A method for producing a potassium carnallite double salt

Abstract

The present application relates to the field of inorganic salt production process, disclose a kind of preparation method of potassium carnallite complex salt.The method comprises the following steps: sodium removal treatment is carried out to salt field potassium carnallite, and low-sodium potassium carnallite is obtained;The low-sodium potassium carnallite and magnesium chloride solution are hot dissolved, then cooling crystallization and filtration are carried out, and potassium carnallite complex salt and filtration mother liquor are obtained, the method can control the formation of potassium carnallite complex salt and the growth of crystal particle size, obtain a kind of low impurity and pure component potassium carnallite, provide high-quality raw materials for electrolytic production of magnesium metal.Simultaneously, the filtration mother liquor and water are mixed in proportion, and the hot dissolution recrystallization process is recycled, to form a stable mother liquor circulation preparation process of potassium carnallite complex salt.

Description

Technical Field

[0001] This invention relates to the field of inorganic salt production processes, specifically to a method for preparing potassium carnallite double salt. Background Technology

[0002] Potassium carnallite (KCl) MgCl2 Potassium carnallite (6H2O), a natural double salt containing potassium and magnesium, possesses unique physicochemical properties due to its molecular structure: during dehydration, potassium chloride in the component can effectively inhibit the hydrolysis of magnesium chloride through chemical action, thereby significantly reducing the formation of harmful impurities such as magnesium oxide (MgO). Based on this excellent process characteristic, potassium carnallite is recognized as an ideal raw material for electrolytic magnesium smelting processes, playing a crucial role in optimizing the smelting process and improving product quality.

[0003] However, the raw potassium carnallite ore obtained from the natural salt fields by sun-drying salt lake brine usually contains nearly 20% sodium chloride and various impurities such as boron and sulfate. Its raw material quality cannot directly meet the process requirements for the preparation of metallic magnesium by existing electrolytic methods.

[0004] Given that the electrolytic magnesium smelting process has extremely strict upper limit control standards for the content of impurities in raw materials, specifically: boron (B) < 10 ppm, sulfate (SO4) < 10 ppm, and so on. 2- With impurities of <300ppm, iron (Fe) <200ppm, silicon (Si) <100ppm, and sodium chloride (NaCl) <6%, developing and preparing high-quality potassium carnallite raw materials with extremely low impurity content and uniform and stable chemical composition has become a core technological bottleneck and key prerequisite for improving the stability of subsequent dehydration and electrolytic magnesium smelting processes, enhancing the comprehensive utilization efficiency of magnesium and potassium resources, and improving the quality of final products. Summary of the Invention

[0005] The purpose of this invention is to address the following key problems in the process of synthesizing a complex salt from potassium carnallite in a multi-component system after dissolution and decomposition into magnesium chloride and potassium chloride monosalts, followed by cooling crystallization: poor operational stability and easy precipitation of impurity crystals such as potassium chloride and magnesium chloride; and the need to solve problems such as impurity control, crystal particle size regulation, and industrially feasible mother liquor recycling. This invention provides a method for preparing potassium carnallite complex salts. This method can control the formation and crystal size growth of potassium carnallite complex salts, yielding a low-impurity and pure potassium carnallite, providing a high-quality raw material for the electrolytic production of metallic magnesium. Simultaneously, the filtered mother liquor and water are mixed in a specific ratio and circulated for a hot dissolution and recrystallization process, forming a stable mother liquor recycling process for preparing potassium carnallite complex salts.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing potassium carnallite double salt, the method comprising the following steps:

[0007] (1) Sodium removal treatment was performed on salt field potassium carnallite to obtain low sodium potassium carnallite;

[0008] (2) Dissolve low-sodium potassium carnallite and magnesium chloride by heat, then cool and crystallize and filter to obtain potassium carnallite double salt and mother liquor;

[0009] (3) Mix the mother liquor and water, and then repeat the recrystallization process several times. The recrystallization process includes hot dissolution, cooling crystallization and filtration.

[0010] Preferably, in step (1), the specific process of sodium removal includes: adding sodium chloride flotation reagent to the potassium carnallite in the salt field, and blowing air in under stirring conditions to remove the floating sodium chloride.

[0011] Preferably, the low-sodium potassium carnallite contains 50-60 ppm boron, 2 wt%-5 wt% sodium, 5 wt%-10 wt% magnesium, 5 wt%-20 wt% potassium, 0.2 wt%-0.5 wt% sulfate, 20-50 ppm iron, 10-20 ppm silicon, 38 wt%-40 wt% chlorine, and 30 wt%-40 wt% water.

[0012] Preferably, the particle size D50 of the low-sodium potassium carnallite is 350~450μm.

[0013] Preferably, in step (2), the specific process of hot dissolution includes: preparing magnesium chloride mother liquor, mixing magnesium chloride mother liquor and low sodium potassium carnallite, and hot dissolving under stirring conditions.

[0014] Preferably, the concentration of the magnesium chloride mother liquor is 200 g / L to 400 g / L.

[0015] Preferably, the volume-to-mass ratio of magnesium chloride mother liquor to low-sodium potassium carnallite is 500 mL: 200 g ~ 300 g.

[0016] Preferably, the conditions for hot melting include: a temperature of 80℃~100℃, a time of 10min~30min, and a stirring rate of 200r / min~600r / min.

[0017] Preferably, in step (2), the cooling crystallization conditions include: an endpoint temperature of 30°C or below, a cooling time of 1h to 2h, and a stirring rate of 100r / min to 400r / min.

[0018] Preferably, in step (3), the volume ratio of the mother liquor to water is 1 to 9:1.

[0019] Preferably, in step (3), the volume ratio of the mother liquor to water is 6:4, 7:3, 8:2 or 9:1.

[0020] Preferably, in step (3), the number of cycles is 1 to 10.

[0021] Preferably, in step (3), the conditions for hot dissolution include: a temperature of 80℃~100℃, a time of 10min~30min, and a stirring rate of 200r / min~600r / min.

[0022] Preferably, in step (3), the cooling crystallization conditions include: an endpoint temperature of 30°C or below, a cooling time of 1h to 2h, and a stirring rate of 100r / min to 400r / min.

[0023] This invention obtains a low-impurity and pure potassium carnallite by controlling the formation and crystal growth of potassium carnallite double salt, providing a high-quality raw material for the electrolytic production of metallic magnesium. Furthermore, the method employs a hot dissolution-cooling crystallization cycle process and optimizes the ratio of the filtered crystallization mother liquor to water, enabling the formation of stable potassium carnallite double salt. The one-pass yield of this invention can reach 94%, and the purity of the potassium carnallite double salt can reach 98.13% or higher. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 The XRD pattern of potassium carnallite double salt crystal A1-1 prepared in step (2) of Example 1.

[0026] Figure 2 The XRD pattern of potassium carnallite double salt crystal A1-2 prepared in step (3) of Example 1. Detailed Implementation

[0027] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] The method for preparing potassium carnallite double salt of the present invention includes the following steps:

[0030] (1) Sodium removal treatment was performed on salt field potassium carnallite to obtain low sodium potassium carnallite;

[0031] (2) Dissolve low-sodium potassium carnallite and magnesium chloride by heat, then cool and crystallize and filter to obtain potassium carnallite double salt and mother liquor;

[0032] (3) Mix the mother liquor and water in proportion, and then repeat the recrystallization process several times. The recrystallization process includes hot dissolution, cooling crystallization and filtration.

[0033] In some embodiments, the specific process of sodium removal in step (1) may include: adding sodium chloride flotation reagent to the potassium carnallite in the salt field, and blowing air in under stirring conditions to remove the floating sodium chloride. In this invention, by adding sodium chloride flotation reagent, the hydrophobicity of the sodium chloride crystal surface is increased. When air is blown in under stirring conditions, sodium chloride adheres to the air bubbles and floats to form a foam layer, which is then scraped off, while the carnallite remains in the slurry, thereby achieving reverse flotation to remove sodium. When sodium removal is carried out according to this embodiment, 70wt%~80wt% of sodium chloride can be removed, avoiding the adverse effects of excessive NaCl causing a sharp drop in current efficiency, a surge in power consumption, and excessive sodium content in magnesium metal products during electrolysis.

[0034] In this invention, the low-sodium potassium carnallite may contain 50-60 ppm boron, 2 wt%-5 wt% sodium, 5 wt%-10 wt% magnesium, 5 wt%-20 wt% potassium, 0.2 wt%-0.5 wt% sulfate, 20-50 ppm iron, 10-20 ppm silicon, 38 wt%-40 wt% chlorine, and 30 wt%-40 wt% water.

[0035] In this invention, the particle size D50 of low-sodium potassium carnallite can be 350~450μm. In this invention, the crystal size growth of potassium carnallite complex salt is controlled by controlling the cooling curve to prevent sudden temperature drops and explosive nucleation.

[0036] In some embodiments, the specific process of thermal dissolution in step (2) may include: preparing magnesium chloride mother liquor, mixing magnesium chloride mother liquor and low sodium potassium carnallite, and thermally dissolving it under stirring conditions.

[0037] In a preferred embodiment, the conditions for thermal dissolution in step (2) include: a temperature of 80°C to 100°C, more preferably 90°C to 100°C; a stirring rate of 200 r / min to 600 r / min, more preferably 400 r / min to 500 r / min; and a time of 10 min to 30 min, more preferably 10 min to 15 min. When the thermal dissolution conditions are within the above-mentioned preferred range, potassium carnallite double salt can be effectively prepared. If the temperature is too high, it will lead to increased energy consumption and a large amount of water evaporation, resulting in a deviation in the crystallization path, an increase in sodium chloride in the crystallized product, and the presence of magnesium chloride impurities. If the temperature is too low, potassium carnallite cannot be completely dissolved, and a homogeneous solution cannot be formed, resulting in a deviation in the crystallization path and an increase in impurity content, making it impossible to obtain high-purity potassium carnallite raw material.

[0038] In a preferred embodiment, the concentration of the magnesium chloride mother liquor is 200 g / L to 400 g / L, more preferably 280 g / L to 350 g / L. When the concentration of the magnesium chloride mother liquor is within the above-mentioned preferred range, potassium carnallite double salt can be effectively prepared while avoiding the formation of magnesium chloride and potassium chloride impurities, and the first-pass yield of the crystallized product can be improved.

[0039] In a preferred embodiment, the volume-to-mass ratio of magnesium chloride mother liquor to low-sodium potassium carnallite can be 500 mL: 200 g to 300 g, more preferably 500 mL: 240 g to 260 g. When the volume-to-mass ratio of magnesium chloride mother liquor to low-sodium potassium carnallite is within the above-mentioned preferred range, potassium carnallite double salt can be effectively prepared while avoiding the formation of magnesium chloride and potassium chloride impurities and reducing the impurity content in the crystals, thereby obtaining high-purity potassium carnallite.

[0040] In the method of the present invention, the cooling crystallization conditions in step (2) may include: an endpoint temperature of 30°C or below, more preferably 20°C or below; a cooling time of 1 h to 2 h, more preferably 1.5 h to 1.8 h; and a stirring rate of 100 r / min to 400 r / min, more preferably 200 r / min to 300 r / min. When the cooling crystallization conditions are within the above-mentioned more preferred range, low-potassium carnallite double salt crystals can be effectively obtained while avoiding the formation of potassium chloride and magnesium chloride impurities.

[0041] In some specific embodiments, step (2) may specifically include: preparing a magnesium chloride mother liquor with a concentration of 280 g / L to 350 g / L; mixing the magnesium chloride mother liquor and low-sodium potassium carnallite at a volume-to-mass ratio of 500 mL: 240 g to 2600 g; hot-dissolving the mixture at 90°C to 100°C and a stirring rate of 400 r / min to 600 r / min for 10 min to 15 min; then controlling the cooling and crystallization process to cool to 20°C or below and a stirring rate of 200 r / min to 300 r / min for 1 h to 2 h; and finally filtering to obtain potassium carnallite double salt and filtrate mother liquor. In these specific embodiments, when step (2) is carried out in the above manner, low-pollution potassium carnallite double salt crystals can be effectively obtained while avoiding the formation of potassium chloride and magnesium chloride impurities.

[0042] In the method of the present invention, in step (3), the volume ratio of the filtration mother liquor to water can be 1 to 9:1, preferably 6:4, 7:3, 8:2 or 9:1, and more preferably 8:2. In the present invention, by optimizing the ratio of crystallization mother liquor to water, a stable low-potassium carnallite complex salt mother liquor recycling process can be formed, while avoiding the generation of potassium chloride and magnesium chloride impurities.

[0043] In the method of the present invention, in step (3), the number of cycles can be 1 to 10, preferably 1 to 6. In the present invention, a stable low-potassium carnallite complex salt can be formed by using a hot dissolution-cooling crystallization cycle process, while avoiding the formation of potassium chloride and magnesium chloride impurities.

[0044] In the method of the present invention, in step (3), the conditions for hot dissolution may include: a temperature of 80°C to 100°C, preferably 90°C to 100°C; a time of 10 min to 30 min, more preferably 10 min to 15 min; and a stirring rate of 200 r / min to 600 r / min, more preferably 400 r / min to 500 r / min.

[0045] In the method of the present invention, the cooling crystallization conditions in step (3) may include: an endpoint temperature of 30°C or below, more preferably 20°C or below; a cooling time of 1 h to 2 h, more preferably 1.5 h to 1.8 h; and a stirring rate of 100 r / min to 400 r / min, more preferably 200 r / min to 300 r / min. When the cooling crystallization conditions are within the above-mentioned more preferred range, low-potassium carnallite double salt crystals can be effectively obtained while avoiding the formation of potassium chloride and magnesium chloride impurities.

[0046] In some specific embodiments, step (3) may specifically include: mixing the mother liquor and water in a more preferred ratio of 8:2, and cyclically performing hot dissolution, cooling crystallization, and filtration 1 to 6 times. The conditions for hot dissolution include: a temperature of 90°C to 100°C, a time of 10 min to 15 min, and a stirring rate of 400 r / min to 500 r / min. The conditions for cooling crystallization include: an endpoint temperature of 20°C or below, a stirring rate of 200 r / min to 300 r / min, and a cooling time of 1.5 h to 1.8 h. When the conditions are within the above range, low-potassium carnallite double salt crystals can be effectively obtained while avoiding the formation of potassium chloride and magnesium chloride impurities.

[0047] The following examples further illustrate the preparation method of potassium carnallite double salt of the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0048] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods in the art.

[0049] Unless otherwise specified, all experimental materials used in the following examples are commercially available.

[0050] Example 1

[0051] Sodium removal treatment of potassium carnallite in salt fields:

[0052] (1) By adding sodium chloride flotation reagent, the hydrophobicity of the sodium chloride crystal surface is increased. When air is blown in during stirring, sodium chloride adheres to the air bubbles and floats to form a foam layer, which is then scraped off, while carnallite remains in the slurry, thus achieving reverse flotation to remove sodium. The resulting low-sodium potassium carnallite, by mass percentage, mainly consists of: 55.4 ppm B, 6.65% NaCl, 30.88% MgCl2, 22.43% KCl, and 0.39% SO4. 2- It contains 38 ppm Fe, 13 ppm Si, and 39.92% water. The particle size D50 of the low-sodium potassium carnallite is 397 μm.

[0053] Preparation of potassium carnallite double salt:

[0054] (2) Prepare a mother liquor with a magnesium chloride concentration of 284 g / L. Add 500 mL of the mother liquor and 250 g of low-sodium potassium carnallite to a beaker. Dissolve and stir at 500 r / min. Dissolve at 90 °C for 10 min. After complete dissolution, cool the mixture. Control the cooling stirring speed at 200 r / min. Cool to a final crystallization temperature of 25 °C for 1.5 h. After cooling and crystallization, filter to obtain potassium carnallite double salt crystals and the mother liquor. The potassium carnallite double salt crystals are denoted as A1-1. Figure 1 The image shows the XRD pattern of potassium carnallite double salt crystal A1-1. Figure 1 As shown, the results indicate that the complex salt crystals are composed of potassium carnallite, and no other impurity diffraction peaks were found.

[0055] (3) The mother liquor collected in the filtration process of step (2) and water are diluted in a volume ratio of 8:2. The mixture is then heated to dissolve at a stirring speed of 500 r / min and a temperature of 90°C for 10 min. After complete dissolution, the mixture is cooled at a stirring speed of 200 r / min and a final temperature of 25°C for 1.5 h. After cooling and crystallization, the mixture is filtered. The above process is repeated 6 times to obtain the remaining potassium carnallite double salt crystals, which are denoted as A1-2. Figure 2 The XRD pattern of potassium carnallite double salt crystal A1-2 is shown. Figure 2 As shown, the results indicate that the complex salt crystals are composed of potassium carnallite, and no other impurity diffraction peaks were found.

[0056] Example 2

[0057] Sodium removal treatment of potassium carnallite in salt fields:

[0058] (1) By adding sodium chloride flotation reagent, the hydrophobicity of the sodium chloride crystal surface is increased. When air is blown in during stirring, sodium chloride adheres to the air bubbles and floats to form a foam layer, which is then scraped off, while carnallite remains in the slurry, thus achieving reverse flotation to remove sodium. The resulting low-sodium potassium carnallite, by mass percentage, mainly consists of: 55.4 ppm B, 6.65% NaCl, 30.88% MgCl2, 22.43% KCl, and 0.39% SO4. 2- It contains 38 ppm Fe, 13 ppm Si, and 39.92% water. The particle size D50 of the low-sodium potassium carnallite is 397 μm.

[0059] Preparation of potassium carnallite double salt:

[0060] (2) Prepare a mother liquor with a magnesium chloride concentration of 300 g / L. Add 500 mL of the mother liquor and 250 g of low-sodium potassium carnallite to a beaker. Dissolve and stir at 500 r / min, dissolve at 100 ℃, and dissolve for 10 min. After complete dissolution, cool the mixture. Control the cooling stirring speed at 200 r / min, cool to a final crystallization temperature of 20 ℃, and cool for 1.5 h. After cooling and crystallization, filter the mixture to obtain potassium carnallite double salt crystals and the mother liquor. The potassium carnallite double salt crystals are denoted as A2-1.

[0061] (3) The mother liquor and water were diluted in a volume ratio of 8:2 and then hot-dissolved at 500 r / min and 100℃ for 10 min. After complete dissolution, the solution was cooled, and the cooling stirring speed was controlled at 200 r / min. The final temperature of the cooling crystallization was 20℃ and the cooling time was 1.5 h. After the cooling crystallization was completed, the solution was filtered. The above process was repeated 6 times to obtain the remaining potassium carnallite double salt crystals, which were denoted as A2-2.

[0062] Example 3

[0063] Sodium removal treatment of potassium carnallite in salt fields

[0064] (1) By adding sodium chloride flotation reagent, the hydrophobicity of the sodium chloride crystal surface is increased. When air is blown in during stirring, sodium chloride adheres to the air bubbles and floats to form a foam layer, which is then scraped off, while carnallite remains in the slurry, thus achieving reverse flotation to remove sodium. The resulting low-sodium potassium carnallite, by mass percentage, mainly consists of: 55.4 ppm B, 6.65% NaCl, 30.88% MgCl2, 22.43% KCl, and 0.39% SO4. 2- It contains 38 ppm Fe, 13 ppm Si, and 39.92% water. The particle size D50 of the low-sodium potassium carnallite is 397 μm.

[0065] Preparation of potassium carnallite double salt:

[0066] (2) Prepare a mother liquor with a magnesium chloride concentration of 284 g / L. Add 500 mL of the mother liquor and 250 g of low-sodium potassium carnallite to a beaker. Dissolve and stir at 400 r / min, dissolve at 95 ℃, and dissolve for 15 min. After complete dissolution, cool the mixture by controlling the cooling stirring speed at 300 r / min, cooling to a final crystallization temperature of 30 ℃, and cooling for 1.5 h. After cooling and crystallization, filter the mixture to obtain potassium carnallite double salt crystals and the mother liquor. The potassium carnallite double salt crystals are denoted as A3-1.

[0067] (3) The mother liquor and water were diluted in a volume ratio of 8:2 and then hot-dissolved at 400 r / min and 95℃ for 15 min. After complete dissolution, the solution was cooled, and the cooling stirring speed was controlled at 300 r / min. The final temperature of the cooling crystallization was 30℃ and the cooling time was 1.5 h. After the cooling crystallization was completed, the solution was filtered. The above process was repeated 3 times to obtain the remaining potassium carnallite double salt crystals, which were denoted as A3-2.

[0068] Example 4

[0069] This embodiment is implemented according to the method of Example 1, except that in step (2), the concentration of magnesium chloride mother liquor is 100 g / L.

[0070] The potassium carnallite double salt crystals obtained in step (2) are denoted as A4-1.

[0071] The potassium carnallite double salt crystals obtained in step (3) are denoted as A4-2.

[0072] Example 5

[0073] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the concentration of magnesium chloride mother liquor is 400 g / L.

[0074] The potassium carnallite double salt crystals obtained in step (2) are denoted as A5-1.

[0075] The potassium carnallite double salt crystals obtained in step (3) are denoted as A5-2.

[0076] Example 6

[0077] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the amount of low sodium potassium carnallite used is 100g.

[0078] The potassium carnallite double salt crystals obtained in step (2) are denoted as A6-1.

[0079] The potassium carnallite double salt crystals obtained in step (3) are denoted as A6-2.

[0080] Example 7

[0081] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the amount of low sodium potassium carnallite used is 300g.

[0082] The potassium carnallite double salt crystals obtained in step (2) are denoted as A7-1.

[0083] The potassium carnallite double salt crystals obtained in step (3) are denoted as A7-2.

[0084] Example 8

[0085] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the temperature of thermal dissolution is 70°C.

[0086] The potassium carnallite double salt crystals obtained in step (2) are denoted as A8-1.

[0087] The potassium carnallite double salt crystals obtained in step (3) are denoted as A8-2.

[0088] Example 9

[0089] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the temperature of thermal dissolution is 110°C.

[0090] The potassium carnallite double salt crystals obtained in step (2) are denoted as A9-1.

[0091] The potassium carnallite double salt crystals obtained in step (3) are denoted as A9-2.

[0092] Example 10

[0093] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the cooling and stirring speed is 100 r / min.

[0094] The potassium carnallite double salt crystals obtained in step (2) are denoted as A10-1.

[0095] The potassium carnallite double salt crystals obtained in step (3) are denoted as A10-2.

[0096] Example 11

[0097] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the cooling and stirring speed is 500 r / min.

[0098] The potassium carnallite double salt crystals obtained in step (2) are denoted as A11-1.

[0099] The potassium carnallite double salt crystals obtained in step (3) are denoted as A11-2.

[0100] Example 12

[0101] This embodiment is implemented according to the method of embodiment 1, except that in step (3), the mother liquor and water are in a volume ratio of 6:4.

[0102] The potassium carnallite double salt crystals obtained in step (2) are denoted as A12-1.

[0103] The potassium carnallite double salt crystals obtained in step (3) are denoted as A12-2.

[0104] Example 13

[0105] This embodiment is implemented according to the method of embodiment 1, except that in step (3), the mother liquor and water are in a volume ratio of 9:1.

[0106] The potassium carnallite double salt crystals obtained in step (2) are denoted as A13-1.

[0107] The potassium carnallite double salt crystals obtained in step (3) are denoted as A13-2.

[0108] Example 14

[0109] This embodiment is implemented according to the method of embodiment 1. The difference is that in step (3), the conditions for hot dissolution include: rotation speed of 100 r / min, temperature of 70°C, and time of 1 h.

[0110] The potassium carnallite double salt crystals obtained in step (2) are denoted as A14-1.

[0111] The potassium carnallite double salt crystals obtained in step (3) are denoted as A14-2.

[0112] Example 15

[0113] This embodiment is implemented according to the method of embodiment 1. The difference is that in step (2), the cooling crystallization conditions include: the final temperature of cooling crystallization is 40°C.

[0114] The potassium carnallite double salt crystals obtained in step (2) are denoted as A15-1.

[0115] The potassium carnallite double salt crystals obtained in step (3) are denoted as A15-2.

[0116] Example 16

[0117] This embodiment is implemented according to the method of embodiment 1. The difference is that in step (2), the cooling crystallization conditions include: the final temperature of cooling crystallization is 50°C.

[0118] The potassium carnallite double salt crystals obtained in step (2) are denoted as A16-1.

[0119] The potassium carnallite double salt crystals obtained in step (3) are denoted as A16-2.

[0120] Example 17

[0121] This embodiment is implemented according to the method of embodiment 1, except that in step (2), the cooling stirring speed is 500 r / min and the cooling crystallization endpoint temperature is 60℃.

[0122] The potassium carnallite double salt crystals obtained in step (2) are denoted as A17-1.

[0123] The potassium carnallite double salt crystals obtained in step (3) are denoted as A17-2.

[0124] Test Example 1

[0125] This test example tests the yield of potassium carnallite double salts obtained in Examples 1-17. The yield of potassium carnallite double salts is calculated according to the following formula:

[0126] The results are shown in Table 1.

[0127] Table 1

[0128]

[0129] As shown in Table 1, when the hot melting conditions are within the optimal range, changing the cooling crystallization process and the number of cycles does not affect the yield, but only the particle size, impurities, and impurity content. Therefore, even in some non-optimal implementation cases (Examples 4-17), there are still high yields.

[0130] Test Example 2

[0131] In this test example, X-ray diffraction (XRD) was used to detect the composition of potassium carnallite double salts obtained in Examples 1-17. The results are shown in Table 2.

[0132] Table 2

[0133]

[0134] As shown in Table 2, the iron and silicon impurities are present in small amounts in the raw materials, so their accumulation during cycles is not significant, and the detected levels are all within 5 ppm. The main impurities, boron and sulfate, are primarily related to high temperature, increased dosage, high magnesium chloride concentration, and the number of cycles, increasing with these factors. Changing the cooling crystallization method does not affect the impurities. Therefore, the above-mentioned impurity patterns fluctuate, and even in non-preferred cases (Examples 4-17), the impurity content indicators are relatively good.

[0135] Test Example 3

[0136] This test case examines the particle size of the potassium carnallite double salts obtained in Examples 1-17, and the results are shown in Table 3.

[0137] Table 3

[0138]

[0139] As shown in Table 3, in this invention, the final crystallization size of potassium carnallite is greatly related to the cooling and stirring rate. This invention controls the crystal growth of potassium carnallite complex salt by controlling the cooling curve to prevent sudden temperature drops and explosive nucleation.

[0140] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing potassium carnallite double salt, characterized in that, The method includes the following steps: (1) Sodium removal treatment was performed on salt field potassium carnallite to obtain low sodium potassium carnallite; (2) The low-sodium potassium carnallite and magnesium chloride are thermally dissolved, followed by cooling, crystallization and filtration to obtain potassium carnallite double salt and mother liquor. (3) The mother liquor and water are mixed and then recrystallized several times. The recrystallization process includes hot dissolution, cooling crystallization and filtration.

2. The method according to claim 1, characterized in that, In step (1), the specific process of sodium removal includes: adding sodium chloride flotation reagent to the potassium carnallite in the salt field, and blowing air in under stirring conditions to remove the floating sodium chloride.

3. The method according to claim 1 or 2, characterized in that, The low-sodium potassium carnallite contains 50-60 ppm boron, 2 wt%-5 wt% sodium, 5 wt%-10 wt% magnesium, 5 wt%-20 wt% potassium, 0.2 wt%-0.5 wt% sulfate, 20-50 ppm iron, 10-20 ppm silicon, 38 wt%-40 wt% chlorine, and 30 wt%-40 wt% water.

4. The method according to claim 1 or 2, characterized in that, The particle size D50 of the low-sodium potassium carnallite is 350~450μm.

5. The method according to claim 1 or 2, characterized in that, In step (2), the specific process of thermal dissolution includes: preparing magnesium chloride mother liquor, mixing the magnesium chloride mother liquor and the low sodium potassium carnallite, and thermally dissolving it under stirring conditions; Preferably, the concentration of the magnesium chloride mother liquor is 200 g / L to 400 g / L; Preferably, the volume-to-mass ratio of the magnesium chloride mother liquor to the low-sodium potassium carnallite is 500 mL: 200 g ~ 300 g; Preferably, the conditions for thermal dissolution include: a temperature of 80℃~100℃, a time of 10min~30min, and a stirring rate of 200r / min~600r / min.

6. The method according to claim 1 or 2, characterized in that, In step (2), the conditions for cooling crystallization include: an endpoint temperature of 30°C or below, a cooling time of 1 h to 2 h, and a stirring rate of 100 r / min to 400 r / min.

7. The method according to claim 1 or 2, characterized in that, In step (3), the volume ratio of the mother liquor to the water is 1~9:1; Preferably, in step (3), the volume ratio of the mother liquor to the water is 6:4, 7:3, 8:2 or 9:

1.

8. The method according to claim 1 or 2, characterized in that, In step (3), the number of cycles is 1 to 10.

9. The method according to claim 1 or 2, characterized in that, In step (3), the conditions for thermal dissolution include: a temperature of 80℃~100℃, a time of 10min~30min, and a stirring rate of 200r / min~600r / min.

10. The method according to claim 1 or 2, characterized in that, In step (3), the conditions for cooling crystallization include: an endpoint temperature of 30°C or below, a cooling time of 1 h to 2 h, and a stirring rate of 100 r / min to 400 r / min.

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