An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures： low-temperature roasting of vanadium-bearing titanomagnetite and water leaching of roasting slag. During the roasting process, the reduction of iron oxides to metallic iron, the sodium oxidation of vanadium oxides to water-soluble sodium vanadate, and the smelting separation of metallic iron and slag were accomplished simultaneously. Optimal roasting conditions for iron/slag separation were achieved with a mixture thickness of 42.5 mm, a roasting temperature of 1200°C, a residence time of 2 h, a molar ratio of C/O of 1.7, and a sodium carbonate addition of 70 wt%, as well as with the use of anthracite as a reductant. Under the optimal conditions, 93.67% iron from the raw ore was recovered in the form of iron nugget with 95.44% iron grade. After a water leaching process, 85.61% of the vanadium from the roasting slag was leached, confirming the sodium oxidation of most of the vanadium oxides to water-soluble sodium vanadate during the roasting process. The total recoveries of iron, vanadium, and titanium were 93.67%, 72.68%, and 99.72%, respectively.
A hydrometallurgical process for the selective removal of silicon from titanium-vanadium slag by alkaline leaching was investigated. X-ray diffraction, scanning electron microscopy and electron dispersive spectroscopy were used to characterize the samples. The results show that anosovite, pyroxene and metallic iron are the major components of the titanium-vanadium slag. Anosovite is presented in granular and plate shapes, and pyroxene is distributed in the anosovite crystals. Metallic iron is spheroidal and wrapped in anosovite. Silicon is mainly in the pyroxene, and titanium and vanadium are mainly in the anosovite. The effects of agitation speed, leaching temperature, leaching time, sodium hydroxide concentration and liquid-solid （L/S） mass ratio on the leaching behavior of silica from titanium-vanadium slag were investigated. The leaching temperature and L/S mass ratio played considerable role in the desilication process. Under the optimal conditions, 88.2% silicon, 66.3% aluminum, 27.3% manganese, and only 1.2% vanadium were leached out. The desilication kinetics of the titanium-vanadium slag was described by the chemical control model. The apparent activation enerffv of the desilication orocess was found to be 46.3 kJ/mol.
A process of NaOH molten salt roasting-water leaching to treat titanium-vanadium slag obtained by direct reduction of titanomagnetite concentrates was investigated.X-ray diffraction(XRD), scanning electron microscopy(SEM) equipped with energy dispersive spectroscopy(EDS), and thermogravimetry-differential scanning calorimetry(TG-DSC) techniques were used to characterize the samples. The results show that anosovite(Mg_(x)Ti_(3-x)O_(5))and clinopyroxene [Ca(Ti,MgAl)(SiAl)_(2)O_(6)] are the major phases of titanium-vanadium slag. In the NaOH molten salt roasting process, titanium is converted to intermediate product Na_(2)TiO_(3) and vanadium is converted to water-soluble vanadate. The response surface methodology(RSM) was used to optimize the roasting process conditions. NaOH to slag mass ratio(N/S) and roasting temperature are the main influential factors. Under the optimal roasting conditions,i.e., roasting temperature of 550℃, N/S of 1.20, and roasting time of 80 min, the conversions of titanium and vanadium are 96.5 % and 93.0 %, respectively. In the water leaching process, Na_(2)TiO_(3) is converted to amorphous structure of H_(2)TiO_(3) since Na^(+)is exchanged with H^(+). Up to 93.0 % vanadium is leached out under the optimal leaching conditions. Titanium and vanadium in the titanium-vanadium slag can be separated and then recovered.
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 stud- ied. The optimal conditions were found as the following： pH value, 〈5.5; molar ratio of NaF to TiQ, 0.6; retention time, 80 min and temperature, 80℃. 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）2SOt（OH2） on the （001） crystal surface of HTD was determined by theo- retical calculation. The possible mechanism of the removal process was also discussed.
The reduction behaviors of FeO·V2O3 and FeO·Cr2O3 during coal-based direct reduction have a decisive impact on the efficient utilization of high-chromium vanadium-bearing titanomagnetite concentrates. The effects of molar ratio of C to Fe n(C)/n(Fe) and temperature on the behaviors of vanadium and chromium during direct reduction and magnetic separation were investigated. The reduced samples were characterized by X-ray diffraction(XRD), scanning election microscopy(SEM) and energy dispersive spectrometry(EDS) techniques. Experimental results indicate that the recoveries of vanadium and chromium rapidly increase from 10.0% and 9.6% to 45.3% and 74.3%, respectively, as the n(C)/n(Fe) increases from 0.8 to 1.4. At n(C)/n(Fe) of 0.8, the recoveries of vanadium and chromium are always lower than 10.0% in the whole temperature range of 1100-1250 °C. However, at n(C)/n(Fe) of 1.2, the recoveries of vanadium and chromium considerably increase from 17.8% and 33.8% to 42.4% and 76.0%, respectively, as the temperature increases from 1100 °C to 1250 °C. At n(C)/n(Fe) lower than 0.8, most of the FeO·V2O3 and FeO·Cr2O3 are not reduced to carbides because of the lack of carbonaceous reductants, and the temperature has little effect on the reduction behaviors of FeO·V2O3 and FeO·Cr2O3, resulting in very low recoveries of vanadium and chromium during magnetic separation. However, at higher n(C)/n(Fe), the reduction rates of FeO·V2O3 and FeO·Cr2O3 increase significatly because of the excess amount of carbonaceous reductants. Moreover, higher temperatures largely induce the reduction of FeO·V2O3 and FeO·Cr2O3 to carbides. The newly formed carbides are then dissolved in the γ(FCC) phase, and recovered accompanied with the metallic iron during magnetic separation.
