CN118290048A - A high water resistance and low toxicity phosphogypsum curing agent and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of curing agents, and discloses a phosphogypsum curing agent with high water resistance and low toxicity, the components of which include ground phosphorus slag, calcined red sandstone powder, a binder, a waterproofing agent, and a toxicity reducing agent. The binder includes sodium alginate, cement kiln dust, red mud, alum stone powder, sodium silicate powder, agar and the like, which are mixed and ground. The waterproofing agent is a composite of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide. The toxicity reducing agent is a mixture of petroleum coke desulfurization ash, slaked lime and carbide slag. The curing agent is applied to curing phosphogypsum. The unconfined compressive strength of the cured phosphogypsum roadbed material sample is greatly improved, the softening coefficient is up to 0.8 or more, the leaching concentration of fluorine and phosphorus can meet the first-level limit of GB 8978-1996 "Comprehensive Sewage Discharge Standard", the curing effect is remarkable, the process is simple, energy-saving and environmentally friendly, and the curing effect is broad.

Description

A high water resistance and low toxicity phosphogypsum curing agent and preparation method thereof

Technical Field

The invention relates to a phosphogypsum curing agent with high water resistance and low toxicity, and applies the same to curing phosphogypsum roadbed materials, and studies the performance changes of phosphogypsum roadbed material samples before and after curing.

Background technique

Phosphogypsum (PG) is a byproduct produced by chemical plants when phosphoric acid is produced by wet process using phosphate lime and sulfuric acid. Its main component is CaSO ₄ ·2H ₂ O, which accounts for more than 90% of its total components. In addition, phosphogypsum also contains phosphorus, fluorine, organic matter and other impurities. Every ton of phosphoric acid produced will produce 4.5-5.5 tons of phosphogypsum. In recent years, the production of phosphogypsum in China has increased year by year, while the increase in utilization has been relatively slow. The phosphogypsum piled in the open air has caused pollution to the soil, atmosphere and water system due to wind erosion and rain erosion, which not only reduces the yield and quality of crops, but also affects the health of local residents, causing inestimable losses. A large number of studies have been carried out at home and abroad on the comprehensive utilization of phosphogypsum. At present, a large number of potential application pathways have been proposed. Among them, the more mature utilization pathways mainly include ecological restoration and mine filling, agricultural soil improvement, building materials, cement industry, phosphogypsum building materials and other fields. Although it has alleviated the pollution of phosphogypsum to the environment to a certain extent, the large-scale comprehensive utilization of phosphogypsum is difficult to achieve due to the scattered phosphate resources in my country, the small scale of most phosphate fertilizer enterprises, and the defects in the utilization technology of phosphogypsum. Therefore, a new technology is urgently needed to deal with these large amounts of waste phosphogypsum. Compared with other application fields, the use of phosphogypsum in the road industry has a large workload and high consumption of phosphogypsum, which can solve the problem of large accumulation of phosphogypsum inventory. In addition, if phosphogypsum is used in road construction, it can not only consume a large amount of phosphogypsum, but also greatly reduce the construction cost of the road, with significant social and economic benefits. However, in the phosphogypsum road industry, whether phosphogypsum is used in road subgrade fillers or road base materials, its strength and durability must be considered, because phosphogypsum and its products have low mechanical strength, poor water stability, strong water absorption, soften when exposed to water, and greatly reduce strength. At the same time, there is also the problem of environmental pollution caused by the dissolution of fluorine and phosphorus in phosphogypsum. These are the critical problems currently faced by the application of phosphogypsum in the road industry, and are also the research purpose and direction of phosphogypsum soil stabilizers. Therefore, the research on phosphogypsum soil stabilizers has broad application prospects and commercial value.

At present, many scholars in my country have also carried out research on the resource utilization of phosphogypsum in the road industry. Most of them focus on using a small amount of phosphogypsum as a retarder for cement, or adding a small amount of phosphogypsum as a composite cementitious material to provide sulfate for the formation of calcium sulfoxide, or using phosphogypsum as a lightweight aggregate to replace part of the crushed stone. However, there are few studies on the direct solidification of original phosphogypsum. In the existing literature, only Ji Xiaoping, Zhang Houji and others have carried out research on phosphogypsum curing agent. However, the CA curing agent studied by Ji Xiaoping and others is used to stabilize the phosphogypsum roadbed filler. The content of sodium methyl silicate in the curing agent reaches 85%, which makes the actual engineering cost too high and is not conducive to actual use; the weight percentage of each raw material in lime, red mud and phosphogypsum in the cured phosphogypsum roadbed filler studied by Zhang Houji and others is: lime 4-15%, red mud 30-50%, phosphogypsum 35-60%, and the maximum amount of phosphogypsum can only reach 60%, and it is impossible to use phosphogypsum in large quantities to solve the problem of phosphogypsum accumulation.

The phosphorus slag used in the present invention is commercially available, with a specific surface area of ^300m2 /kg and a fineness modulus of 3.65. After drying, it needs to be ball-milled in a ball mill for 60min until the specific surface area of the phosphorus slag is greater than ^500m2 /kg. The red sandstone used is calcined at 500℃ for 2h, cooled to room temperature, and then ball-milled in a ball mill for 60min until the specific surface area is greater than ^500m2 /kg before use. The solidified original phosphogypsum is taken from the phosphogypsum yard. The phosphorus content in the phosphogypsum is 52.32 mg/L, the fluoride ion concentration is 32.52 mg/L, the pH is 3.25, and other heavy metal ions meet the relevant standards. The chemical composition of the main raw materials of phosphogypsum and curing agent is shown in the following table.

Table 1 Chemical composition of raw materials (wt/%)

Summary of the invention

The purpose of the present invention is that phosphorus slag is an industrial solid waste material, but has strong volcanic ash activity and needs to be fully stimulated. The present invention combines the physical stimulation method of ball mill grinding with the chemical stimulation of alkaline materials in the detoxification agent to stimulate the hydration activity of phosphorus slag to generate a large amount of hydrated calcium silicate gel and calcium sulfonate crystals to provide a skeleton structure. Red sandstone is a common rock with high durability and strength, but red sandstone has strong water absorption. Therefore, if it is exposed to a humid or rainy environment without proper protective measures, it may absorb a large amount of water and accelerate structural damage. The physical and chemical properties of red sandstone can be changed by calcining and grinding red sandstone, increasing its strength, weathering resistance and reducing water absorption. In this process, the moisture and organic impurities in the red sandstone will be evaporated and decomposed, making the structure more stable. Cement kiln dust is the dust discharged from the kiln tail with the gas when the rotary kiln produces silicate cement clinker. It is collected by dust collecting equipment to obtain dry powder. Its main components include: calcium carbonate, free calcium oxide, potassium (sodium) sulfate, calcium sulfate, α-quartz, β-C ₂ S, C ₂ F, C ₄ AF, etc. The pores of phosphogypsum are filled by the cementing action of the binder prepared by cement kiln dust, sodium alginate and red mud, thereby improving the density of the phosphogypsum sample. Petroleum coke desulfurization ash is a byproduct, which is a solid residue produced by the reaction of sulfide and catalyst in the desulfurization process of petroleum coke. By adding a detoxification agent composed of alkaline materials such as petroleum coke desulfurization ash, slaked lime and carbide slag containing a large amount of CaO and Ca(OH)2, on the one hand, it can stimulate the hydration reaction to generate hydrated calcium silicate gel and calcium aluminate crystals to optimize the pore structure and block the dissolution of toxic ions. On the other hand, Ca ⁽ OH) ₂ combines with _PO43- and ^F- to generate stable insoluble substances such as _Ca2 ( _PO4 ) ₃ , _CaF2 , _Ca10 ( _PO4 ) _{6F2 ,} thereby playing a detoxification role. And through the reaction of the waterproofing agent with carbon dioxide and water molecules in the air, a tightly bound and impermeable waterproof film is formed, which improves the waterproof performance of the sample. Through the combined action of the components in the curing agent studied, the compressive strength and water resistance of the phosphogypsum roadbed material sample are improved, and the leaching toxicity is reduced, so as to achieve the purpose of improving the road performance of phosphogypsum and reducing its pollution to the environment.

The present invention achieves the above object by:

A high water-resistant and low-toxic phosphogypsum curing agent comprises the following raw materials in percentage by weight: 40%-60% ground phosphorus slag, 20%-40% calcined red sandstone powder, 10%-20% binder, 2%-4% waterproofing agent, and 1%-3% toxicity reducing agent.

More preferably, the mixture comprises 51% ground phosphorus slag, 25% calcined red sandstone, 15% binder, 2% waterproofing agent and 2% toxicity reducing agent.

The phosphorus slag used needs to be ball-milled in a ball mill for 60 minutes after being dried, until the specific surface area of the phosphorus slag is greater than ^500m2 /kg.

The red sandstone used was calcined at 500°C for 2 hours, cooled to room temperature, and then ball-milled in a ball mill for 60 minutes until the specific surface area was greater than ^500m2 /kg.

The binder is prepared by mixing 20%-40% sodium alginate, 10%-40% cement kiln dust, 10%-20% red mud, 10%-20% alum stone powder, 10-25% sodium silicate powder and 6%-10% agar, drying and grinding to a specific surface area greater than ^500m2 /kg.

More preferably, the binder is prepared by mixing 20% sodium alginate, 25% cement kiln dust, 10% red mud, 10% alum stone powder, 25% sodium silicate powder, 10% agar, etc., drying and grinding to a specific surface area greater than ^500m2 /kg.

The detoxification agent is prepared by mixing 40%-60% petroleum coke desulfurization ash, 20%-40% slaked lime and 10%-30% carbide slag.

It is further preferred that the detoxification agent is a mixture of 50% petroleum coke desulfurization ash, 40% slaked lime, and 10% carbide slag.

The waterproofing agent is a composite of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

The method for preparing a high water-resistant and low-toxic phosphogypsum curing agent using the above-mentioned materials comprises the following steps: adding ground phosphorus slag and calcined and ground red sandstone powder into a mixer and mixing evenly for 30-40 seconds, then adding a gelling agent and a toxicity reducing agent and stirring for 30-40 seconds, and finally adding a waterproofing agent and stirring for 3-5 minutes.

The application of the highly water-resistant and low-toxic phosphogypsum curing agent prepared in the above method for curing phosphogypsum roadbed materials comprises the following steps: testing the moisture content and pollutants of the original phosphogypsum, uniformly mixing the original phosphogypsum with the above phosphogypsum curing agent to obtain a mixture, wherein the amount of the phosphogypsum curing agent is 5%-10% of the mass of the phosphogypsum, and curing the mixture according to JTG E51-2009 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" The cylindrical specimens were prepared by static pressure method, with a moisture content of 15%-20% and a compaction degree of not less than 96%. After 8 hours, they were demolded and placed in a standard curing box for 28 days. After curing, the unconfined compressive strength and softening coefficient of the roadbed material were tested according to the relevant provisions of the "Test Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), and the total phosphorus and soluble fluoride concentrations were measured after the leachate was prepared according to the "Toxicity Leaching Method of Solid Waste Leaching - Horizontal Oscillation Method" (HJ 557-2010) with reference to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry" (GB 11893-89) and the "Determination of Water-soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

The main component of phosphogypsum is calcium sulfate dihydrate, which is slightly soluble in water and has a retarding effect. This results in low strength and poor water resistance of phosphogypsum roadbed material samples. The concentrations of F and P in the leaching solution are high, which makes it difficult to use phosphogypsum in large quantities in the field of road materials. Phosphorus slag and red sandstone have strong volcanic ash activity. Through grinding excitation, calcination excitation and alkali excitation of detoxification agents such as petroleum coke desulfurization ash, slaked lime and carbide slag, the volcanic ash reaction produced by the excited phosphorus slag and red sandstone generates a large amount of hydrated calcium silicate gel and calcium sulfonite crystals. The formation of these hydration products constitutes a skeleton structure that provides strength for the sample. With the addition of binder, sodium silicate and cement kiln dust further strengthen the hydration reaction. The generated calcium silicate and sodium sulfate fill the pores between phosphogypsum particles. Sodium alginate, red mud, agar, etc. have strong viscosity after mixing with water, which increases the viscosity of the sample. In addition to chemically stimulating phosphate slag and red sandstone to produce hydration products to optimize the pore structure and thus reduce the dissolution of toxic ions, the Ca(OH) ₂ in the detoxifier can combine with PO ₄ ^3- and F ^- to generate stable insoluble substances such as Ca ₂ (PO ₄ ) ₃ , CaF ₂ , Ca ₁₀ (PO ₄ ) ₆ F ₂ , thereby playing a detoxifying role.

With the addition of a waterproofing agent composed of one or more of sodium methyl silicate, polyacrylate and nano-silicon dioxide, the nano-silicon dioxide in the waterproofing agent can modify the polyacrylate, and the copolymer emulsion of the two has excellent hydrophobicity and oleophobicity. After addition, a latex film is formed on the surface of the sample, giving the phosphogypsum sample excellent water resistance. Sodium methyl silicate can react chemically with water molecules and react with the surface of the material to form a tightly bound, impermeable waterproof film on the phosphogypsum, thereby further improving the strength and water resistance of the phosphogypsum.

Compared with the prior art, the present invention has the following advantages: (1) The curing agent process studied in the present invention is simple and feasible, energy-saving and environmentally friendly, and has broad market prospects and industrial value; (2) The components of the curing agent studied in the present invention work synergistically, so that the solidified phosphogypsum has better performance, high strength, high water resistance, and low toxicity; (3) The phosphogypsum dosage is large and the utilization rate is high, which can effectively alleviate the problem of large-scale accumulation of phosphogypsum.

Detailed ways

The following experiments were carried out using the raw materials in Table 1:

Example 1

The phosphorus slag was dried and then ball-milled in a ball mill for 60 minutes. The specific surface area of the phosphorus slag after ball milling was 512 m ² /kg.

The red sandstone powder was calcined at 500°C for 2 hours, cooled to room temperature and then ball-milled in a ball mill for 60 minutes. The specific surface area of the red sandstone powder after ball milling was 526 m ² /kg.

Take 106.3g of ground phosphorus slag, 74.4g of calcined red sandstone, 21.3g of binder, 6.38g of waterproofing agent, and 4.25g of detoxification agent.

The binder is mixed with 30% sodium alginate, 10% cement kiln dust, 20% red mud, 20% alum stone powder, 10% sodium silicate powder, 10% agar, etc., dried and ground to a specific surface area of ^523m2 /kg.

The waterproofing agent is a compound of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

The detoxification agent is a mixture of 60% petroleum coke desulfurization ash, 20% slaked lime, and 20% carbide slag.

The preparation method of the high water-resistant and low-toxic phosphogypsum curing agent is as follows: add the ground phosphorus slag and the calcined and ground red sandstone powder into a mixer and mix them for 30 seconds, then add the gelling agent and the toxicity reducing agent and stir for 30 seconds, and finally add the waterproofing agent and stir for 3 minutes.

The specific steps include:

S1: Detect the moisture content and pollutants of the original phosphogypsum.

S2: The original phosphogypsum and the phosphogypsum curing agent are uniformly mixed to obtain a mixture, wherein the curing agent accounts for 10% of the mass of the phosphogypsum.

S3: The mixture of step S2 is treated according to JTG E51-2009 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" The cylindrical specimens were prepared by static pressure method, with a moisture content of 15% and a compaction degree of 96%. After 8 hours, they were demolded and placed in a standard curing box for 28 days to obtain high water resistance and low toxicity phosphogypsum roadbed materials. After curing, the unconfined compressive strength and softening coefficient of the roadbed materials were tested according to the relevant provisions of the "Test Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), and the total phosphorus and soluble fluoride concentrations were measured after the leachate was prepared according to the "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method" (HJ 557-2010) with reference to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry" (GB 11893-89) and the "Determination of Water-soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

The average compressive strength of the sample in Example 1 at 28 days was 8.62 MPa, the softening coefficient was 0.81, and the leaching concentrations of soluble fluorine and phosphorus were 7.42 mg/L and 0.05 mg/L, respectively, which met the first-level limit of GB 8978-1996 Integrated Wastewater Discharge Standard.

Example 1-1

The components and steps of the high water-resistant and low-toxic phosphogypsum curing agent, preparation method and curing phosphogypsum roadbed material are the same as those in Example 1, except that the phosphorus slag is dried and then ball-milled in a ball mill for 30 minutes. The specific surface area of the phosphorus slag after ball milling is 328 m ² /kg.

The average compressive strength of the sample 28d in Example 1-1 was 6.58 MPa, the softening coefficient was 0.75, and the leaching concentrations of soluble fluorine and phosphorus were 8.14 mg/L and 0.19 mg/L.

Example 1-2

The components and preparation method of the high water-resistant and low-toxic phosphogypsum curing agent and the components and steps of the curing phosphogypsum roadbed material are the same as those in Example 1, except that the red sandstone is not calcined at high temperature and is ball-milled in a ball mill for 60 minutes. After ball milling, the specific surface area is 526 m ² /kg.

The average compressive strength of the sample 28d in Example 1-2 was 5.88 MPa, the softening coefficient was 0.71, and the leaching concentrations of soluble fluorine and phosphorus were 10.6 mg/L and 0.28 mg/L.

Examples 1-3

Highly water-resistant and low-toxic phosphogypsum curing agent components, preparation method and steps for curing phosphogypsum roadbed materials The components are the same as those in Example 1, except that the red sandstone is calcined at 500°C for 2h and used directly after cooling to room temperature without ball milling, and the specific surface area is 206 ^m2 /kg.

The average compressive strength of the sample 28d in Example 1-2 was 6.74 MPa, the softening coefficient was 0.72, and the leaching concentrations of soluble fluorine and phosphorus were 7.16 mg/L and 0.15 mg/L.

Example 2

The phosphorus slag was dried and then ball-milled in a ball mill for 60 minutes. The specific surface area of the phosphorus slag after ball milling was 525 m ² /kg.

The red sandstone powder was calcined at 500°C for 2 hours, cooled to room temperature and then ball-milled in a ball mill for 60 minutes. The specific surface area of the red sandstone after ball milling was 522 m ² /kg.

Take 127.6g of ground phosphorus slag, 42.5g of calcined red sandstone, 27.6g of binder, 8.5g of waterproofing agent, and 6.38g of detoxification agent.

The binder is mixed with 20% sodium alginate, 40% cement kiln dust, 10% red mud, 10% alum stone powder, 14% sodium silicate powder, 6% agar, etc., dried and ground to a specific surface area of ^525m2 /kg.

The waterproofing agent is a compound of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

The detoxification agent is a mixture of 50% petroleum coke desulfurization ash, 30% slaked lime, and 20% carbide slag.

The preparation method of the high water-resistant and low-toxic phosphogypsum curing agent is as follows: add the ground phosphorus slag and the calcined and ground red sandstone powder into a mixer and mix them evenly for 35 seconds, then add the gelling agent and the toxicity reducing agent and stir for 35 seconds, and finally add the waterproofing agent and stir for 4 minutes.

Solidification of phosphogypsum roadbed materials includes the following steps:

S1: Detect the moisture content and pollutants of the original phosphogypsum.

S2: The original phosphogypsum and the phosphogypsum curing agent are uniformly mixed to obtain a mixture, wherein the curing agent accounts for 8% of the mass of the phosphogypsum.

S3: The mixture of step S2 is treated according to JTG E51-2009 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" The cylindrical specimens were prepared by static pressure method, with a moisture content of 17.5% and a compaction degree of 97%. After 8 hours, they were demolded and placed in a standard curing box for 28 days to obtain high water resistance and low toxicity phosphogypsum roadbed materials. After curing, the unconfined compressive strength and softening coefficient of the roadbed materials were tested according to the relevant provisions of the "Test Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), and the total phosphorus and soluble fluoride concentrations were measured after the leachate was prepared according to the "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method" (HJ 557-2010) with reference to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry" (GB 11893-89) and the "Determination of Water-soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

The average compressive strength of the sample in Example 2 at 28d is 7.82MPa, the softening coefficient is 0.76, and the leaching concentrations of soluble fluorine and phosphorus are 7.84mg/L and 0.14mg/L, which can meet the first-level limit of GB 8978-1996 "Integrated Wastewater Discharge Standard".

Example 3

The phosphorus slag was dried and then ball-milled in a ball mill for 60 minutes. The specific surface area of the phosphorus slag after ball milling was 516 m ² /kg.

The red sandstone powder was calcined at 500°C for 2 hours, cooled to room temperature and then ball-milled in a ball mill for 60 minutes. The specific surface area of the red sandstone after ball milling was 524 m ² /kg.

Take 85.0g of ground phosphorus slag, 85.0g of calcined red sandstone, 36.2g of binder, 4.25g of waterproofing agent, and 2.13g of detoxification agent.

The binder is mixed with 40% sodium alginate, 10% cement kiln dust, 15% red mud, 12% alum stone powder, 15% sodium silicate powder, 8% agar, etc., dried and ground to a specific surface area of ^516m2 /kg.

The waterproofing agent is a compound of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

The detoxification agent is a mixture of 40% petroleum coke desulfurization ash, 30% slaked lime, and 30% carbide slag.

The preparation method of the high water-resistant and low-toxic phosphogypsum curing agent is as follows: add the ground phosphorus slag and the calcined and ground red sandstone powder into a mixer and mix them for 30 seconds, then add the gelling agent and the toxicity reducing agent and stir for 40 seconds, and finally add the waterproofing agent and stir for 5 minutes.

Solidification of phosphogypsum roadbed materials includes the following steps:

S1: Detect the moisture content and pollutants of the original phosphogypsum.

S2: The original phosphogypsum and the phosphogypsum curing agent are uniformly mixed to obtain a mixture, wherein the curing agent accounts for 6% of the mass of the phosphogypsum.

S3: The mixture of step S2 is treated according to JTG E51-2009 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" The cylindrical specimens were prepared by static pressure method, with a moisture content of 20% and a compaction degree of 96%. After 8 hours, they were demolded and placed in a standard curing box for 28 days to obtain high water resistance and low toxicity phosphogypsum roadbed materials. After curing, the unconfined compressive strength and softening coefficient of the roadbed materials were tested according to the relevant provisions of the "Test Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), and the total phosphorus and soluble fluorine concentrations were measured after the leachate was prepared according to the "Toxicity Leaching Method of Solid Waste Leaching Horizontal Oscillation Method" (HJ 557-2010) with reference to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry" (GB 11893-89) and the "Determination of Water-soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

The average compressive strength of the sample in Example 3 at 28 days is 6.96 MPa, the softening coefficient is 0.72, and the leaching concentrations of soluble fluorine and phosphorus are 7.12 mg/L and 0.14 mg/L, which can meet the first-level limit of GB 8978-1996 "Integrated Wastewater Discharge Standard".

Example 4

The phosphorus slag was dried and then ball-milled in a ball mill for 60 minutes. The specific surface area of the phosphorus slag after ball milling was 514 m ² /kg.

The red sandstone powder used was calcined at 500°C for 2 hours, cooled to room temperature and then ball-milled in a ball mill for 60 minutes. The specific surface area of the red sandstone after ball milling was 518 m ² /kg.

Take 95.7g of ground phosphorus slag, 74.4g of calcined red sandstone, 29.8g of binder, 6.38g of waterproofing agent, and 6.38g of detoxification agent.

The binder is mixed with 25% sodium alginate, 15% cement kiln dust, 15% red mud, 13% alum stone powder, 25% sodium silicate powder, 7% agar, etc., dried and ground to a specific surface area of ^520m2 /kg.

The waterproofing agent is a compound of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

The detoxification agent is a mixture of 45% petroleum coke desulfurization ash, 30% slaked lime, and 25% carbide slag.

The preparation method of the high water-resistant and low-toxic phosphogypsum curing agent is as follows: add the ground phosphorus slag and the calcined and ground red sandstone powder into a mixer and mix them evenly for 40 seconds, then add the gelling agent and the toxicity reducing agent and stir for 30 seconds, and finally add the waterproofing agent and stir for 4 minutes.

Solidification of phosphogypsum roadbed materials includes the following steps:

S1: Detect the moisture content and pollutants of the original phosphogypsum.

S2: The original phosphogypsum and the phosphogypsum curing agent are uniformly mixed to obtain a mixture, wherein the curing agent accounts for 7% of the mass of the phosphogypsum.

S3: The mixture of step S2 is treated according to JTG E51-2009 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" The cylindrical specimens were prepared by static pressure method, with a moisture content of 18% and a compaction degree of 97%. After 8 hours, they were demolded and placed in a standard curing box for 28 days to obtain high water resistance and low toxicity phosphogypsum roadbed materials. After curing, the unconfined compressive strength and softening coefficient of the roadbed materials were tested according to the relevant provisions of the "Test Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), and the total phosphorus and soluble fluorine concentrations were measured after the leachate was prepared according to the "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method" (HJ 557-2010) with reference to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry" (GB 11893-89) and the "Determination of Water-soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

The average compressive strength of the sample in Example 4 at 28d is 8.32MPa, the softening coefficient is 0.79, and the leaching concentrations of soluble fluorine and phosphorus are 7.66mg/L and 0.09mg/L, which can meet the first-level limit of GB 8978-1996 "Integrated Wastewater Discharge Standard".

Example 5

The phosphorus slag was dried and then ball-milled in a ball mill for 60 minutes. The specific surface area of the phosphorus slag after ball milling was 520 m ² /kg.

The red sandstone powder used was calcined at 500°C for 2 hours, cooled to room temperature and then ball-milled in a ball mill for 60 minutes. The specific surface area of the red sandstone after ball milling was 527m ² /kg.

Take 98.6g of ground phosphorus slag, 63.8g of calcined red sandstone, 42.5g of binder, 4.25g of waterproofing agent, and 4.25g of detoxification agent.

The binder is mixed with 20% sodium alginate, 25% cement kiln dust, 10% red mud, 10% alum stone powder, 25% sodium silicate powder, 10% agar, etc., dried and ground to a specific surface area of ^526m2 /kg.

The waterproofing agent is a compound of one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

The detoxification agent is a mixture of 50% petroleum coke desulfurization ash, 40% slaked lime, and 10% carbide slag.

The preparation method of the high water-resistant and low-toxic phosphogypsum curing agent is as follows: add the ground phosphorus slag and the calcined and ground red sandstone powder into a mixer and mix them for 30 seconds, then add the gelling agent and the toxicity reducing agent and stir for 40 seconds, and finally add the waterproofing agent and stir for 5 minutes.

Solidification of phosphogypsum roadbed materials includes the following steps:

S1: Detect the moisture content and pollutants of the original phosphogypsum.

S2: The original phosphogypsum and the phosphogypsum curing agent are uniformly mixed to obtain a mixture, wherein the curing agent accounts for 10% of the mass of the phosphogypsum.

S3: The mixture of step S2 is treated according to JTG E51-2009 "Testing Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" The cylindrical specimens were prepared by static pressure method, with a moisture content of 17.5% and a compaction degree of 98%. After 8 hours, they were demolded and placed in a standard curing box for 28 days to obtain high water resistance and low toxicity phosphogypsum roadbed materials. After curing, the unconfined compressive strength and softening coefficient of the roadbed materials were tested according to the relevant provisions of the "Test Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), and the total phosphorus and soluble fluorine concentrations were measured after the leachate was prepared according to the "Toxicity Leaching Method of Solid Waste Leaching Horizontal Oscillation Method" (HJ 557-2010) with reference to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry" (GB 11893-89) and the "Determination of Water-soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

The average compressive strength of the sample in Example 5 at 28d was 9.12MPa, the softening coefficient was 0.83, and the leaching concentrations of soluble fluorine and phosphorus were 7.02mg/L and 0.03mg/L, respectively, which met the first-level limit of GB 8978-1996 Integrated Wastewater Discharge Standard.

Claims (9)

1. The phosphogypsum curing agent with high water resistance and low toxicity is characterized by comprising the following raw materials in percentage by weight: 40-60% of ground phosphorous slag, 20-40% of calcined red sandstone powder, 10-20% of cementing agent, 2-4% of waterproof agent and 1-3% of antidote.

2. The high water resistance low toxicity phosphogypsum curing agent of claim 1, which is characterized by comprising the following raw materials in percentage by weight: 51% of ground phosphorus slag, 25% of calcined red sandstone powder, 20% of cementing agent, 2% of waterproof agent and 2% of toxin reducing agent.

3. The high water resistance and low toxicity phosphogypsum curing agent according to claim 1, wherein the cementing agent is prepared by mixing 20% -40% of sodium alginate, 10% -40% of cement kiln dust, 10% -20% of red mud, 10% -20% of alum stone powder, 10% -25% of sodium silicate powder and 6% -10% of agar, drying and grinding to a specific surface area of more than 500m ²/kg.

4. The phosphogypsum curing agent with high water resistance and low toxicity according to claim 1, wherein the waterproof agent is compounded by one or more of sodium methyl silicate, polyacrylate and nano silicon dioxide.

5. The phosphogypsum curing agent with high water resistance and low toxicity according to claim 1, wherein the antidote is prepared by mixing 40% -60% of petroleum coke desulfurization ash, 20% -40% of slaked lime and 10% -30% of carbide slag.

6. The phosphogypsum curing agent with high water resistance and low toxicity according to claim 1, wherein the ground phosphorus slag is prepared by ball milling the dried phosphorus slag in a ball mill until the specific surface area is more than 500m ²/kg.

7. The phosphogypsum curing agent with high water resistance and low toxicity according to claim 1, wherein the used red sandstone powder is prepared by calcining at a high temperature of 500-600 ℃ for 2-3 hours and then ball milling until the specific surface area is more than 500m ²/kg.

8. The method for preparing the phosphogypsum curing agent with high water resistance and low toxicity according to any one of claims 1 to 7, which is characterized by comprising the following preparation method:

Adding the ground phosphorus slag and the calcined red sandstone powder into a stirrer, uniformly mixing for 30-40s, adding the cementing agent and the antidote, stirring for 30-40s, adding the waterproofing agent, and stirring for 3-5min, thus obtaining the phosphogypsum curing agent with high water resistance and low toxicity.

9. The method for preparing the phosphogypsum roadbed material cured by the phosphogypsum curing agent with high water resistance and low toxicity according to any one of claims 1 to 7, which is characterized in that the preparation process comprises the following steps:

s1: detecting the water content and pollutants of the undisturbed phosphogypsum;

S2: uniformly mixing undisturbed phosphogypsum and a phosphogypsum curing agent with high water resistance and low toxicity to obtain a mixture, wherein the phosphogypsum curing agent with high water resistance and low toxicity accounts for 5-10% of the mass of phosphogypsum;

S3: the mixture in the step S2 is processed according to JTG E51-2009 in the test procedure of inorganic binder stabilization materials for Highway engineering The cylindrical test piece is prepared and molded by adopting a static pressure method, the water content is 15% -20%, the compactness is not less than 96%, and the phosphogypsum roadbed material with high water resistance and low toxicity is obtained by demoulding and curing.