Disposal of reactive compounds and salts in secondary aluminum dross: A critical review

Abstract

Massive secondary aluminum dross is annually produced globally, posing a serious threat to the environment. Existing reviews have mainly focused on alumina extraction and material preparation methods, neglecting toxic properties. In this study, its environmental impact was analyzed, and disposal of reactive compounds and salts in secondary aluminum dross were reviewed. The harmful effects of alumina result from their reactivity and salt content; the former can be eliminated hydrolysis and high-temperature oxidation, and the latter may be separated via aqueous washing and high-temperature evaporation. Solution washing can efficiently remove chloride and produce a gas mixture composed mainly of hydrogen and ammonia, and containing some toxic gas. High-temperature elimination can be implemented in the ways, oxidizing by oxygen or the oxides in hazardous wastes and flue gas, and acting as foaming agent for fabricating aerated concrete and foaming ceramic. However, these methods risk generating harmful gases, fail to fully utilize the reducibility of aluminum nitride and metallic aluminum in the dross, and overlook integrated considerations of reducibility, salt separation, and resource planning. Consequently, a method for recycling aluminum dross has been proposed. Thus, a cyclic method for utilizing the dross is proposed. The dross is processed at high-temperature for separating salt and producing ladle refining slag. The obtained salt is returned to aluminum industry, and the slag is used in the process of steel refining. The spent slag can be utilized as raw material for alumina preparation, and the alumina can be reused in aluminum industry. This method fully considers the utilization of the reducibility and composition of the dross, maximizing its economic value while minimizing environmental impacts.