Weijing Wang

An extraction process to recover vanadium from low-grade vanadium-bearing titanomagnetite

An extraction process to recover vanadium from low-grade vanadium-bearing titanomagnetite was developed. In this study, a mixed solvent system of di(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP) diluted with kerosene was used for the selective extraction of vanadium from a hydrochloric acid leaching solution that contained low vanadium concentration with high concentrations of iron and impurities of Ca, Mg, and Al. In the extraction process, the initial solution pH and the phase ratio had considerable functions in the extraction of vanadium from the hydrochloric acid leaching solution. Under optimal extraction conditions (i.e., 30-40°C for 10min, 1:3 phase ratio (O/A), 20% D2EHPA concentration (v/v), and 0-0.8 initial solution pH), 99.4% vanadium and only 4.2% iron were extracted by the three-stage counter-current extraction process. In the stripping process with H2SO4 as the stripping agent and under optimal stripping conditions (i.e., 20% H2SO4 concentration, 5:1 phase ratio (O/A), 20min stripping time, and 40°C stripping temperature), 99.6% vanadium and only 5.4% iron were stripped by the three-stage counter-current stripping process. The stripping solution contained 40.16g/LV2O5,0.691g/L Fe, 0.007g/L TiO2, 0.006g/L SiO2 and 0.247g/L CaO. A V2O5 product with a purity of 99.12% V2O5 and only 0.026% Fe was obtained after the oxidation, precipitation, and calcination processes. The total vanadium recovered from the hydrochloric acid leaching solution was 85.5%.

The study of thermal stability during wet oxidation of AlAs

A structure in which a 1000 Angstrom thick AlAs layer is sandwiched between 1000 Angstrom thick GaAs cap layer and 2000 A GaAs buffer layer was subsequently grown by molecular beam epitaxy on the GaAs substrate. The AlAs layer was laterally oxidized in N-2 bubbled H2O vapor ambient at 400 degreesC for 20, 30, 40, 60, and 120 min. It was found that the thermal stability of the mesas is very dependent on the removal rate of volatile products, such as As and As2O3. The removal of volatile products is dependent on the oxidation time and temperature. The Raman spectra presented here proved that the spectra were different from samples, oxidized for different time durations

Evolution from point defects to arsenic clusters in low-temperature grown GaAs/AlGaAs multiple quantum wells

Optical transient current spectroscopy (OTCS), photoluminescence (PL) spectroscopy and excitonic electroabsorption spectroscopy have been used to investigate the evolution of defects in the low-temperature grown GaAs/AlGaAs multiple quantum well structures during the postgrowth rapid thermal annealing. The sample was grown at 350 degrees C by molecular beam epitaxy on miscut (3.4 degrees off (001) towards (111)A) (001) GaAs substrate. After growth, the sample was subjected to 30s rapid thermal annealing in the range of 500-800 degrees C. It is found that the integrated PL intensity first decreases with the annealing temperature, then gets a minimum at 600 degrees C and finally recovers at higher temperatures. OTCS measurement shows that besides As,, antisites and arsenic clusters, there are several relatively shallower deep levels with excitation energies less than 0.3 eV in the as-grown and 500 degrees C-annealed samples. Above 600 degrees C, OTCS signals from As,, antisites and shallower deep levels become weaker, indicating the decrease of these defects. It is argued that the excess arsenic atoms group together to form arsenic clusters during annealing

Preparation of rutile TiO2 by hydrolysis of TiOCl2 solution: experiment and theory

Titanium slag with a perovskite phase (CaTiO3) is difficult to use in traditional titanium dioxide production. Herein, we demonstrate that HCl can decompose CaTiO3 with a high acidolysis ratio of >97 wt% to obtain a TiOCl2 solution. With subsequent hydrolysis and calcination, rutile TiO2 was synthesised in one step without crystalline-structure transformation. As hydrolysis of the TiOCl2 solution to prepare metatitanic acid (H2TiO3) is an essential step in the process, a simulated pure TiOCl2 solution (prepared from TiCl4 and H2O) was confirmed to have the same structure in water as HCl-treated CaTiO3 slag by Raman spectroscopy. The TiOCl2 solution was also concluded to have the Ti compound cluster of (Ti2O2)(H2O)4Cl4, based on DFT calculations from the Raman data and the curve fit for the hydrolysis ratio. By elucidating the relationship between the H2TiO3 particle size and the concentration of Ti4+ and HCl, we identified the nuclear energy as -19.46 kJ mol−1. Moreover, a complete scheme for the production of rutile TiO2, induced by TiOCl2 solution hydrolysis, was proposed. Periodic structures show the feasibility of the following transformation occurring through a simple structural rearrangement: (Ti2O2)(H2O)4Cl4 (in solution)–Ti(OH)(H2O)2Cl3 (with addition of HCl)–Ti(OH)2Cl2 (1-dimentional growth and removal of HCl)–rutile-type Ti(OH)2Cl2 (stack)–rutile TiO2 (with removal of HCl).

A novel process for the recovery of iron, titanium, and vanadium from vanadium-bearing titanomagnetite: sodium modification–direct reduction coupled process

A sodium modification–direct reduction coupled process was proposed for the simultaneous extraction of V and Fe from vanadium- bearing titanomagnetite. The sodium oxidation of vanadium oxides to water-soluble sodium vanadate and the transformation of iron oxides to metallic iron were accomplished in a single-step high-temperature process. The increase in roasting temperature favors the reduction of iron oxides but disfavors the oxidation of vanadium oxides. The recoveries of vanadium, iron, and titanium reached 84.52%, 89.37%, and 95.59%, respectively. Moreover, the acid decomposition efficiency of titanium slag reached 96.45%. Compared with traditional processes, the novel process provides several advantages, including a shorter flow, a lower energy consumption, and a higher utilization efficiency of vanadium-bearing titanomagnetite resources.

Structures, formation mechanisms, and ion-exchange properties of α-, β-, and γ-Na2TiO3

α-, β-, and γ-Na2TiO3 were prepared from rutile TiO2 and molten NaOH. Three models of β-Na2TiO3 with space groups of R, P, and P were proposed, and the R model was refined from the experimental data by using the Rietveld method. The structure of β-Na2TiO3 is a superstructure of α-Na2TiO3 and supposedly contains Ti6O19 clusters. The structures of Na2TiO3 were mainly determined by the particle sizes of rutile and the reaction temperatures. α-Na2TiO3 could be prepared from fine rutile particles (D(50) < 25.8 μm) and molten NaOH at 500 °C or quenching the melt of Na2TiO3 at 1000 °C quickly. γ- and β-Na2TiO3 were the thermodynamically stable phases of Na2TiO3 at around 500 °C and above 800 °C, respectively. α-Na2TiO3 was formed far beyond the thermodynamically stable state. The Na+ in α-Na2TiO3 was easier to exchange with H+ in water than that in β or γ phases. They all converted to amorphous phases after the 2nd, 6th, and 4th water washings at 25 °C, respectively. β-Na2TiO3 followed similar paths of ion-exchange as α-Na2TiO3, which was different from that of γ-Na2TiO3.

Strong room-temperature exciton-photon coupling in low-finesse microcavities grown by molecular-beam epitaxy

Room-temperature strong exciton-photon coupling phenomena was studied in a low-finesse quantum microcavity entirely filled with 17.5 pairs of GaAs (80 Angstrom )Al0.3Ga0.7As (42 Angstrom) quantum wells. The front and back distributed Bragg reflectors of the microcavity consist of only 6 and 8 pairs of lambda /4 stacks of GaAs (30 Angstrom)/AlAs (5 Angstrom) superlattices and AlAs layers. And the lambda /4 GaAs (30 Angstrom)/AlAs (5 Angstrom) superlattices are equal to the Al0.2Ga0.8As layer in thc distributed Bragg reflector. Large Rabi splitting of 9.4meV was observed at resonance with heavy-hole excitons at room temperature. Photoluminescence spectra show cd a transition from linear regime to high carrier density nonlinear regime due to loss of oscillator strength and collapse of the coupling at high excitation intensity

A method for recovery of iron, titanium, and vanadium from vanadium-bearing titanomagnetite

An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures: low-temperature roasting of vanadium-bearing titanomagnetite and water leaching of roasting slag. During the roasting process, the reduction of iron oxides to metallic iron, the sodium oxidation of vanadium oxides to water-soluble sodium vanadate, and the smelting separation of metallic iron and slag were accomplished simultaneously. Optimal roasting conditions for iron/slag separation were achieved with a mixture thickness of 42.5 mm, a roasting temperature of 1200°C, a residence time of 2 h, a molar ratio of C/O of 1.7, and a sodium carbonate addition of 70wt%, as well as with the use of anthracite as a reductant. Under the optimal conditions, 93.67% iron from the raw ore was recovered in the form of iron nugget with 95.44% iron grade. After a water leaching process, 85.61% of the vanadium from the roasting slag was leached, confirming the sodium oxidation of most of the vanadium oxides to water-soluble sodium vanadate during the roasting process. The total recoveries of iron, vanadium, and titanium were 93.67%, 72.68%, and 99.72%, respectively.

Influence of magnesium and aluminum salts on hydrolysis of titanyl sulfate solution

The influence of magnesium and aluminum salts as impurities on the hydrolysis of titanyl sulfate was investigated. The degree of TiOSO4 conversion to hydrated titanium dioxide (HTD) and the particle size of HTD were measured as functions of the concentrations of MgSO4 and Al-2(SO4)(3) in the TiOSO4 solution. The Boltzmann growth model, which focuses on two main parameters, namely the concentrations of Mg2+ and Al3+ (rho(Mg2+) and rho(Al3+), respectively), fits the data from the hydrolysis process well with R-2>0.988. The samples were characterized by ICP, SEM, XRD, and laser particle size analyzer. It is found that the addition of MgSO4 simultaneously improves the hydrolysis ratio and the hydrolysis rate, especially when F (the mass ratio of H2SO4 to TiO2) is high, hydrolysis ratio increases from 42.8% to 83.0%, whereas the addition of Al-2(SO4)(3) has negligible effect on the chemical kinetics of HTD precipitation during the hydrolysis process, hydrolysis ratio increases from 42.8% to 51.9%. An investigation on the particle size of HTD reveals that the addition of MgSO4 and Al-2(SO4)(3) clearly increases the size of the crystallites and decreases the size of the aggregates.