Removal of Impurity Elements from Molten Aluminum: A Review

In the current paper, the technical progress of aluminum refining over the past 30 years has been summarized, including the improvement of batch reactor and in-line continuous reactors, the evolution of gas purging methods by nozzle, porous plug, and rotating impellor, and the use of fluxing by using gas mixtures (including argon, nitrogen, and chlorine) and solid salts (such as AlF3, MgCl2, and KCl). The mathematical models developed for the removal of impurity elements from molten aluminum were also reviewed. Thermodynamic factors were summarized, including the Gibbs free energy of the chemical reactions, activity coefficients of the impurity elements, and the melting and boiling points of impurity elements and related compounds. Kinetic factors used and derived by researchers are also reviewed, such as mass transfer coefficient of impurity elements, mixing power and mixing time in reactors stirred by gas, impellor and circulation of the fluid, and the size, residence time, and terminal velocity of bubbles. The current review provides useful information for the future study of the removal of impurity elements from aluminum.