Xuewei Lv

Removal of Impurity Elements from Molten Aluminum: A Review

In the current paper, the technical progress of aluminum refining over the past 30 years has been summarized, including the improvement of batch reactor and in-line continuous reactors, the evolution of gas purging methods by nozzle, porous plug, and rotating impellor, and the use of fluxing by using gas mixtures (including argon, nitrogen, and chlorine) and solid salts (such as AlF3, MgCl2, and KCl). The mathematical models developed for the removal of impurity elements from molten aluminum were also reviewed. Thermodynamic factors were summarized, including the Gibbs free energy of the chemical reactions, activity coefficients of the impurity elements, and the melting and boiling points of impurity elements and related compounds. Kinetic factors used and derived by researchers are also reviewed, such as mass transfer coefficient of impurity elements, mixing power and mixing time in reactors stirred by gas, impellor and circulation of the fluid, and the size, residence time, and terminal velocity of bubbles. The current review provides useful information for the future study of the removal of impurity elements from aluminum.

Determination of optimum blast furnace slag cooling rate for slag recycling in cement manufacture

Abstract The crystallisation behaviour of molten blast furnace slag was observed in situ using the single hot thermocouple technique. Isothermal and non-isothermal experiments were conducted to construct the diagrams for time temperature transformation and continuous cooling transformation. The molten slag should be cooled at a minimum critical cooling rate of 10°C s−1. During crystallisation, melilite is the main crystal phase and rankinite is the primary phase. The crystallisation mechanism of the melilite crystal phase involves one-dimensional direction growth with bulk nucleation, whereas the growth mechanism of the rankinite crystal phase is between the surface nucleation mechanism and the one-dimensional direction growth mechanism. The crystallisation activation energies of the melilite and rankinite crystal phases are 238.07±28.81 and 523.52±58.56 kJ mol−1 respectively.

Solid state and smelting reduction of Panzhihua ilmenite concentrate with coke

Abstract Solid state and smelting reduction of ilmenite is an important process of upgrading ilmenite to high titania feedstock. In this study, an ilmenite concentrate supplied by Panzhihua Iron and Steel (Group) Co. was first reduced at solid state in an electric resistance furnace, followed by smelting reduction in an induction furnace. The effects of reducing agent (carbon) amount on the chemical composition of the solid state reduction sample and the titania slag reduced from them, were analysed. It was found that the metallisation of iron in the solid reduction samples and the grade of titania slag generally increased with increasing carbon amount from 8 to 12%, and then remained constant when the carbon amount was increased above 12%. The content of metallic iron in the titania slag increased with increasing carbon amount, because the slag viscosity and liquidus temperature increased with decreasing FeO content. It was also known that the content of Ti2O3 increased with decreasing the content of FeO in the slag. Some metallic iron particles were found in the high titania slag samples. The liquidus lines and viscosity of the slag were calculated using FactSage to explain the experimental results. La réduction à l’état solide et par fusion de l’ilménite est un procédé important de valorisation de l’ilménite pour charge d’alimentation à haute teneur en dioxyde de titane. Dans cette étude, un concentré d’ilménite fourni par le groupe Panzhihua Iron and Steel Co. a d’abord été réduit à l’état solide dans un four électrique à résistances, suivi par la réduction par fusion dans un four à induction. On a analysé les effets de la quantité d’agent réducteur (carbone) sur la composition chimique de l’échantillon de réduction à l’état solide et de la scorie de dioxyde de titane réduit à partir de lui. On a trouvé que la métallisation du fer dans les échantillons de réduction solide et la qualité de la scorie de dioxyde de titane augmentaient généralement avec une augmentation de la quantité de carbone de 8 à 12%, et ensuite restaient constantes lorsqu’on augmentait la quantité de carbone au-delà de 12%. La teneur en fer métallique dans la scorie de dioxyde de titane augmentait avec l’augmentation de la quantité de carbone, parce que la viscosité de la scorie et la température du liquidus augmentaient avec une diminution de la teneur en FeO. On sait également que la teneur en Ti2O3 augmentait avec une diminution de la teneur en FeO dans la scorie. On a trouvé quelques particules de fer métallique dans les échantillons de scorie à haute teneur en dioxyde de titane. On a calculé les lignes de liquidus et la viscosité de la scorie en utilisant FactSage pour expliquer les résultats expérimentaux.

Transition of Blast Furnace Slag from Silicates-Based to Aluminates-Based: Viscosity

The effect of Al2O3 and the Al2O3/SiO2(A/S) ratio on the viscosity of the CaO-SiO2-Al2O3-MgO-TiO2 slag system was studied in the present work. At a fixed CaO/SiO2(C/S) ratio of 1.20, 9 mass pct MgO, and 1 mass pct TiO2, the viscosity increases with an increase in Al2O3 content at a range of 16 to 24 mass pct due to the polymerization of the aluminosilicate structures, while it decreases when the Al2O3 is higher than 24 mass pct, which means that Al2O3 acts as a network modifier at higher content. Increasing A/S from 0.47 to 0.92 causes a slight decrease in viscosity of the slags and has an opposite effect when A/S is more than 0.92. The free running temperature increases with the Al2O3 content and appears to show a peak at an A/S ratio of 0.92. The change of the apparent activation energy is in accordance with the change of viscosity. When Al2O3 content is more than 24 mass pct with low SiO2, CaO content ranges from 35 to 45 mass pct, and the slag transform from silicates-based to aluminates-based can still get a good operation region. Four different viscosity models were employed to predict the viscosity and RIBOUD’s model was found to be the best in predicting the viscosity by comparing the estimated viscosity with the measured viscosity.

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 composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al2O3 and binary basicity (CaO/SiO2) on the critical cooling rate of the CaO–SiO2–MgO–Al2O3 slags were studied under conditions of CaO/SiO2 = 1.1–1.4, 6–12 mass% MgO and 10–16 mass% Al2O3. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al2O3 content decreased the critical cooling rate; higher CaO/SiO2 increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.

Influence of MgO, Al2O3 and CaO/SiO2 on the viscosity of blast furnace type slag with high Al2O3 and 5 wt-% TiO2

The effect of MgO, Al2O3 and CaO/SiO2 on the viscosity of CaO–SiO2–Al2O3–MgO–5 wt-% TiO2 slag was studied in the temperature range of 1673–1773 K. At a fixed CaO/SiO2 ratio of 1·17 and 12 wt-% Al2O3, the viscosity of the slag decreased with increasing MgO content because of depolymerisation of the silicate structures. At a fixed CaO/SiO2 ratio of 1·17 and 8 wt-% MgO, the viscosity of the slag increased with increasing Al2O3 content. At 8 wt-% MgO and 12 wt-% Al2O3 wt-%, increasing the CaO/SiO2 ratio from 1·07 to 1·50 resulted in lower slag viscosity. The temperature dependencies of the viscosity on MgO addition, Al2O3 addition, and CaO/SiO2 ratio were analyzed, and the apparent activation energies of each system were found to be between 178 and 232 kJ/mol, 273 and 360 kJ/mol, and 204 and 233 kJ/mol, respectively. Five different viscosity models were employed to predict slag viscosity, and the Riboud model was found to be the best for predicting this parameter.

Effect of ultrasonic vibration treatment on solid-state reactions between Fe2O3 and CaO

In the present study, ultrasonic vibration was applied to the solid-state reaction between Fe2O3 and CaO. The effect of the ultrasonic vibration treatment on the formation of CaFe2O4 (CF) from the solid-state reaction was investigated by X-ray diffraction (XRD) and the Rietveld structure refinement method. The results indicated that the solid-state reaction between Fe2O3 and CaO was accelerated by ultrasonic treatment (UT), which efficiently lowered the formation temperature of the solid-state CF and increased the quantity formed by enhancing the mass transfer process of the reactions. Without the UT, CF and Ca2Fe2O5 (C2F) were produced at 750°C and the mass fractions of CF and C2F increased with the experiment temperature, with approximately 47.76% CF and 40.66% C2F produced at 850°C. With the UT, mass fractions of 5.67% CF and 18.20% C2F were formed at 700°C, and increasing the experiment temperature enhanced the formation of CF and C2F. Moreover, a significantly greater amount of CF than C2F was formed when the temperature exceeded 700°C. A CF mass fraction of approximately 98.73% was obtained by UT at 850°C, much higher than the 47.76% obtained without UT. In addition, increasing the ultrasonic power influenced the formation of the CF phase. The CF content increased from 19% to 77.34% with increasing ultrasonic power from 0 to 89%×2kW. Furthermore, a prolonged UT time also promoted the formation of solid phase CF. The mass fraction of CF ranged from 19% to 77.34% when the UT time was varied from 0 to 150min.

Dehydrating and sintering of Philippine nickel laterite

Abstract Dehydrating of nickel laterite is necessary when high magnesium laterite ores are treated by pyrometallurgical means. In this work, the Philippine nickel laterite was dehydrated and sintered simultaneously in a laboratory scale sintering apparatus. The original nickel laterite was characterised using thermogravimetric (TG) analysis, differential thermal analysis (DTA) and X‐ray diffraction (XRD) experiments. The measurements indicate that chlorite (Fe,Mg,Al)3(Si,Al)2O5(OH)4 and serpentine Mg21Si2O28(OH)34H2O are the primary phases, while FeO(OH) and (Fe,Mg,)3Si4O10(OH)2 are the minor phases in Philippine nickel laterite. The laterite contains free water, water of crystallisation and hydroxyl group; these can be removed in that order during the heating. The temperature range for the removal of free water is 25–140°C, for water of crystallisation it is 200–480°C, and for hydroxyl group it is 500–800°C. Sintering experiments with various coal additions show that sintering time, sintering product ratio, mass loss and the temperatures of off‐gas and burden increase with increasing coal addition. The sintered samples were analysed using XRD, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results demonstrate that olivine (Mg,Fe)2SiO4 and spinel MgFe2O4 are the main bonding phases during the sintering. La déshydratation de la latérite de nickel est nécessaire lorsque des minerais de latérite à haute teneur en magnésium sont traités par méthodes pyrométallurgiques. Dans ce travail, on a déshydraté et fritté simultanément la latérite de nickel des Philippines dans un appareil de frittage à l’échelle du laboratoire. On a caractérisé la latérite de nickel originale en utilisant des expériences de thermogravimétrie (TG), d’analyses thermiques différentielles (DTA) et de diffraction des rayons X. Les mesures indiquent que le chlorite (Fe,Mg,Al)3(Si,Al)2O5(OH)4 et la serpentine Mg21Si2O28(OH)34H2O sont les phases primaires alors que FeO(OH) et (Fe,Mg)3Si4O10(OH)2sont les phases mineures de la latérite de nickel des Philippines. La latérite contient de l’eau libre, de l’eau de cristallisation et le groupe hydroxyle; on peut les enlever dans cet ordre lors du chauffage. La gamme de température pour l’enlèvement de l’eau libre est de ∼25 à 140°C, elle est de ∼200 à 480°C pour l’eau de cristallisation et de ∼500 à 800°C pour le groupe hydroxyle. Les expériences de frittage, avec additions variées de charbon, montrent que le temps de frittage, le ratio du produit de frittage, la perte de masse et les températures du gaz de dégagement et du lit de fusion, augmentent avec une augmentation d’addition de charbon. On a analysé les échantillons frittés en utilisant la XRD, la microscopie à balayage d’électrons (SEM) et la spectroscopie à dispersion d’énergie (EDS). Les résultats démontrent que l’olivine (Mg,Fe)2SiO4 et le spinelle MgFe2O4 sont les principales phases de liaison lors du frittage.

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.