| Vitrification is the most common treatment for the significant amount of the High Level Liquid Waste (HLLW) generated in the rapid development of nuclear industry. However, the platinum group metals (PGMs) contained in HLLW have adverse effect on the equipment during the vitrification process since they have high melting points. Therefore, many approaches have been adopted to extract platinum group elements from HLLW. The photochemical reduction method, compared with ion exchange method and electrochemical separation method, is a "clean" technique and has several adventages:Light sources can be placed far from the reaction solution avoiding direct contact with HLLW, thus reducing the requirements of the radiation-resistant materials for the equipments. No secondary radioactive wastes were produced since only a few small organic molecules were introduced into the system.In this paper, the photochemical method is proposed to reduce and separate platinum group elements (Pd, Ru) from simulated high level liquid waste. The metal ions were reduced to atoms and reduced atoms congregated into particles under appropriate conditions, and were collected by centrifugation at last. The structure and morphology of these particles were characterized. Our experimental works were carried out according to the sequence of "single metal ions-multi-metal ions mixture-multi-metal ions mixture containing neodymium (Nd) metal ions". Continuous ultraviolet light sources (high, medium and low pressure mercury lamps) were used to irradiate samples after deaeration. UV-Vis spectrophotometer was used to measure the absorption spectra of samples; TEM was used to observe of the morphology of particles; XPS was used to measure the composition of particles. The main contents of the paper are summarized as follows:1. Pd(â…¡) ions in aqueous solution can be reduced successfully by the photoreduction method by a ratio of 98.4%, and the generation of Pd atoms was more efficient in the presence of 2-propanol than ethanol, methanol or tertiary butanol. The presence of high concentration Cl- would suppress the reduction of Pd(â…¡), and high pH value can enhance the reduction of Pd(â…¡).2. Ru(â…¢) ions in aqueous solution can be reduced successfully by the photoreduction method by a ratio of 95.8% in the presence of 2-propanol. The presence of high concentration of Cl- would enhance the reduction of Ru (â…¢), and high pH value can enhance the reduction of Ru (â…¢). The mechanism of photochemical reduction of Pd (â…¡) and Ru (â…¢) ions is also discussed.3. In addition, the separation of Pd(â…¡)/Nd(â…¢), Ru(â…¢)/Nd(â…¢), Pd(â…¡)/Ru(â…¢), Pd(â…¡)/Ru(HI)/Nd(â…¢) by photochemical method was also investigated. High separation efficiencies were obtained.
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