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Thermodynamic description of Be(II) solubility and hydrolysis in acidic to hyperalkaline NaCl and KCl solutions
Applied Geochemistry ( IF 3.4 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.apgeochem.2020.104601
Neşe Çevirim-Papaioannou , Xavier Gaona , Melanie Böttle , Ezgi Yalçıntaş Bethune , Dieter Schild , Christian Adam , Thomas Sittel , Marcus Altmaier

Abstract The solubility of Be(II) is investigated in carbonate-free dilute to concentrated HCl–NaCl–NaOH, KCl–KOH, NaOH and KOH solutions. Undersaturation experiments were performed under Ar atmosphere at T= (22 ± 2) °C. XRD, XPS, SEM and quantitative chemical analysis confirm that α-Be(OH)2(cr) is the solid phase controlling the solubility in all evaluated systems. No transformation of α-Be(OH)2(cr) to β-Be(OH)2(cr) or ternary solid phases Na/K–Be(II)–OH(s) is observed in the investigated systems within the timeframe of this study (t ≤ 600 days). An amphoteric solubility behaviour of Be(II) is observed with a solubility minimum at pHm ≈ 9.5 (with [Be(II)] ≈ 10−6.8 M), regardless of the ionic strength. The combination of solubility data determined in acidic pHm conditions and the hydrolysis scheme reported in the literature for cationic hydrolysis species of Be(II) is used for the determination of the solubility constant of α-Be(OH)2(cr), log *K°s,0 = (6.9 ± 0.4). Slope analysis of the solubility data in alkaline to hyperalkaline conditions and 9Be NMR support the predominance of the monomeric hydrolysis species Be(OH)2(aq), Be(OH)3– and Be(OH)42− within the strongly alkaline pHm-conditions relevant in cementitious systems. The comprehensive solubility dataset collected within this study in combination with extensive solid and aqueous phase characterization allow the development of a complete chemical, thermodynamic and (SIT) activity model for the system Be2+–Na+–K+–H+–Cl––OH––H2O(l). This model provides an accurate and robust tool for the evaluation of Be(II) solubility and speciation in a diversity of geochemical conditions, including source term calculations of beryllium in the context of the nuclear waste disposal Safety Case.

中文翻译:

Be(II) 在酸性至高碱性 NaCl 和 KCl 溶液中溶解度和水解的热力学描述

摘要 研究了 Be(II) 在无碳酸盐稀释至浓 HCl-NaCl-NaOH、KCl-KOH、NaOH 和 KOH 溶液中的溶解度。在 T = (22 ± 2) °C 的 Ar 气氛下进行欠饱和实验。XRD、XPS、SEM 和定量化学分析证实,α-Be(OH)2(cr) 是控制所有评估系统中溶解度的固相。在所研究的系统中未观察到 α-Be(OH)2(cr) 向 β-Be(OH)2(cr) 或三元固相 Na/K-Be(II)-OH(s) 的转变本研究(t ≤ 600 天)。无论离子强度如何,都观察到 Be(II) 的两性溶解行为,其溶解度最小值为 pHm ≈ 9.5([Be(II)] ≈ 10-6.8 M)。在酸性 pHm 条件下测定的溶解度数据与文献中报道的 Be(II) 阳离子水解物质的水解方案相结合,用于测定 α-Be(OH)2(cr) 的溶解度常数,log * K°s,0 = (6.9 ± 0.4)。碱性至高碱性条件下溶解度数据的斜率分析和 9Be NMR 支持单体水解物质 Be(OH)2(aq)、Be(OH)3- 和 Be(OH)42- 在强碱性 pHm-胶凝体系中的相关条件。本研究中收集的综合溶解度数据集与广泛的固相和水相表征相结合,可以为 Be2+–Na+–K+–H+–Cl––OH––H2O 系统开发完整的化学、热力学和 (SIT) 活性模型(l)。
更新日期:2020-06-01
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