Qingyun Huang

Multistage utilization process for the gradient-recovery of V, Fe, and Ti from vanadium-bearing converter slag

A multistage utilization process was developed to fully recover valuable metals from vanadium-bearing converter slag and reduce the content of hazardous elements, such as vanadium and chromium, in the tailings. A mechanical activation-calcification roasting-acid leaching process was firstly employed to recover vanadium. This process generated two products, viz. a V-bearing solution accounting for ∼95% V recovery and vanadium tailings with Fe and Ti contents of 31.85% and 8.94%, respectively. Then, based on theoretical calculations and physical measurements, a coal-based direct reduction-magnetic separation process and a hydrochloric acid leaching process were employed for the stepwise recovery of iron and titanium, respectively, from the vanadium tailings. Iron was recovered in the form of high chromium-vanadium iron with 81.53% Fe, 1.31% Cr, and 2.04% V, and titanium was recovered as titanium dioxide pigment with 85-90% yield. Such a comprehensive and clean utilization of vanadium-bearing converter slag has great potential for practical application.

Effect of Mechanical Activation Treatment on the Recovery of Vanadium from Converter Slag

The high roasting temperature and low leaching efficiency of vanadium from vanadium-bearing converter slag are regarded as the main factors significantly influencing the application of calcification roasting–acid leaching processes in the cleaner production of vanadium. In this study, a mechanical activation treatment was performed to enhance the extraction of vanadium from converter slag. The enhancement effects obtained from mechanical activation were comprehensively evaluated through indices such as the roasting temperature and leaching efficiency. The effects of mechanical activation time, roasting temperature, leaching temperature, solid to liquid ratio, particle size, and acid concentration on the leaching efficiency were investigated. Microstructure morphology and elemental analyses of the raw materials and leaching residue were also investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results demonstrated that the mechanical activation significantly decreased the optimum roasting temperature from 1173 K to 1073 K (900 °C to 800 °C) and increased the leaching efficiency from 86.0 to 90.9 pct.

Oxidation kinetics of vanadium-bearing LD converter slag by mechanical activation

ABSTRACT A thermogravimetric investigation was performed to evaluate the kinetic and thermodynamic parameters and the influence of mechanical activation on oxidation of vanadium-bearing LD (Linz–Donawitz) converter slag. Results indicate that the particle size of d0.5 significantly decreased from 29 μm to 0.266 μm after activation, and the specific surface area based on the BET model increased from 1.324 m2/g to 3.289 mm2/g. Thermogravimetric investigations were separately performed at 650, 700, 750, 800, 850, 900, 950 and 1000°C. Two distinct stages in the oxidation process were identified. The first stage was controlled by nucleation and growth and the second stage was controlled by 3D diffusion. However, the first stage relatively contributed more to the entire process than the second stage. Kinetic study also reveals that mechanical activation exhibited a significant effect on the oxidation of LD converter slag. Mechanical activation significantly reduced the roasting temperature and shortened the roasting time. The corresponding apparent activation energy Ea and frequency factor A changed from 13.01 kJ/mol to 6.59 kJ/mol and 0.247 min−1 to 0.141 min−1 for unmilled and milled slags, respectively.

Thermogravimetric Analysis and Kinetic Study of the Calcification Roasting of Vanadium Slag

The roasting is the key step for the extraction of vanadium from vanadium slag by calcification roasting–acid leaching process. In this study, thermogravimetric analysis and kinetic study of vanadium slag in the presence of calcium oxide was investigated. The maximum oxidation degree was slightly increased by increasing temperature from 700 to 900 °C then almost unchanged further increasing temperature to 1000 °C. The reaction mechanism was analyzed through both Sharp method and ln-ln method. Results showed that the mechanism the reaction in the α range of 0.1–0.8 corresponded to the random nucleation and subsequent growth, as represented as (G(α) = [−ln(1−α)]1/3 = kt. The apparent activation energy was calculated to be 3.5 kJ/mol according to Arrhenius equation.

Effects of Pre-oxidation on the Kinetics of Iron Leaching from Ilmenite in Hydrochloric Acid Solution

The kinetics of iron leaching from ilmenite in hydrochloric acid solutions were investigated. The effects of pre-oxidation roasting, leaching temperature, and holding time on iron extraction rate were determined. The results obtained show that the extraction of iron is significantly enhanced by pre-oxidation roasting and increasing leaching temperature from 75 to 108 °C. The results of the kinetic analysis of the leaching data indicate that the reaction is controlled by diffusion through the product layer. The apparent activation energy for the extraction of iron has been calculated to be 62.5 and 55.1 kJ/mol for untreated and oxidized ilmenite, respectively.

Recovery of tailings from the vanadium extraction process by carbothermic reduction method: Thermodynamic, experimental and hazardous potential assessment

A cleaner process is tremendously required to deal with the vanadium tailings, which may cause serious environmental problem due to the high content of water soluble hazardous elements such as V and Cr. This problem can be possibly solved by proposed high temperature reduction-magnetic separation process, in which, V, Cr and Fe can be recycled as ferroalloy. The thermodynamic calculation results reveal that a higher temperature (>1127.8 °C) promotes the reduction of Fe, V and Cr, and improves the recovery rates of V and Cr in liquid iron. The reduction behavior of vanadium tailings was investigated using XRD, TG/DSC, SEM, EDS and ICP-OES techniques. The EDS results show that a small portion of V was remained in the slag phase when roasted at 1300 °C, while nearly all of V and Cr can concentrate in ferroalloy at 1400 °C. Approximatly 90% of V and 95% of Cr recovery in magnetic fraction can be obtained for the magnetic separation step. A small portion of V and Cr is remained in the non-magnetic final tailings, however, the hazardous potential assessments results indicate that such kind of tailings can safely use as secondary materials or stockpiled as an end-waste.

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

ABSTRACT 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.

Sulfuric Acid Leaching of Mechanically Activated Vanadium–Bearing Converter Slag

The extraction of vanadium from mechanically activated converter slag was studied in dilute sulfuric acid solution. The effects of roasting and leaching parameters were investigated. The results show that Ca/V mole ratio, roasting temperature, leaching temperature, S/L ratio and leaching time significantly affected the dissolution of vanadium while only roasting time has relatively minor effects under the conditions in this work. The over-high roasting temperatures and Ca/V mole ratios performed negative effects on the dissolution of vanadium. The optimum conditions for roasting was found to be 800 °C, 60 min and 1:1 Ca/V mole ratio, and that for leaching conditions was pH 2.5, 60 °C, 20:1 L/S ratio,—150 mesh and 40–80 min. More than 90% of vanadium was leached from the converter slag under these optimum conditions.

Kinetic Study on the Leaching of Vanadium-Bearing Converter Slag with Dilute Sulfuric Acid

Calcification roasting-sulfuric acid leaching process was used to extract vanadium from converter slag. The kinetics of the extraction process based on both unmilled and ball milled slags in dilute sulfuric acid solution (pH = 2.5 ± 0.2) were investigated. The results showed that the extraction of vanadium was a rapid process with particularly a considerable proportion of vanadium rapidly dissolved in the first 10 min. The kinetics analysis showed that the diffusion through product layer was rate-determining step in the course of the dissolution of vanadium. The linear relationship between the rate constant and the inverse square of the particle diameter also illustrated this phenomenon. Mechanical activation can significantly accelerate the vanadium leaching efficiency, and decrease the corresponding apparent activation energy from 9.94 to 7.63 kJ/mol.