Method for preparing lithium nitrate based on strong-acid-free cyclic metathesis reaction

Abstract

The invention provides a method for preparing lithium nitrate based on a strong-acid-free cyclic metathesis reaction, which is characterized by comprising the following steps: mixing lithium carbonate and water, introducing carbon dioxide for carbonization, slowly adding a calcium nitrate solution for cyclic metathesis reaction, and sequentially heating, filtering, adsorbing to remove impurities and crystallizing after the reaction is finished, thereby obtaining the lithium nitrate. According to the method, a high-purity and high-yield lithium nitrate product can be obtained only by adopting lithium carbonate, calcium nitrate and carbon dioxide through a cyclic double decomposition reaction, strong acid and other chemical reagents do not need to be added in the whole reaction process, on the premise that no waste water or waste gas is generated, introduction of new impurities is effectively avoided, the impurity removal process is greatly simplified, and the production cost is reduced. The technical problems of high production cost, complicated impurity removal process and low yield in the prior art are fundamentally solved.

Description

Technical Field

[0001] The present invention relates to a preparation method of lithium nitrate, in particular to a method for preparing lithium nitrate based on a double decomposition reaction without strong acid circulation, belonging to the technical field of inorganic chemical industry. Background Art

[0002] Lithium nitrate is an important lithium salt product and has important applications in fields such as mobile phone glass panel manufacturing and battery manufacturing. In the existing technology, it is mainly obtained by reacting lithium carbonate with nitric acid. Chinese Patent (CN102807236A) discloses a method for preparing lithium nitrate, which includes the following steps: (1) adding nitric acid with a weight concentration of 40 - 98% to pure water, adding lithium carbonate or lithium hydroxide for a neutralization reaction, and then neutralizing with lithium hydroxide to a pH of 7 ± 0.5 to obtain a lithium nitrate solution, adding a precipitant, and filtering; (2) feeding the lithium nitrate solution obtained in step (1) into an evaporator and evaporating until the temperature of the solution is 150°C ± 10°C; (3) cooling the product obtained in step (2) to 50°C ± 10°C for crystallization; (4) separating the solid and liquid of the product in step (3), collecting the separated solid product, which is lithium nitrate hemihydrate, and performing vacuum drying to obtain an anhydrous lithium nitrate product. However, on the one hand, this method requires the use of dangerous chemical nitric acid, resulting in the need for the preparation process to be carried out in a Class A workshop, greatly increasing its fixed asset investment and production safety supervision costs. On the other hand, due to the introduction of nitric acid, some waste gas and waste water are generated during the preparation process, which also has potential impacts on the environment and personnel health.

[0003] To solve the above problems, Chinese Patent (CN102602967A) discloses a method for preparing lithium nitrate, which is characterized by including the following steps: (1) transferring a lithium sulfate solution into a beaker, adding LiOH to adjust the pH to 11 - 12, keeping warm for 30 - 40 min, and filtering; (2) placing the beaker in step (1) in a constant temperature water bath, adding a calcium nitrate solution, reacting, and keeping warm; (3) filtering the product obtained in step (2), and washing the filter cake with deionized hot water at 80 - 95°C to obtain mother liquor 1; (4) concentrating mother liquor 1, measuring the contents of SO 4 2- , Ca 2+ content, adding a impurity removal agent, stirring and reacting for 30 - 40 min, then filtering, and washing the filter cake with deionized hot water at 80 - 95°C to remove SO 4 2- , Ca 2+, mother liquor 2 is obtained; (5) The mother liquor 2 obtained in step (4) is concentrated to a saturated state in a secondary concentration, cooled, crystallized, and separated. The mother liquor 3 obtained after separation is returned to the secondary concentration, and the wet crystal obtained after separation is dried to obtain lithium nitrate. Although this preparation method does not require the introduction of nitric acid, on the one hand, the impurity content of commercially available lithium sulfate is relatively high, and it is difficult to remove impurities in the lithium nitrate solution subsequently, resulting in a relatively low purity of the obtained product. On the other hand, it is necessary to additionally remove the sulfur-containing impurities mixed in the product, which not only increases the overall production cost but also greatly limits its production capacity and is difficult to meet the requirements of process applications.

[0004] Therefore, there is an urgent need in the existing market for a safe, environmentally friendly, rapid, and efficient method for preparing lithium nitrate to meet the current industrial application requirements. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction. By only using lithium carbonate, calcium nitrate, and carbon dioxide, a high-purity and high-yield lithium nitrate product can be obtained through a cyclic double decomposition reaction. Throughout the reaction process, no strong acid or other chemical reagents need to be added. On the premise of realizing no waste water and waste gas, it effectively avoids the introduction of new impurities, greatly simplifies the impurity removal process, and fundamentally solves the technical problems of high production cost, cumbersome impurity removal process, and low output in the prior art.

[0006] To achieve the above technical purpose, the present invention provides a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction, including: slurrying lithium carbonate with water, introducing carbon dioxide for carbonization, and then slowly adding a calcium nitrate solution for a cyclic double decomposition reaction. After the reaction is completed, it is successively subjected to heating, filtration, adsorption impurity removal, and crystallization to obtain it;

[0007] The amount of carbon dioxide introduced is 0.5 - 2 mol / L of the slurry;

[0008] The calcium nitrate solution and lithium carbonate are in a molar ratio of calcium ions to lithium ions of 0.5 - 0.52:1.

[0009] Before the reaction between solid lithium carbonate and liquid calcium nitrate, introducing carbon dioxide into the lithium carbonate slurry is the most crucial innovation of the present invention. By adding carbon dioxide, lithium bicarbonate solution with high solubility is generated by reacting with lithium carbonate. In this way, when the calcium nitrate solution is added subsequently, the calcium ions therein first react with a large amount of bicarbonate ions in the slurry solution to form calcium carbonate solid precipitation, avoiding the formation of a calcium carbonate blocking film on the surface of solid lithium carbonate, which would wrap the solid lithium carbonate. Once the blocking film is formed, it will greatly reduce the conversion rate of lithium carbonate to lithium nitrate and ultimately increase the production cost.

[0010] As a preferred solution, the lithium carbonate is industrial-grade lithium carbonate and / or battery-grade lithium carbonate, and its purity ≥ 98%.

[0011] As a preferred solution, during the slurry preparation process, the mass ratio of lithium carbonate to water is 37 - 500:1000. During the slurry preparation process, the mass ratio of lithium carbonate to water must be strictly implemented according to the above requirements. If the addition amount of lithium carbonate is too low, it will cause excessive heat energy consumption during the evaporation and crystallization of the subsequent obtained lithium nitrate concentrated solution, increasing production costs; if the addition amount of lithium carbonate is too high, it will greatly increase the probability of forming a blocking film on the surface with calcium carbonate, hindering the dissolution of lithium carbonate, and then resulting in a decrease in the yield of lithium nitrate.

[0012] As a preferred solution, the temperature of the carbonization process ≤ 35°C.

[0013] As a preferred solution, the chemical reaction formula of the cyclic double decomposition reaction is:

[0014] Formula 1: H 2 CO 3 + Li 2 CO 3(s) = 2LiHCO 3(aq) ;

[0015] Formula 2: 2LiHCO 3(aq) + Ca(NO 3 ) 2(aq) = CaCO 3(s) + 2LiNO 3(aq) + H 2 CO 3 .

[0016] As a preferred solution, for the calcium nitrate solution in terms of the solute, the molar ratio of it to lithium carbonate is the stoichiometric ratio of the chemical reaction formula of the cyclic double decomposition reaction. During the reaction process involved in the present invention, under the action of carbon dioxide, there are two processes: the conversion of solid lithium carbonate into highly soluble lithium bicarbonate and the reaction of lithium bicarbonate with calcium nitrate to form precipitated calcium carbonate. Therefore, precisely controlling the concentrations of lithium bicarbonate and calcium nitrate in the solution during the reaction process can, on the one hand, ensure the smooth progress of the reaction and avoid the occurrence of reverse side reactions, and on the other hand, reduce the residual calcium ions in the lithium nitrate concentrated solution, ultimately improving the purity of the obtained lithium nitrate solid product.

[0017] As a preferred solution, the concentration of calcium nitrate in the calcium nitrate solution is 40 - 55 wt%, and its addition time is 1 - 10 hours. Further preferably, the addition method of calcium nitrate is: slowly dropwise add under stirring.

[0018] As a preferred solution, the temperature during the heating process is 70 - 100 °C, and the heating time continues until the precipitation dissolution equilibrium of the system is reached. The main function of heating is to convert the soluble calcium bicarbonate in the solution into calcium carbonate precipitate by evaporating carbon dioxide, thereby reducing the calcium content in the solution.

[0019] As a preferred solution, the filtration method is one of suction filtration, centrifugal filtration, and plate and frame pressure filtration, to obtain a crude lithium nitrate solution and wet calcium carbonate residue.

[0020] As a preferred solution, after the wet calcium carbonate residue is washed with water, pure calcium carbonate by - product and wash water are obtained, and the wash water is returned to the slurry - making process for recycling.

[0021] As a preferred solution, the process of adsorption and impurity removal is as follows: using ion - exchange resin to remove metal cation impurities in the crude lithium nitrate solution to obtain a refined lithium nitrate solution.

[0022] As a preferred solution, the ion - exchange resin is at least one of carboxylic acid resin, iminodiacetic acid resin, and aminophosphonic acid resin.

[0023] As a preferred solution, when the ion - exchange resin is carboxylic acid resin, its model is D113.

[0024] As a preferred solution, when the ion - exchange resin is iminodiacetic acid resin, its model is at least one of CR11, TP207, and D401.

[0025] As a preferred solution, when the ion - exchange resin is aminophosphonic acid resin, its model is D418 and / or LSC - 500.

[0026] Compared with the prior art, the beneficial technical effects of the technical solution provided by the present invention are as follows:

[0027] 1) In the method provided by the present invention, using lithium carbonate and calcium nitrate as raw materials, by introducing carbon dioxide, a recyclable double - decomposition reaction is triggered between them. On the one hand, part of the lithium carbonate is converted into lithium bicarbonate with high solubility, which can not only significantly increase the solid content of lithium carbonate in the slurry, greatly reduce the heat energy required for subsequent solution evaporation, but also effectively inhibit the blocking film formed on the surface during the reaction between calcium nitrate and solid lithium carbonate, promote the dissolution of lithium carbonate, and thus improve the yield and purity of lithium nitrate.

[0028] 2) In the technical solution provided by the present invention, only lithium carbonate, calcium nitrate and carbon dioxide are used, and high-purity and high-yield lithium nitrate products can be obtained through cyclic metathesis reactions. Throughout the reaction process, no strong acid or other chemical reagents need to be added. On the premise of achieving no waste water and waste gas, new impurities are effectively avoided, the impurity removal process is greatly simplified, and the technical problems of high production cost, cumbersome impurity removal process and low output in the prior art are fundamentally solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the lithium nitrate preparation method adopted in Examples 1 to 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described clearly and completely below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0031] The present invention can be implemented in other specific forms without departing from its basic attributes. It should be understood that, on the premise of no conflict, any and all embodiments of the present invention can be combined with the technical features in any other embodiment or multiple other embodiments to obtain additional embodiments. The present invention includes such additional embodiments obtained by such combinations.

[0032] All publications and patents mentioned in the present invention are hereby incorporated by reference in their entirety into the present invention. If there are conflicts between the uses or terms used in any incorporated publication and patent and the uses or terms used in the present invention, then the uses and terms of the present invention shall prevail.

[0033] The chapter titles used in the content of the present invention are only for the purpose of organizing the article and should not be construed as a limitation of the subject matter described.

[0034] The following provides embodiments to further illustrate the present invention. It should be understood that these embodiments are only used to illustrate the content of the present invention and are not used to limit the protection scope of the claims of the present invention. For those technical or conditions not specified in the embodiments, the techniques or conditions described in the literature in the art or according to the product specifications are followed. For reagents or instruments not specified by the manufacturer, all are conventional products that can be obtained through commercial purchase.

[0035] Example 1

[0036] This example provides a method for preparing lithium nitrate based on a strong acid-free cyclic metathesis reaction, and its process flow is asFigure 1 As shown in the figure, specifically:

[0037] 1) Add 37 g of industrial-grade lithium carbonate solid to 1000 g of water, stir to make a slurry, and introduce 0.5 mol of carbon dioxide gas into the slurry at room temperature to completely carbonate lithium carbonate into lithium bicarbonate, obtaining a lithium bicarbonate solution;

[0038] 2) Slowly drip 164 g of 50 wt% calcium nitrate solution into the lithium bicarbonate solution under stirring for a cyclic double decomposition reaction. After the reaction ends, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate residue;

[0039] 3) Wash the wet calcium carbonate residue with water to obtain a pure calcium carbonate by-product and washing water, and the washing water is returned to the slurry preparation process for recycling;

[0040] 4) Remove the high-valence metal impurities in the crude lithium nitrate solution through D401 resin to obtain a refined lithium nitrate solution, then heat and evaporate part of the water, and successively carry out cooling crystallization, separation and drying to obtain anhydrous lithium nitrate.

[0041] In this example, the obtained pure calcium carbonate by-product and anhydrous lithium nitrate were subjected to component analysis. Among them, the lithium content in the pure calcium carbonate by-product was only 0.001%, indicating that the loss of lithium was very low; the purity of anhydrous lithium nitrate ≥ 99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.001%.

[0042] Example 2

[0043] This example provides a method for preparing lithium nitrate based on a cyclic double decomposition reaction without strong acid, and its process flow is as Figure 1 shown, specifically:

[0044] 1) Add 500 g of industrial-grade lithium carbonate solid to 1000 g of water, stir to make a slurry, and introduce 1 mol of carbon dioxide gas into the slurry at room temperature to partially carbonate lithium carbonate into lithium bicarbonate, obtaining a mixed slurry;

[0045] 2) Slowly drip 1378 g of 50 wt% calcium nitrate solution into the mixed slurry under stirring for a cyclic double decomposition reaction. After the reaction ends, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate residue;

[0046] 3) Wash the wet calcium carbonate residue with water to obtain a pure calcium carbonate by-product and washing water, and the washing water is returned to the slurry preparation process for recycling;

[0047] 4) The crude lithium nitrate solution is passed through D401 resin to remove the high-valent metal impurities in the solution, obtaining a refined lithium nitrate solution. Then, part of the water is evaporated by heating, followed by cooling crystallization, separation, and drying in sequence to obtain anhydrous lithium nitrate.

[0048] In this example, the obtained pure calcium carbonate by-product and anhydrous lithium nitrate were subjected to component analysis. Among them, the lithium content in the pure calcium carbonate by-product was only 0.01%, indicating that the loss of lithium was very low, only 0.075%; the purity of anhydrous lithium nitrate was ≥99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.002%.

[0049] Example 3

[0050] This example provides a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction, and its process flow is as Figure 1 shown, specifically as follows:

[0051] 1) Add 500 g of industrial-grade lithium carbonate solid to 1000 g of water, stir to make a slurry, and introduce 2 mol of carbon dioxide gas into the slurry at 35 °C to partially carbonize lithium carbonate into lithium bicarbonate to obtain a mixed slurry;

[0052] 2) Slowly drip 1378 g of 50 wt% calcium nitrate solution into the mixed slurry under stirring for a cyclic double decomposition reaction. After the reaction ends, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate residue;

[0053] 3) After washing the wet calcium carbonate residue with water, obtain a pure calcium carbonate by-product and washing water, and the washing water is returned to the slurry-making process for recycling;

[0054] 4) The crude lithium nitrate solution is passed through D401 resin to remove the high-valent metal impurities in the solution, obtaining a refined lithium nitrate solution. Then, part of the water is evaporated by heating, followed by cooling crystallization, separation, and drying in sequence to obtain anhydrous lithium nitrate.

[0055] In this example, the obtained pure calcium carbonate by-product and anhydrous lithium nitrate were subjected to component analysis. Among them, the lithium content in the pure calcium carbonate by-product was only 0.1%, indicating that when the temperature was raised from room temperature to 35 °C during carbonization, the loss of lithium in calcium carbonate increased slightly, only 0.75%; the purity of anhydrous lithium nitrate was ≥99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.002%.

[0056] Example 4

[0057] This example provides a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction, and its process flow is as Figure 1 shown, specifically as follows:

[0058] 1) Add 500 g of industrial-grade lithium carbonate solid to 1000 g of water, stir to make a slurry, and introduce 1 mol of carbon dioxide gas into the slurry at 35 °C to partially carbonize lithium carbonate into lithium bicarbonate to obtain a mixed slurry;

[0059] 2) Slowly drop 1378 g of 50 wt% calcium nitrate solution into the mixed slurry under stirring for cyclic double decomposition reaction. After the reaction ends, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate residue;

[0060] 3) After washing the wet calcium carbonate residue with water, obtain pure calcium carbonate by-product and washing water, and the washing water is returned to the slurry preparation process for recycling;

[0061] 4) Remove the high-valent metal impurities in the crude lithium nitrate solution through D418 resin to obtain a refined lithium nitrate solution, then heat and evaporate part of the water, and successively carry out cooling crystallization, separation and drying to obtain anhydrous lithium nitrate.

[0062] This example analyzed the components of the obtained pure calcium carbonate by-product and anhydrous lithium nitrate. Among them, the lithium content in the pure calcium carbonate by-product was 0.1%, indicating that the loss of lithium was very low; the purity of anhydrous lithium nitrate ≥ 99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.002%.

[0063] Comparative Example 1

[0064] This comparative example provides a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction, specifically as follows:

[0065] 1) Add 3.7 g of industrial-grade lithium carbonate solid to 1000 g of water, stir to make a slurry, and introduce carbon dioxide gas into the slurry at room temperature to completely carbonize lithium carbonate into lithium bicarbonate to obtain a lithium bicarbonate solution;

[0066] 2) Slowly drop 16.4 g of 50 wt% calcium nitrate solution into the lithium bicarbonate solution under stirring for cyclic double decomposition reaction. After the reaction ends, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate residue;

[0067] 3) After washing the wet calcium carbonate residue with water, a pure calcium carbonate by-product and wash water are obtained, and the wash water is returned to the pulp mixing process for recycling.

[0068] 4) The crude lithium nitrate solution is passed through D401 resin to remove the high-valent metal impurities in the solution, obtaining a refined lithium nitrate solution. Then, part of the water is evaporated by heating, followed by cooling crystallization, separation, and drying in sequence to obtain anhydrous lithium nitrate.

[0069] In this comparative example, the obtained pure calcium carbonate by-product and anhydrous lithium nitrate were subjected to component analysis. Among them, the lithium content in the pure calcium carbonate by-product was only 0.001%, indicating that the loss of lithium was very low; the purity of anhydrous lithium nitrate was ≥99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.001%.

[0070] Although too little addition of lithium carbonate during the pulp mixing process does not have much impact on the quality of the obtained anhydrous lithium nitrate, the amount of lithium nitrate product obtained by evaporating the same amount of water is only 10% of that in Example 1, and the energy consumption per unit product increases significantly, significantly increasing the production cost, which is not suitable for industrial application.

[0071] Comparative Example 2

[0072] This comparative example provides a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction, specifically as follows:

[0073] 1) Add 500 g of industrial-grade lithium carbonate solid to 1000 g of water, stir to form a pulp, and introduce 1 mol of carbon dioxide gas into the pulp at 60 °C to partially carbonize lithium carbonate into lithium bicarbonate to obtain a mixed pulp.

[0074] 2) Slowly drip 1378 g of 50 wt% calcium nitrate solution into the mixed pulp under stirring for a cyclic double decomposition reaction. After the reaction ends, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and a wet calcium carbonate residue.

[0075] 3) After washing the wet calcium carbonate residue with water, a calcium carbonate by-product and wash water are obtained, and the wash water is returned to the pulp mixing process for recycling.

[0076] 4) The crude lithium nitrate solution is passed through D401 resin to remove the high-valent metal impurities in the solution, obtaining a refined lithium nitrate solution. Then, part of the water is evaporated by heating, followed by cooling crystallization, separation, and drying in sequence to obtain anhydrous lithium nitrate.

[0077] In this comparative example, component analysis was carried out on the obtained pure calcium carbonate by-product and anhydrous lithium nitrate. Among them, the lithium content in the calcium carbonate by-product was 0.51%, and the loss of lithium increased significantly; the purity of anhydrous lithium nitrate was ≥99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.002%.

[0078] Comparing this comparative example with Example 3, it can be seen that since the temperature of the system was 60 °C when carbon dioxide was introduced, a blocking film was formed on the surface of lithium carbonate when calcium nitrate was added, hindering the dissolution of lithium carbonate. As a result, a large amount of lithium was mixed in the calcium carbonate residue, and the loss rate of lithium was as high as more than 3.8%.

[0079] Comparative Example 3

[0080] This comparative example provides a method for preparing lithium nitrate based on a non-strong acid cyclic double decomposition reaction, specifically as follows:

[0081] 1) Add 500 g of industrial-grade lithium carbonate solid to 1000 g of water, stir and adjust to a slurry to obtain a mixed slurry;

[0082] 2) Slowly drop 1378 g of a 50 wt% calcium nitrate solution into the mixed slurry under stirring for a cyclic double decomposition reaction. After the reaction is completed, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate residue;

[0083] 3) After washing the wet calcium carbonate residue with water, obtain a calcium carbonate by-product and wash water, and the wash water is returned to the slurry adjustment process for recycling;

[0084] 4) Remove the high-valent metal impurities in the solution from the crude lithium nitrate solution through D401 resin to obtain a refined lithium nitrate solution, then heat and evaporate part of the water, and successively carry out cooling crystallization, separation and drying to obtain anhydrous lithium nitrate.

[0085] In this comparative example, component analysis was carried out on the obtained pure calcium carbonate by-product and anhydrous lithium nitrate. Among them, the lithium content in the calcium carbonate by-product was 5.4%, and the loss of lithium increased significantly to 40%; the purity of anhydrous lithium nitrate was ≥99.9 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.001%, Ca 0.002%.

[0086] It can be seen from the comparison between this comparative example and Example 3 that since carbon dioxide was not introduced before adding calcium nitrate, a calcium carbonate blocking film was formed on the surface of solid lithium carbonate when calcium nitrate was added, which hindered the further dissolution of lithium carbonate. As a result, a large amount of lithium was mixed in the calcium carbonate slag, and the loss rate of lithium was as high as 40%.

[0087] Comparative Example 4

[0088] This comparative example provides a method for preparing lithium nitrate based on the double decomposition reaction without strong acid circulation, specifically as follows:

[0089] 1) Add 500 g of industrial-grade solid lithium carbonate to 1000 g of water, stir to make a slurry, and introduce 2 mol of carbon dioxide gas into the slurry at room temperature to partially carbonize lithium carbonate into lithium bicarbonate to obtain a mixed slurry;

[0090] 2) Slowly drop 1378 g of 50 wt% calcium nitrate solution into the mixed slurry under stirring for the double decomposition reaction in a cycle. After the reaction is completed, raise the temperature to 90 °C, keep warm for 30 min to reduce the calcium content in the solution, and then filter to obtain a crude lithium nitrate solution and wet calcium carbonate slag;

[0091] 3) After washing the wet calcium carbonate slag with water, obtain a pure calcium carbonate by-product and washing water, and the washing water is returned to the slurry preparation process for recycling;

[0092] This comparative example analyzed the components of the obtained pure calcium carbonate by-product and anhydrous lithium nitrate. Among them, the lithium content in the pure calcium carbonate by-product was only 0.01%, indicating that the loss of lithium was very low; the purity of anhydrous lithium nitrate ≥ 98 wt%, and its main impurity components were: SO 4 0.001%, Cl 0.001%, PO4 0.0001%, Na 0.001%, Mg 0.02%, Ca 0.2%.

[0093] It can be seen from this comparative example that after not passing through the resin impurity removal process, the content of high-valent metal impurities in the obtained lithium nitrate product increased significantly, and it was difficult to guarantee the purity. In addition, since the lithium content in the pure calcium carbonate by-product in this comparative example was still at a low level, this also proved that in the technical solution provided by the embodiments of the present invention, high-valent metal cations would not directly affect the progress of the double decomposition reaction in a cycle, indicating that this reaction has excellent stability and anti-interference ability.

Claims

1. A method for preparing lithium nitrate based on a strong acid-free cyclic metathesis reaction, characterized in that: include: Lithium carbonate and water are mixed into a slurry, and then carbon dioxide is introduced for carbonization, and then calcium nitrate solution is slowly added for cyclic double decomposition reaction. After the reaction is completed, heating, filtering, adsorption and impurity removal, and crystallization are performed in sequence to obtain; The amount of carbon dioxide introduced is 0.5-2 mol / L slurry; The molar ratio of calcium ion to lithium ion in the calcium nitrate solution and lithium carbonate is 0.5-0.52:

1.

2. A method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 1, characterized in that: The lithium carbonate is industrial grade lithium carbonate and / or battery grade lithium carbonate, and its purity is ≥98%.

3. A method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 1, characterized in that: In the slurry preparation process, the mass ratio of lithium carbonate to water is 37-500:1000; and the temperature of the carbonization process is ≤35°C.

4. The method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 1, characterized in that: The chemical reaction formula of the cyclic metathesis reaction is: Formula 1: H2CO3 + Li2CO 3(s) = 2LiHCO 3(aq) ; Formula 2: 2LiHCO 3(aq) + Ca(NO3)2 = CaCO 3(s) + 2LiNO 3(aq) + H2CO3。 5. A method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 4, characterized in that: The molar ratio of the calcium nitrate solution to the lithium carbonate is the ratio of the stoichiometric numbers of the chemical reaction formula of the cyclic double decomposition reaction.

6. The method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 1, characterized in that: The concentration of calcium nitrate in the calcium nitrate solution is 40-55wt%, and the addition time is 1-10 hours.

7. The method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 1, characterized in that: The temperature of the heating process is 70-100° C., and the heating time is continued until the precipitation and dissolution equilibrium of the system is reached; the filtering method is one of suction filtration, centrifugal filtration and plate and frame filter press to obtain a crude lithium nitrate solution and a calcium carbonate wet residue.

8. A method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 7, characterized in that: The calcium carbonate wet slag is washed with water to obtain pure calcium carbonate by-product and washing water, and the washing water is returned to the slurry preparation process for recycling.

9. The method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 1, characterized in that: The process of adsorption and impurity removal is: using ion exchange resin to remove metal cation impurities in the lithium nitrate crude solution to obtain a lithium nitrate refined solution.

10. A method for preparing lithium nitrate based on strong acid-free cyclic metathesis reaction according to claim 9, characterized in that: The ion exchange resin is at least one of a carboxylic acid resin, an iminodiacetic acid resin and an aminophosphonic acid resin.

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