A method for reducing thallium toxicity and soluble salt content of lithium residue by micro-bubble carbonization

Abstract

The present application belongs to the technical field of solid waste treatment, and provides a method for reducing thallium toxicity and soluble salt content of lithium residue by micro-bubble carbonization, which comprises the following steps: continuously introducing carbon dioxide micro-bubbles into lithium residue slurry for reaction, and then performing solid-liquid separation and washing after the reaction to obtain purified lithium residue; the lithium residue slurry comprises lithium residue and a micro-bubble stabilizer, and the lithium residue comprises thallium and calcium sulfate. According to the method, a weakly acidic leaching environment is formed by carbonization of CO2 micro-bubbles, and a large amount of carbonate is formed at the same time, which promotes the dissolution of thallium ions and the conversion of soluble calcium sulfate into insoluble calcium carbonate, so that the leaching toxicity of thallium and the content of soluble salt in the lithium residue are reduced.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment technology and relates to a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. Background Technology

[0002] Lithium slag is an industrial waste generated during the extraction of lithium salts from lithium ore. The sulfuric acid process for lithium extraction plays a crucial role in lithium ore extraction and utilization due to its high reaction efficiency and mature technology, and is currently the most commonly used lithium extraction process. The soluble salts in the lithium slag produced by the sulfuric acid process mainly include sulfates, such as residual sodium sulfate (Na₂SO₄), potassium sulfate (K₂SO₄), and calcium sulfate (CaSO₄). Simultaneously, because lithium ore contains a certain amount of thallium minerals, these minerals readily enter the lithium smelting slag during the smelting process, causing the thallium leaching toxicity of the lithium slag to far exceed the national standard concentration (5 μg / L). If lithium slag is openly piled up or simply landfilled, the leaching of thallium and soluble salts will pose a serious threat to the surrounding environment and groundwater resources.

[0003] In the prior art, CN118558703A discloses a method for the harmless treatment of lithium slag to remove thallium and beryllium. This method uses ball milling to increase the surface area of ​​the waste lithium slag, releasing soluble salts such as potassium, sodium, beryllium, and thallium encapsulated within the slag, allowing them to dissolve in water during washing. However, this method can only remove soluble sodium and potassium salts, and cannot effectively separate slightly soluble substances such as gypsum (calcium sulfate).

[0004] Therefore, it is necessary to provide a method to reduce the thallium toxicity and soluble salt content in lithium slag, so as to effectively reduce the thallium leaching toxicity and soluble salt content in lithium slag, which is beneficial to the subsequent storage or resource utilization of lithium slag. Summary of the Invention

[0005] The purpose of this invention is to provide a method for reducing the thallium toxicity and soluble salt content in lithium slag using microbubble carbonization. The method utilizes CO2 microbubble carbonization to create a weakly acidic leaching environment, while simultaneously forming a large amount of carbonates, promoting the dissolution of thallium ions and promoting the conversion of soluble calcium sulfate and other substances into insoluble calcium carbonate, thereby reducing the thallium leaching toxicity and soluble salt content in lithium slag.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] This invention provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization, the method comprising the following steps:

[0008] Carbon dioxide microbubbles are continuously introduced into the lithium slag slurry for reaction. After the reaction is completed, solid-liquid separation and washing are performed to obtain purified lithium slag.

[0009] The lithium slag slurry includes lithium slag and a microbubble stabilizer, and the lithium slag includes thallium and calcium sulfate.

[0010] This invention introduces CO2 microbubbles into lithium slag slurry. The carbonization of the CO2 microbubbles creates a weakly acidic leaching environment, while simultaneously generating a large number of carbonate ions in situ. Under these weakly acidic chemical conditions, on the one hand, it facilitates the dissolution of thallium ions adsorbed on the surface of lithium slag particles and entrained within them; on the other hand, the carbonate ions generated in situ can react with calcium sulfate to transform into insoluble calcium carbonate, which also facilitates the dissolution of thallium ions and other soluble sulfates encapsulated within calcium sulfate crystals. This results in a reduction of thallium leaching toxicity and soluble salt content in lithium slag.

[0011] In addition, the present invention also adds a microbubble stabilizer to the lithium slag slurry, which can stabilize CO2 microbubbles, prevent them from rapidly merging, growing, floating and breaking, so that they can remain in the solution, continuously carbonize to maintain a weakly acidic dissolution environment and continuously react to generate carbonates.

[0012] It is understood that the microbubbles described in this invention refer to bubbles with a size on the micrometer scale.

[0013] Preferably, the size of the carbon dioxide microbubbles is 100μm-500μm, for example, it can be 100μm, 200μm, 300μm, 400μm or 500μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] The size of the carbon dioxide microbubbles described in this invention refers to the average particle size of the microbubbles. By controlling the size of the carbon dioxide microbubbles, the CO2 gas content, bubble stability, and residence time can be regulated. If the size of the carbon dioxide microbubbles is too small, the CO2 gas content remaining in the solution will be low, making it difficult to maintain a weakly acidic system for a long time and resulting in a low carbonate content. If the size of the carbon dioxide microbubbles is too large, the bubble stability will be poor, the bubble will rise quickly, and the residence time will be short, resulting in a low carbonate content.

[0015] Preferably, the method for continuously introducing carbon dioxide microbubbles into lithium slag slurry includes: introducing carbon dioxide gas into lithium slag slurry through micropore aeration or dissolved gas-release method to form carbon dioxide microbubbles.

[0016] This invention uses a microporous aeration method or a dissolved-gas-release method to generate microbubbles in lithium slag slurry. The size of the carbon dioxide microbubbles can be controlled by changing the aeration or dissolved-gas-release pressure, the aperture of the aeration head, or the structure of the dissolved-gas-release release device.

[0017] Preferably, the ratio of the flow rate of the carbon dioxide gas to the volume of the lithium slag slurry is (1-4) m³. 3 / h:10m3 For example, it could be 1m 3 / h:10m 3 1.5m 3 / h:10m 3 2m 3 / h:10m 3 2.5m 3 / h:10m 3 3m 3 / h:10m 3 3.5m 3 / h:10m 3 or 4m 3 / h:10m 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0018] The ratio of the carbon dioxide gas flow rate to the volume of lithium slag slurry, as described in this invention, affects the effectiveness of reducing the thallium toxicity and soluble salt content of lithium slag. If the carbon dioxide gas flow rate is too low, the effectiveness of reducing the thallium toxicity and soluble salt content of lithium slag will decrease. However, if the carbon dioxide gas flow rate is too high, the number of microbubbles generated will increase, and the bubbles will easily merge and grow into large bubbles. The lifespan of CO2 bubbles will be shortened, and they will quickly rise and break down, resulting in less CO2 gas remaining in the solution and a decrease in the effectiveness of reducing the thallium toxicity and soluble salt content of lithium slag.

[0019] Preferably, the microbubble stabilizer comprises any one or a combination of at least two of sodium dodecyl sulfate, sodium dodecyl sulfate, or sodium stearate.

[0020] Preferably, the content of microbubble stabilizer in the lithium slag slurry is 0.02wt%-0.2wt%, for example, it can be 0.02wt%, 0.04wt%, 0.06wt%, 0.08wt%, 0.1wt%, 0.12wt%, 0.14wt%, 0.16wt%, 0.18wt% or 0.2wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] The amount of microbubble stabilizer added in this invention also affects the effect of reducing the toxicity of lithium slag thallium and the content of soluble salts. If the content of microbubble stabilizer is too small, the bubble stability will be poor and it will be difficult to stabilize in the system for a long time. However, if the content of microbubble stabilizer is too large, a dense adsorption layer will easily form at the gas-liquid interface, which will limit surface renewal, hinder gas dissolution and diffusion, reduce the effective mass transfer efficiency of CO2 carbonation, and also cause the bubbles to be over-stabilized, forming a large number of foam layers that are difficult to eliminate, causing the system to accumulate bubbles, overflow, or fail to defoam naturally.

[0022] Preferably, the lithium slag content in the lithium slag slurry is 40wt%-60wt%, for example, it can be 40wt%, 45wt%, 50wt%, 55wt% or 60wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the thallium content in the lithium slag slurry is 200 μg / L-500 μg / L, for example, it can be 200 μg / L, 250 μg / L, 300 μg / L, 350 μg / L, 400 μg / L, 450 μg / L or 500 μg / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the calcium sulfate content in the lithium slag is 15wt%-20wt%, for example, it can be 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the thallium leaching toxicity in the lithium slag is 20 μg / L-40 μg / L, for example, it can be 20 μg / L, 25 μg / L, 30 μg / L, 35 μg / L or 40 μg / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the pH of the reaction is 6.0-7.0, for example, it can be 6.0, 6.2, 6.4, 6.6, 6.8 or 7.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the reaction temperature is 30℃-50℃, for example, 30℃, 35℃, 40℃, 45℃ or 50℃, and the reaction time is 0.5h-1h, for example, 0.5h, 0.7h, 0.9h or 1h, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0028] Preferably, the washing method is spray washing.

[0029] Preferably, the detergent used for washing is water.

[0030] Preferably, the mass ratio of the detergent to the lithium slag is (0.3-0.5):1, for example, it can be 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 0.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] As a preferred method of the present invention, the method includes the following steps:

[0032] A lithium slag slurry was prepared by mixing lithium slag with a calcium sulfate content of 15wt%-20wt%, a thallium leaching toxicity of 20μg / L-40μg / L, a microbubble stabilizer, and water. The lithium slag slurry contained 40wt%-60wt% lithium slag, 200μg / L-500μg / L thallium, and 0.02wt%-0.2wt% microbubble stabilizer.

[0033] Carbon dioxide gas is introduced into the lithium slag slurry through microporous aeration or dissolved gas-release method to form carbon dioxide microbubbles with a size of 100μm-500μm. The reaction is carried out at a temperature of 30℃-50℃ and a pH of 6.0-7.0 for 0.5h-1h. The resulting slurry is filtered, and then the filter cake is washed by spraying at a mass ratio of water to lithium slag of (0.3-0.5):1 to obtain purified lithium slag.

[0034] The ratio of the flow rate of carbon dioxide gas to the volume of lithium slag slurry is (1-4) m³. 3 / h:10m 3 .

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention introduces CO2 microbubbles into lithium slag slurry. The carbonization of the CO2 microbubbles creates a weakly acidic leaching environment, while simultaneously generating a large number of carbonate ions in situ. Under these weakly acidic chemical conditions, on the one hand, it facilitates the dissolution of thallium ions adsorbed on the surface of lithium slag particles and entrained within them; on the other hand, the carbonate ions generated in situ can react with calcium sulfate to transform into insoluble calcium carbonate, which also facilitates the dissolution of thallium ions and other soluble sulfates encapsulated within calcium sulfate crystals. This results in a reduction of thallium leaching toxicity and soluble salt content in lithium slag. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] Example 1

[0039] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization, the method comprising the following steps:

[0040] A lithium slag slurry was prepared by mixing lithium slag (lepidolite smelting slag) with a calcium sulfate content of 18 wt%, a thallium leaching toxicity of 30 μg / L, a microbubble stabilizer (sodium dodecyl sulfate), and water. The lithium slag slurry contained 50 wt% lithium slag, 300 μg / L thallium, and 0.05 wt% microbubble stabilizer.

[0041] Carbon dioxide gas was introduced into the lithium slag slurry through a microporous aeration method (aeration pressure 0.15 MPa, pore size 5 μm) to form carbon dioxide microbubbles with a size of 200 μm. The reaction was carried out at a temperature of 40℃ and a pH of 6.5 for 0.8 h. The resulting slurry was filtered, and then the filter cake was washed by spraying at a mass ratio of water to lithium slag of 0.4:1 to obtain purified lithium slag.

[0042] The ratio of the flow rate of the carbon dioxide gas to the volume of the lithium slag slurry is 2m³. 3 / h:10m 3 .

[0043] Example 2

[0044] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization, the method comprising the following steps:

[0045] A lithium slag slurry was prepared by mixing lithium slag (spodumene smelting slag) with a calcium sulfate content of 15 wt%, a thallium leaching toxicity of 20 μg / L, a microbubble stabilizer (sodium dodecyl sulfate), and water. The lithium slag slurry contained 40 wt% lithium slag, 500 μg / L thallium, and 0.2 wt% microbubble stabilizer.

[0046] Carbon dioxide gas was introduced into the lithium slag slurry via a dissolved gas-release method (dissolved gas pressure 0.15 MPa, Venturi jet release device) to form carbon dioxide microbubbles with a size of 100 μm. The reaction was carried out at a temperature of 30℃ and a pH of 7.0 for 0.5 h. The resulting slurry was filtered, and then the filter cake was washed by spraying at a mass ratio of water to lithium slag of 0.3:1 to obtain purified lithium slag.

[0047] The ratio of the flow rate of carbon dioxide gas to the volume of lithium slag slurry is 4m³. 3 / h:10m 3 .

[0048] Example 3

[0049] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization, the method comprising the following steps:

[0050] A lithium slag slurry was prepared by mixing lithium slag (lepidolite smelting slag) with a calcium sulfate content of 20 wt%, a thallium leaching toxicity of 40 μg / L, a microbubble stabilizer (sodium dodecyl sulfate), and water. The lithium slag slurry contained 60 wt% lithium slag, 200 μg / L thallium, and 0.02 wt% microbubble stabilizer.

[0051] Carbon dioxide gas was introduced into the lithium slag slurry through a microporous aeration method (aeration pressure 0.13 MPa, pore size 10 μm) to form carbon dioxide microbubbles with a size of 500 μm. The reaction was carried out at a temperature of 50℃ and a pH of 6.0 for 1 hour. The resulting slurry was filtered, and then the filter cake was washed by spraying at a mass ratio of water to lithium slag of 0.5:1 to obtain purified lithium slag.

[0052] The ratio of the flow rate of the carbon dioxide gas to the volume of the lithium slag slurry is 1 m³. 3 / h:10m 3 .

[0053] Example 4

[0054] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. The method is the same as in Example 1, except that the size of the carbon dioxide microbubbles is 50 μm (aeration pressure 0.21 MPa, pore size 0.22 μm).

[0055] Example 5

[0056] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. The method is the same as in Example 1, except that the size of the carbon dioxide microbubbles is 600 μm (aeration pressure 0.12 MPa, pore size 20 μm).

[0057] Example 6

[0058] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. The method is the same as in Example 1, except that the ratio of the carbon dioxide gas flow rate to the volume of the lithium slag slurry is 0.5:10.

[0059] Example 7

[0060] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. The method is the same as in Example 1, except that the ratio of the carbon dioxide gas flow rate to the volume of the lithium slag slurry is 5:10.

[0061] Example 8

[0062] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. The method is the same as in Example 1, except that the content of microbubble stabilizer in the lithium slag slurry is 0.01 wt%.

[0063] Example 9

[0064] This embodiment provides a method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization. The method is the same as in Example 1, except that the content of microbubble stabilizer in the lithium slag slurry is 0.3 wt%.

[0065] Comparative Example 1

[0066] This comparative example provides a method for treating lithium slag, which is the same as in Example 1 except that carbon dioxide gas is not introduced, i.e., carbon dioxide microbubbles are not introduced.

[0067] Comparative Example 2

[0068] This comparative example provides a method for treating lithium slag, which is the same as in Example 1 except that no microbubble stabilizer is added to the lithium slag slurry.

[0069] The purified lithium slag obtained from the above examples and comparative examples was tested for thallium leaching toxicity and soluble salt content. The thallium leaching toxicity test was conducted according to the standard "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid Nitric Acid Method (HJ / T 299-2007)". The soluble salt content in the purified lithium slag was determined according to "NY / T 1121.16-2006 Soil Testing Part 16: Determination of Total Water-Soluble Salts in Soil".

[0070] The test results are shown in Table 1 below:

[0071] Table 1

[0072]

[0073] As can be seen from Table 1 above:

[0074] As shown in Examples 1-3 and Comparative Example 1, the present invention can significantly reduce the thallium leaching toxicity and soluble salt content of lithium slag by introducing carbon dioxide microbubbles into the lithium slag slurry. As shown in Examples 1 and Comparative Example 2, the addition of the microbubble stabilizer of the present invention can promote the effect of carbon dioxide microbubbles, thereby further reducing the thallium leaching toxicity and soluble salt content of lithium slag. As shown in Examples 1 and Examples 4-5, the size of the carbon dioxide microbubbles of the present invention affects the thallium ion dissolution and calcium sulfate reaction effect, thereby affecting the thallium leaching toxicity and soluble salt content of the purified lithium slag. As shown in Examples 1 and Examples 6-7, the ratio of the carbon dioxide gas flow rate to the volume of the lithium slag slurry of the present invention affects the effect of reducing the thallium toxicity and soluble salt content of lithium slag, preferably within a specific range. As shown in Examples 1 and Examples 8-9, the amount of microbubble stabilizer added also affects the effect of reducing the thallium toxicity and soluble salt content of lithium slag.

[0075] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for reducing the thallium toxicity and soluble salt content of lithium slag using microbubble carbonization, characterized in that, The method includes the following steps: Carbon dioxide microbubbles are continuously introduced into the lithium slag slurry for reaction. After the reaction is completed, solid-liquid separation and washing are performed to obtain purified lithium slag. The lithium slag slurry includes lithium slag and a microbubble stabilizer, and the lithium slag includes thallium and calcium sulfate.

2. The method according to claim 1, characterized in that, The carbon dioxide microbubbles have a size of 100μm-500μm.

3. The method according to claim 1 or 2, characterized in that, The method for continuously introducing carbon dioxide microbubbles into lithium slag slurry includes: introducing carbon dioxide gas into lithium slag slurry through micropore aeration or dissolved gas-release method to form carbon dioxide microbubbles. The ratio of the carbon dioxide gas flow rate to the volume of the lithium slag slurry is (1-4) m³. 3 / h:10m 3 .

4. The method according to claim 1 or 2, characterized in that, The microbubble stabilizer includes any one or a combination of at least two of sodium dodecyl sulfate, sodium dodecyl sulfate, or sodium stearate. The content of microbubble stabilizer in the lithium slag slurry is 0.02wt%-0.2wt%.

5. The method according to claim 1 or 2, characterized in that, The lithium slag slurry contains 40wt%-60wt% lithium slag. The thallium content in the lithium slag slurry is 200 μg / L-500 μg / L.

6. The method according to claim 1 or 2, characterized in that, The calcium sulfate content in the lithium slag is 15wt%-20wt%; The thallium leaching toxicity in the lithium slag is 20 μg / L-40 μg / L; The lithium slag is smelting slag of spodumene and / or smelting slag of lepidolite.

7. The method according to claim 1 or 2, characterized in that, The pH of the reaction is 6.0-7.

0.

8. The method according to claim 1 or 2, characterized in that, The reaction temperature is 30℃-50℃, and the reaction time is 0.5h-1h.

9. The method according to claim 1 or 2, characterized in that, The washing method is spray washing.

10. The method according to claim 9, characterized in that, The detergent used for the washing process is water; The mass ratio of the detergent to lithium slag is (0.3-0.5):1.

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