Bayer Process

• Bauxite, the most important ore of aluminum, contains only 30-54% alumina, Al2O3, the rest being a mixture of silica, various iron oxides, and titanium dioxide. The alumina must be purified before it can be refined to aluminum metal.
• In the Bayer process, bauxite is digested by washing with a hot solution of sodium hydroxide, NaOH, at 175°C. This converts the alumina to aluminum hydroxide, Al(OH)₃, which dissolves in the hydroxide solution according to the chemical equation: Al₂O₃ + 2 OH^- + 3 H2O → 2 [Al(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.