A method for preparing a lithium smectite by steam crystallization

Abstract

The application discloses a method for preparing a lithium smectite by steam crystallization, and directly obtains the lithium smectite by steam crystallization of a lithium smectite precursor gel, and comprises the following steps: first, a certain amount of lithium salt is dissolved in water to form a uniform dispersion liquid by stirring; second, a certain amount of soluble magnesium salt is dissolved in water to form a magnesium salt solution, a certain amount of alkali is added, and Mg(OH)2 precipitate is obtained by reaction, and then the obtained wet filter cake is transferred into the lithium salt dispersion liquid to form a uniform mixed slurry by stirring; third, a certain amount of water glass is added with a certain amount of inorganic strong acid to obtain SiO2 precipitate by reaction, and then the obtained wet filter cake is transferred into the mixed slurry of Mg(OH)2 and lithium salt; fourth, the slurry is rapidly stirred at a certain temperature to form a gel by pre-reaction; finally, the gel is subjected to crystallization reaction in steam at a certain temperature and pressure, and after the reaction is completed, the gel is dried to obtain a lithium smectite product.

Description

Technical Field

[0001] This invention relates to the field of lithium saponite preparation technology, and in particular to a method for preparing lithium saponite by water vapor crystallization. Background Technology

[0002] Lithium saponite is a 2:1 type layered clay mineral material with the general molecular formula M. x [Li x Mg 6-x Si8O 20 [(OH·F)4](M=Na,Li). It consists of Si-O tetrahedra and Mg-O octahedra arranged in a 2:1 ratio in the vertical direction. The average layer thickness is approximately 1 nm, and the diameter is approximately 30 nm. Due to the presence of Mg in the layers... 2+ By Li + Substitution, negatively charged, therefore Li adsorbed between layers + Or Na + Equal cations are used to balance the charge.

[0003] When lithium saponite is dispersed in water, the adsorbed cations in the interlayer structure undergo hydration, increasing in volume and resulting in a peeling dissolution that forms thin, sheet-like particles approximately 1 nm thick and 30 nm in diameter. The surface of these sheets carries a certain number of negative charges, while the Mg-OH groups at the edges are protonated, acquiring a certain number of positive charges. Figure 1 As shown, the negative charges on the surface of the sheet and the positive charges at the edge of the sheet attract each other, forming a continuous network structure. This network structure is figuratively called a "house of cards" structure, as shown in the image. Figure 2 As shown, this "house-like" structure remains stable under static conditions, but it is disrupted when a certain external force is applied. However, once the external force is removed, the stable "house-like" structure reforms. This is the thixotropic property of lithium saponite in water. Due to its excellent swelling, thixotropic, and stable properties in water, lithium saponite is widely used as an excellent suspending agent and thickener in industries such as coatings, cosmetics, and pharmaceuticals.

[0004] Natural lithium saponite minerals are scarce and typically contain numerous impurities, making purification extremely difficult. Synthetic lithium saponite, on the other hand, has fewer impurities, higher purity, and allows for the control of interlayer charge, leading to increasing market demand. Currently, the most mature industrial method for synthesizing lithium saponite is the hydrothermal method. However, this method has several drawbacks: firstly, it requires highly alkaline conditions, generating large amounts of difficult-to-treat mixed wastewater containing alkali and salts; secondly, due to the gelling properties of lithium saponite, a solid content of around 3% can form a viscous solid, and the hydrothermal reaction results in a very low solid content, typically not exceeding 7%, leading to low yields; thirdly, the gelling properties of lithium saponite make the aqueous solution very viscous, making filtration and cleaning of the product extremely difficult; and fourthly, the washed lithium saponite filter cake has a very low solid content, making drying very difficult and costly. These drawbacks of the hydrothermal method make the production process of lithium saponite complex, cumbersome, low-yield, and costly.

[0005] Based on the current disadvantages of hydrothermal production of lithium saponite, this patent develops a new method for preparing lithium saponite by steam crystallization. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing lithium saponite by steam crystallization, which solves the problems existing in the current hydrothermal method for preparing lithium saponite. Specifically, lithium saponite is directly prepared by steam crystallization of the precursor gel that forms lithium saponite.

[0007] To achieve the above objectives, the present invention provides a method for preparing lithium saponite by water vapor crystallization, comprising the following steps:

[0008] S1. Weigh a certain amount of lithium salt and add a certain amount of deionized water to disperse it to obtain a lithium salt dispersion.

[0009] S2. Weigh a certain amount of magnesium salt and put it into a beaker. Add a certain amount of deionized water to dissolve it and obtain a magnesium salt solution. Under stirring conditions, add a certain amount of alkali and react to obtain Mg(OH)2 precipitate. Then filter and wash with deionized water. Transfer the washed Mg(OH)2 wet filter cake to the lithium salt dispersion obtained in S1 and stir to form a uniform mixed slurry.

[0010] S3. Weigh a certain amount of water glass, add a certain amount of inorganic acid under stirring conditions, react to obtain solid SiO2, then filter and wash with deionized water; transfer the washed SiO2 wet filter cake to the mixed slurry of Mg(OH)2 and lithium salt in S2 above.

[0011] S4. Within a certain temperature range, the mixture of the above S3 is rapidly stirred and reacted to obtain a gel;

[0012] S5. The gel obtained in S4 above is crystallized in water vapor at a certain temperature and pressure.

[0013] S6. Finally, dry the crystallized gel to obtain lithium saponite.

[0014] Preferably, in the above-mentioned method for preparing lithium saponite by water vapor crystallization, the lithium salt in step S1 is lithium fluoride or lithium hydroxide; the magnesium salt in step S2 is magnesium chloride, magnesium sulfate or magnesium nitrate, and the alkali is sodium hydroxide, potassium hydroxide or ammonia; the inorganic acid in step S3 is hydrochloric acid, sulfuric acid or nitric acid.

[0015] Preferably, in the above-mentioned method for preparing lithium saponite by water vapor crystallization, the gel prepared in step S4 has a Li:Mg:Si molar ratio of (0.8-1.6):(5.2-5.6):8 and a gel solid content of 30-65%.

[0016] Preferably, in the above-mentioned method for preparing lithium saponite by water vapor crystallization, the temperature range of step S4 is 30-90℃ and the time is 2-6 hours.

[0017] Preferably, in the above-mentioned method for preparing lithium saponite by water vapor crystallization, the water vapor crystallization in step S5 is carried out in a sealed environment with water vapor, the water vapor pressure is 400-1900 kPa, the temperature is 150-210℃, and the time is 8-36 hours.

[0018] Preferably, in the above-mentioned method for preparing lithium saponite by water vapor crystallization, the gel drying temperature after crystallization in step S6 is 105-150℃, and the time is 10-24 hours.

[0019] Preferably, in the above-mentioned method for preparing lithium saponite by water vapor crystallization, the prepared lithium saponite has a Li composition and structure. (0.4-0.8) [Li (0.4-0.8) Mg (5.2-5.6) Si8O 20 (OH·F)4.

[0020] Therefore, the present invention employs the above-described method for preparing lithium saponite via water vapor crystallization, achieving the following technical effects:

[0021] (1) In the second and third steps of this method, salts are also produced when Mg(OH)2 and SiO2 are generated. However, the composition of the salts produced is simple. For example, in the second step, magnesium chloride is added to sodium hydroxide, mainly producing sodium chloride brine. In the third step, water glass is added to sulfuric acid, mainly producing sodium sulfate brine. The treatment of such brine with a simple composition is relatively easy. This solves the problem that the wastewater from the current hydrothermal production of lithium saponite contains not only salts but also excess alkalis, making the treatment of such wastewater containing both salts and alkalis very complicated.

[0022] (2) This method directly pre-reacts the raw materials to form a gel. Since the gel has not yet turned into lithium saponite, a very high solid content can be achieved. In the steam crystallization process, the gel can be placed in a filter cloth with a certain pore size, placed on a perforated tray, and the tray is placed in a sealed oven for high-temperature and high-pressure steam crystallization reaction. After the crystallization reaction is completed, the sealed oven is opened, and the product in the tray is taken out. This solves the problem of low solid content in the hydrothermal production process, and the difficulty in discharging the product if a gel product has formed in the reactor after the reaction is completed.

[0023] (3) This method directly uses the raw materials for forming lithium saponite. After the water vapor crystallization reaction is completed, lithium saponite is directly obtained. For example, with a Li:Mg:Si molar ratio of 1:5.5:8 ​​gel, and lithium salt being lithium fluoride, the reaction formula is LiF + 5.5Mg(OH)2 + 8SiO2 → Li 0.5 [Li 0.5 Mg 5.5 Si8O 20 The reaction [(OH)3F] + 4H2O results in only lithium saponite product and water, requiring no washing. This solves the problem of difficult filtration and washing of lithium saponite products prepared by hydrothermal reactions, as they are present in water containing salt and alkali.

[0024] (4) This method yields lithium saponite gel products with a high solid content, reaching 30-65%, resulting in very low drying costs. It solves the problem that the filter cake obtained after washing and pressing lithium saponite in hydrothermal reaction has a low solid content, which is difficult to reach 20%, and its drying cost is very high.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a sealed stainless steel crystallization reactor filled with gel, representing an embodiment of a method for preparing lithium saponite by water vapor crystallization according to the present invention.

[0027] Figure 2 This is a powder X-ray diffraction (XRD) pattern of a sample prepared according to an embodiment of the method for preparing lithium saponite by water vapor crystallization of the present invention. Detailed Implementation

[0028] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0030] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0031] Example 1

[0032] The method for preparing lithium saponite by water vapor crystallization includes the following steps:

[0033] ① Weigh 1.15g (0.0274mol) LiOH·H2O into a 500mL beaker, add 30g of deionized water, and disperse evenly to obtain a LiOH dispersion.

[0034] ② Weigh 18.24 g (0.192 mol) of anhydrous MgCl2 and place it in a 500 mL beaker. Add 100 mL of deionized water to dissolve it and obtain a MgCl2 solution. Add 288 mL of 2 mol·L⁻¹ sodium hydroxide solution. -1 Ammonia water was used to react fully to obtain Mg(OH)2 precipitate, which was then filtered and washed with deionized water. The washed Mg(OH)2 wet filter cake was transferred to the above LiOH dispersion and stirred to form a homogeneous mixed slurry.

[0035] ③ Weigh 63.30 g of water glass (weight content: SiO2 26%, Na2O 8.2%) (containing 0.274 mol SiO2), place it in a 500 mL beaker, and add 55.81 mL of 3 mol·L⁻¹ solution. -1 Hydrochloric acid was used to react fully to obtain SiO2 precipitate, which was then filtered and washed with deionized water. The washed SiO2 wet filter cake was then transferred to the above mixed slurry of Mg(OH)2 and LiOH.

[0036] ④ Under reflux conditions at a temperature of 55℃, the above mixed slurry was rapidly stirred and reacted for 3 hours to obtain a gel with a solid content of approximately 38%.

[0037] ⑤ Place this gel in Figure 1The sealed stainless steel crystallization reactor shown is filled with a certain amount of water at the bottom. The gel is placed in a sieve with a 200-mesh screen. The crystallization reactor is heated to 200°C and the crystallization reaction is carried out for 16 hours.

[0038] ⑥ After the crystallization reaction is complete, wait for the temperature of the crystallization reactor to drop to room temperature, open the reactor, remove the gel, and dry it at 110℃ for 12 hours to obtain lithium saponite with the composition Li. 0.4 [Li 0.4 Mg 5.6 Si8O 20 [(OH)4],

[0039] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the lithium saponite powder prepared in Example 1. Strong diffraction peaks appear near 2-theta of 6.0°, 19.5°, 29.0°, 36.5°, 61.0°, and 72.3°. These diffraction peaks are completely identical to the characteristic diffraction peaks of lithium saponite, indicating that lithium saponite was successfully prepared by this water vapor crystallization method.

[0040] Example 2

[0041] The method for preparing lithium saponite by water vapor crystallization includes the following steps:

[0042] ① Weigh 0.72g (0.0274mol) of LiF into a 500mL beaker, add 30g of deionized water, and disperse evenly to obtain a LiF dispersion.

[0043] ② Weigh 23.04 g (0.192 mol) of anhydrous MgSO4 and place it in a 500 mL beaker. Add 100 mL of deionized water to dissolve it and obtain a MgSO4 solution. Add 192 mL of 2 mol·L⁻¹ sodium hydroxide solution. -1 The NaOH solution was reacted completely to obtain Mg(OH)2 precipitate, which was then filtered and washed with deionized water. The washed Mg(OH)2 wet filter cake was transferred to the above LiF dispersion and stirred to form a homogeneous mixed slurry.

[0044] ③ Weigh 63.30 g of water glass (weight content: SiO2 26%, Na2O 8.2%) (containing 0.274 mol SiO2), place it in a 500 mL beaker, and add 55.81 mL of 3 mol·L⁻¹ solution. -1 Hydrochloric acid was used to react fully to obtain SiO2 precipitate, which was then filtered and washed with deionized water. The washed SiO2 wet filter cake was then transferred to the above-mentioned Mg(OH)2 and LiF mixed slurry.

[0045] ④ At 60℃ and under reflux conditions, the above mixed slurry was rapidly stirred and reacted for 3 hours to obtain a gel with a solid content of approximately 38%. The resulting gel had a Li:Mg:Si molar ratio of 1:5.5:8, and the lithium salt was lithium fluoride. The reaction formula is as follows:

[0046] LiF + 5.5Mg(OH)₂ + 8SiO₂ → Li 0.5 [Li 0.5 Mg 5.5 Si8O 20 [(OH)3F]+4H2O.

[0047] ⑤ Place this gel in Figure 1 The sealed stainless steel crystallization reactor shown is filled with a certain amount of water at the bottom. The gel is placed in a sieve with a 200-mesh screen. The crystallization reactor is heated to 180°C and the crystallization reaction is carried out for 24 hours.

[0048] ⑥ After the crystallization reaction is complete, wait for the temperature of the crystallization reactor to drop to room temperature, open the reactor, remove the gel, and dry it at 120℃ for 12 hours to obtain lithium saponite with the composition Li. 0.4 [Li 0.4 Mg 5.6 Si8O 20 (OH) 3.2 F 0.8 Its XRD pattern is similar to Figure 2 Similarly, this demonstrates that lithium saponite was prepared using this steam crystallization method.

[0049] Comparative Example 1

[0050] Preparation of lithium saponite by hydrothermal method

[0051] First, you need to prepare LiOH, Mg(OH)2, diatomaceous earth, and deionized water.

[0052] LiOH, Mg(OH)₂, and deionized water were mixed in a ratio of 1:20:60. First, the magnesium and lithium sources were dissolved in the water, and then the mixture was stirred magnetically until homogeneous. A silicon source and diatomaceous earth were added to the mixture, and the mixture was stirred magnetically again to ensure the silicon source was evenly dispersed in the solution.

[0053] The mixture was transferred to an autoclave, which was then sealed and placed in an oven to be heated at approximately 180°C for 29 hours.

[0054] After the reaction was completed, the autoclave was naturally cooled to room temperature. The product was then filtered and washed repeatedly with deionized water to remove residual salts and other impurities. The solid content of the washed filter cake was 15%. The washed solid was dried at 120°C for 24 hours. Using X-ray diffraction (XRD), lithium saponite similar to that in Example 1 was observed.

[0055] As can be seen, compared with Comparative Example 1, Examples 1 and 2 of this application yielded a gel with a solid content of 38%, and the subsequent drying time of 12 hours reduced the drying cost; while in Comparative Example 1, the solid content of the filter cake after washing was 15%, and the washed solids needed to be dried at 120°C for 24 hours to obtain lithium saponite. Examples 1 and 2 of this application reduced the drying cost by utilizing the method of this application. In the second and third steps, when generating Mg(OH)2 and SiO2, salt is produced. However, the salt produced in the examples of this application has a single composition. For example, in the second step, magnesium chloride is added to sodium hydroxide, mainly producing sodium chloride brine; in the third step, water glass is added to sulfuric acid, mainly producing sodium sulfate brine. Such a single-composition brine is relatively easy to process. In Example 2 of this application, a gel with a Li:Mg:Si molar ratio of 1:5.5:8 ​​was obtained, and the lithium salt was lithium fluoride. The reaction formula is as follows: LiF + 5.5Mg(OH)2 + 8SiO2 → Li 0.5 [Li 0.5 Mg 5.5 Si8O 20 The reaction [(OH)3F] + 4H2O produces only lithium saponite and water, requiring no washing. In contrast, Comparative Example 1 uses a hydrothermal reaction to prepare lithium saponite, which requires filtration and washing. This application eliminates the washing step, simplifying the preparation process. Pre-reacting the raw materials to form a gel, before it transforms into lithium saponite, results in a high solids content. The precursor gel is then crystallized with steam to directly obtain lithium saponite, allowing for a simpler preparation process that reduces intermediate steps and improves efficiency compared to the hydrothermal method.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing lithium saponite by water vapor crystallization, characterized in that, Includes the following steps: S1. Weigh a certain amount of lithium salt and add a certain amount of deionized water to disperse it to obtain a lithium salt dispersion. S2. Weigh a certain amount of magnesium salt and put it into a beaker. Add a certain amount of deionized water to dissolve it and obtain a magnesium salt solution. Under stirring conditions, add a certain amount of alkali and react to obtain Mg(OH)2 precipitate. Then filter and wash with deionized water. Transfer the washed Mg(OH)2 wet filter cake to the lithium salt dispersion obtained in S1 and stir to form a uniform mixed slurry. S3. Weigh a certain amount of water glass, add a certain amount of inorganic acid under stirring conditions, react to obtain solid SiO2, then filter and wash with deionized water; transfer the washed SiO2 wet filter cake to the mixed slurry of Mg(OH)2 and lithium salt in S2 above. S4. Within a certain temperature range, the mixture of the above S3 is rapidly stirred and reacted to obtain a gel; S5. The gel obtained in S4 above is crystallized in water vapor at a certain temperature and pressure. Water vapor crystallization is carried out in a sealed environment with water vapor, with a water vapor pressure of 400-1900 kPa, a temperature of 150-210℃, and a time of 8-36 hours. S6. Finally, the crystallized gel is dried to obtain lithium saponite; the prepared lithium saponite has the following structure: Li (0.4-0.8) [Li (0.4-0.8) Mg (5.2-5.6) Si8O 20 (OH·F)4.

2. The method for preparing lithium saponite by steam crystallization according to claim 1, characterized in that, In step S1, the lithium salt is lithium fluoride or lithium hydroxide; in step S2, the magnesium salt is magnesium chloride, magnesium sulfate or magnesium nitrate, and the alkali is sodium hydroxide, potassium hydroxide or ammonia; in step S3, the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid.

3. The method for preparing lithium saponite by steam crystallization according to claim 2, characterized in that, The gel prepared in step S4 has a Li:Mg:Si molar ratio of (0.8-1.6):(5.2-5.6):8 and a gel solid content of 30-65%.

4. The method for preparing lithium saponite by water vapor crystallization according to claim 3, characterized in that, The temperature range for step S4 is 30-90℃, and the time is 2-6 hours.

5. The method for preparing lithium saponite by steam crystallization according to claim 1, characterized in that, In step S6, the gel is dried at a temperature of 105-150℃ for 10-24 hours after crystallization.

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