Role of thermal activation in alumina production from low-quality bauxites

The purpose of this article is giving the rationale for preliminary thermal activation under alumina production from low-quality bauxites via a comparative analysis of liquid and solid phases of desiliconization of initial and calcined bauxite. The following methods are used: thermal activation of the product through firing of initial bauxite at the temperature of 1000 ºC, its desiliconization by alkaline solutions of 150 g/dm³ of Na₂O_к where the liquid-to solid ratio is 10:1, production of the concentrate suitable for refining by the Bayer method. The chemical analysis of solid phase is determined by the x-ray fluorescence method using XRF-1800 spectrometer ("Shimadzu", Japan). The content of SiO₂ in the liquid phase is determined using PE-5400UF spectrophotometer. Phase separation is intensified by means of a centrifuge. The solid phase in the sample cell (after liquid phase sampling) is washed by decantation, dried and analyzed. Graphs are built that describe the dependence of silica extraction degree on desiliconization time for different temperatures. Graphic dependences also take into consideration the use of raw material thermoactivation, show the variations of the process rate depending on the desiliconization temperature, reflect the changes in the apparent activation energy of desiliconization depending on the degree of silica extraction in solution. Conclusions are drawn on the expediency of firing for increasing the silica extraction degree and obtaining a higher value of the silicon modulus of bauxite concentrate. The feasibility of thermal activation in processing of high-silicon bauxites is proved as it allows to increase the degree of silica extraction from calcined bauxite into an alkaline solution as well as to intensify the desiliconization process. Based on the variations of the apparent activation energy for different temperature intervals and SiO₂ extraction degree for thermoactivated and initial bauxite an attempt is made to reveal the mechanism and chemical nature of the desiliconization process.

low-quality bauxites, thermochemical activation, leaching, desiliconization, apparent activation energy