Explain leaching of alumina from bauxite?

Pure alumina( Al2O3) is obtained from bauxite ore by baeyer's process . The bauxite ore is usually contains impurities of iron oxide (Fe2O3 ),silica( SiO3) and titanium oxide (TiO3).the powdered ore is heayedwith a concentrated 45%solution of NaOH at 573-523k and 35-36 bar pressure .under these conditions alumina (Al2O3) dissolves forming sodium meta aluminate and silica as sodium silicate leaving behind the impurities. The resulting solution is filtered cooled and its ph adjusted downwards either by dilution or by neutralization with carbon dioxide.thereafyer the solution is seeded with freshly prepared samples of hydrated alumina when hydrated alumina gets precipitated leaving sodium silicate in the solution. Hydrated alumina obtained as above is filtered washed and finally heated to about 1473k to get pure alumina