transition metal.

Catalytic Mechanism of KCl during Carbothermic Reduction of Pre-Oxidized Ilmenite

As alkali additive, KCl catalyzes effectively the carbothermic reduction of pre-oxidized ilmenite, and the catalytic effect becomes more remarkable as the amount of KCl increases. During the carbothermic reduction, the gaseous product consists mainly of CO, and the partial pressure of which increases with reaction temperature. The EPMA and XPS of the partially reduced ilmenite ore and that of the used graphite as reductant showed that the potassium ions enter both ilmenite particles and graphite powders during reduction. The above-mentioned phenomena result in the distortion of ilmenite and carbon structure by potassium ions and reaction activity of carbon and ilmenite was enhanced. As a result, the overall carbothermic reduction was catalyzed by KCl.

Catalytic effect of alkali chlorides on carbothermic reduction of pre oxidized ilmenite

A computer monitoring thermogravimetric system was used to study the effect of alkali chlorides(MCl, M=Li, Na, K and Cs) on the carbothermic reduction of pre oxidized ilmenite in the course of a linear rise in temperature from 600 ℃ to 1 000 ℃. The experimental results indicate that all the alkali chlorides can speed up the reduction process of pre oxidized ilmenite, moreover, KCl is the most effective catalyst of the chlorides, while the catalytic effects of LiCl and CsCl are relatively weaker. It seems that the catalytic mechanism of LiCl is different from those of the other alkali chlorides. The cross sectional morphology of the partially reduced pre oxidized ilmenite particles and the distribution of potassium ions within them were examined by means of scanning electronic microscopy and electronic probe microanalysis, respectively, which shows that the reduction proceeds topochemically and the alkali ion enriches at the periphery of the particles.[

Carbothermic reduction behaviors of Ti–Nb-bearing Fe concentrate from Bayan Obo ore in China

To support the development of technology to utilize low-grade Ti–Nb-bearing Fe concentrate, the reduction of the concentrate by coal was systematically investigated in the present paper. A liquid phase formed when the Ti–Nb-bearing Fe concentrate/coal composite pellet was reduced at temperatures greater than 1100℃. The addition of CaCO_3 improved the reduction rate when the slag basicity was less than 1.0 and inhibited the formation of the liquid phase. Mechanical milling obviously increased the metallization degree compared with that of the standard pellet when reduced under the same conditions. Evolution of the mineral phase composition and microstructure of the reduced Ti–Nb-bearing Fe concentrate/coal composite pellet at 1100℃ were analyzed by X-ray diffraction and scanning electron microscopy–energy-dispersive spectroscopy. The volume shrinkage value of the reduced Ti–Nb-bearing Fe concentrate/coal composite pellet with a basicity of 1.0 was approximately 35.2% when the pellet was reduced at 1100℃ for 20 min, which enhanced the external heat transfer to the lower layers when reduced in a practical rotary hearth furnace. The present work provides key parameters and mechanism understanding for the development of carbothermic reduction technology of a Ti–Nb-bearing Fe concentrate incorporated in a pyrometallurgical utilization flow sheet.

Thermodynamic analysis of the carbothermic reduction of a high-phosphorus oolitic iron ore by FactSage

A thermodynamic analysis of the carbothermic reduction of high-phosphorus oolitic iron ore(HPOIO) was conducted by the Fact Sage thermochemical software. The effects of temperature, C/O ratio, additive types, and dosages both on the reduction of fluorapatite and the formation of liquid slag were studied. The results show that the minimum thermodynamic reduction temperature of fluorapatite by carbon decreases to about 850°C, which is mainly ascribed to the presence of SiO_2, Al_2O_3, and Fe. The reduction rate of fluorapatite increases and the amount of liquid slag decreases with the rise of C/O ratio. The reduction of fluorapatite is hindered by the addition of CaO and Na_2CO_3, thereby allowing the selective reduction of iron oxides upon controlled C/O ratio. The thermodynamic results obtain in the present work are in good agreement with the experimental results available in the literatures.

Enhanced leaching of metals from spent lithium-ion batteries by catalytic carbothermic reduction

Spent Li-ion battery(LIB)recycling has become a challenge with the rapidly developing electric vehicle(EV)industry.To address the problems of high cost and low recovery of Li in the recycling of spent LIBs using traditional hydrometallurgical processes,we developed an alkali metal catalytic carbothermic reduction method to recover spent LiNi_(x)Co_(y)Mn_(z)O_(2)(NCM).Using alkali metal catalysts,such as NaOH,significantly reduced the temperature required for carbothermic NCM material reduction and realized targeted control of the phase of the reduction product,where Li was first separated by prior water leaching,followed by Ni,Co,and Mn recycling by acid leaching.The optimized carbothermic reduction conditions were a reaction time of 3 h,temperature of 550℃,NaOH dosage of 15 wt%,and graphite dosage of 15 wt%.The Li leaching efficiency reached 78.5 wt%during water leaching.And during acid leaching,the Ni,Co and Mn leaching efficiencies were 99.8 wt%,99.7 wt%,and 99.5wt%,respectively.This study provides strong technical support for the development of LIB industry.

Synthesis of Al_(4)SiC_(4) powders via carbothermic reduction: Reaction and grain growth mechanisms

Highly pure Al_(4)SiC_(4) powders were prepared by carbothermic reduction at 2173 K using Al_(2)O_(3),SiO_(2),and graphite as raw materials.The obtained Al_(4)SiC_(4) powders owned hexagonal plate-like grains with a diameter of about 200-300μm and a thickness of about 2-6μm.Based on the experimental results,the reaction of Al_(4)SiC_(4) formation and grain evolution mechanisms were determined from thermodynamic and first-principles calculations.The results indicated that the synthesis of Al_(4)SiC_(4) by the carbothermic reduction consisted of two parts,i.e.,solid-solid reactions initially followed by complex gas-solid and gas-gas reactions.The grain growth mechanism of Al_(4)SiC_(4) featured a two-dimensional nucleation and growth mechanism.The gas phases formed during the sintering process favored the preferential grain growth of(0010)and(110)planes resulting in formation of hexagonal plate-like Al_(4)SiC_(4) grains.

Phase Evolution during Carbothermic Reduction Process of Ilmenite for TiC_xN_(1-x) Composite Powders

As cutting materials and wear-resistant materials, the composites reinforced by Ti(C,N) have very high performances. The super-high cost of these composites, however, limits apparently their wider application to industry due to use of very expensive Ti(C,N) powders. Therefore, it is very necessary to develop a new process technology with low fabrication cost. In the present work, ilmenite (FeTiO3), which is very cheap and very rich in China, was used to fabricate the Ti(C,N) powder directly. The phase evolution during carbothermic reduction process of ilmenite was investigated by XRD, TG-DSC and thermodynamic calculation. The ilmenite and graphite were mixed by high energy ball milling and then sintered in pure flowing nitrogen atmosphere. The experimental results showed that a new phase, Ti4O7, appeared at 900 ℃ and disappeared at 1100 ℃ while sintered in pure flowing nitrogen atmosphere. The phase evolution during carbothermic reduction process of ilmenite was found to be continuous as FeTiO3→Ti4O7→T3O5→TiCN. XRD results showed that the composite powders produced in the present reaction were composed of α-Fe and TiC1-xNx. The thermodynamic calculation results were agreeable with experimental results.

Dual-Schottky-junctions coupling device based on ultra-longβ-Ga_(2)O_(3)single-crystal nanobelt and its photoelectric properties

High qualityβ-Ga_(2)O_(3)single crystal nanobelts with length of 2−3 mm and width from tens of microns to 132μm were synthesized by carbothermal reduction method.Based on the grown nanobelt with the length of 600μm,the dual-Schottky-junctions coupling device(DSCD)was fabricated.Due to the electrically floating Ga_(2)O_(3)nanobelt region coupling with the double Schottky-junctions,the current I_(S2)increases firstly and rapidly reaches into saturation as increase the voltage V_(S2).The saturation current is about 10 pA,which is two orders of magnitude lower than that of a single Schottky-junction.In the case of solar-blind ultraviolet(UV)light irradiation,the photogenerated electrons further aggravate the coupling physical mechanism in device.I_(S2)increases as the intensity of UV light increases.Under the UV light of 1820μW/cm^(2),I_(S2)quickly enters the saturation state.At V_(S2)=10 V,photo-to-dark current ratio(PDCR)of the device reaches more than 104,the external quantum efficiency(EQE)is 1.6×10^(3)%,and the detectivity(D*)is 7.5×10^(12)Jones.In addition,the device has a very short rise and decay times of 25−54 ms under different positive and negative bias.DSCD shows unique electrical and optical control characteristics,which will open a new way for the application of nanobelt-based devices.

Investigation of β-Ga_(2)O_(3) thick films grown on c-plane sapphire via carbothermal reduction

We investigated the influence of the growth temperature, O_(2) flow, molar ratio between Ga_(2)O_(3) powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire(0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga_(2)O_(3) illustrate that β-Ga_(2)O_(3) growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga_(2)O_(3) films was produced when the O_(2) flow was 20 sccm. To guarantee that β-Ga_(2)O_(3) films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga_(2)O_(3) powder should be set at 10 : 1.

Recent Progress on Fabrication of Thermal Conductive Aluminum Nitride Fibers

Among nitride fibers,aluminum nitride(AlN)fibers have been developed for various advanced applications due to their mechanical flexibility,high thermal conductivity,and excellent electrical insulation and chemical stability.This article presents an overview on the recent progress of AlN fibers.The properties of AlN,particularly the thermal conductivity of AlN in polymer matrix composites are introduced.Afterward,two major approaches,carbothermal reduction and nitriding polycrystalline alumina fiber,for the preparation of AlN fibers are discussed.The carbothermal reduction includes electrospinning,solution blow spinning,and chemical vapor deposition.Furthermore,some perspectives on the future directions for the preparation and application of fibrous AlN are highlighted.This review is expected to provide readers with valuable guidance on the preparation of AlN fibers and inspire researchers to explore more potential applications.

Preparation of ZrB_(2)-ZrO_(2)-SiC Composite Powder by Carbothermal Reduction from Zircon

Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.