Method for elution end point control in a lithium ion scavenger preparation process

Abstract

The application discloses a method for controlling elution end point in lithium ion trapping agent preparation process, and relates to the field of liquid lithium resource recycling. Based on the positive correlation between the conductivity of eluent and the concentration of free ions in solution, the best conductivity setting value considering structural stability and lithium removal activation effect is determined through the corresponding relationship between step elution test and product trapping performance. In the process of trapping agent elution and activation, the conductivity of eluent is monitored in real time online by using a conductivity meter. If the measured value is greater than the setting value, the cycle elution is carried out; if the measured value is less than or equal to the setting value, it indicates that the elution and activation are completed and the elution is terminated, so that the lithium ion trapping agent with high activity and stable structure is obtained. The conductivity test method is simple and fast, and replaces the inductively coupled plasma emission spectrometry test method, so that the quality fluctuation problem caused by the difficulty in judging the elution end point in the preparation of lithium ion trapping agent can be solved, and the monitoring technical support for the preparation of lithium ion trapping agent with high activity and stability is provided.

Description

Technical Field

[0001] This invention belongs to the field of liquid lithium resource recycling technology, specifically relating to a method for controlling the elution endpoint in the preparation process of lithium ion trapping agents. Background Technology

[0002] Lithium / aluminum double hydroxide (Li / Al-LDH) is currently the most widely used and industrially promising scavenging agent material in the field of liquid lithium resource recovery due to its advantages such as neutral desorption and resistance to solvent loss. Its structure consists of a positively charged aluminum hydroxide host layer and interlayer anions and water molecules; its chemical composition can be represented as LiCl· m Al(OH)3· n H2O. In this structure, Al 3+ It serves as a framework support and does not dissolve, while Li + Reversible insertion and extraction can occur between the layers. The stability and trapping performance of Li / Al-LDH crystals are closely related to the degree of lithium-ion insertion and extraction between the layers. Appropriate lithium-ion insertion and extraction can form highly active trapping sites. However, once excessive delithiation occurs, the main layers will undergo irreversible structural rearrangement and gradually collapse into inactive gibbsite (γ-Al(OH)3). Therefore, in the delithiation activation process using deionized water as the eluent, real-time monitoring of the lithium-ion concentration change in the eluent is crucial for accurately controlling the elution endpoint and preventing material structural collapse.

[0003] Currently, in industrial applications, inductively coupled plasma optical emission spectrometry (ICP-OES) is mainly used to determine the elution endpoint during trap preparation. However, this technology has the following problems: First, it suffers from significant detection lag. The ICP-OES detection process is cumbersome, with a delay of several hours from sampling to data acquisition, making it impossible to provide real-time feedback on the elution status. Second, it is costly and inefficient. ICP-OES equipment is expensive, consumes large amounts of consumables such as argon, and has high instrument maintenance costs, making it difficult to deploy in industrial production sites. Third, it is difficult to achieve precise process control. Due to the lack of real-time online monitoring methods, the controllability of the elution process is poor, especially in large-scale preparation processes, which seriously affects the stability of the product's trapping performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the elution endpoint in the preparation process of lithium-ion traps, thereby solving the problems of strong lag, high cost, and difficulty in accurately controlling the elution endpoint in existing ICP-OES detection technologies. This invention achieves precise control of the delithiation and activation process of the trap precursor by accurately determining the optimal elution equilibrium point through online monitoring of changes in the conductivity of the eluent.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for controlling the elution endpoint in the preparation process of a lithium-ion trap includes the following steps: (1) Add aluminum source and lithium source to water and heat to form lithium aluminum intercalation compound; (2) React the lithium aluminum intercalation compound obtained in step (1) with alkaline solution, adjust the pH value to 6.5~7.5, and age it to obtain a structurally stable lithium ion capture agent precursor slurry. (3) The precursor slurry obtained in step (2) is placed in a mixing tank for stepwise elution. Water is added and stirred to release lithium ions between the layers of the precipitant precursor into the aqueous phase. After elution, the mixture is allowed to stand and separate into layers. The conductivity of the supernatant is monitored in real time using a conductivity meter. (4) Compare the measured conductivity value in step (3) with the set conductivity value when elution equilibrium is reached. If the measured value is greater than the set value, remove the supernatant and add water for cyclic elution. If the measured value is less than or equal to the set value, terminate elution and obtain the lithium ion trap by filtration, drying and grinding.

[0006] Preferably, in step (1), the aluminum source is one of polyaluminum chloride (Al2O3 content ≥28.0%), polyaluminum ferric chloride (Al2O3 content ≥23.0%), aluminum chloride hexahydrate, and sodium aluminate; the lithium source is one of anhydrous lithium chloride and lithium chloride monohydrate; and the Li / Al molar ratio in the lithium aluminum intercalation compound is 1:1~2.5.

[0007] Preferably, in step (2), the alkaline solution is one of sodium hydroxide, ammonia, or urea solution.

[0008] Preferably, in step (2), the temperature of the coprecipitation reaction is 80 ℃ and the time of the coprecipitation reaction is 30~60 min; the aging temperature is 80 ℃ and the aging time is 30~60 min.

[0009] Preferably, in step (3), the elution temperature is room temperature, the eluent-to-solid ratio is 100 mL: 1 g (deionized water: dry weight of the precipitant), the stirring time is 10 min, and the stirring speed is 500~800 r / min.

[0010] Preferably, in step (4), the conductivity setting value at elution equilibrium is 2.50 mS / cm; this setting value is determined by the step-by-step elution process, that is, by synchronously monitoring the conductivity and lithium ion concentration of the supernatant after each elution operation, and taking the conductivity value corresponding to the lithium ion concentration in the supernatant dropping to below 8 mg / L as the setting value.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a simple and rapid conductivity testing method to replace inductively coupled plasma atomic emission spectrometry (ICP-AES), significantly improving the efficiency of lithium-ion trapping agent preparation. This method can accurately determine the elution equilibrium point, effectively avoiding insufficient elution leading to a reduction in lithium-capturing sites or excessive elution causing structural deactivation, thus ensuring high activity and stability of the product. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of the elution endpoint control in the preparation process of a lithium-ion trapping agent according to the present invention.

[0013] Figure 2 This is a graph showing the relationship between the conductivity of the eluent and the performance of the trapping agent in Example 1 of the present invention.

[0014] Figure 3 The images show the XRD patterns of the lithium-ion traps prepared in Examples 1 and 2 of this invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. The specific embodiments described herein are only for illustrating the invention and are not intended to limit the scope of the invention.

[0016] Example 1 A method for controlling the elution endpoint in the preparation process of a lithium-ion trap, the process flow is as follows: Figure 1 As shown, the specific steps include the following: 16.5 g of polyaluminum chloride (Al2O3 content ≥28.0%) and 4.6 g of anhydrous lithium chloride were weighed and dissolved in 200 mL of deionized water. The solution was stirred at 500 r / min for 10 min under constant temperature water bath conditions at 80 ℃ to obtain a mixed salt solution. Subsequently, the mixture was added to 20 mL of 6 mol / L NaOH solution, and the pH of the reaction system was adjusted and maintained at 6.5~7.5. After aging at 80 ℃ for 30 min, the slurry of the scavenging agent precursor was obtained. The precursor slurry was placed in a mixing tank, and 800 mL of deionized water was added at a liquid-to-solid ratio of 100 mL: 1 g. The mixture was stirred at 500 rpm for 10 min and then allowed to stand for 10 min. The conductivity of the supernatant was measured using a conductivity meter. If the measured conductivity was greater than the set value of 2.50 mS / cm, the supernatant was removed, and deionized water was added for elution until the conductivity of the supernatant dropped below the set value. Elution was then stopped, and the mixture was filtered and dehydrated. The resulting filter cake was dried at 60 °C for 6 h, and after pulverization and grinding, a highly active and structurally stable lithium-ion scavenger was obtained.

[0017] To determine the rationality of the set value of conductivity at the elution endpoint (2.50 mS / cm), this embodiment records in detail the relationship between the conductivity of the supernatant and the concentration of lithium and sodium ions during the step-elution process. The measured data are shown in Table 1.

[0018] Table 1. Changes in conductivity and ion concentration of the supernatant during the elution process. Table 1 shows a significant positive correlation between the conductivity of the supernatant and the lithium content in the solution. With increasing elution cycles, free ions are continuously removed, and the conductivity and lithium ion concentration decrease synchronously. At the 5th elution, the lithium ion concentration was 8.2 mg / L, and the conductivity was 4.02 mS / cm; at the 6th elution, the lithium ion concentration decreased to 7.0 mg / L, and the conductivity decreased to 2.06 mS / cm. To ensure that the lithium ion concentration in the supernatant stably decreases to below 8 mg / L, this embodiment selects a value between the 5th and 6th elution results, and close to the endpoint of the 6th elution—2.50 mS / cm—as the conductivity setpoint for the elution endpoint.

[0019] 5 g of lithium-ion scavenging agent with different elution cycles was added to 100 mL of heavy oil thermal recovery produced fluid with a lithium concentration of 85 mg / L. After reaching scavenging equilibrium, the lithium-ion content in the produced fluid was analyzed. When the measured value (2.06 mS / cm) ≤ 2.50 mS / cm, the lithium-ion scavenging rate of the obtained product was 73.21%. Figure 2 This is a graph showing the relationship between the conductivity of the eluent and the performance of the lithium-ion trap in this embodiment. It can be seen that the lower the conductivity of the eluent, the higher the capture rate of the lithium-ion trap, indicating that the conductivity can precisely control the elution equilibrium endpoint.

[0020] Example 2 The difference between this embodiment and Example 1 is that the amounts of reaction raw materials and eluent are increased by 400 times in equal proportion.

[0021] 6.6 kg of polyaluminum chloride (Al2O3 content ≥28.0%) and 1.84 kg of anhydrous lithium chloride were weighed and dissolved in 75 L of deionized water. The solution was stirred at 800 r / min for 10 min under constant temperature water bath conditions at 80 ℃ to obtain a mixed salt solution. Subsequently, the mixture was added to 8 L of 6 mol / L NaOH solution, and the pH of the reaction system was adjusted and maintained at 6.5~7.5. After aging at 80 ℃ for 30 min and solid-liquid separation, the slurry of the scavenging agent precursor was obtained. The precursor slurry was placed in a mixing tank, and 320 L of deionized water was added at a liquid-to-solid ratio of 100 mL: 1 g. The mixture was stirred at 800 rpm for 10 min and then allowed to stand for 10 min. The conductivity of the supernatant was measured using a conductivity meter. If the measured conductivity was greater than the set value of 2.50 mS / cm, the supernatant was removed, and deionized water was added for elution. Elution continued until the conductivity of the supernatant dropped below the set value (corresponding to 6 cycles), at which point elution was stopped and the mixture was filtered and dehydrated. The resulting filter cake was dried at 60 °C for 6 h, and after pulverization and grinding, a highly active and structurally stable lithium-ion scavenger was obtained.

[0022] Ten batches of lithium-ion trapping agent produced continuously were sampled and tested. Under the same test conditions as in Example 1, the lithium-ion trapping rate of all batches remained in the range of 70.63% to 82.28%, showing excellent batch stability.

[0023] Figure 3 The XRD patterns of the lithium-ion traps prepared in Examples 1 and 2 show that the diffraction peak shapes and positions of the traps from Example 1 (gram-scale preparation) and Example 2 (kilogram-scale preparation) are highly consistent, and both correspond one-to-one with the characteristic diffraction peaks of the standard card (JCPDS No. 31-0700). These results fully demonstrate that the elution endpoint control method provided by this invention is fully applicable to the kilogram-scale and larger-scale preparation of LiCl·2Al(OH)3·xH2O. This elution technique effectively maintains the integrity of the Li / Al-LDH crystal structure, avoids the formation of gibbsite, and significantly improves product stability while ensuring a high lithium-ion capture rate.

[0024] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger, characterized in that, Includes the following steps: (1) Add aluminum source and lithium source to water and react them by heating to form lithium aluminum intercalation compound; (2) The lithium aluminum intercalation compound obtained in step (1) is added to an alkaline solution for co-precipitation reaction. The pH value at the reaction endpoint is adjusted and controlled to be 6.5~7.

5. After aging, lithium ion capture agent precursor slurry is obtained. (3) Place the precursor slurry obtained in step (2) into a mixing tank for stepwise elution, add water and stir to release lithium ions between the layers of the scavenging agent precursor into the liquid phase; After elution, the supernatant was allowed to stand and separate into layers, and the conductivity of the supernatant was monitored in real time using a conductivity meter. (4) Compare the measured conductivity value in step (3) with the set conductivity value when elution equilibrium is reached. If the measured value is greater than the set value, remove the supernatant and add water for cyclic elution. If the measured value is less than or equal to the set value, terminate elution and obtain the lithium ion trap by filtration, drying and grinding.

2. The method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger according to claim 1, characterized in that, In step (1), the aluminum source is one of polyaluminum chloride with an Al2O3 content ≥28.0%, polyaluminum ferric chloride with an Al2O3 content ≥23.0%, aluminum chloride hexahydrate, and sodium aluminate; the lithium source is one of anhydrous lithium chloride and lithium chloride monohydrate; and the Li / Al molar ratio in the lithium aluminum intercalation compound is 1:1~2.

5.

3. The method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger according to claim 1, characterized in that, In step (2), the alkaline solution is one of sodium hydroxide solution, ammonia water, or urea solution.

4. The method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger according to claim 1, characterized in that, In step (2), the temperature of the coprecipitation reaction is 80 °C and the time of the coprecipitation reaction is 30 min.

5. The method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger according to claim 1, characterized in that, In step (2), the aging temperature is 80 ℃ and the aging time is 60 min.

6. The method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger according to claim 1, characterized in that, In step (3), the eluent-to-solid ratio is 100 mL: 1 g, the stirring time is 10 min, and the stirring speed is 500~800 r / min.

7. The method for controlling the elution endpoint in the preparation process of a lithium-ion scavenger according to claim 1, characterized in that, In step (4), the conductivity is set to 2.50 mS / cm at elution equilibrium. The set value corresponds to the conductivity value when the lithium ion concentration in the supernatant drops to below 8 mg / L. This value is determined by the synchronous monitoring relationship between the conductivity of the supernatant and the lithium ion concentration during the step elution process.

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