Kinetic Evaluation of the Possibility of Aluminum and Magnesium Recovery from Aqueous Solutions of Their Salts as an Alternative to the Electrolysis of Melts

Abstract

Electrolytic production, which is one of the most power-consuming and environmentally dangerous technologies, occupies a special place in nonferrous metallurgy. For example, aluminum production by the electrolysis of cryolite–alumina melts is accompanied by atmospheric emissions of fluorine-containing substances, sulfur-containing substances, and hydrocarbons, while magnesium production is accompanied by emissions of chlorine and organochlorine compounds. As of now, any proposals in the field of production of metals such as aluminum and magnesium directed at improving the environmental situation near metallurgical enterprises should be considered urgent. Despite the fact that the improvement of occurring production technologies of aluminum and magnesium has favorable developmental tendencies and actual possibilities for incorporation at operating enterprises, there are ideas and proposals on the development of new technologies based on scientific achievements in the field of the electrolytic production of light metals. Magnesium and aluminum were used as the objects of investigation. The interaction of metals with aqueous solutions of their salts—chlorides and sulfates such as MgSO4, MgCl2, Al2(SO4)3, and AlCl3—is considered. It is shown that such interactions always proceed in a diffusion region, which opens up possibilities of using various design solutions when selecting the hardware implementation of the process. The reaction order with respect to the solvent, rate constants, and activation energies are found based on the experimental data. The results prove the preference of applying the chloride media that provide the process behavior based on basic electrode reactions and excluding the appearance of side interactions. It is shown that chloride solutions can serve operating electrolytes and be carriers of ions of recovered metal. Herewith, the electrolyte saturation is the guarantee of the impossibility of the reversible process—the secondary dissolution of metal, which lowers the main characteristics of electrolysis of the cryolite–alumina melts.