The quality of sinter is mainly manifested in its mechanical strength and reduction properties, and these characteristics are closely related to the mineral composition and structure of the sinter.
   Sinter is a complex of multiple minerals. It consists of iron-containing minerals and gangue minerals from the adhesive composition of the liquid phase. The mineral composition varies according to the raw material conditions and sintering process conditions. In general, the mineral composition of iron ore sinter: iron-bearing minerals are magnetite, florist, hematite ; in the binder phase, there are fayalite (2FeO•SiO 2 ) and calcium iron sapphire (CaO x FeO 2-x • SiO 2 , x = 0.25 ~ 1.5) wollastonite (βCaO•SiO 2 ) , dicalcium silicate (2CaO•SiO) , tricalcium silicate (3CaO•SiO 2 ) , ferric acid calcium (CaO • Fe 2 O 3, 2CaO • Fe 2 O 3), (CaO • 2Fe 2 O 3), hedenbergite (CaO • FeO • 2SiO 2) ; when the gangue contained in iron oxide in a high aluminum In the case of sinter, aluminum yellow feldspar (2CaO•Al 2 O 3 •SiO 2 ) , tetracalcium aluminoferrite (4CaO•Al 2 O 3 •Fe 2 O 3 ) , iron yellow feldspar (2CaO•Fe 2 O) 3 • SiO 2) and andradite (3CaO • Fe 2 O 3 • 3SiO 2); when the gangue content of more magnesium oxide, may appear monticellite (CaO • MgO • SiO 2) , akermanite (2CaO • MgO • 2SiO 2) and merwinite (3CaO • MgO • 2SiO 2) and the like; and when containing gangue fluorite (CaF 2) are cuspidine (3CaO • 2SiO 2 • CaF 2 ) occurs; containing perovskite and so when titanium ore. In addition, there are a small amount of free quartz and free lime which are incompletely reacted.
   The structure of the sintered ore generally refers to the shape and size of the mineral composition under the microscope and their relationship with each other. Due to the different production process conditions, there are also significant differences in the microstructure. The characteristics of the microstructure are also important factors influencing the quality. The following is a common microstructure of sinter:
1) Granular structure : The self-formed crystal, semi-automorphic crystal or other crystal magnetite crystallized first in the sinter, and the mineral crystal grains of the binder phase form a granular structure.
2) Patchy structure : magnetite speckle crystals with strong self-crystallinity in the sinter ore and fine-grained binder phase minerals combine to form a patchy structure.
3) Twin structure: In the early crystallized magnetite crystals in the sinter, the binder mineral is often filled therein, but the original crystal shape and edge portion of the magnetite are still substantially maintained to form a twin structure.
4) Dan point-like eutectic structure: in the sintered ore, magnetite is present in the form of dots in the crystal of olivine. The magnetite dendritic crystal is formed by the eutectic portion of the Fe 3 O 4 —Ca x •Fe 2-x •SiO 4 system. In the sinter, hematite is also distributed as a dot-like crystal in the silicate crystal, which is formed by oxidation of the Fe 3 O 4 —Ca x •Fe 2-x •SiO 4 system eutectic.
5) Corrosion structure: In the sinter ore, the magnetite is mostly a remnant of his crystal, and the crystal grains are small, mostly 浑 round and special, forming an ablated structure with calcium ferrite. This type is common in high alkalinity sinter and is also a structural feature of high alkalinity sinter.
(1) Quartz gangue magnetite concentrate ore
Most of our sinter plants produce this type of sinter. In acid sinter, when the carbon is normal, its structure is bonded by the iron-bearing mineral as a binder phase mineral ( fayalite or fayalite-magnetite or floc eutectic ) . When higher alkalinity (basicity of 1.0 or less), the main iron minerals magnetite iron San olivine, calcium iron San olivine, hedenbergite and silicate glass bonding. Generally, magnetite grains and binder phase minerals form a granular structure. In self-fluxing sinter, the main iron-bearing mineral magnetite is bound by calcium iron olivine, calcium ferrite, calcium silicate and a small amount of vitreous, generally also in granular structure . High alkalinity sinter The main mineral composition of magnetite, iron, calcium (CaO • Fe 2 O 3, 2CaO • Fe 2 O 3), dicalcium silicate (β • 2CaO • SiO 2) , calcium silicate three its microstructure Generally, calcium ferrite and calcium silicate are used as binder phase minerals, and magnetite ore forms a network-like ablation structure or a columnar interweaving structure. [next]
   Figure 1 shows the change of mineral composition in different alkalinity of Shougang high-silica Qian'an concentrate sinter. Figure 2 shows the change of mineral composition under different carbon mixing conditions of Qian'an concentrate ore.
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   Under low carbon conditions (C=3.2%), the sinter contains more hematite and calcium ferrite. There are few or no floats. Dicalcium silicate and other silicate minerals are also less abundant. With the increase of carbon content, the floc body in the sinter increased significantly, and the silicate binder phase also increased. However, hematite and calcium ferrite have decreased significantly. In the sinter containing 11% carbon , the content of β-C 2 S decreased slightly, mainly due to the fact that part of CaO was dissolved in the float, as shown in Fig . 3 , and also confirmed by the electron probe.
   Acid gangue magnetite self-dissolving sinter mineral composition, due to various minerals undergoing different physical and chemical changes during the sintering process, resulting in a phase change.
(1) Magnetite. There are self-shaped crystals and polyhedral crystals of different sizes, which are produced by recrystallization of the sinter. It can also be precipitated from the slow cooling liquid phase; there is a dendritic or spherical shape which is precipitated from the liquid phase of iron silicate. , skeletal precipitates; isometric aggregates grown from raw magnetite sintered at low temperatures and partially recrystallized; there is a very small (0.007 to 0.002 mm ) circular and olivine Dot-shaped precipitates; point-like and pearlite magnetites in the combination of dicalcium silicate, which are symbiotic in the eutectic region of the Fe 3 O 4 -2CaO•SiO 2 system; Or all oxidized to form a pseudo-magnetite pseudo-crystal, which has the same shape as the floating soil, and is formed into strips, needles, and grids when partially decomposed and partially oxidized by the authorities; and in low-carbon sintering, Residual magnetite in the form of raw concentrate grains.
(2) Hematite. Due to the oxidation and recrystallization of magnetite, the hematite self-formed crystal ( Rhombic body ) is called pseudo-hematite ; there is a hematite self-crystal which precipitates directly from the liquid phase, which is a high alkali. The characteristics of the sinter, the inside is the oxidized magnetite particles, and the outside is the result of the liquid phase precipitation; in the lower temperature oxidizing atmosphere, the hematite pseudocrystals appear on the magnetite (the illusion of hematite The hematite band and lattice-like precipitates appearing in magnetite are mostly the products of the decomposition of hematite solid solution in magnetite; the hematite point precipitates in the silicate, which is The result of oxidation of the eutectic Fe 3 O 4 -Ca 2 Fe 2-x •SiO 4 system; the hematite dendrites crystallized in the silicate binder phase and the hematite dendrites; the original magnetite The particles form a structure similar to hematite during oxidation and sintering.
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