Method for co-producing lithium sulfate and lithium carbonate from lithium concentrate

Abstract

The invention discloses a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, and belongs to the technical field of lithium salt production. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate comprises the following steps: performing transformation roasting, acidizing roasting, size mixing, neutralizing and refining on spodumene concentrate to obtain a lithium sulfate purified solution; evaporating and crystallizing one part of the lithium sulfate purified liquid to obtain wet lithium sulfate and lithium sulfate crystallization mother liquor, and drying the wet lithium sulfate to obtain lithium sulfate; freezing the lithium sulfate crystallization mother liquor to obtain mirabilite and frozen mother liquor; re-dissolving the mirabilite, evaporating and crystallizing to obtain anhydrous sodium sulphate and a sodium thermal precipitation mother solution, and returning the sodium thermal precipitation mother solution to be mixed with the lithium sulfate crystallization mother solution; and carrying out evaporation concentration, lithium precipitation, cleaning and drying on the other part of the lithium sulfate purified liquid to obtain lithium carbonate. According to the method, the procedures of lithium sulfate products and lithium carbonate products can be linked together through the procedures of sodium sulfate evaporative crystallization, freezing, mirabilite redissolution and the like, and co-production of lithium sulfate and lithium carbonate is realized.

Description

A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate Technical Field

[0001] This invention relates to the field of lithium salt production technology, specifically to a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate. Background Technology

[0002] Lithium sulfate is a colorless monoclinic crystal. One part of lithium sulfate monohydrate dissolves in 2.6 parts of water, forming a neutral solution. It is almost insoluble in 80% ethanol, acetone, or pyridine, and loses its water of crystallization when heated to 130°C. It is mainly used as an analytical reagent, in the separation of calcium and magnesium, and in the pharmaceutical industry. It is also used in the manufacture of fireworks. At high temperatures, lithium sulfate can be used to prepare high-conductivity solid electrodes and as an ion conductor in high-temperature hydrogen-oxygen batteries. It is also widely used as a high-temperature heat storage material and as a commonly used reference material for calibrating thermal analysis instruments. These facts demonstrate the wide range of applications and high demand for lithium sulfate. Meanwhile, influenced by market factors, the prices of lithium carbonate and lithium hydroxide are gradually decreasing; while lithium sulfate has a promising application prospect and considerable profits. Therefore, the search for technologies for large-scale production of lithium sulfate has attracted much attention.

[0003] Lithium sulfate is an intermediate material in the production of basic lithium salts (lithium carbonate, lithium hydroxide, and lithium chloride). Current lithium battery (lithium iron phosphate and ternary lithium batteries) production processes generally use lithium carbonate or lithium hydroxide as raw materials. Lithium chloride is mainly used to produce metallic lithium. Therefore, there is currently virtually no industrial demand or driving force for large-scale production of lithium sulfate.

[0004] Currently, the production processes for lithium sulfate and lithium sulfate monohydrate are similar, both using spodumene concentrate as raw material and employing the sulfuric acid process: spodumene concentrate → transformation roasting → acid roasting → slurry preparation → leaching, neutralization, and filtration → refining to remove calcium and magnesium → lithium sulfate evaporation and crystallization. Transformation roasting: Within the temperature range of 1100-1250℃, spodumene transforms from α-type to β-type. α-type is insoluble, while β-type is soluble. Through transformation roasting, spodumene can dissolve in the aqueous phase during subsequent processing. Acid roasting: β-type spodumene concentrate is mixed with concentrated sulfuric acid, converting lithium in the β-type spodumene into solid lithium sulfate. Slurry preparation: The acid-roasted clinker is leached with water, dissolving the solid lithium sulfate into the solution. Leaching, neutralization, and filtration: The acid-roasted clinker slurry after slurry preparation is generally acidic. Calcium carbonate is added to neutralize excess sulfuric acid. After neutralization, the slurry is filtered through a filter press to obtain leaching residue and leachate. The main components of the leachate are lithium sulfate, sodium sulfate, calcium sulfate, and magnesium sulfate. Refining to remove calcium and magnesium: Impurities in the leachate, such as calcium and magnesium, are removed by adding impurity removal reagents such as sodium carbonate and sodium hydroxide. Calcium and magnesium precipitates as calcium carbonate and magnesium hydroxide, which are then removed by filtration. For further removal of calcium and magnesium impurities, ion exchange resin can be used for adsorption, resulting in a purified lithium sulfate solution. Lithium sulfate evaporation and crystallization: Lithium sulfate is evaporated and concentrated to a Li₂O concentration of approximately 55 g / L, yielding a concentrated lithium sulfate solution. Lithium precipitation: Sodium carbonate is added to the concentrated lithium sulfate solution to obtain wet lithium carbonate precipitate and a lithium precipitation mother liquor. Lithium precipitation mother liquor treatment: The lithium precipitation mother liquor is neutralized with concentrated sulfuric acid to obtain a neutralized solution. The neutralized solution is evaporated and crystallized to produce sodium sulfate and sodium precipitation mother liquor. Secondary lithium precipitation: Sodium carbonate is added to the sodium precipitation mother liquor to precipitate lithium again, yielding wet lithium carbonate and a lithium precipitation mother liquor. The lithium precipitation mother liquor is returned to the neutralization process. The above process route is the conventional route for producing lithium carbonate from spodumene, but the only product produced is lithium carbonate, and the lithium carbonate obtained by secondary lithium precipitation is of industrial grade, accounting for about 10-20% of the total lithium carbonate product.

[0005] Patent CN113735142A discloses a method for preparing lithium sulfate monohydrate using spodumene. Specifically, the main process of preparing lithium sulfate monohydrate is the spodumene sulfuric acid process. The process route is: spodumene concentrate → transformation roasting → acidification roasting → slurry preparation → leaching neutralization filtration → refining to remove calcium and magnesium → lithium sulfate evaporation and crystallization → hot filtration → washing and drying → lithium sulfate. Compared with the existing sulfuric acid process using spodumene concentrate as raw material, it is basically the same, except that a washing and drying step is added. The washing and drying step is: lithium sulfate wet material → rinsing to remove soluble impurities in lithium sulfate. The amount of rinsing water is 1 to 1.5 times the amount of pure water in the lithium sulfate wet material. The washing is done once or in multiple stages. However, this patent can only produce one type of lithium sulfate, and the wet lithium sulfate material is rinsed with 1-1.5 times the amount of pure water. Because lithium sulfate is easily soluble in water and has a solubility of about 330g / L, a large amount of lithium sulfate dissolves into the solution during the pure water rinsing process, which greatly reduces the direct recovery rate of lithium sulfate. In addition, the consumption of pure water is high due to the increased pure water rinsing.

[0006] In summary, there is an urgent need to provide a process for producing lithium sulfate by incorporating an existing lithium concentrate-to-lithium carbonate production process, and to improve the quality of lithium carbonate. Summary of the Invention

[0007] The purpose of this invention is to provide a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, thereby filling the gap in the prior art where lithium concentrate cannot be co-produced with lithium sulfate and lithium carbonate.

[0008] To achieve the above objectives, one embodiment of the present invention provides a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, comprising the following steps: spodumene concentrate is subjected to transformation roasting, acid roasting, slurry preparation, neutralization, and refining to obtain a purified lithium sulfate solution; a portion of the purified lithium sulfate solution is evaporated and crystallized to obtain wet lithium sulfate and lithium sulfate crystallization mother liquor, the wet lithium sulfate is dried to obtain lithium sulfate; the lithium sulfate crystallization mother liquor is frozen to obtain sodium sulfate and a frozen mother liquor; the sodium sulfate is redissolved and evaporated and crystallized to obtain sodium sulfate and a hot-precipitated sodium mother liquor, the hot-precipitated sodium mother liquor is returned to be mixed with the lithium sulfate crystallization mother liquor; another portion of the purified lithium sulfate solution is evaporated and concentrated, lithium is precipitated, washed, and dried to obtain lithium carbonate.

[0009] In one preferred embodiment of the present invention, the mother liquor of pyrolysis sodium and the mother liquor of lithium sulfate crystallization are mixed and then frozen together to obtain sodium sulfate. The sodium sulfate is then dissolved, evaporated and crystallized to obtain sodium sulfate.

[0010] In one preferred embodiment of the present invention, the frozen mother liquor is returned to the slurry preparation and lithium sulfate purification liquid evaporation and crystallization steps.

[0011] In one preferred embodiment of the present invention, during the evaporation and crystallization process of lithium sulfate purification solution, the concentration of sodium sulfate in the mother liquor is 10 g / L-250 g / L, and the temperature is 80℃-100℃.

[0012] In one preferred embodiment of the present invention, the freezing is a two-stage freezing process, wherein the temperature of the first stage of freezing is 10℃-50℃ and the temperature of the second stage of freezing is 0℃-10℃.

[0013] In one preferred embodiment of the present invention, the sodium sulfate concentration is controlled to be 200g / L-400g / L during the redissolution of Glauber's salt.

[0014] In one preferred embodiment of the present invention, steam is introduced during the redissolution of Glauber's salt, and the temperature is controlled between 10°C and 90°C.

[0015] In one preferred embodiment of the present invention, another portion of the purified lithium sulfate solution is evaporated and concentrated, lithium precipitation is performed, washed, and dried to obtain lithium carbonate, comprising: evaporating and concentrating the other portion of the purified lithium sulfate solution to obtain a completed lithium sulfate solution; precipitating the completed lithium sulfate solution to obtain wet lithium carbonate and a lithium precipitation mother liquor; and washing and drying the wet lithium carbonate to obtain lithium carbonate.

[0016] In one preferred embodiment of the present invention, the lithium oxide concentration in the lithium sulfate solution is 50 g / L-55 g / L.

[0017] In one preferred embodiment of the present invention, after neutralization and evaporation and crystallization of sodium sulfate mother liquor, sodium sulfate and hot-precipitated sodium mother liquor are obtained.

[0018] In one preferred embodiment of the present invention, the lithium oxide concentration in the pyrolysis sodium mother liquor is 15 g / L-30 g / L.

[0019] In summary, the beneficial effects of the present invention are as follows: 1. The method of the present invention for the co-production of lithium sulfate and lithium carbonate from lithium concentrate enables the processes of lithium sulfate product and lithium carbonate product to be connected through the processes of sodium sulfate evaporation and crystallization, freezing, and sodium sulfate redissolution, thereby realizing the co-production of lithium sulfate and lithium carbonate.

[0020] 2. This invention achieves complete separation of lithium sulfate and sodium sulfate. Sodium sulfate is frozen and enters Glauber's salt. After Glauber's salt is dissolved, it is evaporated and crystallized to obtain sodium sulfate. All sodium sulfate in the lithium sulfate purification solution is ultimately produced in the form of sodium sulfate.

[0021] 3. The lithium sulfate product produced by this invention has high purity, which can meet the lithium sulfate standard (YS / T1241-2018), and the Li2SO4•H2O purity can reach more than 97%.

[0022] 4. This invention combines the process with the lithium sulfate production process. The mother liquor from the hot sodium precipitation and the mother liquor from the lithium sulfate evaporation and crystallization process are combined and then frozen to obtain sodium sulfate. The sodium sulfate is then dissolved and returned to the sodium sulfate evaporation and crystallization process. The lithium in the hot sodium precipitation mother liquor from the above process enters the frozen mother liquor, which is then returned to the lithium sulfate evaporation and crystallization process and slurry preparation. This process eliminates the need for secondary lithium precipitation, allowing lithium sulfate to enter the lithium sulfate evaporation and crystallization system and the slurry preparation system, ultimately yielding lithium sulfate and lithium carbonate products. Because the above process eliminates the secondary lithium precipitation step, the resulting lithium sulfate and lithium carbonate products have high purity.

[0023] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention will be apparent from the effects described in the description and the accompanying drawings. Attached Figure Description

[0024] Figure 1 is a schematic diagram of the method for co-producing lithium sulfate and lithium carbonate from lithium concentrate in an embodiment of the present invention; Figure 2 is a process flow diagram for co-producing lithium sulfate and lithium carbonate from lithium concentrate in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0027] This invention provides a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, as shown in Figure 1, including the following steps: Step (1): Spodumene concentrate is subjected to transformation roasting, acid roasting, slurry preparation, neutralization, and refining to obtain lithium sulfate purified solution; wherein, the concept of lithium sulfate purified solution is a solution whose main component is lithium sulfate, containing a small amount of sodium sulfate and impurities such as calcium and magnesium; specifically, it includes the following steps: Step (101): Transformation roasting: roasting for 2-4 hours in the range of 1100℃-1250℃, spodumene is transformed from α-type to β-type, α-type is an insoluble substance, and β-type is a soluble substance; through transformation roasting, spodumene can enter the aqueous phase and dissolve into the solution in the subsequent process; Step (102): Acid roasting: after the transformation roasting in the above step (101) is completed, acid roasting is carried out, β-type spodumene concentrate is mixed with concentrated sulfuric acid, and the lithium in β-type spodumene is converted into solid lithium sulfate, wherein the acid roasting temperature is 220℃. -280℃, time is 2h-4h, concentrated sulfuric acid added is 20%-30% of the mass ratio of concentrated sulfuric acid / spodumene concentrate; Step (103): Slurry preparation: the clinker after acid roasting in step (102) is leached with water, and the lithium sulfate solid dissolves into the solution. During the slurry preparation process, the liquid-solid ratio is controlled at 1.8-2.4:1; Step (104): Leaching neutralization: the acid clinker slurry after slurry preparation in step (103) is generally an acidic slurry. Calcium carbonate is added to neutralize it. Excess sulfuric acid is used to control the pH to 6.5-7. After neutralization, the solution is filtered through a filter press to obtain leaching residue and leachate. The main components of the leachate are lithium sulfate, sodium sulfate, calcium sulfate, and magnesium sulfate. Step (105): Refining to remove calcium and magnesium: Impurities in the leachate in the above step (104), such as calcium and magnesium, are removed by adding impurity removal reagents such as sodium carbonate and sodium hydroxide to the leachate. The calcium and magnesium are precipitated as calcium carbonate and magnesium hydroxide, and then the precipitate is removed by filtration.To further remove calcium and magnesium impurities, calcium and magnesium can be further removed by adsorption with ion exchange resin to obtain lithium sulfate purified solution; wherein, the refining temperature is 90℃-95℃ and the pH is controlled at 11-11.5; Step (2): A portion of the lithium sulfate purified solution is evaporated and crystallized to obtain wet lithium sulfate and lithium sulfate crystallization mother liquor, and the wet lithium sulfate is dried to obtain lithium sulfate; Specifically, a portion of the lithium sulfate purified solution obtained in step (1) is evaporated and crystallized to obtain wet lithium sulfate and lithium sulfate crystallization mother liquor. In this process, the sodium sulfate concentration in the mother liquor is controlled at 10g / L-250g / L and the temperature is 80℃-100℃ during the lithium sulfate evaporation and crystallization process; the obtained wet lithium sulfate is dried to obtain lithium sulfate, and the lithium sulfate crystallization mother liquor enters the following steps ( 3); Step (3): The lithium sulfate crystallization mother liquor is frozen to obtain sodium sulfate and frozen mother liquor; Specifically, the lithium sulfate crystallization mother liquor in step (2) is frozen to obtain sodium sulfate and frozen mother liquor. The freezing here is a two-stage freezing. The temperature of the first stage freezing is 10℃-50℃, and the temperature of the second stage freezing is 0℃-10℃. The obtained frozen mother liquor is returned to the slurry preparation step (103) and the lithium sulfate purification liquid evaporation and crystallization step (2). The proportion of frozen mother liquor returned to the lithium sulfate purification liquid evaporation and crystallization step is about 0%-100%, and the proportion of frozen mother liquor returned to the slurry preparation step is about 0%-100%. The freezing process of the present invention refers to the process device that reduces the temperature of the lithium sulfate evaporation and crystallization mother liquor (above 50℃) to 0-50℃.The freezing methods and equipment include flash cooling, circulating water cooling, and refrigeration unit cooling, all of which are freezing and cooling methods mentioned in this invention patent and are within the protection scope of this invention patent; Step (4): Glauber's salt is redissolved and evaporated to crystallize, resulting in sodium sulfate and hot-precipitated sodium mother liquor. The hot-precipitated sodium mother liquor is returned to be mixed with lithium sulfate crystallization mother liquor; Specifically, the following steps are included: Step (401): Glauber's salt is redissolved to obtain a heavy solution; Specifically, water is added to dissolve Glauber's salt, and the sodium sulfate concentration in the solution is controlled to be approximately 2. 00g / l-400g / l, and steam is introduced during the redissolution process, and the temperature is controlled at 10℃-90℃ to obtain a heavy solution; Step (402): The heavy solution obtained in step (401) is evaporated and crystallized by sodium sulfate to obtain sodium sulfate and hot sodium precipitation mother liquor; wherein, the hot sodium precipitation mother liquor is returned and mixed with the lithium sulfate crystallization mother liquor, and then frozen together to obtain sodium sulfate, and the sodium sulfate is dissolved, evaporated and crystallized to obtain sodium sulfate, and the lithium oxide concentration in the hot sodium precipitation mother liquor is 15g / L-30g / L; Step (5): Another A portion of the lithium sulfate purification solution is evaporated, concentrated, precipitated, washed, and dried to obtain lithium carbonate; specifically, the following steps are included: Step (501): The remaining portion of the lithium sulfate purification solution in step (2) is evaporated and concentrated to obtain lithium sulfate finished solution; wherein, the lithium oxide concentration in the lithium sulfate finished solution is 50g / L-55g / L, and the temperature of sodium sulfate evaporation crystallization is 80℃-100℃; Step (502): The lithium sulfate finished solution obtained in step (501) is subjected to lithium precipitation treatment to obtain wet lithium carbonate and lithium precipitation mother liquor; wherein, after neutralization treatment, the lithium precipitation mother liquor is entered into the sodium sulfate evaporation crystallization in step (402) above to obtain sodium sulfate and hot sodium precipitation mother liquor; the neutralization treatment of the lithium precipitation mother liquor includes: first adding concentrated sulfuric acid to adjust the pH to about 2, and then adding sodium hydroxide solution to adjust the pH to 5-7; Step (503): The wet lithium carbonate is washed and dried to obtain lithium carbonate; specifically, the wet lithium carbonate is washed twice, dried, crushed, deionized, mixed, and packaged to obtain lithium carbonate product.

[0028] The process flow for the co-production of lithium sulfate and lithium carbonate from lithium concentrate in this invention is shown in Figure 2. It includes: spodumene concentrate → transformation roasting → acidification roasting → slurry preparation → leaching, neutralization, and filtration → refining to remove calcium and magnesium → lithium sulfate evaporation and crystallization to obtain crystallization mother liquor and wet lithium sulfate; the lithium sulfate evaporation and crystallization mother liquor → freezing to obtain sodium sulfate and frozen mother liquor; sodium sulfate → redissolve → the heavy solution is sent to sodium sulfate for evaporation and crystallization to obtain sodium sulfate powder and hot-precipitated sodium mother liquor; the hot-precipitated sodium mother liquor is returned to freezing; part of the frozen mother liquor is returned to lithium sulfate evaporation and crystallization, and part is returned to slurry preparation; the purified lithium sulfate solution, after purification and impurity removal, except for the portion sent to lithium sulfate evaporation and crystallization, is used to produce lithium carbonate. The main process is: lithium sulfate evaporation and concentration to obtain lithium sulfate finished solution; lithium precipitation, two washings, drying, pulverizing, impurity removal, mixing, and packaging to obtain lithium carbonate product; the lithium precipitation mother liquor is neutralized with concentrated sulfuric acid, and then sodium sulfate is evaporated and crystallized to obtain sodium sulfate powder and hot-precipitated sodium mother liquor.

[0029] In traditional lithium carbonate production, the hot-melt sodium mother liquor undergoes a secondary lithium precipitation process, resulting in lithium carbonate products with low purity and grade. However, this invention combines the hot-melt sodium mother liquor with the lithium sulfate evaporation and crystallization mother liquor from the lithium sulfate process, merging them together for freezing to obtain sodium sulfate. The sodium sulfate is then dissolved and returned to the sodium sulfate evaporation and crystallization process. In this process, lithium from the hot-melt sodium mother liquor enters the frozen mother liquor, which is then returned to the lithium sulfate evaporation and crystallization and slurry preparation processes, eliminating the need for secondary lithium precipitation. This allows lithium sulfate to enter both the lithium sulfate evaporation and crystallization system and the slurry preparation system, ultimately yielding lithium sulfate and lithium carbonate products. Furthermore, because this process eliminates the secondary lithium precipitation process, the resulting lithium sulfate and lithium carbonate products have high purity.

[0030] The working principle of this invention is as follows: the solubility of lithium sulfate is shown in Table 1, and the solubility of sodium sulfate is shown in Table 2.

[0031] Table 1: Lithium Sulfate Solubility

[0032] Table 2: Solubility of Sodium Sulfate

[0033] (1) Principle of lithium sulfate evaporation and crystallization: The solubility of lithium sulfate at 90℃-100℃ is 309 g / L, while the solubility of sodium sulfate is 427-425 g / L. The mass fraction of lithium sulfate in the lithium sulfate purification solution is about 80 g / L, and the mass fraction of sodium sulfate is 25 g / L. During the evaporation and crystallization process of lithium sulfate, the mass fraction of lithium sulfate can reach about 300 g / L, with a concentration ratio of 3.75. At 300 g / L, the mass fraction of sodium sulfate is about 93 g / L, which is far from the maximum saturation solubility of sodium sulfate. Therefore, this characteristic can be used to control the concentration of sodium sulfate during the evaporation and crystallization process of lithium sulfate, ensuring that sodium sulfate does not crystallize out, thereby obtaining clean lithium sulfate crystals.

[0034] (2) Freeze-crystallization principle: By controlling the final freezing point temperature to 5℃, the solubility of lithium sulfate is approximately 360 g / L, while the solubility of sodium sulfate is only 5-10 g / L. Utilizing this property, a high-concentration sodium sulfate solution obtained by evaporating and concentrating lithium sulfate is frozen to approximately 5℃ to reduce the mass fraction of sodium sulfate, thereby allowing sodium sulfate to crystallize while lithium sulfate remains in solution. Since Glauber's salt is a solid, a small amount of lithium sulfate may be trapped within the Glauber's salt crystals during the crystallization process.

[0035] (3) Evaporation and crystallization of heavy solution: Glauber's salt is redissolved, and Glauber's salt, lithium sulfate, potassium sulfate, etc., all dissolve into the solution. The solution is mostly sodium sulfate and potassium sulfate, with very little lithium sulfate. Through evaporation and crystallization again, potassium sulfate and sodium sulfate are preferentially saturated, while lithium sulfate is not saturated, thus achieving the crystallization of sodium sulfate and potassium sulfate to form sodium sulfate. The mother liquor of evaporation and crystallization contains a small amount of lithium sulfate, and the mother liquor is returned to the freezing process.

[0036] The present invention provides a method for the co-production of lithium sulfate and lithium carbonate from lithium concentrate. This method integrates the processes of sodium sulfate evaporation and crystallization, freezing, and sodium sulfate redissolution, thereby achieving the co-production of lithium sulfate and lithium carbonate.

[0037] Example 1 A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, comprising the following steps: (1) Spodumene concentrate is converted and roasted (1150℃, 3h) to obtain converted clinker. The converted clinker is added to concentrated sulfuric acid (acid-to-ore ratio 25%) for acidification roasting (280℃, 3h) to obtain acidified clinker. The acidified clinker is added to water to adjust the slurry (liquid-to-solid ratio 2.1:1), and calcium carbonate slurry is added to neutralize to pH 6.5. After neutralization, the slurry is filtered to separate the solid and the leachate; (2) The leachate is added to 300g / L sodium carbonate and 50% sodium hydroxide solution to remove calcium and magnesium impurities, and the slurry is filtered to obtain lithium sulfate purified solution. Conditions: 90-95℃, pH 11-11.5; (3) A portion of the lithium sulfate purified solution and 80% of the frozen mother liquor are combined and entered into the lithium sulfate evaporation and crystallization process. The lithium sulfate is evaporated and crystallized to obtain lithium sulfate product. Conditions: Control the sodium sulfate concentration in the mother liquor of lithium sulfate evaporation and crystallization process to 123 g / L; (4) Combine the mother liquor of lithium sulfate evaporation and crystallization and the mother liquor of hot sodium precipitation into the freezing process. Crystallize out Glauber's salt, dissolve Glauber's salt and add water, and pass in steam; control the temperature to 90℃ and the sodium sulfate concentration to 300 g / L. Obtain a heavy solution. Freezing conditions: Two-stage freezing, first-stage freezing temperature controlled at 15℃, second-stage freezing temperature controlled at 5℃, 80% of the mother liquor obtained from freezing is sent to lithium sulfate evaporation and crystallization, and 20% is sent to the slurry preparation process; (5) Sodium sulfate evaporation and crystallization to produce sodium sulfate, and the hot sodium precipitation mother liquor is returned to the freezing process; conditions: control the sodium sulfate concentration of the heavy solution at 300g / L and the temperature at 46℃; enter sodium sulfate evaporation and crystallization, control the lithium oxide concentration of the hot sodium precipitation mother liquor at 18g / L; (6) The lithium sulfate purified liquid obtained from evaporation and concentration is transferred to the lithium precipitation reactor; conditions: control the lithium oxide concentration of the lithium sulfate purified liquid at approximately 50-55g / L; (7) Add 300g / L sodium carbonate solution to the reactor, sodium carbonate excess coefficient Control at 5%-10%, stir and react at 80-95℃ for 2-3 hours to produce lithium precipitation reaction. After the reaction is completed, filter and separate to obtain lithium carbonate precipitate and lithium precipitation mother liquor; (8) Transfer the lithium carbonate precipitate to the stirring and washing equipment, add pure water for two stirring and washing, and filter after each stirring and washing to remove impurities such as sodium sulfate attached to the surface of lithium carbonate; conditions: 80-100℃, the mass liquid-solid ratio of pure water and solid lithium carbonate is controlled at 1-4:1; (9) Dry the lithium carbonate precipitate after two stirring and washing at 120℃ for 4-5 hours to obtain lithium carbonate product; (10) Collect the lithium precipitation mother liquor, first add concentrated sulfuric acid to adjust the pH to about 2, then add sodium hydroxide solution to adjust the pH to 5-7, and the treated mother liquor will then enter the sodium sulfate evaporation and crystallization process.

[0038] Example 2 is a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, which is basically the same as Example 1, except that the lithium oxide concentration of the lithium sulfate finishing liquid is changed. Except that the lithium oxide concentration of the lithium sulfate finishing liquid is controlled to be 65-70 g / L in step (6), the parameters of the other steps are completely consistent with those of Example 1.

[0039] Results: Example 2 successfully prepared lithium sulfate and lithium carbonate, but during the lithium precipitation reaction, the high concentration of the solution led to severe local supersaturation. The lithium carbonate crystals were large and contained a large amount of sodium sulfate impurities, resulting in a wet purity of only 92.3% after filtration (compared to 97.5% in Example 1). Due to the excessively high concentration, the sodium carbonate reaction was incomplete, and the excess coefficient actually decreased to 3%, reducing the lithium precipitation rate from 95.2% in Example 1 to 88.7%. The lithium oxide concentration in the lithium precipitation mother liquor reached 42 g / L, increasing lithium loss by 42.9% and subsequent recovery energy consumption by 30%.

[0040] Example 3 is a method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, which is basically the same as Example 1, except that the washing process is simplified to one washing. Except for step (8), which is changed to one washing, the temperature is maintained at 80-100℃, the liquid-solid ratio is 1-4:1, and the other step parameters are completely consistent with those of Example 1.

[0041] Results: Example 3 successfully prepared lithium sulfate and lithium carbonate, but a single high-temperature washing process was insufficient to completely remove the sodium sulfate impurities adhering to the surface of the lithium carbonate. After drying, the purity of the lithium carbonate was 95.8%, with a sodium sulfate residue of 3.9%, which failed to meet the purity requirements for battery-grade lithium carbonate (≥99.0%). This necessitates an additional purification process if used in subsequent battery material production, increasing processing costs by 8%.

[0042] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate, characterized in that, Includes the following steps: Lithium spodumene concentrate is subjected to transformation roasting, acid roasting, slurry preparation, neutralization, and refining to obtain lithium sulfate purified solution. Part of the lithium sulfate purified solution is evaporated and crystallized to obtain wet lithium sulfate and lithium sulfate crystallization mother liquor. The wet lithium sulfate is dried to obtain lithium sulfate. The lithium sulfate crystallization mother liquor is frozen to obtain sodium sulfate and frozen mother liquor. The sodium sulfate is redissolved and evaporated and crystallized to obtain sodium sulfate and pyrolysis sodium mother liquor. The pyrolysis sodium mother liquor is returned to be mixed with the lithium sulfate crystallization mother liquor. Another part of the lithium sulfate purified solution is evaporated, concentrated, precipitated, washed, and dried to obtain lithium carbonate.

2. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: The sodium pyrolysis mother liquor and lithium sulfate crystallization mother liquor are mixed and then frozen together to obtain sodium sulfate. The sodium sulfate is dissolved, evaporated and crystallized to obtain sodium sulfate.

3. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: The frozen mother liquor is returned to the slurry preparation and lithium sulfate purification solution evaporation and crystallization steps.

4. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: During the evaporation and crystallization process of the lithium sulfate purification solution, the concentration of sodium sulfate in the mother liquor is 10g / L-250g / L, and the temperature is 80℃-100℃.

5. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: The freezing process is a two-stage freezing process, with the first stage freezing temperature ranging from 10℃ to 50℃ and the second stage freezing temperature ranging from 0℃ to 10℃.

6. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: In the redissolution of Glauber's salt, the concentration of sodium sulfate is controlled at 200g / L-400g / L.

7. A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1 or 6, characterized in that: Steam is introduced during the redissolution of Glauber's salt, and the temperature is controlled between 10℃ and 90℃.

8. The method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: The other portion of the purified lithium sulfate solution is evaporated, concentrated, precipitated, washed, and dried to obtain lithium carbonate, including: evaporating and concentrating the other portion of the purified lithium sulfate solution to obtain a completed lithium sulfate solution; precipitating the completed lithium sulfate solution to obtain wet lithium carbonate and a lithium precipitation mother liquor; and washing and drying the wet lithium carbonate to obtain lithium carbonate.

9. A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 8, characterized in that: The lithium oxide concentration in the lithium sulfate solution is 50 g / L-55 g / L.

10. A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 8, characterized in that: The lithium precipitation mother liquor was neutralized and then evaporated and crystallized with sodium sulfate to obtain sodium sulfate and pyrolysis sodium mother liquor.

11. A method for co-producing lithium sulfate and lithium carbonate from lithium concentrate as described in claim 1, characterized in that: The lithium oxide concentration in the pyrolysis sodium mother liquor is 15 g / L-30 g / L.

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