A novel crystallization additive and its application in crystallization phosphogypsum

Abstract

This invention relates to the field of phosphogypsum treatment technology, specifically to a novel crystallization additive and its application in crystallized phosphogypsum. The specific technical solution involves uniformly mixing phosphogypsum and the crystallization additive, followed by stirring and reaction in an acidic environment; the amount of the crystallization additive is 0.1%-1.5 wt% of the phosphogypsum. This invention achieves the conversion of dihydrate gypsum to anhydrous gypsum by controlling the concentration of the crystallization additive and the stirring reaction time. The method provided by this invention does not require high-temperature calcination and can be achieved at low crystallization additive concentrations, saving costs and realizing the high-value utilization of phosphogypsum.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum treatment technology, specifically to a novel crystallization additive and its application in crystallization phosphogypsum. 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 total production of wet-process phosphoric acid 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 has become the primary disposal method, which not only requires substantial financial investment and occupies significant land, but also poses a risk of continuous pollution to the atmosphere, groundwater systems, and soil due to wind and rain erosion over extended periods. Therefore, effectively treating phosphogypsum to prevent pollution has become an urgent problem to be solved in order to achieve green, sustainable, and circular development of the phosphate fertilizer chemical industry.

[0003] At present, producing sulfuric acid and cement from phosphogypsum is an effective way to comprehensively utilize phosphogypsum. However, this method requires huge investment, is energy-intensive, polluting, and produces unstable product quality. Furthermore, technological bottlenecks hinder its widespread adoption. Applying phosphogypsum to building materials, soil conditioners, and road construction also presents challenges such as secondary pollution and low added value. Therefore, it is necessary to develop high-value-added products to achieve sustainable development of the wet-process phosphoric acid industry while reducing environmental pollution.

[0004] Phosphogypsum crystallization technology is a technique that transforms the industrial byproduct phosphogypsum into a high-value-added product. Although it offers both environmental and economic benefits, it still has some drawbacks in existing technologies. For example, current processes for converting phosphogypsum to anhydrous gypsum face challenges such as complex solvent systems and high acid concentration requirements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a novel crystallization additive and its application in crystallization phosphogypsum, solving problems such as complex processes and complex solvent systems in existing technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a novel crystal transformation additive, wherein the crystal transformation additive is a polymeric thiocyanate.

[0007] Preferably, the polymeric thiocyanate is polymeric potassium thiocyanate.

[0008] Correspondingly, a novel crystallization additive is applied in crystallization phosphogypsum.

[0009] Preferably, the application method is as follows: after mixing phosphogypsum and crystal transformation additive evenly, the mixture is stirred and reacted in an acidic environment; the amount of the crystal transformation additive is 0.1-1.5 wt% of the phosphogypsum.

[0010] Preferably, the acidic environment is a sulfuric acid solution, and the solid-liquid ratio of the phosphogypsum to the sulfuric acid solution is 2:15.

[0011] Preferably, the sulfuric acid solution has a mass fraction of 8-10 wt%.

[0012] Preferably, the stirring reaction is carried out at a temperature of 100°C for 2-6 hours.

[0013] Preferably, the stirring time is 2h, 4h or 6h.

[0014] The present invention has the following beneficial effects: This invention achieves the conversion of dihydrate gypsum into micron-sized anhydrous gypsum under low acid concentrations by controlling the sulfuric acid and the stirring reaction time.

[0015] This invention achieves increased whiteness by adding a crystallization additive to a mixture of sulfuric acid and phosphogypsum, thereby enabling the phosphogypsum to undergo crystallization.

[0016] 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

[0017] Figure 1 The image shows the XRD pattern of the phosphogypsum transformation product in 0.1-1.5 wt% transformation additive solution in Example 1. Figure 2 The XRD patterns of phosphogypsum in Example 2, with an additive dosage of 0.1 wt%, after crystallization for 6 hours in 8 wt% and 10 wt% sulfuric acid solutions; Figure 3 The XRD patterns of phosphogypsum in 10wt% sulfuric acid solution at different crystallization times in Example 3 are shown. Figure 4 The image shows the XRD pattern of phosphogypsum in Comparative Example 4 without additives. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0020] This invention provides a novel crystal transformation additive, wherein the crystal transformation additive is a polymeric thiocyanate. As a preferred embodiment, the polymeric thiocyanate is potassium polymeric thiocyanate.

[0021] This invention provides a novel method for converting phosphogypsum into a crystallizer using a crystallizer additive. The method involves mixing phosphogypsum and the crystallizer additive evenly in a low-concentration sulfuric acid solution and then stirring the mixture to react. The amount of the crystallizer additive used is 0.1-1.5 wt% of the phosphogypsum.

[0022] With the increase of the amount of crystallization additive, the dihydrate gypsum can be converted into anhydrous gypsum. When the amount of crystallization additive is 0.1 wt%, the acid concentration is 10 wt%, and the crystallization time is 6 hours, the dihydrate gypsum is directly converted into anhydrous gypsum. When the concentration of the additive exceeds 0.1 wt%, the dihydrate gypsum can also be directly converted into anhydrous gypsum.

[0023] In some embodiments, the ratio of phosphogypsum to sulfuric acid solution is 2g:15mL, and the mass fraction of sulfuric acid solution is 8-10wt%.

[0024] In some embodiments, the temperature of the stirring reaction is 100°C, and the stirring reaction time is 2-6 hours.

[0025] In some embodiments, the stirring reaction is carried out for 2 hours, 4 hours, or 6 hours.

[0026] In this invention, the conversion of dihydrate gypsum to anhydrous gypsum can be achieved even with lower additive and acid concentrations. This is because the additive contains 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. Simultaneously, impurity ions gradually diffuse into the solution during dissolution, thereby improving whiteness. Even with a 6-hour reaction time, the whiteness continues to increase. Considering time constraints, the reaction time is controlled to be 6 hours. Therefore, this invention controls the reaction time to within 6 hours.

[0027] In some embodiments, the method for controlling the crystallization of phosphogypsum specifically includes the following steps: Phosphogypsum was added to a sulfuric acid solution and stirred until homogeneous. Polythiocyanate was then added and the mixture was stirred to react. After the reaction was complete, the mixture was cooled to room temperature, then filtered and washed until neutral. It was then dried in a forced-air drying oven (at 80°C for 12 hours). The whiteness of the dried sample was measured using a whiteness meter, and the crystal structure of the resulting transcrystalline product was characterized using X-ray scanning diffraction (XRD).

[0028] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0029] The phosphogypsum used in the examples came from a chemical plant in Guizhou.

[0030] Example 1 20g of phosphogypsum was added to 150mL of 10wt% sulfuric acid solution and stirred until homogeneous. Poly(potassium thiocyanate) was then added (the amount of poly(potassium thiocyanate) was 0.1-1.5wt% of the phosphogypsum). The mixture was stirred at 100℃ for 6 hours, filtered, and washed until neutral. The sample was then dried at 80℃ for 12 hours. The whiteness of the dried sample was measured using a whiteness meter, and the crystal form change process was simultaneously determined using X-ray diffraction. The whiteness changes with different amounts of crystal transformation additives are shown in Table 1.

[0031] Table 1. Whiteness variation with different amounts of crystal transformation additives

[0032] As shown in Table 1, the whiteness of phosphogypsum initially increases and then decreases with increasing crystallization additive content. This is because phosphogypsum often contains impurities such as iron and aluminum (coloring ions). The adsorption layer of poly(potassium thiocyanate) can prevent these impurity ions from embedding into the anhydrous gypsum lattice, forming a dense adsorption layer on the crystal surface, thus significantly improving the whiteness of the phosphogypsum crystallization product. A 0.1% addition amount is sufficient to induce crystallization (critical concentration), and as the addition amount increases to 1.5%, the whiteness stabilizes at 72%. This is because at low concentrations, the additive has already reached saturated adsorption on the crystal surface; excessive addition will not further alter the surface coverage, thus the crystallization efficiency and whiteness tend to stabilize.

[0033] Example 2 20g of phosphogypsum was added to 150mL of sulfuric acid solutions with concentrations of 8wt% and 10wt%, stirred until homogeneous, and then poly(potassium thiocyanate) (the amount of poly(potassium sulfate) was 0.1wt% of the phosphogypsum) was added. The mixture was stirred at 100℃ for 6h, filtered and washed until neutral, and then dried at 80℃ for 12h. The whiteness of the dried sample was measured using a whiteness meter, and the crystal form change process was determined simultaneously using an X-ray diffractometer.

[0034] Example 3 20g of phosphogypsum was added to 150mL of 10wt% sulfuric acid solution and stirred until homogeneous. Polysodium thiocyanate (0.1wt% of phosphogypsum) was then added and stirred at 100℃ for different times (2h, 4h and 6h respectively). The mixture was filtered and washed until neutral, and then dried at 80℃ for 12h. The crystal form change process was determined using X-ray diffraction.

[0035] Comparative Example 1 Add 20g of phosphogypsum to 150mL of deionized water, stir well, add only 10wt% sulfuric acid solution, stir and react at 100℃ for 6h, filter and wash until neutral, then dry at 80℃ for 12h, and use X-ray diffraction to determine the crystal form change process.

[0036] The crystallization products in Examples 1-3 and Comparative Example 1 were characterized by XRD. Figure 1 The XRD pattern of Example 1 is shown below. Figure 1 As can be seen, anhydrous gypsum can also be observed at lower additive mass fractions. From Figure 2 (XRD pattern of Example 2) and Figure 3 As can be seen from the XRD pattern of Example 3, increasing the acid concentration is more conducive to the transformation of the crystal form. At a 10 wt% acid concentration, with the reaction time extended to 6 hours, phosphogypsum directly transformed from dihydrate gypsum to anhydrous gypsum. Figure 4 (XRD pattern of Comparative Example 1) It can be seen that, without the addition of additives, the crystal form of phosphogypsum did not change when sulfuric acid was added, and it remained gypsum dihydrate.

[0037] Therefore, the above analysis shows that adding 0.1%-1.5% of the phosphogypsum additive can achieve the transformation of dihydrate gypsum into anhydrous gypsum under low acid concentrations. Simultaneously, whiteness gradually increases; at the same acid concentration, whiteness increases with increasing additive mass fraction.

[0038] 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 novel crystal transformation additive, characterized in that: The crystallization additive is a polymeric thiocyanate.

2. The novel crystal transformation additive according to claim 1, characterized in that: The polymeric thiocyanate is a polymeric potassium thiocyanate.

3. The application of the novel crystallization additive as described in claim 1 or 2 in crystallization phosphogypsum.

4. The application according to claim 3, characterized in that: The application method is as follows: after mixing phosphogypsum and crystal transformation additive evenly, stir and react in an acidic environment; the amount of crystal transformation additive is 0.1-1.5 wt% of phosphogypsum.

5. The application according to claim 4, characterized in that: The acidic environment is a sulfuric acid solution, and the solid-liquid ratio of the phosphogypsum to the sulfuric acid solution is 2:

15.

6. The application according to claim 5, characterized in that: The sulfuric acid solution has a mass fraction of 8-10 wt%.

7. The application according to claim 4, characterized in that: The stirring reaction is carried out at a temperature of 100℃ for 2-6 hours.

8. The method for producing a novel crystallization additive, crystallization phosphogypsum, according to claim 7, is characterized in that: The stirring time is 2 hours, 4 hours, or 6 hours.

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