Method for preparing calcium sulfate whisker by wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum

Abstract

The application discloses a method for preparing calcium sulfate whiskers from yellow phosphorus slag by wet desulfurization and by-product gypsum resource utilization, and belongs to the technical field of industrial waste gas treatment and solid waste resource utilization. The method comprises the following steps: pretreating the yellow phosphorus slag to improve the release efficiency of active calcium, and preparing yellow phosphorus slag slurry by mixing the pretreated yellow phosphorus slag with water; realizing SO2 removal by countercurrent contact of the pretreated yellow phosphorus slag slurry and industrial waste gas containing SO2 in a desulfurization tower; removing impurities by purifying the by-product gypsum after desulfurization; mixing the purified gypsum with water to obtain a mixture, adding a crystal modifier and a surfactant, and preparing calcium sulfate whiskers by hydrothermal reaction. The method realizes the preparation of whiskers from yellow phosphorus slag pretreatment, wet desulfurization and gypsum resource utilization, reduces the environmental risk caused by the storage of yellow phosphorus slag, realizes the high value of by-product gypsum, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste gas treatment and solid waste resource utilization technology, specifically involving a method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers. Background Technology

[0002] The chemical composition of yellow phosphorus slag is mainly calcium oxide (CaO, content approximately 40%–70%) and silicon dioxide (SiO2, content approximately 25%–30%), while also containing small amounts of phosphorus (P2O5) and fluorine (F). - The accumulation of large quantities of yellow phosphorus slag, containing impurities such as phosphorus and fluorine, not only occupies land resources, but also poses a continuous threat to soil, groundwater, and ecosystems due to the leaching of these impurities by rainwater, leading to increased total phosphorus concentrations in surrounding water bodies. Currently, the main ways to utilize yellow phosphorus slag include cement admixtures, roadbed materials, ceramic raw materials, and soil conditioners. However, because industry standards stipulate that the maximum amount of yellow phosphorus slag in ordinary silicate cement is only 20%, and because its harmful components such as phosphorus and fluorine pose a risk of leaching, the resource utilization rate is low, the added value of the products is not high, and it is difficult to achieve large-scale application.

[0003] SO2 is a major air pollutant in industrial flue gas, and its control and emission reduction are crucial for achieving sustainable environmental development. Currently, wet desulfurization technology is widely used in industrial flue gas desulfurization due to its high efficiency. However, existing wet desulfurization technologies largely rely on high-cost raw materials such as limestone, and the gypsum byproduct generated during the desulfurization process contains high levels of impurities, making it difficult to utilize at a high value, resulting in low overall economic benefits. While the sodium alkali method has a fast reaction rate, it is costly to operate and produces high-salt wastewater; the ammonia method has high desulfurization efficiency but requires strict control over equipment materials and carries the risk of ammonia escape. To reduce desulfurization costs and achieve "waste-to-waste treatment," domestic and international research has attempted to use calcium-containing solid wastes such as steel slag and carbide slag to replace traditional desulfurizing agents. However, these technologies generally suffer from low active calcium utilization (typically <60%), poor desulfurization product quality, and severe interference from impurity elements, limiting their industrial application.

[0004] Patent CN202210921292.7 proposes a method for flotation purification of phosphogypsum for the preparation of hemihydrate calcium sulfate whiskers, providing an integrated solution that optimizes the entire process from pretreatment of yellow phosphorus slag to wet desulfurization and resource utilization of by-product gypsum. However, this patent mainly focuses on the flotation purification process of phosphogypsum and does not address the efficient utilization of active calcium in yellow phosphorus slag. Although the degree of automation is improved, the integrated optimization of wet desulfurization and gypsum whisker preparation in the overall process is insufficient, limiting the efficiency and sustainability of phosphogypsum resource utilization. Patent CN201810574567.8 provides a method for the cyclic decomposition of phosphogypsum to produce calcium sulfate whiskers and co-produce ammonium sulfate. It prepares high-purity calcium sulfate whiskers and ammonium sulfate with high aspect ratio through low-temperature cyclic decomposition of phosphogypsum. However, the calcium carbonate slag generated during the preparation of ammonium sulfate is difficult to utilize at high value.

[0005] Therefore, how to efficiently remove SO2 while precisely controlling the release of active calcium and the migration path of impurities in yellow phosphorus slag, to obtain high-purity desulfurized gypsum and further prepare high-value-added calcium sulfate whiskers, has become a key scientific issue and technological challenge for the green and low-carbon development of the phosphorus chemical industry. Summary of the Invention

[0006] To address the issue of low application value of desulfurized gypsum obtained from SO2 removal from flue gas, the present invention aims to provide a method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers. This invention optimizes the calcium-sulfur reaction pathway through pretreatment methods and desulfurization operating conditions, suppresses impurity interference, and improves desulfurization efficiency and gypsum quality. This achieves efficient SO2 removal while simultaneously maximizing the value of by-product gypsum, resulting in calcium sulfate whiskers with advantages of high aspect ratio and high purity.

[0007] The objective of this invention is achieved by including the following steps: (1) Pre-treat the yellow phosphorus slag to improve the release efficiency of active calcium, and mix the pre-treated yellow phosphorus slag with water to prepare yellow phosphorus slag slurry; (2) The yellow phosphorus slag slurry after pretreatment in step (1) is brought into countercurrent contact with the industrial waste gas containing SO2 in the desulfurization tower to achieve SO2 removal; (3) Purify the by-product gypsum after desulfurization in step (2) to remove impurities; (4) Mix the purified gypsum from step (3) with water to obtain a mixture, add a crystallizing agent and a surfactant, and carry out a hydrothermal reaction to prepare calcium sulfate whiskers.

[0008] Preferably, the pretreatment in step (1) is acid leaching, microwave activation or heat treatment.

[0009] More preferably, the acid leaching specifically involves using a 1 mol / L sulfuric acid solution for leaching, controlling the leaching temperature at 90°C for 60 minutes; the leached yellow phosphorus residue undergoes solid-liquid separation, is then washed with deionized water until neutral, and then dried; the microwave activation specifically involves setting the microwave power to 800W for 20 minutes, followed by pulverization; the heat treatment specifically involves calcining at 500°C for 2 hours, cooling to room temperature, and then pulverizing.

[0010] Preferably, the solid content of the yellow phosphorus slag slurry in step (1) is 25% to 30%.

[0011] Preferably, in step (2), the temperature of the industrial waste gas is 65℃~80℃ and the oxygen content is ≥8%.

[0012] Preferably, the purification process in step (3) is a fractional washing or magnetic separation.

[0013] Preferably, the purified gypsum from step (4) is mixed with water at a liquid-to-solid mass ratio of 10-12:1.

[0014] Preferably, in step (4), the crystallization agent is CaCl2, and the amount used is 1% of the weight of the mixture, and the surfactant is polyethylene glycol, and the amount used is 0.3% of the weight of the mixture.

[0015] Preferably, in step (4), the crystallization agent is Na2SO4, and the amount used is 1.5% of the weight of the mixture, and the surfactant is sodium dodecyl sulfonate, and the amount used is 0.2% of the weight of the mixture.

[0016] Preferably, the hydrothermal reaction in step (4) is to first react at 120℃~140℃ for 1 to 2 hours to promote the formation of crystal nuclei, and then raise the temperature to 160℃~180℃ for 2 to 4 hours to promote the directional growth of whiskers, which is beneficial to improving the uniformity of the whisker aspect ratio.

[0017] The beneficial effects of this invention are: 1. The method of the present invention pretreats yellow phosphorus slag for wet desulfurization, which not only effectively utilizes the active calcium resources in yellow phosphorus slag, replaces traditional desulfurizing agents and reduces desulfurization costs, but also achieves the environmental protection goal of "treating waste with waste". The pretreatment step significantly improves the calcium release efficiency in yellow phosphorus slag, providing a sufficient calcium source for subsequent desulfurization reactions. 2. By optimizing the desulfurization operating conditions, this invention achieves efficient countercurrent contact between yellow phosphorus slag slurry and SO2-containing flue gas, with a desulfurization efficiency of over 95%. At the same time, the purity of CaSO4•2H2O in the by-product gypsum can reach over 90%, laying a high-quality foundation for further resource utilization. 3. This invention purifies desulfurized gypsum, removes impurities, and then, through hydrothermal reaction and the addition of crystallizing agents and surfactants, produces high-purity calcium sulfate whiskers with a high aspect ratio, thus realizing the high value of desulfurized gypsum and possessing good prospects for industrial application. 4. The hydrothermal reaction of this invention adopts a two-stage heating process, which effectively promotes uniform nucleation and directional growth of whiskers, significantly improves the aspect ratio uniformity and structural integrity of whiskers, and avoids the problems of uneven whisker growth and unstable quality in traditional methods. 5. The method of the present invention, from the pretreatment of yellow phosphorus slag and wet desulfurization to the resource utilization of gypsum to prepare whiskers, not only reduces the environmental risks caused by the stockpiling of yellow phosphorus slag, but also realizes the high value of by-product gypsum, which has good environmental and economic benefits. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the method of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention. Example 1

[0020] As attached Figure 1 The method for preparing calcium sulfate whiskers by wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum shown in this embodiment includes the following steps: (1) Take yellow phosphorus slag from a certain place for heat treatment, specifically, the roasting temperature is 500℃ and the roasting time is 2 hours, and then mechanically crush it to control the particle size at 150 mesh; the pretreated yellow phosphorus slag is mechanically crushed to control the particle size at 150 mesh; the crushed yellow phosphorus slag is mixed with water to prepare a yellow phosphorus slag slurry with a solid content of 25%, and the pH value is adjusted to 6.0; (2) The yellow phosphorus slag slurry pretreated in step (1) is fed into the top of the desulfurization tower and sprayed, with an SO2 concentration of 3200 mg / m³. 3 Industrial waste gas enters from the bottom of the desulfurization tower and rises upwards, where it comes into countercurrent contact with the waste gas. The temperature of the industrial waste gas is 80℃, and the oxygen content is 8%. Testing showed that the desulfurization efficiency reached 95%, and the purity of CaSO4•2H2O in the by-product gypsum was 90%. (3) The by-product gypsum from step (2) is subjected to solid-liquid separation, and then impurities are removed by a graded washing process, increasing the purity to 96%; (4) The gypsum purified in step (3) was mixed with water at a liquid-solid mass ratio of 10:1 to obtain a mixture. The pH value was adjusted to 7.0. CaCl2 was added as a crystallizing agent at 1% of the weight of the mixture, and polyethylene glycol was added as a surfactant at 0.3% of the weight of the mixture. The mixture was first hydrothermally reacted at 120°C for 1 hour, and then heated to 180°C for 2 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain calcium sulfate whiskers. The whisker aspect ratio was 120:1, the purity was 97%, the tensile strength was 22 GPa, and the whiteness was 92%. Example 2

[0021] The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers in this embodiment is based on Example 1, but differs from Example 1 in that: Step (1) Pretreatment is acid leaching, specifically using a 1 mol / L sulfuric acid solution, controlling the acid leaching temperature at 90℃ for 60 minutes; after acid leaching, the yellow phosphorus slag is separated into solid and liquid, then washed with deionized water until neutral, and then dried; the pretreated yellow phosphorus slag is mixed with water to prepare a yellow phosphorus slag slurry with a solid content of 30%, and the pH value is adjusted to 5.5; Step (2) The SO2 concentration in the industrial waste gas is 2500 mg / m³. 3 The temperature was 75℃; after testing, the desulfurization efficiency reached 97%, and the purity of CaSO4•2H2O in the by-product gypsum was 93%. Example 3

[0022] The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers in this embodiment is based on Example 1, but differs from Example 1 in that: Step (1) Pretreatment is microwave activation, specifically: microwave power is set to 800W, treatment time is 20 minutes; the pretreated yellow phosphorus slag is mixed with water to prepare a yellow phosphorus slag slurry with a solid content of 28%, and the pH value is adjusted to 5.8; Step (2) The SO2 concentration in the industrial waste gas is 2800 mg / m³. 3 The temperature was 65℃; the desulfurization efficiency reached 96%, and the purity of CaSO4•2H2O in the by-product gypsum was 92%. Example 4

[0023] The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers in this embodiment is based on Example 1, but differs from Example 1 in that: Step (4) The purified gypsum was mixed with water at a liquid-solid mass ratio of 12:1 to obtain a mixture. The pH value was adjusted to 8.0. Na2SO4 was added as a crystallizing agent at 1.5% of the weight of the mixture, and sodium dodecyl sulfonate was added as a surfactant at 0.2% of the weight of the mixture. The mixture was first hydrothermally reacted at 140℃ for 2 hours, and then the temperature was raised to 170℃ for 2 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain calcium sulfate whiskers. The whiskers were tested and found to have an aspect ratio of 150:1, a purity of 96%, a tensile strength of 25 GPa, and a whiteness of 90%. Example 5

[0024] The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers in this embodiment is based on Example 1, but differs from Example 1 in that: Step (1) The solid content of the yellow phosphorus slag slurry is 27.5%; Step (2) The temperature of the industrial waste gas is 72.5℃; Step (4) The purified gypsum is mixed with water at a liquid-solid mass ratio of 11:1; the hydrothermal reaction is first carried out at 130℃ for 1.5 hours, and then the temperature is raised to 160℃ for 4 hours. Example 6

[0025] The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers in this embodiment is based on Example 1, but differs from Example 1 in that: Since iron-containing impurities remain in the by-product gypsum from step (2), magnetic separation is used for purification in step (3). Specifically, the by-product gypsum obtained in step (2) is separated into solid and liquid phases, dried to constant weight, and pulverized to a particle size of less than 200 mesh. The pulverized gypsum powder is then separated by a high-gradient magnetic separator with a magnetic field strength of 1.5 T to remove iron-containing impurities. The gypsum after magnetic separation is washed with deionized water and dried to obtain purified gypsum. Step (4) The hydrothermal reaction is to react at 140℃ for 1 hour, and then raise the temperature to 160℃ for 3 hours.

Claims

1. A method for preparing calcium sulfate whiskers from wet desulfurization of yellow phosphorus slag and by-product gypsum, characterized in that... Includes the following steps: (1) Pre-treat the yellow phosphorus slag to improve the release efficiency of active calcium, and mix the pre-treated yellow phosphorus slag with water to prepare yellow phosphorus slag slurry; (2) The yellow phosphorus slag slurry after pretreatment in step (1) is brought into countercurrent contact with the industrial waste gas containing SO2 in the desulfurization tower to achieve SO2 removal; (3) Purify the by-product gypsum after desulfurization in step (2) to remove impurities; (4) Mix the purified gypsum from step (3) with water to obtain a mixture, add a crystallizing agent and a surfactant, and carry out a hydrothermal reaction to prepare calcium sulfate whiskers.

2. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... Step (1) Pretreatment is acid leaching, microwave activation or heat treatment.

3. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 2, characterized in that... The acid leaching specifically involves using a 1 mol / L sulfuric acid solution, controlling the leaching temperature at 90°C for 60 minutes; the yellow phosphorus residue after acid leaching undergoes solid-liquid separation, is then washed with deionized water until neutral, and then dried; the microwave activation specifically involves setting the microwave power to 800W and the processing time to 20 minutes; the heat treatment specifically involves calcining at 500°C for 2 hours, followed by cooling to room temperature and then pulverizing.

4. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... Step (1) The solid content of the yellow phosphorus slag slurry is 25%~30%.

5. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... Step (2) The temperature of the industrial waste gas is 65℃~80℃ and the oxygen content is ≥8%.

6. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... Step (3) purification treatment is either fractional washing or magnetic separation.

7. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... Step (4) The purified gypsum is mixed with water at a liquid-solid mass ratio of 10~12:

1.

8. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... In step (4), the crystallization agent is CaCl2, and the amount used is 1% of the weight of the mixture. The surfactant is polyethylene glycol, and the amount used is 0.3% of the weight of the mixture.

9. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... In step (4), the crystallization agent is Na2SO4, and the amount used is 1.5% of the weight of the mixture. The surfactant is sodium dodecyl sulfonate, and the amount used is 0.2% of the weight of the mixture.

10. The method for wet desulfurization of yellow phosphorus slag and resource utilization of by-product gypsum to prepare calcium sulfate whiskers according to claim 1, characterized in that... Step (4) The hydrothermal reaction is to first react at 120℃~140℃ for 1 to 2 hours, and then raise the temperature to 160℃~180℃ for 2 to 4 hours.

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