Sustainable Production of Alumina through Iron Separation by Smelting-Reduction of Bauxite

Bauxite ore is the main raw material for aluminum production; it is converted into alumina (Al2O3) to obtain a proper charge material for aluminum production in Hall-Héroult process. Bayer process is the main commercial alumina production method in which bauxite ore is first digested by NaOH at moderate hydrothermal conditions, followed by aluminum hydroxide (Al(OH)3) precipitation from the obtained sodium aluminate solution. Calcination of the hydroxide to alumina yields a high purity alumina feedstock for aluminum production. One of the main by-products of the Bayer process is red mud, which is separated from the bauxite solution after digestion and contains significant amount of iron oxide. Red mud is one of the most important disposal materials in the world with no commercial use. Alternative sustainable process for bauxite treatment to alumina is Pedersen process, which was patented in 1920s. This process was run for 40 years on a commercial scale before it was closed down due to the economic reasons. The Pedersen process is more sustainable compared to Bayer process regarding no rd mud production, lower CO2 emission and energy consumption. In this process, iron (the main impurity in European bauxites) is removed from the ore through a smelting reduction process, which yields pig iron and a high alumina containing slag. The slag is further hydrothermally treated to alumina through an economical process. In the present study, Bayer and Pedersen processes are compared and their advantages and disadvantages are presented. Moreover, the experimental results on the smelting-reduction of different bauxites and the distribution of the metallic impurities in the ore such as Si, Ti, Ca,… between the obtained metal and slag phases are presented. It is shown that a modernized Pedersen process will solve serious present environmental challenges such as red mud production and CO2 emissions in the alumina industry.