Phase equilibria of the systems of CsCl + ErCl3 + H2O and CsCl + ErCl3 + HCl (∼10.7%, ∼14.4%) + H2O at T = 298.15 K and the standard molar enthalpies of formation of solid phase compounds

• Solubility was measured for CsCl + ErCl3 + H2O and CsCl + ErCl3 + HCl (∼10.7%, ∼14.4%) + H2O systems at T = 298.15 K.
• The corresponding phase diagrams were plotted.
• Two new solid phase compounds 3CsCl · ErCl3 · 6H2O and 3CsCl · 2ErCl3 · 14H2O were characterized.
• The enthalpies of solution of two new solid phase compounds were measured.
• ΔfHm⊖ for two new solid phase compounds were determined.

Solubility were studied for the two systems of CsCl + ErCl3 + H2O and CsCl + ErCl3 + HCl + H2O in the (∼10.7%, ∼14.4%) HCl regions at T = 298.15 K using the isothermal solubility method, the corresponding phase diagrams were constructed. The solid phases were determined by the Schreinemakers wet residues technique. Four solid phases of CsCl, 3CsCl · ErCl3 · 6H2O, 3CsCl · 2ErCl3 · 14H2O and ErCl3 · 6H2O in the ternary system, and those of CsCl, nCsCl·ErCl3 · 6H2O (not-identify solid), 3CsCl · 2ErCl3 · 14H2O and ErCl3 · 6H2O in the quaternary system were obtained, respectively. The compounds 3CsCl · ErCl3 · 6H2O and 3CsCl · 2ErCl3 · 14H2O were incongruently soluble in water. The compound 3CsCl · 2ErCl3 · 14H2O is congruently soluble in an average medium of ∼10 mass% HCl and incongruently soluble in an average medium of ∼14 mass% HCl. The new solid phase compounds 3CsCl · ErCl3 · 6H2O and 3CsCl · 2ErCl3 · 14H2O were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of 3CsCl · ErCl3 · 6H2O and 3CsCl · 2ErCl3 · 14H2O in water were measured to be (24.67 ± 0.50) and −(12.43 ± 0.31) kJ · mol−1 by microcalorimetry and their standard molar enthalpies of formation were determined as being −(4222.8 ± 1.2) kJ · mol−1 and −(7679.3 ± 1.2) kJ · mol−1, respectively.

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