Sustainable recovery of metallic Al and reuse of molten salt in Al dross: Salt flux erosion and super-gravity separation

Abstract

Al dross is a hazardous solid waste produced in the smelting of electrolytic Al and contains amounts of metallic Al droplets encapsulated by dense oxidized films. The conventional Al recycling processes from Al dross are either inefficient or prone to producing harmful gases and salt cake. In this study, equimolar amounts of KCl and NaCl were employed to attack and erode the solid oxidized films and the metallic Al and molten salt were recovered simultaneously via super-gravity separation. The erosion behavior of salt flux on Al dross indicated that the Al–Al2O3 interface structure was changed, and the cracks and fractures were formed on the oxidized films, which provided the prerequisite conditions for the movement of Al liquid. On this basis, the metallic Al and molten salt were efficiently recovered from Al dross by the enhanced separation of super-gravity with recovery ratios of 98.51 % and 99.03 %, respectively, preventing the production of hazardous gases and unmanageable salt cake. The recovered molten salt was reused in the process of erosion on oxidized films and Al separation from Al dross, where the recovery ratios of metallic Al and molten salt were also up to 94.87 % and 98.58 % after five cycles of recycling. The final residue can also be utilized in appropriate ways and further provides a sustainable method for Al recovery and resource recycling from Al dross.