How is the aluminium produced ?
Aluminum is common in the Earth's crust but rare in its free form. Aluminum is difficult to extract because its primary ore, aluminum oxide (Al2O3), is so stable. The following steps will explain how aluminum is isolated.
- Mine bauxite. Bauxite is not a specific mineral, but a group of minerals containing aluminum hydroxides. Wash the bauxite in hot sodium hydroxide (NaOH) at 250 degrees Celsius to produce aluminum hydroxide by the following equation: Al2O3 + 2NaOH + 3H2O -> 2Al(OH)4 + 2Na
- Filter out the other components of bauxite as solid impurities. Cool the solution and the aluminum hydroxide will precipitate out. Remove the aluminum hydroxide from the solution and heat it to 1,050 degrees Celsius, yielding aluminum oxide by the following equation: 2Al(OH)3 -> Al2O3 +3H2O.
- Heat aluminum oxide in the presence of carbon to obtain aluminum by direct reduction using the following equation: 2Al2O3 + heat + 3C -> 4Al + 3CO2. This method is useful for demonstration purposes but is not commercially practical because aluminum melts at 2,000 degrees Celsius.
- Mix sodium hexafluoroaluminate (Na3AlF6) with aluminum fluoride (AlF3) in a carbon-lined bath. Heat this mixture until it melts and dissolve the aluminum oxide. Run an electric current through this mixture to cause the reaction given in Step 2. The carbon dioxide (CO2) will collect at the anode and the pure aluminum will collect at the cathode. This step is more economical than Step 2 because this mixture melts at 950 degrees Celsius.
- Recycle aluminum. This method has become increasingly common since the manufacture of soft drink cans began in the 1960s. Recycling requires 5 percent of the energy that the initial production does.