Shang Chengming, Reiller Pascal E, Vercouter Thomas
Université Paris-Saclay, CEA, Service d'Études Analytiques et de Réactivité des Surfaces (SEARS), F-91191 Gif-sur-Yvette CEDEX, France.
Dalton Trans. 2020 Nov 10;49(43):15443-15460. doi: 10.1039/d0dt03164j.
The stability constants of ternary calcium uranyl tricarbonate complexes, CaUO2(CO3)32- and Ca2UO2(CO3)3(aq), were determined in NaClO4 medium at various ionic strengths using time-resolved laser-induced luminescence spectroscopy (TRLS) - also known as time-resolved laser-induced fluorescence spectroscopy (TRLFS). As in a previous study, the potential precipitation of schoepite (UO3·2H2O) and calcite (CaCO3) was avoided via titration of the triscarbonatouranyl complex with Ca2+ at varying pH values. The Ringböm coefficients relative to UO2(CO3)34- were individually evaluated under test sample conditions. Steadily enhanced luminescence intensity and increased decay-times were representative of complexation processes. The stoichiometry of calcium was quantified by slope analysis, and its measured intensity was corrected by using the corresponding Ringböm coefficient. The conditional formation constants, i.e. log10 Kn.1.3, were then assessed after rounding off the slope values to their nearest integers. Cumulative formation constants at infinite dilution log10 β°n.1.3, and specific ion interaction parameters ε were determined based on the experimental origin and slope values, respectively, over the range of 0.1-2.46 mol kgw-1 NaClO4 using the specific ion interaction theory (SIT) approach. The cumulative stability constants are log10 β°(CaUO2(CO3)32-) = 27.26 ± 0.04 and log10 β°(Ca2UO2(CO3)3(aq)) = 30.53 ± 0.06. The specific ion interaction coefficients are estimated to be ε(CaUO2(CO3)32-,Na+) = (0.02 ± 0.04) kgw mol-1 and ε(Ca2UO2(CO3)3(aq),NaClO4) = (0.18 ± 0.07) kgw mol-1. These latter values are different from the ones that were previously obtained in NaCl, and underlying causes are discussed from different aspects. This work provides valuable information to address the interaction effects between Ca-UO2-CO3 species and 1 : 1 type electrolytes. It is suggested that the affinity of the cation in a background electrolyte with CanUO2(CO3)3(4-2n)- (n = {1;2}) has to be taken into consideration at high ionic strengths, especially for globally non-charged species.
在不同离子强度的高氯酸钠介质中，使用时间分辨激光诱导发光光谱法（TRLS，也称为时间分辨激光诱导荧光光谱法，TRLFS）测定了三元碳酸铀酰钙络合物CaUO2(CO3)32-和Ca2UO2(CO3)3(aq)的稳定常数。与之前的研究一样，通过在不同pH值下用Ca2+滴定三碳酸铀酰络合物，避免了柱磷铀矿（UO3·2H2O）和方解石（CaCO3）的潜在沉淀。在测试样品条件下分别评估了相对于UO2(CO3)34-的林邦系数。发光强度的稳定增强和衰减时间的增加是络合过程的代表。通过斜率分析对钙的化学计量进行了定量，并使用相应的林邦系数对其测量强度进行了校正。然后将斜率值四舍五入到最接近的整数后，评估条件形成常数，即log10 Kn.1.3。使用特定离子相互作用理论（SIT）方法，根据实验原点和斜率值，在0.1 - 2.46 mol kgw-1高氯酸钠范围内分别确定了无限稀释时的累积形成常数log10 β°n.1.3和特定离子相互作用参数ε。累积稳定常数为log10 β°(CaUO2(CO3)32-) = 27.26 ± 0.04和log10 β°(Ca2UO2(CO3)3(aq)) = 30.53 ± 0.06。特定离子相互作用系数估计为ε(CaUO2(CO3)32-,Na+) = (0.02 ± 0.04) kgw mol-1和ε(Ca2UO2(CO3)3(aq),NaClO4) = (0.18 ± 0.07) kgw mol-1。后一组值与之前在氯化钠中获得的值不同，并从不同方面讨论了其潜在原因。这项工作为解决Ca-UO2-CO3物种与1 : 1型电解质之间的相互作用效应提供了有价值的信息。建议在高离子强度下，尤其是对于整体不带电的物种，必须考虑背景电解质中阳离子与CanUO2(CO3)3(4-2n)-（n = {1;2}）的亲和力。
