A method, apparatus, and application for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution.

Abstract

This invention relates to the technical field of processing calcium-magnesium concentrate and crude calcium nitrate solution, and particularly to a method, apparatus, and application for preparing molten salt-grade sodium nitrate and potassium nitrate using calcium-magnesium concentrate and crude calcium nitrate solution. This application discloses a method for preparing molten salt-grade sodium nitrate and potassium nitrate using calcium-magnesium concentrate and crude calcium nitrate solution, comprising the following steps: S1. Decalcification stage; S2. Demagnesification stage; S3. Concentration and crystallization stage, concentrating and crystallizing the second filtrate to obtain primary sodium nitrate and sodium mother liquor; recrystallizing the primary sodium nitrate to obtain molten salt-grade sodium nitrate; S4. Resizing stage; S5. Production of potassium nitrate, with sodium chloride as a byproduct. The method and apparatus described in this application, using sodium sulfate, crude calcium nitrate solution, calcium-magnesium concentrate, and lime as raw materials, can produce high-value-added molten salt-grade sodium nitrate and molten salt-grade potassium nitrate, and has the advantage of a simple process flow, while also producing sodium chloride and gypsum as byproducts.

Description

Technical Field

[0001] This invention relates to the technical field of processing calcium-magnesium concentrate and crude calcium nitrate solution, and in particular to a method, apparatus and application for preparing molten salt grade sodium nitrate and potassium nitrate using calcium-magnesium concentrate and crude calcium nitrate solution. Background Technology

[0002] Sodium nitrate is a raw material for manufacturing mining explosives, widely used in the glass manufacturing industry and enamel production, used as a metal cleaning agent in the machinery industry, used as a heat treatment agent for steelmaking and aluminum alloys in the metallurgical industry, used as a decolorizing agent for molten caustic soda, used as a raw material for manufacturing potassium nitrate and picric acid, and is gradually replacing other chemical raw materials as a fracturing agent in oil extraction.

[0003] In solar thermal power generation, molten salt is a crucial system. Molten salt is primarily potassium nitrate or a mixture mainly composed of sodium nitrate. Due to its corrosiveness to equipment and stringent requirements, the quality of the potassium nitrate used in molten salt is extremely stringent. Besides high purity, the content of impurity ions, especially chloride ions (Cl), must be extremely low. - The content of ) is required to be below 0.01%.

[0004] In phosphate mining and fertilizer processing enterprises, chemical beneficiation byproducts such as calcium-magnesium concentrate and crude calcium nitrate solution contain large amounts of calcium, magnesium, potassium and other ionic compounds. If these calcium-magnesium concentrate and crude calcium nitrate solution are not treated and are discharged directly, it will result in a large waste of resources and pollution to the environment.

[0005] Therefore, it is necessary to provide a method, apparatus, and application for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method, apparatus, and application for preparing molten salt-grade sodium nitrate and potassium nitrate using calcium-magnesium concentrate and crude calcium nitrate solution. Using sodium sulfate, crude calcium nitrate solution, calcium-magnesium concentrate, and lime as raw materials, it can produce high-value-added molten salt-grade sodium nitrate and molten salt-grade potassium nitrate. It has the advantage of simple process flow and can also produce sodium chloride and gypsum as byproducts.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] The first objective of this invention is to provide a method for preparing molten salt-grade sodium nitrate and potassium nitrate using a calcium-magnesium concentrate and a crude calcium nitrate solution, comprising the following steps:

[0009] S1. Decalcification Section

[0010] The calcium-magnesium concentrate, crude calcium nitrate solution, and sodium sulfate were thoroughly mixed; then lime was added to carry out the decalcification reaction; after the reaction was completed, the mixture was filtered to obtain gypsum filter cake and the first filtrate.

[0011] S2. Demagnesification Section

[0012] The first filtrate and soda ash were thoroughly mixed to carry out a magnesium precipitation reaction; after the reaction was completed, the mixture was filtered to obtain a magnesium carbonate filter cake and a second filtrate.

[0013] S3. Concentration and Crystallization Section

[0014] The second filtrate was concentrated and crystallized to obtain primary sodium nitrate and sodium mother liquor; the primary sodium nitrate was recrystallized to obtain molten salt grade sodium nitrate.

[0015] S4. Re-slurry section

[0016] The magnesium carbonate filter cake is mixed with water and pulped, then filtered and dried to obtain refined magnesium carbonate.

[0017] S5. Production of potassium nitrate, with sodium chloride as a byproduct.

[0018] After thoroughly mixing sodium mother liquor and potassium chloride, the mixture is concentrated and crystallized to obtain potassium nitrate precipitate and potassium nitrate mother liquor.

[0019] The potassium nitrate mother liquor was concentrated and crystallized to obtain sodium chloride precipitate.

[0020] Furthermore, the amount of Glauber's salt added is 0.01-0.02 times the weight of the calcium and magnesium concentrate.

[0021] Furthermore, in step S1, the decalcification reaction is carried out at a temperature of 80-90°C for 10-12 hours.

[0022] Furthermore, in step S2, the primary sodium nitrate magnesium precipitation reaction is carried out at 80-90°C for 5-8 hours.

[0023] Furthermore, in step S2, the feeding ratio of the first filtrate and soda ash is calculated according to the molar ratio, and the ratio of magnesium ions in the first filtrate to carbonate ions in the soda ash is 1:1.1-1.2.

[0024] Furthermore, in step S3, the recrystallization process involves mixing primary sodium nitrate with 0.3-0.5 times the weight of primary sodium nitrate in water and dissolving it at 80-90°C; after dissolution, the temperature is lowered to 30-40°C for crystallization.

[0025] Furthermore, in step S4, the magnesium carbonate filter cake is mixed and pulped with 0.5-1 times the weight of the magnesium carbonate filter cake.

[0026] Furthermore, in step S5, the second filtrate and potassium chloride are thoroughly mixed and then concentrated and crystallized at 80-90°C.

[0027] Furthermore, in step S5, the potassium nitrate mother liquor is concentrated and crystallized at 80-90°C to obtain sodium chloride precipitate.

[0028] A second objective of this invention is to provide an apparatus for preparing molten salt-grade sodium nitrate and potassium nitrate using calcium-magnesium concentrate and crude calcium nitrate solution, applicable to the method described above. The apparatus includes a decalcification section unit, a demagnesification section unit, a concentration and crystallization section unit, a reslurry section unit, and a potassium nitrate production unit connected by pipelines.

[0029] The decalcification section unit is used to carry out a decalcification reaction on calcium-magnesium concentrate, crude calcium nitrate solution, sodium sulfate, and lime.

[0030] The magnesium removal section unit is used to perform a magnesium removal reaction on the first filtrate and soda ash;

[0031] The concentration and crystallization section unit is used to concentrate and crystallize the second filtrate;

[0032] The repulping section unit is used to pulp the magnesium carbonate filter cake.

[0033] The potassium nitrate production unit is used to convert sodium mother liquor into mother liquor containing potassium nitrate and sodium chloride.

[0034] The third objective of this application is to provide an application of molten salt grade sodium nitrate and molten salt grade potassium nitrate in solar thermal power generation, wherein the molten salt grade sodium nitrate and molten salt grade potassium nitrate are obtained by the preparation method or apparatus described above.

[0035] Preferably, the molten salt grade sodium nitrate contains ≥99.9% sodium nitrate, ≤0.001% water-insoluble matter by weight, ≤0.005% chloride by weight, ≤0.005% sodium carbonate by weight, ≤0.005% calcium nitrate by weight, ≤0.005% magnesium nitrate by weight, and ≤0.001% iron by weight.

[0036] Preferably, the molten salt grade potassium nitrate contains ≥99.9% potassium nitrate, ≤0.001% water-insoluble matter by weight, ≤0.005% chloride by weight, ≤0.005% carbonate by weight, ≤0.005% ammonium salt by weight, ≤0.005% sulfate by weight, and ≤0.001% iron by weight.

[0037] The beneficial effects of this invention are as follows:

[0038] 1. The method and apparatus described in this application use Glauber's salt, primary nitrate solution, calcium magnesium concentrate, and lime as raw materials to produce sodium nitrate and potassium nitrate. The process is simple and can also produce sodium chloride and gypsum as byproducts.

[0039] 2. The method described in this application has a simple production process, no special requirements for process equipment, is easy for production workers to control, and can quickly reach production targets.

[0040] 3. The method described in this application can efficiently produce high-value molten salt grade sodium nitrate and molten salt grade potassium nitrate, with low manufacturing costs and strong market competitiveness. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] Figure 1 This is a process flow diagram of a method for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution, as described in this application. Detailed Implementation

[0043] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0044] As used herein, “and / or” includes all combinations of any and one or more of the associated listed items. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. Further understanding is needed; when used in this specification, “comprising” designates the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0045] The applicant currently has a 150,000-ton / year chemical mineral processing plant, producing approximately 100,000 tons of calcium and magnesium concentrate as a byproduct annually. Due to sales restrictions on liquid fertilizers and medium-element fertilizers, and the inability to effectively utilize the calcium and magnesium concentrate, the plant frequently experiences overstocking, leading to shutdowns of the chemical mineral processing plant.

[0046] In addition, the crude calcium nitrate solution, a byproduct of nitrate phosphate fertilizer, is used to produce ammonium calcium nitrate fertilizer, resulting in a large backlog due to market reasons, which ties up a lot of warehouse space and working capital.

[0047] Current solar thermal power generation and energy storage devices require large amounts of sodium nitrate and potassium nitrate as heat storage materials. In order to quickly and efficiently consume calcium magnesium concentrate and crude calcium nitrate solution, and obtain high-value by-products, this application provides a method, apparatus and application for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution.

[0048] like Figure 1 The method shown includes the following steps for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution:

[0049] S1. Decalcification Section

[0050] The calcium-magnesium concentrate, crude calcium nitrate solution, and sodium sulfate were thoroughly mixed; then lime was added, and the decalcification reaction was carried out at 80-90℃ for 10-12 hours; after the reaction was completed, the mixture was filtered to obtain gypsum filter cake and the first filtrate.

[0051] Specifically, calcium-magnesium concentrate, crude calcium nitrate solution, sodium sulfate (solid), and lime are fed in a mass ratio of 1:1-0.8:0.3-0.4:0.01-0.02. Through the decalcification section, calcium ions in the calcium-magnesium concentrate and the crude calcium nitrate solution are converted into gypsum, and the pH of the decalcified solution is adjusted to weakly alkaline.

[0052] S2. Demagnesification Section

[0053] The first filtrate and soda ash are thoroughly mixed and subjected to a magnesium precipitation reaction at 80-90℃ for 5-8 hours. After the reaction is completed, the mixture is filtered to obtain a magnesium carbonate filter cake and a second filtrate.

[0054] The ratio of magnesium ions in the first filtrate to carbonate ions in the soda ash, calculated according to the molar ratio, is 1:1.1-1.2.

[0055] Magnesium ions are removed from the first filtrate by converting them into magnesium carbonate precipitate.

[0056] S3. Concentration and Crystallization Section

[0057] The second filtrate is concentrated at 80-90℃. When the volume of the second filtrate is reduced to 1 / 3-1 / 2, the temperature is lowered to 30-40℃ for incubation and crystallization, followed by filtration to obtain primary sodium nitrate filter cake and sodium mother liquor. The primary sodium nitrate filter cake is mixed with 0.3-0.5 times its weight of water, dissolved and concentrated at 80-90℃. When the volume of the liquid is reduced to 1 / 3-1 / 2, the temperature is lowered to 30-40℃ for incubation and crystallization, followed by filtration to obtain refined sodium nitrate filter cake.

[0058] The primary sodium nitrate filter cake is obtained by concentrating the second filtrate from crystallization. This primary sodium nitrate filter cake is then recrystallized to obtain a refined sodium nitrate filter cake. The refined sodium nitrate filter cake is then dried to obtain molten salt grade sodium nitrate. The recrystallization of the primary sodium nitrate filter cake can be performed according to conventional sodium nitrate recrystallization procedures.

[0059] S4. Re-slurry section

[0060] At room temperature, magnesium carbonate filter cake is mixed with 0.5-1 times the weight of magnesium carbonate filter cake in water and pulped for 1-2 hours. After filtration and drying, refined magnesium carbonate is obtained.

[0061] S5. Production of potassium nitrate, with sodium chloride as a byproduct.

[0062] After thoroughly mixing sodium mother liquor and potassium chloride, the mixture is evaporated and concentrated at 80-90℃. When the volume of the liquid is reduced to 1 / 3-1 / 4, the temperature is lowered to 30-40℃ for heat preservation and crystallization. After filtration, primary potassium nitrate filter cake and potassium nitrate mother liquor are obtained.

[0063] The potassium nitrate mother liquor is evaporated and concentrated at 80-90℃. When the volume of the liquid is reduced to 1 / 2-2 / 3, the temperature is lowered to 30-40℃ for heat preservation and crystallization. After filtration, sodium chloride filter cake is obtained.

[0064] The primary potassium nitrate filter cake is recrystallized to obtain molten salt grade potassium nitrate. The specific recrystallization process for the primary potassium nitrate filter cake can be performed according to the conventional recrystallization process for potassium nitrate.

[0065] An apparatus for preparing molten salt grade sodium nitrate and potassium nitrate using calcium-magnesium concentrate and crude calcium nitrate solution, the apparatus comprising a decalcification section unit, a demagnesification section unit, a concentration and crystallization section unit, a reslurry section unit, and a potassium nitrate production unit connected by pipelines;

[0066] The decalcification section unit is used to carry out a decalcification reaction on calcium-magnesium concentrate, crude calcium nitrate solution, sodium sulfate, and lime.

[0067] The magnesium removal section unit is used to perform a magnesium removal reaction on the first filtrate and soda ash;

[0068] The concentration and crystallization section unit is used to concentrate and crystallize the second filtrate;

[0069] The repulping section unit is used to pulp the magnesium carbonate filter cake.

[0070] The potassium nitrate production unit is used to convert sodium mother liquor into mother liquor containing potassium nitrate and sodium chloride.

[0071] Specifically, the decalcification section unit includes a decalcification kettle, a first dissolving kettle, and a first filter connected by pipelines. The decalcification kettle is connected to the first filter. The first dissolving kettle is used to dissolve sodium sulfate to form a sodium sulfate solution. The decalcification kettle carries out the decalcification reaction. After the reaction is completed, the first filter is used for filtration to obtain gypsum filter cake and first filtrate.

[0072] Specifically, the magnesium removal section unit includes a settling tank, a second dissolving tank, and a second filter connected by pipelines; the first filtrate is introduced into the settling tank, and the soda ash solution dissolved in the second dissolving tank is introduced into the settling tank; the first filtrate and soda ash are thoroughly mixed in the settling tank to carry out the magnesium precipitation reaction; after the reaction is completed, the second filter is used for filtration to obtain magnesium carbonate filter cake and second filtrate;

[0073] Specifically, the concentration and crystallization section includes the first crystallization kettle and the second crystallization kettle;

[0074] The second filtrate is concentrated and crystallized in the first crystallization vessel to obtain primary sodium nitrate and sodium mother liquor; the primary sodium nitrate is recrystallized in the second crystallization vessel to obtain molten salt grade sodium nitrate.

[0075] Specifically, the resizing section unit includes a resizing tank, a fourth filter, and a dryer connected by pipelines; magnesium carbonate filter cake and water are introduced into the resizing tank for mixing and pulping; the fourth filter is used for filtration, and the dryer is used for drying to obtain solid magnesium carbonate (refined magnesium carbonate).

[0076] Specifically, the potassium nitrate production unit includes a conversion tank, a third filter, and a third crystallizer connected by pipelines. Sodium mother liquor and potassium chloride are thoroughly mixed in the conversion tank and then concentrated and crystallized. The third filter is used to obtain potassium nitrate precipitate and potassium nitrate mother liquor. The potassium nitrate mother liquor is introduced into the third crystallizer for concentrated crystallization to obtain sodium chloride precipitate.

[0077] The following three specific embodiments are listed to further illustrate the present invention:

[0078] Example 1

[0079] A method for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution includes the following steps:

[0080] S1. Decalcification Section

[0081] The calcium-magnesium concentrate, crude calcium nitrate solution, and sodium sulfate were thoroughly mixed; then lime was added, and the decalcification reaction was carried out at 80°C for 12 hours; after the reaction was completed, the mixture was filtered to obtain gypsum filter cake and the first filtrate.

[0082] Calcium magnesium concentrate, crude nitrate calcium solution, sodium sulfate (solid), and lime are fed in a mass ratio of 1:1:0.3:0.01.

[0083] S2. Demagnesification Section

[0084] The first filtrate and soda ash were thoroughly mixed and subjected to a magnesium precipitation reaction at 80°C for 8 hours. After the reaction was completed, the mixture was filtered to obtain a magnesium carbonate filter cake and a second filtrate.

[0085] The ratio of magnesium ions in the first filtrate to carbonate ions in the soda ash, calculated according to the molar ratio, is 1:1.1.

[0086] S3. Concentration and Crystallization Section

[0087] The second filtrate was concentrated at 80°C. When the volume of the second filtrate was reduced to 1 / 3, the temperature was lowered to 30°C for incubation and crystallization. The mixture was then filtered to obtain a primary sodium nitrate filter cake and a sodium mother liquor. The primary sodium nitrate filter cake was mixed with 0.3 times its weight of water and dissolved and concentrated at 80°C. When the volume of the liquid was reduced to 1 / 3, the temperature was lowered to 30°C for incubation and crystallization. The mixture was then filtered to obtain a refined sodium nitrate filter cake.

[0088] The primary sodium nitrate filter cake is recrystallized according to conventional sodium nitrate recrystallization methods, and then dried to obtain molten salt grade sodium nitrate.

[0089] S4. Re-slurry section

[0090] At room temperature, magnesium carbonate filter cake and 0.5 times the weight of magnesium carbonate filter cake in water are mixed and pulped for 2 hours. After filtration and drying, refined magnesium carbonate is obtained.

[0091] S5. Production of potassium nitrate, with sodium chloride as a byproduct.

[0092] After thoroughly mixing sodium mother liquor and potassium chloride, the mixture is evaporated and concentrated at 80°C. When the volume of the liquid is reduced to 1 / 3, the temperature is lowered to 30°C for heat preservation and crystallization. After filtration, primary potassium nitrate filter cake and potassium nitrate mother liquor are obtained.

[0093] The potassium nitrate mother liquor was evaporated and concentrated at 80°C. When the volume of the liquid was reduced to 1 / 2, the temperature was lowered to 30°C for heat preservation and crystallization. After filtration, sodium chloride filter cake was obtained.

[0094] The primary potassium nitrate filter cake was recrystallized and dried to obtain molten salt grade potassium nitrate.

[0095] Example 2

[0096] A method for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution includes the following steps:

[0097] S1. Decalcification Section

[0098] The calcium-magnesium concentrate, crude calcium nitrate solution, and sodium sulfate were thoroughly mixed; then lime was added, and the decalcification reaction was carried out at 90°C for 12 hours; after the reaction was completed, the mixture was filtered to obtain gypsum filter cake and the first filtrate.

[0099] Calcium magnesium concentrate, crude calcium nitrate solution, sodium sulfate (solid), and lime are added in a mass ratio of 1:0.8:0.4:0.02. The composition of the calcium magnesium concentrate is as follows:

[0100] S2. Demagnesification Section

[0101] The first filtrate and soda ash were thoroughly mixed and subjected to a magnesium precipitation reaction at 90°C for 5 hours. After the reaction was completed, the mixture was filtered to obtain a magnesium carbonate filter cake and a second filtrate.

[0102] The ratio of magnesium ions in the first filtrate to carbonate ions in the soda ash, calculated according to the molar ratio, is 1:1.2.

[0103] S3. Concentration and Crystallization Section

[0104] The second filtrate was concentrated at 90°C. When the volume of the second filtrate was reduced to 1 / 2, the temperature was lowered to 40°C for incubation and crystallization. The mixture was then filtered to obtain a primary sodium nitrate filter cake and a sodium mother liquor. The primary sodium nitrate filter cake was mixed with 0.5 times its weight of water and dissolved and concentrated at 90°C. When the volume of the liquid was reduced to 1 / 2, the temperature was lowered to 40°C for incubation and crystallization. The mixture was then filtered to obtain a refined sodium nitrate filter cake.

[0105] The primary sodium nitrate filter cake is recrystallized according to conventional sodium nitrate recrystallization methods, and then dried to obtain molten salt grade sodium nitrate.

[0106] S4. Re-slurry section

[0107] At room temperature, magnesium carbonate filter cake and water with an equal weight of magnesium carbonate filter cake are mixed and pulped for 2 hours. After filtration and drying, refined magnesium carbonate is obtained.

[0108] S5. Production of potassium nitrate, with sodium chloride as a byproduct.

[0109] After thoroughly mixing sodium mother liquor and potassium chloride, the mixture is evaporated and concentrated at 90°C. When the volume of the liquid is reduced to 1 / 4, the temperature is lowered to 40°C for heat preservation and crystallization. After filtration, primary potassium nitrate filter cake and potassium nitrate mother liquor are obtained.

[0110] The potassium nitrate mother liquor was evaporated and concentrated at 90°C. When the volume of the liquid was reduced to 2 / 3, the temperature was lowered to 40°C for heat preservation and crystallization. After filtration, sodium chloride filter cake was obtained.

[0111] The primary potassium nitrate filter cake was recrystallized and dried to obtain molten salt grade potassium nitrate.

[0112] Example 3

[0113] A method for preparing molten salt grade sodium nitrate and potassium nitrate using calcium magnesium concentrate and crude calcium nitrate solution includes the following steps:

[0114] S1. Decalcification Section

[0115] The calcium-magnesium concentrate, crude calcium nitrate solution, and sodium sulfate were thoroughly mixed; then lime was added, and the decalcification reaction was carried out at 85°C for 11 hours; after the reaction was completed, the mixture was filtered to obtain gypsum filter cake and the first filtrate.

[0116] Calcium magnesium concentrate, crude nitrate calcium solution, sodium sulfate (solid), and lime are added in a mass ratio of 1:0.9:0.35:0.015.

[0117] S2. Demagnesification Section

[0118] The first filtrate and soda ash were thoroughly mixed and subjected to a magnesium precipitation reaction at 85°C for 7 hours. After the reaction was completed, the mixture was filtered to obtain a magnesium carbonate filter cake and a second filtrate.

[0119] The ratio of magnesium ions in the first filtrate to carbonate ions in the soda ash, calculated according to the molar ratio, is 1:1.1.

[0120] S3. Concentration and Crystallization Section

[0121] The second filtrate was concentrated at 85°C. When the volume of the second filtrate was reduced to 1 / 3, the temperature was lowered to 35°C for incubation and crystallization. The mixture was then filtered to obtain a primary sodium nitrate filter cake and a sodium mother liquor. The primary sodium nitrate filter cake was mixed with 0.4 times its weight of water and dissolved and concentrated at 85°C. When the volume of the liquid was reduced to 1 / 3, the temperature was lowered to 35°C for incubation and crystallization. The mixture was then filtered to obtain a refined sodium nitrate filter cake.

[0122] The primary sodium nitrate filter cake is recrystallized according to conventional sodium nitrate recrystallization methods, and then dried to obtain molten salt grade sodium nitrate.

[0123] S4. Re-slurry section

[0124] At room temperature, magnesium carbonate filter cake and water with 0.8 times the weight of magnesium carbonate filter cake were mixed and pulped for 1.5 hours. After filtration and drying, refined magnesium carbonate was obtained.

[0125] S5. Production of potassium nitrate, with sodium chloride as a byproduct.

[0126] After thoroughly mixing sodium mother liquor and potassium chloride, the mixture is evaporated and concentrated at 85°C. When the volume of the liquid is reduced to 1 / 3, the temperature is lowered to 35°C for heat preservation and crystallization. After filtration, primary potassium nitrate filter cake and potassium nitrate mother liquor are obtained.

[0127] The potassium nitrate mother liquor was evaporated and concentrated at 85°C. When the volume of the liquid was reduced to 1 / 2, the temperature was lowered to 35°C for heat preservation and crystallization. After filtration, sodium chloride filter cake was obtained.

[0128] The primary potassium nitrate filter cake was recrystallized and dried to obtain molten salt grade potassium nitrate.

[0129] The components of the calcium and magnesium concentrate used in Examples 1-3 are as follows:

[0130] project HNO3 Ca(NO3)2 Mg(NO3)2 H3PO4 Weight content (%) 3.17 34.68 22.1 0.05

[0131] The composition of the crude calcium nitrate solution used is as follows:

[0132] project N P2O5 CaO pH Weight content (%) 5.77 0.02 16.24 7.33

[0133] The molten salt grade potassium nitrate and molten salt grade sodium nitrate prepared in steps 1-3 were subjected to the following performance tests, and the relevant results are summarized in Tables 1 and 2:

[0134] 1. The detection of potassium nitrate shall be carried out in accordance with GB / T 1918-2021 for industrial potassium nitrate;

[0135] 2. The detection of sodium nitrate shall be carried out in accordance with GB / T 4553-2016 for industrial sodium nitrate.

[0136] Table 1

[0137] content(%) Example 1 Example 2 Example 3 Sodium nitrate 99.95 99.98 99.96 Water-insoluble matter 0.0003 0.0005 0.0004 chloride 0.002 0.003 0.003 Sodium carbonate 0.003 0.004 0.003 Calcium nitrate 0.002 0.005 0.003 Magnesium nitrate 0.004 0.002 0.003 iron Not detected Not detected Not detected

[0138] Table 2

[0139] content(%) Example 1 Example 2 Example 3 potassium nitrate 99.92 99.97 99.93 Water-insoluble matter 0.0007 0.0008 0.0009 chloride 0.003 0.002 0.002 carbonates 0.0009 0.002 0.001 ammonium salts 0.0004 0.0003 0.0003 sulfates 0.0003 0.0004 0.0005 iron Not detected Not detected Not detected

[0140] As can be seen from Tables 1 and 2, the molten salt-grade potassium nitrate prepared in Examples 1-3 has a potassium nitrate content of 99.92-99.97%, a water-insoluble matter content of 0.0007-0.0009% by weight, a chloride content of 0.002-0.003% by weight, a carbonate content of 0.0009-0.002% by weight, an ammonium salt content of 0.0003-0.0004% by weight, and a sulfate content of 0.0003-0.0005% by weight. This meets the requirements for molten salt-grade potassium nitrate.

[0141] The molten salt grade sodium nitrate prepared in Examples 1-3 has a sodium nitrate content of 99.95-99.98%, a water-insoluble matter content of 0.0003-0.0005% by weight, a chloride content of 0.002-0.003% by weight, a sodium carbonate content of 0.003-0.004% by weight, a calcium nitrate content of 0.002-0.005% by weight, and a magnesium nitrate content of 0.002-0.004% by weight, meeting the requirements for molten salt grade sodium nitrate.

[0142] The above-described method for preparing molten salt-grade sodium nitrate and potassium nitrate using concentrated calcium and magnesium solutions and crude calcium nitrate solutions can produce 76,000 tons of sodium nitrate, 50,000 tons of potassium nitrate, 10,000 tons of magnesium carbonate, and 60,000 tons of powder (gypsum) annually. Based on prices of 2,641.9 yuan / ton for industrial sodium nitrate, 5,141.2 yuan / ton for agricultural potassium nitrate, 233.9 yuan / ton for powder materials, 1,285.6 yuan / ton for industrial magnesium carbonate, 3,039.9 yuan / ton for molten salt sodium nitrate, and 5,714.9 yuan / ton for molten salt potassium nitrate, the investment cost can be recovered in approximately two years, with an annual profit exceeding 70 million yuan.

[0143] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing molten salt-grade sodium nitrate and potassium nitrate using concentrated calcium and magnesium solution and crude calcium nitrate solution, characterized in that, Includes the following steps: S1. Decalcification Section The calcium-magnesium concentrate, crude calcium nitrate solution, and sodium sulfate were thoroughly mixed; then lime was added to carry out the decalcification reaction; after the reaction was completed, the mixture was filtered to obtain gypsum filter cake and the first filtrate; the mass ratio of calcium-magnesium concentrate, crude calcium nitrate solution, sodium sulfate, and lime was 1:1-0.8:0.3-0.4:0.01-0.02; the decalcification reaction temperature was 80-90℃ and the time was 10-12 hours. S2. Demagnesification Section The first filtrate and soda ash were thoroughly mixed to carry out a magnesium precipitation reaction. After the reaction was completed, the mixture was filtered to obtain a magnesium carbonate filter cake and a second filtrate. The magnesium precipitation reaction was carried out at 80-90℃ for 5-8 hours. S3. Concentration and Crystallization Section The second filtrate is concentrated and crystallized at 80-90℃ to obtain primary sodium nitrate and sodium mother liquor; the primary sodium nitrate is recrystallized to obtain molten salt grade sodium nitrate; the recrystallization process involves mixing primary sodium nitrate with 0.3-0.5 times the weight of primary sodium nitrate in water and dissolving it at 80-90℃; after dissolution, the temperature is lowered to 30-40℃ for crystallization. The molten salt grade sodium nitrate contains ≥99.9% sodium nitrate, ≤0.001% water-insoluble matter by weight, ≤0.005% chloride by weight, ≤0.005% sodium carbonate by weight, ≤0.005% calcium nitrate by weight, ≤0.005% magnesium nitrate by weight, and ≤0.001% iron by weight. S4. Re-slurry section The magnesium carbonate filter cake is mixed with water and pulped, then filtered and dried to obtain refined magnesium carbonate. S5. Production of potassium nitrate, with sodium chloride as a byproduct. After thoroughly mixing sodium mother liquor and potassium chloride, the mixture is concentrated and crystallized at 80-90℃ to obtain potassium nitrate precipitate and potassium nitrate mother liquor. The potassium nitrate mother liquor was concentrated and crystallized to obtain sodium chloride precipitate; The potassium nitrate contains ≥99.9% potassium nitrate, ≤0.001% water-insoluble matter by weight, ≤0.005% chloride by weight, ≤0.005% carbonate by weight, ≤0.005% ammonium salt by weight, ≤0.005% sulfate by weight, and ≤0.001% iron by weight.

2. The method according to claim 1, characterized in that, In step S2, the feeding ratio of the first filtrate and soda ash is calculated according to the molar ratio, and the ratio of magnesium ions in the first filtrate to carbonate ions in the soda ash is 1:1.1-1.

2.

3. The method according to claim 1, characterized in that, In step S4, Mix the magnesium carbonate filter cake with water at a ratio of 0.5 to 1 times the weight of the magnesium carbonate filter cake and pulverize.

4. The method according to claim 1, characterized in that, In step S5, the potassium nitrate mother liquor is concentrated and crystallized at 80-90℃ to obtain sodium chloride precipitate.

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