Chemistry of Metal Chloride Complexes in Aprotic Systems

A study of metal chloride solubility in aprotic solvents has been initiated. These solvent systems have very low hydrogen ion activities and thus allow chloride ion activities which are much higher than those attainable in water. The high chloride ion activities can be generated by the dissolution of soluble salts, such as calcium chloride or sodium chloride, in the aprotic media. Metals that normally form aqueous-insoluble chlorides or exist as cations in aqueous solutions (e.g., Ag, Pb, Cd, or Au) may be readily dissolved in aprotic solvent systems as anionic chloride complexes or as solvation complexes. To understand such systems, we constructed ternary phase diagrams for dimethylsulfoxide-water-calcium chloride (DMSO-IO-CaC) and DMSO-ONaCl systems. These diagrams were used to establish the solution regions available for the solubilization of Pb, Ag, Au, Cd, Cu, Zn, and Al. Measurements of Pb and Ag solubilities in the DMSO-to-CaC system gave concentrations as high as ~1.5 and ~0.9 M, respectively. Similar measurements showed concentrations of ~0.8, ~3.0, ~0.65, ~4.0, and MD.85 11 for Au, Cd, Cu, Zn, and Al, respectively. The concentrations of Pb and Ag in the NaCl system, ~0.45 and ~0.11 M, were much less than those obtained in the CaCl₂system. Dissolution/precipitation steps, controlled by varying the ternary system composition, could lead to the development of useful methods for recovering, purifying, or separating various metal chloride compounds.