Investigation of the Phase Equilibria in the Systems Cs2SeO4-CoSeO4-H2Oand Cs2SeO4-NiSeO4-H2O at 25.0°C

Thermodynamics of formation of double salts M2SO4·M′SO4·6H2O and M2SeO4·M′SeO4·6H2O where M denotes Rb, or Cs and M′ denote Co, Ni, or Zn

“…For (m 1 Rb 2 SeO 4 + m 2 ZnSeO 4 )(aq) and (m 1 Cs 2 SeO 4 + m 2 ZnSeO 4 )(aq) systems, the ternary solubility data of Ojkova et al [9] was used. The model for the (m 1 Cs 2 SeO 4 + m 2 CoSeO 4 )(aq) system is developed on the basis of the data from reference [8]. There are no data in the literature on the solubility in (m 1 In constructing the mixing solutions model for the above four systems, an approach that was proposed in a previous study [28] has been used.…”

“…According to the experimental solubility data [6][7][8][9][10][11], the type of solubility isotherms of the rubidium and cesium selenate (m 1 M 2 SeO 4 + m 2 M 0 SeO 4 )(aq) systems [6][7][8][9], and of (m 1 Rb 2 SO 4 + m 2 Co SO 4 )(aq), and (m 1 Rb 2 SO 4 + m 2 NiSO 4 )(aq) sulfate systems [10] [6][7][8][9][10]. According to Pabalan and Pitzer [37], any negative values of mixing parameters tend to increase the solubility in ternary systems, while positive values have the opposite effect.…”

“…The increased hole volume is evidently the reason for the crystallization of a lower crystalline hydrate (1-1-2 double salt) from the (m 1 Na 2 SeO 4 + m 2 ZnSeO 4 )(aq) as compared to the corresponding sulfate solution (1-1-4 double salt) [14]. The double salts with the stoichiometric composition 1-1-6 (M 2 SO 4 ÁM 0 SO 4 Á6H 2 O and M 2 SeO 4 Á M 0 SeO 4 Á 6H 2 O) crystallize from the saturated (m 1 Rb 2 SO 4 + m 2 M 0 SO 4 ) (aq) [10,11], (m 1 Rb 2 SeO 4 + m 2 M 0 SeO 4 )(aq) [7,9], (m 1 Cs 2 SO 4 + m 2 M 0 SO 4 )(aq) [11], and (m 1 Cs 2 SeO 4 + m 2 M 0 SeO 4 )(aq) [6,8,9] ternary solutions, where M 0 denotes Co, Ni, or Zn. It is of interest to investigate the rubidium, and cesium sulfate, and selenate solutions with a view to estimate the effect of the ionic radii of univalent {r(Rb þ ) < r(Cs þ )} and bivalent {r(Ni 2þ ) < r(Co 2þ ) < r(Zn 2þ )} metal cations and of the sulfate and selenate anions on the thermodynamic characteristics of the double salt with the same stoichiometric composition (1-1-6).…”

“…Comparative analysis of the ternary selenate solutions of the type (m 1 M 2 SeO 4 + m 2 M 0 SeO 4 )(aq) where M denotes Na, K, NH 4 , Rb, or Cs, M 0 denotes Mg, Ni, Co, Zn, Fe, Cu, Mn, or Cd, and m denotes molality, with the corresponding sulphate solutions (m 1 M 2 SO 4 + m 2 M 0 SO 4 )(aq) shows that in most of the cases double salts with the stoichiometric composition 1-1-2, 1-1-4, and 1-1-6 crystallize from the saturated ternary solutions [6][7][8][9][10][11]. The existence of these double salts and its stoichiometric composition depend on the ion radii of the cations {r(M þ ) and r(M 0 2þ )} and of the sulfate and selenate ions [2,3].…”