Phosphogypsum microporous aggregate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of solid waste recycling, in particular to ardealite microporous aggregate as well as a preparation method and application thereof. The ardealite microporous aggregate provided by the invention is prepared from the following preparation raw materials in percentage by mass: 70 to 85 percent of modified ardealite, 5 to 10 percent of a cementing material, 5 to 15 percent of slag powder, 3 to 8 percent of carbide slag, 0.5 to 1.5 percent of a foaming agent and 0.1 to 0.8 percent of a coagulant, the interior of the ardealite microporous aggregate is of a micron-sized hole structure; the pH value of the modified phosphogypsum is 6.5-11, the water-soluble total phosphorus content is less than or equal to 100mg / kg, the water-soluble fluoride content is less than or equal to 200mg / kg, and the average particle size is less than or equal to 100mu m. The ardealite microporous aggregate realizes a water quality purification function through a micron-sized pore structure and a multi-component chemical synergistic effect.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a phosphogypsum microporous aggregate, its preparation method, and its application. Background Technology

[0002] Phosphogypsum is an industrial waste residue generated during the wet-process phosphoric acid production. Due to its large localized volume and poor economic viability, large-scale utilization of phosphogypsum is difficult, making its high-volume utilization a persistent challenge. Existing high-volume utilization technologies primarily use phosphogypsum in the preparation of roadbed materials, lightweight aggregates, or cementitious materials. However, its limited functionality and low price prevent its high-value utilization. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a phosphogypsum microporous aggregate, its preparation method, and its application. The phosphogypsum microporous aggregate achieves water purification through its micron-level pore structure and the synergistic effect of multiple chemical components.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a phosphogypsum microporous aggregate, comprising the following raw materials by mass percentage: 70-85% modified phosphogypsum, 5-10% cementitious material, 5-15% slag powder, 3-8% carbide slag, 0.5-1.5% foaming agent, and 0.1-0.8% coagulant.

[0006] The internal structure of the phosphogypsum microporous aggregate is a micron-sized pore structure.

[0007] The modified phosphogypsum has a pH value of 6.5–11, a water-soluble total phosphorus content of ≤100 mg / kg, a water-soluble fluoride content of ≤200 mg / kg, and an average particle size of ≤100 μm.

[0008] Preferably, the preparation process of the modified phosphogypsum includes the following steps:

[0009] Modified phosphogypsum is obtained by mixing phosphogypsum, an alkaline neutralizer, and water.

[0010] Preferably, the pH value of the phosphogypsum is 2.5 to 4.0;

[0011] The alkaline neutralizer includes calcium hydroxide and / or calcium oxide;

[0012] The mass ratio of the phosphogypsum to the alkaline neutralizer is 100:(2-5).

[0013] Preferably, the cementing material includes ordinary silicate cement and aluminate cement;

[0014] The mass ratio of ordinary silicate cement to aluminate cement is (4-8):1.

[0015] Preferably, the pH value of the carbide slag is 12-13, the average particle size is ≤100μm, the mass percentage of calcium hydroxide in the carbide slag is ≥90%, and the moisture content is ≤5%.

[0016] Preferably, the foaming agent includes hydrogen peroxide or aluminum powder.

[0017] Preferably, the coagulant includes one or more of triethanolamine, sodium sulfate, and sodium silicate.

[0018] The present invention also provides a method for preparing the phosphogypsum microporous aggregate described in the above technical solution, comprising the following steps:

[0019] Modified phosphogypsum, cementitious materials, slag powder, carbide slag and coagulant are mixed and then foaming agent and water are added to obtain slurry;

[0020] The slurry is granulated, foamed, and cured sequentially to obtain the phosphogypsum microporous aggregate.

[0021] Preferably, the mass ratio of the water to the total mass of the modified phosphogypsum, cementing material, slag powder, carbide slag, coagulant and foaming agent is (25-40):100;

[0022] The foaming molding temperature is 30-60℃, and the time is 2-4 hours;

[0023] The curing process involves a humidity level of ≥90%, a temperature of 25–35℃, and a duration of 3–7 days.

[0024] The present invention also provides the application of the phosphogypsum microporous aggregate described in the above technical solution or the phosphogypsum microporous aggregate prepared by the preparation method described in the above technical solution in the fields of wetland wastewater ecological regulation, industrial water and slag yard leaching wastewater treatment.

[0025] This invention provides a phosphogypsum microporous aggregate, comprising the following raw materials by mass percentage: 70-85% modified phosphogypsum, 5-10% cementitious material, 5-15% slag powder, 3-8% carbide slag, 0.5-1.5% foaming agent, and 0.1-0.8% coagulant; the internal structure of the phosphogypsum microporous aggregate is a micron-sized pore structure; the modified phosphogypsum has a pH value of 6.5-11, a water-soluble total phosphorus content ≤100mg / kg, a water-soluble fluoride content ≤200mg / kg, and an average particle size ≤100μm.

[0026] The water purification mechanism of the phosphogypsum microporous aggregate described in this invention is as follows:

[0027] 1. Physical interception and adsorption: The porous structure formed by foaming phosphogypsum microporous aggregate can enhance the surface area and increase the adsorption capacity of pollutants. The good micron-level pore structure can intercept and adsorb suspended solids, colloids and other pollutants in the water. At the same time, the filter bed formed by the accumulation of the phosphogypsum microporous aggregate can effectively intercept larger particles (such as silt and algal residues) and reduce the turbidity of the water.

[0028] 2. Chemical precipitation adsorption: The microporous aggregate of phosphogypsum is rich in active groups such as hydroxyl groups (-OH) and metal oxides (e.g., Al2O3, Fe2O3), which can adsorb heavy metal ions (e.g., Pb) through coordination and electrostatic interactions. 2+ Cd 2+ Cu 2+ ) and phosphate (PO4) 2- The active components and hydration products in the aggregates (such as CSH gel and alumina gel) can further adsorb heavy metal ions (Pb). 2+ Cd 2+ (etc.). With the slow release of alkaline oxides (such as CaO and MgO), acidic water can be neutralized, stabilizing the pH value of the water within a suitable range of 6–9; simultaneously, due to the presence of CaO in the entire system... 2+ Excessive amounts will cause the aggregate to slowly release Ca through its micropores. 2+ PO4 in wastewater within micropores 3- The F- reacts to generate Ca5(PO4)3OH and CaF2 precipitate, which are adsorbed by the micropores of the aggregate. At the same time, the generated Ca5(PO4)3OH can further adsorb free F- in the water.

[0029] The reason why the phosphogypsum microporous aggregate described in this invention has the above-mentioned purification effect is as follows:

[0030] 1. Formation of micron-sized pore structures: The foaming agent will react to generate gas and form cavities in the material (for example, hydrogen peroxide decomposes to produce oxygen, and aluminum powder reacts with alkali to produce hydrogen). At the same time, in a humid and hot environment, the mineral phase of aluminate cement will also transform and lead to an increase in porosity, forming a small number of slurry micropores.

[0031] 2. The main sources of hydroxyl groups (-OH) are hydroxide ions produced by the decomposition of calcium hydroxide in carbide slag, calcium hydroxide produced by the hydration of ordinary silicate cement, aluminum hydroxide produced by the hydration of aluminate cement and the activation of mineral powder by alkali. Among the active groups such as metal oxides (e.g., Al2O3, Fe2O3), Al2O3 generally comes from aluminate cement and mineral powder, while Fe2O3 generally comes from aluminate cement and ordinary silicate cement.

[0032] 3. CSH gel and aluminate gel are the main products of the hydration reaction of ordinary silicate cement and aluminate cement, respectively.

[0033] 4. Alkaline oxides (such as CaO and MgO) mainly come from calcium hydroxide in the system and mineral powder that has been activated by alkali.

[0034] 5. Ca in the entire system 2+ The excessive amount is because the cement, mineral powder, and carbide slag added are all calcium-based materials. Detailed Implementation

[0035] This invention provides a phosphogypsum microporous aggregate, comprising the following raw materials by mass percentage: 70-85% modified phosphogypsum, 5-10% cementitious material, 5-15% slag powder, 3-8% carbide slag, 0.5-1.5% foaming agent, and 0.1-0.8% coagulant.

[0036] The internal structure of the phosphogypsum microporous aggregate is a micron-sized pore structure.

[0037] The modified phosphogypsum has a pH value of 6.5–11, a water-soluble total phosphorus content of ≤100 mg / kg, a water-soluble fluoride content of ≤200 mg / kg, and an average particle size of ≤100 μm.

[0038] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0039] In this invention, the particle size of the phosphogypsum microporous aggregate is preferably 5-10 mm.

[0040] Based on mass percentage, the phosphogypsum microporous aggregate of the present invention comprises 70-85% modified phosphogypsum, preferably 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%. In embodiments of the present invention, the mass percentage of modified phosphogypsum in the phosphogypsum microporous aggregate is specifically 81%, 75%, 70%, or 73%.

[0041] In this invention, the preparation process of the modified phosphogypsum preferably includes the following steps:

[0042] Modified phosphogypsum is obtained by mixing phosphogypsum, an alkaline neutralizer, and water.

[0043] In this invention, the pH value of the phosphogypsum is preferably 2.5 to 4.0. In this invention, the phosphogypsum is preferably derived from industrial by-product phosphogypsum.

[0044] In this invention, the alkaline neutralizer preferably includes calcium hydroxide and / or calcium oxide. When the alkaline neutralizer includes calcium hydroxide and calcium oxide, this invention does not impose any particular limitation on the amount of calcium hydroxide and calcium oxide used; they can be mixed in any ratio. In embodiments of this invention, the alkaline neutralizer can be either calcium hydroxide or calcium oxide.

[0045] In this invention, the mass ratio of the phosphogypsum to the alkaline neutralizer is preferably 100:(2-5), more preferably 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5, or 100:5. In embodiments of this invention, the mass ratio of the phosphogypsum to the alkaline neutralizer can be 100:4.94 or 100:2.

[0046] In this invention, the preferred mass ratio of phosphogypsum to water is (0.5-1):1, more preferably 0.5:1, 0.55:1, 0.60:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, or 1.0:1. In embodiments of this invention, the mass ratio of phosphogypsum to water can be 0.8:1 or 0.85:1.

[0047] In this invention, the mixing is preferably carried out under stirring conditions. The stirring process is not particularly limited and can be performed using a process well-known to those skilled in the art. The preferred mixing order is to mix the phosphogypsum and the alkaline neutralizer, followed by the addition of water.

[0048] In this invention, the modification process occurs during the mixing process.

[0049] After the modification treatment is completed, the present invention preferably includes sequential filtration, washing, drying, and grinding. The present invention does not have any special limitations on the filtration process; any process well-known to those skilled in the art can be used. The present invention does not have any special limitations on the washing process; any process well-known to those skilled in the art can be used, ensuring that the filter residue obtained from filtration is washed until the pH value is 6.5–11. In the present invention, the drying method is preferably oven drying; the present invention does not have any special limitations on the drying process; any process well-known to those skilled in the art can be used. In an embodiment of the present invention, the drying temperature can be 40°C. The present invention does not have any special limitations on the grinding process; any process well-known to those skilled in the art can be used. In the present invention, the washing process preferably involves modification.

[0050] In this invention, the purpose of pretreating the phosphogypsum is: 1. To remove soluble impurities: soluble phosphorus, such as H3PO4, H2PO4-, HPO4.2- etc.; soluble fluorine, such as F-, HF, SiF6 2- etc.; soluble salts, such as Na + K + Mg 2+ SO4 2- 1. Residual acids, such as H3PO4 and H2SO4. 2. Transformation of harmful impurities: 2.1 Neutralization of soluble phosphorus: By adding an alkaline neutralizing agent (usually slaked lime Ca(OH)2 or quicklime CaO), soluble phosphate ions are converted into insoluble or slightly soluble calcium phosphate precipitates (such as Ca5(PO4)3OH, Ca3(PO4)2, etc.), thus eliminating their retarding effect. 2.2 Precipitation of soluble fluoride: During neutralization, fluoride ions combine with calcium ions to form calcium fluoride precipitates with low solubility. 3. Improvement of physical properties: 3.1 Reduction of viscosity / improvement of flowability: After removing soluble salts, the viscosity of the slurry is reduced, making it easier to transport, filter, and dewater. 3.2 Improvement of particle surface properties: Removing the impurity film attached to the surface of gypsum crystals makes the particles purer and improves their gelling activity. 3.3 Stabilization of setting time: Eliminating the retarding effect of soluble phosphorus and fluoride makes the setting and hardening time of gypsum more stable and controllable. 3.4 Improved Whiteness: Removing some organic matter and colored impurities can slightly improve the whiteness of the product. 4. Improved Product Quality and Performance: 4.1 Increased Strength: After removing retarding impurities, gypsum hydration is more complete, the hardened body structure is denser, and the strength is significantly improved. 4.2 Improved Durability: Reducing soluble salt content lowers the risk of "blooming" and improves the water resistance and long-term stability of the product. 5. Promoted Resource Utilization and Reduced Environmental Pressure: The performance of the treated phosphogypsum is fundamentally improved, greatly broadening its resource utilization pathways and reducing the risks of land occupation and environmental pollution (dust, acidic leachate, fluoride and phosphorus migration, etc.) caused by stockpiling. Changes in phosphogypsum during the modification process: Physical Changes: Particle Dispersion and Washing: During the washing process, water flow or mechanical stirring disperses the phosphogypsum particles, dissolving soluble impurities coated on the particle surface or filling the interparticle gaps and carrying them away with the washing liquid. Changes in Particle Size Distribution: Some fine particles or flocculent matter may be washed away or removed during the washing process, resulting in a slight change in the overall particle size distribution. Changes in moisture content: The moisture content of the material increases significantly after washing, requiring subsequent dewatering (filtration, centrifugation) treatment. Decrease in viscosity: With the removal of soluble salts, the viscosity of the slurry decreases significantly. Chemical changes: Dissolution and removal of soluble impurities: Soluble P₂O₅, F... - Na + K + Mg 2+ SO4 2- Cl -A large amount of these dissolves into the washing solution. Some residual free acids (H3PO4, H2SO4) also dissolve. Neutralization reactions: Acid neutralization: CaO + H2O → Ca(OH)2; Ca(OH)2 + H2SO4 → CaSO4·2H2O; Ca(OH)2 + 2H3PO4 → Ca(H2PO4)2 + 2H2O (initial reaction). Phosphorus precipitation: As the pH increases (the target is usually 6.5-7.5), soluble phosphates (H2PO4-, HPO4-) precipitate. 2- ) and Ca 2+ The reaction produces insoluble calcium phosphate precipitates, primarily hydroxyapatite or tricalcium phosphate: 5Ca 2+ +3PO4 3- +OH - →Ca5(PO4)3OH or 3Ca 2+ +2PO4 3- →Ca3(PO4)2. Precipitation of fluorine: Ca 2+ +2F -→CaF2↓ (fluorite). pH change: After initial washing to remove some acid and salt, the pH of the original acidic phosphogypsum (pH 2-5) may rise slightly but remain acidic. After neutralization with alkaline materials, the pH rises significantly to near neutral or weakly alkaline (target pH). Impurity morphology transformation: Harmful soluble phosphorus and fluorine are transformed into chemically stable, extremely low-solubility solid precipitates (calcium phosphate, calcium fluoride) that no longer have a retarding or corrosive effect, encapsulating or dispersing within the gypsum particles. Mineralogical / phase change: Main phase unchanged: Under mild washing and neutralization conditions (low temperature), the main component of phosphogypsum, calcium sulfate dihydrate, retains its crystal structure and phase composition essentially unchanged, remaining CaSO4·2H2O. Impurity phase formation: Newly formed precipitates such as calcium phosphate and calcium fluoride become new impurity phases in phosphogypsum, but they exist as inert solids and no longer possess the harmfulness of soluble impurities. Surface purification: The soluble salt film adhering to the surface of the gypsum crystals is washed away, making the crystal surface "cleaner". In summary, the above modification process combines physical cleaning with chemical reaction. Washing removes a large amount of soluble impurities, and neutralization converts residual harmful soluble impurities (especially phosphorus and fluorine) into harmless inert precipitates, while simultaneously adjusting the pH value. The result is a significant increase in the purity of phosphogypsum (reducing the total amount of impurities and their harmfulness), improved physical properties (flowability, dehydration) and gelling properties (setting time, strength), ultimately making it a valuable renewable resource that can be used to produce high-quality building materials, achieving the resource utilization of waste. Furthermore, while undisturbed phosphogypsum does have low mechanical strength, the modified washing process improves its physical properties to some extent. Combined with other components and undergoing a series of hydration reactions, the physical properties of the phosphogypsum are significantly improved, ultimately forming a relatively stable hardened structure that does not easily pulverize during water treatment. The pulverization problem is essentially a significant carbonization reaction that occurs in the material's usage environment (the hydration reaction of the material generates excessive calcium hydroxide, which reacts with carbon dioxide in the air to form fine calcium carbonate powder). For the material composition system in this invention, firstly, the combination of other materials avoids the generation of excessive calcium hydroxide in the system's hydration reaction (consumption of aluminate cement and activation of mineral powder). Secondly, the aggregate is used in wastewater, so the hydration products have limited opportunities to be exposed to the carbon dioxide environment, and the probability of pulverization is relatively low.

[0051] The phosphogypsum microporous aggregate of the present invention comprises 5% to 10% cementitious material, preferably 5%, 6%, 7%, 8%, 9%, or 10%, by weight percentage. In embodiments of the present invention, the weight percentage of cementitious material in the phosphogypsum microporous aggregate may be 7%, 6%, or 9%.

[0052] In this invention, the cementitious material preferably comprises ordinary Portland cement and aluminate cement; the mass ratio of the ordinary Portland cement to the aluminate cement is preferably (4-8):1, more preferably 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, or 8:1. The ordinary Portland cement is preferably PO42.5 ordinary Portland cement; the aluminate cement is preferably CA-50 aluminate cement. In embodiments of this invention, the cementitious material comprises PO42.5 ordinary Portland cement and CA-50 aluminate cement in a mass ratio of 6:1 or 7:1.

[0053] In this invention, the preparation of the cementitious material preferably includes mixing the ordinary silicate cement and aluminate cement to obtain the cementitious material. This invention does not impose any special limitations on the mixing process; any process well-known to those skilled in the art can be used.

[0054] In this invention, phosphogypsum itself has low mechanical strength, and its strength is even lower after foaming. Therefore, it must be modified to improve its initial mechanical strength. Simultaneously, cementitious materials need to be added as strength stabilizers to improve the overall mechanical strength of the material. However, the compatibility between cement types and phosphogypsum must also be considered. Therefore, the advantages of using the two types of cement mentioned above are: 1. Improved early strength: Aluminate cements are known for their extremely fast hydration rate and extremely high early strength. Therefore, adding a small amount to ordinary Portland cement can significantly improve the early strength of the composite cement. Because calcium sulfate dihydrate is itself a retarder, the combination of these two cements with a accelerator can effectively reduce the setting time of phosphogypsum aggregate, improve early strength, shorten the curing cycle, and increase turnover rate. 2. Improved later-stage strength stability: After hydration, aluminate cements generally suffer from strength reduction or long-term strength decline because the initial hydration products of aluminate cement (CAH... 10 The hydration products (C2AH8) are metastable phases. Under conditions of increased temperature and sufficient moisture, they irreversibly transform into a denser, stable phase (C3AH6 + AH3), creating voids and leading to reduced strength. Therefore, it is necessary to rely on ordinary silicate cement + mineral powder + phosphogypsum (to generate ettringite) to stabilize their hydration products, ensuring long-term strength stability and durability, and avoiding the potential long-term strength risks of aluminate cement. 3. Improved resistance to sulfate attack: Aluminate hydration produces almost no calcium hydroxide, while ordinary silicate cement hydration produces Ca(OH)2. Ca(OH)2 is the main target of sulfate attack. Therefore, the addition of aluminate consumes some Ca(OH)2 (through reaction to form more stable hydrated calcium aluminate), thereby reducing the content of free calcium hydroxide in the system and reducing the probability of carbonation reaction.

[0055] The raw materials for preparing the phosphogypsum microporous aggregate of the present invention, based on mass percentage, include 5-15% slag powder, preferably 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. In embodiments of the present invention, the mass percentage of slag powder in the phosphogypsum microporous aggregate can be 5%, 10%, 11%, or 12%.

[0056] In this invention, the slag powder is preferably commercially available blast furnace granulated slag powder of grade S95 or higher.

[0057] The raw materials for preparing the phosphogypsum microporous aggregate of the present invention, based on mass percentage, include 3-8% carbide slag, more preferably 3%, 4%, 5%, 6%, 7%, or 8%. In embodiments of the present invention, the mass percentage of carbide slag in the phosphogypsum microporous aggregate can be 4.5%, 8%, 7%, or 5.5%.

[0058] In this invention, the pH value of the calcium carbide slag is preferably 12-13, the average particle size is preferably ≤100μm, the mass percentage of calcium hydroxide in the calcium carbide slag is preferably ≥90%, and the moisture content is preferably ≤5%. In this invention, the calcium carbide slag is preferably an industrial waste residue with calcium hydroxide as the main component obtained after the hydrolysis of calcium carbide to obtain acetylene gas.

[0059] The raw materials for preparing the phosphogypsum microporous aggregate of the present invention, based on mass percentage, include 0.5% to 1.5% foaming agent, preferably 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%. In embodiments of the present invention, the mass percentage of the foaming agent in the phosphogypsum microporous aggregate can be 1.3%, 1.5%, or 0.8%.

[0060] In this invention, the foaming agent preferably includes hydrogen peroxide or aluminum powder; the mass concentration of the hydrogen peroxide is preferably 10% to 30%, more preferably 10%, 15%, 20%, 25% or 30%.

[0061] The raw materials for preparing the phosphogypsum microporous aggregate of the present invention, based on mass percentage, include 0.1% to 0.8% of a coagulant accelerator, preferably 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%. In embodiments of the present invention, the mass percentage of the coagulant in the phosphogypsum microporous aggregate may be 0.7%, 0.5%, or 0.2%.

[0062] In this invention, the coagulant preferably includes one or more of triethanolamine, sodium sulfate, and sodium silicate. When the coagulant is two or more of the above-mentioned specific selections, this invention does not impose any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In the embodiments of this invention, the coagulant can be triethanolamine, sodium silicate, or sodium sulfate.

[0063] In this invention, the interior of the phosphogypsum microporous aggregate has a micron-sized pore structure; the pore size of the phosphogypsum microporous aggregate is preferably 100-900 μm, and the porosity is preferably 20%-30%.

[0064] The present invention also provides a method for preparing the phosphogypsum microporous aggregate described in the above technical solution, comprising the following steps:

[0065] Modified phosphogypsum, cementitious materials, slag powder, carbide slag and coagulant are mixed and then foaming agent and water are added to obtain slurry;

[0066] The slurry is granulated, foamed, and cured sequentially to obtain the phosphogypsum microporous aggregate.

[0067] This invention involves mixing modified phosphogypsum, cementitious materials, slag powder, carbide slag, and a coagulant, then adding a foaming agent and water to obtain a slurry.

[0068] Before the mixing, the present invention preferably includes drying and grinding the modified phosphogypsum and carbide slag separately in sequence. The present invention does not impose any special limitations on the drying and grinding process; any process well-known to those skilled in the art can be used, ensuring that the modified phosphogypsum or carbide slag has an average particle size ≤50μm.

[0069] In this invention, the mixing is preferably carried out under stirring conditions, and the stirring speed is preferably 30-100 r / min, more preferably 30 r / min, 40 r / min, 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min or 100 r / min; the stirring time is preferably 5-10 min, more preferably 5 min, 6 min, 7 min, 8 min, 9 min or 10 min. In an embodiment of this invention, the stirring is carried out in a mixer, and the stirring speed is specifically 60 r / min, and the stirring time is specifically 8 min or 6 min.

[0070] The present invention does not impose any special limitations on the process of adding the foaming agent and water; any process known to those skilled in the art can be used.

[0071] In this invention, the preferred mass ratio of the water to the total mass of the modified phosphogypsum, cementitious material, slag powder, carbide slag, coagulant, and foaming agent is (25-40):100, more preferably 25:100, 30:100, 35:100, or 40:100. In an embodiment of this invention, the specific mass ratio of the water to the total mass of the modified phosphogypsum, cementitious material, slag powder, carbide slag, coagulant, and foaming agent is 40:100.

[0072] After adding the foaming agent and water, the present invention preferably includes a process of continued stirring. The present invention does not have any special limitations on the process of continued stirring, and any process known to those skilled in the art can be used.

[0073] After obtaining the slurry, the present invention sequentially granulates, foams, and cures the slurry to obtain phosphogypsum microporous aggregate.

[0074] In this invention, the granulation method is preferably extrusion granulation or rolling granulation; this invention does not impose any special limitations on the extrusion granulation or rolling granulation process, and any process well known to those skilled in the art can be used to ensure that particles with a diameter of 5 to 10 mm are obtained.

[0075] In this invention, the foaming temperature is preferably 30–60°C, more preferably 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C; the time is preferably 2–4 hours, more preferably 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. In embodiments of this invention, the foaming temperature is specifically 55°C, 45°C, or 60°C, and the time is specifically 4 hours or 2.5 hours.

[0076] In this invention, the curing humidity is preferably ≥90%, the temperature is preferably 25-35℃, more preferably 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, 31℃, 32℃, 33℃, 34℃, or 35℃; and the curing time is preferably 3-7 days, more preferably 3 days, 4 days, 5 days, 6 days, or 7 days. In an embodiment of this invention, the curing temperature is specifically 35℃, and the curing time is specifically 7 days, 5 days, or 3 days.

[0077] In this invention, during the curing process, the foaming agent hydrogen peroxide can decompose to generate oxygen and form micron-sized pores; or the foaming agent aluminum powder can react with an alkaline environment to generate hydrogen gas and form micron-sized pores.

[0078] After the curing process is completed, the present invention preferably includes drying. The present invention does not impose any special limitations on the drying process; any process well-known to those skilled in the art can be used, ensuring that the moisture content of the resulting phosphogypsum microporous aggregate is ≤5%. In an embodiment of the present invention, the drying method is specifically natural drying.

[0079] The present invention also provides the application of the phosphogypsum microporous aggregate described in the above technical solution or the phosphogypsum microporous aggregate prepared by the preparation method described in the above technical solution in the fields of wetland wastewater ecological regulation, industrial water and slag yard leaching wastewater treatment.

[0080] In this invention, the phosphogypsum microporous aggregate is preferably used for the purification of suspended solids, water-soluble phosphorus, water-soluble fluoride and heavy metal ions in water.

[0081] In this invention, the preferred method of application includes: filling the phosphogypsum microporous aggregate into a filter device, and passing the water to be treated through the filter device filled with the phosphogypsum microporous aggregate for adsorption.

[0082] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0083] Example 1

[0084] Add 4.2 kg of calcium hydroxide to 85 kg of phosphogypsum with a pH of 2.91 and stir until homogeneous. Add 100 kg of water and stir to form a homogeneous slurry. Filter the slurry and wash the residue with water until the pH of the residue is 9.5. Then dry the residue at 40℃ and grind it to an average particle size ≤50 μm to obtain modified phosphogypsum.

[0085] 8 kg of carbide slag was dried at 105℃ for 1 hour and then ground to an average particle size of ≤50 μm to obtain pretreated carbide slag.

[0086] 7 kg of ordinary Portland cement (P.O42.5) and 1 kg of aluminate cement (CA-50) are mixed evenly to obtain a cementitious material.

[0087] Add 81 kg of the modified phosphogypsum, 7 kg of the cementitious material, 5 kg of slag powder, 5.5 kg of pretreated carbide slag and 0.2 kg of triethanolamine to a mixer and dry mix for 10 minutes. Then add 1.3 kg of aluminum powder and 30 kg of water and stir until a uniform slurry is formed.

[0088] The slurry is injected into a granulator and granulated by extrusion or rolling to form particles with a diameter of 5-10 mm. After foaming and curing at 55°C for 4 hours, it is cured (cured for 7 days at 35°C and humidity ≥90%, and then naturally dried until the moisture content is ≤5%) to obtain phosphogypsum microporous aggregate (average pore size of 745 μm and porosity of 27%).

[0089] Example 2

[0090] Add 1.6 kg of calcium oxide to 80 kg of phosphogypsum with pH 3.05 and stir until homogeneous. Add 100 kg of water and stir into a homogeneous slurry. Filter the slurry and wash the residue with water until the pH of the residue is 11. Then dry the residue at 40℃ and grind it to an average particle size ≤ 50 μm to obtain modified phosphogypsum.

[0091] 10 kg of carbide slag was dried at 105℃ for 1 hour and then ground to an average particle size of ≤50 μm to obtain pretreated carbide slag.

[0092] Mix 6 kg of ordinary Portland cement (P.O42.5) and 1 kg of aluminate cement (CA-50) evenly to obtain a cementitious material.

[0093] Add 75 kg of the modified phosphogypsum, 6 kg of the cementitious material, 10 kg of slag powder, 7 kg of pretreated carbide slag and 0.5 kg of sodium silicate to a mixer and dry mix for 8 minutes. Then add 1.5 kg of hydrogen peroxide (mass concentration of 15%) and 38 kg of water and stir until a uniform slurry is formed.

[0094] The slurry is injected into a granulator and granulated by extrusion or rolling to form particles with a diameter of 5-10 mm. After foaming and curing at 45°C for 4 hours, it is cured (cured for 5 days at 35°C and humidity ≥90%, and then naturally dried until the moisture content is ≤5%) to obtain phosphogypsum microporous aggregate (average pore size of 680 μm and porosity of 26%).

[0095] Example 3

[0096] The process for obtaining modified phosphogypsum, pretreated carbide slag, and cementitious materials is described in Example 1.

[0097] Add 70 kg of the modified phosphogypsum, 9 kg of the cementitious material, 11 kg of slag powder, 8 kg of pretreated carbide slag and 0.5 kg of triethanolamine to a mixer and dry mix for 8 minutes. Then add 1.5 kg of aluminum powder and 40 kg of water and stir until a uniform slurry is formed.

[0098] The slurry is injected into a granulator and granulated by extrusion or rolling to form particles with a diameter of 5-10 mm. After foaming and curing at 60°C for 2.5 h, it is then cured (cured for 3 days at 35°C and humidity ≥90%) and naturally dried until the moisture content is ≤5%) to obtain phosphogypsum microporous aggregate (average pore size of 760 μm and porosity of 23%).

[0099] Example 4

[0100] The process for obtaining modified phosphogypsum, pretreated carbide slag, and cementitious materials is described in Example 2.

[0101] Add 73 kg of the modified phosphogypsum, 9 kg of the cementitious material, 12 kg of slag powder, 4.5 kg of pretreated carbide slag and 0.7 kg of sodium sulfate to a mixer and dry mix for 6 minutes. Then add 0.8 kg of aluminum powder and 40 kg of water and stir until a uniform slurry is formed.

[0102] The slurry is injected into a granulator and granulated by extrusion or rolling to form particles with a diameter of 5-10 mm. After foaming and curing at 45°C for 4 hours, it is cured (cured for 5 days at 35°C and humidity ≥90%, and then naturally dried until the moisture content is ≤5%) to obtain phosphogypsum microporous aggregate (average pore size of 410 μm and porosity of 20%).

[0103] Comparative Example 1

[0104] The process for obtaining modified phosphogypsum is described in Example 1.

[0105] 12 kg of ordinary Portland cement (P.O42.5) and 1.5 kg of aluminate cement (CA-50) are mixed evenly to obtain a cementitious material.

[0106] Add 85 kg of the modified phosphogypsum, 13 kg of the cementitious material, and 0.5 kg of the complex of triethanolamine and sodium sulfate (the mass ratio of triethanolamine to sodium sulfate is 9.5:1) to a mixer and dry mix for 10 min. Then add 1.5 kg of aluminum powder and 30 kg of water and stir until a uniform slurry is formed.

[0107] The slurry is injected into a granulator and granulated by extrusion or rolling to form particles with a diameter of 5-10 mm. After foaming and curing at 55°C for 4 hours, it is cured (cured for 7 days at 35°C and humidity ≥90%) and then naturally dried to a moisture content ≤5% to obtain phosphogypsum microporous aggregate (average pore size of 180 μm and porosity of 28%).

[0108] Comparative Example 2

[0109] The process for obtaining modified phosphogypsum, pretreated carbide slag, and cementitious materials is described in Example 2.

[0110] Add 75 kg of the modified phosphogypsum, 6 kg of the cementitious material, 10 kg of slag powder, 7 kg of pretreated carbide slag and 0.5 kg of sodium silicate to a mixer and dry mix for 8 minutes. Then add 38 kg of water and stir until a uniform slurry is formed.

[0111] The slurry is injected into a granulator and granulated by extrusion or rolling to form particles with a diameter of 5-10 mm. After foaming and curing at 45°C for 4 hours, it is cured (cured for 5 days at 35°C and humidity ≥90%) and then naturally dried to a moisture content ≤5% to obtain phosphogypsum aggregate.

[0112] Application examples

[0113] After filling the phosphogypsum microporous aggregate described in Example 3 into the phosphogypsum slag field water treatment filter, phosphorus- and fluoride-containing wastewater (PO4) was introduced. 3- 77mg / L, F - 130 mg / L, suspended solids 108 mg / L, hydraulic retention time 4 h), the resulting effluent (PO4) 3- ≤0.5mg / L, F - The concentration of pollutants (≤10mg / L, suspended solids ≤70mg / L) meets the Class I standard of the Integrated Wastewater Discharge Standard (GB8978-1996).

[0114] Test case

[0115] The phosphogypsum microporous aggregates described in Examples 1-4 and Comparative Example 1, as well as the phosphogypsum aggregates described in Comparative Example 2, were used as test samples, and their cylinder compressive strength was determined in accordance with GB / T17431 "Lightweight Aggregates and Their Test Methods".

[0116] Water from a wastewater collection tank of a chemical plant was used as the water to be purified. Test samples were immersed in the water for 4 hours at a solid-liquid ratio of 1:2. After removing the samples, the purified water was allowed to stand for 1 hour. The concentration of total phosphorus in the water before and after purification was determined according to GB11893 "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method". The concentration of fluoride in the water before and after purification was determined according to GB / T7484 "Determination of Fluoride in Water - Ion Selected Electrode Method". The content of suspended solids in the water before and after purification was determined according to GB11901 "Determination of Suspended Solids in Water - Gravimetric Method". The concentrations of lead and chromium in the water before and after purification were determined according to HJ700 "Determination of 65 Elements in Water - Inductively Coupled Plasma Mass Spectrometry".

[0117] The water quality of the water body to be purified was tested and found to be as follows: pH value 4.12, total phosphorus 47.55 mg / L, fluoride 119.05 mg / L, total lead 0.51 mg / L, total chromium 0.29 mg / L, and suspended solids 58 mg / L.

[0118] Test results: The compressive strength and water purification results of the phosphogypsum microporous aggregates described in Examples 1-4 and Comparative Example 1, as well as the phosphogypsum aggregate described in Comparative Example 2, are shown in Table 1.

[0119] Table 1 shows the compressive strength and water purification results of the phosphogypsum microporous aggregates described in Examples 1-4, Comparative Example 1, and Comparative Example 2.

[0120]

[0121] Note: The reason why the total chromium removal rate of Examples 1 to 4 in Table 1 is 89.66% is that the total chromium in the water to be purified is 0.29 mg / L. After purification, the total chromium content in the water is significantly reduced. However, the detection instrument has a detection limit of 0.03 mg / L. That is to say, even if the total chromium concentration in the purified water is lower than 0.03 mg / L, the instrument can only display 0.03 mg / L. Therefore, the maximum total chromium removal rate can only be 89.66%.

[0122] As shown in Table 1, the phosphogypsum microporous aggregates in Examples 1-4, due to their unique micron-sized pore structure and chemical composition, can achieve removal or adsorption rates of over 92%, 80%, and 80% for phosphorus and fluoride, heavy metals, and suspended solids in water after purification. Comparative Example 1 shows that, without the addition of pretreated carbide slag and slag powder, the phosphogypsum microporous aggregates prepared solely with phosphogypsum and cement exhibit significantly lower removal or adsorption rates for fluorides and heavy metals. This demonstrates that Ca(OH)2 and active Al2O3 play a crucial role in the chemical precipitation of fluorides and heavy metals in water. Comparative Example 2 shows that the phosphogypsum aggregates prepared without the addition of a foaming agent show a significant decrease in the removal or adsorption rates of heavy metals and suspended solids, proving that the micron-sized pore structure plays a key role in the retention and adsorption of relevant substances (heavy metals and suspended solids) in water. In summary, this invention achieves the dual goals of efficient resource utilization of phosphogypsum and water purification through multi-component synergy and micron-level pore structure design, resulting in significant environmental and social benefits.

[0123] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A microporous aggregate of phosphogypsum, characterized in that, The raw materials, by weight percentage, include: 70-85% modified phosphogypsum, 5-10% cementitious material, 5-15% slag powder, 3-8% carbide slag, 0.5-1.5% foaming agent and 0.1-0.8% coagulant. The internal structure of the phosphogypsum microporous aggregate is a micron-sized pore structure. The modified phosphogypsum has a pH value of 6.5–11, a water-soluble total phosphorus content of ≤100 mg / kg, a water-soluble fluoride content of ≤200 mg / kg, and an average particle size of ≤100 μm.

2. The phosphogypsum microporous aggregate as described in claim 1, characterized in that, The preparation process of the modified phosphogypsum includes the following steps: Modified phosphogypsum is obtained by mixing phosphogypsum, an alkaline neutralizer, and water.

3. The phosphogypsum microporous aggregate as described in claim 2, characterized in that, The pH value of the phosphogypsum is 2.5–4.0; The alkaline neutralizer includes calcium hydroxide and / or calcium oxide; The mass ratio of the phosphogypsum to the alkaline neutralizer is 100:(2-5).

4. The phosphogypsum microporous aggregate as described in claim 1, characterized in that, The cementitious materials include ordinary silicate cement and aluminate cement; The mass ratio of ordinary silicate cement to aluminate cement is (4-8):

1.

5. The phosphogypsum microporous aggregate as described in claim 1, characterized in that, The pH value of the carbide slag is 12-13, the average particle size is ≤100μm, the mass percentage of calcium hydroxide in the carbide slag is ≥90%, and the moisture content is ≤5%.

6. The phosphogypsum microporous aggregate as described in claim 1, characterized in that, The foaming agent includes hydrogen peroxide or aluminum powder.

7. The phosphogypsum microporous aggregate as described in claim 1, characterized in that, The coagulant includes one or more of triethanolamine, sodium sulfate, and sodium silicate.

8. The method for preparing the phosphogypsum microporous aggregate according to any one of claims 1 to 7, characterized in that, Includes the following steps: Modified phosphogypsum, cementitious materials, slag powder, carbide slag and coagulant are mixed and then foaming agent and water are added to obtain slurry; The slurry is granulated, foamed, and cured sequentially to obtain the phosphogypsum microporous aggregate.

9. The preparation method according to claim 8, characterized in that, The mass ratio of the water to the total mass of the modified phosphogypsum, cementing material, slag powder, carbide slag, coagulant and foaming agent is (25-40):

100. The foaming molding temperature is 30-60℃, and the time is 2-4 hours; The curing process involves a humidity level of ≥90%, a temperature of 25–35℃, and a duration of 3–7 days.

10. The application of the phosphogypsum microporous aggregate according to any one of claims 1 to 7 or the phosphogypsum microporous aggregate prepared by the preparation method according to claim 8 or 9 in the fields of wetland wastewater ecological regulation, industrial water and slag yard leaching wastewater treatment.

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