A method for separating lithium and magnesium ions in a salt lake by precipitation and application thereof

Abstract

The application provides a precipitation method for separating lithium and magnesium ions in a salt lake and application, and belongs to the field of separation engineering. In the application, magnesium and lithium ions in the salt lake are separated through a coupling reaction of an organic acid and a water-soluble solid base. Although the traditional method of adding an organic acid to separate magnesium and lithium can separate magnesium ions, a large amount of lithium ions are removed in the precipitation process, so that the retention rate of lithium ions is greatly reduced. The removal rate of magnesium ions in the precipitation method of the application can reach 85-100%, and the retention rate of lithium ions is 96-100%. In the coupling reaction process, the organic acid and the water-soluble solid base used are green and non-toxic, the coupling process is simple, and only the salt lake, the organic acid and the water-soluble solid base need to be mixed and stirred at a specific feeding amount and temperature to precipitate magnesium ions, and lithium ions remain in the solution. The precipitation method in the application has wide application.

Description

Technical Field

[0001] This invention belongs to the field of separation engineering, specifically a precipitation method for separating lithium and magnesium ions in salt lakes and its application. Background Technology

[0002] Lithium, the first metallic element in the periodic table, is an important metallic resource with wide applications in nuclear energy, chemistry, manufacturing, and metallurgy. It is also a key component of the popular new energy batteries. Its main sources include lithium-bearing ores and lithium-bearing brine from salt lakes. China possesses extremely rich lithium deposits in its salt lake brines. Compared to calcining lithium-bearing ores to obtain lithium products, recovering lithium from salt lake brines is a relatively simple and cost-effective method. However, lithium extraction from salt lakes is a global challenge. my country's salt lake resources are mainly concentrated in the Qinghai-Tibet Plateau and Qinghai Province. Qinghai salt lakes generally have a high magnesium-to-lithium ratio and low lithium content, making extraction particularly difficult.

[0003] Methods for lithium extraction from salt lake brine mainly include extraction, adsorption, electrodialysis, and precipitation. Solvent extraction is an effective method, typically exhibiting high selectivity for lithium ions; however, most extractants are organic chemicals, which can severely corrode separation equipment. Adsorption methods often utilize layered adsorbents, aluminum salt adsorbents, and ion sieves, but some adsorbents suffer from problems such as easy solubility, poor recyclability, and insufficient capacity to support industrial applications, thus hindering their practical development. Electrodialysis has gained widespread attention due to its environmental friendliness and high lithium extraction efficiency. However, the complex composition of the brine system and the pH value of the solution negatively impact electrode stability, creating numerous unfavorable factors in practical electrodialysis processes. Precipitation is a traditional method for recovering lithium from salt lakes, utilizing solar and wind power to evaporate and concentrate the brine, followed by a series of chemical reactions and physical processes to precipitate and separate lithium. For example, CN111484046A discloses a method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio. The method mainly involves using magnesium in the brine as raw material, adding an aluminum source and a precipitant, precipitating magnesium and aluminum into layered bimetallic hydroxides (MgAl-LDHs), separating them by filtration, leaving lithium ions in the filtrate, and then enriching the lithium by concentration or ion selective adsorption before precipitating it with carbonate ions to obtain lithium carbonate.

[0004] CN115321705B discloses a method for separating magnesium and lithium from high magnesium-to-lithium ratio salt lake brines. It utilizes the selective complexing ability of complexes for alkali metal ions, increasing the magnesium ion rejection rate of nanofiltration membranes after complexation with magnesium ions, and then producing lithium carbonate through concentration and precipitation. However, the precipitation method results in significant lithium loss during evaporation and precipitation, leading to a low overall recovery rate. Furthermore, this method is not suitable for salt lake brines with high magnesium-to-lithium ratios.

[0005] In summary, the method for extracting lithium from salt lakes is relatively simple and low-cost in industrial applications, and precipitation is commonly used. However, due to the high magnesium and lithium content in some salt lakes, problems such as long precipitation time, low lithium ion recovery rate, and poor ion selectivity remain to be solved during the extraction process. Summary of the Invention

[0006] To address the above problems, this invention provides a precipitation method and application for separating lithium and magnesium ions in salt lakes. This method uses a reaction coupling approach to precipitate magnesium ions from salt lakes, while lithium ions remain in the solution, thereby separating magnesium and lithium ions. The separation process is simple and efficient, with high lithium ion retention, high magnesium removal rate, and few impurities. Furthermore, the obtained magnesium precipitate can be used as a carbon dioxide adsorbent, solving the problem of post-treatment of solid waste.

[0007] This invention provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 85-100% and a lithium retention rate of 96-100%.

[0008] Furthermore, the precipitation method includes the following steps:

[0009] The organic acid and the water-soluble solid alkali were added to the simulated salt lake solution, and the mixture was sonicated and then heated and stirred until completely dissolved. The reaction was continued by heating and stirring. After the reaction was completed, the mixture was allowed to stand to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed alternately with deionized water and ethanol, dried under vacuum, and cooled to room temperature to obtain a magnesium precipitate.

[0010] Furthermore, the simulated salt lake solution includes magnesium chloride, lithium chloride, and deionized water.

[0011] Furthermore, the simulated salt lake solution also includes calcium chloride, and the concentration of calcium chloride in the simulated salt lake solution is 0.001-0.01 g / L.

[0012] Furthermore, the concentration of magnesium chloride in the simulated salt lake solution is 4-100 g / L, and the concentration of lithium chloride is 0.01-10 g / L.

[0013] Furthermore, the mass-to-volume ratio of the organic acid to the simulated salt lake solution is 60-750 g / L.

[0014] Furthermore, the mass-to-volume ratio of the water-soluble solid alkali to the simulated salt lake solution is 25-400 g / L.

[0015] Furthermore, the organic acid is 3,4,5-trihydroxybenzoic acid, and the water-soluble solid base is potassium hydroxide.

[0016] Furthermore, the reaction coupling process mechanism in the precipitation method is as follows:

[0017] .

[0018] Furthermore, the frequency of the ultrasound is 20-50 Hz, and the duration of the ultrasound is 5-20 min.

[0019] Furthermore, the heating and stirring temperature is 110-140℃, and the heating and stirring speed is 300-500 r / min.

[0020] Furthermore, the temperature for continued heating is 110-140℃, the heating time is 12-24h, and the stirring speed during heating is 300-500r / min.

[0021] Furthermore, the settling time is 0.5-1 hour.

[0022] Furthermore, the washing process involves washing with deionized water and ethanol 1-3 times respectively.

[0023] Furthermore, the ethanol is 75% ethanol or anhydrous ethanol.

[0024] Furthermore, the vacuum drying temperature is 50-100℃, the vacuum drying time is 12-24h, and the vacuum degree of the vacuum drying is -0.08 to -0.1MPa.

[0025] The present invention also provides a lithium-containing solution, which is prepared by the precipitation method described above.

[0026] The present invention also provides a lithium battery, which is prepared from the lithium-containing solution.

[0027] This invention also provides a magnesium precipitate, prepared by the precipitation method, wherein the magnesium precipitate has a metal-organic framework structure; in the infrared spectroscopy test of the magnesium precipitate, the range of 3800-2800 cm⁻¹ is [not specified in the original text]. -1 ±0.01cm -1 The region shows a characteristic peak of OH in the carboxyl functional group, at 1622 cm⁻¹. -1 ±0.01cm -1 Characteristic peaks for C=O appear at 1554, 1462, and 1376 cm⁻¹. -1 ±0.01cm -1The three characteristic peaks are typical tensile vibration peaks of the C-C bonds in the aromatic ring, 1300-1000 cm⁻¹. -1 ±0.01cm -1 The characteristic peaks in the region indicate the stretching vibration peaks of the CO bond and the bending vibration peaks of the OH bond in the aromatic ring, at 748 cm⁻¹. -1 ±0.01cm -1 The characteristic peak of the aromatic ring CH appeared at the location; after the magnesium precipitate was soaked for one week under the condition of pH 2-12, obvious diffraction peaks appeared in powder X-ray diffraction (PXRD) at 2θ of 11.35°±0.02°, 14.05°±0.02° and 24.53°±0.02°, respectively, corresponding to the Miller index (hkl) values ​​of (010), (011) and (221), respectively. The peak positions did not change after soaking, and the properties were stable.

[0028] The present invention also provides an adsorbent comprising or prepared from the magnesium precipitate, wherein the adsorbent is used for the adsorption of carbon dioxide gas and the separation of a carbon dioxide-methane mixture; at 25°C and 1.0 bar, the adsorbent has an adsorption capacity of 75-90 cm³ for carbon dioxide. 3 / g, the selectivity of the adsorbent for separating carbon dioxide in the carbon dioxide-methane mixture was calculated to be 1600-1900 based on the adsorption isotherm using the Ideal Adsorption Solution Theory (IAST).

[0029] The beneficial effects of this invention are:

[0030] 1. In this invention, magnesium and lithium ions in a salt lake are separated through a coupling reaction of organic acid and water-soluble solid alkali. Traditional methods of separating magnesium and lithium by adding organic acid can separate magnesium ions, but a large number of lithium ions are carried away during the precipitation process, which greatly reduces the lithium ion retention rate. However, the precipitation method in this invention has a high magnesium ion removal rate of 85-100% and a lithium ion retention rate of 96-100%. Moreover, the organic acid and water-soluble solid alkali used in the coupling reaction process of this invention are green and non-toxic raw materials, and the coupling process is simple. It only requires mixing and stirring the salt lake, organic acid and water-soluble solid alkali at specific feed amounts and temperatures to precipitate magnesium ions, while lithium ions remain in the solution.

[0031] 2. In addition to its simplicity and good separation effect, the precipitation method of this invention can maintain a high removal and retention rate even when other interfering ions are present in the salt lake. It can be applied to any mixed solution of magnesium and lithium ions, and the magnesium precipitate obtained after precipitation has adsorption properties, especially for mixed gases of carbon dioxide and methane. It has good adsorption properties for carbon dioxide and high selectivity, which solves the problem of recycling the precipitate after separating magnesium and lithium. At the same time, the magnesium precipitate can maintain stable performance under pH conditions of 2-12 and still has an advantage in adsorption effect on carbon dioxide. Attached Figure Description

[0032] Figure 1 The images show powder X-ray diffraction (PXRD) patterns of the magnesium precipitate described in Example 1 after being soaked for one week at pH values ​​of 2-12.

[0033] Figure 2 The infrared spectra of magnesium precipitates obtained from the precipitation methods in Examples 3 and 4 are shown below.

[0034] Figure 3 This is an adsorption isotherm diagram of carbon dioxide (CO2) and methane (CH4) by the adsorbent described in Example 11.

[0035] Figure 4 The above are powder X-ray diffraction (PXRD) patterns of magnesium precipitates obtained in the precipitation methods of Example 3 and Comparative Example 1. Detailed Implementation

[0036] The invention will be described in detail below with reference to the embodiments:

[0037] This invention discloses a precipitation method and application for separating lithium and magnesium ions in a salt lake. The method separates magnesium and lithium ions in the salt lake through a simple reaction process. Magnesium ions are removed by precipitation, while lithium ions remain in the solution. Using this precipitation method, the removal rate of magnesium ions is high, and the retention rate of lithium ions is also high.

[0038] Example 1

[0039] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 92.38% and a lithium retention rate of 98.45%.

[0040] In this embodiment, the precipitation method includes the following steps:

[0041] 5.25 g of 3,4,5-trihydroxybenzoic acid and 2.25 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0042] In this embodiment, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19; the amount of organic acid fed is 70g / L, and the amount of water-soluble solid alkali fed is 30g / L.

[0043] like Figure 1 The images show the powder X-ray diffraction (PXRD) patterns of the magnesium precipitate described in Example 1 after soaking for one week at pH values ​​of 2-12. In the PXRD, obvious diffraction peaks appear at 2θ of 11.35°±0.02°, 14.05°±0.02°, and 24.53°±0.02°, respectively, corresponding to the Miller index (hkl) values ​​of (010), (011), and (221). The peak positions do not change after soaking, indicating that the properties are stable.

[0044] The horizontal axis (2 Theta) in the figure represents the diffraction angle, and the vertical axis (Intensity) represents the relative intensity.

[0045] Example 2

[0046] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, so that the magnesium ions in the simulated salt lake solution form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 89.62% and a lithium retention rate of 100%.

[0047] In this embodiment, the precipitation method includes the following steps:

[0048] 5.25 g of 3,4,5-trihydroxybenzoic acid and 2.63 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 110 °C and 300 r / min until completely dissolved. The reaction was continued at 110 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0049] In this embodiment, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19; the amount of organic acid fed is 70g / L, and the amount of water-soluble solid alkali fed is 35g / L.

[0050] Example 3

[0051] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, so that the magnesium ions in the simulated salt lake solution form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 86.71% and a lithium retention rate of 98.64%.

[0052] In this embodiment, the precipitation method includes the following steps:

[0053] 5.25 g of 3,4,5-trihydroxybenzoic acid and 3 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the mixture was heated and stirred at 110 °C and 300 r / min until completely dissolved. The reaction was continued at 110 °C and 300 r / min for 12 h. After the reaction was completed, the mixture was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0054] In this embodiment, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19; the amount of organic acid fed is 70g / L, and the amount of water-soluble solid alkali fed is 40g / L.

[0055] Example 4

[0056] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, so that the magnesium ions in the simulated salt lake solution form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 98.44% and a lithium retention rate of 100%.

[0057] In this embodiment, the precipitation method includes the following steps:

[0058] 5.25 g of 3,4,5-trihydroxybenzoic acid and 2.63 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed once with deionized water and once with anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0059] In this embodiment, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19; the amount of organic acid fed is 70g / L, and the amount of water-soluble solid alkali fed is 35g / L.

[0060] Table 1 shows the inductively coupled plasma optical emission spectrometry (ICP) test results of the magnesium precipitate described in Example 4.

[0061]

[0062] As shown in Table 1, the precipitation method of this invention was used to separate lithium and magnesium ions in the simulated salt lake solution. The lithium content in the separated magnesium precipitate was extremely low, which proves that the precipitation method of this invention has a low lithium ion loss rate and a high retention rate.

[0063] like Figure 2 The figures show the infrared spectra of magnesium precipitates obtained from the precipitation methods in Examples 3 and 4. As can be seen from the figures, the magnesium precipitates obtained from the precipitation methods in Examples 3 and 4 are all within the range of 3800-2800 cm⁻¹. -1 ±0.01cm -1 The region shows a characteristic peak of OH in the carboxyl functional group, at 1622 cm⁻¹. -1 ±0.01cm-1 Characteristic peaks for C=O appear at 1554, 1462, and 1376 cm⁻¹. -1 ±0.01cm -1 The three characteristic peaks are typical tensile vibration peaks of the C-C bonds in the aromatic ring, 1300-1000 cm⁻¹. -1 ±0.01cm -1 The characteristic peaks in the region indicate the stretching vibration peaks of the CO bond and the bending vibration peaks of the OH bond in the aromatic ring, at 748 cm⁻¹. -1 ±0.01cm -1 The characteristic peak of the aromatic ring CH appears at this location;

[0064] In the figure, the horizontal axis (Wavenumbers) represents wavelength, and the vertical axis (transmittance) represents transmittance.

[0065] Example 5

[0066] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, so that the magnesium ions in the simulated salt lake solution form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 92.73% and a lithium retention rate of 97.83%.

[0067] In this embodiment, the precipitation method includes the following steps:

[0068] 5.63 g of 3,4,5-trihydroxybenzoic acid and 2.63 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0069] In this embodiment, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19; the amount of organic acid fed is 75g / L, and the amount of water-soluble solid alkali fed is 35g / L.

[0070] Example 6

[0071] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, so that the magnesium ions in the simulated salt lake solution form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 98.81% and a lithium retention rate of 100%.

[0072] In this embodiment, the precipitation method includes the following steps:

[0073] 4.77 g of 3,4,5-trihydroxybenzoic acid and 2.15 g of potassium hydroxide were added to 77 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0074] In this embodiment, the simulated salt lake solution includes 0.37g magnesium chloride, 0.0034g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 4.86g / L, the concentration of lithium chloride is 0.044g / L, and the magnesium-to-lithium concentration ratio is 109.73; the amount of organic acid fed is 62g / L, and the amount of water-soluble solid alkali fed is 28g / L.

[0075] Example 7

[0076] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 98.96% and a lithium retention rate of 96.03%.

[0077] In this embodiment, the precipitation method includes the following steps:

[0078] 5.01 g of 3,4,5-trihydroxybenzoic acid and 2.31 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0079] In this embodiment, the simulated salt lake solution includes 0.37g magnesium chloride, 0.36g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 4.95g / L, the concentration of lithium chloride is 4.82g / L, and the magnesium-to-lithium concentration ratio is 1.03; the amount of organic acid fed is 65g / L, and the amount of water-soluble solid alkali fed is 30g / L.

[0080] Example 8

[0081] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 99.63% and a lithium retention rate of 97.14%.

[0082] In this embodiment, the precipitation method includes the following steps:

[0083] 10.4 g of 3,4,5-trihydroxybenzoic acid and 4.8 g of potassium hydroxide were added to 80 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0084] In this embodiment, the simulated salt lake solution includes 0.79g magnesium chloride, 0.0028g lithium chloride, and deionized water, wherein the concentration of magnesium chloride is 9.86g / L, the concentration of lithium chloride is 0.035g / L, and the magnesium-to-lithium concentration ratio is 281.71; the amount of organic acid fed is 130g / L, and the amount of water-soluble solid alkali fed is 60g / L.

[0085] Example 9

[0086] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, so that the magnesium ions in the simulated salt lake solution form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 98.71% and a lithium retention rate of 99.85%.

[0087] In this embodiment, the precipitation method includes the following steps:

[0088] 70 g of 3,4,5-trihydroxybenzoic acid and 35 g of potassium hydroxide were added to 100 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the mixture was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the mixture was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0089] In this embodiment, the simulated salt lake solution includes 7.659g of magnesium chloride, 0.0268g of lithium chloride, and deionized water. The concentration of magnesium chloride is 76.59g / L, the concentration of lithium chloride is 0.268g / L, and the magnesium-to-lithium concentration ratio is 285.78. The amount of organic acid fed is 700g / L, and the amount of water-soluble solid alkali fed is 350g / L.

[0090] Example 10

[0091] This embodiment provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 97.20% and a lithium retention rate of 99.26%.

[0092] In this embodiment, the precipitation method includes the following steps:

[0093] 5.25 g of 3,4,5-trihydroxybenzoic acid and 2.63 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 130 °C and 300 r / min until completely dissolved. The reaction was continued at 130 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0094] In this embodiment, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, 0.00045g calcium chloride, and deionized water. The concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, the concentration of calcium chloride is 0.006g / L, and the magnesium-to-lithium concentration ratio is 82.19. The amount of organic acid added is 70g / L, and the amount of water-soluble solid alkali added is 35g / L.

[0095] Example 11

[0096] The present invention also provides an adsorbent comprising the magnesium precipitate described in Example 1, wherein the adsorbent is used for the adsorption of carbon dioxide gas and the separation of a carbon dioxide-methane mixture; at 25°C and 1.0 bar, the adsorbent has an adsorption capacity of 81.56 cm³ for carbon dioxide. 3 / g, the selectivity of the adsorbent for separating carbon dioxide in the carbon dioxide-methane mixture was calculated to be 1753 based on the adsorption isotherm using the Ideal Adsorption Solution Theory (IAST) method.

[0097] like Figure 3 The figure shows the adsorption isotherms of carbon dioxide (CO2) and methane (CH4) by the adsorbent described in Example 11. As can be seen from the figure, the adsorbent exhibits good adsorption performance for carbon dioxide, with an adsorption capacity of 81.56 cm⁻¹. 3 / g, therefore, carbon dioxide and methane can be separated, and its separation selectivity for carbon dioxide can reach 1753;

[0098] The horizontal axis (P / P0) in the figure represents relative pressure, and the vertical axis (Gas uptake) represents adsorption capacity.

[0099] The testing process for the adsorption isotherm is as follows:

[0100] 100 mg of the adsorbent was activated at 80 °C for 12 h. The activated adsorbent was degassed and loaded into a sample tube. Carbon dioxide and methane gases were introduced into the sample tube containing the adsorbent using a BSD-660M A6M high-performance gas adsorption and microporous analyzer. The adsorption performance of the adsorbent was tested at 25 °C and 1.0 bar.

[0101] Comparative Example 1

[0102] This comparative example provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 71.66% and a lithium retention rate of 96.65%.

[0103] In this comparative example, the precipitation method includes the following steps:

[0104] 5.25 g of 3,4,5-trihydroxybenzoic acid and 2.25 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 170 °C and 300 r / min until completely dissolved. The reaction was continued at 170 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0105] In this comparative example, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water. The concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19. The amount of organic acid fed is 70g / L, and the amount of water-soluble solid alkali fed is 30g / L.

[0106] like Figure 4 The figures show the powder X-ray diffraction (PXRD) patterns of magnesium precipitates in the precipitation methods of Example 3 and Comparative Example 1. As can be seen from the figures, the magnesium precipitate in Comparative Example 1 shows a small number of impurity peaks and peak fluctuations compared to Example 3, indicating that its crystal structure has some defects.

[0107] The horizontal axis (2 Theta) in the figure represents the diffraction angle, and the vertical axis (Intensity) represents the relative intensity.

[0108] Comparative Example 2

[0109] This comparative example provides a precipitation method for separating lithium and magnesium ions in a salt lake. The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling, causing the magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing the magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 69.96% and a lithium retention rate of 93.51%.

[0110] In this comparative example, the precipitation method includes the following steps:

[0111] 6.75 g of 3,4,5-trihydroxybenzoic acid and 3.75 g of potassium hydroxide were added to 75 mL of the simulated salt lake solution. After sonication at 20 Hz for 10 min, the solution was heated and stirred at 110 °C and 300 r / min until completely dissolved. The reaction was continued at 110 °C and 300 r / min for 12 h. After the reaction was completed, the solution was allowed to stand for 0.5 h to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed twice alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80 °C and -0.1 MPa for 12 h. After cooling to room temperature, a magnesium precipitate was obtained.

[0112] In this comparative example, the simulated salt lake solution includes 0.45g magnesium chloride, 0.0055g lithium chloride, and deionized water. The concentration of magnesium chloride is 6g / L, the concentration of lithium chloride is 0.073g / L, and the magnesium-to-lithium concentration ratio is 82.19. The amount of organic acid fed is 90g / L, and the amount of water-soluble solid alkali fed is 50g / L.

[0113] Table 2 shows the data for the precipitation methods in Examples 1-10 and Comparative Examples 1-2.

[0114]

[0115] Table 2 shows the test results of the precipitation methods described in Examples 1-10 and Comparative Examples 1-2. As can be seen from the table, when the magnesium content in the simulated salt lake solution increases (Examples 6, 8 and 9) or when other interfering ions are present in the simulated salt lake solution (Example 10), the precipitation method of the present invention can still better separate magnesium and lithium ions, with a high magnesium removal rate and a high lithium ion retention rate. However, in Comparative Examples 1 and 2, the increased temperature or excessive increase in the amount of organic acid and water-soluble solid alkali led to insufficient reaction, thus reducing the magnesium removal rate.

[0116] As can be seen from the above, the precipitation method described in this invention has a very wide range of applications, low cost, and a very high market prospect.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A precipitation method for separating lithium and magnesium ions in a salt lake, characterized in that, The precipitation method involves adding an organic acid and a water-soluble solid alkali to a simulated salt lake solution for reaction coupling. This causes magnesium ions in the simulated salt lake solution to form a complex precipitate with the organic acid and the water-soluble solid alkali, thereby removing magnesium ions from the simulated salt lake solution. The precipitation method achieves a magnesium removal rate of 85-100% and a lithium retention rate of 96-100%. The precipitation method includes the following steps: The organic acid and the water-soluble solid alkali were added to the simulated salt lake solution, and the mixture was sonicated and then heated and stirred until completely dissolved. The reaction was continued by heating and stirring. After the reaction was completed, the mixture was allowed to stand to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a lithium-containing solution and a solid complex. The solid complex was washed alternately with deionized water and ethanol, dried under vacuum, and cooled to room temperature to obtain a magnesium precipitate. The simulated salt lake solution includes magnesium chloride, lithium chloride, and deionized water. The organic acid is 3,4,5-trihydroxybenzoic acid, and the water-soluble solid base is potassium hydroxide; The heating and stirring temperature is 110-140℃, and the heating and stirring speed is 300-500 r / min; The magnesium precipitate has a metal-organic framework structure.

2. The precipitation method according to claim 1, characterized in that, The concentration of magnesium chloride in the simulated salt lake solution is 4-100 g / L, and the concentration of lithium chloride is 0.01-10 g / L.

3. The precipitation method according to claim 1, characterized in that, The mass-to-volume ratio of the organic acid to the simulated salt lake solution is 60-750 g / L.

4. The precipitation method according to claim 1, characterized in that, The mass-to-volume ratio of the water-soluble solid alkali to the simulated salt lake solution is 25-400 g / L.

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