Method for rapidly preparing polyhalite

Abstract

The invention discloses a method for rapidly preparing polyhalite, which comprises the following steps: carrying out hydrothermal phase inversion reaction on a mixed system containing a K < + > source, a Mg < 2 + > source, a Ca < 2 + > source, a SO4 < 2-> source and water, and then carrying out cooling treatment to prepare the polyhalite, wherein in the mixed system, the content of K < + > is 1.31 wt% to 10.10 wt%, the content of Mg < 2 + > is 1.31 wt% to 3.16 wt%, the content of Ca < 2 + > is 0.96 wt% to 12.5 wt%, the content of SO4 < 2-> is 9.09 wt% to 54.86 wt%, and the content of H2O is 87.33 wt% to 19.38 wt%. According to the method provided by the invention, phase inversion and phase chemical equilibrium of polyhalite are realized under a hydrothermal condition, and the polyhalite can be rapidly prepared through a temperature changing process.

Description

Technical Field

[0001] The invention relates to the technical field of polyhalite synthesis, and in particular to a method for rapidly preparing polyhalite. Background Art

[0002] Potash is a key raw material for industrial production and one of the three major agricultural fertilizers. It plays a vital role in improving the yield and quality of agricultural products, crucial for national agricultural production and grain production, and a key strategic resource indispensable for national economic development. The agricultural sector alone consumes approximately tens of millions of tons of potash fertilizer annually. However, there is a serious supply-demand imbalance between the demand for resources and the availability of reserves (my country's potassium reserves account for only approximately 5% of the world's total). As a major agricultural country with limited potash resources, efforts to identify potential potash resources are of great significance to improving my country's potash fertilizer supply.

[0003] Polyhalite (K2SO4·MgSO4·2CaSO4·2H2O) is a sulfate mineral rich in potassium, magnesium, calcium, sulfur, and other elements. It contains 12.97% potassium, 4.03% magnesium, 13.29% calcium, 63.73% sulfate, and a whopping 28.9% potassium sulfate, making it a potential potash resource. Although polyhalite deposits have been discovered in Sichuan, Hubei, Shandong, Shaanxi, and Qinghai provinces in my country, large-scale mining and utilization have yet to be achieved due to its complex composition, poor water solubility, and deep burial depths. It is often considered a difficult-to-use "dead end ore."

[0004] Given my country's limited potassium resources, the development and utilization of insoluble potassium salts such as polyhalite to broaden the source of potash fertilizer has become a research hotspot. However, the complex composition of natural polyhalite minerals, often coexisting with impurities (such as soil, rock salt, and calcium sulfate), has led to current research focusing primarily on its sedimentary genesis, dissolution characteristics, and potassium sulfate preparation processes. However, fundamental research on the separation mechanism of potassium and magnesium ions in pure polyhalite is severely lacking. The fundamental reason is that the unique chemical composition of polyhalite makes it difficult to prepare through conventional experiments. Related research has long been limited to the theoretical level of phase chemistry, and to date, there has been a lack of effective artificial synthesis methods. Therefore, the development of technologies for the artificial synthesis of polyhalite is urgently needed. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for quickly preparing polyhalite to overcome the shortcomings of the prior art.

[0006] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0007] The present invention provides a method for rapidly preparing polyhalite, which comprises: + Source, Mg 2+ Source, Ca 2+ Source, SO42- The mixed system of the source and water undergoes a hydrothermal phase conversion reaction, and then undergoes a cooling treatment to obtain polyhalite;

[0008] Wherein, K in the mixed system + The content of Mg is 1.31~10.10wt%, Mg 2+ The content of Ca is 1.31~3.16wt%, 2+ The content is 0.96~12.5wt%, SO4 2- The content of is 9.09-54.86wt%, and the content of H2O is 87.33-19.38wt%;

[0009] The temperature of the hydrothermal phase conversion reaction is 80-170° C., and the reaction time is 4-10 hours.

[0010] Compared with the prior art, the present invention has at least the following advantages:

[0011] The method provided by the present invention is to + Source, Mg 2+ Source, Ca 2+ Source, SO4 2- The mixed system of the source and water directly undergoes high-temperature hydrothermal phase transformation to achieve polyhalite phase transformation and phase chemical equilibrium. Polyhalite can be quickly prepared through the temperature-varying process, which has the advantages of simple operation and rapid reaction. The synthesized polyhalite does not contain impurities, has high purity, and has an appropriate ratio of components. It has broad application prospects in the field of preparing compound fertilizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 This is a process flow chart for preparing polyhalite in a typical embodiment of the present invention;

[0014] Figure 2 Schematic diagram of the polyhalite preparation process in a typical embodiment of the present invention;

[0015] Figure 3 is the XRD diffraction pattern of the polyhalite prepared in Example 1 of the present invention;

[0016] Figure 4 is a SEM image of the polyhalite prepared in Example 1 of the present invention;

[0017] Figure 5 This is the XRD diffraction pattern of the low-purity polyhalite prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be more fully understood by reading the following detailed description. However, it should be understood that the detailed description disclosed below is merely exemplary of the present invention, and that the present invention may be embodied in a variety of forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art to variously employ the present invention in virtually any appropriately detailed embodiment.

[0019] As one aspect of the technical solution of the present invention, a method for rapidly preparing polyhalite comprises: + Source, Mg 2+ Source, Ca 2+ Source, SO4 2- A mixed system of the source and water undergoes a hydrothermal phase conversion reaction to produce polyhalite;

[0020] Wherein, K in the mixed system + The content of Mg is 1.31~10.10wt%, Mg 2+ The content of Ca is 1.31~3.16wt%, 2+ The content is 0.96~12.5wt%, SO4 2- The content of is 9.09-54.86wt%, and the content of H2O is 87.33-19.38wt%;

[0021] The temperature of the hydrothermal phase conversion reaction is 80-170° C., and the reaction time is 4-10 hours.

[0022] In some embodiments, the method for rapidly preparing polyhalite specifically comprises: + Source, Mg 2+ Source, Ca 2+ Source, SO4 2- A mixed system of the source and water undergoes a hydrothermal phase conversion reaction in a reactor. After the reaction is completed, the reactor is cooled and subjected to the cooling treatment, and solid-liquid separation is performed to obtain polyhalite.

[0023] In some embodiments, the temperature of the cooling treatment is 25-50°C.

[0024] In some embodiments, the K + The source includes, but is not limited to, any one of anhydrous potassium salt, potassium salt containing crystalline water, or a combination of the two.

[0025] In some embodiments, the Mg 2+The source includes, but is not limited to, any one of anhydrous magnesium salts, magnesium salts containing crystalline water, or a combination of both.

[0026] In some embodiments, the Ca 2+ The source includes, but is not limited to, any one of anhydrous calcium salt, calcium salt containing crystal water, or a combination of the two.

[0027] In some embodiments, the SO4 2- Sources include but are not limited to SO4 2- Sources include K + Sulfate, Mg 2+ Sulfate, Ca 2+ Any one or a combination of two or more of the sulfates.

[0028] For more specific implementations, see Figure 1 and Figure 2 A method for rapidly preparing polyhalite comprises the following steps:

[0029] S1: First, prepare the materials required for synthesizing polyhalite. The materials contain K in percentage by mass. + :1.31~10.10%、Mg 2+ :1.31~3.16%, Ca 2+ :0.96~12.5%、SO4 2- :9.09~54.86%, H2O: 87.33~19.38%;

[0030] S2: Stir and mix the materials in step S1 evenly;

[0031] S3: Add the material stirred in step S2 directly into the reactor, heat it to 80-170°C, and keep it at high temperature for 4-10 hours;

[0032] S4: Stop heating and cool the reactor in step S3 to a temperature of 25-50°C;

[0033] S5: Open the reactor, separate the solid and liquid phases, and dry them. The solid phase is a polyhalite phase.

[0034] As another aspect of the technical solution of the present invention, it relates to polyhalite prepared by the above method.

[0035] As another aspect of the technical solution of the present invention, it also involves the application of the aforementioned polyhalite in chlorine-free compound fertilizers.

[0036] In summary, the preparation method provided by the present invention is based on the chemical composition of polyhalite, and utilizes a hydrothermal phase transformation reaction at high temperature to promote polyhalite phase transformation and phase equilibrium between potassium, magnesium, calcium, and sulfate ions, and then realizes the synthesis of polyhalite by cooling operation. This method has the advantages of simple operation and rapid reaction, and has broad application prospects in the field of synthesizing other insoluble inorganic salt minerals. It can not only provide an ideal pure phase model to replace natural ore, but also be used to deeply explore the separation mechanism of potassium and magnesium ions, and lay a solid theoretical foundation for the efficient and comprehensive utilization of natural polyhalite resources. At the same time, it also has the potential to be directly applied to agricultural planting as a high-quality chlorine-free composite slow-release fertilizer.

[0037] The present invention is further illustrated by way of examples below, but the invention is not limited to the scope of the examples. The reagents and raw materials used in the following examples are commercially available, and the experimental methods where specific conditions are not specified are generally carried out under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0038] Example 1

[0039] Prepare the material, wherein potassium sulfate 1.46g, magnesium sulfate 3.24g, calcium sulfate 1.63g and water 43.67g (i.e., K + :1.31%、Mg 2+ :1.31%、Ca 2+ :0.96%、SO4 2- :9.09%,H2O:87.33%), put the material into a beaker, stir evenly and pour into a reactor, put into an oven and heat to 120℃, keep it for 7 hours and then stop heating, sprinkle water on the reactor to cool it down, and after it drops to 25℃, open the reactor, separate the solid and liquid phases, wash and dry to obtain 3.28g of polyhalite. The XRD diffraction pattern of the polyhalite prepared in this example is shown in Figure 3 , the SEM image of polyhalite is shown in Figure 4 .

[0040] Example 2

[0041] Prepare the material, wherein potassium sulfate 3.13g, magnesium sulfate 6.96g, calcium sulfate 6.45g and water 33.46g (i.e., K + :2.81%、Mg 2+ :2.81%、Ca 2+ :3.8%、SO4 2- : 23.67%, H2O: 66.91%), the materials were placed in a beaker, stirred evenly and poured into a reactor, placed in an oven and heated to 100°C, and kept for 9 hours before stopping heating, the reactor was cooled by pouring water, and after the temperature dropped to 30°C, the reactor was opened, the solid and liquid phases were separated, and 16.37 g of polyhalite was obtained after washing and drying.

[0042] Example 3

[0043] Prepare the material, wherein potassium sulfate 6.57g, magnesium sulfate 4.38g, calcium sulfate 12.74g and water 26.30g (i.e., K + :5.90%、Mg 2+ :1.77%、Ca 2+ :7.5%、SO4 2- : 32.22%, H2O: 52.61%), the materials were placed in a beaker, stirred evenly and poured into a reactor, placed in an oven and heated to 170°C, and kept for 5 hours before stopping heating, the reactor was cooled by pouring water, and after the temperature dropped to 35°C, the reactor was opened, the solid and liquid phases were separated, and 34.41 g of polyhalite was obtained after washing and drying.

[0044] Example 4

[0045] Prepare the material, wherein potassium sulfate 7.99g, magnesium sulfate 5.61g, calcium sulfate 15.28g and water 21.11g, (i.e., K + :7.97%、Mg 2+ :2.52%、Ca 2+ :10.0%、SO4 2- : 43.72%, H2O: 35.79%), the materials were placed in a beaker, stirred evenly and poured into a reactor, placed in an oven and heated to 150°C, and kept for 4 hours before stopping the heating, the reactor was cooled by pouring water, and after the temperature dropped to 45°C, the reactor was opened, the solid and liquid phases were separated, and 51.99 g of polyhalite was obtained after washing and drying.

[0046] Example 5

[0047] Prepare the material, wherein potassium sulfate 11.25g, magnesium sulfate 7.82g, calcium sulfate 21.23g and water 9.69g (i.e., K + :10.10%、Mg 2+ :3.16%、Ca 2+ :12.5%、SO4 2- : 54.86%, H2O: 19.38%), the materials were placed in a beaker, stirred evenly and poured into a reactor, placed in an oven and heated to 80°C, and kept for 10 hours before stopping the heating, the reactor was cooled by pouring water, and after the temperature dropped to 50°C, the reactor was opened, the solid and liquid phases were separated, and 68.27 g of polyhalite was obtained after washing and drying.

[0048] Comparative Example 1

[0049] Compared with Example 1, the difference is that the temperature is raised to 70°C. After washing and drying, 2.79g of polyhalite and 0.49g of calcium sulfate are obtained. The temperature is lower than 80°C, and the conversion between the materials is incomplete, there is residual calcium sulfate, and the purity is low. The XRD diffraction pattern of the low-purity polyhalite prepared in this comparative example is shown in Figure 5 .

[0050] Comparative Example 2

[0051] Compared with Example 1, the difference is that the temperature is raised to 180°C. After washing and drying, 3.28g of polyhalite is obtained. The high temperature limit of the reactor is 180°C, which has little effect on the product, but the high temperature leads to excessive energy consumption.

[0052] Comparative Example 3

[0053] Compared with Example 1, the difference is that heating was stopped after 3.5 hours, the reactor was cooled by pouring water, and after the temperature dropped to 25°C, the reactor was opened, the solid and liquid phases were separated, and after washing and drying, 2.95g of polyhalite and 0.33g of calcium sulfate were obtained. The time was too short, the reaction was incomplete, and there was residual calcium sulfate in the product.

[0054] Comparative Example 4

[0055] Compared with Example 1, the difference is that the raw materials include 11.37g of potassium sulfate, 7.92g of magnesium sulfate, 21.40g of calcium sulfate, and 9.31g of water. After washing and drying, 68.05g of polyhalite and 0.28g of calcium sulfate are obtained. The raw material ratio exceeds the parameters specified in the present invention, the purity of the polyhalite decreases, and calcium sulfate is present.

[0056] Comparative Example 5

[0057] Compared with Example 1, the difference is that the reactor was cooled to 20°C by spraying water. After washing and drying, 3.45g of polyhalite and 0.18g of calcium sulfate were obtained. The cooling temperature exceeded the limit parameters of the present invention, the purity of the polyhalite decreased, and calcium sulfate was accompanied.

[0058] Comparative Example 6

[0059] Compared with Example 1, the difference is that the reaction kettle was cooled to 52°C by spraying water. After washing and drying, 2.9 g of polyhalite was obtained. The cooling temperature exceeded the limit parameters of the present invention, and the polyhalite yield was reduced.

[0060] In summary, polyhalite is a mineral that is difficult to form. Natural minerals generally contain soil and other salt mines and have very low grade. The polyhalite prepared by the present invention has high purity and can be used as a slow-release fertilizer and directly used as agricultural potash fertilizer. It has broad application prospects in the field of agricultural planting.

[0061] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0062] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for rapidly preparing polyhalite, characterized in that: include: Make K + Source, Mg 2+ Source, Ca 2+ Source, SO4 2- The mixed system of the source and water undergoes a hydrothermal phase conversion reaction, and then undergoes a cooling treatment to obtain polyhalite; Wherein, K in the mixed system + The content of Mg is 1.31~10.10wt%, Mg 2+ The content of Ca is 1.31~3.16wt%, 2 + The content is 0.96~12.5wt%, SO4 2- The content of is 9.09-54.86wt%, and the content of H2O is 87.33-19.38wt%; The temperature of the hydrothermal phase conversion reaction is 80-170° C., and the reaction time is 4-10 hours.

2. The method according to claim 1, characterized in that Specifically include: Make K + Source, Mg 2+ Source, Ca 2+ Source, SO4 2- A mixed system of the source and water undergoes a hydrothermal phase conversion reaction in a reactor. After the reaction is completed, the reactor is cooled and subjected to the cooling treatment, and solid-liquid separation is performed to obtain polyhalite.

3. The method according to claim 1, characterized in that The temperature of the cooling treatment is 25-50°C.

4. The K + The source includes any one of anhydrous potassium salt, potassium salt containing crystal water, or a combination of the two.

5. The method according to claim 1, characterized in that The Mg 2+ The source includes any one of anhydrous magnesium salts, magnesium salts containing crystal water, or a combination of the two.

6. The method according to claim 1, characterized in that The Ca 2+ The source includes any one of anhydrous calcium salt, calcium salt containing crystal water, or a combination of the two.

7. The method according to claim 1, characterized in that The SO4 2- Sources include K + Sulfate, Mg 2+ Sulfate, Ca 2+ Any one or a combination of two or more of the sulfates.

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