The other components of bauxite do not dissolve and are filtered from the solution as solid impurities (
clarification)
Solubility/particle size i guess.
When then heated to 1050°C, the aluminium hydroxide decomposes to alumina (
calcination), giving off water vapor in the process:
mmm...some kind of chemical property.
The problem with your process is that it involves ALOT of chemical properties.
Where the year 11 syllabus focuses on (and defines) mixtures as those that can be separated physically.