Phosphogypsum-red mud-based artificial fish reef ecological material as well as preparation method and application thereof

Abstract

The invention discloses an ardealite-red mud-based artificial fish reef ecological material and a preparation method and application thereof, and the ardealite-red mud-based artificial fish reef ecological material is prepared by pretreating 40-60 parts of ardealite, 20-40 parts of red mud, 10-20 parts of oyster shell powder and 5-10 parts of diatomite, adding an alkali activator and a bioactive agent, and carrying out molding, maintenance and seawater mineralization treatment. A stable pH buffer system is constructed by utilizing the acid-base neutralization effect of the ardealite and the red mud, and the biocompatibility of the oyster shell powder and the porous adsorption characteristic of the diatomite are combined to realize the coordination of triple functions: the red mud iron-aluminum oxide and ettringite generated by the ardealite efficiently solidify heavy metals; the material continuously releases Ca < 2 + >, SiO2 and other elements, neutralizes H < + > in seawater, and relieves ocean acidification; and the multi-stage pore structure and the aragonite type CaCO3 coating layer improve the biological adhesion amount. The problem of solid waste pollution of ardealite and red mud is solved, a high-performance functional material is provided for marine ecological restoration, and remarkable environmental benefits and ecological values are achieved.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, and in particular to a phosphogypsum-red mud-based artificial reef ecological material, its preparation method, and its application. Background Technology

[0002] Phosphogypsum, a major industrial solid waste generated during the wet-process phosphoric acid production, has a global annual emission exceeding 300 million tons. Its open-air storage not only occupies land resources but also poses risks of groundwater pollution and soil acidification due to its content of soluble phosphorus, fluorine, and heavy metals. Red mud, a highly alkaline residue from alumina smelting, has a global annual emission of approximately 180 million tons. Its high alkalinity and sodium salt content easily trigger soil salinization, and the residual aluminum and iron oxides and trace amounts of radioactive substances further exacerbate environmental risks. Although current technologies attempt to use phosphogypsum as a cement retarder or roadbed material, and red mud for sintered bricks or soil amendment, the individual use of either has significant drawbacks: impurities in phosphogypsum inhibit cementitious activity, resulting in low product strength and poor water resistance; and the unstable alkaline release of red mud easily causes secondary pollution. In the field of marine ecological restoration, traditional artificial reefs mostly use concrete or stone. The extraction of raw materials exacerbates ecological damage, and the materials are biologically inert, unable to address the increasingly serious problem of ocean acidification. While research has explored red mud-based artificial reefs or phosphogypsum-based cementitious materials, the former has not addressed the toxicity of alkaline leaching to marine organisms, while the latter, due to its slow solidification and weak corrosion resistance, fails to meet the requirements of the deep-sea environment. Furthermore, neither material achieves the synergistic treatment and ecological function integration of the two types of solid waste—that is, simultaneously possessing the triple benefits of heavy metal stabilization, seawater pH buffering, and biofouling promotion. Therefore, developing an environmentally compatible artificial reef material that synergistically combines resource recycling and ecological benefits has become a key path to solving the dual challenges of solid waste disposal and marine governance. Summary of the Invention

[0003] The purpose of this invention is to provide a phosphogypsum-red mud-based artificial reef ecological material, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a phosphogypsum-red mud-based artificial reef ecological material and its preparation method and application, comprising the following components by dry basis mass: 40-60 parts phosphogypsum, 20-40 parts red mud, 10-20 parts oyster shell powder, and 5-10 parts diatomaceous earth. After alkali-activated molding and seawater mineralization treatment, the artificial reef ecological material is obtained.

[0005] The phosphogypsum is the portion passing through a 200-mesh sieve, with a calcium sulfate dihydrate content ≥80%, dried at 150℃ to a moisture content ≤3%, removing soluble phosphorus and fluorine impurities; the red mud is calcined at 300℃ for 2 hours to decompose organic matter, ball-milled to 100 mesh, reducing sodium ion dissolution rate by >40%; the oyster shell powder is washed, calcined at 1000℃ for 1 hour, and ball-milled to D50 ≤50μm, enhancing calcium dissolution activity.

[0006] Its core mechanism is shown in the table below:

[0007] Components Function implementation mechanism phosphogypsum Ca 2+ reacts with AI02 - to form ettringite, solidifying heavy metals, SO4 2- promoting calcification of corals Red mud Fe2O3 and Al2O3 provide adsorption sites to lock Pb and Cd, and the alkaline components neutralize the H + of seawater, and relieve acidification Oyster shell powder Micro-sized CaCO3 increases surface roughness, inducing barnacle, coral larvae attachment diatomite <![CDATA[Nanometer SiO2 constructs a microporous network to adsorb eutrophic pollutants]]>

[0008] The preparation method of phosphogypsum-red mud-based artificial reef ecological materials includes the following steps:

[0009] SS1. Dry phosphogypsum at 150℃ until the moisture content is ≤3%, pulverize it through a 200-mesh sieve to remove soluble phosphorus and fluorine impurities, roast red mud at 300℃ for 2 hours to decompose organic matter, ball mill it to 100 mesh to reduce sodium ion dissolution rate by >40%, wash oyster shell powder and calcine it at 1000℃ for 1 hour, ball mill it to D50≤50μm to improve calcium dissolution activity;

[0010] SS2. Add 50 parts of pretreated phosphogypsum, 30 parts of red mud, 15 parts of oyster shell powder, and 7 parts of diatomaceous earth into a mixer and mix at 120 r / min for 5 minutes.

[0011] SS3, add 5 parts of water glass with a modulus of 2.0 as an alkali activator and 2 parts of seaweed polysaccharide as a bioactive agent, adjust the water-solid ratio to 0.26-0.30, and continue mixing for 10 minutes to form a homogeneous slurry;

[0012] SS4. After injection into the steel mold, maintain pressure at 20MPa for 30 minutes to form a porous structure, maintaining a porosity of 35%±3% and a pore size gradient of 50μm~8mm.

[0013] SS5, after curing for 24 hours, is demolded and placed in an environment of 80℃ and 95% humidity for 48 hours to form ettringite reinforcement;

[0014] SS6, after being immersed in artificial seawater with a salinity of 3.5% for 7 days, has a 10-15 μm thick aragonite-type CaCO3 layer deposited on its surface, which promotes the attachment of marine organisms and completes the mineralization of seawater.

[0015] The technical effects and advantages of this invention are as follows:

[0016] (1) This invention fundamentally solves the environmental risk problem of the co-utilization of phosphogypsum and red mud: by precisely controlling the ratio of phosphogypsum (pH 4-5) to red mud (pH 12-13), a stable pH buffer system of 7.5-8.5 is formed inside the material, completely eliminating the risk of marine organism toxicity caused by the alkaline leaching of red mud. Verification through a 180-day seawater immersion experiment shows that the material surface continuously releases beneficial elements such as calcium and silicon, including Ca... 2+ The average daily leaching amount was 2.5 mg / L, and the average daily leaching amount of SiO2 was 1.8 mg / L, while the heavy metal leaching concentrations were far below the limits of the national standard GB 5085.3, with Pb at 0.08 mg / L and Cd at 0.05 mg / L. This is attributed to the chemical chelation effect of iron and aluminum oxides in the red mud on heavy metals and the encapsulation effect of ettringite minerals formed by phosphogypsum. Simultaneously, the micron-sized calcium carbonate coating induced by oyster shell powder during the seawater mineralization stage reached a thickness of 10-15 μm, which not only enhanced surface biocompatibility but also more effectively adsorbed phosphates in the water, inhibiting red tide occurrence and achieving a revolutionary transformation from a "pollution source" to an "ecological beneficiary."

[0017] (2) This material exhibits significantly superior comprehensive performance compared to traditional artificial reefs in marine ecological restoration: its multi-level pore structure, ranging from 50μm micropores to 8mm macropores, provides diverse habitats for marine organisms. The measured biological attachment amount reached 12.8kg / m², a 212% increase compared to 4.1kg / m² for concrete artificial reefs, and the biodiversity index of attachment increased by 40%. The key innovation lies in simultaneously solving two major problems: "marine acidification control" and "biological community construction." The alkaline components in the red mud continuously neutralize H⁺ in seawater; while the sulfate and calcium ions released by phosphogypsum promote the calcification metabolism of coral polyps, resulting in a significantly higher coral larval attachment density of 35 larvae / cm² compared to natural reefs. In simulated ocean current scouring experiments, the compressive strength of the material decreased by only 7%, far lower than the 25% decrease rate of concrete. Its durability stems from the synergistic strengthening mechanism of the ettringite network generated by steam curing and the aragonite crystals formed by seawater mineralization. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a phosphogypsum-red mud-based artificial reef ecological material, its preparation method, and its application. The preferred embodiment (Example 2) of the artificial reef used in the following sample is prepared using the following method:

[0020] SS1. Dry phosphogypsum at 150℃ until the moisture content is ≤3%, pulverize it through a 200-mesh sieve to remove soluble phosphorus and fluorine impurities, roast red mud at 300℃ for 2 hours to decompose organic matter, ball mill it to 100 mesh to reduce sodium ion dissolution rate by >40%, wash oyster shell powder and calcine it at 1000℃ for 1 hour, ball mill it to D50≤50μm to improve calcium dissolution activity;

[0021] SS2. Add 50 parts of pretreated phosphogypsum, 30 parts of red mud, 15 parts of oyster shell powder, and 7 parts of diatomaceous earth into a mixer and mix at 120 r / min for 5 minutes.

[0022] SS3, add 5 parts of water glass with a modulus of 2.0 as an alkali activator and 2 parts of seaweed polysaccharide as a bioactive agent, adjust the water-solid ratio to 0.26-0.30, and continue mixing for 10 minutes to form a homogeneous slurry;

[0023] SS4. After injection into the steel mold, maintain pressure at 20MPa for 30 minutes to form a porous structure, maintaining a porosity of 35%±3% and a pore size gradient of 50μm~8mm.

[0024] SS5, after curing for 24 hours, is demolded and placed in an environment of 80℃ and 95% humidity for 48 hours to form ettringite reinforcement;

[0025] SS6, after being immersed in artificial seawater with a salinity of 3.5% for 7 days, has a 10-15 μm thick aragonite-type CaCO3 layer deposited on its surface, which promotes the attachment of marine organisms and completes the mineralization of seawater.

[0026] Following the above steps, 10 sets of implementation test cases and 10 sets of comparative test cases were prepared. The raw material formulations and preparation processes for each implementation case and comparative example are shown in Tables 1 and 2.

[0027] Table 1. Examples (in copies)

[0028] Group number phosphogypsum Red mud Oyster shell powder diatomite Alkali activator Special treatment Example 1 40 40 15 5 Water glass modulus 1.8 conventional process Example 2 50 30 15 7 Water glass modulus 2.0 +0.5% carbon fiber Example 3 60 20 20 10 Water glass modulus 2.2 conventional process Example 4 45 35 10 5 Sodium silicate immersion in seawater for 14 days Example 5 55 25 20 10 Sodium hydroxide conventional process Example 6 50 30 10 5 Water glass modulus 2.0 Steam curing at 60℃ Example 7 50 30 20 7 Water glass modulus 2.0 +3% zeolite powder Example 8 40 30 15 10 Water glass modulus 1.8 conventional process Example 9 60 40 10 5 Potassium silicate No seaweed polysaccharide Example 10 50 30 15 7 Water glass modulus 2.0 <![CDATA[+0.1% CeO2]]>

[0029] Table 2 Comparative Examples (portions)

[0030] Group number Design Purpose Key changes For 1 Red mud lacks neutral alkalinity Red mud 0 parts, phosphogypsum 70 parts 2 Phosphorus-deficient gypsum solidification of heavy metals 0 parts phosphogypsum, 70 parts red mud 3 Insufficient oyster shell powder 2 parts oyster shell powder 4 Excessive red mud triggers strong alkali 50 portions of red mud 5 Alkali-free activator Unwater glass 6 No seawater mineralization Skip seawater soaking 7 Insufficient steam curing Curing temperature 60℃, time 24h 8 Diatomaceous earth replaces non-porous materials Diatomaceous earth was replaced with an equal amount of quartz sand. 9 Ineffective alternatives to bioactive agents Seaweed polysaccharide was replaced with an equal amount of starch. 10 Untreated phosphogypsum Use raw phosphogypsum directly

[0031] The purpose and related performance indicators of each embodiment are as follows:

[0032] Example 1: Verifying the feasibility of the lower limit of the claimed ratio, it proves that even with the lowest proportion of phosphogypsum, a pH of 7.9±0.1 can still be achieved through sufficient neutralization with red mud, while the degree of deterioration in compressive strength is controllable at 35 MPa. Example 2: 50 parts phosphogypsum + 30 parts red mud is the core preferred solution of this invention, with the addition of 0.5% carbon fiber to enhance crack resistance, providing a data anchor for the optimal value of the claim. Example 3: Examining the extreme ratios of the upper limit of phosphogypsum and the lower limit of red mud, it confirms that even with insufficient red mud, alkalinity can still be maintained by relying on oyster shell powder, but the leaching of heavy metal Cd is 0.07 mg / L, slightly higher than in Example 2, clarifying the necessity of red mud ≥20 parts. Example 4: Extending seawater mineralization to 14 days revealed an 18% increase in biofilm formation compared to 7-day treatment, but with increased costs. Example 5: Replacing the alkali activator with sodium hydroxide resulted in excessively rapid reaction and microcracks, proving the necessity of the water glass / silicate process. Example 6: Lowering the steam curing temperature to 60℃ reduced the formation of ettringite by 40% and increased the erosion resistance attenuation rate to 12%, confirming that 80℃ is the critical value for curing. Example 7: Adding zeolite powder to replace diatomaceous earth, PO4... 3- The adsorption rate remained the same, but the change in microporous structure led to a 15% decrease in coral attachment density. Example 8: Combining the lower limit of phosphogypsum and the upper limit of diatomaceous earth, PO4 was measured. 3- An adsorption rate of 91% was optimal, but 30 parts of red mud resulted in insufficient alkaline buffering capacity. Example 9: Removing the bioactive agent resulted in a 36% loss in bio-attachment after 6 months, decreasing to 8.2 kg / m², demonstrating its crucial role in inducing microbial colonization. Example 10: Incorporating 0.1% CeO2 enhanced coral metabolism, increasing the survival rate to 92%, extending the high-value-added improvement scheme.

[0033] The key performance indicators of the artificial reefs in each embodiment and comparative example are shown in the table below. Among them, the molding of comparative example 10 failed because the phosphogypsum was not pretreated and had too high water content.

[0034] Table 3 Mechanical Properties

[0035] Group Compressive strength (MPa) Group Compressive strength (MPa) Example 1 35.2 For 1 14.5 Example 2 45.4 2 18.4 Example 3 38.4 3 40.2 Example 4 43.3 4 28.8 Example 5 28.0 5 18.4 Example 6 32.9 6 43.6 Example 7 44.4 7 26.3 Example 8 36.5 8 44.7 Example 9 42.1 9 44.3 Example 10 46.3 10 /

[0036] Table 4 pH value, heavy metal leaching and phosphorus adsorption rate

[0037] Group seawater pH Pb leaching (mg / L) Cd leaching (mg / L) <![CDATA[PO4 3- Adsorption rate (%) Example 1 7.9 0.09 0.06 82 Example 2 8.0 0.08 0.05 85 Example 3 8.1 0.10 0.07 88 Example 4 8.0 0.07 0.04 87 Example 5 7.8 0.12 0.08 76 Example 6 8.1 0.11 0.07 80 Example 7 8.0 0.08 0.05 87 Example 8 7.9 0.09 0.06 91 Example 9 8.0 0.08 0.05 83 Example 10 8.0 0.07 0.04 86 For 1 9.3 0.15 0.80 45 2 10.2 1.20 0.11 32 3 8.0 0.08 0.05 50 4 9.5 0.13 0.09 69 5 7.9 0.10 0.07 71 6 8.1 0.05 6.1 58 7 8.0 0.08 9.8 77 8 8.0 0.05 10.5 28 9 8.0 0.05 4.5 80 10 / / / /

[0038] Table 5 Bioattachment and Structural Durability

[0039] Group Bioattachment rate (kg / m²) Coral survival rate (%) Structural durability Example 1 10.2 78 7.5% Example 2 12.8 85 7.0% Example 3 14.2 82 8.2% Example 4 15.1 88 6.8% Example 5 9.5 70 15.0% Example 6 11.0 75 12.0% Example 7 10.9 72 7.3% Example 8 11.5 80 8.5% Example 9 8.2 74 7.2% Example 10 13.5 92 6.5% For 1 4.9 35 Shatter 2 0 (Poisoning) 0 (Poisoning) Powdering 3 5.7 38 8.0% 4 0 (desorption) 0 (desorption) 12.5% 5 7.3 65 disintegration 6 6.1 60 9.0% 7 9.8 68 15.0% 8 10.5 70 7.8% 9 4.5 62 7.1% 10 / / /

[0040] Each comparative example exhibits significant performance defects. In Comparative Example 1, the red mud content was reduced to zero, causing the material to lose its alkaline neutralization ability. Seawater immersion resulted in a pH spike to 9.3. Furthermore, the lack of red mud iron and aluminum oxides to fix heavy metals led to Cd leaching at 0.8 mg / L, and biofilm attachment at only 4.9 kg / m², demonstrating the indispensability of the dual-waste synergy. In Comparative Example 2, the phosphogypsum content was reduced to zero, triggering strong alkaline leaching that directly killed 98% of barnacle larvae in the test area. The absence of phosphogypsum resulted in the formation of ettringite to encapsulate heavy metals, with Pb leaching at 1.2 mg / L. The structure also pulverized due to the lack of sulfate activation. In Comparative Example 3, the oyster shell powder content was reduced to 2 parts, resulting in a surface roughness Ra of only 1.2 μm. Coral larvae attachment density plummeted to 16 larvae / cm², primarily due to the lack of micron-sized calcium carbonate inducing groups. In Comparative Example 4, the red mud content increased to 50 parts, causing alkaline overload. Although the alkalinity was later reduced to 9.5, it still exceeded the tolerance limit of marine organisms, leading to 100% shellfish detachment and death. Excessive sodium ions also weakened the structure. Comparative Example 5, without the addition of an alkali activator, failed to form an ettringite gel network, resulting in a compressive strength of only 18 MPa. It disintegrated after 90 days of ocean current simulation testing, confirming that the activation reaction is the core of structure formation. Comparative Example 6, skipping seawater mineralization treatment, failed to form a calcium carbonate coating on the surface, resulting in a biofilm adhesion rate of only 6.1 kg / m². Comparative Example 7, with insufficient steam curing, showed a 52% decrease in the intensity of the characteristic peaks of ettringite detected by XRD, leading to a 15% decrease in compressive strength and structural cracking during simulated deep-sea pressure testing. Comparative Example 8, replacing diatomaceous earth with quartz sand, sharply reduced the microporous surface area from 42 m² / g to 5 m² / g, and increased PO₄² / g. 3- The adsorption rate was only 28%. In Comparative Example 9, the bioactive agent was replaced with starch, resulting in the loss of microbial induction function, a 64% decrease in surface bacterial biofilm coverage, delayed attachment of large organisms, and a reduction in the total amount to 4.5 kg / m². In Comparative Example 10, undried phosphogypsum was used, and excessive moisture during wet mixing caused phase separation, resulting in 100% cracking during the pressure molding stage, confirming that a moisture content of ≤3% is a prerequisite for process implementation.

[0041] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A phosphogypsum-red mud-based artificial reef ecological material, characterized in that, The material comprises the following components by dry basis mass: 40-60 parts phosphogypsum, 20-40 parts red mud, 10-20 parts oyster shell powder, and 5-10 parts diatomaceous earth; the phosphogypsum is dried at 150℃ to a moisture content ≤3%, pulverized through a 200-mesh sieve, and soluble phosphorus and fluorine impurities are removed; the red mud is calcined at 300℃ for 2 hours, ball-milled to 100 mesh, and the sodium ion dissolution rate is reduced to >40%; the oyster shell powder is washed, calcined at 1000℃ for 1 hour, and ball-milled to D50 ≤ 50μm; the material is prepared by alkali-activated molding and seawater mineralization treatment.

2. The phosphogypsum-red mud-based artificial reef ecological material according to claim 1, its preparation method and application, characterized in that, The phosphogypsum has a calcium sulfate dihydrate content of ≥80%; the red mud has an aluminum and iron oxide content of ≥30%; and the diatomaceous earth has a specific surface area of ​​≥40 m² / g.

3. The phosphogypsum-red mud-based artificial reef ecological material according to claim 1, its preparation method and application, characterized in that, The alkaline activator used in the alkaline activation molding is water glass, sodium silicate, or potassium silicate with a modulus of 1.8 to 2.2, and the amount added is 3 to 8% of the total mass of the system.

4. The phosphogypsum-red mud-based artificial reef ecological material according to claim 1, its preparation method and application, characterized in that, The seawater mineralization treatment involves immersing the molded material in artificial seawater with a salinity of 3.5% for 7 to 14 days, forming an aragonite-type CaCO3 layer with a thickness of 10 to 15 μm on the surface.

5. The phosphogypsum-red mud-based artificial reef ecological material according to claim 1, its preparation method and application, characterized in that, The porosity of the material is 35%±3%, and the pore size gradient distribution is 50μm~8mm.

6. A method for preparing a phosphogypsum-red mud-based artificial reef ecological material according to any one of claims 1-5, characterized in that, Includes the following steps: SS1: Pretreatment of phosphogypsum, red mud, and oyster shell powder respectively; SS2: Add the pretreated phosphogypsum, red mud, oyster shell powder, and diatomaceous earth into the mixer in proportion and mix at 120 r / min for 5 minutes; SS3: Add alkali activator and bioactive agent, adjust the water-to-solid ratio to 0.26-0.30, and continue mixing for 10 minutes to form a homogeneous slurry; SS4: Inject the slurry into the steel mold and hold it under pressure at 20MPa for 30 minutes to form the final product; SS5: After curing for 24 hours, demold and cure in an environment of 80℃ and 95% humidity for 48 hours; SS6: Seawater mineralization is completed after immersion in artificial seawater with a salinity of 3.5% for 7 days.

7. The method for preparing a phosphogypsum-red mud-based artificial reef ecological material according to claim 6, characterized in that, The bioactive agent mentioned in step SS3 is seaweed polysaccharide, and the amount added is 1-3% of the total mass of the system.

8. The method for preparing an artificial reef ecological material based on phosphogypsum and red mud according to claim 6, wherein the preferred proportions of each component in step SS2 are: 50 parts phosphogypsum, 30 parts red mud, 15 parts oyster shell powder, and 7 parts diatomaceous earth.

9. In the preparation method of the phosphogypsum-red mud-based artificial reef ecological material according to claim 6, 0.5-3% of a reinforcing agent may be added during the curing process in step SS5, wherein the reinforcing agent is selected from carbon fiber, zeolite powder or CeO2.

10. The application of a phosphogypsum-red mud-based artificial reef ecological material according to any one of claims 1-5 in marine ecological restoration, characterized in that, The material is used to construct artificial reefs, achieving synergistic functions of heavy metal stabilization, seawater pH adjustment, and improvement of marine organism habitats.