Densities and excess molar volumes of binary and ternary melts of MgCl2, CaCl2and AlkCl

Abstract

Densities of binary liquid mixtures of AlkCl + CaCl2 and AlkCl + MgCl2 have been measured. Molar excess volumes VEm of mixing are given. In the CaCl2-system the excess volumes are always positive, while both positive and negative excess volumes are always positive, while both positive and negative excess volumes are found in the MgCl2-systems. The excess volume curves show pronounced maxima near the composition 33 mol % MgCl2 in the systems KCl+, RbCl+, and CsCl + MgCl2. It is suggested that VEm can be separated into two principal parts. One part is positive and associated with changes in ionic interactions (the Coulomb interaction); the other part is negative and is attributed to the effect of changing the covalent bridging interaction in liquid magnesium chloride when mixing the two components. Densities of six mixtures in each of the two ternary systems NaCl + CaCl2+ MgCl2 and KCl + CaCl2+ MgCl2 have also been measured and the excess volumes determined for each mixture. These values are compared with the excess volumes calculated from the component binaries. Densities of several binary and ternary liquid chloride mixtures of potential interest have been measured as a part of an investigation of the physicochemical properties of the magnesium chloride electrolyte for the electrowinning of magnesium.