Hungary Sludge Disaster - How alumina is made from bauxite

[sharon sanders]

STEP 1- Crushing and Grinding: Alumina recovery begins by passing the bauxite through screens to sort it by size. It is then crushed to produce relatively uniformly sized material. The ore is then fed into large grinding mills and mixed with a caustic soda solution (sodium hydroxide) at high temperature and pressure. The grinding mill rotates like a huge drum while steel rods - rolling around loose inside the mill - grind the ore to an even finer consistency. The process is a lot like a kitchen blender only much slower and much larger. The material finally discharged from the mill is called slurry.
The resulting liquor contains a solution of sodium aluminate and undissolved bauxite residues containing iron, silicon, and titanium. These residues - commonly referred to as "red mud" - gradually sink to the bottom of the tank and are removed.

more...

http://www.rocksandminerals.com/aluminum/process.htm