Significant amounts of uranium (U) and thorium (Th) exist in the earth ores and in the nuclear fuel reprocessing process, which needs separation and extraction. Reprocessing the spent fuel not only reduces the volume and radio toxicity of the high-level waste, but also can be used to produce new fuel.The separation techniques for reprocessing include precipitation, ion exchange, and solvent extraction. Solvent extraction has several advantages for use in the large scale reprocessing of spent nuclear fuel, including the ability for continuous operation, high throughput, and solvent recycling.