Method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride from gypsum at low cost

Abstract

The invention discloses a low-cost method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride from gypsum, and belongs to the technical field of resource utilization of gypsum solid waste. The method comprises the following steps: (1) dissolving excessive gypsum in a first mixed solution, and filtering to obtain a first filtrate; (2) adding a carbon source into the first filtrate, filtering to obtain a first filter cake and a second filtrate, and separating and purifying the first filter cake to obtain CaCO3; (3) adding KCl into the second filtrate, filtering to obtain a second filter cake and a third filtrate, and separating and purifying the second filter cake to obtain K2SO4 and NH4Cl; the first mixed solution comprises an aqueous solution of ammonia water and a phase transfer reagent, the concentration of the ammonia water is 2-3 mol / L, and the concentration of the phase transfer reagent is not less than 1 mol / L. On one hand, high-purity potassium sulfate and co-production of calcium carbonate and ammonium chloride are obtained, generation of impurities is avoided, and the product value and the economic value are high; the method is simple, saves energy, reduces consumption, reduces cost and is beneficial to large-scale utilization of gypsum solid waste.

Description

Technical Field

[0001] The present application relates to a method for preparing high-purity potassium sulfate by using gypsum at low cost and co-producing calcium carbonate and ammonium chloride, and belongs to the technical field of resource utilization of gypsum solid waste. Background Art

[0002] Industrial by-product gypsum is a solid waste generated in the industrial production process, and its sources mainly include desulfurized gypsum, phosphogypsum, fluorogypsum, titanium gypsum, etc., and its main component is calcium sulfate dihydrate. The annual discharge of industrial by-product gypsum in China is as high as 258 million tons, and the historical stockpile exceeds 11 billion tons. With a large stockpile, increasing increment, and many potential hazards, traditional treatment methods such as stacking, landfilling, and dumping not only occupy a large amount of land resources, but also pose great potential ecological and environmental hazards and safety risks. At present, the comprehensive utilization of gypsum solid waste mainly includes the production of building materials, cement retarders, chemical raw materials, road construction, etc., but the utilization rate of gypsum solid waste is still relatively low, and the high-value utilization of gypsum solid waste resources is imminent.

[0003] Potassium fertilizers are generally produced at home and abroad using KCl in natural potassium mines and potassium salt lakes as raw materials. However, potassium required for the growth of agricultural plants, especially economic crops such as tobacco, mulberry, citrus, sugarcane, watermelon, grape, tea, and sugar beet, is particularly chlorine-intolerant. Otherwise, the yield and quality will be reduced. Therefore, converting the valuable elements calcium and sulfur rich in gypsum into calcium carbonate and chlorine-free potassium fertilizer - potassium sulfate respectively is a feasible route for its high-value utilization of resources.

[0004] In the prior art, there are mainly two processes for preparing potassium sulfate by the gypsum conversion method: the one-step method is to react phosphogypsum and potassium chloride in a high-concentration ammonia solution to obtain potassium sulfate in one step; the two-step method uses ammonium bicarbonate (or ammonium carbonate) instead of ammonia solution, and the reaction system proceeds in two steps. It consists of processes such as ammonia absorption, limestone calcination, carbonation, gypsum conversion, potassium sulfate crystallization and drying, gypsum precipitation, and distillation.

[0005] Chinese Patent CN 111592014 A discloses a method and system device for preparing potassium sulfate, calcium carbonate, and ammonium chloride from phosphogypsum, specifically discloses that phosphogypsum, ammonia added, and CO2 by-produced from synthetic ammonia are used as raw materials to obtain ammonium sulfate and calcium carbonate precipitate containing impurities. Among them, the ammonium sulfate solution is added with potassium chloride for a double decomposition reaction to obtain potassium sulfate products and a mixed solution of potassium chloride and ammonium chloride. The mixed solution of potassium chloride and ammonium chloride and the calcium carbonate precipitate containing impurities are subjected to a decomposition reaction of calcium carbonate and ammonium chloride in a specific ammonia distillation reactor, and the resulting solution is a mixture of potassium chloride and calcium chloride. After filtration and cooling crystallization, the obtained potassium chloride is recycled as a raw material for producing potassium sulfate. The calcium chloride solution reacts with ammonia and CO2 to obtain light calcium carbonate products and ammonium chloride solution, and the ammonium chloride solution is subjected to evaporation crystallization to obtain ammonium chloride products.

[0006] Chinese Patent CN 109748296 A discloses a technology and method for preparing potassium sulfate products by using phosphogypsum, co-producing lime and ammonium chloride. First, phosphogypsum and ammonium bicarbonate are added to a reaction tank in proportion. After the reaction, the material is filtered by a rotary table filter. The residue after filtration is calcium carbonate co-producing lime; the solution is ammonium sulfate solution. The ammonium sulfate solution and potassium chloride are dissolved in a dissolving tank, filtered by a plate filter, crystallized in a crystallizer, and filtered to produce ammonium chloride solution and potassium sulfate crystals. The ammonium chloride solution is separated by a triple-effect concentrator centrifuge and then dried by a dryer to prepare ammonium chloride products; the potassium sulfate crystals are dried by a dryer to prepare potassium sulfate products required by the market.

[0007] The above patents disclose the preparation of potassium sulfate products by using phosphogypsum, but there are many problems. First, the reaction processes disclosed in the above patents all require heating, which is energy-consuming and increases the cost of gypsum resource utilization. Second, since calcium sulfate is slightly soluble, the solubility of calcium sulfate in the saturated solutions of the three products is only 0.0034 mol / L at room temperature, resulting in a low reaction rate and making it difficult to achieve large-scale production. And in Chinese Patent CN 109748296 A, the mass concentration of ammonia water used is 20-25%. On the one hand, too high ammonium concentration is prone to react with SO4 2- and Ca 2+ to form ammonium gypsum. On the other hand, due to the extremely volatile high-concentration ammonia water, it causes pollution, waste and unstable reaction conditions. And during continuous production, Ca 2+ , NH4 + , K + , Cl - , SO4 2- and CO3 2- will exist in the solution at the same time. Adjusting the mixed solution containing K + , SO4 2- and Ca 2+ to be weakly acidic to alkaline will generate potassium gypsum and ammonium gypsum; finally, since the ammonium ion and potassium ion have similar radii, most of the actually produced final products are co-precipitated potassium ammonium sulfate and potassium chloride ammonium compound fertilizers, which not only seriously affect the purity and yield of potassium sulfate products, but also seriously affect their product value and economic benefits.

[0008] Based on the above problems, it is urgent to develop a method for low-cost preparation of high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride from gypsum to realize the resource utilization and high-value utilization of gypsum waste residue, relieve environmental pressure, and at the same time be able to produce high-value products such as high-purity potassium sulfate with low energy consumption and create certain economic benefits. Summary of the Invention

[0009] To solve the above problems, a method for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride with gypsum at low cost is provided. By defining the method steps for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride, on the one hand, in this application, a solubilization reaction, a carbonation reaction, and a double decomposition reaction are carried out in sequence to obtain high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride. The preparation method is simple, the phase transfer reagent can be recycled, energy is saved and consumption is reduced, the emission of three wastes can be reduced, and the production cost can be lowered, which is conducive to the large-scale utilization of gypsum solid waste; on the other hand, the potassium sulfate, calcium carbonate, and ammonium chloride prepared in this application are all high-purity products, avoiding the generation of impurities, and having high product value and economic value.

[0010] According to one aspect of the present application, a method for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride with gypsum at low cost is provided, including the following steps:

[0011] (1) Dissolve excessive gypsum in the first mixed solution, carry out a solubilization reaction under normal temperature and pressure conditions, and filter after the reaction ends to obtain a first filtrate;

[0012] (2) Add a carbon source to the first filtrate, carry out a carbonation reaction under normal temperature and pressure conditions, filter after the reaction is completed to obtain a first filter cake and a second filtrate, separate and purify the first filter cake to obtain CaCO3 and NH4Cl;

[0013] (3) Add KCl to the second filtrate, carry out a double decomposition reaction under normal temperature and pressure conditions, filter after the reaction is completed to obtain a second filter cake and a third filtrate, separate and purify the second filter cake to obtain K2SO4 and NH4Cl;

[0014] The first mixed solution includes an aqueous solution of ammonia water and a phase transfer reagent, the concentration of the ammonia water is 2-3 mol / L, and the concentration of the aqueous solution of the phase transfer reagent is not less than 1 mol / L.

[0015] Optionally, it further includes step (4) returning the third filtrate to step (1) for recycling, and repeating steps (1)-(3) to continuously obtain CaCO3, K2SO4, and NH4Cl.

[0016] Specifically, in step (1), the slightly soluble gypsum undergoes a solubilization reaction under the action of the first mixed solution, and Ca and S existing in solid form in the gypsum are transferred to the liquid phase and exist in the form of Ca 2+ and SO4 2- . Therefore, the first filtrate includes Ca 2+ , NH4 + and SO4 2- ; in step (2), a carbon source is added to the first filtrate to carry out a carbonation reaction to convert Ca 2+It is converted into CaCO3 precipitate, that is, the main components in the first filter cake are CaCO3 and NH4Cl products. After separation and purification, CaCO3 products are obtained, and the second filtrate contains NH4 + and SO4 2- ; In step (3), KCl is added to the second filtrate for a metathesis reaction to obtain a second filter cake mainly composed of K2SO4 and NH4Cl. After separation and purification, K2SO4 and NH4Cl products are obtained, and the third filtrate contains a phase transfer reagent, which can be recycled to continue dissolving gypsum; repeating the above steps can continuously obtain CaCO3 products, K2SO4 products and NH4Cl products.

[0017] Specifically, the first mixed solution includes aqueous ammonia and an aqueous solution of a phase transfer reagent. The combined action of the two greatly promotes the dissolution of gypsum, significantly increases the reaction rate, and is beneficial to the large-scale treatment of gypsum solid waste.

[0018] Specifically, the combined action of aqueous ammonia with a specific concentration and an aqueous solution of a phase transfer reagent, on the one hand, the combined action of aqueous ammonia and an aqueous solution of a phase transfer reagent increases the dissolution of calcium ions and promotes the dissolution of gypsum; on the other hand, it can also inhibit the formation of impurities such as potassium gypsum and ammonium gypsum.

[0019] Specifically, the present application makes specific limitations on the mass concentration of aqueous ammonia in the first solution. The concentration of aqueous ammonia in the present application can be as low as 2 mol / L at least, that is, the mass concentration is 3.7%. On the one hand, low-concentration aqueous ammonia is easy to prepare and not easy to volatilize, which is beneficial to maintaining the relative stability of the reaction conditions; on the other hand, if the concentration of aqueous ammonia is too low, potassium gypsum impurities are likely to be generated, affecting the purity of the product and the yield of potassium sulfate. By limiting the concentrations of aqueous ammonia and the phase transfer reagent, the present application avoids the generation of impurity potassium gypsum.

[0020] Optionally, the phase transfer reagent includes one or more of sucrose, glucose, ammonium formate, citric acid, ammonium citrate, sodium citrate, sodium acetate or ammonium acetate;

[0021] Preferably, the phase transfer reagent is at least one of sodium acetate or ammonium acetate.

[0022] More preferably, the phase transfer reagent is ammonium acetate.

[0023] Specifically, when ammonium acetate is used as the phase transfer reagent, its concentration is 1 - 3 mol / L.

[0024] Specifically, when ammonium acetate is used as the phase transfer reagent, ammonium acetate is a strong electrolyte and its ammonium ions can be completely ionized. When the concentration of ammonium acetate is too low, its solubilization effect is not good; but when its concentration is too high, ammonium gypsum will be generated. The present invention controls its concentration, and thus a relatively high Ca 2+It not only avoids the generation of ammonium gypsum impurities but also controls the concentration.

[0025] Optionally, the carbon source includes carbon dioxide, ammonium carbonate, or ammonium bicarbonate.

[0026] Specifically, carbon dioxide, ammonium carbonate, or ammonium bicarbonate can provide carbonate ions or bicarbonate ions, which can combine with Ca 2+ to form CaCO3.

[0027] Optionally, the separation and purification in step (2) specifically include separating and purifying the first filter cake with a washing solvent, and the washing solvent includes water, alcohol, or liquid ammonia.

[0028] Specifically, in step (2), water is used as the washing solvent to separate and purify the first filter cake, and then the washing solvent water and NH4Cl are separated by evaporation crystallization;

[0029] Optionally, the separation and purification in step (3) specifically include separating and purifying the second filter cake with a washing solvent, and the washing solvent includes alcohol or liquid ammonia.

[0030] Specifically, in steps (2) and (3), alcohol is used as the washing solvent, and the washing solvent alcohol and NH4Cl are separated by evaporation crystallization or rectification;

[0031] Specifically, during the process of recycling the third filtrate, ammonium is introduced while adding the carbon source, increasing the concentration of NH4 + in the solution. The third filtrate contains saturated ammonium chloride, which may cause ammonium chloride and potassium sulfate to crystallize out simultaneously. In the present invention, alcohol or liquid ammonia is used as the washing solvent to dissolve ammonium chloride in the washing solvent, thereby separating and purifying the mixture of potassium sulfate and ammonium chloride. After purification, the purity of both potassium sulfate and ammonium chloride products reaches 100%, greatly improving the conversion rate of potassium ions and the economy of gypsum conversion.

[0032] Specifically, the washing solvent alcohol includes one or more of methanol, ethanol, or glycerol.

[0033] Specifically, in steps (2) and (3), liquid ammonia is used as the washing solvent, and the washing solvent liquid ammonia and NH4Cl are separated by ammonia evaporation or decompression.

[0034] Specifically, the same washing solvent is used in steps (2) and (3) to facilitate the combined treatment of the washed filtrates.

[0035] Specifically, the present application makes specific limitations on the dosages of ammonia water, phase transfer reagent, and gypsum to maximize the dissolution of gypsum, increase the concentration of Ca 2+ and improve the reaction rate.

[0036] Optionally, the reaction time in step (1) is 10 to 60 minutes.

[0037] Specifically, the entire reaction process of this application is carried out under normal temperature and pressure, achieving energy conservation and consumption reduction, cost reduction, and being conducive to the large-scale utilization and popularization of this method.

[0038] Optionally, the gypsum includes desulfurized gypsum or phosphogypsum.

[0039] Specifically, the main component of the gypsum is calcium sulfate dihydrate.

[0040] Optionally, when adding a carbon source in step (2), the step of adding ammonia or quicklime simultaneously is also included.

[0041] Specifically, when adding a carbon source, adding ammonia or quicklime simultaneously can neutralize hydrogen ions, provide an alkaline environment, and promote the precipitation of CaCO3.

[0042] Specifically, when using carbon dioxide as the carbon source, ammonia with a molar amount twice that of carbon dioxide is added for reaction simultaneously;

[0043] Specifically, when carbon dioxide is used as the carbon source, carbon dioxide dissolves in water to produce carbonic acid, which further ionizes to produce hydrogen ions. In order to convert more carbon dioxide into carbonate ions, these hydrogen ions need to be neutralized. Therefore, ammonia with a molar amount twice that of carbon dioxide is added for reaction simultaneously. Each mole of carbon dioxide produces 2 moles of hydrogen ions, and each mole of ammonia produces 1 mole of hydroxide ions. Therefore, to neutralize the hydrogen ions produced by carbon dioxide, ammonia with a molar amount twice that of carbon dioxide needs to be added for reaction simultaneously.

[0044] Specifically, when using ammonium bicarbonate as the carbon source, ammonia with the same molar amount as ammonium bicarbonate is added for reaction simultaneously, or quicklime with 0.5 times the molar amount of ammonium bicarbonate is added for reaction simultaneously.

[0045] Specifically, when ammonium bicarbonate is used as the carbon source, ammonium bicarbonate dissociates to produce ammonium ions and bicarbonate ions, and the bicarbonate ions further ionize to produce hydrogen ions. In order to convert more bicarbonate ions into carbonate ions, these hydrogen ions also need to be neutralized. Each mole of ammonium bicarbonate produces 1 mole of hydrogen ions, each mole of ammonia can produce 1 mole of hydroxide ions, and each mole of quicklime can produce 2 moles of hydroxide ions. Therefore, to neutralize the hydrogen ions produced by ammonium bicarbonate, ammonia with the same molar amount as ammonium bicarbonate needs to be added for reaction simultaneously, or quicklime with 0.5 times the molar amount of ammonium bicarbonate needs to be added for reaction simultaneously.

[0046] Optionally, the number of times the third filtrate is recycled in step (4) is infinite.

[0047] The beneficial effects of this application include but are not limited to:

[0048] 1. A method for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride from gypsum at low cost according to the present application. By defining the method steps for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride, on the one hand, the present application successively conducts a solubilization reaction, a carbonation reaction, and a double decomposition reaction to obtain high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride. The preparation method is simple, energy-saving and consumption-reducing, and cost-effective, which is conducive to the large-scale utilization of gypsum solid waste. On the other hand, the potassium sulfate, calcium carbonate, and ammonium chloride prepared by the present application are all high-purity products, and the purities of the calcium carbonate, potassium sulfate, and ammonium chloride products are all 100%, avoiding the generation of impurities, and the product value and economic value are relatively high.

[0049] 2. A method for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride from gypsum at low cost according to the present application. The present application makes specific limitations on the mass concentration of ammonia water in the first solution. The lowest concentration of ammonia water in the present application can be 2 mol / L, that is, the mass concentration is 3.7%. On the one hand, low-concentration ammonia water is easy to prepare and not easy to volatilize, which is conducive to maintaining the relative stability of the reaction conditions. On the other hand, if the concentration of ammonia water is too low, it is easy to generate potassium gypsum impurities, which will affect the purity of the product and the yield of potassium sulfate. By limiting the concentrations of ammonia water and the phase transfer reagent, the present application avoids the generation of impurity potassium gypsum and ammonium gypsum.

[0050] 3. A method for preparing high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride from gypsum at low cost according to the present application is carried out under normal temperature and pressure throughout the process, and the target products generated are only high-purity potassium sulfate and ammonium chloride, and there are no compound fertilizers such as potassium ammonium sulfate and potassium chloride ammonium; and the phase transfer reagent and the washing solvent can be recycled, which is suitable for industrial large-scale production and has high economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0052] Figure 1 is the process flow chart adopted in Example 1 of the present invention;

[0053] Figure 2 is the process flow chart adopted in Example 2 of the present invention;

[0054] Figure 3 is the SEM image of the calcium carbonate product in Example 2;

[0055] Figure 4 is the XRD pattern of the calcium carbonate product in Example 2;

[0056] Figure 5XRD pattern of the potassium sulfate and ammonium chloride mixture in Example 2;

[0057] Figure 6 SEM image of the potassium sulfate product in Example 2;

[0058] Figure 7 XRD pattern of the potassium sulfate product in Example 2;

[0059] Figure 8 SEM image of the ammonium chloride product in Example 2;

[0060] Figure 9 XRD pattern of the ammonium chloride product in Example 2;

[0061] Figure 10 Physical image of the potassium gypsum impurity in Comparative Example 2;

[0062] Figure 11 XRD pattern of the potassium gypsum impurity in Comparative Example 2;

[0063] Figure 12 Physical image of the ammonium gypsum impurity in Comparative Example 3;

[0064] Figure 13 XRD pattern of the ammonium gypsum impurity in Comparative Example 3. Detailed implementation manners

[0065] The present application will be described in detail below with reference to the examples, but the present application is not limited to these examples.

[0066] Unless otherwise specified, the raw materials in the examples and comparative examples of the present application are all purchased through commercial channels.

[0067] Unless otherwise specified, the methods used in the examples and comparative examples of the present application are conventional methods in the prior art.

[0068] Example 1

[0069] A method for low-cost preparation of high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride using gypsum:

[0070] (1) Dissolve 10 g of desulfurized gypsum in 100 ml of a first mixed solution, which includes an aqueous solution of ammonia water and a phase transfer reagent. Among them, the concentration of ammonia water is 2 mol / L, and the phase transfer reagent includes sucrose, ammonium citrate, sodium acetate, and ammonium acetate. Among them, the sucrose concentration is 0.01 mol / L, the ammonium citrate concentration is 0.3 mol / L, the sodium acetate concentration is 0.2 mol / L, and the ammonium acetate concentration is 1.0 mol / L. Carry out a solubilization reaction, react for 10 min under normal temperature and pressure conditions, and filter after the reaction to obtain a first filtrate. Measure Ca in the first filtrate with a potentiometric titrator 2+The concentration is 0.055 mol / L;

[0071] (2) Ammonium carbonate is added to the first filtrate so that the molar ratio of carbonate to calcium ions is 1:1, and a carbonation reaction is carried out under normal temperature and pressure conditions. Ca 2+ precipitates as CaCO3. After the reaction is completed, filtration is carried out to obtain the first filter cake and the second filtrate. The first filter cake is washed with clear water and dried to obtain the CaCO3 product, and the concentration of SO4 2- in the second filtrate is measured with a potentiometric titrator to be 0.055 mol / L;

[0072] (3) 0.11 mol of KCl is added to the second filtrate, and a metathesis reaction is carried out under normal temperature and pressure conditions. After the reaction is completed, filtration is carried out to obtain the second filter cake and the third filtrate. The second filter cake is washed with ethanol and dried to obtain the K2SO4 product, and the third filtrate is evaporated and crystallized to obtain the NH4Cl product.

[0073] In this example, desulfurized gypsum is used as the raw material and an intermittent operation mode is adopted. The process flow chart of Example 1 is as Figure 1 shown.

[0074] Example 2

[0075] A method for low-cost preparation of high-purity potassium sulfate with co-production of calcium carbonate and ammonium chloride from gypsum:

[0076] (1) 20 g of phosphogypsum is dissolved in 500 ml of the first mixed solution. The first mixed solution includes an aqueous solution of ammonia and a phase transfer reagent. Among them, the concentration of ammonia water is 2 mol / L, and the phase transfer reagent includes glucose, ammonium formate, citric acid, and sodium citrate. Among them, the concentration of glucose is 0.02 mol / L, the concentration of ammonium formate is 2.5 mol / L, the concentration of citric acid is 0.6 mol / L, and the concentration of sodium citrate is 0.8 mol / L. Then 10 g of CaCO3, 200 g of NH4Cl, and 15 g of K2SO4 are added, and a dissolution-promoting reaction is carried out. The reaction is carried out at normal temperature and pressure for 60 min. After the reaction is completed, filtration is carried out to obtain the first filtrate. The concentration of Ca 2+ in the first filtrate is measured with a potentiometric titrator to be 0.25 mol / L;

[0077] (2) 0.125 mol of CO2 and 0.25 mol of ammonia are introduced into the first filtrate, and a carbonation reaction is carried out under normal temperature and pressure conditions. Ca 2+ precipitates as CaCO3. After the reaction is completed, filtration is carried out to obtain the first filter cake and the second filtrate. The first filter cake is washed with a methanol-glycerol mixture and filtered and dried to obtain the CaCO3 product. Then, through rectification operation, the NH4Cl product and the washing solvent methanol-glycerol mixture can be separated;

[0078] (3) Add 0.25 mol of KCl to the second filtrate and conduct a metathesis reaction under normal temperature and pressure. After the reaction is completed, filter to obtain a second filter cake and a third filtrate. Wash the second filter cake with a methanol-glycerol mixture, filter, and dry to obtain the K2SO4 product. The rectification operation can separate the NH4Cl product and the washing solvent methanol-glycerol mixture;

[0079] (4) The third filtrate is returned to step (1) for recycling, and the washing solvent can also be recycled. Repeat steps (1) to (3) to continuously obtain CaCO3, K2SO4, and NH4Cl.

[0080] In this example, using phosphogypsum as the raw material, the composition of the phosphogypsum is shown in Table 1. Simulate the continuous operation mode, that is, during continuous operation, calcium carbonate, potassium sulfate, and ammonium chloride continuously react and crystallize out, and calcium carbonate, potassium sulfate, and ammonium chloride in the solution are all in a saturated state. Therefore, add 10 g of CaCO3, 200 g of NH4Cl, and 15 g of K2SO4 to obtain a simulated saturated solution. The process flow chart of Example 2 is as Figure 2 shown. As Figures 3 to 9 shown, the CaCO3 product obtained in this example is calcite with a purity of 100%, indicating that after promoting the dissolution of phosphogypsum with the first mixed solution in this application, not only can its solubility in water be increased, but also solid impurities such as silica, alumina, and calcium silicate in industrial by-product gypsum can be removed to obtain a pure calcium carbonate product; the purities of the potassium sulfate and ammonium chloride obtained in this example are also both 100%, indicating that the washing solvent has a good separation and purification effect on their mixture after washing.

[0081] Table 1 Composition analysis of phosphogypsum (XRF)

[0082] Component Mass fraction % Component Mass fraction % CaO 41.9 <![CDATA[K2O]]> 0.458 <![CDATA[SO3]]> 52.6 BaO 0.156 <![CDATA[SiO2]]> 2.71 ZnO 0.108 F 1.26 <![CDATA[Al2O3]]> 0.0998 <![CDATA[P2O5]]> 0.461 <![CDATA[Fe2O3]]> 0.0727

[0083] Example 3

[0084] A method for low-cost preparation of high-purity potassium sulfate co-producing calcium carbonate and ammonium chloride from gypsum:

[0085] (1) Dissolve 20 g of phosphogypsum in 500 ml of the first mixed solution. The first mixed solution includes an aqueous solution of ammonia and a phase transfer reagent. Among them, the concentration of ammonia is 3 mol / L, and the phase transfer reagent includes ammonium acetate. Among them, the concentration of ammonium acetate is 2.5 mol / L. Then add 10 g of CaCO3, 200 g of NH4Cl, and 15 g of K2SO4, and conduct a promoting dissolution reaction. React at normal temperature and pressure for 15 minutes. After the reaction is completed, filter to obtain the first filtrate. Use a potentiometric titrator to measure the Ca 2+ concentration in the first filtrate is 0.080 mol / L;

[0086] (2) Add 0.04 mol of ammonium bicarbonate and 0.02 mol of quicklime to the first filtrate, and carry out a carbonation reaction under normal temperature and pressure conditions. Ca 2+ precipitates as CaCO3. After the reaction is completed, filtration is carried out to obtain the first filter cake and the second filtrate. The first filter cake is washed, filtered, and dried with liquid ammonia to obtain the CaCO3 product. Then, through the ammonia evaporation operation, the NH4Cl product and the washing solvent liquid ammonia can be separated;

[0087] (3) Add 0.08 mol of KCl to the second filtrate, and carry out a metathesis reaction under normal temperature and pressure conditions. After the reaction is completed, filtration is carried out to obtain the second filter cake and the third filtrate. The second filter cake is washed, filtered, and dried with liquid ammonia to obtain the K2SO4 product. The ammonia evaporation operation can separate the NH4Cl product and the washing solvent liquid ammonia. The third filtrate is returned to step (1) for recycling, and ammonia water and a phase transfer reagent are supplemented to make the concentration of ammonia water 3 mol / L and the concentration of the phase transfer reagent ammonium acetate 2.5 mol / L. Continue to dissolve phosphogypsum, and use a potentiometric titrator to measure the Ca 2+ concentration to be 0.079 mol / L;

[0088] (4) Repeat steps (2) to (3) to continuously obtain CaCO3, K2SO4, and NH4Cl, and it is obtained that as the number of cycles increases, the soluble Ca 2+ concentration is shown in Table 2.

[0089] Table 2 Soluble calcium ion concentration

[0090]

[0091] As can be seen from Table 2, as the number of cycles increases, the dissolution effect of the first mixed solution on calcium ions slightly decreases. The concentration of calcium ions dissolved when initially dissolving phosphogypsum is 0.080 mol / L, and the concentration of calcium ions dissolved when recycled to the 20,000th time is 0.076 mol / L. It can be seen that the phase transfer effect of the first mixed solution in the method proposed by the present invention is relatively stable and can be recycled infinitely.

[0092] Comparative Example 1

[0093] The difference between Comparative Example 1 and Example 2 is that the first mixed solution does not include a phase transfer reagent, and the rest are the same.

[0094] Comparative Example 2

[0095] The difference between Comparative Example 2 and Example 2 is that the concentration of ammonia water is 0.5 mol / L, and the rest are the same.

[0096] Comparative Example 3

[0097] The difference between Comparative Example 3 and Example 3 is that the concentration of the aqueous solution of the phase transfer reagent is 6 mol / L, and the rest are the same.

[0098] Comparative Example 4

[0099] The difference between Comparative Example 4 and Example 3 is that the first mixed solution does not include ammonia water, and the rest are the same.

[0100] From Figures 10 to 13 it can be seen that in Comparative Example 2, the concentration of ammonia water is too low, resulting in the formation of a large amount of by-product potassium gypsum. In Comparative Example 3, the concentration of the aqueous solution of the phase transfer reagent is too high, resulting in the formation of ammonium gypsum, which affects the purity and yield of the product. In Comparative Example 1, the aqueous solution of the phase transfer reagent is not added to the first mixed solution, and the Ca 2+ concentration in the first filtrate is measured to be 0.013 mol / L. Compared with the case where the Ca 2+ concentration in the first filtrate is only 0.0034 mol / L without ammonia water and without the phase transfer reagent, it shows that although ammonia water can promote the dissolution of gypsum to a certain extent, without adding the aqueous solution of the phase transfer reagent, the Ca 2+ concentration is greatly reduced; in Comparative Example 4, the first mixed solution does not include ammonia water, resulting in the formation of a large amount of potassium gypsum impurities and the solution becoming very viscous.

[0101] As mentioned above, only the embodiments of the present application are described. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the technical idea and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost, characterized in that: The following steps are involved: (1) dissolving excess gypsum in the first mixed solution, performing a dissolution-promoting reaction under normal temperature and pressure, and filtering after the reaction to obtain a first filtrate; (2) adding a carbon source to the first filtrate, carrying out a carbonation reaction under normal temperature and pressure, filtering after the reaction is completed to obtain a first filter cake and a second filtrate, separating and purifying the first filter cake to obtain CaCO3 and NH4Cl; (3) adding KCl to the second filtrate, carrying out double decomposition reaction under normal temperature and pressure conditions, filtering after the reaction is completed to obtain a second filter cake and a third filtrate, separating and purifying the second filter cake to obtain K2SO4 and NH4Cl; The first mixed solution includes ammonia water and an aqueous solution of a phase transfer agent, the concentration of the ammonia water is 2-3 mol / L, and the concentration of the aqueous solution of the phase transfer agent is not less than 1 mol / L.

2. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: The method further comprises step (4) of returning the third filtrate to step (1) for recycling, and repeating steps (1) to (3) to continuously obtain CaCO3, K2SO4 and NH4Cl.

3. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: The phase transfer reagent includes one or more of sucrose, glucose, ammonium formate, citric acid, ammonium citrate, sodium citrate, sodium acetate or ammonium acetate; Preferably, the phase transfer reagent is at least one of sodium acetate or ammonium acetate.

4. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: The carbon source includes carbon dioxide, ammonium carbonate or ammonium bicarbonate.

5. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride by using gypsum at low cost according to claim 1, characterized in that: The separation and purification in step (2) specifically includes separating and purifying the first filter cake using a washing solvent, wherein the washing solvent includes water, alcohol or liquid ammonia.

6. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: The separation and purification in step (3) specifically includes separating and purifying the second filter cake using a washing solvent, wherein the washing solvent includes alcohol or liquid ammonia.

7. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: The reaction time of step (1) is 10 to 60 minutes.

8. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: The gypsum includes desulfurized gypsum or phosphogypsum.

9. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 1, characterized in that: When the carbon source is added in step (2), the step of adding ammonia or quicklime at the same time is also included.

10. The method for preparing high-purity potassium sulfate and co-producing calcium carbonate and ammonium chloride using gypsum at low cost according to claim 2, characterized in that: The third filtrate in step (4) can be recycled an unlimited number of times.

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