Yanqing Hou

The “high-temperature carbonization and low-temperature chlorination process” can recover titanium from high-titanium blast furnace slag containing 20–25% TiO₂ at 1450–1700 °C and 500–600 °C. The carbonization process was carried out in an industrial three-phase AC electric furnace with a rated power of 9000 kVA. Through Factsage calculations, XRD, SEM-EDS, and industrial data collection, the mechanism of carbonization and the impact of smelting parameters were illustrated. The results indicated that Ti primarily existed as titanaugite or perovskite in the slag, and the reduction reaction of TiO₂ began at 1301 °C. But to complete perovskite transformation, a temperature exceeding 1550 °C was necessary. When the reaction began, the reaction rate of TiO₂ to Ti₂O₃ was faster than that of Ti₂O₃ to TiC, and TiC grains appeared as small island-shaped particles (0–3 μm) and larger aggregates (0–10 μm) surrounding Fe. Furthermore, as the molten pool was agitated, the TiC particles detached from the surface of the carbon and it became very difficult for them to grow. In the final reaction stage, most of the TiC contained a certain amount of oxygen and was dispersed, with a particle size of 0–5 μm and a settling tendency. In terms of industrial production, the results indicate that employing coke with a particle size of 0.074–1 mm, maintaining a bath temperature ≥1550 °C, and implementing stage-specific power supply protocols (particularly for the high-conductivity final stage) are crucial for achieving a ≥88% industrial carbonization rate.

TiC-bearing slag is an intermediate product in the titanium extraction process following the “high-temperature carbonization and low-temperature chlorination” method. It exhibits complex grinding characteristics, and traditional grinding methods often yield issues such as broad particle size distribution (PSD) and overgrinding, adversely affecting process efficiency. In this study, TiC-bearing slag was investigated as the raw material. Through methods such as SEM-EDS, MLA, and scientific experiments, we established quantitative relationships between mechanical inputs and product granulometry. The results indicate that the coexistence of TiC and pyroxene-group minerals leads to poor grinding selectivity, causing TiC to resist fracturing while pyroxene minerals are prone to overgrinding. Furthermore, the experiments demonstrated that high circulating-load grinding combined with staged sieving is most effective for producing narrow PSD products. This research explores the methods and paths for achieving controlled narrow PSD of TiC-containing slag in the crushing process, and providing data support for the selection of industrial-scale grinding processes.

With the growing demand for polysilicon, scaling up Siemens reactors (SR) has become a crucial approach to improving production efficiency and reducing unit production costs. However, the increased SR size has led to a significant rise in total energy consumption, necessitating efforts to address the challenge of reducing energy consumption while maintaining production output. This study focuses on a 40-pair silicon rod large-capacity SR with a high silicon core and novel inlet–outlet ports, investigating the effects of parameters such as the inlet gas velocity (v), silicon rod surface temperature (Ts), wall emissivity (ε), and silicon rod diameter (d) on energy consumption, as well as their interaction effects. The results indicate that an increase in v raises convective heat loss (CHL) by 29.40%. An elevated Ts increases radiative heat loss (RHL) by 46.18%. Reducing ε effectively decreases RHL by 33.94%. Although increasing the d leads to higher RHL and CHL, it significantly reduces the specific energy consumption per unit mass of polysilicon by 76.69%. The synergistic influence of Ts and d has the most substantial impact on energy consumption, increasing by 62.48%. In conclusion, optimizing v, Ts, ε, and d are effective strategies for achieving energy savings and reducing energy consumption in SR. This study provides a theoretical foundation for the high-efficiency, low-energy operation of the Siemens process and holds significant importance for promoting the green and sustainable development of the high-purity polysilicon industry.

The gas-liquid flow and oxygen content in a pressurized leaching stirred tank significantly influence the chemical reaction rates, while the specific dynamics of gas-liquid flow in the sulfuric acid system remain largely unexplored. In this study, a mathematical model of gas-liquid flow within a stirred tank is developed using the Euler-Euler approach, with the turbulence and drag force models being validated against experimental data. Utilizing this validated and reliable model, this study investigates the impacts of the sulfuric acid concentration, baffles, air inlet velocity, and bubble diameter on the flow field and gas holdup in a two-phase system consisting of a sulfuric acid solution and oxygen. The findings indicate that introducing a specific concentration of sulfuric acid decreases the solution velocity and increases the gas holdup within the tank. However, once the sulfuric acid concentration reaches a certain threshold, further increases have a diminished effect on the gas-liquid phases. The installation of baffles enhances the turbulent kinetic energy and increases the gas holdup while only resulting in a minimal 1.2% increase in power consumption. Additionally, the inlet velocity and bubble diameter have a relatively minor impact on the tank’s flow field. However, increasing the inlet velocity significantly boosts the gas holdup, whereas an increase in the bubble diameter marginally reduces it. Furthermore, introducing a sulfuric acid solution into the tank can enhance the gas holdup when the gas inlet velocity is low. Conversely, when the gas inlet velocity is high, the addition of sulfuric acid results in a decrease in the gas holdup. The conclusions from this study contribute to enhancing the mixing effectiveness and oxygen content within the tank, providing a substantial theoretical basis for optimizing the design and operating conditions of pressurized leaching stirred tanks.