Influence of Cryolite Content on the Thermal Properties and Coalescence Efficiency of NaCl-KCl salt flux

Abstract

Salt fluxes with fluoride additions are necessary for the treatment and recycling of contaminated or oxidized aluminium scrap. This study aims to investigate the effect of cryolite additions on the thermal properties and the coalescence efficiency of a NaCl–KCl salt flux mixture. Thermodynamic calculations were carried out to examine the phase diagram of the salt mixture as the cryolite content increases. The study of the melting properties of the salt was carried out by means of differential scanning calorimetry. The coalescence efficiency of the salts was assessed by re-melting coated aluminium chips. The experimental results show a decrease in the liquidus temperature as the cryolite content increases; this differs from the thermodynamical calculations. For cryolite contents up to 3 wt%, higher cryolite content in the salt leads to higher coalescence of re-melted chips. However, the coalescence differences observed between the recycling products for cryolite contents of 3% and higher were minor.