Aluminium is widely used in sectors such as building, transportation, and packaging thanks to its lightness, good corrosion resistance, and thermal and electrical conductivity. Its prevalence in transportation, especially in lightweight vehicle production, contributes to reduced fuel consumption and emissions. However, the energy-intensive primary production of Al poses sustainability challenges. Aluminium recycling emerges as a crucial solution, reducing energy consumption and emissions by up to 95% compared to primary production. Yet, the recycling process raises issues such as the oxidation of the molten metal and the accumulation of impurities in recycled Al products. The present work highlights the role of salt fluxes in improving secondary aluminium quality. The fluxes consist mainly of chlorides mixtures with fluorides additions, and they are added during the re-melting process of Al scrap to reduce metal oxidation and remove impurities. Moreover, they improve metal recovery by releasing the metal entrapped in the dross. The mechanisms lying underneath the action of fluxes are covered in detail in the present work. Despite the advantages of introducing fluxes in the melt, a consolidated procedure to characterize their efficiency is still lacking. Given this, a laboratory-scale procedure to characterise the efficiency of fluxes is proposed in this study, with a particular focus on their chemical and physical features. X-ray diffraction (XRD), X-ray fluorescence and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) were used for elemental analysis and phase identification of the salt flux’s components. The melting characteristics of the salt were analysed using differential scanning calorimetry (DSC). The salt was added to a stirred molten bath of AlSi9Cu3(Fe) alloy scrap and ingot. To assess melt cleanliness, reduced pressure test (RPT) samples were collected from the bath, while hydrogen was monitored throughout the process. The resulting dross was collected and investigated using SEM and XRD techniques. The findings demonstrate the reliability of the experimental approach and its ability to determine the chemical and physical characteristics of the salt flux. The identified compounds in the flux consisted mainly of NaCl, KCl, NaF, and K2CO3. When salt is added, the hydrogen levels in the melt are reduced, and melt cleanliness is improved as shown from the analysis of the RPT samples. Reaction products in the dross were primarily aluminium oxides and chlorides, with limited metal losses observed. With the developed experimental procedure, it is possible to reliably assess the chemical and physical properties of a salt flux and correlate them with its efficiency in delivering satisfactory metal cleanliness.