Red mud is the by-product of the Bayer-processing of bauxites, one of the oldest large-scale industries in the world. In 1892 Karl Joseph Bayer, an Austrian chemist, applied for a patent on the digestion of bauxite, an aluminium-containing ore, by means of a concentrated sodium hydroxide solution employed at elevated temperature and pressure, which enables dissolution of the aluminium content and its separation from other bauxite components. From the caustic solution the dissolved aluminium hydroxide can be precipitated by dilution. Then the hydroxide is subjected to calcinations to form alumina, from which metallic aluminium is produced by e...