Method for preparing lithium dihydrogen phosphate by utilizing amblygonite
Through the calcination acid dissolution method and impurity removal treatment, the problem of impurity elements in phosphate lithium aluminite is solved, and the preparation of high-purity lithium dihydrogen phosphate is realized, which improves the recovery rate of lithium elements and the purity of the product, and reduces production costs.
Patent Information
- Application Number
- CN202411933479.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-05-06
AI Technical Summary
In the prior art, when lithium dihydrogen phosphate is prepared by using phosphate lithium aluminite, it is difficult to effectively remove impurities, resulting in low purity and yield of lithium dihydrogen phosphate.
The phosphorus and lithium elements in the phosphate and lithium aluminite were fully dissolved by calcining acid dissolution method, and purified by decomposition treatment and concentration to obtain high-purity lithium dihydrogen phosphate.
The recovery rate of lithium elements in phosphate lithium aluminite has reached more than 90%, and the purity of lithium dihydrogen phosphate produced has reached more than 99.0%, which has significantly reduced production costs.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for preparing lithium dihydrogen phosphate by utilizing pyroxenite. Background Art
[0002] Lithium dihydrogen phosphate, with the chemical formula LiH2PO4, is a colorless cubic crystal. Lithium dihydrogen phosphate has a high specific capacity of about 150mAh / g, which is much higher than traditional oxide positive electrode materials such as lithium cobalt oxide and lithium iron phosphate. It also has a high conductivity at high temperature, which is beneficial to improve the discharge performance of the battery. In addition, it has good cycle stability and can maintain a long cycle life. It is an ideal battery positive electrode material. At present, lithium dihydrogen phosphate is mainly prepared by using pure materials containing lithium source and phosphorus source as raw materials, but the production cost of this preparation method is generally high. In addition, lithium dihydrogen phosphate can also be prepared by recycling waste batteries, but due to the complex composition of the battery and the low content of valuable elements that can be recovered in the battery, it can be seen that this method has the problems of greater difficulty in separation and purification and unstable product quality.
[0003] Lithium aluminum phosphate, with the chemical formula LiAl(PO4)(OHF), is one of the industrial minerals with a high lithium content. The journal "Technology Research on the Preparation of Lithium Carbonate from Lithium aluminum phosphate" (Huang Guangzhu et al., Phosphate Fertilizer and Compound Fertilizer, Vol. 34, No. 11, November 2019) mentioned that X-ray diffraction analysis of lithium aluminum phosphate ore samples showed that the ore samples mainly existed in the form of phosphates. Specifically, the mass fraction of Li2O was 8.46%, the mass fraction of P2O3 was 37.13%, the mass fraction of Al2O3 was 28.33%, and the mass fraction of SiO2 was 14.37%. It can be seen that the content of impurity elements such as Al in lithium aluminum phosphate is relatively high. Therefore, when using lithium aluminum phosphate as a raw material, it is very necessary to fully dissolve the phosphorus and lithium elements in it, efficiently remove the impurity elements, and obtain battery-grade lithium dihydrogen phosphate.
[0004] In the prior art, CN117003264A discloses a method for preparing lithium carbonate using phosphate lithium aluminum stone, and the specific steps are: after pulverizing the phosphate lithium aluminum stone, adding concentrated sulfuric acid to mix, a mixture is obtained, and the mixture is heated at 500-600 ° C for sulfuric acid pyrolysis treatment to obtain clinker, and the clinker is leached and the pH is adjusted to remove impurities to obtain a Li-containing solution, and then the solution is added to a carbonate solution to obtain lithium carbonate. In the journal "Technology Research on Preparation of Lithium Carbonate from Phosphorus Lithium Aluminum Stone" (Huang Guangzhu et al., Phosphate Fertilizer and Compound Fertilizer, November 2019, Vol. 34, No. 11), the phosphate lithium aluminum stone is acidified and roasted, and high-temperature leached to obtain a mother liquor, and then ammonia water is added to adjust the pH of the mother liquor to remove Fe and Al impurities to obtain a primary purified liquid, and the pH of the primary purified liquid is further adjusted to remove P impurities to obtain a Li-containing purified liquid, and saturated sodium carbonate is added to the Li-containing purified liquid to obtain a lithium carbonate product. In the above patents and journals, lithium carbonate is prepared using lithium aluminum phosphate as a raw material. During the preparation of lithium carbonate, it is necessary to prevent the phosphorus element in the lithium aluminum phosphate from being leached into the solution as much as possible to ensure the purity of the lithium carbonate. During the preparation of lithium dihydrogen phosphate, it is necessary to control the preparation process so that the phosphorus element is leached into the solution as completely as possible.
[0005] Therefore, when using pyrophosphate as a raw material to prepare lithium dihydrogen phosphate, how to reduce the dissolution of impurity elements in pyrophosphate and increase the dissolution of phosphorus and lithium elements in pyrophosphate to improve the purity and yield of lithium dihydrogen phosphate is a problem that needs to be solved urgently. Summary of the invention
[0006] In view of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing lithium dihydrogen phosphate using phosphate lithium aluminum stone. Specifically, phosphate lithium aluminum stone is calcined and crushed to obtain phosphate lithium aluminum stone powder, and then the phosphate lithium aluminum stone powder is mixed with acid solution for calcination and acid dissolution reaction, and water is added for leaching to obtain an acidic solution containing lithium dihydrogen phosphate, and an impurity remover is added to the above solution to remove impurity elements. After concentration, a concentrated solution is obtained, and then an organic reagent is added to the concentrated solution, and after purification, lithium dihydrogen phosphate is obtained. The present invention adopts the method of calcination and acid dissolution to dissolve phosphate lithium aluminum stone, and the phosphorus element and lithium element in the phosphate lithium aluminum stone are fully dissolved. The method provided by the present invention can ensure that the recovery rate of lithium element in the phosphate lithium aluminum stone is more than 90%, and the purity of the obtained lithium dihydrogen phosphate is more than 99.0%.
[0007] To achieve the above object, the present invention adopts the following technical solution:
[0008] The present invention provides a method for preparing lithium dihydrogen phosphate by using pyrophosphate, comprising the following steps:
[0009] (1) mixing phosphate aluminum powder and acid solution and heating them to react, after the reaction is completed, cooling and crushing the reaction product, adding water to leach, filtering, and collecting the filtrate to obtain an acidic solution containing lithium dihydrogen phosphate;
[0010] (2) The acidic solution containing lithium dihydrogen phosphate is treated to remove impurities and then concentrated to obtain a concentrated solution. An organic solvent and a salting-out agent are added to the concentrated solution, and the solution is stirred and filtered. The filtered solid is collected, and the solid is recrystallized and dried to obtain lithium dihydrogen phosphate.
[0011] Preferably, in step (1), the pyrophosphate powder is prepared by the following method:
[0012] The phosphate lithium aluminum stone is calcined at 700-1000°C for 1-3 hours and then crushed to obtain the phosphate lithium aluminum stone powder with a particle size of 10-100 μm.
[0013] Preferably, in step (1), the acid solution is one of concentrated sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid or acetic acid, and the concentration of the acid solution is 50wt%-98wt%.
[0014] Preferably, in step (1), the material-liquid ratio of phosphate lithium aluminum stone powder to acid solution is 1g:(1-5)mL.
[0015] Preferably, in step (1), the heating temperature is 200-300° C. and the reaction time is 1-3 h.
[0016] Preferably, in step (1), the reaction product is cooled to below 50° C. and the particle size of the pulverized reaction product is 10-100 μm.
[0017] Preferably, during the water leaching process, the solid-liquid ratio of the crushed reaction product to water is 1 g: (2-10) mL, the leaching temperature is 20-100° C., and the leaching time is 1-5 h.
[0018] Preferably, in step (2), the specific operation of the impurity removal treatment is: adding an impurity remover to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements.
[0019] Further preferably, the impurity remover is one or more of ammonia water, sodium hydroxide, EDTA, oxalic acid, cuproferric reagent, polyaluminium chloride, polyacrylamide, thiourea or activated carbon.
[0020] More preferably, the material-liquid ratio of the acidic solution containing lithium dihydrogen phosphate and the impurity remover is (80-120) mL:1 g.
[0021] Preferably, in step (2), the concentrated solution contains Li + The concentration is 1-15mol / L.
[0022] Preferably, in step (2), the organic solvent is at least one of methanol, ethanol, formic acid or acetic acid.
[0023] Preferably, in step (2), the salting-out agent is ammonium sulfate or sodium sulfate.
[0024] Preferably, in step (2), the material-liquid ratio of the concentrate, the organic solvent and the salting-out agent is 1 mL: (0.1-10) mL: (2-4) g.
[0025] Preferably, in step (2), the stirring time is 0.5-2h.
[0026] Preferably, in step (2), during the recrystallization process, the solid is recrystallized 2-3 times using pure water, wherein the mass ratio of pure water to solid is (2-5):1.
[0027] Preferably, in step (2), the drying temperature is 100-180° C., the drying pressure is -0.06 MPa to -0.1 MPa, and the drying time is 1-5 h.
[0028] Beneficial effects of the present invention:
[0029] The present invention provides a method for preparing lithium dihydrogen phosphate using pyrophosphate. Specifically, pyrophosphate is calcined and then crushed to obtain pyrophosphate powder, and then the pyrophosphate powder is mixed with an acid solution for calcination and acid dissolution reaction, and then water is added for leaching to obtain an acid solution containing lithium dihydrogen phosphate, and an impurity remover is added to the solution to remove impurity elements, and after concentration, a concentrated solution is obtained, and then an organic reagent is added to the concentrated solution, and after purification, lithium dihydrogen phosphate is obtained.
[0030] The present invention adopts a calcination and acid dissolution method to dissolve phosphate lithium aluminum stone, and fully dissolves the phosphorus element and lithium element in the phosphate lithium aluminum stone. The method of the present invention can ensure that the recovery rate of the lithium element in the phosphate lithium aluminum stone is more than 90%, and the purity of the prepared lithium dihydrogen phosphate is more than 99.0%. At the same time, the method of the present invention can significantly reduce the production cost and has a good application prospect. In addition, the preparation method of lithium dihydrogen phosphate of the present invention is also simple and easy to implement, and the selected organic solvent is safe and non-toxic, which is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 : The present invention utilizes phosphate lithium aluminum stone to prepare lithium dihydrogen phosphate flow chart. DETAILED DESCRIPTION
[0032] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.
[0033] Apatite is one of the industrial minerals with a high lithium content and is often used as a raw material to prepare lithium salts. However, the prior art only discloses the use of apatite as a raw material to prepare lithium carbonate. However, in the process of preparing lithium carbonate, it is necessary to prevent the phosphorus element in apatite from being leached into the solution as much as possible to ensure the purity of lithium carbonate, while in the process of preparing lithium dihydrogen phosphate, it is necessary to control the preparation process so that the phosphorus element is leached into the solution as completely as possible.
[0034] As a mineral with high lithium content, the theoretical lithium content of Li2O in pyroxenite is as high as 10.1%, and the typical value of Li2O is 8-9%, which is much higher than other lithium minerals. From the perspective of mineral composition, the main body of the mineral is AlPO4, which can be regarded as AlPO4 and Li(OH x F 1-x ) combination, through appropriate processes, Li(OH x F 1-x ) After separation, the remaining AlPO4 can be used as a high-quality raw material for extracting Al and P, which can realize the high-value utilization of phosphate lithium aluminum stone. It can be seen that phosphate lithium aluminum stone is a lithium resource with high lithium content, low impurity content and strong comprehensive utilization. However, in addition to Li, it also contains other impurity elements such as Al and Si. These impurity elements restrict the use of phosphate lithium aluminum stone as a raw material for the preparation of high-purity lithium dihydrogen phosphate.
[0035] Based on this, the present invention provides a method for preparing lithium dihydrogen phosphate using phosphate lithium aluminum stone, such as Figure 1 Specifically, calcine the lithium aluminum phosphate and then crush it to obtain the lithium aluminum phosphate powder, then mix the lithium aluminum phosphate powder with acid solution, heat and calcine it, add water to leach it, and obtain an acid solution containing lithium dihydrogen phosphate, add an impurity remover to the above solution to remove impurity elements, concentrate it to obtain a concentrated solution, then add an organic reagent to the concentrated solution, and purify it to obtain lithium dihydrogen phosphate. Specifically:
[0036] The activated phosphate lithium aluminum stone is calcined to activate the phosphate lithium aluminum stone. Only the activated phosphate lithium aluminum stone can react with the acid solution. The unactivated phosphate lithium aluminum stone does not react after contacting with the acid solution. In principle, calcining and activating the phosphate lithium aluminum stone can change its crystal structure so that it can react with the acid solution. The uncalcined phosphate lithium aluminum stone has tight internal chemical bonds, and the lithium element is difficult to be dissolved by the acid solution. After calcination, the chemical bonds in the crystal structure break or become unstable, which increases the activity of the reaction with the acid solution. The activated phosphate lithium aluminum stone is crushed to make the particle size of the phosphate lithium aluminum stone powder 10-100μm. The crushing process can increase the reaction contact area between the phosphate lithium aluminum stone and the acid solution, thereby accelerating the mixed reaction of the phosphate lithium aluminum stone and the acid solution, and improving the dissolution rate and recovery rate of lithium.
[0037] After mixing the phosphate lithium aluminum stone powder with the acid solution, heating and calcining reaction are carried out, and the reaction process is as follows:
[0038] LiAl(FOH)PO4+H + →LiH2PO4+AlO2ˉ+P04 3- +AlF3↓;
[0039] After the lithium aluminum phosphate reacts with the acid solution, a mixture of lithium dihydrogen phosphate, phosphate, aluminate and aluminum fluoride is obtained as a reaction product. During the heating and calcining reaction process, the acid solution is mainly mixed with the lithium aluminum phosphate powder in the form of a concentrated solution. The present invention can accelerate the acidification reaction rate and avoid the increase in cost caused by adding too much acid by optimizing the ratio of the lithium aluminum phosphate powder to the acid. At the same time, by optimizing the mixed reaction conditions, the acidification reaction rate can be accelerated, the lithium element is fully dissolved, and the recovery rate of the lithium dihydrogen phosphate is improved. At the same time, the present invention ensures that the lithium element and the phosphorus element in the lithium aluminum phosphate are fully dissolved by controlling the heating temperature during the reaction process.
[0040] Since lithium dihydrogen phosphate, phosphates, and aluminates are easily soluble in water, while aluminum fluoride is an insoluble impurity, the insoluble impurity aluminum fluoride can be removed by leaching with water to obtain an acidic solution containing lithium dihydrogen phosphate. In addition to lithium dihydrogen phosphate, the acidic solution also contains impurities such as sulfate, iron, and aluminum.
[0041] In the subsequent purification and impurity removal process, impurity removers are added to remove iron and aluminum elements in the solution. Specifically, the impurity removers include ammonia water, sodium hydroxide, EDTA, oxalic acid, copper iron reagent, polyaluminium chloride, polyacrylamide, thiourea or activated carbon. Ammonia water and sodium hydroxide are mainly used to adjust the pH of the solution so that Fe 3+ and Al 3+ It precipitates in the form of a precipitate; EDTA and thiourea can react with Fe 3+ and Al 3+ Forming a complex to achieve the purpose of impurity removal; oxalic acid can react with Fe 3+ and Al 3+ Combine to form oxalate precipitate to achieve the purpose of impurity removal; copper iron reagent can be combined with Fe 3+ and Al 3+ A specific reaction occurs to generate a precipitate or complex to achieve the purpose of impurity removal; polyaluminium chloride can be hydrolysed to produce Al(OH)3 colloid, and the adsorption of the colloid can be used to remove Fe 3+ and Al 3+ ; Polyacrylamide as a flocculant can make Fe 3+ and Al 3+ Form flocculation precipitation to achieve the purpose of impurity removal; activated carbon has adsorption properties and can adsorb and remove Fe 3+ and Al 3+.
[0042] The solution after concentrating and removing impurities is obtained as a concentrated solution, and there are acid anion impurities remaining in the concentrated solution. For example, if the acid used is sulfuric acid, the concentrated solution contains sulfate, and an organic solvent is added. The organic solvent is methanol, ethanol, formic acid or acetic acid. The separation of sulfate can be achieved by mixing with organic solvents. Specifically, when an organic solvent is added and mixed with a solution containing sulfate and lithium dihydrogen phosphate, the dielectric constant of the solution will decrease. According to Coulomb's law, a decrease in the dielectric constant will increase the electrostatic attraction between the solute molecules. For ionic compounds such as lithium dihydrogen phosphate and sulfate, the attraction between their ions is enhanced, prompting them to aggregate with each other, so that lithium dihydrogen phosphate is precipitated. Then add the salting-out agent ammonium sulfate or sodium sulfate. Since the ions in the salting-out agent have a strong hydration effect, the hydration film on the surface of the organic solvent will be destroyed, causing the organic solvent to lose stability and aggregate, and the solution is divided into an aqueous phase and an organic phase. In this process, the solubility of lithium dihydrogen phosphate in organic solvents is relatively low, and it will preferentially precipitate and crystallize as a solid, while the sulfate ions combine with the added ammonium ions or sodium ions and remain in the solution in the form of sodium sulfate or ammonium sulfate, thereby achieving the separation of sulfate ions and lithium dihydrogen phosphate.
[0043] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.
[0044] The experimental materials used in the embodiments of the present invention are all conventional experimental materials in the art and can be purchased through commercial channels.
[0045] The main components of the phosphate lithium aluminum stone used in the present invention are shown in Table 1.
[0046] Table 1 Main components of phosphate lithium aluminum stone
[0047]
[0048]
[0049] Example 1: Method for preparing lithium dihydrogen phosphate using lithium aluminum phosphate
[0050] (1) calcining the pyrophosphate at 750° C. for 2 h and then pulverizing the pyrophosphate to obtain pyrophosphate powder with a particle size of 60 μm;
[0051] (2) mixing phosphate lithium aluminum stone powder with 98wt% sulfuric acid at a solid-liquid ratio of 1g:1.5mL, heating at 260°C for reaction for 2h, cooling to 50°C after the reaction, crushing to a particle size of 60μm, adding water to the crushed product, stirring and leaching at 60°C for 1h, the solid-liquid ratio of the crushed product to water being 1g:3mL, filtering, and collecting the filtrate, which is an acidic solution containing lithium dihydrogen phosphate;
[0052] (3) Adding EDTA to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements, wherein the material-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to EDTA is 100 mL: 1 g, and heating the solution after impurity removal to obtain a concentrated solution. + The concentration is 10 mol / L, ethanol and ammonium sulfate are added to the concentrated solution, and the mixture is stirred. The solid-liquid ratio of the concentrated solution, ethanol and ammonium sulfate is 1 mL:2 mL:3 g. The mixture is stirred for 1 hour, filtered, and the filtered solid is collected. The solid is washed with water twice, and pure water is added to the washed solid for recrystallization twice, wherein the solid-liquid ratio of the solid to pure water is 4:1. The mixture is dried at 140°C and -0.09 MPa for 2 hours to obtain lithium dihydrogen phosphate.
[0053] The purity of potassium dihydrogen phosphate prepared in this embodiment is 99.22%, and the recovery rate of lithium element is 92.21%.
[0054] Among them, the calculation formula for the recovery rate of lithium element is:
[0055] Recovery rate of lithium element (%) = (mass of lithium element in lithium dihydrogen phosphate / mass of lithium element in phosphate lithium aluminum stone) × 100%;
[0056] Among them, the mass of lithium element in lithium dihydrogen phosphate = the mass of lithium dihydrogen phosphate × the mass fraction of lithium element in lithium dihydrogen phosphate; the mass of lithium element in phosphate lithium aluminum stone = the mass of phosphate lithium aluminum stone × 7.89% × the mass fraction of lithium element in lithium oxide.
[0057] Embodiment 2:
[0058] (1) calcining the pyrophosphate at 750° C. for 2 h and then pulverizing the pyrophosphate to obtain pyrophosphate powder with a particle size of 50 μm;
[0059] (2) mixing phosphate lithium aluminum stone powder with sulfuric acid having a concentration of 98 wt % at a solid-liquid ratio of 1 g:1.5 mL, heating the mixture at 280° C. for reaction for 2 h, cooling the mixture to 50° C. after the reaction is completed, and crushing the mixture to a particle size of 60 μm. Adding water to the crushed mixture, stirring and leaching the mixture at 80° C. for 1 h, wherein the solid-liquid ratio of the crushed mixture to water is 1 g:3 mL, filtering the mixture, and collecting the filtrate, which is an acidic solution containing lithium dihydrogen phosphate;
[0060] (3) Adding EDTA to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements, wherein the material-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to EDTA is 100 mL: 1 g, and heating the solution after impurity removal to obtain a concentrated solution. + The concentration is 10 mol / L, ethanol and ammonium sulfate are added to the concentrated solution, and the mixture is stirred. The solid-liquid ratio of the concentrated solution, ethanol and ammonium sulfate is 1 mL:2 mL:3 g. The mixture is stirred for 1 hour, filtered, and the filtered solid is collected. Pure water is added to the solid for recrystallization 3 times. The solid-liquid ratio of the solid to pure water is 4:1. The mixture is dried at 120°C and -0.09 MPa for 2 hours to obtain lithium dihydrogen phosphate.
[0061] The purity of the lithium dihydrogen phosphate prepared in this embodiment is 99.24%, and the recovery rate of lithium element is 91.09%.
[0062] Embodiment 3:
[0063] (1) calcining the pyrophosphate at 750° C. for 2 h and then pulverizing the pyrophosphate to obtain pyrophosphate powder with a particle size of 60 μm;
[0064] (2) mixing phosphate lithium aluminum stone powder with 98wt% sulfuric acid at a solid-liquid ratio of 1g:1.5mL, heating at 280°C for reaction for 2h, cooling to 50°C after the reaction, crushing to a particle size of 60μm, adding water to the crushed product and stirring and leaching at 90°C for 1h, wherein the solid-liquid ratio of the crushed product to water is 1g:3mL, filtering, and collecting the filtrate, which is an acidic solution containing lithium dihydrogen phosphate;
[0065] (3) Adding EDTA to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements, wherein the material-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to EDTA is 100 mL: 1 g, and heating the solution after impurity removal to obtain a concentrated solution. + The concentration is 10 mol / L, ethanol and ammonium sulfate are added to the concentrated solution, and the mixture is stirred. The solid-liquid ratio of the concentrated solution, ethanol and ammonium sulfate is 1 mL:2 mL:3 g. The mixture is stirred for 1 hour, filtered, and the filtered solid is collected. Pure water is added to the solid for recrystallization 3 times. The solid-liquid ratio of the solid to pure water is 4:1. The mixture is dried at 150°C and -0.1 MPa for 2 hours to obtain lithium dihydrogen phosphate.
[0066] The purity of potassium dihydrogen phosphate prepared in this embodiment is 99.51%, and the recovery rate of lithium element is 93.11%.
[0067] Embodiment 4:
[0068] (1) calcining the pyrophosphate at 750° C. for 2 h and then pulverizing the pyrophosphate to obtain pyrophosphate powder with a particle size of 60 μm;
[0069] (2) mixing phosphate lithium aluminum stone powder with sulfuric acid having a concentration of 98 wt % at a solid-liquid ratio of 1 g:1 mL, heating the mixture at 280° C. for 2 h, cooling the mixture to 50° C. after the reaction is completed, and crushing the mixture to a particle size of 60 μm. Adding water to the crushed mixture and stirring the mixture at 90° C. for 1 h, wherein the solid-liquid ratio of the crushed mixture to water is 1 g:3 mL, filtering the mixture, and collecting the filtrate, which is an acidic solution containing lithium dihydrogen phosphate;
[0070] (3) Adding EDTA to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements, wherein the material-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to EDTA is 100 mL: 1 g, and heating the solution after impurity removal to obtain a concentrated solution. + The concentration is 10 mol / L, ethanol and ammonium sulfate are added to the concentrated solution, and the mixture is stirred. The solid-liquid ratio of the concentrated solution, ethanol and ammonium sulfate is 1 mL:2 mL:3 g. The mixture is stirred for 1 hour, filtered, and the filtered solid is collected. Pure water is added to the solid for recrystallization 3 times. The solid-liquid ratio of the solid to pure water is 4:1. The mixture is dried at 120°C and -0.09 MPa for 2 hours to obtain lithium dihydrogen phosphate.
[0071] The purity of potassium dihydrogen phosphate prepared in this embodiment is 99.46%, and the recovery rate of lithium element is 90.46%.
[0072] Embodiment 5:
[0073] (1) calcining the pyroxenite at 1000° C. for 3 h and then pulverizing the pyroxenite to obtain pyroxenite powder with a particle size of 10 μm;
[0074] (2) mixing phosphate lithium aluminum stone powder and sulfuric acid with a concentration of 98wt% in a mass ratio of 1g:5mL, heating the mixture at 300°C for 3h, cooling the mixture to 50°C after the reaction is completed, and crushing the mixture to a particle size of 10μm. Adding water to the crushed mixture and stirring the mixture at 100°C for 1h, wherein the material-liquid ratio of the crushed mixture to water is 1g:10mL, filtering the mixture, and collecting the filtrate, which is an acidic solution containing lithium dihydrogen phosphate;
[0075] (3) Adding EDTA to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements, wherein the solid-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to EDTA is 120 mL: 1 g, and heating the solution after impurity removal to obtain a concentrated solution. +The concentration is 15 mol / L, ethanol and ammonium sulfate are added to the concentrated solution and stirred, wherein the solid-liquid ratio of the concentrated solution, ethanol and ammonium sulfate is 1 mL:10 mL:4 g, stirred for reaction for 2 h, filtered, and the filtered solid was collected, pure water was added to the solid for recrystallization 3 times, wherein the mass ratio of the solid to pure water is 5:1, and dried at 180°C and -0.1 MPa for 5 h to obtain lithium dihydrogen phosphate.
[0076] The purity of the lithium dihydrogen phosphate prepared in this embodiment is 99.34%, and the recovery rate of lithium element is 92.50%.
[0077] Embodiment 6:
[0078] (1) calcining the pyroxenite at 700° C. for 1 h and then pulverizing the pyroxenite to obtain pyroxenite powder with a particle size of 100 μm;
[0079] (2) mixing phosphate lithium aluminum stone powder and sulfuric acid with a concentration of 98wt% in a mass ratio of 1g:1mL, heating the mixture at 200°C for reaction for 1h, cooling the mixture to 40°C after the reaction is completed, crushing the mixture to a particle size of 100μm, adding water to the crushed mixture, stirring and leaching the mixture at 20°C for 5h, wherein the material-liquid ratio of the crushed mixture to water is 1g:2mL, filtering the mixture, and collecting the filtrate, which is an acidic solution containing lithium dihydrogen phosphate;
[0080] (3) Adding EDTA to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements, wherein the solid-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to EDTA is 80 mL:1 g, and heating the solution after impurity removal to obtain a concentrated solution. + The concentration is 1 mol / L, ethanol and ammonium sulfate are added to the concentrated solution and stirred, wherein the solid-liquid ratio of the concentrated solution, ethanol and ammonium sulfate is 1 mL: 0.1 mL: 2 g, the reaction is stirred for 0.5 h, filtered, and the filtered solid is collected. Pure water is added to the solid for recrystallization 3 times, wherein the mass ratio of the solid to pure water is 2: 1, and dried at 100 ° C and -0.06 MPa for 1 h to obtain lithium dihydrogen phosphate.
[0081] The purity of the lithium dihydrogen phosphate prepared in this embodiment is 99.62%, and the recovery rate of lithium element is 91.42%.
[0082] Comparative Example 1:
[0083] The difference between this comparative example and Example 3 is that in step (1), the pyroxenite is not calcined. Specifically, the pyroxenite is directly crushed to obtain pyroxenite powder with a particle size of 60 μm.
[0084] In this comparative example, the yield of lithium dihydrogen phosphate is 0%. The main reason is that the crystal structure of lithium aluminum phosphate is relatively stable, and the lithium element inside it is wrapped in the crystal lattice, and the chemical bonds are tightly combined, making it difficult for the lithium element to directly react with the acid solution and dissolve. Therefore, the calcination and activation treatment of lithium aluminum phosphate can provide sufficient energy to break the chemical bonds in the lithium aluminum phosphate, thereby making it easier for the lithium element to react with the acid solution. The activation treatment of lithium aluminum phosphate was not performed on the lithium aluminum phosphate, and the crystal structure of the lithium aluminum phosphate was not destroyed, and there were very few active sites on the surface for sulfuric acid molecules to contact and react. It is difficult for sulfuric acid molecules to reach the location of the lithium element to react with it, resulting in the inability of the lithium element to dissolve.
[0085] Comparative Example 2:
[0086] The difference between this comparative example and Example 3 is that in step (1), the reaction temperature is 180° C. Specifically, after the phosphate lithium aluminum stone powder and sulfuric acid are mixed, they are heated at 180° C. for reaction.
[0087] In this comparative example, the yield of potassium dihydrogen phosphate is 0%. The main reason is that the crystal structure of phosphate lithium aluminum stone is relatively stable, and the chemical bond inside it is strong, which is difficult to destroy at a relatively low temperature. Therefore, it is necessary to reach a certain temperature condition to make the crystal structure of phosphate lithium aluminum stone change significantly, thereby exposing the active site so that it can react chemically with sulfuric acid. The temperature of controlling the calcined acid dissolution in this comparative example is 180 ° C. At this reaction temperature, the energy provided is not enough to break the chemical bond in the phosphate lithium aluminum stone crystal. At the same time, at this temperature, the crystal structure of phosphate lithium aluminum stone changes less, and the active site on the surface of phosphate lithium aluminum stone that can be contacted and reacted by sulfuric acid molecules is not fully exposed, making sulfuric acid difficult to react with the lithium element in phosphate lithium aluminum stone. Therefore, the main component of the solution after the reaction is sulfuric acid, which does not contain lithium ions, and thus, the yield of lithium dihydrogen phosphate is 0%.
[0088] Comparative Example 3:
[0089] The difference between this comparative example and Example 3 is that in step (1), the reaction temperature is 320° C. Specifically, after the phosphate lithium aluminum stone powder and sulfuric acid are mixed, they are heated at 320° C. for reaction.
[0090] In this comparative example, the yield of potassium dihydrogen phosphate is 0%. The main reason is that: due to the high reaction temperature of calcination acid solution, the reaction system of phosphate lithium aluminum stone powder and sulfuric acid is seriously damaged at a high temperature of 320°C. The volatilization and decomposition of sulfuric acid make the reaction raw materials insufficient, the interference of acidic smoke makes the reaction unable to proceed normally, and the damage of the muffle furnace makes the reaction unable to reach the expected temperature conditions and reaction time. The combined effect of various factors makes it impossible for the lithium, aluminum and other elements in phosphate lithium aluminum stone to be effectively converted into lithium dihydrogen phosphate, which ultimately leads to a yield of lithium dihydrogen phosphate of 0%.
[0091] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims
1. A method for preparing lithium dihydrogen phosphate using pyrophosphate, characterized in that: The following steps are involved: (1) mixing phosphate aluminum powder and acid solution and heating them to react, after the reaction is completed, cooling and crushing the reaction product, adding water to leach, filtering, and collecting the filtrate to obtain an acidic solution containing lithium dihydrogen phosphate; (2) The acidic solution containing lithium dihydrogen phosphate is treated to remove impurities and then concentrated to obtain a concentrated solution. An organic solvent and a salting-out agent are added to the concentrated solution, and the solution is stirred and filtered. The filtered solid is collected, and the solid is recrystallized and dried to obtain lithium dihydrogen phosphate.
2. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (1), the pyrophosphate powder is prepared by the following method: The phosphate lithium aluminum stone is calcined at 700-1000°C for 1-3 hours and then crushed to obtain the phosphate lithium aluminum stone powder with a particle size of 10-100 μm.
3. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (1), the acid solution is one of concentrated sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid or acetic acid, and the concentration of the acid solution is 50wt%-98wt%.
4. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (1), the material-liquid ratio of phosphate lithium aluminum stone powder to acid solution is 1g: (1-5)mL; the heating temperature is 200-300°C, and the reaction time is 1-3h.
5. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (1), during the water leaching process, the solid-liquid ratio of the crushed reaction product to water is 1 g: (2-10) mL, the leaching temperature is 20-100° C., and the leaching time is 1-5 h.
6. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (2), the specific operation of the impurity removal treatment is: adding an impurity remover to the acidic solution containing lithium dihydrogen phosphate to remove Fe and Al impurity elements.
7. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 6, characterized in that: The impurity remover is one or more of ammonia water, sodium hydroxide, EDTA, oxalic acid, copper iron reagent, polyaluminium chloride, polyacrylamide, thiourea or activated carbon; the material-liquid ratio of the acidic solution containing lithium dihydrogen phosphate to the impurity remover is (80-120) mL: 1 g.
8. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (2), Li in the concentrated solution + The concentration is 1-15mol / L.
9. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (2), the organic solvent is at least one of methanol, ethanol, formic acid or acetic acid; the salting-out agent is ammonium sulfate or sodium sulfate; and the solid-liquid ratio of the concentrate, the organic solvent and the salting-out agent is 1 mL: (0.1-10) mL: (2-4) g.
10. The method for preparing lithium dihydrogen phosphate using pyrophosphate as claimed in claim 1, characterized in that: In step (2), the stirring time is 0.5-2h; the drying temperature is 100-180°C, the drying pressure is -0.06MPa to -0.1MPa, and the drying time is 1-5h.