A kind of gypsum and its preparation method and application

Abstract

The invention discloses a gypsum and a preparation method and application thereof. The preparation method of gypsum comprises the following steps: acid treatment: placing natural gypsum particles in dilute sulfuric acid, wherein the concentration of the dilute sulfuric acid does not exceed 15%, and then adding oxalic acid, and stirring for reaction; removing inorganic minerals: standing the mixed solution obtained in the acid treatment step to obtain a solution and a precipitate, removing the black impurities on the upper layer of the precipitate, and then uniformly mixing the remaining precipitate and the solution; extraction: adding an extractant to the mixed solution obtained in the inorganic mineral removal step, wherein the extractant comprises a non-polar solvent, standing for stratification, and obtaining a lower layer of white precipitate and an upper layer of black filtrate; washing and drying: washing the white precipitate obtained in the extraction step with clean water, and drying. The purity of the gypsum product obtained by the invention reaches more than 99%, and the whiteness reaches more than 94%.

Description

Technical Field

[0001] The invention relates to the field of natural gypsum, and more particularly to gypsum and a preparation method and application thereof. Background Art

[0002] Gypsum is an important industrial raw material. Gypsum includes two categories: phosphogypsum and natural gypsum. Phosphogypsum is a solid waste produced in the wet phosphoric acid process. Its composition is complex. In addition to calcium sulfate, there are also incompletely decomposed phosphate rock, residual phosphoric acid, fluoride, acid insoluble matter, organic matter, etc. The presence of fluorine and phosphorus limits its application in the field of high-end gypsum. For example, phosphogypsum cannot be used in the field of food additives due to the presence of fluorine and phosphorus. Natural gypsum, as an environmentally friendly material, has a wide range of uses in food additives, high-end building materials and other fields.

[0003] my country is rich in natural gypsum ore resources, but the current utilization rate of natural gypsum ore is extremely low (generally no more than 10%), the production cost is high, and it cannot meet the needs of modern industrialization. Natural gypsum contains black humic acid and a small amount of black inorganic minerals. Therefore, the industry generally adopts color sorting combined with calcination to prepare high-purity, high-whiteness natural gypsum. However, after color sorting, more than 80% to 90% of gray natural gypsum remains. In other words, the utilization rate of natural gypsum by color sorting combined with calcination does not exceed 10%, resulting in a large amount of waste natural gypsum, which greatly increases the production cost of the enterprise. Improving the utilization rate of natural gypsum is a key issue that needs to be solved in this technical field.

[0004] The patent "A calcination device and production process for purifying and whitening natural anhydrous gypsum" (publication number CN106800306A) states that the whiteness of anhydrite can reach more than 98% through one-time calcination. However, the one-time calcination method can only remove humic acid, but cannot remove the black inorganic minerals in natural gypsum. In addition, the calcination temperature of this method is controlled at 750-800℃, which consumes a lot of energy (electricity, heat, etc.), making the enterprise cost high and not environmentally friendly.

[0005] The patent "Method for Deep Purification of Phosphogypsum by Extraction" (Publication No. CN 106044828 A) mentions that organic matter in phosphogypsum can be removed by extraction. Specifically, the method uses high-concentration sulfuric acid (sulfuric acid concentration is stable at 30-40%) and a composite extractant (the composite extractant is composed of component A and component B, wherein component A is at least one of n-butanol, n-octanol, methyl isobutyl ketone, and tributyl phosphate, and component B is at least one of sulfonated kerosene and cyclohexane). This method is a method for treating phosphogypsum. The composition of phosphogypsum and natural gypsum is different (phosphogypsum is a secondary mineral obtained after artificial treatment, which contains almost no humic acid; while natural gypsum is a primary mineral mined directly from a mine, and the black impurities are mainly humic acid). This method cannot be used for the treatment of natural gypsum. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a gypsum and a preparation method and application thereof to improve the whiteness and purity of natural gypsum ore, which is suitable for preparing food additives in view of the deficiencies in the prior art.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing gypsum, comprising the following steps:

[0008] Acid treatment: natural gypsum particles are placed in dilute sulfuric acid, the concentration of which does not exceed 15%, and then oxalic acid is added and stirred for reaction;

[0009] Removal of inorganic minerals: The mixed solution obtained in the acid treatment step is allowed to stand to obtain a solution and a precipitate, the black impurities on the upper layer of the precipitate are removed, and the remaining precipitate and the solution are mixed evenly;

[0010] Extraction: adding an extractant to the mixed solution obtained in the inorganic mineral removal step, wherein the extractant includes a non-polar solvent, and standing the mixture to separate layers to obtain a lower white precipitate and an upper black filtrate;

[0011] Washing and drying: The white precipitate obtained in the extraction step is washed with clean water and dried.

[0012] In the patent "Method for deep purification of phosphogypsum by extraction method" (publication number CN 106044828 A), the phosphogypsum processed by this method comes from phosphate rock, and phosphogypsum contains almost no humic acid. However, the humic acid content in natural gypsum is high, and this method cannot remove the humic acid in natural gypsum. High concentration of sulfuric acid makes natural gypsum passivated, and part of the humic acid in natural gypsum cannot be separated from gypsum, resulting in a low whiteness of the treated natural gypsum.

[0013] The present invention adopts a low-concentration sulfuric acid treatment process, wherein the mass concentration of sulfuric acid does not exceed 15%. If the concentration exceeds 15%, the gypsum will be passivated, so that the humic acid in the natural gypsum ore cannot be separated. Therefore, the low-concentration sulfuric acid treatment process completely separates the humic acid in the natural gypsum from the gypsum, thereby improving the whiteness of the natural gypsum.

[0014] The oxalic acid in the acid treatment reacts with inorganic minerals such as iron oxide to form complex precipitates (black impurities are inorganic minerals complexed with oxalic acid). The density of the complex precipitate is lower than that of the gypsum precipitate, so the complex precipitate can be removed by density stratification, thereby improving the whiteness of natural gypsum.

[0015] The synergistic effect of oxalic acid and dilute sulfuric acid makes the separation of humic acid and gypsum better.

[0016] Humic acid is not dissolved by the non-polar extractant, but is dispersed in the extractant by physical action. Therefore, after standing, the humic acid is separated from the extractant, making the recycling rate of the extractant high.

[0017] In a preferred embodiment of the present invention, the volume ratio of the natural gypsum particles to the dilute sulfuric acid is 1:2-6. Too high a volume of dilute sulfuric acid will cause gypsum loss in the "washing and drying" step: although the solubility of gypsum in dilute sulfuric acid is very low, too high a volume of dilute sulfuric acid will increase the amount of dissolution and reduce the output of gypsum products. Too low a volume of dilute sulfuric acid will result in incomplete separation of humic acid and gypsum, reducing the purity and whiteness of the gypsum product.

[0018] In a preferred embodiment of the present invention, the mass ratio of the oxalic acid to the natural gypsum particles is 2:50 to 100. If the amount of oxalic acid is too high, oxalic acid will form calcium oxalate with gypsum, reducing the purity of the gypsum product. If the amount of oxalic acid is too low, inorganic minerals such as iron oxide will remain in the gypsum product, reducing the purity and whiteness of the gypsum product.

[0019] In a preferred embodiment of the present invention, the extractant is one of acetone, dichloromethane, n-hexane and tetrachloromethane.

[0020] The composite extractant in the patent "Method for deep purification of phosphogypsum by extraction method" (publication number CN 106044828 A) is used to extract phosphogypsum to achieve better results. For the extraction of natural gypsum, the extractant needs to be further adjusted. The use of composite extractants is more complicated than that of single extractants, which reduces the stability of the extraction process.

[0021] This patent selects a single non-polar extractant to form a stable extraction process, which makes the recycling rate of the extractant high.

[0022] In a preferred embodiment of the present invention, the volume ratio of the extractant to the mixed solution obtained in the inorganic mineral removal step is 2 to 6: 1. If the amount of the extractant is too high, the consumption of the extractant will increase. Even if the recovery rate of the extractant is high, the cost increase caused by the increased consumption of the extractant cannot be recovered. If the amount of the extractant is too low, the humic acid cannot be completely removed, thereby reducing the purity and whiteness of the gypsum product.

[0023] In a preferred embodiment of the present invention, after the black filtrate is allowed to stand, a clear extractant on the upper layer is obtained and retained for reuse.

[0024] Humic acid is physically dispersed in the extractant and separated from the extractant after standing. The separated humic acid is harmlessly treated by burning or comprehensively reused.

[0025] In a preferred embodiment of the present invention, the preparation method further comprises acid-treating the dried white precipitate again, removing inorganic minerals, extracting and washing, and drying.

[0026] In a preferred embodiment of the present invention, the specific preparation method of the natural gypsum particles comprises:

[0027] Crushing: crushing natural gypsum ore into particles of 0.1-8mm;

[0028] Color sorting: Select the fine particles with whiteness greater than 90% to obtain the remaining natural gypsum particles.

[0029] The remaining gray particles of 0-8 mm (waste from the traditional calcination process) are obtained by crushing and color sorting, and the gray particles are separated from the fine particles. The fine particles are collected and used to produce ultra-high purity fine gypsum. The 0-8 mm gray particles are the natural gypsum raw materials of this method. The process of the present invention can dissolve 4-8 mm large particles of natural gypsum.

[0030] Preferably, the stirring time in the acid treatment step is 1 to 2 hours and the temperature is room temperature.

[0031] Preferably, the drying temperature is 50-70° C. and the drying time is 0.5-1.5 hours.

[0032] Preferably, the dried white precipitate is subjected to acid treatment again, inorganic mineral removal, extraction, washing, and drying, which specifically include the following steps:

[0033] Place the dried white precipitate in a concentrated solution of dilute sulfuric acid (the concentration of dilute sulfuric acid does not exceed 10%, and the volume ratio of gray particles to dilute sulfuric acid is 1:2-6), stir, and react at room temperature for 1-2 hours. Take the extractant, add it to the reaction solution in the previous step, and stir and react at room temperature for 1 hour. The volume ratio of the extractant to the reaction solution is 1-3:1. Let it stand and separate to obtain a lower layer of white precipitate and an upper layer of filtrate. After the filtrate is allowed to stand, a clear extractant is obtained on the upper layer, which is retained for reuse. Wash the white precipitate with clean water and dry it at 60 degrees Celsius for 1 hour to obtain the final product, natural gypsum.

[0034] The invention also discloses gypsum prepared by the preparation method.

[0035] The invention also discloses an application of the gypsum in food additives.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The purity of the obtained natural gypsum product reaches more than 99%, and the whiteness reaches more than 94%, so that the natural gypsum product can be applied to the fields of food additives with high industrial added value, thereby improving the utilization rate of natural gypsum ore.

[0038] (2) The extraction agent reuse rate is over 95%, saving costs.

[0039] (3) The large particle (0-8mm) crushing method is adopted to further reduce the production cost (the larger the ore particles, the lower the crushing cost). The utilization rate of natural gypsum ore is greatly improved, and the utilization rate exceeds 80%, which solves the key problem that restricts the application of natural gypsum in the field and turns waste into treasure. The overall cost is low, especially getting rid of the traditional and costly high-temperature calcination.

[0040] In summary, this method improves the utilization rate of natural gypsum and broadens the application field of natural gypsum while saving production costs and maximizing economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a comparison chart of the whiteness of the products of Example 1 of the present invention and Comparative Example 1.

[0042] Figure 1 In the figure, the left side is the product of Example 1, and the right side is the product of Comparative Example 1. DETAILED DESCRIPTION

[0043] Example 1

[0044] The specific composition of the natural gypsum raw material (gray particles after separation of fine particles) described in the present method is as follows: calcium sulfate content 85%-88%, inorganic mineral content 3%-6%, humic acid content 5%-8%, and other 1%.

[0045] Crushing: Use a crusher to crush natural gypsum ore into particles of 0-8mm;

[0046] Color sorting: select the fine particles with whiteness greater than 90%, remove the fine particles, and obtain the remaining gray particles;

[0047] Acid treatment: place the gray particles in a concentrated solution of dilute sulfuric acid (concentration of dilute sulfuric acid is 10%, the volume ratio of gray particles to dilute sulfuric acid is 1:4), add oxalic acid (mass ratio of oxalic acid to gray particles is 2:75), stir, and react at room temperature for 1.5 hours.

[0048] Removal of inorganic minerals: Let stand to obtain a solution and a precipitate, remove the black impurities (oxalic acid complexed inorganic minerals) on the upper layer of the precipitate, and remix the above solution and precipitate.

[0049] Extraction: Take the extractant, add it to the reaction solution in the previous step, and stir at room temperature for 1 hour. The extractant is acetone. The volume ratio of the extractant to the reaction solution is 2:1. Let it stand for stratification to obtain a white precipitate at the lower layer and a black filtrate at the upper layer. After the black filtrate is left to stand, a clear extractant is obtained at the upper layer, which is retained for reuse. The reuse rate of the extract is 98%.

[0050] Washing and drying: Wash the white precipitate from the previous step with clean water and dry it at 60 degrees Celsius for 1 hour.

[0051] Acid treatment and re-extraction again: Place the dried white precipitate in a concentrated solution of dilute sulfuric acid (5% dilute sulfuric acid concentration, the volume ratio of gray particles to dilute sulfuric acid is 1:4), stir, and react at room temperature for 1.5 hours. Take the extractant, add it to the reaction solution in the previous step, and stir and react at room temperature for 1 hour. The volume ratio of the extractant to the reaction solution is 2:1. Let it stand and separate to obtain a lower white precipitate and an upper filtrate. After the filtrate is allowed to stand, a clear extractant is obtained on the upper layer, which is retained for reuse. Wash the white precipitate with clean water and dry it at 60 degrees Celsius for 1 hour to obtain the final product, natural gypsum. Its purity is 99% and its whiteness is 97%.

[0052] Example 2

[0053] Crushing: Use a crusher to crush natural gypsum ore into particles of 0-8mm;

[0054] Color sorting: select the fine particles with whiteness greater than 90%, remove the fine particles, and obtain the remaining gray particles;

[0055] Acid treatment: place the gray particles in a concentrated solution of dilute sulfuric acid (concentration of dilute sulfuric acid is 8%, volume ratio of gray particles to dilute sulfuric acid is 1:2), add oxalic acid (mass ratio of oxalic acid to gray particles is 2:50), stir, and react at room temperature for 1 hour.

[0056] Removal of inorganic minerals: Let stand to obtain a solution and a precipitate, remove the black impurities (oxalic acid complexed inorganic minerals) on the upper layer of the precipitate, and remix the above solution and precipitate.

[0057] Extraction: Take the extractant, add it to the reaction solution in the previous step, and stir at room temperature for 1 hour. The extractant is n-hexane. The volume ratio of the extractant to the reaction solution is 4:1. Let it stand for stratification to obtain a white precipitate at the lower layer and a black filtrate at the upper layer. After the black filtrate is left to stand, a clear extractant is obtained at the upper layer, which is retained for reuse. The reuse rate of the extract is 97%.

[0058] Washing and drying: Wash the white precipitate from the previous step with clean water and dry it at 60 degrees Celsius for 1 hour.

[0059] Acid treatment and re-extraction again: Place the dried white precipitate in a concentrated solution of dilute sulfuric acid (4% dilute sulfuric acid concentration, the volume ratio of gray particles to dilute sulfuric acid is 1:2), stir, and react at room temperature for 1 hour. Take the extractant, add it to the reaction solution in the previous step, and stir and react at room temperature for 1 hour. The volume ratio of the extractant to the reaction solution is 2:1. Let it stand and separate to obtain a lower white precipitate and an upper filtrate. After the filtrate is allowed to stand, a clear extractant is obtained on the upper layer, which is retained for reuse. Wash the white precipitate with clean water and dry it at 60 degrees Celsius for 1 hour to obtain the final product, natural gypsum. Its purity is 99% and its whiteness is 96%.

[0060] Example 3

[0061] Crushing: Use a crusher to crush natural gypsum ore into particles of 0-8mm;

[0062] Color sorting: select the fine particles with whiteness greater than 90%, remove the fine particles, and obtain the remaining gray particles;

[0063] Acid treatment: place the gray particles in a concentrated solution of dilute sulfuric acid (concentration of dilute sulfuric acid is 15%, the volume ratio of gray particles to dilute sulfuric acid is 1:6), add oxalic acid (the mass ratio of oxalic acid to gray particles is 2:100), stir, and react at room temperature for 2 hours.

[0064] Removal of inorganic minerals: Let stand to obtain a solution and a precipitate, remove the black impurities (oxalic acid complexed inorganic minerals) on the upper layer of the precipitate, and remix the above solution and precipitate.

[0065] Extraction: Take the extractant, add it to the reaction solution in the previous step, stir and react at room temperature for 1 hour. The extractant is tetrachloromethane. The volume ratio of the extractant to the reaction solution is 6:1. Let it stand and separate into layers to obtain a white precipitate at the lower layer and a black filtrate at the upper layer. After the black filtrate is left to stand, a clear extractant is obtained at the upper layer, which is retained and reused. The reuse rate of the extract is 96%.

[0066] Washing and drying: Wash the white precipitate from the previous step with clean water and dry it at 60 degrees Celsius for 1 hour.

[0067] Acid treatment and re-extraction again: Place the dried white precipitate in a concentrated solution of dilute sulfuric acid (4% dilute sulfuric acid concentration, the volume ratio of gray particles to dilute sulfuric acid is 1:6), stir, and react at room temperature for 1.5 hours. Take the extractant, add it to the reaction solution in the previous step, and stir and react at room temperature for 1 hour. The volume ratio of the extractant to the reaction solution is 2:1. Let it stand and separate to obtain a lower white precipitate and an upper filtrate. After the filtrate is allowed to stand, a clear extractant is obtained on the upper layer, which is retained for reuse. Wash the white precipitate with clean water and dry it at 60 degrees Celsius for 1 hour to obtain the final product, natural gypsum. Its purity is 99% and its whiteness is 96%.

[0068] Example 4

[0069] The difference between Example 4 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is dichloromethane. The reuse rate of the extract is 95%. The final product, natural gypsum, has a purity of 99% and a whiteness of 94%.

[0070] Example 5

[0071] The difference between Example 5 and Example 1 is that in the acid treatment step, the concentration of dilute sulfuric acid is 5%. The reuse rate of the extract is 96%. The final product, natural gypsum, has a purity of 99% and a whiteness of 95%.

[0072] Example 6

[0073] The difference between Example 6 and Example 1 is that in the acid treatment step, the mass ratio of oxalic acid to gray particles is 2:100. The reuse rate of the extract is 96%. The final product, natural gypsum, has a purity of 99% and a whiteness of 96%.

[0074] Example 7

[0075] The difference between Example 7 and Example 1 is that no acid treatment and re-extraction are performed. The reuse rate of the extract is 98%. The final product, natural gypsum, has a purity of 99% and a whiteness of 95%.

[0076] Comparative Example 1

[0077] The difference between Comparative Example 1 and Example 1 is that in the acid treatment step, the concentration of dilute sulfuric acid is 20%. The reuse rate of the extract is 94%. The final product, natural gypsum, has a purity of 97% and a whiteness of 92%.

[0078] Comparative Example 2

[0079] The difference between Comparative Example 2 and Example 1 is that in the acid treatment step, the concentration of dilute sulfuric acid is 40%. The reuse rate of the extract is 94%. The final product, natural gypsum, has a purity of 96% and a whiteness of 90%.

[0080] Comparative Example 3

[0081] The difference between Comparative Example 3 and Example 1 is that no oxalic acid is added in the acid treatment step. The reuse rate of the extract is 94%. The final product, natural gypsum, has a purity of 94% and a whiteness of 89%.

[0082] Comparative Example 4

[0083] The difference between Comparative Example 4 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is ethyl acetate. The reuse rate of the extract is 70%. The final product, natural gypsum, has a purity of 90% and a whiteness of 82%.

[0084] Comparative Example 5

[0085] The difference between Comparative Example 5 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is ethanol. The reuse rate of the extract is 50%. The final product, natural gypsum, has a purity of 90% and a whiteness of 78%.

[0086] Comparative Example 6

[0087] The difference between Comparative Example 6 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is a composite extractant of acetone and tetrachloromethane. The reuse rate of the extract is 90%. The final product, natural gypsum, has a purity of 97% and a whiteness of 92%.

[0088] Table 1 Recycling rate of extract, purity and whiteness of final product natural gypsum

[0089]

[0090]

[0091] As shown in Table 1, the reuse rate of the extracts in Examples 1-6 is above 95%, and the purity of the final product natural gypsum is 99%, and the whiteness is above 94%. The reuse rate of the extracts in Comparative Examples 1-6 is 50% to 94%, and the purity of the final product natural gypsum is 90% to 97%, and the whiteness is 78% to 92%.

[0092] The difference between Comparative Example 1 and Example 1 is that in the acid treatment step, the concentration of dilute sulfuric acid is 20%. The above three indicators all decrease. The scientific problem in the content of the invention is verified: the low-concentration sulfuric acid treatment process, in which the mass concentration of sulfuric acid does not exceed 15%, will passivate gypsum, making it impossible to separate the humic acid in the natural gypsum ore. Therefore, the low-concentration sulfuric acid treatment process completely separates the humic acid in the natural gypsum from the gypsum, thereby improving the whiteness of the natural gypsum.

[0093] The difference between Comparative Example 2 and Example 1 is that in the acid treatment step, the concentration of dilute sulfuric acid is 40%. The above three indicators all decrease. The scientific problem in the content of the invention is verified: the low-concentration sulfuric acid treatment process, in which the mass concentration of sulfuric acid does not exceed 15%, will passivate gypsum, making it impossible to separate the humic acid in the natural gypsum ore. Therefore, the low-concentration sulfuric acid treatment process completely separates the humic acid in the natural gypsum from the gypsum, thereby improving the whiteness of the natural gypsum.

[0094] The difference between Comparative Example 3 and Example 1 is that oxalic acid is not added in the acid treatment step. The above three indicators all decrease. The precipitate generated when oxalic acid is not added is a white precipitate such as calcium sulfate, and the separation effect of white precipitates such as calcium sulfate and natural gypsum ore with similar color is not good. The scientific problem in the content of the invention is verified: the oxalic acid in the acid treatment reacts with inorganic minerals such as iron oxide to generate a complex precipitate. The density of the complex precipitate is lower than that of the gypsum precipitate, so the complex precipitate can be removed by density stratification, thereby improving the whiteness of the natural gypsum. The synergistic effect of oxalic acid and dilute sulfuric acid makes the separation effect of humic acid and gypsum better, and can dissolve large particles of natural gypsum of 4-8mm.

[0095] The difference between Comparative Example 4 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is ethyl acetate, which is a polar solvent. After standing, the humic acid is not well separated from the ethyl acetate, so that the recycling rate of the extractant is low, so the above three indicators are all reduced. The scientific problem in the content of the invention is verified: the humic acid is not dissolved by the non-polar extractant, but is dispersed in the extractant by physical action. Therefore, after standing, the humic acid is separated from the extractant, so that the recycling rate of the extractant is high.

[0096] The difference between Comparative Example 5 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is ethanol. The above three indicators all decrease. The scientific problem in the content of the invention is verified: humic acid is not dissolved by the non-polar extractant, but is dispersed in the extractant by physical action. Therefore, after standing, the humic acid is separated from the extractant, so that the recycling rate of the extractant is high.

[0097] The difference between Comparative Example 6 and Example 1 is that in the extraction, acid treatment and re-extraction steps, the extractant is a composite extractant of acetone and tetrachloromethane. The above three indicators all decreased. The scientific problem in the content of the invention was verified: the method selects a non-polar single extractant, forms a stable extraction process, and makes the recycling rate of the extractant high.

[0098] like Figure 1 As shown, the whiteness of the natural gypsum of the final product of Example 1 is 97%, and the whiteness of the natural gypsum of the final product of Comparative Example 1 is 92%.

Claims

1. A method for preparing gypsum, characterized in that The following steps are involved: Acid treatment: natural gypsum particles are placed in dilute sulfuric acid, the concentration of which does not exceed 15%, and then oxalic acid is added and stirred for reaction; Removal of inorganic minerals: The mixed solution obtained in the acid treatment step is allowed to stand to obtain a solution and a precipitate, the black impurities on the upper layer of the precipitate are removed, and the remaining precipitate and the solution are mixed evenly; Extraction: adding an extractant to the mixed solution obtained in the inorganic mineral removal step, wherein the extractant includes a non-polar solvent, and standing the mixture to separate layers to obtain a lower white precipitate and an upper black filtrate; Washing and drying: washing the white precipitate obtained in the extraction step with clean water and drying to obtain gypsum; The extractant is one of acetone, dichloromethane, n-hexane and tetrachloromethane; The volume ratio of the extractant to the mixed solution obtained in the inorganic mineral removal step is 2-6:1; The volume ratio of the natural gypsum particles to the dilute sulfuric acid is 1:2-6; The mass ratio of the oxalic acid to the natural gypsum particles is 2:50-100; The specific composition of natural gypsum particles is: calcium sulfate content 85-88%, inorganic mineral content 3-6%, humic acid content 5-8%, and other 1%.

2. The method for preparing gypsum according to claim 1, characterized in that: After the black filtrate is allowed to stand, a clear extractant on the upper layer is obtained and retained for reuse.

3. The method for preparing gypsum according to any one of claims 1 to 2, characterized in that: The preparation method further comprises acid treatment of the dried white precipitate, removal of inorganic minerals, extraction, washing and drying.

4. The method for preparing gypsum according to any one of claims 1 to 2, characterized in that: The specific preparation method of the natural gypsum particles comprises: Crushing: crushing natural gypsum ore into particles of 0.1-8mm; Color sorting: Select the fine particles with whiteness greater than 90% to obtain the remaining natural gypsum particles.

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