The titanium hydrolysis in the concentrated titanyl sulfate solution is essential to the TiO2 production by using the new NaOH roasting method proposed by authors, which is undergoing to scale up. The experimental titanium hydrolysis was detected by the infrared and Raman spectra for the first time to reveal the significant role of SO42- ions. The bridging bidentate SO42- ligands arrange the Ti-O octahedra of hydrated titanium dioxide (HTD) in zigzag chains along the crystal face (221) to form anatase structure and are changed into unidentate SO42- ligands and free bisulfate ions step by step with increasing hydrolysis time. This proposed mechanism of titanium hydrolysis in titanyl sulfate solution was applied to establish a new kinetic model x=1 -k(n)e(-kn)(2k(m)c(Tl)(0)/1-+1)/2k(m)C(Tl)(0) [Ei(k(n)t+2k(m)C(Tl)(0)/k(n)) - Ei(2k(m)C(Tl)(0)/k(n))] - e(-knt), which indicates the important effect of initial concentrations of titanium, sulfuric acid, and water on the titanium hydrolysis. The hydrolysis kinetic model is capable of describing the behavior of the system and can provide basic knowledge for scale-up of TiO2 production. (C) 2015 Elsevier Ltd. All rights reserved.