Method for producing sodium carbonate and high-strength gypsum by using calcium carbonate and sodium sulfate as raw materials

Abstract

The present application discloses a method for producing sodium carbonate and high-strength gypsum by using calcium carbonate and sodium sulfate as raw materials. In the present application, two low-value-added salts, sodium sulfate and calcium carbonate, are used as raw materials, and are combined with an ammonia cycle to produce a high-value-added product, i.e., sodium bicarbonate or sodium carbonate, and high-strength gypsum; by means of a calcium-oxide-based deamination unit, full cycling of an ammonia raw material in a production process is realized; and by producing the high-strength gypsum, the economic efficiency of the process is improved. The method provided in the present application has the advantages of a simple process, stable operation, low investment and low production costs.

Description

A method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials

[0001] This application claims priority to a Chinese patent application filed with the Patent Office of China on February 4, 2024, with application number CN202410153178.3 and application name “A method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of fine chemical technology, and in particular to a method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials. Background Art

[0003] With the rapid development of industry, especially in coal chemical industry, steel and other industries, a large amount of sodium sulfate and calcium carbonate waste salts are generated in the process of zero wastewater discharge and ultra-low waste gas discharge. These two types of waste salts have low added value, are difficult to be absorbed by the market, and have high disposal costs for enterprises. With the idea of ​​short process and high added value, a new resource utilization idea is formed to use calcium carbonate and sodium sulfate as raw materials to prepare baking soda or soda ash and high-strength gypsum.

[0004] There are many processes reported for preparing baking soda using sodium sulfate as a raw material. Most of the ideas use sodium sulfate as a raw material and adopt ammoniaation + carbonization or double decomposition with ammonium bicarbonate to produce sodium bicarbonate products. The separated mother liquor is disposed of and ammonium sulfate is recovered. These ideas generally have high investment and operating costs, and the operation process involves multiple evaporation, cooling, and freezing processes of the mother liquor. The process is complicated and difficult to operate, making it difficult to operate stably and not easily accepted by enterprises. A new process that can solve the above problems and meet the needs of enterprises is needed. In addition, the above process consumes a large amount of ammonia to produce ammonium sulfate during the sodium sulfate alkali production process, and the process is highly dependent on ammonia resources. Calcium carbonate is used in the Solvay alkali production process to provide calcium oxide and carbon dioxide to realize the circulation of ammonia. However, the traditional Solvay process has the problems of sodium resource waste and high-salt wastewater pollution, which greatly limits the application of the process.

[0005] Summary of the Invention

[0006] To this end, this application provides a method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials. This method uses sodium sulfate and calcium carbonate as raw materials, combined with an ammonia cycle, to produce sodium bicarbonate or soda ash. The high-strength gypsum recycling method utilizes a calcium oxide-based deamination unit to achieve full recycling of the ammonia raw material in the production process, while also improving the economic benefits of the process by producing high-strength gypsum. This method offers the advantages of a simple process, stable operation, and low investment and production costs.

[0007] In order to achieve the above objectives, this application provides the following technical solutions:

[0008] A method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials, the method comprising the following steps:

[0009] (1) Calcium carbonate is calcined to produce calcium oxide and carbon dioxide;

[0010] (2) ammoniating the mother liquor I, sodium sulfate and the carbon dioxide produced in step (1) to undergo a carbonization reaction to produce a slurry containing sodium bicarbonate crystals, performing solid-liquid separation to obtain a sodium bicarbonate product and the mother liquor II, and calcining the sodium bicarbonate product to prepare a sodium carbonate product;

[0011] (3) the mother liquor II produced in step (2) reacts with the calcium oxide produced in step (1) to convert bicarbonate ions into calcium carbonate precipitate, and the solid-liquid separation is performed to obtain calcium carbonate and carbon removal mother liquor II, and the calcium carbonate is returned to step (1) for calcination to produce carbon dioxide and calcium oxide;

[0012] (4) reacting the carbon removal mother liquor II produced in step (3) with the calcium oxide produced in step (1) to convert ionic ammonia into ammonia gas, and then undergoing deamination treatment to produce ammonia gas. The sulfate radicals and calcium ions are converted into a slurry containing dihydrate gypsum crystals, and the solid-liquid separation is performed to obtain dihydrate gypsum and the mother liquor I;

[0013] (5) introducing the carbon dioxide produced in step (1) into the mother liquor I produced in step (4), or directly adding the sodium carbonate product produced in step (2), separating the solid and liquid to obtain calcium carbonate and the decalcified mother liquor I, and returning the calcium carbonate to step (1) for calcination to produce calcium oxide and carbon dioxide;

[0014] (6) introducing ammonia produced in step (4) into the decalcified mother liquor I produced in step (5) to obtain an ammoniated mother liquor I, and returning the ammoniated mother liquor I to step (2) to undergo a carbonization reaction with sodium sulfate and carbon dioxide;

[0015] (7) The dihydrate gypsum produced in step (4) is made into high-strength gypsum under the action of an accelerator.

[0016] Furthermore, in step (2), the total ammonia content in the ammoniated mother liquor I is 4.5-5.5 mol / L, and the temperature of the ammoniated mother liquor I is controlled at 30°C-40°C; the molar ratio of sodium sulfate, carbon dioxide and total ammonia in the ammoniated mother liquor I is (0.2-0.8):(0.5-2):(0.5-2); the temperature of the slurry is controlled at 30-40°C; and the free ammonia content in the mother liquor II is 1.1-1.2 mol / L.

[0017] Furthermore, in step (2), the water content of the sodium bicarbonate product is 5-20%; and the calcination temperature is 200-280°C.

[0018] Furthermore, in step (3), the molar ratio of bicarbonate to calcium oxide in the mother liquor II is 1:0.5-2, the reaction temperature is 40-100° C., and the reaction time is 0.5-6 h.

[0019] Furthermore, in step (4), the molar ratio of total ammonia to calcium oxide in the carbon removal mother liquor II is 1:0.5-1, the reaction temperature is 40-100° C., and the reaction time is 0.5-6 h.

[0020] Furthermore, in step (4), the deamination treatment includes ammonia evaporation, stripping, and natural volatilization.

[0021] Furthermore, in step (4), the total ammonia content in the mother liquor I is 0.001-0.002 mol / L, and the calcium ion content is 10-1000 mg / L.

[0022] Furthermore, in step (5), the molar ratio of calcium ions to carbon dioxide or sodium carbonate in the mother liquor I is 1:0.5-2; and the temperature of the mother liquor I is controlled at 40-100°C.

[0023] Furthermore, in step (6), the temperature of the decalcified mother liquor I is 25-30° C., and the total ammonia content in the ammoniated mother liquor I is 4.5-5.5 mol / L.

[0024] Furthermore, in step (7), the accelerator is selected from one or more of sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, magnesium nitrate, magnesium chloride, aluminum chloride, and aluminum nitrate. Based on the mass of dihydrate gypsum, the amount of any one of the accelerators is 0.2-4.0 mol / kg, the reaction solid-liquid ratio is 0.5-4:1, the reaction temperature is 50-100°C, and the reaction time is 0.5-5h.

[0025] Compared with the prior art, this application has at least the following beneficial effects:

[0026] 1. This application has the advantages of high resource utilization and no secondary pollution. Compared with the traditional sodium chloride Solvay process, the utilization rate of sodium in the Solvay process is about 70%, while this process is close to 100%; the Solvay process produces about 5.0-6.0m3 of high-salt wastewater (containing sodium chloride and calcium chloride). 3 / t soda ash. This process can achieve water balance and no waste liquid is discharged.

[0027] 2. The economic benefits of this application are outstanding. The traditional sodium chloride Solvay alkali production process only produces one product, soda ash, and calcium resources and part of the sodium resources are discharged as high-salt wastewater. The calcium ions and sulfate ions of this application are used to produce high-strength gypsum, with an output of about 1.2 tons / ton of soda ash, which increases the economic benefits by about 900-1200 yuan / ton. In addition, since this process does not discharge wastewater, the ammonia loss of this process is less than 0.2kg ammonia / ton of soda ash, compared with 1.0-1.5kg ammonia / ton of soda ash in the traditional Solvay process.

[0028] 3. The traditional process of high-strength gypsum is to steam-refine under saturated water vapor at 124°C at 1.3 atmospheres. In this application, when a crystallization inducer is used, it can be carried out at normal pressure and 50-100°C, which has a great cost advantage.

[0029] In summary, this application uses industrial waste salt or low-value calcium sulfate and calcium carbonate as raw materials to produce high-value-added products such as sodium carbonate and high-strength gypsum. The process is simple, with low investment and operating costs. The process operates at room or medium temperatures, without any low-temperature crystallization, resulting in stable operation and simple operation. Ammonia circulates as a medium in the system, eliminating wastewater discharge and significantly reducing ammonia loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more intuitively illustrate the prior art and the present application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be considered as limiting conditions for implementing the present application; for example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are capable of easily making routine adjustments or further optimizations to the addition / reduction / attribution division, specific shapes, positional relationships, connection methods, dimensional ratios, etc. of certain units (components).

[0031] FIG1 is a process flow chart for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials provided in this application. DETAILED DESCRIPTION

[0032] The following specific embodiments illustrate the implementation of this application. Those familiar with the art can easily understand the other advantages and functions of this application from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of this application, but not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] As shown in Figure 1, the process flow is as follows: calcium carbonate is calcined to obtain calcium oxide and carbon dioxide, which are then absorbed by ammonia to obtain ammoniated mother liquor I. The ammoniated mother liquor I reacts with sodium sulfate and carbon dioxide to produce sodium bicarbonate through carbonization, which is separated to obtain a sodium bicarbonate product and mother liquor II. The sodium bicarbonate product is calcined to obtain a sodium carbonate product. Mother liquor II is decarbonized and deaminated to obtain ammonia, dihydrate gypsum and mother liquor I. Dihydrate gypsum reacts with a accelerator to obtain high-strength gypsum (α-hemihydrate gypsum). Mother liquor I is decalcified and absorbed by ammonia to obtain ammoniated mother liquor I, and ammoniated mother liquor I is subjected to the next round of cyclic production.

[0034] The main reactions of this process include:

[0035] ①Calcium carbonate calcination: CaCO3→CaO+CO2

[0036] ② Sodium sulfate ammoniated and carbonized to produce sodium bicarbonate:

[0037] Na2SO4+2H2O+2NH3+CO2→(NH4)2SO4+2NaHCO3↓

[0038] ③ Calcination of sodium bicarbonate: 2NaHCO3→Na2CO3+H2O+CO2↑

[0039] ④Calcification slurry: CaO+H2O→Ca(OH)2

[0040] ⑤ Sodium sulfate carbonization mother liquor II decarbonization: HCO3 - +Ca 2+ →CaCO3↓+OH -

[0041] ⑥ Ammonia evaporation from carbon removal mother liquor II: (NH4)2SO4+Ca(OH)2→NH3↑+CaSO4·2H2O (natural gypsum)

[0042] ⑦ Preparation of high-strength gypsum from dihydrate gypsum: CaSO4·2H2O (natural gypsum) → CaSO4·1 / 2H2O (α-type high-strength gypsum)

[0043] ⑧ Calcium removal from mother liquor I: Ca 2+ +CO3 2- =CaCO3↓, or Ca 2+ +CO2+H2O=CaCO3↓+2H +

[0044] Overall reaction formula: Na2SO4+CaCO3→CaSO4↓+Na2CO3↓

[0045] The process includes the following steps:

[0046] (1) Calcium carbonate is calcined at 800-1200°C to produce calcium oxide and carbon dioxide.

[0047] (2) The mother liquor I is ammoniated by a three-phase reaction with sodium sulfate and carbon dioxide to obtain sodium bicarbonate. Sodium bicarbonate has a low solubility and precipitates after saturation to form a slurry containing sodium bicarbonate crystals. The slurry is filtered, washed, dehydrated, dried or calcined (200-280° C.) to obtain a qualified baking soda or soda ash product.

[0048] In some specific embodiments, the total ammonia content in the ammoniation mother liquor I is 4.5-5.5 mol / L, and the temperature is 30°C-40°C. The molar ratio of sodium sulfate, carbon dioxide, and the total ammonia in the ammoniation mother liquor I is (0.2-0.8):(0.5-2):(0.5-2). The temperature of the slurry is controlled at 30-40°C, and the concentration of free ammonia in the mother liquor II obtained by solid-liquid separation of the slurry is reduced to 1.1-1.2 mol / L.

[0049] (3) After separating the sodium bicarbonate crystals, a large amount of bicarbonate exists in the mother liquor II. First, calcium oxide is added. The calcium oxide dissolves in water to form calcium hydroxide. The calcium hydroxide reacts with the bicarbonate in the mother liquor II to form calcium carbonate. The reaction is filtered to obtain calcium carbonate and decarbonization mother liquor II. The calcium carbonate can be calcined to produce carbon dioxide and calcium oxide. Calcium oxide is further added to the decarbonization mother liquor II to react with ions and ammonia, which is converted into free ammonia and ammonia gas is obtained through deamination treatment. The sulfate is converted into slightly soluble dihydrate gypsum slurry. The mother liquor I and dihydrate gypsum crystals are obtained through solid-liquid separation.

[0050] In some specific embodiments, the molar ratio of bicarbonate to calcium oxide in mother liquor II is 1:0.5-2, the reaction temperature is 40-100°C, and the reaction time is 0.5-6 hours. The molar ratio of total ammonia to calcium oxide in carbon removal mother liquor II is 1:0.5-1, the reaction temperature is 40-100°C, and the reaction time is 0.5-6 hours. Ammonia can be removed by ammonia evaporation, stripping, or natural volatilization. The ammonia evaporation operation is performed at a temperature of 40-100°C. The stripping temperature is the reaction tank temperature and is not controlled. Air, oxygen, or nitrogen can be used as the gas source for stripping. Natural volatilization utilizes the heat released by the reaction of calcium oxide with water to promote the volatilization of ammonia. After solid-liquid separation, the total ammonia content in mother liquor I is 0.001-0.002 mol / L, and the calcium ion content is 10-1000 mg / L.

[0051] (4) In order to prevent the residual calcium in the mother liquor I from causing scaling on the equipment in the multiphase reaction process for preparing sodium bicarbonate and affecting the purity of the product, the mother liquor I needs to be decalcified. Carbon dioxide or sodium carbonate is used for decalcification. After solid-liquid separation, the obtained precipitated calcium carbonate can be calcined to produce CaO and CO2. The decalcified mother liquor I is subjected to ammonia absorption, and the obtained aminated mother liquor I reacts with sodium sulfate and carbon dioxide to prepare a baking soda product.

[0052] In some specific embodiments, the amount of carbon dioxide introduced needs to be controlled to ensure that carbonate ions generated after carbon dioxide dissolves in water will not be converted into bicarbonate ions. The molar ratio of calcium ions to carbon dioxide or sodium carbonate in the mother liquor I is 1:0.5-2, and the temperature of the mother liquor I is 40-100° C. After the decalcified mother liquor I is cooled to 25-30° C., ammonia absorption is directly performed to obtain an ammoniated mother liquor I with a total ammonia concentration of 4.5-5.5 mol / L for the carbonization reaction in step (2), thereby achieving water balance.

[0053] (5) Dihydrate gypsum is converted into high-strength gypsum in the presence of accelerator and water.

[0054] In some specific embodiments, the accelerator includes one or more of sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, magnesium nitrate, magnesium chloride, aluminum chloride, and aluminum nitrate. Based on the mass of dihydrate gypsum, the amount of any of the accelerators is 0.2-4.0 mol / kg, the reaction solid-to-liquid ratio (volume ratio of dihydrate gypsum to water) is 0.5-4:1, the reaction temperature is 50-100°C, and the reaction time is 0.5-5 hours.

[0055] Example 1

[0056] This embodiment provides a method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials. The production process includes the following steps:

[0057] (1) Calcium carbonate is calcined to produce calcium oxide and carbon dioxide.

[0058] (2) Sodium sulfate is added to an ammonia-containing mother liquor I having a total ammonia content of 5.0 mol / L and a temperature of 35° C., and carbon dioxide produced in step (1) is introduced, and the molar ratio of sodium sulfate, carbon dioxide, and total ammonia in the ammonia-containing mother liquor I is controlled to be 0.5:1:1 to obtain a slurry containing sodium bicarbonate crystals, and the slurry temperature is controlled at 30° C. The slurry is subjected to solid-liquid filtration to obtain a sodium bicarbonate product and a mother liquor II, wherein the concentration of free ammonia in the mother liquor II is reduced to 1.1 mol / L, and the obtained sodium bicarbonate product is washed, dehydrated, dried, or calcined to obtain a qualified baking soda or soda ash product.

[0059] (3) adding calcium oxide produced in step (1) to the mother liquor II after separating the sodium bicarbonate crystals in step (2), wherein the molar ratio of bicarbonate to calcium oxide in the mother liquor II is 1:1, the reaction temperature is 80° C., the reaction time is 2 h, and the reaction is carried out after filtering. The calcium oxide produced in step (1) is added to the obtained liquid phase decarbonization mother liquor II, wherein the molar ratio of total ammonia to calcium oxide in the decarbonization mother liquor II is 1:0.8, the reaction temperature is 80° C., the reaction time is 3 h, and the reaction is carried out after filtering to obtain a mother liquor I having a total ammonia concentration of 0.0015 mol / L and a calcium ion content of 210 mg / L and dihydrate gypsum crystals.

[0060] (4) CO2 is introduced into the mother liquor I produced in step (3) to remove excess calcium. The temperature of the mother liquor I is controlled at 50°C. 2+ The molar ratio of calcium carbonate to CO2 is 1:1. The generated calcium carbonate is filtered and calcined to produce CaO and CO2. The resulting liquid decalcified mother liquor I is cooled to 25°C and subjected to ammonia absorption to form an ammoniated mother liquor I with a total ammonia concentration of 5.0 mol / L. This ammoniated mother liquor I is used for the carbonization reaction in step (2).

[0061] (5) The dihydrate gypsum formed in step (3) is converted into high-strength gypsum (α hemihydrate gypsum) with sodium chloride and aluminum nitrate in the presence of water. The amounts of sodium chloride and aluminum nitrate used are 0.2 mol / kg and 4.0 mol / kg, respectively, based on the mass of the dihydrate gypsum. The reaction solid-liquid ratio is 2:1, the reaction temperature is 70°C, and the reaction time is 3 h.

[0062] The conversion rate of baking soda or soda ash products obtained by this process is greater than 90%, and the product purity is greater than 98%. The conversion rate of high-strength gypsum products is greater than 90%, and the purity is greater than 96%.

[0063] Example 2

[0064] This embodiment provides a method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials. The production process includes the following steps:

[0065] (1) Calcium carbonate is calcined to produce calcium oxide and carbon dioxide.

[0066] (2) adding sodium sulfate to an ammonia-containing mother liquor I having a total ammonia content of 4.5 mol / L and a temperature of 40° C., and introducing carbon dioxide produced in step (1), controlling the molar ratio of sodium sulfate, carbon dioxide, and total ammonia in the ammonia-containing mother liquor I to be 0.8:1:1, and obtaining a slurry containing sodium bicarbonate crystals, wherein the temperature of the slurry is controlled at 35° C., performing solid-liquid filtration on the slurry to obtain a sodium bicarbonate product and a mother liquor II, wherein the concentration of free ammonia in the mother liquor II is reduced to 1.1 mol / L, and washing, dehydrating, drying, or calcining the obtained sodium bicarbonate product to obtain a qualified baking soda or soda ash product.

[0067] (3) adding the calcium oxide produced in step (1) to the mother liquor II after separating the sodium bicarbonate crystals in step (2), wherein the molar ratio of bicarbonate to calcium oxide in the mother liquor II is 1:2, the reaction temperature is 50° C., the reaction time is 1 h, and the reaction is carried out after filtering. The calcium oxide produced in step (1) is added to the obtained liquid phase decarbonization mother liquor II, wherein the molar ratio of total ammonia to calcium oxide in the decarbonization mother liquor II is 1:1, the reaction temperature is 60° C., the reaction time is 3 h, and the reaction is carried out after filtering to obtain a mother liquor I having a total ammonia concentration of 0.0012 mol / L and a calcium ion content of 350 mg / L and dihydrate gypsum crystals.

[0068] (4) Sodium carbonate was added to the mother liquor I produced in step (3) to remove excess calcium. The temperature of the mother liquor I was controlled at 60°C. 2+ :CO3 2- The molar ratio is 1:1. The generated calcium carbonate is filtered and calcined to produce CaO and CO2. The resulting liquid decalcified mother liquor I is cooled to 25°C and subjected to ammonia absorption to form an ammoniated mother liquor I with a total ammonia concentration of 4.5 mol / L, which is then used for the carbonization reaction in step (2).

[0069] (5) The dihydrate gypsum formed in step (3) is converted into high-strength gypsum (α-hemihydrate gypsum) with sodium chloride and magnesium chloride in the presence of water. The amounts of sodium chloride and magnesium chloride used are 0.5 mol / kg and 3.0 mol / kg, respectively, based on the mass of the dihydrate gypsum. The reaction solid-liquid ratio is 1:1, the reaction temperature is 80°C, and the reaction time is 4 hours.

[0070] The conversion rate of baking soda or soda ash products obtained by this process is greater than 95%, and the product purity is greater than 98%. The conversion rate of high-strength gypsum products is greater than 90%, and the purity is greater than 96%.

[0071] Example 3

[0072] This embodiment provides a method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials. The production process includes the following steps:

[0073] (1) Calcium carbonate is calcined to produce calcium oxide and carbon dioxide.

[0074] (2) adding sodium sulfate to an ammonia-containing mother liquor I having a total ammonia content of 5.5 mol / L and a temperature of 30° C., and introducing carbon dioxide from step (1), controlling the molar ratio of sodium sulfate, carbon dioxide, and ammonia in the mother liquor I after ammoniation to be 0.8:1.5:1.5, to obtain a slurry containing sodium bicarbonate crystals, and controlling the temperature of the slurry at 30° C., performing solid-liquid filtration on the slurry to obtain a sodium bicarbonate product and a mother liquor II, wherein the concentration of free ammonia in the mother liquor II is reduced to 1.1 mol / L, and washing, dehydrating, drying, or calcining the obtained sodium bicarbonate product to obtain a qualified baking soda or soda ash product.

[0075] (3) adding the calcium oxide produced in step (1) to the mother liquor II after separating the sodium bicarbonate crystals in step (2), wherein the molar ratio of bicarbonate to calcium oxide in the mother liquor II is 1:0.5, the reaction temperature is 60° C., the reaction time is 2 h, and the reaction is carried out after filtering. The calcium oxide produced in step (1) is added to the obtained liquid phase decarbonization mother liquor II, wherein the molar ratio of total ammonia to calcium oxide in the decarbonization mother liquor II is 1:0.8, the reaction temperature is 60° C., the reaction time is 5 h, and the reaction is carried out after filtering to obtain a mother liquor I having a total ammonia concentration of 0.0018 mol / L and a calcium ion content of 560 mg / L and dihydrate gypsum crystals.

[0076] (4) CO2 is introduced into the mother liquor I produced in step (3) to remove excess calcium. The temperature of the mother liquor I is controlled at 40°C. 2+ The molar ratio of calcium carbonate to CO2 is 1:1. The generated calcium carbonate is filtered and calcined to produce CaO and CO2. The resulting liquid decalcified mother liquor I is cooled to 30°C and subjected to ammonia absorption to form an ammoniated mother liquor I with a total ammonia concentration of 5.0 mol / L, which is used for the carbonization reaction in step (2).

[0077] (5) The dihydrate gypsum formed in step (3) is converted into high-strength gypsum (α-hemihydrate gypsum) by reacting with sodium chloride, potassium chloride, and sodium nitrate in the presence of water. The amounts of sodium chloride, potassium chloride, and sodium nitrate used are 1 mol / kg, 1 mol / kg, and 4.0 mol / kg, respectively, based on the mass of the dihydrate gypsum. The reaction solid-liquid ratio is 2:1, the reaction temperature is 70° C., and the reaction time is 2 h.

[0078] The conversion rate of baking soda or soda ash products obtained by this process is greater than 90%, and the product purity is greater than 98%. The conversion rate of high-strength gypsum products is greater than 90%, and the purity is greater than 96%.

[0079] The technical features of the above embodiments can be combined arbitrarily (as long as there is no contradiction in the combination of these technical features). In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described; these embodiments that are not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials, characterized in that: The method comprises the following steps: (1) Calcium carbonate is calcined to produce calcium oxide and carbon dioxide; (2) ammoniating the mother liquor I, sodium sulfate and the carbon dioxide produced in step (1) to undergo a carbonization reaction to produce a slurry containing sodium bicarbonate crystals, performing solid-liquid separation to obtain a sodium bicarbonate product and the mother liquor II, and calcining the sodium bicarbonate product to prepare a sodium carbonate product; (3) the mother liquor II produced in step (2) reacts with the calcium oxide produced in step (1) to convert bicarbonate ions into calcium carbonate precipitate, and the solid-liquid separation is performed to obtain calcium carbonate and carbon removal mother liquor II, and the calcium carbonate is returned to step (1) for calcination to produce carbon dioxide and calcium oxide; (4) reacting the carbon removal mother liquor II produced in step (3) with the calcium oxide produced in step (1) to convert ionic ammonia into ammonia gas, and then undergoing deamination treatment to produce ammonia gas. The sulfate radicals and calcium ions are converted into a slurry containing dihydrate gypsum crystals, and the solid-liquid separation is performed to obtain dihydrate gypsum and the mother liquor I; (5) introducing the carbon dioxide produced in step (1) into the mother liquor I produced in step (4), or directly adding the sodium carbonate product produced in step (2), separating the solid and liquid to obtain calcium carbonate and the decalcified mother liquor I, and returning the calcium carbonate to step (1) for calcination to produce calcium oxide and carbon dioxide; (6) introducing ammonia produced in step (4) into the decalcified mother liquor I produced in step (5) to obtain an ammoniated mother liquor I, and returning the ammoniated mother liquor I to step (2) to undergo a carbonization reaction with sodium sulfate and carbon dioxide; (7) The dihydrate gypsum produced in step (4) is made into high-strength gypsum under the action of an accelerator.

2. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (2), the total ammonia content in the ammoniated mother liquor I is 4.5-5.5 mol / L, and the temperature of the ammoniated mother liquor I is controlled at 30°C-40°C; the molar ratio of sodium sulfate, carbon dioxide and total ammonia in the ammoniated mother liquor I is (0.2-0.8):(0.5-2):(0.5-2); the temperature of the slurry is controlled at 30-40°C; and the free ammonia content in the mother liquor II is 1.1-1.2 mol / L.

3. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (2), the water content of the sodium bicarbonate product is 5-20%; and the calcination temperature is 200-280°C.

4. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (3), the molar ratio of bicarbonate to calcium oxide in the mother liquor II is 1:0.5-2, the reaction temperature is 40-100° C., and the reaction time is 0.5-6 h.

5. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (4), the molar ratio of total ammonia to calcium oxide in the carbon removal mother liquor II is 1:0.5-1, the reaction temperature is 40-100° C., and the reaction time is 0.5-6 h.

6. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (4), the deamination treatment includes ammonia evaporation, stripping, and natural volatilization.

7. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (4), the total ammonia content in the mother liquor I is 0.001-0.002 mol / L, and the calcium ion content is 10-1000 mg / L.

8. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (5), the molar ratio of calcium ions to carbon dioxide or sodium carbonate in the mother liquor I is 1:0.5-2; and the temperature of the mother liquor I is controlled at 40-100°C.

9. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (6), the temperature of the decalcified mother liquor I is 25-30° C., and the total ammonia content in the ammoniated mother liquor I is 4.5-5.5 mol / L.

10. The method for producing soda ash and high-strength gypsum using calcium carbonate and sodium sulfate as raw materials according to claim 1, characterized in that: In step (7), the accelerator is selected from one or more of sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, magnesium nitrate, magnesium chloride, aluminum chloride, and aluminum nitrate. Based on the mass of dihydrate gypsum, the amount of any one of the accelerators is 0.2-4.0 mol / kg, the reaction solid-liquid ratio is 0.5-4:1, the reaction temperature is 50-100° C., and the reaction time is 0.5-5 h.

Images