A novel process to prepare titanium dioxide from Ti-bearing electric furnace slag by NH4HF2-HF leaching and hydrolyzing process has been developed. In this present study, the effects of [NH4+]/[F] mXolar ratio, leaching temperature, [F] concentration, liquid/solid mass ratio, leaching time on the Ti extraction, and the phase transformations have been investigated to reveal the leaching mechanism of Ti-bearing electric furnace slag in NH4HF2-HF solution. In the NH4HF2-HF leaching process, the MgTi2O5 and Al2TiO5 are converted to TiF62- and Mg-Al-bearing precipitate. Ti extraction rate reached 98.84% under the optimal conditions. In addition, 98.25% iron ions can be removed in the presence of NaCl prior to hydrolysis process. The effects of pH and temperature on the selective hydrolysis of TiF62- during hydrolysis process were also studied. In the hydrolysis process, the TiF62- is converted to (NH4)(2)center dot TiOF4 By calcination, high grade TiO2 powder with its purity of 99.88% was obtained, using which the products, well crystallized anatase and rutile, were obtained through roasting at 800 degrees C and 1000 degrees C, respectively. (C) 2017 Elsevier B.V. All rights reserved.