The solubility of ⁹⁹Tc(IV) was investigated in dilute to concentrated carbonate solutions (0.01 M ≤ C_tot ≤ 1.0 M, with C_tot = [HCO₃⁻] + [CO₃²⁻]) under systematic variation of ionic strength (I = 0.3–5.0 M NaHCO₃–Na₂CO₃–NaCl–NaOH) and pH_m (−log[H⁺] = 8.5–14.5). Strongly reducing conditions (pe + pH_m ≈ 2) were set with Sn(II). Carbonate enhances the solubility of Tc(IV) in alkaline conditions by up to 3.5 log₁₀-units compared to carbonate-free systems. Solvent extraction and XANES confirmed that Tc was kept as +IV during the timeframe of the experiments (≤ 650 days). Solid phase characterization performed by XAFS, XRD, SEM-EDS, chemical analysis and TG-DTA confirmed that TcO₂·0.6H₂O(am) controls the solubility of Tc(IV) under the conditions investigated. Slope analysis of the solubility data in combination with solid/aqueous phase characterization and DFT calculations indicate the predominance of the species Tc(OH)₃CO₃⁻ at pH_m ≤ 11 and C_tot ≥ 0.01 M, for which thermodynamic and activity models are derived. Solubility data obtained above pH_m ≈ 11 indicates the formation of previously unreported Tc(IV)–carbonate species, possibly Tc(OH)₄CO₃²⁻, although the likely formation of additional complexes prevents deriving a thermodynamic model valid for this pH_m-region. This work provides the most comprehensive thermodynamic dataset available for the system Tc⁴⁺–Na⁺–Cl⁻–OH⁻–HCO₃⁻–CO₃²⁻–H₂O(l) valid under a range of conditions relevant for nuclear waste disposal.

中文翻译：

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碱性NaHCO ₃ -Na ₂ CO ₃ -NaCl体系 中Tc（iv）溶解度和碳酸盐络合的热力学描述†

的溶解度⁹⁹ TC（IV）在稀进行了研究，以浓缩的碳酸盐溶液（0.01M≤Ç_地合计≤1.0M，以C _TOT = [HCO ₃ ^- ] + [CO ₃ ^2- ]）下的离子强度的系统性变化（I = 0.3–5.0 M NaHCO ₃ –Na ₂ CO ₃ –NaCl–NaOH）和pH _m（-log [H ⁺ ] = 8.5-14.5）。强还原条件下（PE + pH值_米≈2）与锡（设置II）。碳酸盐可提高Tc（IV）在碱性条件下的溶解度，最高可达3.5 log ₁₀-单位与无碳酸盐的系统相比。溶剂萃取和XANES证实，在实验期间（≤650天），Tc保持为+ IV。通过XAFS，XRD，SEM-EDS，化学分析和TG-DTA进行的固相表征证实，在研究的条件下，TcO ₂ ·0.6H ₂ O（am）控制Tc（IV）的溶解度。与固相/水相的表征和DFT计算组合中的溶解度数据的斜率分析指示物种TC（OH）的优势₃ CO ₃ ^-在pH_米≤11和C_地合计≥0.01μm时，对于其中的热力学和活动模型是衍生的。在pH以上获得的溶解度数据_米≈11指示以前未报告的TC（形成IV） -碳酸酯物种，可能TC（OH） ₄ CO ₃ ^2-，虽然附加的复合物防止了可能形成导出热力学模型有效该pH_米-region。这项工作为系统Tc ⁴⁺ –Na ⁺ –Cl ^– –OH ^– –HCO ₃ ^– –CO ₃ ^2– –H ₂ O（l）提供了最全面的热力学数据集，在与核废料有关的一系列条件下有效处理。