Mechanism of Electrolytic Reduction of Coarse Boehmitic Bauxite in Alkaline Media Before Bayer Process

The Bayer process, the dominant method of alumina production for over a century, faces several challenges, including low iron content in bauxite residue, increased caustic alkali consumption and low alumina recovery rates. This article focuses on studying electrolytic reduction processes of bauxite iron minerals in alkaline solutions as a potential improvement to the traditional Bayer process for producing alumina. The research employs a metal mesh cathode at the bottom of an electrochemical cell to simultaneously reduce iron minerals and leach aluminium and silica from coarse boehmite bauxite before milling and high-pressure leaching. Preliminary thermodynamic research indicates that the presence of both hematite (α-Fe2O3) and chamosite ((Fe2+,Mg,Al,Fe3+)6(Si,Al)4O10(OH,O)8) in this type of bauxite helps to achieve a higher iron concentration in the solution. Cyclic voltammetry revealed that, in the initial stage of electrolysis, overvoltage at the cathode decreases as metallic iron deposited and conductive magnetite form on the surface of the particles. After 60 min, the reduction efficiency begins to decrease. The proportion of the current used for magnetization and iron deposition on the cathode decreased from 89.5% after 30 min to 67.5% after 120 min. Studying the electrolysis product using SEM-EDS revealed the formation of a dense, iron-containing reaction product on the particles' surface, preventing diffusion of the reaction products. Mössbauer spectroscopy of the high-pressure leaching product revealed that the primary iron-containing phases of bauxite residue are maghemite (Fe3O4), formed during the hydrolysis of sodium ferrite (Na2FeO4).