Anti-caking in the production of titanium dioxide using low-grade titanium slag via the NaOH molten salt method

The caking and adhesion of intermediate product on reactor surfaces during TiO2 production via the NaOH molten salt method are a serious problem. The consolidation of intermediate product can lead to low heat transfer efficiency and low titanium fractional conversion. Furthermore, frequent cleaning is generally required. An anti-caking method that can be applied during low-grade titanium slag decomposition in the NaOH system was studied. The method, which involves the two-step reaction of low-grade titanium slag with molten NaOH without the introduction of additives, can significantly reduce the extent of caking. The NaOH and low-grade titanium slag mixture was first reacted at 350 °C for 60 min. The temperature was then increased to 550 °C in 40 min. Finally, the mixture was reacted at 550 °C for 75 min. The effects of the reaction temperatures, NaOH-to-slag mass ratio and the reaction time on the titanium extraction were investigated. The Brunauer–Emmett–Teller (BET) surface area and apparent density were used to characterize the extent of caking. In the low grade titanium slag, silicate phase prior to pseudobrookite phase reacts with molten NaOH at 350 °C in the process of two-step molten reaction and formed sodium silicate. Microstructural and Fourier transform infrared (FT-IR) absorption results show that the firstly formed sodium silicate did not diffuse into the entire reaction system and powder-shaped intermediate product was formed. Approximately 97% of titanium in the titanium slag could be extracted under the optimal reaction conditions. In addition, the content of TiO2 obtained in the product reached 99.3%.

Graphical abstractAnti-caking in the process of produce titanium dioxide without introducing additives has been achieved successfully. Powder shaped intermediate product can be obtained by the two-step molten salt reaction process. Silicate phase in the low-grade titanium slag was reacted with molten NaOH ahead of pseudobrookite at 350 °C.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Anti-caking in the process of produce titanium dioxide without introducing additives has been achieved successfully. ► Powder shaped intermediate product was obtained through new method. ► BET surface area and apparent density were used to characterize the extent of caking. ► Silicate phase in the low-grade titanium slag was reacted with molten NaOH ahead of pseudobrookite at 350 °C.