Extraction of zinc oxide from electric arc furnace dust. Solubilities of zinc chloride and zinc oxide in aqueous ammonium chloride solutions from 303–363 K

Abstract

Through our waste minimization studies in the SC 33/50 Technical Assistance Program (SC TAP), we found the Burrows process as modified by Myerson [1] to be attractive for South Carolina industry because of its low capital cost and its simplicity. However, many thermo‐dynamic properties are not available for practical application of the process. Therefore, our objective was to determine key solubility data: (1) the ZnCl2 + NH4Cl + H2O system and (2) the ZnO + NH4Cl + H2O system. The first system is important because the diamino zinc chloride compounds are known to form. The second system provides the thermodynamic behavior of the zinc oxide in the presence of chloride ion important for crystallizer design. At 363 K, the solubility of ZnCl2 decreased from 85 wt % at 1.49 wt % ammonium chloride to 79.3 wt % at 6.22 wt % ammonium chloride. As the temperature approached 333 K and 4.55 wt % NH4Cl, the solubility seemed to show a minimum. At 303 K, the phase boundary showed a sharp transition with two branches indicating more than one solid phase or the formation of chemical complexes. The point of intersection of these two curves was at 76.85 wt % ammonium chloride and 4.63 wt % ammonium chloride. Solubility measurements were made of zinc oxide in 30 wt % aqueous ammonium chloride solutions. The solubility of ZnO ranged from approximately 2.06 wt % at 312.9 K to 8.26 wt % at 364.7 K and increased approximately linearly with increasing temperature. The data were correlated with a modified relative activity model of Nývlt. The model could provide good correlation of the data with up to two fitting constants for each isotherm. The model was shown to provide reliable predictions of solubilities at other temperatures and ammonium chloride concentrations.