Influence of Sodium Sulfate Addition on Iron Grain Growth during Carbothermic Roasting of Red Mud Samples with Different Basicity

Abstract

Red mud is an iron-containing waste of alumina production with high alkalinity. A promising approach for its recycling is solid-phase carbothermic roasting in the presence of special additives followed by magnetic separation. The crucial factor of the separation of the obtained iron metallic particles from gangue is sufficiently large iron grains. This study focuses on the influence of Na2SO4 addition on iron grain growth during carbothermic roasting of two red mud samples with different (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21, respectively. Iron phase distribution in the red mud and roasted samples were investigated in detail by Mössbauer spectroscopy method. Based on thermodynamic calculations and results of multifactorial experiments, the optimal conditions for the roasting of the red mud samples with (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21 were duration of 180 min with the addition of 13.65% Na2SO4 at 1150 °C and 1350 °C followed by magnetic separation that led to 97% and 83.91% of iron recovery, as well as 51.6% and 83.7% of iron grade, respectively. The mechanism of sodium sulfate effect on iron grain growth was proposed. The results pointed out that Na2SO4 addition is unfavorable for the red mud carbothermic roasting compared with other alkaline sulfur-free additives.

Research on High-Pressure Hydrochloric Acid Leaching of Scandium, Aluminum and Other Valuable Components from the Non-Magnetic Tailings Obtained from Red Mud after Iron Removal

“…Furthermore, it contains small amounts of Mg3Al2Si3O12 (pyrope), MgAl2O4 (magnesium aluminum oxide), and Fe (iron). The major phases of the SSAT sam- [53]. It should be noted that there is an absence of gehlenite and grossular in the SSAT compared to the WAT, as well as a similarity of other minerals to the WAT sample.…”

“…Figure 1 shows diffractograms of the WAT and SSAT samples with phase signs. The phase composition of the RM sample is in our previous paper [53]. The mineral compositions of the samples are quite different.…”

“…Two samples of non-magnetic tailings were derived by reduction roasting-a magnetic separation process of red mud (RM) from the Bogoslovsky Aluminium Plant (Russian Federation, Krasnoturyinsk, 59.84 • N, 60.19 • E) at optimal conditions according to our previous work [53]. The first sample codenamed as without addition tailings (WAT) was obtained by the reduction roasting of RM at 1300 • C for 1 h. The second sample codenamed as sodium sulfate addition tailings (SSAT) was obtained by reduction roasting of the mixture of 84.6 wt.% RM and 15.4 wt.% Na 2 SO 4 at 1150 • C for 3 h. Both the roasted samples were ground, screened through a 300-mesh sieve, and magnetically separated using a wet method by the Davis tube XCGS-50 (Shaoxing Weibang Mining Machinery Manufacturing Co., Ltd., Zhejiang, China) at magnetic field intensity of 0.1 T. Table 1 demonstrates the chemical compositions including iron content of the RM, WAT, and SSAT samples.…”

Research on High-Pressure Hydrochloric Acid Leaching of Scandium, Aluminium and Other Valuable Components from the Non-Magnetic Residues Obtained from Red Mud after Iron Removal

“…Also, it contains small amounts of Mg3Al2Si3O12 (pyrope), MgAl2O4 (magnesium aluminum oxide), and Fe (iron). The major phases of the SSAT sample are NaAlSiO4 (nepheline) and CaS (oldhamite), which were formed by chemical reactions between Na2SO4 and calcium-aluminum-silicon oxides during the carbothermic roasting of red mud [49]. It should be noted an absence of gehlenite and grossular in the SSAT compared to the WAT, as well as a similarity of other minerals to the WAT sample.…”

“…Two samples of non-magnetic tailings were derived by reduction roasting -magnetic separation process of red mud (RM) from Bogoslovsky Aluminium Plant (Russian Federation, Krasnoturyinsk, 59.84°N, 60.19°E) at optimal conditions according with our previous work [49]. The first sample codenamed as without addition tailings (WAT) was obtained by reduction roasting of RM at 1300 °C during 1 hour.…”