Solubility equilibria in the ternary systems Rb2SO4 – CaSO4 – H2O and Cs2SO4 – CaSO4 – H2O at ambient temperature, and the crystal structure of rubidium syngenite

Abstract For the ternary systems, Rb 2 SO 4 – CaSO H O and Cs O, solubility data have been determined at ambient temperatures (22 25 °C). In both gypsum is found as stable -phase in presence of low alkali metal sulfate concentrations. addition, two double salts exist Rb-system: Rb-disalt (Rb ·2CaSO ) Rb-syngenite ·CaSO ·H O) addition to . Rb-syngenite, crystal structure was by single analysis (space group P 21/ m (11), a = 6.323 Å, b 7.223 c 10.044 β 102.96°, Z 2, V 447.03 Å 3 ), which isomorphous potassium syngenite (K O). Cs-system, besides , only salt exists. Graphical abstract