Method for recovering titanium from titanium-containing blast furnace slag through hydrogen-based low-temperature reduction

Abstract

The invention discloses a method for recovering titanium from titanium-containing blast furnace slag through hydrogen-based low-temperature reduction, and belongs to the field of solid waste comprehensive utilization. The method comprises the following steps: finely grinding, uniformly mixing and agglomerating raw materials containing high-silicon hematite and titanium-containing blast furnace slag to obtain agglomerates; roasting and cooling the block mass to obtain a mixed molten block mass of ferrotitanium spar and silicate; and the mixed molten block mass is subjected to crushing, ore grinding and magnetic separation, and the high-purity ferrotitanium spar is obtained. The roasting is carried out in a hydrogen-based reducing atmosphere. According to the method, SiO2 is introduced into a roasting system, stable structures of titanium phases such as perovskite are destroyed through silicate, and meanwhile, the atmosphere of reduction roasting is controlled, so that a titanium component and an iron component in the blast furnace slag can be directionally converted into a ferrotitanium spar phase at a relatively low temperature. The ferrotitanium spar obtained by the method is pure in crystal phase and high in titanium recovery rate.

Description

Technical Field

[0001] The present invention relates to a method for recovering titanium components, in particular to a method for hydrogen-based low-temperature reduction of titanium-containing blast furnace slag to recover titanium components therein, belonging to the field of comprehensive utilization of solid waste. Background Art

[0002] China is rich in titanium resources, mainly vanadium-titanium magnetite, and the blast furnace method is mainly used for its utilization. During the smelting process, titanium elements are more difficult to reduce than iron, resulting in some titanium entering the blast furnace slag, with a content of about 20%. These titanium mainly exist in the form of perovskite, with low titanium grade and high impurity content, and cannot be directly used as raw materials for producing titanium products. The existing methods for utilizing titanium-containing blast furnace slag are mainly divided into pyrometallurgy and hydrometallurgy processes. Among them, the pyrometallurgy process is carbonitriding treatment and smelting ferrotitanium alloy, and the hydrometallurgy process is acid leaching to extract titanium. However, due to the low titanium grade, stable phase, and complex intergrowth relationship in the slag, high temperature (>1500°C), high pressure, and strong acid environment are often required for titanium extraction treatment to enrich and selectively separate titanium components. The above processes have high equipment requirements, high costs, high energy consumption, and heavy pollution, resulting in difficulty in large-scale industrial application. Therefore, the utilization rate of this type of titanium-containing metallurgical slag is still very low, and it is urgent to develop and utilize it.

[0003] Due to the complex phase, dispersed intergrowth, and fine crystal grain size of titanium components in titanium-containing blast furnace slag, it is difficult to achieve the enrichment and recovery of titanium components by traditional physical separation. From the earlier research results, to achieve the separation and enrichment of titanium components in titanium-containing blast furnace slag, it is necessary to construct a new titanium-rich phase that is easy to recycle. Based on the differences in magnetic, density, and surface chemical properties between the titanium-rich phase and gangue minerals, titanium components are enriched and recovered by traditional low-cost means. Titanomagnetite is a spinel-type titanium iron oxide, with the chemical formula Fe 2 TiO 4 , and the theoretical TiO 2 grade is 35.70%, and the total iron grade is 49.96%. It has good magnetic properties, low synthesis temperature, fast crystal transformation and growth rate, and can be recovered by magnetic separation, which is an ideal phase for constructing titanium-rich compounds. At present, titanomagnetite is mostly synthesized from rutile as raw material, while the titanium phases in titanium-containing blast furnace slag mainly exist in stable phases such as perovskite and titanaugite, making it difficult to carry out phase transformation to generate titanomagnetite phase.

[0004] At present, there is no method for synergistic hydrogen-based reduction and low-temperature titanium extraction of titanium-containing blast furnace slag and high-silica hematite in the existing technology. If the silicon component in high-silica hematite can be utilized to promote the decomposition of titanium phases in titanium-containing blast furnace slag and induce the directional transformation of titanium components and iron components into titanomagnetite phase, then the efficient recovery of titanium components in titanium-containing blast furnace slag can be achieved at a lower temperature, which is of great significance to China's iron and steel and titanium smelting industries. Summary of the Invention

[0005] Aiming at the problem that the existing process cannot recycle titanium components in titanium-bearing blast furnace slag at low cost, the purpose of the present invention is to provide a method for hydrogen-based low-temperature reduction of titanium-bearing blast furnace slag to recover titanium. In this method, SiO is introduced into the roasting system 2 , to destroy the stable structure of perovskite and other titanium phases through silicate, and at the same time control the atmosphere of reduction roasting, so that the titanium components in the blast furnace slag can be directionally transformed into ilmenite phase (Fe 2 TiO 4 ) together with iron components at a lower temperature. The ilmenite obtained by this method has a pure crystal phase and a high titanium recovery rate.

[0006] To achieve the above technical purpose, the present invention provides a method for hydrogen-based low-temperature reduction of titanium-bearing blast furnace slag to recover titanium. In this method, raw materials containing high-silica hematite and titanium-bearing blast furnace slag are finely ground, mixed evenly and pelletized to obtain pellets; after the pellets are roasted and cooled, a mixed molten pellet of ilmenite and silicate is obtained; the mixed molten pellet is crushed, ground and subjected to magnetic separation to obtain high-purity ilmenite; the roasting is carried out under a hydrogen-based reducing atmosphere.

[0007] The present invention first proposes to directionally synthesize ilmenite by high-temperature molten reduction of titanium-bearing blast furnace slag and high-silica hematite raw materials, and then obtain high-purity ilmenite materials through magnetic separation enrichment. The main titanium-containing components in titanium-bearing blast furnace slag are perovskite and titanaugite and other phases, which have stable properties and are difficult to decompose and extract titanium. However, the present invention cleverly utilizes that the formation enthalpy of calcium silicate is lower than that of perovskite, selects high-silica hematite, and by reasonably designing the slag system composition, SiO is introduced into the CaTiO 3 -Fe 2 O 3 system 2 , to destroy the stable crystal structure of perovskite, induce the calcium-containing components to preferentially combine with SiO 2 to form calcium silicate phase. Therefore, the titanium-containing components can react with iron oxides at a lower temperature to form ilmenite. And during the roasting process, ilmenite has a high melting point and a higher density than silicate. The ilmenite phase precipitates in a solid state at the bottom of the molten pool, which is conducive to the growth of ilmenite grains. Subsequently, based on the magnetic difference between ilmenite and silicate gangue minerals, high-purity ilmenite materials can be obtained through magnetic separation enrichment.

[0008] The inventors found that when hydrogen in a hydrogen-based reducing atmosphere is used as the reducing gas, iron oxide and perovskite can react at 1200 °C to form the ilmenite phase, while when CO is used as the reducing agent, it is necessary to reach 1700 °C to form the ilmenite phase. At the same time, the present invention can use the reducibility of hydrogen to directionally reduce Fe 3+ in high-silica hematite to Fe 2+ in ilmenite.

[0009] As a preferred embodiment, silica and high-silica hematite can be added to the raw materials to jointly adjust the acidity of the system, where the acidity refers to the ratio of the molar amount of SiO 2 in the system to the molar amount of CaO.

[0010] As a preferred embodiment, the TiO 2 content in the titanium-bearing blast furnace slag is 15 wt% to 40 wt%; the titanium-bearing blast furnace slag used in the present invention is a common blast furnace slag in the field of vanadium-titanium magnetite smelting, including low-titanium slag, medium-titanium slag, high-titanium slag, etc. The recovery and utilization of titanium components in the blast furnace slag can be achieved by using the method of the present invention.

[0011] As a preferred embodiment, the SiO 2 content in the high-silica hematite is 5 wt% to 15 wt%, and the Fe 2 O 3 content is 60 wt% to 90 wt%; the SiO 2 content in the silica is 90 wt% to 99.5 wt%. The main purpose of selecting high-silica hematite in the present invention is that on the one hand, it serves as an iron source to form perovskite, and on the other hand, the acidity of the roasting system can be adjusted by using the silicon component therein. When silica is added, the acidity of the system can be further appropriately increased, thereby improving the recovery rate of titanium.

[0012] As a preferred embodiment, the fine grinding particle size range of the raw materials is 60 wt% to 99 wt% of -0.074 mm. The reason for using fine grinding in the present invention is that when finer raw materials are pelletized, the contact area between particles is larger, which is beneficial to the migration of mass points and the formation of perovskite phase.

[0013] As a preferred embodiment, the acidity range is 0.8 to 1.5. If the SiO 2 is too low, the decomposition of perovskite is incomplete, the utilization rate of titanium components is low, and due to the incomplete destruction of the perovskite structure, a higher temperature is required for the reaction of titanium-containing components with iron oxides to form perovskite. Because the stable perovskite structure makes it difficult for titanium-containing components to participate in the reaction, higher energy is required to overcome this stability, resulting in an increase in the reaction temperature. If the SiO 2 is too high, there are too many silicate gangue minerals in the system, which affects the effect of subsequent magnetic separation to enrich high-purity perovskite. It is further preferably 1.0 to 1.4, and more preferably 1.0 to 1.1.

[0014] As a preferred embodiment, the size of the pellets is 5 to 8 mm. A smaller pellet size helps the heat to be more evenly transferred to the inside of the pellets during roasting, thereby forming a uniform molten phase. Generally, the pellets include, but are not limited to, cylindrical pellets with a diameter and height of 5 to 8 mm or spherical pellets with a diameter of 5 to 8 mm.

[0015] As a preferred solution, the hydrogen-based reducing atmosphere consists of H 2 and N 2 . Among them, the content of H 2 is 0.5 vol% to 30 vol%, and the rest is N 2 . The partial pressure of H 2 required for TiO 2 O 3 to react with Fe 2 O 2 to form ilmenite is extremely low. In the reaction process of the present invention, in order to accelerate the formation rate of ilmenite, the partial pressure of H 2 can be appropriately increased. However, when the partial pressure of H 3 is too high, ilmenite will transform into the FeTiO 2 phase, affecting the purity.

[0016] As a preferred solution, the conditions for roasting are as follows: the roasting temperature is 1200 to 1500 °C, and the roasting time is 0.5 to 6 h. The method of the present invention significantly reduces the roasting temperature, reduces the requirements for equipment and energy consumption. However, when the roasting temperature in the present invention is too low, a large amount of perovskite in the system is not decomposed, resulting in that hematite cannot be completely transformed into the ilmenite phase, and is reduced to metallic iron by hydrogen and enters the magnetic separation product. At the same time, the unreacted quartz and perovskite will also be wrapped with ilmenite and enter the magnetic separation product, thus resulting in a significant decrease in the titanium recovery rate of the product.

[0017] As a preferred solution, the particle size range of the crushed and ground mixed molten agglomerates is that the proportion of -0.074 mm accounts for 50 wt% to 90 wt%.

[0018] As a preferred solution, the magnetic field strength for magnetic separation is 2 kA / m to 45 kA / m. Within the range of magnetic separation intensity selected in the present invention, ilmenite and the silicate gangue minerals transformed by the introduction of silicon in the present invention can be effectively separated.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] 1) In the present invention, by mixing and roasting the titanium-bearing blast furnace slag and high-silica hematite, SiO 2 is induced to form silicate in the slag phase by non-titanium elements in the titanium-bearing blast furnace slag, and the titanium and iron components are promoted to be directionally transformed into the ilmenite phase.

[0021] 2) The process provided by the present invention can synergistically utilize the refractory high-silica hematite and the titanium-bearing blast furnace slag solid waste, skillfully construct the ilmenite phase, and complete the directional migration, transformation and recovery of valuable components in the two raw materials in one step.

[0022] 3) Based on the design principle of slag phase components, by adjusting the acidity of the system, the decomposition temperature of titanium-containing phases such as perovskite can be significantly reduced, and fayalite can be synthesized at low temperature. Compared with the traditional high-temperature conversion-crystallization / flotation or gravity separation process for titanium-containing blast furnace slag, the process provided by the present invention can reduce the roasting temperature by more than 400 °C. At the same time, fayalite has excellent magnetism, is easy to be enriched by magnetic separation, and has a high titanium recovery rate.

[0023] 4) The roasting temperature of the present invention is relatively low, only 1200-1500 °C, which has low requirements for equipment and can be completed using general equipment in the field of iron and steel smelting, facilitating popularization. Brief Description of the Drawings

[0024] Figure 1 It is the XRD pattern of the magnetic separation product of Example 1 of the present invention.

[0025] Figure 2 It is the XRD pattern of the magnetic separation product of Example 2 of the present invention.

[0026] Figure 3 It is the XRD pattern of the magnetic separation product of Example 3 of the present invention.

[0027] Figure 4 It is the XRD pattern of the magnetic separation product of Comparative Example 1 of the present invention.

[0028] Figure 5 It is the XRD pattern of the magnetic separation product of Comparative Example 2 of the present invention. Detailed Embodiments

[0029] The following examples are intended to further illustrate the content of the present invention rather than limit the protection scope of the claims of the present invention.

[0030] Example 1

[0031] In this example, a certain titanium-containing blast furnace slag and high-silica hematite are selected as raw materials, and the specific components are shown in Table 1. 70 wt% of the titanium-containing blast furnace slag and 30 wt% of the high-silica hematite are mixed and pelletized. At this time, the molar ratio of titanium to iron elements in the mixture is 1:1, and the acidity (SiO 2 :CaO) molar ratio is 0.9. The mixture is pressed into pellets, and the size of each pellet is controlled at 5-8 mm. The mixture pellets are placed in a corundum crucible and heated using an electric furnace. First, N 2 is introduced, and the mixture is heated to 1300 °C. Subsequently, the atmosphere is converted to 10 vol% H 2 + 90 vol% N 2 , and roasted for 2 h. Then, the atmosphere is changed to pure N 2, the sample was cooled to room temperature in the furnace and then taken out. The molten mass was crushed and ground to a particle size of -0.074 mm with a proportion of 78.21 wt%, and magnetic separation was carried out using a magnetic field intensity of 45 kA / m. The XRD pattern of the obtained high-purity ilmenite material is shown in Figure 1 .

[0032] From Figure 1 it can be seen that after hydrogen-based reduction and magnetic separation, the main phase in the magnetic separation product transformed into ilmenite (Fe 2 TiO 4 ). In addition, there were also some unreacted CaTiO 3 and the formed CaSiO 3 phase peaks. The TiO 2 content in the magnetic separation product was 31.68 wt%, and the titanium recovery rate was 80.87 wt%.

[0033] Table 1 Main chemical components of raw materials / wt%

[0034]

[0035] Example 2

[0036] In this example, the titanium-bearing blast furnace slag and high-silica hematite in Example 1 were selected as raw materials. At the same time, in order to increase the acidity of the system, some silica was added. The specific composition of the silica is shown in Table 2. 67 wt% of titanium-bearing blast furnace slag, 28.7 wt% of high-silica hematite, and 4.3 wt% of silica were mixed evenly and pelletized. At this time, the molar ratio of titanium to iron elements in the mixture was 1:1, and the acidity (SiO 2 :CaO) molar ratio was 1.1. The mixture was pressed into pellets, and the size of each pellet was controlled within 5 - 8 mm. The mixture pellets were placed in a corundum crucible and heated using an electric furnace. First, N 2 was introduced, and the mixture was heated to 1300 °C. Subsequently, the atmosphere was changed to 10 vol% H 2 + 90 vol% N 2 , and roasted for 2 h. Then, the atmosphere was changed to pure N 2 , and the sample was cooled to room temperature in the furnace and then taken out. The molten mass was crushed and ground to a particle size of -0.074 mm with a proportion of 70.35 wt%, and magnetic separation was carried out using a magnetic field intensity of 45 kA / m. The XRD pattern of the obtained high-purity ilmenite material is shown in Figure 1 .

[0037] From Figure 1 it can be seen that after hydrogen-based reduction and magnetic separation, the main phase in the magnetic separation product transformed into ilmenite (Fe 2 TiO 4 ). Compared with the magnetic separation product in Example 1, after increasing the acidity of the system, CaTiO 3 decomposed more completely, and CaTiO 3The peak disappears, but there is some FeTiO 3 by-product generated. The TiO 2 content in the magnetic separation product is 33.16 wt%, and the titanium recovery rate is 86.93 wt%.

[0038] Table 2 Main chemical components of silica / wt%

[0039]

[0040] Example 3

[0041] In this example, the titanium-bearing blast furnace slag and high-silica hematite in Example 1 are selected as raw materials, and the specific components are shown in Table 1. 64 wt% of titanium-bearing blast furnace slag, 27.86 wt% of high-silica hematite and 8.14 wt% of silica are mixed and pelletized. At this time, the molar ratio of titanium to iron elements in the mixed material is 1:1, and the acidity SiO 2 :CaO molar ratio is 1.4. The mixed material is pressed into pellets, and the size of each pellet is controlled at 5-8 mm. The mixed material pellets are placed in a corundum crucible and heated by an electric furnace. First, N 2 is introduced, and the mixed material is heated to 1300 °C. Subsequently, the atmosphere is converted to 30 vol% H 2 + 70 vol% N 2 , roasted for 3 h, and then the atmosphere is changed to pure N 2 . The sample is cooled to room temperature in the furnace and taken out. The molten pellets are crushed and ground to a particle size of -0.074 mm accounting for 76.35 wt%, and magnetic separation is carried out using a magnetic field intensity of 45 kA / m. The XRD pattern of the obtained high-purity titanomagnetite material is shown in Figure 3 .

[0042] It can be seen from Figure 3 that after increasing the acidity of the system, the main phases in the magnetic separation product change little. However, in the high-acidity system, Fe 2 TiO 4 is further converted into non-magnetic FeTiO 3 , which affects the titanium recovery rate during magnetic separation. The TiO 2 content in the magnetic separation product is 28.68 wt%, and the titanium recovery rate is 74.26 wt%.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 2 is only that the roasting temperature is replaced with 1100 °C, and the other steps and conditions are the same. The XRD pattern of the obtained magnetic separation product is shown in Figure 4 .

[0045] From Figure 4It can be seen that at a reduction temperature of 1100 °C, a small amount of ilmenite phase appears in the system. A large amount of unreacted quartz and perovskite are wrapped with each other and ilmenite, and are separated by magnetic separation. At the same time, due to the large amount of perovskite in the system not being decomposed, hematite fails to be completely transformed into the ilmenite phase and is reduced to metallic iron by hydrogen, and enters the magnetic product together. The above results show that at low temperature, the siliceous component cannot fully react with perovskite to form a silicate slag phase. At this time, the formation of ilmenite is incomplete and the crystal grain size is small, and high-purity products cannot be obtained by magnetic separation. The TiO 2 content in the magnetic separation product is 12.35 wt%, and the titanium recovery rate is 21.19 wt%.

[0046] Comparative Example 2

[0047] All reaction conditions in this comparative example are the same as those in Example 2, except that H 2 is replaced by CO, and the gas composition of the system is 10 vol% CO + 90 vol% N 2 . The XRD pattern of the magnetic separation product obtained is shown in Figure 5 .

[0048] It can be seen from Figure 5 that when using CO as a reducing agent, perovskite cannot be decomposed at a reduction temperature of 1300 °C. At this temperature, the iron oxide in the system will be reduced to metallic iron by CO and thus recovered by magnetic separation. The main phases in the magnetic separation product are undecomposed perovskite and metallic iron. The above results show that when using CO as a reducing agent, ilmenite phase cannot be prepared at low temperature.

Claims

1. A method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction, characterized in that: The raw materials including high-silicon hematite and titanium-containing blast furnace slag are finely ground, mixed and agglomerated to obtain agglomerates; the agglomerates are roasted and cooled to obtain mixed molten agglomerates of ilmenite and silicate; the mixed molten agglomerates are crushed, ground and magnetically separated to obtain high-purity ilmenite; The calcination is performed under a hydrogen-based reducing atmosphere.

2. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 1, characterized in that: Silica and high-silicon hematite can be added to the raw materials to jointly adjust the acidity of the system, wherein the acidity refers to the ratio of the molar amount of SiO2 to the molar amount of CaO in the system.

3. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 2, characterized in that: The titanium-containing blast furnace slag contains TiO2 at a content of 15wt% to 40wt%; The high-silicon hematite contains 5wt% to 15wt% SiO2 and 60wt% to 90wt% Fe2O3. The SiO2 content in the silica is between 90wt% and 99.5wt%.

4. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 3, characterized in that: The fine grinding particle size range of the raw materials is -0.074 mm, accounting for 60wt% to 99wt%.

5. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 1 or 2, characterized in that: The acidity range is 0.8 to 1.

5.

6. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 5, characterized in that: The size of the agglomerates is 5 to 8 mm.

7. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 1, characterized in that: The hydrogen-based reducing atmosphere is composed of H2 and N2, wherein the content of H2 is 0.5 vol% to 30 vol%, and the rest is N2.

8. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 7, characterized in that: The calcination conditions are as follows: the calcination temperature is 1200-1500° C. and the calcination time is 0.5-6 hours.

9. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 8, characterized in that: The crushing and grinding particle size range of the mixed molten agglomerate is -0.074 mm, accounting for 50wt% to 90wt%.

10. The method for recovering titanium from titanium-containing blast furnace slag by hydrogen-based low-temperature reduction according to claim 1, characterized in that: The field strength of the magnetic separation is 2kA / m to 45kA / m.

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