我们研究了Cs吸附后粘土矿物的结构变化,并使用离子交换剂了解了它们的低解吸效率。我们专注于中间层在2:1粘土矿物中Cs吸附和解吸中的作用,即伊利石,水黑云母,和蒙脱石,使用批量实验以及XRD和EXAFS分析。利用阳离子交换容量(CEC)分析了粘土矿物的吸附特性,最大吸附等温线(Qmax),和放射性铯截获潜力(RIP)实验。虽然伊利石表现出较低的CEC值,它对具有相对高的RIP/CEC比率的Cs表现出高选择性。用NaCl离子交换剂处理后,伊利石的Cs解吸效率最高(74.3%),其次是水黑云母(45.5%)和蒙脱石(30.3%);因此,Cs吸附在平面位点上,而不是在夹层或磨损的边缘位点(FES)上,很容易解吸。NaCl处理后,XRD分析表明,解吸效率低的原因是层间固定的Cs塌陷,由于二价阳离子(Mg2或Ca2)与一价阳离子(Na)的离子交换,使夹层\'水黑云母变窄。此外,EXAFS分析表明,水黑云母在NaCl解吸后形成内球结构,表明由于水黑云母和蒙脱石夹层的塌陷以及伊利石在FES中的牢固结合,很难从NaCl解吸中去除Cs。相比之下,使用草酸的螯合解吸有效地溶解了水黑云母(98%)和蒙脱石(85.26%)的狭窄夹层,提高解吸效率。因此,由于一价阳离子和二价阳离子之间的交换,夹层塌陷导致使用离子交换剂的Cs粘土的解吸效率低。
We investigated the structural changes in clay minerals after Cs adsorption and understood their low desorption efficiency using an ion-exchanger. We focused on the role of interlayers in Cs adsorption and desorption in 2:1 clay minerals, namely illite, hydrobiotite, and montmorillonite, using batch experiments and XRD and EXAFS analyses. The adsorption characteristics of the clay minerals were analyzed using cation exchange capacity (CEC), maximum adsorption isotherms (Qmax), and radiocesium interception potential (RIP) experiments. Although illite showed a low CEC value, it exhibited high selectivity for Cs with a relatively high RIP/CEC ratio. The Cs desorption efficiency after treatment with a NaCl ion exchanger was the highest for illite (74.3%), followed by hydrobiotite (45.5%) and montmorillonite (30.3%); thus, Cs adsorbed onto planar sites, rather than on interlayers or frayed edge sites (FESs), is easily desorbed. After NaCl treatment, XRD analysis showed that the low desorption efficiency was due to the collapse of the interlayer-fixed Cs, which tightly narrowed the interlayers\' hydrobiotite due to the ion exchange of divalent cations (Mg2+ or Ca2+) into the monovalent cation (Na+). Moreover, EXAFS analysis showed that hydrobiotite formed inner-sphere structures after NaCl desorption, indicating that it was difficult to remove Cs from NaCl desorption due to the collapsed hydrobiotite and montmorillonite interlayers as well as the strong bonding in FESs of illite. In contrast, chelation desorption using oxalic acid effectively dissolved the narrowed interlayers of hydrobiotite (98%) and montmorillonite (85.26%), enhancing the desorption efficiency. Therefore, low desorption efficiency for Cs clays using an ion exchanger was caused by the collapsed interlayer due to the exchange between monovalent cation and divalent cation.