Method for recovering iron from iron-containing waste residues

Abstract

The invention provides a method for recovering iron from iron-containing waste residues, which comprises the following steps: (1) slurrying the iron-containing waste residues, carrying out first water washing treatment, and carrying out first solid-liquid separation treatment to obtain first water washing residues; (2) carrying out alkali treatment on the first water washing slag by using an alkali source to obtain alkali treatment slag; (3) slurrying the alkali treatment slag, carrying out second water washing treatment, and carrying out second solid-liquid separation treatment to obtain second water washing slag; and (4) the second washing slag and a reducing agent are mixed for reduction roasting treatment, a roasted material is obtained, magnetic separation treatment is conducted on the roasted material, and iron powder is obtained. According to the method, impurities such as aluminum, silicon and sulfur in the iron slag can be fully removed, the content of the impurities is reduced to an extremely low level, and high-purity and high-value iron powder is obtained while the high recovery rate is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrometallurgy and relates to a method for recovering iron from iron-containing waste slag. Background Art

[0002] Currently, hydrometallurgical slag generated during nickel smelting is generally landfilled due to its low value. However, due to its high iron content, the iron content of ferrous slag is significant from a resource perspective. For example, iron alum slag, the largest and most difficult hazardous waste generated during hydrometallurgical zinc smelting, typically accounts for 20-30% of the total elemental content in the ferrous slag.

[0003] Existing technology generally recovers iron by combining reduction roasting with magnetic separation. However, due to the high content of impurities such as Al, Si, and S in the product, it is difficult to achieve sufficient separation and purification. The resulting iron concentrate is difficult to meet the application standards of the steelmaking industry.

[0004] CN119569129A discloses a method for recovering iron ore concentrate, which adopts a process route of hydrochloric acid leaching - iron powder reduction - sulfidation impurity removal - evaporation crystallization - slurry washing - roasting. Impurities such as Cu and Co can be removed by iron powder reduction. Then, taking advantage of the fact that the Ksp of NiS and CoS is smaller than that of FeS, FeS is used for sulfidation impurity removal, thereby completing the precipitation and recovery of Ni and Co without losing Fe. Finally, through evaporation crystallization, the trace impurity elements remaining in the impurity removal solution can be enriched in the solution to prevent them from entering the ferrous chloride crystals. The roasting process can efficiently convert the ferrous chloride into iron red.

[0005] CN103721845A discloses a method for separating and extracting elemental iron from iron-containing waste slag produced by fire smelting: 1. crushing the iron-containing waste slag and wet-milling it in a ball mill to a size of less than 20 mesh; 2. wet-milling the tail iron powder and coarse iron powder by magnetic separation; 3. wet-milling the coarse iron powder in a ball mill to a size of less than 40 mesh; 4. wet-milling the tail iron powder and iron powder by magnetic separation; 5. sorting the iron powder to remove iron oxide therein to obtain refined iron powder.

[0006] The purity of the iron powder obtained by the above scheme is low, and the iron loss during the recovery process is large, and the practicality is poor. Summary of the Invention

[0007] The object of the present invention is to provide a method for recovering iron from iron-containing waste slag. The method of the present invention can fully remove impurities such as aluminum, silicon, and sulfur from the iron slag, reducing the impurity content to an extremely low level, while ensuring a high recovery rate and obtaining high-purity, high-value iron powder.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for recovering iron from iron-containing waste slag, the method comprising the following steps:

[0010] (1) slurrying the iron-containing waste slag, performing a first water washing treatment, and performing a first solid-liquid separation treatment to obtain a first water-washed slag;

[0011] (2) using an alkali source to perform alkali treatment on the first water-washed slag to obtain alkali-treated slag;

[0012] (3) slurrying the alkali-treated slag, subjecting it to a second water washing treatment, and subjecting it to a second solid-liquid separation treatment to obtain a second water-washed slag;

[0013] (4) Mixing the second washed slag with a reducing agent and performing reduction roasting treatment to obtain a roasted material, and performing magnetic separation treatment on the roasted material to obtain iron powder.

[0014] The present invention pre-slurries the iron-containing waste slag and then washes it with water, which can remove soluble salts and some surface impurities and reduce the burden of subsequent alkali treatment. Targeted removal of water-soluble pollutants can also avoid volatilization and corrosion of equipment or affecting iron purity during the high-temperature roasting stage. Non-iron impurities are efficiently removed by alkali treatment, and then the alkali-treated slag is slurried and then washed with water to thoroughly remove alkali-treated products such as NaAlO2, Na2SiO3, etc., to avoid them reacting with iron in the reduction stage to form aluminosilicate eutectic or iron olivine, etc., which affects the purity of the iron powder. The iron-containing material after alkali treatment has a high degree of dissociation, and the reducing agent is more easily contacted with iron, and the metallization rate is high, which can make the reduction reaction more sufficient and the iron powder purity higher. The removal of impurities Al / Si makes the reduced iron particles purer and enhances magnetism. Finally, after reduction roasting, fine grinding is carried out and high-purity iron powder can be obtained through magnetic separation.

[0015] Preferably, the temperature of the first water washing treatment in step (1) is 40°C to 80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0016] Preferably, the alkali source in step (2) comprises sodium hydroxide.

[0017] Preferably, the alkali treatment in step (2) includes solid phase sintering and / or alkali leaching treatment.

[0018] Preferably, the solid phase sintering treatment comprises mixing the first water-washed slag with an alkali source and sintering the mixture to obtain alkali-treated slag.

[0019] The present invention uses an alkali treatment method using solid-phase sintering. At high temperatures, SiO2 and Al2O3 react with NaOH / Na2CO3 to generate soluble Na2SiO3 or NaAlO2, which can be removed by subsequent water washing to prevent them from encapsulating iron oxides and affecting reduction. Alkali roasting loosens the waste residue structure, making it easier for subsequent reducing agents to penetrate and achieve more complete reduction. This alkali treatment method is particularly suitable for treating waste residues containing high silicon and aluminum content and insoluble minerals, achieving iron enrichment through high-temperature conversion.

[0020] Preferably, the sintering temperature is 350°C to 500°C, for example, 350°C, 380°C, 400°C, 450°C or 500°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the sintering time is 1 h to 2 h, for example, 1 h, 1.2 h, 1.5 h, 1.8 h or 2 h, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, during the solid-phase sintering process, the mass ratio of the first water-washed slag to the alkali source is 1:(0.2~0.4), for example: 1:0.2, 1:0.25, 1:0.3, 1:0.35 or 1:0.4, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0023] Preferably, the alkali leaching treatment comprises mixing the first water-washed slag, an alkali source and water for leaching treatment.

[0024] The alkaline treatment method of the present invention through leaching treatment can treat iron-containing waste at a relatively low temperature, which is more economical for high-silicon-aluminum waste slag, but the reaction rate is slow.

[0025] Preferably, the temperature of the leaching treatment is 200°C to 300°C, for example, 200°C, 220°C, 250°C, 280°C or 300°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the leaching treatment time is 1 h to 4 h, for example, 1 h, 1.5 h, 2 h, 3 h or 4 h, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, during the alkali leaching process, the mass ratio of the first water-washed slag to the alkali source is 1:(0.2-0.4), for example: 1:0.2, 1:0.25, 1:0.3, 1:0.35 or 1:0.4, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0028] If the present invention adopts the alkali treatment method of solid phase sintering, the alkali treatment slag needs to be ground into fine powder before the second water washing treatment.

[0029] Preferably, the temperature of the second water washing treatment in step (3) is 40°C to 80°C, for example: 40°C, 50°C, 60°C, 70°C or 80°C, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the reducing agent in step (4) includes any one of coke, anthracite or lignite, or a combination of at least two of them. Typical but non-limiting combinations include a combination of coke and anthracite, a combination of coke and lignite, or a combination of anthracite and lignite.

[0031] Preferably, in step (4), the mass ratio of the second water-washed slag to the reducing agent is 1:(0.1-0.3), for example: 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0032] Preferably, the temperature of the reduction roasting treatment in step (4) is 1100°C to 1200°C, for example: 1100°C, 1120°C, 1150°C, 1180°C or 1200°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0033] Preferably, the time of the reduction roasting treatment in step (4) is 2h to 4h, for example: 2h, 2.5h, 3h, 3.5h or 4h, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the magnetic field intensity of the magnetic separation treatment in step (4) is 100mT to 500mT, for example: 100mT, 200mT, 300mT, 400mT or 500mT, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] The present invention requires grinding the calcined material before magnetic separation.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The present invention addresses the problems of high content of aluminum, silicon and sulfur impurities in iron slag and incomplete magnetic separation. The present invention adopts a method of alkali treatment combined with reduction roasting and magnetic separation to effectively remove the impurities aluminum, silicon and sulfur in iron products. While ensuring a high recovery rate, high-purity and high-value iron powder is obtained, thereby realizing the resource disposal and utilization of iron slag.

[0038] (2) The method for recovering iron from iron-containing waste slag of the present invention can produce iron powder with a purity of over 90.8% and an iron recovery rate of over 90%. The temperature and amount of alkali treatment significantly affect the recovery of iron. If the temperature and amount of alkali are too low, the purity and recovery rate of the iron powder will decrease significantly. If the temperature and amount of alkali are too high, the investment and operating costs will increase significantly. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a process flow chart for recovering iron from iron-containing waste slag provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0041] The composition of the iron-containing waste slag used in the examples of the present invention and the comparative examples is as follows:

[0042] Fe: 43%, Al: 3.5%, Si: 6.5%, S: 3%.

[0043] Example 1

[0044] This embodiment provides a method for recovering iron from iron-containing waste slag. The process flow chart of the method is as follows: Figure 1 As shown, the method includes the following steps:

[0045] (1) slurrying the iron-containing waste slag with water, washing it with water at 60° C., and obtaining a first washed slag by solid-liquid separation;

[0046] (2) mixing the first water-washed slag with sodium hydroxide in a mass ratio of 1:0.3, and sintering at 450° C. for 1.5 h to obtain an alkali-treated slag;

[0047] (3) grinding the alkali-treated slag, slurrying the alkali-treated slag with water, washing the slag with water at 60° C., and performing solid-liquid separation to obtain a second washed slag;

[0048] (4) The second washed slag and coke were mixed in a mass ratio of 1:0.2, and reduction roasted at 1150°C for 3 hours to obtain a roasted material. The roasted material was finely ground, and then magnetically separated under a magnetic field intensity of 300 mT, and vacuum dried to obtain iron powder.

[0049] Example 2

[0050] This embodiment provides a method for recovering iron from iron-containing waste slag. The process flow chart of the method is as follows: Figure 1 As shown, the method includes the following steps:

[0051] (1) slurrying the iron-containing waste slag with water, washing the slag with water at 80° C., and obtaining a first washed slag by solid-liquid separation;

[0052] (2) mixing the first washed residue with sodium hydroxide and water in a mass ratio of 1:0.4, leaching the residue at 250° C. for 3 h, and performing solid-liquid separation to obtain an alkali-treated residue;

[0053] (3) grinding the alkali-treated slag, slurrying the alkali-treated slag with water, washing the slag with water at 80° C., and obtaining a second washed slag by solid-liquid separation;

[0054] (4) The second washed slag and anthracite were mixed in a mass ratio of 1:0.3, and reduction roasted at 1200°C for 2 hours to obtain a roasted material. The roasted material was finely ground, and then magnetically separated under a magnetic field intensity of 100 mT, and vacuum dried to obtain iron powder.

[0055] Example 3

[0056] This embodiment provides a method for recovering iron from iron-containing waste slag. The process flow chart of the method is as follows: Figure 1 As shown, the method includes the following steps:

[0057] (1) slurrying the iron-containing waste slag with water, washing it with water at 40° C., and obtaining a first washed slag through solid-liquid separation;

[0058] (2) mixing the first water-washed slag with sodium hydroxide in a mass ratio of 1:0.2, and sintering at 350° C. for 2 h to obtain an alkali-treated slag;

[0059] (3) grinding the alkali-treated slag, slurrying the alkali-treated slag with water, washing the slag with water at 40° C., and obtaining a second washed slag by solid-liquid separation;

[0060] (4) The second washed slag and coke were mixed in a mass ratio of 1:0.1, and reduction roasted at 1100°C for 4 hours to obtain a roasted material. The roasted material was finely ground, and then magnetically separated under a magnetic field intensity of 300 mT, and vacuum dried to obtain iron powder.

[0061] Example 4

[0062] The only difference between this embodiment and embodiment 1 is that the sintering temperature is 300° C., and other conditions and parameters are exactly the same as those in embodiment 1.

[0063] Example 5

[0064] The only difference between this embodiment and embodiment 1 is that the sintering temperature is 600° C., and other conditions and parameters are exactly the same as those in embodiment 1.

[0065] Example 6

[0066] The only difference between this embodiment and embodiment 2 is that the alkali leaching temperature is 150° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0067] Example 7

[0068] The only difference between this embodiment and embodiment 1 is that the mass ratio of the first water-washed slag to sodium hydroxide is 1:0.1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 1 is that step (2) is not performed, and the other conditions and parameters are exactly the same as those in Example 1.

[0071] Performance testing:

[0072] The purity of the iron powder obtained in the embodiment and the comparative example was tested, and the recovery rate was calculated. The test results are shown in Table 1:

[0073] Table 1

[0074] Iron powder purity (%) Recovery rate (%) Example 1 92.5 91 Example 2 92.8 91 Example 3 90.8 90 Example 4 85.4 84 Example 5 80.5 82 Example 6 84.6 81 Example 7 82.5 78 Comparative Example 1 78.2 75

[0075] As can be seen from Table 1, from Examples 1-7, the method for recovering iron from iron-containing waste slag of the present invention can obtain an iron powder with a purity of more than 80.5% and an iron recovery rate of more than 78%. Suitable alkali treatment can effectively improve the purity and recovery rate of the iron powder, obtaining an iron powder with a purity of more than 90.8% and an iron recovery rate of more than 90%. The temperature and alkali dosage of the alkali treatment have a significant effect on the recovery of iron. If the temperature and alkali dosage are too low, the purity and recovery rate of the iron powder will decrease significantly. If the temperature and alkali dosage are too high, the investment and operating costs will also increase significantly.

[0076] Comparison of Examples 1 and 4-5 reveals that, in the method for recovering iron from iron-containing waste slag of the present invention, if a solid-phase sintering alkali treatment method is used, the sintering temperature will affect the recovery effect. Controlling the sintering temperature between 350°C and 500°C achieves better recovery. If the sintering temperature is too low, the residual silicon and aluminum content is high, and low-melting-point silicates such as Fe2SiO4 are easily formed during subsequent reduction roasting, encapsulating the iron particles and reducing the magnetic separation recovery rate. If the sintering temperature is too high, melt bonding occurs between the waste slag particles, forming a dense mass, reducing porosity, making it difficult for subsequent reducing agents to penetrate, reducing reduction efficiency, and reducing the iron metallization rate. Furthermore, high temperatures may cause some Fe2O3 to convert into non-magnetic FeO·Al2O3 spinel or to form fayalite with SiO2, making it difficult to recover by magnetic separation, resulting in a reduced iron recovery rate.

[0077] By comparison of Example 1 and Example 6, it can be seen that in the method for recovering iron from iron-containing waste slag according to the present invention, if an alkali treatment method of alkali leaching is adopted, the temperature of the alkali leaching will affect the recovery effect. The recovery effect is better when the temperature of the alkali leaching is controlled at 200°C to 300°C. If the temperature of the alkali leaching is too low, the residual aluminum and silicon content in the alkali leaching slag is high, and low-melting-point aluminosilicates are easily formed during subsequent reduction roasting, which encapsulates iron oxides and reduces the reduction efficiency and magnetic separation recovery rate. If the temperature of the alkali leaching is too high, the energy consumption is too high, and the equipment investment and operating costs will increase significantly.

[0078] By comparison between Example 1 and Example 7, it can be seen that in the method for recovering iron from iron-containing waste slag according to the present invention, the amount of alkali source added will affect the recovery effect. The recovery effect is better when the mass ratio of the first water-washed slag to the alkali source is controlled at 1:0.2~0.4. If the amount of alkali source added is too low, the impurity reaction is incomplete, and a low-melting-point eutectic is formed in the reduction stage, which hinders iron reduction and leads to a decrease in the purity of magnetically separated iron powder. If the amount of alkali source added is too high, the cost is significantly increased, but the improvement in the results is not obvious.

[0079] By comparing Example 1 and Comparative Example 1, it can be seen that in the method for recovering iron from iron-containing waste slag of the present invention, the purity and recovery rate of iron powder are significantly improved by alkali treatment. Alkali treatment can effectively remove impurities such as aluminum and silicon in the waste slag, reduce the encapsulation of impurities on the iron oxide phase, make the subsequent reducing agent easier to contact the iron oxide, and reduce more fully, so that high-purity iron powder can be obtained.

[0080] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for recovering iron from iron-containing waste slag, characterized in that: The method comprises the following steps: (1) slurrying the iron-containing waste slag, performing a first water washing treatment, and performing a first solid-liquid separation treatment to obtain a first water-washed slag; (2) using an alkali source to perform alkali treatment on the first water-washed slag to obtain alkali-treated slag; (3) slurrying the alkali-treated slag, subjecting it to a second water washing treatment, and subjecting it to a second solid-liquid separation treatment to obtain a second water-washed slag; (4) Mixing the second washed slag with a reducing agent and performing reduction roasting treatment to obtain a roasted material, and performing magnetic separation treatment on the roasted material to obtain iron powder.

2. The method according to claim 1, wherein The temperature of the first water washing treatment in step (1) is 40°C to 80°C.

3. The method according to claim 1 or 2, wherein: The alkali source in step (2) includes sodium hydroxide.

4. The method according to any one of claims 1 to 3, wherein The alkali treatment in step (2) includes solid phase sintering and / or alkali leaching.

5. The method according to claim 4, wherein The solid phase sintering treatment comprises mixing the first water-washed slag with an alkali source and sintering the mixture to obtain an alkali-treated slag; Preferably, the sintering temperature is 350°C to 500°C; Preferably, the sintering time is 1 h to 2 h; Preferably, during the solid-phase sintering process, the mass ratio of the first water-washed slag to the alkali source is 1:(0.2-0.4).

6. The method according to claim 4, wherein The alkali leaching treatment includes mixing the first water-washed slag, an alkali source and water to perform a leaching treatment; Preferably, the leaching treatment temperature is 200°C to 300°C; Preferably, the leaching treatment time is 1h to 4h; Preferably, during the alkali leaching process, the mass ratio of the first water-washed slag to the alkali source is 1:(0.2-0.4).

7. The method according to any one of claims 1 to 6, wherein: The temperature of the second water washing treatment in step (3) is 40°C to 80°C.

8. The method according to any one of claims 1 to 7, wherein: The reducing agent in step (4) comprises any one of coke, anthracite or blue charcoal, or a combination of at least two thereof; Preferably, in step (4), the mass ratio of the second water-washed slag to the reducing agent is 1:(0.1-0.3).

9. The method according to any one of claims 1 to 8, wherein The temperature of the reduction roasting treatment in step (4) is 1100° C. to 1200° C.; Preferably, the reduction roasting treatment in step (4) is carried out for 2 to 4 hours.

10. The method according to any one of claims 1 to 9, wherein The magnetic field intensity of the magnetic separation treatment in step (4) is 100mT to 500mT.

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