How the Kroll Process Produces Titanium Sponge

1. Converting Titanium Ore to Titanium Tetrachloride

The conversion process begins with titanium ore, primarily rutile. Once the ore is collected, it is placed into a specialized apparatus known as a chlorinator. Here, ore is reduced with the introduction of coke and treated with chlorine gas at high temperatures. When chlorine gas is introduced, it reacts with titanium to generate titanium tetrachloride, a colorless and volatile liquid with a distinctive, pungent odor. This step isolates titanium from oxygen and effectively removes various impurities, producing a purified form of titanium in its chlorinated state.

2. Purification of Titanium Tetrachloride

The crude titanium tetrachloride is accompanied by various undesirable byproducts that can affect its purity. To achieve a high level of refinement, the titanium tetrachloride undergoes a process known as fractional distillation. This technique leverages the differences in boiling points to effectively separate TiCl₄ from its impurities, allowing the more volatile titanium tetrachloride to rise through the distillation column. As a result, a highly purified form of titanium tetrachloride is obtained, ensuring it is ready for the subsequent processing stages. Fractions close to titanium are further separated by precipitation. 

3. Reduction to Titanium Sponge

The purified titanium tetrachloride is meticulously transferred to a sealed reactor, where it is combined with molten magnesium. This process occurs at extremely high temperatures and reduces titanium tetrachloride to pure titanium metal.

The outcome of this reaction is the production of a porous, sponge-like form of titanium metal, known as titanium sponge. Additionally, magnesium chloride is generated as a byproduct of the reaction, which can be further processed or reused.

4. Purification of Titanium Sponge

After initial processing, the titanium sponge retains some residual magnesium and magnesium chloride. These impurities are eliminated by leaching with a suitable acid or vacuum distillation to purify it. This process effectively vaporizes the unwanted materials while preserving the integrity of the titanium.

The Kroll Process Step-by-Step: Diagram and Explanation

1. Ore Preparation: Titanium ore, most commonly rutile, is mixed with coke.
2. Chlorination: At high temperatures, coke reduces the ore, and chlorine gas produces TiCl₄.
3. Distillation: TiCl₄ is purified through fractional distillation and precipitation.
4. Reduction: TiCl₄ is reduced with molten magnesium in a sealed reactor to create titanium sponge.
5. Purification: Byproducts are removed from the titanium sponge through leaching or distillation.