Production of Pigments on the Basis of Titanium Tetrachloride

The article describes the manufacture of titanium dioxide, or titania, on the basis of titanium tetrachloride. The main technological requirements for the production of titania are listed, the most prospective raw materials for the chlorination method are given, the description of the technological process for the yield of titania is described.


Introduction
Titania, or titanium dioxide [1,2,3,4,5], is a polymorphous pigment found naturally in several crystal modifications. Titania forms solid solutions with transition metal oxides hereby distorting its crystal lattice and acquiring a coloured tinge. The phenomena of phototropy and photochemical activity are also inherent in titania.

Requirements for the yield of titania
To produce any kind of pigment, including titania [22,23], the following requirements must be fulfilled: 1. The sufficient amount of direct and auxiliary materials of the specified quality. 2. The main and auxiliary equipment of the specified capacity. 3. The power (viz. electric energy, technical and fresh water, steam, etc.) and human resources of the specified amount.
4. The economically achievable technology for the production of the specified high quality product.

Preparation of titanium raw materials for the yield of titania from titanium tetrachloride
The technology of titanium slag chlorination has been developed and applied at titaniummagnesium plants in order to yield titania, by means of the chlorination method. Machinebuilding enterprises produce special equipment both for slag chlorination, and for titanium tetrachloride purification. An example of such equipment is an oxidation unit for titanium tetrachloride, which is supplied with an arc plasmatron having annual yield capacity equal to 3000 tons of titania. The quality of titania yielded in this unit is on a level with the quality of titania yielded by the sulphatation method.
The most promising raw material for the yield of titania by the chlorination method is a titanium-quartz ore deposit, with the ore purification technology developed at a specially built ore processing plant. The plant has a yield capacity equal to 240 thousand tons of titanium concentrate containing 50 ... 52% of titania; 41 ... 45% of silica; 2 ... 3.5% of ferric oxide; 2 ... 3% of alumina; 0.5 ... 1.0% of sodium oxide; 0.06% of sulphur and 0.18% of phosphorus pentoxide.
The technology of silica pressure leaching with sodium hydroxide applied for initial concentration of ilmenite has been developed and tested in order to yield titanium-silicon of a higher concentration value than has been applied by far. When processing by pressure leaching, two chemical products are obtained: titanium-processed concentrate containing 88 ... 90% of titania and alkaline-siliceous solutions subsequently subject to filtration, crystallization and centrifugation, and finally converted into sodium metasilicate [24].
It has been stated that the supply of rutile concentrate containing 94 ... 95% of titania from ore processing factories provides the most economically reasonable yield of titania further on.

Development of the technology for the yield of titania from titanium tetrachloride
As it was stated above, various technologies for titanium slag chlorination, also of titanium tetrachloride purification, and titanium tetrachloride oxidation with oxygen and preliminary heating of reagents have been developed at a titanium-magnesium plant with annual yield capacity equal to 3000 tons. The technology of titanium concentrate chlorination, and titanium tetrachloride oxidation with oxygen using arc plasmatron heating has been developed at a pilot plant with annual yield capacity equal to 200 tons of titania. The quality of titania produced in this unit is on a level with the best foreign samples.
The pilot plant affords full facilities not only for testing the obtaining technology of high quality anatase-phase and rutile-phase titania, but also for titania modification with the obtaining of different-purpose pigment grades.
The research of the surface condition of titania samples obtained by the chlorination method has stated that the electric double layer of titania samples consists mainly of components of acid-base dissociation of alumina, which has a significant effect on the properties of the electric double layer and the pH value of the isotopes. The pH value of the isoelectric point and the isoelectric adsorption point of H + and OH-ions are close to each other and both equal to 6.5 ... 8.0 [25].
In accordance with the above-given diagram, titania ore is fed from hopper 1 into bead mill 4 for future dechlorination. Besides, the specified amount of chemically purified water and caustic magnesite is also fed from tank 3 and hopper 2 to bead mill 4. In bead mill 4, while heating, the titania ore is ground to the specified size, and the chlorine bound by caustic magnesite passes into the solution according to the reaction (1): The obtained pigment slurry is subsequently fed from bead mill 2 to filter press 6 by pump 5, whereas the filtrate from filter press 6 is fed to collector 7, with the obtained paste fed primarily to centrifuge 8 and finally to hydroseparator 9 where the paste is separated into coarse and fine fractions. The coarse paste fraction is subject to additional microniziation in steam-jet mill 11, then refed to the centrifuge 8, whereas the fine paste fraction is fed from collector 12 to reactor 13 for the final surface treatment. Reagents in specified amounts are fed into reactor 13 in the following sequence: firstly, aluminium sulphate and sodium carbonate, and secondly, liquid glass and alkali. The obtained stabilized slurry is next fed to filter press 6, and then flushed from the filter press surface with condensate supplied from vapour condenser 20 as well as chemically purified water, to the condition with complete absence of water-soluble salts in the obtained paste.
The flushed paste is fed to combined dryer 17, then dried and ground to the specified size. The ground pigment, during the accumulation process, is transferred by the auger to hopper 19, from where, when needed, is either packed into containers or additionally micronized in steam jet mill 11, and finally sent to finished product hopper 21. Titania modified by the described technology fully complies with its technical requirements. The combined feed of aluminium-, silicon-, and zinc-containing additives at the stage of titanium tetrachloride oxidation provides good physical and technical properties and weather resistance of the yielded titania [26].

Conclusions
The study have stated that 1. The most promising raw material for the yield of titania by the chlorination method is a titanium-quartz ore deposit. 2. The most economically reasonable method is to supply rutile concentrate from ore processing factories with a content of titania equal to 94 ... 95%.
3. The quality of titania produced with titanium concentrate chlorination, and titanium tetrachloride oxidation with oxygen using arc plasmatron heating in this unit is on a level with the best foreign samples. 4. The combined feed of aluminium-, silicon-, and zinc-containing additives at the stage of titanium tetrachloride oxidation provides high properties of the yielded titania.