By Intratec Solutions |
This column is based on “Titanium Dioxide Production Process – Cost Analysis,” a report published by Intratec. It can be found at: www.intratec.us/analysis/titanium-dioxide-production-cost.
Titanium dioxide (TiO2) is the naturally occurring oxide of titanium, and is found particularly in rutile ores. The compound has great technological importance: it is a commodity chemical widely used in paints, coatings, plastics, food, cosmetics and pharmaceuticals. The vast majority of titanium ore is processed into titanium dioxide, the most used titanium product.
The process under analysis comprises three major sections: (1) ilmenite processing; (2) titanium dioxide hydration; and (3) titanium dioxide treatment (Figure 1).
Ilmenite processing. Initially, ilmenite ores are dried to a moisture content of less than 0.1% and ground to give a mean particle size of less than 40 mm. This prevents heating and premature reactions downstream. The finely ground, titanium-bearing ore is dissolved in sulfuric acid and water, forming a solution rich in metal sulfates. The digester effluent is dissolved in cold water, forming a solution of sulfate salts of iron, titanium and other trace metals. This solution is processed for the removal of impurities (for example, silica and silicates) and contacted with iron scrap for the reduction of Fe3+ (ferric salts) to Fe2+ (ferrous salts). The solution is separated from unreacted solids and cooled in such a way that crystals of iron(ll) sulfate precipitate and are removed. The crystals are subsequently concentrated in a vacuum evaporator.
Titanium dioxide hydration. The solution, at this point rich in titanyl sulfate (TiOSO4), is mixed with rutile seed crystals and submitted to a hydrolysis reactor, where the titanyl sulfate is converted to insoluble, hydrated titanium dioxide. The hydrolysis effluent is passed through vacuum filters in such a way that the titanium oxide hydrate is separated from the solution and washed with water. The acid solution is concentrated in multiple columns and recycled to be reused in the digestion.
Titanium dioxide treatment. The hydrated titanium dioxide is heated in a rotary kiln, which evaporates water and decomposes residual sulfuric acid in the solid. The weak acid from the calcination and sludge from titanyl sulfate purification is neutralized with lime. After a filtration step, the resulting sludge is discharged, while the filtrate is recycled to the first section. The titanium dioxide crystals obtained are milled to a specific size, coated, dried and packed.
Titanium dioxide is largely produced by the reduction of titanium tetrachloride, obtained in turn from the chlorination of natural rutile, synthetic rutile derived from ilmenite, or even slags rich in TiO2 produced by metallurgical treatment of ilmenite. TiO2 is also manufactured by treatment of ilmenite with sulfuric acid. These two pathways for TiO2 production are presented in Figure 2.
The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce titanium dioxide was about $1,800 per ton of titanium dioxide in the third quarter of 2015. The analysis was based on a plant constructed in the U.S. with capacity to produce 120,000 metric ton per year of titanium dioxide.
Edited by Scott Jenkins