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The stability relations of cerium and its species in the hydrometallurgical processing of bastnasite were studied using Pourbaix diagrams. Different systems of Ce-(F)-(CO 3 )-(SO 4 )-(C 2 O 4 )-H 2 O were constructed using HSC Chemistry software with the necessary thermodynamic data. The Ce-F-H 2 O system exhibits a large stability region for CeF 3 (pH∼ −1.5 -12). The stability domain of was determined by Ce-CO 3 -H 2 system in the pH of 4.5 -12. The decomposition behaviours of CeFCO 3 were studied by Ce-F-CO 3 -H 2 O system which shows the stability domain of CeFCO 3 from neutral to basic media. The treatment of CeFCO 3 with H 2 SO 4 was investigated by depicting diagrams of Ce-F-CO 3 -SO 4 -H 2 O system. According to this system, CeFCO 3 can be decomposed to produce soluble Ce sulphates at around pH 6.2. In contrast, alkaline treatment of CeFCO 3 converts it to Ce(OH) 3 at pH 11. Finally, the recovery of Ce by oxalate precipitation was studied by Ce-C 2 O 4 -H 2 O system which showed the domain of Ce oxalate decahydrate.

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