Preparation method of food-grade potassium chloride based on salt lake brine

Abstract

The invention relates to the technical field of potassium chloride extraction, and discloses a preparation method of food-grade potassium chloride based on salt lake brine. The method comprises the following steps of cold crystallization, direct flotation, re-pulp washing, hot melting ultrafiltration, precipitation adsorption and concentration drying. By adopting a multi-stage impurity removal mechanism combining elution crystallization, physical adsorption and a chelating resin column, the entrainment loss caused in an intermittent production process can be effectively reduced, the utilization rate of potassium resources is improved, other extra impurity ions are not introduced in the whole impurity removal process, the subsequent impurity removal burden is relieved, and the production cost is reduced. The method is simple, convenient, green and environment-friendly, the advantages of salt lake potassium resources are fully played, the potassium resources are comprehensively utilized to produce food-grade potassium chloride which is increasingly short in supply, and the great requirements of China for food-grade potassium chloride products are met.

Description

Technical Field

[0001] The invention relates to the technical field of potassium chloride extraction, and in particular to a method for preparing food-grade potassium chloride based on salt lake brine. Background Art

[0002] Potassium chloride is a white crystalline powder or colorless crystal. Like sodium chloride, it is used as a flavoring agent for various foods such as agricultural products, aquatic products, livestock products, fermentation, seasoning, canned foods and convenience foods. In recent years, with the continuous expansion of social production scale, the demand for potassium chloride has also increased day by day. However, although my country has the advantage of vast salt lakes, the existing production process of edible potassium chloride cannot remove impurities such as ammonium chloride, calcium chloride, magnesium chloride, octadecylamine anti-caking agents and flotation agents in the raw materials to the maximum extent, resulting in high production cost, low purity and peculiar smell of edible potassium chloride, which is difficult to meet the quality requirements of the low-sodium salt industry and export potassium chloride. Most of the existing production processes of food-grade potassium chloride use chemical or physical impurity removal methods. For example, Zhao Sizhu of Jiangsu Salt Industry Research Institute proposed a process for preparing food-grade potassium chloride using 90% potassium chloride in 2000. A variety of agents such as impurity removers, bleaching agents and flocculants were added, which inevitably introduced other impurity ions, ultimately affecting the purity of the product. In 2010, Liu Liping et al. of Tianjin Changlu Hangu Salt Field Co., Ltd. proposed a potassium chloride refining process without adding other auxiliary agents, and only used physical methods to remove impurities, so the purity of the obtained product was not high. In 2014, Zhu Guilin of Lianyungang Shuren Kechuang Food Additive Co., Ltd. proposed a method of flotation agent in high-quality edible potassium chloride, and the process method proposed by Zhong Lin et al. in 2014 both used activated carbon adsorption to assist filtration, which may affect the whiteness of the product. In 2015, Xie Chao et al. of Changsha Design Institute of Chemical Industry proposed a preparation process for high-purity potassium chloride. The technical solution uses acid method to remove calcium ions and sulfate, alkali method to remove magnesium, sodium hexametaphosphate dispersion and cyclone high temperature to remove organic amines. Although the purity of the obtained product is relatively high, the use of sodium hexametaphosphate dispersion introduces additional ionic impurities and the long-term use of acid method to remove impurities has a certain degree of corrosion to the equipment. The raw materials for the above-mentioned processes for preparing food-grade potassium chloride are all industrial potassium chloride semi-finished products. Compared with the process of directly producing food-grade potassium chloride from salt lake brine, the comprehensive utilization rate of salt lake potassium resources is low, and the advantages of potassium resources cannot be fully utilized, resulting in waste of potassium resources and low product purity. Summary of the invention

[0003] The purpose of the present invention is to overcome the problems of low comprehensive utilization rate of salt lake potassium resources, serious waste of potassium resources and low economic benefits in the prior art, and to provide a method for preparing food-grade potassium chloride based on salt lake brine. The method for preparing food-grade potassium chloride based on salt lake brine of the present invention can simply and conveniently prepare high-purity potassium chloride.

[0004] In order to achieve the above object, the present invention provides a method for preparing food-grade potassium chloride based on salt lake brine, the method comprising the following steps:

[0005] (1) Cold crystallization: Use fresh water to crush the salt ore particles formed by drying the brine in the salt lake, then mix them with magnesium-containing mother liquor for wet grinding, and then crystallize the obtained mixture to obtain ore pulp;

[0006] (2) positive flotation: the ore pulp is mixed with a flotation agent, and the mixed slurry is subjected to flotation treatment, and then the magnesium-containing mother liquor is removed to obtain a crude potassium filter cake;

[0007] (3) Re-slurry washing: the crude potassium filter cake is subjected to a hot-melt washing with fresh water, and then subjected to centrifugal dehalogenation to obtain a wet refined potassium product;

[0008] (4) hot melt ultrafiltration: using pure water to perform a secondary hot melt on the wet refined potassium product, and then removing impurities to obtain a primary refined potassium solution;

[0009] (5) Precipitation adsorption: adding potassium carbonate and potassium hydroxide to the first-level refined potassium solution to adjust the pH value of the system, heating and reacting to generate a precipitate, then adding a filter aid, and then removing the precipitate to obtain a second-level refined potassium solution;

[0010] (6) Concentration and drying: the secondary refined potassium solution is passed through a chelating resin column to obtain a tertiary refined potassium solution, hydrochloric acid is added to the tertiary refined potassium solution to adjust the pH value of the system for a second time, and then potassium chloride is concentrated and precipitated by evaporation to supersaturation, and potassium chloride crystals are separated and dried.

[0011] Preferably, in step (1), the mass ratio of the salt ore particles to the fresh water is 1:(2-4), preferably 1:(2.5-3.5).

[0012] Preferably, in step (2), the mass ratio of the flotation agent to the slurry is 1:(3.5-6), preferably 1:(4.5-5.5).

[0013] Preferably, the flotation agent is at least one of octadecylamine, No. 2 oil and hydrochloric acid.

[0014] Preferably, in step (3), the mass ratio of the crude potassium filter cake to the fresh water is 1:(0.5-1.5), preferably 1:(0.9-1.1).

[0015] Preferably, in step (4), the mass ratio of the wet refined potassium product to the pure water is 1:(1.5-3.5).

[0016] Preferably, in step (5), the potassium carbonate and the potassium hydroxide are used in the form of an aqueous solution, and the mass concentration of the potassium carbonate solution is 25-50wt%.

[0017] Preferably, in step (5), the mass concentration of the potassium hydroxide solution is 20-25 wt %.

[0018] Preferably, in step (5), the pH value of the system after the first pH adjustment is 7-8.5.

[0019] Preferably, the filter aid is at least one of diatomaceous earth, activated carbon, expanded perlite and vermiculite.

[0020] Preferably, in step (6), the pH value of the system after the secondary pH adjustment is 6-7.5.

[0021] Preferably, in step (6), the drying conditions include: temperature of 250-350° C. and time of 20-40 min.

[0022] According to the method for preparing food-grade potassium chloride based on salt lake brine of the present invention, a multiple-stage impurity removal mechanism combining dissolution crystallization, physical adsorption and chelating resin column is adopted, which can effectively reduce the entrainment loss caused by the intermittent production process, improve the utilization rate of potassium resources, and no other additional impurity ions are introduced in the entire impurity removal process, which reduces the burden of subsequent impurity removal and further improves the purity of the product. The method is simple, convenient, green and environmentally friendly, and is more suitable for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention provides a process flow chart of a method for preparing food-grade potassium chloride based on salt lake brine. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0025] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] The method for preparing food-grade potassium chloride based on salt lake brine of the present invention comprises the following steps:

[0027] (1) Cold crystallization: Use fresh water to crush the salt ore particles formed by drying the brine in the salt lake, then mix them with magnesium-containing mother liquor for wet grinding, and then crystallize the obtained mixture to obtain ore pulp;

[0028] (2) positive flotation: the ore pulp is mixed with a flotation agent, and the mixed slurry is subjected to flotation treatment, and then the magnesium-containing mother liquor is removed to obtain a crude potassium filter cake;

[0029] (3) Re-slurry washing: the crude potassium filter cake is subjected to a hot-melt washing with fresh water, and then subjected to centrifugal dehalogenation to obtain a wet refined potassium product;

[0030] (4) hot melt ultrafiltration: using pure water to perform a secondary hot melt on the wet refined potassium product, and then removing impurities to obtain a primary refined potassium solution;

[0031] (5) Precipitation adsorption: adding potassium carbonate and potassium hydroxide to the first-level refined potassium solution to adjust the pH value of the system, heating and reacting to generate a precipitate, then adding a filter aid, and then removing the precipitate to obtain a second-level refined potassium solution;

[0032] (6) Concentration and drying: the secondary refined potassium solution is passed through a chelating resin column to obtain a tertiary refined potassium solution, hydrochloric acid is added to the tertiary refined potassium solution to adjust the pH value of the system for a second time, and then potassium chloride is concentrated and precipitated by evaporation to supersaturation, and potassium chloride crystals are separated and dried.

[0033] In step (1), the beach drying process can be carried out according to conventional operation methods in the art.

[0034] In step (1), the salt mine contains potassium chloride, sodium chloride, magnesium chloride, magnesium sulfate and water, and relative to 100 parts by weight of the salt mine, the content of potassium chloride can be 12.2-15.8 parts by weight, the content of sodium chloride can be 45.5-60.2 parts by weight, the content of magnesium chloride can be 1-2.5 parts by weight, the content of magnesium sulfate can be 9.5-12 parts by weight, and the content of water can be 5-8 parts by weight.

[0035] In a preferred embodiment, relative to 100 parts by weight of the salt ore, the content of potassium chloride is 13-14.5 parts by weight, the content of sodium chloride is 50-55.6 parts by weight, the content of magnesium chloride is 1.2-2 parts by weight, the content of magnesium sulfate is 10-11.5 parts by weight, and the content of water is 6.1-7.2 parts by weight.

[0036] In step (1), the mass ratio of the salt ore particles to the fresh water may be 1:(2-4), preferably 1:(2.5-3.5), specifically, for example, 1:2.5, 1:2.8, 1:3, 1:3.2 or 1:3.5.

[0037] In step (1), the specific process of the crushing treatment may include: crushing the salt ore particles to control the particle size to be less than 2 cm, and then performing ball milling. The crushing process can be implemented in various conventional crushers in the art. The feed rate of the ball milling process can be 150-190 t / h, preferably 160-180 t / h. In a specific embodiment, the ball milling process is implemented in an overflow ball mill.

[0038] In step (1), the mixing process can be carried out under stirring, and the stirring frequency can be 38-45 Hz. The crystallization process can be carried out in a crystallizer. The specific gravity of the crystallizer can be 1.254-1.265.

[0039] In step (1), the mixing process also includes processing according to the following method: mixing the crushed salt ore particles with the magnesium-containing mother liquor. The solid-liquid ratio of the salt ore particles to the magnesium-containing mother liquor can be 1: (1-2), preferably 1: (1-1.5). In a preferred case, the magnesium-containing mother liquor contains potassium chloride, sodium chloride, magnesium chloride and magnesium sulfate, and relative to 100 parts by weight of the magnesium-containing mother liquor, the content of potassium chloride is 2-4 parts by weight, the content of sodium chloride is 2-4 parts by weight, the content of magnesium chloride is 17.4-20.5 parts by weight, and the content of magnesium sulfate is 3.5-5.5 parts by weight. In a more preferred case, relative to 100 parts by weight of the magnesium-containing mother liquor, the content of potassium chloride is 2.5-3.5 parts by weight, the content of sodium chloride is 2.5-3.5 parts by weight, the content of magnesium chloride is 18-19.8 parts by weight, and the content of magnesium sulfate is 4-5 parts by weight.

[0040] In step (2), the mass ratio of the flotation agent to the ore pulp may be 1:(3.5-6), preferably 1:(4.5-5.5), specifically, for example, 1:4.5, 1:4.8, 1:5, 1:5.2 or 1:5.5.

[0041] In the present invention, the flotation reagent can be at least one of octadecylamine, No. 2 oil and hydrochloric acid. In a preferred embodiment, the flotation reagent is a combination of octadecylamine, No. 2 oil and hydrochloric acid, and the mass ratio of the pulp, the octadecylamine, the No. 2 oil and the hydrochloric acid can be 1: (0.5-0.8): (0.1-0.4): (0.5-2.5), preferably 1: (0.6-0.7): (0.2-0.3): (1-2).

[0042] In step (2), the mixing process further comprises the following treatment: adding water to the mixed slurry, the temperature of the water may be 80-100° C. In a specific embodiment, the mixing process is carried out in a blending tank.

[0043] In step (2), the specific operation steps of the flotation treatment may include: conveying the mixed slurry to a roughing flotation machine for roughing, conveying the product in the roughing foam tank to a fine I flotation machine for treatment, and then conveying it to a fine II flotation machine for treatment, and conveying the product in the bottom tank to a scavenging flotation machine. The flotation treatment process may be implemented in a flotation machine conventionally used in the art.

[0044] In step (2), the specific operation process of removing the magnesium-containing mother liquor can be: pumping the slurry after flotation treatment into a filter for filtration. The filtering conditions can include: the belt machine frequency is 15-40Hz, the vacuum degree is (-0.4)-0MPa, and the mesh number of the belt machine filter cloth is 165-250 mesh; in a preferred case, the filtering conditions include: the belt machine frequency is 20-35Hz, the vacuum degree is (-0.3)-0MPa, and the mesh number of the belt machine filter cloth is 175-200 mesh. In a specific embodiment, the filter is a vacuum belt filter, and the filter cake thickness of the vacuum belt filter can be 20-35mm, preferably 25-30mm.

[0045] In step (2), the moisture content of the crude potassium filter cake can be 0-25wt%, preferably 0-15wt%. In a preferred case, the crude potassium filter cake contains potassium chloride, sodium chloride, magnesium chloride and magnesium sulfate; and relative to 100 parts by weight of the crude potassium filter cake, the content of potassium chloride is 57.5-60.5 parts by weight, the content of sodium chloride is 15.5-19.2 parts by weight, the content of magnesium chloride is 1-4.5 parts by weight, and the content of magnesium sulfate is 4-7.5 parts by weight. In a further preferred case, relative to 100 parts by weight of the crude potassium filter cake, the content of potassium chloride is 58.1-59.5 parts by weight, the content of sodium chloride is 16.5-18.2 parts by weight, the content of magnesium chloride is 1.5-3.2 parts by weight, and the content of magnesium sulfate is 4.5-6.5 parts by weight.

[0046] In step (3), the mass ratio of the crude potassium filter cake to the fresh water may be 1:(0.5-1.5), preferably 1:(0.8-1.2), and further preferably 1:(0.9-1.1).

[0047] In step (3), the conditions of the first hot-melt washing may include: a stirring frequency of 40-50 Hz, a washing concentration of 45-60 wt%. The number of times of the first hot-melt washing may be one or more times, preferably multiple times. The first hot-melt washing process may be implemented in a repulping washing tank.

[0048] In step (3), the feed concentration of the centrifugal dehalogenation is 40-60wt%, preferably 45-55wt%. The centrifugal dehalogenation process can be implemented in various conventional centrifuges in the art.

[0049] In step (3), the wet refined potassium product contains potassium chloride, sodium chloride, magnesium chloride, magnesium sulfate and water, and relative to 100 parts by weight of the wet refined potassium product, the content of potassium chloride is 70.5-85.5 parts by weight, the content of sodium chloride is 2-5 parts by weight, the content of magnesium chloride is 0.01-0.2 parts by weight, the content of magnesium sulfate is 1-2.5 parts by weight, and the content of water is 8.5-12.5 parts by weight. In a preferred embodiment, relative to 100 parts by weight of the wet refined potassium product, the content of potassium chloride is 75.5-83.5 parts by weight, the content of sodium chloride is 3-4 parts by weight, the content of magnesium chloride is 0.02-0.1 parts by weight, the content of magnesium sulfate is 1.5-2 parts by weight, and the content of water is 9-12 parts by weight.

[0050] In step (4), the mass ratio of the wet refined potassium product to the pure water can be 1:(1.5-3.5), preferably 1:(2-3).

[0051] In step (4), the temperature of the secondary thermal dissolution may be 80-110°C, preferably 82-85°C.

[0052] In step (4), the secondary heat dissolution time may be 3-5 min, preferably 3.5-4.5 min. The secondary heat dissolution process may be carried out in a heat dissolution buffer tank.

[0053] In step (4), the impurity removal process may specifically be: the wet refined potassium product is mixed with pure water and then transported to an ultrafiltration device to remove impurities such as mud, insoluble suspended matter, sodium chloride, etc. mixed in the slurry. In a specific embodiment, the ultrafiltration device is an external pressure ultrafiltration device, and the ultrafiltration conditions include: the membrane inlet pressure may be 0.1-0.7MPa, preferably 0.1-0.5MPa; the feed temperature may be 22-25°C, preferably 22-24°C; the feed conductivity may be 18-22ms / cm, preferably 18-20ms / cm.

[0054] In step (4), the mass concentration of the primary refined potassium solution may be 25-35 wt %.

[0055] In step (5), the potassium carbonate is used in the form of an aqueous solution, and the mass concentration of the potassium carbonate solution can be 25-50wt%, preferably 28-40wt%. In a preferred case, the purpose of adding the potassium carbonate to the solution after the secondary thermal dissolution is to remove calcium ions in the solution. The content of carbonate ions in the potassium carbonate is 102-105 molar parts relative to 100 molar parts of the calcium ions in the solution.

[0056] In step (5), the potassium hydroxide is used in the form of an aqueous solution, and the concentration of the potassium hydroxide solution can be 18-25wt%, preferably 20-23wt%. In a preferred case, the purpose of adding the potassium hydroxide is to remove magnesium ions in the solution. The content of hydroxide ions in the potassium hydroxide is 204-210 molar parts relative to 100 molar parts of the magnesium ions in the solution.

[0057] In step (5), the specific process of heating can be: heating to a temperature of 80-110°C, preferably 80-90°C.

[0058] In step (5), the pH value of the system after the first pH adjustment can be 7-8.5, preferably 8.5-10. Adjusting the pH value of the system by adjusting the amount of potassium carbonate and potassium hydroxide is more conducive to the subsequent impurity removal process.

[0059] In step (5), the solid precipitated during the dissolution and crystallization process may include at least one of potassium salt, sodium salt and magnesium salt.

[0060] In step (5), the specific operation process of the solid-liquid separation may include: pumping the mixture after dissolution and crystallization into an automatic slag discharge filter for filtration. The filtration pressure may be 0.3-0.392 MPa.

[0061] In step (5), the filter aid may be at least one of diatomaceous earth, activated carbon, expanded perlite and vermiculite. In the most preferred embodiment, the filter aid is expanded perlite. The impurities removed by the adsorption process may include at least one of octadecylamine and No. 2 oil. The weight of the adsorbent is 110-150 parts by weight relative to 100 parts by weight of the impurities in the primary potassium chloride solution.

[0062] In step (5), the mass concentration of the secondary refined potassium solution can be 30-40wt%.

[0063] In step (6), the pH value of the system after the secondary pH adjustment can be 6-7.5, preferably 6.5-7.2. The pH value of the system is adjusted by adding hydrochloric acid, and the concentration of the hydrochloric acid can be 0.3-1.0wt%, preferably 0.4-0.8wt%.

[0064] In step (6), the material of the chelating resin column can be at least one of D401 type, D402 type and D403 type. In the most preferred embodiment, the material of the chelating resin column is D402 type.

[0065] In step (6), the evaporation conditions may include: a temperature of 80-85° C. and a vacuum degree of (-0.072)-0.095 MPa. The evaporation process may be carried out in a reduced pressure evaporation crystallizer.

[0066] In step (6), the separation process can be carried out in a centrifuge. The conditions for the centrifugal separation include: the current can be 75-100A, and the screen gap can be 0.1-0.2mm.

[0067] In step (6), the drying temperature may be 250-350°C, preferably 250-300°C; the spray drying time may be 20-40 min, preferably 25-35 min. The drying equipment may be at least one of a pressure spray dryer, a centrifugal spray dryer, an airflow spray dryer and a disc dryer. In the most preferred embodiment, the spray drying equipment may be a disc dryer.

[0068] In the specific implementation process, the process flow of the method for preparing food-grade potassium chloride based on salt lake brine of the present invention is as follows: Figure 1 As shown, it mainly includes the following steps:

[0069] (1) Cold crystallization: placing the brine outdoors for drying to form salt ore particles, wherein the salt ore contains 12.2-15.8wt% potassium chloride, 45.5-60.2wt% sodium chloride, 1-2.5wt% magnesium chloride, 9.5-12wt% magnesium sulfate and 5-8wt% water, followed by crushing and ball milling in sequence, with the feed rate of the ball milling being 150-190t / h, and the treated salt ore particles and fresh water being mixed in a mass ratio of 1:(2-4) The magnesium-containing mother liquor is transported to a crystallizer for uniform mixing, wherein the specific gravity of the crystallizer is 1.254-1.265 and the stirring frequency is 38-45 Hz; then the magnesium-containing mother liquor is transported to a crystallizer for mixing, decomposition and crystallization according to a mass ratio of salt ore particles to magnesium-containing mother liquor of 1:(1-2) to obtain a slurry, wherein the magnesium-containing mother liquor contains 2-4wt% of potassium chloride, 2-4wt% of sodium chloride, 17.4-20.5wt% of magnesium chloride, 3.5-5.5wt% of magnesium sulfate and water;

[0070] (2) positive flotation: the ore pulp obtained in step (1) and the flotation agent are mixed and stirred in a blending tank in a mass ratio of 1:(3.5-6), wherein the flotation agent is a combination of octadecylamine, No. 2 oil and hydrochloric acid, and the mass ratio of the ore pulp, the octadecylamine, the No. 2 oil and the hydrochloric acid is 1:(0.5-0.8):(0.1-0.4):(0.5-2.5), and hot water with a temperature of 80-100° C. is added; the mixed ore pulp is then pumped into a flotation machine for flotation operation, and the slurry after flotation treatment is pumped into a filter for filtration, wherein the thickness of the filter cake layer is 20-35 mm, the belt machine frequency is 15-40 Hz, the vacuum degree is (-0.4)-0 MPa, and the mesh number of the belt machine filter cloth is 165-250 meshes, to obtain a crude potassium filter cake;

[0071] (3) Repulping and washing: the crude potassium filter cake obtained in step (2) is placed in a repulping washing tank with fresh water in a mass ratio of 1:(0.5-1.5) for hot dissolution washing, with a stirring frequency of 40-50 Hz and a washing concentration of 45-60 wt %. The washed crude potassium filter cake is then centrifuged with a feed concentration of 40-60 wt % to obtain a wet refined potassium product;

[0072] (4) hot melt ultrafiltration: the wet refined potassium product obtained in step (3) and pure water are placed in a hot melt buffer tank at a mass ratio of 1: (1.5-3.5), and fresh water at 82-85° C. is added for secondary hot melt, the duration of which is 3-5 min, and then the mixture is transported to an external pressure ultrafiltration device for filtration, the membrane pressure is 0.1-0.7 MPa, the feed temperature is 22-25° C., and the feed conductivity is 18-22 ms / cm, to obtain a first-grade refined potassium solution;

[0073] (5) Precipitation adsorption: The first-grade refined potassium solution in step (4) is added with stirring to a potassium carbonate solution with a mass concentration of 25-50 wt% and a potassium hydroxide solution with a mass concentration of 18-25 wt% and heated, and tested with a pH meter to adjust the solution pH to 7-8.5, the heating temperature is 80-110° C., and then a filter aid is added to mix and stir evenly, and pumped into an automatic slag discharge filter to remove excess impurities, the filter pressure is 0.3-0.392 MPa, and a second-grade refined potassium solution is obtained;

[0074] (6) Concentrating and drying: passing the secondary refined potassium solution obtained in step (5) through a chelating resin column to obtain a tertiary refined potassium solution; gradually adding a hydrochloric acid solution with a concentration of 0.3-1.0 wt % to the tertiary refined potassium solution until the pH value of the solution is adjusted to 6-7.5; then placing the pH-adjusted solution in a reduced pressure evaporation crystallizer for evaporation at a vacuum degree of (-0.072)-0.095 MPa, separating the liquid and the potassium chloride solid by centrifugation at a current of 75-100 A and a screen gap of 0.1-0.2 mm, and placing the potassium chloride solid in a disc dryer for spray drying at 250-350° C. for 20-40 min.

[0075] The following examples further illustrate the method for preparing food-grade potassium chloride based on salt lake brine of the present invention. The examples are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0076] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0077] Example 1

[0078] The composition of the salt ore used in this embodiment is: 13.5wt% potassium chloride, 52.3wt% sodium chloride, 1.4wt% magnesium chloride, 10.6wt% magnesium sulfate, and 6.8wt% water;

[0079] The composition of the magnesium-containing mother solution used is: 2.9wt% potassium chloride, 2.6wt% sodium chloride, 3.1wt% magnesium chloride and 4.5wt% magnesium sulfate;

[0080] The flotation reagent used is a mixture of octadecylamine, No. 2 oil (No. 2 flotation oil in the mineral processing reagent, purchased from Sichuan Suihui Trading Co., Ltd.) and hydrochloric acid (concentration of 36-38%, purchased from Golmud Shuangqiang Chemical Products Sales Co., Ltd.) in a mass ratio of 0.6:0.3:1;

[0081] The filter aid used was expanded perlite, brand 50, purchased from Tianjin Julong Insulation Material Manufacturing Co., Ltd.

[0082] The chelating resin column used was a D402 chelating resin column purchased from Langfang Senate Chemical Co., Ltd.

[0083] (1) Cold crystallization: Place the brine outdoors to dry in the sun to form salt ore particles, and then crush and ball mill the particles in turn. The feed rate of the ball milling process is 170t / h. The treated salt ore particles and fresh water are transported to the crystallizer at a mass ratio of 1:3 and mixed evenly. The specific gravity of the crystallizer is set to 1.255 and the stirring frequency is 40Hz. Then, the magnesium-containing mother liquor is transported to the crystallizer at a mass ratio of 1:1.25 to mix, decompose, and crystallize to obtain ore slurry.

[0084] (2) Positive flotation: the ore pulp obtained in step (1) and the flotation agent are mixed and stirred in a blending tank at a mass ratio of 5:1, and hot water at a temperature of 90° C. is added; the mixed ore pulp is pumped into a flotation machine for flotation operation, and the slurry after flotation treatment is pumped into a filter for filtration, wherein the thickness of the filter cake layer is 25 mm, the belt frequency is 25 Hz, the vacuum degree is -0.4 MPa, and the mesh number of the belt filter cloth is 190 meshes, to obtain a crude potassium filter cake;

[0085] (3) Repulping and washing: the crude potassium filter cake obtained in step (2) is placed in a repulping and washing tank with fresh water in a mass ratio of 1:1 for hot dissolution washing, with a stirring frequency of 45 Hz and a washing concentration of 50 wt %. The washed crude potassium filter cake is then centrifuged with a feed concentration of 48 wt % to obtain a wet refined potassium product;

[0086] (4) hot melt ultrafiltration: the wet refined potassium product obtained in step (3) and pure water are placed in a hot melt buffer tank at a mass ratio of 1:2, and fresh water at 85° C. is added for secondary hot dissolution for 4 min. The mixture is then pumped into an external pressure ultrafiltration device for filtration at a pressure of 0.4 MPa, a feed temperature of 23° C., and a feed conductivity of 18 ms / cm. Impurities such as silt, insoluble suspended matter, and sodium chloride mixed in the slurry are removed to obtain a first-grade refined potassium solution;

[0087] (5) Precipitation adsorption: The first-level refined potassium solution in step (4) is added with a potassium carbonate solution having a mass concentration of 30 wt% and a potassium hydroxide solution having a mass concentration of 22 wt% under stirring and heated, and tested with a pH meter, and the pH value of the solution is adjusted to 7.8, the heating temperature is 85° C., and the time is 3 h; then it is allowed to stand for 2.5 h, and then expanded perlite is added and mixed and stirred evenly, and then pumped into an automatic slag discharge filter to remove excess impurities, and the pressure of the filter is 0.382 MPa, to obtain a second-level refined potassium solution;

[0088] (6) Concentration and drying: the secondary refined potassium solution obtained in step (5) is passed through a chelating resin column to obtain a tertiary refined potassium solution; a 0.5% hydrochloric acid solution is gradually added to the tertiary refined potassium solution, the pH value of the solution is detected in real time using a pH meter, and the pH value of the solution is adjusted to 6.5; the pH-adjusted solution is then placed in a reduced pressure evaporation crystallizer for evaporation at a vacuum degree of -0.081 MPa, the liquid and the potassium chloride solid are separated by centrifugation at a current of 75 A and a screen gap of 0.15 mm, and the potassium chloride solid is placed in a disc dryer for spray drying at 280° C. for 30 min to obtain the potassium chloride crystal A1 of the present invention.

[0089] Example 2

[0090] The salt mine, magnesium-containing mother liquor, filter aid and chelating resin column used in this embodiment are the same as those in Example 1, and the flotation reagent used is a mixture of octadecylamine, No. 2 oil (No. 2 flotation oil in the ore dressing reagent, purchased from Sichuan Suihui Trading Co., Ltd.) and hydrochloric acid (concentration of 36-38%, purchased from Golmud Shuangqiang Chemical Products Sales Co., Ltd.) in a mass ratio of 0.65:0.25:1.5.

[0091] (1) Cold crystallization: Place the brine outdoors to form salt ore particles, and then crush and ball mill the particles in turn. The feed rate of the ball milling process is 180t / h. The treated salt ore particles and fresh water are transported to the crystallizer at a mass ratio of 1:2.5 and mixed evenly. The specific gravity of the crystallizer is 1.254 and the stirring frequency is 45Hz. Then, the magnesium-containing mother liquor is transported to the crystallizer at a mass ratio of 1:1.5 between the salt ore particles and the magnesium-containing mother liquor to mix, decompose, and crystallize to obtain a slurry.

[0092] (2) Positive flotation: the ore pulp obtained in step (1) and the flotation agent are mixed and stirred in a blending tank at a mass ratio of 5.5:1, and then hot water at a temperature of 80° C. is added; the mixed ore pulp is then pumped into a flotation machine for flotation operation, and then the flotation-treated slurry is pumped into a filter for filtration, the thickness of the filter cake layer is 25 mm, the belt frequency is 35 Hz, the vacuum degree is -0.4 MPa, and the mesh number of the belt filter cloth is 200 meshes, to obtain a crude potassium filter cake;

[0093] (3) Repulping and washing: the crude potassium filter cake obtained in step (2) is placed in a repulping washing tank with fresh water in a mass ratio of 1:0.9 for hot dissolution washing, with a stirring frequency of 50 Hz and a washing concentration of 45 wt %. The washed crude potassium filter cake is then centrifuged at a feed concentration of 55 wt % to obtain a wet refined potassium product;

[0094] (4) hot melt ultrafiltration: the wet refined potassium product obtained in step (3) and pure water are placed in a hot melt buffer tank at a mass ratio of 1:3, fresh water at 85° C. is added for secondary hot dissolution for 4.5 min, and then the mixture is pumped into an external pressure ultrafiltration device for filtration at a pressure of 0.4 MPa, a feed temperature of 22° C., and a feed conductivity of 18 ms / cm. Impurities such as silt, insoluble suspended matter, and sodium chloride mixed in the slurry are removed to obtain a first-grade refined potassium solution;

[0095] (5) Precipitation adsorption: The first-grade refined potassium solution in step (4) is added with stirring to a potassium carbonate solution with a mass concentration of 40 wt% and a potassium hydroxide solution with a mass concentration of 23 wt% and heated, and tested with a pH meter to adjust the solution pH to 8.2, the heating temperature is 85° C., and the time is 3 h; then allowed to stand for 2.5 h, and then expanded perlite is added and mixed and stirred evenly, and pumped into an automatic slag discharge filter to remove excess impurities, and the pressure of the filter is 0.382 MPa, to obtain a second-grade refined potassium solution;

[0096] (6) Concentration and drying: the secondary potassium chloride solution obtained in step (5) is passed through a chelating resin column to obtain a tertiary refined potassium solution; a 0.6% hydrochloric acid solution is gradually added to the tertiary refined potassium solution, the pH value of the solution is detected in real time using a pH meter, and the pH value of the solution is adjusted to 7.2; the pH-adjusted solution is then placed in a reduced pressure evaporation crystallizer for evaporation at a vacuum degree of 0.095 MPa; the liquid and the potassium chloride solid are separated by centrifugation at a current of 75 A and a screen gap of 0.12 mm; the potassium chloride solid is placed in a disc dryer at 300° C. for drying for 25 min to obtain potassium chloride crystals A2 of the present invention.

[0097] Example 3

[0098] The salt mine, magnesium-containing mother liquor, filter aid and chelating resin column used in this embodiment are the same as those in Example 1, and the flotation reagent used is a mixture of octadecylamine, No. 2 oil (No. 2 flotation oil in the ore dressing reagent, purchased from Sichuan Suihui Trading Co., Ltd.) and hydrochloric acid (concentration of 36-38%, purchased from Golmud Shuangqiang Chemical Products Sales Co., Ltd.) in a mass ratio of 0.7:0.2:2.

[0099] (1) Cold crystallization: Place the brine outdoors to form salt ore particles, and then crush and ball mill the particles in turn. The feed rate of the ball milling process is 160t / h. The treated salt ore particles and fresh water are transported to the crystallizer at a mass ratio of 1:3.5 and mixed evenly. The specific gravity of the crystallizer is 1.265 and the stirring frequency is 38Hz. Then, the magnesium-containing mother liquor is transported to the crystallizer at a mass ratio of 1:1 between the salt ore particles and the magnesium-containing mother liquor to mix, decompose, and crystallize to obtain a slurry.

[0100] (2) Positive flotation: the ore pulp obtained in step (1) and the flotation reagent are mixed and stirred in a blending tank at a mass ratio of 4.5:1, and hot water at a temperature of 100° C. is added; the mixed ore pulp is pumped into a flotation machine for flotation operation, and the flotation-treated slurry is pumped into a filter for filtration, the thickness of the filter cake layer is 25 mm, the belt frequency is 20 Hz, the vacuum degree is -0.4 MPa, and the mesh number of the belt filter cloth is 175 meshes, to obtain a crude potassium filter cake;

[0101] (3) Repulping and washing: the crude potassium filter cake obtained in step (2) is placed in a repulping washing tank with fresh water in a mass ratio of 1:1.1 for washing, the stirring frequency is 40 Hz, the washing concentration is 60 wt %, and the washed crude potassium filter cake is then centrifuged at a feed concentration of 45 wt % to obtain a wet refined potassium product;

[0102] (4) hot melt ultrafiltration: the wet refined potassium product obtained in step (3) and pure water are placed in a hot melt buffer tank at a mass ratio of 1:2.5, and fresh water at 85° C. is added for secondary hot dissolution for 3.5 min. The mixture is then pumped into an external pressure ultrafiltration device for filtration at a pressure of 0.4 MPa, a feed temperature of 23° C., and a feed conductivity of 18 ms / cm. Impurities such as silt, insoluble suspended matter, and sodium chloride mixed in the slurry are removed to obtain a first-grade refined potassium solution;

[0103] (5) Precipitation adsorption: The first-grade refined potassium solution in step (4) is added with stirring to a potassium carbonate solution with a mass concentration of 28 wt% and a potassium hydroxide solution with a mass concentration of 20 wt% and heated, and tested with a pH meter to adjust the solution pH to 7.2, the heating temperature is 85° C., and the time is 3 h; then allowed to stand for 2.5 h, and then expanded perlite is added and mixed and stirred evenly, and pumped into an automatic slag discharge filter to remove excess impurities, and the pressure of the filter is 0.3 MPa, to obtain a second-grade refined potassium solution;

[0104] (6) Concentrating and drying: passing the secondary potassium chloride solution obtained in step (5) through a chelating resin column to obtain a tertiary potassium chloride solution; gradually adding a 0.7% hydrochloric acid solution to the tertiary potassium chloride solution, using a pH meter to detect the pH value of the solution in real time, and adjusting the pH value of the solution to 6.9; then placing the pH-adjusted solution in a reduced pressure evaporation crystallizer for evaporation at a vacuum degree of -0.072 MPa; separating the liquid and the potassium chloride solid by centrifugation at a current of 90 A and a screen gap of 0.18 mm; placing the potassium chloride solid in a disc dryer for spray drying at 250° C. for 35 min to obtain the potassium chloride crystal A3 of the present invention.

[0105] Example 4

[0106] Potassium chloride crystals were prepared according to the method of Example 1, except that in step (2), the mass ratio of the ore pulp to the flotation agent was 1:6.0, and potassium chloride crystals A4 were finally prepared.

[0107] Example 5

[0108] Potassium chloride crystals were prepared according to the method of Example 1, except that in step (2), the mass ratio of the ore pulp to the flotation agent was 1:3.5, and potassium chloride crystals A5 were finally prepared.

[0109] Comparative Example 1

[0110] The system of salt lake brine used in this comparative example is Na + ,K + Mg 2+ / / Cl - ,SO4 2- -H2O five-element water-salt system, according to the law of brine evaporation and salt precipitation, when the brine evaporates to Na + The content of is 0.32%, the content of K is 1.39%, and the content of Mg is 2+ The content of Cl is 6.93%, - The content is 19.74%, SO4 2- When the content is 3.08%, carnallite potassium ore is saturated and precipitated. The obtained potassium ore is subjected to cold crystallization, positive flotation and centrifugal drying to prepare potassium chloride crystal D1.

[0111] Test Case

[0112] The potassium chloride crystals A1-A5 obtained in Examples 1-5 and the potassium chloride crystals D1 obtained in Comparative Example 1 were tested for purity, and the testing method was as follows:

[0113] Reagents required for the test: nitric acid, hydrochloric acid (superior purity), potassium nitrate, silver nitrate, sodium hydroxide, chloroform, sodium hypochlorite, cesium chloride, sodium standard solution, lead standard solution, arsenic standard solution, phenolphthalein, bromophenol blue, etc.

[0114] Instruments required for the test: liquid chromatograph, inductively coupled plasma emission spectrometer Avio550, atomic absorption spectrophotometer, scanning electron microscope SU3800, Rigaku MiniFlex600 desktop powder diffractometer, muffle furnace, electric oven, etc.

[0115] Purity test of potassium chloride crystals: weigh about 0.25g of the sample after drying for 2h, accurate to 0.0001g, place it in a 100mL beaker, add 40mL of water to dissolve, add 1 drop of bromophenol blue indicator solution, add 1 drop to 2 drops of nitric acid solution to make the solution just yellow, use a standard silver nitrate titration solution with a concentration of about 0.1mol, and then start the operation according to the standard steps in 46 of GB / T 3050-2000, record the total volume and corresponding potential value after each addition of the standard silver nitrate titration solution, and calculate the volume (V) of the standard silver nitrate titration solution consumed by the titration to the endpoint.

[0116] The mass fraction of potassium chloride is ω1, the value is expressed in %, and the calculation formula is as follows:

[0117]

[0118] Where:

[0119] V--The volume of the silver nitrate standard titration solution consumed in the titration, in milliliters (mL);

[0120] c--The exact value of the concentration of the standard silver nitrate titration solution, in moles per liter (mol);

[0121] ω0--The mass fraction of the measured drying loss, expressed in %;

[0122] m--the numerical value of the sample mass, in grams (g);

[0123] M - the numerical value of the molar mass of potassium chloride (KC1), in grams per mole (g / mol) (M = 74.55).

[0124] The arithmetic mean of the parallel determination results was taken as the determination result. The absolute difference between the two parallel determination results was no greater than 0.2%. The test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] It can be seen from the data in Table 1 that the potassium chloride crystals prepared by the method for preparing food-grade potassium chloride based on salt lake brine described in the present invention are obviously higher in purity and lower in sodium ion content. Specifically, in a preferred case, the potassium chloride crystals prepared in the embodiment have a purity of up to 99.9%, and a sodium ion content as low as 0.2%. Therefore, according to the method for preparing food-grade potassium chloride based on salt lake brine described in the present invention, the multiple classification impurity removal mechanisms combining dissolution crystallization, physical adsorption, and chelating resin columns are adopted, which can effectively reduce the entrainment loss brought in the discontinuous production process, improve the utilization rate of potassium resources, and do not introduce other additional impurity ions in the whole impurity removal process, thereby reducing the subsequent impurity removal burden and further improving the product purity. The method is simple, convenient, green and environmentally friendly, gives full play to the salt lake potassium resource advantage, comprehensively utilizes potassium resources to produce the increasingly scarce food-grade potassium chloride, and meets the great demand for food-grade potassium chloride products in my country.

[0128] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing food-grade potassium chloride based on salt lake brine, characterized in that: The method comprises the following steps: (1) Cold crystallization: Use fresh water to crush the salt ore particles formed by drying the brine in the salt lake, then mix them with magnesium-containing mother liquor for wet grinding, and then crystallize the obtained mixture to obtain ore pulp; (2) positive flotation: the ore pulp is mixed with a flotation agent, and the mixed slurry is subjected to flotation treatment, and then the magnesium-containing mother liquor is removed to obtain a crude potassium filter cake; (3) Re-slurry washing: the crude potassium filter cake is subjected to a hot-melt washing with fresh water, and then subjected to centrifugal dehalogenation to obtain a wet refined potassium product; (4) hot melt ultrafiltration: using pure water to perform a secondary hot melt on the wet refined potassium product, and then removing impurities to obtain a primary refined potassium solution; (5) Precipitation adsorption: adding potassium carbonate and potassium hydroxide to the first-level refined potassium solution to adjust the pH value of the system, heating and reacting to generate a precipitate, then adding a filter aid, and then removing the precipitate to obtain a second-level refined potassium solution; (6) Concentration and drying: the secondary refined potassium solution is passed through a chelating resin column to obtain a tertiary refined potassium solution, hydrochloric acid is added to the tertiary refined potassium solution to adjust the pH value of the system for a second time, and then potassium chloride is concentrated and precipitated by evaporation to supersaturation, and potassium chloride crystals are separated and dried.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of the salt ore particles to the fresh water is 1:(2-4), preferably 1:(2.5-3.5).

3. The method according to claim 1, characterized in that: In step (2), the mass ratio of the flotation reagent to the ore pulp is 1:(3.5-6), preferably 1:(4.5-5.5).

4. The method according to claim 1 or 3, characterized in that: The flotation reagent is at least one of octadecylamine, No. 2 oil and hydrochloric acid.

5. The method according to claim 1, characterized in that In step (3), the mass ratio of the crude potassium filter cake to the fresh water is 1:(0.5-1.5), preferably 1:(0.9-1.1).

6. The method according to claim 1, characterized in that In step (4), the mass ratio of the wet refined potassium product to the pure water is 1:(1.5-3.5).

7. The method according to claim 1, characterized in that In step (5), the potassium carbonate and the potassium hydroxide are used in the form of an aqueous solution, and the mass concentration of the potassium carbonate solution is 25-50wt%; and / or The mass concentration of the potassium hydroxide solution is 20-25wt%; and / or After the first pH adjustment, the pH value of the system is 7-8.

5.

8. The method according to claim 1 or 7, characterized in that: The filter aid is at least one of diatomaceous earth, activated carbon, expanded perlite and vermiculite.

9. The method according to claim 1, characterized in that: In step (6), the pH value of the system after the secondary pH adjustment is 6-7.

5.

10. The method according to claim 1 or 9, characterized in that: In step (6), the drying conditions include: temperature of 250-350° C. and time of 20-40 min.

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