Aluminium oxide is an amphoteric compound which means that it reacts with acid and base to produce salts and water. It is used in various chemical, industrial and commercial applications.
Aluminum is a metal which occurs naturally as various minerals. It has an incredible affinity towards oxygen and forms a protective layer of oxide on its surface when exposed to air.
It is very sensitive to acids and alkalis resulting in corrosion of aluminium alloys. This is caused by the fact that the oxide layer carries a negative charge, which means that when it breaks under acidic conditions it will grab the hydrogens in water molecules to form hydroxide ions.
When the oxide reaches an electronegativity of 1.5, the element will grab the oxygens in water more strongly and will start to form acid anions. This happens because the bonding between the oxide and oxygen atoms becomes ionic and thus a negative charge will be generated in the oxygen atoms.
This process is irreversible and if the oxide is not replaced, it can lead to a phase separation of aluminium. This can be a significant problem when using aluminium for industrial purposes as it can result in a risk to human health.
To study the action of alkali and acid on aluminium oxide, we performed extractions in the presence of HCl at different concentrations and with a S:L ranging from 3:10 to 4:10. The results showed that the highest percentage of aluminum extracted was achieved when the acid concentration was 2 mol/L and the time was 2 h. Increasing the HCl concentration to 4 or 8 mol/L led to a slight increase in the percentage of extracted aluminum but this was rather small.