Thermodynamic description of Be(II) solubility and hydrolysis in acidic to hyperalkaline NaCl and KCl solutions.

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 pH m ≈ 9.5 (with [Be(II)] ≈ 10−6.8 M), regardless of the ionic strength. The combination of solubility data determined in acidic pH m 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) 4 2− within the strongly alkaline pH m -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––H 2 O(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. • Systematic solubility and spectroscopic study with Be(II) in NaCl and KCl systems. • α-Be(OH) 2 (cr) controls the solubility of Be(II) in the investigated systems. • Comprehensive thermodynamic, chemical and SIT activity models derived. • Accurate description of the system Be2+–Na+–K+–H+–Cl––OH––H 2 O(l) provided. • Be(OH) 3 – and Be(OH) 4 2− confirmed as relevant species in cementitious systems. [ABSTRACT FROM AUTHOR]