Method for separating alkali metal from aqueous solution by using beta-diketone eutectic solvent

Abstract

The invention relates to a process for separating alkali metal from an aqueous solution by using a beta-diketone eutectic solvent. According to the process, a deep eutectic solvent synthesized by trioctylphosphine oxide and thiophenoyl trifluoroacetone as well as dibenzoylmethane and benzoyl trifluoroacetone in a molar ratio of 1 is used as an extracting agent, and simulated brine containing alkali metals such as lithium, sodium and potassium is used as an extraction water phase. The optimal extraction agent and pH conditions are screened out by investigating the extraction efficiency of the extraction agent on metal ions in different acid-base environments; the optimal extraction process conditions are researched by changing the extraction temperature, the extraction time, the stirring rotating speed and comparison. A large number of metal ions are loaded on the organic phase after the extraction experiment is finished, the research of the back extraction experiment is carried out by adopting 1.5 M LiCl and 0.3 M HCl under the condition that the phase ratio is 1, a high-purity LiCl solution is finally obtained, and the organic phase after the back extraction experiment is finished can be washed by a NaOH solution to be subjected to multiple circulation experiments. According to the method, the eutectic solvent is used as the extraction agent, the method has the advantages of being simple in synthesis, convenient to operate and low in cost, the extraction agent can be recycled after extraction, the production cost is effectively reduced, and the resource utilization rate is increased.

Description

[Technical field]

[0001] The invention belongs to the field of extraction chemistry, chemical purification and separation processes, and specifically relates to a method for separating alkali metals from aqueous solutions using a β-diketone low eutectic solvent. [Background technology]

[0002] With the rise of renewable energy and the popularity of electric vehicles, the demand for lithium resources continues to grow. Lithium-ion batteries are the main energy storage method for electric vehicles, mobile devices, and renewable energy storage systems, and Li2CO3 is one of the important raw materials for manufacturing positive electrode materials for lithium-ion batteries. In the process of Li2CO3 production, sodium carbonate is usually added as a precipitant during the carbonation reaction stage, which results in a relatively high sodium content in the generated mother liquor.

[0003] The most studied lithium extraction technologies include precipitation, adsorption, membrane separation, electrochemical and extraction. Solvent extraction is an efficient metal ion separation method. Its main advantages are its simple operation and high capacity. It is widely used in different processes involving lithium and performs outstandingly.

[0004] In past studies, a large number of extractants for lithium extraction have been developed. Traditional organic extractants often face the problem of large water-soluble losses in practical applications, which not only leads to waste of resources, but also may affect the efficiency and economy of the process. When faced with aqueous solutions containing high concentrations of sodium, the separation of lithium and sodium becomes extremely challenging. Because they are relatively similar in chemical properties, conventional methods may be difficult to achieve effective separation. Low eutectic solvents provide new ideas for the separation and recovery of metal ions due to their green characteristics and high solubility in metal materials. Since Abbott et al. first discovered low eutectic solvents in 2003, researchers have developed a large number of hydrogen bond donors and hydrogen bond acceptors that can form low eutectic solvents (Chem. Commun. 1, (2003) 70-71). However, the high solubility of a large number of low eutectic solvents in aqueous solutions limits their application in aqueous system extraction. Van Osch first synthesized a hydrophobic low eutectic solvent in 2015, and its solubility in water can be as low as 11 mg / g (Green Chemistry. 17 (9) (2015) 4518-4521). The P=O group in trioctylphosphine oxide has a large electron cloud density, strong extraction ability, and good coordination ability for metal ions. It has been reported that it can be used as a hydrogen bond donor to form a low eutectic solvent. Studies have shown that β-diketone has a strong selectivity for lithium ions and can be used as a hydrogen bond donor to form a hydrophobic low eutectic solvent with a synergistic effect with trioctylphosphine oxide. Although researchers have recently increased their research on the use of hydrophobic low eutectic solvents for metal extraction, research on the extraction of alkali metals is still in its early stages. [Summary of the invention]

[0005] In order to solve the above-mentioned technical problems, the present invention provides a method for separating alkali metals from an aqueous solution using a β-diketone deep eutectic solvent. The method uses a hydrophobic deep eutectic solvent composed of trioctylphosphine oxide and thenoyltrifluoroacetone, dibenzoylmethane and benzoyltrifluoroacetone as an extractant, which not only solves the problem of large water solubility loss of traditional extractants during the extraction process, but also solves the problem of difficulty in separating lithium / sodium in an aqueous solution containing high sodium concentration.

[0006] [Technical solution]

[0007] In view of the problem of selectively extracting lithium from an aqueous solution containing alkali metals, the present invention proposes a method for separating alkali metals from an aqueous solution using a β-diketone low eutectic solvent, which not only achieves the purpose of selectively extracting lithium, but also reduces the loss of the selected extractant in the aqueous solution, and the single extraction efficiency of lithium reaches 83.96%.

[0008] The present invention is achieved through the following technical solutions.

[0009] A method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent comprises the following steps:

[0010] (1) The extractant is synthesized by a one-step method, wherein the extractant is mainly composed of three low eutectic solvents consisting of a hydrogen bond acceptor and a hydrogen bond donor acceptor; wherein the hydrogen bond acceptor is trioctylphosphine oxide, and the hydrogen bond donors are thenoyltrifluoroacetone, dibenzoylmethane and benzoyltrifluoroacetone; (2) A simulated salt solution is prepared, wherein the components in the simulated solution mainly include: LiCl, NaCl, KCl; (3) The influence of different extraction process conditions is investigated; wherein the conditions involved include: pH value, temperature, extraction time, stirring speed and relative ratio; (4) The extraction equilibrium of alkali metals is studied by a constant temperature water ring liquid-liquid phase equilibrium kettle, the metal residual concentration in the extract phase is analyzed by atomic absorption spectroscopy, and the extraction efficiency and selectivity of different metal ions are calculated by mass conservation; (5) The influence of different stripping process conditions is investigated; wherein the conditions involved include: LiCl concentration, HCl concentration, relative ratio.

[0011] According to another preferred embodiment of the present invention, it is characterized in that: the extractant is a low eutectic solvent composed of trioctylphosphine oxide and β-diketone.

[0012] According to another preferred embodiment of the present invention, it is characterized in that the molar ratio of the hydrogen bond donor and the hydrogen bond acceptor forming the low eutectic solvent is 1:1, and the synthesis experiment temperature is 25°C.

[0013] According to another preferred embodiment of the present invention, it is characterized in that thenoyltrifluoroacetone is selected as the hydrogen bond donor for the final synthesis of the deep eutectic solvent.

[0014] According to another preferred embodiment of the present invention, it is characterized in that the extraction pH value is 8-12.

[0015] According to another preferred embodiment of the present invention, it is characterized in that the temperature of the extraction experiment is 30-50°C.

[0016] According to another preferred embodiment of the present invention, it is characterized in that the extraction experiment lasts for 1 to 20 minutes.

[0017] According to another preferred embodiment of the present invention, it is characterized in that the stirring speed of the extraction experiment is 120-600 rpm.

[0018] According to another preferred embodiment of the present invention, it is characterized in that the ratio of extractant to water is 0.5-2.5:1.

[0019] According to another preferred embodiment of the present invention, it is characterized in that: the concentrations of the metal ions are: Li + 1~5g / L -1 ,Na + 10~100g / L -1 ,K + 1~5g / L -1 .

[0020] According to another preferred embodiment of the present invention, it is characterized in that: in the process conditions of the stripping process, the LiCl concentration is 0.1-2 mol / L, the HCl concentration is 0.1-0.5 mol / L, and the ratio of the low eutectic solvent to the acid is 1:2-2:1.

[0021] [Beneficial Effects]

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) This method can be used to selectively extract lithium from a simulated solution containing alkali metals, ultimately obtaining a high-purity LiCl solution.

[0024] (2) This method uses a low eutectic solvent as an extractant, which has the advantages of simple synthesis, convenient operation, and low cost. In addition, during the extraction process, there is almost no loss of the extractant in the aqueous solution, thus avoiding the problem of contaminating the aqueous solution.

[0025] (3) The low eutectic solvent used is relatively cheap and can be recycled and reused after extraction, which effectively reduces production costs and improves resource utilization.

Brief Description of the Drawings

[0026] Figure 1 The present invention is a process flow chart for separating alkali metals from aqueous solutions using a β-diketone low eutectic solvent. [Specific implementation method]

[0027] Test process:

[0028] The simulated solution and the extractant were subjected to extraction experiments in an assembled constant temperature water ring liquid-liquid phase equilibrium reactor. After the extraction experiment, the two phases were allowed to stand to completely separate, the upper organic phase was taken out with a pipette, and the aqueous phase flowed out from the lower layer. About 1g of the aqueous phase was weighed for dilution, and the concentration of alkali metals in the aqueous solution was determined by an atomic absorption spectrophotometer, and the concentration of alkali metals in the low eutectic solvent was obtained by the law of conservation of mass. The distribution ratio (D) and separation factor (β) were calculated by the following formula:

[0029]

[0030] Embodiment 1:

[0031] When a low eutectic solvent synthesized by trioctylphosphine oxide and thenoyltrifluoroacetone, dibenzoylmethane and benzoyltrifluoroacetone in a molar ratio of 1 is used as an extractant, the low eutectic solvent formed by trioctylphosphine oxide and thenoyltrifluoroacetone has good lithium extraction performance at a pH value of 12, with a lithium extraction efficiency of 77.92%, a separation coefficient of lithium and sodium of 279.92, and a separation coefficient of lithium and potassium of 415.69.

[0032] Embodiment 2:

[0033] Under the conditions of extraction temperature of 20°C, extraction time of 10 min, stirring speed of 480 rpm and phase ratio of 0.5, the extraction efficiency of lithium was 73.56%, the separation coefficient of lithium and sodium was 172.1, and the separation coefficient of lithium and potassium was 431.09.

[0034] Embodiment 3:

[0035] Under the conditions of extraction temperature of 20°C, extraction time of 10 min, stirring speed of 480 rpm and phase ratio of 1, the extraction efficiency of lithium was 83.96%, the separation coefficient of lithium and sodium was 283.51, and the separation coefficient of lithium and potassium was 583.92.

[0036] Embodiment 4:

[0037] Under the conditions of extraction temperature of 20°C, extraction time of 10 min, stirring speed of 540 rpm and phase ratio of 1, the extraction efficiency of lithium was 83.86%, the separation coefficient of lithium and sodium was 1199.37, and the separation coefficient of lithium and potassium was 585.18 for trioctylphosphine oxide and thenoyltrifluoroacetone.

[0038] Embodiment 5:

[0039] After the extraction experiment, the low eutectic solvent and the stripping agent were subjected to stripping experiments under different extraction conditions in an assembled constant temperature water ring liquid-liquid phase equilibrium kettle. After the stripping experiment, the two phases were allowed to stand to completely separate, the upper organic phase was taken out with a pipette, and the aqueous phase flowed out from the lower layer. About 1g of the aqueous phase was weighed for dilution, and the concentration of alkali metals in the aqueous solution was determined by an atomic absorption spectrophotometer. In the stripping process conditions, the LiCl concentration was 2mol / L, the HCl concentration was 0.3mol / L, and when the ratio was 0.5, 85.65% of the sodium, 91.94% of the potassium, and 83.89% of the lithium were stripped from the low eutectic solvent.

[0040] Embodiment 6:

[0041] After the extraction experiment, the low eutectic solvent and the stripping agent were subjected to stripping experiments under different extraction conditions in the assembled constant temperature water ring liquid-liquid phase equilibrium reactor. In the stripping process conditions, the LiCl concentration was 2 mol / L, the HCl concentration was 0.3 mol / L, and when the phase ratio was 1, 99.59% of the sodium, 99.76% of the potassium, and 99.37% of the lithium were stripped from the low eutectic solvent.

Claims

1. A method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent, characterized in that: Includes steps: (1) synthesizing an extractant by a one-step method, wherein the extractant is mainly composed of three low eutectic solvents consisting of a hydrogen bond acceptor and a hydrogen bond donor; wherein the hydrogen bond acceptor is trioctylphosphine oxide, and the hydrogen bond donors are thenoyltrifluoroacetone, dibenzoylmethane and benzoyltrifluoroacetone; (2) preparing a simulated salt solution, wherein the components of the simulated solution mainly include: LiCl, NaCl, and KCl; (3) Investigate the effects of different extraction process conditions; the conditions involved include: pH value, temperature, extraction time, stirring speed and ratio; (4) The extraction equilibrium of alkali metals was studied by a constant temperature water ring liquid-liquid phase equilibrium kettle, the metal residual concentration in the raffinate phase was analyzed by atomic absorption spectroscopy, and the extraction efficiency and selectivity of different metal ions were calculated by mass conservation; (5) Investigate the influence of different stripping process conditions; Among them, the conditions involved are: LiCl concentration, HCl concentration, compared.

2. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor of the extractant is 1:1, and the synthesis temperature condition is 25°C.

3. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: Finally, thenoyltrifluoroacetone was selected as the hydrogen bond donor for the synthesis of deep eutectic solvents.

4. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The pH value in the extraction process conditions is 5-12.

5. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The extraction temperature in the extraction process conditions is 20-80°C.

6. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The extraction time in the extraction process conditions is 1 to 30 minutes.

7. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The stirring speed in the extraction process conditions is 10 to 600 rpm.

8. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The ratio of low eutectic solvent to water is 0.5 to 2.5:

1.

9. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: The concentrations of metal ions are: Li + 1~10g / L -1 ,Na + 10~100g / L -1 ,K + 1~10g / L -1 g / L -1 .

10. The method for separating alkali metals from aqueous solutions using a β-diketone deep eutectic solvent according to claim 1, characterized in that: In the stripping process conditions, the LiCl concentration is 0.1-2 mol / L, the HCl concentration is 0.1-0.5 mol / L, and the ratio of the low eutectic solvent to the acid is 1:3-3:1.

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