Method for separating and extracting lithium and magnesium from salt lake brine

Abstract

The invention provides a method for separating and extracting lithium and magnesium from salt lake brine. The method comprises the following steps: pretreating the salt lake brine; adding an organic extraction agent into the pretreated salt lake brine, and transferring lithium and magnesium into an organic phase; preparing a mixed solution of sodium ascorbate and hydrochloric acid, mixing the mixed solution with the organic phase containing lithium and magnesium, carrying out reverse extraction, and carrying out solid-liquid separation after the reverse extraction is ended, so as to respectively obtain a magnesium ascorbate precipitate and a solution containing lithium ascorbate; and evaporating and concentrating the solution containing the lithium ascorbate to obtain a lithium ascorbate solid. The separation and extraction method is environment-friendly and low in cost, and lithium and magnesium in the salt lake brine can be efficiently separated and extracted.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium extraction from salt lakes, and specifically relates to a method for separating and extracting lithium and magnesium from salt lake brine. Background Art

[0002] Salt lake brines contain abundant lithium and magnesium resources, but lithium-magnesium separation remains a key challenge in salt lake resource development. Commonly used methods include precipitation, solvent extraction, ion exchange adsorption, membrane separation technology, and calcination leaching, but all present significant drawbacks. Precipitation achieves initial separation through stepwise precipitation or aluminum salt precipitation, but this method consumes large amounts of reagents and is prone to lithium loss due to lithium co-precipitation with magnesium. Solvent extraction relies on organic extractants for selective lithium extraction, but high magnesium ion concentrations interfere with extraction efficiency. Ion exchange and adsorption methods offer high selectivity, but the adsorbent material has low capacity and poor stability in complex brines, and the regeneration process produces acidic wastewater. Membrane separation technologies (such as nanofiltration and electrodialysis) can physically separate ions, but their large-scale application is hampered by severe membrane fouling, high energy consumption, and insufficient selectivity. Calcination leaching is uneconomical due to high-temperature energy consumption, lithium volatilization losses, and carbon emissions. Furthermore, the high magnesium-to-lithium ratio results in low resource utilization, and the by-product magnesium is often discharged as waste slag, exacerbating environmental pressures. Efficient and environmentally friendly lithium-magnesium separation remains an urgent challenge. Summary of the Invention

[0003] In view of the shortcomings of the prior art, one of the objectives of the present invention is to solve one or more problems existing in the prior art. For example, one of the objectives of the present invention is to provide an efficient, environmentally friendly, and low-cost method for separating and extracting lithium and magnesium from salt lake brine.

[0004] The present invention provides a method for separating and extracting lithium and magnesium from salt lake brine, which can include the following steps: pretreating the salt lake brine; adding an organic extractant to the pretreated salt lake brine to transfer lithium and magnesium into an organic phase; preparing a mixed solution of sodium ascorbate and hydrochloric acid, mixing the mixed solution with an organic phase containing lithium and magnesium for back extraction, and separating the solid and liquid after the back extraction to obtain a magnesium ascorbate precipitate and a solution containing lithium ascorbate, respectively; and evaporating and concentrating the solution containing lithium ascorbate to obtain a lithium ascorbate solid.

[0005] Furthermore, the stripping temperature may be 15°C to 30°C.

[0006] Furthermore, the water content in the mixture of sodium ascorbate and hydrochloric acid may be 31 wt% to 35 wt%.

[0007] Furthermore, the stripping temperature may be 20° C., and the water content in the mixed solution of sodium ascorbate and hydrochloric acid may be 31 wt %.

[0008] Furthermore, the stripping time may be 50 minutes to 70 minutes.

[0009] Furthermore, in the mixed solution of sodium ascorbate and hydrochloric acid, the concentration of sodium ascorbate may be 0.1 mol / L to 0.5 mol / L, and the concentration of hydrochloric acid may be 0.5 mol / L to 1.5 mol / L.

[0010] Furthermore, the extractant may be P204, P507 or Cyanex 272.

[0011] Furthermore, after adding the organic extractant to the pretreated salt lake brine, the volume ratio of the organic phase to the aqueous phase can be (4-5):1.

[0012] Compared with the prior art, the beneficial effects of the present invention include at least: the separation and extraction method of the present invention is environmentally friendly, low-cost, and can efficiently separate and extract lithium and magnesium from salt lake brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects and features of the present invention will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0014] Figure 1 This is the XRD pattern of the magnesium product obtained in Example 1.

[0015] Figure 2 This is the XRD pattern of the lithium product obtained in Example 1.

[0016] Figure 3 This is the product diagram after the stripping in Comparative Example 1.

[0017] Figure 4 This is the product diagram after the stripping in Comparative Example 2.

[0018] Figure 5 This is the product diagram after the stripping in Comparative Example 3.

[0019] Figure 6 This is the product diagram after the stripping in Comparative Example 4. DETAILED DESCRIPTION

[0020] Hereinafter, a method for separating and extracting lithium and magnesium from salt lake brine according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0021] Specifically, the present invention first adds an extractant to salt lake brine for a co-extraction operation, thereby transferring lithium and magnesium elements in the salt lake brine from the brine into an organic phase. Next, the organic phase containing lithium and magnesium is contacted with a mixed solution of sodium ascorbate and hydrochloric acid. The temperature of the entire stripping process and the water content of the mixed solution are controlled to perform a stripping operation. During the stripping process, lithium and magnesium are separated from the organic phase, wherein magnesium reacts with sodium ascorbate to form a magnesium ascorbate precipitate, while lithium enters the aqueous phase to form a lithium ascorbate solution. The stripping mixture is then subjected to solid-liquid separation to obtain a magnesium ascorbate precipitate and an aqueous phase containing lithium ascorbate, completing the separation of lithium and magnesium and achieving magnesium recovery. Finally, the aqueous phase containing lithium ascorbate is evaporated and concentrated to obtain a lithium ascorbate solid. The lithium ascorbate solid is further processed to obtain a high-purity lithium product, achieving lithium recovery.

[0022] The present invention provides a method for separating and extracting lithium and magnesium from salt lake brine. In some embodiments, the method may include the following steps:

[0023] Step 01: Pre-treat the salt lake brine.

[0024] Step 02: Add an organic extractant to the pretreated salt lake brine to transfer lithium and magnesium into the organic phase.

[0025] Step 03: Prepare a mixture of sodium ascorbate and hydrochloric acid. This mixture is then mixed with the organic phase containing lithium and magnesium for stripping. After stripping, the solid and liquid are separated to produce a magnesium ascorbate precipitate and a solution containing lithium ascorbate. During the stripping process, lithium and magnesium are separated from the organic phase. Magnesium reacts with sodium ascorbate to form a magnesium ascorbate precipitate, while lithium enters the aqueous phase to form a lithium ascorbate solution.

[0026] Step 04: Evaporating and concentrating the solution containing lithium ascorbate to obtain lithium ascorbate solid.

[0027] Step 05, washing the magnesium ascorbate precipitate with anhydrous ethanol 3 to 5 times, transferring it to an oven at 65°C for heating and drying to obtain magnesium acetate; washing the lithium ascorbate precipitate with anhydrous ethanol 3 to 5 times, transferring it to an oven at 65°C for heating and drying to obtain a lithium maleate product.

[0028] In some embodiments, the salt lake brine is pretreated to remove suspended matter and impurities in the salt lake brine. For example, suspended matter can be removed by allowing the brine to stand for a while, and then impurities such as potassium salts can be removed by evaporating the brine and cooling and crystallizing it.

[0029] In some embodiments, the stripping temperature may be 15° C. to 30° C. If the stripping temperature is less than 15° C. or greater than 30° C., the magnesium in the organic phase cannot react with ascorbic acid to form magnesium ascorbate precipitate, resulting in the inability to separate lithium and magnesium. Therefore, the stripping temperature must be controlled between 15° C. and 30° C. In certain embodiments, the stripping temperature may be 17° C. to 26° C., 19° C. to 23° C., 20° C. to 22° C., or a combination thereof.

[0030] In some embodiments, the water content in the mixture of sodium ascorbate and hydrochloric acid can be 31wt% to 35wt%. The water content in the mixture of sodium ascorbate and hydrochloric acid has an important impact on the separation of magnesium and lithium in brine. If the water content in the mixture is less than 31wt%, lithium and magnesium will co-precipitate, resulting in the inability to separate and extract lithium and magnesium. If the water content in the mixture is greater than 35wt%, the magnesium in the organic phase cannot form ascorbic acid magnesium precipitate with ascorbic acid, resulting in the inability to separate lithium and magnesium. Therefore, the water content in the mixture of sodium ascorbate and hydrochloric acid is set to 31wt% to 35wt%. In certain embodiments, the water content in the mixture can be a combination of 32wt% to 34wt%, 32.5wt% to 33wt% or above. Preferably, the stripping temperature is 20°C and the water content in the mixture of sodium ascorbate and hydrochloric acid is 31%, which can maximize the recovery rate of magnesium and lithium elements.

[0031] In some embodiments, the stripping time can be set to 50 minutes to 70 minutes. For example, the stripping time can be set to 53 minutes to 67 minutes, 58 minutes to 65 minutes, 62 minutes to 64 minutes, or a combination of the above ranges.

[0032] In some embodiments, the concentration of sodium ascorbate in the mixture of sodium ascorbate and hydrochloric acid can be 0.1mol / L to 0.5mol / L, and the concentration of hydrochloric acid can be 0.5mol / L to 1.5mol / L. When the concentration of hydrochloric acid is within the range of 0.5mol / L to 1.5mol / L, the hydrogen ions provided by hydrochloric acid can provide an acidic environment, facilitating the extraction of lithium ions and magnesium ions from P204, and the chloride ions provided by hydrochloric acid can coordinate with the lithium ions and magnesium ions first. When the concentration of sodium ascorbate is controlled at 0.1mol / L to 0.5mol / L, the ascorbate ions provided by sodium ascorbate can cause the lithium ions and magnesium ions to switch from coordination with chloride ions to coordination with ascorbate ions, causing the magnesium ions to precipitate and the lithium ions to enter the solution.

[0033] In some embodiments, the organic extractant may be P204, P507, or Cyanex 272. Of course, the present invention is not limited thereto, and other conventional existing extractants may be used.

[0034] In some embodiments, after adding the organic extractant to the pretreated salt lake brine, the volume ratio of the organic phase to the aqueous phase can be (4-5):1. This volume ratio can improve the extraction rate. For example, the volume ratio can be 4.5:1.

[0035] In some embodiments, the solution containing lithium ascorbate is evaporated and concentrated to reduce the water content, for example, to 17.8%, to obtain lithium ascorbate solid.

[0036] In order to better understand the present invention, the content of the present invention is further explained below with reference to specific examples, but the content of the present invention is not limited to the following examples.

[0037] Example 1

[0038] A method for separating and extracting lithium and magnesium from salt lake brine, comprising the following steps:

[0039] Step 1: Take 1000L of salt lake brine and filter it through a sand filter to remove suspended matter and impurities, thereby pretreating the salt lake brine.

[0040] Step 2: adding extractant P204 to the pretreated brine, controlling the extraction temperature to 25° C. and the extraction time to 60 minutes, so that lithium and magnesium are transferred from the brine to the organic phase.

[0041] Step 3, mix the organic phase containing lithium and magnesium with a mixed solution of sodium ascorbate and hydrochloric acid, control the water content of the mixed solution of sodium ascorbate and hydrochloric acid to 31%, the stripping temperature to 25°C, and the stripping time to 60 minutes. During the stripping process, lithium and magnesium are separated from the organic phase, wherein magnesium reacts with sodium ascorbate to form a magnesium ascorbate precipitate, while lithium enters the aqueous phase to form a lithium ascorbate solution. The mixture after stripping is centrifuged to obtain a magnesium ascorbate precipitate and an aqueous phase containing lithium ascorbate. Wash the magnesium ascorbate precipitate with anhydrous ethanol 3 to 5 times, transfer to an oven to heat and dry at 65°C to obtain magnesium acetate, whose XRD is as follows: Figure 1 shown.

[0042] Step 4: Evaporate and concentrate the aqueous phase containing lithium ascorbate to reduce the water content to 18.7% to obtain lithium ascorbate solid. Wash the lithium ascorbate precipitate 3 to 5 times with anhydrous ethanol, transfer to an oven and heat and dry at 65°C to obtain the lithium maleate product, whose XRD is as follows: Figure 2 shown.

[0043] Example 2

[0044] A method for separating and extracting lithium and magnesium from salt lake brine, comprising the following steps:

[0045] Step 1: Take 1000L of salt lake brine and filter it through an activated carbon filter to remove suspended matter and impurities, thereby achieving pretreatment of the salt lake brine.

[0046] Step 2: adding extractant P204 to the pretreated brine, controlling the extraction temperature to 25° C. and the extraction time to 60 minutes, so that lithium and magnesium are transferred from the brine to the organic phase.

[0047] Step 3, mix the organic phase containing lithium and magnesium with a mixed solution of sodium ascorbate and hydrochloric acid (the water content of the mixed solution of sodium ascorbate and hydrochloric acid is 33%), control the stripping temperature to 18°C, and the stripping time to 65 minutes. During the stripping process, lithium and magnesium are separated from the organic phase, wherein magnesium reacts with sodium ascorbate to form a magnesium ascorbate precipitate, while lithium enters the aqueous phase to form a lithium ascorbate solution. The mixture after stripping is subjected to filter press separation to obtain a magnesium ascorbate precipitate and an aqueous phase containing lithium ascorbate. Wash the magnesium ascorbate precipitate with anhydrous ethanol 3 to 5 times, transfer to an oven at 65°C for heating and drying, and obtain magnesium acetate, whose XRD pattern is as shown below. Figure 1 shown.

[0048] Step 4: Evaporate and concentrate the aqueous phase containing lithium ascorbate to remove water and obtain lithium ascorbate solid. Wash the lithium ascorbate precipitate with anhydrous ethanol for 3 to 5 times, transfer to an oven and heat and dry at 65°C. The obtained lithium maleate product has an XRD pattern as shown below: Figure 2 shown.

[0049] Example 3

[0050] A method for separating and extracting lithium and magnesium from salt lake brine, comprising the following steps:

[0051] Step 1: Take 1000L of salt lake brine and filter it through an activated carbon filter to remove suspended matter and impurities, thereby achieving pretreatment of the salt lake brine.

[0052] Step 2: adding extractant P204 to the pretreated brine, controlling the extraction temperature to 25° C. and the extraction time to 60 minutes, so that lithium and magnesium are transferred from the brine to the organic phase.

[0053] Step 3, the organic phase containing lithium and magnesium is contacted with a mixed solution of sodium ascorbate and hydrochloric acid (the water content of the mixed solution of sodium ascorbate and hydrochloric acid is 35%), and the stripping temperature is controlled to be 28 ° C, and the stripping time is 55 minutes. During the stripping process, lithium and magnesium are separated from the organic phase, wherein magnesium reacts with sodium ascorbate to generate a magnesium ascorbate precipitate, while lithium enters the aqueous phase to form a lithium ascorbate solution. The mixture after stripping is subjected to press filtration separation to obtain a magnesium ascorbate precipitate and an aqueous phase containing lithium ascorbate. The magnesium ascorbate precipitate is washed 3 to 5 times with absolute ethanol and transferred to a baking oven at 65 ° C for heating and drying to obtain magnesium acetate.

[0054] Step 4: Evaporating and concentrating the aqueous phase containing lithium ascorbate to remove water and obtain lithium ascorbate solid. Washing the lithium ascorbate precipitate with anhydrous ethanol 3 to 5 times, and drying it in an oven at 65°C to obtain a lithium maleate product.

[0055] Comparative Example 1

[0056] Compared with Example 1, the difference is that the stripping temperature is controlled to 10° C. and the stripping time is 60 minutes. Other aspects are the same as Example 1.

[0057] Comparative Example 2

[0058] Compared with Example 1, the difference is that the stripping temperature is controlled to 35° C. and the stripping time is 60 minutes. Other aspects are the same as Example 1.

[0059] The product after the stripping of Comparative Example 1 is as follows Figure 3 As shown, from Figure 3 It can be seen that when the stripping temperature is 10°C, magnesium ions cannot form magnesium ascorbate precipitate normally during the stripping process, and the separation of magnesium and lithium cannot be achieved. Figure 4 As shown, from Figure 4 It can be seen that when the stripping temperature is 35°C, magnesium ions cannot normally form magnesium ascorbate precipitate during the stripping process, and the separation of magnesium and lithium cannot be achieved. Comparison of Example 1, Comparative Example 1, and Comparative Example 2 shows that when the stripping temperature is too high or too low, the magnesium in the organic phase cannot form magnesium ascorbate precipitate with ascorbic acid, resulting in the inability to separate lithium and magnesium. Therefore, the stripping temperature needs to be controlled at 15°C to 30°C.

[0060] Comparative Example 3

[0061] Compared with Example 1, the difference is that the water content of the mixed solution of sodium ascorbate and hydrochloric acid is 28%, and the other conditions are the same as those of Example 1.

[0062] Comparative Example 4

[0063] Compared with Example 1, the difference is that the water content of the mixed solution of sodium ascorbate and hydrochloric acid is 40%, and the other conditions are the same as those of Example 1.

[0064] The product after the stripping of Comparative Example 3 is as follows Figure 5 As shown, from Figure 5 It can be seen that when the water content of the mixed solution of sodium ascorbate and hydrochloric acid is 18%, the magnesium ions cannot form magnesium ascorbate precipitate normally during the stripping process, and the separation of magnesium and lithium cannot be achieved. Figure 6 As shown, from Figure 6 It can be seen that when the water content of the mixed solution of sodium ascorbate and hydrochloric acid is 40%, lithium and magnesium coprecipitate during the stripping process, and separation of magnesium and lithium cannot be achieved. Therefore, the water content of the mixed solution of sodium ascorbate and hydrochloric acid needs to be controlled at 31wt% to 35wt%.

[0065] Although the present invention has been described above with reference to the exemplary embodiments, it will be apparent to those skilled in the art that various modifications and variations may be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined in the claims.

Claims

1. A method for separating and extracting lithium and magnesium from salt lake brine, characterized in that: The following steps are involved: Pretreatment of salt lake brine; adding an organic extractant to the pretreated salt lake brine to transfer lithium and magnesium into the organic phase; A mixture of sodium ascorbate and hydrochloric acid is prepared, and the mixture is mixed with an organic phase containing lithium and magnesium for stripping. After stripping, solid-liquid separation is performed to obtain a magnesium ascorbate precipitate and a solution containing lithium ascorbate, respectively; The solution containing lithium ascorbate is evaporated and concentrated to obtain lithium ascorbate solid.

2. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1, characterized in that: The stripping temperature is 15°C to 30°C.

3. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1 or 2, characterized in that: The water content in the mixed solution of sodium ascorbate and hydrochloric acid is 31wt% to 35wt%.

4. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1 or 2, characterized in that: The stripping temperature was 20° C., and the water content in the mixed solution of sodium ascorbate and hydrochloric acid was 31 wt %.

5. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1 or 2, characterized in that: The stripping time is 50 to 70 minutes.

6. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1 or 2, characterized in that: In the mixed solution of sodium ascorbate and hydrochloric acid, the concentration of sodium ascorbate is 0.1 mol / L to 0.5 mol / L, and the concentration of hydrochloric acid is 0.5 mol / L to 1.5 mol / L.

7. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1 or 2, characterized in that: The organic extractant is P204, P507 or Cyanex 272.

8. The method for separating and extracting lithium and magnesium from salt lake brine according to claim 1 or 2, characterized in that: After adding the organic extractant to the pretreated salt lake brine, the volume ratio of the organic phase to the aqueous phase is (4-5):1.

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