Coalescence behaviour of aluminum droplets under a molten salt flux cover

The formation of a suspension of aluminum droplets in salt fluxes used during the refining and recycling of aluminum, leads to decreased aluminum recovery. To enhance the coalescence and recovery, it is required to remove the oxide layer formed on the surface of these small aluminum drops. The coalescence behaviour of aluminum droplets under a molten salt flux cover was investigated using a hot stage microscope at a temperature of 740 degrees C. Two salt systems were studied: i) an equal weight mixture of NaCl-KCl with chloride and fluoride additives and ii) the MgCl2-KCl system with fluoride additives. Chloride salts did nothing to enhance coalescence but fluoride additions to both salt systems removed the oxide film from die metal. NaF, KF and Na3AlF6 additives were the most effective salts at stripping away the oxide layer and promoting coalescence. As the concentration of MgCl2 increased, the ability of the droplets to coalesce decreased.