Method for preparing high-whiteness superfine anhydrous gypsum by purifying industrial byproduct gypsum

Abstract

The invention discloses a method for preparing high-whiteness superfine anhydrous gypsum by purifying industrial by-product gypsum, which comprises the following steps: by taking the industrial by-product gypsum as a raw material, firstly, carrying out deep purification pretreatment to obtain gypsum of which the whiteness is greater than or equal to 55% and the content of CaSO4. 2H2O is greater than or equal to 95%; and sequentially carrying out dilute acid dissolution, organic matter extraction and crystal transformation whitening treatment on the pretreated gypsum to obtain the high-whiteness superfine anhydrous gypsum with the whiteness of more than or equal to 90%. The obtained high-whiteness superfine anhydrous gypsum is high in whiteness, finer in fineness and controllable in crystal form and crystal appearance, and compared with anhydrous gypsum obtained through a calcination method, the high-whiteness superfine anhydrous gypsum is low in energy consumption, small in carbon emission, high in benefit and suitable for wide popularization and implementation.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing anhydrite from industrial by-product gypsum, in particular, a method for preparing high-white ultra-fine anhydrite from industrial by-product gypsum. BACKGROUND

[0002] Industrial by-product gypsum, including phosphogypsum, fluorogypsum, desulfurization gypsum, etc., is a large amount of industrial solid waste discharged in the industrial production process. For example, in the wet-process phosphoric acid industry, about 4.5-5 tons of industrial by-product gypsum are generated for every ton of phosphoric acid produced. The main component of industrial by-product gypsum is calcium sulfate dihydrate CaSO4·2H2O. Industrial by-product gypsum generally contains a large amount of impurities, such as un-decomposed phosphate rock, free phosphoric acid, fluorides, organic matter, and trace amounts of heavy metals, etc. These impurities cause the industrial by-product gypsum to be yellow or black in color, and unstable in performance, greatly limiting its resource utilization. At present, the global stockpile of industrial by-product gypsum is huge, not only occupying land resources, but also posing a risk of environmental pollution. Therefore, efficient and high-value resource utilization of industrial by-product gypsum is an urgent problem to be solved in the industry.

[0003] In the prior art, the purification treatment methods of industrial by-product gypsum mainly include water washing, flotation, lime neutralization, calcination, etc. The water washing method can remove part of the soluble impurities, but the water consumption is large, and the removal effect on the wrapped impurities and organic matter is limited, and the whiteness of the obtained product is generally low (usually less than 50), which is difficult to meet the demand of high-end applications. The calcination method is a common method for preparing building gypsum (β-hemihydrate gypsum), but the traditional calcination process has high energy consumption, and the impurities may react at high temperatures, resulting in deterioration of product performance, darkening of color, and unstable setting time.

[0004] Anhydrite (type II) is a kind of cementing material with excellent performance, which has the advantages of high strength, good water resistance, small shrinkage, etc., and can be used as high-grade building material filler, self-leveling mortar, adhesive, papermaking filler, etc. However, the preparation of anhydrite from industrial by-product gypsum usually requires high-temperature calcination (>600℃), which has huge energy consumption, and it is difficult to solve the problem of low whiteness caused by impurities. Chemical dehydration, such as using electrolyte solution for crystal transformation, can reduce the reaction temperature, but the current dehydration system has insufficient impurity removal capacity, and the whiteness and purity of the product still need to be improved.

[0005] Therefore, it is of great significance to develop a new method that has low energy consumption, short process, good impurity removal effect, and can significantly improve the whiteness and fineness of the product of industrial by-product gypsum, for promoting the high-value utilization of industrial by-product gypsum.

[0006] The present application relates to a method for preparing anhydrite from industrial by-product gypsum, in particular, a method for preparing high-white ultra-fine anhydrite from industrial by-product gypsum. The present application has low energy consumption and low carbon emission, and the crystal type and morphology of the prepared anhydrite are controllable, with high whiteness and finer fineness, which is suitable for wide implementation and promotion.

[0007] The application discloses a method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, which comprises the following steps: S1, taking industrial by-product gypsum as raw material; S2, performing purification and pretreatment on the industrial by-product gypsum to obtain pretreated gypsum with a calcium sulfate dihydrate content of greater than or equal to 95% and a whiteness of greater than or equal to 55%; S3, immersing the pretreated gypsum in a dilute mixed acid system of sulfuric acid and phosphoric acid to perform dissolution, then adding a mixture of phosphoric acid tributyl ester and EDTA-2Na to perform organic extraction, and then adding a mixture of ammonium persulfate and NaCl to perform crystal transformation and whitening, so as to obtain anhydrous gypsum slurry; and S4, performing post-treatment on the anhydrous gypsum slurry to obtain high-white superfine anhydrous gypsum with a whiteness of greater than or equal to 90%.

[0008] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum comprises the following steps: S1, taking industrial by-product gypsum as raw material; S2, performing purification and pretreatment on the industrial by-product gypsum to obtain pretreated gypsum with a calcium sulfate dihydrate content of greater than or equal to 95% and a whiteness of greater than or equal to 55%; S3, immersing the pretreated gypsum in a dilute mixed acid system of sulfuric acid and phosphoric acid to perform dissolution, then adding a mixture of phosphoric acid tributyl ester and EDTA-2Na to perform organic extraction, and then adding a mixture of ammonium persulfate and NaCl to perform crystal transformation and whitening, so as to obtain anhydrous gypsum slurry; and S4, performing post-treatment on the anhydrous gypsum slurry to obtain high-white superfine anhydrous gypsum with a whiteness of greater than or equal to 90%.

[0009] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum comprises the following steps: S1, taking industrial by-product gypsum as raw material; S2, performing purification and pretreatment on the industrial by-product gypsum to obtain pretreated gypsum with a calcium sulfate dihydrate content of greater than or equal to 95% and a whiteness of greater than or equal to 55%; S3, immersing the pretreated gypsum in a dilute mixed acid system of sulfuric acid and phosphoric acid to perform dissolution, then adding a mixture of phosphoric acid tributyl ester and EDTA-2Na to perform organic extraction, and then adding a mixture of ammonium persulfate and NaCl to perform crystal transformation and whitening, so as to obtain anhydrous gypsum slurry; and S4, performing post-treatment on the anhydrous gypsum slurry to obtain high-white superfine anhydrous gypsum with a whiteness of greater than or equal to 90%. S1. Taking industrial by-product gypsum as raw material; S2. Performing purification and pretreatment on the industrial by-product gypsum to obtain pretreated gypsum with a calcium sulfate dihydrate content of greater than or equal to 95% and a whiteness of greater than or equal to 55%; S3. Immersing the pretreated gypsum in a dilute mixed acid system of sulfuric acid and phosphoric acid to perform dissolution, then adding a mixture of phosphoric acid tributyl ester and EDTA-2Na to perform organic extraction, and then adding a mixture of ammonium persulfate and NaCl to perform crystal transformation and whitening, so as to obtain anhydrous gypsum slurry; In this step, the pretreated gypsum is added into the dilute mixed acid system, at this time, the dihydrate gypsum only undergoes the dissolution step and is not transformed into anhydrous gypsum, at this time, the organic and inorganic impurities wrapped in the dihydrate gypsum crystals are fully released, at this time, the addition of EDTA-2Na can chelate calcium ions to further increase the dissolution of dihydrate gypsum, at the same time, the addition of phosphoric acid tributyl ester extractant can extract the organic matters released in the dihydrate gypsum dissolution process to the surface of the crystal transformation solution, so as to achieve the purpose of organic matter aggregation. At this time, further addition of ammonium persulfate and NaCl can supplement sulfate ions by using ammonium persulfate to promote the efficient transformation of dihydrate gypsum into anhydrous gypsum, at the same time, the organic matters extracted to the surface of the solution can be oxidized to achieve the purpose of high whiteness; secondly, the mixed acid system creates favorable conditions for the reaction of ammonium persulfate and sodium chloride, under the catalysis of heating and the metal Fe 2+ / Fe 3+ ions released in the phosphogypsum, the chlorine ions ionized from the sodium chloride form chlorine gas, the chlorine gas can react with most other developing metals to generate chlorides, at the same time, the chlorine gas can react with water to generate hypochlorous acid HClO, so as to achieve the purpose of further whitening.

[0010] S4. Performing post-treatment on the anhydrous gypsum slurry to obtain high-white superfine anhydrous gypsum with a whiteness of greater than or equal to 90%.

[0011] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the conventional pretreatment of S2 comprises phosphorus-fluorine separation, organic matter separation, magnetic separation of iron, multi-stage impurity removal and ultrasonic whitening.

[0012] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the mass concentration of sulfuric acid in the mixed acid system is 25-30%, and the mass concentration of phosphoric acid is 3-5%.

[0013] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the solid-liquid ratio of the pretreated industrial by-product gypsum to the mixed acid system in S3 is 1:3-5.

[0014] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the dissolution time in S3 is 0.5-1.5h; the extraction time is 20-40min; and the crystal transformation and whitening time is 0.5-2h.

[0015] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the addition amount of ammonium persulfate is 5-10% of the mass of the mixed acid system, the addition amount of tributyl phosphate is 1-5% of the mass of the mixed acid system, the addition amount of EDTA-2Na is 0.1-0.5% of the mass of the mixed acid system, and the addition amount of NaCl is 5-15% of the mass of the mixed acid system.

[0016] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the post-treatment in S4 is filtering separation of the anhydrous gypsum slurry, then washing the filter cake with hot water to neutral, drying at 100-120℃ to constant weight, and finally modifying, grinding and grading.

[0017] Preferably, the method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the washing liquid generated by the washing is neutralized by calcium hydroxide to recover calcium phosphofluoridate.

[0018] 1、The method for preparing high-white superfine anhydrous gypsum from industrial by-product gypsum, the pretreatment of the industrial by-product gypsum removes the soluble phosphorus-fluorine and organic matter and other impurities wrapped on the surface of the industrial by-product gypsum particles and doped in the crystal lattice, so that a high-purity and high-whiteness industrial by-product gypsum raw material is obtained, which is beneficial to the subsequent preparation of high-white superfine anhydrous gypsum.

[0019] 2. This invention first dissolves pretreated gypsum in a dilute mixed acid system, extracts it in its pre-crystallization state, and then performs crystallization and impurity removal and whitening treatments, resulting in an anhydrous gypsum with a whiteness of ≥90%, far exceeding the approximately 60% whiteness of anhydrous gypsum made from industrial by-product gypsum currently on the market. Simultaneously, the use of a composite regulator not only enhances the whitening effect but also achieves crystal form control, yielding granular anhydrous gypsum with a finer particle size, reaching up to 2500 mesh or finer, which is more conducive to the application of anhydrous gypsum made from industrial by-product gypsum in fields such as papermaking.

[0020] 3. The industrial by-product gypsum of the present invention is recrystallized in a low-temperature environment below 100°C to obtain anhydrous gypsum, which has low energy consumption.

[0021] 4. The process flow of this invention is short and easy to operate, which is conducive to industrial promotion and implementation; moreover, the solution system can be recycled, which is in line with the concept of green circular economy development. Attached Figure Description

[0022] Appendix Figure 1 SEM images and actual whiteness photos of the pretreated industrial by-product gypsum with super-high purity obtained after purification pretreatment according to the present invention; whiteness 58%.

[0023] Appendix Figure 2 The image shows the whiteness of the high-whiteness ultrafine anhydrous gypsum prepared in Example 1 of this invention; whiteness 90%.

[0024] Appendix Figure 3 The images show SEM images and actual whiteness photos of the high-whiteness ultrafine anhydrous gypsum prepared in Example 2 of this invention; whiteness 95%.

[0025] Appendix Figure 4 The images show the SEM image and actual whiteness photo of the high-whiteness ultrafine anhydrous gypsum prepared in Example 3 of this invention; whiteness 92%.

[0026] Appendix Figure 5 The images show the SEM image and actual whiteness photo of the high-whiteness ultrafine anhydrous gypsum prepared in Example 4 of this invention; whiteness 90%.

[0027] from Figures 1-5 The comparison shows that the high-whiteness ultrafine anhydrous gypsum produced by the process of the present invention is whiter and has a finer particle size. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0029] Embodiments of the present invention The purification pretreatment method in this embodiment of the invention is as follows: 1. At room temperature, feed the raw phosphogypsum residue into a slurry at a solid-liquid ratio of 1:2 and stir. Add a polycarboxylate dispersant at a ratio of 150-200g / t to separate phosphorus, fluorine and organic matter from the surface of the phosphogypsum. 2. Magnetic levitation separation is performed with a magnetic field strength of 0.8-1.0T to remove iron and fine impurities such as floatable organic matter; 3. The slurry after removing organic matter and iron is passed through 80-mesh, 100-mesh and 150-mesh screens to remove metal oxides such as silicon, aluminum and magnesium and un-acidified phosphate rock in stages, and to remove impurities through multi-stage filtration. 4. Use ultrasound at a frequency of 20-40KHZ, add conventional decolorizing agent at a dosage of 50-100g / T, and perform ultrasonic decolorization and whitening for 10-20 minutes to remove the fine chromosomes removed by ultrasound. 5. Remove soluble impurities by pressure filtration and washing, adjust the pH value of the filtered gypsum to the range of 6-9, and control the water content between 10-20% to obtain high-purity, high-whiteness phosphogypsum with a calcium sulfate dihydrate content ≥95%. 6. Extract and purify the soluble phosphorus and fluoride in the washing solution to obtain high-grade calcium phosphofluoride ≥35%, and achieve water treatment and recycling during the phosphorus and fluoride extraction process. Example 1

[0030] The method for purifying industrial by-product gypsum to prepare high-whiteness, ultrafine anhydrous gypsum comprises the following steps: S1. Take industrial by-product phosphogypsum as raw material; S2. Purify and pretreat the phosphogypsum raw material to obtain pretreated gypsum with a super-purity of ≥95% calcium sulfate dihydrate and ≥55% whiteness. S3. The pretreated phosphogypsum was immersed in a mixed acid system of sulfuric acid and phosphoric acid for 1 hour at a solid-liquid ratio of 1 kg: 4 L. The mass concentration of sulfuric acid in the mixed acid system was 25% and the mass concentration of phosphoric acid was 5%. Then, a mixture of tributyl phosphate and EDTA-2Na was added for organic extraction. After extraction for 35 min, a mixture of ammonium persulfate and NaCl was added and reacted for 1.5 h. The amount of ammonium persulfate added was 8% of the mass of the mixed acid system, the amount of tributyl phosphate added was 3% of the mass of the mixed acid system, the amount of EDTA-2Na added was 0.3% of the mass of the mixed acid system, and the amount of NaCl added was 10% of the mass of the mixed acid system. The mixture was stirred at 94 °C for 3 h to obtain anhydrous gypsum slurry. S4. Filter and separate the anhydrous gypsum slurry, then wash the filter cake with hot water until neutral, dry it at 110℃ to constant weight, and finally crush and classify it to obtain high whiteness ultrafine anhydrous gypsum with a whiteness ≥95%. Example 2

[0031] The method for purifying industrial by-product gypsum to prepare high-whiteness, ultrafine anhydrous gypsum comprises the following steps: S1. Take industrial by-product phosphogypsum as raw material; S2. Purify and pretreat the phosphogypsum raw material to obtain pretreated gypsum with a super-purity of ≥95% calcium sulfate dihydrate and ≥55% whiteness. S3. The pretreated phosphogypsum was immersed in a mixed acid system of sulfuric acid and phosphoric acid for 0.5 h at a solid-liquid ratio of 1 kg: 3 L. The mass concentration of sulfuric acid in the mixed acid system was 26% and the mass concentration of phosphoric acid was 5%. Then, a mixture of tributyl phosphate and EDTA-2Na was added for organic extraction. After extraction for 20 min, a mixture of ammonium persulfate and NaCl was added and reacted for 0.5 h. The amount of ammonium persulfate added was 5% of the mass of the mixed acid system, the amount of tributyl phosphate added was 1% of the mass of the mixed acid system, the amount of EDTA-2Na added was 0.1% of the mass of the mixed acid system, and the amount of NaCl added was 5% of the mass of the mixed acid system. The mixture was stirred at 90 °C for 4 h to obtain anhydrous gypsum slurry. S4. Filter and separate the anhydrous gypsum slurry, then wash the filter cake with hot water until it is neutral, dry it at 100℃ to constant weight, and finally crush and classify it to obtain high whiteness ultrafine anhydrous gypsum with a whiteness ≥90%. Example

[0032] The method for purifying industrial by-product gypsum to prepare high-whiteness, ultrafine anhydrous gypsum comprises the following steps: S1. Take industrial by-product phosphogypsum as raw material; S2. Purify and pretreat the phosphogypsum raw material to obtain pretreated gypsum with a super-purity of ≥95% calcium sulfate dihydrate and ≥55% whiteness. S3. The pretreated phosphogypsum was immersed in a mixed acid system of sulfuric acid and phosphoric acid for 1.5 hours at a solid-liquid ratio of 1 kg: 5 L. The mass concentration of sulfuric acid in the mixed acid system was 29% and the mass concentration of phosphoric acid was 3%. Then, a mixture of tributyl phosphate and EDTA-2Na was added for organic extraction. After extraction for 40 minutes, a mixture of ammonium persulfate and NaCl was added and reacted for 2 hours. The amount of ammonium persulfate added was 10% of the mass of the mixed acid system, the amount of tributyl phosphate added was 5% of the mass of the mixed acid system, the amount of EDTA-2Na added was 0.5% of the mass of the mixed acid system, and the amount of NaCl added was 15% of the mass of the mixed acid system. The mixture was stirred at 98℃ for 1 hour to obtain anhydrous gypsum slurry. S4. Filter and separate the anhydrous gypsum slurry, then wash the filter cake with hot water until neutral, dry it at 120℃ to constant weight, and finally crush and classify it to obtain high whiteness ultrafine anhydrous gypsum with a whiteness ≥90%. Example 3

[0033] The method for purifying industrial by-product gypsum to prepare high-whiteness, ultrafine anhydrous gypsum comprises the following steps: S1. Take industrial by-product phosphogypsum as raw material; S2. Purify and pretreat the phosphogypsum raw material to obtain pretreated phosphogypsum with a calcium sulfate dihydrate content ≥95% and a whiteness of ≥55, which is of extra-high purity. S3. The pretreated phosphogypsum was immersed in a mixed acid system of sulfuric acid and phosphoric acid for 1.2 hours at a solid-liquid ratio of 1 kg: 5 L. The mass concentration of sulfuric acid in the mixed acid system was 30% and the mass concentration of phosphoric acid was 3%. Then, a mixture of tributyl phosphate and EDTA-2Na was added for organic extraction. After extraction for 26 minutes, a mixture of ammonium persulfate and NaCl was added and reacted for 1 hour. The amount of ammonium persulfate added was 9% of the mass of the mixed acid system, the amount of tributyl phosphate added was 2% of the mass of the mixed acid system, the amount of EDTA-2Na added was 0.4% of the mass of the mixed acid system, and the amount of NaCl added was 8% of the mass of the mixed acid system. The mixture was stirred at 94℃ for 2 hours to obtain anhydrous gypsum slurry. S4. Filter and separate the anhydrous gypsum slurry, then wash the filter cake with hot water until it is neutral, dry it at 110℃ to constant weight, and finally crush and classify it to obtain high whiteness ultrafine anhydrous gypsum with whiteness ≥90%. The washing liquid generated by S5 and S4 is neutralized with calcium hydroxide to obtain calcium sulfate and calcium phosphate precipitates, and calcium is recovered.

[0034] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for purifying industrial by-product gypsum to prepare high-whiteness, ultrafine anhydrous gypsum, characterized in that: It uses industrial by-product gypsum as raw material. First, it undergoes deep purification pretreatment to obtain gypsum with a whiteness ≥55% and a CaSO4·2H2O content ≥95%. Then, the pretreated gypsum is subjected to dilute acid dissolution, organic matter extraction and crystallization whitening treatment in sequence to obtain high whiteness ultrafine anhydrous gypsum with a whiteness ≥90%.

2. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 1, characterized in that: The industrial by-product gypsum includes one or more of phosphogypsum, desulfurized gypsum, titanium gypsum, or salt gypsum.

3. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 1, characterized in that, The method includes the following steps: S1. Obtain industrial by-product gypsum raw materials; S2. Purify and pretreat industrial by-product gypsum raw materials to obtain pretreated gypsum with a super-purity grade of calcium sulfate dihydrate content ≥95% and whiteness ≥55%. S3. The pretreated gypsum is immersed in a dilute mixed acid system of sulfuric acid and phosphoric acid for dissolution. After dissolution, a mixture of tributyl phosphate and EDTA-2Na is added for organic extraction. After extraction, a mixture of ammonium persulfate and NaCl is added for crystallization and whitening to obtain anhydrous gypsum slurry. S4. Post-process the anhydrous gypsum slurry to obtain high-whiteness ultrafine anhydrous gypsum with a whiteness ≥90%.

4. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 3, characterized in that: The purification and pretreatment described in S2 includes phosphorus and fluorine separation, organic matter separation, magnetic separation for iron removal, multi-stage impurity removal, and ultrasonic whitening of industrial by-product gypsum.

5. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 3, characterized in that: The mass concentration of sulfuric acid in the mixed acid system is 25-30%, and the mass concentration of phosphoric acid is 3-5%.

6. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 3, characterized in that: The solid-liquid ratio of the pretreated industrial by-product gypsum and the mixed acid system described in S3 is 1:3-5.

7. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 3, characterized in that: The dissolution time in S3 is 0.5-1.5 h; the extraction time is 20-40 min; and the crystallization and whitening time is 0.5-2 h.

8. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 3, characterized in that: The amount of ammonium persulfate added is 5-10% of the mass of the mixed acid system, tributyl phosphate is 1-5% of the mass of the mixed acid system, EDTA-2Na is 0.1-0.5% of the mass of the mixed acid system, and NaCl is 5-15% of the mass of the mixed acid system.

9. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 3, characterized in that: The post-processing described in S4 involves filtering and separating the anhydrous gypsum slurry, then washing the filter cake with hot water until it is neutral, drying it at 100-120℃ to constant weight, and finally modifying, grinding, and classifying it.

10. The method for purifying industrial by-product gypsum to prepare high-whiteness ultrafine anhydrous gypsum according to claim 9, characterized in that: The washing liquid generated during the washing process is neutralized with calcium hydroxide to recover calcium fluoride.

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