Experimental investigation on the direct crystallization of high-purity AlCl3·6H2O from the AlCl3-NaCl-H2O(-HCl-C2H5OH) system

Abstract

Equilibrium and nonequilibrium phase diagrams of the AlCl3-NaCl-H2O(-HCl-C2H5OH) salt water system were drawn and these were used to optimize the separation technology for solving the problem of aluminum chloride hexahydrate extracted from hydrochloric acid leach liquor with low purity because of the contamination of sodium chloride. The phase diagram of the AlCl3-NaCl-H2O(-HCl-C2H5OH) system is a simple eutonic type. It is weakly dependent on temperature but is greatly affected by hydrochloric acid and ethanol. Acidity can nonselectively decrease the solubility of the two salts, and this leads to similar aluminum/sodium ratios in the co-saturated liquid phase with different acidities and temperatures. As a result, the obtained aluminum chloride hexahydrate has a maximum purity of 96.65%. Adding ethanol to the system can increase the differences in solubility and crystal size between the two salts. Thus, in accordance with the theoretical route of evaporation and ethanol-assisted re-dissolution, aluminum chloride hexahydrate crystals were precipitated with a higher purity of 99.50%.