Method for preparing potassium chloride by double flotation and its application

Abstract

The invention provides a method for preparing potassium chloride by double flotation. The preparation method comprises: step S1, performing primary flotation on carnallites to remove a first tail salt, thereby obtaining low-sodium carnallites; step S2, mixing the low-sodium carnallites with water, performing decomposition and crystallization, obtaining a crystallizer underflow slurry, and screening the crystallizer underflow slurry to obtain a first crude potassium slurry, wherein the particle size of sodium chloride crystals in the first crude potassium slurry is less than or equal to 0.6 mm; step S3, performing secondary flotation on the first crude potassium slurry to remove a second tail salt, thereby obtaining a second crude potassium slurry; and step S4, performing thickening, a first solid-liquid separation, repulping and washing, and a second solid-liquid separation on the second crude potassium slurry in sequence, thereby obtaining potassium chloride. By adding the secondary flotation process after the decomposition and crystallization step, the amount of water used in the subsequent repulping and washing process is reduced, the loss of potassium chloride in the repulping and washing process is avoided, and the recovery rate of potassium chloride is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of salt chemical industry, in particular to a method for preparing potassium chloride by double flotation and application thereof. Background Art

[0002] Currently, several potassium resource processing technologies have been industrialized, including "cold decomposition-flotation," "cold crystallization-flotation," "reverse flotation-cold crystallization," "halogen salt addition," and "hot melt crystallization." The "reverse flotation-cold crystallization" process offers outstanding advantages, including high-quality potassium chloride, large particle size, low moisture content, low processing energy consumption, and minimal corrosion to equipment. According to this production process, after initially removing a large amount of sodium chloride through flotation, low-sodium carnallite is formed. At this point, small amounts of sylvite and large sodium chloride particles (particle size > 0.4 mm) still remain within the low-sodium carnallite. This material is easily broken down into small sodium chloride particles during crystallizer decomposition and crystallization. This material then mixes with the potassium chloride produced from the crystallizer to form a crude potassium material that enters the next slurry washing process. Fresh water is added during this process to remove the sodium chloride contaminants from the crude potassium material. The washed potassium chloride slurry undergoes dehalogenation, drying, and packaging to produce the potassium chloride product.

[0003] Because the current slurry mixing process is mainly based on the different solubilities of potassium chloride and sodium chloride, fresh water is used to mix the mother liquor for slurry mixing and washing. Combined with the solubility of the two at the temperature of the existing production system, the main components of the slurry during the slurry mixing operation are potassium chloride and a small amount of sodium chloride and magnesium chloride. Since the solubility of sodium chloride is 1 to 2 times that of potassium chloride, removing the sodium chloride impurity by adding water for washing will also lead to the loss of potassium chloride, which will ultimately affect the overall recovery rate of the potash fertilizer production system.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The main purpose of the present application is to provide a method for preparing potassium chloride by double flotation, so as to solve the problem that in the prior art, washing is directly performed after crystallization and decomposition, resulting in the use of a large amount of water in the washing process, causing potassium chloride loss and resulting in a low potassium chloride recovery rate.

[0006] To achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing potassium chloride by double flotation is provided, the preparation method comprising: step S1, subjecting a carnallitite ore to a primary flotation to remove a first tail salt, and then subjecting the ore to solid-liquid separation to obtain low-sodium carnallitite; step S2, mixing the low-sodium carnallitite with water to decompose and crystallize the ore to obtain a crystallizer underflow slurry and a crystallizer overflow liquid, and screening the crystallizer underflow slurry to obtain a first crude potassium slurry, wherein the particle size of the sodium chloride crystals in the first crude potassium slurry is ≤0.6 mm; step S3, subjecting the first crude potassium slurry to a secondary flotation to remove a second tail salt, and obtaining a second crude potassium slurry; and step S4, subjecting the second crude potassium slurry to sequential thickening, a primary solid-liquid separation, re-pulp washing, and a secondary solid-liquid separation to obtain potassium chloride.

[0007] Furthermore, a first reverse flotation agent is used for primary flotation, and a second reverse flotation agent is used for secondary flotation. Both the first reverse flotation agent and the second reverse flotation agent are dodecylmorpholine.

[0008] Furthermore, in step S3, the time for secondary flotation is 15 to 25 minutes.

[0009] Furthermore, in step S3, the mass ratio of the second reverse flotation agent to the solid in the first crude potassium slurry is 0.015‰ to 0.025‰:1.

[0010] Furthermore, in step S1, the flotation time is 15 to 25 minutes.

[0011] Furthermore, in step S1, the mass ratio of the first reverse flotation agent to the carnallite ore is 0.050‰ to 0.060‰:1.

[0012] Furthermore, in step S2, the low-sodium carnallite is in granular form, and its particle size is 0.1 to 3 mm.

[0013] Furthermore, in step S2, the solid-to-liquid ratio of low-sodium carnallite to water is 1.5-2 g / mL.

[0014] Furthermore, water is used for repulping and washing, the mass ratio of water to the second crude potassium slurry is 3.0% to 4.5%:1, and the repulping and washing time is 25 to 35 minutes.

[0015] To achieve the above object, according to one aspect of the present invention, a method for preparing potassium chloride by double flotation is provided, and the potassium chloride produced can be used in chemical, fertilizer and other industries.

[0016] Applying the technical solution of the present application, the present application provides a method for preparing potassium chloride by double flotation. By adding a secondary flotation process after the decomposition and crystallization step, the second tail salt in the underflow liquid of the crystallizer is removed to obtain a crude potassium slurry, thereby reducing the amount of water used in the subsequent re-pulping and washing process, avoiding the loss of potassium chloride in the re-pulping and washing process, and thus improving the potassium chloride recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0018] Figure 1 A schematic diagram of a process for preparing potassium chloride by double flotation in one embodiment of the present application is shown; and

[0019] Figure 2 The figure shows a schematic flow chart of preparing potassium chloride by single flotation in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] As analyzed in the background of this application, the prior art uses a reverse flotation-cold crystallization process. The flotation process initially removes a large amount of sodium chloride, forming low-sodium carnallite. This is then decomposed and crystallized in a crystallizer to form a crude potassium material, which is then washed to produce a potassium chloride product. However, the washing process requires the addition of a large amount of water, causing some potassium chloride to dissolve in the water, resulting in potassium chloride loss and a reduced potassium chloride recovery rate. To address this issue, this application provides a method for preparing potassium chloride using double flotation and its application.

[0022] In a typical embodiment of the present application, a method for preparing potassium chloride by double flotation is as follows: Figure 1 As shown, the preparation method includes: step S1, flotation of carnallites to remove the first tail salt, and then solid-liquid separation to obtain low-sodium carnallites; step S2, mixing the low-sodium carnallites with water to decompose and crystallize to obtain crystallizer underflow slurry and crystallizer overflow liquid, screening the crystallizer underflow slurry to obtain a first crude potassium slurry, wherein the particle size of the sodium chloride crystals in the first crude potassium slurry is ≤0.6 mm; step S3, flotation of the first crude potassium slurry to remove the second tail salt to obtain a second crude potassium slurry; step S4, thickening the second crude potassium slurry, performing the first solid-liquid separation, re-pulping and washing, and the second solid-liquid separation in sequence to obtain potassium chloride.

[0023] In the present application, the water used in step S2 is fresh water, and the water used for repulping and washing in step S4 is also fresh water.

[0024] Applying the technical solution of the present application, the present application provides a method for preparing potassium chloride by double flotation. By adding a secondary flotation process after the decomposition and crystallization step, the second tail salt in the underflow liquid of the crystallizer is removed to obtain a second crude potassium slurry, so that the amount of water used in the subsequent re-pulping and washing process is reduced, and the loss of potassium chloride in the re-pulping and washing process is avoided, thereby improving the potassium chloride recovery rate.

[0025] In the above-mentioned step S1, the carnallites are composed of carnallites and a certain amount of fine-grained salt, and the above-mentioned fine-grained salt mainly includes sodium chloride. In order to remove the sodium chloride in the carnallites, the carnallites are subjected to a flotation treatment. The flotation process is carried out in a flotation machine. The carnallites are slurried with carnallites saturated brine and then mixed with a first reverse flotation agent. The first reverse flotation agent can increase the hydrophobicity of the sodium chloride surface without increasing the hydrophobicity of the carnallites. The flotation machine stirs and inhales air, and the water layer on the surface of the sodium chloride quickly breaks up and closely combines with the bubbles to form foam (also called the first tail salt), which rises to the surface of the carnallites slurry. A scraper is used to scrape out the first tail salt, and most of the sodium chloride in the carnallites is selected to obtain a low-sodium carnallites slurry containing less sodium chloride. The first tail salt floated out is stored as waste. The low-sodium carnallites cannot adhere to the bubbles and rise to the surface of the slurry due to the strong wetting ability of the mineral surface, and remain in the slurry.

[0026] The above-mentioned low-sodium carnallites slurry is subjected to solid-liquid separation to obtain low-sodium carnallites and a liquid phase, and the low-sodium carnallites obtained by solid-liquid separation enter the next process as a raw material for decomposition and crystallization. In the present application, the low-sodium carnallites slurry is subjected to solid-liquid separation to obtain low-sodium carnallites, which are then mixed with water for decomposition and crystallization. The crystallizer underflow slurry and the crystallizer overflow liquid are obtained by rate-controlled decomposition and rate-controlled crystallization in a crystallizer, and then the crystallizer underflow slurry is screened using a sieve plate with an aperture of 0.6 mm to obtain an upper sieve and a lower sieve, wherein the lower sieve is the first coarse potassium slurry, and the particle size of the sodium chloride crystals in the first coarse potassium slurry is ≤0.6 mm. In order to further save energy, it is preferred that the crystallizer overflow is returned to the salt field for sun-drying carnallites.

[0027] In order to improve the effect of the primary flotation, a first reverse flotation agent is used for primary flotation. The first reverse flotation agent is a commonly used reverse flotation agent in the art, including but not limited to at least one of C10-C18 alkyl morpholine and fatty amide.

[0028] In order to further improve the effect of primary flotation, the first reverse flotation agent is preferably dodecylmorpholine. Dodecylmorpholine is a cationic surfactant. Compared with other reverse flotation agents, it has stronger hydrophobicity and can be selectively adsorbed on the surface of sodium chloride particles. It also has a strong hydration repulsion with the surface of carnallites. Dodecylmorpholine cannot be adsorbed on the surface of carnallites. In addition, dodecylmorpholine has a high action efficiency. A small amount of dodecylmorpholine can float out a large amount of sodium chloride in the flotation of carnallites. The use of the above-mentioned first reverse flotation agent can effectively remove a large amount of sodium chloride in the carnallites, thereby improving the effect of primary flotation.

[0029] In order to further improve the effect of the primary flotation, the primary flotation time is preferably 15 to 25 minutes, such as 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes or a range consisting of any two values. If the primary flotation time is too short, sodium chloride cannot be completely adsorbed, resulting in poor quality of low-sodium carnallite. If the time is too long, after the adsorption limit of sodium chloride by the first reverse flotation agent is reached, further increasing the flotation time will not increase the amount of sodium chloride adsorbed by the first reverse flotation agent, but will increase the preparation time cost. In addition, if the time is too long, part of the potassium chloride will be adsorbed, resulting in a reduced recovery rate of potassium chloride.

[0030] In the present application, the mass ratio of the first reverse flotation agent to the carnallites is 0.050‰ to 0.060‰:1. When the amount of the first reverse flotation agent added is too much, the selectivity of the flotation process is destroyed, resulting in a decrease in the quality of the low-sodium carnallites, causing a waste of the first reverse flotation agent and an increase in the preparation cost. When the amount of the first reverse flotation agent added is too little, the amount of sodium chloride adsorbed is reduced, resulting in a decrease in the quality of the low-sodium carnallites and an increase in the difficulty of subsequent removal of the sodium chloride.

[0031] In the above step S2, decomposition and crystallization are carried out in a crystallizer to obtain a crystallizer underflow slurry and a crystallizer overflow liquid. The decomposition process realizes the decomposition of low-sodium carnallite by adding water. The crystallization process includes the generation of crystal nuclei and the growth of crystal grains. When the generation rate of crystal nuclei exceeds the growth rate of crystal grains, a large number of crystals with too small particle size are obtained. When the generation rate of crystal nuclei is less than the growth rate of crystal grains, a small number of coarse-grained crystals are generated. The crude potassium product is obtained by controlled decomposition and controlled crystallization in the crystallizer. The crystallizer underflow slurry contains the crude potassium product, and then a 0.6 mm aperture screening device is used to screen the crystallizer bottom. The flowing slurry is screened to obtain an upper screen and a lower screen. The lower screen is the first crude potassium slurry. The particle size of the sodium chloride crystals in the first crude potassium slurry is ≤0.6mm. Among them, when the particle size of the sodium chloride crystals is ≤0.4mm, it meets the standard of secondary flotation. Removing sodium chloride through secondary flotation is not only more efficient in removing sodium chloride, but also avoids the need to add a large amount of water for washing in the subsequent re-pulping and washing process, resulting in potassium chloride loss and waste of water resources. Among them, sodium chloride crystals with a particle size between 0.4mm and 0.6mm are mainly removed through the re-pulping and washing process. In addition, to further avoid the loss of potassium chloride during the decomposition crystallization process, the overflow liquid of the crystallizer is returned to the salt field to produce carnallite.

[0032] In some embodiments, low-sodium carnallites are granular with a particle size of 0.1 to 3 mm. The decomposition and crystallization process is carried out in a crystallizer. If the particle size of the low-sodium carnallites is too small, they will dissolve rapidly after entering the crystallizer, resulting in excessively high saturation of potassium chloride and the generation of a large number of small potassium chloride crystals, which will lead to a large loss of potassium chloride in the subsequent processing process, thereby reducing the recovery rate of potassium chloride. If the particle size of the low-sodium carnallites is too large, the dissolution rate will be reduced, and the saturation of potassium chloride will not be met, resulting in insufficient crystal generation rate, thereby reducing the recovery rate of potassium chloride. Within the above range, the particle size of the sodium chloride crystals in the underflow of the crystallizer can be effectively controlled, which is beneficial to the subsequent secondary flotation and further improves the recovery rate and purity of potassium chloride.

[0033] In the above step S3, in order to further remove sodium chloride, the first crude potassium slurry is subjected to secondary flotation. The first crude potassium slurry is mixed with a second reverse flotation agent. The second reverse flotation agent is added to adsorb sodium chloride, thereby increasing the hydrophobicity of the surface of sodium chloride, forming a second tail salt which is removed, and further removing sodium chloride from the first crude potassium slurry to obtain a second crude potassium slurry. The second reverse flotation agent is also a commonly used reverse flotation agent in the art, and is the same as the first reverse flotation agent. Its specific composition is as described above and will not be repeated here.

[0034] In the present application, the particle size of the sodium chloride crystals in the crystallizer underflow slurry is made smaller by controlling the rate of decomposition and crystallization in the crystallizer, and then the crystallizer underflow slurry is screened using a screening device with an aperture of 0.6 mm to obtain an upper screen and a lower screen, wherein the lower screen is the first coarse potassium slurry, and the particle size of the sodium chloride crystals in the first coarse potassium slurry is ≤0.6 mm. If the particle size of the sodium chloride crystals is too large (>0.6 mm), the second reverse flotation agent will not be able to select and remove the sodium chloride crystals in the first coarse potassium slurry, so that a large amount of water will be needed for subsequent re-pulping and washing, resulting in a waste of water resources and a reduction in the recovery rate of potassium chloride. The present application uses a crystallizer to control rate decomposition and crystallization, and then screens the crystals to make the particle size of sodium chloride crystals in the first crude potassium slurry ≤0.6 mm. The sodium chloride can be further removed through secondary flotation, thereby further improving the purity of potassium chloride, reducing the amount of water used in the subsequent repulping and washing process, and preventing part of the potassium chloride from dissolving in water during the repulping and washing process, resulting in a lower potassium chloride recovery rate.

[0035] In order to further improve the effect of secondary flotation, a second reverse flotation agent is used for secondary flotation, and the second reverse flotation agent is preferably dodecylmorpholine.

[0036] In some embodiments, in order to further remove sodium chloride from the first crude potassium slurry, the time of the secondary flotation is 15 to 25 minutes, such as 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, or a range of any two values. If the time of the secondary flotation is too short, the second reverse flotation agent cannot maximize the selection of sodium chloride in the underflow slurry of the crystallizer, resulting in a large amount of sodium chloride in the crude potassium slurry. If the time is too long, when the second reverse flotation agent adsorbs sodium chloride crystals to the maximum limit, increasing the flotation time will not reduce the content of sodium chloride in the crude potassium slurry, resulting in too low potassium chloride preparation efficiency. The time of the secondary flotation is within the above range, which can effectively remove sodium chloride from the first crude potassium slurry and thereby reduce the content of sodium chloride in the first crude potassium slurry.

[0037] In order to further reduce the sodium chloride content in the first crude potassium slurry, the mass ratio of the second reverse flotation agent to the solids in the first crude potassium slurry is preferably 0.015‰ to 0.025‰:1. A relatively small amount of the second reverse flotation agent cannot completely adsorb the sodium chloride in the first crude potassium slurry, resulting in a lower purity of the potassium chloride in the second crude potassium slurry. Within the above range, the sodium chloride content in the first crude potassium slurry can be effectively reduced, reducing the amount of water used in the subsequent re-pulping and washing process, saving water resources, and avoiding the problem of some potassium chloride dissolving in water due to excessive water use, which reduces the potassium chloride recovery rate.

[0038] In the above step S4, in order to further improve the quality of potassium chloride, the second crude potassium slurry is preferably subjected to thickening, first solid-liquid separation, re-pulping and washing, and second solid-liquid separation in sequence to obtain potassium chloride. In some embodiments, the thickening equipment is not limited. The present application adopts a thickener, and the crude potassium slurry is thickened by pumping the thickener. The thickened second crude potassium slurry is subjected to a first solid-liquid separation. In order to reduce the loss of potassium chloride, the liquid phase obtained by the first solid-liquid separation is again thickened by pumping the thickener. The solid obtained by the first solid-liquid separation contains a small amount of sodium chloride. In order to remove a small amount of sodium chloride in the solid, the solid is added with water for re-pulping and washing, and then a centrifuge is used to perform a second solid-liquid separation to obtain potassium chloride.

[0039] In order to further improve the recovery rate of potassium chloride, the mass ratio of water to the second crude potassium slurry is 3.0% to 4.5%:1. If the amount of water added is too large, the sodium chloride can be fully removed and the quality of potassium chloride can be improved. However, on the one hand, the amount of water used is large, which wastes water resources. On the other hand, part of the potassium chloride is dissolved in water, resulting in a lower recovery rate of potassium chloride. If the amount of water added is too small, the sodium chloride cannot be fully removed, resulting in poor quality of the obtained potassium chloride. Within the above range, the recovery rate of potassium chloride can be improved while ensuring good quality of potassium chloride.

[0040] In some embodiments, the repulping and washing time is 25 to 35 minutes. If the repulping and washing time is too long, a small amount of potassium chloride will dissolve in the water, resulting in potassium chloride loss. If the repulping and washing time is too short, sodium chloride cannot be completely dissolved, resulting in poor quality of the obtained potassium chloride.

[0041] In the present application, a secondary flotation process is added after the decomposition and crystallization process to remove sodium chloride impurities in crude potassium, thereby reducing the amount of water added during the repulping and washing process, improving the recovery rate of potassium chloride, and achieving efficient utilization of resources.

[0042] In the second typical embodiment of the present application, the potassium chloride prepared in the first typical embodiment is used in chemical, fertilizer and other industries.

[0043] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0044] Example 1

[0045] This embodiment provides a potassium chloride, which is prepared according to the following steps:

[0046] (1) Carnallite ore (1000 kg) was placed in a flotation machine and slurried with 2000 kg of carnallite saturated brine. Then, dodecylmorpholine (55 g) was added as a reverse flotation agent as the first reverse flotation agent to perform a flotation for 20 minutes. After the first flotation, the first tail salt was removed and solid-liquid separation was performed to obtain low-sodium carnallite (761 kg). The particle size of the low-sodium carnallite was 0.1 to 3 mm.

[0047] (2) Low sodium carnallite (761 kg) is placed in a crystallizer, and water (381 kg) is added to decompose and crystallize. A crude potassium product is obtained by rate-controlled decomposition and rate-controlled crystallization in the crystallizer. The crude potassium product is deposited at the bottom of the crystallizer by gravity to obtain a crystallizer underflow slurry and a crystallizer overflow liquid. The underflow slurry is passed through a screening device with an aperture of 0.6 mm to form a first crude potassium slurry, wherein the mass of sodium chloride crystals with a particle size of ≤0.6 mm accounts for approximately 80% of the total amount of sodium chloride crystals.

[0048] (3) The solid phase mass of the first crude potassium slurry is about 158 ​​kg. It is sent to a secondary flotation device, and then dodecylmorpholine (3.2 g) is added for secondary flotation to remove the second tail salt, thereby obtaining a second crude potassium slurry containing a solid phase mass (136 kg); wherein the mass ratio of the second reverse flotation agent to the solid phase in the first crude potassium slurry is 0.0032:158, and the secondary flotation time is 20 min.

[0049] (4) The second crude potassium slurry after the secondary flotation is first thickened and then subjected to the first solid-liquid separation. Water (5.5 kg) is added to the obtained solid to remove sodium chloride by re-slurry washing, and then the second solid-liquid separation is performed to obtain the potassium chloride product.

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that the mass ratio of the second reverse flotation reagent in step (3) to the solid in the first crude potassium slurry is 0.015‰:1.

[0052] Example 3

[0053] The difference between this embodiment and embodiment 1 is that the mass ratio of the second reverse flotation reagent in step (3) to the solid in the first crude potassium slurry is 0.025‰:1.

[0054] Example 4

[0055] The difference between this embodiment and embodiment 1 is that the mass ratio of the second reverse flotation reagent in step (3) to the solid in the first crude potassium slurry is 0.035‰:1.

[0056] Example 5

[0057] The difference between this embodiment and embodiment 1 is that the mass ratio of the second reverse flotation reagent in step (3) to the solids in the first crude potassium slurry is 0.005‰:1.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing potassium chloride by single flotation, and its flow chart is as follows: Figure 2 As shown, it is prepared according to the following steps:

[0060] (1) Carnallite ore (1000 kg) was placed in a flotation machine and slurried with 2000 kg of carnallite saturated brine. Then, dodecylmorpholine (55 g) was added as a reverse flotation agent as the first reverse flotation agent to perform a flotation for 20 minutes. After the first flotation, the first tail salt was removed and solid-liquid separation was performed to obtain low-sodium carnallite (761 kg). The particle size of the low-sodium carnallite was 0.1 to 3 mm.

[0061] (2) Low sodium carnallite (761 kg) is placed in a crystallizer, and water (381 kg) is added to decompose and crystallize. A crude potassium product is obtained by rate-controlled decomposition and rate-controlled crystallization in the crystallizer. The crude potassium product is deposited at the bottom of the crystallizer by gravity to obtain a crystallizer underflow slurry and a crystallizer overflow liquid. The underflow slurry is passed through a screening device with an aperture of 0.6 mm to form a first crude potassium slurry, wherein the mass of sodium chloride crystals with a particle size of ≤0.6 mm accounts for approximately 80% (or 70-90%) of the total amount of sodium chloride crystals.

[0062] (3) The first crude potassium slurry is first thickened and then subjected to a first solid-liquid separation. A large amount of water (42 kg) is added to the obtained solid to remove sodium chloride by re-slurry washing, and finally a second solid-liquid separation is performed to obtain a potassium chloride product.

[0063] Test Example 1

[0064] The potassium chloride products prepared in the above examples and comparative examples were subjected to purity tests and the mass of the potassium chloride products was recorded to calculate the recovery of the potassium chloride products. The results are shown in Table 1:

[0065] Among them: 1) The purity test method of potassium chloride is: GB / T 37918-2019, volumetric analysis method.

[0066] 2) The quality test method of potassium chloride is: zero measurement method, the laboratory balance is zeroed, and the sample to be tested is placed in it for direct weighing and counting.

[0067] 3) The calculation method of the recovery rate of potassium chloride is:

[0068] Potassium chloride recovery rate = (product potassium chloride content * mass) / (carnallite potassium chloride content * mass) * 100%.

[0069] Table 1

[0070]

[0071]

[0072] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: It can be seen from Example 1 and Comparative Example 1 that Comparative Example 1 only performs one flotation. In order to achieve the purity of potassium chloride in Example 1, a large amount of water needs to be added during the repulping and washing process. Moreover, due to the addition of a large amount of water, the potassium chloride is partially lost and dissolved during the repulping and washing process, resulting in a significant decrease in the recovery rate of potassium chloride. The present application provides a method for preparing potassium chloride by double flotation, which removes the second tail salt in the crystallizer underflow liquid by adding a secondary flotation process after the decomposition and crystallization step to obtain a crude potassium slurry, thereby reducing the amount of water used in the subsequent repulping and washing process, avoiding the loss of potassium chloride during the repulping and washing process, and thus improving the potassium chloride recovery rate.

[0073] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing potassium chloride by double flotation, characterized in that: The preparation method comprises: Step S1, flotation of the carnallites to remove the first tail salt, and then solid-liquid separation to obtain low-sodium carnallites; Step S2, mixing the low-sodium carnallite with water for decomposition and crystallization to obtain a crystallizer underflow slurry and a crystallizer overflow liquid, and screening the crystallizer underflow slurry to obtain a first crude potassium slurry, wherein the particle size of the sodium chloride crystals in the first crude potassium slurry is ≤0.6 mm; Step S3, performing secondary flotation on the first crude potassium slurry to remove the second tail salt, thereby obtaining a second crude potassium slurry; Step S4, sequentially performing thickening, first solid-liquid separation, re-slurry washing, and second solid-liquid separation on the second crude potassium slurry to obtain the potassium chloride; A first reverse flotation agent is used for the primary flotation, and a second reverse flotation agent is used for the secondary flotation, wherein both the first reverse flotation agent and the second reverse flotation agent are dodecylmorpholine; In step S3, the secondary flotation time is 15 to 25 minutes; the mass ratio of the second reverse flotation agent to the solid in the first crude potassium slurry is 0.015‰ to 0.025‰:

1.

2. The method for preparing potassium chloride by double flotation according to claim 1, wherein In step S1, the time for one flotation is 15 to 25 minutes.

3. The method for preparing potassium chloride by double flotation according to claim 1, wherein In step S1, the mass ratio of the first reverse flotation agent to the carnallite ore is 0.050‰~0.060‰:

1.

4. The method for preparing potassium chloride by double flotation according to claim 1, wherein In the step S2, the low-sodium carnallite is in granular form with a particle size of 0.1-3 mm.

5. The method for preparing potassium chloride by double flotation according to claim 1, wherein In step S2, the solid-to-liquid ratio of the low-sodium carnallite to the water is 1.5-2 g / mL.

6. The method for preparing potassium chloride by double flotation according to claim 1, wherein: In step S4, water is used for the repulping and washing, the mass ratio of the water to the second crude potassium slurry is 3.0% to 4.5%:1, and the repulping and washing time is 25 to 35 minutes.

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