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Investigation of dephosphorization of brown iron ore concentrates by sintering and magnetic beneficiation
International Journal of Mineral Processing 126 (2014) 136–140
Contents lists available at ScienceDirect
International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro
Investigation of dephosphorization of brown iron ore concentrates by sintering and magnetic beneficiation B. Khassen a,⁎, N. Baltynova a, L. Dakhno b a b
The Institute of Problems of Complex Development of Mineral Resources, Karaganda, Kazakhstan Karaganda State Technical University, Karaganda, Kazakhstan
a r t i c l e
i n f o
Article history: Received 29 July 2013 Received in revised form 25 November 2013 Accepted 29 November 2013 Available online 5 December 2013
a b s t r a c t The results of investigation of sintering and magnetic beneficiation of brown iron ore concentrate are presented. The investigations are based on using a possibility of redistribution of phosphorus from the ore constituents into slag-forming ones in the process of sinter roasting. © 2013 Elsevier B.V. All rights reserved.
Keywords: Dephosphorization Brown iron ore concentrate Sinter roasting Magnetic separation Micro-X-ray spectral analysis
1. Introduction The aim of this work is to study the behavior of phosphorus in the process of sinter roasting of brown iron ores to develop a technology for obtaining high-quality iron ore concentrates. The reserves of brown iron ore are known to rank third in the world and they are common in North America, Australia, China, Kazakhstan, and other countries. Ores of most brown iron deposits are readily and inexpensively mineable and require low power for crushing and beneficiation. However, the mechanical methods of their beneficiation do not provide high-quality iron ore products that meet modern requirements (Zhu and Zhang, 1996; Zima, 2011; Khassen et al., 2004). The needs of metallurgy in industrial countries are met at the expense of import of high-quality concentrates (iron content is higher than 64% and that of phosphorus is less than 0.07%). In the Republic of Kazakhstan the following trend is observed: about 67% of the registered reserves of iron ores are represented by brown iron ores of two largest deposits (Lisakovsk, Ayatsk). The import of high-quality iron ores to Kazakhstan is problematic due to its continental location and lack of such ores in neighboring countries. The Republic of Kazakhstan has an integrated iron-and-steel mill of the complete cycle (“ArcelorMittal Temirtau”), which annually produces over 6 million tons of steel products (sheet metal and ⁎ Corresponding author at: The Institute of Problems of Complex Development of Mineral Resources, 5 Ippodromnaya Str., 100019 Karaganda, Kazakhstan. Tel.: +7 7212 414 520. E-mail address: [email protected] (N. Baltynova). 0301-7516/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.minpro.2013.11.013
tin-plate). Therefore, it is very important to involve into processing the iron ores of the country's own mineral resources. Neither the existing gravity-magnetic scheme nor the roasting-magnetic scheme can solve the issue of simultaneously increasing the iron content and reducing the content of phosphorus in Kazakhstan brown iron ore concentrates (Mirko et al., 2002). Such a situation is typical for many brown iron ores (Panychev, 2006; Tuo et al., 2008). This explains an intensive research into processing of brown iron ores according to complex process flow schemes. Among them are roasting of concentrate and acid leaching of phosphorus (Belikov et al., 2003), sintering with soda and water leaching of aluminum (Li et al., 2008), pressure leaching of impurities (Maximov et al., 2003), using of bacteria and their waste products for flocculation and flotation separation of hematite from oxides of Al, Si, and Сa (Sarvamangala and Natarajan, 2011), roasting and metallic coating (Panychev, 2006; Zima, 2011), agglomeration sintering and acid leaching of phosphorus and other contaminants from sinter (Patrick and Lovel, 2001). These works are in different stages of research. The researchers (Patrick and Lovel, 2001) carry out agglomeration sintering of brown iron ores at basicity of 1.84. They observe the concentration of phosphorus in 2CaOSiO2 and the absence of phosphorus in Fe3O4. Khassen B.P. (Khassen, 2005) notes the attractiveness of using a sintering machine for sintering brown iron ores since this reduces the costs for an expensive heating procedure. According to this work, phosphorus is accumulated in olivine (CaO)х·(FeO)2−x·SiO2, where х b 1.1, and it is absent in Fe3O4. The object of agglomeration sintering is brown iron ore having basicity 2 and higher, which is necessary to form individual phosphorus-containing phases: 7CaO·P2O5·2SiO2
B. Khassen et al. / International Journal of Mineral Processing 126 (2014) 136–140
137
(nagelschmidtite) and 5CaO·Р2O5·SiO2 (silicocarnatite). The work (Baltynova et al., 2009) is a continuation of these investigations. It has studied the composition and physical mechanical properties of sinter (basicity 0.6; coke consumption 18%) obtained from the hematite concentrate. In the sinter, phosphorus is also redistributed from ore components into slag-forming ones. This work investigates:
the center (0.9%) in dense oolites of GMC, while in zonal-concentric oolites it is distributed as 0.7 and 0.6%, respectively. A diagram of phosphorous content also confirms a uniform distribution of phosphorus over the cross-section of oolite (Fig. 1).
– the regularities of redistribution of phosphorus between ore and slag-forming minerals at sintering the brown iron ore concentrate while varying the basicity of the charge from 0 to 2; – the possibility to separate ore and slag-forming minerals of the sintering products by magnetic separation.
When sintering GMC without fluxing agents, high temperatures have a refining effect on the minerals of ore grains. In particular, magnetite without phosphorus impurities has been obtained. This fact is illustrated by the results of scanning of the structure of nonfluxed sinter of GMC (Fig. 2) and the micro-X-ray spectral analysis (Table 2). According to the crystal optical analysis (Fig. 3a) a ferrous-silicate matrix has a distinctive structure: 1—a semiopaque silicate glass, depositions of magnetite in a dendritic form were observed on some of its parts; 2—non-decrystallized glass enriched with iron oxides. The data on their micro-X-ray spectral analysis are given in Table 2. As follows from Fig. 3b, the ore component of the sinter (basicity 0.6) is represented mainly by magnetite. Тhe silicate matrix is the glass phase, which is nonhomogeneous in its structure and contains dendrites of magnetite, gehlenite, and wustite. An increase of basicity of the charge up to 1.9 (Fig. 3c and d) leads to a further increase of inhomogeneity of the microstructure and an occurrence of new phases (calcium ferrites, calcium silicates, individual minerals of phosphorus, sweat balls of metallic iron are observed). Crystals of magnetite are of a regular shape, with the sizes within the range of 1.0 to 50 μm. According to the data of the micro-X-ray spectral analysis (Table 2), phosphorus was not detected in the structure of magnetite, wustite, and metallic iron. Thus it has been established that during sinter-roasting GMC there is a large-scale transfer of phosphorus from ore minerals into slag-forming minerals. To separate those minerals and obtain iron-ore concentrates free of phosphorous impurities it is expedient to use magnetic separation.
2. Experimental 2.1. Materials and equipment The material used for this study was the concentrate of gravitymagnetic separation (GMC) of brown iron ores of the Lisakovsk deposit. Composition of the concentrates and by-products of their roasting was determined by chemical, crystal-optical, X-ray diffraction and micro-X-ray spectral analyses. The following instruments were used: microscope (Axioskop 40 Pol from Zeiss, Germany), electron-probe microanalyzer (JEOL ISM-6510, Japan), X-ray diffractometer (BRUKER D8 ADVANCE, Germany). The polished sections were made on grinding-and-polishing machines of S-1000 type of LECO (USA). The quantitative evaluation of the structure of mineral phases was performed with the help of the computer program Video-Test Structure (Russia). The experiments on roasting of GMC were carried out in a sintering plant (the bowl of 350 mm in diameter and 500 mm in height). In all the laboratory experiments the thickness of the charge layer was 250 mm, the charge weight was 20 kg; the coke consumption ranged from 3 to 20% of the weight of charge and basicity (ratio CaO:SiO2) was varied from 0 to 2. The wet magnetic separation was carried out in a tubular magnetic analyzer of 25 T type at the magnetic field intensity of 120 kA/m.
2.3. Sinter roasting of GMC
2.2. Analysis of the initial concentrates The brown iron ore concentrates of the Lisakovsk deposit have the following chemical composition, %: 49 Fe; 0.5 FeO; 10.7 SiO2; 4.5 Al2O3; 0.3 CaO; 1.6 P2O5; 0.3 MgO; 0.3 MnO and 12.4 is the loss on ignition. They are represented mainly by oolites of the minerals of goethite, hydrogoethite and inclusions of quartz. Oolites have a rounded, elliptical and clastic shape; their size varies from 200 to 700 μm, predominantly 300 to 400 μm. Quartz is in the free state in the form of independent phase-grains of angular shape of 50 to 90 μm in size. According to their structure oolites can be classified into two types: 1) dense homogeneous ones, having a high reflection power, 2) concentrically-zonal ones. Table 1 shows distribution of elements over the cross-section of oolite found by the micro-X-ray spectral analysis. As can be seen, phosphorus is distributed relatively evenly between the edge and Table 1 Distribution of elements in the microstructure of oolites. Structure
Position
Content of elements, % О
Fe
Al
P
Ca
Si
Oolite of GMC, dense Oolite of GMC, zonal-concentric
Edge Center Edge Center
38.9 40.0 32.5 32.4
54.3 53.4 57.7 57.3
3.7 3.6 3.6 3.6
0.9 0.9 0.7 0.6
0.1 0.2 0.2 0.2
1.4 1.6 1.4 1.6
Fig. 1. Distribution of phosphorus over the gross-section of oolite.
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Fig. 2. X-ray spectral scanning of the structure of non-fluxed sinter of GMC: o—general view.
2.4. Magnetic concentration of the products of sinter roasting of GMC The crystal-optical analysis helped in the determination of the optimal degree of grinding of the sinter roasting products as 95 to 99% of the class minus 0.044 mm. To improve the indicators of magnetic concentration a preliminary desliming of the finely ground products (the class of 0.010 mm) was carried out. Table 3 contains the results of magnetic concentration of the products of sinter roasting of GMC. When increasing the basicity of the charge from 0 to 2 in the obtained magnetic fractions, the content of Fe is shown to decrease from 61.8 to 51.4% and that of P2O5 from 1.6 to 1.2%. 3. Results and discussion The experimental data (Table 1, Fig. 1) show that hydrogoethite– goethite oolites of brown iron ores of the Lisakovsk deposit are characterized by a uniform distribution of phosphorus and aluminum in the structure of oolites. These data are confirmed by the analysis of a state diagram of the system Fe2O3–P2O5: when the content of P2O5 in oolites is within 1.27–1.92%, phosphorus can predominantly be in the form of an isomorphic impurity in the crystal lattice of goethite α-Fe2O3·H2O or hematite α-Fe2O3; in addition, phosphorus does not form individual phases in the structure of oolite (Dakhno, 2002). The impact of high temperatures on the mechanism of recrystallization can be presented as follows. During the agglomerative heating the
moisture is removed from the non-fluxed charge (minerals goethite, hydrogoethite), and hematite is formed, which then reduces to magnetite and wustite. At high temperatures magnetite and wustite react with silica (SiO2) in the charge and form fayalite. Thus, by the time of melting, the mixture is formed in the charge, consisting of magnetite, fayalite and small amounts of wustite and quartz. The melting of fayalite proceeds in accordance with the state diagram of the system Fe3 O 4 – Fe 2SiO 4 (magnetite–fayalite), magnetite gradually dissolves in fayalite, with the ferrous silicate melt on the base of fayalite becoming more heat-resistant. It allows the solid charge to be heated up to high temperatures. In the process of cooling, magnetite crystals of a regular shape, with sizes of 1.0 to 50 μm, are the first to be separated out in this melt (Fig. 3). According to the data of the micro-X-ray spectral analysis, phosphorus is not detected in the grains of magnetite (Table 2). On solidifying of the melt, phosphorus is likely to liquate into a liquid phase that crystallizes in the form of a eutectic mixture of fayalite and magnetite. Phosphorus is evenly distributed over the volume of eutectics without forming any individual phase. Formation of the structure occurs in a similar way on agglomeration of the fluxed charge. The difference is the following: phosphorus segregates into calc-ferrous olivine (CaO)x·(FeO)2 − x·SiO2, where the value of x does not exceed 1.1. When increasing basicity of the sinter charge CaO: SiO2 ≥ 2, the conditions are created for the formation of individual phosphorus-containing phases, represented by silicocarnatite and nagelschmidtite (Fig. 3d4).
Table 2 Micro-X-ray spectral analysis of the phases after the sinter roasting of GMC. Conditions of roasting: basicity, coke consumption, %
Phase
Content of oxides, % FeО
Р2О5
Al2O3
SiO2
СаО
МnО
MgO
0 7:0
Magnetite Glass phase semiopaque Glass phase opaque Magnetite Wustite Glass phase Magnetite Wustite Glass phase Nagelschmidtite
94.8 12.2 46.2 81.7 93.0 37.4 84.7 94.9 15.9 13.7
– 7.4 2.2 – – 5.0 – – 2.4 28.1
0.9 14.3 7.6 8.0 0.8 4.1 5.6 0.2 9.0 2.0
0.5 52.1 41.1 0.3 0.1 33.1 0.3 0.2 32.1 10.7
– 9.1 1.8 0.2 0.3 17.8 0.4 0.3 39.7 43.8
0.4 0.8 0.4 0.2 0.3 0.4 0.1 0.3 0.2 0.2
– 1.8 0.9 0.4 0.4 0.8 0.3 0.5 0.7 –
0:6 10:0
1:9 10:0
B. Khassen et al. / International Journal of Mineral Processing 126 (2014) 136–140
139
Fig. 3. Microstructure of products of the agglomeration sintering of GMC: a) ×500, basicity 0 and coke consumption 7%, b) × 125, basicity 0.6 and coke consumption 10%; c) × 125 and d) × 100, basicity 1.9 and coke consumption 10%. 1—iron–silicate matrix (FeO content less than 25%), 2) iron–silicate matrix (FeO content higher than 25%), 3—magnetite, 4—silicocarnatite.
Hence it is demonstrated that there is phosphorus transfer from ore minerals into slag-forming ones over the entire range of the changing basicity of the charge (from 0 to 2). That is why it was supposed that magnetic separation would provide a selective isolation of ore minerals from phosphorus-containing phases concentrated in slag-forming minerals. However, the obtained magnetic fractions of the products of sinter roasting of GMC cannot be classified as a qualitative magnetite concentrate. The crystal optical analysis showed that intergranular space of the aggregates of fine grains of magnetite is filled with a phosphorus-containing glass phase (Fig. 3b, c). Therefore, even fine grinding of these aggregates (less than 0.040 mm) did not provide the selective extraction of magnetite grains. To obtain a qualitative magnetite concentrate containing not more than 0.3% of P2O5, it is obviously essential, while sintering, to get a purposeful formation of crystal silicates having a lesser strength of interphase boundaries.
4. Conclusions Sintering followed by magnetic separation has been considered as one of the possible ways of processing brown iron ore phosphorous concentrates. Experiments have demonstrated that on sinter roasting of the concentrate over the entire range of the studied parameters (basicity from 0 to 2 and coke consumption from 3 to 10%) there occurs the transfer of phosphorus from ore constituents into slagforming ones. The micro-X-ray spectral analysis confirms the absence of phosphorus in ore minerals (magnetite, wustite). The composition of iron-silicate and phosphorus-containing phases depending on the basicity of the charge has been determined. The research into wet magnetic separation of the finely ground products of sinter roasting has been carried out. According to the content of iron and phosphorus, magnetic fractions do not correspond to qualitative magnetite concentrates. The crystal optical analysis had
Table 3 Results of magnetic separation of the products of sinter roasting of GMC. Basicity of initial charge, unit
Fractions
0
Magnetic Nonmagnetic Slimes Total Magnetic Nonmagnetic Slimes Total Magnetic Nonmagnetic Slimes Total Magnetic Nonmagnetic Slimes Total
0.8
1.5
2.0
Output, %
Content, % Fetotal
Р2О5
SiO2
Fetotal
Recovery, % Р2О5
SiO2
60.39 27.78 11.83 100.00 65.58 18.40 16.02 100.00 69.47 18.75 11.78 100.00 62.15 23.46 14.39 100.00
61.83 47.20 39.90 55.17 55.65 45.26 36.60 50.69 51.11 42.23 31.97 47.19 51.45 41.75 30.29 46.13
1.64 1.64 1.71 1.65 1.29 1.66 2.30 1.52 1.23 1.49 2.43 1.42 1.22 1.37 2.02 1.37
11.20 18.78 14.88 13.74 9.28 15.28 10.00 10.50 8.49 8.15 12.35 8.88 6.79 9.83 10.18 7.99
67.68 23.77 8.55 100.00 72.00 16.43 11.57 100.00 75.24 16.78 7.98 100.00 69.32 21.23 9.45 100.00
60.09 27.65 12.26 100.00 55.66 20.09 24.25 100.00 60.17 19.67 20.16 100.00 55.34 23.46 21.20 100.00
49.22 37.97 12.81 100.00 57.96 26.78 15.26 100.00 66.42 17.20 16.38 100.00 52.81 28.86 18.33 100.00
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shown that gaps between the grains of magnetite in the sinter were filled with a glass phase of a complex composition containing phosphorus oxides. Further work on obtaining a qualitative concentrate will be focused, while sintering, on the target-oriented formation of crystal silicates having a lesser strength of interphase boundaries. Acknowledgments This article is dedicated to the memory of Maximov Ye. V.—Professor, Doctor of Technical Sciences, who was the author of the idea and research supervisor of the project. The work was carried out within the framework of the state program for basic research of the Ministry of Education and Science of the Republic of Kazakhstan on the theme: Physical and chemical fundamentals of thermal selection of products of solid-phase recovery of brown iron ore raw materials. References Baltynova, N.Z., Dakhno, L.A., Maximov, E.V., Nadyrbekov, А.К., Khassen, B.P., 2009. Osobennosti formirovaniya mineral'nogo sostava i svoistv aglomerata. Izvestiya VUZov. Chornaya metallurgiya (4), 6–9. Belikov, V.V., Ogorodov, V.B., Yadryshkov, А.О., Mikhailovina, N.А., 2003. Obesfosforivanie burozheleznyakovykh rud i kontsentratov. Obogaschenie rud (3), 8–12.
Dakhno, L.A., 2002. Fosfor v burozheleznyakovykh rudakh Lisakovskogo mestorozhdeniya. Journal Promyshlennost' Kazakhstana 02, 64–65. Khassen, B.P., 2005. Problemy ispolzovaniya burozheleznyakovyx rud Lisacovskogo mestorozhdeniya. Izvestiya VUZov. Chornaya metallurgiya (3), 8–11. Khassen, B.P., Baltynova, N.Z., Dakhno, L.A., Kazantseva, G.V., Schaisultanov, E.S., 2004. Perspectivy obogascheniya burozheleznyakovoi rudy Ayatskogo mestorozhdeniya. Obogascheniе rud (3), 3–6. Li, Guang-Hui, Zhou, Tai-Hua, Liu, Mu-Dan, Jiang, Tao, Fan, Xiao-Hui, 2008. Novel process and mechanisms of aluminum-iron separation of high-aluminum limonite ore. Zhongguo Youse Jinshu Xuebao/Chin. J.Nonferrous Met. 18 (11), 2087–2093. Maximov, E.V., Bekturganov, N.S., Katkeeva, G.A., 2003. Vyschelachivanie primesei iz burozheleznyakovoy oolitovoi rudy i zhelezorudnyx kontsentratov. Obogaschenie rud (2), 6–8. Panychev, A.A., 2006. Vozmozhnosti rasshireniya syrevoi bazy chernoi metallurgii za schet vovlecheniya burozheleznyakovyh rud. Metallurg (5), 33–40. Patrick, Tim R.C., Lovel, Roy R., 2001. Leaching dicalcium silicates from iron ore sinter to remove phosphorus and other contaminants. ISIJ Int. 41 (2), 128–135. Sarvamangala, H., Natarajan, K.A., 08.07.2011. Microbially induced flotation of alumina, silica/calcite from haematite. IJMP 100, 27–32. Tuo, B.J., Zhang, Q., Xie, F., Wang, J.L., 2008. Study of the separation of low grade limonite. Proceedings of 24 International Mineral Processing Congress (JMPC), Beijing, 24–28 sept. Sci Press, Beijing, pp. 1212–1220. Zhu, Jianhua, Zhang, Liling, 1996. Industrial tests of technology of enrichment on decrease content of phosphorus in an iron concentrate. Jinshu kuangshan = Metal. Mine (3), 15–18. Zima, S.N., 2011. Sostav i structura burozheleznyakovyh rud mestorozhdeniya Lyubiya (Bosnia i Gertsegovina) i ih izmenenie v protsesse magnetiziruiyschego obzhiga i metallizatsii. Geologo- m neralog cheski visnik (25), 27–37. Мirko, V., Kabanov, Yu., Naidenov, V., 2002. Sovremennoe sostoyanie razvitiya mestorozhdeniy burykh zheleznyakov Kazakhstana. J. Promyshlennost' Kazakhstana 02, 79–82.
Contents lists available at ScienceDirect
International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro
Investigation of dephosphorization of brown iron ore concentrates by sintering and magnetic beneficiation B. Khassen a,⁎, N. Baltynova a, L. Dakhno b a b
The Institute of Problems of Complex Development of Mineral Resources, Karaganda, Kazakhstan Karaganda State Technical University, Karaganda, Kazakhstan
a r t i c l e
i n f o
Article history: Received 29 July 2013 Received in revised form 25 November 2013 Accepted 29 November 2013 Available online 5 December 2013
a b s t r a c t The results of investigation of sintering and magnetic beneficiation of brown iron ore concentrate are presented. The investigations are based on using a possibility of redistribution of phosphorus from the ore constituents into slag-forming ones in the process of sinter roasting. © 2013 Elsevier B.V. All rights reserved.
Keywords: Dephosphorization Brown iron ore concentrate Sinter roasting Magnetic separation Micro-X-ray spectral analysis
1. Introduction The aim of this work is to study the behavior of phosphorus in the process of sinter roasting of brown iron ores to develop a technology for obtaining high-quality iron ore concentrates. The reserves of brown iron ore are known to rank third in the world and they are common in North America, Australia, China, Kazakhstan, and other countries. Ores of most brown iron deposits are readily and inexpensively mineable and require low power for crushing and beneficiation. However, the mechanical methods of their beneficiation do not provide high-quality iron ore products that meet modern requirements (Zhu and Zhang, 1996; Zima, 2011; Khassen et al., 2004). The needs of metallurgy in industrial countries are met at the expense of import of high-quality concentrates (iron content is higher than 64% and that of phosphorus is less than 0.07%). In the Republic of Kazakhstan the following trend is observed: about 67% of the registered reserves of iron ores are represented by brown iron ores of two largest deposits (Lisakovsk, Ayatsk). The import of high-quality iron ores to Kazakhstan is problematic due to its continental location and lack of such ores in neighboring countries. The Republic of Kazakhstan has an integrated iron-and-steel mill of the complete cycle (“ArcelorMittal Temirtau”), which annually produces over 6 million tons of steel products (sheet metal and ⁎ Corresponding author at: The Institute of Problems of Complex Development of Mineral Resources, 5 Ippodromnaya Str., 100019 Karaganda, Kazakhstan. Tel.: +7 7212 414 520. E-mail address: [email protected] (N. Baltynova). 0301-7516/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.minpro.2013.11.013
tin-plate). Therefore, it is very important to involve into processing the iron ores of the country's own mineral resources. Neither the existing gravity-magnetic scheme nor the roasting-magnetic scheme can solve the issue of simultaneously increasing the iron content and reducing the content of phosphorus in Kazakhstan brown iron ore concentrates (Mirko et al., 2002). Such a situation is typical for many brown iron ores (Panychev, 2006; Tuo et al., 2008). This explains an intensive research into processing of brown iron ores according to complex process flow schemes. Among them are roasting of concentrate and acid leaching of phosphorus (Belikov et al., 2003), sintering with soda and water leaching of aluminum (Li et al., 2008), pressure leaching of impurities (Maximov et al., 2003), using of bacteria and their waste products for flocculation and flotation separation of hematite from oxides of Al, Si, and Сa (Sarvamangala and Natarajan, 2011), roasting and metallic coating (Panychev, 2006; Zima, 2011), agglomeration sintering and acid leaching of phosphorus and other contaminants from sinter (Patrick and Lovel, 2001). These works are in different stages of research. The researchers (Patrick and Lovel, 2001) carry out agglomeration sintering of brown iron ores at basicity of 1.84. They observe the concentration of phosphorus in 2CaOSiO2 and the absence of phosphorus in Fe3O4. Khassen B.P. (Khassen, 2005) notes the attractiveness of using a sintering machine for sintering brown iron ores since this reduces the costs for an expensive heating procedure. According to this work, phosphorus is accumulated in olivine (CaO)х·(FeO)2−x·SiO2, where х b 1.1, and it is absent in Fe3O4. The object of agglomeration sintering is brown iron ore having basicity 2 and higher, which is necessary to form individual phosphorus-containing phases: 7CaO·P2O5·2SiO2
B. Khassen et al. / International Journal of Mineral Processing 126 (2014) 136–140
137
(nagelschmidtite) and 5CaO·Р2O5·SiO2 (silicocarnatite). The work (Baltynova et al., 2009) is a continuation of these investigations. It has studied the composition and physical mechanical properties of sinter (basicity 0.6; coke consumption 18%) obtained from the hematite concentrate. In the sinter, phosphorus is also redistributed from ore components into slag-forming ones. This work investigates:
the center (0.9%) in dense oolites of GMC, while in zonal-concentric oolites it is distributed as 0.7 and 0.6%, respectively. A diagram of phosphorous content also confirms a uniform distribution of phosphorus over the cross-section of oolite (Fig. 1).
– the regularities of redistribution of phosphorus between ore and slag-forming minerals at sintering the brown iron ore concentrate while varying the basicity of the charge from 0 to 2; – the possibility to separate ore and slag-forming minerals of the sintering products by magnetic separation.
When sintering GMC without fluxing agents, high temperatures have a refining effect on the minerals of ore grains. In particular, magnetite without phosphorus impurities has been obtained. This fact is illustrated by the results of scanning of the structure of nonfluxed sinter of GMC (Fig. 2) and the micro-X-ray spectral analysis (Table 2). According to the crystal optical analysis (Fig. 3a) a ferrous-silicate matrix has a distinctive structure: 1—a semiopaque silicate glass, depositions of magnetite in a dendritic form were observed on some of its parts; 2—non-decrystallized glass enriched with iron oxides. The data on their micro-X-ray spectral analysis are given in Table 2. As follows from Fig. 3b, the ore component of the sinter (basicity 0.6) is represented mainly by magnetite. Тhe silicate matrix is the glass phase, which is nonhomogeneous in its structure and contains dendrites of magnetite, gehlenite, and wustite. An increase of basicity of the charge up to 1.9 (Fig. 3c and d) leads to a further increase of inhomogeneity of the microstructure and an occurrence of new phases (calcium ferrites, calcium silicates, individual minerals of phosphorus, sweat balls of metallic iron are observed). Crystals of magnetite are of a regular shape, with the sizes within the range of 1.0 to 50 μm. According to the data of the micro-X-ray spectral analysis (Table 2), phosphorus was not detected in the structure of magnetite, wustite, and metallic iron. Thus it has been established that during sinter-roasting GMC there is a large-scale transfer of phosphorus from ore minerals into slag-forming minerals. To separate those minerals and obtain iron-ore concentrates free of phosphorous impurities it is expedient to use magnetic separation.
2. Experimental 2.1. Materials and equipment The material used for this study was the concentrate of gravitymagnetic separation (GMC) of brown iron ores of the Lisakovsk deposit. Composition of the concentrates and by-products of their roasting was determined by chemical, crystal-optical, X-ray diffraction and micro-X-ray spectral analyses. The following instruments were used: microscope (Axioskop 40 Pol from Zeiss, Germany), electron-probe microanalyzer (JEOL ISM-6510, Japan), X-ray diffractometer (BRUKER D8 ADVANCE, Germany). The polished sections were made on grinding-and-polishing machines of S-1000 type of LECO (USA). The quantitative evaluation of the structure of mineral phases was performed with the help of the computer program Video-Test Structure (Russia). The experiments on roasting of GMC were carried out in a sintering plant (the bowl of 350 mm in diameter and 500 mm in height). In all the laboratory experiments the thickness of the charge layer was 250 mm, the charge weight was 20 kg; the coke consumption ranged from 3 to 20% of the weight of charge and basicity (ratio CaO:SiO2) was varied from 0 to 2. The wet magnetic separation was carried out in a tubular magnetic analyzer of 25 T type at the magnetic field intensity of 120 kA/m.
2.3. Sinter roasting of GMC
2.2. Analysis of the initial concentrates The brown iron ore concentrates of the Lisakovsk deposit have the following chemical composition, %: 49 Fe; 0.5 FeO; 10.7 SiO2; 4.5 Al2O3; 0.3 CaO; 1.6 P2O5; 0.3 MgO; 0.3 MnO and 12.4 is the loss on ignition. They are represented mainly by oolites of the minerals of goethite, hydrogoethite and inclusions of quartz. Oolites have a rounded, elliptical and clastic shape; their size varies from 200 to 700 μm, predominantly 300 to 400 μm. Quartz is in the free state in the form of independent phase-grains of angular shape of 50 to 90 μm in size. According to their structure oolites can be classified into two types: 1) dense homogeneous ones, having a high reflection power, 2) concentrically-zonal ones. Table 1 shows distribution of elements over the cross-section of oolite found by the micro-X-ray spectral analysis. As can be seen, phosphorus is distributed relatively evenly between the edge and Table 1 Distribution of elements in the microstructure of oolites. Structure
Position
Content of elements, % О
Fe
Al
P
Ca
Si
Oolite of GMC, dense Oolite of GMC, zonal-concentric
Edge Center Edge Center
38.9 40.0 32.5 32.4
54.3 53.4 57.7 57.3
3.7 3.6 3.6 3.6
0.9 0.9 0.7 0.6
0.1 0.2 0.2 0.2
1.4 1.6 1.4 1.6
Fig. 1. Distribution of phosphorus over the gross-section of oolite.
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Fig. 2. X-ray spectral scanning of the structure of non-fluxed sinter of GMC: o—general view.
2.4. Magnetic concentration of the products of sinter roasting of GMC The crystal-optical analysis helped in the determination of the optimal degree of grinding of the sinter roasting products as 95 to 99% of the class minus 0.044 mm. To improve the indicators of magnetic concentration a preliminary desliming of the finely ground products (the class of 0.010 mm) was carried out. Table 3 contains the results of magnetic concentration of the products of sinter roasting of GMC. When increasing the basicity of the charge from 0 to 2 in the obtained magnetic fractions, the content of Fe is shown to decrease from 61.8 to 51.4% and that of P2O5 from 1.6 to 1.2%. 3. Results and discussion The experimental data (Table 1, Fig. 1) show that hydrogoethite– goethite oolites of brown iron ores of the Lisakovsk deposit are characterized by a uniform distribution of phosphorus and aluminum in the structure of oolites. These data are confirmed by the analysis of a state diagram of the system Fe2O3–P2O5: when the content of P2O5 in oolites is within 1.27–1.92%, phosphorus can predominantly be in the form of an isomorphic impurity in the crystal lattice of goethite α-Fe2O3·H2O or hematite α-Fe2O3; in addition, phosphorus does not form individual phases in the structure of oolite (Dakhno, 2002). The impact of high temperatures on the mechanism of recrystallization can be presented as follows. During the agglomerative heating the
moisture is removed from the non-fluxed charge (minerals goethite, hydrogoethite), and hematite is formed, which then reduces to magnetite and wustite. At high temperatures magnetite and wustite react with silica (SiO2) in the charge and form fayalite. Thus, by the time of melting, the mixture is formed in the charge, consisting of magnetite, fayalite and small amounts of wustite and quartz. The melting of fayalite proceeds in accordance with the state diagram of the system Fe3 O 4 – Fe 2SiO 4 (magnetite–fayalite), magnetite gradually dissolves in fayalite, with the ferrous silicate melt on the base of fayalite becoming more heat-resistant. It allows the solid charge to be heated up to high temperatures. In the process of cooling, magnetite crystals of a regular shape, with sizes of 1.0 to 50 μm, are the first to be separated out in this melt (Fig. 3). According to the data of the micro-X-ray spectral analysis, phosphorus is not detected in the grains of magnetite (Table 2). On solidifying of the melt, phosphorus is likely to liquate into a liquid phase that crystallizes in the form of a eutectic mixture of fayalite and magnetite. Phosphorus is evenly distributed over the volume of eutectics without forming any individual phase. Formation of the structure occurs in a similar way on agglomeration of the fluxed charge. The difference is the following: phosphorus segregates into calc-ferrous olivine (CaO)x·(FeO)2 − x·SiO2, where the value of x does not exceed 1.1. When increasing basicity of the sinter charge CaO: SiO2 ≥ 2, the conditions are created for the formation of individual phosphorus-containing phases, represented by silicocarnatite and nagelschmidtite (Fig. 3d4).
Table 2 Micro-X-ray spectral analysis of the phases after the sinter roasting of GMC. Conditions of roasting: basicity, coke consumption, %
Phase
Content of oxides, % FeО
Р2О5
Al2O3
SiO2
СаО
МnО
MgO
0 7:0
Magnetite Glass phase semiopaque Glass phase opaque Magnetite Wustite Glass phase Magnetite Wustite Glass phase Nagelschmidtite
94.8 12.2 46.2 81.7 93.0 37.4 84.7 94.9 15.9 13.7
– 7.4 2.2 – – 5.0 – – 2.4 28.1
0.9 14.3 7.6 8.0 0.8 4.1 5.6 0.2 9.0 2.0
0.5 52.1 41.1 0.3 0.1 33.1 0.3 0.2 32.1 10.7
– 9.1 1.8 0.2 0.3 17.8 0.4 0.3 39.7 43.8
0.4 0.8 0.4 0.2 0.3 0.4 0.1 0.3 0.2 0.2
– 1.8 0.9 0.4 0.4 0.8 0.3 0.5 0.7 –
0:6 10:0
1:9 10:0
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Fig. 3. Microstructure of products of the agglomeration sintering of GMC: a) ×500, basicity 0 and coke consumption 7%, b) × 125, basicity 0.6 and coke consumption 10%; c) × 125 and d) × 100, basicity 1.9 and coke consumption 10%. 1—iron–silicate matrix (FeO content less than 25%), 2) iron–silicate matrix (FeO content higher than 25%), 3—magnetite, 4—silicocarnatite.
Hence it is demonstrated that there is phosphorus transfer from ore minerals into slag-forming ones over the entire range of the changing basicity of the charge (from 0 to 2). That is why it was supposed that magnetic separation would provide a selective isolation of ore minerals from phosphorus-containing phases concentrated in slag-forming minerals. However, the obtained magnetic fractions of the products of sinter roasting of GMC cannot be classified as a qualitative magnetite concentrate. The crystal optical analysis showed that intergranular space of the aggregates of fine grains of magnetite is filled with a phosphorus-containing glass phase (Fig. 3b, c). Therefore, even fine grinding of these aggregates (less than 0.040 mm) did not provide the selective extraction of magnetite grains. To obtain a qualitative magnetite concentrate containing not more than 0.3% of P2O5, it is obviously essential, while sintering, to get a purposeful formation of crystal silicates having a lesser strength of interphase boundaries.
4. Conclusions Sintering followed by magnetic separation has been considered as one of the possible ways of processing brown iron ore phosphorous concentrates. Experiments have demonstrated that on sinter roasting of the concentrate over the entire range of the studied parameters (basicity from 0 to 2 and coke consumption from 3 to 10%) there occurs the transfer of phosphorus from ore constituents into slagforming ones. The micro-X-ray spectral analysis confirms the absence of phosphorus in ore minerals (magnetite, wustite). The composition of iron-silicate and phosphorus-containing phases depending on the basicity of the charge has been determined. The research into wet magnetic separation of the finely ground products of sinter roasting has been carried out. According to the content of iron and phosphorus, magnetic fractions do not correspond to qualitative magnetite concentrates. The crystal optical analysis had
Table 3 Results of magnetic separation of the products of sinter roasting of GMC. Basicity of initial charge, unit
Fractions
0
Magnetic Nonmagnetic Slimes Total Magnetic Nonmagnetic Slimes Total Magnetic Nonmagnetic Slimes Total Magnetic Nonmagnetic Slimes Total
0.8
1.5
2.0
Output, %
Content, % Fetotal
Р2О5
SiO2
Fetotal
Recovery, % Р2О5
SiO2
60.39 27.78 11.83 100.00 65.58 18.40 16.02 100.00 69.47 18.75 11.78 100.00 62.15 23.46 14.39 100.00
61.83 47.20 39.90 55.17 55.65 45.26 36.60 50.69 51.11 42.23 31.97 47.19 51.45 41.75 30.29 46.13
1.64 1.64 1.71 1.65 1.29 1.66 2.30 1.52 1.23 1.49 2.43 1.42 1.22 1.37 2.02 1.37
11.20 18.78 14.88 13.74 9.28 15.28 10.00 10.50 8.49 8.15 12.35 8.88 6.79 9.83 10.18 7.99
67.68 23.77 8.55 100.00 72.00 16.43 11.57 100.00 75.24 16.78 7.98 100.00 69.32 21.23 9.45 100.00
60.09 27.65 12.26 100.00 55.66 20.09 24.25 100.00 60.17 19.67 20.16 100.00 55.34 23.46 21.20 100.00
49.22 37.97 12.81 100.00 57.96 26.78 15.26 100.00 66.42 17.20 16.38 100.00 52.81 28.86 18.33 100.00
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shown that gaps between the grains of magnetite in the sinter were filled with a glass phase of a complex composition containing phosphorus oxides. Further work on obtaining a qualitative concentrate will be focused, while sintering, on the target-oriented formation of crystal silicates having a lesser strength of interphase boundaries. Acknowledgments This article is dedicated to the memory of Maximov Ye. V.—Professor, Doctor of Technical Sciences, who was the author of the idea and research supervisor of the project. The work was carried out within the framework of the state program for basic research of the Ministry of Education and Science of the Republic of Kazakhstan on the theme: Physical and chemical fundamentals of thermal selection of products of solid-phase recovery of brown iron ore raw materials. References Baltynova, N.Z., Dakhno, L.A., Maximov, E.V., Nadyrbekov, А.К., Khassen, B.P., 2009. Osobennosti formirovaniya mineral'nogo sostava i svoistv aglomerata. Izvestiya VUZov. Chornaya metallurgiya (4), 6–9. Belikov, V.V., Ogorodov, V.B., Yadryshkov, А.О., Mikhailovina, N.А., 2003. Obesfosforivanie burozheleznyakovykh rud i kontsentratov. Obogaschenie rud (3), 8–12.
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