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Chloride Process Titanium Dioxide

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Sulphate Process Titanium Dioxide

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In the sulfate process, ilmenite (FeTiO3), a common iron/titanium oxide material, is used. It is treated with concentrated sulfuric acid (H2SO4) and the titanium oxygen sulfate (TiOSO4) is selectively extracted and converted into titanium dioxide.

1. Ilmenite is treated (digested) with a 60% excess of concentrated sulfuric acid at a temperature around 100 °C. The following reaction takes place:

FeTiO3 + 2H2SO4 → FeSO4 + TiOSO4 + 2H2O

2. In the next stage, the waste product iron(II)sulfate is removed. As FeSO4 is not very soluble at low temperatures, the solution is cooled to around 15 °C and FeSO4 crystallises out. It can then be removed by filtration.
The remaining aqueous digestion products are heated to around 110 °C in order to hydrolyse the titanium oxygen sulphate.

TiOSO4 + (n+1)H2O → TiO2•nH2O + H2SO4

The hydrolysis stage of the process produces sulfuric acid waste and a precipitate gel containing hydrated titanium dioxide.

3. In the last stage, the hydrated titanium dioxide is heated in large rotary kilns to drive off the water and produce crystals of anatase or rutile (2 forms of titanium dioxide).

TiO2•nH2O → TiO2 + nH2O

Water is removed at temperatures between 200–300°C. Seed crystals are added to start the crystallisation process. Depending on the final heating temperature (800−850°C or 900−930°C), either anatase or rutile is formed, respectively.
The sulfate process requires the use of very large quantities of sulfuric acid and produces copious amounts of acidic waste. This acidic waste could cause significant damage to the environment, if not disposed of responsibly.