Research On The Phase Restructuring And Resource Utilization Of Ferrotitanium Slag

The increasing public awareness of environmental issues has led to a growing interest in the comprehensive utilization of metallurgical waste.In China,ferrotitanium slag is mainly a byproduct of traditional aluminothermy-based ferrotitanium production.Owing to the addition of lime flux during smelting and the presence of titanium oxides in the slag,its chemical composition is based on the Ca O-Ti O₂-Al₂O₃ system.In recent years,China has made significant efforts to enhance resource utilization efficiency and mitigate environmental problems,with a particular focus on the fundamental research and comprehensive utilization of ferrotitanium slag.Based on the alumina content above 75%in the chemical composition,ferrotitanium slag has been used as a low-grade and inexpensive substitute for high-alumina refractory materials in refractories.However,its basic research has been found to have certain shortcomings during practical applications.For instance,the problems of macroscopic discoloration,phase evolution,volume instability,and high-temperature liquid phase increase have not been fully explained in theory.Therefore,improving the basic research for ferrotitanium slag and developing control methods for steady-state reconstruction would be of great theoretical and practical significance.This would promote the stable and efficient utilization of ferrotitanium slag.This study focuses on ferrotitanium slag in Northeast China,using various analytical equipments such as powder X-ray diffractometer,X-ray photoelectron spectroscopy,plasma emission spectrometer,scanning electron microscope,and energy spectrometer to analyze the sample.The X-ray diffraction data is refined using the Unit Cell computer program to determine the main phases present in ferrotitanium slag,along with mineralogical analysis.Additionally,Low-fluxing Ferrotitanium Slag（LFS）obtained without adding lime flux is used as an auxiliary research sample to observe the impact of the evolution of ferrotitanium alloy production technology on the formation of the phase and structure of ferrotitanium slag.The formation mechanism of the phase and structure distribution in ferrotitanium slag are discussed,combining theoretical analysis with experimental data.Furthermore,based on the characteristics of phase and structure evolution of ferrotitanium slag in different environments,the study summarizes the phase reconstruction laws that control the phase evolution process of ferrotitanium slag.The series of basic theoretical research results on the efficient resource utilization of ferrotitanium slag are then validated through practical application of the ferrotitanium slag reconstruction law.The study concludes with several meaningful research findings:（1）The analysis of phase and chemical composition reveals that ferrotitanium slag in China is a molten calcium aluminate material that differs from other thermite slags.Its primary phase composition belongs to the Ca O-Al₂O₃-Ti O₂-Ti₂O₃high-temperature phase system.Crystallography and microstructure analysis indicate that ferrotitanium slag has a heterogeneous phase distribution structure,and its primary phase is hibonite(Ca Al₁₂O₁₉)with mixed doping of Ti³⁺and Ti⁴⁺.Ti⁴⁺doping occurs in the form of coupling with Mg²⁺,which accounts for approximately 29%to 56%of the total Ti doping concentration.The minimum size of hibonite coarse crystals within ferrotitanium slag particles exceeds 100μm,and they form the main body of ferrotitanium slag.Coarse crystal gaps are distributed with secondary crystal phases covered by the amorphous phase,and the size is approximately 1 to 10μm hibonite fine crystal.Tracing studies reveal that the coarse crystal of hibonite is formed through the peritectic reaction during cooling,and the formation of a heterogeneous structure is caused by crystal competitive growth and component segregation during cooling.（2）The doping equilibrium of low valent titanium elements in ferrotitanium slag is imbalanced during the process of oxidation and temperature rise,leading to phase and structural reforms.Temperature rise tests from room temperature to 1100℃under the oxidation atmosphere show that the color of ferrotitanium slag changes from black to blue at approximately 600℃and turns white at approximately 900℃due to the influence of Ti³⁺in hibonite shifting to Ti⁴⁺.In this process,the cell doping of hibonite is reconstructed,and the cell volume decreases in the range of 597.59×10⁶ pm³ to586.94×10⁶ pm³.This phenomenon directly causes the change of phase and structure of ferrotitanium slag particles,which is one of the main factors that decrease the volume stability of ferrotitanium slag.During the process of high-temperature usage,the amorphous phase in ferrotitanium slag is liquefied and partially eutectic to form a low melting system,which reduces the structural stability of ferrotitanium slag.（3）After holding for three hours at 1100℃in an air atmosphere,the structure and phase composition of ferrotitanium slag changed,and the complete aggregate disintegrated into several coarse units of hibonite.The disintegration became more apparent with the increase of aggregate particle size.The study on the structure of ferrotitanium slag in castables with different matrix environments shows that sintering and interfacial reaction promote the transformation of ferrotitanium slag to a more stable structure.When using the matrix environment with the chemical composition of the Al₂O₃-Si O₂ system,the liquid phase in the matrix increases at high temperature,and the liquid phase sintering in the material is promoted.The disintegrated hibonite unit can be reconstructed as a whole through liquid phase sintering.When using the matrix environment with the Al₂O₃-Mg O system as the chemical component,the phase in the ferrotitanium slag is reconstructed under the action of the aggregate-matrix reaction to form a more stable Mg²⁺and Ti⁴⁺coupling doped hibonite,which enhances the interfacial bonding strength.（4）Ferrotitanium slag has significant potential for development and utilization as a source of calcium hexaaluminate to maximize its resource efficiency.The application research in the castables of aluminum electrolytic cells reveals that the castables prepared by entirely using titanium iron slag instead of high-alumina bauxite and synthetic calcium hexaaluminate have better resistance to cryolite melt.The calculation of the low melting system in ferrotitanium slag shows that there are nine eutectic systems in the temperature range from 1300℃to 1600℃.The research on refining and impurity removal shows that the content of the low melting system in ferrotitanium slag is reduced by hot processing,and the primary phase is reconstructed into Ti⁴⁺doped hibonite,resulting in a material that is closer to the theoretical properties of calcium hexaaluminate.