Method for gradient separation and recovery of metal components based on microwave hydrocarbon coupling reduction of ferrous metallurgy dust

Abstract

The invention discloses a method for gradient separation and recovery of metal components based on microwave hydrocarbon coupling reduction of ferrous metallurgy dust, and belongs to the field of secondary resource recycling, and the method specifically comprises the following steps: mixing and pressing ferrous metallurgy dust and biochar to obtain a block mass, putting the block mass in a microwave oven for reduction roasting, and drying to obtain the metal components. Volatile components generated in the reduction roasting process are condensed and recycled to obtain lead and zinc, and metallized blocks obtained after reduction roasting are subjected to magnetic separation to obtain reduced iron powder and magnetic separation tailings; the ferrous metallurgy dust is treated by synergistically utilizing clean microwave energy, carbon-neutral biochar and biomass gas resources, metal components are recycled in a cascade separation mode, and a feasible technical scheme is provided for clean, low-carbon and efficient all-component resource utilization of the ferrous metallurgy dust; the method is simple in process flow and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of recycling harmful secondary resources, and in particular to a method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction. Background Technology

[0002] Steel is an essential functional material, and no other material is expected to replace its application in the foreseeable future. Steel is widely used not only in critical sectors such as national defense, aerospace, and urban construction, but is also ubiquitous in daily life. In the steel production process, in addition to producing steel and ferroalloy products, a large amount of waste gas, slag, and dust are generated as byproducts. Dust, in particular, is characterized by its fine particle size and heavy metal content, posing potential hazards to the environment and human health. Furthermore, steel metallurgical dust is diverse, including electric furnace dust, blast furnace dust, converter dust, and sintering dust. Electric furnace dust, due to its content of heavy metals such as lead, zinc, and manganese, is currently classified as hazardous waste. Electric furnace dust is generated during the decarburization reaction in electric arc furnace steelmaking, causing CO bubbles on the surface of the molten pool to burst, resulting in slag splashing. Statistics show that an electric arc furnace produces approximately 15-20 kg of dust for every ton of crude steel produced. Currently, over 30% of global steel production comes from electric arc furnaces, and in some developed countries, this proportion exceeds 80%. This means that the global annual production of electric furnace dust will reach as high as 8.48 million to 11.31 million tons.

[0003] The main chemical components of electric arc furnace (EAF) dust include metallic elements such as Fe, Zn, Pb, and Mn, with the main phases being zinc ferrite (ZnFe2O4), zinc oxide (ZnO), and magnetite (Fe3O4). Generally, based on the Zn content, dust can be classified into low-zinc dust (<4 wt%), medium-zinc dust (4-20 wt%), and high-zinc dust (>20 wt%). This characteristic is mainly influenced by the proportion of scrap steel used in EAF steelmaking; dust with higher scrap steel usage has a relatively higher zinc content. Due to the scarcity of scrap steel in China, direct reduced iron is the primary raw material for EAF steelmaking, resulting in EAF dust being high in iron and low in zinc, with an iron content typically between 40 and 50 wt%. Given my country's current situation of iron ore shortage and long-term reliance on imports, EAF dust is undoubtedly an important iron-containing secondary resource. Furthermore, the fine particle size of EAF slag (>90% of particles less than 100 μm) poses a significant air pollution risk when stored in the open. Traditional landfill disposal not only wastes resources but also causes soil pollution. Therefore, as a valuable secondary resource, electric furnace dust urgently needs appropriate treatment measures.

[0004] Currently, pyrometallurgical and hydrometallurgical processes are the two main methods for the resource recovery of electric furnace dust. Hydrometallurgical processes mainly include acid leaching, alkaline leaching, and ammonia leaching. The principle is to use various leaching solutions to dissolve elements such as Zn and Fe from the dust. After separating the leaching solution, the cathode deposit is melted through electrode reactions to ultimately obtain the corresponding metal product, primarily zinc. However, hydrometallurgical processes generally suffer from low efficiency, large slag production, and the inability to effectively utilize iron in the dust, thus limiting their large-scale application. In contrast, pyrometallurgical processes have the advantages of large processing capacity and can fully utilize the low boiling points and high volatility of lead and zinc to separate them from electric furnace dust, thereby achieving the separation and recovery of iron, lead, and zinc. Among all pyrometallurgical processes, reduction roasting is widely used due to its simple operation and high efficiency. Typical processes include the Wiltz rotary kiln method, the rotary hearth furnace (RHF) method, and the PRIMUS method. However, existing processes still have significant drawbacks. For example, they consume large quantities of non-renewable energy sources such as coke and coal, and generate substantial amounts of carbon dioxide during production, contradicting the principles of green and sustainable development. Using hydrogen as a reducing agent promises to solve the inherent emission problems of carbonaceous reducing agents, but the unique endothermic nature of the hydrogen reduction reaction imposes more stringent thermodynamic requirements on the reduction process. Furthermore, the high cost of hydrogen poses a significant challenge to its industrial application, resulting in an electric furnace dust resource recovery rate of less than 30%. Therefore, innovating energy structures and processing methods has become a key strategy for improving the utilization rate of electric furnace dust resources.

[0005] In fact, not only electric furnace dust, but other types of steel metallurgical dust also face similar challenges in resource utilization. Patents CN110004291A, CN114686689B, and CN101457269B disclose a series of technologies for the resource recovery and utilization of steel metallurgical dust. However, these technologies still suffer from drawbacks such as complex processes, high energy consumption, high carbon dioxide emissions, and low metal element recovery efficiency. These processes have not simultaneously brought about changes in energy structure and processing methods. Therefore, developing low-carbon and efficient steel metallurgical dust resource utilization technologies is crucial for improving resource recovery efficiency. Summary of the Invention

[0006] To address the common challenges in the resource utilization of iron and steel metallurgical dust, such as low energy efficiency, high pollutant emissions, complex processing procedures, and low metal element recovery efficiency, this invention aims to provide a method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction. The method involves thoroughly mixing dried iron and steel metallurgical dust with biochar and pressing it into uniform lumps. These lumps are then placed in a microwave tube furnace. Under conditions of microwave radiation, biochar-biomass gas coupling, and controlled reduction temperature, the dust undergoes graded reduction, promoting the separation of volatile components such as Zn and Pb, which are then recovered through condensation. The reduced lumps are then crushed and subjected to grinding and magnetic separation to obtain high-purity direct reduced iron powder and magnetic separation tailings. After further separation, the volatile components containing lead, zinc, etc., can be used for the preparation of related materials. Directly reduced iron powder can be used for electric arc furnace steelmaking, and magnetic separation tailings can be used as raw materials for the production of building materials such as cement. This invention treats iron and steel metallurgical dust by synergistically utilizing clean microwave energy, carbon-neutral biochar, and biomass gas resources. It achieves the recovery and utilization of metal components through a cascade separation method, providing a practical and feasible technical solution for the clean, low-carbon, and efficient utilization of all components of iron and steel metallurgical dust. The process is simple and has good prospects for industrial application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction. Iron and steel metallurgical dust and biochar are mixed, pressed to obtain lumps, and the lumps are placed in a microwave oven for reduction roasting. The volatile components generated during the reduction roasting process are condensed and recovered to obtain lead and zinc. The metallized lumps obtained after reduction roasting are separated by magnetic separation to obtain reduced iron powder and magnetic separation tailings.

[0009] The reduction roasting process is as follows: first, the temperature is raised to 950~1200 ℃, preferably 1000~1100 ℃, under a protective atmosphere; then, the protective atmosphere is switched to biomass gas; after holding at the temperature, the biomass gas is switched back to the protective atmosphere and cooled to room temperature.

[0010] The biomass gas, by volume percentage, has the following composition: H2 35~65 vol%, CO 10~45 vol%, CO2 10~45 vol%.

[0011] The solution provided by this invention involves introducing biomass gas to deeply reduce the agglomerates during microwave-assisted roasting of agglomerates obtained by mixing iron and steel metallurgical dust and biochar. This process enhances the removal of Zn and Pb and promotes the growth of iron particles, facilitating subsequent separation and recovery. Experiments have shown that under the deep reduction effect of biomass gas, the size of metallic iron particles in the agglomerates increases significantly, making them easier to separate from gangue impurities during subsequent grinding. Therefore, both the magnetic separation recovery rate and the product grade are improved.

[0012] However, to achieve good performance, a protective atmosphere must be used during both the heating and cooling processes. Biomass gas can only be introduced during the sintering and heat preservation process. If biomass gas is introduced directly during the heating process, the outer layer of the agglomerates will be metallized first, forming a metallic iron layer. This prevents the reducing gas from effectively penetrating into the agglomerates. At the same time, the gas produced by the decomposition of biochar inside the agglomerates cannot volatilize in time. The large pressure difference between the inside and outside of the agglomerates will cause them to crack. In actual production, this phenomenon will lead to ring formation, affecting the normal operation of the process. Using biomass gas during the cooling process will result in energy waste and will not significantly improve the agglomerate reduction effect.

[0013] In addition, during the experimental exploration, the inventors also tried many other types of gases, such as converter gas and blast furnace gas, which all reduced the reduction effect. This is because the ratio of H2 to CO in them is different from that in biomass gas. H2 reduction is an endothermic reaction at the thermodynamic level, while CO reduction is an exothermic reaction. A reasonable ratio of the two can make up for the heat difference between the reactions and improve the reduction efficiency. If the H2 content in the biomass gas is too high, although it can improve the reduction effect of the agglomerates to a certain extent, the utilization rate of H2 will be reduced, resulting in unnecessary energy waste. CO2 is a substance that is inevitably produced in the process of biomass pyrolysis to produce biomass gas. Its presence has little impact on the reduction. Its main role is to dilute the gas concentration. However, too high a CO2 concentration will also lead to a decrease in the reduction effect. The composition of the biomass gas selected in this invention is similar to the gas composition of the current Midrex process. It has a high overall energy utilization efficiency and biomass energy is easy to obtain.

[0014] In a preferred embodiment, both the steel metallurgical dust and the biochar have a particle size of less than 0.074 mm.

[0015] In a preferred embodiment, the biochar content in the agglomerates is 5-25 wt%, preferably 12-18 wt%.

[0016] In a preferred embodiment, the protective atmosphere is nitrogen.

[0017] In a preferred embodiment, the heating rate is 10~50 ℃ / min, more preferably 25~45 ℃ / min.

[0018] The highest recovery rate is achieved by controlling the heating rate within the above range.

[0019] After heating, the temperature reaches the holding temperature for reduction roasting, which must be higher than the boiling point temperature of the volatile components (lead, zinc, etc.).

[0020] In a preferred embodiment, the heat preservation time is 5 to 30 minutes, and more preferably 10 to 20 minutes.

[0021] In the preferred embodiment, during the heating and cooling processes of reduction roasting, the flow rate of the protective atmosphere introduced per gram of ag of ag is 1.0~2.0 L / min.

[0022] In the preferred embodiment, during the heat preservation process of reduction roasting, the flow rate of biomass gas introduced per gram of pellet is 0.6~1.2 g / L. Controlling the flow rate of the protective atmosphere within this range yields the highest reduction efficiency.

[0023] In this invention, the volatile components generated during the reduction process are recovered through conventional condensation.

[0024] In a preferred embodiment, the metallized agglomerates are crushed to below 0.1 mm, then wet-milled for 5–25 min, preferably 10–20 min, to obtain a slurry with a mass concentration of 40–60%, which is then subjected to magnetic separation. Experiments have shown that magnetic separation is most effective when using slurry of the above concentration.

[0025] In a preferred embodiment, the magnetic field strength for magnetic separation is 500~1000 Gs, preferably 700~900 Gs.

[0026] Principles and advantages

[0027] This invention innovatively combines clean energy sources such as microwaves, biochar, and biomass gas. By controlling key parameters such as the amount of biochar added, reduction temperature, and gas composition, it achieves the tiered separation and recovery of important metal components in steelmaking dust. Utilizing the strong microwave absorption properties of iron and other metal elements in the dust, as well as biochar, the agglomerates can rapidly heat up in a microwave field, with a heating rate significantly superior to traditional heating. Furthermore, the overall heating effect of microwaves and the "lens effect" enhance the dust reduction efficiency. In addition, the combined use of biochar and biomass gas not only avoids carbon dioxide emissions but also improves the reduction process of the agglomerates, strengthening the dust reduction effect. The final separated product can be used in electric arc furnace steelmaking and the preparation of functional materials, realizing the value-added utilization of steelmaking dust.

[0028] In this invention, typical electric furnace dust was used as the object of verification. The iron metallization rate in the reduced agglomerates was as high as 97.18%, and the zinc volatilization rate reached 99.60%. After grinding and magnetic separation, the total iron grade of the magnetically separated concentrate was 89.84 wt%, the iron metallization rate was 94.47%, and the iron recovery rate was 90.06%, which is significantly better than the results reported by other methods.

[0029] Therefore, this invention has the advantages of short process flow, high processing efficiency, low cost and high metal component recovery rate; the obtained direct reduced iron powder is of excellent quality and can be directly used as raw material for electric arc furnace steelmaking. Attached Figure Description

[0030] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Figure 1 Microscopic morphology and phase analysis of volatiles recovered through condensation separation.

[0032] Figure 2 Microstructure and phase analysis of directly reduced iron powder obtained by grinding and magnetic separation. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To avoid repetition, the raw materials involved in this specific embodiment are described uniformly as follows, and will not be repeated in the specific embodiments:

[0035] In this invention, the main chemical composition of the electric furnace dust is as follows: total iron content (TFe) of 43.94 wt%, FeO content of 3.80 wt%, Zn content of 6.05 wt%, Pb content of 0.10 wt%, CaO content of 9.09 wt%, SiO2 content of 4.94 wt%, MnO content of 2.71 wt%, and MgO content of 2.54 wt%.

[0036] In this invention, the biochar used has a fixed carbon content of 80.80 wt% and an ash content of 5.65 wt%.

[0037] In the following cases, unless otherwise stated, the ratio of dust to biochar is by weight.

[0038] Example 1

[0039] The dried electric furnace dust and biochar were mixed in a ratio of 20:3 and pressed into lumps. After drying, the lumps were placed in a microwave oven and heated to 1050 °C at a rate of 40 °C / min in a nitrogen atmosphere (flow rate: 1.75 L / min per gram of lumps). The nitrogen atmosphere was then switched to biomass gas (50 vol% H2 + 25 vol% CO + 25 vol% CO2, flow rate: 1 L / min per gram of lumps). After 15 min, the atmosphere was switched back to nitrogen (flow rate: 1.75 L / min per gram of lumps) and cooled to room temperature to obtain metallized lumps. The lead and zinc volatiles were collected.

[0040] The metallized agglomerates obtained from the reduction were then crushed to less than 0.1 mm and placed in a conventional ball mill for 15 minutes. The slurry concentration was set to 50%. After the ball milling was completed, the agglomerates were separated in a conventional magnetic separator with a magnetic field strength of 800 Gs. Finally, direct reduced iron powder and magnetic separation tailings were obtained by filtration.

[0041] In this embodiment, the total iron content of the agglomerates obtained after reduction is 63.37 wt%, the iron metallization rate is 97.18%, the zinc volatility rate is 99.60%, and the lead volatility rate is 84.94%. After grinding and magnetic separation, the total iron content of the direct reduced iron powder is 89.84%, the metallization rate is 94.47%, and the iron recovery rate is 90.06%.

[0042] Example 2

[0043] The only difference from Example 1 is that the ratio of electric furnace dust to biochar is 5:1.

[0044] In this comparative example, the total iron content of the agglomerates obtained after reduction was 56.59 wt%, the iron metallization rate was 96.90%, the zinc volatility rate was 99.74%, and the lead volatility rate was 85.50%.

[0045] Comparative Example 1

[0046] Compared with Example 1, the only difference is that the reduction is carried out under conventional heating conditions, and the heating rate is 10 °C / min due to the influence of the equipment.

[0047] In this comparative example, the total iron content of the agglomerates obtained after reduction was 54.61 wt%, the iron metallization rate was 96.65%, the zinc volatility rate was 99.12%, and the lead volatility rate was 82.43%. After grinding and magnetic separation, the total iron content of the direct reduced iron powder obtained was 86.38 wt%, the metallization rate was 93.17%, and the iron recovery rate was 87.27%.

[0048] Comparative Example 2

[0049] Compared with Example 1, the only difference is that the ratio of electric furnace dust to biochar is 10:1.

[0050] In this comparative example, the total iron content of the agglomerates obtained after reduction was 49.94 wt%, the iron metallization rate was 86.22%, the zinc volatility rate was 92.76%, and the lead volatility rate was 82.93%.

[0051] Comparative Example 3

[0052] Compared with Example 1, the only difference is that the ratio of electric furnace dust to biochar is 5:2.

[0053] In this comparative example, the total iron content of the agglomerates obtained after reduction was 50.64 wt%, the iron metallization rate was 83.67%, the zinc volatility rate was 98.01%, and the lead volatility rate was 80.29%.

[0054] Comparative Example 4

[0055] Compared with Example 1, the only difference is that the reduction temperature is 1150 °C.

[0056] In this comparative example, the total iron content of the agglomerates obtained after reduction was 51.64 wt%, the iron metallization rate was 85.43%, the zinc volatility rate was 79.03%, and the lead volatility rate was 77.07%.

[0057] Comparative Example 5

[0058] Compared with Example 1, the only difference is that the atmosphere used for reduction is oxygen blast furnace gas (H2: 20~25 vol%, CO: 48~52 vol%, CO2: 20~25 vol%, N2: 2~5 vol%).

[0059] In this comparative example, the total iron content of the agglomerates obtained after reduction was 61.32 wt%, the iron metallization rate was 95.86%, the zinc volatility rate was 99.05%, and the lead volatility rate was 82.62%.

[0060] Comparative Example 6

[0061] Compared with Example 1, the only difference is that the atmosphere used for reduction is converter gas (H2: 1~3 vol%, CO: 60~70 vol%, CO2: 15~18 vol%, N2: 15~18 vol%).

[0062] In this comparative example, the total iron content of the agglomerates obtained after reduction was 60.80 wt%, the iron metallization rate was 95.59%, the zinc volatility rate was 99.04%, and the lead volatility rate was 82.61%.

[0063] Comparative Example 7

[0064] Compared with Example 1, the only difference is that no biomass gas is introduced during the reduction process, and all stages are completed under an N2 atmosphere.

[0065] In this comparative example, the total iron content of the agglomerates obtained after reduction was 58.95 wt%, the iron metallization rate was 95.17%, the zinc volatility rate was 86.23%, and the lead volatility rate was 30.74%.

[0066] Comparative Example 8

[0067] Compared with Example 1, the only difference is that the biomass gas flow rate used per gram of pellet during the heat preservation process is 0.4 L / min.

[0068] In this comparative example, the total iron content of the agglomerates obtained after reduction was 61.94 wt%, the iron metallization rate was 92.78%, the zinc volatility rate was 98.93%, and the lead volatility rate was 79.75%.

[0069] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

[0070] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation schemes that can be understood by those skilled in the art.

Claims

1. A method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction, characterized in that: Iron and steel metallurgical dust and biochar are mixed, pressed to obtain lumps, and the lumps are placed in a microwave oven for reduction roasting. The volatile components generated during the reduction roasting process are condensed and recovered to obtain lead and zinc. The metallized lumps obtained after reduction roasting are separated by magnetic separation to obtain reduced iron powder and magnetic separation tailings. The reduction roasting process is as follows: first, the temperature is raised to 950~1200 ℃, preferably 1000~1100 ℃, under a protective atmosphere; then, the protective atmosphere is switched to biomass gas; after holding at the temperature, the biomass gas is switched back to the protective atmosphere and cooled to room temperature. The biomass gas, by volume percentage, has the following composition: H2 35~65 vol%, CO 10~45 vol%, CO2 10~45 vol%.

2. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The particle size of both the iron and steel metallurgical dust and the biochar is less than 0.074 mm.

3. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The biochar in the agglomerates has a mass fraction of 5-25 wt%, preferably 12-18 wt%.

4. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The protective atmosphere is nitrogen.

5. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The heating rate is 10~50 ℃ / min, preferably 25~45 ℃ / min.

6. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The heat preservation time is 5 to 30 minutes, preferably 10 to 20 minutes.

7. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: During the heating and cooling processes of reduction roasting, the flow rate of the protective atmosphere introduced per gram of pellet is 1.0~2.0 L / min.

8. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: During the heat preservation process of reduction roasting, the flow rate of biomass gas introduced per gram of pellet is 0.6~1.2 g / L.

9. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The metallized lumps are crushed to below 0.1 mm, then wet ball milled for 5-25 minutes to obtain a slurry with a mass concentration of 40-60%, which is then separated by magnetic separation.

10. The method for the graded separation and recovery of metal components from iron and steel metallurgical dust based on microwave carbon-hydrogen coupling reduction according to claim 1, characterized in that: The magnetic field strength for magnetic separation is 500~1000 Gs, preferably 700~900 Gs.

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