Purification and impurity removal method for lithium-containing liquid

Abstract

The invention provides a purification and impurity removal method for lithium-containing liquid. The purification and impurity removal method comprises the following steps: (1) mixing a lithium-containing liquid with solid alkali, carrying out a first precipitation reaction to convert iron ions, aluminum ions and magnesium ions in the lithium-containing liquid into hydroxide precipitates, and then carrying out solid-liquid separation to obtain first separation residues and a separation liquid; (2) detecting the pH value of the separation liquid, when the pH value of the separation liquid is greater than or equal to a preset value, judging that the separation liquid is qualified, and entering the next process; and (3) mixing the qualified separation liquid with soluble carbonate, carrying out a second precipitation reaction to convert calcium ions in the separation liquid into precipitates, and then carrying out solid-liquid separation to obtain second separation residues and an impurity-removed lithium-containing liquid. The lithium-containing liquid is subjected to two-step impurity removal through the solid alkali and the soluble carbonate, the lithium loss rate is low, the impurity removal rate is high, the process is simple, operation is easy, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium resource extraction and relates to a method for purifying and removing impurities from lithium-containing liquid. Background Art

[0002] Lithium is known as a key strategic resource in the development of high technology. It is an ideal electrode material for batteries and a core metal that supports the development of the lithium-ion new energy industry. Clay-type lithium ore is a new type of lithium ore. With the popularization of new energy electric vehicles in recent years, its production and consumption have increased year by year. Extracting lithium from clay-type lithium ore will be one of the important sources of lithium. At present, the main methods for extracting lithium from lithium ore include limestone calcination, sulfuric acid method, sulfate mixed roasting method and chlorination roasting, etc., and then through the leaching process, the leachate is obtained, and then the leachate is removed. Removing impurities from the lithium leachate is an important part of the lithium extraction process. The lithium leachate generally contains impurity ions such as iron ions, aluminum ions, magnesium ions and calcium ions.

[0003] Chinese patent CN115970653A adopts a resin impurity removal method to remove iron and copper from lithium liquid. Although the resin is simple to prepare and has good iron and copper removal effects, the resin is expensive and not suitable for industrial applications. It also does not specify whether impurity ions such as aluminum ions, magnesium ions and calcium ions can be removed.

[0004] Therefore, there is an urgent need to provide a lithium leaching solution impurity removal method that can remove iron ions, aluminum ions, magnesium ions and calcium ions in the lithium leaching solution, and has low cost, which can solve the problem that industrial economic feasibility of lithium leaching solution impurity removal is unfeasible. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for purifying and removing impurities from lithium-containing liquid. The present invention uses a solid alkali and a soluble carbonate to remove impurities from the lithium-containing liquid in two steps, which can effectively remove iron ions, aluminum ions, magnesium ions and calcium ions in the lithium-containing liquid, has a low lithium loss rate, a high impurity removal rate, a simple process, easy operation, low cost, and can be industrially applied and has economic feasibility.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for purifying and removing impurities from a lithium-containing liquid, the method comprising:

[0008] (1) mixing a lithium-containing liquid and a solid base, performing a first precipitation reaction, converting iron ions, aluminum ions, and magnesium ions in the lithium-containing liquid into hydroxide precipitates, and then performing solid-liquid separation to obtain a first separation slag and a separation liquid;

[0009] (2) detecting the pH value of the separation liquid, and when the pH value of the separation liquid is ≥ a preset value, determining that the separation liquid is a qualified separation liquid and proceeding to the next step;

[0010] (3) The qualified separation liquid is mixed with a soluble carbonate, and a second precipitation reaction is performed to convert calcium ions in the separation liquid into precipitates, and then solid-liquid separation is performed to obtain a second separation slag and a lithium-containing liquid after impurities are removed.

[0011] The invention provides a method for purifying and removing impurities from a lithium-containing liquid. The lithium-containing liquid is subjected to two-step impurity removal by solid alkali and soluble carbonate. The first step is to introduce solid alkali to remove iron ions, aluminum ions and magnesium ions in the lithium-containing liquid. Then, the pH value of the separated liquid after impurity removal is detected. When the pH value of the separated liquid is greater than or equal to a preset value, most of the iron ions, aluminum ions and magnesium ions are removed in the form of hydroxide precipitation. At this time, the separated liquid is a qualified separated liquid and can enter the next step of impurity removal. The second step is to introduce soluble carbonate to effectively remove calcium ions in the qualified separated liquid in the form of calcium carbonate precipitation. After solid-liquid separation, the lithium-containing liquid after impurity removal and the second separated slag are obtained. The second separated slag can also be used as a solid alkali, which can not only recover the residual lithium in the second separated slag, but also realize the comprehensive utilization of materials.

[0012] In summary, the purification and impurity removal method of the present invention can effectively remove iron ions, aluminum ions, magnesium ions and calcium ions in lithium-containing liquid, with low lithium loss rate and high impurity removal rate. It also has a simple process, is easy to operate, and has low cost. It can be industrially applied and is economically feasible.

[0013] Preferably, the lithium-containing liquid is a lithium-extracted liquid obtained after lithium is extracted from clay-type lithium ore.

[0014] Preferably, the concentration of lithium ions in the lithium-containing liquid is 500-3000 mg / L, for example, 800 mg / L, 1200 mg / L, 1500 mg / L, 2000 mg / L or 2500 mg / L, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] Preferably, in the lithium-containing liquid, the concentrations of iron ions, aluminum ions, magnesium ions and calcium ions are independently 100-2000 mg / L, for example, 500 mg / L, 800 mg / L, 1000 mg / L, 1300 mg / L, 1500 mg / L or 1800 mg / L, etc., but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] In the present invention, when the lithium-containing liquid is a lithium extraction liquid obtained after lithium extraction from clay-type lithium ore, it often contains impurity ions such as iron ions, aluminum ions, magnesium ions and calcium ions, and the concentrations of the four impurity ions are independently 100-2000 mg / L.

[0017] Preferably, the anions in the lithium-containing solution include at least one of nitrate ions, chloride ions and sulfate ions.

[0018] Preferably, the solid base in step (1) comprises at least one of calcium carbonate, calcium oxide, calcium hydroxide and sodium hydroxide.

[0019] Preferably, the molar amount of the solid base is greater than the molar amount of the theoretical solid base required to precipitate the iron ions, aluminum ions and magnesium ions.

[0020] In the present invention, the solid base used is excessive to improve the impurity removal effect.

[0021] Preferably, the mixing in step (1) specifically comprises: passing the lithium-containing liquid into a reactor containing a solid base.

[0022] Preferably, the volume of the solid base is 1 / 30-1 / 10 of the inner cavity volume of the reactor, for example, it can be 1 / 30, 1 / 25, 1 / 20, 1 / 18, 1 / 15, 1 / 12 or 1 / 10, etc., but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 1 / 20-1 / 15.

[0023] Preferably, the temperature of the first precipitation reaction is 25-95°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 60-95°C.

[0024] In the present invention, the solid alkali has low solubility at high temperature. Therefore, at the temperature of the first precipitation reaction, the solid alkali dissolves slowly during the first precipitation reaction, which can maintain the pH value of the system constant. The addition of the solid alkali and the treatment time of the first separation slag can be determined without too much operation.

[0025] Preferably, the time of the first precipitation reaction is 0.2-6h, for example, it can be 0.2h, 0.5h, 1h, 1.5h, 2h, 3h, 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 0.5-2h.

[0026] Preferably, step (2) further comprises: when the pH value of the separation liquid is less than a preset value, determining that the separation liquid is an unqualified separation liquid, and repeating step (1) with the unqualified separation liquid as a new lithium-containing liquid.

[0027] It should be noted that when the unqualified separated liquid is used as a new lithium-containing liquid to repeat step (1), it is mixed with a new solid base. Further, the unqualified separated liquid is introduced into a new reactor containing a solid base.

[0028] In the present invention, when the pH value of the separation liquid is less than the preset value, the iron, aluminum and magnesium ions in the separation liquid are not completely removed, and the separation liquid is unqualified, and it is necessary to return to step (1) for re-removal of impurities. This can improve the removal rate and effectively remove iron ions, aluminum ions and magnesium ions.

[0029] Preferably, the preset value in step (2) is 11-13, for example, it can be 11.5, 12 or 12.5, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, step (2) further comprises: performing a first washing and a second washing on the first separation slag to obtain a lithium recovery liquid.

[0031] In the present invention, the lithium recovery liquid can be recycled and used as a lithium-containing liquid for two-step impurity removal. The first washing and the second washing of the present invention can reduce the loss of lithium and further reduce the lithium loss rate.

[0032] Preferably, the washing reagents used in the first washing and the second washing both include water.

[0033] Preferably, the first washing and the second washing are specifically: the second washing is performed with pure water as a washing agent, the washing liquid obtained after the second washing is used as a washing agent for the first washing, and the washing liquid obtained after the first washing is a lithium recovery liquid. This can not only recover lithium ions, but also reduce the amount of water used, enrich lithium to reduce the burden of impurity removal, and save resources.

[0034] Furthermore, in the present invention, the first washing and the second washing can be directly performed in the reactor, further saving the investment in equipment.

[0035] Preferably, the soluble carbonate in step (3) includes at least one of potassium carbonate, sodium carbonate and ammonium carbonate.

[0036] Preferably, the molar amount of the soluble carbonate is 0.9-1.5 times the molar amount of calcium ions in the qualified separation liquid, for example, it can be 0.9 times, 1 times, 1.1 times, 1.2 times, 1.3 times, 1.4 times or 1.5 times, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable, preferably 1.0-1.2 times.

[0037] Preferably, the temperature of the second precipitation reaction is 25-95°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 60-95°C.

[0038] In the present invention, when the temperature of the second precipitation reaction is controlled within a limited range, it is more conducive to removing calcium ions and improving the calcium ion removal rate.

[0039] Preferably, the time of the second precipitation reaction is 0.2-6h, for example, it can be 0.2h, 0.5h, 1h, 1.5h, 2h, 3h, 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 0.5-2h.

[0040] As a preferred technical solution of the present invention, the purification and impurity removal method specifically comprises the following steps:

[0041] (I) introducing the lithium-containing liquid into a reactor containing a solid base, and carrying out a first precipitation reaction at 25-95° C. for 0.2-6 h under stirring conditions to convert iron ions, aluminum ions and magnesium ions in the lithium-containing liquid into hydroxide precipitates, and then filtering to obtain a first separation slag and a separation liquid;

[0042] Wherein, the lithium-containing liquid is a lithium-extracting liquid obtained after lithium is extracted from a clay-type lithium ore; in the lithium-containing liquid, the concentration of lithium ions is 500-3000 mg / L, and the concentrations of iron ions, aluminum ions, magnesium ions and calcium ions are independently 100-2000 mg / L; the solid alkali includes at least one of calcium carbonate, calcium oxide, calcium hydroxide and sodium hydroxide; the molar amount of the solid alkali is greater than the theoretical molar amount of the solid alkali required to precipitate the iron ions, aluminum ions and magnesium ions;

[0043] (II) performing a first washing and a second washing on the first separation slag to obtain a lithium recovery liquid;

[0044] Detecting the pH value of the separation liquid; when the pH value of the separation liquid is ≥ a preset value, the separation liquid is determined to be a qualified separation liquid and proceeds to the next step; when the pH value of the separation liquid is < the preset value, the separation liquid is determined to be an unqualified separation liquid, and the unqualified separation liquid is used as a new lithium-containing liquid to repeat step (I); wherein the preset value is 11-13;

[0045] (III) adding a soluble carbonate to the qualified separated liquid, performing a second precipitation reaction at 25-95° C. for 0.2-6 h to convert the calcium ions in the separated liquid into precipitates, and then filtering to obtain a second separated slag and a lithium-containing liquid after impurities are removed;

[0046] Wherein, the soluble carbonate includes at least one of potassium carbonate, sodium carbonate and ammonium carbonate; the molar amount of the soluble carbonate is 0.9-1.5 times the molar amount of calcium ions in the qualified separation liquid.

[0047] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The invention provides a method for purifying and removing impurities from a lithium-containing liquid. The lithium-containing liquid is subjected to two-step impurity removal by solid alkali and soluble carbonate. The first step is to introduce solid alkali to remove iron ions, aluminum ions and magnesium ions in the lithium-containing liquid. Then, the pH value of the separated liquid after impurity removal is detected. When the pH value of the separated liquid is greater than or equal to a preset value, most of the iron ions, aluminum ions and magnesium ions are removed in the form of hydroxide precipitation. At this time, the separated liquid is a qualified separated liquid and can enter the next step of impurity removal. The second step is to introduce soluble carbonate to effectively remove calcium ions in the qualified separated liquid in the form of calcium carbonate precipitation. After solid-liquid separation, the lithium-containing liquid after impurity removal and the second separated slag are obtained. The second separated slag can also be used as a solid alkali, which can not only recover the residual lithium in the second separated slag, but also realize the comprehensive utilization of materials.

[0050] In summary, the purification and impurity removal method of the present invention can effectively remove iron ions, aluminum ions, magnesium ions and calcium ions in lithium-containing liquid, with low lithium loss rate and high impurity removal rate. It also has a simple process, is easy to operate, and has low cost. It can be industrially applied and is economically feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic flow chart of a method for purifying and removing impurities from a lithium-containing liquid provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In one embodiment, the present invention provides a method for purifying and removing impurities from a lithium-containing solution, the process of which is as follows: Figure 1 As shown, the purification and impurity removal method comprises:

[0053] (1) passing the lithium-containing liquid into a reactor containing an excess of solid alkali to perform a first precipitation reaction, so that the iron ions, aluminum ions and magnesium ions in the lithium-containing liquid are converted into hydroxide precipitates, and then filtering to obtain a first separation slag and a separation liquid;

[0054] (2) detecting the pH value of the separation liquid, and determining that the separation liquid is qualified separation liquid when the pH value of the separation liquid is ≥ a preset value; adding a soluble carbonate to the qualified separation liquid to perform a second precipitation reaction, so that the calcium ions in the separation liquid are converted into precipitates, and then filtering while hot to obtain a second separation residue and a lithium-containing liquid after impurity removal; the second separation residue can be placed in a reactor containing an excess of solid alkali for reuse; when the pH value of the separation liquid is less than a preset value, determining that the separation liquid is unqualified separation liquid, and passing the unqualified separation liquid into a new reactor containing an excess of solid alkali to continue to remove impurities;

[0055] (3) performing a first washing and a second washing on the first separation slag in sequence, wherein the second washing is performed using pure water as a washing agent, the washing liquid obtained after the second washing is used as a washing agent for the first washing, and the washing liquid obtained after the first washing is used as a lithium-containing liquid and introduced into a new reactor containing excess solid alkali to continue removing impurities.

[0056] Example 1

[0057] This embodiment provides a method for purifying and removing impurities from a lithium-containing liquid, the method comprising:

[0058] (1) passing 1L of lithium-containing liquid into a reactor containing a solid base, wherein the lithium-containing liquid is a lithium-extracting liquid obtained after lithium extraction from a clay-type lithium ore, comprising: 1100mg / L of lithium ions, 850mg / L of iron ions, 1900mg / L of magnesium ions, 1000mg / L of aluminum ions, 790mg / L of calcium ions and 13750mg / L of anions, wherein the anions are nitrate ions, chloride ions and sulfate ions; the solid base is calcium oxide, the volume of the solid base is 1 / 25 of the volume of the reactor cavity, and the molar amount of the solid base is 1.5 times the theoretical molar amount of the solid base required for precipitating the iron ions, aluminum ions and magnesium ions; then, a first precipitation reaction is carried out at 60°C for 2h under stirring conditions to convert the iron ions, aluminum ions and magnesium ions in the lithium-containing liquid into iron hydroxide, aluminum hydroxide and magnesium hydroxide precipitates, and then filtering to obtain a first separation slag and a separation liquid;

[0059] (2) detecting the pH value of the separation liquid, specifically 10, which is less than the preset value 11, determining that the separation liquid is unqualified separation liquid, and the unqualified separation liquid proceeds to step (3);

[0060] (3) passing the unqualified separation liquid into a new reactor containing solid alkali which is the same as step (1); washing the first separation slag twice, wherein the washing liquid after the second washing can be used for the first washing to achieve recycling, and the washing liquid obtained after the two washings is also passed into a new reactor containing solid alkali, and the first precipitation reaction is continued. After filtering, the pH value of the separated liquid obtained by filtration is detected to be 12.6, which is greater than the preset value 11, and the separated liquid is determined to be a qualified separated liquid, and the process proceeds to step (4);

[0061] (4) adding soluble potassium carbonate to the qualified separation liquid, wherein the molar amount of the soluble potassium carbonate is 1.1 times the molar amount of calcium ions in the qualified separation liquid, and performing a second precipitation reaction at 60° C. for 2 h to convert the calcium ions in the separation liquid into calcium carbonate precipitates, which are then filtered to obtain a second separation slag and a lithium-containing liquid after impurities are removed.

[0062] Example 2

[0063] This embodiment provides a method for purifying and removing impurities from a lithium-containing liquid, the method comprising:

[0064] (1) passing 1L of lithium-containing liquid into a reactor containing a solid base, wherein the lithium-containing liquid is a lithium extraction liquid obtained after lithium extraction from a clay-type lithium ore, comprising: 1300mg / L of lithium ions, 800mg / L of iron ions, 1700mg / L of magnesium ions, 900mg / L of aluminum ions, 650mg / L of calcium ions and 12000mg / L of anions, wherein the anions are nitrate ions, chloride ions and sulfate ions; the solid base is calcium oxide, the volume of the solid base is 1 / 15 of the volume of the reactor cavity, and the molar amount of the solid base is 2.5 times the theoretical molar amount of the solid base required to precipitate the iron ions, aluminum ions and magnesium ions; then, a first precipitation reaction is carried out at 90°C for 1h under stirring conditions to convert the iron ions, aluminum ions and magnesium ions in the lithium-containing liquid into iron hydroxide, aluminum hydroxide and magnesium hydroxide precipitates, and then filtering to obtain a first separation slag and a separation liquid;

[0065] (2) detecting the pH value of the separation liquid, specifically 12, which is greater than the preset value 11, determining that the separation liquid is a qualified separation liquid and proceeding to the next step;

[0066] (3) adding soluble ammonium carbonate to the qualified separated liquid obtained in step (2), wherein the molar amount of the soluble ammonium carbonate is 1.2 times the molar amount of calcium ions in the qualified separated liquid, performing a second precipitation reaction at 90° C. for 1 hour to convert the calcium ions in the separated liquid into calcium carbonate precipitates, and then filtering to obtain a second separated slag and a lithium-containing liquid after impurities are removed.

[0067] Example 3

[0068] This embodiment provides a method for purifying and removing impurities from a lithium-containing liquid, the method comprising:

[0069] (1) passing 1L of lithium-containing liquid into a reactor containing a solid base, wherein the lithium-containing liquid is a lithium extraction liquid obtained after lithium extraction from a clay-type lithium ore, comprising: 2100mg / L of lithium ions, 900mg / L of iron ions, 2000mg / L of magnesium ions, 670mg / L of aluminum ions, 720mg / L of calcium ions and 15600mg / L of anions, wherein the anions are nitrate ions, chloride ions and sulfate ions; the solid base is calcium hydroxide, the volume of the solid base is 1 / 20 of the volume of the reactor cavity, and the molar amount of the solid base is twice the theoretical molar amount of the solid base required to precipitate the iron ions, aluminum ions and magnesium ions; then, a first precipitation reaction is carried out at 80°C for 1.5h under stirring conditions to convert the iron ions, aluminum ions and magnesium ions in the lithium-containing liquid into iron hydroxide, aluminum hydroxide and magnesium hydroxide precipitates, and then filtering to obtain a first separation slag and a separation liquid;

[0070] (2) detecting the pH value of the separation liquid, specifically 11.7, which is greater than the preset value 11, and determining that the separation liquid is a qualified separation liquid, and proceeding to the next step;

[0071] (3) adding soluble ammonium carbonate to the qualified separation liquid obtained in step (2), wherein the molar amount of the soluble ammonium carbonate is 1.2 times the molar amount of calcium ions in the qualified separation liquid, performing a second precipitation reaction at 80° C. for 1.5 h to convert the calcium ions in the separation liquid into calcium carbonate precipitates, and then filtering to obtain a second separation slag and a lithium-containing liquid after impurities are removed.

[0072] Example 4

[0073] The difference between this embodiment and embodiment 3 is that the temperature of the second precipitation reaction is adjusted to 100°C.

[0074] The remaining parameters remain the same as those in Example 3.

[0075] Example 5

[0076] The difference between this embodiment and embodiment 3 is that the temperature of the second precipitation reaction is adjusted to 40°C.

[0077] The remaining parameters remain the same as those in Example 3.

[0078] Example 6

[0079] The difference between this embodiment and embodiment 3 is that the temperature of the second precipitation reaction is adjusted to 20°C.

[0080] The remaining parameters remain the same as those in Example 3.

[0081] Comparative Example 1

[0082] The difference between this comparative example and Example 1 is that step (3) is omitted and soluble potassium carbonate is directly added to the unqualified separated liquid.

[0083] The rest is the same as in Example 1.

[0084] test

[0085] The concentrations of lithium ions, iron ions, magnesium ions, aluminum ions and calcium ions in the lithium-containing solution after impurity removal provided in the above embodiments and comparative examples were tested by inductively coupled plasma spectrometer (ICP), and the lithium loss rate and the removal rates of iron ions, magnesium ions, aluminum ions and calcium ions were calculated.

[0086] The test results are shown in Table 1.

[0087] Table 1

[0088]

[0089] analyze:

[0090] It can be seen from Examples 1-3 that after the lithium-containing liquid is impurity-removed by the impurity-removal process provided by the present invention, the lithium recovery rate can exceed 95%, and the impurity ion removal rate is above 95%, which has industrial application feasibility.

[0091] It can be seen from Examples 1 and 4-6 that when the temperature of the second precipitation reaction is too high, the calcium ion removal rate will be appropriately increased, but the energy consumption will be correspondingly increased. If the temperature of the second precipitation reaction decreases, the calcium ion removal rate will also decrease, and when the temperature of the second precipitation reaction is too low, the calcium ion removal rate will be significantly reduced.

[0092] It can be seen from Example 1 and Comparative Example 1 that if the unqualified separation liquid is directly decalcified, the magnesium ions in the solution cannot be completely removed, which affects the subsequent removal of calcium ions.

[0093] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for purifying and removing impurities from a lithium-containing liquid, characterized in that: The purification and impurity removal method comprises: (1) mixing a lithium-containing liquid and a solid base, performing a first precipitation reaction, converting iron ions, aluminum ions, and magnesium ions in the lithium-containing liquid into hydroxide precipitates, and then performing solid-liquid separation to obtain a first separation slag and a separation liquid; (2) detecting the pH value of the separation liquid, and when the pH value of the separation liquid is ≥ a preset value, determining that the separation liquid is a qualified separation liquid and proceeding to the next step; (3) The qualified separation liquid is mixed with a soluble carbonate, and a second precipitation reaction is performed to convert calcium ions in the separation liquid into precipitates, and then solid-liquid separation is performed to obtain a second separation slag and a lithium-containing liquid after impurities are removed.

2. The purification and impurity removal method according to claim 1, characterized in that: The lithium-containing liquid is a lithium-extracting liquid obtained after lithium is extracted from a clay-type lithium ore; Preferably, the concentration of lithium ions in the lithium-containing solution is 500-3000 mg / L; Preferably, in the lithium-containing solution, the concentrations of iron ions, aluminum ions, magnesium ions and calcium ions are independently 100-2000 mg / L; Preferably, the anions in the lithium-containing solution include at least one of nitrate ions, chloride ions and sulfate ions.

3. The purification and impurity removal method according to claim 1 or 2, characterized in that: The solid base in step (1) comprises at least one of calcium carbonate, calcium oxide, calcium hydroxide and sodium hydroxide; Preferably, the molar amount of the solid base is greater than the molar amount of the theoretical solid base required to precipitate the iron ions, aluminum ions and magnesium ions.

4. The purification and impurity removal method according to any one of claims 1 to 3, characterized in that: The mixing in step (1) specifically comprises: passing the lithium-containing liquid into a reactor containing a solid base; Preferably, the volume of the solid base is 1 / 30-1 / 10 of the inner cavity volume of the reactor, preferably 1 / 20-1 / 15.

5. The purification and impurity removal method according to any one of claims 1 to 4, characterized in that: The temperature of the first precipitation reaction is 25-95°C, preferably 60-95°C; Preferably, the first precipitation reaction time is 0.2-6h, preferably 0.5-2h.

6. The purification and impurity removal method according to any one of claims 1 to 5, characterized in that: Step (2) also includes: when the pH value of the separated liquid is less than a preset value, determining that the separated liquid is an unqualified separated liquid, and using the unqualified separated liquid as a new lithium-containing liquid to repeat step (1); Preferably, the preset value in step (2) is 11-13.

7. The purification and impurity removal method according to any one of claims 1 to 6, characterized in that: Step (2) also includes: performing a first washing and a second washing on the first separation slag to obtain a lithium recovery liquid.

8. The purification and impurity removal method according to any one of claims 1 to 7, characterized in that: The soluble carbonate in step (3) comprises at least one of potassium carbonate, sodium carbonate and ammonium carbonate; Preferably, the molar amount of the soluble carbonate is 0.9-1.5 times, preferably 1.0-1.2 times, the molar amount of calcium ions in the qualified separation liquid.

9. The purification and impurity removal method according to any one of claims 1 to 8, characterized in that: The temperature of the second precipitation reaction is 25-95°C, preferably 60-95°C; Preferably, the second precipitation reaction time is 0.2-6h, preferably 0.5-2h.

10. The purification and impurity removal method according to any one of claims 1 to 9, characterized in that: The purification and impurity removal method specifically comprises the following steps: (I) introducing the lithium-containing liquid into a reactor containing a solid base, and carrying out a first precipitation reaction at 25-95° C. for 0.2-6 h under stirring conditions to convert iron ions, aluminum ions and magnesium ions in the lithium-containing liquid into hydroxide precipitates, and then filtering to obtain a first separation slag and a separation liquid; Wherein, the lithium-containing liquid is a lithium-extracting liquid obtained after lithium is extracted from a clay-type lithium ore; in the lithium-containing liquid, the concentration of lithium ions is 500-3000 mg / L, and the concentrations of iron ions, aluminum ions, magnesium ions and calcium ions are independently 100-2000 mg / L; the solid alkali includes at least one of calcium carbonate, calcium oxide, calcium hydroxide and sodium hydroxide; the molar amount of the solid alkali is greater than the theoretical molar amount of the solid alkali required to precipitate the iron ions, aluminum ions and magnesium ions; (II) performing a first washing and a second washing on the first separation slag to obtain a lithium recovery liquid; Detecting the pH value of the separation liquid; when the pH value of the separation liquid is ≥ a preset value, the separation liquid is determined to be a qualified separation liquid and proceeds to the next step; when the pH value of the separation liquid is < the preset value, the separation liquid is determined to be an unqualified separation liquid, and the unqualified separation liquid is used as a new lithium-containing liquid to repeat step (I); wherein the preset value is 11-13; (III) adding a soluble carbonate to the qualified separated liquid, performing a second precipitation reaction at 25-95° C. for 0.2-6 h to convert the calcium ions in the separated liquid into precipitates, and then filtering to obtain a second separated slag and a lithium-containing liquid after impurities are removed; Wherein, the soluble carbonate includes at least one of potassium carbonate, sodium carbonate and ammonium carbonate; the molar amount of the soluble carbonate is 0.9-1.5 times the molar amount of calcium ions in the qualified separation liquid.

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