Ardealite source harmless pollution treatment method

Abstract

The invention discloses an ardealite source harmless pollution treatment method, and relates to the technical field of industrial waste treatment.The ardealite source harmless pollution treatment method comprises the steps that a continuous reaction device is arranged at a discharge port of ardealite slurry produced by wet-process phosphoric acid, the solid-liquid mass-volume ratio of the ardealite slurry is adjusted to be 1: 2-1: 3, the temperature of the ardealite slurry is controlled to be 30-45 DEG C, and the temperature of the ardealite slurry is controlled to be 30-45 DEG C; and adding a composite phosphorus and fluorine removal agent of hydroxyapatite and magnesium oxide into the phosphogypsum slurry. The wet-process phosphoric acid production source continuous treatment mode is adopted, the defect of traditional treatment after stockpiling is abandoned, synchronous removal of phosphorus, fluorine, heavy metal, organic matter and other multi-element impurities is achieved through cooperative treatment, the pollutant migration path caused by rainwater leaching in the phosphogypsum stockpiling process is blocked from the source, and the production efficiency of phosphogypsum is improved. Therefore, the effect of controlling environmental pollution from the source is achieved, the pollution risk of soil and underground water is effectively avoided, meanwhile, land resources needed by stockpiling are saved, and the land occupation pressure of solid waste treatment in the phosphorus chemical industry is relieved.

Description

Technical Field

[0001] This invention relates to the field of industrial waste treatment technology, specifically a method for the harmless treatment of phosphogypsum pollution at its source. Background Technology

[0002] Phosphogypsum is a solid waste generated by phosphate chemical companies during the production of phosphoric acid and other chemicals using wet processes (decomposing phosphate rock with sulfuric acid, nitric acid, or hydrochloric acid). Typically, producing 1 ton of phosphoric acid generates 4-5 tons of phosphogypsum. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains free phosphoric acid, fluorides, phosphorus pentoxide, phosphates, and small amounts of heavy metals. Currently, my country's annual phosphogypsum emissions have exceeded 78 million tons, mainly disposed of through stockpiling. This not only occupies a large amount of land resources but also risks leaching pollutants into the soil and groundwater through rainwater, causing serious environmental pollution problems.

[0003] Existing technologies for the harmless treatment of phosphogypsum mostly adopt a stockpiling and subsequent treatment model, lacking efficient and synergistic treatment solutions for phosphogypsum slurry from the source of wet-process phosphoric acid production. Furthermore, existing treatment agents have a single function and cannot simultaneously and efficiently remove multiple impurities such as phosphorus, fluorine, heavy metals, and organic matter. This makes phosphogypsum susceptible to rainwater leaching during stockpiling, leading to pollutants seeping into the soil and groundwater. After treatment, the phosphogypsum crystal form is unstable and its performance varies greatly, making it difficult to accurately match resource utilization scenarios. This not only causes serious risks of soil and groundwater pollution but also results in low resource utilization rates and low added value of phosphogypsum. At the same time, stockpiling occupies a large amount of land resources, further exacerbating the environmental pressure and economic burden of solid waste disposal in the phosphorus chemical industry. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for the harmless treatment of phosphogypsum pollution at its source, solving the problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for harmless treatment of phosphogypsum pollution at its source, comprising the following steps: S1. A continuous reaction device is set up at the discharge port of the phosphogypsum slurry produced by wet-process phosphoric acid production. The solid-liquid mass-volume ratio of the phosphogypsum slurry is adjusted to 1:2-1:3, and the temperature of the phosphogypsum slurry is controlled at 30-45℃. A composite phosphorus and fluoride removal agent of hydroxyapatite and magnesium oxide is added to the phosphogypsum slurry, and a composite buffer of wood ash and calcium dihydrogen phosphate is added at the same time. The mixture is then stirred at a rate of 50-80 rpm for 30-45 min, and the pH of the reaction process is maintained at 2.5-3.0. After the reaction is completed, the phosphogypsum slurry is introduced into an adjustment tank, and low-pressure air is introduced and stirred for 10-15 min. The pH of the phosphogypsum slurry is adjusted to 4.0-5.0 to obtain a pretreated slurry. S2. A basic composite modifier is obtained by mixing iron-modified bentonite, polyphosphate bacteria and humic acid in a mass ratio of 10:3:2. The composite modifier is mixed with a composite adhesive in a mass ratio of 10:1 and stirred into a paste. The paste is then spray-granulated to form coated particles. The coated particles are added to the pretreated slurry and stirred at a constant temperature of 35-45℃ for 30-40 minutes. Then, the composite modified bentonite is added, and the stirring speed is adjusted to 100-120 rpm. The reaction is carried out at a pH of 3.5-5.0 for 20-30 minutes. At the end of the reaction, a calcium silicate crystal inducing agent is added, and stirring is continued for 10-15 minutes to obtain the reaction slurry. S3. The reaction slurry is fed into the curing reactor and heated to 50-60℃. A mixed crystalline guiding gas of carbon dioxide and nitrogen is introduced and kept at the temperature for 20-25 minutes. Then, the composite curing agent is added and stirred evenly. The mixture is first pre-cured at room temperature for 4-6 hours, and then transferred to the low-temperature steam curing stage. The curing temperature is controlled at 40-50℃, the relative humidity is ≥90%, and the curing time is 8-18 hours to allow impurities to form stable precipitates. After curing, the cured mixture is separated by pressure filtration to obtain a harmless phosphogypsum filter cake and a treatment liquid. The treatment liquid is filtered through quartz sand and returned to the equalization tank for recycling. S4. The phosphogypsum filter cake is subjected to a 28-day compressive strength test. Based on the strength difference, it is divided into three levels: high strength, medium strength and low strength. The three levels are then applied to different resource utilization applications.

[0006] Preferably, the mass ratio of hydroxyapatite to light magnesium oxide in the composite phosphorus and fluorine removal agent is 3:1-5:1, wherein the hydroxyapatite is in powder form with a particle size of 5-20 μm, and the purity of the light magnesium oxide is ≥92%.

[0007] Preferably, the composite buffer is prepared by mixing and grinding wood ash and calcium dihydrogen phosphate at a mass ratio of 2:1, and the particle size after grinding is ≤200μm.

[0008] Preferably, the composite modified bentonite is prepared by modifying bentonite through a combination of mercapto and aluminum, and the preparation method is as follows: After sodium treatment, calcium-based bentonite is soaked in a 5%–8% aluminum sulfate solution for 2–3 hours, filtered and dried, and then reacted with a 3%–5% mercaptosilane reagent at 60–70°C for 1.5–2 hours. After cooling, it is ground to a particle size ≤100μm to obtain the composite modified bentonite.

[0009] Preferably, the calcium silicate crystal form inducer is nano-calcium silicate modified with an aluminate coupling agent, and the calcium silicate crystal form inducer has a particle size ≤50nm and a purity ≥95%.

[0010] Preferably, the composite curing agent is obtained through a calcination activation treatment, specifically: Red mud was calcined at 600-700℃ for 2 hours to remove organic impurities. After cooling, it was mixed with cement clinker and slag powder in a certain proportion to obtain the composite curing agent. The mass ratio of red mud, cement clinker, and slag powder in the composite curing agent is 4:3:3.

[0011] Preferably, in step S4, the resource recovery of the phosphogypsum filter cake at the three levels adopts a standard reuse based on strength grading and performance adaptation, specifically as follows: High strength grade: Suitable for modification with 0.5%-1.0% polypropylene fiber, used in the production of high-strength gypsum building materials; Medium strength grade: Suitable for use with 1%-2% polymer waterproofing agent, and can be used as a cement retarder; Low strength grade: Suitable for use with 2%-3% fly ash expansion agent for ecological restoration filler.

[0012] Preferably, a micro-negative pressure gas collection hood is installed at the top of the regulating tank, the composite modified reactor, and the solidification reactor to pass the captured acidic tail gas into a dilute ammonia water absorption tower. The absorbed mixture is then reused in the regulating tank in step S1 for the treatment of the phosphogypsum slurry.

[0013] Preferably, the low-pressure air introduction rate in step S1 is 0.5-0.8 m / s. 3 / (m 2 •h), the stirring speed is 120-150 r / min, the amount of the composite phosphorus and fluoride removal agent added is 4%-6% of the dry weight of phosphogypsum in the phosphogypsum slurry, and the amount of the composite buffer added is 1%-2% of the dry weight of phosphogypsum in the phosphogypsum slurry; The amount of calcium silicate crystal inducing agent added is 0.5%-1.0% of the dry weight of phosphogypsum in the pretreated slurry, and the amount of composite curing agent added is 8%-12% of the dry weight of phosphogypsum in the reaction slurry.

[0014] Preferably, the composite adhesive in step S2 is a starch and sodium alginate composite adhesive, which is prepared by dissolving amylose and sodium alginate in deionized water at a mass ratio of 3:1, with a concentration of 5%-8%. The coated particles have a particle size of 0.5-1 mm and are added at a rate of 0.8%-1.2% of the dry weight of phosphogypsum in the pretreated slurry. The polyphosphate-accumulating agent is prepared by mixing *Pseudomonas* and *Pseudomonas putida* at a 1:1 ratio, with an effective viable count ≥5×10⁻⁶. 6 cfu / mL.

[0015] This invention provides a method for the harmless treatment of phosphogypsum pollution at its source. It has the following beneficial effects: (1) This invention adopts a continuous treatment mode at the source of wet phosphoric acid production, which eliminates the drawbacks of traditional stockpiling and subsequent treatment. Through synergistic treatment, it achieves the simultaneous removal of multiple impurities such as phosphorus, fluorine, heavy metals and organic matter, thereby blocking the migration path of pollutants caused by rainwater leaching during the stockpiling of phosphogypsum from the source, thus achieving the effect of controlling environmental pollution from the root, effectively avoiding the risk of soil and groundwater pollution, while saving the land resources required for stockpiling and alleviating the land occupation pressure of solid waste disposal in the phosphoric chemical industry.

[0016] (2) By integrating composite modification and crystal form regulation, the problem of the single function of existing treatment agents has been improved, the stable regulation of phosphogypsum crystal form has been achieved, the problem of unstable phosphogypsum crystal form and large performance difference after traditional treatment has been solved, the performance stability of phosphogypsum treatment products has been improved, and the treated phosphogypsum can be accurately matched with the needs of different resource utilization scenarios. This breaks through the limitation of low resource utilization rate of traditional treatment products and promotes the transformation of phosphogypsum from solid waste to highly adaptable resources.

[0017] (3) By constructing a closed-loop process for exhaust gas recovery, water resource recycling and graded resource utilization, the efficient reuse of materials and energy during the treatment process is guaranteed, the material consumption and secondary pollutant emissions during the treatment process are reduced, and the effect of synergistic promotion of environmental governance and resource utilization is achieved. This not only reduces the overall cost of harmless treatment of phosphogypsum, but also increases the added value of resource utilization products, effectively alleviates the environmental pressure and economic burden of solid waste disposal in the phosphate chemical industry, and helps the industry achieve green and sustainable development. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the steps of the method for harmlessly treating phosphogypsum pollution at its source according to the present invention. Figure 2 Line graphs showing the harmlessness index data of the embodiments and comparative examples of the present invention; Figure 3 This is a line graph showing the performance stability index data of the embodiments and comparative examples of the present invention; Figure 4 This is a line graph showing the environmental protection indicator data of the embodiments and comparative examples of the present invention. Detailed Implementation

[0019] 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.

[0020] Please see Figure 1 This invention provides a method for the harmless treatment of phosphogypsum pollution at its source. To achieve the above objectives, this invention employs the following technical solution, comprising the following steps: S1. A continuous reaction device is set up at the discharge port of the phosphogypsum slurry produced by wet-process phosphoric acid. The solid-liquid mass-volume ratio of the phosphogypsum slurry is adjusted to 1:2-1:3, and the temperature of the phosphogypsum slurry is controlled at 30-45℃. A composite phosphorus and fluoride removal agent of hydroxyapatite and magnesium oxide is added to the phosphogypsum slurry, and a composite buffer of wood ash and calcium dihydrogen phosphate is added at the same time. The mixture is then stirred at a rate of 50-80 rpm for 30-45 min, and the pH of the reaction process is maintained at 2.5-3.0. After the reaction is completed, the phosphogypsum slurry is introduced into the conditioning tank, and low-pressure air is introduced and stirred for 10-15 min. The pH of the phosphogypsum slurry is adjusted to 4.0-5.0 to obtain the pretreated slurry. S2. Iron-modified bentonite, polyphosphate-producing bacteria and humic acid are mixed in a mass ratio of 10:3:2 to obtain a basic composite modifier. The composite modifier and composite adhesive are mixed in a mass ratio of 10:1 and stirred into a paste. The paste is then spray-granulated to form coated particles. The coated particles are added to the pretreated slurry and stirred at a constant temperature of 35-45℃ for 30-40 minutes. Then, the composite modified bentonite is added and the stirring speed is adjusted to 100-120 rpm. The reaction is carried out at a pH of 3.5-5.0 for 20-30 minutes. At the end of the reaction, calcium silicate crystal inducing agent is added and stirring is continued for 10-15 minutes to obtain the reaction slurry. S3. The reaction slurry is fed into the curing reactor and heated to 50-60℃. A mixed crystalline guiding gas of carbon dioxide and nitrogen is introduced and kept at the temperature for 20-25 minutes. Then, the composite curing agent is added and stirred evenly. The mixture is first pre-cured at room temperature for 4-6 hours, and then transferred to the low-temperature steam curing stage. The curing temperature is controlled at 40-50℃ and the relative humidity is ≥90%. The curing time is 8-18 hours to allow impurities to form stable precipitates. After curing, the cured mixture is separated by pressure filtration to obtain harmless phosphogypsum filter cake and treatment liquid. The harmless phosphogypsum filter cake is obtained, and the treatment liquid is returned to the equalization tank for recycling after being filtered by quartz sand. S4. The phosphogypsum filter cake is subjected to 28-day compressive strength testing and divided into three grades according to the strength difference: high strength, medium strength and low strength. The three grades are then applied to different resource utilization applications according to their differences.

[0021] The mass ratio of hydroxyapatite to light magnesium oxide in the composite phosphorus and fluorine removal agent is 3:1-5:1, wherein the hydroxyapatite is in powder form with a particle size of 5-20μm, and the purity of the light magnesium oxide is ≥92%.

[0022] The composite buffer is made by grinding wood ash and calcium dihydrogen phosphate in a mass ratio of 2:1, and the particle size after grinding is ≤200μm.

[0023] The composite modified bentonite is prepared by modifying bentonite through the composite modification of mercapto and aluminum. The preparation method is as follows: After sodium treatment, calcium-based bentonite is soaked in a 5%–8% aluminum sulfate solution for 2–3 hours, filtered and dried, and then reacted with a 3%–5% mercaptosilane reagent at 60–70°C for 1.5–2 hours. After cooling, it is ground to a particle size ≤100μm to obtain composite modified bentonite.

[0024] The calcium silicate crystal form inducer is nano-calcium silicate modified with an aluminate coupling agent. The calcium silicate crystal form inducer has a particle size ≤50nm and a purity ≥95%.

[0025] The composite curing agent is prepared by calcination activation treatment, specifically as follows: Red mud was calcined at 600-700℃ for 2 hours to remove organic impurities. After cooling, it was mixed with cement clinker and slag powder in a certain proportion to obtain a composite curing agent. The mass ratio of red mud, cement clinker, and slag powder in the composite curing agent is 4:3:3.

[0026] In step S4, the resource utilization of the three grades of phosphogypsum filter cake adopts a standard of strength grading and performance adaptation for reuse, specifically as follows: High strength grade: Suitable for modification with 0.5%-1.0% polypropylene fiber, used in the production of high-strength gypsum building materials; Medium strength grade: Suitable for use with 1%-2% polymer waterproofing agent, and can be used as a cement retarder; Low strength grade: Suitable for use with 2%-3% fly ash expansion agent for ecological restoration filler.

[0027] A micro-negative pressure gas collection hood is installed at the top of the equalization tank, the composite modified reactor, and the solidification reactor. The captured acidic tail gas is passed into a dilute ammonia water absorption tower. The absorbed mixture is reused in the equalization tank in step S1 for the treatment of phosphogypsum slurry.

[0028] In step S1, the low-pressure air is introduced at a rate of 0.5-0.8 m / s. 3 / (m 2 •h), the stirring speed is 120-150 r / min, the amount of compound phosphorus and fluoride removal agent added is 4%-6% of the dry weight of phosphogypsum in the phosphogypsum slurry, and the amount of compound buffer added is 1%-2% of the dry weight of phosphogypsum in the phosphogypsum slurry; The amount of calcium silicate crystal inducing agent added is 0.5%–1.0% of the dry weight of phosphogypsum in the pretreated slurry, and the amount of composite curing agent added is 8%–12% of the dry weight of phosphogypsum in the reaction slurry.

[0029] In step S2, the composite adhesive is a starch and sodium alginate composite adhesive, which is made by dissolving amylose and sodium alginate in deionized water at a mass ratio of 3:1, with a concentration of 5%-8%. The particle size of the coated particles is 0.5-1 mm, and the addition amount is 0.8%-1.2% of the dry weight of phosphogypsum in the pretreated slurry; Polyphosphate-accumulating bacteria are prepared by mixing *Pseudomonas* and *Pseudomonas putida* in a 1:1 ratio, with an effective viable count ≥ 5 × 10⁻⁶. 6 cfu / mL.

[0030] Unless otherwise specified, all raw materials used in this invention are commercially available products well known to those skilled in the art.

[0031] Example 1 A continuous reaction device is set up at the discharge port of phosphogypsum slurry produced by wet-process phosphoric acid. Fresh phosphogypsum slurry (30% dry basis content) discharged from this port is taken, and its solid-liquid mass-volume ratio is adjusted to 1:2.5. The slurry temperature is controlled at 38℃. A composite phosphorus and fluoride removal agent with a mass ratio of hydroxyapatite to light magnesium oxide of 4:1 is added to the slurry. The hydroxyapatite is in powder form with a particle size of 12μm, and the light magnesium oxide has a purity of 95%. The amount added is 5% of the dry weight of phosphogypsum. At the same time, a composite buffer agent with a mass ratio of wood ash to calcium dihydrogen phosphate of 2:1 and ground to a particle size of 150μm is added. The amount added is 1.5% of the dry weight of phosphogypsum. The reaction was stirred at 65 rpm for 38 minutes, and the pH was maintained at 2.8 by adding dilute phosphoric acid dropwise. After the reaction was completed, the slurry was introduced into an equalization tank at a rate of 0.65 m³ / min. 3 / (m 2 Low-pressure air is introduced at a rate of h), and the mixture is stirred at 135 rpm for 12 min. Dilute ammonia is added dropwise to adjust the pH of the slurry to 4.5, thus obtaining the pretreated slurry. Iron-modified bentonite and polyphosphate-rich bacteria (effective viable count 5×10⁻⁶) were mixed in a mass ratio of 10:3:2. 6 The basic composite modifier was obtained by mixing (cfu / mL) and humic acid, and the composite adhesive was prepared by dissolving amylose and sodium alginate in deionized water at a mass ratio of 3:1 to prepare a 6% starch-sodium alginate composite adhesive. The basic composite modifier and the composite adhesive were mixed at a mass ratio of 10:1 and stirred into a uniform paste. Then, the coated particles with a particle size of 0.8 mm were prepared by spray granulation. The coated particles were added to the pretreated slurry at a rate of 1.0% of the dry weight of phosphogypsum. The mixture was stirred at a constant temperature of 38°C for 35 min. Then, composite modified bentonite was added at a rate of 4% of the dry weight of phosphogypsum. The composite modified bentonite was prepared by soaking calcium-based bentonite in a 6% aluminum sulfate solution for 2.5 h after sodium treatment, filtering and drying, and then reacting it with a 4% mercaptosilane reagent at 65°C for 1.8 h. After cooling, the mixture was ground to a particle size of 80 μm. Adjust the stirring speed to 110 rpm, maintain the pH at 4.2 and react for 25 min; at the end of the reaction, add nano-calcium silicate crystal form inducer modified with aluminate coupling agent, with a particle size of 30 nm and a purity of 97%, and add 0.75% of the dry weight of phosphogypsum, and continue stirring for 12 min to obtain the reaction slurry. The reaction slurry was fed into a solidification reactor and heated to 55°C. A mixed crystalline guiding gas with a carbon dioxide to nitrogen volume ratio of 1:5 was then introduced at a gas introduction rate of 0.25 m / s. 3 / (m 2 •h), keep warm and stand for 22min; then add composite curing agent, the amount of which is 10% of the dry weight of phosphogypsum. The preparation method of composite curing agent is as follows: calcine red mud at 650℃ for 2h to remove organic impurities, and after cooling, mix it with 42.5 grade cement clinker with a specific surface area of ​​450m². 2 / kg of slag powder is mixed at a mass ratio of 4:3:3; After mixing evenly, the mixture is pre-cured at room temperature for 5 hours, and then transferred to the low-temperature steam curing stage. The curing temperature is controlled at 45℃ and the relative humidity at 95%, and the curing time is 13 hours, so that the impurities form stable precipitates. After curing, the mixture is sent to a plate and frame filter press and filtered at 0.7MPa pressure for 28 minutes to obtain harmless phosphogypsum filter cake and treatment liquid. The treatment liquid is returned to the equalization tank for recycling after being filtered by quartz sand. The phosphogypsum filter cake was cured in a standard curing environment for 28 days and then subjected to compressive strength testing. Based on the strength differences, it was divided into three grades: high strength (compressive strength ≥15MPa), medium strength (compressive strength 8-15MPa), and low strength (compressive strength <8MPa). The high strength grade was modified with 0.8% polypropylene fiber and used in the production of high-strength gypsum building materials. The medium strength grade was modified with 1.5% polymer waterproofing agent and used as a cement retarder. The low strength grade was modified with 2.5% fly ash expansion agent and used as an ecological restoration filler.

[0032] Example 2 A continuous reaction device was set up at the discharge port of the phosphogypsum slurry produced by wet-process phosphoric acid. Fresh phosphogypsum slurry was taken and the solid-liquid mass-to-volume ratio was adjusted to 1:2. The temperature was controlled at 30℃. A composite phosphorus and fluoride removal agent with a mass ratio of hydroxyapatite and light magnesium oxide of 3:1 (hydroxyapatite particle size 5μm, light magnesium oxide purity 92%) was added at 4% of the dry weight of the phosphogypsum. At the same time, a composite buffer with a mass ratio of wood ash and calcium dihydrogen phosphate of 2:1 (particle size 200μm) was added at 1% of the dry weight of the phosphogypsum. The reaction was stirred at 50 rpm for 30 min, maintaining the pH at 2.5. After the reaction was completed, the slurry was introduced into an equalization tank at a flow rate of 0.5 m³ / min. 3 / (m 2 •h) Introduce low-pressure air, stir at 120 rpm for 10 min, adjust pH to 4.0, and obtain pretreated slurry; Iron-modified bentonite and polyphosphate-rich bacteria (effective viable count 5×10⁻⁶) were mixed in a mass ratio of 10:3:2. 6 The basic composite modifier was obtained by mixing phosphogypsum (cfu / mL) and humic acid. The basic composite modifier was then mixed with a 5% starch and sodium alginate composite adhesive at a mass ratio of 10:1. The mixture was spray-granulated to form coated particles with a particle size of 0.5 mm. The amount added was 0.8% of the dry weight of phosphogypsum. The mixture was stirred at a constant temperature of 35°C for 30 min. Subsequently, composite modified bentonite was added at a rate of 3% of the dry weight of phosphogypsum. The preparation method of composite modified bentonite was as follows: after sodium-modified calcium-based bentonite, it was soaked in 5% aluminum sulfate solution for 2 hours, filtered and dried, and then reacted with 3% mercaptosilane reagent at 60℃ for 1.5 hours. After cooling and grinding, the particle size was adjusted to 100 μm, the stirring speed was adjusted to 100 rpm, and the pH was maintained at 3.5 for 20 minutes. At the end of the reaction, a calcium silicate crystal inducing agent with a particle size of 50 nm and a purity of 95% was added at a rate of 0.5% of the dry weight of phosphogypsum. The mixture was stirred for another 10 minutes to obtain the reaction slurry. The reaction slurry was fed into a curing reactor, heated to 50°C, and a mixture of carbon dioxide and nitrogen in a volume ratio of 1:4 was introduced. The mixture was kept at this temperature and allowed to stand for 20 minutes. A composite curing agent was then added, at a rate of 8% of the dry weight of the phosphogypsum. The composite curing agent was prepared by calcining red mud at 600°C for 2 hours and mixing it with 42.5 grade cement clinker with a specific surface area of ​​400 m². 2 / kg of slag powder is mixed in a ratio of 4:3:3, stirred evenly, and then pre-cured at room temperature for 4 hours. Then it is transferred to an environment of 40℃ and 90% relative humidity for 8 hours. The phosphogypsum filter cake and treatment liquid are obtained by pressure filtration and separation. The treatment liquid is recycled. After curing the phosphogypsum filter cake for 28 days, its compressive strength was tested, and it was then graded and applied for resource utilization according to the corresponding plan.

[0033] Example 3 Step S1: A continuous reaction device is set up at the discharge port of the phosphogypsum slurry produced by wet-process phosphoric acid. Fresh phosphogypsum slurry is taken and the solid-liquid mass-volume ratio is adjusted to 1:3. The temperature is controlled at 45℃. A composite phosphorus and fluoride removal agent with a mass ratio of hydroxyapatite and light magnesium oxide of 5:1 (hydroxyapatite particle size 20μm, light magnesium oxide purity 98%) is added at 6% of the dry weight of the phosphogypsum. At the same time, a composite buffer with a mass ratio of wood ash and calcium dihydrogen phosphate of 2:1 and a particle size of 100μm is added at 2% of the dry weight of the phosphogypsum. The mixture is stirred at 80 rpm for 45 min, maintaining the pH at 3.0. After the reaction is completed, the slurry is introduced into an equalization tank at a flow rate of 0.8 m³ / min. 3 / (m 2 •h) Introduce low-pressure air, stir at 150 rpm for 15 min, adjust pH to 5.0, and obtain pretreated slurry; Iron-modified bentonite and polyphosphate-rich bacteria (effective viable count 10×10⁶) were mixed in a mass ratio of 10:3:2. 6 The basic composite modifier was prepared by mixing phosphogypsum (cfu / mL) and humic acid. The basic composite modifier was then mixed with 8% starch-sodium alginate composite adhesive at a mass ratio of 10:1. The mixture was spray-granulated to form coated particles with a particle size of 1.0 mm. The amount added was 1.2% of the dry weight of phosphogypsum. The mixture was stirred at 45℃ for 40 min. Then, composite modified bentonite was added at a mass ratio of 5% of the dry weight of phosphogypsum. The preparation method of composite modified bentonite was as follows: after sodium-modified calcium-based bentonite, it was soaked in 8% aluminum sulfate solution for 3 h, filtered and dried, and then reacted with 5% mercaptosilane reagent at 70℃ for 2 h. After cooling and grinding, the particle size was reduced to 50 μm. The stirring speed was adjusted to 120 rpm, and the pH was maintained at 5.0 for 30 min. At the end of the reaction, calcium silicate crystal inducing agent with a particle size of 20 nm and a purity of 99% was added at a mass ratio of 1.0% of the dry weight of phosphogypsum. The mixture was stirred for another 15 min to obtain the reaction slurry. Step S3: The reaction slurry is fed into the curing reactor, heated to 60℃, and a mixture of carbon dioxide and nitrogen in a volume ratio of 1:6 is introduced. The mixture is kept at this temperature and allowed to stand for 25 minutes. A composite curing agent is then added, with the addition amount being 12% of the dry weight of the phosphogypsum. The composite curing agent is prepared by calcining red mud at 700℃ for 2 hours, and then mixing it with 42.5 grade cement clinker with a specific surface area of ​​500 m². 2 / kg of slag powder is mixed in a 4:3:3 ratio, stirred evenly, and then pre-cured at room temperature for 6 hours. It is then transferred to an environment of 50℃ and 98% relative humidity for 18 hours. The phosphogypsum filter cake and treatment liquid are obtained by pressure filtration and separation. The treatment liquid is recycled.

[0034] After curing the phosphogypsum filter cake for 28 days, its compressive strength was tested, and it was then graded and applied for resource utilization according to the corresponding plan.

[0035] Comparative Example 1 The phosphogypsum slurry produced by wet-process phosphoric acid was directly stored for 7 days. The stored phosphogypsum was then mixed with water to adjust the solid-liquid mass-volume ratio to 1:2.5, and the temperature was controlled at 38°C. The subsequent addition of composite phosphorus removal agent and composite buffer, as well as the stirring parameters, were the same as in Example 1. After the reaction was completed, the mixture was introduced into an adjustment tank, and the remaining steps were exactly the same as in Example 1.

[0036] Comparative Example 2 involved mixing and granulating the basic composite modifier with the composite adhesive, and then directly adding the uncoated basic composite modifier to the pretreated slurry in the same amount as in Example 1. The remaining steps were exactly the same as in Example 1.

[0037] Comparative Example 3 Without introducing a mixed crystalline guiding gas of carbon dioxide and nitrogen, the composite curing agent is directly added after heat preservation and standing. After curing, the filter cake is obtained by pressure filtration. Without grading the compressive strength after 28 days, it is directly used for the production of single gypsum building materials. The remaining steps are exactly the same as in Example 1.

[0038] Test case The phosphogypsum filter cakes treated in Examples 1-3 and Comparative Examples 1-3, as well as related pollution control indicators, were tested. Harmlessness indicators: The soluble phosphorus content in the filter cake was detected by the molybdenum antimony spectrophotometric method, the fluoride content was detected by the ion-selective electrode method, and the cadmium and lead heavy metal content was detected by atomic absorption spectrophotometry. Performance stability indicators: The 28-day compressive strength of the filter cake was tested using a pressure testing machine, and the moisture absorption and reabsorption rate of the filter cake was tested using a constant temperature and humidity chamber method. Environmental indicators: The amount of exhaust gas emitted during the treatment process is detected using gas detection tubes, and the recycling rate of the treated liquid is calculated; Resource adaptability index: Observe whether the product performance of filter cake of different strength grades meets the standards for resource utilization application scenarios; Table 1 shows the pollutant content of the filter cake from the harmless treatment of phosphogypsum (refer to...). Figure 2 ): ; Note: Industrial solid waste Class I standard limits: soluble phosphorus content ≤0.01%, fluoride content ≤0.1 mg / L, cadmium content ≤0.01 mg / kg, lead content ≤0.1 mg / kg Table 2 shows the performance stability and environmental indicators of the harmless treatment of phosphogypsum (refer to...). Figure 3 , 4 ): ; Table 3 shows the resource utilization suitability indicators for filter cake after harmless treatment of phosphogypsum: ; From Tables 1, 2, and 3, we can see that: The test results of Examples 1-3 show that the treatment process of the present invention can effectively remove soluble phosphorus, fluoride and heavy metal impurities from phosphogypsum. The filter cake indexes after treatment are all far below the Class I standard limit for industrial solid waste. Among them, Example 1 has the best treatment effect, which takes into account the treatment effect, cost and resource utilization adaptability. The results of Comparative Example 1 show that abandoning the continuous reaction device at the source and adopting the stockpiling and post-treatment mode will lead to the migration and leakage of impurities in phosphogypsum, resulting in excessive indicators after treatment and poor performance stability, proving that continuous treatment at the source is the core prerequisite for achieving harmlessness. The results of Comparative Example 2 show that adding modifier directly without using coated particles reduces the effectiveness of the modifier, resulting in lower filter cake strength. This indicates that the structural design of the coated particles can improve the utilization rate of the modifier and ensure the performance of the filter cake. The results of Comparative Example 3 show that removing the crystal-guided gas and the graded resource utilization steps leads to large fluctuations in filter cake strength and poor resource utilization adaptability, proving that crystal form regulation and graded application are key technical features for achieving high-value-added utilization of phosphogypsum. In summary, this invention achieves the harmless and high-value utilization of phosphogypsum through the synergistic effects of continuous source treatment, coated particle composite modification, crystal-guided solidification, and graded resource utilization, and has significant technical advantages and reusability.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for harmlessly treating phosphogypsum pollution at its source, characterized in that: Includes the following steps: S1. A continuous reaction device is set up at the discharge port of the phosphogypsum slurry produced by wet-process phosphoric acid production. The solid-liquid mass-volume ratio of the phosphogypsum slurry is adjusted to 1:2-1:3, and the temperature of the phosphogypsum slurry is controlled at 30-45℃. A composite phosphorus and fluoride removal agent of hydroxyapatite and magnesium oxide is added to the phosphogypsum slurry, and a composite buffer of wood ash and calcium dihydrogen phosphate is added at the same time. The mixture is then stirred at a rate of 50-80 rpm for 30-45 min, and the pH of the reaction process is maintained at 2.5-3.

0. After the reaction is completed, the phosphogypsum slurry is introduced into an adjustment tank, and low-pressure air is introduced and stirred for 10-15 min. The pH of the phosphogypsum slurry is adjusted to 4.0-5.0 to obtain a pretreated slurry. S2. A basic composite modifier is obtained by mixing iron-modified bentonite, polyphosphate bacteria and humic acid in a mass ratio of 10:3:

2. The composite modifier is mixed with a composite adhesive in a mass ratio of 10:1 and stirred into a paste. The paste is then spray-granulated to form coated particles. The coated particles are added to the pretreated slurry and stirred at a constant temperature of 35-45℃ for 30-40 minutes. Then, the composite modified bentonite is added, and the stirring speed is adjusted to 100-120 rpm. The reaction is carried out at a pH of 3.5-5.0 for 20-30 minutes. At the end of the reaction, a calcium silicate crystal inducing agent is added, and stirring is continued for 10-15 minutes to obtain the reaction slurry. S3. The reaction slurry is fed into the curing reactor and heated to 50-60℃. A mixed crystalline guiding gas of carbon dioxide and nitrogen is introduced and kept at the temperature for 20-25 minutes. Then, the composite curing agent is added and stirred evenly. The mixture is first pre-cured at room temperature for 4-6 hours, and then transferred to the low-temperature steam curing stage. The curing temperature is controlled at 40-50℃, the relative humidity is ≥90%, and the curing time is 8-18 hours to allow impurities to form stable precipitates. After curing, the cured mixture is separated by pressure filtration to obtain a harmless phosphogypsum filter cake and a treatment liquid. The treatment liquid is filtered through quartz sand and returned to the equalization tank for recycling. S4. The phosphogypsum filter cake is subjected to a 28-day compressive strength test. Based on the strength difference, it is divided into three levels: high strength, medium strength and low strength. The three levels are then applied to different resource utilization applications.

2. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: The mass ratio of hydroxyapatite to light magnesium oxide in the composite phosphorus and fluorine removal agent is 3:1-5:1, wherein the hydroxyapatite is in powder form with a particle size of 5-20μm, and the purity of the light magnesium oxide is ≥92%.

3. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: The composite buffer is prepared by grinding wood ash and calcium dihydrogen phosphate in a mass ratio of 2:1, and the particle size after grinding is ≤200μm.

4. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: The composite modified bentonite is prepared by modifying bentonite through a combination of mercapto and aluminum, and its preparation method is as follows: After sodium treatment, calcium-based bentonite is soaked in a 5%–8% aluminum sulfate solution for 2–3 hours, filtered and dried, and then reacted with a 3%–5% mercaptosilane reagent at 60–70°C for 1.5–2 hours. After cooling, it is ground to a particle size ≤100μm to obtain the composite modified bentonite.

5. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: The calcium silicate crystal form inducer is nano-calcium silicate modified with an aluminate coupling agent, and the calcium silicate crystal form inducer has a particle size ≤50nm and a purity ≥95%.

6. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: The composite curing agent is prepared by calcination activation treatment, specifically as follows: Red mud was calcined at 600-700℃ for 2 hours to remove organic impurities. After cooling, it was mixed with cement clinker and slag powder in a certain proportion to obtain the composite curing agent. The mass ratio of red mud, cement clinker, and slag powder in the composite curing agent is 4:3:

3.

7. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: In step S4, the resource utilization of phosphogypsum filter cake at the three levels adopts a standard reuse based on strength grading and performance adaptation, specifically as follows: High strength grade: Suitable for modification with 0.5%-1.0% polypropylene fiber, used in the production of high-strength gypsum building materials; Medium strength grade: Suitable for use with 1%-2% polymer waterproofing agent, and can be used as a cement retarder; Low strength grade: Suitable for use with 2%-3% fly ash expansion agent for ecological restoration filler.

8. The method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: A micro-negative pressure gas collection hood is installed at the top of the conditioning tank, the composite modified reactor, and the solidification reactor. The captured acidic tail gas is passed into a dilute ammonia water absorption tower. The absorbed mixture is reused in the conditioning tank in step S1 to treat the phosphogypsum slurry.

9. A method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: In step S1, the low-pressure air is introduced at a rate of 0.5-0.8 m / s. 3 / (m 2 •h), the stirring speed is 120-150 r / min, the amount of the composite phosphorus and fluoride removal agent added is 4%-6% of the dry weight of phosphogypsum in the phosphogypsum slurry, and the amount of the composite buffer added is 1%-2% of the dry weight of phosphogypsum in the phosphogypsum slurry; The amount of calcium silicate crystal inducing agent added is 0.5%-1.0% of the dry weight of phosphogypsum in the pretreated slurry, and the amount of composite curing agent added is 8%-12% of the dry weight of phosphogypsum in the reaction slurry.

10. A method for harmless treatment of phosphogypsum pollution at its source according to claim 1, characterized in that: The composite adhesive mentioned in step S2 is a starch and sodium alginate composite adhesive, which is made by dissolving amylose and sodium alginate in deionized water at a mass ratio of 3:1, with a concentration of 5%-8%. The coated particles have a particle size of 0.5-1 mm and are added at a rate of 0.8%-1.2% of the dry weight of phosphogypsum in the pretreated slurry. The polyphosphate-accumulating agent is prepared by mixing *Pseudomonas* and *Pseudomonas putida* at a 1:1 ratio, with an effective viable count ≥5×10⁻⁶. 6 cfu / mL.

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