Method for preparing potassium chloride to promote grain growth

Abstract

The present application relates to potassium chloride preparation technical field, disclose a kind of preparation method of promoting grain growth of potassium chloride.The method includes the following steps: (1) decomposition cold crystallization: after halite ore is crushed, add water and carry out decomposition crystallization, obtain mixed potassium salt slurry;(2) direct flotation: the mixed potassium salt slurry is mixed with flotation reagent, and the slurry obtained after mixing is treated by direct flotation, and the mother liquor is removed, to obtain crude potassium filter cake;(3) slurry washing: the crude potassium filter cake is washed with fresh water, to obtain crude potassium mixed slurry;(4) secondary crystallization: the crude potassium mixed slurry is passed into crystallizer and secondary crystallization is carried out, to obtain crystal slurry;(5) dehydration and drying: the obtained crystal slurry is dehydrated and dried to obtain potassium chloride.The technical scheme of the present application is beneficial to prepare large-particle potassium chloride product with high purity, improve the dehydration performance of the product, and reduce the energy consumption per unit product.

Description

Technical Field

[0001] This invention relates to the field of potassium chloride preparation technology, and more specifically to a method for preparing potassium chloride that promotes grain growth. Background Technology

[0002] Potassium chloride is an essential raw material for the production of agricultural compound fertilizers and is also an important raw material for the chemical, metallurgical, pharmaceutical, and food industries. The main raw materials for potassium chloride production include halite and carnallite. Carnallite's main chemical composition is KCl-MgCl2-6H2O, along with sodium salts (NaCl) derived from sedimentary environments; its resources are relatively abundant.

[0003] Common methods for producing potassium chloride from carnallite include direct flotation, reverse flotation-cold crystallization, and cold crystallization-direct flotation. Among these, cold crystallization-direct flotation is a relatively new technology that utilizes controlled supersaturation in the carnallite decomposition system to achieve potassium chloride crystal growth at room temperature. However, current cold crystallization-direct flotation processes still face challenges such as small potassium chloride crystal size, high impurity content, and low purity of the resulting potassium chloride product. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of small particle size of potassium chloride crystals, high impurity content, and low purity of potassium chloride products in the existing technology, and to provide a method for preparing potassium chloride that promotes crystal growth. This method involves adding a secondary crystallization process after the slurry washing process to reduce the impact of gradual particle size breakage during the washing and desalination process, thereby facilitating the preparation of large-particle, high-purity potassium chloride products.

[0005] To achieve the above objectives, the present invention provides a method for preparing potassium chloride that promotes grain growth, comprising the following steps: (1) Decomposition and cold crystallization: After crushing carnallite, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry; (2) Direct flotation: The mixed potassium salt slurry is mixed with flotation reagents, and the slurry obtained after mixing is subjected to direct flotation to remove the mother liquor and obtain crude potassium filter cake; (3) Washing: The crude potassium filter cake is washed with fresh water to obtain a crude potassium mixed slurry; (4) Secondary crystallization: The crude potassium mixed slurry is passed into a crystallizer for secondary crystallization to obtain crystal slurry; (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride.

[0006] Preferably, in step (4), the conditions for secondary crystallization include: an initial feed rate of 180 m³ / h-200 m³ / h, an initial stirring speed of 20-48 rpm, and a crystallization time of 4-6 hours.

[0007] Preferably, in step (4), the conditions for secondary crystallization include: adjusting the stirring speed according to the solid-liquid ratio of the slurry in the crystallizer; when the solid-liquid ratio of the slurry is less than the preset solid-liquid ratio, reducing the stirring speed; when the solid-liquid ratio of the slurry is greater than the preset solid-liquid ratio, increasing the stirring speed; preferably, the preset solid-liquid ratio is 35%~45%.

[0008] Preferably, in step (3), the washing time is 0.5-1 hour.

[0009] Preferably, in step (2), the flotation reagent includes aliphatic amine cationic collector and a frother; preferably, the aliphatic amine cationic collector is dodecylamine and / or octadecylamine, and the frother is pine oil.

[0010] Preferably, in step (5), the moisture content of the crystal slurry after dehydration is 10-15%.

[0011] Preferably, in step (2), the potassium chloride content in the crude potassium filter cake is ≥60%.

[0012] Preferably, the average crystal grain size of the potassium chloride is 96~125μm.

[0013] Preferably, in step (4), the crystallizer comprises: A housing, wherein a feed inlet is provided at the top of the housing and a discharge outlet is provided at the bottom of the housing; A flow guide tube is disposed inside the housing. An annular baffle is arranged around the outer wall of the flow guide tube, and an annular channel is formed between the annular baffle and the inner wall of the housing. The top of the flow guide tube is closed, and the bottom is open. Several flow guide holes are provided on the flow guide tube. A stirrer is located inside the guide tube.

[0014] Preferably, the agitator includes a first agitator blade and a second agitator blade arranged from top to bottom. The first stirring blade is an inclined blade stirring blade, and the second stirring blade is a turbine blade stirring blade.

[0015] The technical solution of the present invention has at least the following beneficial effects: By adding a secondary crystallization process after the slurry washing treatment, the impact of gradual particle size breakage during the washing and desalination process is reduced, thus facilitating the preparation of large-particle, high-purity potassium chloride products. Using the preparation method of this invention, the average crystal particle size of the potassium chloride product can be increased from approximately 100 μm to 150 μm, an increase of up to 50%. The increased crystal size contributes to improved purity of the potassium chloride product. Simultaneously, with the increase in crystal particle size, the product's dehydration performance is significantly improved, which helps reduce moisture content, effectively reducing the load on subsequent drying processes, lowering energy consumption per unit product, and providing strong support for achieving green and low-carbon production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the crystallizer provided in an embodiment of the present invention.

[0017] The attached figures are labeled as follows: 1. Shell; 2. Flow guide tube; 3. Agitator; 4. Annular baffle; 11. Feed inlet; 12. Discharge outlet; 31. First stirring blade; 32. Second stirring blade. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] This invention provides a method for preparing potassium chloride that promotes grain growth, comprising the following steps: (1) Decomposition and cold crystallization: After crushing carnallite, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry; (2) Direct flotation: The mixed potassium salt slurry is mixed with flotation reagents, and the slurry obtained after mixing is subjected to direct flotation to remove the mother liquor and obtain crude potassium filter cake; (3) Washing: The crude potassium filter cake is washed with fresh water to obtain a crude potassium mixed slurry; (4) Secondary crystallization: The crude potassium mixed slurry is passed into a crystallizer for secondary crystallization to obtain crystal slurry; (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride.

[0021] By adding a secondary crystallization process after the slurry washing treatment, the impact of gradual particle size breakage during the washing and desalination process is reduced, which is beneficial for preparing large-particle, high-purity potassium chloride products. Simultaneously, with the increase in crystal particle size, the product's dehydration performance is significantly improved, which helps reduce the moisture content, effectively reducing the load on subsequent drying processes, lowering energy consumption per unit product, and providing strong support for achieving green and low-carbon production.

[0022] In this invention, in step (1), the carnallite ore can be carnallite ore produced by sun-drying in salt fields, and decomposition and crystallization can be carried out by a high-efficiency decomposition machine. The carnallite ore contains potassium chloride, sodium chloride, magnesium chloride, magnesium sulfate and water, and relative to 100 parts by weight of carnallite ore, the content of potassium chloride can be 10-13 parts by weight, the content of sodium chloride can be 10-25 parts by weight, the content of magnesium chloride can be 18-24 parts by weight, the content of magnesium sulfate can be 8-14 parts by weight, and the content of water can be 24-45 parts by weight.

[0023] In this invention, step (1), the decomposition and cold crystallization of carnallite are carried out simultaneously. First, the carnallite is decomposed to form a potassium chloride saturated slurry, and then the potassium chloride in the slurry is kept crystallized at room temperature. To obtain potassium chloride crystals with good particle size, the first process must be controlled well, that is, the decomposition rate of carnallite should not be too fast, otherwise excessive magnesium chloride supersaturation will be formed, producing a large amount of fine potassium chloride crystals. To reduce the decomposition rate of carnallite, part of the mother liquor during the crystallization process can be recycled to the decomposition process of carnallite, thereby reducing the driving force for the decomposition of carnallite.

[0024] In some embodiments, in step (2), the flotation reagent includes aliphatic amine cationic collectors and frothers; preferably, the aliphatic amine cationic collector is dodecylamine and / or octadecylamine, and the frother is pine oil.

[0025] In step (2) of the positive flotation process, the target mineral is KCl. Pure KCl crystals are initially weakly hydrophilic, but under the influence of aliphatic amine cationic collectors in the flotation reagents, the hydrophobic groups (such as hydrocarbon chains) of the collector are directionally adsorbed onto the KCl surface, while the hydrophilic groups (such as amino groups) face the aqueous phase, making the KCl surface hydrophobic, non-repellent, and prone to bubble adhesion. Impurity minerals (such as NaCl) have a stronger surface polarity, and their adsorption force on water molecules is much greater than that of the collector, maintaining strong hydrophilicity and easily adsorbing water, thus preventing bubble adhesion and ultimately remaining in the slurry. Therefore, under the stirring and aeration of the flotation machine, a large number of tiny bubbles with a diameter of approximately 0.1-1 mm are generated in the slurry. The hydrophobic KCl particles adhere to the bubble surface and rise with the bubbles to the slurry surface, forming a foam layer, which is then scraped off by the scraper to remove the mother liquor, resulting in a crude potassium filter cake. The hydrophilic impurity particles settle due to gravity and are discharged from the bottom of the flotation machine.

[0026] In addition, in actual implementation, step (2) can include roughing, scavenging, primary cleaning, secondary cleaning and other processing steps, depending on the actual process conditions.

[0027] In some embodiments, in step (2), the crude potassium filter cake contains potassium chloride, sodium chloride, magnesium chloride and magnesium sulfate, and the potassium chloride content in the crude potassium filter cake is ≥60%.

[0028] In some embodiments, the washing time in step (3) is 0.5-1 hour. Typically, the washing time in the prior art is about 30 minutes, while in this embodiment of the invention, the washing time can be appropriately extended, resulting in a higher sodium chloride content in the liquid phase compared to the shorter washing time in the prior art. In this embodiment of the invention, by extending the washing time of the crude potassium, the sodium chloride in the liquid phase reaches saturation more quickly during the slurry crystallization process, significantly reducing the amount of washing water used, achieving a water saving rate of over 40%. This measure significantly improves the production yield while reducing potassium ion loss in the liquid phase, increasing it from 55% to 60%, with a simultaneous increase in output of over 5%, achieving a dual improvement in resource efficiency and production benefits.

[0029] In some embodiments, the conditions for secondary crystallization in step (4) include: an initial feed rate of 180 m³ / h-200 m³ / h, an initial stirring speed of 20-48 rpm, and a crystallization time of 4-6 hours. Under these suitable conditions, secondary crystallization is beneficial for obtaining a product with a suitable particle size. Generally, the longer the crystallization time, the better it is to obtain a larger average crystal particle size of potassium chloride, higher purity, and lower moisture content. However, from an economic perspective, the crystallization time should not be too long.

[0030] In some embodiments, the conditions for secondary crystallization in step (4) include: adjusting the stirring speed according to the solid-liquid ratio of the slurry in the crystallizer; reducing the stirring speed when the solid-liquid ratio is less than a preset solid-liquid ratio, and increasing the stirring speed when the solid-liquid ratio is greater than the preset solid-liquid ratio; preferably, the preset solid-liquid ratio is 35%~45%. This improves the product's dehydration performance. In some embodiments, in step (5), the moisture content of the crystal slurry after dehydration is 10~15%, effectively reducing the load on subsequent drying processes. Based on this, in some embodiments, the natural gas consumption per unit of the subsequent drying process is reduced from approximately 18 m³ / t to approximately 16 m³ / t, achieving an overall gas saving rate of 11%, which not only reduces the energy consumption per unit product but also provides strong support for achieving green and low-carbon production.

[0031] In some embodiments, the average crystal grain size of the potassium chloride is 96~125 μm.

[0032] In some implementations, in step (4), see Figure 1 The crystallizer includes a shell 1, a guide cylinder 2, and a stirrer 3. The shell 1 has a feed inlet 11 at its top and a discharge outlet 12 at its bottom. The guide cylinder 2 is located inside the shell 1, and an annular baffle 4 is arranged around its outer wall, forming an annular channel between the baffle 4 and the inner wall of the shell 1. The top of the guide cylinder 2 is closed, while the bottom is open, and several guide holes are provided on the guide cylinder 2. The stirrer 3 is located inside the guide cylinder 2. The function of the guide cylinder 2 is to guide the flow direction of the slurry, enabling it to form an orderly circulation within the crystallizer. Under the action of the stirrer, the solution enters from the bottom of the guide cylinder 2, flows upward to the top of the guide cylinder 2, then enters the annular channel through the guide holes, and then flows downward along the annular channel to the bottom of the crystallizer, forming a cycle.

[0033] In some embodiments, the agitator 3 includes a first agitator blade 31 and a second agitator blade 32 arranged from top to bottom, wherein the first agitator blade 31 is an inclined blade agitator blade, and the second agitator blade 32 is a turbine blade agitator blade. Using these two types of agitator blades allows the slurry to form a uniform circulation within the crystallizer, promoting heat and mass transfer and preventing crystal deposition on the walls and bottom of the crystallizer.

[0034] In specific implementation, the process flow of the potassium chloride preparation method for promoting grain growth described in this invention mainly includes the following steps: (1) Decomposition and cold crystallization: After the carnallite ore produced by sun-drying in the salt field is crushed, water is added and it is put into a high-efficiency decomposition machine for decomposition and crystallization to obtain a mixed potassium salt slurry; wherein, the carnallite ore contains potassium chloride, sodium chloride, magnesium chloride, magnesium sulfate and water, and relative to 100 parts by weight of carnallite ore, the content of potassium chloride can be 10-13 parts by weight, the content of sodium chloride can be 10-25 parts by weight, the content of magnesium chloride can be 18-24 parts by weight, the content of magnesium sulfate can be 8-14 parts by weight, and the content of water can be 24-45 parts by weight.

[0035] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:(0.0054-0.0024), and the resulting slurry is subjected to direct flotation to remove the mother liquor and obtain crude potassium filter cake; wherein, the flotation reagents are octadecylamine, pine oil and hydrochloric acid. And the mass ratio of slurry, octadecylamine, pine oil and hydrochloric acid is 1:(0.0054-0.0065):(0.0024-0.004):(0.0108-0.013).

[0036] (3) Washing: Wash the crude potassium filter cake with fresh water to obtain crude potassium slurry; wash the crude potassium filter cake obtained in step (2) with fresh water at a mass ratio of 1:(0.5-1.2) for 0.5-1 hours.

[0037] (4) Secondary crystallization: The crude potassium slurry is fed into a crystallizer for secondary crystallization to obtain crystal slurry; wherein the initial feed rate is 180m³ / h-200m³ / h, the initial stirring speed is 20-48 rpm, and the crystallization time is 4-6 hours.

[0038] (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 100-120℃.

[0039] The present invention will be further described below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0041] In the following embodiments, the carnallite contains potassium chloride, sodium chloride, magnesium chloride, magnesium sulfate and water, and relative to 100 parts by weight of carnallite, the content of potassium chloride is 13 parts by weight, the content of sodium chloride is 20 parts by weight, the content of magnesium chloride is 23 parts by weight, the content of magnesium sulfate may be 10 parts by weight, and the content of water is 34 parts by weight.

[0042] Example 1 This embodiment illustrates a method for preparing potassium chloride that promotes grain growth.

[0043] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0044] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0045] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 0.5 hours.

[0046] (4) Secondary crystallization: The crude potassium slurry is fed into a crystallizer for secondary crystallization to obtain a crystal slurry; wherein the initial feed rate is 180 m³ / h, the initial stirring speed is 45 rpm, and the crystallization time is 4 hours. The stirring speed is adjusted according to the solid-liquid ratio of the slurry in the crystallizer. When the solid-liquid ratio of the slurry is less than the preset solid-liquid ratio, the stirring speed is reduced; when the solid-liquid ratio of the slurry is greater than the preset solid-liquid ratio, the stirring speed is increased; thereby maintaining the solid-liquid ratio of the slurry in the crystallizer at 40%.

[0047] (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0048] In step (4), the crystallizer includes a shell 1, a guide tube 2, and a stirrer 3. The shell 1 has an inlet 11 at its top and an outlet 12 at its bottom. The guide tube 2 is located inside the shell 1, and an annular baffle 4 surrounds its outer wall, forming an annular channel between the baffle 4 and the inner wall of the shell 1. The top of the guide tube 2 is closed, while the bottom has an opening, and several guide holes are provided on the guide tube. The stirrer is located inside the guide tube. Under the action of the stirrer 3, the solution enters from the bottom of the guide tube, flows upward to the top of the guide tube, then enters the annular channel through the guide holes, and then flows downward along the annular channel to the bottom of the crystallizer, forming a cycle.

[0049] In some embodiments, the agitator includes a first agitator blade 31 and a second agitator blade 32 arranged from top to bottom, wherein the first agitator blade 31 is an inclined blade agitator blade and the second agitator blade 32 is a turbine blade agitator blade.

[0050] Example 2 This embodiment illustrates a method for preparing potassium chloride that promotes grain growth. The difference between this embodiment and Embodiment 1 lies in the different parameters in step (4).

[0051] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0052] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0053] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 0.5 hours.

[0054] (4) Secondary crystallization: The crude potassium slurry is fed into a crystallizer for secondary crystallization to obtain a crystal slurry; wherein the initial feed rate is 180 m³ / h, the initial stirring speed is 45 rpm, and the crystallization time is 5 hours. The stirring speed is adjusted according to the solid-liquid ratio of the slurry in the crystallizer. When the solid-liquid ratio is less than the preset solid-liquid ratio, the stirring speed is reduced; when the solid-liquid ratio is greater than the preset solid-liquid ratio, the stirring speed is increased; thereby maintaining the solid-liquid ratio of the slurry in the crystallizer at 40%.

[0055] (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0056] Example 3 This embodiment illustrates a method for preparing potassium chloride that promotes grain growth. The difference between this embodiment and Embodiment 1 lies in the different parameters in step (4).

[0057] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0058] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0059] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 0.5 hours.

[0060] (4) Secondary crystallization: The crude potassium slurry is fed into a crystallizer for secondary crystallization to obtain a crystal slurry; wherein the initial feed rate is 180 m³ / h, the initial stirring speed is 45 rpm, and the crystallization time is 6 hours. The stirring speed is adjusted according to the solid-liquid ratio of the slurry in the crystallizer. When the solid-liquid ratio is less than the preset solid-liquid ratio, the stirring speed is reduced; when the solid-liquid ratio is greater than the preset solid-liquid ratio, the stirring speed is increased; thereby maintaining the solid-liquid ratio of the slurry in the crystallizer at 40%.

[0061] (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0062] Example 4 This embodiment illustrates a method for preparing potassium chloride that promotes grain growth. The difference between this embodiment and Embodiment 1 lies in the different parameters in step (4).

[0063] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0064] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0065] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 0.5 hours.

[0066] (4) Secondary crystallization: The crude potassium slurry is fed into a crystallizer for secondary crystallization to obtain a crystal slurry; wherein the initial feed rate is 180 m³ / h, the initial stirring speed is 45 rpm, and the crystallization time is 2 hours. The stirring speed is adjusted according to the solid-liquid ratio of the slurry in the crystallizer. When the solid-liquid ratio is less than the preset solid-liquid ratio, the stirring speed is reduced; when the solid-liquid ratio is greater than the preset solid-liquid ratio, the stirring speed is increased; thereby maintaining the solid-liquid ratio of the slurry in the crystallizer at 40%.

[0067] (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0068] Example 5 This embodiment illustrates a method for preparing potassium chloride that promotes grain growth. The difference between this embodiment and Embodiment 1 lies in the different parameters in step (3).

[0069] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0070] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0071] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 1 hour.

[0072] (4) Secondary crystallization: The crude potassium slurry is fed into a crystallizer for secondary crystallization to obtain a crystal slurry; wherein the initial feed rate is 180 m³ / h, the initial stirring speed is 45 rpm, and the crystallization time is 4 hours. The stirring speed is adjusted according to the solid-liquid ratio of the slurry in the crystallizer. When the solid-liquid ratio of the slurry is less than the preset solid-liquid ratio, the stirring speed is reduced; when the solid-liquid ratio of the slurry is greater than the preset solid-liquid ratio, the stirring speed is increased; thereby maintaining the solid-liquid ratio of the slurry in the crystallizer at 40%.

[0073] (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0074] Comparative Example 1 The difference between this comparative example and Example 1 is that secondary crystallization is not performed in this comparative example.

[0075] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0076] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0077] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 0.5 hours.

[0078] (4) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0079] Comparative Example 2 The difference between this comparative example and Example 1 is that secondary crystallization is not performed in this comparative example, and the washing time in step (3) is different.

[0080] (1) Decomposition and cold crystallization: After crushing the carnallite ore, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry.

[0081] (2) Direct flotation: The slurry obtained in step (1) is mixed with flotation reagents at a mass ratio of 1:0.0054, and the resulting slurry is subjected to direct flotation to remove the mother liquor, resulting in a crude potassium filter cake. The flotation reagents are octadecylamine, pine oil, and hydrochloric acid. The mass ratio of the slurry, octadecylamine, pine oil, and hydrochloric acid is 1:0.0054:0.0024:0.0108. The potassium chloride content in the crude potassium filter cake is 60%.

[0082] (3) Washing: The crude potassium filter cake is washed with fresh water to obtain crude potassium slurry; the crude potassium filter cake obtained in step (2) is washed with fresh water at a mass ratio of 1:0.5 for 1 hour.

[0083] (4) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride, wherein the drying temperature is 120℃.

[0084] Test case In step (5), the moisture content of the crystal slurry is obtained by drying the sample in a drying oven at 120±2℃ and then measuring the mass reduction of the sample.

[0085] Average crystal particle size test of potassium chloride: The average crystal particle size is tested by sieving. The vortex vibration generated by the oscillator is used to screen and classify the material by the high-frequency vibration of the sieve body. The standard sieve mesh number is selected as 60-160 mesh (pore size 250-96μm).

[0086] Potassium chloride purity test: Tetraphenylborate sodium-quaternary ammonium salt volumetric method: Potassium ions react with tetraphenylborate sodium to form a stable tetraphenylborate potassium precipitate. Excess tetraphenylborate sodium is titrated with a quaternary ammonium salt to form an insoluble tetraphenylborate quaternary ammonium salt. The potassium ion content is determined by indirect volumetric method.

[0087] The test results are shown in Table 1.

[0088] Table 1

[0089] As can be seen from the data in Table 1, compared to Comparative Examples 1 and 2 which did not employ secondary crystallization, the addition of secondary crystallization in the embodiments of this application effectively improves the average crystal particle size and purity of potassium chloride. Examples 1-4 show that increasing the crystallization time can increase the average crystal particle size of potassium chloride and reduce the moisture content. Examples 1 and 5 show that extending the washing time can increase the sodium chloride saturation in the crude potassium slurry liquid phase, reduce the potassium chloride content in the liquid phase, and simultaneously reduce the sodium chloride content in the solid phase, thereby improving the purity of potassium chloride.

[0090] 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 combinations of 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 chloride that promotes grain growth, characterized in that, Includes the following steps: (1) Decomposition and cold crystallization: After crushing carnallite, water is added to decompose and crystallize it to obtain a mixed potassium salt slurry; (2) Direct flotation: The mixed potassium salt slurry is mixed with flotation reagents, and the slurry obtained after mixing is subjected to direct flotation to remove the mother liquor and obtain crude potassium filter cake; (3) Washing: The crude potassium filter cake is washed with fresh water to obtain a crude potassium mixed slurry; (4) Secondary crystallization: The crude potassium mixed slurry is passed into a crystallizer for secondary crystallization to obtain crystal slurry; (5) Dehydration and drying: The obtained crystal slurry is dehydrated and dried to obtain potassium chloride.

2. The method for preparing potassium chloride according to claim 1, characterized in that, In step (4), the conditions for secondary crystallization include: The initial feed rate is 180 m³ / h-200 m³ / h, the initial stirring speed is 20-48 rpm, and the crystallization time is 4-6 hours.

3. The method for preparing potassium chloride according to claim 1 or 2, characterized in that, In step (4), the conditions for secondary crystallization include: The stirring speed is adjusted according to the solid-liquid ratio of the slurry in the crystallizer. When the solid-liquid ratio of the slurry is less than the preset solid-liquid ratio, the stirring speed is reduced; when the solid-liquid ratio of the slurry is greater than the preset solid-liquid ratio, the stirring speed is increased. Preferably, the preset solid-liquid ratio is 35% to 45%.

4. The method for preparing potassium chloride according to claim 3, characterized in that, In step (3), the washing time is 0.5-1 hour.

5. The method for preparing potassium chloride according to any one of claims 1-4, characterized in that, In step (2), the flotation reagents include aliphatic amine cationic collectors and frothers; preferably, the aliphatic amine cationic collectors are dodecylamine and / or octadecylamine, and the frothers are pine oil.

6. The method for preparing potassium chloride according to claim 3, characterized in that, In step (5), the moisture content of the crystal slurry after dehydration is 10-15%.

7. The method for preparing potassium chloride according to any one of claims 1-6, characterized in that, In step (2), the potassium chloride content in the crude potassium filter cake is ≥60%.

8. The method for preparing potassium chloride according to any one of claims 1-6, characterized in that, The average crystal size of the potassium chloride is 96~125μm.

9. The method for preparing potassium chloride according to any one of claims 1-8, characterized in that, In step (4), the crystallizer includes: A housing (1) is provided with a feed inlet (11) at the top and a discharge outlet (12) at the bottom. A flow guide tube (2) is disposed inside the housing (1). An annular baffle (4) is arranged around the outer wall of the flow guide tube (2). An annular channel is formed between the annular baffle (4) and the inner wall of the housing (1). The top of the flow guide tube (2) is closed, and the bottom is open. Several flow guide holes are provided on the flow guide tube (2). A stirrer (3) is installed inside the guide tube (2).

10. The method for preparing potassium chloride according to claim 9, characterized in that, The agitator (3) includes a first agitator blade (31) and a second agitator blade (32) arranged from top to bottom. The first stirring blade (31) is an inclined blade stirring blade, and the second stirring blade (32) is a turbine stirring blade.

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