添加剂Na2CO3对钛精矿碳热还原的影响

研究添加不同含量的Na2CO3对钛精矿强化还原机理和动力学的影响,以不同的升温速率进行还原过程,并采用Starink方法研究其动力学.结果表明:Na2CO3的加入强化还原效果,并通过以反应物的形式增加其活性来降低还原反应的初始温度和表观活化能;然而,Na2CO3的加入会形成熔融相恶化还原后期的动力学条件,从而降低还原后...     

Effect of additives on growth of ferronickel grains and metal–slag separation behavior

Na₂S, Na₂CO₃, FeO, FeS and carbon were used to regulate the properties of slag or metal fractions, and their effects on metal growth and metal–slag separation behavior were investigated. The growth of ferronickel grains can be enhanced by adding these additives, and Na₂S was the most effective. Na₂S, Na₂CO₃ and FeO mainly affected the properties of slag, while carbon and FeS affected the metal fraction. The onset temperature of metal–slag separation was 1297 °C for the sample without additive, which was decreased to 1123 and 1101 °C after adding 3.30 wt.% Na₂S and 4.47 wt.% Na₂CO₃, respectively. The onset temperature of metal–slag separation was mainly controlled by the slag fraction. The average apparent activation energy of metal grain growth was 125.32 kJ/mol without additive, and it decreased obviously after adding different additives. Na₂S also had the most remarkable effect on the decrease in activation energy.     

Study of Reaction Mechanisms for Copper-Cobalt-Iron Sulfide Concentrates in the Presence of Lime and Carbon

The reaction mechanisms for the carbothermic reduction of complex mineral sulfide concentrates in the presence of lime were studied between 1073 K and 1323 K. The reaction mechanisms were studied by stopping the reduction experiments at different times and analyzing the reaction products by x-ray diffraction and scanning electron microscopy techniques. Magnetite (Fe₃O₄) and digenite (Cu_1.8S) were the initial phases formed during reduction of CuFeS₂ and Cu₅FeS₄ mineral particles, such that metallization of iron occurred before copper above 1173 K and at an equal stoichiometric ratio of CaO and C. The metallization of iron was found to take place via reduction of intermediate oxide phase (Fe₃O₄/FeO), whereas metallization of copper occurred via diffusion of S^2? ions away from the mineral particles or via formation of Cu-O-S liquid phase. Metallic iron and cobalt were embedded in the copper matrix due to a preferential reduction of iron and cobalt from the Cu-Fe-S and Cu-Co-S type of mineral particles. The effects of CaO/C ratio were analyzed and the rate of reactions was increasing with an increase in the CaO/C ratio. The formation of liquid phase has been discussed. The experimental results were found to be in good agreement with the thermodynamic predictions.     

Synthesis of TiO<Subscript>2</Subscript> Nanoparticles from Ilmenite Through the Mechanism of Vapor-Phase Reaction Process by Thermal Plasma Technology

Synthesis of nanoparticles of TiO₂ was carried out by non-transferred arc thermal plasma reactor using ilmenite as the precursor material. The powder ilmenite was vaporized at high temperature in plasma flame and converted to a gaseous state of ions in the metastable phase. On cooling, chamber condensation process takes place on recombination of ions for the formation of nanoparticles. The top-to-bottom approach induces the disintegration of complex ilmenite phases into simpler compounds of iron oxide and titanium dioxide phases. The vapor-phase reaction mechanism was carried out in thermal plasma zone for the synthesis of nanoparticles from ilmenite compound in a plasma reactor. The easy separation of iron particles from TiO₂ was taken place in the plasma chamber with deposition of light TiO₂ particles at the top of the cooling chamber and iron particles at the bottom. The dissociation and combination process of mechanism and synthesis are studied briefly in this article. The product TiO₂ nanoparticle shows the purity with a major phase of rutile content. TiO₂ nanoparticles produced in vapor-phase reaction process shows more photo-induced capacity.     

Mechano-thermal reduction of molybdenite (MoS2) in the presence of Sulfur scavenger: New method for production of molybdenum carbide

In this research, carbothermic reduction of molybdenite in the presence of sodium carbonate as sulfur scavenger by mechanical activation and heat treatment was studied. Mechanical activation of the mixed powders of molybdenite, graphite and sodium carbonate with 1:4:2 mol ratios were carried out by ball milling process under argon atmosphere for 10,20,40,50 and 70 h. The X-ray diffraction (XRD) patterns of samples revealed that no reaction occurred in the mill even after 70 h of milling. In order to study the mechanism of carbothermic reduction of molybdenite in the presence of sodium carbonate, simultaneous thermal analysis (STA) under heating rate of 10, 15 and 20 °C/min was carried out on the activated samples. XRD patterns and thermodynamic analysis of reaction products indicated that carbothermic reduction of molybdenite in the presence of sodium carbonate was advanced through the formation of intermediate phases Na₂MoO₄, MoO₂ in which the final products were Mo₂C, Na₂S. For separation of these two products, leaching by HCl and hot water was used. The XRD patterns of leached products were shown that molybdenum carbide with high purity was produced. The kinetics of reduction reaction was investigated and it was found that mechanical activation lowered the reaction temperature and activation energy.     

Preparation of titanium mineral from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching

Titanium mineral was prepared from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching. The leaching behaviors of elements like Fe, V, Mn, Al, Mg, Ca, and Si were highly related to the reduction degree. The phase compositions of the reduced materials and the leached residues were analyzed by XRD to identify the effect of reduction degree on the leaching mechanisms. The results showed that the concentrates were reduced to iron metal and titanomagnetite at 800?1000 °C for 0.5 h, and the above elements of Fe and impurities were easily leached. Deeper reduction led to the formation of ilmenite and Mg?Al spinel, which hindered leaching. Mg-bearing anosovite appeared in the further reduced materials, and the leaching rates of impurities became much lower. An upgraded titanium mineral with a normalized TiO₂ grade of 70.3% was achieved by H₂ reduction at 850 °C for 0.5 h and acid leaching, which is a satisfactory Ti resource for the preparation of titanium oxide by sulfate process.     

The effect of Fe2Al5 as reducing agent in intermediate steps of 'Al2O3/TiC-Fe composite production process

Al₂O₃/TiC-Fe cutting tools can be produced in-situ by using ilmenite, aluminum and graphite. The formation mechanism of the system was investigated in some researches. Most of them have diagnosed the aluminum as reducing agent of TiO₂, but in this study, it is proven that Fe₂Al₅ acts as the reducing agent for TiO₂ in the intermediate steps of the reactions. To achieve this goal, firstly, the reactions of synthesized ilmenite, aluminum and graphite system were investigated in detail. Then, pure Fe₂Al₅ was synthesized, and mixed with definite amount of TiO₂. The sample mixture was heat treated at the same temperature at the real reaction temperature, namely, 930 °C. The final products were analyzed with XRD. It was found that the product heat treatment of F₂Al₅ and TiO₂ mixture was the same as the sample of ilmenite, aluminum and graphite mixture with a molar ratio of 1:2:1 heat treated at 930 °C.     

Reduction roasting–magnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90 wt% and TiO_2 content of 17.40 wt%. The results show that after reduction roasting–magnetic separation with sodium sulfate dosage of 2 wt% at roasting temperature of 1150 °C for roasting time of 120 min, metallic iron concentrate with total iron grade of 90.20 wt%, iron recovery rate of 97.56 % and TiO_2 content of 4.85 wt% is obtained and high-titanium slag with TiO_2 content of 57.31 wt% and TiO_2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy(SEM) and X-ray diffraction(XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO_2 content is obtained.     

Effects of MgO on the Reduction of Vanadium Titanomagnetite Concentrates with Char

The effects of MgO on the carbothermic reduction behavior of vanadium titanomagnetite concentrates (VTC) from Chengde, China, were investigated via temperature-programmed heating under nitrogen atmosphere in a sealed furnace. Gaseous product content was measured by using an infrared gas analyzer, and it was found that the addition of MgO to VTC with char decreased the reduction rate and reduction degree, and the utilization of CO in VTC reduction was also reduced. X-ray diffraction results showed that magnesium titanate (Mg₂TiO₄) was formed but FeTi₂O₅ was not observed in the VTC reduction process by adding 6 wt.% MgO, which can be explained by thermodynamic analysis. Scanning electron microscopy revealed that the enrichment of Mg in the unreacted core was the main reason that the further reduction of VTC was restricted. However, comparatively pure particles of Mg₂TiO₄ were generated, and the titanium and iron were separated well due to the combination of magnesium and titanium.     

Effect of microwave radiation and mechanical activation on the Carbothermic reduction of molybdenum trioxide: Improving the practical efficiency

In this research two different paths were used to cabothermic reduction of MoO₃. In the first and second path, as received MoO₃ and graphite with stoichiometric ratios were mixed and mechanically activated at 5, 10, 15 and 24 h and heating by microwave oven (first path) and furnace at 700 and 1000 °C in second path. The XRD results of activated samples before heating showed that, MoO₂ was produced in the planetary ball mill after 5 h milling and don't change to another phase during milling up to 24 h. the SEM and XRD results in first and second path showed that the final product was molybdenum carbide but in the non-activated samples the final products were molybdenum carbide and unreacted MoO₂. The practical efficiency calculations in first and second method showed that heating of samples by microwave radiation and mechanical activation increase the practical efficiency and decrease the sublimation of molybdenum trioxide. The TGA analysis of non-activated MoO₃+ C mixture indicated that the reduction goes with three steps but in the 24 h activated sample, it was seen that the reduction goes with one peak. In other words, the first and second peaks in non-activated sample were not detected in the activated sample that increases the practical efficiency due to prevent the sublimation of MoO₃     

Microwave irradiation effects on reversible hydrogen desorption in sodium aluminum hydrides (NaAlH4)

The effect of microwave irradiation on the reversible desorption reaction in sodium aluminum hydride (NaAlH₄) is explored. NaAlH₄ is doped with 2 mol% TiCl₂ and pre-activated by high energy ball milling and aging to show the presence of metallic aluminum phase. As a catalyst, Ti²⁺ has been used to improve desorption kinetics in sodium alanate. X-ray diffraction was performed on the samples exposed to microwave irradiation for 10, 20, 30, 40 and 50 min. Results show that when the powders show the presence of aluminum, a steady increase in the formation of the hexahydride (Na₃AlH₆) phase and Al occurs during microwave irradiation; and is accompanied by a steady reduction in the NaAlH₄ phase XRD peak (h k l) intensities. This data suggests that microwave irradiation drives the reversible H₂ desorption reaction in NaAlH₄. NaAlH₄ doped with 2 mol% TiCl₂ which does not show the presence of Al phase, undergoes a reduction in NaAlH₄ peak intensities with increasing microwave exposure (and no reversible product phases are detected in this case). Dielectric studies on NaAlH₄ indicate that microwave penetration is low. Therefore, it is proposed that microwave irradiation heating of the Al particulate phase is responsible for the hydrogen desorption reaction pathway which is similar to that of conventional heating.     

Rapid anodic oxidation of highly ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays prepared by anodic oxidation have attracted increasing research interests due to their promising applications in many scientific areas. To the best of our knowledge, a factor limiting the application of TiO₂ nanotube arrays was their long sustaining reaction time by anodic oxidation, usually lasting 6-12 h and even longer when synthesizing thicker nanotubular layers. In the present paper, we reported for the first time a facile but effective approach to accelerate the anodic formation of TiO₂ nanotube arrays by proper addition of sodium carbonate (Na₂CO₃) into the anodization electrolyte. We adopted the 0.3 M NH₄F + 0.03 M Na₂CO₃ + EG (ethylene glycol) + 3.0 vol.% H₂O electrolyte and the average growth rate of the nanotubes achieved in our experiments could be accelerated to 1100 nm/min. The possible mechanism of the rapid electrochemical process was also presented.     

Upgrading ilmenite into a high-grade synthetic rutile

Titanium, the ninth most abundant element, occurs mainly in minable form as ilmenite (95%) and rutile (5%) minerals. The current world consumption of these minerals is used mainly to produce titanium dioxide pigments, with the balance in welding rod flux and titanium metal. Ilmenite is currently being mined in annual quantities eight times larger than rutile. In the past 35 years, an increasing percentage of the pigments have been produced via the chloride method, which requires rutile. This has caused the need to produce a synthetic rutile of more than 90% TiO₂ content and large amounts of an 85% TiO₂ slag from ilmenite. The direct chlorination of 61% TiO₂ ilmenite is being done on a large scale in the United States.     

In situ composite coating of titania-hydroxyapatite on commercially pure titanium by microwave processing

Microwave (MW) processing has been studied as an alternative method of hydroxyapatite (HA) based composite coatings on commercially pure titanium (CPTi) to enhance the bioactivity for orthopaedic and dental implant applications. The coating was formed by processing CPTi metal packed in HA and at 800 W microwave power for 22 min. The composition of the coating was found to be TiO₂ (rutile) as major phase along with HA as minor phase. The MW absorption of non-stoichiometric TiO₂ layer, which was grown during the initial hybrid heating, resulted in sintering of apatite particles interfacing them. The non-stoichiometric nature of TiO₂ was evident from the observed mid-gap bands in ultraviolet-visible diffusive reflectance (UV-VIS-DR) spectrum. The lamellar α structure of the substrate suggests that the processing temperature was above β transus of CPTi (1155 K). The oxygen stabilized α phase whose thickness increased with microwave processing time, was likely to be the reason for the increase in Young's Modulus and hardness of the substrate. The coating induced apatite precipitation in bioactivity test. The osteoblast cell adhesion test demonstrated cell spreading which is considered favourable for cell proliferation and differentiation. Thus, in situ composite coating of titania and HA on CPTi was obtained by a simple one-step process.     

Hot-Corrosion Behavior of TiAl-Base Intermetallics in Molten Salts

The hot-corrosion behavior of Ti-50Al,Ti-48Al-2Cr-2Nb, and Ti-50Al10Cr alloys was investigatedin (Na, K)₂SO₄ andNa₂SO₄ + NaCl melts. TiAlintermetallics showed much better hot-corrosionresistance in (Na, K)₂SO₄ at900°C than the Ni-base superalloy K38G. Two types ofcorrosion products formed on Ti-50Al: some areas werecovered with a continuous Al2O3 scale, whereas otherareas formed a mixed Al₂O₃ +TiO₂ scale; TiS existed at the scale-alloyinterface. A mixed Al₂O₃ +TiO₂ scale formed on Ti-48Al-2Cr 2Nb, and nosulfide was found beneath the scale. An adherentAl₂O₃ scale, however, formed onTi-50Al-10Cr, which provided excellent hot-corrosionresistance. All three alloys suffered severe hotcorrosion in Na₂SO₄ + NaCl meltsat 850°C. A mixed Al₂O₃ +TiO₂ scale formed on all three alloys andmany voids and pits existed in the scale-alloy interface. Thehot-corrosion mechanisms are discussed.     

Formation behavior of CaTiO<Subscript>3</Subscript> during electrochemical deoxidation of ilmenite concentrate to prepare Fe–Ti alloy

The formation behavior of CaTiO₃ during electro-deoxidization of ilmenite concentrate to prepare Fe–Ti alloy was investigated by experiments and simulation. The results indicate that the formation and decomposition of intermediate products, CaTiO₃, are inevitable steps during electro-deoxidization of ilmenite concentrate. CaTiO₃ can be generated through the hydrolyzation of molten salt and electrochemistry reaction during electrochemical process. The main reason for the generation of CaTiO₃ is the electrochemistry reaction between Ca²⁺ from molten salt and TiO₂ in the cathode. With the proceeding of the electro-deoxidization, CaTiO₃ is further electrolyzed to form titanium sub-oxide. The current efficiency can be improved when CaTiO₃ forms in the cathode by adding CaCO₃ during sintering process.     

A New Technique for Preparation of High-Grade Titanium Slag from Titanomagnetite Concentrate by Reduction–Melting–Magnetic Separation Processing

This paper proposes a new technique for preparation of high-grade titanium slag from Panzhihua vanadium titanomagnetite concentrate by reduction–melting–magnetic separation processing. Chemical analysis, x-ray diffraction, and scanning electron microscopy in conjunction with energy-dispersive spectroscopy were used to characterize the samples. The effective separation of iron and titanium slag could be realized by melting metallized pellets at 1550°C for 60 min with the addition of 1% CaO (basicity of 1.1) and 2% graphite powder. The small iron particles embedded in the slag could be removed by fine grinding and magnetic separation process. The grade of TiO₂ in the obtained high-grade titanium slag reached 60.68% and the total recovery of TiO₂ was 91.25%, which could be directly applied for producing titanium white by the sulfuric acid process. This technique provides an alternative method to use vanadium titanomagnetite concentrate of the Panzhihua area in China.     

钒渣提钒和铬循环冶金工艺:(II)沉钒后液分离回收铬

研究通过用PbCO3沉淀并用Na2CO3溶液浸出从钒沉淀溶液中分离和回收铬的循环冶金工艺.沉钒后液pH调至3.0后,按Pb/Cr摩尔比2.5加入PbCO3,在30℃搅拌180 min,铬浓度从2.360 g/L降到0.001 g/L.过滤后,沉铬富集渣用热Na2CO3溶液浸出得到含有Na2CrO4的浸出液和含有PbCO...     

Surface modification of ilmenite and its accompanied gangue minerals by thermal pretreatment: Application in flotation process

The effect of conventional thermal pretreatment on the surface properties of ilmenite and its accompanied gangue minerals was investigated using flotation experiments (microflotation and laboratory cell flotation), XRD, XPS and FT-IR analysis and zeta potential and contact angle measurements. After treatment at 600 °C for 25 min as optimal condition, the floatability of ilmenite is improved from 73.5% to 91% at a pH value of 6.3. As demonstrated by XRD and XPS analysis, under this pretreatment condition, the Fe³⁺ content increases by almost 16.5% without any phase decomposition and structural changes in ilmenite. FT-IR analysis and contact angle and zeta potential measurements give evidences that the improvement of ilmenite floatability can be related to the enhancement of collector adsorption and the formation of a more insoluble hydrophobic layer of ferric iron oleate. The ore flotation experiments show that the thermal pretreatment process without making a significant change in TiO₂ content of ilmenite concentrate enhances the TiO₂ recovery from 65.4% to 73.7%.     

Effects of R2CO3 (R = Li,Na and K) on the reduction of MoO2 to Mo by hydrogen

In the present work, the influence of different factors (additives and temperatures) on the morphologies and sizes of as-prepared metal Mo powders by the hydrogen reduction of MoO₂ in the temperature range of 1053 K to 1353 K are investigated. When pure MoO₂ powders are reduced, the morphologies and sizes of as-prepared metal Mo powders are nearly kept the same as the raw materials. However, it is found that adding a small amount of additives (Li₂CO₃, Na₂CO₃ and K₂CO₃) into MoO₂ has a great influence on that of prepared metal Mo powders. The particles become uniformed, ultrafine and spherical powders. In addition, the particles size of the as-prepared metal Mo powders will become larger as the increase of reaction temperature due to the grains growth. This work provides a new method for the preparation of uniformed, ultrafine and spherical metal Mo powders.