Sodium recovery from crystallization waste of Bayer liquor in alumina beneficiation

The residue generated in the crystallization stage of the Bayer process to obtain alumina may be used for sodium recovery. The addition of calcium hydroxide (Ca(OH) 2 ) to the residues of the Bayer process may become an alternative study for recovering the caustic soda (NaOH) inserted in the process, so the objective of this work is to utilize the causticization technique in a real residue obtained from the crystallization step of the Bayer liquor. The residue characterized presented 13% Al, so this indicated that there were losses of this element in the Bayer process. Also, the presence of Na 2 C 2 O 4 , Na 2 CO 3 , and NaAlO 2 were observed. The total sodium recovery was 87%, and the best condition for causticization to occur was in the use of a 1:1 molar ratio (Na 2 C 2 O 4 and Ca(OH) 2 ), during 6 h of reaction, and at 80°C, with the conversion of 96% of the organic carbons present in the solution. The causticization was effective in separating sodium from residue in the removal of oxalates, organics, and aluminium, and it provided a reaction that separated oxalates and carbonates that are harmful to the aluminium obtaining process.