A highly water-resistant and low-toxicity phosphogypsum curing agent and its preparation method

Abstract

This invention belongs to the field of curing agents and discloses a highly water-resistant and low-toxicity phosphogypsum curing agent. Its components include finely ground phosphogypsum slag, calcined red sandstone powder, a binder, a waterproofing agent, and a detoxifying agent. The binder is a mixture of sodium alginate, cement kiln ash, red mud, alunite powder, sodium silicate powder, agar, etc., ground together. The waterproofing agent is a composite of one or more of sodium methylsilicate, polyacrylate, and nano-silica. The detoxifying agent is a mixture of petroleum coke desulfurization ash, slaked lime, and carbide slag. This invention applies this curing agent to the curing of phosphogypsum. The unconfined compressive strength of the cured phosphogypsum roadbed material samples is significantly improved, with a softening coefficient reaching over 0.8. The leaching concentrations of fluorine and phosphorus meet the Class I limits of GB 8978—1996 "Integrated Wastewater Discharge Standard," demonstrating significant curing effect. Furthermore, the process is simple, energy-saving, and environmentally friendly, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to a highly water-resistant and low-toxicity phosphogypsum curing agent, and applies it to the curing of phosphogypsum roadbed materials, and studies the performance changes of phosphogypsum roadbed material samples before and after curing. Background Technology

[0002] Phosphogypsum (PG) is a byproduct of the wet process production of phosphoric acid using phosphate lime and sulfuric acid in chemical plants. Its main component is CaSO4·2H2O, accounting for over 90% of its total composition. In addition, phosphogypsum contains phosphorus, fluorine, organic matter, and other impurities. The production of 1 ton of phosphoric acid generates 4.5-5.5 tons of phosphogypsum. Open-air stockpiles of phosphogypsum cause pollution to soil, air, and water systems due to wind and rain erosion, reducing crop yields and quality, impacting the health of local residents, and resulting in incalculable losses. Extensive research has been conducted both domestically and internationally on the comprehensive utilization of phosphogypsum, and numerous potential applications have been proposed. Among the more mature applications are ecological restoration and mine backfilling, agricultural soil improvement, building materials, the cement industry, and phosphogypsum building materials. While these methods have alleviated phosphogypsum pollution to some extent, large-scale comprehensive utilization of phosphogypsum remains difficult to achieve due to the scattered nature of phosphate rock resources, the small scale of many phosphate fertilizer enterprises, and deficiencies in phosphogypsum utilization technology. Therefore, a new technology is urgently needed to handle these large quantities of waste phosphogypsum. Compared with other application areas, the application of phosphogypsum in the road industry involves a large workload and high consumption, which can solve the problem of large stockpiles of phosphogypsum. Furthermore, using phosphogypsum in road construction can not only consume large quantities of phosphogypsum but also significantly reduce road construction costs, resulting in significant social and economic benefits. However, in the phosphogypsum road industry, whether applied as roadbed filler or road base material, the issues of strength and durability must be considered. This is because phosphogypsum and its products have low mechanical strength, poor water stability, and strong water absorption, softening upon contact with water and experiencing a significant reduction in strength. Additionally, the leaching of fluorine and phosphorus from phosphogypsum causes environmental pollution. These are the pressing challenges currently facing the application of phosphogypsum in the road industry, and also the research objectives and directions for phosphogypsum soil stabilizers. Therefore, research on phosphogypsum-based soil stabilizers has broad application prospects and commercial value.

[0003] Currently, many scholars in my country have also conducted research on the resource utilization of phosphogypsum in the road industry. Most of these studies focus on using a small amount of phosphogypsum as a cement retarder, adding a small amount of phosphogypsum as a composite cementitious material to provide sulfate for the formation of ettringite, or using phosphogypsum as a lightweight aggregate to replace part of the crushed stone. However, there are few studies on the direct solidification of undisturbed phosphogypsum. In existing literature, only Ji Xiaoping, Zhang Houji, and others have conducted research on phosphogypsum curing agents. However, the CA curing agent studied by Ji Xiaoping and others is used to stabilize phosphogypsum roadbed filler. The sodium methylsilicate content in the curing agent reaches 85%, which makes the actual engineering cost too high and is not conducive to practical use. The weight percentage of each raw material in lime, red mud, and phosphogypsum in the solidified phosphogypsum roadbed filler studied by Zhang Houji and others is as follows: lime 4-15%, red mud 30-50%, and phosphogypsum 35-60%. The maximum amount of phosphogypsum can only reach 60%, which cannot be used in large quantities to solve the problem of phosphogypsum accumulation.

[0004] The phosphorus slag used in this invention is commercially available and has a specific surface area of ​​300 m². 2 / kg, with a fineness modulus of 3.65, after drying, it needs to be ball-milled for 60 minutes until the specific surface area of ​​the phosphorus slag is greater than 500m². 2 / kg, the red sandstone used was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes until the specific surface area was greater than 500m². 2 / kg after use. The solidified undisturbed phosphogypsum was taken from the phosphogypsum stockpile. The phosphogypsum contained 52.32 mg / L phosphorus, 32.52 mg / L fluoride ion concentration, and pH 3.25. Other heavy metal ions met the relevant standards. The chemical composition of the main raw materials of phosphogypsum and curing agent is shown in the table below.

[0005] Table 1 Chemical composition of raw materials (wt / %)

[0006] Summary of the Invention

[0007] The purpose of this invention is to address the issue that phosphorus slag, an industrial solid waste material, possesses strong pozzolanic activity and requires thorough activation. This invention combines physical activation through ball milling with chemical activation through alkaline materials in a detoxifying agent. This activates the hydration activity of the phosphorus slag, generating a large amount of hydrated calcium silicate gel and ettringite crystals to provide the skeletal structure. Red sandstone is a common rock with high durability and strength, but it also has strong water absorption. Therefore, when exposed to humid or rainy environments without proper protection, it may absorb large amounts of moisture, accelerating structural damage. Calcination and grinding of red sandstone alters its physical and chemical properties, increasing its strength, weathering resistance, and reducing water absorption. During this process, moisture and organic impurities in the red sandstone are evaporated and decomposed, making the structure more stable. Cement kiln ash is a dry powder collected by dust collection equipment during the production of silicate cement clinker in rotary kilns. It is produced by the flow of air into the kiln tail and discharged through a dust collection system. Its main components include calcium carbonate, free calcium oxide, potassium (sodium) sulfate, calcium sulfate, α-quartz, β-C2S, C2F, C4AF, etc. Through the cementing effect of a binder prepared from cement kiln ash, sodium alginate, and red mud, the pores of phosphogypsum are filled, thereby increasing the density of the phosphogypsum sample. Petroleum coke desulfurization ash is a byproduct, a solid residue produced during the desulfurization process of petroleum coke when sulfides react with the catalyst. By adding a detoxifying agent composed of alkaline materials containing large amounts of CaO and Ca(OH)2, such as petroleum coke desulfurization ash, slaked lime, and carbide slag, it can, on the one hand, stimulate the hydration reaction, generating hydrated calcium silicate gel and ettringite crystals to optimize the pore structure and block the dissolution of toxic ions; on the other hand, Ca(OH)2 and PO4... 3- and F - Combine to form Ca2(PO4)3, CaF2, and Ca 10 Stable, insoluble compounds such as (PO4)6F2 are incorporated to reduce toxicity. The waterproofing agent reacts with carbon dioxide and water molecules in the air to form a tightly bonded, impermeable waterproof membrane, improving the waterproof performance of the sample. The combined effect of the components in the studied curing agent enhances the compressive strength and water resistance of the phosphogypsum roadbed material samples, reduces leaching toxicity, and ultimately improves the road performance of phosphogypsum while minimizing its environmental pollution.

[0008] The present invention achieves the above objectives as follows:

[0009] A highly water-resistant and low-toxicity phosphogypsum curing agent comprises the following raw materials in weight percentages: 40%-60% finely ground phosphogypsum slag, 20%-40% calcined red sandstone powder, 10%-20% binder, 2%-4% waterproofing agent, and 1%-3% detoxifying agent.

[0010] Further preferred components include 51% finely ground phosphorus slag, 25% calcined red sandstone, 15% cementing agent, 2% waterproofing agent, and 2% detoxifying agent.

[0011] The dried phosphorus slag needs to be ball-milled for 60 minutes until the specific surface area of ​​the phosphorus slag is greater than 500 m². 2 / kg.

[0012] The red sandstone used was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes until the specific surface area was greater than 500 m². 2 Use after / kg.

[0013] The binder is composed of 20%-40% sodium alginate, 10%-40% cement kiln ash, 10%-20% red mud, 10%-20% alum stone powder, 10-25% sodium silicate powder, and 6%-10% agar, which are then mixed, dried, and ground to a specific surface area greater than 500 m². 2 It is made per kg.

[0014] A further preferred binder is a mixture of 20% sodium alginate, 25% cement kiln ash, 10% red mud, 10% alum powder, 25% sodium silicate powder, and 10% agar, which is then dried and ground to a specific surface area greater than 500 m². 2 It is made per kg.

[0015] The detoxification agent is composed of 40%-60% petroleum coke desulfurization ash, 20%-40% slaked lime, and 10%-30% carbide slag.

[0016] A further preferred detoxification agent is a mixture of 50% petroleum coke desulfurization ash, 40% slaked lime, and 10% carbide slag.

[0017] The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano silica.

[0018] The method for preparing a high water-resistant, low-toxicity phosphogypsum curing agent using the materials described above includes the following steps: adding finely ground phosphorus slag and calcined, finely ground red sandstone powder into a mixer and mixing for 30-40 seconds, then adding a gelling agent and a detoxifying agent and mixing for 30-40 seconds, and finally adding a waterproofing agent and mixing for 3-5 minutes.

[0019] The application of the high water-resistant, low-toxicity phosphogypsum curing agent prepared above for curing phosphogypsum subgrade materials includes the following steps: testing the moisture content and contaminants of the undisturbed phosphogypsum; mixing the undisturbed phosphogypsum with the above-mentioned phosphogypsum curing agent to obtain a uniform mixture; the dosage of the phosphogypsum curing agent is 5%-10% of the phosphogypsum mass; and mixing the mixture according to JTG E51—2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing 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 chamber for 28 days. After curing, the subgrade material was tested for unconfined compressive strength and softening coefficient according to the relevant provisions in the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG E51-2009). The leachate was prepared according to the "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ 557-2010). The total phosphorus and soluble fluoride concentrations were measured with reference to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89) and the "Determination of Water-Soluble Fluoride and Total Fluoride in Soil - Ion Electrode Method" (HJ 873-2017).

[0020] 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 in phosphogypsum roadbed material samples, and high concentrations of phosphogypsum (F) and phosphorus (P) in the leachate, making it difficult to use phosphogypsum in large quantities in the road materials field. Phosphate slag and red sandstone have strong pozzolanic activity. Through grinding activation, calcination activation, and alkaline activation by petroleum coke desulfurization ash, slaked lime, and carbide slag in detoxification agents, the pozzolanic reaction of activated phosphogypsum and red sandstone produces a large amount of hydrated calcium silicate gel and ettringite crystals. The formation of these hydration products constitutes the skeleton structure, providing strength to the sample. With the addition of cementitious agents, sodium silicate and cement kiln ash further enhance the hydration reaction. The generated calcium silicate and sodium sulfate fill the pores of phosphogypsum particles. Sodium alginate, red mud, agar, etc., have strong viscosity when mixed with water, increasing the viscosity of the sample. Besides chemically activating the hydration products of phosphorus slag and red sandstone to optimize the pore structure and thus reduce the leaching of toxic ions, the Ca(OH)2 in the detoxifying agent can react with PO42-. 3- and F - Combine to form Ca2(PO4)3, CaF2, and Ca 10 Stable, insoluble compounds such as (PO4)6F2 can reduce toxicity.

[0021] With the addition of a waterproofing agent composed of one or more of sodium methylsilicate, polyacrylate, and nano-silica, the nano-silica in the waterproofing agent can modify the polyacrylate. The copolymer emulsion of the two has excellent hydrophobic and oleophobic properties. After addition, a latex film is formed on the surface of the sample, giving the phosphogypsum sample excellent water resistance. Sodium methylsilicate can react chemically with water molecules and react with the material surface to form a tightly bonded, impermeable waterproof film on the phosphogypsum, thereby further improving the strength and water resistance of the phosphogypsum.

[0022] Compared with the prior art, the present invention has the following advantages: (1) The curing agent process studied in the present invention is simple, feasible, energy-saving and environmentally friendly, and has a wide market prospect and industrial value; (2) The curing agent components studied in the present invention have a synergistic effect, which makes the phosphogypsum after curing have good performance, high strength, high water resistance and low toxicity; (3) The phosphogypsum has a large dosage and high utilization rate, which can effectively alleviate the problem of large accumulation of phosphogypsum. Detailed Implementation

[0023] The following experiments were conducted using the raw materials listed in Table 1:

[0024] Example 1

[0025] After drying, the phosphorus slag was ball-milled for 60 minutes. The specific surface area of ​​the phosphorus slag after ball milling was 512 m². 2 / kg.

[0026] The red sandstone powder was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes. The specific surface area of ​​the ball-milled red sandstone powder was 526 m². 2 / kg.

[0027] Take 106.3g of finely ground phosphorus slag, 74.4g of calcined red sandstone, 21.3g of cementing agent, 6.38g of waterproofing agent, and 4.25g of detoxifying agent.

[0028] The binder is made by mixing 30% sodium alginate, 10% cement kiln ash, 20% red mud, 20% alum stone powder, 10% sodium silicate powder, and 10% agar, drying, and grinding to a specific surface area of ​​523 m². 2 / kg.

[0029] The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano silica.

[0030] The detoxification agent is composed of 60% petroleum coke desulfurization ash, 20% slaked lime, and 20% carbide slag.

[0031] The preparation method of high water resistance and low toxicity phosphogypsum curing agent is as follows: finely ground phosphorus slag and calcined and finely ground red sandstone powder are added to a mixer and mixed for 30 seconds. Then, a gelling agent and a detoxifying agent are added and mixed for 30 seconds. Finally, a waterproofing agent is added and mixed for 3 minutes.

[0032] Specifically, the steps include the following:

[0033] S1: Test the moisture content and contaminants of the undisturbed phosphogypsum.

[0034] S2: Mix the raw phosphogypsum with the phosphogypsum curing agent evenly to obtain a mixture, wherein the curing agent accounts for 10% of the mass of the phosphogypsum.

[0035] S3: The mixture from step S2 shall be prepared in accordance with JTG E51—2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing with a moisture content of 15% and a compaction degree of 96%. After 8 hours, the specimens were demolded and cured in a standard curing chamber for 28 days to obtain a high-water-resistant, low-toxicity phosphogypsum subgrade material. After curing, the subgrade material was tested for unconfined compressive strength and softening coefficient according to the relevant provisions in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). Leachate was prepared according to the "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ 557-2010). Total phosphorus and soluble fluoride concentrations were measured with reference to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89) and the "Determination of Water-Soluble Fluorides and Total Fluorides in Soil - Ion Electrode Method" (HJ 873-2017).

[0036] In Example 1, the average compressive strength of the sample after 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 meet the Class I limit of GB 8978—1996 "Integrated Wastewater Discharge Standard".

[0037] Example 1-1

[0038] The components, preparation method, and steps of the high water-resistant, low-toxicity phosphogypsum curing agent for curing phosphogypsum roadbed materials are the same as in Example 1, except that the phosphogypsum slag is ball-milled for 30 minutes after drying. The specific surface area of ​​the phosphogypsum slag after ball milling is 328 m². 2 / kg.

[0039] In Example 1-1, the average compressive strength of the sample after 28 days 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, respectively.

[0040] Examples 1-2

[0041] The components, preparation method, and steps of the high water-resistant, low-toxicity phosphogypsum curing agent for curing phosphogypsum roadbed materials are the same as in Example 1, except that the red sandstone was not calcined at high temperature and was ball-milled for 60 minutes. The specific surface area after ball milling was 526 m². 2 / kg.

[0042] In Examples 1-2, the average compressive strength of the samples after 28 days 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, respectively.

[0043] Examples 1-3

[0044] The components, preparation method, and steps for curing phosphogypsum roadbed materials using a high water-resistant, low-toxicity phosphogypsum curing agent are the same as in Example 1, except that the red sandstone was calcined at 500℃ for 2 hours, cooled to room temperature, and used directly without ball milling, resulting in a specific surface area of ​​206 m². 2 / kg.

[0045] In Examples 1-2, the average compressive strength of the samples after 28 days 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, respectively.

[0046] Example 2

[0047] After drying, the phosphorus slag was ball-milled for 60 minutes. The specific surface area of ​​the phosphorus slag after ball milling was 525 m². 2 / kg.

[0048] The red sandstone powder was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes. The specific surface area of ​​the ball-milled red sandstone was 522 m². 2 / kg.

[0049] Take 127.6g of finely ground phosphorus slag, 42.5g of calcined red sandstone, 27.6g of cementing agent, 8.5g of waterproofing agent, and 6.38g of detoxifying agent.

[0050] The binder is a mixture of 20% sodium alginate, 40% cement kiln ash, 10% red mud, 10% alum stone powder, 14% sodium silicate powder, and 6% agar, which is then dried and ground to a specific surface area of ​​525 m². 2 / kg.

[0051] The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano silica.

[0052] The detoxification agent is composed of 50% petroleum coke desulfurization ash, 30% slaked lime, and 20% carbide slag.

[0053] The preparation method of high water resistance and low toxicity phosphogypsum curing agent is as follows: finely ground phosphorus slag and calcined and finely ground red sandstone powder are added to a mixer and mixed for 35 seconds. Then, a gelling agent and a detoxifying agent are added and mixed for 35 seconds. Finally, a waterproofing agent is added and mixed for 4 minutes.

[0054] The solidification of phosphogypsum subgrade materials includes the following steps:

[0055] S1: Test the moisture content and contaminants of the undisturbed phosphogypsum.

[0056] S2: The raw phosphogypsum and phosphogypsum curing agent are mixed evenly to obtain a mixture, wherein the curing agent accounts for 8% of the mass of the phosphogypsum.

[0057] S3: The mixture from step S2 shall be prepared in accordance with JTG E51—2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing with a moisture content of 17.5% and a compaction degree of 97%. After 8 hours, the specimens were demolded and cured in a standard curing chamber for 28 days to obtain a high-water-resistant, low-toxicity phosphogypsum subgrade material. After curing, the subgrade material was tested for unconfined compressive strength and softening coefficient according to the relevant provisions in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). Leachate was prepared according to the "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ 557-2010). Total phosphorus and soluble fluoride concentrations were measured with reference to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89) and the "Determination of Water-Soluble Fluorides and Total Fluorides in Soil - Ion Electrode Method" (HJ 873-2017).

[0058] In Example 2, the average compressive strength of the sample after 28 days was 7.82 MPa, the softening coefficient was 0.76, and the leaching concentrations of soluble fluorine and phosphorus were 7.84 mg / L and 0.14 mg / L, respectively, which meet the Class I limit of GB 8978—1996 "Integrated Wastewater Discharge Standard".

[0059] Example 3

[0060] After drying, the phosphorus slag was ball-milled for 60 minutes. The specific surface area of ​​the phosphorus slag after ball milling was 516 m². 2 / kg.

[0061] The red sandstone powder was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes. The specific surface area of ​​the ball-milled red sandstone was 524 m². 2 / kg.

[0062] Take 85.0g of finely ground phosphorus slag, 85.0g of calcined red sandstone, 36.2g of cementing agent, 4.25g of waterproofing agent, and 2.13g of detoxifying agent.

[0063] The binder is made by mixing 40% sodium alginate, 10% cement kiln ash, 15% red mud, 12% alum stone powder, 15% sodium silicate powder, and 8% agar, drying, and grinding to a specific surface area of ​​516 m². 2 / kg.

[0064] The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano silica.

[0065] The detoxification agent is composed of 40% petroleum coke desulfurization ash, 30% slaked lime, and 30% carbide slag.

[0066] The preparation method of high water resistance and low toxicity phosphogypsum curing agent is as follows: finely ground phosphorus slag and calcined and finely ground red sandstone powder are added to a mixer and mixed for 30 seconds. Then, a gelling agent and a detoxifying agent are added and mixed for 40 seconds. Finally, a waterproofing agent is added and mixed for 5 minutes.

[0067] The solidification of phosphogypsum subgrade materials includes the following steps:

[0068] S1: Test the moisture content and contaminants of the undisturbed phosphogypsum.

[0069] S2: The raw phosphogypsum and phosphogypsum curing agent are mixed evenly to obtain a mixture, wherein the curing agent accounts for 6% of the mass of the phosphogypsum.

[0070] S3: The mixture from step S2 shall be prepared in accordance with JTG E51—2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing with a moisture content of 20% and a compaction degree of 96%. After 8 hours, the specimens were demolded and cured in a standard curing chamber for 28 days to obtain a high-water-resistant, low-toxicity phosphogypsum subgrade material. After curing, the subgrade material was tested for unconfined compressive strength and softening coefficient according to the relevant provisions in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). Leachate was prepared according to the "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ 557-2010). Total phosphorus and soluble fluoride concentrations were measured with reference to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89) and the "Determination of Water-Soluble Fluorides and Total Fluorides in Soil - Ion Electrode Method" (HJ 873-2017).

[0071] In Example 3, the average compressive strength of the sample after 28 days was 6.96 MPa, the softening coefficient was 0.72, and the leaching concentrations of soluble fluorine and phosphorus were 7.12 mg / L and 0.14 mg / L, respectively, which meet the Class I limit of GB 8978—1996 "Integrated Wastewater Discharge Standard".

[0072] Example 4

[0073] After drying, the phosphorus slag was ball-milled for 60 minutes. The specific surface area of ​​the phosphorus slag after ball milling was 514 m². 2 / kg.

[0074] The red sandstone powder used was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes. The specific surface area of ​​the ball-milled red sandstone was 518 m². 2 / kg.

[0075] Take 95.7g of finely ground phosphorus slag, 74.4g of calcined red sandstone, 29.8g of cementing agent, 6.38g of waterproofing agent, and 6.38g of detoxifying agent.

[0076] The binder is a mixture of 25% sodium alginate, 15% cement kiln ash, 15% red mud, 13% alum stone powder, 25% sodium silicate powder, and 7% agar, which is then dried and ground to a specific surface area of ​​520 m². 2 / kg.

[0077] The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano silica.

[0078] The detoxification agent is composed of 45% petroleum coke desulfurization ash, 30% slaked lime, and 25% carbide slag.

[0079] The preparation method of high water resistance and low toxicity phosphogypsum curing agent is as follows: finely ground phosphorus slag and calcined and finely ground red sandstone powder are added to a mixer and mixed for 40 seconds. Then, a gelling agent and a detoxifying agent are added and mixed for 30 seconds. Finally, a waterproofing agent is added and mixed for 4 minutes.

[0080] The solidification of phosphogypsum subgrade materials includes the following steps:

[0081] S1: Test the moisture content and contaminants of the undisturbed phosphogypsum.

[0082] S2: The raw phosphogypsum and phosphogypsum curing agent are mixed evenly to obtain a mixture, wherein the curing agent accounts for 7% of the mass of the phosphogypsum.

[0083] S3: The mixture from step S2 shall be prepared in accordance with JTG E51—2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing with a moisture content of 18% and a compaction degree of 97%. After 8 hours, the specimens were demolded and cured in a standard curing chamber for 28 days to obtain a high-water-resistant, low-toxicity phosphogypsum subgrade material. After curing, the subgrade material was tested for unconfined compressive strength and softening coefficient according to the relevant provisions in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). Leachate was prepared according to the "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method" (HJ 557-2010), and the total phosphorus and soluble fluoride concentrations were measured with reference to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89) and the "Determination of Water-Soluble Fluorides and Total Fluorides in Soil - Ion Electrode Method" (HJ 873-2017).

[0084] In Example 4, the average compressive strength of the sample after 28 days was 8.32 MPa, the softening coefficient was 0.79, and the leaching concentrations of soluble fluorine and phosphorus were 7.66 mg / L and 0.09 mg / L, respectively, which meet the Class I limit of GB 8978—1996 "Integrated Wastewater Discharge Standard".

[0085] Example 5

[0086] After drying, the phosphorus slag was ball-milled for 60 minutes. The specific surface area of ​​the phosphorus slag after ball milling was 520 m². 2 / kg.

[0087] The red sandstone powder used was calcined at 500℃ for 2 hours, cooled to room temperature, and then ball-milled for 60 minutes. The specific surface area of ​​the ball-milled red sandstone was 527 m². 2 / kg.

[0088] Take 98.6g of finely ground phosphorus slag, 63.8g of calcined red sandstone, 42.5g of cementing agent, 4.25g of waterproofing agent, and 4.25g of detoxifying agent.

[0089] The binder is made by mixing 20% ​​sodium alginate, 25% cement kiln ash, 10% red mud, 10% alum stone powder, 25% sodium silicate powder, and 10% agar, drying, and grinding to a specific surface area of ​​526 m². 2 / kg.

[0090] The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano silica.

[0091] The detoxification agent is composed of 50% petroleum coke desulfurization ash, 40% slaked lime, and 10% carbide slag.

[0092] The preparation method of high water resistance and low toxicity phosphogypsum curing agent is as follows: finely ground phosphorus slag and calcined and finely ground red sandstone powder are added to a mixer and mixed for 30 seconds. Then, a gelling agent and a detoxifying agent are added and mixed for 40 seconds. Finally, a waterproofing agent is added and mixed for 5 minutes.

[0093] The solidification of phosphogypsum subgrade materials includes the following steps:

[0094] S1: Test the moisture content and contaminants of the undisturbed phosphogypsum.

[0095] S2: The raw phosphogypsum and phosphogypsum curing agent are mixed evenly to obtain a mixture, wherein the curing agent accounts for 10% of the mass of the phosphogypsum.

[0096] S3: The mixture from step S2 shall be prepared in accordance with JTG E51—2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing with a moisture content of 17.5% and a compaction degree of 98%. After 8 hours, the specimens were demolded and cured in a standard curing chamber for 28 days to obtain a high-water-resistant, low-toxicity phosphogypsum subgrade material. After curing, the subgrade material was tested for unconfined compressive strength and softening coefficient according to the relevant provisions in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). Leachate was prepared according to the "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ 557-2010). Total phosphorus and soluble fluoride concentrations were measured with reference to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89) and the "Determination of Water-Soluble Fluorides and Total Fluorides in Soil - Ion Electrode Method" (HJ 873-2017).

[0097] In Example 5, the average compressive strength of the sample after 28 days was 9.12 MPa, the softening coefficient was 0.83, and the leaching concentrations of soluble fluorine and phosphorus were 7.02 mg / L and 0.03 mg / L, respectively, which meet the Class I limit of GB 8978—1996 "Integrated Wastewater Discharge Standard".

Claims

1. A highly water-resistant, low-toxicity phosphogypsum curing agent, characterized in that, The curing agent comprises the following raw materials in weight percentages: 40%-60% finely ground phosphorus slag, 20%-40% calcined red sandstone powder, 10%-20% cementitious agent, 2%-4% waterproofing agent, and 1%-3% detoxifying agent; The binder is composed of 20%-40% sodium alginate, 10%-40% cement kiln ash, 10%-20% red mud, 10%-20% alum stone powder, 10-25% sodium silicate powder, and 6%-10% agar, which are then mixed, dried, and ground to a specific surface area greater than 500 m². 2 / kg The waterproofing agent is composed of one or more of sodium methylsilicate, polyacrylate, and nano-silica; The phosphorus slag used is dried and then ball-milled in a ball mill until the specific surface area is greater than 500 m². 2 / kg was used to prepare finely ground phosphorus slag; The red sandstone powder used was calcined at 500-600℃ for 2-3 hours and then ball-milled to a specific surface area greater than 500 m². 2 / kg was used to prepare calcined red sandstone powder; The detoxification agent is composed of 40%-60% petroleum coke desulfurization ash, 20%-40% slaked lime, and 10%-30% carbide slag.

2. The high water resistance and low toxicity phosphogypsum curing agent according to claim 1, characterized in that, The curing agent comprises the following raw materials in weight percentages: 51% finely ground phosphorus slag, 25% calcined red sandstone powder, 20% binder, 2% waterproofing agent, and 2% detoxifying agent.

3. The method for preparing the highly water-resistant and low-toxicity phosphogypsum curing agent according to any one of claims 1-2, characterized in that, The preparation methods include the following: Finely ground phosphorus slag and calcined red sandstone powder are added to a mixer and mixed for 30-40 seconds. Then, a binder and a detoxifying agent are added and mixed for 30-40 seconds. Finally, a waterproofing agent is added and mixed for 3-5 minutes to prepare a highly water-resistant and low-toxicity phosphogypsum curing agent.

4. The method for preparing phosphogypsum roadbed materials using the highly water-resistant and low-toxicity phosphogypsum curing agent according to any one of claims 1-2, characterized in that, The preparation process includes the following steps: S1: Test the moisture content and contaminants of the undisturbed phosphogypsum; S2: Mix the undisturbed phosphogypsum with a highly water-resistant and low-toxicity phosphogypsum curing agent to obtain a mixture. The highly water-resistant and low-toxicity phosphogypsum curing agent accounts for 5%-10% of the phosphogypsum mass. S3: The mixture from step S2 shall be prepared in accordance with JTG E51-2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Cylindrical specimens were prepared by static pressing with a moisture content of 15%-20% and a compaction degree of not less than 96%. After demolding and curing, a highly water-resistant and low-toxicity phosphogypsum roadbed material was obtained.

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