Method for recovering iron from iron-rich waste residue by alkali synergistic reduction roasting-water leaching-magnetic separation

Abstract

This invention belongs to the field of metallurgical engineering and solid waste resource utilization technology, specifically involving a method for recovering iron from iron-rich waste slag through alkali-co-reduction roasting-water leaching-magnetic separation. The method includes the following steps: (1) drying and crushing the iron-containing waste slag, then adding solid alkali and reducing agent and mixing evenly to obtain a mixture; (2) roasting the mixture at 900~1100℃ under an inert atmosphere, cooling the roasted product to room temperature and then leaching it with water, filtering, washing, and drying to obtain a desiliconized solid residue; (3) magnetically separating the desiliconized solid residue to obtain a magnetic concentrate enriched with iron resources. The method of this invention introduces solid alkali during the reduction roasting process, and achieves efficient recovery of iron resources through a combination of water leaching desiliconization and magnetic separation. It overcomes the problems of stable silicate matrix and difficult iron phase dissociation in the existing technology of amorphous iron-containing waste slag.

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 recovering iron from iron-rich waste slag through alkali-co-reduction roasting-water leaching-magnetic separation. Background Technology

[0002] Amorphous iron-containing waste slag is widely derived from the high-temperature melting-quenching process in non-ferrous metal pyrometallurgical processes, such as smelting slag for lead, zinc, copper, and nickel. This type of waste slag typically has a glassy silicate structure as its main component, with iron elements highly dispersed in the form of iron oxide microcrystals, spinel-type or olivine-type minerals, and silicate solid solutions, all encapsulated by an amorphous matrix. This results in a tight bond between the iron phase and gangue minerals, making efficient dissociation and recovery difficult.

[0003] Patent document CN105618254B ​​discloses a method for treating iron-containing waste slag by roasting and magnetic separation, which involves refining the slag through wet grinding followed by multi-stage magnetic separation to recover iron concentrate. However, this method has limited damage to the amorphous silicate matrix, often requires high-intensity grinding, consumes a lot of energy, and results in insufficient iron dissociation. Patent document CN111057858A discloses a method for comprehensively recovering multiple metals from smelting slag through molten alkali leaching. Although this method can achieve the transfer of iron to the liquid phase, the process is complex, consumes a large amount of reagents, and easily generates waste liquid containing salt or heavy metals, increasing the environmental burden. Patent document CN102658369A discloses a method for producing iron powder by direct reduction of lead slag and coal, which involves obtaining elemental iron through high-temperature carbothermic reduction followed by magnetic separation. However, when treating amorphous iron-containing waste slag, this method still retains a large amount of silicate glass matrix, and iron particles are easily encapsulated by gangue, affecting the subsequent magnetic separation effect.

[0004] In addition, existing patents rarely combine the "solid alkali activation of amorphous silicates" with the "iron reduction-magnetic separation recovery" process. There is still a lack of a technical solution that takes into account both process feasibility and resource utilization efficiency, which is necessary to address the problem that the silicate matrix in amorphous iron-containing waste is difficult to destroy and the iron phase is difficult to fully dissociate. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a method for recovering iron from iron-rich waste slag through alkali-coordinated reduction roasting, water leaching, and magnetic separation. This method introduces a solid alkali during the reduction roasting process and combines water leaching desilication with magnetic separation to achieve efficient iron resource recovery. It overcomes the problems of unstable silicate matrix and difficulty in iron phase dissociation in existing technologies for amorphous iron-containing waste slag.

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

[0007] A method for recovering iron from iron-rich waste slag through alkaline synergistic reduction roasting-water leaching-magnetic separation includes the following steps:

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

[0009] (2) The mixture from step (1) is heated to 900~1100℃ under an inert atmosphere and calcined. The calcined product is cooled to room temperature and then subjected to water immersion treatment, filtered, washed and dried to obtain the desiliconized solid residue.

[0010] (3) The solid residue after desiliconization is subjected to magnetic separation to obtain magnetic concentrate enriched with iron resources.

[0011] Furthermore, the iron-containing waste slag mentioned in step (1) is a smelting slag containing amorphous silicates produced during the pyrometallurgical smelting of non-ferrous metals such as lead, zinc, copper, and nickel.

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

[0013] Furthermore, the solid alkali mentioned in step (1) is one or more of sodium carbonate and potassium carbonate. The solid alkali is pretreated by drying before use.

[0014] The amount of solid alkali added is 5-20% of the mass of the iron-containing waste residue.

[0015] Further, the reducing agent mentioned in step (1) is one or more of waste graphite, coal powder or coke powder.

[0016] The amount of reducing agent added is 5-15% of the mass of the iron-containing waste slag.

[0017] Furthermore, the heating rate in step (2) is 5~15℃ / min, and the holding time of the calcination treatment is 60~180 min.

[0018] During the roasting process, solid alkali reacts with amorphous silicates in iron-containing waste residue to generate soluble silicates, while iron oxides and solid-solution iron are reduced to elemental iron or iron-rich phases to obtain roasting products.

[0019] Further, in step (2), the liquid-to-solid mass ratio of the water immersion treatment is 5:1 to 20:1, the water immersion treatment temperature is 80 to 120°C, and the water immersion treatment time is 10 to 120 min.

[0020] Soluble silicates generated during roasting are dissolved into the liquid phase by water immersion treatment, resulting in desiliconized solid residue.

[0021] Furthermore, the magnetic field strength of the magnetic separation process in step (3) is 0.2~0.6 T.

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

[0023] Introducing solid alkali as an alkali activator during the reduction roasting process can, on the one hand, lower the reduction reaction temperature of iron oxides and solid-solution iron in the amorphous iron-containing waste slag system, allowing iron to undergo reduction transformation at relatively low temperatures; on the other hand, solid alkali can react with encapsulated silicates in the amorphous iron-containing waste slag at high temperatures, transforming the originally stable and difficult-to-dissociate glassy silicate network into water-soluble or easily soluble alkali metal silicates, thereby significantly weakening the encapsulation effect of the silicate matrix on the iron phase.

[0024] Under the aforementioned synergistic effect, iron oxides and dissolved iron in amorphous iron-containing waste slag can be effectively reduced to elemental iron or iron-rich phases at approximately 900℃, while silicate impurities are converted into soluble silicates. Subsequent water leaching selectively dissolves and removes soluble silicate impurities, further improving the exposure and dissociation of the iron phase. Ultimately, utilizing the significant magnetic differences between elemental iron and gangue minerals, efficient enrichment and recovery of iron resources are achieved through magnetic separation.

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

[0026] (1) Through the synergistic effect of solid alkali activation-reduction roasting-water leaching desilication, the amorphous silicate matrix structure is effectively destroyed, and the iron phase dissociation conditions are significantly improved.

[0027] (2) To achieve selective removal of silicate impurities without relying on strong acid or strong alkali leaching, thereby reducing the risk of secondary pollution.

[0028] (3) The process flow is clear, the parameter adjustment range is wide, and it is applicable to amorphous iron-containing waste residues from various sources, and has good engineering 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] A method for recovering iron from iron-rich waste slag through alkaline synergistic reduction roasting-water leaching-magnetic separation includes the following steps:

[0032] (1) Weigh 5.0 g of dried amorphous iron-containing waste slag. The waste slag was obtained from water-quenched lead-zinc smelting slag of China Minmetals Corporation. Its main chemical components, by mass percentage, include: 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 showed obvious diffuse peaks in the 2θ range of 20° to 40°, indicating that the phase composition of the sample was mainly amorphous glass, with a small amount of crystalline phases, including ferroalloy (FeO) and magnetite (Fe3O4). Crush to a particle size ≤200 μm. Then mix thoroughly with 0.5 g of waste graphite and 0.75 g of dried sodium carbonate to obtain a mixture.

[0033] (2) The mixture from step (1) was placed in an alumina crucible and heated to 1000°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and held for 120 min. After calcination, it was cooled to room temperature and then soaked in water at 100°C for 30 min at a liquid-to-solid mass ratio of 10:1. The resulting solid residue was filtered, washed, and dried to obtain the desiliconized solid residue.

[0034] (3) The solid residue after desiliconization is subjected to magnetic separation under a magnetic field strength of 0.3 T to obtain a magnetic concentrate enriched with iron resources.

[0035] The magnetic concentrate obtained after magnetic separation had an iron grade of 77.86% and an iron recovery rate of 82.47%. The iron in the obtained magnetic concentrate mainly existed in the form of metallic iron, while the silicate-related impurity peaks were significantly weakened. This indicates that, under the synergistic effect of solid alkali and reducing agent, the amorphous silicate matrix in the iron-containing waste slag was effectively activated during roasting and partially desiliconized during subsequent water leaching, thus significantly improving the exposure and dissociation of the iron phase. The results show that the method of this invention can effectively promote the reduction, transformation, separation, and enrichment of the iron phase in iron-rich waste slag, achieving efficient recovery of iron resources.

[0036] Example 2

[0037] A method for recovering iron from iron-rich waste slag through alkaline synergistic reduction roasting-water leaching-magnetic separation includes the following steps:

[0038] (1) Weigh 5.0 g of dried amorphous iron-containing waste residue, which is the same as in Example 1, and crush it to a particle size ≤200 μm. Then mix it thoroughly with 0.5 g of waste graphite and 0.75 g of dried potassium carbonate to obtain a mixture.

[0039] (2) The mixture from step (1) was placed in a corundum crucible and heated to 900°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and held for 150 min. After calcination, it was cooled to room temperature and then soaked in water at 90°C for 30 min at a liquid-to-solid mass ratio of 12:1. The resulting solid residue was filtered, washed, and dried to obtain the desiliconized solid residue.

[0040] (3) The solid residue after desiliconization is subjected to magnetic separation under a magnetic field strength of 0.25 T to obtain a magnetic concentrate enriched with iron resources.

[0041] The results showed that potassium carbonate could also activate the amorphous silicate matrix and promote the reduction and transformation of the iron phase during roasting, even at lower roasting temperatures. Magnetic concentrate was obtained after magnetic separation, with an iron grade of 75.94% and an iron recovery rate of 79.68%.

[0042] Example 3

[0043] A method for recovering iron from iron-rich waste slag through alkaline synergistic reduction roasting-water leaching-magnetic separation includes the following steps:

[0044] (1) Weigh 5.0 g of dried amorphous iron-containing waste residue, which is the same as in Example 1, and crush it to a particle size ≤200 μm. Then mix it thoroughly with 0.5 g of waste graphite and 0.75 g of dried sodium carbonate-potassium carbonate composite alkali (mass ratio 1:1) to obtain a mixture.

[0045] (2) The mixture from step (1) was placed in an alumina crucible and heated to 900°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and held for 90 min. After calcination, it was cooled to room temperature and then soaked in water at 120°C for 20 min at a liquid-to-solid mass ratio of 15:1. The resulting solid residue was filtered, washed, and dried to obtain the desiliconized solid residue.

[0046] (3) The solid residue after desiliconization is subjected to magnetic separation under a magnetic field strength of 0.35 T to obtain a magnetic concentrate enriched with iron resources.

[0047] Magnetic concentrate was obtained after magnetic separation, with an iron grade of 76.32% and an iron recovery rate of 80.41%. This example demonstrates that by controlling the activation level of silicates through a composite alkali, effective enrichment of iron resources can be achieved under conditions of shortened holding time. The sodium carbonate and potassium carbonate composite alkali system can jointly participate in the activation of the amorphous silicate matrix during roasting, transforming some structurally stable glassy silicates into alkali metal silicate phases that are easier to remove with subsequent water leaching; simultaneously, under the reducing atmosphere provided by waste graphite, the conversion of the iron phase to metallic iron is promoted.

[0048] Example 4

[0049] A method for recovering iron from iron-rich waste slag through alkaline synergistic reduction roasting-water leaching-magnetic separation includes the following steps:

[0050] (1) Weigh 5.0 g of dried amorphous iron-containing waste residue, which is the same as in Example 1, and crush it to a particle size ≤200 μm. Then mix it thoroughly with 0.25 g of coke powder and 1.0 g of dried sodium carbonate-potassium carbonate composite alkali (mass ratio 1:1) to obtain a mixture.

[0051] (2) The mixture from step (1) was placed in an alumina crucible and heated to 950°C at a heating rate of 5°C / min under a nitrogen protective atmosphere and held for 60 min. After calcination, it was cooled to room temperature and then soaked in water at 100°C for 60 min at a liquid-to-solid mass ratio of 18:1. The resulting solid residue was filtered, washed, and dried to obtain the desiliconized solid residue.

[0052] (3) The solid residue after desiliconization is subjected to magnetic separation under a magnetic field strength of 0.5T to obtain a magnetic concentrate enriched with iron resources.

[0053] Magnetic concentrate was obtained after magnetic separation, with an iron grade of 72.84% and an iron recovery rate of 74.36%. The results show that, under the conditions of using coke powder as a reducing agent, a relatively high amount of composite alkali, and a short holding time, the method of the present invention can still achieve effective recovery of iron resources from amorphous iron-containing waste slag, indicating that the method has a certain degree of adaptability to changes in the type of reducing agent and process parameters.

[0054] Example 5

[0055] A method for recovering iron from iron-rich waste slag through alkaline synergistic reduction roasting-water leaching-magnetic separation includes the following steps:

[0056] (1) Weigh 5.0 g of dried amorphous iron-containing waste residue, which is the same as in Example 1, and crush it to a particle size ≤200 μm. Then mix it thoroughly with 0.75 g of coal powder and 0.25 g of dried sodium carbonate-potassium carbonate composite alkali (mass ratio 1:1) to obtain a mixture.

[0057] (2) The mixture from step (1) was placed in a corundum crucible and heated to 1100°C at a heating rate of 15°C / min under a nitrogen protective atmosphere and held for 180 min. After calcination, it was cooled to room temperature and then soaked in water at 120°C for 120 min at a liquid-to-solid mass ratio of 20:1. The resulting solid residue was filtered, washed, and dried to obtain the desiliconized solid residue.

[0058] (3) The solid residue after desiliconization is subjected to magnetic separation under a magnetic field strength of 0.6T to obtain a magnetic concentrate enriched with iron resources.

[0059] Magnetic concentrate was obtained after magnetic separation, with an iron grade of 71.56% and an iron recovery rate of 72.83%. The iron grade and iron recovery rate of the magnetic concentrate obtained under these conditions are lower than those in Example 1, indicating that excessively high roasting temperature, excessively long holding time, and low alkali addition are not conducive to obtaining better iron enrichment effect. The reason may be that under high temperature and long time conditions, iron particles are prone to agglomeration and growth, and some iron phases are re-densified with gangue minerals, thus affecting the subsequent magnetic separation effect.

[0060] Comparative Example 1

[0061] A method for recovering iron from iron-rich waste residue by alkaline synergistic reduction roasting-water leaching-magnetic separation is identical to Example 1 except that solid sodium carbonate is not added.

[0062] Magnetic concentrate was obtained after magnetic separation, with an iron grade of 61.84% and an iron recovery rate of 67.23%. Compared with Example 1, under the condition of no addition of solid alkali, the amorphous silicate matrix was difficult to be effectively activated and destroyed during roasting, and the iron phase was still easily encapsulated by gangue minerals. This resulted in limited removal of silicate impurities during subsequent water leaching, and a low degree of exposure and dissociation of the iron phase, ultimately affecting the magnetic separation effect.

[0063] 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 recovering iron from iron-rich waste slag through alkali-co-reduction roasting-water leaching-magnetic separation, characterized in that... Includes the following steps: (1) The iron-containing waste residue is dried and crushed, and then solid alkali and reducing agent are added and mixed evenly to obtain a mixture; (2) The mixture from step (1) is heated to 900~1100℃ under an inert atmosphere and calcined. The calcined product is cooled to room temperature and then subjected to water immersion treatment, filtered, washed and dried to obtain the desiliconized solid residue. (3) The solid residue after desiliconization is subjected to magnetic separation to obtain magnetic concentrate enriched with iron resources.

2. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 1, characterized in that: The iron-containing waste slag mentioned in step (1) is a smelting slag containing amorphous silicates produced during the pyrometallurgical smelting of lead, zinc, copper and nickel non-ferrous metals.

3. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation 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 recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 1, characterized in that: The solid alkali mentioned in step (1) is one or more of sodium carbonate and potassium carbonate.

5. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 4, characterized in that: The amount of solid alkali added is 5-20% of the mass of the iron-containing waste residue.

6. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 1, characterized in that: The reducing agent mentioned in step (1) is one or more of waste graphite, coal powder or coke powder.

7. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 6, characterized in that: The amount of reducing agent added is 5-15% of the mass of the iron-containing waste slag.

8. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation 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 60~180min.

9. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 1, characterized in that: The liquid-to-solid mass ratio of the water immersion treatment in step (2) is 5:1 to 20:1, the water immersion treatment temperature is 80 to 120°C, and the water immersion treatment time is 10 to 120 min.

10. The method for recovering iron from iron-rich waste slag by alkali-co-reduction roasting-water leaching-magnetic separation according to claim 1, characterized in that: The magnetic field strength of the magnetic separation process in step (3) is 0.2~0.6 T.