PU 12 Aluminate Slurry Make-up
Digested slurry from Pu 11 is pumped into mixed tanks where dilution of slurry takes place and afterdesilication continues. slurry is diluted by wash water coming from PU 14 red mud washing and filtration to the required concentration.
To keep the temperature of aluminate slurry on desired level, the wash water is heated by steam from PU 24 Boiler house. Aluminate slurry is from PU 12 pumped into sedimentation tanks of PU 13.
PU 13 Aluminate Liquor Separation
Aluminate slurry from PU 12 is fed into sedimentation tanks and flocculant solution is simultaneously added. In the sedimentation tanks the red mud sedimentates and is drawn off to Unit PU 14 in such way to keep steady required solids content of red mud slurry.
Overflow from sedimentation tanks-aluminate liquor is collected in collecting tank from where it is pumped to control filtration where the rest red mud particles are caught.
After control filtration in kelly filters the alumiate liquor is routed to unit PU 17A.
Preparation of flocculant solution takes place in the unit PU 13 too. the concentrated flocculant is diluted to required concentration by overflow wash water from PU 14.
PU 14 Red Mud Washing and Filtration
Thickened red mud from PU 13 contains solids of red mud and aluminate liquor which has to be washed out.
The washing takes place in three thickeners and it is done counter currently by process water coming from PU 35.
Washed red mud is filtered on vacuum drum filters but before filtration red mud is causticized by addition of lime milk to decrease the losses of soda. In the caustification step about 42.5% of Na2O which is contained in red mud is diluted to the concentration of solids about 50% wt. by waste water and pumped away to the disposal area.