Simultaneous Application of Oxalic Acid and Sodium Dithionite for Synchronous Removal of Iron and Silica from Low-Grade Bauxite: Kinetics and Mechanism

Bauxite is widely used to produce alumina. There are many bauxite resources with high iron content. These resources could not be processed and utilized efficiently due to the high concentration of iron (Fe). The alkaline leaching process has been proposed to remove iron from these bauxite resources. Therefore, in this study, the alkaline leaching process was employed, and the effects of sodium dithionite (on the decomposition of iron oxides), sodium carbonate (adjustment of the solution pH), and oxalic acid (on the prevention of precipitation of Fe2+ complexes and the decomposition of kaolinite) were investigated using a central composite design. The results showed that 77 and 54% of iron and silica were removed under optimum operating conditions. These conditions included the use of oxalic acid at a dosage of 24 g and sodium dithionite at a concentration of 0.08 M, reaction time of 75 min, solid content of 10%, pH of 8-8.2, and stirring speed of 700 rpm. The kinetics modeling indicated that the alkaline leaching of iron from high-iron bauxite was controlled by the product layer diffusion mechanism. In addition, the calculated activation energy was 18.8 kJ/mol. The removal mechanism was studied by X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy analysis.