Process method for recovering iron by reducing copper slag through hydrogen and application

Abstract

The invention belongs to the technical field of copper slag treatment, and discloses a process method for recovering iron by reducing copper slag through hydrogen and application. According to the process method for recovering the iron by reducing the copper slag through the hydrogen, calcium oxide is added into the copper slag, and efficient reduction and directional polymerization of the iron element are achieved through the hydrogen; according to the process, hydrogen is used as a clean reducing agent, and a reaction byproduct is only water vapor, so that the problem of carbon emission of a carbon-based reduction process is fundamentally avoided; a gradient dissociation process of pre-reduction, grinding and secondary reduction is further adopted, that is, primary pre-reduction is firstly carried out, so that primary polymerization of the iron element is realized; grinding and crushing the pre-reduced product to destroy a symbiotic structure of an iron phase and gangue minerals, so that an iron-containing phase is effectively separated from other phases; and finally, secondary reduction is carried out, the iron phase is promoted to further aggregate and grow, high-purity metal iron particles existing in a monomer form are formed, and the problem that in a traditional method, iron phase dissociation is not sufficient is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of copper slag treatment technology, and specifically relates to a process and application of hydrogen reduction of copper slag to recover iron. Background Technology

[0002] Copper, as an important basic metallic material, plays an irreplaceable role in key sectors of the national economy such as construction, power, and transportation. Copper smelting generates a large amount of copper slag, which is high in iron and possesses significant potential for iron resource recovery. However, the iron in copper slag is mainly found in fir olivine (Fe2SiO4) and magnetite (Fe3O4), and is closely associated with gangue minerals such as silicates and glass phases, exhibiting a fine particle size. This makes it difficult to achieve efficient enrichment and recovery of iron using traditional physical separation methods such as magnetic separation and flotation.

[0003] Currently, a large amount of copper slag is still disposed of through stockpiling or landfilling, which not only occupies land resources but also poses a potential threat to soil and water pollution due to its heavy metal content, threatening ecological and environmental safety. While existing technologies have attempted to treat copper slag through carbothermic reduction and smelting tempering, these methods generally suffer from high energy consumption, complex processes, low iron recovery rates, or secondary pollution. Traditional processes, in particular, still face technological bottlenecks in achieving efficient reduction of fir olivine and directional migration of the iron phase.

[0004] With the increasing demands for green and low-carbon smelting, the development of efficient and clean technologies for the resource utilization of copper slag and iron has become an urgent need in the industry. Hydrogen, as a clean reducing agent, can selectively reduce metal oxides at high temperatures, and the reaction product is only water, avoiding the carbon emission problems of carbon-based reduction processes. Therefore, based on the reduction characteristics of hydrogen, designing a new process for the efficient activation and separation of iron components in copper slag is of great significance for realizing the high-value-added utilization of copper slag and promoting the sustainable development of the metallurgical industry. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the purpose of this invention is to provide a process and application for recovering iron from copper slag using hydrogen reduction. This invention uses hydrogen reduction to recover iron from copper slag, fundamentally avoiding the carbon emission problem of traditional carbon-based reduction processes. It utilizes hydrogen to achieve efficient reduction and directional polymerization of iron. Furthermore, it employs a gradient dissociation process of "pre-reduction-grinding-secondary reduction" to promote further aggregation and growth of the iron phase, forming high-purity, monomeric metallic iron particles, effectively solving the problem of insufficient iron phase dissociation in traditional methods.

[0006] In a first aspect, the present invention provides a process for recovering iron from copper slag by hydrogen reduction, comprising the following steps: S1. Mix copper slag and calcium oxide to obtain a mixture; S2. Under the protection of nitrogen and / or inert gas, the mixture is heated to a buffer temperature and held at that temperature; the buffer temperature is 400-500℃. S3. After the heat preservation is completed, continue to heat to the reduction temperature, and replace the nitrogen and / or inert gas with a reducing gas to carry out the reduction reaction; the reduction temperature is 1000-1150℃; S4. After the reduction reaction in step S3 is completed, replace the reducing gas with nitrogen and / or an inert gas, cool, and obtain the reduction product; S5. Grind the reduction product and separate it by magnetic separation to obtain metallic iron.

[0007] Specifically, this invention involves adding a certain proportion of calcium oxide to copper slag (the amount of calcium oxide added is calculated based on the elemental analysis of the copper slag, and should be sufficient to completely replace the iron in the fuchsite or magnetite). Utilizing the reducing effect of hydrogen at high temperatures, the iron in the copper slag is reduced, maximizing the recovery of iron resources from the slag. This method uses hydrogen reduction, and the hydrogen reduction reaction only produces water vapor as a byproduct. The entire reaction process is clean and pollution-free, meeting green environmental protection requirements and fundamentally avoiding the carbon emission problems of traditional carbon-based reduction processes.

[0008] In some embodiments of the present invention, before performing step S3, the following steps are also included: a) After the mixture in step S2 has been kept at a certain temperature, heat it to the pre-reduction temperature and replace the nitrogen and / or inert gas with a reducing gas to carry out the pre-reduction reaction; the pre-reduction temperature is 900-1000℃. b) After the pre-reduction reaction in step a) is completed, replace the reducing gas with nitrogen and / or an inert gas, cool, and obtain the pre-reduction product; c) After grinding the pre-reduced product, it is heated to the buffer temperature under the protection of nitrogen and / or inert gas, and then kept at that temperature.

[0009] Specifically, in order to better reduce iron and facilitate subsequent magnetic separation, this invention designs a process flow of "pre-reduction-grinding-secondary reduction". First, pre-reduction causes the iron in the copper slag to polymerize. Then, the pre-reduction product is ground and crushed to separate the iron-containing phase from other phases. Then, the crushed and separated sample is reduced again (secondary reduction). The iron in the sample after pre-reduction has been well polymerized. Secondary reduction can maximize the yield of metallic iron particles and improve the purity of the metallic iron particles.

[0010] In some embodiments of the present invention, the calcium oxide accounts for 10-20% of the mass percentage of the mixture.

[0011] In some embodiments of the present invention, the heating rate is 5-10°C / min.

[0012] In some embodiments of the present invention, the heat preservation time in step S2 is 20-40 minutes.

[0013] In some embodiments of the present invention, the reduction reaction time in step S3 is 0.25-1h, preferably 0.5-1h.

[0014] In some embodiments of the present invention, the reducing gas contains hydrogen, and the volume percentage of the hydrogen is 30-60%.

[0015] In some embodiments of the present invention, the flow rate of the reducing gas is 90-180 mL / min.

[0016] In some embodiments of the present invention, in step S5, the reduction product is ground to 1000-2000 mesh.

[0017] In some embodiments of the present invention, the metallic iron accounts for a mass percentage of the iron element in the copper slag > 70 wt%.

[0018] In some embodiments of the present invention, the process for recovering iron from copper slag by hydrogen reduction (direct reduction), with programmed temperature control executed in a high-temperature tubular furnace, specifically includes the following steps: 1) Initial preparation and purging: Place the sample (copper slag + calcium oxide) in the constant temperature zone of the tube furnace, and then seal the reaction tube; before the start of the entire program and during the subsequent heating stage, continuously introduce high-purity nitrogen into the reaction tube to completely remove the air from the furnace tube and the environment around the sample, ensuring that the reaction is always carried out under anaerobic conditions.

[0019] 2) Programmed temperature rise and initial holding: Heat from room temperature (25±5℃) to an intermediate buffer temperature (400-500℃) at a set heating rate (5-10℃ / min); after reaching the buffer temperature, hold for 20-40 minutes. This process aims to ensure that the sample is heated evenly and release some physically adsorbed water and other substances, while maintaining a nitrogen atmosphere.

[0020] 3) Reaching the target temperature and switching the gas: After completing the buffer temperature holding, continue heating to the target reaction temperature at a set heating rate under nitrogen protection (controlling the reduction temperature at 1000-1150℃); when the system stably reaches this target temperature, immediately switch the gas from nitrogen to a reducing gas with a specific composition and concentration (H2 / N2 mixed gas containing 30-60% hydrogen by volume, with a gas flow rate of 90-180mL / min); under the target reaction temperature and reducing gas, perform continuous treatment for a preset holding time (i.e., reduction reaction time of 0.25-1h); this holding time can be set according to the specific material and processing requirements, and is a key stage for completing the core reduction or phase change process of the material.

[0021] 4) Reaction Termination and Gas Protection: After the preset reduction holding time is completed, heating is stopped, and the gas is switched from reducing gas back to nitrogen. This nitrogen gas will be maintained until the sample cools down to the end of the entire program. The purpose is to terminate the reduction reaction and prevent the high-temperature sample from being oxidized by contact with air during the cooling process. Under the continuous protection of nitrogen, the furnace is allowed to cool naturally or the step cooling function of the program is activated until the temperature drops below room temperature and the reduction product is obtained.

[0022] 5) Crushing and separation: Stop the nitrogen gas supply, take out the reduction product, put it into a ball mill and grind it to 1000-2000 mesh, and then use a magnetic separator to separate the ground product and recover metallic iron.

[0023] In some embodiments of the present invention, the process for recovering iron from copper slag by hydrogen reduction (pre-reduction-grinding-secondary reduction), with programmed temperature control, is executed in a high-temperature tubular furnace, specifically including the following steps: 1) Initial preparation and purging: Place the sample (copper slag + calcium oxide) in the constant temperature zone of the tube furnace, and then seal the reaction tube; before the start of the entire program and during the subsequent heating stage, continuously introduce high-purity nitrogen into the reaction tube to completely remove the air from the furnace tube and the environment around the sample, ensuring that the reaction is always carried out under anaerobic conditions.

[0024] 2) Programmed temperature rise and initial holding: Heat from room temperature (25±5℃) to an intermediate buffer temperature (400-500℃) at a set heating rate (5-10℃ / min); after reaching the buffer temperature, hold for 20-40 minutes. This process aims to ensure that the sample is heated evenly and release some physically adsorbed water and other substances, while maintaining a nitrogen atmosphere.

[0025] 3) Reaching the pre-reduction temperature and switching the gas: After completing the buffer temperature holding, continue heating to the target reaction temperature at a set heating rate under nitrogen protection (controlling the pre-reduction temperature at 900-1000℃, the purpose of which is to allow the iron element in the sample to polymerize first); when the system stably reaches this temperature, immediately switch the gas from nitrogen to a reducing gas with a specific composition and concentration (H2 / N2 mixed gas containing 30-60% hydrogen by volume, gas flow rate of 90-180mL / min); under the target reaction temperature and reducing gas, perform a preset holding time (i.e., pre-reduction reaction time of 0.25-1h); this holding time can be set according to the specific material and processing requirements, and is a key stage for completing the core reduction or phase change process of the material.

[0026] 4) Termination of pre-reduction reaction and gas protection: After the preset reduction holding time is completed, heating is stopped, and the gas is switched from reducing gas back to nitrogen. This nitrogen will be maintained until the sample cools down to the end of the entire program. The purpose is to terminate the reduction reaction and prevent the high-temperature sample from being oxidized by contact with air during the cooling process. Under the continuous protection of nitrogen, the furnace is naturally cooled or the step cooling function of the program is activated until the temperature drops below room temperature, and the pre-reduction product is obtained.

[0027] 5) Crushing and separation: Stop the nitrogen gas supply, take out the pre-reduction product, put it into a ball mill and grind it to 200-400 mesh. Then, repeat the process of steps 2)-4) on the ground pre-reduction product. At this time, the target reaction temperature in step 3) should be raised to 1000-1150℃ to carry out the reduction reaction (secondary reduction) so that the pre-reduction product can be completely reduced to obtain the reduced product.

[0028] 6) Crushing and magnetic separation: The extracted reduction product is put into a ball mill and ground to 1000-2000 mesh. Then, the ground product is separated by magnetic separation equipment to recover metallic iron.

[0029] Specifically, this invention precisely calculates the elemental composition of copper slag and adds an appropriate amount of calcium oxide as an activator to ensure complete replacement of iron in fritillary olivine or magnetite. Under strictly controlled temperature and time conditions, hydrogen is used to achieve efficient reduction and directional polymerization of iron. This process uses hydrogen as a clean reducing agent, and the only reaction byproduct is water vapor, fundamentally avoiding the carbon emission problem of carbon-based reduction processes. This invention further employs a gradient dissociation process of "pre-reduction-grinding-secondary reduction," whereby an initial pre-reduction is performed to achieve preliminary polymerization of iron; subsequently, the pre-reduction product is ground and crushed to disrupt the symbiotic structure of the iron phase and gangue minerals, effectively separating the iron-containing phase from other phases; finally, a secondary reduction is performed to promote further aggregation and growth of the iron phase, forming high-purity, monomeric metallic iron particles. The "pre-reduction-grinding-secondary reduction" process effectively solves the problem of insufficient iron phase dissociation in traditional methods.

[0030] A second aspect of the present invention provides the application of the hydrogen reduction copper slag recovery iron process described in the first aspect of the present invention in the recovery of iron metal from copper slag.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The process method for recovering iron from copper slag by hydrogen reduction provided by the present invention significantly improves the recovery rate of metallic iron. Through the synergistic effect of two reductions and intermediate grinding, the iron resources in the copper slag are recovered to the maximum extent. Moreover, the product quality is excellent, and metallic iron particles with higher purity and easier magnetic separation are finally obtained.

[0032] (2) The process for recovering iron from copper slag by hydrogen reduction provided by the present invention is clean and environmentally friendly throughout the entire recovery process. Hydrogen is used as the reducing agent, and there is no carbon emission or other pollutant generation.

[0033] (3) The process method for recovering iron from copper slag by hydrogen reduction provided by the present invention has a reasonable process flow. Through segmented reduction and intermediate grinding, energy consumption is effectively reduced and technical economy is improved.

[0034] (4) The process method for recovering iron from copper slag by hydrogen reduction provided by the present invention has achieved a major breakthrough in reaction mechanism and process design. It not only solves the technical problem of iron resource recovery from copper slag, but also provides a new way for green and sustainable development in the metallurgical industry. It is of great significance to promote the high value-added utilization of copper slag. Attached Figure Description

[0035] Figure 1 The process flow diagrams for recovering iron from copper slag by hydrogen reduction in Examples 1-4 of this invention are shown below. Figure 2 This is a process flow diagram of hydrogen reduction of copper slag to recover iron in Embodiment 5 of the present invention; Figure 3The XRD patterns of the reduction products obtained in Examples 1-4 of this invention are shown below. Figure 4 This is an EMPA diagram of the reduction product obtained in Example 4 of the present invention; Figure 5 This is an EMPA diagram of the reduction product obtained in Example 5 of the present invention; Figure 6 The images show the XRD patterns of the reduction products obtained in Comparative Examples 1 and 2 of this invention. Detailed Implementation

[0036] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0037] Example 1 (Direct Reduction) Reference Figure 1 This embodiment provides a process for recovering iron from copper slag by hydrogen reduction, including the following steps: 1) Initial preparation and purging: Place the sample (copper slag + calcium oxide) in the constant temperature zone of the tube furnace, and then seal the reaction tube. The calcium oxide accounts for 15% of the sample mass. Before the start of the entire procedure and during the subsequent heating stage, continuously introduce high-purity nitrogen into the reaction tube to completely remove the air from the furnace tube and the environment around the sample, ensuring that the reaction is always carried out under anaerobic conditions.

[0038] 2) Programmed temperature rise and initial holding: Heat from room temperature to an intermediate buffer temperature of 450°C at a set temperature rise rate (10°C / min); after reaching the buffer temperature, hold for 30 minutes. This process is intended to ensure that the sample is heated evenly and to release some physically adsorbed water and other substances, while maintaining a nitrogen atmosphere.

[0039] 3) Reaching the target temperature and switching the gas: After completing the buffer temperature holding, continue heating under nitrogen protection at the set heating rate to the final target reaction temperature (controlling the reduction temperature at 1100℃); when the system stably reaches this target temperature, immediately switch the gas from nitrogen to a reducing gas with a specific composition and concentration (H2 / N2 mixed gas containing 50% hydrogen by volume, with a gas flow rate of 180mL / min); under the target reaction temperature and reducing gas, continue treatment for a preset holding time (i.e., reduction reaction time of 0.25h).

[0040] 4) Reaction Termination and Gas Protection: After the preset reduction holding time is completed, heating is stopped, and the gas is switched from reducing gas back to nitrogen. This nitrogen gas will be maintained until the sample cools down to the end of the entire process. The purpose is to terminate the reduction reaction and prevent the high-temperature sample from being oxidized by contact with air during the cooling process. Under the continuous protection of nitrogen, the furnace cools naturally until the temperature drops below room temperature, and the reduction product is obtained.

[0041] 5) Crushing and separation: Stop the nitrogen gas supply, take out the reduction product, put it into a ball mill and grind it to 1500 mesh, and then use a magnetic separator to separate the ground product and recover metallic iron.

[0042] Example 2 The only difference from Example 1 is that the reduction reaction time in step 3) is adjusted from 0.25h to 0.5h.

[0043] Example 3 The only difference from Example 1 is that the reduction reaction time in step 3) is adjusted from 0.25h to 0.75h.

[0044] Example 4 The only difference from Example 1 is that the reduction reaction time in step 3) is adjusted from 0.25h to 1h.

[0045] Example 5 (Pre-reduction-grinding-secondary reduction) Reference Figure 2 This embodiment provides a process for recovering iron from copper slag by hydrogen reduction, including the following steps: 1) Initial preparation and purging: Place the sample (copper slag + calcium oxide) in the constant temperature zone of the tube furnace, and then seal the reaction tube. The calcium oxide accounts for 15% of the sample mass. Before the start of the entire procedure and during the subsequent heating stage, continuously introduce high-purity nitrogen into the reaction tube to completely remove the air from the furnace tube and the environment around the sample, ensuring that the reaction is always carried out under anaerobic conditions.

[0046] 2) Programmed temperature rise and initial holding: Heat from room temperature to an intermediate buffer temperature of 450°C at a set temperature rise rate (10°C / min); after reaching the buffer temperature, hold for 30 minutes. This process is intended to ensure that the sample is heated evenly and to release some physically adsorbed water and other substances, while maintaining a nitrogen atmosphere.

[0047] 3) Reaching the target temperature and switching the gas: After completing the buffer temperature holding, continue heating under nitrogen protection at the set heating rate to the final target reaction temperature (controlling the pre-reduction temperature at 900℃, the purpose of which is to allow the iron element in the sample to polymerize first); when the system stably reaches this target temperature, immediately switch the gas from nitrogen to a reducing gas with a specific composition and concentration (H2 / N2 mixed gas containing 50% hydrogen by volume, gas flow rate of 180mL / min); under the target reaction temperature and reducing gas, continue the treatment for a preset holding time (i.e., pre-reduction reaction time of 1h).

[0048] 4) Reaction Termination and Gas Protection: After the preset pre-reduction holding time is completed, heating is stopped, and the gas is switched from reducing gas back to nitrogen. This nitrogen gas will be maintained until the sample cools down to the end of the entire process. The purpose is to terminate the reduction reaction and prevent the high-temperature sample from being oxidized by contact with air during the cooling process. Under the continuous protection of nitrogen, the furnace cools naturally until the temperature drops below room temperature, and the pre-reduced product is obtained.

[0049] 5) Crushing and separation: Stop the nitrogen gas supply, take out the pre-reduction product, put it into a ball mill and grind it to 300 mesh. Then, repeat the process of steps 2)-4) on the ground pre-reduction product. At this time, change the target reaction temperature in step 3) (that is, increase the original pre-reduction temperature to 1100℃) and carry out the reduction reaction for 1 hour so that the pre-reduction product can be completely reduced to obtain the reduced product.

[0050] 6) Crushing and magnetic separation: The extracted reduction product is put into a ball mill and ground to 1500 mesh. Then, the ground product is separated by magnetic separation equipment to recover metallic iron.

[0051] The reduction products obtained in Examples 1-4 have X-ray diffraction (XRD) patterns as follows: Figure 3 As shown. By Figure 3 It can be seen that, compared with the original sample, after reduction for t=0.25h (Example 1), the characteristic peak intensities of major components such as fir olivine (Fe2SiO4), magnetite (Fe3O4), and CaO decreased significantly, while the characteristic peak of metallic Fe increased significantly. With the increase of reduction time t (Examples 2-4), the characteristic peaks of Fe2SiO4, Fe3O4, CaO, and other phases continued to decrease until they essentially disappeared, and the characteristic peak intensity of metallic Fe also reached its maximum. Furthermore, it can be seen that the content of metallic Fe in the original sample was essentially 0%, and with the increase of reduction time, the iron element in the sample was gradually reduced.

[0052] The electron microscopy probe microanalysis (EMPA) image of the reduction product obtained in Example 4 is shown below. Figure 4 As shown. By Figure 4 It can be seen that most of the reduced metallic iron in the sample aggregates around the particles and exists in a symbiotic relationship with other phases, and metallic Fe is clearly distinguishable from other phases.

[0053] The EMPA diagram of the reduction product obtained in Example 5 is shown below. Figure 5 As shown. By Figure 5 It is known that the small particles adhering to the sample surface are the metallic iron phase generated during the secondary reduction process. In this invention, after preliminary reduction under pre-reduction conditions, the sample undergoes mechanical grinding, which effectively separates metallic iron (Fe) from silicon (Si) and other phases. Subsequently, a secondary reduction process is performed, which on the one hand helps to promote a more thorough reduction of Fe to metallic iron, increasing the reduction rate; on the other hand, it provides conditions for the aggregation and growth of the reduced metallic iron particles, thus facilitating the formation of larger and more prominent iron particles, further enhancing phase differentiation and identification. This two-stage "pre-reduction-grinding-secondary reduction" treatment strategy significantly optimizes the reduction efficiency and microstructure of metallic iron. The staged "pre-reduction-grinding-secondary reduction" strategy effectively promotes the separation of metallic iron and silicate phases: high-temperature pre-reduction promotes the aggregation and growth of metallic iron particles, preliminary grinding achieves physical desorption between the two phases, and subsequent high-temperature secondary reduction further enhances the reduction and aggregation of iron, thus creating favorable conditions for the efficient extraction of high-purity metallic iron through subsequent mechanical crushing and magnetic separation.

[0054] Comparative Example 1 (Traditional Carbon-based Reduction) A process for recovering iron from copper slag by reducing it with pulverized coal includes the following steps: 1) Initial preparation and purging: The sample (copper slag + calcium oxide + coal powder) was placed in the constant temperature zone of the tube furnace, and then the reaction tube was sealed. The ratio of calcium oxide to copper slag was the same as in Example 1, and the mass ratio of coal powder to (the mixture of calcium oxide and copper slag) was 1:1. Before the start of the entire process and during the subsequent heating stage, high-purity nitrogen was continuously introduced into the reaction tube to completely remove the air from the furnace tube and the environment around the sample, ensuring that the reaction was always carried out under anaerobic conditions.

[0055] 2) Programmed temperature rise and initial holding: Heat from room temperature to an intermediate buffer temperature of 450°C at a set temperature rise rate (10°C / min); after reaching the buffer temperature, hold for 30 minutes. This process is intended to ensure that the sample is heated evenly and to release some physically adsorbed water and other substances, while maintaining a nitrogen atmosphere.

[0056] 3) Reaching the target temperature and switching gases: After completing the buffer temperature holding, continue heating under nitrogen protection at the set heating rate to the final target reaction temperature (controlling the reduction temperature at 1100℃); when the system stably reaches this target temperature, continue treatment at the target reaction temperature for a preset holding time (i.e., reduction reaction time 1h).

[0057] 4) Reaction termination and gas protection: After the preset reduction holding time is completed, heating is stopped, and the furnace is naturally cooled under continuous nitrogen protection until the temperature drops below room temperature to obtain the reduction product.

[0058] 5) Crushing and separation: Stop the nitrogen gas supply, take out the reduction product, put it into a ball mill and grind it to 1500 mesh, and then use a magnetic separator to separate the ground product and recover metallic iron.

[0059] Comparative Example 2 (Traditional Carbon-based Reduction) A process for recovering iron from copper slag by reducing it with pulverized coal includes the following steps: 1) Initial preparation and purging: The sample (copper slag + calcium oxide + coal powder) was placed in the constant temperature zone of the tube furnace, and then the reaction tube was sealed. The ratio of calcium oxide to copper slag was the same as in Example 1, and the mass ratio of coal powder to (the mixture of calcium oxide and copper slag) was 1:1. Before the start of the entire process and during the subsequent heating stage, high-purity nitrogen was continuously introduced into the reaction tube to completely remove the air from the furnace tube and the environment around the sample, ensuring that the reaction was always carried out under anaerobic conditions.

[0060] 2) Programmed temperature rise and initial holding: Heat from room temperature to an intermediate buffer temperature of 450°C at a set temperature rise rate (10°C / min); after reaching the buffer temperature, hold for 30 minutes. This process is intended to ensure that the sample is heated evenly and to release some physically adsorbed water and other substances, while maintaining a nitrogen atmosphere.

[0061] 3) Reaching the target temperature and switching the gas: After completing the buffer temperature holding, continue heating under nitrogen protection at the set heating rate to the final target reaction temperature (controlling the reduction temperature at 1100℃); when the system stably reaches this target temperature, immediately switch the gas from nitrogen to a reducing gas with a specific composition and concentration (H2 / N2 mixed gas containing 50% hydrogen by volume, with a gas flow rate of 180mL / min); under the target reaction temperature and reducing gas, continue treatment for a preset holding time (i.e., reduction reaction time of 1 hour).

[0062] 4) Reaction Termination and Gas Protection: After the preset reduction holding time is completed, heating is stopped, and the gas is switched from reducing gas back to nitrogen. This nitrogen gas will be maintained until the sample cools down to the end of the entire process. The purpose is to terminate the reduction reaction and prevent the high-temperature sample from being oxidized by contact with air during the cooling process. Under the continuous protection of nitrogen, the furnace cools naturally until the temperature drops below room temperature, and the reduction product is obtained.

[0063] 5) Crushing and separation: Stop the nitrogen gas supply, take out the reduction product, put it into a ball mill and grind it to 1500 mesh, and then use a magnetic separator to separate the ground product and recover metallic iron.

[0064] The percentage of metallic iron obtained in Examples 1-4 and Comparative Examples 1-2, representing the mass percentage of iron in the copper slag, is shown in Table 1.

[0065] Table 1

[0066] As shown in Table 1, the process of recovering iron from copper slag by hydrogen reduction provided by the present invention significantly improves the recovery rate of metallic iron.

[0067] The XRD patterns of the reduction products obtained from Comparative Example 1 and Comparative Example 2 are shown below. Figure 6 As shown; where Comparative Example 1 corresponds to Figure 6 The "copper slag + CaO + pulverized coal (N2)" in Comparative Example 2 corresponds to Figure 6 The formula is "copper slag + CaO + pulverized coal (N2 + H2)". Figure 6 It is known that using pulverized coal also has a reducing effect; at the same time, under the condition of pulverized coal as a reducing agent, the introduction of H2 helps to eliminate some small impurity peaks, especially the impurity peaks between 50 and 65° of 2θ, which are almost completely eliminated. However, it is inevitable that using pulverized coal as a reducing agent will introduce new impurities, such as carbon. Most importantly, using carbon-based reducing agents will result in high CO2 emissions, which is inconsistent with green environmental protection requirements. Therefore, in comparison, the reduction advantage of using H2 in this invention is not only improved reduction efficiency, but also clean and pollution-free.

[0068] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A process for recovering iron from copper slag by hydrogen reduction, characterized in that, Includes the following steps: S1. Mix copper slag and calcium oxide to obtain a mixture; S2. Under the protection of nitrogen and / or inert gas, the mixture is heated to a buffer temperature and held at that temperature; the buffer temperature is 400-500℃. S3. After the heat preservation is completed, continue to heat to the reduction temperature, and replace the nitrogen and / or inert gas with a reducing gas to carry out the reduction reaction; the reduction temperature is 1000-1150℃; S4. After step S3 is completed, replace the reducing gas with nitrogen and / or an inert gas, cool, and obtain the pre-reduction product; S5. Grind the reduction product and separate it by magnetic separation to obtain metallic iron.

2. The process method according to claim 1, characterized in that, Before performing step S3, the following steps are also included: a) After the mixture in step S2 has been kept at a certain temperature, heat it to the pre-reduction temperature and replace the nitrogen and / or inert gas with a reducing gas to carry out the pre-reduction reaction; the pre-reduction temperature is 900-1000℃. b) After the pre-reduction reaction in step a) is completed, replace the reducing gas with nitrogen and / or an inert gas, cool, and obtain the pre-reduction product; c) After grinding the pre-reduced product, it is heated to the buffer temperature under the protection of nitrogen and / or inert gas, and then kept at that temperature.

3. The process method according to claim 1, characterized in that, The calcium oxide accounts for 10-20% of the mass of the mixture.

4. The process method according to claim 1, characterized in that, The heating rate is 5-10℃ / min.

5. The process method according to claim 1, characterized in that, The heat preservation time in step S2 is 20-40 minutes.

6. The process method according to claim 1, characterized in that, The reduction reaction in step S3 takes 0.25-1 hour.

7. The process method according to claim 1, characterized in that, The reducing gas contains hydrogen, and the volume percentage of hydrogen is 30-60%.

8. The process method according to claim 1, characterized in that, In step S5, the reduction product is ground to 1000-2000 mesh.

9. The process method according to claim 1, characterized in that, The mass percentage of metallic iron in the copper slag is >70wt%.

10. The application of the process method as described in any one of claims 1-9 in the recovery of iron metal from copper slag.

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