Process
In the Bayer process, bauxite is digested by washing with a hot solution of sodium hydroxide, NaOH, at 175 °C. This converts the aluminium oxide in the ore to sodium aluminate, 2NaAl(OH)4, according to the chemical equation:
- Al2O3 + 2 NaOH + 3 H2O → 2 NaAl(OH)4
The other components of bauxite do not dissolve. The solution is clarified by filtering off the solid impurities. The mixture of solid impurities is called red mud, and presents a disposal problem. Next, the alkaline solution is cooled, and aluminium hydroxide precipitates as a white, fluffy solid:
- NaAl(OH)4 → Al(OH)3 + NaOH
Then, when heated to 980°C (calcined), the aluminium hydroxide decomposes to aluminium oxide, giving off water vapor in the process:
- 2 Al(OH)3 → Al2O3 + 3 H2O
A large amount of the aluminium oxide so produced is then subsequently smelted in the Hall–Héroult process in order to produce aluminium.
Read more about this topic: Bayer Process
Famous quotes containing the word process:
“It haunts me, the passage of time. I think time is a merciless thing. I think life is a process of burning oneself out and time is the fire that burns you. But I think the spirit of man is a good adversary.”
—Tennessee Williams (1914–1983)
“The process of discovery is very simple. An unwearied and systematic application of known laws to nature causes the unknown to reveal themselves.”
—Henry David Thoreau (1817–1862)
“[Wellesley College] is about as meaningful to the educational process in America as a perfume factory is to the national economy.”
—Nora Ephron (b. 1941)