Method for improving conversion rate and length-diameter ratio of calcium sulfate hemihydrate whiskers

Abstract

The invention provides a method for improving the conversion rate and the length-diameter ratio of calcium sulfate hemihydrate whiskers. According to the method for improving the conversion rate and the length-diameter ratio of the calcium sulfate hemihydrate whiskers, impurities, including phosphate radicals, fluorine ions, magnesium ions and iron ions, contained in ardealite are added into natural gypsum, the mass content of the phosphate radicals is controlled to be 0-0.5%, the mass content of the fluorine ions is controlled to be 0-0.4%, the mass content of the magnesium ions is controlled to be 1-2%, and the mass content of the iron ions is controlled to be 1-2%, so that the conversion rate and the length-diameter ratio of the calcium sulfate hemihydrate whiskers are improved. The conversion rate and the length-diameter ratio of the calcium sulfate hemihydrate whisker are further improved; according to the method disclosed by the invention, impurities contained in the ardealite are added into the natural gypsum, and the scene of preparing the hemihydrate gypsum from the ardealite is simulated by exploring the mutual relationship between the concentrations of phosphate ions, magnesium ions, fluorine ions and iron ions in the ardealite and the conversion rate and the length-diameter ratio of the calcium sulfate hemihydrate whiskers, so that theoretical support is provided for efficiently utilizing the ardealite.

Description

Technical Field

[0001] This invention relates to the field of calcium sulfate hemihydrate preparation technology, and in particular to a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers. Background Technology

[0002] Currently, the main methods for preparing calcium sulfate hemihydrate (CaSO4·0.5H2O) whiskers, both domestically and internationally, are the autoclaving method, the atmospheric pressure solution method, and the pressurized solution method. All of these methods require relatively long reaction times, increasing energy consumption. Existing technologies for preparing calcium sulfate whiskers often involve reacting high-purity calcium salts with sulfuric acid / sulfate, requiring high purity raw materials. In technologies using gypsum, a byproduct of the process, as a raw material, most methods only involve simple pretreatment processes such as crushing, screening, acid washing, and water washing. Because the inhibitory effect of numerous complex ions in the gypsum raw material on the growth of calcium sulfate whiskers is ignored, the purity and aspect ratio of the resulting product are low, and the dehydration rate of dihydrate gypsum is also slowed down. Furthermore, the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers prepared using existing technologies are not high. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers.

[0004] The present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers, comprising the following steps:

[0006] Phosphate, fluoride, magnesium, and iron salts are added to natural gypsum to obtain treated natural gypsum.

[0007] The treated natural gypsum was mixed with a salt-ethanol mixture, heated to react, filtered, washed, and dried to obtain calcium sulfate hemihydrate whiskers.

[0008] The treated natural gypsum contains 0-0.5% phosphate, 0-0.4% fluoride, 1-2% magnesium, and 1-2% iron.

[0009] Preferably, the salt-alcohol mixture is obtained by mixing glycerol, sodium chloride, and water.

[0010] Preferably, the mass ratio of glycerol, sodium chloride, and water is (40-50):(10-20):(20-30).

[0011] Preferably, the treated natural gypsum is mixed with the salt-alcohol mixed solution, and the step of heating reaction is carried out at a temperature of 90-100 DEG C for 60-90 minutes.

[0012] Preferably, the mass ratio of the treated natural gypsum to the salt-alcohol mixed solution is 1: (10-15).

[0013] Preferably, the phosphate salt is potassium dihydrogen phosphate;

[0014] The fluorine salt is sodium fluoride;

[0015] The magnesium salt is magnesium chloride;

[0016] The iron salt is ferric chloride.

[0017] Preferably, the mass ratio of the glycerol, sodium chloride and water is 50:20:30.

[0018] Preferably, the mass content of phosphate in the treated natural gypsum is 0%, the mass content of fluorine ion is 0%, the mass content of magnesium ion is 2%, and the mass content of iron ion is 2%.

[0019] Preferably, the treated natural gypsum is mixed with the salt-alcohol mixed solution, and the step of heating reaction is carried out at a temperature of 90-100 DEG C for 60-90 minutes.

[0020] In the second aspect, the application further provides a calcium sulfate hemihydrate whisker prepared by the method.

[0021] The calcium sulfate hemihydrate whisker and the preparation method thereof have the following effects compared with the prior art.

[0022] 1. The method for improving the conversion rate and aspect ratio of the calcium sulfate hemihydrate whisker adds the impurities contained in phosphogypsum, i.e. phosphate, fluorine ion, magnesium ion and iron ion, to the natural gypsum, controls the mass content of phosphate to be 0-0.5%, the mass content of fluorine ion to be 0-0.4%, the mass content of magnesium ion to be 1-2%, and the mass content of iron ion to be 1-2%, and thus improves the conversion rate and aspect ratio of the calcium sulfate hemihydrate whisker.

[0023] 2. The method for improving the conversion rate and aspect ratio of the calcium sulfate hemihydrate whisker adds the impurities contained in phosphogypsum to the natural gypsum, explores the mutual relationship between the concentrations of phosphate ion, magnesium ion, fluorine ion and iron ion in the phosphogypsum and the conversion rate and aspect ratio of the calcium sulfate hemihydrate whisker, simulates the scenario of preparing the calcium sulfate hemihydrate whisker from the phosphogypsum, and provides theoretical support for efficient utilization of the phosphogypsum. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0025] Figure 1 SEM image of the calcium sulfate hemihydrate whisker prepared according to the method in Comparative Example 2;

[0026] Figure 2 SEM image of the calcium sulfate hemihydrate whisker prepared according to the method in Example 1. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present application, the following will be a more comprehensive description of the present application combined with specific embodiments. The preferred embodiments of the present application are given in the specific embodiments. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0028] The sequence of the following embodiment description is not limited as the preferred sequence of the embodiments. In addition, in the description of the present application, the term "comprising" means "including but not limited to". Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limit to the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this text, it means that any cited number (fraction or integer) within the indicated range is included.

[0029] The present application provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whisker, comprising the following steps:

[0030] S1, adding phosphate, fluoride, magnesium salt, iron salt to natural gypsum to obtain treated natural gypsum;

[0031] S2, mixing the treated natural gypsum with a salt-alcohol mixed solution, heating and reacting, filtering, washing and drying to obtain calcium sulfate hemihydrate whisker;

[0032] The treated natural gypsum has a mass content of phosphate ions of 0-0.5%, a mass content of fluoride ions of 0-0.4%, a mass content of magnesium ions of 1-2%, and a mass content of iron ions of 1-2%.

[0033] Specifically, the dehydration process of dihydrate gypsum (calcium sulfate dihydrate (CaSO4·2H2O)) is regulated by adding a certain amount of reagent, so that the dehydration rate is accelerated, and the reaction time for preparing calcium sulfate hemihydrate whiskers is shortened. Some impurity ions in phosphogypsum can play this role. Fluoride ions, magnesium ions, phosphate ions and iron ions can affect the dehydration rate of dihydrate gypsum to some extent and have a great influence on the growth of calcium sulfate hemihydrate. At the same time, some impurity ions in phosphogypsum can also regulate the micro-morphology of calcium sulfate hemihydrate and promote the aspect ratio of calcium sulfate hemihydrate whiskers. By adding the impurities contained in phosphogypsum, i.e. phosphate ions, fluoride ions, magnesium ions and iron ions, to natural gypsum (main component: calcium sulfate dihydrate (CaSO4·2H2O)), and by controlling the concentrations of phosphate ions, fluoride ions, magnesium ions and iron ions, the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers are improved.

[0034] Further, by adding the impurities contained in phosphogypsum to natural gypsum, the mutual relationship between the concentrations of phosphate ions, magnesium ions, fluoride ions and iron ions in phosphogypsum and the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers is explored, the preparation of calcium sulfate hemihydrate from phosphogypsum is simulated, and theoretical support is provided for efficient utilization of phosphogypsum.

[0035] In some embodiments, the salt-alcohol mixed solution is obtained by mixing glycerol, sodium chloride and water; wherein the sodium chloride can improve the solubility of dihydrate gypsum in the solution and improve the supersaturation degree of the solution, and the glycerol can reduce the activity of the solution, and the improvement of the supersaturation degree and the reduction of the water activity can promote the dehydration reaction of dihydrate gypsum.

[0036] In some embodiments, the mass ratio of glycerol, sodium chloride and water is (40-50):(10-20):(20-30).

[0037] In some embodiments, in the step of mixing the treated natural gypsum with the salt-alcohol mixed solution and heating for reaction, the reaction temperature is 90-100 DEG C, and the reaction time is 60-90 min.

[0038] In some embodiments, the mass ratio of the treated natural gypsum to the salt-alcohol mixed solution is 1:(10-15).

[0039] In some embodiments, the phosphate salt is potassium dihydrogen phosphate;

[0040] The fluoride salt is sodium fluoride;

[0041] The magnesium salt is magnesium chloride;

[0042] The iron salt is ferric chloride.

[0043] In some embodiments, the mass ratio of glycerol, sodium chloride and water is 50:20:30.

[0044] In some embodiments, the mass content of phosphate in the treated natural gypsum is 0%, the mass content of fluoride is 0%, the mass content of magnesium ions is 2%, and the mass content of iron ions is 2%.

[0045] Specifically, when the mass content of phosphate is 0% and the mass content of fluoride is 0%, i.e., no phosphate salt and fluoride salt is added.

[0046] In some embodiments, the treated natural gypsum is mixed with a salt-alcohol mixed solution, heated and reacted, washed with water at a temperature of 90-100°C, then washed with ethanol, and dried to obtain calcium sulfate hemihydrate whiskers.

[0047] The method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers provided by the application has a conversion rate of hemi-gypsum (i.e., the conversion rate of natural gypsum into hemi-gypsum) of 95-100% during preparation, and the aspect ratio (i.e., the ratio of length to diameter) of the prepared calcium sulfate hemihydrate whiskers is 60-80.

[0048] Based on the same inventive concept, the application further provides a calcium sulfate hemihydrate whisker prepared by the above preparation method.

[0049] The method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers provided by the application is further described in the following specific embodiments, and this part further describes the content of the application in combination with specific embodiments, but should not be understood as a limitation of the application. Unless otherwise specified, the technical means used in the embodiments are conventional means familiar to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the art.

[0050] The natural gypsum in the following embodiments is from the National Pharmaceutical Group Chemical Reagent Co., Ltd., and the mass content of calcium sulfate dihydrate is 99.99%.

[0051] Embodiment 1

[0052] The embodiment provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers, comprising the following steps:

[0053] S1, potassium dihydrogen phosphate, sodium fluoride, magnesium chloride and ferric chloride are added to natural gypsum to obtain treated natural gypsum; wherein the mass content of phosphate in the treated natural gypsum is 0%, the mass content of fluoride is 0%, the mass content of magnesium ions is 2%, and the mass content of iron ions is 2%;

[0054] S2, the treated natural gypsum and salt-alcohol mixed solution are mixed, and reacted at 100 DEG C for 60 min, and then washed with water at 95 DEG C and then washed with ethanol, and dried to obtain calcium sulfate hemihydrate whiskers;

[0055] The salt-alcohol mixed solution is obtained by mixing glycerol, sodium chloride and water in a mass ratio of 50:20:30.

[0056] The mass ratio of the treated natural gypsum to the salt-alcohol mixed solution is 1:10.

[0057] Example 2

[0058] The embodiment provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers, which comprises the following steps:

[0059] S1, potassium dihydrogen phosphate, sodium fluoride, magnesium chloride and ferric chloride are added into natural gypsum to obtain treated natural gypsum; wherein the mass content of phosphate in the treated natural gypsum is 0.5%, the mass content of fluoride ion is 0.4%, the mass content of magnesium ion is 1%, and the mass content of iron ion is 1%;

[0060] S2, the treated natural gypsum and salt-alcohol mixed solution are mixed, and reacted at 100 DEG C for 80 min, and then washed with water at 95 DEG C and then washed with ethanol, and dried to obtain calcium sulfate hemihydrate whiskers;

[0061] The salt-alcohol mixed solution is obtained by mixing glycerol, sodium chloride and water in a mass ratio of 50:20:30.

[0062] The mass ratio of the treated natural gypsum to the salt-alcohol mixed solution is 1:10.

[0063] Comparative Example 1

[0064] The embodiment provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers, which comprises the following steps:

[0065] S1, potassium dihydrogen phosphate, sodium fluoride, magnesium chloride and ferric chloride are added into natural gypsum to obtain treated natural gypsum; wherein the mass content of phosphate in the treated natural gypsum is 0.5%, the mass content of fluoride ion is 0.4%, the mass content of magnesium ion is 0%, and the mass content of iron ion is 0%;

[0066] S2, the treated natural gypsum and salt-alcohol mixed solution are mixed, and reacted at 100 DEG C for 90 min, and then washed with water at 95 DEG C and then washed with ethanol, and dried to obtain calcium sulfate hemihydrate whiskers;

[0067] The salt-alcohol mixed solution is obtained by mixing glycerol, sodium chloride and water in a mass ratio of 50:20:30.

[0068] The mass ratio of the treated natural gypsum and the salt-alcohol mixed solution is 1:10.

[0069] Comparative Example 2

[0070] The present comparative example provides a method for improving the conversion rate and aspect ratio of calcium sulfate hemihydrate whiskers, comprising the following steps:

[0071] S1, mixing natural gypsum and a salt-alcohol mixed solution, reacting at 100°C for 90 min, and then washing with water at a temperature of 95°C and then with ethanol after filtration, and drying to obtain calcium sulfate hemihydrate whiskers;

[0072] The salt-alcohol mixed solution is obtained by mixing glycerol, sodium chloride and water in a mass ratio of 50:20:30.

[0073] The mass ratio of the natural gypsum and the salt-alcohol mixed solution is 1:10.

[0074] Performance test

[0075] Calcium sulfate hemihydrate whiskers were prepared according to the methods in Examples 1-2 and Comparative Examples 1-2, and the conversion rate of hemihydrate gypsum and the aspect ratio of calcium sulfate hemihydrate whiskers were tested, and the results are shown in Table 1 below.

[0076] The conversion rate of hemihydrate gypsum is calculated as follows:

[0077] The conversion rate of hemihydrate gypsum = (1-(HH%-6.21%) / (DH%)) x 100%;

[0078] In the formula: DH% represents the crystallization water content of CaSO4.2H2O in the raw material (i.e. natural gypsum), %;

[0079] HH%: the crystallization water content of CaSO4.2H2O and CaSO4.0.5H2O in the product (i.e. the final prepared calcium sulfate hemihydrate whisker product), %; in theory, the mass percentage of CaSO4.0.5H2O crystallization water is 6.21%;

[0080] The crystallization water is calculated as follows:

[0081] W = (m-m1) / m x 100%;

[0082] In the formula: W - crystallization water content, %; m - sample mass before heating, g; m1 - sample mass after heating, g.

[0083] Table 1 - Conversion rate of hemihydrate gypsum and aspect ratio of calcium sulfate hemihydrate whiskers in different examples

[0084]

[0085] As shown in Table 1, in Examples 1 and 2, the conversion rate of hemihydrate gypsum (i.e., the conversion rate of natural gypsum to hemihydrate gypsum) reached 95%-100% within 60-80 minutes, and the aspect ratio of the hemihydrate calcium sulfate whiskers was 60-80; while in Comparative Examples 1 and 2, the conversion rate of hemihydrate gypsum was 90%-100% within 90 minutes, and the aspect ratio of the hemihydrate calcium sulfate whiskers was 35-40. The hemihydrate calcium sulfate whiskers prepared by the method of the present invention have a higher conversion rate of hemihydrate gypsum and a higher aspect ratio.

[0086] Figure 1 SEM image of calcium sulfate hemihydrate whiskers prepared according to the method in Comparative Example 2;

[0087] Figure 2 SEM image of calcium sulfate hemihydrate whiskers prepared according to the method in Example 1;

[0088] from Figures 1-2 As can be seen, the aspect ratio of the calcium sulfate hemihydrate whiskers prepared according to the method in Comparative Example 2 is about 40; while in Example 1, after adding specific impurity ions, the aspect ratio of the prepared calcium sulfate hemihydrate whiskers increased to 80.

[0089] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this interpretation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for improving the conversion rate, aspect ratio of calcium sulphate hemi-hydrate whiskers, characterized in that, The method comprises the following steps: adding phosphate, fluoride, magnesium salt and iron salt into natural gypsum to obtain treated natural gypsum; mixing the treated natural gypsum with a salt-alcohol mixed solution, heating and reacting, filtering, washing and drying to obtain calcium sulfate hemihydrate whiskers; The mass content of phosphate in the treated natural gypsum is 0-0.5%, the mass content of fluoride is 0-0.4%, the mass content of magnesium ion is 1-2%, and the mass content of iron ion is 1-2%.

2. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 1, wherein, The salt-alcohol mixed solution is obtained by mixing glycerol, sodium chloride and water.

3. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 2, wherein, The mass ratio of glycerol, sodium chloride and water is (40-50):(10-20):(20-30).

4. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 1, wherein, In the step of mixing the treated natural gypsum with the salt-alcohol mixed solution and heating and reacting, the reaction temperature is 90-100 DEG C, and the reaction time is 60-90 min.

5. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 1, wherein, The mass ratio of the treated natural gypsum and the salt-alcohol mixed solution is 1:(10-15).

6. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 1, wherein, The phosphate is potassium dihydrogen phosphate. The fluoride is sodium fluoride. The magnesium salt is magnesium chloride. The iron salt is ferric chloride.

7. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 3, wherein, The mass ratio of glycerol, sodium chloride and water is 50:20:

30.

8. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 1, wherein, The mass content of phosphate in the treated natural gypsum is 0%, the mass content of fluoride is 0%, the mass content of magnesium ion is 2%, and the mass content of iron ion is 2%.

9. The method of improving the conversion and aspect ratio of calcium sulphate hemi-hydrate whiskers according to claim 1, wherein, After filtering, the treated natural gypsum is washed with water with a temperature of 90-100 DEG C and then washed with ethanol, drying to obtain calcium sulfate hemihydrate whiskers.

10. A calcium sulphate hemihydrate whisker, characterized in that, The calcium sulfate hemihydrate whiskers are prepared by the method as claimed in any one of claims 1-9.

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