Arab-Chapelet B, Martin P M, Costenoble S, Delahaye T, Scheinost A C, Grandjean S, Abraham F
CEA, DEN, DRCP, SERA/ Laboratoire de Conversion des Actinides et Radiolyse, BP 17171, F-30207 Bagnols sur Cèze Cedex, France.
CEA, DEN, DEC, 13108 St Paul Lez Durance, France.
Dalton Trans. 2016 Apr 28;45(16):6909-19. doi: 10.1039/c5dt04312c.
Mixed actinide(III,IV) oxalates of the general formula M2.2UAn(C2O4)5·nH2O (An = Pu or Am and M = H3O(+) and N2H5(+)) have been quantitatively precipitated by oxalic precipitation in nitric acid medium (yield >99%). Thorough multiscale structural characterization using XRD and XAS measurements confirmed the existence of mixed actinide oxalate solid solutions. The XANES analysis confirmed that the oxidation states of the metallic cations, tetravalent for uranium and trivalent for plutonium and americium, are maintained during the precipitation step. EXAFS measurements show that the local environments around U(+IV), Pu(+III) and Am(+III) are comparable, and the actinides are surrounded by ten oxygen atoms from five bidentate oxalate anions. The mean metal-oxygen distances obtained by XAS measurements are in agreement with those calculated from XRD lattice parameters.
通式为M2.2UAn(C2O4)5·nH2O（An = Pu或Am，M = H3O(+)和N2H5(+)）的混合锕系元素（III,IV）草酸盐已在硝酸介质中通过草酸沉淀法进行了定量沉淀（产率>99%）。使用XRD和XAS测量进行的全面多尺度结构表征证实了混合锕系元素草酸盐固溶体的存在。XANES分析证实，在沉淀步骤中，金属阳离子的氧化态得以保持，铀为四价，钚和镅为三价。EXAFS测量表明，U(+IV)、Pu(+III)和Am(+III)周围的局部环境具有可比性，并且锕系元素被来自五个双齿草酸根阴离子的十个氧原子所包围。通过XAS测量获得的平均金属-氧距离与根据XRD晶格参数计算得出的距离一致。
