Method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing lepidolite decomposition byproducts

Abstract

The method comprises the following steps: mixing sodium sulfate, ammonium bicarbonate and a salting-out agent to obtain sodium bicarbonate and double decomposition mother liquor containing the salting-out agent; adjusting the pH value of the double decomposition mother liquor containing the salting-out agent to be neutral; mixing the double salt and the double decomposition mother liquor containing the salting-out agent, and performing evaporative crystallization to obtain sodium sulfate and a double salt solution containing the salting-out agent; cooling and crystallizing the double salt solution to obtain double salt and an ammonium sulfate-rich solution containing a salting-out agent; evaporating and crystallizing the ammonium sulfate-rich solution to obtain ammonium sulfate and an evaporation mother solution containing a salting-out agent; the evaporation mother liquor containing the salting-out agent is recycled for the double decomposition reaction for circulation. According to the method provided by the invention, the problems of excess of a lepidolite decomposition byproduct sodium sulfate and environmental pollution are relieved, value-added utilization of sodium sulfate is realized, meanwhile, the sodium carbonate yield is increased, the energy consumption is reduced, the technological process is simplified, and environmental protection and economical efficiency are both considered.

Description

Technical Field

[0001] The invention relates to a method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing byproducts of decomposing lepidolite. Background Art

[0002] As an ideal secondary battery, lithium-ion batteries have attracted widespread attention due to their high energy density and long cycle life. In recent years, the output of lithium-ion batteries has shown explosive growth. As an indispensable raw material for the preparation of lithium-ion battery materials, the demand for lithium carbonate has also shown a sustained growth momentum. my country's salt lake lithium resources are rich, but the grade is low, the content of impurities such as Mg and B is high, and the comprehensive utilization is difficult. The obtained lithium carbonate is difficult to meet the battery grade standards. Yichun City, Jiangxi Province has a large amount of ore lithium resources, which mainly exist in the form of lithium mica. The mineral phase structure of lithium mica is complex and difficult to process. At present, the methods for extracting lithium salts from lithium mica include chlorination roasting, defluorination roasting acid leaching, and sulfate pressure cooking. Among them, a large amount of sodium sulfate by-product is produced in the process of producing lithium salts from lithium mica using sulfuric acid (salt) method. Sodium sulfate itself is of low value, and the direct sale income is low, and a large amount of accumulation will cause environmental pollution. If the by-product sodium sulfate can be processed and converted into bulk chemical raw materials such as sodium carbonate and ammonium sulfate, it will greatly alleviate the problem of sodium sulfate surplus, which is a method with both environmental and economic significance.

[0003] CN110563007A discloses a method for converting sodium sulfate into sodium bicarbonate using calcium oxide and carbon dioxide, but this method requires the introduction of excessive carbon dioxide, which will produce carbon dioxide waste gas, and a small amount of calcium carbonate will also exist in the gypsum, reducing the quality of the gypsum, and the solubility of sodium bicarbonate is very low, and excessive water needs to be introduced into the whole system to increase the residual calcium, so that the subsequent use of sodium bicarbonate for desulfurization is very likely to cause serious scarring of the reactor. CN112850747A discloses a method and device for preparing ammonium sulfate and sodium bicarbonate from sodium sulfate and ammonium bicarbonate, but this method and device have strict requirements on raw materials. If the raw materials contain chloride ions, metal ions or organic matter, it will not only have an adverse effect on product quality, but also damage the equipment. In addition, due to the structural complexity of the electrodialysis equipment, the control is relatively cumbersome, and the maintenance and replacement costs of the equipment in the later stage are high.

[0004] It can be seen that how to provide a method for preparing sodium carbonate and ammonium sulfate by using sodium sulfate, a byproduct of lithium mica decomposition, to alleviate the problem of excess sodium sulfate, realize the value-added utilization of sodium sulfate, reduce energy consumption, simplify the process flow, and take into account environmental protection and economy has become an urgent problem that technicians in this field need to solve. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing the byproducts of decomposing lepidolite, aiming to solve the above technical problems.

[0006] To achieve the above object, the present invention proposes a method for preparing sodium carbonate and co-producing ammonium sulfate by using lepidolite decomposition byproducts, comprising:

[0007] (1) mixing sodium sulfate, ammonium bicarbonate and a salting-out agent, a byproduct of decomposition of lepidolite, wherein the molar ratio of total sodium to total ammonium in the reaction system is 1:(0.8-1.4), performing a double decomposition reaction at 20-45° C., filtering and washing to obtain sodium bicarbonate and a double decomposition mother liquor containing a salting-out agent; and calcining the obtained sodium bicarbonate to obtain sodium carbonate;

[0008] (2) adjusting the pH of the double decomposition mother liquor containing the salting-out agent obtained in step (1) to 4-7 with sulfuric acid;

[0009] (3) mixing the double salt and the double decomposition mother liquor containing the salting-out agent obtained in step (2), evaporating and crystallizing, and filtering to obtain sodium sulfate and a double salt solution containing the salting-out agent; the obtained sodium sulfate is reused in step (1);

[0010] (4) cooling and crystallizing the complex salt solution obtained in step (3), filtering to obtain a complex salt and an ammonium sulfate-rich solution containing a salting-out agent; and recycling the complex salt obtained in step (3);

[0011] (5) evaporating and crystallizing the ammonium sulfate-rich solution obtained in step (4), filtering to obtain ammonium sulfate and an evaporation mother liquor containing a salting-out agent; and returning the evaporation mother liquor containing a salting-out agent to step (1).

[0012] In one embodiment, the molar ratio of total sodium to total ammonium in step (1) is 1:(0.9-1.1).

[0013] In one embodiment, the salting-out agent is one of n-butanol, propylene glycol, triethanolamine, ethanol, and methanol.

[0014] In one embodiment, the molar ratio of sodium sulfate to the salting-out agent in step (1) is 1:(0.8-1.8).

[0015] In one embodiment, the time of the metathesis reaction in step (1) is 0.5-3h.

[0016] In one embodiment, the pH of the metathesis mother liquor in step (2) is 4-7.

[0017] In one embodiment, the temperature during the evaporation crystallization in step (3) is 70-130°C.

[0018] In one embodiment, the temperature during cooling crystallization in step (4) is 0-30°C.

[0019] In one embodiment, the temperature during evaporation and crystallization in step (5) is 70-110°C.

[0020] In the technical scheme of the present invention, sodium carbonate and ammonium sulfate are prepared as raw materials using sodium sulfate, a byproduct of lithium mica decomposition, as raw materials. In the method, sodium sulfate and ammonium bicarbonate undergo metathesis reaction to obtain sodium bicarbonate and metathesis mother liquor, and sodium bicarbonate is calcined to obtain sodium carbonate. On the one hand, compared with not adding a salting-out agent or adding an electrolyte salting-out agent, the present invention uses organic alcohols and organic amines as salting-out agents, which can improve the conversion rate of sodium bicarbonate in the metathesis reaction, improve the sodium carbonate yield, and the organic salting-out agent can be recycled and non-toxic. On the other hand, the main components of the metathesis mother liquor are ammonium bicarbonate, sodium sulfate and ammonium sulfate, which are different from the combined alkali process that recovers ammonium bicarbonate in the form of ammonia distillation. The present invention uses a sulfuric acid neutralization method to convert ammonium bicarbonate into ammonium sulfate and carbon dioxide, and carbon dioxide can be reused for metathesis reaction, thereby avoiding the problem of device corrosion in the ammonia distillation process and simplifying the process flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0022] Figure 1 The present invention is a flow chart of a method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing lepidolite decomposition byproducts according to an embodiment of the present invention.

[0023] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0026] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0027] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] The invention provides a method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing byproducts of decomposing lepidolite.

[0029] like Figure 1 As shown, the method for preparing sodium carbonate and co-producing ammonium sulfate by using lepidolite decomposition byproducts provided in an embodiment of the present invention comprises:

[0030] (1) mixing sodium sulfate, ammonium bicarbonate and a salting-out agent (or an evaporation mother liquor containing a salting-out agent) which are byproducts of decomposition of lepidolite, and controlling the molar ratio of total sodium to total ammonium in the reaction system to be 1:(0.8-1.4), performing a double decomposition reaction at 20-45° C., filtering and washing to obtain sodium bicarbonate and a double decomposition mother liquor containing a salting-out agent; and calcining the obtained sodium bicarbonate to obtain sodium carbonate;

[0031] (2) adjusting the pH of the double decomposition mother liquor containing the salting-out agent obtained in step (1) to 4-7 with sulfuric acid;

[0032] (3) mixing the double salt and the double decomposition mother liquor containing the salting-out agent obtained in step (2), evaporating and crystallizing, and filtering to obtain sodium sulfate and a double salt solution containing the salting-out agent; the obtained sodium sulfate is reused in step (1);

[0033] (4) cooling and crystallizing the complex salt solution obtained in step (3), filtering to obtain a complex salt and an ammonium sulfate-rich solution containing a salting-out agent; and recycling the complex salt obtained in step (3);

[0034] (5) evaporating and crystallizing the ammonium sulfate-rich solution obtained in step (4), filtering to obtain ammonium sulfate and an evaporation mother liquor containing a salting-out agent; and returning the evaporation mother liquor containing a salting-out agent to step (1).

[0035] The method provided by the present invention uses sodium sulfate, a byproduct of lithium mica decomposition, as a raw material to prepare sodium carbonate and ammonium sulfate. In the method, sodium sulfate and ammonium bicarbonate undergo a double decomposition reaction to obtain sodium bicarbonate and a double decomposition mother liquor, and sodium bicarbonate is calcined to obtain sodium carbonate. On the one hand, compared with not adding a salting-out agent or adding an electrolyte salting-out agent, the present invention uses organic alcohols and organic amines as salting-out agents, which can improve the conversion rate of sodium bicarbonate in the double decomposition reaction, improve the sodium carbonate yield, and the organic salting-out agent can be recycled and non-toxic. On the other hand, the main components of the double decomposition mother liquor are ammonium bicarbonate, sodium sulfate and ammonium sulfate. Unlike the combined alkali process that recycles ammonium bicarbonate in the form of ammonia distillation, the present invention uses a sulfuric acid neutralization method to convert ammonium bicarbonate into ammonium sulfate and carbon dioxide, and carbon dioxide can be reused for double decomposition reaction, thereby avoiding the problem of device corrosion during ammonia distillation and simplifying the process flow.

[0036] In addition, according to the change law of the phase diagram of the water-salt system of sodium sulfate and ammonium sulfate at different temperatures, the present invention sequentially adopts the methods of heating crystallization, cooling crystallization and evaporation crystallization to achieve the separation of ammonium sulfate. The whole process is simple to operate, high in efficiency, low in cost, and no waste gas or waste liquid is generated.

[0037] The product obtained by the method provided by the present invention has high purity. The purity of the sodium carbonate product meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022, and the purity of the ammonium sulfate product meets the requirements of Type I products in GB / T 535-2020.

[0038] In the present invention, the sodium sulfate described in step (1) is a byproduct obtained by crystallization after treating lepidolite to produce lithium salt.

[0039] In the present invention, the double salt in step (3) and step (4) includes Na2SO4·(NH4)2SO4·4H2O.

[0040] Preferably, the temperature of the double decomposition reaction is 20-45°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C or 45°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the molar ratio of total sodium to total ammonium in the double decomposition reaction of step (1) is 1:(0.8-1.4), for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3 or 1:1.4, and is further preferably 1:(0.9-1.1), but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the salting-out agent in step (1) is one of n-butanol, propylene glycol, triethanolamine, ethanol and methanol.

[0043] Preferably, the molar ratio of sodium sulfate, a byproduct of the decomposition of lithium mica, and the salting-out agent in step (1) is 1:(0.8-1.8), for example, it can be 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6 or 1:1.8, and is further preferably 1:(0.8-1.2), but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the time of the metathesis reaction in step (1) is 0.5-3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h,

[0045] 2.5h or 3h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the pH of the metathesis mother liquor in step (2) is adjusted to 4-7, for example, 4, 5, 6 or 7, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the temperature of the crystallization in step (3) is 70-130°C, for example, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C or 130°C, more preferably 80-100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] Preferably, the cooling crystallization temperature in step (4) is 0-30°C, for example, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C or 30°C, more preferably 15-30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] Preferably, the temperature of the evaporation product in step (5) is 70-110°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C or 110°C, more preferably 80-100°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] The method provided by the present invention uses sodium sulfate, a byproduct of lithium mica decomposition, as a raw material to prepare sodium carbonate and ammonium sulfate. In the method, sodium sulfate and ammonium bicarbonate undergo a double decomposition reaction to obtain sodium bicarbonate and a double decomposition mother liquor, and sodium bicarbonate is calcined to obtain sodium carbonate. On the one hand, compared with not adding a salting-out agent or adding an electrolyte salting-out agent, the present invention uses organic alcohols and organic amines as salting-out agents, which can improve the conversion rate of sodium bicarbonate in the double decomposition reaction, thereby improving the sodium carbonate yield, and the organic salting-out agent can be recycled and non-toxic. On the other hand, the main components of the double decomposition mother liquor are ammonium bicarbonate, sodium sulfate and ammonium sulfate. Unlike the combined alkali process that recycles ammonium bicarbonate in the form of ammonia distillation, the present invention uses a sulfuric acid neutralization method to convert ammonium bicarbonate into ammonium sulfate and carbon dioxide, and carbon dioxide can be reused for double decomposition reaction, thereby avoiding the problem of device corrosion during ammonia distillation and simplifying the process flow.

[0051] According to the change law of the phase diagram of the water-salt system of sodium sulfate and ammonium sulfate at different temperatures, the invention sequentially adopts the methods of heating crystallization, cooling crystallization and evaporation crystallization to realize the separation of ammonium sulfate. The whole process is simple to operate, high in efficiency, low in cost, and no waste gas or waste liquid is generated.

[0052] The product obtained by the method provided by the present invention has high purity. The purity of the sodium carbonate product meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022, and the purity of the ammonium sulfate product meets the requirements of Type I products in GB / T 535-2020.

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the implementation of the present invention is not limited thereto.

[0054] Example 1

[0055] This embodiment provides a method for preparing sodium carbonate and co-producing ammonium sulfate by using sodium sulfate, a byproduct of decomposing lepidolite, such as Figure 1 As shown, the method comprises the following steps:

[0056] (1) mixing sodium sulfate, ammonium bicarbonate and n-butanol (or an evaporation mother liquor containing n-butanol), which are byproducts of lepidolite decomposition, and controlling the molar ratio of total sodium to total ammonium in the reaction system to be 1:1.1, and the molar ratio of sodium sulfate to n-butanol to be 1:1.2, performing a double decomposition reaction at 35° C. for 1 hour, filtering and washing to obtain sodium bicarbonate and a double decomposition mother liquor containing a salting-out agent; and calcining the obtained sodium bicarbonate to obtain sodium carbonate;

[0057] (2) adjusting the pH of the metathesis mother liquor containing n-butanol obtained in step (1) to 6 with sulfuric acid;

[0058] (3) mixing the double salt and the double decomposition mother liquor containing n-butanol obtained in step (2), evaporating and crystallizing at 100° C., and filtering to obtain sodium sulfate and a double salt solution containing n-butanol; the obtained sodium sulfate is reused in step (1);

[0059] (4) cooling the double salt solution obtained in step (3) at 20° C. for crystallization, filtering to obtain a double salt and an ammonium sulfate solution rich in n-butanol; the obtained double salt is reused in step (3);

[0060] (5) evaporating and crystallizing the ammonium sulfate-rich solution obtained in step (4) at 90° C., filtering to obtain ammonium sulfate and an evaporation mother liquor containing n-butanol; and recycling the obtained evaporation mother liquor containing n-butanol to step (1);

[0061] After calculation and detection, the yield of the sodium carbonate product obtained in this embodiment is 65.96%, and the total alkali content of the sodium carbonate product is 98.63%, which meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022; the nitrogen content of the obtained ammonium sulfate product is 20.95%, which meets the requirements of Type I products in GB / T 535-2020.

[0062] Example 2

[0063] This embodiment provides a method for preparing sodium carbonate and co-producing ammonium sulfate by using sodium sulfate, a byproduct of decomposing lepidolite, such as Figure 1 As shown, the method comprises the following steps:

[0064] (1) mixing sodium sulfate, ammonium bicarbonate and evaporation mother liquor, byproducts of lithium mica decomposition, and controlling the molar ratio of total sodium to total ammonium in the reaction system to be 1:1, performing double decomposition reaction at 30° C. for 2 hours, filtering and washing to obtain sodium bicarbonate and double decomposition mother liquor; and calcining the obtained sodium bicarbonate to obtain sodium carbonate;

[0065] (2) adjusting the pH of the metathesis mother liquor obtained in step (1) to 7 with sulfuric acid;

[0066] (3) mixing the double salt and the double decomposition mother liquor obtained in step (2), evaporating and crystallizing at 120° C., and filtering to obtain sodium sulfate and a double salt solution; the obtained sodium sulfate is reused in step (1);

[0067] (4) cooling the double salt solution obtained in step (3) at 10° C. for crystallization, filtering to obtain a double salt and a rich ammonium sulfate solution; the obtained double salt is reused in step (3);

[0068] (5) evaporating and crystallizing the rich ammonium sulfate solution obtained in step (4) at 110° C., filtering to obtain ammonium sulfate and evaporation mother liquor; and recycling the obtained evaporation mother liquor to step (1);

[0069] After calculation and detection, the yield of the sodium carbonate product obtained in this embodiment is 40.51%, and the total alkali content of the sodium carbonate product is 98.85%, which meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022; the nitrogen content of the obtained ammonium sulfate product is 20.61%, which meets the requirements of Type I products in GB / T 535-2020.

[0070] Example 3

[0071] This embodiment provides a method for preparing sodium carbonate and co-producing ammonium sulfate by using sodium sulfate, a byproduct of decomposing lepidolite, such as Figure 1 As shown, the method comprises the following steps:

[0072] (1) mixing sodium sulfate, ammonium bicarbonate and glycerol (or evaporation mother liquor containing glycerol), which are byproducts of lepidol mica decomposition, and controlling the molar ratio of total sodium to total ammonium in the reaction system to be 1:1.2, and the molar ratio of sodium sulfate to glycerol to be 1:1.4, performing double decomposition reaction at 40° C. for 3 hours, filtering and washing to obtain sodium bicarbonate and double decomposition mother liquor containing glycerol; and calcining the obtained sodium bicarbonate to obtain sodium carbonate;

[0073] (2) adjusting the pH of the double decomposition mother liquor containing glycerol obtained in step (1) to 4 with sulfuric acid;

[0074] (3) mixing the double salt and the double decomposition mother liquor containing glycerol obtained in step (2), evaporating and crystallizing at 90° C., and filtering to obtain sodium sulfate and a double salt solution containing glycerol; the obtained sodium sulfate is reused in step (1);

[0075] (4) cooling and crystallizing the double salt solution obtained in step (3) at 0° C., filtering to obtain a double salt and a glycerol-rich ammonium sulfate solution; the obtained double salt is reused in step (3);

[0076] (5) evaporating and crystallizing the ammonium sulfate-rich solution obtained in step (4) at 80° C., filtering to obtain ammonium sulfate and an evaporation mother liquor containing glycerol; and returning the obtained evaporation mother liquor containing the salting-out agent to step (1);

[0077] After calculation and detection, the yield of the sodium carbonate product obtained in this embodiment is 51.01%, and the total alkali content of the sodium carbonate product is 98.51%, which meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022; the nitrogen content of the obtained ammonium sulfate product is 20.73%, which meets the requirements of Type I products in GB / T 535-2020.

[0078] Example 4

[0079] This embodiment provides a method for preparing sodium carbonate and co-producing ammonium sulfate by using sodium sulfate, a byproduct of decomposing lepidolite, such as Figure 1 As shown, the method comprises the following steps:

[0080] (1) mixing sodium sulfate, ammonium bicarbonate and triethanolamine (or evaporation mother liquor containing triethanolamine), which are byproducts of lepidolite decomposition, and controlling the molar ratio of total sodium to total ammonium in the reaction system to be 1:1.4, and the molar ratio of sodium sulfate to triethanolamine to be 1:0.9, performing double decomposition reaction at 25° C. for 0.5 h, filtering and washing to obtain sodium bicarbonate and double decomposition mother liquor containing triethanolamine; and calcining the obtained sodium bicarbonate to obtain sodium carbonate;

[0081] (2) adjusting the pH of the double decomposition mother liquor containing triethanolamine obtained in step (1) to 5 with sulfuric acid;

[0082] (3) mixing the double salt and the double decomposition mother liquor containing triethanolamine obtained in step (2), evaporating and crystallizing at 80° C., and filtering to obtain sodium sulfate and a double salt solution containing triethanolamine; the obtained sodium sulfate is reused in step (1);

[0083] (4) cooling the double salt solution obtained in step (3) at 30° C. for crystallization, filtering to obtain a double salt and a triethanolamine-containing ammonium sulfate-rich solution; the obtained double salt is reused in step (3);

[0084] (5) evaporating and crystallizing the ammonium sulfate-rich solution obtained in step (4) at 70° C., filtering to obtain ammonium sulfate and an evaporation mother liquor containing triethanolamine; and returning the obtained evaporation mother liquor containing triethanolamine to step (1);

[0085] After calculation and detection, the yield of the sodium carbonate product obtained in this embodiment is 45.82%, and the total alkali content of the sodium carbonate product is 98.11%, which meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022; the nitrogen content of the obtained ammonium sulfate product is 20.68%, which meets the requirements of Type I products in GB / T 535-2020.

[0086] Example 5

[0087] The present embodiment provides a method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing sodium sulfate, a byproduct of decomposing lepidolite. The method is the same as that of Example 1 except that the salting-out agent n-butanol in the reaction system of step (1) is replaced with ethanol. Therefore, the remaining steps and conditions are not described in detail here.

[0088] After calculation and detection, the yield of the sodium carbonate product obtained in this embodiment is 54.64%, and the total alkali content of the sodium carbonate product is 98.55%, which meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022; the nitrogen content of the obtained ammonium sulfate product is 20.65%, which meets the requirements of Type I products in GB / T 535-2020.

[0089] Compared with Example 1, the boiling point of the salting-out agent ethanol used in the reaction system of this embodiment is only 78.3° C., which is lower than the boiling point of water. During subsequent recovery, the ethanol needs to be evaporated first, and then the water is evaporated to obtain sodium sulfate and ammonium sulfate. It cannot be directly recycled like the n-butanol in Example 1 (the boiling point of n-butanol is higher than that of water, and the salting-out agent will not volatilize when the water is evaporated), which will increase material consumption and equipment costs, and the economy is not good.

[0090] Example 6

[0091] The present embodiment provides a method for preparing sodium carbonate and co-producing ammonium sulfate by utilizing sodium sulfate, a byproduct of decomposing lepidolite. The method is the same as that of Example 1 except that the salting-out agent n-butanol in the reaction system of step (1) is replaced with methanol. Therefore, the remaining steps and conditions are the same as those of Example 1 and are not described in detail here.

[0092] After calculation and detection, the yield of the sodium carbonate product obtained in this embodiment is 45.08%, and the total alkali content of the sodium carbonate product is 98.88%, which meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022; the nitrogen content of the obtained ammonium sulfate product is 20.81%, which meets the requirements of Type I products in GB / T 535-2020.

[0093] Compared with Example 1, the boiling point of the salting-out agent methanol used in the reaction system of this embodiment is only 64.7°C, which is lower than the boiling point of water. During subsequent recovery, methanol must be evaporated first, and then water must be evaporated to obtain sodium sulfate and ammonium sulfate, which will increase material consumption and equipment costs, and the economy is not as good as Example 1.

[0094] In summary, the method provided by the present invention uses sodium sulfate, a byproduct of lithium mica decomposition, as a raw material to prepare sodium carbonate and ammonium sulfate, wherein sodium sulfate and ammonium bicarbonate undergo a double decomposition reaction to obtain sodium bicarbonate and a double decomposition mother liquor, and sodium bicarbonate is calcined to obtain sodium carbonate. On the one hand, compared with not adding a salting-out agent or adding an electrolyte salting-out agent, the present invention uses organic alcohols and organic amines as salting-out agents, which can increase the conversion rate of sodium bicarbonate in the double decomposition reaction, improve the yield of sodium carbonate, and the organic salting-out agent can be recycled and is non-toxic and harmless. On the other hand, the main components of the double decomposition mother liquor are ammonium bicarbonate, sodium sulfate and ammonium sulfate. Different from the combined alkali production method in which ammonium bicarbonate is recovered by distilling ammonia, the present invention adopts a sulfuric acid neutralization method to convert ammonium bicarbonate into ammonium sulfate and carbon dioxide, and the carbon dioxide can be reused for the double decomposition reaction, thereby avoiding the problem of equipment corrosion in the process of distilling ammonia and simplifying the process flow; according to the change law of the water-salt system phase diagram of sodium sulfate and ammonium sulfate at different temperatures, the present invention sequentially adopts the methods of heating crystallization, cooling crystallization and evaporation crystallization to achieve the separation of ammonium sulfate, and the whole process is simple to operate, high in efficiency, low in cost, and no waste gas and waste liquid are generated; in addition, the product obtained by the method provided by the present invention has high purity, the purity of the sodium carbonate product meets the requirements of Class II qualified light sodium carbonate in GB / T 210-2022, and the purity of the ammonium sulfate product meets the requirements of Type I products in GB / T 535-2020.

[0095] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing sodium carbonate and co-producing ammonium sulfate by using lepidolite decomposition byproducts, characterized in that: The method for preparing sodium carbonate and co-producing ammonium sulfate by using lepidolite decomposition byproducts comprises: (1) mixing sodium sulfate, ammonium bicarbonate and a salting-out agent, a byproduct of decomposition of lepidolite, wherein the molar ratio of total sodium to total ammonium in the reaction system is 1:(0.8-1.4), performing a double decomposition reaction at 20-45° C., filtering and washing to obtain sodium bicarbonate and a double decomposition mother liquor containing a salting-out agent; and calcining the obtained sodium bicarbonate to obtain sodium carbonate; (2) adjusting the pH of the double decomposition mother liquor containing the salting-out agent obtained in step (1) to 4-7 with sulfuric acid; (3) mixing the double salt and the double decomposition mother liquor containing the salting-out agent obtained in step (2), evaporating and crystallizing, and filtering to obtain sodium sulfate and a double salt solution containing the salting-out agent; the obtained sodium sulfate is reused in step (1); (4) cooling and crystallizing the complex salt solution obtained in step (3), filtering to obtain a complex salt and an ammonium sulfate-rich solution containing a salting-out agent; and recycling the complex salt obtained in step (3); (5) evaporating and crystallizing the ammonium sulfate-rich solution obtained in step (4), filtering to obtain ammonium sulfate and an evaporation mother liquor containing a salting-out agent; and returning the evaporation mother liquor containing a salting-out agent to step (1).

2. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The molar ratio of total sodium to total ammonium in step (1) is 1:(0.9-1.1).

3. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The salting-out agent is one of n-butanol, propylene glycol, triethanolamine, ethanol and methanol.

4. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The molar ratio of sodium sulfate to the salting-out agent in the step (1) is 1:(0.8-1.8).

5. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The time of the double decomposition reaction in step (1) is 0.5-3h.

6. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The pH value of the double decomposition mother liquor in the step (2) is 4-7.

7. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The temperature during the evaporation crystallization in step (3) is 70-130°C.

8. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The temperature during cooling and crystallization in step (4) is 0-30°C.

9. The method for preparing sodium carbonate and co-producing ammonium sulfate by decomposing lepidolite as a byproduct according to claim 1, characterized in that: The temperature during evaporation and crystallization in step (5) is 70-110°C.

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