Phosphogypsum-based curing material and preparation method thereof

Abstract

The invention relates to the technical field of low-carbon building materials, in particular to an ardealite-based curing material and a preparation method thereof.Active ardealite obtained through pretreatment serves as a main raw material, mineral powder and carbide slag are added to be matched to form a cementing material system, a modifier is added to be matched with a cementing material hydration product to cure Pb < 2 + > in the ardealite, and the curing material is prepared. The leaching concentration is obviously reduced, the mechanical property of the curing material is enhanced, the resource utilization value of the ardealite is improved, and a more competitive solution is provided for the fields of building materials and environmental pollution abatement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-carbon building materials, and in particular to a phosphogypsum-based solidification material and a preparation method thereof. BACKGROUND

[0002] Phosphogypsum is a large amount of solid waste produced in the process of wet-process phosphoric acid, and its main component is calcium sulfate dihydrate. About 5-5.5 tons of phosphogypsum are discharged for every ton of phosphoric acid produced. For a long time, due to the limitation of comprehensive utilization technology, the comprehensive utilization rate of phosphogypsum is less than 40%, and most of it is disposed of by piling. This method not only occupies a large amount of land resources, but also causes serious environmental problems. The residual heavy metals in phosphogypsum may migrate with rainwater or groundwater, posing a threat to water bodies, soil and ecosystems, and even endangering human health. In view of the technical bottleneck of phosphogypsum resource utilization, the current focus is on reducing the Pb 2+ leaching concentration and improving the adsorption capacity through modification processes.

[0003] Solidification and adsorption of heavy metal ions are relatively mature in the field of water treatment, however, the addition of adsorbents has a great influence on the performance of phosphogypsum-based cementitious materials and solidification bodies, and there is still a great gap in the study of solidification of heavy metals in phosphogypsum.

[0004] Industrial production produces a lot of industrial waste slag, such as fly ash, mineral powder, calcium carbide slag, etc. Mineral powder is a by-product formed during the blast furnace ironmaking industry, which is rapidly quenched and does not have time to crystallize, thus forming particles with glassy properties. The cooled particles are dried and ground to make fine powder. It contains 90-95% glass body, which gives it high potential hydration activity. Calcium carbide slag is a by-product produced when calcium carbide reacts with water to produce acetylene, and its pH value is usually not less than 12.4. The existing technology is commonly used as an alkaline activator.

[0005] Chinese patent CN202011400623.X discloses a phosphogypsum-containing multi-layer foamed plastic board and a preparation method thereof. The multi-layer structure is composed of a calcium plastic paper on the surface layer, a phosphogypsum-containing single-layer foamed plastic board on the core layer, and a calcium plastic paper on the bottom layer. The raw materials for the core layer include, by mass fraction: 55-60 parts of polyethylene, 20-30 parts of phosphogypsum, 2.5-3 parts of polyethylene glycol, 1.5-2 parts of polyvinyl alcohol, 0.5-1.0 parts of stearic acid, 0.02-0.04 parts of antioxidant, 2.0-2.5 parts of titanium white, and 2.0-2.5 parts of zinc stearate. Through the hydrogen bonding and cross-linking effect of polyethylene glycol and polyvinyl alcohol with the crystal water in phosphogypsum, the heavy metals in the solidified phosphogypsum can be solidified, and the interfacial interaction and interlayer adhesion can be improved, thus solving the problem of the need for adhesive bonding for multi-layer calcium plastic boards. However, it does not show specific data in solidifying heavy metals in phosphogypsum. ​

[0006] Chinese patent CN202311391556.3 discloses a phosphogypsum slag-based functional material and its method for solidifying / stabilizing heavy metal-polluted water or soil, comprising the following components by mass percentage: 50-80% blast furnace slag, 10-45% phosphogypsum, and 3-25% lime. It features rapid solidification rate and good solidification effect. However, it mainly relies on the hydration reaction between phosphogypsum and blast furnace slag, resulting in a single material system and a lack of further means to reduce the risk of heavy metal migration. Furthermore, while it exhibits a certain solidification effect, specific data on the heavy metal leaching concentration are not clearly provided, and the strength index is relatively low. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a phosphogypsum-based curing material. It uses pretreated activated phosphogypsum as the main raw material, adds mineral powder and carbide slag to form a cementitious material system, and adds a modifier to work with the hydration products of the cementitious material to improve the curing effect of the phosphogypsum. The curing process significantly reduces the leaching concentration and enhances the mechanical properties of the cured material, thereby increasing the resource utilization value of phosphogypsum and providing a more competitive solution for the fields of building materials and environmental pollution control.

[0008] Specifically, the phosphogypsum-based curing material of the present invention is composed of the following raw materials in parts by weight: 65-80 parts of active phosphogypsum, 15-30 parts of mineral powder, 3-10 parts of carbide slag, 5-10 parts of modifier, 0.01-0.1 parts of retarder, 0.1-0.4 parts of water-reducing agent, 0.01-0.05 parts of water-retaining agent, and a water-cement ratio of 0.56-0.65.

[0009] This invention relates to phosphogypsum. Multi-stage curing involves both physical adsorption of modifiers and coating of hydration products, enabling the development of multi-purpose materials through "waste-to-waste" treatment.

[0010] Preferably, the preparation process of the active phosphogypsum is as follows: phosphogypsum and water glass are mixed evenly at a mass ratio of 1:(0.1-0.2), and then stir-fried and dehydrated to obtain the product.

[0011] Preferably, the preparation process of the modifier is as follows: chitosan and acetic acid are mixed evenly at a mass ratio of 1:(40-50), and 10-20% of its volume of acetone is added and mixed evenly to obtain a modification solution. Diatomaceous earth is microwave-strengthened, acid-washed, and dried to obtain modified diatomaceous earth. The modification solution and modified diatomaceous earth are mixed evenly at a ratio of (200-300):1 and dried to obtain the final product.

[0012] The main components of the modifier in this invention are chitosan and modified diatomaceous earth. The amino (-NH2) and hydroxyl (-OH) groups in the chitosan molecule can interact with the phosphogypsum... The chitosan can play the role of adhesive and form stable composite material with other cementitious materials, the modified diatomite has excellent specific surface area and porous structure, which can significantly improve the overall porosity of the composite material and make the pore structure more uniform, and can provide more adsorption sites for the active sites of the chitosan, so that the overall adsorption capacity is improved. The present application adopts high water-binder ratio, so that the phosphogypsum forms a microporous matrix, the modifiers can be connected with each other through the micropores of the matrix, and a graded pore network is formed. The network is beneficial to diffusion into the material and combination with the active sites of the chitosan, so that the overall adsorption capacity is improved.

[0013] In addition, the chitosan is a natural biological macromolecule, which will first ionize after being contacted with water, and the active -NH2 and -OH functional groups on the molecular chain can not only adsorb the impurities such as P and F in the phosphogypsum. , but also can adsorb the soluble P and F on the surface of the phosphogypsum crystal, which greatly increases the solubility of the phosphogypsum. On the other hand, the chitosan can also be adsorbed on the generated calcium sulfate dihydrate (DH) crystal embryo through complexation, which reduces the surface energy and prolongs the time to reach the critical nucleation size, not only has a retarding effect on the system, but also affects the early strength of the solidified body. 2+ Therefore, the present application mixes the phosphogypsum with water glass first, and then fries and dehydrates, so as to reduce the influence of the chitosan on the early strength of the solidified body. In addition, in the hydration process of the modified active phosphogypsum, the Ca 2+ enrichment, the chitosan will be selectively adsorbed on the crystal face, which affects the growth of the DH crystal in the c-axis, so that the growth rate of the crystal in different directions is different, the DH crystal size is refined, and the crystal packing density is improved, so that the mechanical properties of the solidified body are enhanced. In addition, in the strong alkali environment, the proportion of soluble silicic acid in the modified diatomite can reach 60%-80%, a large amount of amorphous SiO2 can react with calcium hydroxide to generate C-S-H gel which is beneficial to strength and water resistance, and can further seal . Therefore, the addition of the modifier and the synergistic effect of the mineral components of the present application finally form a more compact microstructure, which also leads to the increase of the mechanical properties.

[0014] Preferably, in the preparation process of the active phosphogypsum, the frying temperature is 60-70 DEG C, and the frying time is 3-4h.

[0015] Preferably, in the modification agent preparation process, the microwave enhancement is irradiated for 15-20 minutes with a microwave power of 700-800W, and the pickling is performed by soaking in a nitric acid solution and then cleaning to neutral.

[0016] Preferably, the modified phosphogypsum particle size is ≤150μm.

[0017] Preferably, the mineral powder is at least one of S95, S105 grade, and the specific surface area is ≥450m 2 / kg.

[0018] Preferably, the carbide slag has a specific surface area of ≥350m 2 / kg.

[0019] The present application adds carbide slag, which is a waste residue generated during the preparation of acetylene. The alkaline environment provided by the carbide slag can partially remove soluble impurities (such as P and F) in the phosphogypsum, and on the other hand, it can make the phosphogypsum and the mineral powder well hydrated to generate hydrated calcium silicate gel or / and hydrated calcium silicate aluminum gel and hydrated ettringite, etc. These products not only can wrap , reduce the risk of dissolution, but also can fill the internal pores of the composite material to enhance the mechanical properties of the material, and, The introduction of the carbide slag also increases the chain length of the silicate chain, improves the polymerization of the silicate chain, and thus improves the mechanical properties of the material.

[0020] Preferably, the retarder is at least one of citric acid and tartaric acid.

[0021] Preferably, the water reducing agent is at least one of melamine-based water reducing agent and polycarboxylic acid water reducing agent, and the water reducing rate is ≥18%.

[0022] Preferably, the water retaining agent is hydroxyethyl methyl cellulose ether.

[0023] The present application also relates to a preparation method of the above-mentioned phosphogypsum-based solidified material, specifically comprising the following steps:

[0024] 1) weighing each raw material by weight parts,

[0025] 2) mixing each raw material uniformly, and obtaining.

[0026] The present application uses phosphogypsum as the main raw material, modifies it with chitosan and diatomite, and adds mineral powder and carbide slag as active materials to prepare a phosphogypsum-based solidified material, which significantly reduces the leaching concentration, so that <0.08mg / L, and the mechanical properties of the solidified material are improved, with 28d flexural strength of no less than 9 MPa and 28d compressive strength of no less than 45 MPa. The present application not only realizes efficient resource utilization of phosphogypsum and industrial solid waste, but also effectively solves the problems of poor stability and poor adsorption capacity in traditional solidified materials, and provides a green, low-carbon and economic technical solution for phosphogypsum resource utilization and heavy metal pollution treatment. DETAILED DESCRIPTION

[0027] To characterize the technical effect of the present application, the solidified material is prepared and its performance is tested, wherein The leaching concentration test measures the net paste sample by the heavy metal ion leaching method specified in the standard HJ / T 300-2007 “Solid Waste Leaching Toxicity Leaching Method Acetate Buffer Solution Method”.

[0028] During the test, the retarder is citric acid, the water reducing agent is melamine type water reducing agent, and the water retaining agent is hydroxyethyl methyl cellulose ether. The modification agent preparation process is as follows: uniformly mix chitosan and acetic acid at a mass ratio of 1:50, add 10% of its volume of acetone and mix uniformly to obtain a modified liquid. The modified diatomite is obtained by microwave intensification, acid washing and drying. The modified liquid and the modified diatomite are uniformly mixed at a ratio of 240:1, and then dried to obtain the modified agent. The performance of the modified agent is tested. The adsorption performance test is 81.5mg / g, and the test process is as follows: 200mg / L of nitrate solution is prepared, 0.2g of the modified agent is added to 200mL of the above solution, shaken for 5h, filtered with filter paper with a pore size of 0.45μm, and the filtrate is determined by ICP-MS. The filtered product is dried and used for XPS test. The adsorption amount of the modified agent to Pb is calculated by the formula: Q=V*(C0-C e ) / m, wherein Q is the adsorption amount of Pb 2+ , mg / g; C0and C e are the initial concentration and the equilibrium concentration of the solution, mg / L; V is the volume of the solution, L; and m is the mass of the composite system, g.

[0029] Example 1

[0030] The phosphogypsum-based solidified material is composed of the following raw materials by weight: active phosphogypsum 75 parts, mineral powder 20 parts, carbide slag 7 parts, modified agent 8 parts, retarder 0.03 parts, water reducing agent 0.3 parts, water retaining agent 0.02 parts, and water binder ratio of 0.62. The preparation process of the active phosphogypsum is as follows: uniformly mix phosphogypsum and water glass at a mass ratio of 1:0.2, and then dehydrate by frying at 70℃ for 3h to obtain the active phosphogypsum.

[0031] After detection, the leaching concentration of Pb 2+The leaching concentration is 0.08 mg / L, the 3d compressive strength of the solidified body is 13.5 MPa, and the 28d compressive strength is 46.3 MPa.

[0032] Example 2

[0033] The phosphogypsum-based solidified material is composed of the following raw materials in parts by weight: active phosphogypsum 72 parts, mineral powder 25 parts, carbide slag 8 parts, modifier 9 parts, retarder 0.03 parts, water reducing agent 0.3 parts, water retaining agent 0.02 parts, and the water-binder ratio is 0.62. The preparation process of the active phosphogypsum is as follows: uniformly mix phosphogypsum and water glass at a mass ratio of 1:0.2, and dehydrate at 70°C for 3h.

[0034] After detection, Pb 2+ The leaching concentration is 0.07 mg / L, the 3d compressive strength of the solidified body is 13.9 MPa, and the 28d compressive strength is 47.0 MPa.

[0035] Comparative Example 1

[0036] The phosphogypsum-based solidified material is composed of the following raw materials in parts by weight: phosphogypsum 72 parts, mineral powder 25 parts, carbide slag 8 parts, modifier 9 parts, retarder 0.03 parts, water reducing agent 0.3 parts, and water retaining agent 0.02 parts, and the water-binder ratio is 0.62.

[0037] After detection, Pb 2+ The leaching concentration is 0.25 mg / L, the 3d compressive strength of the solidified body is 8.6 MPa, and the 28d compressive strength is 32.5 MPa.

[0038] Comparative Example 2

[0039] The phosphogypsum-based solidified material is composed of the following raw materials in parts by weight: active phosphogypsum 72 parts, mineral powder 25 parts, carbide slag 8 parts, modifier 9 parts, retarder 0.03 parts, water reducing agent 0.3 parts, water retaining agent 0.02 parts, and the water-binder ratio is 0.62. The preparation process of the active phosphogypsum is as follows: dehydrate phosphogypsum at 70°C for 3h.

[0040] After detection, Pb 2+ The leaching concentration is 0.16 mg / L, the 3d compressive strength of the solidified body is 9.3 MPa, and the 28d compressive strength is 39.6 MPa.

[0041] Comparative Example 3

[0042] The phosphogypsum-based solidified material is composed of the following raw materials in parts by weight: active phosphogypsum 72 parts, mineral powder 25 parts, carbide slag 8 parts, modifier 9 parts, retarder 0.03 parts, water reducing agent 0.3 parts, water retaining agent 0.02 parts, and the water-binder ratio is 0.62. The preparation process of the active phosphogypsum is as follows: uniformly mix phosphogypsum and water glass at a mass ratio of 1:0.2, and dehydrate at 70°C for 3h.

[0043] The detection result of Pb is 0.18 mg / L. 2+ The leaching concentration is 0.18 mg / L, the 3d compressive strength of the solidified body is 10.7 MPa, and the 28d compressive strength is 40.5 MPa.

[0044] Comparative Example 4

[0045] The phosphogypsum-based solidified material is composed of the following raw materials in parts by weight: active phosphogypsum 72 parts, mineral powder 25 parts, carbide slag 8 parts, chitosan 1 part, diatomite 8 parts, retarder 0.03 parts, water reducing agent 0.3 parts, water retaining agent 0.02 parts, and the water-binder ratio is 0.62. The preparation process of the active phosphogypsum is as follows: the phosphogypsum and water glass are uniformly mixed at a mass ratio of 1:0.2, and then dehydrated by frying at 70°C for 3h, and the active phosphogypsum is obtained.

[0046] The detection result of Pb is 0.18 mg / L. 2+ The leaching concentration is 0.30 mg / L, the 3d compressive strength of the solidified body is 5.1 MPa, and the 28d compressive strength is 33.4 MPa.

[0047] Comparative Example 5

[0048] The phosphogypsum-based solidified material is composed of the following raw materials in parts by weight: active phosphogypsum 72 parts, mineral powder 25 parts, carbide slag 8 parts, diatomite 9 parts, retarder 0.03 parts, water reducing agent 0.3 parts, water retaining agent 0.02 parts, and the water-binder ratio is 0.62. The preparation process of the active phosphogypsum is as follows: the phosphogypsum and water glass are uniformly mixed at a mass ratio of 1:0.2, and then dehydrated by frying at 70°C for 3h, and the active phosphogypsum is obtained.

[0049] The detection result of Pb is 0.18 mg / L. 2+ The leaching concentration is 0.27 mg / L, the 3d compressive strength of the solidified body is 9.6 MPa, and the 28d compressive strength is 35.1 MPa.

[0050] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A phosphogypsum-based curing material, characterized in that, It is composed of the following raw materials in parts by weight: 65-80 parts activated phosphogypsum, 15-30 parts mineral powder, 3-10 parts carbide slag, 5-10 parts modifier, 0.01-0.1 parts retarder, 0.1-0.4 parts water-reducing agent, and 0.01-0.05 parts water-retaining agent, with a water-cement ratio of 0.56-0.

65. The preparation process of the active phosphogypsum is as follows: phosphogypsum and water glass are mixed evenly at a mass ratio of 1:(0.1-0.2), then stir-fried and dehydrated to obtain the final product. The preparation process of the modifier is as follows: chitosan and acetic acid are mixed evenly at a mass ratio of 1:(40-50), and 10-20% of its volume of acetone is added and mixed evenly to obtain a modification solution. Diatomaceous earth is microwave-strengthened, acid-washed, and dried to obtain modified diatomaceous earth. The modification solution and modified diatomaceous earth are mixed evenly at a ratio of (200-300):1 and dried to obtain the final product.

2. The phosphogypsum-based curing material according to claim 1, characterized in that, In the preparation process of the active phosphogypsum, the frying temperature is 60-70℃ and the frying time is 3-4 hours.

3. The phosphogypsum-based curing material according to claim 1, characterized in that, In the preparation process of the modifier, microwave strengthening is performed by irradiating with a microwave power of 700-800W for 15-20 minutes, and acid washing is performed by soaking in nitric acid solution and then washing until neutral.

4. The phosphogypsum-based curing material according to claim 1, characterized in that, The modified phosphogypsum has a particle size ≤150μm.

5. The phosphogypsum-based curing material according to claim 1, characterized in that, The mineral powder is at least one of grades S95 and S105, with a specific surface area ≥450m². 2 / kg.

6. The phosphogypsum-based curing material according to claim 1, characterized in that, The specific surface area of ​​the carbide slag is ≥350m² 2 / kg.

7. The phosphogypsum-based curing material according to claim 1, characterized in that, The retarder is at least one of citric acid and tartaric acid.

8. The phosphogypsum-based curing material according to claim 1, characterized in that, The water-reducing agent is at least one of melamine-based water-reducing agents and polycarboxylate-based water-reducing agents, with a water reduction rate ≥18%.

9. The phosphogypsum-based curing material according to claim 1, characterized in that, The water-retaining agent is hydroxyethyl methyl cellulose ether.

10. The method for preparing the phosphogypsum-based curing material according to any one of claims 1-9, characterized in that, Includes the following steps: 1) Weigh each ingredient according to its weight. 2) Mix all the ingredients evenly to obtain the final product.