Application Of Fatty Acid-based Green Extractant In Rare Earth And Thorium Recovery

Rare earth elements are known as"the treasure house of new materials in the 21st century"and"modern industrial vitamins".With the large-scale exploitation of rare earth resources,it has caused serious damage to the ecosystem,and there are also supply risks of rare earth elements.In addition,the thorium resources associated with rare earths have not been effectively recovered,resulting in waste of resources and environmental pollution.Therefore,it is very important to recover rare earth?thorium?resources from secondary resources.This dissertation focuses on how to efficiently and greenly recover rare earth and thorium resources.Fatty acid-based green extractants-ionic liquids and eutectic solvents has been developed for the recovery of rare earth elements and thorium,the following conclusions were reached:Methyltrioctylammonium capric acid?[N1888][DA]?,methyltrioctylammonium lauric acid?[N1888][LA]?and methyltrioctylammonium palmitate?[N1888][PA]?were synthesized and used for separating Sm?III?/Co?II?from simulated leaching solution of waste SmCo permanent magnet.Under the optimal extraction conditions,a high-purity CoCl₂?99.5%?product could be obtained through a simple extraction-stripping-scrubbing process.The entire process consumed only Na₂C₂O₄and NH₃·H₂O,and the low concentration of salt wastewater could be recycled.Sm₂O₃ with a purity of 99%could be obtained by washing and roasting at 800°C for 2 hours.The whole process is simple,environmentally friendly and has the potential for industrial applications.The possibility of extracting and separating La?III?/Ni?II?from fatty acid ionic liquid[N1888][LA]was also studied.The results have shown that[N1888][LA]could selectively extract La?III?,and the separation coefficient of La?III?/Ni?II?could reach 1.06×10⁴,which has a good separation effect.It is expected to be used for selective recovery of rare earth elements from waste nickel-hydrogen batteries.Developed eutectic solvents based on natural products terpenes and fatty acids for the separation of Th?IV?/REEs?III?,including menthol/capric acid?B/G?,menthol/oleic acid?B/Y?,thymol/capric acid?BA/G?and thymol/oleic acid?BA/Y?.The results show that the synthesized eutectic solvents could extract Th?IV?with high selectivity under short time and low acidity conditions,and low concentration of acid could be used for the strippin.Taking BA/G as an example,Th?IV?was extracted and separated from the simulated leach solution of radioactive waste residue under the optimal conditions.The final recovery of Th?IV?was 96.4%after single stage extraction-scrubbing-stripping process,and the purity was 94.2%,the concentration of Th?IV?in the raffinate was lower than 2 mg/L,and the separation coefficient of Th?IV?/REEs?III?reached 3223.During the Th?IV?/REEs?III?separation process,the acid consumption was low,no volatile organic solvents were needed,the process was green and environmentally friendly,and the raw materials were widely sourced,non-toxic,easily degradable,and revealed potential application value.In short,fatty acids could be extracted from plants,renewable,biocompatible and non-toxic.The synthetic route of fatty acid ionic liquids/eutectic solvents was simple,and had good extraction ability and selectivity,which is expected to be applied to selective separation of rare earths and other elements from secondary resources.