Method for recovering valuable elements from lithium-containing acid solution

Abstract

The invention relates to a method for recovering valuable elements from a lithium-containing acid solution, and solves the problems of difficulty in product recycling, low lithium recovery rate and the like in a traditional purification process. The method comprises the following steps: firstly, precipitating silicon and aluminum in the lithium-containing acidic leaching solution step by step to obtain fluosilicate and fluoroaluminate products, then precipitating lithium in the solution to obtain a lithium phosphate product, and carrying out evaporative crystallization on the precipitated solution to obtain a product which can be returned to the impurity removal step. The core of the method is that silicon and aluminum impurities are produced in the form of high-purity byproducts and efficient closed-loop recovery of lithium is realized by utilizing the coordination state difference of silicon, aluminum and fluorine ions in an acid solution. The method provided by the invention has the characteristics of short process flow, high product purity and appreciation in the process.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, in particular to a method for selectively removing impurities from a lithium-containing acidic leaching solution and preparing a high-purity product. Background Art

[0002] Acid leaching is an efficient and low-cost method for lithium extraction. During the acidic lithium leaching process, the dissociation of aluminosilicates in the raw materials causes silicon and aluminum to enter the leachate simultaneously, making solution purification a necessary step for further lithium purification and separation. However, efficient separation and purification of lithium from leachates with low lithium concentrations and high silicon and aluminum impurity concentrations remains a challenge in the industry.

[0003] Currently, the separation and purification of lithium from lithium-containing acidic leachates primarily relies on precipitation to remove impurities. For example, Chinese patent CN110983041A discloses a "method for purifying and removing impurities from lepidolite leachates." The method uses solid caustic soda to adjust the pH of the lepidolite leachate to 12-12.5. After initially removing aluminum, magnesium, manganese, iron, and silicon impurities, sodium carbonate solution is added at high temperature and stirred for 45 minutes to remove calcium impurities. Filtering yields a clear lepidolite leachate. However, this method suffers from high precipitant consumption, the generation of waste residue containing a mixture of various impurities, and difficulties in resource utilization. Furthermore, the hydrolysis and gelation of silicon and aluminum under high pH conditions leads to lithium entrainment and loss.

[0004] In summary, existing purification technologies present challenges such as difficulty in resource utilization of impurity removal products and low lithium recovery rates. Therefore, to address these issues with existing lithium-containing acidic solution purification methods, the present invention proposes a method for selectively separating impurities from lithium-containing acidic solutions, providing a new and effective technology for the efficient separation and purification of lithium from leachates with low lithium concentrations and high silicon and aluminum impurity concentrations. Summary of the Invention

[0005] The object of the present invention is to provide a method for selectively recovering elements from a lithium-containing acidic solution.

[0006] To achieve the above objectives, the technical solution employed is as follows: first, fluoride and alkali metal salts are added to a lithium-containing acidic leachate, allowing for stepwise precipitation at a specific pH to produce fluorosilicate and fluoroaluminate products. Phosphate is then added to the purified solution to produce lithium phosphate. The precipitated solution is then evaporated and crystallized, and the resulting product is returned to the impurity removal step. The essence of the present invention lies in utilizing the differences in the ability of silicon and aluminum to bind fluorine to selectively produce high-purity byproducts, while also achieving efficient closed-loop recovery of lithium from the acidic leachate.

[0007] The specific process and parameters of the above technical solution are as follows:

[0008] (1) Fluoride and alkali metal salt are added to a lithium-containing acidic solution, the pH of the system is controlled to be 0.9-1.6, the fluoride ion concentration is 1.80-2.0 mol / L, the alkali metal ion concentration is 1.0-2.0 mol / L, the precipitation temperature is 25-40°C, the precipitation is stirred for 30-60 minutes, and the solid-liquid separation is performed to obtain fluorosilicate and a primary precipitate. The main reactions that occur are:

[0009] 6H + +SiO3 2- +6F - +M2SO4=M2SiF6↓+SO4 2- +3H2O (M=Na or K)

[0010] 6H + +SiO3 2- +6F - +2MNO3=M2SiF6↓+2NO3 - +3H2O (M=Na or K)

[0011] 6H + +SiO3 2- +6F - +2MCl=M2SiF6↓+2Cl - +3H2O (M=Na or K)

[0012] (2) Fluoride is added to the desiliconization solution, the fluoride ion concentration is controlled to 0.7-0.9 mol / L, the precipitation temperature is 25-40°C, and the precipitation is stirred for 30-60 minutes. The solid-liquid separation is performed to obtain fluoroaluminate and secondary precipitate. The main reactions are:

[0013] Al 3+ +3M + +6F - =M3AlF6↓(M=Na or K)

[0014] (3) Adjust the pH value of the secondary precipitate to 11-13, add phosphate, control the phosphate concentration to 0.045-0.18 mol / L, the precipitation temperature to 70-90°C, the precipitation time to 90-120 min, and separate the solid and liquid to obtain the lithium phosphate product and the tertiary precipitate. The reaction that occurs is:

[0015] 2M3PO4+3Li2SO4=2Li3PO4↓+3M2SO4(M=Na or K)

[0016] (4) The precipitate is evaporated and crystallized three times, and the crystallized product is returned to step (1).

[0017] The concentrations of lithium, aluminum, and silicon in the lithium-containing acidic solution of step (1) are 0.5-3 g / L, 4.5-6.0 g / L, and 5.0-7.5 g / L, respectively;

[0018] The base metal salt in step (1) is one or more of sodium or potassium sulfate, nitrate and chloride;

[0019] The fluoride in steps (1) and (2) is one or more of hydrofluoric acid, sodium fluoride and potassium fluoride;

[0020] The phosphate in step (3) is one or more of sodium phosphate or potassium phosphate;

[0021] Compared with the traditional purification method of lithium-containing solution, the advantages of the present invention are:

[0022] (1) By utilizing the difference in coordination between silicon, aluminum and fluoride ions in an acidic system, the silicon and aluminum in the acidic solution are efficiently removed in a step-by-step manner, with a removal rate greater than 96% and a purity of silicon and aluminum products exceeding 98%.

[0023] (2) Lithium was purified and separated from a lithium-containing solution with low lithium content and high impurity concentration, with a lithium recovery rate greater than 98.0% and a lithium product purity of 99.7%;

[0024] (3) The evaporated crystallized product can replace the pure reagent and return to the impurity removal step, thus achieving a closed-loop process without secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Process flow chart for selective separation of impurities from lithium-containing acidic solution

[0026] Figure 2 X-ray diffraction patterns of different products

[0027] Figure 3 Scanning electron microscope image of silicon product

[0028] Figure 4 Scanning electron microscope image of aluminum products

[0029] Figure 5 Scanning electron microscope image of lithium products

[0030] Figure 6 X-ray diffraction pattern of the crystalline product DETAILED DESCRIPTION

[0031] The following implementation rules are intended to illustrate the present invention rather than to further limit the present invention.

[0032] Example 1

[0033] The separation and purification process of impurities in lithium-containing acidic solution is as follows: Figure 1 shown.

[0034] The main components of the lithium-containing acidic leachate are: Li: 0.73g / L, Si: 6.80g / L, Al: 5.33g / L. Hydrofluoric acid and sodium sulfate are added to the lithium-containing acidic solution, the system pH is controlled at 0.90, the fluoride ion concentration is 2.0mol / L, and the sodium ion concentration is 1.0mol / L. The precipitation temperature is 25°C and the precipitation time is 60 minutes. Solid-liquid separation is performed to obtain a sodium fluorosilicate product and a primary precipitate. The silicon removal rate is 96.7%, and the purity of the sodium fluorosilicate product is 99.6%. Hydrofluoric acid is added to the primary precipitate, the fluoride ion concentration is controlled at 0.88mol / L, the precipitation temperature is 25°C and the precipitation time is 60 minutes. Solid-liquid separation is performed to obtain a sodium fluoroaluminate product and a secondary precipitate. The aluminum removal rate is 98.6%, and the purity of the sodium fluoroaluminate product is 98.6%. The pH value of the secondary precipitation liquid was adjusted to 12.3, sodium phosphate was added, the sodium phosphate concentration was controlled to 0.09 mol / L, the precipitation temperature was 80°C, and the precipitation time was 100 min to obtain a lithium phosphate product with a purity of 99.7%. After the lithium phosphate precipitation liquid was evaporated and crystallized, the obtained crystalline product was returned to the desiliconization step. The solution composition before and after separation is shown in Table 1, the composition of the silicon product, aluminum product, and lithium product are shown in Tables 2, 3, and 4, and the X-ray diffraction pattern is shown in Table 1. Figure 2 As shown in the scanning electron microscope image Figure 3 、 4 , 5, the X-ray diffraction pattern of the crystalline product is as shown in Figure 6 shown.

[0035] Table 1 Solution composition before and after separation (g / L)

[0036]

[0037] Table 2 Example silicon product composition (mass percentage)

[0038]

[0039] Table 3 Composition of aluminum products in the embodiment (mass percentage)

[0040]

[0041] Table 4 Example lithium product composition (mass percentage)

[0042]

[0043] Example 2

[0044] The main components of the lithium-containing acidic leachate are: Li: 0.51 g / L, Si: 7.42 g / L, Al: 5.91 g / L. Potassium fluoride and potassium chloride are added to the lithium-containing acidic solution, the system pH is controlled to 1.60, the fluoride ion concentration is 1.80 mol / L, and the potassium ion concentration is 2.0 mol / L. The precipitation temperature is 40°C and the precipitation time is 30 minutes. Solid-liquid separation is performed to obtain a potassium fluorosilicate product and a primary precipitate. The silicon removal rate is 95.3%, and the potassium fluorosilicate product purity is 99.1%. Potassium fluoride is added to the primary precipitate, the fluoride ion concentration is controlled to 0.72 mol / L, the precipitation temperature is 40°C and the precipitation time is 30 minutes. Solid-liquid separation is performed to obtain a potassium fluoroaluminate product and a secondary precipitate. The aluminum removal rate is 97.8%, and the sodium fluoroaluminate product purity is 98.1%. The pH of the secondary precipitate was adjusted to 11.2, and potassium phosphate was added to control the concentration to 0.045 mol / L. The precipitation temperature was set at 90°C and the precipitation time was 120 minutes. A lithium phosphate product with a purity of 99.1% was obtained. The composition of the solution before and after separation is shown in Table 1, and the compositions of the silicon, aluminum, and lithium products are shown in Tables 2, 3, and 4.

[0045] Example 3

[0046] The main components of the lithium-containing acidic leachate are: Li: 2.97g / L, Si: 5.16g / L, Al: 4.57g / L. Sodium fluoride and sodium nitrate are added to the lithium-containing acidic solution, the system pH is controlled to 1.32, the fluoride ion concentration is 1.90mol / L, and the sodium ion concentration is 1.5mol / L. The precipitation temperature is 30°C and the precipitation time is 45 minutes. Solid-liquid separation is performed to obtain a sodium fluorosilicate product and a primary precipitate. The silicon removal rate is 95.9%, and the purity of the sodium fluorosilicate product is 99.3%. Sodium fluoride is added to the primary precipitate, the fluoride ion concentration is controlled to 0.83mol / L, the precipitation temperature is 30°C and the precipitation time is 45 minutes. Solid-liquid separation is performed to obtain a sodium fluoroaluminate product and a secondary precipitate. The aluminum removal rate is 98.1%, and the purity of the sodium fluoroaluminate product is 98.4%. The pH of the secondary precipitation solution was adjusted to 13, potassium phosphate was added, and the sodium phosphate concentration was controlled at 0.18 mol / L. The precipitation temperature was 70°C and the precipitation time was 90 minutes. A lithium phosphate product with a purity of 99.3% was obtained. The composition of the solution before and after separation is shown in Table 1, and the compositions of the silicon, aluminum, and lithium products are shown in Tables 2, 3, and 4.

Claims

1. A method for recovering valuable elements from a lithium-containing acidic solution, characterized in that: The following steps are involved: (a) adding fluoride and alkali metal salt to a lithium-containing acidic solution, controlling the system pH to 0.9-1.6, the fluoride ion concentration to 1.80-2.0 mol / L, the alkali metal ion concentration to 1.0-2.0 mol / L, the precipitation temperature to 25-40° C., stirring and precipitating for 30-60 minutes, and solid-liquid separation to obtain fluorosilicate and a primary precipitate; (b) adding fluoride to the desiliconization solution, controlling the fluoride ion concentration to 0.7-0.9 mol / L, the precipitation temperature to 25-40° C., stirring and settling for 30-60 minutes, and performing solid-liquid separation to obtain fluoroaluminate and a secondary precipitate; (c) adjusting the pH of the secondary precipitate to 11-13, adding phosphate to control the phosphate concentration to 0.045-0.18 mol / L, the precipitation temperature to 70-90° C., the precipitation time to 90-120 min, and performing solid-liquid separation to obtain a lithium phosphate product and a tertiary precipitate; (d) The precipitate is evaporated and crystallized three times, and the resulting crystalline product is returned to step (a).

2. The method for recovering valuable elements from a lithium-containing acidic solution according to claim 1, wherein: The contents of lithium, aluminum and silicon in the lithium-containing acidic solution of step (a) are 0.5-3 g / L, 4.5-6.0 g / L and 5.0-7.5 g / L respectively.

3. The method for recovering valuable elements from a lithium-containing acidic solution according to claim 1, wherein: The alkali metal salt in step (a) is one or more of sodium or potassium sulfate, nitrate and chloride.

4. The method for recovering valuable elements from a lithium-containing acidic solution according to claim 1, wherein: The fluoride in steps (a) and (b) is one or more of hydrofluoric acid, sodium fluoride and potassium fluoride.

5. The method for recovering valuable elements from a lithium-containing acidic solution according to claim 1, wherein: In step (c), the phosphate is one or more of sodium phosphate or potassium phosphate.

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