Method for producing salt lake potassium chloride

Abstract

The application provides a production method of salt lake potassium chloride. The method comprises the following steps: adding fresh water into carnallite to perform decomposition, then filtering to obtain a solid-phase mixture; adding fresh water into the solid-phase mixture to perform dissolution to obtain a liquid-phase mixture; using a composite adsorption membrane to perform treatment on the liquid-phase mixture to obtain a filtrate; heating the filtrate to boiling, then cooling and crystallizing, and finally drying to obtain potassium chloride; the composite adsorption membrane comprises a first sodium ion adsorption membrane, a nano-alumina modified nanofiltration membrane and a second sodium ion adsorption membrane which are stacked in sequence. The nano-alumina modified nanofiltration membrane can effectively adsorb the residual divalent ions in the coexisting liquid, and the sodium ion adsorption membrane can fully adsorb sodium ions, so that the potassium ions and sodium ions and the divalent impurity ions can be separated. The method has the advantages of short process flow, simple operation, low production cost, high quality of the prepared potassium chloride product, good recovery rate and large particle size, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of inorganic salt production technology, and more specifically, to a method for producing potassium chloride from salt lakes. Background Technology

[0002] Potassium chloride has a wide range of uses. Industrially, it is a basic raw material for manufacturing other potassium salts, such as potassium carbonate, potassium hydroxide, potassium chlorate, and potassium nitrate. In national defense, potassium chloride is often used as a smoke suppressant. In medicine, it can be used to produce diuretics and drugs to prevent potassium deficiency. In the metallurgical industry, it is a component of the electrolyte in the process of electrolyzing magnesium chloride to produce metallic magnesium. In chemical analysis, it is used as an analytical reagent and a standard buffer for nitrate solutions. It is also used in heat treatment and photography. In the synthetic fiber, electroplating, and food industries, it is used as a nutritional supplement, gelling agent, and salt substitute. In agricultural production, it is used as a fertilizer, both as a base fertilizer and as a top dressing.

[0003] Currently, the demand for potassium chloride in various industries is increasing daily, and most of the potassium chloride in China is produced from salt lakes. There are several technologies for producing potassium chloride from salt lakes, commonly including cold decomposition flotation, hot dissolution crystallization, reverse flotation cold crystallization, and brine blending. Among these, hot dissolution crystallization yields higher potassium chloride yields and larger particle sizes, but it consumes more energy, suffers from severe corrosion of the hot dissolution equipment, and has high equipment investment and costs. Cold decomposition flotation offers strong production reliability and simple operation, but its recovery rate is poor, the quality of the finished potassium chloride is low, and the resulting potassium chloride particles are extremely small, with over 80% having a diameter of less than 0.088 mm, making separation and drying difficult. Reverse flotation cold crystallization can be operated continuously with good output, but it incurs high mechanical construction costs and reagent expenses. Brine blending technology produces high-quality products and allows for resource recycling, but it has excessive geographical requirements, is significantly affected by the environment, and has a low recovery rate of only about 38%. Summary of the Invention

[0004] The main objective of this invention is to provide a method for producing potassium chloride from salt lakes, in order to solve the problems of low product quality, poor recovery rate, large particle size, and high cost in the existing potassium chloride production process from salt lakes.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for producing potassium chloride from a salt lake is provided, comprising the following steps: Step S1, adding fresh water to carnallite for decomposition, followed by filtration to obtain a solid mixture; Step S2, adding fresh water to the solid mixture for dissolution to obtain a liquid mixture; Step S3, treating the liquid mixture using a composite adsorption membrane to obtain a filtrate; Step S4, heating the filtrate to boiling, then cooling to crystallize, and drying to obtain potassium chloride; wherein the composite adsorption membrane comprises a first sodium ion adsorption membrane, a nano-alumina modified nanofiltration membrane, and a second sodium ion adsorption membrane stacked sequentially.

[0006] Furthermore, in step S1, the decomposition temperature is 10–15°C, the time is 30–40 min, and the freshwater redundancy is 0–10%.

[0007] Further, in step S3, the thickness ratio of the first sodium ion adsorption membrane, the modified nanofiltration membrane, and the second sodium ion adsorption membrane is (1.5~2.5):1:(1.5~2.5).

[0008] Furthermore, the composite adsorption membrane is prepared by the following method: a first sodium ion adsorption membrane, a nanofiltration membrane modified with nanoalumina, and a second sodium ion adsorption membrane are subjected to co-pressure to obtain a composite adsorption membrane; preferably, the co-pressure pressure is 0.15 to 0.25 MPa.

[0009] Further, in step S3, the nano-alumina modified nanofiltration membrane is prepared using the following method: Step S311, piperazine and sodium lauryl sulfate are dissolved in water to obtain an aqueous solution; Step S312, phthaloyl chloride and polyisobutylene are dissolved in isoparaffin solvent oil to obtain an oil solution; Step S313, polysulfone and ethylene glycol dimethyl ether are dissolved in N,N-dimethylformamide to obtain a casting solution; the casting solution is coated on the surface of a nonwoven fabric and formed in a water bath, and after washing with water, a polysulfone-based membrane is obtained; Step S314, the polysulfone-based membrane is sequentially immersed in the aqueous solution, the oil solution, nano-alumina, and water, and after drying, a nano-alumina modified nanofiltration membrane is obtained.

[0010] Further, in the aqueous phase solution, the mass percentage concentration of piperazine is 0.05–0.07%, and the mass percentage concentration of sodium lauryl sulfate is 0.002–0.004%; and / or in the oil phase solution, the mass percentage concentration of phthaloyl chloride is 0.004–0.005%, and the mass percentage concentration of polyisobutylene is 0.0001–0.0003%; and / or in the casting solution, the mass percentage concentration of polysulfone is 1.9–2.0%, and the mass percentage concentration of ethylene glycol dimethyl ether is 0.4–0.6%.

[0011] Further, in step S311, piperazine and sodium lauryl sulfate are dissolved in water, and sodium hydroxide is added to adjust the pH of the solution to 8.5-9 to obtain an aqueous solution; and / or in step S313, polysulfone and ethylene glycol dimethyl ether are dissolved in N,N-dimethylformamide, stirred at 65-70°C and allowed to stand to remove bubbles, and cooled for 24-36 hours to obtain a casting solution; preferably, the water bath film formation temperature is 25-28°C, and the thickness of the polysulfone-based membrane is 40-60 μm; and / or in step S314, the polysulfone-based membrane is immersed in the aqueous solution and allowed to stand for 1-2 minutes, dried, then immersed in the oil phase solution and allowed to stand for 1-2 minutes, dried, then immersed in nano-alumina and allowed to stand for 5-10 minutes, then immersed in water and allowed to stand for 24-36 hours, and dried to obtain a nano-alumina modified nanofiltration membrane.

[0012] Further, in step S3, the sodium ion adsorption membrane is prepared using the following method: Step S321, copper sulfide and dopamine hydrochloride are dissolved in Tris buffer to obtain a first solution, and the first solution is annealed in a nitrogen atmosphere to obtain C@Cu2S nanomaterials; Step S322, C@Cu2S nanomaterials, potassium hexahydroxyantimonate and sulfobetaine are dissolved in water to obtain a second solution, and the second solution is dried and ball-milled to obtain a composite powder; Step S323, the composite powder is pre-pressed to obtain a precursor; Step S324, the precursor is calcined to obtain a sodium ion adsorption membrane.

[0013] Further, in step S321, the weight ratio of copper sulfide to dopamine hydrochloride is (1.5-2.5):1; and / or the solid-liquid ratio of copper sulfide to Tris buffer is (3.5-4.6):1; preferably, before annealing, the step further includes stirring the first solution for 4-6 hours and washing it sequentially with distilled water and ethanol; more preferably, the annealing temperature is 500-600°C and the time is 2-4 hours.

[0014] Further, in step S322, the weight ratio of C@Cu2S to potassium hexahydroxyantimonate is (1.5-2.5):1; and / or the weight ratio of C@Cu2S to sulfobetaine is 1:(0.0004-0.0006); and / or the solid-liquid ratio of C@Cu2S to water is 1:(5-7); preferably, the ball milling speed is 1000-1200 rpm and the time is 6-8 h; and / or in step S324, the calcination temperature is 500-600℃ and the time is 6-8 h.

[0015] By applying the technical solution of this invention, magnesium chloride in carnallite raw materials is completely introduced into the liquid phase through cold decomposition, separating it from potassium chloride and sodium chloride. A three-layer composite adsorption membrane with a sandwich structure is used to treat the coexisting solution of potassium chloride and sodium chloride. The nanofiltration membrane modified with nano-alumina effectively adsorbs residual divalent ions in the coexisting solution, such as magnesium ions, sulfate ions, and calcium ions. The sodium ion adsorption membrane achieves sufficient adsorption of sodium ions, thereby separating potassium ions from sodium ions and divalent impurity ions. The resulting potassium chloride product has high purity, high recovery rate, and a suitable large particle size, significantly superior to potassium chloride particles prepared by cold decomposition flotation. Furthermore, compared to the hot melt crystallization method, the method of this invention causes less corrosion to equipment and requires less equipment investment; compared to the reverse flotation cold crystallization process, it does not require a large amount of reagents, resulting in lower overall costs. In summary, the method of this invention has a short process flow, simple operation, low production cost, and produces potassium chloride products with high quality, good recovery rate, and large particle size, showing broad application prospects. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0017] As described in the background section of this invention, existing technologies suffer from problems such as low product quality, poor recovery rate, large particle size, and high cost in the production of potassium chloride from salt lakes. To address these issues, in a typical embodiment of this invention, a method for producing potassium chloride from salt lakes is provided, comprising the following steps: Step S1, adding fresh water to carnallite for decomposition, followed by filtration to obtain a solid-phase mixture; Step S2, adding fresh water to the solid-phase mixture for dissolution to obtain a liquid-phase mixture; Step S3, treating the liquid-phase mixture using a composite adsorption membrane to obtain a filtrate; Step S4, heating the filtrate to boiling, then cooling to crystallize, and drying to obtain potassium chloride; wherein the composite adsorption membrane comprises a first sodium ion adsorption membrane, a nano-alumina modified nanofiltration membrane, and a second sodium ion adsorption membrane stacked sequentially.

[0018] This invention first involves adding fresh water to carnallite obtained by sun-drying in salt lakes and salt pans for cold decomposition, allowing all magnesium chloride in the carnallite raw material to enter the liquid phase and separate from potassium chloride and sodium chloride. After filtration, a solid mixture with most of the magnesium chloride removed is obtained. Then, fresh water is added to the solid mixture to fully dissolve it, resulting in a liquid mixture in which potassium chloride and sodium chloride coexist. This mixture is then treated using a three-layer composite adsorption membrane with a sandwich structure. The nanofiltration membrane modified with nanoalumina can effectively adsorb residual divalent ions in the coexisting liquid, such as magnesium ions, sulfate ions, and calcium ions. The sodium ion adsorption membrane can fully adsorb sodium ions, thereby separating potassium ions, sodium ions, and divalent impurity ions in the liquid mixture.

[0019] Finally, the filtrate is heated to boiling and then cooled to room temperature to separate the precipitated potassium chloride crystals, yielding a potassium chloride product with high purity, high recovery rate, and large particle size. The purity can reach 90.55–92.33 wt%, the recovery rate can reach 92.63–95.94%, and the particle size can reach 0.18 mm or larger, for example, 0.18–0.27 mm, which is larger than the potassium chloride particles prepared by the cold decomposition flotation process (0.088 mm). Furthermore, compared with the hot melt crystallization method, the method of this invention causes less corrosion to equipment and requires less equipment investment; compared with the reverse flotation cold crystallization process, it does not require a large amount of reagents, resulting in lower overall costs. In summary, the method of this invention has a short process flow, simple operation, low production cost, and produces a high-quality potassium chloride product with good recovery rate and large particle size.

[0020] Among them, the nanofiltration membrane modified with nanoalumina can be any conventional nanofiltration membrane modified with nanoalumina in this field, and the sodium ion adsorption membrane can be any conventional type in this field.

[0021] It should be noted that the term "freshwater" can be defined using the conventional definition used in the field of inorganic salt production in salt lakes; "first sodium ion adsorption membrane" and "second sodium ion adsorption membrane" are only used to distinguish sodium ion adsorption membranes located at different positions on both sides of the nano-alumina modified nanofiltration membrane, and are not used to limit the materials or thicknesses of the two membranes to a specific range.

[0022] To further promote the decomposition of carnallite and more fully achieve the initial removal of magnesium chloride, in a preferred embodiment, in step S1, the decomposition temperature is 10–15°C, the time is 30–40 min, and the freshwater redundancy is 0–10%. Here, freshwater redundancy refers to the volume percentage of the difference between the actual and theoretical water addition during carnallite decomposition, relative to the theoretical water addition. The theoretical water addition is calculated based on the magnesium chloride content in carnallite and the solubility of magnesium chloride in a co-saturated solution of magnesium chloride, sodium chloride, and potassium chloride at 10–15°C (31.6–34.6 g / 100 g water). These are concepts understood by those skilled in the art and will not be elaborated further here.

[0023] In a preferred embodiment, in step S3, the thickness ratio of the first sodium ion adsorption membrane, the modified nanofiltration membrane, and the second sodium ion adsorption membrane is (1.5-2.5):1:(1.5-2.5), which can further enable potassium ions, sodium ions, and divalent impurity ions to be fully separated, which is more conducive to improving the recovery rate and purity of potassium chloride products.

[0024] To further improve the mechanical properties of the composite adsorption membrane, in a preferred embodiment, the composite adsorption membrane is prepared by the following method: a first sodium ion adsorption membrane, a nano-alumina modified nanofiltration membrane, and a second sodium ion adsorption membrane are co-pressed to obtain the composite adsorption membrane; preferably, the co-pressing pressure is 0.15 to 0.25 MPa.

[0025] Specifically, in a preferred embodiment, in step S3, the nano-alumina modified nanofiltration membrane is prepared using the following method: Step S311, piperazine and sodium lauryl sulfate are dissolved in water to obtain an aqueous solution; Step S312, phthaloyl chloride and polyisobutylene are dissolved in isoparaffin solvent oil to obtain an oil solution; Step S313, polysulfone and ethylene glycol dimethyl ether are dissolved in N,N-dimethylformamide to obtain a casting solution; the casting solution is coated on the surface of a nonwoven fabric and formed in a water bath, and after washing with water, a polysulfone-based membrane is obtained; Step S314, the polysulfone-based membrane is sequentially immersed in the aqueous solution, the oil solution, nano-alumina, and water, and after drying, a nano-alumina modified nanofiltration membrane is obtained.

[0026] In this invention, a polysulfone-based membrane prepared from polysulfone and ethylene glycol dimethyl ether is immersed in an aqueous solution of piperazine and sodium lauryl sulfate. After drying, it is immersed in an oil solution of phthaloyl chloride and polyisobutylene, allowing the two monomers to polymerize at their immiscible interfaces, forming a dense polymeric thin layer and promoting interfacial cross-linking. After drying again, it is immersed in nano-alumina, thereby enhancing the membrane's hydrophilicity and antifouling properties, inhibiting macropore formation, strengthening the membrane's spatial connectivity, improving membrane strength, and extending its lifespan, thus modifying the nanofiltration membrane. Finally, it is immersed in water to control the surface porosity and ensure it is as thin as possible. After drying, a nano-alumina-modified nanofiltration membrane is obtained. The nano-alumina-modified nanofiltration membrane prepared using the above method can further improve the adsorption effect on residual divalent ions in the coexisting solution, with better removal effects for magnesium ions, sulfate ions, calcium ions, etc., thereby further improving the purity of potassium chloride products.

[0027] For similar reasons, further, in a preferred embodiment, the aqueous phase solution contains 0.05–0.07% by mass and sodium lauryl sulfate contains 0.002–0.004% by mass; and / or the oil phase solution contains 0.004–0.005% by mass and polyisobutylene contains 0.0001–0.0003% by mass; and / or the casting solution contains 1.9–2.0% by mass and 0.4–0.6% by mass, preferably using IsoparG solvent as the isoparaffin solvent.

[0028] For similar reasons, in a preferred embodiment, in step S311, piperazine and sodium lauryl sulfate are dissolved in water, and sodium hydroxide is added to adjust the pH of the solution to 8.5-9 to obtain an aqueous solution; and / or in step S313, polysulfone and ethylene glycol dimethyl ether are dissolved in N,N-dimethylformamide, stirred at 65-70°C and allowed to stand to degas, and cooled for 24-36 hours to obtain a casting solution; preferably, the water bath film formation temperature is 25-28°C, and the thickness of the polysulfone-based membrane is 40-60 μm; and / or in step S314, the polysulfone-based membrane is immersed in the aqueous solution and allowed to stand for 1-2 minutes, dried, then immersed in the oil phase solution and allowed to stand for 1-2 minutes, dried, then immersed in nano-alumina and allowed to stand for 5-10 minutes, then immersed in water and allowed to stand for 24-36 hours, and dried to obtain a nano-alumina modified nanofiltration membrane. Under the above conditions, the interfacial cross-linking reaction can be further promoted to occur fully.

[0029] Specifically, in a preferred embodiment, in step S3, the sodium ion adsorption membrane is prepared using the following method: Step S321, copper sulfide and dopamine hydrochloride are dissolved in Tris buffer to obtain a first solution, and the first solution is annealed in a nitrogen atmosphere to obtain C@Cu2S nanomaterials; Step S322, C@Cu2S nanomaterials, potassium hexahydroxyantimonate and sulfobetaine are dissolved in water to obtain a second solution, and the second solution is dried and ball-milled to obtain a composite powder; Step S323, the composite powder is pre-pressed to obtain a precursor; Step S324, the precursor is calcined to obtain a sodium ion adsorption membrane.

[0030] In this invention, copper sulfide and dopamine hydrochloride are dissolved in Tris buffer and annealed in a nitrogen atmosphere, thereby coating the C element of dopamine hydrochloride onto the surface of copper sulfide to obtain C@Cu2S nanomaterials. Then, the C@Cu2S nanomaterials, potassium hexahydroxyantimonate, and sulfobetaine are dissolved in water, dried, and ball-milled. During this process, potassium hexahydroxyantimonate adheres to the surface of C@Cu2S under the action of a surfactant, obtaining a composite powder. Finally, the composite powder is pre-pressed and calcined. During this process, the internal tension of the molecular structure is eased, allowing it to adapt to the increasing forces during the shaping process, resulting in a sodium ion adsorption membrane. C@Cu2S has a stable hollow cubic structure, and hexahydroxyantimonate ions can be stably and uniformly distributed on the surface of the cube, increasing the specific surface area of ​​the cube and providing numerous anchor points for sodium ions. The sodium ion adsorption membrane obtained using the above preparation method can further improve the adsorption effect of sodium ions, thereby further improving the purity of potassium chloride products.

[0031] To further achieve high-efficiency and low-cost preparation of sodium ion adsorption membranes, in a preferred embodiment, in step S321, the weight ratio of copper sulfide to dopamine hydrochloride is (1.5–2.5):1; and / or the solid-liquid ratio of copper sulfide to Tris buffer is (3.5–4.6):1; preferably, before annealing, the first solution is stirred for 4–6 hours and washed sequentially with distilled water and ethanol; more preferably, the annealing temperature is 500–600°C and the time is 2–4 hours, thereby further improving the uniformity of composition and the degree of grain refinement.

[0032] For similar reasons, in a preferred embodiment, in step S322, the weight ratio of C@Cu2S to potassium hexahydroxyantimonate is (1.5-2.5):1; and / or the weight ratio of C@Cu2S to sulfobetaine is 1:(0.0004-0.0006); and / or the solid-liquid ratio of C@Cu2S to water is 1:(5-7); preferably, the ball milling speed is 1000-1200 rpm and the time is 6-8 h; and / or in step S324, the calcination temperature is 500-600℃ and the time is 6-8 h. Under the above conditions, the sodium ion adsorption membrane has the best quality.

[0033] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0034] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0035] Unless otherwise specified, "%" in the following examples and comparative examples refers to weight percentage.

[0036] 1. Regarding raw materials

[0037] Carnallite was obtained by sun-drying in the salt fields of Qarhan Salt Lake. The composition of the carnallite was analyzed and is shown in Table 1.

[0038] Table 1

[0039] Carnallite 18.43 35.75 24.77 1.28 0.86 margin

[0040] 2. Regarding the amount of water added for cold decomposition

[0041] At 10℃ and 15℃, a mixture of KCl, NaCl and MgCl2 in a mass ratio of 1:1:1 was gradually added to 100g of water while stirring until the added mixture became significantly insoluble and crystals precipitated. The content of each component in the solution was then measured, and the solubility of the co-saturated solution of KCl, NaCl and MgCl2 was obtained, as shown in Table 2.

[0042] Table 2

[0043]

[0044] Table 2 shows that the solubility of MgCl2 in a co-saturated solution of KCl, NaCl, and MgCl2 at 10–15℃ is 31.6–34.6. Since carnallite is an asymmetrical double salt, it completely decomposes upon the addition of water. After decomposition, all MgCl2 enters the liquid phase, a small amount of KCl and NaCl enter the liquid phase, and the remaining KCl and NaCl exist in the solid phase. KCl undergoes a process of dissolution followed by crystallization. Therefore, the theoretical amount of water required for carnallite decomposition can be calculated based on the MgCl2 content in carnallite and the solubility of MgCl2 in a co-saturated solution of KCl, NaCl, and MgCl2. The actual amount of fresh water added is 100–110% of the theoretical amount. Table 3 shows the theoretical and actual amounts of water required to decompose 1000g of carnallite at 10–15℃.

[0045] Table 3

[0046]

[0047] Example 1

[0048] An optimized method for the production of potassium chloride from salt lakes is provided, which specifically includes the following steps:

[0049] S1: Using 1000g of carnallite as raw material, add 784g of fresh water (0% fresh water redundancy) at 10℃, stir for 30min to decompose the carnallite, and obtain a solid-liquid mixture slurry. Filter to obtain a solid phase mixture.

[0050] S2: Add fresh water to the solid mixture to fully dissolve it, and a liquid mixture is obtained;

[0051] S3: Prepare nanofiltration membranes modified with nanoalumina and sodium ion filtration membranes respectively. Then, use a tablet press (pressure 0.15MPa) to co-press a three-layer structure consisting of a sodium ion adsorption membrane, a nanofiltration membrane modified with nanoalumina, and another sodium ion adsorption membrane with a thickness ratio of 1.5:1:1.5 to form a three-layer adsorption membrane with a sandwich structure. Treat the liquid mixture through the three-layer composite adsorption membrane to obtain the filtrate.

[0052] S4: Heat the filtrate to boiling, then cool to allow crystals to precipitate, and dry to obtain potassium chloride product.

[0053] The preparation method of the above-mentioned nanofiltration membrane modified with alumina is as follows:

[0054] S311: Dissolve 30g of 2% piperazine and 3g of 1% sodium lauryl sulfate in 967g of water, stir well, add sodium hydroxide to adjust the pH to 8.5, stir well to obtain an aqueous solution;

[0055] S312: Dissolve 3g of 1.5% phthaloyl chloride and 1g of 0.2% polyisobutylene in 996g of IsoparG solvent, and stir until homogeneous to obtain an oil phase solution;

[0056] S313: Dissolve 130g of 15% polysulfone and 5g of ethylene glycol dimethyl ether in 865g of N,N-dimethylformamide, stir at 65℃, let stand at constant temperature to remove bubbles, and then cool for 24h to obtain a cooled casting solution. Coat the casting solution onto the surface of a 110μm thick nonwoven fabric and place it in a 25℃ water bath to solidify into a film. Rinse with deionized water to obtain a 40μm thick polysulfone-based film.

[0057] S314: Immerse the polysulfone-based membrane in an aqueous solution, let it stand for 1 minute, pour off the excess aqueous phase, and air dry. Then immerse the membrane in an oil solution, let it stand for 1 minute, pour off the excess oil phase, and air dry again. Immerse the membrane in nano-alumina for 5 minutes, then immerse it in deionized water for 30 hours. After air drying, the nano-alumina modified nanofiltration membrane is obtained.

[0058] The method for preparing the sodium ion adsorption membrane is as follows:

[0059] S321: Dissolve 60g of copper sulfide powder and 30g of dopamine hydrochloride in 15mL of Tris buffer, stir for 4h, wash with distilled water and ethanol, and anneal at 550℃ for 3h in a nitrogen atmosphere to obtain C@Cu2S nanomaterials.

[0060] S322: Add 20g C@Cu2S, 10g potassium hexahydroxyantimonate, and 0.01g sulfobetaine to 100mL of deionized water and stir thoroughly. After stirring, dry the mixture and ball mill it at 1000r / min for 8h to obtain the composite powder.

[0061] S323: The composite powder is evenly sprinkled into a stainless steel mold and pre-pressed using a tablet press to obtain the precursor;

[0062] S324: The precursor is placed in a muffle furnace and calcined at 550°C for 8 hours to obtain a sodium ion adsorption membrane.

[0063] Example 2

[0064] An optimized method for the production of potassium chloride from salt lakes is provided, which specifically includes the following steps:

[0065] S1: Using 1000g of carnallite as raw material, add 823g of fresh water (5% fresh water redundancy) at 10℃, stir for 35min to decompose the carnallite, and obtain a solid-liquid mixture slurry. Filter to obtain a solid phase mixture.

[0066] S2: Add fresh water to the solid mixture to fully dissolve it, and a liquid mixture is obtained;

[0067] S3: Prepare nanofiltration membranes modified with nanoalumina and sodium ion filtration membranes respectively. Then, use a tablet press (pressure 0.2MPa) to co-press a three-layer structure with a thickness ratio of 2:1:2, consisting of a sodium ion adsorption membrane, a nanofiltration membrane modified with nanoalumina, and another sodium ion adsorption membrane, to form a three-layer adsorption membrane with a sandwich structure. Treat the liquid mixture through the three-layer composite adsorption membrane to obtain the filtrate.

[0068] S4: Heat the filtrate to boiling, then cool to allow crystals to precipitate, and dry to obtain potassium chloride product.

[0069] The preparation method of the above-mentioned nanofiltration membrane modified with alumina is as follows:

[0070] S311: Dissolve 30g of 2% piperazine and 3g of 1% sodium lauryl sulfate in 967g of water, stir well, add sodium hydroxide to adjust the pH to 8.8, stir well to obtain an aqueous solution;

[0071] S312: Dissolve 3g of 1.5% phthaloyl chloride and 1g of 0.2% polyisobutylene in 996g of IsoparG solvent, and stir until homogeneous to obtain an oil phase solution;

[0072] S313: Dissolve 130g of 15% polysulfone and 5g of ethylene glycol dimethyl ether in 865g of N,N-dimethylformamide, stir at 68℃, let stand at constant temperature to remove bubbles, and then cool for 24h to obtain a cooled casting solution. Coat the casting solution onto the surface of a 110μm thick nonwoven fabric and place it in a 26℃ water bath to solidify into a film. Rinse with deionized water to obtain a 50μm thick polysulfone-based film.

[0073] S314: Immerse the polysulfone-based membrane in an aqueous solution, let it stand for 1.5 min, pour off the excess aqueous phase, and air dry. Then immerse the membrane in an oil solution, let it stand for 1.5 min, pour off the excess oil phase, and air dry again. Then immerse the membrane in nano-alumina for 8 min, and then immerse it in deionized water for 24 h. After air drying, the nano-alumina modified nanofiltration membrane is obtained.

[0074] The method for preparing the sodium ion adsorption membrane is as follows:

[0075] S321: Dissolve 60g of copper sulfide powder and 30g of dopamine hydrochloride in 15mL of Tris buffer, stir for 5h, wash with distilled water and ethanol, and anneal at 550℃ for 3h in a nitrogen atmosphere to obtain C@Cu2S nanomaterials.

[0076] S322: Add 20g C@Cu2S, 10g potassium hexahydroxyantimonate, and 0.01g sulfobetaine to 100mL of deionized water and stir thoroughly. After stirring, dry the mixture and ball mill it at 1000r / min for 7h to obtain the composite powder.

[0077] S323: The composite powder is evenly sprinkled into a stainless steel mold and pre-pressed using a tablet press to obtain the precursor;

[0078] S324: The precursor is placed in a muffle furnace and calcined at 550°C for 7 hours to obtain a sodium ion adsorption membrane.

[0079] Example 3

[0080] An optimized method for the production of potassium chloride from salt lakes is provided, which specifically includes the following steps:

[0081] S1: Using 1000g of carnallite as raw material, add 862g of fresh water (10% fresh water redundancy) at 10℃, stir for 40min to decompose the carnallite, and obtain a solid-liquid mixture slurry. Filter to obtain a solid phase mixture.

[0082] S2: Add fresh water to the solid mixture to fully dissolve it, and a liquid mixture is obtained;

[0083] S3: Prepare nanofiltration membranes modified with nanoalumina and sodium ion filtration membranes respectively. Then, use a tablet press (pressure 0.25MPa) to co-press a three-layer structure consisting of a sodium ion adsorption membrane, a nanofiltration membrane modified with nanoalumina, and another sodium ion adsorption membrane with a thickness ratio of 2.5:1:2.5 to form a three-layer adsorption membrane with a sandwich structure. Treat the liquid mixture through the three-layer composite adsorption membrane to obtain the filtrate.

[0084] S4: Heat the filtrate to boiling, then cool to allow crystals to precipitate, and dry to obtain potassium chloride product.

[0085] The preparation method of the above-mentioned nanofiltration membrane modified with alumina is as follows:

[0086] S311: Dissolve 30g of 2% piperazine and 3g of 1% sodium lauryl sulfate in 967g of water, stir well, add sodium hydroxide to adjust the pH to 9, stir well to obtain an aqueous solution;

[0087] S312: Dissolve 3g of 1.5% phthaloyl chloride and 1g of 0.2% polyisobutylene in 996g of IsoparG solvent, and stir until homogeneous to obtain an oil phase solution;

[0088] S313: Dissolve 130g of 15% polysulfone and 5g of ethylene glycol dimethyl ether in 865g of N,N-dimethylformamide, stir at 70℃, let stand at constant temperature to remove bubbles, and then cool for 36h to obtain a cooled casting solution. Coat the casting solution onto the surface of a 110μm thick nonwoven fabric and place it in a 28℃ water bath to solidify into a film. Rinse with deionized water to obtain a 60μm thick polysulfone-based film.

[0089] S314: Immerse the polysulfone-based membrane in an aqueous solution, let it stand for 2 minutes, pour off the excess aqueous phase, and air dry. Then immerse the membrane in an oil solution, let it stand for 2 minutes, pour off the excess oil phase, and air dry again. Immerse the membrane in nano-alumina for 10 minutes, then immerse it in deionized water for 36 hours. After air drying, the nano-alumina modified nanofiltration membrane is obtained.

[0090] The method for preparing the sodium ion adsorption membrane is as follows:

[0091] S321: Dissolve 60g of copper sulfide powder and 30g of dopamine hydrochloride in 15mL of Tris buffer, stir for 6h, wash with distilled water and ethanol, and anneal at 600℃ for 2h in a nitrogen atmosphere to obtain C@Cu2S nanomaterials.

[0092] S322: Add 20g C@Cu2S, 10g potassium hexahydroxyantimonate, and 0.01g sulfobetaine to 100mL of deionized water and stir thoroughly. After stirring, dry the mixture and ball mill it at 1200r / min for 6h to obtain the composite powder.

[0093] S323: The composite powder is evenly sprinkled into a stainless steel mold and pre-pressed using a tablet press to obtain the precursor;

[0094] S324: The precursor is placed in a muffle furnace and calcined at 600℃ for 6 hours to obtain a sodium ion adsorption membrane.

[0095] Example 4

[0096] The difference from Example 1 is that in step S2, 716g of fresh water (0% fresh water redundancy) is added at 15°C to decompose carnallite.

[0097] Example 5

[0098] The difference from Example 2 is that in step S2, 752g of fresh water (5% fresh water redundancy) is added at 15°C to decompose carnallite.

[0099] Example 6

[0100] The difference from Example 3 is that in step S2, 788g of fresh water (10% fresh water redundancy) is added at 15°C to decompose carnallite.

[0101] Example 7

[0102] The difference from Example 2 is that the preparation method of the nanofiltration membrane modified with nano-alumina is as follows:

[0103] S311: Dissolve 25g of 2% piperazine and 2g of 1% sodium lauryl sulfate in 973g of water, stir well, add sodium hydroxide to adjust the pH to 8.8, stir well to obtain an aqueous solution;

[0104] S312: Dissolve 2.6g of 1.5% phthaloyl chloride and 0.5g of 0.2% polyisobutylene in 996.9g of IsoparG solvent, and stir until homogeneous to obtain an oil phase solution;

[0105] S313: Dissolve 126g of 15% polysulfone and 4g of ethylene glycol dimethyl ether in 870g of N,N-dimethylformamide, stir at 68℃, let stand at constant temperature to remove bubbles, and then cool for 24h to obtain a cooled casting solution. Coat the casting solution onto the surface of a 110μm thick nonwoven fabric and place it in a 26℃ water bath to solidify into a film. Rinse with deionized water to obtain a 50μm thick polysulfone-based film.

[0106] S314: Immerse the polysulfone-based membrane in an aqueous solution, let it stand for 1.5 min, pour off the excess aqueous phase, and air dry. Then immerse the membrane in an oil solution, let it stand for 1.5 min, pour off the excess oil phase, and air dry again. Then immerse the membrane in nano-alumina for 8 min, and then immerse it in deionized water for 24 h. After air drying, the nano-alumina modified nanofiltration membrane is obtained.

[0107] Example 8

[0108] The difference from Example 2 is that the preparation method of the nanofiltration membrane modified with nano-alumina is as follows:

[0109] S311: Dissolve 35g of 2% piperazine and 4g of 1% sodium lauryl sulfate in 961g of water, stir well, add sodium hydroxide to adjust the pH to 8.8, stir well to obtain an aqueous solution;

[0110] S312: Dissolve 3.5g of 1.5% phthaloyl chloride and 1.5g of 0.2% polyisobutylene in 995g of IsoparG solvent, and stir until homogeneous to obtain an oil phase solution;

[0111] S313: Dissolve 134g of 15% polysulfone and 6g of ethylene glycol dimethyl ether in 860g of N,N-dimethylformamide, stir at 68℃, let stand at constant temperature to remove bubbles, and then cool for 24h to obtain a cooled casting solution. Coat the casting solution onto the surface of a 110μm thick nonwoven fabric and place it in a 26℃ water bath to solidify into a film. Rinse with deionized water to obtain a 50μm thick polysulfone-based film.

[0112] S314: Immerse the polysulfone-based membrane in an aqueous solution, let it stand for 1.5 min, pour off the excess aqueous phase, and air dry. Then immerse the membrane in an oil solution, let it stand for 1.5 min, pour off the excess oil phase, and air dry again. Then immerse the membrane in nano-alumina for 8 min, and then immerse it in deionized water for 24 h. After air drying, the nano-alumina modified nanofiltration membrane is obtained.

[0113] Example 9

[0114] The difference from Example 2 is that the sodium ion adsorption membrane is prepared by:

[0115] S321: Dissolve 60g of copper sulfide powder and 40g of dopamine hydrochloride in 17mL of Tris buffer, stir for 4h, wash with distilled water and ethanol, and anneal at 500℃ for 4h in a nitrogen atmosphere to obtain C@Cu2S nanomaterials.

[0116] S322: Add 20g C@Cu2S, 13.3g potassium hexahydroxyantimonate, and 0.008g sulfobetaine to 120mL of deionized water and stir thoroughly. After stirring, dry the mixture and ball mill it at 1200r / min for 6h to obtain the composite powder.

[0117] S323: The composite powder is evenly sprinkled into a stainless steel mold and pre-pressed using a tablet press to obtain the precursor;

[0118] S324: The precursor is placed in a muffle furnace and calcined at 500°C for 8 hours to obtain a sodium ion adsorption membrane.

[0119] Example 10

[0120] The difference from Example 2 is that the sodium ion adsorption membrane is prepared by:

[0121] S321: Dissolve 60g of copper sulfide powder and 24g of dopamine hydrochloride in 13mL of Tris buffer, stir for 6h, wash with distilled water and ethanol, and anneal at 600℃ for 2h in a nitrogen atmosphere to obtain C@Cu2S nanomaterials.

[0122] S322: Add 20g C@Cu2S, 8g potassium hexahydroxyantimonate, and 0.012g sulfobetaine to 140mL of deionized water and stir thoroughly. After stirring, dry the mixture and ball mill it at 1200r / min for 6h to obtain the composite powder.

[0123] S323: The composite powder is evenly sprinkled into a stainless steel mold and pre-pressed using a tablet press to obtain the precursor;

[0124] S324: The precursor is placed in a muffle furnace and calcined at 600°C for 6 hours to obtain a sodium ion adsorption membrane.

[0125] Comparative Example 1

[0126] The difference from Example 2 is that the nanofiltration membrane used was unmodified, and the preparation method was as follows:

[0127] S311: Preparation of aqueous solution: Dissolve 30g of 2% piperazine and 3g of 1% sodium lauryl sulfate in 967g of water, stir well, add sodium hydroxide to adjust the pH to 8.8, stir well to obtain aqueous solution;

[0128] S312: Preparation of oil phase solution: Dissolve 3g of 1.5% phthaloyl chloride and 1g of 0.2% polyisobutylene in 996g of IsoparG solvent, stir evenly to obtain oil phase solution;

[0129] S313: Preparation of base film: Dissolve 130g of 15% polysulfone and 5g of ethylene glycol dimethyl ether in 865g of N,N-dimethylformamide, stir at 68℃, stand at constant temperature to remove bubbles, and then cool for 24h to obtain a cooled casting solution. Coat the casting solution onto the surface of a 110μm thick nonwoven fabric and place it in a 26℃ water bath to solidify into a film. Rinse with deionized water to obtain a 50μm thick polysulfone base film.

[0130] S314: Preparation of modified nanofiltration membrane: Immerse the polysulfone-based membrane in an aqueous solution, let it stand for 1.5 min, pour off the excess aqueous phase, and air dry. Then immerse the base membrane in an oil solution, let it stand for 1.5 min, pour off the excess oil phase, air dry again, immerse it in deionized water for 24 h, and air dry to obtain the nanofiltration membrane.

[0131] Comparative Example 2

[0132] The difference from Example 2 is that the composite adsorption membrane did not use nanofiltration membrane modified with nano-alumina.

[0133] Comparative Example 3

[0134] The difference from Example 2 is that the composite adsorption membrane does not use a sodium ion adsorption membrane.

[0135] Detection method:

[0136] The retention rate of the nanofiltration membrane modified with nanoalumina prepared in the above examples was determined and calculated using the method described in the paper "Study on the Evolution Law of Membrane Pores during Drying of Hollow Fiber Ultrafiltration Membranes" by Xu Hongmei, Wei Junfu, Wang Xiaolei, et al. [J]. Journal of Tianjin University of Technology, 2014, 33(03):7-11. The Stokes radius and diameter were further calculated, and the effective average pore size was obtained by fitting the diameter and retention rate to the pore size distribution density function. The results showed that the pore size of the nanofiltration membrane modified with nanoalumina was 1.2–1.4 nm, and the retention rate of divalent ions such as magnesium ions, sulfate ions, and calcium ions reached 92.32–96.47%.

[0137] The sodium ion filtration membrane prepared in the above examples was tested for sodium ion content in the solution before and after adsorption using an adsorption experiment. The results showed that the adsorption rate of the sodium ion filtration membrane for 0.2 g / L sodium ions reached 91.05–95.33%.

[0138] The potassium chloride product produced in the above embodiments was screened, and the particle size of the potassium chloride product was all above 0.18 mm.

[0139] The composition and recovery rate of the potassium chloride products obtained in the above embodiments and comparative examples are shown in Table 4.

[0140] Table 4

[0141]

[0142] As can be seen from the above, the potassium chloride products obtained in the various embodiments of the present invention have a KCl content of 90.05–92.33 wt% and a potassium chloride recovery rate of 92.63–95.94%, which is significantly better than that of comparative examples 1 to 3. Therefore, the nano-alumina modified nanofiltration membrane in the various embodiments of the present invention can effectively adsorb residual divalent ions in the coexisting liquid, such as magnesium ions, sulfate ions, and calcium ions; the sodium ion adsorption membrane can achieve sufficient adsorption of sodium ions, thereby separating potassium ions from sodium ions and divalent impurity ions. The resulting potassium chloride product has high purity, high recovery rate, and a suitable large particle size, which is significantly better than potassium chloride particles prepared by the cold decomposition flotation process. Moreover, compared with the hot melt crystallization method, it causes less corrosion to the equipment and has lower equipment investment; compared with the reverse flotation cold crystallization process, it does not require a large amount of reagents, resulting in lower overall cost.

[0143] In summary, the method of the present invention has a short process flow, simple operation, and low production cost. The potassium chloride product obtained is of high quality, has a good recovery rate, and large particle size, and has broad application prospects.

[0144] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing potassium chloride from salt lakes, characterized in that, Includes the following steps: Step S1: Add fresh water to carnallite to decompose it, then filter to obtain a solid mixture; Step S2: Add the fresh water to the solid mixture to dissolve it and obtain a liquid mixture; Step S3: The liquid mixture is treated with a composite adsorption membrane to obtain the filtrate; Step S4: Heat the filtrate to boiling, then cool to crystallize, and dry to obtain the potassium chloride; The composite adsorption membrane comprises a first sodium ion adsorption membrane, a nano-alumina modified nanofiltration membrane, and a second sodium ion adsorption membrane stacked sequentially. The nanofiltration membrane modified with alumina was prepared using the following method: Step S311, piperazine and sodium lauryl sulfate were dissolved in water to obtain an aqueous solution; Step S312, phthaloyl chloride and polyisobutylene were dissolved in isoalkane solvent oil to obtain an oil solution; Step S313, polysulfone and ethylene glycol dimethyl ether were dissolved in N,N-dimethylformamide to obtain a casting solution; the casting solution was coated onto the surface of a nonwoven fabric and formed into a film in a water bath, and after washing with water, a polysulfone-based membrane was obtained; Step S314, the polysulfone-based membrane was sequentially immersed in the aqueous solution, the oil solution, nano-alumina, and water, and after drying, the nanofiltration membrane modified with alumina was obtained. The sodium ion adsorption membrane is prepared using the following method: Step S321, copper sulfide and dopamine hydrochloride are dissolved in Tris buffer to obtain a first solution, and the first solution is annealed in a nitrogen atmosphere to obtain C@Cu2S nanomaterials; Step S322, the C@Cu2S nanomaterials, potassium hexahydroxyantimonate and sulfobetaine are dissolved in water to obtain a second solution, and the second solution is dried and ball-milled to obtain a composite powder; Step S323, the composite powder is pre-pressed to obtain a precursor; Step S324, the precursor is calcined to obtain the sodium ion adsorption membrane.

2. The production method according to claim 1, characterized in that, In step S1, the decomposition temperature is 10~15℃, the time is 30~40min, and the freshwater redundancy is 0~10%, with the unit of freshwater redundancy being volume percentage.

3. The production method according to claim 1 or 2, characterized in that, In step S3, the thickness ratio of the first sodium ion adsorption membrane, the modified nanofiltration membrane and the second sodium ion adsorption membrane is (1.5~2.5):1:(1.5~2.5).

4. The production method according to claim 1 or 2, characterized in that, The composite adsorption membrane is prepared by co-pressing the first sodium ion adsorption membrane, the nano-alumina modified nanofiltration membrane, and the second sodium ion adsorption membrane to obtain the composite adsorption membrane.

5. The production method according to claim 4, characterized in that, The pressure of the co-pressure is 0.15~0.25MPa.

6. The production method according to claim 1, characterized in that, In the preparation of the nanofiltration membrane modified with alumina, In the aqueous solution, the mass percentage concentration of piperazine is 0.05~0.07%, and the mass percentage concentration of sodium lauryl sulfate is 0.002~0.004%; and / or In the oil phase solution, the mass percentage concentration of the phthaloyl chloride is 0.004~0.005%, and the mass percentage concentration of the polyisobutylene is 0.0001~0.0003%; and / or In the casting solution, the mass percentage concentration of polysulfone is 1.9~2.0%, and the mass percentage concentration of ethylene glycol dimethyl ether is 0.4~0.6%.

7. The production method according to claim 1 or 6, characterized in that, In the preparation of the nanofiltration membrane modified with alumina, In step S311, after dissolving the piperazine and sodium lauryl sulfate in water, sodium hydroxide is added to adjust the pH of the solution to 8.5-9 to obtain the aqueous solution; and / or In step S313, after dissolving the polysulfone and the ethylene glycol dimethyl ether in the N,N-dimethylformamide, the mixture is stirred at 65-70°C and allowed to stand to remove bubbles, then cooled for 24-36 hours to obtain the casting solution; and / or In step S314, the polysulfone-based membrane is immersed in the aqueous solution and allowed to stand for 1-2 minutes. After drying, the polysulfone-based membrane is immersed in the oil solution and allowed to stand for 1-2 minutes. After drying, the polysulfone-based membrane is immersed in the nano-alumina and allowed to stand for 5-10 minutes. Then, the polysulfone-based membrane is immersed in water and allowed to stand for 24-36 hours. After drying, the nano-alumina modified nanofiltration membrane is obtained.

8. The production method according to claim 7, characterized in that, In step S313, the temperature of the water bath film formation is 25~28℃, and the thickness of the polysulfone-based film is 40~60μm.

9. The production method according to claim 1, characterized in that, In the preparation of the sodium ion adsorption membrane, In step S321, the weight ratio of copper sulfide to dopamine hydrochloride is (1.5~2.5):1; and / or the solid-liquid ratio of copper sulfide to Tris buffer is (3.5~4.6g):1mL.

10. The production method according to claim 1 or 9, characterized in that, In the preparation of the sodium ion adsorption membrane, In step S321, before the annealing, the first solution is stirred for 4-6 hours and washed sequentially with distilled water and ethanol.

11. The production method according to claim 10, characterized in that, The annealing temperature is 500~600℃, and the time is 2~4h.

12. The production method according to claim 1 or 9, characterized in that, In the preparation of the sodium ion adsorption membrane, In step S322, the weight ratio of C@Cu2S to potassium hexahydroxyantimonate is (1.5~2.5):1; and / or the weight ratio of C@Cu2S to sulfobetaine is 1:(0.0004~0.0006); and / or the solid-liquid ratio of C@Cu2S to water is 1g:(5~7 mL); and / or In step S324, the calcination temperature is 500~600℃ and the time is 6~8h.

13. The production method according to claim 12, characterized in that, In step S322, the ball mill rotates at a speed of 1000-1200 rpm for 6-8 hours.

Images