A method for separating and recovering iron from iron-rich smelting waste residue by using waste graphite to reduce roasting

Abstract

This invention belongs to the field of metallurgical engineering and solid waste resource utilization technology, specifically relating to a method for separating and recovering iron from iron-rich smelting slag using waste graphite reduction roasting. The method includes the following steps: (1) drying and crushing the iron-containing slag, then adding waste graphite as a reducing agent and mixing evenly to obtain a mixture; (2) roasting the mixture from step (1) at 900~1100℃ under an inert atmosphere to obtain a roasting product; (3) ball milling the roasting product, followed by magnetic separation to obtain a magnetic concentrate enriched with elemental iron. This invention uses waste graphite as a reducing agent and achieves efficient recovery of iron resources from amorphous iron-containing slag through a direct reduction roasting-mechanical ball milling-magnetic separation coupling process. It realizes the synergistic resource utilization of amorphous iron-containing slag and waste graphite.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical engineering and solid waste resource utilization technology, specifically relating to a method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag. Background Technology

[0002] Amorphous iron-containing slag is a high-temperature water-quenched solid waste generated during the pyrometallurgical process of non-ferrous metals. It is characterized by large emissions, high disposal costs, and potential environmental risks. This type of smelting slag typically contains 30%–45% iron resources, possessing the potential for recycling as a secondary iron resource. However, because amorphous iron-containing slag is formed by rapid cooling after high-temperature melting, its phase structure is mainly amorphous glass, with iron elements primarily existing as dendritic iron oxides and dissolved Fe. 2+ The iron exists in the form of silicate minerals and is closely embedded or wrapped around them, resulting in a complex state of iron phase occurrence, making it difficult to achieve effective recovery through conventional physical sorting methods.

[0003] Patent document CN108531740A discloses a process for recovering lead, zinc, carbon, silver, and iron from zinc smelting leaching slag, including high-temperature roasting followed by grinding, combined with flotation and magnetic separation to recover valuable components from the slag. This type of process is highly dependent on the grindability and dissociation of iron phases and gangue in the slag. For amorphous iron-containing waste slag, which is mainly composed of amorphous glass and where iron exists in solid solution or fine-grained dissemination, problems such as high grinding energy consumption, insufficient iron dissociation, and limited concentrate grade and recovery rate often arise. Patent document CN111057858A discloses a method for comprehensively recovering copper, iron, zinc, and lead from copper slag, including steps such as molten alkali leaching and multi-stage alkali leaching. While such methods can improve iron extraction rates in certain systems, they typically involve high reagent consumption, lengthy processes, and the generation of secondary wastewater containing salts or heavy metals, placing a heavy burden on post-treatment. Furthermore, the encapsulation / solution of iron by the amorphous silicate matrix further reduces leaching selectivity and efficiency, limiting their engineering applicability in the recovery of iron resources from amorphous iron-containing waste slag. Patent document CN105618254B ​​discloses a roasting and magnetic separation process, which obtains iron concentrate through roasting followed by wet grinding and multi-step magnetic separation. However, this route uses pulverized coal as a reducing agent and combines it with wet grinding. When processing amorphous iron-containing waste slag, which is mainly composed of glassy silicates, it still suffers from insufficient reduction and transformation of the iron phase and limited dissociation of iron particles from gangue minerals after reduction. Carbothermic reduction / reduction smelting patents achieve deep reduction and enrichment of iron at higher temperatures. For example, patent document CN102658369A discloses a method for directly reducing lead slag with coal to produce metallic iron powder (typical conditions are 1150-1250℃, 45-60min, with multi-stage grinding and wet magnetic separation). Patent document CN104789724A discloses a method for iron extraction by reduction smelting of lead slag, achieving slag-iron separation by adding slag-forming agents and reducing agents in an inert atmosphere. These patents primarily use primary carbonaceous reducing agents such as coal and coke, resulting in significant energy consumption and carbon emission pressure. Furthermore, when processing amorphous iron-containing waste slag, problems may still arise such as the tight bonding between the iron phase and the silicate matrix, and insufficient magnetic separation recovery efficiency due to the encapsulation of reduced iron particles. High-temperature or high-intensity grinding is often required to ensure separation effectiveness.

[0004] On the other hand, with the rapid development of the lithium-ion battery industry, a large amount of waste lithium-ion battery negative electrode graphite is generated. Existing patents focus more on the utilization of waste graphite in electrode material regeneration, conductive materials, or fuels, while patents using waste graphite as a reducing agent for the recovery of smelting slag and iron resources are relatively few. Waste graphite has the characteristics of high fixed carbon content and good reactivity. If it is introduced into the direct reduction process of amorphous iron-containing waste slag and coupled with subsequent ball milling and magnetic separation, it is expected to reduce the consumption of primary carbonaceous reducing agent while improving the metallization degree and recovery efficiency of iron, realizing the synergistic resource utilization of smelting slag and waste graphite. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a method for separating and recovering iron from iron-rich smelting slag using waste graphite reduction roasting. This method uses waste graphite as a reducing agent and employs a coupled process of direct reduction roasting, mechanical ball milling, and magnetic separation to efficiently recover iron resources from amorphous iron-containing waste slag. This achieves the synergistic resource utilization of amorphous iron-containing waste slag and waste graphite.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag includes the following steps:

[0008] (1) The iron-containing waste residue is dried and crushed, and then waste graphite is added as a reducing agent and mixed evenly to obtain a mixture;

[0009] (2) The mixture from step (1) is heated to 900~1100℃ under an inert atmosphere to obtain the calcined product;

[0010] (3) The roasted product is ball-milled and then magnetically separated to obtain a magnetic concentrate enriched with elemental iron.

[0011] Furthermore, the iron-containing waste slag mentioned in step (1) is an amorphous iron-containing waste slag generated during the pyrometallurgical process of non-ferrous metals.

[0012] Further, the crushing process described in step (1) is carried out until the particle size of the iron-containing waste slag is ≤200μm.

[0013] Furthermore, the waste graphite mentioned in step (1) originates from waste lithium-ion battery anode materials, with a fixed carbon content ≥95% and a particle size preferably below 200 μm. Finer-grained waste graphite facilitates thorough mixing and contact with iron-containing waste slag, thereby improving the reduction reaction efficiency. This invention uses waste graphite as a high-fixed-carbon-content reducing agent, which, compared to conventional primary carbonaceous reducing agents such as coal powder and coke, is more conducive to the conversion of complex iron phases in amorphous iron-containing waste slag into elemental iron. It also better promotes the relaxation and reconstruction of the glassy silicate structure, creating favorable conditions for subsequent ball milling dissociation of the iron phase, thereby improving the magnetic separation effect.

[0014] More preferably, the amount of waste graphite added is 10% to 40% of the mass of iron-containing waste slag.

[0015] Furthermore, the inert atmosphere mentioned in step (2) is a nitrogen atmosphere or an argon atmosphere. The calcination treatment under an inert atmosphere prevents secondary oxidation of elemental iron at high temperatures.

[0016] Furthermore, the heating rate in step (2) is 5~15℃ / min, and the holding time of the calcination treatment is 30~180 min.

[0017] The iron oxides and silicate-bound iron in the amorphous iron-containing waste residue are reduced by roasting to produce elemental iron, thus obtaining the roasted product.

[0018] Furthermore, the grinding media for the ball milling process in step (3) is zirconia balls or corundum balls, with a ball-to-material ratio of 5:1 to 15:1.

[0019] More preferably, the ball milling process in step (3) is dry ball milling, with a ball milling speed of 200~500 rpm and a ball milling time of 10~60 min.

[0020] By ball milling to disrupt the structure of silicate minerals, effective liberation of elemental iron from gangue minerals is achieved. Compared to conventional wet grinding, this invention uses dry ball milling, which eliminates the need for a liquid medium. This avoids the dispersion and loss of fine-grained elemental iron in the slurry from the roasted product and reduces the adverse effects of iron particle surface oxidation or mud formation in a liquid environment on subsequent magnetic separation. Furthermore, dry ball milling is more effective in applying direct mechanical impact and shearing to the roasted and reduced product, promoting effective liberation between elemental iron particles and silicate gangue minerals, thereby improving the iron grade and iron recovery rate of the magnetic concentrate.

[0021] Furthermore, the magnetic field strength for magnetic separation in step (3) is 0.2~0.5 T.

[0022] The principle of this invention is as follows:

[0023] During the high-temperature melting and rapid cooling process, amorphous iron-containing waste slag forms an amorphous structure dominated by glassy silicates. Iron elements are highly dispersed and encapsulated in the matrix as fine iron oxide grains, spinel or olivine minerals, and dissolved silicates, making it difficult to effectively dissociate the iron phase using conventional physical methods. This invention introduces waste graphite as a reducing agent to directly reduce and roast the amorphous iron-containing waste slag under an inert atmosphere. This causes the iron oxides and dissolved iron dispersed in the glassy matrix to undergo a reduction reaction at high temperatures, transforming them into elemental iron particles or iron phase aggregates with significant magnetic properties. This thermodynamically and kinetically weakens the bond strength between the iron phase and the silicate matrix. During the reduction roasting process, the fixed carbon in the waste graphite reacts with the iron oxides to generate elemental iron, while simultaneously promoting the relaxation and reconstruction of the glassy silicate structure, creating favorable conditions for subsequent dissociation of the iron phase. Subsequently, mechanical ball milling applies shear and impact forces to the roasted product, further disrupting the silicate matrix structure and allowing the reduced elemental iron particles to fully dissociate from the gangue minerals. Ultimately, by utilizing the significant magnetic differences between elemental iron and gangue minerals, efficient enrichment and recovery of iron resources can be achieved through magnetic separation.

[0024] Compared to existing reduction roasting processes that use primary carbonaceous reducing agents such as coal and coke, along with wet grinding, this invention uses waste graphite as a reducing agent and combines it with a dry ball milling-magnetic separation process to treat amorphous iron-containing waste slag, which is mainly composed of glassy silicates. The difference in effectiveness mainly stems from the difference in the type of reducing agent and the subsequent grinding and separation methods. On the one hand, waste graphite has a higher fixed carbon content, allowing for more thorough contact with the iron-containing waste slag, which is more conducive to the conversion of complex iron phases into elemental iron and can better promote the relaxation and reconstruction of the glassy silicate structure. On the other hand, dry ball milling is more effective in applying mechanical impact and shearing to the roasting and reduction products of this invention, promoting the dissociation of elemental iron particles from the silicate matrix, while avoiding the dispersion and loss of fine iron particles in the slurry or surface oxidation during wet grinding, thereby improving the subsequent magnetic separation effect.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] (1) Using waste graphite as a highly active reducing agent can achieve deep reduction of complex iron phases in amorphous iron-containing waste slag to elemental iron, thereby improving the metallization degree of iron. Moreover, compared with other reducing agents, it can better promote the relaxation and reconstruction of glassy silicate structures, creating favorable conditions for the subsequent dissociation of iron phases.

[0027] (2) By using direct reduction roasting and ball milling-magnetic separation coupled processes, the problem of the iron phase and silicate minerals being tightly embedded and difficult to separate is effectively solved, and the iron recovery rate and concentrate grade are significantly improved.

[0028] (3) This invention realizes the synergistic resource utilization of amorphous iron-containing waste slag and waste graphite. The process is relatively simple, the environmental impact is low, and it has good industrial application prospects. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0030] Example 1

[0031] 5.0 g of dried, water-quenched lead-zinc smelting slag was weighed and crushed to a particle size ≤200 μm. The main chemical components of the lead-zinc smelting slag, by mass percentage, included: TFe 33.42%, Si 11.36%, Ca 8.51%, Al 2.93%, Mg 3.27%, with the remainder being Pb, Zn, and other trace components. XRD analysis showed that the slag exhibited obvious diffuse peaks in the 2θ range of 20°–40°, indicating that it was predominantly a glassy phase, while also containing small amounts of FeO and Fe3O4 crystalline phases. The slag was thoroughly mixed with 2.0 g of waste graphite (fixed carbon content ≥95%, particle size ≤200 μm) derived from waste lithium-ion battery anode materials and placed in a corundum crucible. The mixture was heated to 1000°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and held for 150 min. After calcination, the mixture was cooled to room temperature to obtain the calcined product. The calcined product was ball-milled in a planetary ball mill (the grinding media was zirconia balls, and the ball-to-material ratio was 10:1) at 300 rpm for 30 min, and then magnetically separated under a magnetic field strength of 0.3 T to obtain magnetic concentrate.

[0032] The obtained magnetic concentrate had a total iron content of 73.84% and an iron recovery rate of 80.26%. XRD results showed that the diffraction peaks of metallic iron in the obtained magnetic concentrate were significantly enhanced, while the peaks of silicate-related impurities were significantly weakened. This indicates that the waste graphite reduction roasting combined with dry ball milling-magnetic separation process can effectively promote the transformation of complex iron phases in amorphous iron-containing waste slag into elemental iron and improve the dissociation effect between it and gangue minerals, thereby achieving effective enrichment and recovery of iron resources.

[0033] Example 2

[0034] 5.0 g of dried lead smelting water-quenched slag was crushed to a particle size ≤200 μm and thoroughly mixed with 1.0 g of waste graphite derived from waste lithium-ion battery anode material. The mixture was then placed in a corundum crucible and heated to 950 °C at a heating rate of 10 °C / min under an argon protective atmosphere, and held for 120 min. After calcination, the mixture was allowed to cool naturally to room temperature to obtain the calcined product. The calcined product was then dry-milled in a planetary ball mill (grinding media: zirconia balls, ball-to-material ratio: 15:1) at 400 rpm for 60 min, followed by magnetic separation under a magnetic field strength of 0.25 T to obtain a magnetic concentrate.

[0035] The obtained magnetic concentrate had a total iron content of 71.84% and an iron recovery rate of 76.92%. The iron in the magnetic concentrate mainly existed in the form of elemental iron. The results indicate that even under low roasting temperatures and low amounts of waste graphite, waste graphite can still promote the conversion of complex iron phases in lead smelting water-quenched slag into elemental iron. Subsequent dry ball milling further enhanced the dissociation of the iron phase from gangue minerals, thus achieving effective enrichment and recovery of iron resources.

[0036] Example 3

[0037] 5.0 g of dried water-quenched lead-zinc smelting slag was crushed to a particle size ≤200 μm and thoroughly mixed with 0.5 g of waste graphite derived from waste lithium-ion battery anode material. The mixture was then placed in a corundum crucible and heated to 1100 °C at a heating rate of 10 °C / min under a nitrogen atmosphere and held for 180 min. After calcination, the mixture was cooled to room temperature to obtain the calcined product. The calcined product was then dry-milled in a planetary ball mill (grinding media: zirconia balls, ball-to-material ratio: 5:1) at 300 rpm for 50 min, followed by magnetic separation under a magnetic field strength of 0.3 T to obtain a magnetic concentrate.

[0038] The obtained magnetic concentrate had a total iron content of 69.48% and an iron recovery rate of 73.26%. The iron in the obtained magnetic concentrate mainly exists in the form of elemental iron. The results show that even with a low amount of waste graphite added, by increasing the roasting temperature, extending the holding time, and combining it with subsequent dry ball milling-magnetic separation, it is still possible to effectively enrich and recover iron resources from water-quenched lead-zinc smelting slag.

[0039] Comparative Example 1

[0040] Compared with Example 1, this comparative example uses an equal amount of coal powder to replace waste graphite, but the rest is the same.

[0041] The obtained magnetic concentrate had a total iron content of 68.27% and an iron recovery rate of 74.85%. Compared with Example 1, when pulverized coal was used as a reducing agent, both the total iron content and iron recovery rate of the obtained magnetic concentrate decreased. This indicates that under the conditions of this invention, waste graphite, as a reducing agent with high fixed carbon content, is more conducive to the conversion of complex iron phases in amorphous iron-containing waste slag into elemental iron, and improves the subsequent ball milling and magnetic separation effects. The reason may be that the higher fixed carbon content of waste graphite allows for more thorough mixing and contact with iron-containing waste slag, which is more conducive to maintaining a local reducing atmosphere and promoting the reduction of iron phases during roasting. At the same time, waste graphite as a reducing agent can better promote the relaxation and reconstruction of the glassy silicate structure, creating favorable conditions for the subsequent ball milling and separation of the iron phase.

[0042] Comparative Example 2

[0043] Compared with Example 1, this comparative example uses an equal amount of coke to replace waste graphite, but the rest are the same.

[0044] The obtained magnetic concentrate had a total iron content of 66.94% and an iron recovery rate of 73.12%. Compared with Example 1, when coke was used as a reducing agent, the total iron content and iron recovery rate of the obtained magnetic concentrate both decreased significantly. This indicates that waste graphite, under the process conditions of this invention, is more conducive to promoting the conversion of complex iron phases in amorphous iron-containing waste slag into elemental iron, and improves the subsequent ball milling and magnetic separation effects. The reason may be that waste graphite has a higher fixed carbon content and finer particle size, resulting in more uniform mixing and more thorough contact with iron-containing waste slag, which is more conducive to the reduction reaction during roasting. At the same time, waste graphite as a reducing agent can better promote the relaxation and reconstruction of the glassy silicate structure, creating favorable conditions for the subsequent ball milling and separation of the iron phase.

[0045] Comparative Example 3

[0046] Compared with Example 1, this comparative example uses wet grinding instead of ball milling, but the rest are the same.

[0047] The obtained magnetic concentrate had a total iron content of 69.72% and an iron recovery rate of 76.48%. Compared with Example 1, the total iron content and iron recovery rate of the obtained magnetic concentrate decreased when wet grinding was used. This indicates that under the process conditions of this invention, dry ball milling is more conducive to the effective dissociation of the iron phase from gangue minerals in the roasted product and helps to maintain the separation and recovery effect of the reduced elemental iron particles. The reason may be that after the introduction of liquid medium during wet grinding, fine iron particles are easily dispersed and lost in the slurry, and the liquid environment may weaken the selective separation effect between the reduced iron particles and gangue minerals; in contrast, dry ball milling can more directly apply mechanical impact and shearing to the roasted and reduced product of this invention, which is more conducive to the dissociation of elemental iron particles from the silicate matrix, thereby improving the subsequent magnetic separation effect.

[0048] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag, characterized in that... Includes the following steps: (1) The iron-containing waste residue is dried and crushed, and then waste graphite is added as a reducing agent and mixed evenly to obtain a mixture; (2) The mixture from step (1) is heated to 900~1100℃ under an inert atmosphere to obtain the calcined product; (3) The roasted product is ball-milled and then magnetically separated to obtain a magnetic concentrate enriched with elemental iron.

2. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The iron-containing waste slag mentioned in step (1) is an amorphous iron-containing waste slag generated during the pyrometallurgical process of non-ferrous metals.

3. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The crushing process described in step (1) is carried out until the particle size of the iron-containing waste slag is ≤200μm.

4. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The waste graphite mentioned in step (1) comes from waste lithium-ion battery anode materials, with a fixed carbon content of ≥95% and a particle size of ≤200μm.

5. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 4, characterized in that: The amount of waste graphite added is 10% to 40% of the mass of iron-containing waste slag.

6. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The inert atmosphere mentioned in step (2) is a nitrogen atmosphere or an argon atmosphere.

7. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The heating rate in step (2) is 5~15℃ / min, and the holding time of the calcination treatment is 30~180min.

8. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The grinding media for the ball milling process in step (3) are zirconia balls or corundum balls, with a ball-to-material ratio of 5:1 to 15:

1.

9. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 8, characterized in that: The ball milling process is a dry ball milling process, with a milling speed of 200~500 rpm and a milling time of 10~60 min.

10. The method for separating and recovering iron from waste graphite reduction roasting iron-rich smelting slag according to claim 1, characterized in that: The magnetic field strength for magnetic separation in step (3) is 0.2~0.5 T.