Method for removing soluble phosphorus and fluorine in phosphorite gypsum by electrolytic manganese residue and steel slag

Abstract

The application discloses a method for removing soluble phosphorus and fluorine in phosphogypsum by electrolytic manganese slag and steel slag, and belongs to the technical field of industrial solid waste resource utilization. The method comprises the following steps: grinding the steel slag, mixing the steel slag with the electrolytic manganese slag to stimulate the activity, adding the mixture into the phosphogypsum which has been treated by slurry, stirring, and obtaining the product by pressure filtration after the reaction. The mass fractions of the steel slag, the electrolytic manganese slag and the phosphogypsum are 5%-10%, 1%-3% and 87%-94% respectively. The method uses the alkalinity of the steel slag to neutralize the soluble phosphorus and fluorine in the phosphogypsum, so that the phosphorus and fluorine are converted into insoluble phosphides and fluorides. In addition, the steel slag itself contains active components such as C2S and C3S, and the hydration rate of the steel slag is greatly improved in the sulfate stimulating environment provided by the electrolytic manganese slag, so that the hydrated calcium sulphoaluminate is continuously generated, the mechanical properties of the modified body are improved, the purpose of waste treatment by waste is achieved, and the harmless treatment of the phosphogypsum is realized on a large scale.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization technology, specifically a method for removing soluble phosphorus and fluorine from phosphogypsum in conjunction with electrolytic manganese slag and steel slag. Background Technology

[0002] Steel slag is a solid waste product generated during the steel production process from slag-forming materials such as lime and fluorite, the corrosion of furnace linings, and the oxidation of silicon and iron in molten iron. Approximately 0.15 tons of steel slag are produced for every ton of steel produced. Large quantities of steel slag are stored up for extended periods, occupying land and polluting the environment, necessitating effective and comprehensive utilization. Steel slag contains abundant alkaline oxides such as CaO, MgO, and Fe2O3, exhibiting strong alkalinity. According to the alkalinity calculation formula R=CaO / (SiO2+P2O5), it can be classified into low-alkalinity steel slag (R<1.8), medium-alkalinity steel slag (R=1.8-2.5), and high-alkalinity steel slag (R>2.5). Furthermore, steel slag contains active minerals similar to cement clinker, such as C2S and C3S. However, due to the dense crystals and large grains of these minerals, the hydration rate of the cementing active minerals is relatively slow, reducing early strength. Therefore, activation of the steel slag is necessary to increase its utilization scale.

[0003] Electrolytic manganese slag is the filter residue produced during the electrolytic production of metallic manganese. Producing 1 ton of manganese metal generates 10-12 tons of electrolytic manganese slag. Untreated electrolytic manganese slag contains heavy metals such as Mn, Cr, Pb, Cu, Zn, Se, and Ni, posing serious hazards to land occupied by its storage, surface water, groundwater, and surrounding residents. Electrolytic manganese slag is rich in sulfates, with a content exceeding 30%. During the hydration of steel slag, electrolytic manganese slag dissolves a large amount of SO4. 2- In a sulfate environment, the hydration rate of steel slag is greatly increased, continuously generating hydrated calcium sulfoaluminate. This hydrated calcium sulfoaluminate fills the pores, and the various hydration products exhibit good matching, ultimately forming a dense structure. Using electrolytic manganese slag to activate the hydration activity of steel slag not only achieves the goal of waste treatment and cost reduction, but also produces products that are more beneficial for the production and preparation of downstream products.

[0004] Phosphogypsum is a solid waste byproduct of the wet-process phosphoric acid industry. For every ton of phosphoric acid produced, 4.8-5.0 tons of phosphogypsum are generated. Phosphogypsum contains various impurities, including phosphorus, fluorine, organic matter, and heavy metals. The most problematic impurity is soluble phosphorus (H₂PO₄). - HPO4 2- ) and fluorine (F - Impurities. These impurities not only adhere to the surface of gypsum crystals but also bind within the gypsum lattice, significantly impacting the quality of downstream high-value-added products. How to efficiently and cost-effectively remove these impurities has become a hot research topic in the industry.

[0005] The main methods for removing soluble phosphorus and fluorine from phosphogypsum include physical methods, chemical methods, and heat treatment methods.

[0006] Physical methods mainly include physical flotation and water washing. Physical flotation involves thoroughly mixing water and gypsum in a specific ratio and then feeding the mixture into flotation equipment. Through stirring and settling, organic impurities suspended on the water surface, as well as small amounts of soluble phosphorus and fluoride, are removed. This method offers a high gypsum recovery rate, but it requires high-quality flotation equipment. Water washing involves rinsing the phosphogypsum in a reslurry tank, followed by a secondary rinsing in a filter, and finally purification through pressure filtration. This method can remove most water-soluble phosphorus and fluoride impurities, but effective treatment of the wash water is necessary.

[0007] Chemical methods primarily involve adding acidic or alkaline substances to phosphogypsum, causing impurities to undergo a qualitative change, forming soluble or insoluble substances. These impurities are then removed through washing or filtration. Industrially, lime is commonly used to wash phosphogypsum, utilizing its alkaline neutralization reaction to convert water-soluble phosphates, water-soluble fluoride, and other impurities into inert substances (calcium phosphate, calcium fluoride, etc.). However, some of the inert substances produced by this method can affect the performance of subsequent gypsum products.

[0008] The heat treatment method utilizes phosphogypsum under high temperature conditions to convert the residual soluble fluorine into hydrogen fluoride gas and volatilize it, and convert the soluble phosphorus into stable insoluble phosphate compounds. However, this method requires high energy consumption and has high flue gas purification costs.

[0009] Utilizing the alkalinity of steel slag to neutralize and remove soluble phosphorus and fluorine impurities from phosphogypsum is a slow process with a long cycle. For example, patent application number 202010966060.4 discloses a method for pretreating phosphogypsum using steel slag. This method utilizes the active lime in the steel slag to neutralize the acidity of the phosphogypsum, reducing the content of compounds such as phosphorus and fluorine. Sulfuric acid washing removes soluble compounds such as silicon, aluminum, iron, fluorine, and potassium from the phosphogypsum. The two are then mixed in a predetermined ratio, allowing the phosphogypsum filter residue to fully precipitate in the steel slag filtrate. Finally, further drying and dehydration in an oven removes small amounts of organic impurities from the phosphogypsum, resulting in a relatively pure hemihydrate phosphogypsum with high whiteness.

[0010] Some researchers have also used electrolytic manganese slag in combination with phosphogypsum to reduce the impact of soluble fluorine, phosphorus, manganese and ammonia nitrogen on phosphogypsum. For example, patent application No. 201910149830.3 discloses a method for harmless treatment of electrolytic manganese slag and phosphogypsum in combination. The method has the following steps: (1) Electrolytic manganese slag and phosphogypsum are mixed evenly at a ratio of electrolytic manganese slag: phosphogypsum = 1:2~5 (dry basis mass ratio); (2) The mixture in step (1) is made into a slurry (mass ratio) at a solid-liquid ratio of 1:0.3~0.7. The pH of the slurry is adjusted by an alkaline agent (1~2 parts by weight of calcined raw material, 2~3 parts by weight of calcium oxide, 1~3 parts by weight of magnesium oxide or one or more of these) to ensure that the pH value of the slurry is 6~9; (3) The mixture in step (2) is transported to a storage site for storage or used for other purposes. The drawback of this method is that the resulting mixture contains a large amount of insoluble precipitates formed by manganese, magnesium, calcium, fluoride, phosphate, and hydrogen phosphate ions, which have virtually no hydration activity. This has a significant impact on its later application in the building materials field. In addition, this method requires the addition of alkaline agents to adjust the pH value of the slurry, which increases the production cost. Summary of the Invention

[0011] This invention aims to provide a method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag in conjunction with steel slag. This method utilizes the alkalinity of steel slag to neutralize the soluble phosphorus and fluoride in phosphogypsum, causing them to form insoluble phosphides and fluorides. In addition, steel slag itself contains active components such as dicalcium silicate (C2S) and tricalcium silicate (C3S). At the same time, under the sulfate-activated environment provided by electrolytic manganese slag, the hydration rate of steel slag is greatly increased, continuously generating hydrated calcium sulfoaluminate, which increases the stability of hydration products and improves the mechanical properties of the modified body. This achieves the purpose of treating waste with waste and utilizing waste, and is suitable for the harmless treatment of phosphogypsum on a large-scale industrial basis.

[0012] The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in combination includes the following steps: S1. Grind the dried steel slag and electrolytic manganese slag separately; S2. The pulverized electrolytic manganese slag is mixed into the pulverized steel slag for activation. S3. The electrolytic manganese slag activated steel slag slurry from step S2 is added to the phosphogypsum that has undergone water slurry treatment and stirred. After the removal reaction is completed, the slurry is filtered by pressure to obtain a phosphogypsum slurry with soluble phosphorus and fluorine removed.

[0013] Preferably, the steel slag includes converter steel slag, open-hearth furnace steel slag, electric furnace steel slag, and / or a removal agent formulated from chemical raw materials that has the same main components as the steel slag.

[0014] Preferably, the steel slag is mainly composed of the following components by mass: 40-60 parts CaO, 3-10 parts MgO, 4-12 parts SiO2, 2-8 parts Fe2O3, 1-8 parts MnO and 2-8 parts Al2O3.

[0015] Preferably, the basicity R of the steel slag is greater than 2.5. The basicity R of the steel slag is mainly determined by the ratio of the sum of the contents of CaO, SiO2, and P2O5, i.e., R = CaO / (SiO2 + P2O5). Steel slag can be classified according to its basicity into low-basicity steel slag (R < 1.8), medium-basicity steel slag (R = 1.8~2.5), and high-basicity steel slag (R > 2.5).

[0016] Preferably, the electrolytic manganese slag is mainly composed of the following components by mass: 22-41 parts SiO2, 11-30 parts SO3, 8-19 parts Fe2O3, 2-19 parts CaO, 2-9 parts Al2O3 and 0-4 parts MnO.

[0017] Preferably, in step S1, both the steel slag and the electrolytic manganese slag are dried to constant weight at 80~120 ℃ and then dry-milled using a ball mill to achieve a specific surface area of ​​500 m². 2 / kg.

[0018] Preferably, in step S2, the mass ratio of electrolytic manganese slag to steel slag is 1~3:5~10.

[0019] Preferably, in step S2, the activation specifically includes the following steps: adding water to steel slag at a solid-liquid mass ratio of 1:0.5~2 and stirring evenly, then adding electrolytic manganese slag, and activating at a temperature of 25~60 ℃ for 0.5~12 h.

[0020] Preferably, in step S3, the mass ratio of the steel slag to the dry phosphogypsum is 5~10:87~94.

[0021] Preferably, in step S3, the solid-liquid mass ratio of the phosphogypsum pulping treatment is 1:0.5~2.

[0022] Preferably, in step S3, the reaction temperature of the removal reaction is 25~50 ℃, and the reaction time is 0.5~6 h.

[0023] Preferably, in step S3, the pH value of the phosphogypsum slurry after pressure filtration is 5-8.

[0024] Preferably, in step S3, the water content of the phosphogypsum slurry after pressure filtration is 8%~15%.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes the alkalinity of steel slag to neutralize the soluble phosphorus and fluorine in phosphogypsum, causing it to generate insoluble phosphides and fluorides. In addition, steel slag itself contains active components such as C2S and C3S, and under the sulfate-activated environment provided by electrolytic manganese slag, its hydration rate is greatly improved, continuously generating hydrated calcium sulfoaluminate, which improves the mechanical properties of the modified body. This achieves the purpose of treating waste with waste and utilizing waste, and is suitable for the harmless treatment of phosphogypsum on a large-scale industrial basis.

[0026] 2. The method provided by this invention is used to process phosphogypsum and use it as a raw material to produce building gypsum powder. After testing, the mechanical properties of the specimens are improved by at least 50% compared with the untreated specimens, reaching the quality standard of building gypsum strength grade 3.0. Detailed Implementation

[0027] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.

[0028] The phosphogypsum used in this embodiment of the invention has a soluble phosphorus content of 2500 mg / L and a soluble fluorine content of 4600 mg / L, and was purchased from Yidu Xingfa Chemical Co., Ltd. The electrolytic manganese slag was purchased from Ningxia Tianyuan Manganese Industry Group Co., Ltd., and the steel slag was purchased from Shanxi Jianlong Steel Co., Ltd.

[0029] Example 1 A method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction, comprising the following steps: S1. Weigh 50 g of converter steel slag with an alkalinity R of 2.4 and 10 g of electrolytic manganese slag, and dry them separately in an oven at 100 ℃ until constant weight. Then, dry grind them separately using a ball mill until the specific surface area is 500 m². 2 / kg; S2. Add water to the ground steel slag at a solid-liquid mass ratio of 1:1 and stir evenly. Then add the ground electrolytic manganese slag and activate it at 25 ℃ for 2 h. S3. Weigh 940 g of phosphogypsum, add water at a solid-liquid mass ratio of 1:1 for slurry treatment, and add the electrolytic manganese slag activated steel slag slurry from step S2 into it and stir thoroughly. Remove the slag and react at 25 ℃ for 5 h. Finally, filter the slurry to obtain phosphogypsum slurry with soluble phosphorus and fluorine removed.

[0030] The soluble phosphorus content, soluble fluoride content, moisture content, pH value, and flexural strength of the prepared β-gypsum powder were tested on the filtrate after pressure filtration.

[0031] The test results were as follows: soluble phosphorus content was 0.2 mg / L, soluble fluoride content was 7.1 mg / L, moisture content was 10%, pH value was 7.2, and the flexural strength of the prepared β-gypsum powder was 3.1 MPa. This demonstrates that the phosphogypsum treated by electrolytic manganese slag activation of steel slag has been transformed into general solid waste (P≤0.5 ppm, F≤10 ppm) and still possesses good mechanical properties.

[0032] Example 2 A method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction, comprising the following steps: S1. Weigh 70 g of converter steel slag with an alkalinity R of 2.8 and 20 g of electrolytic manganese slag, and dry them separately in an oven at 100 ℃ until constant weight. Then, dry grind them separately using a ball mill until the specific surface area is 500 m². 2 / kg; S2. Add water to the ground steel slag at a solid-liquid mass ratio of 1:1 and stir. Then add the ground electrolytic manganese slag and activate it at 25 °C for 1.5 h. S3. Weigh 910 g of phosphogypsum, add water at a solid-liquid mass ratio of 1:1.2 for slurry treatment, and add the electrolytic manganese slag activated steel slag slurry from step S2 into it and stir thoroughly. Remove the slag and react at 25 ℃ for 4 h. Finally, filter the slurry to obtain phosphogypsum slurry with soluble phosphorus and fluorine removed.

[0033] The soluble phosphorus content, soluble fluoride content, moisture content, pH value, and flexural strength of the prepared β-gypsum powder were tested on the filtrate after pressure filtration.

[0034] The test results were as follows: soluble phosphorus content was 0.1 mg / L, soluble fluoride content was 6.5 mg / L, moisture content was 12%, pH value was 7.6, and the flexural strength of the prepared β-gypsum powder was 3.3 MPa. This demonstrates that the phosphogypsum treated by electrolytic manganese slag activation of steel slag has been transformed into general solid waste (P≤0.5 ppm, F≤10 ppm) and still possesses good mechanical properties.

[0035] Example 3 A method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction, comprising the following steps: S1. Weigh 100 g of electric furnace steel slag with an alkalinity R of 1.5 and 30 g of electrolytic manganese slag, and dry them separately in an oven at 100 ℃ until constant weight. Then, dry grind them separately using a ball mill until the specific surface area is 500 m². 2 / kg; S2. Add water to the ground steel slag at a solid-liquid mass ratio of 1:1 and stir. Add electrolytic manganese slag and activate at 50 °C for 4 h. S3. Weigh 870 g of phosphogypsum, add water at a solid-liquid mass ratio of 1:1 for slurry treatment, and add the electrolytic manganese slag activated steel slag slurry from step S2 into it and stir thoroughly. Remove the slag and react at 50 ℃ for 6 h. Finally, filter the slurry to obtain phosphogypsum slurry with soluble phosphorus and fluorine removed.

[0036] Finally, the slurry was filtered until the adsorbed water content was reached. The filtered phosphogypsum slurry was then tested for soluble phosphorus content, soluble fluorine content, water content, pH value, and the flexural strength of the prepared β-gypsum powder.

[0037] The test results were as follows: soluble phosphorus content was 0.2 mg / L, soluble fluoride content was 8.3 mg / L, moisture content was 9%, pH value was 6.8, and the flexural strength of the prepared β-gypsum powder was 3.0 MPa. This demonstrates that the phosphogypsum treated by electrolytic manganese slag activation of steel slag has been transformed into general solid waste (P≤0.5 ppm, F≤10 ppm) and still possesses good mechanical properties.

[0038] Comparative Example 1 A method for removing soluble phosphorus and fluorine from phosphogypsum in steel slag includes the following steps: S1. Weigh 50g of converter steel slag with a basicity R of 2.4 and dry it in a 100℃ oven until constant weight. Then, dry grind it using a ball mill until the specific surface area is 500 m². 2 / kg; S2. Add water to the ground steel slag at a solid-liquid mass ratio of 1:1 and stir thoroughly. S3. Weigh 940 g of phosphogypsum, add water at a solid-liquid mass ratio of 1:1 for slurry treatment, and add the steel slag slurry from step S2 into it and stir thoroughly. Remove the slag and react at 25 ℃ for 5 h.

[0039] The soluble phosphorus content, soluble fluoride content, moisture content, pH value, and flexural strength of the prepared β-gypsum powder were tested on the filtrate after pressure filtration. The results were as follows: soluble phosphorus content was 0.55 mg / L, soluble fluoride content was 13.2 mg / L, moisture content was 10%, pH value was 6.3, and the flexural strength of the prepared β-gypsum powder was 2.7 MPa. This indicates that unactivated steel slag has a certain removal capacity for soluble phosphorus and soluble fluoride in phosphogypsum, but it cannot convert it into general solid waste (P≤0.5 ppm, F≤10 ppm), and the mechanical properties of the modified phosphogypsum slurry are poor.

[0040] The experimental data of Examples 1-3 and Comparative Example 1 are shown in Table 1.

[0041] Table 1

[0042] Table 1 shows that the soluble phosphorus and soluble fluoride contents of phosphogypsum treated with electrolytic manganese slag and steel slag are much lower than those of the original phosphogypsum. The soluble phosphorus content is all below 0.2 mg / L, and the soluble fluoride content is all below 10 mg / L, meeting the requirements for general solid waste (P≤0.5 ppm, F≤10 ppm). Furthermore, the flexural strength of the prepared β-gypsum powder is all 3.0 MPa or higher. In contrast, the soluble phosphorus content of phosphogypsum treated only with steel slag is more than twice that of the phosphogypsum treated with electrolytic manganese slag and steel slag, and the soluble fluoride content is also much higher. At the same time, the flexural strength of the prepared β-gypsum powder does not reach 3.0 MPa. This indicates that steel slag without electrolytic manganese slag activation has a certain removal capacity for soluble phosphorus and soluble fluoride in phosphogypsum, but it cannot convert it into general solid waste. Moreover, the mechanical properties of the modified phosphogypsum slurry are poor, making it unsuitable as a main raw material for downstream high-strength gypsum building materials.

[0043] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction, characterized in that, Includes the following steps: S1. Grind the dried steel slag and electrolytic manganese slag separately; S2. The pulverized electrolytic manganese slag is mixed with the pulverized steel slag for activation. The activation specifically includes the following steps: the steel slag is mixed with water at a solid-liquid mass ratio of 1:0.5~2 and stirred evenly. Then, the electrolytic manganese slag is added and activated at a temperature of 25~60℃ for 0.5~12h. S3. The electrolytic manganese slag activated steel slag slurry from step S2 is added to the phosphogypsum that has undergone water slurry treatment and stirred. After the removal reaction is completed, the slurry is filtered by pressure to obtain a phosphogypsum slurry with soluble phosphorus and fluorine removed.

2. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, The steel slag mentioned is one or more of converter steel slag, open-hearth steel slag, and electric furnace steel slag.

3. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, The steel slag, by mass, mainly consists of the following components: CaO 40-60 parts, MgO 3-10 parts, SiO 24-12 parts, Fe 2O 32-8 parts, MnO 1-8 parts, and Al 2O 32-8 parts; the electrolytic manganese slag, by mass, mainly consists of the following components: SiO 22-41 parts, SO 31-30 parts, Fe 2O 38-19 parts, CaO 2-19 parts, Al 2O 32-9 parts, and MnO 0-4 parts.

4. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, In step S1, both the steel slag and the electrolytic manganese slag are dried to constant weight at 80~120℃ and then dry-milled using a ball mill to achieve a specific surface area of ​​500 m². 2 / kg.

5. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, In step S2, the mass ratio of electrolytic manganese slag to steel slag is 1~3:5~10.

6. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, In step S3, the mass ratio of steel slag to dry phosphogypsum is 5~10:87~94.

7. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, In step S3, the solid-liquid mass ratio of the phosphogypsum pulping treatment is 1:0.5~2.

8. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, In step S3, the reaction temperature of the removal reaction is 25~50℃, and the reaction time is 0.5~6h.

9. The method for removing soluble phosphorus and fluoride from phosphogypsum using electrolytic manganese slag and steel slag in conjunction with claim 1, characterized in that, In step S3, the pH value of the phosphogypsum slurry after pressure filtration is 5-8; the water content of the phosphogypsum slurry after pressure filtration is 8%-15%.

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