Synthesis strategies of alumina from aluminum saline slags

Abstract

Aluminum saline slags is a waste of the metallurgical industry that presents serious environmental problems since it needs very extensive areas for its disposal, the toxicity it causes in the atmosphere and groundwater, in addition to high transportation costs. The valorization of this residue by the synthesis of alumina, a compound widely used in the chemical industry, generates a high impact and great interest. In this work, the strategies for synthesizing alumina from aluminum saline slags are reviewed in a context of growing demand for this metal and environmental crisis. The first sections present the aluminum production processes, both from natural bauxite (primary process) and from the recycling of materials with a high aluminum content (secondary process); paying attention to the waste generated and what environmental problems they produce. The main investigations that have allowed to address the recovery of the waste generated are described below, focusing on the processes of recovery/extraction of the aluminum present in its composition. The aluminum in these residues can be found as a metal or forming other compounds such as simple or mixed oxides. Chemical processes are the most relevant, especially those that deal with the acid and alkaline extraction of the metal. The most important section of the work reports on the methods of synthesis of Al2O3, highlighting the methods of precipitation, sol-gel, hydrothermal synthesis, and combustion, among others. The work ends with a summary and conclusions section.