As the serosity of red mud which come from alumyte consist of sodium aluminate solution and red mud, they must be separated to get the pure solution which reaches the requirements of the seed separation. The separated red mud have to be washed so as to reduce the loss of Na₂O and Al₂O₃ of red mud. At present most alumina plant take a settlement tank to separate and wash Bayer red mud.

The separation and washing of red mud generally include following steps:

1. dilution of red mud solution  
The thick dissoluted red mud solution use red mud lotion to dilute so as to settlement separate and reach the requirement of solution concentration and purity (SiO₂ content) which kind asks for.

2. settlement separate
The diluted red mud solution is sent to a settlement tank to separate most solution.

3. backwashing of red mud
Take backwashing several times for the bottom solution of the settlement tank. Control the loss of red mud in the limit of technological requirements.

4. controlled filter of crude solution
Controlled filter generally use leaf filter. America uses a kind of fixed bed sand filter.

(From <The study of processing technique of alumina>  Zhongyu Yang)