Briefly describe the process of aluminum production from bauxite. Describe the electrolyte and write the anode and cathode half-reactions.
Bauxite is dissolved in NaOH to remove impurities and form aluminum hydroxide; the aluminum hydroxide is then precipitated out, and water is removed to produce pure aluminum oxide (alumina). In aluminum production, alumina (Al2O3) is dissolved in molten cryolite (Na3AlF6). This molten mixture is then placed in a container with graphite electrodes (cathode and anode are both graphite). The molten mixture serves as the electrolyte. At the cathode: Al3+ (l) + 3e- ---- Al (l) Aluminum ions gather electrons to form aluminum metal, which is liquid due to the high temperatures. The molten metal sinks to the bottom of the container, and is piped off. At the anode: 2O2- (l) --- O2 (g) + 4e- The oxide ions from alumina lose their electrons to form oxygen gas.
Bauxite is purified by washing with sodium hydroxide and then seeding with dry ice. The purified aluminium oxide is then dissolved in molten cryolite at 900 degrees C (the electrolyte). It is electrolysed with grapite anodes and a graphite cathode that acts as the vessel for the reaction. Anode; 2 O2- - O2(g) + 4e Cathode: Al3+ + 3e - Al(l)
