Clean and efficient utilization of low-grade high‑iron sedimentary bauxite via calcification‑carbonation method

Abstract

With the rapid development of China's aluminum industry and the depletion of high-quality bauxite resources, technology for the clean and efficient utilization of non-traditional bauxite resources has become the focus in related fields.The alumina-to-silica mass ratio of low-grade high-iron sedimentary bauxite from Yunnan, China is 2.65; diaspore and goethite coexist in this bauxite. To enhance the utilization efficiency of bauxite, the hydrometallurgy process of the “calcification-carbonation method” (CCM) had been proposed, and the research results indicated that the addition of lime promoted the transformation of the goethite phase significantly, and the replacement ratio of Al in goethite decreased from 16.02% to 12.15% for a calcification temperature of 200 °C. The Gibbs free energy for the generation of Ca3(Fe0.87Al0.13)2(SiO4)1.65(OH)5.4 decreases gradually with an increase in the reaction temperature, and an excessive decomposition temperature in the carbonization process is not conducive to the decomposition of the garnet phase. The calcification reaction is controlled by diffusion and chemical reaction, and the activation energy in the temperature range from 220 to 260 °C (determined using a high-pressure DSC) is 38.4 kJ/mol; it is 19.6 kJ/mol in the temperature range from 260,276.8 °C. Fe completely dissociates from hydrogarnet upon carbonization, and the main silica-containing phases in the digested slag are unreacted hydrogrossular and calcium silicate. The CCM enhanced the recovery ratios of Al2O3 and Fe from high-iron diasporic bauxite by ~20% and 10%, respectively, compared with those in the Bayer process, and the Na content decreased to lower than 0.1% in the CCM slag; this can be used as cement raw material directly. Thus, the clean and efficient utilization of low-grade high-iron sedimentary bauxite was achieved using the CCM.