Separation and recovery of Th(IV) from rare earth and other cation solutions using pH-responsive ionic liquids at high acidity condition of 1 M HNO3

• Published in: Hydrometallurgy Vol. 214; p. 105953
• Main Authors: Lv, Chuan, Fu, Jie, Wang, Shuang-Long, Zhang, Guo-Hao, Guo, Shi-Jie, He, Ling, Li, Jun-Ling, Tao, Guo-Hong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2022
• Subjects: Ionic liquid; pH-responsive; Selective separation; Self-assembly; Stimulus response material; Thorium; Selective separation; Self-assembly; Stimulus response material; pH-responsive; Ionic liquid; Thorium
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2022.105953

Thorium has received widespread attention as a potential nuclear fuel alternative, but it is still a difficult task to extract thorium from strong HNO3 media. Meanwhile, stimulus-responsive materials have received extensive attention in the field of separation due to their special properties. Herein, we designed and synthesized a new type of stimulus responsive ionic liquid (SIL) material and applied it to solve the problem of low thorium extraction efficiency in strong HNO3 media. By utilizing the pH-response performance of SIL, a SIL and thorium complex (SILTh) is found to self-assemble and precipitate out from solution upon simple adjustment of the pH. We found that the extraction efficiency of thorium can reach 99.6% under high acidity and that it can be even higher than 98.8% when the temperature changes. Under experimental conditions, SIL showed a record-breaking maximum extraction capacity for thorium (644.2 mg g−1) with an excellent selectivity for thorium over lanthanide and transition metal in 1 M HNO3 (S>1400). Studies reveal that PO is complexed with thorium, which also explains the high adsorption capacity and selectivity of SIL for thorium under high acidity. Moreover, the pH-response characteristics of SIL are reversible. The pH-responsive SIL material and the extracted thorium can be recovered, and SIL also shows an excellent recycling ability over five cycles, with extraction and recovery efficiencies for Th(IV) of 98.0% and 98.7%, respectively within five cycles, indicating that the material has a good recycling ability. This study explores the possibility of using pH-responsive materials to recover thorium in strong HNO3 media, and provides ideas for the design and synthesis of new materials for the recovery of thorium. [Display omitted] •Stimulus response material for extraction.•pH-responsive ionic liquids for capture of thorium.•Extraction efficiency for thorium can reach up to 99.5% under high acidity.•Extract thorium at high acidity with the extraction capacity 644.2 mg g−1 under 1 M HNO3.•Selective capture of thorium from lanthanides and transition elements with the selectivity (STh/M) >1400.