Panzhihua ilmenite, located in Sichuan province of southwest China, is thelargest ilmenite reserve in the world, with an estimated reserve of 870million tons. This deposit accounts for more than 90% of the total titanium resource of China and over 35% of the world. In the present processing flowsheet, the ore is first processed with wet low-intensity drum magnetic separator to concentrate strongly magnetic vanadic titano-magnetite, with its tailings classified into coarse and fine fractions; and then the ilmenite is respectively recovered from the two fractions, by high-gradient magnetic separation-reverse flotation flowsheet. Figure21 shows the processing flowsheet for the fine fraction in the ilmenite processing plant of Panshihua Iron and Steel Company, with separation results listed in Table 13.
It can be seen that high-gradient magnetic separation plays a crucially important role in the recovery of fine ilmenite from the ore. In the flowsheet as shown in Figure21, the feed is firstly processed by wet low-intensity drum magnetic separation to concentrate vanadic titano-magnetite, and then is effectively processed through an SLon pulsating high-gradient magnetic separation flowsheet, in which 67.87% by mass weight of the feed is discarded as tailings, at a very low grade of 3.02% TiO2.
It is apparent that high-gradient magnetic separation plays the most significant role in the flowsheet for the production of qualified high-grade ilmenite concentrate, by providing a primary ilmenite concentrate to the reverse flotation flowsheet, at a low mass flow rate.
Ilmenite (FeTiO3) and rutile (TiO2) are the most important ores used as raw material for TiO2. Although natural rutile contains a high amount of TiO2 with low level of impurities, the mineral is becoming scarce and thus more costly. Consequently, ilmenite is currently favored despite its relatively low TiO2 content (approximately 50% TiO2 compared with 96% in case rutile is used) and the presence of Fe impurity .
Manufacturing of nano-sized TiO2 is still rapidly increasing and estimations for the total production of the nano-sized particles are therefore difficult to make. In 2005, however, annual global production of nano-sized TiO2 was estimated at 2000 metric tons (MT) and 5000MT in 2010 with 65% being used for personal care applications like sunscreens and cosmetics [47,62]. It has furthermore been forecasted that the portion of nano-sized TiO2 of the total U.S. TiO2 production would continue to increase .
Three commercial chemical purification processes are commonly applied to produce both nano-sized and conventional, microsized TiO2 pigments: the chloride, the sulfate route , and a route known as the Altair process . The production processes of nano-sized TiO2 sunscreens generally follow the same main phases that comprise nuclei synthesis, coating, filtration (and washing), dispersion, and milling . Briefly, the sulfate process is a wet process that creates primarily microsized TiO2 particles. The more expensive chloride process is a gas-phase method which is able to produce finer particles of different morphology. The Altair procedure is a spray hydrolysis-based process and this method was introduced by Altair Nanotechnologies Inc. (currently Altairnano, Reno, Nevada, USA). The spray hydrolysis of the feedstock solution is used instead of the aqueous filtration step (as applied during the sulfate process). Main differences between the sulfate and chloride process comprise the nuclei synthesis techniques and the feedstocks. For more detail reading, an interesting overview of available synthetic procedures for nano-sized TiO2, including new developments, is given by Chen and Mao .
For sunscreen (formulation) manufacturing, the photostability of the TiO2 particles and the use of a dispersion medium are (apart from particle size) factors of specific importance. As indicated in section 1, various TiO2 mineral forms have different photocatalytic properties with rutile being the most stable and less photocatalytic active than the anatase. Most compositions appear to use a combination of rutile and anatase forms. Anatase particles are, however, still used as sunscreen ingredient (like the S75-O coded anatase material)  and surface treatment of the nano-sized particles is commonly applied to prevent production of harmful ROS. Examples of these surface treatments include particle coating (see also section 1.4.2, nano-sized TiO2) but also doping of the nano-sized particles with metals like Mn, V, Cr, and Fe. It is important to understand that both procedures may change functional properties of the particles and probably associated risk profiles as well . Moreover, as discussed (section 1), the effectiveness of coatings in controlling photocatalytic reactions is not clear. Specific coatings of nano-sized TiO2 particles are combinations of alumina (aluminum oxide) and silica (silicium dioxide) or combination of alumina or silica with simethicone, methicone, lecithin, stearic acid, glycerol, dimethicone, metal soap, isopropyl titanium triisostearate, triethoxy caprylylsilane, or C9-15 fluoroalcohol phosphate. Dispersion media are applied in the manufacture of nano-sized TiO2 sunscreen formulations to reduce the aggregation and/or agglomeration of the particles. The company Kobo Products Inc., specialized in TiO2 and ZnO powders and dispersions is one of the few producers that has provided information on the Internet in a number of attenuation-grade dispersions with nano-sized TiO2 . The dispersion media used by this company are, for example, polyhydroxystearic acid and cyclopentasiloxane. Polyhydroxystearic acid is an oil-soluble compound which is able to attach to the skin and is often applied as a pigment wetting agent, grinding or coating material . Cyclopentasiloxane is commonly used in cosmetic and sun-blocking products but there is also a concern regarding its persistence, bioaccumulation, and nonreproductive organ toxicity properties . Noteworthy is the change in size from the primary nano-sized particles (1015nm) into large microsized aggregates in the dispersions (130164nm). Finally, particle coatings can interact with the dispersion medium and/or other sunscreen ingredients which may affect overall UV attenuation. A recent publication of the Scientific Committee on Consumer Safety (SCCS), however, reported on a scientific proof for the (photo)stability of common coatings in sunscreen formulations and absence of interactions with other formulation ingredients .
Information on the concentrations of nano-sized TiO2 in sunscreens is mostly not given (manufacturers are currently not obliged to mention the presence of nanoparticles in their products). Croda International Plc. (North Humberside, United Kingdom), on the other hand, provided concentrations of 5% and 35% TiO2 in formulation parts before mixing with other parts to produce the final formulation . A study of Botta etal. has given an estimation of 4.6% for the concentration of nano-TiO2 in commercialized sunscreens . It is noticeable that sunscreen spray products with nano-sized TiO2 are formulated with nonvolatile ingredients in pump sprays to minimize aerosol cloud formation and should comply current requirements regarding droplet size (using laser diffraction by Malvern method), a mass median aerodynamic diameter of at least 30m (a maximum allowance of 1% particles with an aerodynamic diameter of 10m or less) .
The stability (including susceptibility to weathering processes) and the type of nano-sized TiO2 particles, their coating and dispersion sunscreen media are factors that determine potential amounts of TiO2 releases during distribution, utilization, and disposal stadia. Ashort lifetime of the nano-sized particles in sunscreen products combined to a low product use and strong particle fixation in the formulation will lower the change of particle releases into the environment. On the other hand, sunscreen formulations with nano-sized particles and a stabilized long lifetime that are easily eliminated from their formulation are more hazardous to humans and their environment .
MgTiO3 has an ilmenite-type structure with r =17, Qf = 160 000 GHz and f = 50 ppm/C [50, 212]. Ferreira et al.  reported that MgTiO3 dielectrics prepared by chemical method have better quality factor (166 400 GHz). It was found  that addition of La2O3, Cr2O3 or Fe2O3 lowered the Qf value although it improved densification. In the La-doped samples, secondary phases of La2Ti2O7 was found which degraded quality factor. MgTiO3 when sintered at 1400C contain MgTi2O5 secondary phase . Ichinose et al.  reported that the addition of 5 mol% B2O3 to MgTiO3 lowers the sintering temperature and suppressed the formation of MgTi2O5. Yoo et al.  reported that the quality factor depends very much on the cooling rate. The slow cooled samples have lower amount of strain and thereby exhibit higher Qf. MgTiO3 sintered at 1350C and cooled at the rate of 1/min had a high Qf of 220 000 GHz, whereas the sample cooled at a rate of 30/min had Qf = 170 000 GHz and quenched sample 150 000 GHz, respectively. To compensate for the negative f of MgTiO3, Wakino  prepared a composite ceramic of MgTiO3CaTiO3 (MCT). It was found that the composition 0.95MgTiO30.05CaTiO3 ceramics has f = 0. They do not form a solid solution because of the large difference in the ionic sizes of Mg2+ and Ca and the difference in the crystallographic structure. The 0.95MgTiO30.05CaTiO3 mixture ceramics have f = 0 with r 21 and Qf 56 000 GHz. Several authors  investigated the effect of small amounts of dopants and glass additives on the sintering temperature and MW dielectric properties of MCT. Ichinose et al.  reported that addition of 5 mol% B2O5 to MCT and fired at 1200C showed a maximum Qf = 86 000 GHz with r = 19.6 and f = 3 ppm/C. Addition of 5 mol% V2O5 in MCT lowers the sintering temperature to about 1000C but the sintered ceramic was multiphase consisting of MgTiO3, MgTi2O5 and Ca5Mg4V6O24  with a degradation in the dielectric properties. Addition of low melting glasses lowered the sintering temperature to <950C suitable for LTCC and are described in Chapter 12 on LTCC. Addition of 0.2wt% Bi2O3 [221, 229] in 0.94MgTiO30.06CaTiO3 lowered sintering temperature to about 1250C resulting a f of 2.9 ppm/C with Qf 53 000 GHz and r 22.6. Further addition of Bi2O3 leads to formation of Bi2Ti2O7 which lowered the Qf value. Cho et al.  reported that (1 x)MgTiO3xSrTiO3 (x = 0.036) sintered at 1270C for 2 hours showed temperature-stable ceramic with Qf = 71 000 GHz. Hence they propose (1 x) MgTiO3xSrTiO3 (MST) superior to MCT as MCT has a higher sintering temperature of 1400C and the properties of MST and MCT are comparable.
Reduction of titanium from ilmenite and rutile by carbon proceeds first with the reduction of iron oxides and later with the reduction of titanium, which partially dissolves in ion melt and partially transforms into carbide (TiC). Smelting of ilmenite with carbon usually leads to the formation of Fe-Ti-C alloy with a high carbon content (35% to 40% Ti; 5% to 8% C; 1% to 3% Si). Such alloys with high carbon content may be used for deoxidation and alloying of carbon steels.
Using silicon as a reductant for titanium is more problematic, as silicon has a lower affinity for oxygen than does titanium, and thus recovery of TiO2 is only possible with a high content of silicon in the ferroalloy. Also, the presence of iron is needed as it decreases titanium activity and promotes reduction. The resulting Fe-Si-Ti alloy has a composition of 20% to 25% Ti, 20% to 25% Si, and ~ 1% C, which has limited application in steelmaking.
The aluminothermic method for ferrotitanium processing is the most common (Gous, 2006). Reduction of titanium by aluminum from ilmenite and rutile proceeds via the formation of intermediate monoxide TiO (TiOx), which, as basic oxide, is able to form titanium aluminate. This decreases the activity of TiO and makes titanium recovery more difficult. To suppress the process of binding TiO with alumina, lime is injected to the charge: CaO replaces TiO, forming CaOAl2O3. However, the balance must be kept, as an excess of CaO in the charge is not desirable: it decreases the activity of titanium dioxide by forming perovskite CaOTiO2. Lime also has a great influence on the viscosity and fluidity of the slag. The optimum amount of it in the charge is about 20% by weight of aluminum (Gasik et al., 2009). This method has been greatly improved and applied in several ways, both by using a conventional furnace and by using an electric furnace with preheating of the charge and the use of iron-thermal (exothermic) mixtures (Kotz et al., 2006). Slag of ferrotitanium is then postprocessed in an electric furnace to recover the rest of titanium and to produce high-alumina (68% to 78% Al2O3, 14% to 17% CaO) slag, which is used as a high-alumina cement addition (Pourabdoli et al., 2007). Although different alternative methods of ferrotitanium processing are being studied (e.g., by electrolysis in molten salts as shown by Shi et al., 2011), these methods still mostly take place in the laboratory.
Titanium is present in the blast furnace as ilmenite (FeOTiO2) in the burden, and is very difficult to reduce. Most of the oxide is reported into slag causing very high viscosity. Reduction of TiO2 in the slag can partially take place in the hearth by carbon and silicon. The reduced Ti metal can form titanium carbide, nitride, or carbonitride, which all have very high melting temperatures and will precipitate as solid from the melt. Deliberate charging of ilmenite to the blast furnace is used for the protection of the hearth refractories and for repair of the damaged area in the hearth .
There are several examples of apparently intrusive masses of ilmenite associated with anorthositic massifs (e.g., Tellnes, Norway; Lac Tio, Quebec; Ilmen Mountains, Russia; Force, 1991). These bodies may exceed 300Mt and show a variety of structural and textural forms. There are clearly discordant bodies resembling dikes and sills, with xenoliths and vein-like apophyses; there are also lenticular or equidimensional masses as well as very extensive concordant layers that apparently form part of the magmatic stratigraphy. There is as yet little petrogenetic evidence to shed light on the origins of these rocks, but their intrusive forms suggest that they are similar in origin to the Ti-magnetite deposits described earlier.
Magnetite is often contaminated with titanium, forming minerals like ilmenite. The contaminated mineral shows an appreciable degree of magnetism. This property is made use of in the separation of ilmenite from other economical minerals such as rutile, monazite, zircon, leucoxene in Western Australia, Weipa in Queensland, Kerala in South India and other places where heavy minerals are present in beach sands.
The ionic model of magnetite is considered as Fe3+ [Fe3+ Fe2+] O42. The crystals are cubic with an inverse spinel structure. The cations [Fe3+, Fe2+] are in the octahedral sites. The Fe3+ is half in tetrahedral and half in the octahedral sites. The spontaneous magnetism exhibited by magnetite is therefore entirely due to Fe2+ per Fe3O4. The electronic configuration of Fe3+ is (3d)5 and that of Fe2+ is (3d)6. Quantum mechanics has helped establish discrete changes in magnetic moments that can occur. The orientations of magnetic moments in the crystals are either parallel or anti-parallel to the applied magnet field.
The beach sand that contains silica, aluminum silicate, titanium (ilmenite), and zircon are found along the seashore in Florida, USA and elsewhere. A process has been developed  by which alumosilicate, zircon, and ilmenite were recovered separately.
Initially ilmenite was recovered using magnetic separation. The nonmagnetic fraction is stage conditioning at 60% solids with HF and alpha sulfostereic acid followed by pulp dilution to 25% solids and zircon+alumosilicate bulk concentrate was recovered while silica reported to the tailing. The concentrate was scrubbed with NaOH to remove residual collectors followed by conditioning with dextrin and amine acetate as zircon collector at pH 8.5. Zircon concentrate was produced while alumosilicate reported to the tailing. Using this method a zircon concentrate assaying 66.0% ZrO2 at 82% recovery was achieved. High-grade alumosilicate was also produced. The separation flow sheet is presented in Figure 31.6.
Titanium is strongly fractionated into FeTi oxides (e.g., ilmenite or titanomagnetite) and to a lesser extent in accessory phases, such as sphene or rutile. Ti oxides and ilmenite are very resistant to weathering and are transported into sediments with only limited decomposition. In this process, Ti is dissolved but quickly transforms into Ti-oxide-aquate and subsequently into anatase or rutile (TiO2). As such Ti is locally accumulated during chemical weathering and reflects residues, new products of weathering, and diagenetic minerals. The distribution of Ti in clays is mostly orientated on the coarser grain size fraction, but differs considerably according to different sources.
Triboelectric separation, as an entirely dry technology, is a prospective method to process fine minerals. The aim of this paper is to investigate the performance of triboelectric separation of ilmenite and quartz minerals in a lab unit and to get ready for the separation of ilmenite ore. A tribocharge measurement system was used to test the triboelectric properties of ilmenite and quartz particles with tribochargers respectively made of PVC, PPR, PMMA, Teflon, copper, stainless steel and quartz glass. The results show that the ilmenite particles charged positively while quartz charged negatively when tribocharged with PVC tribocharger. The mixture of 12% ilmenite and 88% quartz was prepared for the triboelectric separation. The recovery of ilmenite increases with the increase of airflow rate, decreases with the increasing feed rate, and grows up firstly and then decreases with the increasing voltage. A maximum ilmenite recovery of 51.71% with ilmenite content 32.72% was obtained at 40m3/h airflow rate, 6g/s feed rate and 20kV voltage. According to the optimal parameters of the separation of ilmenite and quartz mixture, fine ilmenite ore with 7.55% Ti content was beneficiated using the unit and the Ti content increased to12.32% in concentrate product.
The introduction of centrifugal force in HGMS field improves separation selectivity.The matrix rotation improves capture probability and recovery for magnetic particles.Centrifugal HGMS achieves an improved separation performance for fine ilmenite.Centrifugal HGMS presents a new method for separation of para-magnetic minerals.
High gradient magnetic separation (HGMS) has been an effective method for the concentration or removal of fine para-magnetic particles from suspension, but its powerful magnetic capture to magnetic particles results in the mechanical entrainment of non-magnetic particles in magnetic product, and thus reduces the separation selectivity. HGMS in centrifugal field (CHGMS) is proposed to improve the separation selectivity, and in this investigation a cyclic pilot-scale CHGMS separator was used to concentrate fine ilmenites from slurry. The theoretical descriptions on this CHGMS process indicate that the introduction of centrifugal field in the HGMS field has a promoting effect on the magnetic capture of matrix to magnetic particles and significantly improves the HGMS performance, and a minimum critical magnetic field force is required for the capture of magnetic particles in the centrifugal field. These theoretical descriptions were experimentally verified and the dependence of CHGMS performance on the key parameters such as centrifugal acceleration was determined. This CHGMS method has achieved a significantly improved separation selectivity and performance to the fine ilmenite, and thus provided a potential prospect in the development of CHGMS technology.
The future utilization trend of titanium resource will be largely relied on ilmenite.Combined processing technologies will be more effective in ilmenite dressing.Flotation proves to be an indispensable step for ilmenite upgrading in future.Future research needs on ilmenite beneficiation are discussed.
Ilmenite, as the main titanium source in practice, is of critical importance in meeting the pressing needs of various titanium associated fields. Herein, a review of ilmenite mineral processing by flotation is conducted to systemise the development of technologies in ilmenite upgrading. It proves that Australia and China are the top two countries with higher titanium reserves than other countries but with different metallogenic mechanisms. The basic properties of ilmenite and its metallogenic mechanism codetermine the final choice for ilmenite-containing ores beneficiation. Flotation has been an indispensable step for ilmenite upgrading as time goes and many collector types that can float ilmenite in different pH ranges have been developed. To date, various surface modification methods have proven to be a research hotspot. How to improve the flotability of fine ilmenite and comprehensive recycling of those historic ilmenite-containing tailings are much deserved in future.
Magnetic coating enlarged magnetism difference between ilmenite and titanaugite.SEM/EDS confirmed magnetite selectively coated onto ilmenite surface.Magnetic attraction force dominated magnetite selective coating behavior.
Magnetic separation of ilmenite from titanaugite was conducted by the selectively magnetic coating method in this study, and the mechanism of magnetite coating on ilmenite was investigated by calculating the interaction force. After magnetic coating, the recovery of TiO2 in mixed mineral magnetic separation increased by 36%. Scanning electron microscopy (SEM) confirmed that magnetite preferentially coated onto the ilmenite surface during magnetic coating process, leading to an obvious enhancement of ilmenite magnetism. Furthermore, the selective coating behavior of magnetite was ascribed to a physical interaction and has been confirmed by the Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The calculation of interaction force indicated that the magnetic attraction force between ilmenite and magnetite was stronger than that between magnetite and titanaugite, which resulted in the selective coating of magnetite on the mineral surfaces. Therefore, magnetic coating has potential in improving the magnetic separation of ilmenite from titanaugite.
The effects of corrosion temperature, oxygen flow rate and corrosion time on the transformation of metallic iron were systematically studied, and the effects of mineral phases of Fe-bearing products on TiFe separation were investigated. The reaction mechanism of metallic iron in corrosion process was proposed. The results showed that corrosion temperature played a key role in determining the transformation of metallic iron in reduced ilmenite during corrosion process. Under suitable corrosion conditions, Fe-bearing mineral in reduced ilmenite could be converted to amorphous ferric hydroxide, lepidocrocite, hematite and magnetite, respectively, and lepidocrocite was the most easily separated Fe-bearing mineral from corrosion products owing to the significant density difference between lepidocrocite and Ti-rich materials. The Ti-rich material with 77.81 wt.% TiO2 and Fe-bearing product with 52.69 wt.% total Fe were obtained by gravity separation. The Ti recovery ratio and Fe recovery ratio were 91.16% and 86.27%, respectively.
The authors are grateful to the Natural Science Foundation of Hunan Province, China (Grant No. 2019JJ50816) and the National Natural Science Foundation of China (Grant No. 50504018) for supporting this research, and they acknowledge the support of State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization.
Zheng, Fq., Liu, X., Guo, Yf. et al. Transformation and separation of metallic iron in reduced ilmenite during corrosion process. J. Iron Steel Res. Int. 27, 13721381 (2020). https://doi.org/10.1007/s42243-020-00476-z