Impurities Titanium

Discovered by Gregor in 1791 named by Klaproth in 1795. Impure titanium was prepared by Nilson and Pettersson in 1887 however, the pure metal (99.9%) was not made until 1910 by Hunter by heating TiCk with sodium in a steel bomb. 

The iodide or van Arkel-de Boer process is a volatilization process involving transfer of an involatile metal as its volatile compound. It is used for the purification of titanium. The reaction of iodine gas with impure titanium metal at 175°C yields gaseous titanium iodide and leaves the impurities in the sohd residue. 

Figure 25-4 HPLC column with replaceable guard column to collect irreversibly adsorbed impurities. Titanium frits distribute the liquid evenly over the diameter of the column. [Courtesy Upchurch Scientific, Oak Harbor. WAJ...

The main impurity of the filtrate is the iron(II) sulfate which can be crystallized as the heptahydrate, FeS04-7H2 O, by cooling the solution to a temperature below 15°C. This process is most often carried out in vacuum crystallizers. The crystals of iron sulfate are separated by centrifugation or filtration (qv). To prevent premature hydrolysis of titanium dioxide, the temperature of the above processes should not exceed 70°C. 

The concentrated mother Hquor contains a large amount of sulfuric acid in a free form, as titanium oxy-sulfate, and as some metal impurity sulfates. To yield the purest form of hydrated TiOg, the hydrolysis is carried out by a dding crystallizing seeds to the filtrate and heating the mixture close to its boiling temperature, - 109° C. The crystal stmcture of the seeds (anatase or mtile) and their physical properties affect the pigmentary characteristics of the final product. 

The chlorination is mostly carried out in fluidized-bed reactors. Whereas the reaction is slightly exothermic, the heat generated during the reaction is not sufficient to maintain it. Thus, a small amount of oxygen is added to the mixture to react with the coke and to create the necessary amount of heat. To prevent any formation of HCl, all reactants entering the reactor must be completely dry. At the bottom of the chlorination furnace, chlorides of metal impurities present in the titanium source, such as magnesium, calcium, and zircon, accumulate. 

Impurities that form volatile chlorides leave as gases at the top of the furnace together with the TiCl. By cooling those gases, most impurities, with the exception of vanadium and siUcon chlorides can be separated from the titanium tetrachloride [7550-45-0]. Vanadium chlorides can be reduced to lower oxidation state chlorides that are soHds highly volatile SiCl can be removed from TiCl by fractional distillation. 

Tetrachloride-Reduction Process. Titanium tetrachloride for metal production must be of very high purity. The requited purity of technical-grade TiCl for pigment production is compared with that for metal production in Table 4. Titanium tetrachloride for metal production is prepared by the same process as described above, except that a greater effort is made to remove impurities, especially oxygen- and carbon-containing compounds. 

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