Interfacial tension between aluminum alloy and molten salt flux

Recycling of aluminum scrap is economically sound and saves energy. The aluminum alloy scrap is shredded, decoated, and screened for contaminants, before charging in a bath of molten salt flux, so that the melting of aluminum alloy takes place under the cover of salt flux. Flux prevents oxidation of the aluminum alloy and promotes coalescence of molten metal. The salt flux is usually based on equimolar NaCl-KCl composition corresponding to the eutectic composition, because it is cheap, and its melting point is low. The interfacial tension between aluminum alloy and salt plays an important role in the whole remelting process. The present work describes the variation of interfacial tension between Used Beverage Container (UBC) alloy and ternary salt systems having equimolar NaCl-KCl. In this work, the interfacial tension between UBC alloy and molten salts was measured using the drop detachment method. The salt composition was varied by adding varying amounts of NaF, KF, LiF, Na3AlF6, ALF(3), MgF2, and LiCl in an equimolar NaCl-KCl salt mixture. The variation of interfacial tension with salt composition was related to the adsorption of surface active elements at the metal-salt interface. Adsorption of the surface active elements is dependent on their activity. Measurement of sodium and potassium content in aluminum metal using Electron Probe Micro-Analysis (EPMA) supported this model.