This is a process for the production of
Alumina, which was patented by Karl Josef Bayer in
Austria in 1888. It involves the digestion of crushed
Bauxite in
sodium Hydroxide solution at high temperatures (~240
oC).
Most of the Alumina will dissolve, leaving a "red mud", which is removed by filtration.
The remaining product is then decomposed by reversing the reaction, by cooling and adding the trihydrate, Al2O3.3H2O.
This gives:-
2NaAlO2 + 2H2O -> 2NaOH + Al2O3.3H2O
This is then heated to drive off the water of crystallization, which produces Alumina.