Enhancing separation of cerium(IV) and thorium(IV) from sulfate medium by introducing cyclohexyl group into molecule of an aminophosphorus extractant

• Published in: Journal of rare earths 2024-07
• Main Authors: Li, Songsong, Han, Jinglu, Li, Yanling, Liao, Wuping
• Format: Article
• Language: English
• Subjects: cerium(IV); Extraction; Rare earths; Separation; thorium(IV); α-aminophosphonate
• ISSN: 1002-0721; 2509-4963
• DOI: 10.1016/j.jre.2024.07.021

Enlarging the steric hindrance to the molecular structures of extractants is a common way to improve their selectivity. To improve the separation factor of thorium(IV) and cerium(IV), cyclic groups having large steric hindrance such as phenyl, cyclohexyl, and benzyl were introduced into the α-aminophosphonate extractant molecules. Bis(2-ethylhexyl) ((phenylamino)methyl) phosphonate (PAMP), bis(2-ethylhexyl) ((cyclohexylamino)methyl) phosphonate (CAMP), and bis(2-ethylhexyl) ((benzylamine)methyl) phosphate (BAMP) were synthesized and applied in the separation and recovery of thorium(IV) and cerium(IV) from sulfuric acid solution. The separation ability between cerium(IV) and thorium(IV) descends in the order of CAMP > BAMP ≈ Cextrant230 > DEHAMP >> PAMP, which is consistent with the decreasing order of steric hindrance. Nearly non-extraction of both cerium(IV) and thorium(IV) and the lowest separation ability for PAMP will be due to the conjugation of the lone pair of the amino N atom and benzene ring in PAMP. Furthermore, the extraction of REs(Ⅲ) by CAMP is lower than that of thorium(IV). Thermodynamic parameters (ΔG0, ΔH0, ΔS0) and extraction equilibrium constants were determined. An extraction process was developed to separate and retrieve thorium(IV) and cerium(IV) from a bastnaesite leaching solution. The final product purity of CeO2 and ThO2 is 99% and 98.4%, respectively, and the yields are 90.2% and 97.6%, respectively. CAMP with cyclohexyl group can efficiently separate cerium(IV) and thorium(IV) and the highest separation factor βCe(IV)/Th(IV) reaches 135.4. [Display omitted] •The introduction of cycloalkyl groups into the α-aminophosphonate molecules affects the extraction of Ce(IV) and Th(IV).•The introduction of cyclohexyl group enhances the separation of Ce(IV) and Th(IV).•The maximum separation factor βCe(IV)/Th(IV) reaches 135.43 for the CAMP system.