Tianyan Xue

Recovery of titanium from undissolved residue (tionite) in titanium oxide industry via NaOH hydrothermal conversion and H2SO4 leaching

Abstract To recover titanium from tionite, a new process consisting of NaOH hydrothermal conversion, water washing, and H 2 SO 4 leaching for TiO 2 preparation was developed. The experimental results show that under the optimum hydrothermal conversion conditions, i.e., 50% NaOH (mass fraction) solution, NaOH/tionite mass ratio of 4:1, reaction temperature of 240 °C, reaction time of 1 h and oxygen partial pressure of 0.25 MPa, the titanium was mainly converted into Na 2 TiO 3 , and the conversion was 97.2%. The unwanted product Na 2 TiSiO 5 remained stable in water washing, and its formation was prevented by improving NaOH concentration. In water washing process, about 97.6% of Na + could be recycled by washing the hydrothermal product. The NaOH solutions could be reused after concentration. 96.7% of titanium in the washed product was easily leached in H 2 SO 4 solution at low temperatures, forming titanyl sulfate solution to further prepare TiO 2 .

Removal of zirconium from hydrous titanium dioxide

A method was proposed for removing zirconium (Zr) from hydrous titanium dioxide (HTD) by the NaF solution. The effects of main parameters, i.e. pH values, NaF dosage, temperature and retention time, on the removal of zirconium were studied. The optimal conditions were found as the following: pH value, <5.5; molar ratio of NaF to TiO2, 0.6; retention time, 80 min; and temperature, 80°C. The removal rate of Zr under the optimized conditions was above 87.7%. The adsorption energy of the preferential absorption of hydrofluoric acid for Zr(OH)2SO4(OH2) on the (001) crystal surface of HTD was determined by theoretical calculation. The possible mechanism of the removal process was also discussed.

Structures, formation mechanisms, and ion-exchange properties of α-, β-, and γ-Na2TiO3

α-, β-, and γ-Na2TiO3 were prepared from rutile TiO2 and molten NaOH. Three models of β-Na2TiO3 with space groups of R, P, and P were proposed, and the R model was refined from the experimental data by using the Rietveld method. The structure of β-Na2TiO3 is a superstructure of α-Na2TiO3 and supposedly contains Ti6O19 clusters. The structures of Na2TiO3 were mainly determined by the particle sizes of rutile and the reaction temperatures. α-Na2TiO3 could be prepared from fine rutile particles (D(50) < 25.8 μm) and molten NaOH at 500 °C or quenching the melt of Na2TiO3 at 1000 °C quickly. γ- and β-Na2TiO3 were the thermodynamically stable phases of Na2TiO3 at around 500 °C and above 800 °C, respectively. α-Na2TiO3 was formed far beyond the thermodynamically stable state. The Na+ in α-Na2TiO3 was easier to exchange with H+ in water than that in β or γ phases. They all converted to amorphous phases after the 2nd, 6th, and 4th water washings at 25 °C, respectively. β-Na2TiO3 followed similar paths of ion-exchange as α-Na2TiO3, which was different from that of γ-Na2TiO3.

Influence of magnesium and aluminum salts on hydrolysis of titanyl sulfate solution

The influence of magnesium and aluminum salts as impurities on the hydrolysis of titanyl sulfate was investigated. The degree of TiOSO4 conversion to hydrated titanium dioxide (HTD) and the particle size of HTD were measured as functions of the concentrations of MgSO4 and Al-2(SO4)(3) in the TiOSO4 solution. The Boltzmann growth model, which focuses on two main parameters, namely the concentrations of Mg2+ and Al3+ (rho(Mg2+) and rho(Al3+), respectively), fits the data from the hydrolysis process well with R-2>0.988. The samples were characterized by ICP, SEM, XRD, and laser particle size analyzer. It is found that the addition of MgSO4 simultaneously improves the hydrolysis ratio and the hydrolysis rate, especially when F (the mass ratio of H2SO4 to TiO2) is high, hydrolysis ratio increases from 42.8% to 83.0%, whereas the addition of Al-2(SO4)(3) has negligible effect on the chemical kinetics of HTD precipitation during the hydrolysis process, hydrolysis ratio increases from 42.8% to 51.9%. An investigation on the particle size of HTD reveals that the addition of MgSO4 and Al-2(SO4)(3) clearly increases the size of the crystallites and decreases the size of the aggregates.