Method for recovering sylvite from sylvite-containing water

Abstract

The invention relates to the technical field of water treatment, in particular to a method for recovering sylvite from sylvite-containing water. Potassium salt-containing water and a recrystallization agent are mixed and heated, the recrystallization agent reacts with potassium ions to generate new potassium-containing double salt crystals, the potassium-containing double salt crystals are ground and decomposed to obtain potassium salt crystals, and at least part of the potassium salt crystals are obtained by lattice distortion and chemical bond recombination of the potassium-containing double salt crystals; the sylvite comprises potassium chloride or potassium sulfate. Therefore, the problems of low recovery rate and low product purity of the existing sylvite recovery process are solved. The potassium salt is extracted by adopting a recrystallization method and a grinding decomposition method, so that potassium resources of salt lake chemical engineering, industrial potassium-containing mixed salt and industrial byproduct potassium salt-containing water can be effectively recovered, and an agricultural potassium fertilizer product is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and more particularly to a method for recovering potassium salts from potassium-containing brines. Background Art

[0002] Most of the potassium salt products in the world are produced into fertilizers required for crops, and a small part of potassium salts is used in industrial production, mainly for solid wastes or wastewaters rich in potassium salts generated during the production of products using potassium elements by fertilizer factories, pharmaceutical factories and chemical factories. Potassium fertilizer is one of the three major fertilizers required for crop growth, mainly as a yield-increasing fertilizer for the vast majority of crops. Potassium fertilizer is an acidic fertilizer and can be mainly divided into potassium chloride fertilizer and potassium sulfate fertilizer. Potassium salt ore is one of the national critically scarce mineral resources. With the rapid growth of the world's demand for potassium salts, the recycling of potassium salts is an important task. Therefore, finding new sources of potassium elements and producing inexpensive potassium products has become the top priority in the world potassium salt market. In addition to natural potassium resources and seawater potassium sources, potassium-containing wastewater rich in potassium salts generated during the production or recycling of lithium batteries, fertilizers, glass, medicine or semiconductors in industries and agriculture, as well as potassium-containing brines produced by dissolving industrial by-products containing potassium salts and industrial by-products containing potassium mixed salts are a kind of potassium resource with great development value. Therefore, with the rapid development of industry and agriculture, the discharge of a large amount of potassium salt wastewater has led to a shortage of potassium salts. Extracting potassium salts from potassium-containing wastewater is of great significance and application value in resource recycling and circular utilization.

[0003] The existing potassium salt recovery process is extraction and evaporation crystallization, with great recovery difficulty, low recovery rate, low product purity and relatively high production cost. Summary of the Invention

[0004] To solve the problems of low recovery rate and low product purity in the existing potassium salt recovery process, the present invention provides a method for recovering potassium salts from potassium-containing brines, comprising the following steps:

[0005] The potassium-containing brine is mixed with a recrystallization agent and heated. The recrystallization agent reacts with potassium ions to form potassium-containing double salt crystals. The potassium-containing double salt crystals are ground and decomposed to obtain potassium salt crystals, wherein at least part of the potassium salt crystals are obtained by lattice distortion and chemical bond recombination of the potassium-containing double salt crystals;

[0006] The potassium salts include potassium chloride or potassium sulfate.

[0007] Preferably, the potassium-containing brine is heated under the conditions of a heating temperature range of 40 - 90 °C and a heating time range of 1 - 4 hours, and then the heated potassium-containing brine is mixed with the recrystallization agent and heated.

[0008] Preferably, the potassium salt crystals include potassium chloride, sodium sulfate, potassium sulfate or sodium chloride.

[0009] Preferably, the potassium-containing brine includes water containing potassium salts generated during the production or recycling of lithium batteries, fertilizers, glass, pharmaceuticals, or semiconductors; or the potassium-containing brine includes wastewater containing potassium salts generated from salt lake chemical industry; or the potassium-containing brine includes industrial by-product wastewater containing potassium salts, or the potassium-containing brine is a potassium-containing brine generated by dissolving industrial by-product potassium-containing mixed salts.

[0010] Preferably, the heating temperature range required for mixing and heating the potassium-containing brine with the recrystallization agent is 10-90°C, and the heating time range is 1-4 hours.

[0011] Preferably, the recrystallization agent includes calcium salts, magnesium salts, aluminum salts, or iron salts.

[0012] Preferably, the calcium salt includes calcium chloride or calcium sulfate; the magnesium salt includes magnesium chloride or magnesium sulfate; the aluminum salt includes aluminum sulfate or aluminum chloride; the iron salt includes iron sulfate or iron chloride.

[0013] Preferably, the molar ratio of the recrystallization agent to the potassium salt in the potassium-containing brine is 1:1-1.5.

[0014] Preferably, after the recrystallization agent reacts with potassium ions, a high-potassium suspension containing the potassium-containing double salt crystals is obtained, and the potassium-containing double salt crystals are obtained by solid-liquid separation of the high-potassium suspension through plate-and-frame filtration;

[0015] After the potassium-containing double salt crystals are ground and decomposed, a purified potassium mother liquor containing the potassium salt crystals is obtained, and the potassium salt crystals are obtained by solid-liquid separation of the purified potassium mother liquor through plate-and-frame filtration.

[0016] Preferably, the grinding is ball milling, the ball-to-material ratio of the ball milling is 8-10:1, the rotation speed is 300-400 rpm, the ball milling time is 30-45 minutes, and the ball milling input energy > 15 kwh / t.

[0017] The present invention has the following beneficial effects:

[0018] 1. The method for recovering potassium salts in the present invention is simple, the recovery rate of potassium salts is over 98%, the recovery rate is high, and the purity is as high as over 97%. The method of the present invention does not involve technologies such as evaporation separation and membrane separation, reducing production costs. Extracting potassium salts from potassium-containing brine has important significance and application value in resource recovery and recycling.

[0019] 2. The potassium-containing double salt crystal of the present invention is decomposed by ball milling. The lattice transformation of the potassium-containing double salt crystal generates potassium salt crystals. For example, high-energy ball milling is used to change the lattice of picromerite crystal salt, and it directly decomposes itself into potassium sulfate and magnesium sulfate, avoiding the need for external potassium salts or other crystal conversion agents such as magnesium salts for crystal conversion when the existing picromerite crystal salt is converted into potassium sulfate crystals. By means of grinding and decomposition, the reaction rate of converting picromerite crystal salt into potassium sulfate and magnesium sulfate is faster, and no other substances are introduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The flowchart showing the recovery of potassium salts of the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The present disclosure will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are described only to enable those of ordinary skill in the art to better understand and thus implement the present disclosure, rather than to imply any limitation on the scope of the present disclosure.

[0022] As used herein, the term "comprising" and its variants are to be construed as open-ended terms meaning "including but not limited to". The term "based on" is to be construed as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be construed as "at least one embodiment". The term "another embodiment" is to be construed as "at least one other embodiment". For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances. In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, the meaning of "a plurality" is two or more.

[0023] Specifically, this embodiment discloses a method for recovering potassium salts from potassium-containing brine, as Figure 1 shown, including the following steps:

[0024] The potassium-containing brine is mixed with a recrystallization agent and heated. The recrystallization agent reacts with potassium ions to generate a new potassium-containing double salt crystal. The potassium-containing double salt crystal is ground and decomposed to obtain potassium salt crystals, wherein at least part of the potassium salt crystals are obtained by lattice distortion and chemical bond recombination of the potassium-containing double salt crystal;

[0025] The potassium salts include potassium chloride or potassium sulfate.

[0026] In this embodiment, a chemical agent, the recrystallizing agent, which is only used once, is used to selectively precipitate potassium in water to form a new potassium-containing double salt crystal. The potassium-containing double salt crystal can directly produce a potassium salt crystal through topochemical decomposition after grinding. Specifically, when the potassium-containing double salt crystal is ground and decomposed, lattice distortion and chemical bond recombination occur in the potassium-containing double salt crystal, and then topochemical decomposition is triggered to produce a potassium salt crystal. There is no need to use a crystal conversion agent such as other potassium salts or magnesium salts to convert the potassium-containing double salt crystal into a potassium salt crystal. In this embodiment, grinding is used to change the lattice of the potassium-containing double salt crystal, and it directly decomposes itself into potassium chloride or potassium sulfate crystals. The heat generated during grinding will also accelerate the decomposition of the potassium-containing double salt crystal to produce potassium salts, and no other substances are introduced. The purity of the potassium salt crystal reaches over 97%.

[0027] In some embodiments, the potassium salt crystal is dried to obtain a potassium salt product.

[0028] Preferably, the potassium-containing brine is heated under the conditions of a heating temperature range of 40 - 90 °C and a heating time range of 1 - 4 hours, and then the heated potassium-containing brine wastewater is mixed and heated with the recrystallizing agent.

[0029] In this embodiment, the potassium-containing brine wastewater is heated first and then mixed and heated with the recrystallizing agent to preliminarily concentrate the wastewater and ensure the binding effect with the recrystallizing agent in the subsequent potassium-containing brine wastewater.

[0030] Preferably, the potassium salt crystal includes potassium chloride, sodium sulfate, potassium sulfate or sodium chloride.

[0031] In this embodiment, different potassium salt products can be obtained according to different selections of the recrystallizing agent.

[0032] Preferably, the potassium-containing brine wastewater includes wastewater containing potassium salts generated during the production or recycling of lithium batteries, fertilizers, glass, medicine or semiconductors; or the potassium-containing brine includes wastewater containing potassium salts generated in salt lake chemical industry; or the potassium-containing brine includes industrial by-product potassium salt-containing wastewater or the potassium-containing brine is a potassium-containing brine produced by dissolving industrial by-product potassium-containing mixed salts.

[0033] Preferably, the heating temperature range required for mixing and heating the potassium-containing brine wastewater with the recrystallizing agent is 10 - 90 °C, and the heating time range required is 1 - 4 hours.

[0034] Preferably, the heating temperature range required for mixing and heating the potassium-containing brine wastewater with the recrystallizing agent is 40 - 60 °C.

[0035] In some embodiments, the potassium-containing brine includes potassium ions, sodium ions, magnesium ions, calcium ions, chloride ions and sulfate ions.

[0036] Preferably, the recrystallizing agent includes calcium salts, magnesium salts, aluminum salts or iron salts.

[0037] Preferably, the calcium salt includes calcium chloride or calcium sulfate;

[0038] The magnesium salt includes magnesium chloride or magnesium sulfate;

[0039] The aluminum salt includes aluminum sulfate or aluminum chloride;

[0040] The iron salt includes ferric sulfate or ferric chloride.

[0041] In this embodiment, when the recrystallization agent is magnesium chloride, carnallite is formed; when the recrystallization agent is magnesium sulfate, kainite is formed; when the recrystallization agent is calcium sulfate, potassium gypsum is formed; when the recrystallization agent is aluminum sulfate, potassium alum is formed; when the recrystallization agent is ferric sulfate, jarosite is formed.

[0042] In some embodiments, the first crystal includes carnallite (KCl·MgCl2·6H2O), kainite (K2SO4·MgSO4·6H2O), potassium gypsum (K2SO4·CaSO4·H2O), potassium alum (KAl(SO4)2·12H2O) or jarosite (KFe3(SO4)2(OH)6).

[0043] Preferably, the molar ratio of the recrystallization agent to the potassium salt in the potassium salt-containing wastewater is 1:1 - 1.5.

[0044] Preferably, after the recrystallization agent reacts with potassium ions, a high-potassium suspension containing the potassium-containing double salt crystal is obtained, and the potassium-containing double salt crystal is obtained by solid-liquid separation of the high-potassium suspension through plate-and-frame filtration;

[0045] The potassium-containing double salt crystal is ground and decomposed to obtain a purified potassium mother liquor containing the potassium salt crystal, and the potassium salt crystal is obtained by solid-liquid separation of the purified potassium mother liquor through plate-and-frame filtration.

[0046] Preferably, the grinding is ball milling, the ball-to-material ratio of the ball milling is 8 - 10:1, the rotation speed is 300 - 400 rpm, the ball milling time is 30 - 45 minutes, and the ball milling input energy > 15 kwh / t.

[0047] Preferably, the high-energy ball milling includes high-energy sand milling, high-energy stirring milling, high-energy planetary ball milling or high-energy drum ball milling.

[0048] Example 1

[0049] Potassium-containing brine is provided, and the potassium-containing brine is produced by dissolving potassium-containing waste salt by-produced from the preparation of lithium carbonate from lepidolite. In the potassium-containing brine, by mass percentage, it includes potassium sulfate (K2SO4) 30%, sodium sulfate (Na2SO4) 65% and calcium sulfate (CaSO4) 5%;

[0050] Heat the potassium-containing brine at a temperature of 40 °C for 1 hour to obtain a crude high-potassium mother liquor;

[0051] Filter the crude high-potassium mother liquor to remove suspended impurities to obtain a clarified high-potassium mother liquor. The concentration of potassium ions in the clarified high-potassium mother liquor is 50 g / L;

[0052] Provide magnesium sulfate (MgSO4) as a recrystallization agent. The molar ratio of magnesium sulfate to potassium sulfate in the potassium-containing brine is 1:1. Add magnesium sulfate to the high-potassium mother liquor and heat and stir at a temperature of 60 °C for 2 hours. Magnesium sulfate reacts with potassium ions to form a new schoenite crystal salt (K2SO4·MgSO4·6H2O). After the reaction is completed, a suspension containing schoenite crystal salt is obtained;

[0053] The suspension containing schoenite crystal salt is separated by plate-and-frame filtration to obtain schoenite crystal salt and a low-potassium mother liquor. The purity of the schoenite crystal salt is above 95%, and the concentration of potassium ions in the low-potassium mother liquor is 2 g / L;

[0054] Grind the schoenite crystal salt with a planetary ball mill with high-energy ball milling for 30 minutes. The ball milling energy input is 16 kwh / t, the ball-to-material ratio is 10:1, and the rotation speed is 300 rpm. The crystal lattice of the schoenite crystal salt changes, the schoenite crystal salt is transformed into potassium sulfate crystals, and the schoenite crystal salt dehydrates to produce a solution containing magnesium sulfate. Specifically, high-energy ball milling induces lattice distortion and chemical bond recombination of schoenite (K2Mg(SO4)2·6H2O) by continuously applying high-intensity mechanical energy (such as impact, shear, and friction). During the ball milling process, the high-speed collision of the grinding balls and the material will cause a large number of dislocations, grain boundary slips, and local stress concentrations inside the crystal, making the originally ordered double salt lattice gradually amorphous or nanocrystalline. At the same time, the mechanical energy is converted into heat energy, which may instantaneously raise the local temperature to several hundred degrees Celsius. This mechanical-thermal coupling effect first destroys the crystal water network structure in schoenite, resulting in the desorption of water molecules from the hexahydrate. Subsequently, the coordination environment of Mg 2+ and K + is disrupted, causing the composite structure of [Mg(SO4)2] 2- and K + stabilized by ionic bonds and hydrogen bonds to dissociate. When the lattice distortion reaches the critical threshold, sulfate ions (SO4 2-) The tetrahedral configuration of changes irreversibly with the coordination mode of metal cations, ultimately triggering the topochemical decomposition of the double salt to produce thermodynamically more stable simple sulfates, namely magnesium sulfate (MgSO4) and potassium sulfate (K2SO4). The solubility of potassium sulfate is significantly lower than that of magnesium sulfate. Most of the potassium sulfate is in crystal form, while magnesium sulfate dissolves in water. The heat generated during grinding also accelerates the decomposition of polyhalite. After grinding, the potassium sulfate crystals are separated from the aqueous solution containing magnesium sulfate through plate-and-frame filtration to obtain the target potassium sulfate crystals. The purity of the potassium sulfate crystals is over 98%, and the recovery rate of potassium is over 92%. The potassium sulfate crystals can be used as agricultural potassium salt products.

[0055] Preferably, the low-potassium mother liquor is used to produce sodium sulfate crystals through evaporation crystallization. The obtained sodium sulfate crystals have a purity of over 85%. The sodium sulfate crystals contain a small amount of calcium impurities and can be used as industrial salt. Or the low-potassium mother liquor is directly recycled to the heating step of the potassium-containing brine to recover potassium salts again and improve the recovery rate of potassium salts.

[0056] Preferably, the solution containing magnesium sulfate can be directly used as a recrystallization agent, or the solution containing magnesium sulfate can also be used as a recrystallization agent after evaporation crystallization treatment.

[0057] Preferably, the separated potassium sulfate crystals are further subjected to evaporation crystallization and drying treatment to obtain the final potassium salt product.

[0058] Example 2

[0059] Provide potassium-containing brine. The potassium salt wastewater is the by-product potassium salt wastewater from salt lakes. In the potassium-containing brine, the concentration of potassium ions is 12 g / L, the concentration of sodium ions is 25 g / L, the concentration of chloride ions is 50 g / L, and the concentration of sulfate ions is 10 g / L.

[0060] Heat the potassium-containing brine at 80 °C for 4 hours to obtain a crude high-potassium mother liquor.

[0061] Filter the crude high-potassium mother liquor to remove suspended impurities to obtain a clear high-potassium mother liquor. The concentration of potassium ions in the clear high-potassium mother liquor is 12 g / L.

[0062] Provide magnesium chloride (MgCl2) as a recrystallization agent. The molar ratio of magnesium chloride to potassium chloride in the potassium-containing brine is 1:1. Add magnesium chloride to the clear high-potassium mother liquor and stir and heat at 40 °C for 3 hours. Magnesium chloride reacts with potassium ions to form a new carnallite crystal salt (KCl·MgCl2·6H2O). After the reaction is completed, a suspension containing the carnallite crystal salt is obtained.

[0063] The suspension containing carnallite crystal salt is separated by plate and frame pressure filtration into carnallite crystal salt and low-potassium mother liquor. The purity of the carnallite crystal salt is above 93%, and the concentration of potassium ions in the low-potassium mother liquor is 1.5 g / L.

[0064] The carnallite crystal salt is ground for 45 minutes using a sand mill with high-energy ball milling. The ball-to-material ratio is 8:1, the rotation speed is 400 rpm, and the ball milling energy input is 18 kwh / t. The crystal lattice of the carnallite crystal salt changes, and the carnallite crystal salt is transformed into potassium chloride crystals. Moreover, the carnallite crystal salt dehydrates to produce a solution containing magnesium chloride. Specifically, high-energy ball milling induces lattice distortion and chemical bond recombination of the carnallite crystal salt (KCl·MgCl2·6H2O) by continuously applying high-intensity mechanical energy (such as impact, shear, and friction). During the ball milling process, the high-speed collision between the grinding balls and the material causes a large number of dislocations, grain boundary slips, and local stress concentrations inside the crystal, making the originally ordered double salt lattice gradually undergo amorphization or nanocrystallization. At the same time, the mechanical energy is converted into heat energy, which may instantaneously raise the local temperature to several hundred degrees Celsius. This mechanical-thermal coupling effect first destroys the crystal water network structure in carnallite, resulting in the desorption of water molecules from the hexahydrate. Subsequently, the coordination environment of Mg 2+ and K + is disrupted, causing the composite structure of [Mg(Cl)3] 2- and K + stabilized by ionic bonds and hydrogen bonds to dissociate. When the lattice distortion reaches the critical threshold, the tetrahedral configuration of sulfate ions (Cl - ) and the coordination mode with metal cations undergo irreversible changes, ultimately triggering the topochemical decomposition of the double salt to form thermodynamically more stable simple chlorides, namely magnesium chloride (MgCl2) and potassium chloride (KCl). The solubility of potassium chloride is significantly lower than that of magnesium chloride, and most of the potassium chloride is in crystal form, while magnesium chloride dissolves in water. The heat generated during grinding also accelerates the decomposition of carnallite. The concentration of potassium ions is 35 g / L. After grinding, the potassium chloride crystals are separated from the solution containing magnesium chloride by plate and frame pressure filtration to obtain the target potassium chloride crystals. The purity of the potassium chloride crystals is above 97%, and the potassium recovery rate is above 94%. The potassium sulfate crystals can be used as agricultural potassium salt products.

[0065] Preferably, the low-potassium mother liquor is used to produce a mixture of sodium chloride and sodium sulfate by evaporation crystallization. The purity of this mixture is above 85%, and the mixture of sodium chloride and sodium sulfate can be used as industrial salt. Or the low-potassium mother liquor is directly recycled to the step of heating the potassium-containing brine to recover potassium salts again and improve the potassium salt recovery rate.

[0066] Preferably, the solution containing magnesium chloride can be directly used as a recrystallization agent, or the solution containing magnesium chloride can also be used as a recrystallization agent after evaporation crystallization treatment.

[0067] Preferably, the separated potassium chloride crystals are further subjected to evaporation crystallization and drying treatments to obtain the final potassium chloride product.

[0068] Example 3

[0069] Potassium-containing brine is provided, which is produced by dissolving potassium-containing waste salts by-produced from the preparation of lithium carbonate from lepidolite. In the potassium-containing waste salt water, by mass percentage, it includes potassium sulfate (K2SO4) 30%, sodium sulfate (Na2SO4) 65%, and calcium sulfate (CaSO4) 5%.

[0070] The waste water containing potassium salts is heated at a temperature of 40 °C for 1 hour to obtain a crude high-potassium mother liquor.

[0071] The crude high-potassium mother liquor is filtered to remove suspended impurities to obtain a clarified high-potassium mother liquor, and the concentration of potassium ions in the clarified high-potassium mother liquor is 50 g / L.

[0072] A magnesium sulfate (MgSO4) recrystallization agent is provided. The molar ratio of magnesium sulfate to potassium sulfate in the potassium-containing brine is 1:1. Magnesium sulfate is added to the high-potassium mother liquor and heated and stirred at a temperature of 10 °C for 4 hours. Magnesium sulfate reacts with potassium ions to form a new picromerite crystal salt (K2SO4·MgSO4·6H2O). After the reaction is completed, a suspension containing picromerite crystal salt is obtained.

[0073] The suspension containing picromerite crystal salt is separated by plate-and-frame filtration to obtain picromerite crystal salt and a low-potassium mother liquor. The purity of the picromerite crystal salt is above 96%, and the concentration of potassium ions in the low-potassium mother liquor is 20 g / L.

[0074] The picromerite crystal salt is ground by a planetary ball mill with high-energy ball milling for 30 minutes. The ball milling energy input is 16 kwh / t, the ball-to-material ratio is 10:1, and the rotation speed is 300 rpm. The crystal lattice of the picromerite crystal salt changes, the picromerite crystal salt is transformed into potassium sulfate crystals, and the picromerite crystal salt dehydrates to produce a solution containing magnesium sulfate. Specifically, high-energy ball milling induces lattice distortion and chemical bond recombination of picromerite (K2Mg(SO4)2·6H2O) by continuously applying high-intensity mechanical energy (such as impact, shear, and friction). During the ball milling process, the high-speed collision of the grinding balls and the material will cause a large number of dislocations, grain boundary slips, and local stress concentrations inside the crystal, making the originally ordered double salt lattice gradually amorphous or nanocrystalline. At the same time, the mechanical energy is converted into heat energy, which may cause the local temperature to instantaneously rise to several hundred degrees Celsius. This mechanical-thermal coupling effect first destroys the crystal water network structure in picromerite, resulting in the desorption of water molecules in the hexahydrate, and then the coordination environment of 2+ Mg + with K 2- is disrupted, making the originally stable [Mg(SO4)2] through ionic bonds and hydrogen bonds with K+ Dissociation of the composite structure. When the lattice distortion reaches the critical threshold, the tetrahedral configuration of sulfate ions (SO4 2- ) and the coordination mode of metal cations undergo irreversible changes, ultimately triggering the topochemical decomposition of the double salt to form thermodynamically more stable simple sulfates, namely magnesium sulfate (MgSO4) and potassium sulfate (K2SO4). The solubility of potassium sulfate is significantly lower than that of magnesium sulfate. Most of the potassium sulfate is in crystal form, and magnesium sulfate dissolves in water. The heat generated during grinding also accelerates the decomposition of polyhalite. After grinding, the potassium sulfate crystals are separated from the aqueous solution containing magnesium sulfate by plate and frame filtration to obtain the target potassium sulfate crystals. The purity of the potassium sulfate crystals is over 98%, and the recovery rate of potassium is over 70%. The potassium sulfate crystals can be used as agricultural potassium salt products.

[0075] Preferably, the low-potassium mother liquor is used to produce sodium sulfate by evaporation crystallization, and the obtained sodium sulfate has a purity of over 60% and can be used as industrial salt. Or the low-potassium mother liquor is directly recycled to the heating and dissolving step of the solid waste containing potassium salts to recover potassium salts again and improve the recovery rate of potassium salts.

[0076] In this example, the recrystallization temperature is reduced to provide a lower requirement for the recovery process conditions. Although the recovery rate of potassium is over 70%, potassium can still be recovered to a certain extent through this example, avoiding the loss of potassium resources.

[0077] Comparative Example 1

[0078] Potassium-containing brine is provided, which is produced by dissolving potassium-containing waste salts by-produced from the preparation of lithium carbonate from lepidolite. In the potassium-containing brine, by mass percentage, it includes 30% potassium sulfate (K2SO4), 65% sodium sulfate (Na2SO4), and 5% calcium sulfate (CaSO4);

[0079] The potassium-containing brine is heated at 40 °C for 1 hour to obtain a crude high-potassium mother liquor;

[0080] The crude high-potassium mother liquor is filtered to remove suspended impurities to obtain a clarified high-potassium mother liquor, and the concentration of potassium ions in the clarified high-potassium mother liquor is 50 g / L;

[0081] A magnesium sulfate (MgSO4) recrystallization agent is provided. The molar ratio of magnesium sulfate to potassium sulfate in the potassium-containing brine is 1:1. Magnesium sulfate is added to the high-potassium mother liquor and heated and stirred at 60 °C for 2 hours. Magnesium sulfate reacts with potassium ions to form a new polyhalite crystal salt (K2SO4·MgSO4·6H2O). After the reaction is completed, a suspension containing the polyhalite crystal salt is obtained;

[0082] The suspension containing picromerite crystalline salt is separated by plate-and-frame pressure filtration into picromerite crystalline salt and low-potassium mother liquor. The purity of the picromerite crystalline salt is over 90%, and the concentration of potassium ions in the low-potassium mother liquor is 2 g / L.

[0083] The picromerite crystalline salt is ground for 10 minutes using an ordinary roller ball mill, with a ball milling energy input of 5 kwh / t, a ball-to-material ratio of 10:1, and a rotational speed of 300 rpm. The crystal lattice of the picromerite crystalline salt changes, and the picromerite crystalline salt is transformed into potassium sulfate crystals, and the picromerite crystalline salt dehydrates to produce a solution containing magnesium sulfate. Specifically, high-energy ball milling induces lattice distortion and chemical bond recombination of picromerite (K2Mg(SO4)2·6H2O) by continuously applying high-intensity mechanical energy (such as impact, shear, and friction). During the ball milling process, the high-speed collision between the grinding balls and the material will cause a large number of dislocations, grain boundary slips, and local stress concentrations inside the crystal, making the originally ordered double salt lattice gradually undergo amorphization or nanocrystallization. At the same time, the conversion of mechanical energy into heat may instantaneously raise the local temperature to several hundred degrees Celsius. This mechanical-thermal coupling effect first destroys the crystal water network structure in picromerite, resulting in the desorption of water molecules in the hexahydrate, and then the coordination environment of Mg 2+ and K + is disrupted, causing the composite structure of [Mg(SO4)2] 2- and K + stabilized by ionic bonds and hydrogen bonds to dissociate. When the lattice distortion reaches the critical threshold, the tetrahedral configuration of sulfate ions (SO4 2- ) and the coordination mode of metal cations undergo irreversible changes, ultimately triggering the topochemical decomposition of the double salt to form thermodynamically more stable simple sulfates, namely magnesium sulfate (MgSO4) and potassium sulfate (K2SO4). The solubility of potassium sulfate is significantly lower than that of magnesium sulfate, and most of the potassium sulfate is in crystal form, while magnesium sulfate dissolves in water. The heat generated during grinding also accelerates the decomposition of picromerite. After grinding, the potassium sulfate crystals are separated from the aqueous solution containing magnesium sulfate by plate-and-frame pressure filtration to obtain the target potassium sulfate crystals. The purity of the potassium sulfate crystals is over 90%, and the potassium recovery rate is over 30%. The potassium sulfate crystals can be used as agricultural potassium salt products.

[0084] In Comparative Example 1, the ball milling energy input is insufficient, and picromerite cannot be fully decomposed, resulting in a low potassium recovery rate.

[0085] The low-potassium mother liquor is used to produce sodium sulfate by evaporation crystallization, and the obtained sodium sulfate has a purity of 85%.

[0086] Economic benefit analysis:

[0087] 1. Cost accounting (calculated based on 1 ton of potassium chloride):

[0088] Raw material cost of Example 1 (liquid waste containing potassium salt, magnesium chloride, energy consumption): 1,600 yuan;

[0089] Equipment depreciation and labor: 500 yuan;

[0090] Total cost of producing potassium sulfate in Example 1: 2,100 yuan / ton (market price of potassium chloride is 2,800 yuan / ton);

[0091] According to the above analysis, the cost of producing potassium chloride in Example 1 is significantly lower than the cost of directly purchasing potassium chloride. The potassium salt recovery method provided by the present invention enables the production cost of potassium sulfate per ton to be lower than 2,500 yuan, having significant economic value. It solves the problem that the production cost of potassium sulfate by current evaporation separation, membrane separation and other technologies is higher than the market price and is not economically feasible.

[0092] Those of ordinary skill in the art can understand that the above embodiments are specific cases for implementing the present disclosure, and in actual applications, various changes can be made in form and details without departing from the scope of the present disclosure.

Claims

1. A method for recovering potassium salts from potassium-containing brine, characterized in that, The steps include the following: The potassium-containing brine is mixed with a recrystallization agent and heated. The recrystallization agent reacts with potassium ions to form potassium-containing double salt crystals. The potassium-containing double salt crystals are ground and decomposed to obtain potassium salt crystals, wherein at least part of the potassium salt crystals are obtained by lattice distortion and chemical bond recombination of the potassium-containing double salt crystals; The potassium salt includes potassium chloride or potassium sulfate.

2. The method for recovering potassium salts from potassium salt-containing brine according to claim 1, characterized in that, The potassium-containing brine is heated under the conditions that the heating temperature range is 40 - 90 °C and the heating time range is 1 - 4 hours, and then the heated potassium-containing brine is mixed with the recrystallization agent and heated.

3. A method for recovering potassium salts from potassium-containing brine according to claim 1, characterized in that, The potassium salt crystals include potassium chloride, sodium sulfate, potassium sulfate or sodium chloride.

4. A method for recovering potassium salts from potassium salt-containing brine according to claim 1, characterized in that, The potassium-containing brine includes wastewater containing potassium salts generated in the production or recycling of lithium batteries, fertilizers, glass, medicine or semiconductors; or the potassium-containing brine includes wastewater containing potassium salts generated in salt lake chemical industry; or the potassium-containing brine includes industrial by-product wastewater containing potassium salts or the potassium-containing brine is a potassium-containing brine generated by dissolving industrial by-product potassium-containing mixed salts.

5. A method for recovering potassium salts from potassium-containing brine according to claim 1, characterized in that, The heating temperature range required for mixing and heating the potassium-containing brine with the recrystallization agent is 10 - 90 °C, and the heating time range required is 1 - 4 hours.

6. A method for recovering potassium salts from potassium salt-containing brine according to claim 5, characterized in that, The recrystallization agent includes calcium salts, magnesium salts, aluminum salts or iron salts.

7. A method for recovering potassium salts from potassium-containing brine according to claim 6, characterized in that, The calcium salt includes calcium chloride or calcium sulfate; the magnesium salt includes magnesium chloride or magnesium sulfate; the aluminum salt includes aluminum sulfate or aluminum chloride; the iron salt includes iron sulfate or iron chloride.

8. A method for recovering potassium salts from potassium-containing brine according to claim 1, characterized in that, The molar ratio of the recrystallization agent to the potassium salt in the potassium-containing brine is 1:1 - 1.

5.

9. A method for recovering potassium salts from potassium salt-containing brine according to claim 1, characterized in that, After the reaction between the recrystallization agent and potassium ions is completed, a high-potassium suspension containing the potassium-containing double salt crystals is obtained. The high-potassium suspension is subjected to solid-liquid separation by plate-and-frame filtration to obtain the potassium-containing double salt crystals; After the potassium-containing double salt crystals are ground and decomposed, a purified potassium mother liquor containing the potassium salt crystals is obtained. The purified potassium mother liquor is subjected to solid-liquid separation by plate-and-frame filtration to obtain the potassium salt crystals.

10. A method for recovering potassium salts from potassium-containing brine according to claim 1, characterized in that, The grinding is ball milling. The ball-to-material ratio of the ball milling is 8 - 10:1, the rotation speed is 300 - 400 rpm, the ball milling time is 30 - 45 minutes, and the input energy of the ball milling > 15 kwh / t.

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