使用新型大孔硅基复合树脂分离高放废液中铂族金属的吸附机理研究

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 is the 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 recovery 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 Crea and TODGA two extractants into the macroporous SiO2-P support. Adsorption and desorption behavior of PGMs onto (Crea+TODGA)/SiO2-P adsorbent will be investigated by batch method. In batch adsorption experiments, the effect of HNO3 and metal ions concentrations, contact time, temperature and the choice of elution solution on the adsorption/desorption of PGMs or other simulated FPs ions onto adsorbent will be examined, respectively. In addition, the adsorption isotherms, thermodynamic and kinetics parameters of PGMs in adsorption process will be calculated from the results of batch experiment. Meanwhile, the adsorption mechanism of aim ions onto adsorbent and a reasonable optimization partitioning process will be confirmed from the results of batch experiment for the further extraction chromatography technology using in PGMs separation.

高放废液的处理处置是核燃料循环技术中的关键环节，也是一个世界性难题，对核电的可持续健康发展具有重要意义。稀有铂族金属钯、钌、铑是高放废液中典型的分裂元素之一。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PUREX流程中铂族元素发生沉淀堵塞管道等技术难题，迫切需要一种从高放废液中选择性分离铂族金属的工艺方法。本课题合成并使用一种新型大孔硅基复合吸附树脂(Crea+TODGA)/SiO2-P，通过静态吸附试验，重点研究硝酸浓度、固液相接触时间、温度变化、洗脱液类型等因素对铂族金属在树脂上吸附与脱附行为的影响规律，并计算出吸附过程中吸附等温线、热力学和动力学基本参数，确定树脂对目标元素的吸附机理。结合耐酸性试验结果，计算确定后续柱色谱法分离目标元素工艺的各项最优化操作条件，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。

铂族金属钯、钌、铑是高放废液中典型的分裂元素之一。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PUREX流程中铂族元素发生沉淀堵塞管道等技术难题，迫切需要一种从高放废液中选择性分离铂族金属的工艺方法。本项目选择萃取剂Crea（N’,N’-di-n-hexyl-thiodiglycolamide）和TODGA（正N,N,N’,N’-四辛基-3-氧戊二酰胺）组成协同萃取体系，通过毛细管作用以及分子间相互作用力的方式固定到SiO2-P载体的孔隙中，合成出新型大孔硅基复合树脂(Crea+TODGA)/SiO2-P。从SEM照片可以看出，树脂外形呈均匀的规则球形，直径约50 μm，结构完好。从TG-DTA曲线计算出其组成为萃取剂33 wt%， SiO2-P 67 wt%。从耐酸性实验中发现，萃取剂与3.0 M硝酸溶液接触一周后，在一定程度上发生了裂化，但是裂化量少于树脂中萃取剂总量的1%，这种裂化程度在实际应用中是可以接受的。从静态吸附试验中发现，树脂对Pd(II)有着非常强的吸附亲和力，能完全吸附水相中的离子且吸附能力不随硝酸浓度的变化而变化。树脂对Ru(III)和Rh(III)的吸附能力则较弱。对于锝99的替代元素Re(VII)，在0.1 M HNO3中 (Crea+TODGA)/SiO2-P对Re(VII)有着强烈的吸附，但吸附能力随着酸度的上升急剧下降。使用拟二级动力学方程拟合Pd(II)的吸附，发现吸附速率较高且是由化学吸附控制。Pd(II)在(Crea+TODGA)/SiO2-P上的吸附符合Langmuir等温吸附模型，是单层化学吸附。但Freundlich等温吸附模型不能用来拟合该吸附过程。在色谱柱实验中，11种典型分裂产物可以分为五组流出：Ru(III)和Rh(III)随注入液流出；Re(VII)和Mo(VI)随3.0 M HNO3的洗涤液流出；La(III)，Ce(III)和Nd(III)随洗涤液H2O流出；Pd(II)随硫脲洗脱液流出；Sm(III)和Gd(III)随DTPA溶液流出。从色谱柱分离结果可以看出，Ru(III)、Rh(III)、Pd(II)分别流出色谱柱，完全与其它离子分开，所以将萃取剂TODGA加入到Crea/SiO2-P，与Crea组成协同萃取体系用来从高放废液中一步分离富集铂族金属是可行的，达到本项目预定的目标。