A method for preparing accordion-like micrometer anhydrous gypsum

Abstract

The present application relates to the technical field of phosphogypsum treatment, in particular to a preparation method of accordion-shaped micrometer anhydrous gypsum. The preparation method of the accordion-shaped micrometer anhydrous gypsum comprises the following steps: after phosphogypsum is uniformly mixed in a sulfuric acid solution, a crystal transformation additive is added for stirring reaction, and then the obtained product is washed to neutral by suction filtration and dried to obtain the accordion-shaped micrometer anhydrous gypsum; the crystal transformation additive is a polymeric potassium thiocyanate salt or a polymeric sodium thiocyanate salt. The method provided by the present application can be realized only by adding a crystal transformation additive and a low-concentration acid solution without a complex solvent system, thereby saving cost and realizing high-value utilization of phosphogypsum.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum treatment technology, and in particular to a method for preparing accordion-shaped micron-sized anhydrous gypsum. Background Technology

[0002] Phosphogypsum exists in two forms: dihydrate gypsum (CaSO4·2H2O) and hemihydrate gypsum (CaSO4·1 / 2H2O), with the latter being more prevalent. Currently, the world's annual wet-process phosphoric acid production is approximately 270 million tons (based on P2O5), with about 150 million tons of phosphogypsum as a byproduct, representing a utilization rate of only 4.3%–4.6%. Natural stockpiling of phosphogypsum is the primary disposal method, which not only requires substantial investment and land use but also leads to continuous pollution of the atmosphere, groundwater, and soil due to wind and rain erosion over long periods. Therefore, effectively treating phosphogypsum to avoid pollution has become a pressing issue for achieving green, sustainable, and circular development in the phosphate fertilizer chemical industry. At present, using phosphogypsum to produce sulfuric acid and co-produce cement is an effective way to comprehensively utilize phosphogypsum; however, this method requires significant investment, is energy-intensive, causes substantial pollution, and results in unstable product quality. Furthermore, several technological bottlenecks hinder its widespread adoption. Applying phosphogypsum to building materials, soil conditioners, and road construction still presents challenges such as secondary pollution and low added value. Therefore, it is necessary to develop high-value-added products to achieve the sustainable development of the wet-process phosphoric acid industry while reducing environmental pollution.

[0003] The morphology control technology for phosphogypsum transcrystalline products is a technique for transforming industrial byproduct phosphogypsum into high-value-added products. Although it offers both environmental and economic benefits, it still has some drawbacks in existing technologies. For example, current processes for transcrystallineing anhydrous gypsum with special morphologies are complex and involve challenges such as complex solvent systems. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing accordion-shaped micron-sized anhydrous gypsum. This method achieves control over the preparation of a special accordion-shaped anhydrous gypsum under low acid and low additive concentration conditions.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing accordion-shaped micron-sized anhydrous gypsum, comprising the following steps: After mixing phosphogypsum with sulfuric acid solution, a crystallization additive was added and stirred to react. The mixture was then filtered, washed until neutral, and dried to obtain accordion-shaped micron-sized anhydrous gypsum. The crystallization additive is a poly(potassium) thiocyanate or a poly(sodium) thiocyanate.

[0006] The second technical solution of the present invention is an accordion-shaped micron-sized anhydrous gypsum prepared by the above-mentioned preparation method.

[0007] The third technical solution of this invention is the application of the above-mentioned accordion-shaped micron-sized anhydrous gypsum in the preparation of polymer fillers, environmentally friendly adsorbent materials, or precision building materials.

[0008] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves the preparation of micron-sized accordion-shaped anhydrous gypsum by controlling the sulfuric acid concentration and the stirring reaction time.

[0009] This invention achieves morphology control while phosphogypsum undergoes crystal transformation by adding additives to a mixture of sulfuric acid and phosphogypsum.

[0010] The method provided by this invention does not require high-temperature calcination and can be achieved under low acid and low additive concentration conditions, saving costs and realizing the high-value utilization of phosphogypsum. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 The XRD patterns are of the transcrystallization products prepared in sulfuric acid solutions of different concentrations in Example 1.

[0013] Figure 2 The images show SEM images of the crystallization products prepared in sulfuric acid solutions of different concentrations in Example 1; where A is a 2wt% sulfuric acid solution, B is a 5wt% sulfuric acid solution, C is an 8wt% sulfuric acid solution, D is a 10wt% sulfuric acid solution, E is a 12wt% sulfuric acid solution, and F is a 15wt% sulfuric acid solution.

[0014] Figure 3 The images show SEM images of the crystal-transforming products prepared under different crystal-transforming additive conditions in Example 2; wherein, A and B are poly(potassium) thiocyanate salts, and C and D are poly(sodium) thiocyanate salts.

[0015] Figure 4 The images show SEM images of the crystal-transformed products prepared under different crystal-transformation time conditions in Example 3; wherein, the crystal-transformation time for A and B is 6 hours, and the crystal-transformation time for C and D is 4 hours.

[0016] Figure 5 The images show SEM images of untreated phosphogypsum used in the examples and the crystallization product prepared under conventional additive conditions in Comparative Example 1; where A is untreated phosphogypsum and B is the crystallization product prepared in Comparative Example 1. Detailed Implementation

[0017] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0018] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0019] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0020] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0021] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0022] The first aspect of this invention provides a method for preparing accordion-shaped micron-sized anhydrous gypsum, comprising the following steps: After mixing phosphogypsum with sulfuric acid solution, a crystallization additive was added and stirred to react. The mixture was then filtered, washed until neutral, and dried to obtain accordion-shaped micron-sized anhydrous gypsum. The crystallization additive is a poly(potassium) thiocyanate or a poly(sodium) thiocyanate.

[0023] In a preferred embodiment of the present invention, the concentration of the sulfuric acid solution is 2wt% to 15wt%. The solvent for the sulfuric acid solution is water.

[0024] As the concentration of sulfuric acid solution increases, the accordion morphology becomes more pronounced and the particle size becomes smaller. When the amount of additive is 0.5 wt%, the concentration of sulfuric acid solution is 10 wt%, and the crystallization time (i.e., stirring reaction time) is 6 h, dihydrate gypsum is directly crystallized into anhydrous gypsum, and has a distinct accordion morphology.

[0025] In a preferred embodiment of the present invention, the solid-liquid ratio of the phosphogypsum to the sulfuric acid solution is 1 g: (5~8) mL.

[0026] In a preferred embodiment of the present invention, the amount of the crystallization additive added is 0.5% of the mass of the phosphogypsum.

[0027] In a preferred embodiment of the present invention, the temperature of the stirring reaction is 100°C and the stirring reaction time is 4 to 6 hours.

[0028] The present invention does not impose any particular limitation on the stirring speed of the reaction; a stirring speed commonly used by those skilled in the art, such as 500 r / min, can be used.

[0029] In a preferred embodiment of the present invention, the drying temperature is 60°C and the drying time is 12 hours.

[0030] In this invention, the transformation of dihydrate gypsum into anhydrous gypsum can be achieved even with lower crystallization additives and lower acid concentrations. This is because the additives contain polymeric thiocyanate ions with strong chelating properties, which accelerate the dissolution of dihydrate gypsum and the removal of water of crystallization at low acid concentrations, while simultaneously controlling particle size and morphology. The changes in particle size and morphology become more pronounced with an extended reaction time of 6 hours. Considering time constraints, the reaction time is controlled to 6 hours. Therefore, this invention controls the reaction time to within 6 hours.

[0031] A second aspect of the present invention provides an accordion-shaped micron-sized anhydrous gypsum prepared by the above-described preparation method.

[0032] The third aspect of this invention provides the application of the above-mentioned accordion-shaped micron-sized anhydrous gypsum in the preparation of polymer fillers, environmentally friendly adsorbent materials, or building materials.

[0033] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0034] The phosphogypsum used in this embodiment of the invention comes from a chemical plant in Yunnan.

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1 10 g of phosphogypsum was added to 75 mL of sulfuric acid solution with a concentration of 2–15 wt% (the sulfuric acid solution concentrations were 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, and 15 wt%, respectively), and stirred until homogeneous. Poly(potassium thiocyanate) was then added (the amount of poly(potassium thiocyanate) was 0.5% of the phosphogypsum mass). The mixture was stirred at 100 °C for 6 h, filtered, washed until neutral, and then dried at 60 °C for 12 h to obtain the transcrystalline product. The crystal structure of the transcrystalline product was characterized using X-ray scanning diffraction (XRD), the morphology was analyzed using scanning electron microscopy (SEM), and the particle size was analyzed using a laser particle size analyzer.

[0037] Example 2 10g of phosphogypsum was added to 75mL of 10wt% sulfuric acid solution and stirred until homogeneous. Potassium thiocyanate or sodium thiocyanate was added (the amount of phosphogypsum was 0.5wt% of the phosphogypsum mass). The mixture was stirred at 100℃ for 6h, filtered and washed until neutral, and then dried at 60℃ for 12h. The crystal structure was analyzed by XRD, the morphology was analyzed by SEM, and the particle size was analyzed by laser particle size analyzer.

[0038] Example 3 10g of phosphogypsum was added to 75mL of 12wt% sulfuric acid solution and stirred until homogeneous. Polysodium thiocyanate (0.5wt% of the phosphogypsum mass) was then added. The mixture was stirred at 100℃ for 4h and 6h, filtered and washed until neutral, and then dried at 60℃ for 12h. The crystal structure was analyzed by XRD, the morphology was analyzed by SEM, and the particle size was analyzed by laser particle size analyzer.

[0039] Comparative Example 1 10 g of phosphogypsum was added to 75 mL of a 15 wt% sulfuric acid solution and stirred until homogeneous. A crystallization additive, a mixture of polyaluminum sulfate and sodium ethylenediaminetetraacetate (EDTA-2Na) in a 1:1 mass ratio, was then added at 0.5% of the phosphogypsum mass. The mixture was stirred at 100 °C for 6 h, filtered, washed until neutral, and then dried at 60 °C for 12 h to obtain the crystallized product. The morphology and structure were analyzed using SEM, and the results are as follows: Figure 5 As shown.

[0040] The particle size variation of the transcrystalline product in Example 1 is shown in Table 1.

[0041] As shown in Table 1, with increasing sulfuric acid concentration, the particle size of the phosphogypsum transcrystalline product exhibits a phenomenon of first decreasing, then increasing, and then decreasing again. This is because increasing sulfuric acid concentration facilitates the complete dissolution and recrystallization of phosphogypsum. The adsorption layer of polymeric thiocyanate can prevent impurity ions from embedding into the anhydrous gypsum lattice, causing the transcrystalline product to exhibit an accordion-like shape. The longer the time, the more obvious this phenomenon becomes. At sulfuric acid concentrations of 2% to 8%, phosphogypsum fails to dissolve completely and does not achieve the purpose of transcrystallineization, remaining in a blocky morphology. As the sulfuric acid concentration increases to 10% to 15%, phosphogypsum completely dissolves and recrystallizes, while simultaneously regulating the morphology.

[0042] The crystal transformation products in Examples 1-3 and Comparative Example 1 were characterized by SEM. Figure 1 The XRD pattern of Example 1 is shown below. Figure 1 As can be seen, at lower sulfuric acid concentrations, a small amount of anhydrous gypsum can be observed; as the acid concentration increases to 10% and 15%, the phosphogypsum has completely transformed into anhydrous gypsum. From Figure 2 As can be seen from the SEM image of Example 1, increasing the acid concentration is more conducive to the transformation of crystal form and the formation of accordion-like morphology. At a 10% acid concentration, a more pronounced accordion-like morphology can be observed with the addition of sodium thiocyanate (e.g., Figure 3 As shown); with the reaction time extended to 6 hours, the accordion structure became more apparent (as shown). Figure 4 As shown). By Figure 5 (SEM image of Comparative Example 1) Figure 5 (PG in the image represents untreated phosphogypsum) It can be seen that, without the addition of polythiocyanate, the addition of other crystallization additives results in phosphogypsum exhibiting a micron-sized short rod-like structure rather than an accordion-shaped structure.

[0043] Therefore, the results above show that accordion-sized anhydrous gypsum can be prepared under low acid concentration (10%) and low polymeric thiocyanate addition (0.5%).

[0044] The anhydrous gypsum with a special morphology of the present invention can be applied to the preparation of polymer fillers, environmental adsorption, building materials and other fields. In terms of application, compared with anhydrous gypsum without a special morphology, its unique microstructure brings high specific surface area and good dispersibility.

[0045] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing accordion-shaped micron-sized anhydrous gypsum, characterized in that, Includes the following steps: After mixing phosphogypsum with sulfuric acid solution, a crystallization additive was added and stirred to react. The mixture was then filtered, washed until neutral, and dried to obtain accordion-shaped micron-sized anhydrous gypsum. The crystallization additive is a polymeric thiocyanate.

2. The preparation method according to claim 1, characterized in that, The polymeric thiocyanate is a polymeric potassium thiocyanate or a polymeric sodium thiocyanate; the concentration of the sulfuric acid solution is 2wt%~15wt%.

3. The preparation method according to claim 1, characterized in that, The solid-liquid ratio of the phosphogypsum to the sulfuric acid solution is 1 g: (5~8) mL.

4. The preparation method according to claim 1, characterized in that, The amount of the crystallization additive added is 0.5% of the mass of the phosphogypsum.

5. The preparation method according to claim 1, characterized in that, The stirring reaction is carried out at a temperature of 100°C for 4-6 hours.

6. The preparation method according to claim 1, characterized in that, The drying temperature is 60℃, and the drying time is 12 hours.

7. An accordion-shaped micron-sized anhydrous gypsum prepared by the preparation method according to any one of claims 1-6.

8. The application of the accordion-shaped micron-sized anhydrous gypsum as described in claim 7 in the preparation of polymer fillers, environmentally friendly adsorbent materials, or building materials.

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