2. Experimental
2.1. Materials
The purified sample of natural pyrite ore (the content of FeS2 >98%) was offered by a company in Guangzhou, China. Hematite (α-Fe2O3) was prepared by calcination of iron sulfate (FeSO4·7H2O, reagent grade) in a muffle furnace at 800 °C for 2 h, and the formed hematite was confirmed by TG and XRD. The intermediate product of pyrite was prepared by calcination of pyrite in a tube furnace under N2 atmosphere at 700 °C for 1 h, which is the mixture of pyrite, pyrrhotite and iron monosulfide confirmed by XRD.
The red mud samples discharged by the sintering process or Bayer process were collected from alumina plants in Shanxi and Henan, China, which were dried at 110 °C for 4 h before testing. The chemical composition of these red mud samples was determined by the nonferrous metals industry standard methods (YS/T 575-2007), in which Fe2O3 content was determined by the orthophenanthroline photometric method (YS/T 575.5-2007).
2.2. Roasting experiments
The mixtures of hematite and pyrite in different ratio were constant-temperature roasted in a tube furnace under N2 atmosphere in the range of 500–800 °C for 30–60 min. The products were identified by XRD.
30 g of red mud samples were used in the simulation experiment, and amount of pyrite was calculated based on the content of Fe2O3 in the red mud in which the mole ratio of FeS2 to Fe2O3 was 1:4 or 1:8. After mixed carefully, the mixture of red mud and pyrite was roasted at 600 °C for 30 min under N2 atmosphere. The roasted products were separated into magnetic and nonmagnetic part by a magnet after repetitive operation. The Fe2O3 contents of both parts were determined by the orthophenanthroline photometric method.
2.3. Characterization
The thermogravimetric analysis (TG) and differential thermal analysis (DTA) of the samples were performed on a thermal analyzer (NETZSCH, STA 449 F3). The typical measurements were performed at a heating rate of 10 °C min−1 under N2 atmosphere. The identification of the evolved gas during thermo-analysis was performed by a Fourier IR spectrometer (Bruker Tensor 27) coupling with a thermal analyzer through a transferring tube keeping 250 °C. All of the products were detected by an X-ray diffractometer (Bruker AXS D8) with a Cu-Kα radiation. The specific saturation magnetization of the samples was tested by a vibrating sample magnetometer (VSM, Lake Shore 7410).
2. Experimental2.1. MaterialsThe purified sample of natural pyrite ore (the content of FeS2 >98%) was offered by a company in Guangzhou, China. Hematite (α-Fe2O3) was prepared by calcination of iron sulfate (FeSO4·7H2O, reagent grade) in a muffle furnace at 800 °C for 2 h, and the formed hematite was confirmed by TG and XRD. The intermediate product of pyrite was prepared by calcination of pyrite in a tube furnace under N2 atmosphere at 700 °C for 1 h, which is the mixture of pyrite, pyrrhotite and iron monosulfide confirmed by XRD.The red mud samples discharged by the sintering process or Bayer process were collected from alumina plants in Shanxi and Henan, China, which were dried at 110 °C for 4 h before testing. The chemical composition of these red mud samples was determined by the nonferrous metals industry standard methods (YS/T 575-2007), in which Fe2O3 content was determined by the orthophenanthroline photometric method (YS/T 575.5-2007).2.2. Roasting experimentsThe mixtures of hematite and pyrite in different ratio were constant-temperature roasted in a tube furnace under N2 atmosphere in the range of 500–800 °C for 30–60 min. The products were identified by XRD.30 g of red mud samples were used in the simulation experiment, and amount of pyrite was calculated based on the content of Fe2O3 in the red mud in which the mole ratio of FeS2 to Fe2O3 was 1:4 or 1:8. After mixed carefully, the mixture of red mud and pyrite was roasted at 600 °C for 30 min under N2 atmosphere. The roasted products were separated into magnetic and nonmagnetic part by a magnet after repetitive operation. The Fe2O3 contents of both parts were determined by the orthophenanthroline photometric method.2.3. CharacterizationThe thermogravimetric analysis (TG) and differential thermal analysis (DTA) of the samples were performed on a thermal analyzer (NETZSCH, STA 449 F3). The typical measurements were performed at a heating rate of 10 °C min−1 under N2 atmosphere. The identification of the evolved gas during thermo-analysis was performed by a Fourier IR spectrometer (Bruker Tensor 27) coupling with a thermal analyzer through a transferring tube keeping 250 °C. All of the products were detected by an X-ray diffractometer (Bruker AXS D8) with a Cu-Kα radiation. The specific saturation magnetization of the samples was tested by a vibrating sample magnetometer (VSM, Lake Shore 7410).
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