Low-alkalinity phosphogypsum composite heavy metal curing agent as well as preparation method and application thereof

Abstract

The invention discloses a low-alkalinity phosphogypsum composite heavy metal curing agent as well as a preparation method and application thereof. The low-alkalinity phosphogypsum composite heavy metal curing agent comprises the following components in parts by mass: 5-8 parts of a low-alkalinity gelling agent, 3-6 parts of an activated crystal form regulator, 2-5 parts of a chelating dispersant, 3-7 parts of an enhanced chelating agent, 6-10 parts of an efficient adsorbent and 63-84 parts of a carrier. An aluminate cement-superfine slag powder-metakaolin compound system is created for the first time to replace a traditional high-alkali gelling agent, the pH value of the system is reduced from 10.3-11.5 to 7.2-8.0, meanwhile, by means of the hydration promotion effect of the superfine slag powder, the 3d compressive strength is improved by 60% or above, and the technical contradiction between low alkalinity and high gelling activity is thoroughly solved.

Description

Technical Field

[0001] This invention belongs to the field of harmless phosphogypsum technology, and particularly relates to a low-alkalinity phosphogypsum composite heavy metal curing agent, its preparation method and application. Background Technology

[0002] Phosphogypsum is a major industrial byproduct generated during the wet-process phosphoric acid production, producing approximately 4-5 tons of phosphogypsum for every ton of phosphoric acid produced. The leaching of heavy metal ions (such as Cd, Pb, Cr, and As) and soluble phosphorus and fluorine from phosphogypsum can cause soil and water pollution. Direct stockpiling or simple treatment can easily lead to rainwater leaching and pollution of soil and groundwater, creating significant environmental hazards. Pretreatment is necessary to reduce the impact of impurities on the performance of phosphogypsum. However, while water washing can remove impurities, it is costly, energy-intensive, and causes secondary pollution, making it unsuitable for large-scale application. Biological and adsorption methods also face the problems of high cost and low efficiency. Furthermore, the low utilization rate of phosphogypsum (less than 40%) has become a core bottleneck restricting the green transformation of the phosphoric acid chemical industry.

[0003] Existing heavy metal curing technologies for phosphogypsum mostly employ traditional curing agents such as cement and lime, but these pose risks of expansion and heavy metal leaching due to high-alkali environments. Curing agents often rely on single chelating agents or high-alkali cementitious systems, exhibiting the following drawbacks: First, the curing of heavy metals is not highly targeted, resulting in uneven curing efficiency for complex, multi-component heavy metals; second, high-alkali components easily lead to excessive pH values ​​in the cured body, triggering alkali-aggregate reactions in building materials applications; third, the disordered crystal morphology of phosphogypsum itself results in insufficient mechanical strength after curing, limiting its high-value utilization; and fourth, the binding stability between chelating agents and heavy metal ions is poor, leading to a high risk of long-term leaching.

[0004] Therefore, it is imperative to develop a composite curing agent with low alkalinity that can efficiently cure heavy metals in phosphogypsum. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a low-alkalinity phosphogypsum composite heavy metal curing agent, its preparation method, and its application. This invention synergistically integrates the various components to develop a low-alkalinity, high-strength, and highly stable composite curing agent, thus overcoming existing technical bottlenecks.

[0006] The objective of this invention is achieved through the following technical solution: A low-alkalinity phosphogypsum composite heavy metal curing agent comprises the following components in parts by weight: 5-8 parts low-alkalinity gelling agent, 3-6 parts activating crystal form modifier, 2-5 parts chelating dispersant, 3-7 parts reinforcing chelating agent, 6-10 parts high-efficiency adsorbent, and 63-84 parts carrier. The low-alkali cementitious material is a mixture of CA-50 aluminate cement, ultrafine slag powder and metakaolin in a mass ratio of 2:3:2. The activated crystal form modifier is a mixture of tributyl phosphate (TBP) and anhydrous ethanol in a 1:1 mass ratio; The chelating dispersant is a mixture of polyepoxysuccinic acid (PESA) and aminotrimethylenephosphonic acid (ATMP) in a mass ratio of 3:2; The enhanced chelating agent is a mixture of sodium dimethyl dithiocarbamate and sodium trithiocarbonate (TTC-Na) in a mass ratio of 1 to 4:1; The high-efficiency adsorbent is a mixture of hydrochloric acid activated diatomaceous earth and ultrafine slag powder in a mass ratio of 2:1, or a mixture of iron-modified diatomaceous earth and ultrafine slag powder in a mass ratio of 7:3. The carrier is pretreated phosphogypsum.

[0007] Preferably, the alkali content of the CA-50 aluminate cement is ≤0.5%, the specific surface area of ​​the ultrafine slag powder is ≥500m² / kg, and the activity index of the metakaolin is ≥95%.

[0008] Preferably, the polyepoxysuccinic acid has a molecular weight of 1000-3000.

[0009] In this invention, the low-alkali cementitious material has both low alkali properties and high cementitious activity. Aluminate cement provides early strength, ultrafine slag powder improves density through micro-aggregate effect and hydration cementation, and metakaolin exerts volcanic ash activity to generate stable hydration products, which can stabilize the pH of the system at 7.2~8.0. At the same time, it reacts with soluble phosphorus to generate hydroxyapatite precipitate, achieving a dual gain of strength and harmlessness.

[0010] In the activated crystal form modifier, anhydrous ethanol is used as a dispersion medium to prevent TBP from agglomerating in the dry powder system. TBP activates inert heavy metal ions through complexation and adsorbs onto the growth surface of gypsum crystals, guiding the transformation of calcium sulfate dihydrate crystals from needle-like to short columnar and granular, significantly optimizing the particle packing structure and increasing the 3d compressive strength of the roadbed material by more than 40% compared to the system without TBP.

[0011] In the chelating dispersant, the polymer chains of PESA can effectively disperse phosphogypsum particles, ensuring no agglomeration at a high dosage of 80%; the phosphonic acid groups of ATMP can form stable complexes with soluble phosphorus, and work synergistically with low-alkali gelling active components to precisely control water-soluble P2O5 to below 0.15%.

[0012] Strengthening chelating agents utilize the strong coordination properties of sulfur atoms to form targeted curing: sodium dimethyl dithiocarbamate for Cd 2+ Pb2+ TTC-Na exhibits excellent chelation effects with divalent heavy metals, while it can bind with Cr. 3+ As 3+ It forms stable sulfide chelates with trivalent heavy metals, achieving a solidification rate of over 99.5% for trace heavy metals in roadbed materials, while also assisting in the adsorption of soluble fluoride ions.

[0013] In the high-efficiency adsorbent, diatomaceous earth, after being activated with 3wt% hydrochloric acid, has a more developed mesoporous structure, which significantly improves its specific adsorption capacity for fluoride ions; ultrafine slag powder reacts synergistically with the calcium source in the system to generate hydrated calcium silicate gel, which further densifies the solidified body structure, increasing the 28-day compressive strength by 25% compared to the single adsorbent system.

[0014] The preparation method of the above-mentioned low-alkalinity phosphogypsum composite heavy metal curing agent includes the following steps: Phosphogypsum and water are mixed at a liquid-solid ratio of 3-4:1, stirred evenly, filtered, and the filter cake is calcined at 550-600℃ for 1.5 hours. The calcined product is ball-milled to a fineness of 200 mesh to obtain pretreated phosphogypsum. In this invention, after the filter cake is calcined, the calcium sulfate dihydrate is partially converted into calcium sulfate hemihydrate with higher activity. After cooling, it is ground to 200 mesh by a ball mill. The activity of phosphogypsum is increased by 30% after pretreatment, laying the foundation for high-dosage applications of more than 80%.

[0015] A highly efficient adsorbent is prepared by mixing diatomaceous earth and hydrochloric acid at a liquid-solid ratio of 5:1, activating the mixture by stirring under water bath heating, filtering, washing the filter cake with water until neutral, drying, mixing it with ultrafine slag, and ball milling it to a fineness of 300 mesh. Alternatively, a highly efficient adsorbent can be prepared by mixing diatomaceous earth and ferric chloride solution at a liquid-solid ratio of 5:1, activating the mixture by stirring under water bath heating, filtering, washing the filter cake with water until neutral, drying, mixing it with ultrafine slag, and ball milling it to a fineness of 300 mesh. The chelating dispersant and the reinforcing chelating agent are dry-mixed evenly to obtain a composite chelating agent; First, the pretreated phosphogypsum is mixed evenly with low-alkali cementitious material. Then, the activating crystal form adjuster, composite chelating agent and high-efficiency adsorbent are added in sequence. After each addition, the mixture is stirred thoroughly to obtain the final mixture. After vacuum drying, the mixture is then ground by air jet milling to 350-400 mesh to obtain the low-alkalinity phosphogypsum composite heavy metal curing agent.

[0016] Preferably, in the preparation step of the high-efficiency adsorbent, when activated with hydrochloric acid, the concentration of hydrochloric acid is 3 wt%; the temperature of the water bath heating is 60 ± 5 °C; the stirring rate for stirring activation is 200 r / min; the drying temperature is 105 ± 5 °C, and the drying time is 4 h. When activated with ferric chloride, the concentration of the ferric chloride solution is 0.2 mol / L, the water bath heating temperature is 60±5℃, the stirring rate for activation is 200 r / min, the drying temperature is 105±5℃, and the drying time is 4 h.

[0017] Preferably, in the preparation step of the mixture, the activating crystal form modifier is added within 5 to 8 minutes.

[0018] Preferably, in the preparation step of the low-alkalinity phosphogypsum composite heavy metal curing agent, the vacuum drying temperature is 60°C and the vacuum degree is -0.08MPa. Application of the above-mentioned low-alkalinity phosphogypsum composite heavy metal curing agent in the preparation of roadbed materials.

[0019] Preferably, the content of phosphogypsum in the roadbed material is ≥80%.

[0020] Preferably, the amount of the low-alkalinity phosphogypsum composite heavy metal curing agent added accounts for 8 to 12 wt% of the phosphogypsum content in the roadbed material.

[0021] In some embodiments of the present invention, the specific methods for applying the low-alkalinity phosphogypsum composite heavy metal curing agent in the preparation of roadbed materials are as follows: Add the low-alkalinity phosphogypsum composite heavy metal curing agent at 8-12% of the mass of the phosphogypsum to be treated (ensuring the total phosphogypsum content in the subgrade material is ≥80%). Simultaneously, add 16-22% of the total mass of the mixture (subgrade material + curing agent) of tap water (water temperature controlled at 20-25℃ to avoid low temperature affecting hydration). Use a forced mixer at 300 rpm for 25-28 minutes until the material forms a uniform paste (no lumps, consistent color). Then, spread the mixture in layers according to subgrade construction specifications, with each layer controlled at a thickness of 15-20 cm. Compact the mixture 6-8 times using an 18t vibratory roller to ensure a compaction degree ≥95%. Curing is carried out in a natural environment (temperature 5-35℃, relative humidity 50-80%). For the first 7 days of curing, water twice daily to keep the surface moist. After 28 days, the cured body meets the performance standards and can be put into use.

[0022] The core mechanism of action of this invention lies in: 1. Tributyl phosphate (TBP) is a highly efficient extractant that can activate heavy metal ions through hydrogen bonding. At the same time, its ester structure can bind to the hydroxyl groups on the surface of gypsum crystals, guiding the directional growth of crystals. 2. The polyepoxysuccinic acid (PESA) and aminotrimethylenephosphonic acid (ATMP) compound system has both chelating and dispersing functions, which can improve the uniformity of component mixing; 3. Both dimethyl dithiocarbamate and trithiocarbonate contain strongly coordinating sulfur atoms, and when combined, they can form stable chelates for heavy metals of different valence states.

[0023] Compared with the prior art, the beneficial effects of the present invention include: (1) Innovation of low-alkali and high-activity system: The first aluminate cement (low alkali) - ultrafine slag powder (active cement) - metakaolin (volcanic ash activity) compound system is created to replace the traditional high-alkali cementitious agent. The pH of the system is reduced from 10.3~11.5 to 7.2~8.0. At the same time, with the help of the hydration promotion effect of ultrafine slag powder, the 3d compressive strength is increased by more than 60%, which completely solves the technical contradiction between "low alkalinity and high cementitious activity".

[0024] (2) Construction of multi-level solidification mechanism: A four-level synergistic mechanism is formed, namely “TBP activation-PESA / ATMP dispersion chelation-sodium dimethyl dithiocarbamate / TTC-Na targeted enhanced chelation-activated diatomaceous earth specific adsorption”, which improves the solidification / adsorption efficiency of heavy metals, soluble phosphorus and fluorine by 7~15% compared with the single system, and achieves precise control of harmful components.

[0025] (3) Significant advantages in construction and resources: The curing agent and phosphogypsum have excellent workability after mixing and can be directly adapted to existing roadbed construction equipment without process modification; the phosphogypsum content is ≥80%, and about 2,000 tons of phosphogypsum can be consumed per kilometer of roadbed, achieving the resource recycling goal of "treating waste with waste" and reducing project costs by more than 30%.

[0026] (4) Significant economic and social benefits: It can not only extend the service life of roads, but also reduce maintenance costs and improve the overall benefits of road engineering. At the same time, it also solves the problems of large stockpiles of phosphogypsum and difficulty in treatment, achieving a win-win situation for both economic and environmental benefits. It is of great significance for realizing the high-value utilization of solid wastes such as phosphogypsum, and is in line with the concept of ecological civilization construction and sustainable development. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Example 1 (Adapted for Cd-containing 2+ Cr 3+ (Conventional phosphogypsum) A low-alkalinity phosphogypsum composite heavy metal curing agent, comprising the following components in parts by weight: 7 kg of low-alkali cementitious agent, 2 kg of CA-50 aluminate cement (alkali content 0.45%), 3 kg of ultrafine slag powder (specific surface area 520 m² / kg), and 2 kg of metakaolin (activity index 96%) are mixed in a mass ratio of 2:3:2. 5 kg of activating crystal form modifier: 2.5 kg of tributyl phosphate (TBP, 99% purity) and 2.5 kg of anhydrous ethanol, mixed in a 5:5 mass ratio; Chelating dispersant 3kg: Polyepoxysuccinic acid (PESA, molecular weight 2000) 1.8kg, aminotrimethylenephosphonic acid (ATMP) 1.2kg, compounded in a mass ratio of 3:2; 6 kg of enhanced chelating agent: 4.8 kg of sodium dimethyl dithiocarbamate and 1.2 kg of sodium trithiocarbonate (TTC-Na), compounded in a mass ratio of 4:1; 9 kg of high-efficiency adsorbent: 6 kg of hydrochloric acid-activated diatomaceous earth (specific surface area 850 m² / g) and 3 kg of ultrafine slag powder are mixed in a mass ratio of 2:1. 70 kg of active phosphogypsum carrier: The raw phosphogypsum was pretreated by washing with water (liquid-solid ratio 3:1), calcining at 580℃ for 1.5 hours, and grinding with 200 mesh.

[0029] The specific steps for preparing the above-mentioned low-alkalinity phosphogypsum composite heavy metal curing agent are as follows: (1) Carrier pretreatment: Remove impurities >5mm from 70kg phosphogypsum, stir and wash with water at 150r / min for 30min, filter, calcine at 560℃ for 1.5h, grind to 200 mesh fineness, and seal for later use; Preparation of high-efficiency adsorbent: 6 kg of diatomaceous earth was added to 30 kg of 3 wt% hydrochloric acid, and activated by stirring in a constant temperature water bath at 60℃ for 2 h (200 r / min). After washing until neutral, it was dried at 105℃ for 4 h. Then it was mixed with 3 kg of ultrafine slag powder and ground to 300 mesh for later use. Preparation of activating crystal form modifier: 2.5 kg TBP and 2.5 kg ethanol are stirred at room temperature for 15 min (120 r / min). Preparation of composite chelating agent: 1.8 kg PESA and 1.2 kg ATMP were dry-mixed for 10 min, and then 4.8 kg sodium dimethyl dithiocarbamate and 1.2 kg TTC-Na were added and dry-mixed for 20 min. Low-alkali cementitious premix: Mix 2kg aluminate cement, 3kg ultrafine slag powder, and 2kg metakaolin for 5 minutes; (2) Basic cementitious construction: 70 kg of pretreated carrier is added to the mixer, and 7 kg of low-alkali cementitious agent is added while stirring at 80 r / min. Stir for 12 min. (3) Activation and chelation: Increase the rotation speed to 120 r / min, add 5 kg of activating crystal form adjuster within 6 min, stir for 8 min; add 3 kg of composite chelating agent, and continue stirring for 15 min; (4) Strength enhancement: Add 9 kg of high-efficiency adsorbent and stir at 150 r / min for 20 min to obtain a mixture; (5) Finished product processing: The mixture is vacuum dried at 60℃ and -0.08MPa for 30 minutes. The dried sample is then ground to a fineness of 380 mesh and a sieve pass rate of 98% through 350 mesh. The sample is then sealed and packaged.

[0030] Application testing: A sample from a phosphate fertilizer plant containing Cd 2+ (12.5 mg / kg), Cr 3+ The raw phosphogypsum (38.2 mg / kg) was pretreated (phosphogypsum and water were mixed at a liquid-solid ratio of 3:1, stirred evenly, filtered, and the filter cake was calcined at 560℃ for 1.5 h. The calcined product was then ball-milled to a fineness of 200 mesh). 830 kg of this pretreated phosphogypsum (accounting for 83% of the total mass of the roadbed material) was then added to 100 kg of the low-alkalinity phosphogypsum composite heavy metal curing agent prepared in Example 1 (containing 7 kg of low-alkalinity gelling active component) and 180 kg of tap water. The mixture was then stirred in a forced mixer for 25 min until a uniform paste was formed. The paste was then poured into standard test blocks of 100 mm × 100 mm × 100 mm and cured at 25℃ and 70% relative humidity.

[0031] Test results of the test blocks: 3-day compressive strength was 3.8 MPa, 7-day compressive strength was 6.2 MPa, and 28-day compressive strength was 11.3 MPa; the system pH was 7.8 (2.5 units lower than the traditional high-alkalinity system), and Cd... 2+ Curing rate 99.8%, Cr 3+ The curing rate was 99.6%, and the strength loss rate after 50 freeze-thaw cycles was only 3.2%. The water-soluble P2O5 content was 0.12%, and the water-soluble fluorine content was 0.07%. All indicators met the requirements of the "Technical Specification for Harmless Treatment of Phosphogypsum (Trial)". The curing rates of heavy metals, phosphorus, and fluorine were calculated by measuring the water-soluble components in the cured body (according to JC / T 2073), with the curing rate = 1 - leaching rate. The freeze-thaw cycle test was conducted according to GB / T 50082. The strength loss rate was expressed as the percentage decrease in strength after freeze-thaw cycles relative to the 28-day strength.

[0032] Example 2 (Adapted for Pb-containing 2+ Zn 2+ (Conventional phosphogypsum) A low-alkalinity phosphogypsum composite heavy metal curing agent, comprising the following components in parts by weight: 6 kg of low-alkali cementitious agent: 1.715 kg of CA-50 aluminate cement (alkali content 0.45%), 2.57 kg of ultrafine slag powder (specific surface area 520 m² / kg), and 1.715 kg of metakaolin (activity index 96%), mixed in a mass ratio of 2:3:2; 4 kg of activating crystal form modifier: 2 kg of tributyl phosphate (TBP, 99% purity) and 2 kg of anhydrous ethanol, mixed in a mass ratio of 5:5; Chelating dispersant 2kg: Polyepoxysuccinic acid (PESA, molecular weight 1500) 1.2kg, aminotrimethylenephosphonic acid (ATMP) 0.8kg, compounded in a mass ratio of 3:2; 5 kg of chelating agent: 4 kg of sodium dimethyl dithiocarbamate and 1 kg of sodium trithiocarbonate (TTC-Na) are compounded in a mass ratio of 4:1. 10 kg of high-efficiency adsorbent: 6.67 kg of hydrochloric acid-activated diatomaceous earth (specific surface area 850 m² / g) and 3.33 kg of ultrafine slag powder, mixed in a mass ratio of 2:1; 63 kg of active phosphogypsum carrier: high-fluorine phosphogypsum was pretreated by washing with water (liquid-solid ratio 4:1), calcining at 560℃ for 1.5 hours, and grinding with 200 mesh.

[0033] The specific steps for preparing the above-mentioned low-alkalinity phosphogypsum composite heavy metal curing agent are as follows: (1) Carrier pretreatment: Remove impurities >5mm from 63kg of phosphogypsum, stir and wash with water at 180r / min for 40min, filter, calcine at 560℃ for 1.5h, grind to 200 mesh fineness, and seal for later use; Preparation of high-efficiency adsorbent: 6.67 kg of diatomaceous earth was added to 33.35 kg of 3 wt% hydrochloric acid, and activated by stirring in a constant temperature water bath at 60 ℃ for 2 h (200 r / min). After washing until neutral, it was dried at 105 ℃ for 4 h. Then it was mixed with 3.33 kg of ultrafine slag powder and ground to 300 mesh for later use. Preparation of activating crystal form modifier: Stir 2 kg TBP and 2 kg ethanol at room temperature for 15 min (120 r / min). Preparation of composite chelating agent: 1.2 kg PESA and 0.8 kg ATMP are dry-mixed for 10 min, then 4 kg sodium dimethyl dithiocarbamate and 1 kg TTC-Na are added and dry-mixed for 20 min; Low-alkali cementitious premix: Mix 1.715 kg aluminate cement, 2.57 kg ultrafine slag powder, and 1.715 kg metakaolin for 5 minutes; (2) Basic cementitious construction: 63 kg of pretreated carrier was added to the mixer, and 6 kg of low-alkali cementitious agent was added while stirring at 80 r / min. The mixture was stirred for 12 min. (3) Activation and chelation: Increase the rotation speed to 120 r / min, add 4 kg of activation crystal form adjuster within 5 min, stir for 8 min; add 2 kg of composite chelating agent, and continue stirring for 15 min; (4) Strength enhancement: Add 10 kg of high-efficiency adsorbent and stir at 150 r / min for 20 min to obtain a mixture; (5) Finished product processing: The mixture is vacuum dried at 60℃ and -0.08MPa for 30 minutes. The dried sample is then ground to a fineness of 350 mesh with a 350 mesh sieve pass rate of 98%, and then sealed and packaged.

[0034] Application testing: Take phosphogypsum from a chemical industrial park, and after pretreatment (phosphogypsum and water are mixed at a liquid-solid ratio of 3:1, stirred evenly, filtered, and the filter cake is calcined at 560℃ for 1.5 hours, and the calcined product is ball-milled to a fineness of 200 mesh), take 850 kg (accounting for 85% of the total mass of the roadbed material), add 90 kg of the low-alkalinity phosphogypsum composite heavy metal curing agent prepared in Example 2 and 190 kg of tap water, put it into a forced mixer and stir for 25 minutes until a uniform paste is formed, pour it into a standard test block of 100 mm × 100 mm × 100 mm, and cure it in an environment of 25℃ and 70% relative humidity.

[0035] Test results of the test block: 3-day compressive strength was 3.5 MPa, 7-day compressive strength was 5.8 MPa, and 28-day compressive strength was 10.5 MPa; water-soluble P₂O₅ content was 0.14%, water-soluble fluorine content was 0.09%, and Pb content was [not specified]. 2+ The leaching concentration was 0.005 mg / L, Pb 2+ Zn 2+ The leaching concentrations of heavy metals are all below the limits of GB 5085.3-2007, making them suitable for use in highway subgrade base courses.

[0036] Example 3 (suitable for high arsenic phosphogypsum, containing As) 3+ (Concentration is 50.2 mg / kg) A low-alkalinity phosphogypsum composite heavy metal curing agent, comprising the following components in parts by weight: 7 kg of low-alkali cementitious agent, 2 kg of CA-50 aluminate cement (alkali content 0.42%), 3 kg of ultrafine slag powder (specific surface area 530 m² / kg), and 2 kg of metakaolin (activity index 97%) are mixed in a mass ratio of 2:3:2. 5 kg of activating crystal form modifier: 2.5 kg of tributyl phosphate (TBP, 99% purity) and 2.5 kg of anhydrous ethanol, mixed in a 5:5 mass ratio; TBP activates As 3+ Enhance reaction activity; Chelating dispersant 3kg: Polyepoxysuccinic acid (PESA, molecular weight 2500) 1.8kg, aminotrimethylenephosphonic acid (ATMP) 1.2kg, compounded in a mass ratio of 3:2; 7 kg of enhanced chelating agent: 3.5 kg of sodium dimethyl dithiocarbamate and 3.5 kg of sodium trithiocarbonate (TTC-Na), compounded in a 1:1 mass ratio; increasing the proportion of TTC-Na to enhance As 3+ Chelation; High-efficiency adsorbent 10kg: 7kg iron-modified diatomaceous earth (specific surface area 920m² / g) and 3kg ultrafine slag powder, mixed in a mass ratio of 7:3; iron modification enhances arsenic adsorption; 68 kg of active phosphogypsum carrier: high arsenic phosphogypsum was pretreated by washing with water (liquid-solid ratio 4:1), calcining at 570℃ for 1.5 hours, and grinding with 200 mesh. 30% of soluble arsenic was removed by washing with water. The specific steps for preparing the above-mentioned low-alkalinity phosphogypsum composite heavy metal curing agent are as follows: (1) Carrier pretreatment: Remove impurities >5mm from 68kg of phosphogypsum, stir and wash with water at 180r / min for 40min, filter, calcine at 570℃ for 1.5h, grind to 200 mesh fineness, and seal for later use; Preparation of high-efficiency adsorbent: 7 kg of diatomaceous earth was added to 35 kg of 0.2 mol / L ferric chloride solution and activated by stirring in a constant temperature water bath at 65℃ for 1.5 h (200 r / min). After filtration, the filter cake was washed until neutral and then dried at 110℃ for 4 h. Subsequently, it was mixed with 3 kg of ultrafine slag powder and ground to a fineness of 300 mesh for later use. Preparation of activating crystal form modifier: 2.5 kg TBP and 2.5 kg ethanol are stirred at room temperature for 15 min (120 r / min). Preparation of composite chelating agent: 1.8 kg PESA and 1.2 kg ATMP were dry-mixed for 10 min, and then 3.5 kg sodium dimethyl dithiocarbamate and 3.5 kg TTC-Na were added and dry-mixed for 25 min (extending the time by 5 min to ensure dispersion of the chelating agent). Low-alkali cementitious premix: Mix 2kg aluminate cement, 3kg ultrafine slag powder, and 2kg metakaolin for 5 minutes; (2) Basic gel construction: 68 kg of pretreated carrier was added to the mixer, and 7 kg of low-alkali gelling agent was added while stirring at 80 r / min. The mixture was stirred for 12 min. (3) Activation and chelation: Increase the rotation speed to 120 r / min, add 5 kg of activation crystal form adjuster within 7 min, stir for 10 min; add 3 kg of composite chelating agent, and continue stirring for 20 min; (4) Strength enhancement: Add 10 kg of high-efficiency adsorbent and stir at 150 r / min for 25 min (extend for 5 min to improve the adsorption and encapsulation effect) to obtain a mixture; (5) Finished product processing: The mixture is vacuum dried at 60℃ and -0.08MPa for 30 minutes. The dried sample is then ground to a fineness of 380 mesh and the 350 mesh sieve passing rate is 98.5%. It is then sealed and packaged.

[0037] Application testing: Take a certain amount of raw phosphogypsum, and after pretreatment (the phosphogypsum and water are mixed at a liquid-solid ratio of 3:1, stirred evenly, filtered, and the filter cake is calcined at 560℃ for 1.5h, and the calcined product is ball-milled to a fineness of 200 mesh), take 820kg (accounting for 82% of the total mass of the roadbed material), add 100kg of the low-alkalinity phosphogypsum composite heavy metal curing agent prepared in Example 3, and 190kg of tap water (water temperature 22℃), put it into a forced mixer and stir for 28min (300r / min) until a uniform paste is formed, spread it according to the roadbed specifications (each layer 16cm), roll it 8 times with an 18t road roller (compaction degree 97%), and cure it at 25℃ and 75% humidity.

[0038] 28-day test results: 3-day compressive strength was 3.6 MPa, 7-day compressive strength was 6.0 MPa, and 28-day compressive strength was 11.0 MPa; system pH = 7.6, As 3+ The curing rate was 99.6% (leaching concentration was 0.21 mg / L, far below the limit of 0.3 mg / L in GB 5085.3-2007); the water-soluble P2O5 content was 0.13%, and the water-soluble fluorine content was 0.08%. All indicators met the requirements of the regulations and roadbed materials.

[0039] Comparative Example 1 (Traditional Cement-Based Hardener) High-alkali curing agent components (total mass 100kg): 15 kg of high-alkali activator; 8 kg of quicklime; 7 kg of PO 42.5 cement; 5 kg of single chelating agent: 5 kg of disodium EDTA; 5 kg of adsorbent: 5 kg of ordinary diatomaceous earth; 75kg of phosphogypsum carrier: only simply crushed (200 mesh fineness), without water washing and calcination pretreatment.

[0040] Preparation and application: Mix the above components dry for 20 minutes (100 r / min) to make a curing agent. Take 830 kg of untreated phosphogypsum, add 100 kg of the curing agent and 180 kg of tap water, and put them into a forced mixer to mix for 28 minutes (300 r / min) until a uniform paste is formed. Spread the paste according to the roadbed specifications (16 cm per layer), and roll it 8 times with an 18t roller (97% compaction degree). Curing is carried out at 25℃ and 75% humidity.

[0041] 28-day test results: pH=11.2 (exceeding standard), 3-day compressive strength 2.3MPa (below standard), 28-day compressive strength 10.1MPa; Cd 2+ The curing rate was 92.0%, the water-soluble P2O5 content was 0.22%, and the water-soluble fluorine content was 0.16%, with many indicators failing to meet the requirements of the regulations.

[0042] As can be seen from the comparison, the curing agent prepared by the present invention is significantly superior to traditional cement-based curing agents in terms of alkalinity control, heavy metal curing rate, and mechanical properties.

[0043] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A low-alkalinity phosphogypsum composite heavy metal curing agent, characterized in that, It comprises the following components in parts by weight: 5-8 parts low-alkali gelling agent, 3-6 parts activated crystal form modifier, 2-5 parts chelating dispersant, 3-7 parts enhanced chelating agent, 6-10 parts high-efficiency adsorbent and 63-84 parts carrier; The low-alkali cementitious material is a mixture of CA-50 aluminate cement, ultrafine slag powder and metakaolin in a mass ratio of 2:3:

2. The activated crystal form modifier is a mixture of tributyl phosphate and anhydrous ethanol in a 1:1 mass ratio; The chelating dispersant is a mixture of polyepoxysuccinic acid and aminotrimethylenephosphonic acid in a mass ratio of 3:2; The enhanced chelating agent is a mixture of sodium dimethyl dithiocarbamate and sodium trithiocarbonate in a mass ratio of 1 to 4:

1. The high-efficiency adsorbent is a mixture of hydrochloric acid-activated diatomaceous earth and ultrafine slag powder in a mass ratio of 2:1; or a mixture of iron-modified diatomaceous earth and ultrafine slag powder in a mass ratio of 7:

3. The carrier is pretreated phosphogypsum.

2. The low-alkalinity phosphogypsum composite heavy metal curing agent according to claim 1, characterized in that, The alkali content of the CA-50 aluminate cement is ≤0.5%, the specific surface area of ​​the ultrafine slag powder is ≥500m² / kg, and the activity index of the metakaolin is ≥95%.

3. The low-alkalinity phosphogypsum composite heavy metal curing agent according to claim 1, characterized in that, The molecular weight of the polyepoxysuccinic acid is 1000~3000.

4. The preparation method of the low-alkalinity phosphogypsum composite heavy metal curing agent according to any one of claims 1 to 3, characterized in that, Includes the following steps: Phosphogypsum and water are mixed at a liquid-solid ratio of 3-4:1, stirred evenly, filtered, and the filter cake is calcined at 550-600℃ for 1.5 hours. The calcined product is ball-milled to a fineness of 200 mesh to obtain pretreated phosphogypsum. A highly efficient adsorbent is prepared by mixing diatomaceous earth and hydrochloric acid at a liquid-solid ratio of 5:1, activating the mixture by stirring under water bath heating, filtering, washing the filter cake with water until neutral, drying, mixing it with ultrafine slag, and ball milling it to a fineness of 300 mesh. Alternatively, a highly efficient adsorbent can be prepared by mixing diatomaceous earth and ferric chloride solution at a liquid-solid ratio of 5:1, activating the mixture by stirring under water bath heating, filtering, washing the filter cake with water until neutral, drying, mixing it with ultrafine slag, and ball milling it to a fineness of 300 mesh. The chelating dispersant and the reinforcing chelating agent are dry-mixed evenly to obtain a composite chelating agent; First, the pretreated phosphogypsum is mixed evenly with low-alkali cementitious material. Then, the activating crystal form adjuster, composite chelating agent and high-efficiency adsorbent are added in sequence. After each addition, the mixture is stirred thoroughly to obtain the final mixture. After vacuum drying, the mixture is then pulverized and ground to 350-400 mesh using airflow to obtain the low-alkalinity phosphogypsum composite heavy metal curing agent.

5. The preparation method of the low-alkalinity phosphogypsum composite heavy metal curing agent according to claim 4, characterized in that, In the preparation steps of the high-efficiency adsorbent, when activated with hydrochloric acid, the concentration of the hydrochloric acid is 3 wt%; the temperature of the water bath is 60 ± 5 °C; the stirring rate for activation is 200 r / min; the drying temperature is 105 ± 5 °C, and the drying time is 4 h; and / or When activated with ferric chloride, the concentration of the ferric chloride solution is 0.2 mol / L, the water bath heating temperature is 60±5℃, the stirring rate for activation is 200 r / min, the drying temperature is 105±5℃, and the drying time is 4 h.

6. The preparation method of the low-alkalinity phosphogypsum composite heavy metal curing agent according to claim 4, characterized in that, In the preparation step of the mixture, the activated crystal form modifier is added within 5 to 8 minutes.

7. The preparation method of the low-alkalinity phosphogypsum composite heavy metal curing agent according to claim 4, characterized in that, In the preparation step of the low-alkalinity phosphogypsum composite heavy metal curing agent, the vacuum drying temperature is 60℃ and the vacuum degree is -0.08MPa.

8. The application of the low-alkalinity phosphogypsum composite heavy metal curing agent according to any one of claims 1 to 3 in the preparation of roadbed materials.

9. The application according to claim 8, characterized in that, The content of phosphogypsum in the roadbed material is ≥80%.

10. The application according to claim 9, characterized in that, The amount of the low-alkalinity phosphogypsum composite heavy metal curing agent added accounts for 8-12 wt% of the phosphogypsum content in the roadbed material.