An Innovative Technique for Comprehensive Utilization of High Aluminum Iron Ore Via Pre-Reduced-Smelting Separation-Alkaline
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metals Article An Innovative Technique for Comprehensive Utilization of High Aluminum Iron Ore via Pre-Reduced-Smelting Separation-Alkaline Leaching Process: Part I: Pre-Reduced-Smelting Separation to Recover Iron Siwei Li, Jian Pan , Deqing Zhu *, Zhengqi Guo *, Yue Shi, Jianlei Chou and Jiwei Xu School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China; [email protected] (S.L.); [email protected] (J.P.); [email protected] (Y.S.); [email protected] (J.C.); [email protected] (J.X.) * Correspondence: [email protected] (D.Z.); [email protected] (Z.G.); Tel.: +86-135-0848-0691(D.Z.); +86-185-7313-1417 (Z.G.) Received: 22 November 2019; Accepted: 24 December 2019; Published: 28 December 2019 Abstract: In this study, a novel process was established for extraction of Fe and Al from a complex high aluminum iron ore (33.43% Fetotal and 19.09% Al2O3). The main steps in the proposed process included pre-reducing high alumina iron ore and subsequent smelting to produce pig iron and rich-alumina slag, followed by alkaline leaching of the slag to obtain sodium aluminate solution and a clean slag. When smelting the pre-reduced high alumina iron ore pellets at 1625 ◦C for 30 min with a slag basicity of 0.40, the pig iron yielded 97.08% Fe and extracted 0.13% Al2O3, together with an iron recovery of 94.54%. In addition, more than 68.93% Al2O3 was recovered by leaching the slag, which was achieved by firstly roasted the slag at 900 ◦C for 2 h and then alkaline leaching at 95 ◦C for 2 h with a liquid-to-solid ratio of 10 mL/g. In addition, the alkaline leaching slag could potentially be used as raw material for construction purpose, which mainly consisted of SiO2 and CaO. Keywords: high-aluminum iron ore; smelting separation; modification; alkaline leaching 1. Introduction With the rapid increasing in demand for metals, the global reserves of high-grade ores are shrinking at an alarming rate. Therefore, it is urgent to develop a novel process to upgrade the complex iron resources [1,2]. High aluminum iron ore (HAIO), a kind of polymetallic complex resources, is widely distributed in nature, which has a high comprehensive utilization value. Moreover, it is abundantly found in China, Australian, India and Indonesia [3]. Typically, it contains 5–20% Al2O3 and 30–60% Fe, indicating that it is difficult to be used as a raw material for ironmaking [4,5]. Thus, it is important to remove alumina from HAIO. The recovery of valuable metals, such as Fe and Al, from HAIO has attracted increasing attention. Many technologies have been reported in previous literature, including physical beneficiation, biological leaching, and smelting. The beneficiation methods include both physical [6–8] and chemical [9] processes. Thella et al. [7] adopted flotation process to treat HAIO slime (4.0% Al2O3 and 61.99% Fe), and the findings demonstrated that the iron recovery is only 70% and the content of Al2O3 in final concentrate remained as high as 2.66%. Generally, it is difficult to effectively remove aluminum by the using the conventional beneficiation process, due to the dissemination of aluminum minerals is complex and micro-grained [10]. Pradhan et al. [2] used Bacillus circulars and Aspergillus niger to Metals 2020, 10, 57; doi:10.3390/met10010057 www.mdpi.com/journal/metals Metals 2020, 10, 57 2 of 17 remove aluminum from iron ore containing Fetotal 52.94%, 9.95% Al2O3 and 6.1% SiO2, and only 40% alumina was removed after 6 or 15 days of in situ leaching at 10% pulp density. Biological method could play a certain role in the separation of iron from alumina, but its effect may be poorer, especially the period is too lengthy compared to smelting processes. Smelting processes consist of coal-based direct reduction-magnetic separation, roasting-magnetic separation, and smelting separation [11–13]. It is effective to recover iron from low-grade refractory iron ore through coal-based direct reduction-magnetic separation. However, there is a problem that exists in this process, low reduction rate [14,15]. Zhou et al. [13] proposed a high temperature reduction followed by magnetic separation for high aluminum hematite-limonite ore treatment. Their findings indicated that approximately 90.25% of iron recovery was obtained, but the recovery of Al2O3 was not considered. Sellaeg et al. [16] adopted a direct smelting reduction process to recover iron from red mud, and the result showed that only 70% of iron was recovered and an Al2O3-containing slag was obtained. He et al. [17] proposed a slag-iron bath smelting reduction process for the treatment of alumina-rich iron ore, and more than 90% iron was recovered using this method. It is worth noting that the smelting separation process can achieve the separation of iron and alumina. However, the slag could not be effectively used, resulting in a difficulty of extracting aluminum. Considering that the existing processes for HAIO treatment have highly energy consumption and are economically impractical, it is urgent to develop a more economical and valid process. In this work, a new process was developed through the pre-reduction of high alumina iron ore and subsequent smelting to produce pig iron and rich-alumina slag, followed by alkali leaching to extract aluminum and generate a clean slag for cement industry. 2. Materials and Methods 2.1. Materials 2.1.1. High Aluminum Iron Ore The HAIO used in this study was supplied by Guang Xi Province, China. To remove all free moisture, the sample was pre-dried for 10 h at 100 ◦C prior to chemical analysis, and the findings are shown in Table1. The major ingredients of HAIO included 33.43 wt. % Fe, 19.09 wt. % Al 2O3 and 18.36% SiO2. Table 1. Chemical compositions of high aluminum iron ore (HAIO) (wt. %). Element TFe Al2O3 SiO2 K2O Na2O MgO CaO P S LOI Content 33.43 19.09 18.36 0.12 0.033 0.063 0.039 0.20 0.028 12.34 LOI: Loss on ignition. As shown in Figure1, the minerals compositions of the main phases of the iron ore cover goethite (35%), hematite (33%) and kaolinite (32%). The distributions of iron and aluminum in the ore are summarized in Tables2 and3, showing that the iron is predominantly found in the form of hematite and goethite, while aluminum is dominantly presented in the form of kaolinite. Figure2 reveals the microstructure of HAIO. The results of EDS analysis for the areas in Figure2 is demonstrated in Table4. It was observed that the main iron minerals existed within 10 µm and embedded closely with gangue minerals, which in turn could impart a great challenge for the removal of aluminum from HAIO through physical beneficiation processes. 3 of 17 3 of 17 Minerals Diasporite Gibbsite Kaolinite TAl2O3 Al MineralsContent Diasporite3.03 Gibbsite2.59 Kaolinite16.16 21.78TAl2 O3 FractionAl Content 13.933.03 11.892.59 74.1816.16 10021.78 Fraction 13.93 11.89 74.18 100 Metals 2020, 10, 57 3 of 17 Figure 1. XRD diffraction diffraction pattern of HAIO.HAIO. Figure 1. XRD diffraction pattern of HAIO. Figure 2. MMicrostructureicrostructure of the HAIO (G-Goethite,(G-Goethite, H-Hematite,H-Hematite, K-Kaolinite).K-Kaolinite). Figure 2. Microstructure of the HAIO (G-Goethite, H-Hematite, K-Kaolinite). Table 2.TableDistributions 4. The EDS of ironanalysis in mineral results phasesfor areas of thein Figure HAIO 2 (wt.. %). Table 4. The EDS analysis results for areas in Figure 2. AreaMinerals No. Iron CarbonateElemental IronCompositions/ SulfideMagnetite (atomic conc, Hematite %) /GoethiteMineral Fayalite Phase TFe FeArea Content No. 0.14Elemental C 0.020ompositions/ 0.050(atomic conc, %) 37.46Mineral 0.47 Phase 38.14 Fraction 0.36 0.06 0.14 98.21 1.23 100 Metals 2020, 10, 57 4 of 17 Table 3. Distributions of aluminum in mineral phases of the HAIO (wt. %). Minerals Diasporite Gibbsite Kaolinite TAl2O3 Al Content 3.03 2.59 16.16 21.78 Fraction 13.93 11.89 74.18 100 Table 4. The EDS analysis results for areas in Figure2. Elemental Compositions/(atomic conc, %) Area No. Mineral Phase Fe Al Si O 1 33.49 6.57 4.89 55.13 hematite 2 18.19 12.51 8.66 60.64 goethite 3 5.34 18.53 18.19 57.94 kaolinite 4 6.82 18.34 18.34 56.50 kaolinite 5 18.82 14.66 12.18 54.34 hematite/kaolinite 6 30.77 8.34 6.69 54.20 hematite 7 29.29 8.47 6.50 55.74 hematite 8 20.21 12.58 6.42 60.79 goethite 9 38.55 3.18 57.89 0.38 hematite 10 4.66 19.31 19.70 56.32 kaolinite 11 18.19 12.51 8.66 60.64 goethite 12 5.34 18.53 18.19 57.94 kaolinite 13 20.21 12.58 6.42 60.79 goethite 14 32.96 7.73 52.36 6.95 hematite 2.1.2. Flux and Additive In this study, limestone was employed as a flux to modify the binary basicity of pre-reduced-smelting separation process, which contains 55.73% of CaO and 41.52% of loss on ignition. Analytical grade Na2CO3 was used as the additive in this study for reconstructing the mineral phases of smelting separation slag by modifying the firing process. 2.1.3. Reductant Soft coal was selected as a reductant in this study, which was crushed and screened to a size of 1–5 mm. A proximate analyzer (SDTGA5000, Hunan Sundy, Changsha, China) was used for the proximate analysis of soft coal, while the chemical compositions of ash were evaluated by chemical titration method [18,19].