On oxoacidic properties and solubilities of beryllium and magnesium oxides in molten (CsCs + KCl + NaCl) eutectic at T = 783 K

Reactions of Be2+ and Mg2+ with O2– in molten eutectic mixture (CsCs + KCl + NaCl) (0.455:0.245:0.30) at T = 783 K were studied by a potentiometric method using Pt(O2)|ZrO2(Y2O3) indicator electrode. Addition of O2– ions to the melt containing Mg2+ results in precipitation of MgO (pKs,MgO = 11.89 ± 0.3, molality) whereas interaction of Be2+ with O2– is accompanied with sequential formation of Be2O2+ (pK = 15.68 ± 0.5, molality) and precipitation of BeO (pKs,BeO = 9.62 ± 0.3, molality). On the basis of the obtained and known data pKs,MgO–T−1 dependence in molten (CsCs + KCl + NaCl) eutectic is constructed. The slope of the said dependence in T/K = (from 583 to 1073) range is in good agreement with the value predicted by the Shreder equation, that extends the range of use of the Shreder equation for predictions of metal oxide solubilities in molten halides.

► Solubility product index of MgO in CsCl–KCl–LiCl eutectic melt is 11.89, molality.
► Solubility product index of BeO in CsCl–KCl–LiCl eutectic melt is 9.62, molality.
► Dissociation constant index of Be2O2+ in the said melt is 15.68, molality.
► Solutions of MgO in the said melt demonstrate positive deviations from ideality.