Defect-induced regulation of crystal growth and phase transition of TiO2 synthesized from Ti-bearing blast furnace slag

Ti-bearing blast furnace slag (TBFS) is an essential secondary Ti resource for TiO2 production. However, the TiO2 is sintered and does not meet the pigment requirements. This study investigated the effect of surface/bulk dis-tribution of defect structures on the crystal growth and phase transition of TiO2 based on the Rietveld method. For the defects of Xn+ (Al3+/Mg2+/Zn2+), the interstitial Xn+ (Xint) is mainly located on the surface of TiO2 particles and inhibits the crystal growth. The substituted Xn+ (Xsub) is primarily located in the bulk and promotes the phase transition. The radius of Xn+ affects the stability of Xint and determines the distribution of Xint/Xsub. Thus, the major defect structures of Al3+, Mg2+, and Zn2+ (increasing radius) are Alint, Mgint/Mgsub, and Znsub, respectively. Based on this, a new co-doping method was proposed. Co-doping modifies the distribution of Xint/ Xsub to regulating the crystal growth and phase transition. Finally, TiO2 for pigment with a small particle size (220 +/- 60 nm) and high rutile conversion (98.1%) was synthesized from TBFS. The results will help to optimize the process for producing TiO2 pigment from TBFS and provide new insights into the structure regulation of TiO2 materials.