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

Abstract

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=298.15K 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.