Method for synchronous potassium removal of thickening material and potassium-rich mother liquor in lithium salt production

Abstract

The application relates to the technical field of lithium metallurgy, in particular to a method for synchronously removing potassium from slurry and potassium-rich mother liquor in lithium salt production, which comprises the following steps: taking slurry and potassium-rich mother liquor from a lithium salt production process, adding the potassium-rich mother liquor into the slurry, stirring uniformly to obtain a mixed solution; the volume ratio of the slurry to the potassium-rich mother liquor is (5-15):1, and the potassium ion concentration in the potassium-rich mother liquor is 5-20 g / L; S2, adding jarosite seeds, ferrous sulfate and an oxidizing agent into the mixed solution to perform a potassium precipitation reaction; S3, after the potassium precipitation reaction is completed, returning the reaction mixture to a process before a lithium residue separation step in the lithium salt production process. According to the method, potassium is synchronously removed from the slurry and the potassium-rich mother liquor, high-concentration potassium in the potassium-rich mother liquor is removed, the potassium ion concentration in the slurry is simultaneously reduced, the potassium ion concentration in the main process is reduced, the purity of the product is improved, the recyclable times of the mother liquor are increased, and the production cost is reduced.

Description

Technical Field

[0001] This application relates to the field of lithium metallurgy technology, specifically to a method for simultaneous potassium removal from slurry and potassium-rich mother liquor during lithium salt production. Background Technology

[0002] With the vigorous development of research and development and industry of new energy materials such as lithium-ion batteries, the efficient utilization of lithium resources has become particularly important. Spodumene is an important lithium ore resource; however, spodumene ore generally contains a certain amount of potassium. Due to the high solubility of potassium salts, potassium in the ore can easily enter the slurry after the acid roasting process. During lithium salt production, potassium impurities accumulate continuously as the mother liquor is recycled during production, gradually transforming it from low-potassium mother liquor to potassium-rich mother liquor. The high concentration of potassium ions in the potassium-rich mother liquor, when returned to the main process, reduces the purity of the lithium salt product. If the liquor is discarded directly, the lithium yield will decrease. Therefore, it is necessary to remove potassium from the potassium-rich mother liquor in a timely manner.

[0003] Several methods for removing potassium from mother liquor have been reported. Patent CN102010991B discloses a method for extracting lithium and removing potassium from lepidolite raw materials, which involves adding aluminum sulfate or aluminum hydroxide to the acid leaching solution to reduce potassium content. 3+ The concentration is saturated / supersaturated, and then potassium is removed by freezing. However, the resulting potassium aluminum sulfate is a soluble substance, resulting in low potassium removal efficiency, and further aluminum removal is still required, making the process cumbersome. Patent CN112978769B discloses a method for removing potassium using sodium sulfate in lithium hydroxide production. Sodium and potassium sources are added to the filtered and neutralized mother liquor to obtain a saturated solution, which is then heated to evaporate the water, and finally filtered to remove the filter cake. However, this method has high production costs and low potassium removal efficiency, making it unsuitable for industrial production. Patent CN113387374B discloses a potassium removal process in an ore-based lithium extraction system. The pH of the potassium-rich sodium precipitation mother liquor is adjusted to 1.5-2.5 with concentrated sulfuric acid, and then iron salt is added and heated to produce potassium alum crystals. Solid-liquid separation reduces the potassium ion concentration in the system. However, this method has a long process flow, high raw material costs, and a slow rate of potassium alum crystal production, making it unsuitable for continuous industrial production. Summary of the Invention

[0004] To address the problems of existing technologies, this application provides a method for simultaneous potassium removal from slurry and potassium-rich mother liquor in lithium salt production. This method adds a potassium removal sub-process outside the main process, seamlessly integrating with the main process to avoid lithium loss during potassium removal. This method not only removes the high concentration of potassium from the potassium-rich mother liquor but also simultaneously reduces the potassium ion concentration in the slurry, thereby lowering the potassium ion concentration in the main process. This improves product purity, increases the number of times the mother liquor can be recycled, and reduces production costs.

[0005] First, this application provides a method for simultaneous potassium removal from slurry and potassium-rich mother liquor in lithium salt production, comprising the following steps:

[0006] S1. Take slurry and potassium-rich mother liquor from the lithium salt production process, add the potassium-rich mother liquor to the slurry, stir evenly to obtain a mixed solution; the volume ratio of the slurry to the potassium-rich mother liquor is (5~15):1, the pH value of the mixed solution is 2~4, and the potassium ion concentration in the potassium-rich mother liquor is 5~20g / L.

[0007] S2. Add potassium ferric sulfate seed crystals, ferrous sulfate and oxidant to the mixture obtained in step S1 to carry out potassium precipitation reaction;

[0008] S3. After the potassium precipitation reaction is completed, the reaction mixture is returned to the process before the lithium slag separation step in the lithium salt production process.

[0009] Preferably, the concentration of potassium ions in the slurry is 1.76~1.87 g / L.

[0010] Preferably, the oxidant is selected from at least one of hydrogen peroxide (molecular formula H2O2), sodium peroxide (molecular formula Na2O2), and sodium percarbonate (molecular formula 2Na2CO3·3H2O2).

[0011] Preferably, the amount of potassium ferrous sulfate seed crystals added is 0.09 to 0.35 times the mass of potassium in the mixture. For example, the amount of potassium ferrous sulfate seed crystals added is 0.09, 0.1, 0.12, 0.15, 0.16, 0.2, 0.24, 0.25, 0.3, or 0.35 times the mass of potassium in the mixture; alternatively, it can be a range of values ​​formed by using any two of the above points as endpoints.

[0012] Preferably, the amount of ferrous sulfate added is 9.71 to 15.55 times the mass of potassium in the mixture.

[0013] Preferably, the molar ratio of peroxide to ferrous sulfate in the oxidant is (0.5~2):1.

[0014] Preferably, the potassium precipitation reaction is carried out at a temperature of 90-98°C for 20-40 minutes.

[0015] Preferably, the potassium precipitation reaction is carried out under stirring conditions of 300-500 r / min. When the stirring speed is lower than this range, the formation rate of potassium ferric sulfate is slow, and the generated crystals tend to aggregate into large particles, leading to increased lithium loss after potassium removal. When the stirring speed is higher than this range, the generated potassium ferric sulfate crystals are too small, and their excessively large specific surface area also leads to increased lithium loss after potassium removal.

[0016] Preferably, the ferrous sulfate is selected from ferrous sulfate heptahydrate, anhydrous ferrous sulfate, ferrous sulfate monohydrate, or ferrous sulfate tetrahydrate.

[0017] Preferably, during the potassium precipitation reaction, air or oxygen is introduced into the reaction solution through a microbubble generator to form bubbles. Introducing air or oxygen promotes the oxidation of ferrous ions and accelerates the growth of potassium ferrous alum crystals, thus improving potassium removal efficiency. Introducing air or oxygen through a microbubble generator creates fine bubbles in the reaction solution, which improves the contact area and uniformity between ferrous ions and oxygen or air, resulting in the uniform production of potassium ferrous alum throughout the system.

[0018] Preferably, when introducing air or oxygen, the flow rate is 0.05~0.30VVM; that is, the volume of gas introduced per minute is 0.05~0.3 times the volume of liquid.

[0019] Preferably, the slurry is a slurry obtained by roasting, acid roasting and water conditioning of spodumene ore.

[0020] Preferably, the potassium-rich mother liquor is the separated mother liquor obtained after multiple cycles of lithium precipitation in the lithium salt production process.

[0021] Compared with the prior art, this application has the following beneficial effects:

[0022] 1. This application ingeniously utilizes the strong acidity of the slurry and the strong alkalinity of the potassium-rich mother liquor. The potassium-rich mother liquor is slowly added to the slurry to obtain a mixed solution. By optimizing the ratio of the slurry and the potassium-rich mother liquor, the pH of the mixed solution is adjusted to the range where potassium ferric sulfate can be formed. This removes potassium from both the potassium-rich mother liquor and the slurry simultaneously, eliminating the need for additional sulfuric acid to adjust the pH and reducing raw material costs. The simultaneous removal of potassium from both the potassium-rich mother liquor and the slurry lowers the potassium ion concentration in the main process, thereby improving product purity, increasing the number of times the mother liquor can be recycled, increasing lithium yield, and reducing production costs.

[0023] 2. This application accelerates the formation rate of potassium ferric sulfate by adding seed crystals, and at the same time uses oxidants such as hydrogen peroxide to oxidize ferrous ions to ferric ions. The newly generated highly active ferric ions can quickly react with potassium ions to form potassium ferric sulfate, which further accelerates the reaction rate and significantly shortens the reaction time. This technical solution only requires 20 to 40 minutes, while the existing technology requires at least 60 minutes or even longer.

[0024] 3. Because sulfuric acid is generated during the precipitation of potassium ferric alum, the pH of the solution gradually deviates from the acceptable range for potassium ferric alum formation, requiring continuous addition of alkali to maintain the reaction. This application, however, consumes sulfuric acid when using oxidants such as hydrogen peroxide to oxidize ferrous ions to ferric ions, keeping the pH of the solution consistently within the acceptable range for potassium ferric alum formation, eliminating the need for continuous alkali addition. Furthermore, the potassium-removed slurry is directly returned to the main process for leaching and neutralization, and the potassium-removed slag and lithium slag are removed simultaneously, eliminating the need for an additional post-potassium-removal filtration step, further simplifying the production process and reducing production costs.

[0025] 4. The method of this application has a high potassium removal efficiency. The potassium ion concentration in the mixed liquor after potassium removal is lower than that in the slurry preparation in the main process. After returning the mixed liquor after potassium removal to the main process, the potassium ion concentration in the main process is reduced to a certain extent, and the number of times the mother liquor can be recycled is increased. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the process for simultaneous potassium removal from the slurry and potassium-rich mother liquor in the lithium hydroxide production process of Example 1. Detailed Implementation

[0028] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0029] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0030] Those skilled in the art will understand that the order in which the steps are written in the various embodiments or examples does not imply a strict execution order and does not limit the implementation process in any way. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but sequentially is preferred.

[0031] See Figure 1 The traditional process for preparing lithium hydroxide includes: first, roasting, ball milling, acid roasting, and cooling raw materials such as spodumene; then, preparing a slurry, followed by leaching, neutralization, and filtration to separate lithium slag and leaching solution; the leaching solution is then purified and filtered to remove metal impurities, improving solution purity and preparing for deep lithium purification; the filtered liquid undergoes causticization to convert lithium ions into lithium hydroxide, followed by freezing and separation to separate sodium sulfate decahydrate crystals and lithium hydroxide solution; the lithium hydroxide solution undergoes primary and secondary evaporation and centrifugation to obtain solid lithium hydroxide; the lithium hydroxide is dried and packaged to obtain lithium hydroxide monohydrate product; the low-potassium mother liquor formed during the centrifugation process after evaporation is transferred to the causticization step to further precipitate residual lithium ions in the mother liquor; after multiple cycles, the potassium-rich mother liquor produced during the centrifugation process can no longer be directly introduced into the production system.

[0032] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0033] The following embodiments and comparative examples are as follows: Figure 1 The lithium hydroxide production process shown includes a slurry and a potassium-rich mother liquor; the potassium ion concentration in the slurry is 1.76~1.87 g / L. After the potassium precipitation reaction, the reactants are returned to the leaching and neutralization step. The resulting potassium ferric sulfate solid (i.e., potassium-removed slag) can be discharged along with the undissolved lithium slag during the filtration step in the main process.

[0034] Example 1

[0035] Step 1: From such Figure 1 In the main process of lithium hydroxide production shown, 1500 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 5 g / L were taken. The potassium-rich mother liquor was slowly added to the slurry and stirred evenly at a speed of 500 r / min to obtain a mixed solution with a pH value of 2.

[0036] Step 2: Add 0.33g of potassium ferric sulfate seed crystals, 93.15g of ferrous sulfate heptahydrate and 19.00g of 30% hydrogen peroxide solution to the mixture obtained in Step 1. Introduce air through a microbubble at a flow rate of 0.30VVM and heat to 98℃ for 20min to obtain the reaction mixture.

[0037] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0038] Example 2

[0039] Step 1: Take 1000 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 10 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 400 r / min to obtain a mixed solution with a pH value of 3.

[0040] Step 2: Add 0.56g of potassium ferric sulfate seed crystals, 48.10g of ferrous sulfate tetrahydrate and 24.63g of 30% hydrogen peroxide solution to the mixture obtained in Step 1. Introduce air through a microbubble at a flow rate of 0.20VVM and heat to 95℃ for 30min to obtain the reaction mixture.

[0041] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0042] Example 3

[0043] Step 1: Take 800 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 12 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 350 r / min to obtain a mixed solution with a pH value of 3.2.

[0044] Step 2: Add 0.40g of potassium ferric sulfate seed crystals, 29.15g of anhydrous ferrous sulfate and 26.95g of sodium peroxide to the mixture obtained in Step 1. Introduce air through a microbubble apparatus at a flow rate of 0.1VVM and heat to 96℃ for 35min to obtain the reaction mixture.

[0045] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0046] Example 4

[0047] Step 1: Take 1200 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 15 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 450 r / min to obtain a mixed solution with a pH value of 2.5.

[0048] Step 2: Add 0.90g of potassium ferric sulfate seed crystals, 54.93g of ferrous sulfate monohydrate and 37.84g of sodium peroxide to the mixture obtained in Step 1. Introduce oxygen through a microbubble at a flow rate of 0.05VVM and heat to 93℃ for 25min to obtain the reaction mixture.

[0049] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0050] Example 5

[0051] Step 1: Take 500 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 20 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 300 r / min to obtain a mixed solution with a pH value of 4.

[0052] Step 2: Add 0.88g of potassium ferric sulfate seed crystals, 52.17g of ferrous sulfate heptahydrate and 39.31g of sodium percarbonate to the mixture obtained in Step 1. Introduce oxygen through a microbubble at a flow rate of 0.2VVM and heat to 90℃ for 40min to obtain the reaction mixture.

[0053] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0054] Comparative Example 1

[0055] Step 1: Take 1500 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 3 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 500 r / min to obtain a mixed solution with a pH value of 2.

[0056] Step 2: Add 0.30g of potassium ferric sulfate seed crystals, 47.31g of anhydrous ferrous sulfate and 17.67g of 30% hydrogen peroxide solution to the mixture obtained in Step 1. Introduce oxygen through a microbubble at a flow rate of 0.1VVM and heat to 98℃ for 20min to obtain the reaction mixture.

[0057] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0058] Comparative Example 2

[0059] Step 1: Take 500 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 4 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 300 r / min to obtain a mixed solution with a pH value of 4.

[0060] Step 2: Add 0.39g of potassium ferric sulfate seed crystals, 22.93g of ferrous sulfate heptahydrate and 12.86g of sodium peroxide to the mixture obtained in Step 1. Introduce air through a microbubble at a flow rate of 0.3VVM and heat to 90℃ for 40 minutes to obtain the reaction mixture.

[0061] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0062] Comparative Example 3

[0063] Step 1: Take 500 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 22 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 300 r / min to obtain a mixed solution with a pH value of 4.

[0064] Step 2: Add 0.93g of potassium ferric sulfate seed crystals, 54.84g of ferrous sulfate heptahydrate and 30.78g of sodium peroxide to the mixture obtained in Step 1. Introduce oxygen through a microbubble apparatus at a flow rate of 0.05VVM and heat to 90℃ for 40min to obtain the reaction mixture.

[0065] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0066] Comparative Example 4

[0067] Step 1: Take 1500 mL of slurry and 100 mL of potassium-rich mother liquor with a potassium ion concentration of 25 g / L from the main process of lithium hydroxide production. Slowly add the potassium-rich mother liquor to the slurry and stir evenly at a speed of 500 r / min to obtain a mixed solution with a pH value of 2.

[0068] Step 2: Add 0.52g of potassium ferric sulfate seed crystals, 90.65g of ferrous sulfate monohydrate and 27.94g of sodium percarbonate to the mixture obtained in Step 1. Introduce air through a microbubble apparatus at a flow rate of 0.2VVM, and heat to 98℃ for 20min to obtain the reaction mixture.

[0069] Step 3: Return the reacted mixture to the leaching and neutralization step of the main process.

[0070] The potassium ion concentration in the slurry, the potassium ion concentration in the potassium-rich mother liquor, the potassium ion concentration in the mixed liquor after potassium removal, and the potassium removal rate in Examples 1-5 and Comparative Examples 1-4 were statistically analyzed and summarized in Table 1.

[0071] Table 1. Potassium removal rates in each example and comparative example.

[0072]

[0073] In the table, potassium removal rate = 1 - potassium ion concentration in the mixed solution after potassium removal × (volume of slurry + volume of potassium-rich mother liquor) / (potassium ion concentration in slurry × volume of slurry + potassium ion concentration in potassium-rich mother liquor × volume of potassium-rich mother liquor).

[0074] Table 1 shows that when the potassium ion concentration in the potassium-rich mother liquor is between 5 and 20 g / L, the potassium removal rate using this method is >80%; when the potassium ion concentration in the potassium-rich mother liquor is below 5 g / L or above 20 g / L, the potassium removal rate using this method is lower. This may be because when the potassium ion concentration is too low, the reaction rate is low, resulting in a low conversion rate of potassium ions at that reaction time; when the potassium ion concentration is too high, more ferric hydroxide precipitate byproducts are produced, reducing the number of iron ions that can react with potassium ions, thus leading to a decrease in the potassium ion conversion rate.

[0075] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for simultaneous potassium removal from slurry and potassium-rich mother liquor in lithium salt production, characterized in that, The method is as follows: S1. Take slurry and potassium-rich mother liquor from the lithium hydroxide production process, add the potassium-rich mother liquor to the slurry, and stir evenly to obtain a mixed solution; the volume ratio of the slurry to the potassium-rich mother liquor is (5~15):1, the pH value of the mixed solution is 2~4, and the potassium ion concentration in the potassium-rich mother liquor is 5~20g / L; the slurry is obtained by roasting, acid roasting and water conditioning of spodumene ore. S2. Add potassium ferric sulfate seed crystals, ferrous sulfate and oxidant to the mixture obtained in step S1, and carry out potassium precipitation reaction under stirring conditions of 300~500 r / min; the oxidant is selected from at least one of hydrogen peroxide, sodium peroxide and sodium percarbonate; the molar ratio of peroxide to ferrous sulfate in the oxidant is (0.5~2):

1. S3. After the potassium precipitation reaction is completed, the reaction mixture is returned to the process before the lithium slag separation step in the lithium salt production process.

2. The method according to claim 1, characterized in that, The amount of potassium ferrous sulfate seed crystals added is 0.09 to 0.35 times the mass of potassium in the mixture; the amount of ferrous sulfate added is 9.71 to 15.55 times the mass of potassium in the mixture.

3. The method according to claim 1, characterized in that, The potassium precipitation reaction is carried out at a temperature of 90-98°C for 20-40 minutes.

4. The method according to claim 1, characterized in that, The concentration of potassium ions in the slurry is 1.76~1.87 g / L.

5. The method according to claim 1, characterized in that, The ferrous sulfate is selected from ferrous sulfate heptahydrate, anhydrous ferrous sulfate, ferrous sulfate monohydrate, or ferrous sulfate tetrahydrate.

6. The method according to claim 1, characterized in that, During the potassium precipitation reaction, air or oxygen is introduced into the reaction solution through a microbubble generator to form bubbles in the reaction solution.

7. The method according to claim 1, characterized in that, The potassium-rich mother liquor is the separated mother liquor obtained after multiple cycles of lithium precipitation steps in the lithium salt production process.

Images