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:
“I believe that history might be, and ought to be, taught in a new fashion so as to make the meaning of it as a process of evolution intelligible to the young.”
—Thomas Henry Huxley (1825–95)
“... geometry became a symbol for human relations, except that it was better, because in geometry things never go bad. If certain things occur, if certain lines meet, an angle is born. You cannot fail. It’s not going to fail; it is eternal. I found in rules of mathematics a peace and a trust that I could not place in human beings. This sublimation was total and remained total. Thus, I’m able to avoid or manipulate or process pain.”
—Louise Bourgeois (b. 1911)
“Thinking is seeing.... Every human science is based on deduction, which is a slow process of seeing by which we work up from the effect to the cause; or, in a wider sense, all poetry like every work of art proceeds from a swift vision of things.”
—Honoré De Balzac (1799–1850)