Production of Rutile TiO2 Pigment from Titanium Slag Obtained by Hydrochloric Acid Leaching of Vanadium-Bearing Titanomagnetite

Co-Removal of Fe/V Impurity in H2TiO3 Synthesized from Ti-Bearing Blast Furnace Slag

Ti-bearing blast furnace slag (TBFS) can be converted to impurity bearing TiOSO4 solution for TiO2 pigment production. However, the H2TiO3 (MTA) hydrolyzed from the solution has too high Fe/V impurity to meet the standard for TiO2 pigment. In this study, we found that Fe3+ and V3+ were easily hydrolyzed and entered the MTA lattice, and hence could not be removed by washing. Furthermore, Fe/V was hard to co-remove by the traditional reduction method. Therefore, the Fe/V non-hydrolysis condition (Ti3+ = 0.01 M, F = 3.0, T = 130 °C; Ti3+ = 0.01 M, F = 3.5, T = 150 °C) was determined by thermodynamic calculations. However, at these conditions, the Ti hydrolysis ratio was low or the reaction time was long. Therefore, a new two-step hydrothermal hydrolysis process was proposed. Step 1 (130 °C, 2 h) ensured the non-hydrolysis of V3+, and Ti was partially hydrolyzed to increase the H2SO4 concentration. Step 2 (150 °C, 2 h) ensured a high Ti hydrolysis ratio (>0.95) and short total reaction time (4-6 h). Finally, a high-purity MTA was obtained (Fe = 21 ppm, V = 145 ppm). These results provide new insights into the control of the hydrolysis of impurity ions in solutions and help to optimize the process of TiO2 pigment preparation from TBFS.

Hydrolysis Kinetics of Low-Concentration Industrial TiOSO4 Solution and Structural Evolution of Metatitanic Acid

Using the industrial low-concentration TiOSO4 solution as the raw material, the hydrolysis kinetics and structural evolution of metatitanic acid was investigated. The samples were characterized by TiO2 content, XRD analysis, particle size distribution, FT-IR spectroscopy, Raman analysis, and HRTEM. The curves of hydrolysis yield showed S type shape, and the hydrolysis process consisted of the induction period, rapid hydrolysis period, and mature period. The rapid hydrolysis period was the first-order reaction, and increasing of hydrolysis temperature would shorten the induction period and hydrolysis period while prolonging the mature period had an approximate linear positive correlation on the hydrolysis yield and hydrolysis rate. The actual hydrolysis yield at the graying point was consistent with the calculated hydrolysis yield. The calculated pre-exponential factor k0 was 1.40 × 1018 min-1 and activation energy Ea was of 147.6 kJ/mol. With the hydrolysis temperature increasing, the grain size increased, the lattice stress decreased, the average particle size of metatitanic acid decreased, and the sulfur content decreased, resulting from the growth and adjustment of crystals and colloidal particles. Also, the SO42- ions promoted the formation of anatase TiO2 crystals. The formation of the precipitated particles underwent processes such as gel, crystal growth, aggregation, and condensation.

Physical and chemical separation of Ti, rare earth elements, Fe, and Al from red mud by carbothermal reduction, magnetic separation, and leaching

In this study, a combination of physical and chemical separation processes was used to recover the metallic components of red mud. At first, the impact of carbothermal reduction on magnetic separation of iron was studied. Low magnetic properties of iron minerals resulted in insignificant separation of iron from other components in the non-carbothermally reduced sample. Various carbothermal reduction parameters were optimized to maximize iron separation from other components. The optimum conditions were found T = 1350 °C, t = 120 min, coal/red mud ratio of 3, reaction time of 120 min, and the soda ash/red mud ratio of 0.2. Under the optimum condition, the iron recovery of the magnetic product was observed 91% with 81% Fe content, while the non-magnetic product has contained 90% of Ti and Al and 80% of rare earth elements (REEs). Following the physical separation of iron, the chemical separation of remaining red mud components was investigated using leaching with sulfuric, hydrochloric, and nitric acids. The leaching experiments were performed on two samples, treated red mud with carbothermal reduction and an untreated sample. The untreated sample had a higher dissolution efficiency for Ti and REEs than the carbothermally reduced sample. Different dissolution behavior of the red mud components was explained by samples' mineralogy. In the end, considering the obtained results, various scenarios for the recovery of red mud components were evaluated from technical and environmental aspects.

Visible light activation of photocatalysts formed from the heterojunction of sludge-generated TiO2 and g-CN towards NO removal

The feasibility of preparing TiO₂/g-CN heterojunction from Ti-incorporated dried dye wastewater sludge is explored in this study. Two reaction routes of composite formation were evaluated. In the initial approach, one-step calcination of dried sludge and melamine mixture @600 °C was carried out. Detailed morphological and chemical characterizations showed that the one-step calcination route did not create TiO₂/g-CN composites; instead, only N-doped anatase TiO₂ composites were formed. Moreover, due to the non-uniform composition of organic content in the dried sludge, it was not easy to control the N doping level by varying melamine content (0-100%) in the precursor mix. However, successful formation of anatase TiO₂ and g-CN was observed when a two-step calcination route was followed, i.e., via synthesis of anatase TiO₂ from dried sludge, and later development of heterojunction by calcining (@550 °C) the TiO₂ and melamine mixture. X-ray diffraction along with infrared and X-ray photoelectron spectroscopy verified the effective heterojunction. In addition, maximum atmospheric NO removal under UV and visible light were observed for the prepared composite when the melamine content in the precursor mixture was 70%. After 1 h of UV and visible light irradiation, the best TiO₂/g-CN composite removed 25.71% and 13.50% of NO, respectively. Optical characterization suggested that the enhanced NO oxidation under UV/visible light was due to the bandgap narrowing and diminished photogenerated electron-hole recombination.

Modified Hydrothermal Route for Synthesis of Photoactive Anatase TiO2/g-CN Nanotubes from Sludge Generated TiO2

Titania nanotube was prepared from sludge generated TiO2 (S-TNT) through a modified hydrothermal route and successfully composited with graphitic carbon nitride (g-CN) through a simple calcination step. Advanced characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, UV/visible diffuse reflectance spectroscopy, and photoluminescence analysis were utilized to characterize the prepared samples. A significant improvement in morphological and optical bandgap was observed. The effective surface area of the prepared composite increased threefold compared with sludge generated TiO2. The optical bandgap was narrowed to 3.00 eV from 3.18 in the pristine sludge generated TiO2 nanotubes. The extent of photoactivity of the prepared composites was investigated through photooxidation of NOx in a continuous flow reactor. Because of extended light absorption of the as-prepared composite, under visible light, 19.62% of NO removal was observed. On the other hand, under UV irradiation, owing to bandgap narrowing, although the light absorption was compromised, the impact on photoactivity was compensated by the increased effective surface area of 153.61 m2/g. Hence, under UV irradiance, the maximum NO removal was attained as 32.44% after 1 h of light irradiation. The proposed facile method in this study for the heterojunction of S-TNT and g-CN could significantly contribute to resource recovery from water treatment plants and photocatalytic atmospheric pollutant removal.

Characterisation of polyphosphate coated aluminium-doped titania nanoparticles during milling

This paper investigates the characterisation of alumina-doped titania nanoparticles, milled under high-shear over time, in the presence of sodium hexametaphosphate (SHMP) dispersant. Transmission electron microscopy (TEM) indicated that prolonged milling times led to the formation of 10 nm particle fines which were electrostatically attracted to larger particles, where no change in the crystal structure was observed. Primary particle sizes measured by dynamic light scattering (DLS) and TEM were in agreement and showed no change in primary particle size (∼250 nm) with respect to milling time, however, there was a clear reduction in the magnitude of the slow mode decay associated to aggregates. The TiO₂ was found to have an isoelectric point (iep) in the range of pH 3-4.5, where an increase in milling time led to a lower pH_iep, indicative of an increase in SHMP coverage, which was further supported by an intensification in phosphorus content measured by X-ray fluorescence (XRF). Phosphorus content and zeta potential analysis before and after centrifugal washing showed that SHMP was partially removed or hydrolysed for the longer milled pigment samples, whereas no change was observed for shorter milled samples. Relaxation NMR was also performed, where enhanced relaxation rates at longer milling times were associated partially to increases in surface area and exposure of Al sites, as well as physicochemical changes to SHMP density and structure. It is thought that extended milling times may lead to hydrolysis or other structural changes of the dispersant from the high energy milling conditions, allowing easier removal after washing for longer milled pigments.

A high-efficiency hydrocyclone designed by response surface methodology for acid hydrolysis residue recycling

A high-efficiency hydrocyclone was designed by response surface methodology to evaluate the recycling of acid hydrolysis residues from titanium dioxide (TiO2) production as a study case. TiO2 is an important product and the world's best white pigment. During its production from ilmenite (FeTiO3) by the sulfuric acid method, the incomplete reaction produces large amounts of residue, which also contain unreacted ilmenite. Large amounts of residue are generally accumulated without any treatment. Hydrocyclone use is regarded as a method for separating and recovering chemicals from process residues by which the unreacted components can be recycled efficiently. However, hydrocyclones designed by conventional procedures may have some limitations regarding classification sharpness. In this paper, numerical experiments and laboratory tests were performed to evaluate the classification sharpness of various hydrocyclone designs. Response surface methodology was used to optimize hydrocyclones with different structural configurations. Based on the response models, a designed hydrocyclone with a high sharpness of classification of particles was constructed. The sharpness of the newly designed hydrocyclone increased from 80.5% to 93.3%. The vortex finder separated approximately 89.9% of the fine particles in impurities, while 51.0% of TiO2 was recycled by the spigot. The hydrocyclone proposed in this paper properly minimizes the risk of environmental pollution caused by TiO2 production and provides a significant estimated cost savings.

Influence of Mn on the iron-based friction material directly prepared by in situ carbothermic reaction from vanadium-bearing titanomagnetite concentrates

In this work, we prepared an iron-based frictional material from vanadium-bearing titanomagnetite concentrates by in situ carbothermic reaction with improved tribological properties. Effects of Mn content (1–4 wt%) on the microstructure and properties of iron-based friction material were investigated. The microstructure and properties of iron-based friction material with Mn are significantly improved. In particular, the friction coefficient decreases from 0.54 to 0.40–0.49 and the wear rate reduces from 1.899 × 10⁻⁷ cm³ J⁻¹ to 0.229 × 10⁻⁷ cm³ J⁻¹ – 1.309 × 10⁻⁷ cm³ J⁻¹. Appropriate Mn addition (1–3 wt%) contributes efficiently to the sintering densification and increasing laminated pearlites. Comparatively, the density, hardness and wear resistance are improved. The dominant wear mechanism changes from severe abrasive wear to mild abrasive wear and oxidative wear is also enhanced. However, when Mn content increases to 4 wt%, the microstructure, relative density, hardness and wear performance of iron-based friction material are deteriorated. Consequently, the optimal addition of Mn is 3 wt% in the iron-based friction material.

In this work, we prepared an iron-based frictional material from vanadium-bearing titanomagnetite concentrates by in situ carbothermic reaction with improved tribological properties.

Spatial distribution of vanadium and microbial community responses in surface soil of Panzhihua mining and smelting area, China

Spatial distribution of vanadium in surface soils from different processing stages of vanadium-bearing titanomagnetite in Panzhihua mining and smelting area (China) as well as responses of microbial communities including bacteria and fungi to vanadium were investigated by fieldwork and laboratory incubation experiment. The vanadium contents in this region ranged from 149.3 to 4793.6 mg kg^-1, exceeding the soil background value of vanadium in China (82 mg kg^-1) largely. High-throughput DNA sequencing results showed bacterial communities from different manufacturing locations were quite diverse, but Bacteroidetes and Proteobacteria were abundant in all samples. The contents of organic matter, available P, available S and vanadium had great influences on the structures of bacterial communities in soils. Bacterial communities converged to similar structure after long-term (240 d) cultivation with vanadium containing medium, dominating by bacteria which can tolerate or reduce toxicities of heavy metals. Fungal diversities decreased after cultivation, but Ascomycota and Ciliophora were still the most abundant phyla as in the original soil samples. Results in this study emphasize the urgency of investigating vanadium contaminations in soils and provide valuable information on how vanadium contamination influences bacterial and fungal communities.