Plasma assisted synthesis of γ-alumina from waste aluminium dross

Aluminium dross, a waste generated from aluminium melting process, contains aluminium metal, aluminium oxide, aluminium oxy-nitride and impurities such as sodium chloride and potassium chloride. Since aluminium dross is land filled without treatment, it is hazardous to the environment. Conventional methods for the metal recovery from the recycling of aluminium dross involve chemicals and are time consuming. In this study, an attempt was made to treat aluminium dross using plasma arc melting process. The aluminium dross was melted and evaporated by the plasma arc established between a crucible anode and a rod type hollow cathode made of graphite. Raw dross and products of plasma treated dross such as slag and fine powder were characterized. The generation of ultrafine alumina powder and slag are explained using simulation of the plasma arc inside the crucible and free energy minimization calculations. High temperature and air entrainment into the plasma inside the crucible converted the dross into alumina slag and fine powder. The amount of fine alumina powder produced increased substantially with plasma power initially as seen from the results of alumina obtained at 5 kW and 10 kW. However, further increase in plasma power resulted only in marginal increase in the conversion of Al dross to alumina. Results of this study indicate that arc plasma technology can be effectively applied to convert Al dross into value added fine alumina powder.