Rutile production

An important modification of the Becher process is the development of the Synthetic Rutile Enhancement Process (SREP) route, using various leaching methods to reduce the level of radioactivity in the synthetic rutile product to internationally acceptable levels. 

The demand for TiO is much greater than the annual rutile production from mining, so synthetic TiO is produced in a large scale from ihnenite and titaniferous slag. 

The main electroceramic apphcations of titanium dioxide derive from its high dielectric constant (see Table 6). Rutile itself can be used as a dielectric iu multilayer capacitors, but it is much more common to use Ti02 for the manufacture of alkaline-earth titanates, eg, by the cocalciuation of barium carbonate and anatase. The electrical properties of these dielectrics are extremely sensitive to the presence of small (<20 ppm) quantities of impurities, and high performance titanates require consistently pure (eg, >99.9%) Ti02- Typical products are made by the hydrolysis of high purity titanium tetrachloride. 

Sn02, cassiterite, is the main ore of tin and it crystallizes with a rutile-type structure (p. 961). It is insoluble in water and dilute acids or alkalis but dissolves readily in fused alkali hydroxides to form stannates M Sn(OH)6. Conversely, aqueous solutions of tin(IV) salts hydrolyse to give a white precipitate of hydrous tin(IV) oxide which is readily soluble in both acids and alkalis thereby demonstrating the amphoteric nature of tin(IV). Sn(OH)4 itself is not known, but a reproducible product of empirical formula Sn02.H20 can be obtained by drying the hydrous gel at 110°, and further dehydration... 

It is most economical when high-grade ores are used, becoming less economical with poorer feed materials containing iron, because of the production of chloride wastes from which the chlorine cannot be recovered. By contrast the sulfate process cannot make use of rutile which does not dissolve in sulfuric acid, but is able to operate on lower grade ores. However, the capital cost of plant for the sulfate process is higher, and disposal of waste has proved environmentally more difficult, so that most new plant is designed for the chloride process. 

Under these circumstances the metal s surface within the crevice became active and it corroded with the formation of a yellowish-white corrosion product that was identified as being mainly rutile TiOj. On the other hand, a Ti-0- 13Pd alloy was found to be immune from crevice corrosion, since the presence of the palladium facilitated passivation of the metal surfaces forming the crevice. 

There is a difference of a factor of five in energy consumption between the two processes, largely due to the avoidance of evaporation of large amounts of water in the latter process. Despite this both processes still operate, although the chloride process does dominate. There are two main reasons for this first the sulfate process can use lower grade and therefore less expensive ores and secondly it produces anatase pigments as well as rutile, which is the sole product of the chloride process. 

The commonly used catalyst today is a vanadia on a titania support, which is resistant to the high SO2 content. Usually the titania is in the anatase form since it is easier to produce with large surface areas than the rutile form. Several poisons for the catalyst exist, e.g. arsenic and potassium. The latter is a major problem with biomass fuel. In particular, straw, a byproduct from grain production, seems to be an attractive biomass but contains potassium, which is very mobile at reaction tern-... 

Titanium dioxide (E171, Cl white 6) is a white, opaque mineral occurring naturally in three main forms rutile, anatase, and brookite. More than 4 million tons of titanium dioxide are produced per year and it is widely used for industrial applications (paints, inks, plastics, textiles) and in small amounts as a food colorant. ° "° Production and properties — Titanium oxide is mainly produced from ilmenite, a titaniferous ore (FeTiOj). Rutile and anatase are relatively pure titanium dioxide (Ti02) forms. Titanium oxide pigment is produced via chloride or sulfate processes via the treatment of the titanium oxide ore with chlorine gas or sulfuric acid, followed by a series of purification steps. High-purity anatase is preferred for utilization in the food industry. It may be coated with small amounts of alumina or silica to improve technological properties. 

The photolytic reduction of N2 at TiO -suspensions was at first reported by Schrauzer et al. Small amounts of NH3 and N2H4 were obtained as products. The highest activity was found with anatase containing 20-30 % rutile. Very low yields were also obtained with p-GaP electrodes under illumination It is much easier to produce NH3 from NO -solutions at CdS- and Ti02-particles using S -ions as hole scavengers . Efficiencies are not reported yet. Recently the formation of NH3 from NO was observed at p-GaAs electrodes under illumination. In this case NH3-formation was only found in the presence of transition metal ions or their complex with EDTA. 

In the production of titanium, the chlorination of rutile generates approximately 0.12 tons of waste for every ton of titanium tetrachloride produced. If ilmenite is directly chlorinated, the amount of waste is 1.5 tons for every ton of titanium tetrachloride. Large amounts of ferric chloride are produced along with volatile chlorides and oxychlorides (e.g., aluminum trichloride, silicon tetrachloride, carbon oxychloride, tin tetrachloride, vanadium tetrachloride, vanadium oxychloride) these can be removed by selective distillation. In flu-idized-bed chlorination, the build-up of liquid calcium chloride and magnesium chloride in the fluid bed interferes with the process of fluidization and hence these must be removed. 

Solar light photocatalytic hydrogen production from water over Pt and Au/Ti02 (anatase/rutile) photocatalysts influence of noble metal and porogen promotion. Journal of Catalysis, 269 (1), 179—190. 

Leucoxene has a composition similar to that of rutile, and is a product of alterations of a number of titanium minerals, most often ilmenite and sphene. It contains higher amounts of titanium, compared to ilmenite, and can range from 61% to 75% Ti02. 

Titanium minerals have been recovered from both hard rock and sand deposits. Until 1945, most of the ilmenite and rutile produced commercially came from sand deposits, but nowadays, the production of ilmenite from rock deposits exceeds that of sand deposits. Rutile, however, is exclusively produced from sand deposits, although a new technology exists that recovers rutile from rock deposits. 

The most abundant titanium sand deposits are black sands in streams and on beaches of volcanic regions. The principal black minerals are magnetite, titanoferous magnetite and black silicates, chiefly angite and homblend. It is quite difficult to produce an ilmenite suitable for pigment product from black sand, but other sand deposits that contain rutile, ilmenite and often monazite are found in Australia, USA, India and Africa. These deposits are either alluvial or marine in origin. 

The ilmenite production from heavy mineral sands exclusively utilizes a physical separation method using magnetic separation, gravity concentration and electrostatic separation. Flotation is practiced mainly for beneficiation of fine mineral sands containing rutile, ilmenite and zircon. The ilmenite that is produced in a number of operations in Western Australia, India and the USA is high in chromium, which makes the ilmenite unusable. This section discusses a new process that was developed for chromium removal from ilmenite concentrates. 

The fine -250-mesh product was preconcentrated using gravity (tabling) followed by zircon flotation and magnetic separation to produce rutile and ilmenite concentrate. The process flowsheet with points of reagent additions is presented in Figure 25.14. Using... 

Figure 25.14 Plant flowsheet with reagent additions for production of zircon, rutile and ilmenite from the Sierra Leone fines.

Kim43,49 utilized the effect of water on the activity in FTS patents using un-promoted and promoted cobalt deposited on Ti02 (rutile). For a wide range of external H20 addition levels, beneficial effects of increased productivity could be realised. However, when more than 28% water was added to the feed of the rhenium based version, the CO conversion was affected negatively. More recent experimental investigations of the effect of added water on the rate of the FTS over titania-supported Co are summarized in Table 4. 

---