Method for carbonitriding of titanium-containing blast furnace slag

Abstract

This invention relates to the field of metallurgical technology and discloses a method for carbonitriding titanium-containing blast furnace slag, comprising the following steps: S1, mixing titanium-containing blast furnace slag with a carbonaceous reducing agent and placing it in a reactor, and carrying out a carbonization reaction at a temperature above 1700°C to obtain a primary carbonized slag containing TiC and residual TiO2; S2, lowering the temperature inside the reactor to 1400-1600°C and introducing nitrogen gas into the reactor to carry out a nitriding reaction to obtain a carbonitrided slag containing TiC and TiN. This invention can reduce the consumption of carbonaceous reducing agent and production costs, and can also improve the chlorination reactivity of the product, which is beneficial to improving the efficiency of subsequent titanium extraction processes through chlorination.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a method for carbonitriding treatment of titanium-containing blast furnace slag. Background Technology

[0002] Titanium-containing blast furnace slag is the main solid waste generated during the smelting of vanadium-titanium magnetite. It contains 20%-25% TiO2 and has extremely high recycling value. The current mainstream titanium extraction process is "high-temperature carbonization-low-temperature chlorination", which means that firstly, TiO2 in the slag is reduced and carbonized to TiC with carbon powder at a high temperature (above 1600℃) to obtain carbonized slag; then, TiC is chlorinated by passing chlorine gas at a low temperature (about 500℃) to generate TiCl4 for purification.

[0003] The inventors recognized that the process had significant shortcomings: on the one hand, the high-temperature carbonization stage required the consumption of a large amount of expensive metallurgical coke or petroleum coke, resulting in high costs; on the other hand, there was still room for improvement in the chlorination activity of TiC in the carbonized slag.

[0004] Therefore, developing an improved scheme that can reduce carbon consumption and optimize the performance of intermediate products is of great significance for promoting the industrial application of titanium extraction from titanium-containing blast furnace slag. Summary of the Invention

[0005] The main objective of this invention is to provide a carbonitriding treatment method for titanium-containing blast furnace slag, so as to solve the technical problems of high carbon consumption and insufficient product activity in existing high-temperature carbonization processes.

[0006] According to one aspect of the present invention, a method for carbonitriding titanium-containing blast furnace slag is provided, comprising the following steps: S1, mixing titanium-containing blast furnace slag with a carbonaceous reducing agent and placing it in a reactor, and carrying out a carbonization reaction at a temperature above 1700°C to obtain a primary carbonized slag containing TiC and residual TiO2; S2, lowering the temperature inside the reactor to 1400-1600°C, and introducing nitrogen gas into the reactor to carry out a nitriding reaction to obtain a carbonitrided slag containing TiC and TiN.

[0007] According to one embodiment of the present invention, in step S1, the molar ratio of C in the carbonaceous reducing agent to TiO2 in the titanium-containing blast furnace slag is 1.0-2.0.

[0008] According to one embodiment of the present invention, in step S2, nitrogen gas is delivered below the molten slag surface by a deep blowing device, and a covering nitrogen atmosphere is formed in the space above the molten slag surface by a surface dispersion device.

[0009] According to one embodiment of the present invention, in step S2, the proportion of nitrogen flow rate of the deep blowing device to the total nitrogen flow rate is higher in the early stage of the nitriding reaction than in the middle and late stages of the nitriding reaction; the proportion of nitrogen flow rate of the surface dispersion device to the total nitrogen flow rate is lower in the early stage of the nitriding reaction than in the middle and late stages of the nitriding reaction.

[0010] According to one embodiment of the present invention, in step S2, the nitrogen flow rate of the deep blowing device accounts for 30%-70% of the total nitrogen flow rate, and the nitrogen flow rate of the surface dispersion device accounts for 70%-30% of the total nitrogen flow rate.

[0011] According to one embodiment of the present invention, in step S2, the deep blowing device includes a hollow electrode, and the surface dispersion device includes an annular coil disposed on the lower side of the furnace cover.

[0012] According to one embodiment of the present invention, in step S2, by controlling the nitrogen flow rate and reaction time, the molar amount of TiN in the carbonitriding slag accounts for 10%-50% of the total molar amount of TiC and TiN.

[0013] According to one embodiment of the present invention, in step S2, the nitrogen flow rate is 0.8-1.6 L / min per kilogram of titanium-containing blast furnace slag, and the nitriding reaction time is 60-120 minutes.

[0014] According to one embodiment of the present invention, in step S2, after the nitriding reaction is completed, the slag is cooled to room temperature at a rate of 25-35°C / min under nitrogen protection.

[0015] According to one embodiment of the present invention, in step S1, the carbonaceous reducing agent includes at least one of coke powder, semi-coke and anthracite; the carbonization reaction is carried out under an inert atmosphere or vacuum conditions.

[0016] In the technical solution of this invention, titanium-containing blast furnace slag is first subjected to a carbonization reaction with a carbonaceous reducing agent at a high temperature (>1700℃) to generate TiC; then the temperature is lowered to 1400-1600℃ and nitrogen gas is introduced to carry out a nitriding reaction (TiC + 0.5N2 → TiN + C). The generated free carbon can be recycled for the carbonization reaction, ultimately obtaining a carbonitrided slag containing TiC and TiN. This invention utilizes inexpensive nitrogen gas to achieve internal carbon source recycling, which can significantly reduce the consumption of external carbonaceous reducing agents and production costs. Moreover, the product has better chlorination reactivity, which is beneficial to improving the efficiency of subsequent titanium extraction chlorination processes. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a method for carbonitriding titanium-containing blast furnace slag according to an embodiment of the present invention is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0020] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0021] refer to Figure 1 This invention proposes a carbonitriding treatment method for titanium-containing blast furnace slag, wherein the titanium-containing blast furnace slag is the main solid waste generated during the smelting of vanadium-titanium magnetite, and contains 20-25 wt% TiO2. The treatment method includes the following steps: S1, titanium-containing blast furnace slag is mixed with carbonaceous reducing agent and placed in a reactor, and carbonization reaction is carried out at a temperature of over 1700℃ to obtain primary carbonized slag containing TiC and residual TiO2. S2, the temperature inside the reactor is reduced to 1400-1600℃, and nitrogen is introduced into the reactor to carry out the nitriding reaction, to obtain carbonitriding slag containing TiC and TiN (e.g. Ti(C,N) solid solution).

[0022] In the technical solution of this invention, titanium-containing blast furnace slag is first subjected to a carbonization reaction with a carbonaceous reducing agent at a high temperature (>1700℃) to generate TiC; then the temperature is lowered to 1400-1600℃ and nitrogen gas is introduced to carry out a nitriding reaction (TiC + 0.5N2 → TiN + C). The generated free carbon can be recycled for the carbonization reaction, ultimately obtaining a carbonitrided slag containing TiC and TiN. This invention utilizes inexpensive industrial nitrogen gas (cost approximately 0.13 yuan / kg) to replace part of the expensive solid carbon (cost approximately 1.25 yuan / kg). The free carbon generated by the nitriding reaction can be directly used for the carbonization reaction, realizing the internal recycling of the carbon source. This invention only uses a carbonaceous reducing agent in step S1, and in step S2, the free carbon generated by the nitriding reaction is recycled to participate in the carbonization reaction, eliminating the need for additional carbonaceous reducing agent. Thus, through the internal recycling of the carbon source, the net consumption of external carbon powder and the overall production cost can be significantly reduced. Furthermore, the generated Ti(C,N) solid solution exhibits better chlorination reactivity than pure TiC, which is beneficial for improving the efficiency of subsequent titanium extraction chlorination processes. This invention can provide a new approach for the efficient and economical utilization of titanium-containing blast furnace slag.

[0023] Step S1 mainly involves high-temperature carbonization. Titanium-containing blast furnace slag is mixed with a carbonaceous reducing agent and reacted at a temperature above 1700℃ under an inert atmosphere or vacuum. This causes some of the TiO2 in the titanium-containing blast furnace slag to react and form titanium carbide (TiC), resulting in a primary carbonized slag containing TiC and unreacted residual TiO2. The reaction temperature above 1700℃ accelerates the reaction rate between TiO2 and C, allowing the carbonization reaction (TiO2 + 3C → TiC + 2CO) to proceed rapidly and completely. The temperature can be increased to above 1700℃ at a rate of 8-15℃ / min, and the holding time can be 30-90 minutes. The carbonaceous reducing agent can include at least one of coke powder, semi-coke, and anthracite.

[0024] In some embodiments, in step S1, the molar ratio of C in the carbonaceous reducing agent to TiO2 in the titanium-containing blast furnace slag is 1.0-2.0. This ratio is lower than the theoretical molar ratio of 3.0 required for complete carbonization. Its purpose is to intentionally retain a portion of TiO2 that does not participate in the carbonization reaction, allowing it to enter the primary carbonized slag. This residual TiO2 will react with the active free carbon generated by TiC nitriding in the subsequent step S2, regenerating TiC, thereby achieving an internal cycle of carbon elements between TiC → free C → TiC, significantly reducing the net consumption of external carbonaceous reducing agents and production costs.

[0025] Step S2 mainly involves medium-temperature nitriding. The primary carbide slag obtained in step S1 is cooled to a temperature range of 1400℃-1600℃ at a rate of 3-8℃ / min, and nitrogen gas (N2) is introduced into the reaction system to carry out the nitriding reaction. The main reaction occurring in this stage is: TiC + 0.5N2 → TiN + C. The active free carbon (C) generated by this reaction can immediately react with the residual TiO2 in the slag to form an internal carbon cycle. By controlling the temperature, nitrogen flow rate, reaction time, and nitrogen introduction method during the nitriding stage, a carbonitriding slag containing titanium carbide (TiC) and titanium nitride (TiN) can be finally obtained, where TiC and TiN can form a Ti(C,N) solid solution.

[0026] The TiC nitriding reaction (TiC + 0.5N₂ = TiN + C) proceeds spontaneously at temperatures of 1600°C and below, where the Gibbs free energy is less than 0. However, the reverse reaction (TiN + C = TiC + 0.5N₂) requires temperatures of 1700°C and above to have a Gibbs free energy less than 0, meaning the reverse reaction only occurs at temperatures above 1700°C. Therefore, in this invention, the temperature of step S2 is precisely controlled at a medium temperature (1400-1600°C) to ensure the directional conduction of the nitriding reaction. This medium temperature condition also ensures that the generated active free carbon reacts promptly with the residual TiO₂ to form a carbonization reaction.

[0027] In some embodiments, in step S2, nitrogen is delivered below the molten slag surface via at least one deep-blowing device, and a covering nitrogen atmosphere is formed in the space above the molten slag surface via at least one surface-diffusing device. Delivering nitrogen directly below the molten slag surface via the deep-blowing device enhances mass transfer between the gas, liquid, and solid phases through the strong agitation of nitrogen bubbles, allowing the nitrogen to fully contact the TiC particles suspended in the molten slag, thereby rapidly initiating and accelerating the nitriding reaction. Simultaneously, forming a covering nitrogen atmosphere above the molten slag surface via the surface-diffusing device prevents oxidation of the high-temperature molten slag from contact with residual air in the furnace, and helps maintain the nitrogen partial pressure of the reaction system and stabilize the thermodynamic conditions of the nitriding reaction. The synergistic effect of both ensures efficient initiation and execution of the nitriding reaction while protecting the product from oxidation.

[0028] In some embodiments, the deep blowing device includes a hollow graphite electrode, through which nitrogen gas is delivered to a depth below the molten slag surface. The hollow graphite electrode can be inserted 40-60 mm below the molten slag surface. The surface dispersion device includes an annular coil disposed on the underside of the furnace cover, on which multiple spaced-apart nozzles can be arranged. The diameter of the annular coil can be 8-12 mm, the diameter of the nozzles can be 1-3 mm, and the number of nozzles can be 10-15.

[0029] In some embodiments, the deep blowing device and the surface dispersion device can independently control the gas flow rate to achieve segmented and precise control of the carbonitriding reaction process. The proportion of nitrogen flow rate from the deep blowing device to the total nitrogen flow rate is higher in the early stage of the nitriding reaction than in the middle and later stages; the proportion of nitrogen flow rate from the surface dispersion device to the total nitrogen flow rate is lower in the early stage of the nitriding reaction than in the middle and later stages. In the early stage of the nitriding reaction, increasing the nitrogen proportion from the deep blowing device enhances mass transfer and initiates the reaction; in the middle and later stages of the reaction, increasing the nitrogen proportion from the surface dispersion device maintains the atmosphere and controls the product composition. In some embodiments, the proportion of nitrogen flow rate from the deep blowing device to the total nitrogen flow rate is 30%-70%, and the proportion of nitrogen flow rate from the surface dispersion device is 70%-30%.

[0030] In some embodiments, in step S2, by controlling the nitrogen flow rate and reaction time, the molar amount of TiN in the carbonitriding slag accounts for 10%-50% of the total molar amount of TiC and TiN. Specifically, the total nitrogen flow rate can be 0.8-1.6 L / min per kilogram of titanium-containing blast furnace slag, and the nitriding reaction time can be 60-120 minutes.

[0031] In some embodiments, in step S2, after the nitriding reaction is completed, the slag is cooled to room temperature at a rate of 25-35°C / min under nitrogen protection. This cooling rate can suppress excessive growth or phase separation of the Ti(C,N) solid solution, ensuring that the product maintains suitable grain size and uniformity, which is beneficial to improving the efficiency of the subsequent titanium chlorination process. Simultaneously, a faster cooling rate can also reduce the segregation of titanium components in the slag phase, improving product consistency. By continuously introducing nitrogen to form a protective atmosphere, oxidation of the high-temperature carbonitriding slag during cooling can be avoided, ensuring the grade of TiC and TiN.

[0032] In summary, to overcome the shortcomings of existing high-temperature carbonization processes, such as high carbon consumption, high cost, and low product activity, this invention provides a carbonitriding treatment method that reduces carbonization costs by introducing nitrogen to achieve internal carbon source circulation. This method can inherit existing high-temperature carbonization furnaces and other infrastructure, requiring only the addition of a nitrogen supply and control system. It is easy to modify and promote industrialization.

[0033] The present invention can achieve the following beneficial effects: (1) Significantly reduce carbon consumption and costs: Use inexpensive industrial nitrogen (cost of about RMB 0.13 / kg) to replace part of the expensive solid carbon (cost of about RMB 1.25 / kg). The free carbon generated by the nitriding reaction can be directly used for the carbonization reaction, realizing the internal recycling of carbon source and significantly reducing the net consumption of external carbon powder and the overall production cost.

[0034] (2) Better product activity: The generated Ti(C,N) solid solution may have better chlorination reaction activity than pure TiC, which is beneficial to improving the efficiency of subsequent titanium chlorination process.

[0035] (3) Smooth process integration: This method can inherit existing high-temperature carbonization furnaces and other infrastructure, and only requires the addition of nitrogen supply and control system. The transformation is simple and easy to promote industrially.

[0036] (4) Sufficient thermodynamic basis: The nitriding reaction (TiC nitriding) of this invention has a negative Gibbs free energy below 1600℃, and the reaction can proceed spontaneously; while the reverse reaction can only occur at high temperatures of 1700℃ and above. Therefore, precise control of intermediate temperature nitriding can ensure the directional progress of the reaction.

[0037] The following description is based on specific embodiments.

[0038] Example 1 Step 1: High-temperature carbonization Take 1000g of titanium-containing blast furnace slag and grind it to 100 mesh (i.e., able to pass through a 100-mesh sieve). Add petroleum coke powder at a C / TiO2 molar ratio of 1.5 and mix thoroughly. Place the mixture in a graphite crucible and put it into a high-temperature carbonization furnace. After evacuation, purge with argon gas for protection, and heat to 1750℃ at a rate of 10℃ / min, holding at this temperature for 60 minutes to carry out a high-temperature carbonization reaction, obtaining primary carbonized slag.

[0039] Step 2: Intermittent nitriding After the carbonization reaction, the furnace temperature was lowered to 1550℃ (cooling rate approximately 5℃ / min). The argon gas was shut off, and the dedicated nitrogen injection system was started for the nitriding reaction. Deep blowing: Nitrogen was introduced at a flow rate of 0.8 L / min through a hollow graphite electrode (inserted approximately 50 mm below the molten slag surface); Surface diffusion: Nitrogen was introduced at a flow rate of 0.4 L / min through an annular coil (10 mm diameter, with 12 φ2 mm nozzles) under the furnace cover to create a covering atmosphere. The total nitrogen flow rate was 1.2 L / min, with approximately 67% deep blowing and approximately 33% surface diffusion. The nitriding reaction lasted 90 minutes, during which the reaction temperature was recorded every 30 minutes, maintaining a stable temperature of 1550 ± 10℃.

[0040] Product control: After the nitriding reaction is completed, the slag is cooled to room temperature at a rate of about 30℃ / min under nitrogen protection to obtain black carbonitriding slag.

[0041] The obtained carbonitriding slag was analyzed, and the results showed that the main phases of the product were TiC and TiN, with TiN accounting for about 35% of the total molar amount of titanium compounds (TiC+TiN).

[0042] Example 2 Step 1: High-temperature carbonization Take 2000g of titanium-containing blast furnace slag and grind it to 100 mesh (i.e., able to pass through a 100-mesh sieve). Add petroleum coke powder at a C / TiO2 molar ratio of 1.2 and mix thoroughly. Place the mixture in a graphite crucible and put it into a high-temperature carbonization furnace. After evacuation, purge with argon gas for protection, and heat to 1780℃ at a rate of 10℃ / min, holding at this temperature for 45 minutes to carry out a high-temperature carbonization reaction, obtaining primary carbonized slag.

[0043] Step 2: Intermittent nitriding After the carbonization reaction, the furnace temperature was lowered to 1480℃ (cooling rate approximately 5℃ / min). The argon gas was shut off, and the dedicated nitrogen injection system was started for the nitriding reaction. Deep blowing: Nitrogen was introduced at a flow rate of 1.8 L / min through a hollow graphite electrode (inserted approximately 50 mm below the molten slag surface); Surface diffusion: Nitrogen was introduced at a flow rate of 1.2 L / min through an annular coil (10 mm diameter, with 12 φ2 mm nozzles) under the furnace cover to create a covering atmosphere. The total nitrogen flow rate was 3.0 L / min, with approximately 60% deep blowing and approximately 40% surface diffusion. The nitriding reaction lasted 120 minutes, during which the reaction temperature was recorded every 30 minutes, maintaining a stable temperature of 1480 ± 10℃.

[0044] Product control: After the nitriding reaction is completed, the slag is cooled to room temperature at a rate of about 30℃ / min under nitrogen protection to obtain black carbonitriding slag.

[0045] The obtained carbonitriding slag was analyzed, and the results showed that the main phases of the product were TiC and TiN, with TiN accounting for about 42% of the total molar amount of titanium compounds (TiC+TiN).

[0046] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for carbonitriding titanium-containing blast furnace slag, characterized in that, Includes the following steps: S1, titanium-containing blast furnace slag is mixed with carbonaceous reducing agent and placed in a reactor, and carbonization reaction is carried out at a temperature of over 1700℃ to obtain primary carbonized slag containing TiC and residual TiO2. S2, the temperature inside the reactor is reduced to 1400-1600℃, and nitrogen gas is introduced into the reactor to carry out a nitriding reaction, resulting in carbonitriding slag containing TiC and TiN.

2. The method according to claim 1, characterized in that, In step S1, the molar ratio of C in the carbonaceous reducing agent to TiO2 in the titanium-containing blast furnace slag is 1.0-2.

0.

3. The method according to claim 1, characterized in that, In step S2, nitrogen is delivered below the molten slag surface through a deep blowing device, and a covering nitrogen atmosphere is formed in the space above the molten slag surface through a surface dispersion device.

4. The method according to claim 3, characterized in that, In step S2, the proportion of nitrogen flow rate of the deep blowing device to the total nitrogen flow rate is higher in the early stage of the nitriding reaction than in the middle and late stages; the proportion of nitrogen flow rate of the surface dispersion device to the total nitrogen flow rate is lower in the early stage of the nitriding reaction than in the middle and late stages.

5. The method according to claim 3, characterized in that, In step S2, the nitrogen flow rate of the deep blowing device accounts for 30%-70% of the total nitrogen flow rate, and the nitrogen flow rate of the surface dispersion device accounts for 70%-30% of the total nitrogen flow rate.

6. The method according to claim 3, characterized in that, In step S2, the deep blowing device includes a hollow electrode, and the surface dispersion device includes an annular coil disposed on the underside of the furnace cover.

7. The method according to claim 1, characterized in that, In step S2, by controlling the nitrogen flow rate and reaction time, the molar amount of TiN in the carbonitriding slag is made to account for 10%-50% of the total molar amount of TiC and TiN.

8. The method according to claim 7, characterized in that, In step S2, the nitrogen flow rate is 0.8-1.6 L / min per kilogram of titanium-containing blast furnace slag, and the nitriding reaction time is 60-120 minutes.

9. The method according to claim 1, characterized in that, In step S2, after the nitriding reaction is completed, the slag is cooled to room temperature at a rate of 25-35℃ / min under nitrogen protection.

10. The method according to claim 1, characterized in that, In step S1, the carbonaceous reducing agent includes at least one of coke powder, semi-coke, and anthracite; the carbonization reaction is carried out under an inert atmosphere or vacuum conditions.

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