(1) The chemical composition of vanadium- titanium sinter. In addition to TiO 2 and V 2 O 5 , other chemical components are also significantly different from ordinary sinter. According to the content of TiO 2 , vanadium-titanium sinter can be Divided into high titanium type (Changping Steel), medium titanium type (bearing steel) and low titanium type (Ma Steel).
Compared with the chemical composition of ordinary sinter, vanadium-titanium sinter has the characteristics of “three lows†and “three highsâ€. I.e., low sinter containing iron, low content of FeO and SiO 2, TiO 2, MgO, Al 2 O 3 content is high.
(2) Mineral composition of vanadium-titanium sinter
The phase composition of vanadium-titanium sinter mainly includes: titanium hematite, titanomagnetite, calcium ferrite, titanium garnet, perovskite, diopside, and vitreous.
1. Mineral characteristics of vanadium-titanium sinter. Titanite is the main iron-bearing phase in sinter, generally accounting for 40% to 50% of the total sinter, and is a hematite-ilmenite solid solution. It is a hexagonal crystal system, grayish white under reflected light, strong heterogeneity, opaque, reflectivity 25%, Fe 2 O 3 as a lattice, in addition to Ti, it also solidifies Mg, Al, Mn and other elements. The titanium hematite in vanadium-titanium sinter is mainly granular and porphyritous, and a few are in his shape and self-shaped column. An edging or lace structure is usually formed around the pores or around the titanium magnetite grains. The existence of a large amount of titanium hematite and its crystallisation make the sinter have good reducibility and mechanical strength.
Titanium magnetite is different from the magnetic mineral of ordinary sinter. It is a magnetite-titanite solid solution and is the main iron-bearing mineral in sinter. Its content is between 25% and 35%, which is Fe 3 . O 4 is a solid solution of a crystal lattice in which solid oxides of Ti, Mg, Mn, V, and Al are dissolved. It is grayish-white with brownish hue under reflection, with homogeneity and reflectivity of 18% to 22%. The internal reflection is opaque, strong magnetic, and the surface can be corroded by hydrochloric acid, which is dark brown. It is mainly in the form of self-granular and irregular-shaped columnar. There are also self-formed, semi-self-shaped octahedrons (polygonal sections) and fine dendritic twins precipitated from the silicate phase, and some of the titanomagnetite is often colored by hematite.
Calcium ferrite is mainly found in flux vanadium-titanium sinter and increases with the increase of sintering alkalinity, generally accounting for 3% to 20% of the total amount of sintered ore. It is gray with blue hue under reflection and is heterogeneous. The reflectance is 16%. It is mainly plate-like and needle-like, and forms an ablated structure and a columnar interwoven structure with titanium magnetite. A large amount of calcium ferrite crystals are formed on the edges of the residual lime particles. It has good reducing properties and high compressive strength.
Titanium garnet is a silicate phase in vanadium-titanium sinter, which generally accounts for 3% to 15% of the total amount of sintered ore. It is often seen in fluxed vanadium-titanium sinter. It is mainly composed of granules, round and dendritic aggregates, and titanium garnets in individual areas are connected into pieces. Reflected light is gray, no internal color, low reflectivity (12% ~ 13%). Yellow, yellowish brown under transmission light, no cleavage, no double crystal grain, is a late crystalline silicate phase, Sintered ore has a certain bonding effect. From the chemical composition, the titanium garnet in the vanadium-titanium sinter is close to the natural titanium garnet.
Perovskite is a flux-bearing vanadium-titanium sinter mainly containing titanium minerals, generally accounting for 2% to 10% of the total amount of sinter, belonging to the isometric crystal system, grayish white under reflection, and the reflectivity is 15% to 16%. It is lower than the titanium magnetite solid solution, homogeneous to heterogeneous, and the internal reflection color is yellowish brown. Under transmitted light, it is brown, yellow, purple, reddish brown and other colors. Interference color level, sometimes showing abnormal interference color. The perovskite is mainly in the form of granules, spindles, skeletons and branches in the sinter, and is dispersed between the slag phase or the titanium hematite brown titanomagnetite. Its high melting point (1970 ° C), strong crystallization ability, is the earliest phase of crystal. The hardness is higher than that of titanium magnetite.
Titanite is an orthorhombic system, mostly in the form of short columns, sometimes in the form of massive aggregates, filled between perovskites, titanomagnetite and titanium hematite. It is a vanadium-titanium sinter silicate binder phase. one. It is dark gray under reflected light, the reflectivity is slightly higher than that of the glass phase, and it is yellowish green to light reddish purple under light transmission, which is effective pleochroism. [next]
2. Factors affecting the mineral composition of vanadium-titanium sinter The mineral composition of sinter is different with the changes of sintering raw materials and sintering process conditions.
(1) The effect of alkalinity. The effect of different alkalinity on the mineral composition of vanadium-titanium sinter is shown in Fig. The main minerals of vanadium-titanium sinter are titanium magnetite, titanium hematite, fayalite and glass cryptocrystals, titanium hematite and titanium magnetism. Iron ore is mostly self-shaped or semi-automorphic coarse crystal, and the crystal is tightly combined into a continuous crystal, which is the main connection mode of natural alkalinity vanadium-titanium sinter. Followed by olivine and vitreous, the crystal is bonded to form a sponge-like structure with uniform pores. The pores are generally 1 to 2 mm. The sinter structure is dense, the strength is good, the drum index is high, and the yield is high. However, since a large amount of magnetite is oxidized, it takes a long time, so the vertical sintering speed is low.
A flux-type vanadium-titanium sintered ore having a basicity of 1.0 to 2.0, the main minerals of which are titanomagnetite, titanium hematite, calcium olivine, titanium garnet, perovskite, calcium ferrite, titanium pyroxene and vitreous.
For sinter with alkalinity greater than 3.0, the solid solution of titanium hematite is reduced and the solid solution of titanium magnetite is increased. The appearance of sinter is black, the gloss is dark, and the calcium ferrite is obviously increased.
(2) The effect of fuel usage on mineral composition. The mineral composition of vanadium-titanium sinter varies with the increase or decrease of fuel consumption. When the fuel consumption is low, the content of titanium hematite in sinter is high and the glass quality is small, the binder phase is insufficient, and the strength of sinter is poor. With the increase of fuel, the reducing atmosphere is enhanced, the sintering temperature is increased, the titanomagnetite and the ferrite in the sinter are obviously increased, the silicate binder phase and calcium ferrite are increased, but the titanium hematite is greatly reduced, and the titanium is weakened. Hematite crystallisation. When the fuel exceeds a certain amount, the titanium hematite in the sinter is further reduced, the calcium ferrite content is also low, and the perovskite content is significantly increased, and the silicic acid phase is not changed at this time. Therefore, increasing the carbon content is not advantageous for increasing the strength of vanadium-titanium sinter.
(3) Effect of TiO 2 content on mineral composition. With the increase of TiO 2 content in the sintered ore, the amount of perovskite increases, the amount of calcium ferrite decreases, and the amount of titanium pyroxene increases, and the glass quality decreases. [next]
(III) Metallurgical properties of vanadium-titanium sinter 1. Drum strength of vanadium-titanium sinter The drum strength of vanadium-titanium sinter is generally lower than that of ordinary sinter. The main reasons are as follows: (1) the content of SiO 2 in the sintered ore is low, and the formed silicate has less binder phase; (2) the perovskite which is easily formed with CaO during sintering due to the high content of TiO 2 ; (3) The amount of the sintered liquid phase is small, and the bonding ability is poor. In addition, due to the mineral properties, this type of sinter has the characteristics of wear resistance and fall resistance.
Increasing the carbon content can improve the drum strength of vanadium-titanium ore, but when the carbon content exceeds a certain ratio, the strength decreases. The increase of carbon content can increase the amount of sintering liquid, which is beneficial to the increase of drum strength. At the same time, due to the increase of carbon content, the reducing atmosphere is strengthened, the ferrite is reduced, and the amount of perovskite is increased. Therefore, it should be properly controlled. With carbon.
2. Sinter storage performance Vanadium-titanium sinter has good storage performance, and its natural pulverization rate is much lower than that of ordinary sinter. The reason is that during the cooling process of the sinter, when the temperature drops to 675 °C, the calcium orthosilicate (2CaO•SiO 2 ) in the ordinary sinter undergoes a phase change (transition from β-2CaO•SiO 2 to γ-2CaO), and the volume occurs. Rapid expansion (increased by 10%), causing sinter pulverization; while vanadium-titanium sinter has no 2CaO•SiO 2 formation during sintering, because the SiO 2 content in the sinter is low, even if the sintering alkalinity is 1.70, the CaO content is also of only 9.5 to 9.1%, CaO and TiO 2 and partly forming the perovskite (CaO • TiO 2), so very little free CaO.
3. Reduction performance of vanadium-titanium sinter The vanadium-titanium sinter has better reduction performance than ordinary sinter due to its high degree of oxidation and low FeO content. The factors affecting the reduction of vanadium-titanium sinter mainly include alkalinity and FeO content.
(1) The effect of alkalinity. The effect of alkalinity on the reduction of vanadium-titanium sinter is similar to that of ordinary sinter. With the increase of sinter alkalinity, the degree of reduction increases remarkably.
(2) The influence of FeO content. In the vanadium-titanium sinter, FeO mainly exists in the form of titanomagnetite and calcium olivine, and its reduction is poor, but compared with ordinary sinter, its content is lower, and the reduction is still better. With the increase of FeO content, the reduction degree of vanadium-titanium sinter decreases linearly. Therefore, when the vanadium-titanium magnet concentrate is sintered, the appropriate FeO content should be controlled, and under the condition of ensuring the strength of vanadium-titanium sinter, it has a good Reducing.
(3) The effect of TiO2 content. With the increase of TiO 2 content in vanadium-titanium ore, the degree of reduction of sinter decreased. It is generally believed that due to the increase of TiO 2 content, it is bound to lead to a decrease in iron-containing phases (such as titanium hematite, calcium ferrite, etc.) in sinter, and an increase in gangue minerals (such as perovskite, titanite, etc.). Not conducive to the diffusion of reducing gases.
4. The low-temperature reduction pulverization performance of vanadium-titanium sinter is generally considered to be caused by the reduction of crystallite shape during the reduction of hematite into magnetite at the low temperature (400-500 °C). . Titanite has various crystal forms such as granules, plaques, dendrites, leaves, and crystals. For different crystal forms, the reduction pulverization performance is different, and the reduction and pulverization of the rhodium-shaped diamond hematite is the most serious.
Low vanadium and titanium powder sintered ore reduction rate is much higher than normal RDI -3.15 sinter. The RDI -3.15 of Panzhihua Sinter is generally greater than 55% to 60%, and when some vanadium and titanium materials are added to the ordinary sinter, the reduction pulverization rate of the sinter will also increase significantly.
The reasons for the low reduction pulverization rate of vanadium-titanium sinter are: (1) the sinter contains a large amount of titanium hematite (40% to 50%), of which about 50% is present in the form of rhodium-shaped rhombohedrite. There is also a portion of the titanium hematite that occupies the ilmenite in a grid. At the time of reduction, expansion and pulverization are caused due to crystal transformation. (2) The content of SiO 2 in the sintered ore is low, the silicate phase which acts as a bonding is small, and the presence of the perovskite which does not adhere to it is not only inherently brittle, but also hinders titanium hematite and titanium. The intercalation between magnetites reduces the ability to resist expansion and pulverization. (3) The phase composition of vanadium-titanium sinter is more complex than that of ordinary sinter, and the internal stress caused by different thermal expansion is low. The reduction stage leads to the formation of a large number of microcracks, which also reduces the strength of the sinter.
Although the phenomenon of low-temperature reduction and pulverization of vanadium-titanium sinter is serious, in actual production, the low-temperature reduction pulverization rate of sinter has not caused the deterioration of the upper block of the blast furnace, which has become a link to limit smelting and strengthening. An anatomical investigation of the smelting of vanadium-titanium sinter in a small blast furnace revealed no abnormalities in the particle size composition of the sinter.
Increasing the FeO content in the sinter can reduce the amount of regenerated hematite and reduce the low-temperature reduction pulverization rate, but too high FeO will cause the deterioration of sinter reductivity. To this end, Panzhihua Iron and Steel sprayed a halide aqueous solution on the finished sintered ore, so that the phenomenon of low-temperature reduction and pulverization of the sintered ore was greatly improved.
5. Soft-melt dripping performance of vanadium-titanium sinter The mineral composition of the sinter determines its soft-melt dripping performance. Because of the high melting point minerals of vanadium-titanium sinter, the softening temperature is high, and the melting point of high-melting minerals is different. Large, so its droplet temperature interval is wide, and the slag iron separation is poor during the dripping process, and the slag contains more iron. The main factors affecting the soft-melt dripping performance of vanadium-titanium sinter are the alkalinity of sinter and the content of TiO 2 .
The effect of alkalinity on the soft-melting dripping properties of vanadium-titanium sinter. As the alkalinity increases, the sinter softening start temperature (T a ), the softening end temperature (T s ) (melting start temperature), the starting droplet temperature (T m ) rise, the softening temperature interval (ΔT sa ) and the droplet temperature interval (T c ) narrows, the pressure difference rises sharply, the temperature (T Δp ) rises, the highest pressure difference (ΔP max ) decreases, and the droplet thickness (H) becomes thin.
The effect of TiO 2 content on the soft drop dripping properties of vanadium-titanium sinter. With the increase of TiO 2 content in the sinter, the drip temperature begins to decrease, the pressure difference rises sharply, the highest pressure difference decreases, the reflow temperature range becomes wider, and the dripping time is prolonged.
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