PhreePlot绘制某些可变价核素Eh-pH图

U、Np、Pu、~(99)Tc、~(79)Se等放射性元素或核素对氧化还原条件敏感,存在多种价态,且锕系元素(U、Np、Pu)具有丰富的配位化学,其在生物圈和地质圈中的化学行为较为复杂。电势(Eh)-pH图对解决在水溶液中发生的一系列反应及平衡问题具有广泛的应用。本工作采用PhreePlot软件绘制了这些元素或核素在人体血清、唾液、胃液、DMEM培养基和北山地下水中的Eh-pH图以研究它们的主要氧化态和赋存形态。结果表明,U在生物圈中的主要氧化态是Ⅵ,Np是Ⅳ,Pu是Ⅳ和Ⅲ,99 Tc是Ⅶ和Ⅳ,79Se是0和Ⅳ。相比其他元素或核素,pH对铀的赋存形态影响更大。在地质圈中,根据Eh-pH图来看,北山处置库有利于Np、Pu的长期储存而对于U、99 Tc、79Se的储存不利。本工作的对比研究也表明,在热力学数据库一致的情况下,采用免费软件PhreePlot绘制的元素Eh-pH图与Geochemist’s Workbench(GWB)程序绘制的Eh-pH图具有高度的一致性。

Application of PhreePlot: Drawing the Eh-pH Diagram of Valence-Variable Radionuclides

U,Np,Pu,99Tc,and 79Se are redox-sensitive that can exist in several oxidation states.Moreover,actinides like U,Np,and Pu can form various complexes,making their chemical behavior complicated in the biosphere and geosphere.Eh-pH diagram (Pourbaix diagram) is widely used in solving the chemical reactions occurred in aqueous solution.In this study,PhreePlot was used to draw the Eh-pH diagrams of these elements or nuclides in the human serum,saliva,and gastric juice,as well as in Dulbecco's Modified Eagle's Medium (DMEM) and Beishan groundwater.The results indicate that in the biosphere the prevalent oxidation states are Ⅵ for U,Ⅳ for Np,Ⅳ and Ⅲ for Pu,Ⅶ and Ⅳ for 99Tc,and 0 and Ⅳ for 79Se.Particularly,U is more sensitive to the pH condition than other elements or nuclides.In the study of the geological media,according to the Eh-pH diagrams,Beishan repository is in favor of the long-term storage of Np and Pu,whereas U,99Tc,and 79Se aresusceptible to mobilization.This study also indicates that the Eh-pH diagrams plotted by PhreePlot are comparable to the one(s) plotted by Geochemist's Workbench(GWB) program.