柱色谱法分离富集高放废液中铂族金属的分离机理研究

To ensure a sustainable development of nuclear energy in the future, the establishment of a partitioning process for treatment of high level liquid waste (HLLW) is one of the challenging tasks in closed nuclear fuel cycle. One of the representative valuable fission produces (FPs) in HLLW from PUREX reprocessing are platinum group metals (PGMs) including platinum, rhodium and ruthenium. PGMs are known to obstruct producing of vitrified waste before geologic disposal. Therefore, the selective separation and enrichment of PGMs from HLLW can not only solve the problem in process of vitrification but also reuse the valuable nuclides into useful resource. For this purpose, a novel silica-based macroporous adsorbent (Crea+TODGA)/SiO2-P is synthesized by impregnating two extractants Crea and TODGA into a macroporous SiO2-P support in this study. In batch experiment, Adsorption and desorption behavior of PGMs onto (Crea+TODGA)/SiO2-P adsorbent will be investigated. The effect of HNO3 and metal ions concentrations, contact time, temperature and the choice of elution solution on the adsorption/desorption of PGMs ions onto adsorbent will be examined, respectively. Moreover, adsorption isotherms, thermodynamic and kinetics parameters of PGMs in adsorption process will be calculated from the results of batch experiments. In addition, chromatographic separation thermodynamic and kinetics parameters of PGMs ions will be studied by column method and the optimization separation technology can be confirmed. Finally, a reasonable optimization partitioning process for the separation and enrichment of PGMs from HLLW will be proposed for industrial utilization by means of extraction chromatography technology using (Crea+TODGA)/SiO2-P packed column.

高放废液的处理处置是核燃料循环技术中的关键环节，对核电的可持续健康发展具有重要意义。高放废液中含有约15%的铂族金属钯、钌、铑，基于减少放射性废物总量、充分利用稀有金属资源、解决乏燃料后处理流程中铂族元素沉淀堵塞管道等技术难题，迫切需要一种铂族金属的分离富集方法。本课题采用Crea和TODGA的协同萃取体系，将此萃取剂固定到大孔SiO2-P载体的孔隙中，合成新型(Crea+TODGA)/SiO2-P复合吸附树脂。通过静态吸附试验，探讨各种影响因素对目标离子吸附脱附行为的影响、计算吸附等温线、热力学及动力学数据，确定最佳吸附和脱附条件。探讨目标离子柱色谱分离的热力学和动力学过程，得到三种离子分离与富集的最佳工艺条件。对使用大孔硅基(Crea+TODGA)/SiO2-P复合吸附树脂从高放废液中柱色谱法分离出钯、钌、铑的可行性进行综合评估，为乏燃料后处理工艺提供一种可能的处理方法和理论指导。

高放废液中含有约15 wt%的铂族金属，基于减少放射性废物总量、充分利用稀有贵金属资源并解决乏燃料后处理流程中铂族金属沉淀堵塞管道等技术难题，如何从高放废液中有效分离铂族金属，一直是科学研究领域的热点和难点问题。. 本研究以单步分离高放废液中的铂族金属为目标，采用Crea和TODGA两种萃取剂组成协同萃取体系，将其放入大孔硅基SiO2-P基体中，合成出新型大孔硅基复合吸附树脂(Crea+TODGA)/SiO2-P，研究了树脂对铂族金属静态和动态吸附分离特性以及树脂的耐酸性质。. 树脂对铂族金属离子的吸附亲和力有显著的差异，其亲和程度为：Pd(II)>Ru(III)>Rh(III)。从静态吸附试验中可知，树脂对Pd(II)的吸附过程符合准二级动力学模型，对Pd(II)、Ru(III)的吸附过程符合Langmuir吸附等温模型。且该吸附过程是自发进行的且为放热过程；在脱附实验中发现，洗脱剂硫脲对Pd(II)洗脱效果最好。在耐酸性实验中，树脂在298 K的3.0 M HNO3溶液中表现出良好的稳定性能，树脂在与3.0 M HNO3溶液接触28天后平均TOC泄漏量为720.4 mg/dm3，漏出量低，说明其适用于实际的高酸度高放废液后处理流程。. 从动态色谱柱实验中可以看出，Ru(III)和Rh(III)在(Crea+TODGA)/SiO2-P柱上表现为不吸附或弱吸附，其随着注入液最先流出色谱柱，稀土元素是在柱内短暂停留再随洗涤液H2O流出色谱柱，可实现Ru(III)、Rh(III)组与稀土元素的分离。而Pd(II)随着硫脲溶液从(Crea+TODGA)/SiO2-P柱上脱附分离，三种铂族金属元素分别流出色谱柱，完全与其他实验的离子分开，所以，将萃取剂TODGA加入Crea/SiO2-P，与Crea组成协同萃取体系用来从高放废液中分离富集铂族金属是可行的，能达到本研究预定的目标，实现了高放废液中单步分离三种铂族金属，结合其良好的耐酸性能，本研究为从高放废液中分离出铂族金属的工业化生产提供一种可供选择的新思路和技术指导。