How is pure chromium made through the aluminothermic process?

The aluminothermic process is a method used to produce pure chromium by reducing chromium oxide ($C{r}_2{O}_3$) with aluminum.1

The process follows these key steps:

• Preparation: Fine ore, soda, and lime are roasted at 1,100 °C (2,000 °F) to create a calcine. This material is leached to remove insoluble gangue, then reduced and precipitated to obtain pure $C{r}_2{O}_3$.1
• Reaction: The $C{r}_2{O}_3$ is blended with finely divided aluminum powder and placed into a refractory-lined container.1
• Ignition: Once ignited, the combustion generates temperatures exceeding 2,000 °C (3,600 °F). This intense heat facilitates a clean separation of the chromium metal from the slag.1

Depending on the quality of the starting materials, this method yields chromium with a purity level between 97 and 99 percent. This technique was pioneered by the German chemist Hans Goldschmidt in 1898.12