Co-recovery of iron,chromium, and vanadium from vanadium tailings by semi-molten reduction–magnetic separation process

A co-recovery process used to extract iron, chromium, and vanadium in the form of chromium–vanadium-bearing metallic iron from vanadium tailings via a semi-molten reduction-magnetic separation method was investigated. The effects of the reductant (carbon) dosage, temperature, and time on the recovery rates of iron, chromium, and vanadium were studied. The phase compositions, microstructures, and micro-constitutions of the reduced samples, products, and byproducts were analysed using X-ray powder diffraction, SEM and EDS. As the reduction temperature increased, the recovery of iron, chromium, and vanadium improved. When the carbon dosage was increased from 8 to 11%, the recovery enhanced; however, the recovery deteriorated with carbon dosage of over 11%. Under optimum conditions, two products were obtained, namely a primary product consisting of chromium–vanadium-bearing metallic iron, where the recovery rates of iron, chromium, and vanadium were over 98, 82, and 65%, respectively, and a byproduct consisting of titanium-bearing slag, where the titanium yield was approximately 68%. The co-recovery process exerts a significant influence on the recovery of valuable metals and the minimisation of hazardous materials for clean utilisation of vanadium tailings.     

Slag–graphite wettability and reaction kinetics Part 2 Wettability influenced by reduction kinetics

Abstract

The present paper reports results of experimental investigations into the wettability of graphite by molten slag containing FeO. The wettability was determined by measurement of the graphite–slag contact angle. A higher initial FeO content in the slag phase and higher temperature lead to better wettability of graphite owing to the chemical reaction between the molten FeO in the slag and the graphite surface. The presence of FeO also reduces the surface tension of the slag. The free energy of reaction released per unit area ΔG _r has been estimated and correlated with the wettability parameters. The overall contribution of this factor to lowering the interfacial tension has also been examined.     

The effects of MgO and Al2O3 behaviours on softening–melting properties of high basicity sinter

Because the behaviours of MgO and Al₂O₃ during slag formation of high basicity sinter are not clearly understood, the effects of MgO and Al₂O₃ on softening-melting properties are always arguable. In this paper, four kinds of sinter containing different MgO and Al₂O₃ content are investigated. Some observations are obtained. The mechanism of the influence of MgO and Al₂O₃ on softening properties of sinter are different. Al₂O₃ has priority over MgO to enter into slag phase and forms low-melting point phase while MgO remains unslagged state and mainly exists in wustite as FeO–MgO solid solution. When sinter melts, the viscosity of the slag generated from sinter containing high MgO and Al₂O₃ content is low, which could result in low pressure drop. As MgO and Al₂O₃ content increase, the main minerals of residual slag change from 2CaO?SiO₂ to merwinte and melilite. The changes of the minerals in slag phase can well explain the trend of softening-melting characteristic temperatures.     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.     

“Ridge effect” in oxidation kinetics of hetero-modulus ceramics based on titanium carbide

Recent studies on oxidation kinetics of the TiC-7 vol.% C (graphite) hetero-modulus ceramics at temperatures of 400–1000 °C and oxygen pressures of 0.13–65 kPa have led to the discovery of a temperature-pressure-dependent phenomenon called “ridge effect”. The oxidation rate of the composite rises rapidly to a maximum at ridge values of oxygen pressure or temperature (T), but then it declines with subsequent growth of oxidation parameters. The ridge values mark a change in the prevailing mechanism, as while the ridge parameter traversing the values of apparent activation energy Q or order of reaction m change its sign. The oxidation mechanisms, essentially different within the ranges of parameters, are identified according to the developed ridge-effect model, which can be applied probably to a variety of systems with inorganic compounds. Published in Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 179–195, 2008.     

Processing and properties of sinter hardened Fe–Cr–Mo steels with admixed extra-fine nickel

Abstract

The processing and properties of chromium–molybdenum, powder metallurgy steels with admixed extra-fine nickel (XF Ni) were investigated. Prealloyed Fe–1·5Cr–0·2Mo powder was blended with different quantities of XF Ni, while a hybrid steel with lower Cr content was prepared by blending Fe–1·5Cr–0·2Mo and Fe–0·5Mo prealloyed powders, with additions of XF Ni and copper powders. These steels were compacted into different part shapes in order to evaluate the effect of part thickness on sinterhardening behaviour. These parts were also subjected to different cooling rates after sintering. This study showed that additions of XF Ni improve the compressibility, densification behaviour and mechanical properties of Cr–Mo steels. Furthermore, the properties of the hybrid steel were shown to be either equal to or greater than those of the reference material. Hardenability of all steels was sufficiently high such that part thickness was seen to have negligible impact. Higher cooling rates generally resulted in improved mechanical properties.     

Influence of titanium microalloying on the properties of low-alloy Cr–Mo–V steel

The influence of titanium, which readily forms nitrides, on the structure and the long- and short-term mechanical properties of Cr–Mo–V steel is investigated. Increase in the Ti content to 0.075% increases the thermal stability of the steel. With increase in Ti content to 0.13%, the thermal stability of the steel declines sharply, on account of structural changes.     

A study on precipitation kinetics of sigma phase in a hot-rolled super duplex stainless steel during isothermal aging based on the Johnson–Mehl–Avrami model

Isothermal aging treatment of 2507 super duplex stainless steel (SDSS2507) was conducted at 850°C after solution treatment at 1150°C. The characteristics of sigma (σ) precipitation kinetics in SDSS2507 were discussed and an improved JMA (Johnson–Mehl–Avrami) model had been developed. The results show that, the precipitation mechanism of σ phase in hot-rolled SDSS2507 was quite different to other ordinary DSSs. It can be found that σ phase precipitated via two mechanisms in this experiment. (1) The eutectoid decomposition δ?→?σ?+?γ₂. It dominated the precipitation kinetics of σ phase in aging 0–25?min, and at this time the volume fraction of σ phase increased rapidly. (2) After 25?min, the precipitation of σ phase absolutely relied on the transformation of γ?→?σ which is controlled by the diffusion of Mo and Ni in γ. In this period, the precipitation rate of σ phase was significantly decreased. In this case, the separate modeling on the basis of each transformation mechanism was adopted and then an improved JMA model was developed for the precipitation kinetics of σ phase in the whole aging process. As a result, a good agreement between the experimental data and this developed JMA model can be obtained.     

Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO₂) =–7.194; logK(TiO₂) =–6.125; logK(Ti₃O₅) =–16.793; logK(Ti₂O₃) =–10.224) to cobalt (logK(CoO · TiO₂) =–8.580; logK(TiO₅) =–7.625; logK(Ti₃O₅) =–20.073; logK(Ti₂O₃) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO₂, TiO₂, Ti₃O₅, and Ti₂O₃ are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO₂ ? TiO₂ decreases from 1.0 × 10^–4% Ti in iron to 1.9 × 10^–6% Ti in cobalt. The titanium content at the equilibrium point TiO₂?Ti₃O₅ increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti₃O₅ ? Ti₂O₃ decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.     

The incongruent dissolution of scorodite — Solubility,kinetics and mechanism

This work reports the results of a laboratory investigation on the long-term stability of crystalline scorodite conducted at fixed pH (5–9) and temperature (22 °C, 50 °C and 75 °C). The scorodite used in this work was prepared via a hydrothermal synthesis procedure. The dissolution of scorodite at 22 °C was found to be extremely slow. At neutral pH, the arsenic concentration stabilized after 24 weeks at 5.9 mg/L. Analysis of the solubility data as a function of temperature yielded a scorodite solubility model equation. The solubility product of scorodite was recalculated as 10^− 25.4 using the solubility data generated by the study and the geochemical code PHREEQC for solution modelling. As scorodite dissolved, the iron re-precipitated as 2-line ferrihydrite. The growth and re-crystallization of ferrihydrite was apparently retarded by arsenate adsorption. The dissolution rate of scorodite was modeled with a decreasing exponential equation. The initial rate approached first order dependency on OH⁻ concentration while the apparent activation energy suggested that scorodite dissolution is chemically controlled.     

Physical simulation study of the dynamic recrystallization kinetics of an Ni–Cu–Al alloy

The influence of temperature and deformation on the dynamic recrystallization kinetics of an Ni–30Cu–3Al heat-resistant alloy has been studied on the basis of experiments using a torsion plastometer. The process is simulated and mathematical model is proposed for estimating the dynamically recrystallized grain sizes. Good agreement between the calculated and experimental data is achieved.     

Diffusion mechanism of internal friction in a niobium–titanium alloy

An NT50 alloy of the composition Nb–(48.5 ± 1.5)% Ti is studied after severe plastic deformation and subsequent 100-h annealing. During heating at a rate of 2 K/min, the NT50 alloy subjected to this thermomechanical treatment demonstrates two internal friction peaks at 493 K and 573 K. As the heating rate increases by a factor of three, both peaks shift to higher temperatures and the peak height at 573 K increases. A diffusion mechanism of the temperature-dependent internal friction in the strongly deformed NT50 alloy is proposed. Using this mechanism, the effect of the heating rate on the internal friction in this alloy is explained as the volume titanium diffusion due to the diffusion growth of α-Ti precipitates in subgrains in the alloy. In this case, the first peak is related to the bulk diffusion that accompanies grain-boundary diffusion in subgrains, and the second peak, to usual bulk diffusion in subgrains.     

Numerical simulation and parameters optimization on gas–solid heat transfer process of high temperature sinter

Abstract

Based on the careful analysis of the heat transfer mechanism of the cooling process of high temperature sinter, a one-dimensional unsteady state mathematical model for the gas–solid heat transfer process of high temperature sinter was established according to the energy conservation. The mathematical model was verified by the use of industrial practical data, and the results showed that it was correct and reliable. Lastly, the model was used to investigate the effect of operation parameters (such as the trolley moving speed and the cooling air velocity) on the cooling process of the annular cooler, and the proposals were put forward for optimising operations of the annular cooler.     

The isothermal thickening of cementite allotriomorphs in a 1.5Cr1C steel

The kinetics of isothermal thickening of cementite allotriomorphs in a l%C1.5%Cr steel (AISI 52100) were investigated by quantitative metallographic measurements. Specimens from high phosphorus (0.023%) and low phosphorus (0.009%) heats were fully austenitized and then held at various temperatures between A₁ and A_cm for times up to 6 h. Thickening rates in the later stages were quite sluggish compared with those expected for carbon diffusion controlled processes in austenite. Growth effectively stopped far short of the expected equilibrium volume fractions of cementite. Auger ionsputtering analysis of the fracture surface of specimens isothermally treated to form grain boundary allotriomorphs of cementite showed carbon activities in austenite that were independent of the location in an austenite grain. Therefore, growth was controlled by a mechanism other than carbon diffusion. Structural observations made by transmission and scanning electron microscopy indicated that the carbide thickening occurred by lateral ledge migration on partially coherent interfaces between the cementite and the parent austenite. Cementite growth may proceed rapidly without Cr partitioning in the early stages, but the growth becomes sluggish in the later stages due possibly to Cr partitioning to and/or Si rejection from cementite.     

Preparation of Ti–Ni binary powder via electroless nickel plating of titanium powder

Abstract

In this study, Ti powder (average size: 45 μm) was plated/coated by electroless Ni with hydrazine hydrate as reductant. The Ni plating was carried out at 85°C and pH 9–10. The influence of process parameters such as plating period as well as reductant concentration was investigated. The Ni plated Ti powder was characterised by scanning electron microscopy, energy dispersive spectrometer analysis and X-ray fluorescence. It is found that a pure/uniform Ni layer may be deposited on the Ti powder particles. The deposited mass increases as plating period/reductant concentration increases.     

Regularities of the contact interaction of titanium carbide with Ni and Ni–Mo melts

Regularities of the dissolution, the phase formation, and the structure formation implemented under the contact interaction conditions of titanium carbide of various compositions with Ni and Ni–(5–25%)Mo melts are investigated. It is originally established that the dissolution of carbide TiC_x in nickel-based melts is incongruent. Preferentially, carbon transfers into the melt at x ≥ 0.9 and titanium at x ≤ 0.8. The limiting stage of the dissolution is diffusion of metal atoms in the liquid phase. The formation regularities of carbide Ti_1–nMo_nC_x (K-phase)—the main product of the contact interaction in the TiC/Ni–Mo system—are revealed. It is established that the K-phase is formed under the relative excess conditions of the Ni–Mo melt preferentially according to the dissolution–isolation mechanism. The composition of autonomous isolations of the K-phase depending on the experimental conditions (1450°C, 0–25 h) varies in limits from Ti_0.4Mo_0.6C_0.7 (a = 4.27 Å) to Ti_0.7Mo_0.3C_0.6 (a = 4.29 Å). It is determined by the molybdenum concentration in the melt at the unsteady dissolution stage and by the concentration ratio between titanium and carbon in it at the steady-state dissolution stage.     

Fine structure of interphase boundaries in hard alloys of the chromium carbide–titanium system

The structure of interphase boundaries in hard alloys fabricated by the explosive compacting of the powder mixtures of chromium carbide (Cr₃C₂) and titanium is investigated. It is established by electron microscopy that similar boundaries have thicknesses of about 100 nm, over the extension of which a smooth variation in chromium and titanium contents is observed at the almost identical carbon concentration. The boundary structure is nonuniform over the thickness, notably, a layer with a thickness of 5–7 nm and an amorphous structure is revealed between two crystalline interlayers. It is shown that the revealed layers are the layers of specific “boundary phases” not corresponding to any phase of the equilibrium phase diagram of the Cr–C–Ti system.