PU 06 NaOH Storage
The liquid caustic soda with concentration of 50% is transported to the plant by railway tankers and from them is unloaded into two storage tanks with capacities of 4000m3 .caustic soda from these tanks is delivered to the unit PU18 for preparation of leaching solution and to unit PU unit PU 16 for preparation of cleaning solution.
PU 18 Evaporating and Desalting
Evaporating and desalting unit protects liquor from dilution and from increasing of sodium salt content above admissible limit.
The unit consists of two evaporating line and one common desalting line. Weak caustic solution coming from PU 17A is thickened in five evaporating stages to concentration at which sodium salt falls out from the solution. No formation and fall out of salts is expected under normal operation conditions provided that specified bauxite is processed, therefore desalting system will be put in operation only rarely.
Sodium salts can be separated from the caustic liquor by filtration on vacuum drum filter. Solid salts are dried and transported for use out of the plant.
Strong caustic solution is discharged to prede-silication unit PU 09.
PU 18A H2SO4 Racking
This unit secures the racking of 96% sulphuric acid from railway tanks to PU 18. The sulphuric acid is used for chemical cleaning in PU 13, 14, 16, 18.