A method for solidifying heavy metal ions of lithium slag

Abstract

The present disclosure provides a method for solidifying heavy metal ions in lithium slag, belonging to the technical field of lithium slag treatment. The method for solidifying heavy metal ions in lithium slag comprises: taking lithium slag powder as a base material, adding sodium fluoride, silicon carbide, sodium tetraborate and hydroxyapatite to the base material for dry mixing to obtain a mixed powder; adding deionized water to the mixed powder to prepare a spherical green body; drying the spherical green body to obtain a dry green body; and performing sintering treatment on the dry green body, and cooling to room temperature to obtain solidified lithium slag ceramsite. The method realizes nuisance-free treatment of lithium slag, simplifies the treatment process, reduces environmental damage, and improves the resource utilization of lithium slag.

Description

Technical Field

[0001] This disclosure belongs to the field of solidified lithium slag treatment technology, specifically relating to a method for solidifying heavy metal ions in lithium slag. Background Technology

[0002] Current methods for solidifying heavy metal ions in lithium slag mainly rely on chemical stabilization and traditional solidifying agents (such as cement-based materials). For example, one of the existing technologies, Chinese patent application CN119101811A, proposes a method and apparatus for treating thallium-containing lithium slag based on chemical leaching and biomineralization. By controlling an appropriate batching ratio, thallium in the lithium slag is fully activated and complexed, improving the leaching performance of thallium. By controlling an appropriate solid-liquid ratio, leaching temperature, and leaching time, thallium can be efficiently dissolved. This method is beneficial for achieving the harmless treatment of lithium slag and eliminating the environmental risks of thallium leaching. However, this chemical method has the disadvantages of large reagent consumption, insufficient long-term stability, and potential secondary pollution. Furthermore, one existing technology, Chinese patent application CN119241158A, proposes a method for the harmless treatment of lithium slag and the preparation of water-stabilized materials from the treated lithium slag. This method involves adding materials containing active alumina to the lithium slag for harmless treatment, improving problems such as low hydration activity, high alkali content, and large compositional fluctuations. An activator is used to generate more gel structures, achieving the resource utilization of lithium slag. However, this method using conventional curing agents suffers from low curing efficiency, poor high-temperature resistance, and poor erosion resistance, making it difficult to effectively prevent the leaching of heavy metal ions (such as lithium and thallium) in complex environments. Especially with the expansion of the lithium battery industry, the production of lithium slag has surged, and the enrichment of soluble heavy metals in it severely restricts resource utilization—if directly used in building materials or landfills, heavy metal ions easily migrate into the environment, causing continuous pollution of soil and water bodies. Therefore, developing a curing technology that combines high-efficiency curing capability, high-temperature stability, and environmental adaptability is crucial for solving the lithium slag disposal dilemma and promoting green recycling. Summary of the Invention

[0003] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a method for solidifying heavy metal ions in lithium slag.

[0004] This disclosure provides a method for solidifying heavy metal ions in lithium slag, the method comprising:

[0005] Lithium slag powder was used as the matrix material, and sodium fluoride, silicon carbide, sodium tetraborate, and hydroxyapatite were added to the matrix material and dry-mixed to obtain a mixed powder.

[0006] Deionized water was added to the mixed powder to form a spherical preform;

[0007] The spherical blank is dried to obtain a dried blank;

[0008] The dried blank is sintered and then cooled to room temperature to obtain solidified lithium slag ceramic particles.

[0009] Optionally, the sodium fluoride content is 1.0-5.0 wt.% of the matrix material.

[0010] The silicon carbide content is 0.5-2.0 wt.% of the matrix material.

[0011] The sodium tetraborate content is 3.0-6.0 wt.% of the matrix material.

[0012] The content of hydroxyapatite is 2.0-15.0 wt.% of the mass of the matrix material.

[0013] Optionally, the dry mixing time is 30-60 minutes.

[0014] Optionally, the content of the deionized water is 5-15% of the mass of the matrix material.

[0015] Optionally, the diameter of the spherical blank is 5-20 mm.

[0016] Optionally, the spherical blank is dried at a temperature of 70-90 ℃ for 6-12 h.

[0017] Optionally, the sintering process includes:

[0018] First sintering stage: Increase the temperature from room temperature to 500-700 ℃ at a rate of 2-5 ℃ / min, and hold for 1-3 h;

[0019] Second sintering stage: Heat to 900-1000℃ at a rate of 2-5℃ / min and hold for 3-9 hours.

[0020] Optionally, the second sintering stage includes:

[0021] Heat to 900-950℃ at a heating rate of 2-5℃ / min and hold for 1-3 hours. Then heat to 950-970℃ at the same heating rate and hold for 1-3 hours. Finally, heat to 970-1000℃ at the same heating rate and hold for 1-3 hours.

[0022] This disclosure proposes a method for solidifying heavy metal ions in lithium slag. The method includes: taking lithium slag powder as a matrix material, adding sodium fluoride, silicon carbide, sodium tetraborate, and hydroxyapatite to the matrix material and dry mixing to obtain a mixed powder; adding deionized water to the mixed powder to form a spherical green body; drying the spherical green body to obtain a dried green body; sintering the dried green body and cooling it to room temperature to obtain solidified lithium slag ceramsite. This method achieves pollution-free treatment of lithium slag, simplifies the treatment process, reduces environmental damage, and improves the resource utilization of lithium slag. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating a specific embodiment of the method for solidifying heavy metal ions in lithium slag according to this disclosure.

[0024] Figure 2 SEM image of lithium slag ceramsite prepared in Comparative Example 1 of this disclosure;

[0025] Figure 3 Here is a SEM image of the lithium slag ceramsite prepared in Example 1 of this disclosure; wherein, Figure 3 (b) in the image is a magnified view of a portion of (a).

[0026] Figure 4 Here is a SEM image of the lithium slag ceramsite prepared in Example 2 of this disclosure; wherein, Figure 4 (b) in the image is a magnified view of a portion of (a).

[0027] Figure 5 Here is a SEM image of the lithium slag ceramsite prepared in Example 3 of this disclosure; wherein, Figure 5 (b) in the image is a magnified view of (a). Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0029] As shown in Figure 1, one aspect of this disclosure provides a method S100 for solidifying heavy metal ions in lithium slag, specifically including the following steps S110~S140:

[0030] S110. Take lithium slag powder as the matrix material, and add the following additives according to the mass percentage of the matrix material: sodium fluoride 1.0-5.0 wt.%, silicon carbide 0.5-2.0 wt.%, sodium tetraborate 3.0-6.0 wt.%, hydroxyapatite 2.0-15.0 wt.%. Place the above raw materials in a mixer and dry mix for 30-60 min until uniform.

[0031] In step S110, the sodium fluoride content is preferably 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, etc.

[0032] In step S110, the silicon carbide content is preferably 0.5 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, etc.

[0033] In step S110, the sodium tetraborate content is preferably 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, etc.

[0034] In step S110, the content of hydroxyapatite is preferably 2 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, etc.

[0035] S120. Add 5-15% of the total mass of deionized water to the mixed powder to form a spherical blank with a diameter of 5-20 mm.

[0036] In step S120, the content of deionized water can preferably be 5 wt.%, 8 wt.%, 10 wt.%, 15 wt.%, etc.

[0037] S130. Place the green body in an oven and dry it at 70-90 ℃ for 6-12 h until it is completely dry.

[0038] In step S130, the drying temperature can preferably be 70℃, 80℃, 90℃, etc., and the drying time can preferably be 6h, 8h, 10h, 12h, etc.

[0039] S140. Place the dried green body into a high-temperature electric furnace and raise the temperature from room temperature to 500-700 ℃ at a rate of 2-5 ℃ / min, and hold for 1-3 h. Continue to raise the temperature to the target high-temperature sintering zone (900-1000 ℃) at the same rate and hold for 3-9 h. Stop heating and allow the furnace to cool naturally to room temperature to obtain the solidified lithium slag ceramic particles.

[0040] In step S140, the calcination stage includes a first calcination stage and a second calcination stage. In the first calcination stage, the temperature is preferably 500℃, 600℃, 700℃, etc., and the time is preferably 1h, 2h, 3h, etc. The second sintering stage includes: heating to 900-950℃ at a heating rate of 2-5℃ / min and holding for 1-3h, then heating to 950-970℃ at the same heating rate and holding for 1-3h, and then heating to 970-1000℃ at the same heating rate and holding for 1-3h.

[0041] It should be understood that the solidified lithium slag ceramic can be used directly as a lightweight aggregate or adsorbent to achieve high added value utilization.

[0042] In this embodiment, waste lithium slag is used as the matrix material for ceramsite, hydroxyapatite is used as the heavy metal ion solidification material, commercially available sodium fluoride and silicon carbide are used as foaming agents, and sodium tetraborate is used as a co-solvent. Ceramsite is prepared by uniformly mixing hydroxyapatite and lithium slag, and then sintering at high temperature to form a stable core-shell structure. The hydroxyapatite and lithium slag particles form a complex, interwoven spatial structure, together constituting the ceramsite framework. Simultaneously, hydroxyapatite possesses strong ion exchange capacity and unique multiple adsorption sites, enabling it to firmly adsorb heavy metal ions such as lithium and thallium, with the leaching ion content meeting national emission standards. This method achieves pollution-free treatment of lithium slag, simplifies the treatment process, reduces environmental damage, and improves the resource utilization of lithium slag.

[0043] The method for solidifying heavy metal ions in lithium slag will be further illustrated below with specific examples:

[0044] Comparative Example 1

[0045] Lithium slag powder was used as the matrix material, and the following additives were added according to the mass percentage of the matrix material: sodium fluoride 2.0 wt.%, silicon carbide 0.8 wt.%, sodium tetraborate 4.7 wt.%. The above raw materials were placed in a mixer and dry-mixed for 50 min until uniform. 10% of the total mass of deionized water was added to the mixed powder to form spherical blanks with a diameter of 15 mm. The blanks were placed in an oven and dried at 80℃ for 8 h until dry. The dried blanks were placed in a high-temperature electric furnace and heated from room temperature to 600℃ at a heating rate of 4℃ / min, and held at that temperature for 2 h. The temperature was then increased to the target high-temperature sintering zone of 945℃, 960℃, and 990℃ at the same heating rate, and held for 2 h at each temperature. Heating was then stopped, and the furnace was allowed to cool naturally to room temperature to obtain the solidified finished product.

[0046] The microstructure of the obtained sample is as follows Figure 2As shown in Table 1, the surface structure of the ceramsite is relatively loose, with uneven pore distribution and a lack of dense interwoven network. Combined with Table 1, it can be seen that without the addition of hydroxyapatite, relying solely on physical sintering results in poor encapsulation of heavy metal ions (such as Cd and Tl), leading to a higher leaching concentration.

[0047] Example 1.

[0048] Lithium slag powder was used as the matrix material, and the following additives were added according to the matrix material mass percentage: sodium fluoride 2.0 wt.%, silicon carbide 0.8 wt.%, sodium tetraborate 4.7 wt.%, and hydroxyapatite 4.0 wt.%. The above raw materials were placed in a mixer and dry-mixed for 50 min until homogeneous. 10% of the total mass of deionized water was added to the mixed powder to form spherical blanks with a diameter of 15 mm. The blanks were placed in an oven and dried at 80℃ for 8 h until completely dry. The dried blanks were placed in a high-temperature electric furnace and heated from room temperature to 600℃ at a rate of 4℃ / min, and held for 2 h. The temperature was then increased to the target high-temperature sintering zones of 945℃, 960℃, and 990℃ at the same rate, and held for 2 h at each zone. Heating was then stopped, and the furnace was allowed to cool naturally to room temperature to obtain the solidified finished product.

[0049] The microstructure of the obtained sample is as follows Figure 3 As shown, after adding 4.0 wt.% hydroxyapatite, a partially interwoven structure appeared between the particles, but the interwoven density was low. Combined with Table 1, it can be seen that the Cd leaching concentration decreased to 0.026 mg / L and Tl decreased to 0.0047 mg / L, indicating that the ion exchange function of hydroxyapatite was initially demonstrated.

[0050] Example 2

[0051] Lithium slag powder was used as the matrix material, and the following additives were added by mass percentage: sodium fluoride 2.0 wt.%, silicon carbide 0.8 wt.%, sodium tetraborate 4.7 wt.%, and hydroxyapatite 8.0 wt.%. The above raw materials were dry-mixed in a mixer for 50 min until homogeneous. 10% of the total mass of deionized water was added to the mixed powder to form spherical blanks with a diameter of 15 mm. The blanks were placed in an oven and dried at 80℃ for 8 h until completely dry. The dried blanks were placed in a high-temperature electric furnace and heated from room temperature to 600℃ at a rate of 4℃ / min, and held for 2 h. The temperature was then increased to the target high-temperature sintering zones of 945℃, 960℃, and 990℃ at the same rate, and held for 2 h at each zone. Heating was then stopped, and the furnace was allowed to cool naturally to room temperature to obtain the solidified finished product.

[0052] The microstructure of the obtained sample is as follows Figure 4As shown, with the hydroxyapatite content increased to 8.0 wt.%, the SEM image revealed a denser core-shell interwoven structure and reduced porosity. Combined with Table 1, the leaching concentrations of Cd and Tl further decreased (0.021 mg / L and 0.0040 mg / L), indicating that the increased adsorption sites enhanced the curing effect.

[0053] Example 3

[0054] Lithium slag powder was used as the matrix material, and the following additives were added by mass percentage: sodium fluoride 2.0 wt.%, silicon carbide 0.8 wt.%, sodium tetraborate 4.7 wt.%, and hydroxyapatite 12.0 wt.%. The above raw materials were dry-mixed in a mixer for 50 min until homogeneous. 10% of the total mass of deionized water was added to the mixed powder to form spherical blanks with a diameter of 15 mm. The blanks were placed in an oven and dried at 80℃ for 8 h until completely dry. The dried blanks were placed in a high-temperature electric furnace and heated from room temperature to 600℃ at a rate of 4℃ / min, and held for 2 h. The temperature was then increased to the target high-temperature sintering zones of 945℃, 960℃, and 990℃ at the same rate, and held for 2 h at each zone. Heating was then stopped, and the furnace was allowed to cool naturally to room temperature to obtain the solidified finished product.

[0055] The microstructure of the obtained sample is as follows Figure 5 As shown, hydroxyapatite reached 12.0 wt.%, and the SEM image revealed a highly interwoven three-dimensional network with almost completely filled pores. Combined with Table 1, the lowest leaching concentrations of Cd and Tl (0.018 mg / L and 0.0035 mg / L, respectively) were observed, verifying the synergistic effect of high-proportion hydroxyapatite on the chemical adsorption and physical encapsulation of heavy metals.

[0056] The lithium slag raw materials, Comparative Example 1, and the solidified lithium slag ceramsite from Examples 1-3 were leached using the method described in "Solid Waste Leaching Toxicity Leaching Method: Sulfuric Acid and Nitric Acid Method" (HJ / T299-2007). The toxicity leaching results are shown in Table 1. The toxicity leaching results for Examples 1-3 are all below the Class I discharge standard in the "National Integrated Wastewater Discharge Standard" (GB8978-1996). With the increase of the hydroxyapatite proportion, the heavy metal leaching concentration gradually decreased, indicating that the solidification method provided by this invention has a good solidification effect on lithium slag.

[0057] Table 1 Toxicity Leaching Results

[0058]

[0059] This disclosure proposes a method for solidifying heavy metal ions in lithium slag, which has the following advantages compared to existing technologies:

[0060] First, this disclosure proposes a low-cost, simple, and highly effective method for curing heavy metal ions in lithium slag.

[0061] Secondly, this disclosure utilizes the ion exchange capacity and multiple adsorption sites of hydroxyapatite (such as phosphate forming insoluble salts with heavy metals), combined with the core-shell interwoven structure formed by high-temperature sintering, to achieve dual fixation of heavy metals (such as Cd, Tl, Be, etc.), resulting in high solidification efficiency and significantly reducing the risk of secondary leaching of heavy metals in complex environments.

[0062] Third, the calcium aluminosilicate and apatite mineral phases formed by sintering can resist high-temperature environments. The solidified ceramsite still maintains a low leaching rate in acidic or high-salt environments, which is superior to chemical methods.

[0063] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A method for solidifying heavy metal ions in lithium slag, characterized in that, The method includes: Lithium slag powder was used as the matrix material. Sodium fluoride, silicon carbide, sodium tetraborate, and hydroxyapatite were added to the matrix material and dry-mixed to obtain a mixed powder. The content of sodium fluoride was 1.0-5.0 wt.% of the matrix material, the content of silicon carbide was 0.5-2.0 wt.% of the matrix material, the content of sodium tetraborate was 3.0-6.0 wt.% of the matrix material, and the content of hydroxyapatite was 2.0-15.0 wt.% of the matrix material. Deionized water was added to the mixed powder to form a spherical preform; The spherical blank is dried to obtain a dried blank; The dried blank is sintered and cooled to room temperature to obtain solidified lithium slag ceramsite. The first sintering stage is as follows: the temperature is increased from room temperature to 500-700 ℃ at a heating rate of 2-5 ℃ / min and held for 1-3 h. Second sintering stage: Heat to 900-950℃ at a heating rate of 2-5℃ / min and hold for 1-3 hours, then heat to 950-970℃ at the same heating rate and hold for 1-3 hours, then heat to 970-1000℃ at the same heating rate and hold for 1-3 hours. In the solidified lithium slag ceramsite, hydroxyapatite and lithium slag particles form a complex spatial structure that interweaves and interpenetrates, together forming the ceramsite skeleton; the solidified lithium slag ceramsite can reduce the leaching concentration of various heavy metals such as Cd, Tl, Be, Pb, Hg, Cu, and Zn in the lithium slag powder matrix material.

2. The method according to claim 1, characterized in that, The dry mixing time is 30-60 minutes.

3. The method according to claim 1, characterized in that, The content of deionized water is 5-15% of the mass of the matrix material.

4. The method according to claim 1, characterized in that, The diameter of the spherical blank is 5-20 mm.

5. The method according to claim 1, characterized in that, The spherical blanks are dried at a temperature of 70-90 ℃ for 6-12 h.

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