Preparation and application of metallurgical slag waste alkali balls for treating ardealite leachate

Abstract

The invention discloses a preparation method of metallurgical slag waste alkali balls for treating ardealite leachate, which is used for innocent treatment of leachate generated by ardealite accumulation and secondary resource utilization of metallurgical solid waste. According to the method, metallurgical slag waste alkali balls of solid waste are used as a preparation raw material and are matched with an adhesive and a pore forming agent, and high-concentration phosphate radicals and fluorine ions in the ardealite leachate are deposited on the surface of the ardealite leachate in the form of adsorption and precipitation so as to be removed from water. The metallurgical slag powder can be linked into a millimeter-level spherical material by the adhesive; the pore-forming agent can increase the pore channels in the metallurgical slag waste alkali sphere and enhance the liquidity of the liquid. The prepared metallurgical slag waste alkali balls have high structural stability and high adsorption activity in various water bodies, the limitation that a current powder material is difficult to recycle and prone to loss in phosphorus and fluorine wastewater treatment is overcome, and whole-process recycling of'treating waste with waste 'is achieved.

Description

Technical Field

[0001] This invention relates to a method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate, and also to the application of these metallurgical slag alkali pellets in treating phosphogypsum leachate, belonging to the field of solid waste resource utilization technology. Background Technology

[0002] Phosphogypsum is a solid waste byproduct of the wet-process phosphoric acid production. For every ton of phosphoric acid (calculated as P2O5) produced, this process generates approximately 4-5 tons of phosphogypsum. Based on data from long-term phosphoric acid production using this method, the cumulative stockpile of phosphogypsum produced nationwide currently exceeds 820 million tons.

[0003] Since phosphogypsum's main component is calcium sulfate dihydrate, it also contains soluble phosphorus, fluorine, heavy metals, and organic matter, among other substances. Soluble phosphorus and fluorine are currently the biggest problems with phosphogypsum stockpiling. Due to its solubility, long-term stockpiling may lead to the release of phosphorus and fluorine into natural water bodies through rainwater or other means, and leachate generated during solid waste stockpiling could further contribute to environmental problems such as eutrophication.

[0004] Phosphogypsum leachate is polluted wastewater formed during the stockpiling or landfilling of phosphogypsum solid waste through rinsing, soaking, and dissolution by rainwater or flushing water. It contains high concentrations of phosphorus (2000–15000 mg / L) and fluoride (100–3000 mg / L). Currently, the main treatment methods for phosphogypsum leachate include ion exchange, membrane separation, and chemical precipitation. Among these, the expensive resin materials in ion exchange and the membrane materials in membrane separation lead to high treatment costs for phosphogypsum. Traditional chemical precipitation methods, which involve adding only calcium oxide or calcium hydroxide, struggle to simultaneously achieve compliant phosphorus and fluoride discharge levels and also generate large amounts of precipitates. Therefore, developing novel, low-cost treatment materials capable of simultaneously achieving deep removal of phosphorus and fluoride is crucial to overcoming the bottleneck in the harmless disposal of phosphogypsum leachate.

[0005] In the smelting processes of magnesium, iron, and aluminum, metallurgical slag is a major byproduct, and its generation is significantly positively correlated with the output of magnesium, iron, and aluminum. According to industry statistics, my country's annual metallurgical slag production reaches 200-300 million tons. However, over 70% of the current disposal methods employ extensive treatment methods such as landfilling or open-air storage, which not only occupies valuable land resources but also poses environmental risks such as heavy metal leaching and dust pollution. In light of this situation, developing high-value-added resource utilization technologies for metallurgical slag has significant environmental and economic value.

[0006] Chemical composition analysis of metallurgical slag shows that the key active components in magnesium, iron, and aluminum metallurgical slags are CaO (20–50 wt.%), MgO (6–10 wt.%), and Fe2O3 (2–15 wt.%). These alkaline oxides give the metallurgical slag its strong alkalinity (hence the term "metallurgical slag alkali"), and it exhibits a special coordination affinity for phosphate and fluoride ions in water. This characteristic makes metallurgical slag alkali an ideal candidate material for the deep treatment of phosphorus and fluoride wastewater. However, metallurgical slag alkali is mainly in powder form (0.01–1 mm). When directly treating phosphorus and fluoride wastewater, its powder form makes it impossible to achieve solid-liquid separation in a dynamic water treatment system, and it is also very easy to lose, even causing secondary pollution. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, this invention provides a method for preparing and applying metallurgical slag waste alkali balls for treating phosphogypsum leachate, thereby solving the problems of difficult separation and easy loss in the existing methods for low-value utilization of metallurgical slag waste alkali and treatment of phosphorus and fluorine wastewater.

[0008] To achieve the above objectives, the present invention first provides a method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate, comprising the following steps:

[0009] Step 1: Take metallurgical slag powder, mix it with binder and pore-forming agent by mechanical stirring, and then granulate it in a granulator. During the granulation process of 1 to 3 hours, add 100 to 500 mL of water for every 1000 g of metallurgical slag powder to obtain metallurgical slag waste alkali balls.

[0010] Step 2: After the metallurgical slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven for heat treatment to obtain shaped metallurgical slag waste alkali balls.

[0011] Furthermore, the metallurgical slag powder is any one of steel slag from iron and steel smelting, magnesium slag from magnesium smelting, and red mud; the binder is any one of sodium alginate, polyacrylic acid, and polyvinyl alcohol; and the pore-forming agent is any one of ammonium bicarbonate, ammonium carbonate, and sodium carbonate.

[0012] Furthermore, for every 1000 parts by weight of metallurgical slag powder, the following are respectively formulated: 8-12 parts of polyacrylic acid and 8-12 parts of ammonium bicarbonate, 20-25 parts of sodium alginate and 40-50 parts of sodium carbonate, and 20-30 parts of polyvinyl alcohol and 40-50 parts of sodium carbonate.

[0013] Furthermore, in step 2, the heat treatment in the oven is 300℃~600℃ for 3~6 hours.

[0014] Furthermore, in step 1, the rotation speed of the granulation process is 20-300 r / min.

[0015] The metallurgical slag waste alkali balls prepared by the method described above for treating phosphogypsum leachate have a particle size of 1-8 mm.

[0016] The application of the above-mentioned metallurgical slag alkali balls in the treatment of phosphogypsum leachate includes the following steps:

[0017] Metallurgical slag waste alkali balls are used to fill a fixed bed column with a diameter of 4 cm and a height of 25 cm to treat phosphogypsum leachate. The flow rate of the phosphogypsum leachate is 2 to 10 bed volumes / h.

[0018] Furthermore, in the treated phosphogypsum: the phosphorus concentration in the treated water is less than 0.5 mg / L, and the fluoride concentration is less than 10 mg / L.

[0019] Explanation of principles

[0020] In the current metal smelting industry, the most common metallurgical slags include steel slag, magnesium slag, and red mud. Due to the metal smelting process, these slags contain dicalcium silicate (C2S) or tricalcium silicate (C3S), which react with water to form a cross-linked CaO·SiO2·nH2O (CSH) gel. Because CSH gel itself is cross-linked, and metallurgical slag also contains a large amount of free calcium oxide and magnesium oxide, their hydration produces calcium hydroxide and magnesium hydroxide, resulting in a volume expansion of 90%–150%. This significantly interferes with the hydration process of the metallurgical slag and destroys its microscopic cross-linked structure. Therefore, directly using metallurgical slag to prepare spheres results in low structural strength, leading to cracking and fragmentation during water treatment, failing to solve the problem of easy slag loss.

[0021] On the other hand, the effective active components in the aforementioned industrial metallurgical slag are low, specifically the relative content of free alkaline oxides such as CaO, MgO, and Fe2O3 is low, and some of these alkaline oxides are encapsulated by inert matrices such as silicates. The reaction rate between these effective components in the metallurgical slag and phosphorus and fluorine in the phosphogypsum leachate is slow, or even negligible. Therefore, directly reacting the metallurgical slag with the phosphogypsum leachate results in low adsorption efficiency and fails to meet the requirements for harmless treatment.

[0022] Enhancing the structural stability of metallurgical slag when preparing spherical materials, while maintaining the internal pores of the slag balls, and comprehensively improving the adsorption and long-term effectiveness of metallurgical slag waste alkali balls in removing phosphorus and fluoride from wastewater, has become a pressing technical bottleneck that needs to be addressed.

[0023] This invention enhances the crosslinking density of the CSH gel network by introducing a binder, and simultaneously uses a pore-forming agent to regulate the connectivity of multi-level pores, thereby increasing the specific surface area of ​​the metallurgical slag waste alkali balls and optimizing the mass transfer efficiency, ultimately synergistically improving the phosphorus and fluorine curing performance and long-lasting effect of the metallurgical slag waste alkali balls.

[0024] This invention utilizes added metal oxides to increase the adsorption sites of metallurgical slag. Furthermore, the metallurgical slag and metal oxides are pre-activated in water to form more phosphorus- and fluoride-loving hydroxides, thereby enhancing the adsorption activity of the metallurgical slag waste alkali material and increasing the reaction rate between the metallurgical slag and soluble phosphorus and fluoride in phosphogypsum. This process is easy to scale up for later production and can achieve large-scale preparation of spherical solid waste materials, showing promising industrial application prospects.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention uniquely utilizes the characteristic that metallurgical slag waste alkali (steel slag, magnesium slag, red mud, etc.) is rich in alkaline oxides such as CaO, MgO, and Fe2O3, which have an affinity for phosphorus and fluorine, to prepare a molding material that can deeply treat phosphorus and fluorine wastewater, thereby realizing the high-value utilization of metallurgical slag waste alkali.

[0027] 2. This invention utilizes dicalcium silicate and tricalcium silicate in metallurgical slag to hydrate into CSH gel, which is then used to network metallurgical slag powder. By adding a binder, the cross-linking density of the gel network is enhanced, thereby improving the structural stability of the prepared metallurgical slag waste alkali balls.

[0028] 3. This invention utilizes a high-temperature decomposition method of pore-forming agent to create channels inside metallurgical slag waste alkali balls, thereby enhancing the flow of liquid in the fixed bed column. This method is economical and does not generate secondary pollution.

[0029] 4. The metallurgical slag waste alkali balls prepared by this invention have high structural stability and phosphorus and fluoride adsorption activity. They can maintain a stable structure for a long time in a fixed bed column, and can deeply adsorb and remove phosphorus and fluoride from wastewater, which can solve the problems of difficult separation and easy loss of powder materials. Attached Figure Description

[0030] Figure 1 The images show actual photos of the waste alkali balls prepared in Examples 12, 13, 14 and Comparative Example 1.

[0031] Figure 2 The Raman spectrum of the magnesium slag waste alkali ball material in Example 2;

[0032] Figure 3 The infrared spectrum of magnesium slag waste alkali ball material in Example 3. Detailed Implementation

[0033] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only used to illustrate the technical solution of the present invention and are not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are still within the protection scope of the present invention.

[0034] Example 1: Preparation of steel slag waste alkali balls - 1

[0035] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0036] Step 1: Take 1000g of steel slag powder, 10g of polyacrylic acid, and 10g of ammonium bicarbonate, mechanically mix them, and then place them in a granulator for granulation at a speed of 200r / min. Add 150mL of water during the 1h granulation process to obtain wet steel slag waste alkali balls.

[0037] Step 2: After the wet steel slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 6 hours to obtain the formed steel slag waste alkali balls-1.

[0038] Example 2: Preparation of steel slag waste alkali balls - 2

[0039] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0040] Step 1: Take 1000g of steel slag powder, 8g of polyacrylic acid, and 12g of ammonium bicarbonate, and mix them mechanically. Then, place them in a granulator and granulate them at a speed of 200r / min. Add 100mL of water during the 1.5h granulation process to obtain wet steel slag waste alkali balls.

[0041] Step 2: After the wet steel slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 6 hours to obtain shaped steel slag waste alkali balls.

[0042] Example 3: Preparation of steel slag waste alkali balls - 3

[0043] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0044] Step 1: Take 1000g of steel slag powder, 12g of polyacrylic acid, and 8g of ammonium bicarbonate, and mix them mechanically. Then, place them in a granulator and granulate them at a speed of 180r / min. Add 500mL of water during the 2h granulation process to obtain wet steel slag waste alkali balls.

[0045] Step 2: After the wet steel slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 6 hours to obtain shaped steel slag waste alkali balls.

[0046] Example 4: Preparation of steel slag alkali pellets - 4

[0047] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0048] Step 1: Take 1000g of steel slag powder, 20g of sodium alginate, and 40g of ammonium carbonate, mechanically mix them, and then place them in a granulator for granulation at a speed of 200r / min. Add 300mL of water during the 3h granulation process to obtain wet steel slag waste alkali balls.

[0049] Step 2: After the wet steel slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven and heat-treated at 350℃ for 5 hours to obtain shaped steel slag waste alkali balls.

[0050] Example 5: Preparation of steel slag alkali pellets - 5

[0051] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0052] Step 1: Take 1000g of steel slag powder, 25g of polyvinyl alcohol, and 50g of sodium carbonate, mechanically mix them, and then place them in a granulator for granulation at a speed of 50r / min. Add 500mL of water during the 1h granulation process to obtain wet steel slag waste alkali balls.

[0053] Step 2: After the wet steel slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 600℃ for 3 hours to obtain shaped steel slag waste alkali balls.

[0054] Example 6: Verification Test

[0055] 60g of the steel slag waste alkali balls prepared in Examples 1 to 5 were weighed and filled into a fixed bed column with a diameter of 4cm and a height of 25cm. Leachate from a phosphogypsum stockpile in Hubei Province was selected as the treatment target, with a phosphorus concentration of 1500mg / L and a fluoride concentration of 300mg / L. The flow rate was 20 bed volumes / h, and samples were taken every 30 minutes. The phosphorus concentration in the water was detected using a spectrophotometer according to the national standard for the determination of total phosphorus in water (GB 11893-1989). The experimental results are shown in Table 1 below. The fluoride concentration in the water was detected using ion chromatography according to the national standard for the detection of fluoride ions in water (GB 11894-2014). The experimental results are shown in Table 1 below.

[0056] Table 1. Phosphorus concentration of wastewater after treatment with waste alkali balls from different metallurgical slags

[0057]

[0058] Table 2. Fluorine concentration of wastewater after treatment with waste alkali balls from different metallurgical slags

[0059]

[0060] Example 7: Preparation of Red Mud Waste Alkali Balls - 1

[0061] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0062] Step 1: Take 1000g of red mud powder, 10g of polyacrylic acid, and 10g of ammonium bicarbonate, and mechanically mix them. Then, place them in a granulator and granulate them at a speed of 500r / min. Add 150mL of water during the 1h granulation process to obtain wet red mud waste alkali balls.

[0063] Step 2: After the wet red mud waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 6 hours to obtain shaped red mud waste alkali balls.

[0064] Example 8: Preparation of Red Mud Waste Alkali Balls - 2

[0065] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0066] Step 1: Take 1000g of red mud powder, 20g of sodium alginate, and 40g of ammonium carbonate, and mechanically mix them. Then, place them in a granulator for granulation at a speed of 100r / min. Add 200mL of water during the 1.5h granulation process to obtain wet red mud waste alkali balls.

[0067] Step 2: After the wet red mud waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 400℃ for 5 hours to obtain shaped red mud waste alkali balls.

[0068] Example 9: Preparation of Red Mud Waste Alkali Balls - 3

[0069] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0070] Step 1: Take 1000g of red mud powder, 25g of sodium alginate, and 50g of ammonium carbonate, and mechanically mix them. Then, place them in a granulator for granulation at a speed of 200r / min. Add 500mL of water during the 2h granulation process to obtain wet red mud waste alkali balls.

[0071] Step 2: After the wet red mud waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 5 hours to obtain shaped red mud waste alkali balls.

[0072] Example 10: Preparation of Red Mud Waste Alkali Balls - 4

[0073] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0074] Step 1: Take 1000g of red mud powder, 25g of polyvinyl alcohol, and 50g of sodium carbonate, mechanically stir and mix them, then place them in a granulator for granulation at a speed of 300r / min. Add 400mL of water during the 2h granulation process to obtain wet red mud waste alkali balls.

[0075] Step 2: After the wet red mud waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 600℃ for 5 hours to obtain shaped red mud waste alkali balls.

[0076] Example 11: Verification Test

[0077] 60g of the red mud waste alkali balls prepared in Examples 7-10 were weighed and filled into a fixed bed column with a diameter of 4cm and a height of 25cm. Leachate from a phosphogypsum stockpile in Hubei Province was selected as the treatment target, with a phosphorus concentration of 1500mg / L and a fluoride concentration of 300mg / L. The flow rate was 20 bed volumes / h, and samples were taken every 30 minutes. The phosphorus concentration in the effluent was detected using a spectrophotometer according to the national standard for the determination of total phosphorus in water (GB 11893-1989). The experimental results are shown in Table 3 below. The fluoride concentration in the effluent was detected using ion chromatography according to the national standard for the detection of fluoride ions in water (GB 11894-2014). The experimental results are shown in Table 4 below.

[0078] Table 3. Phosphorus concentration of wastewater after treatment with different red mud alkali balls

[0079] materials Red mud waste alkali ball-1 Red mud waste alkali ball-2 Red mud waste alkali balls-3 Red mud waste alkali balls-4 0 - - - - 30 0.32 0.48 0.22 0.18 60 0.48 0.86 0.39 0.37 90 0.97 1.38 0.48 0.87 120 1.99 4.28 0.91 1.35

[0080] Table 4. Fluorine concentration of wastewater after treatment with different red mud alkali balls

[0081] materials Red mud waste alkali ball-1 Red mud waste alkali ball-2 Red mud waste alkali balls-3 Red mud waste alkali balls-4 0 - - - - 30 6.4 5.3 3.2 2.9 60 9.2 12.5 7.2 6.5 90 15.8 19.7 9.8 8.8 120 22.3 29.4 15.3 10.2

[0082] Example 12: Preparation of magnesium slag waste alkali balls - 1

[0083] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0084] Step 1: Take 1000g of magnesium slag powder, 10g of polyacrylic acid, and 10g of ammonium bicarbonate, mechanically stir and mix them, then place them in a granulator for granulation. Add 150mL of water during the 1-hour granulation process to obtain wet magnesium slag waste alkali balls.

[0085] Step 2: After the wet magnesium slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 6 hours to obtain shaped magnesium slag waste alkali balls.

[0086] Example 13: Preparation of magnesium slag waste alkali balls - 2

[0087] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0088] Step 1: Take 1000g of magnesium slag powder, 20g of sodium alginate, and 40g of ammonium carbonate, mechanically stir and mix them, then place them in a granulator for granulation. Add 100mL of water during the 1-hour granulation process to obtain wet magnesium slag waste alkali balls.

[0089] Step 2: After the wet magnesium slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven and heat-treated at 300℃ for 6 hours to obtain shaped magnesium slag waste alkali balls.

[0090] Example 14: Preparation of magnesium slag waste alkali balls - 3

[0091] A method for preparing metallurgical slag alkali pellets includes the following steps:

[0092] Step 1: Take 1000g of magnesium slag powder, 30g of polyvinyl alcohol, and 50g of sodium carbonate, mechanically stir and mix them, then place them in a granulator for granulation. Add 200mL of water during the 1-hour granulation process to obtain wet magnesium slag waste alkali balls.

[0093] Step 2: After the wet magnesium slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 600℃ for 6 hours to obtain shaped magnesium slag waste alkali balls.

[0094] Example 15: Comparative Example 1: Preparation of magnesium slag waste alkali balls - 4

[0095] Step 1: Take 1000g of magnesium slag powder, place it in a granulator for granulation, and add 100mL of water during the 1h granulation process to obtain wet magnesium slag waste alkali balls;

[0096] Step 2: After the wet magnesium slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 500℃ for 6 hours to obtain shaped magnesium slag waste alkali balls.

[0097] Example 10: Preparation of Red Mud Waste Alkali Balls - 4 A method for preparing metallurgical slag alkali pellets includes the following steps: Step 1: Take 1000g of red mud powder, 25g of polyvinyl alcohol, and 50g of sodium carbonate, mechanically stir and mix them, then place them in a granulator for granulation at a speed of 300r / min. Add 400mL of water during the 2h granulation process to obtain wet red mud waste alkali balls. Step 2: After the wet red mud waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven at 600℃ for 5 hours to obtain shaped red mud waste alkali balls.

[0098] Taking magnesium slag as an example, the Raman and infrared spectra of the material after it was pelletized were measured, such as... Figure 2 and Figure 3 As shown, there are very obvious Si-O bond signals, indicating that the magnesium slag contains dicalcium silicate (C2S) or tricalcium silicate (C3S), which will react with water to form CaO·SiO2·nH2O (CSH) gel with cross-linking properties, which is beneficial to the formation of magnesium slag into spheres.

[0099] Example 16: Application of Example 3

[0100] 60g of each of the steel slag waste alkali balls-1, red mud waste alkali balls-1, and magnesium slag waste alkali balls-1 prepared in Examples 1, 7, and 12 were weighed and filled into a fixed bed column with a diameter of 4cm and a height of 25cm. Leachate from a phosphogypsum stockpile in Hubei Province was selected as the treatment target, with a phosphorus concentration of 1000mg / L and a fluoride concentration of 200mg / L. The flow rate was 20 bed volumes / h, and samples were taken every 20 minutes. The phosphorus concentration in the water was detected using a spectrophotometer according to the national standard for the determination of total phosphorus in water (GB 11893-1989). The experimental results are shown in Table 5 below. The fluoride concentration in the water was detected using ion chromatography according to the national standard for the detection of fluoride ions in water (GB 11894-2014). The experimental results are shown in Table 6 below.

[0101] Table 5. Phosphorus concentration of wastewater after treatment with waste alkali balls from different metallurgical slags

[0102] materials Steel slag waste alkali ball-1 Magnesium slag waste alkali ball-1 Red mud waste alkali ball-1 0 - - - 20 0.06 0.02 0.14 40 0.10 0.04 0.22 60 0.19 0.03 0.24 80 0.32 0.02 0.48 100 0.59 0.02 1.02 120 0.87 0.05 2.54 140 1.58 0.08 6.87 160 5.23 0.02 15.23 180 10.18 0.06 19.34

[0103] Table 6. Fluorine concentration of wastewater after treatment with waste alkali balls from different metallurgical slags

[0104] materials Steel slag waste alkali ball-1 Magnesium slag waste alkali ball-1 Red mud waste alkali ball-1 0 - - - 20 0.5 0.4 0.3 40 1.2 0.9 0.9 60 2.9 1.5 1.8 80 6.3 1.8 4.7 100 12.8 2.5 9.6 120 20.1 3.6 18.3 140 34.5 5.5 29.6 160 47.3 6.3 40.6 180 66.2 8.2 50.8

[0105] According to the "GB 8978-1996 Integrated Wastewater Discharge Standard", as shown in Tables 1 and 2, steel slag waste alkali balls, magnesium slag waste alkali balls, and red mud waste alkali balls all have the ability to remove phosphorus and fluoride. Among them, the magnesium slag waste alkali balls prepared in Example 12 have the best and longest-lasting phosphorus and fluoride removal effects, and can remove phosphorus from the leachate to below 0.5 mg / L and fluoride to below 10 mg / L.

[0106] Example 17: Application of Example 4

[0107] 60g of different types of magnesium slag waste alkali balls prepared in Examples 2 and 12-15 were weighed and filled into a fixed bed column with a diameter of 4cm and a height of 25cm. A phosphogypsum leachate from a phosphogypsum stockpile in Guizhou Province was selected as the treatment target, with a phosphorus concentration of 3000mg / L and a fluoride concentration of 1000mg / L. The phosphorus and fluoride concentrations in this phosphogypsum leachate were higher than those in the phosphogypsum leachate from Hubei Province. The flow rate of the leachate was set to 10 bed volumes / h, and samples were taken every 20 minutes. The phosphorus concentration in the water was detected using a spectrophotometer according to the national standard for the determination of total phosphorus in water (GB 11893-1989). The experimental results are shown in Table 7 below. The fluoride concentration in the water was detected using ion chromatography according to the national standard for the detection of fluoride ions in water (GB 11894-2014). The experimental results are shown in Table 8 below.

[0108] Table 7. Phosphorus concentration of wastewater after treatment with different magnesium slag waste alkali balls

[0109] materials Magnesium slag waste alkali ball-1 Magnesium slag waste alkali ball-2 Magnesium slag waste alkali ball-3 Magnesium slag waste alkali ball-4 0 - - - - 20 0.13 0.05 0.24 0.43 40 0.24 0.05 0.28 0.42 60 0.39 0.05 0.54 0.89 80 0.58 0.12 1.25 2.56 100 0.99 0.16 2.98 6.87 120 1.87 0.20 6.90 10.28 140 5.21 0.25 10.54 15.29 160 9.73 0.23 16.73 24.18 180 16.38 0.30 20.15 35.67

[0110] Table 8. Fluorine concentration of wastewater after treatment with different magnesium slag waste alkali balls

[0111]

[0112]

[0113] The magnesium slag alkali balls in Example 12 showed the best adsorption and removal effects for phosphorus and fluoride. In this example, the magnesium slag alkali balls-1,-2, and-3, which had pore-forming agents added during synthesis, exhibited significantly better phosphorus and fluoride removal effects than the magnesium slag alkali ball-4, which did not have pore-forming agents added.

[0114] Compared to Example 16, this embodiment has higher initial phosphorus and fluoride concentrations, resulting in better and longer-lasting phosphorus and fluoride removal effects. Furthermore, the effectiveness of the magnesium slag waste alkali balls in adsorbing and removing phosphorus and fluoride is related to the ball size. Magnesium slag waste alkali balls-2, with the smallest size, exhibit the best phosphorus and fluoride removal effects, effectively removing phosphorus concentrations from wastewater to below 0.5 mg / L and fluoride concentrations to below 10 mg / L for an extended period. Other sizes of magnesium slag waste alkali balls can also remove phosphorus and fluoride from wastewater to meet standards in a short time.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate, characterized in that... Includes the following steps: Step 1: Take metallurgical slag powder, mix it with binder and pore-forming agent by mechanical stirring, and then granulate it in a granulator. During the granulation process of 1 to 3 hours, add 100 to 500 mL of water for every 1000 g of metallurgical slag powder to obtain metallurgical slag waste alkali balls. Step 2: After the metallurgical slag waste alkali balls obtained in Step 2 are naturally air-dried, they are placed in an oven for heat treatment to obtain shaped metallurgical slag waste alkali balls.

2. The method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate as described in claim 1, characterized in that: The metallurgical slag powder is any one of steel slag from iron and steel smelting, magnesium slag from magnesium smelting, and red mud; the binder is any one of sodium alginate, polyacrylic acid, and polyvinyl alcohol; and the pore-forming agent is any one of ammonium bicarbonate, ammonium carbonate, and sodium carbonate.

3. The method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate as described in claim 1 or 2, characterized in that: For every 1000 parts by weight of metallurgical slag powder, the following are respectively formulated: 8-12 parts of polyacrylic acid and 8-12 parts of ammonium bicarbonate, 20-25 parts of sodium alginate and 40-50 parts of sodium carbonate, and 20-30 parts of polyvinyl alcohol and 40-50 parts of sodium carbonate.

4. The method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate as described in claim 3, characterized in that... In step 2, the heat treatment in the oven is 300℃~600℃ for 3~6 hours.

5. The method for preparing metallurgical slag alkali pellets for treating phosphogypsum leachate as described in claim 1, characterized in that... In step 1, the rotation speed of the granulation process is 20-300 r / min.

6. The metallurgical slag waste alkali pellets obtained by the preparation method of any one of claims 1 to 5 for treating phosphogypsum leachate have a particle size of 1 to 8 mm.

7. An application of the metallurgical slag alkali pellets as described in claim 6 in the treatment of phosphogypsum leachate, characterized in that... Includes the following steps: Metallurgical slag waste alkali balls are used to fill a fixed bed column with a diameter of 4 cm and a height of 25 cm to treat phosphogypsum leachate. The flow rate of the phosphogypsum leachate is 2 to 10 bed volumes / h.

8. The application of the metallurgical slag alkali pellets as described in claim 7 in the treatment of phosphogypsum leachate, characterized in that... In the treated phosphogypsum: the phosphorus concentration in the treated water is less than 0.5 mg / L, and the fluoride concentration is less than 10 mg / L.

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