Bauxite is a mainly a mixture of iron and aluminium hydroxides and oxides of Al, Fe, O and OH. Principal aluminium hydroxide minerals found in varying proportions are gibbsite and the polymorphs of boehmite and diaspore. Other components include SiO2, TiO2 and P2O5. The overall chemistry of bauxite determines its commercial usage.
Gibbsite has the chemical formula Al (OH)3, which is a trihydrate. Boehmite and diaspore have the formula AlO(OH), which is monohydrate. The main mineral of aluminium in our bauxite deposits is gibbsite. Large bauxite deposits in China and Vietnam are either low grade, high in monohydrate minerals, and/or high in reactive silica. Dissolution of monohydrate minerals requires higher temperatures and higher concentration of caustic soda; energy consumption is much higher than for dissolution of trihydrate gibbsite.
Dissolution of gibbsite requires lower temperatures and lower concentration of caustic soda, providing ABx with a significant competitive advantage.
Moreover, our bauxite deposits have low levels of reactive silica and high total alumina to silica ratios. Reactive silica is the most harmful contaminant because it forms insoluble double Al, Na silicate which reports to red mud during conversion to alumina.
High levels of reactive silica causes the loss of alumina and caustic soda, while TiO2 and P2O5 robs sodium. Our bauxite deposits are low in contaminants.