Chloride process, titanium dioxide manufacture

FIGURE 2 Titanium dioxide manufacture by the chloride process. 

Precipitation of a hydrated titanium oxide by mixing aqueous solutions of titanium chloride with alkaU forms the precipitation seeds, which are used to initiate precipitation in the Mecklenburg (50) variant of the sulfate process for the production of pigmentary titanium dioxide. Hydrolysis of aqueous solutions of titanium chloride is also used for the preparation of high purity (>99.999%) titanium dioxide for electroceramic appHcations (see Ceramics). In addition, hydrated titanium dioxide is used as a pure starting material for the manufacture of other titanium compounds. 

Two processes are used in the manufacture of titanium dioxide pigments the sulfate process and the chloride process. The chemistry of the sulfate process, the longer established of the two methods, is illustrated schematically in Scheme 9.1. In this process, crude ilmenite ore, which contains titanium dioxide together with substantial quantities of oxides of iron, is digested with concentrated sulfuric acid, giving a solution containing the sulfates of Ti(iv), Fe(m) and Fe(n). Treatment of this... 

Presently there are two main processes for manufacturing this important white pigment. The main one involves reaction of rutile ore (about 95% Ti02) with chlorine to give titanium tetrachloride. For this reason we have chosen to group this key chemical under chlorine and sodium chloride. The titanium tetrachloride is a liquid and can be purified by distillation, bp 136°C. It is then oxidized to pure titanium dioxide and the chlorine is regenerated. Approximately 94% of all titanium dioxide is made by this process. 

About 70% of all iron oxide pigments are produced synthetically. Copperas or ferrous sulfate heptahydrate (FeS04-7H20) is the primary source of iron. It is a byproduct of the sulfate process for the manufacture of titanium dioxide as well as a by-product of pickling operations in the steel industry. Other sources of iron include ferric sulfate, ferrous chloride, ferric chloride, and the iron oxide slurry from the production of aniline by nitrobenzene reduction. 

There are two major processes for the manufacture of titanium dioxide pigments, namely (1) sulfate route and (2) chloride route. In the sulfate process, the ore limonite, Fe0Ti02, is dissolved in sulfuric acid and the resultant solution is hydrolyzed by boiling to produce a hydrated oxide, while the iron remains in solution. The precipitated titanium hydrate is washed and leached free of soluble impurities. Controlled calcinations at about 1000°C produce pigmentary titanium dioxide of the correct crystal size distribution this material is then subjected to a finishing coating treatment and milling. The process flow sheet is shown in Fig. 7.1 [4],... 

Titanium dioxide is also obtained from the chloride process, which gives an additional option to either hydrolyze titanium tetrachloride with steam or oxidize it with air to the dioxide. In this method, the pigment can be obtained from the gaseous phase. In this method, the feedstock must contain 90% rutile ore. It is not always possible to find such an ore therefore beneficiated feedstock is used which is obtained by various routes. Figure 2.67 compares both manufacturing processes. 

These silicas are produced by a gas phase, as opposed to a solution process. There are a number of possible gas phase routes, but the predominant one is by hydration of silicon tetra-chloride. This is carried out in a flame of hydrogen and oxygen at a temperature of 1000 °C or above, and is similar to the chloride route for the manufacture of titanium dioxide pigments. Details of the process can be found in the work by Watson [39] (see also Figure 2.10). 

These ores are the principal raw materials used in the manufacture of titanium dioxide pigment The first step to purify the ore is basically a refinement, using either sulfuric acid (sulfate process Gesenhues et al., 2003) or chlorine (chloride process) as an extraction agent... 

Inorganic chemicals manufacture has the potential to contaminate water with trace elements. Among the industries regulated for potential trace element pollution of water are those producing chlor-alkali, hydrofluoric acid, sodium dichromate (sulfate process and chloride ilmenite process), aluminum fluoride, chrome pigments, copper sulfate, nickel sulfate, sodium bisulfate, sodium hydrosulfate, sodium bisulfite, titanium dioxide, and hydrogen cyanide. 

Titanium dioxide is manufactured by two processes, the sulfate process and the chloride process. In the sulfate process, ilmenite ore (FeTiOg) is dissolved in concentrated sulfuric acid and insoluble impurities are removed by clarification, flocculation, sedimentation and filtration. The resulting solution is further purified by crystallization to remove ferrous sulfate from titanyl sulfate solution. The titanyl sulfate solution is then hydrolyzed to give hydrated titanium dioxide, which is calcined at about 900 to 1100 °C to give the titanium dioxide pigment. Both anatase and rutile-type titanium dioxide pigments are produced using this method. 

Another method for manufacturing titanium dioxide is the chloride process wherein natural rutile ore is chlorinated to form titanium tetrachloride, which is purified, vaporized and reacted with oxygen at elevated temperature to form the dioxide. 

There are two commercial processes used today to manufacture titanium dioxide. The sulfate process produces titanium dioxide from the mineral ilmenite. The chloride process manufactures titanium dioxide from the mineral rutile. Both of these processes are shown in Figure 8.13. 

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