Method for preparing semi-hydrated gypsum from dihydrate gypsum based on normal temperature and normal pressure

Abstract

The invention relates to the technical field of gypsum material preparation, and discloses a method for preparing semi-hydrated gypsum from dihydrate gypsum based on normal temperature and pressure, which comprises the following steps: S1, adding NaCl into dilute sulfuric acid water, adding calcium hydroxide with the same molar weight as sulfuric acid, and reacting until the solution has a transient transparent stage; s2, adding ethanol with different contents during the period, so that the volume ratios of the ethanol are respectively 40vol%, 45vol%, 50vol%, 55vol%, 60vol% and 70vol%, and the total volume of the solution is fixed to be 100mL; s3, reacting for 10 seconds, performing centrifugal filtration, and analyzing the composition of a precipitation phase and the concentration of SO4 < 2-> in the water body; and S4, performing vacuum drying and analyzing the proportion of the semi-hydrated gypsum. The sulfate concentration in the water body is reduced, meanwhile, the efficiency of treating the sulfate water body by lime is improved, and up-to-standard discharge of the water body is promoted; the method provided by the invention realizes resource utilization of gypsum, and has the advantages of low cost and high efficiency; the preparation method is simple and feasible and can be widely popularized and applied.

Description

Technical Field

[0001] The invention relates to the technical field of gypsum material preparation, in particular to a method for preparing hemihydrate gypsum from dihydrate gypsum based on normal temperature and pressure. Background Art

[0002] Lime treatment of acid mine wastewater is currently the most commonly used method, but it has disadvantages such as large accumulation of gypsum and excessive concentration of residual sulfate. Hemihydrate gypsum is an important functional material. The existing production technology is mainly prepared by dissolving and recrystallizing dihydrate gypsum through heating in an organic solvent water bath. The conversion process requires the addition of organic solvents such as methanol and ethylene glycol to the aqueous solution and maintaining the temperature at 90℃-100℃. High temperature requires a lot of heat consumption, and some difficult-to-degrade organic solvents are prone to secondary pollution. The preparation time is long, and there are problems such as high cost and difficulty in production.

[0003] Therefore, it is necessary to design a practical method for preparing hemihydrate gypsum based on dihydrate gypsum at room temperature and pressure. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing hemihydrate gypsum from dihydrate gypsum at normal temperature and pressure to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, a method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure comprises the following steps:

[0006] S1: Add NaCl to dilute sulfuric acid water, add calcium hydroxide in an equal molar amount to the sulfuric acid to react, and the solution will enter a brief transparent stage;

[0007] S2: different amounts of ethanol were added during the process, making the volume ratio of ethanol 40vol%, 45vol%, 50vol%, 55vol%, and 60vol%, respectively, and the total volume of the solution was fixed at 100mL;

[0008] S3: centrifuge and filter after 10 seconds of reaction to analyze the composition of the precipitate phase and the SO4 in the water 2- concentration;

[0009] S4: Vacuum drying analysis of the proportion of hemihydrate gypsum.

[0010] According to the above technical solution, the NaCl concentration is set to 50mmol / L.

[0011] According to the above technical solution, the NaCl concentration is set to 100 mmol / L.

[0012] According to the above technical solution, the NaCl concentration is set to 150mmol / L.

[0013] According to the above technical solution, the concentration of dilute sulfuric acid is set to 50 mmol / L.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0015] 1. The present invention reduces the sulfate concentration in the water body, while improving the efficiency of lime treatment of sulfate water bodies, and promotes the discharge of water bodies up to standard.

[0016] 2. The present invention realizes the resource utilization of gypsum, and has the advantages of low cost and high efficiency; the preparation method is simple and easy, and can be widely promoted and applied.

[0017] 3. The present invention reduces SO4 in water 2- concentration, in order to solve the residual SO4 caused by the dissolution characteristics of gypsum in traditional lime treatment 2- The problem of excessive concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 is a schematic diagram of the analysis results of Example 1 of the present invention;

[0020] Figure 2 is a schematic diagram of the analysis results of Example 2 of the present invention;

[0021] Figure 3 is a schematic diagram of the analysis results of Example 3 of the present invention;

[0022] Figure 4 is a 50vol% thermogravimetric data diagram of Example 4 of the present invention;

[0023] Figure 5 is a 55 vol% thermogravimetric data diagram of Example 2 of the present invention;

[0024] Figure 6 This is a 60vol% thermogravimetric data diagram of Example 2 of the present invention;

[0025] Figure 7 is a 50vol% thermogravimetric data diagram of Example 3 of the present invention;

[0026] Figure 8 This is a graph of the 55 vol% thermogravimetric data of Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1: A method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure, comprising the following steps:

[0029] S1: Add 50mmol / L NaCl to 50mmol / L dilute sulfuric acid water, add calcium hydroxide in an equal molar amount to the sulfuric acid to react, and the solution will enter a short transparent stage;

[0030] S2: different amounts of ethanol were added during the process, making the volume ratio of ethanol 40vol%, 45vol%, 50vol%, 55vol%, and 60vol%, respectively, and the total volume of the solution was fixed at 100mL;

[0031] S3: centrifuge and filter after 10 seconds of reaction to analyze the composition of the precipitate phase and the SO4 in the water 2- concentration;

[0032] S4: Vacuum drying analysis of the proportion of hemihydrate gypsum.

[0033] like Figure 1 As shown: NaCl concentration is 50mmol / L, and the crystal phase has no characteristic peak of hemihydrate gypsum through XRD structural analysis. The reason may be that the proportion of hemihydrate gypsum is small and the absorption intensity is not enough; after the reaction, SO4 2- The concentration was maintained at 120 mg / L, which is lower than the water discharge standard of 250 mg / L.

[0034] Embodiment 2: A method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure, comprising the following steps:

[0035] S1: Add 100mmol / L NaCl to 50mmol / L dilute sulfuric acid water, add calcium hydroxide in an equal molar amount to the sulfuric acid, and the solution will enter a brief transparent stage;

[0036] S2: different amounts of ethanol were added during the process, making the volume ratio of ethanol 40vol%, 45vol%, 50vol%, 55vol%, and 60vol%, respectively, and the total volume of the solution was fixed at 100mL;

[0037] S3: centrifuge and filter after 10 seconds of reaction to analyze the composition of the precipitate phase and the SO4 in the water 2- concentration;

[0038] S4: Vacuum drying analysis of the proportion of hemihydrate gypsum.

[0039] like Figure 2 and Figure 5-6 As shown: when the NaCl concentration is 100mmol / L and the ethanol volume ratio is 55vol%, 60vol%, the XRD crystal phase shows the characteristic peak of hemihydrate gypsum. After the reaction, SO4 2- The concentration was maintained at 190 mg / L, which is lower than the water discharge standard of 250 mg / L. Thermogravimetric analysis showed that the percentage of crystal water loss in the crystalline phase of ethanol volume ratio 50 vol%, 55 vol%, and 60 vol% was 16.03%, 22.28%, and 24.80% by mole of hemihydrate gypsum, respectively.

[0040] Embodiment 3: A method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure, comprising the following steps:

[0041] S1: Add 150mmol / L NaCl to 50mmol / L dilute sulfuric acid water, add calcium hydroxide in an equal molar amount to the sulfuric acid, and the solution will enter a short transparent stage;

[0042] S2: different amounts of ethanol were added during the process, making the volume ratio of ethanol 40vol%, 45vol%, 50vol%, 55vol%, and 60vol%, respectively, and the total volume of the solution was fixed at 100mL;

[0043] S3: centrifuge and filter after 10 seconds of reaction to analyze the composition of the precipitate phase and the SO4 in the water 2- concentration;

[0044] S4: Vacuum drying analysis of the proportion of hemihydrate gypsum.

[0045] like Figure 3 and Figure 7-8 As shown: when the NaCl concentration is 150mmol / L and the ethanol volume ratio is 50vol%, 55vol%, and 60vol%, the XRD crystal phase shows the characteristic peak of hemihydrate gypsum. After the reaction, SO4 2- The concentration was maintained at 210 mg / L, which is lower than the water discharge standard of 250 mg / L. Thermogravimetric analysis showed that the percentage of crystal water loss in the crystalline phases with a volume ratio of 50 vol% and 55 vol% ethanol, and the molar proportions of hemihydrate gypsum were 28.60% and 38.52%, respectively.

[0046] Example 4: A method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure, comprising the following steps:

[0047] S1: Add 100mmol / L NaCl to 50mmol / L dilute sulfuric acid water, add calcium hydroxide in an equal molar amount to the sulfuric acid, and the solution will enter a brief transparent stage;

[0048] S2: adding ethanol to make the volume ratio of ethanol 70 vol%, and the total volume of the solution is fixed at 100 mL;

[0049] S3: After 10 seconds of reaction, centrifuge and filter. One group is washed with anhydrous ethanol, and the other group is not washed. The composition of the precipitate phase and the concentration of SO42- in the water are analyzed.

[0050] S4: Vacuum drying analysis of the proportion of hemihydrate gypsum.

[0051] like Figure 4 As shown: when the ethanol content is 70 vol% and the NaCl concentration is 100 mmol / L, the XRD results of the crystalline phase directly centrifuged and dried show the presence of two crystalline phases, gypsum and hemihydrate gypsum. The XRD results of the crystalline phase washed with ethanol show only hemihydrate gypsum. The proportion of hemihydrate gypsum in the crystalline phase can be adjusted by adjusting the ethanol content.

[0052] In summary: the present invention utilizes ethanol and NaCl to regulate the crystallization of calcium sulfate, and directly converts the gypsum crystal phase into a semi-hydrated gypsum phase by reacting calcium hydroxide with sulfate water bodies at normal temperature and pressure. Compared with the traditional method, it not only reduces the sulfate concentration in the water body, improves the efficiency of lime treatment of sulfate water bodies, and promotes the discharge of water bodies up to standard; it converts the waste gypsum into semi-hydrated gypsum with high utilization rate, and realizes the resource utilization of gypsum; it realizes the conversion of dihydrate gypsum to semi-hydrated gypsum at normal temperature and pressure, and has the advantages of low cost and high efficiency compared with the traditional water bath heating method; the preparation method is simple and easy, and can be widely promoted and applied.

[0053] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0054] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing hemihydrate gypsum from dihydrate gypsum at normal temperature and pressure, characterized in that: The following steps are involved: S1: Add NaCl to dilute sulfuric acid water, add calcium hydroxide in an equal molar amount to the sulfuric acid to react, and the solution will enter a brief transparent stage; S2: different amounts of ethanol were added during the process, making the volume ratio of ethanol 40vol%, 45vol%, 50vol%, 55vol%, and 60vol%, respectively, and the total volume of the solution was fixed at 100mL; S3: centrifuge and filter after 10 seconds of reaction to analyze the composition of the precipitate phase and the SO4 in the water 2- concentration; S4: Vacuum drying analysis of the proportion of hemihydrate gypsum.

2. The method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure according to claim 1, characterized in that: The NaCl concentration was set to 50 mmol / L.

3. The method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure according to claim 2, characterized in that: The NaCl concentration was set to 100 mmol / L.

4. The method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure according to claim 3, characterized in that: The NaCl concentration was set to 150 mmol / L.

5. The method for preparing hemihydrate gypsum from dihydrate gypsum at room temperature and pressure according to claim 3, characterized in that: The concentration of the dilute sulfuric acid is set to 50 mmol / L.

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