Phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash and application of phosphorus-modified calcium-based biomineral material

Abstract

The invention discloses a phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash and application, and belongs to the technical field of fly ash treatment. The material takes waste oyster shells as a raw material, and is prepared by grinding, sieving, dipotassium phosphate modification, pyrolysis at 400-600 DEG C, grinding and sieving with a 0.15-0.22 mm sieve, the pH is 10.2-11.3, the calcium accounts for 20-30%, and the phosphorus accounts for 6-8%. During application, the mass ratio of the material to fly ash is 0.01-0.1, and the material is cured for 24 hours and dried. The material can efficiently fix seven heavy metals such as As and Cd in the fly ash, the leaching concentration reaches the standard, the secondary release rate is low under the acidic condition, resource utilization of the oyster shells is achieved, the cost is low, and the material is suitable for stabilizing treatment of the waste incineration fly ash.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fly ash treatment, and particularly relates to a phosphorus modified calcium-based biomimetic material for inhibiting leaching of heavy metals in fly ash and application thereof. BACKGROUND

[0002] At present, about 210 million tons of household garbage is treated by means of waste incineration, accounting for about 82% of the total amount of waste incineration. A large amount of ash is generated after waste incineration, and on average, 30 kg to 150 kg of fly ash is generated per ton of incinerated waste. Fly ash is a product collected by a flue gas purification system, and the particle size is concentrated in 10 to 50 microns. In the formation process, heavy metals and organic pollutants are easily adsorbed. These heavy metals enter the environment through percolation during fly ash disposal, threatening human health. Therefore, before fly ash disposal, it needs to be stabilized.

[0003] Calcium-based biomimetic is a kind of biomass material for heavy metal stabilization, which is widely available, has large specific surface area, rich surface charge, high porosity, and rich functional groups. A large amount of discarded shellfish is generated in the production of seafood shellfish. If these discarded shellfish are not effectively treated, they will cause resource waste and environmental pollution. Oyster production accounts for about 4% of the total amount of cultured shellfish, and the resource is abundant. Oyster shells account for more than 60% of the total mass of adult oysters. Oyster shells are mainly composed of calcium carbonate, accounting for about 80% to 90% of the total mass. There are a large amount of calcium ions and carbonate in oyster shells, which have certain fixing capacity for heavy metals through processes such as adjusting the pH of the leaching solution, generating precipitates and adsorption. However, the above-mentioned methods have poor fixing capacity for heavy metals, and the heavy metals can be easily released again under acidic conditions. Moreover, the types of heavy metals that can be fixed are limited, and it is impossible to comprehensively fix the heavy metals contained in fly ash. SUMMARY

[0004] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0005] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of a phosphorus modified calcium-based biomimetic material for inhibiting leaching of heavy metals in fly ash.

[0006] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of a phosphorus modified calcium-based biomimetic material for inhibiting leaching of heavy metals in fly ash, characterized in that it comprises, Raw material pretreatment: grind the oyster shells and sieve to obtain oyster shell powder; Phosphate modification: mix the oyster shell powder with dipotassium hydrogen phosphate uniformly, add ultrapure water, modify for 8 to 12 hours, and dry; Pyrolysis treatment: pyrolyzing the dried mixture at 400-600 DEG C; Grinding and sieving: grinding and sieving the pyrolysis product to obtain the phosphorus-modified calcium-based biomimetic mineral material.

[0007] As a preferred scheme of the preparation method, the mass-volume ratio of K2HPO4 to water is 8-9 g:1 mL.

[0008] As a preferred scheme of the preparation method, the mass ratio of the oyster shell powder to K2HPO4 is 1:0.01-0.2.

[0009] As a preferred scheme of the preparation method, the drying temperature is 30-50 DEG C.

[0010] As a preferred scheme of the preparation method, the pyrolysis time is 0.5-2 h.

[0011] As a preferred scheme of the preparation method, the pyrolysis product is ground and sieved, and the mesh size is 0.15-0.22 mm.

[0012] Another object of the present application is to provide a phosphorus-modified calcium-based biomimetic mineral material, which overcomes the shortcomings of the prior art.

[0013] Another object of the present application is to provide an application of the phosphorus-modified calcium-based biomimetic mineral material in inhibiting heavy metal leaching in fly ash, which overcomes the shortcomings of the prior art.

[0014] As a preferred scheme of the application, the heavy metals include arsenic, cadmium, chromium, copper, lead, nickel and zinc.

[0015] As a preferred scheme of the application, the fly ash is waste incineration fly ash, and the pH of the fly ash is 12.0-12.5, and the water content is ≤25%.

[0016] The present application has the following advantages: (1) The calcium-based biomimetic mineral mainly generates carbonate precipitate and hydroxide precipitate with heavy metals, which are not stable under acidic conditions and are easy to be released again. In comparison, the phosphate precipitate of heavy metals has higher solubility product constant, higher stability and lower ecological risk. Therefore, the present application can not only improve the immobilization efficiency of the material by introducing phosphate into the calcium-based biomimetic mineral, but also convert the heavy metals into the residual state and reduce the ecological risk. In addition, the introduction of phosphate into the calcium-based biomimetic mineral generates hydroxyapatite under pyrolysis conditions, has more adsorption sites, and increases the immobilization of heavy metals.

[0017] (2) The present application prepares a material suitable for fly ash modification by phosphate infiltration of the calcium-based biomimetic mineral oyster shell under high-temperature pyrolysis conditions, introduces phosphate to improve the stabilization efficiency and stability of the material, and reduces the ecological risk of fly ash in the disposal process while improving the ability of the material to stabilize fly ash heavy metals. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The removal effects of K2HPO4 modified oyster shells under different conditions in Examples 1-4 on Cd 2+ and Pb 2+ , a indicates the removal effects of K2HPO4 modified oyster shells on Cd 2+ and Pb 2+ under different mass ratios of K2HPO4 to oyster shell powder; b indicates the removal effects of K2HPO4 modified oyster shells on Cd 2+ and Pb 2+ under different calcination temperatures; c indicates the removal effects of K2HPO4 modified oyster shells on Cd 2+ and Pb 2+ under different calcination times.

[0020] Figure 2 The SEM images of the oyster shells before and after modification in Example 1.

[0021] Figure 3 The electron energy spectrum of the oyster shells before and after modification in Example 1.

[0022] Figure 4 The infrared spectrum of the oyster shells before and after modification in Example 1.

[0023] Figure 5XRD patterns of oyster shell before and after modification in Example 1.

[0024] Figure 6 Heavy metal fixation in fly ash by oyster shell and modified oyster shell with different proportions in Example 7 and Example 8.

[0025] Figure 7 Changes in the form of heavy metals in fly ash fixed by oyster shell in Example 8.

[0026] Figure 8 RAC levels of each heavy metal in fly ash before and after stabilization in Example 8.

[0027] Figure 9 ICF values of each heavy metal in fly ash before and after stabilization in Example 8. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objectives, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the description examples.

[0029] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in other ways that are not specifically described herein, and it is understood that one of ordinary skill in the art, upon reading the present disclosure, can employ a similar methodology in other and different implementations or applications of the present application without departing from the spirit and scope of the present application. Accordingly, the present application is not intended to be limited to the specific illustrative examples described and shown herein.

[0030] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is separate or alternative to other embodiments.

[0031] The reagents used in the embodiments of the present application are all analytical pure, the solvents used in the experiments are all deionized water, and the sodium chloride, cadmium nitrate tetrahydrate, lead nitrate, acetic acid, concentrated nitric acid, sodium hydroxide, dipotassium hydrogen phosphate, concentrated hydrochloric acid, sodium bicarbonate and the like used in the experiments are all analytical pure and purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.

[0032] In the embodiments of the present application, the pH value of the oyster shell powder is 8.84, the total calcium content is 1.65 g kg -1 , and the organic matter content is 5.43 g kg -1 .

[0033] The instruments used in the embodiments of the present application include an environmental scanning electron microscope (ESEM, model: Quattro S, manufacturer: Thermo Fisher Corporation). Fourier Transform Infrared Spectrometer (FTIR, Model: IRPvestige-21, Manufacturer: Shimadzu, Japan); X-ray diffraction (XRD, Model: PANalytical X'pert, Manufacturer: Spectris Pte. Ltd).

[0034] Example 1, the embodiment provides a preparation method of a phosphorus modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash, comprising the following steps: (1) raw material pretreatment: grind the oyster shell and pass it through a 0.149 mm sieve to obtain oyster shell powder; (2) phosphate modification: mix 2 g of oyster shell powder with 0.4 g of dipotassium hydrogen phosphate, add 50 mL of water, stir uniformly, and place in a 35°C oven after 12 h; (3) pyrolysis treatment: calcine the dried mixed material in a muffle furnace at 400°C for 30 min; (4) grinding and sieving: take out the pyrolysis product after cooling at room temperature, grind and sieve through a 100 mesh sieve to obtain the phosphorus modified calcium-based biomineral material.

[0035] Example 2, the difference between this embodiment and Example 1 is that in step (2), the mass of dipotassium hydrogen phosphate is replaced by 0 g, 0.02 g, 0.1 g, 0.2 g and 0.6 g respectively, so that the mass ratio of K2HPO4 to oyster shell powder is 0, 0.01, 0.05, 0.1, 0.3 respectively, and the remaining steps are the same as those of Example 1, to prepare the phosphorus modified calcium-based biomineral material.

[0036] Example 3, the difference between this embodiment and Example 1 is that in step (3), the pyrolysis temperature is replaced by 0°C, 200°C, 300°C, 600°C and 800°C respectively, and the remaining steps are the same as those of Example 1, to prepare the phosphorus modified calcium-based biomineral material.

[0037] Example 4, the difference between this embodiment and Example 1 is that in step (3), the pyrolysis temperature is replaced by 400°C, and the pyrolysis time is replaced by 0 min, 60 min, 90 min, 120 min respectively, and the remaining steps are the same as those of Example 1, to prepare the phosphorus modified calcium-based biomineral material.

[0038] Take 0.1 g of the phosphorus modified oyster shell obtained in Examples 1-4 in a 50 mL centrifuge tube, and use a NaNO3 solution with pH of 7 and 0.01 M as a supporting electrolyte, so that the Cd 2+ and Pb 2+The concentration of Cd 2+ and Pb 2+ was 200ppm, the total volume was 30mL, the centrifuge tube was taken out after shaking for 6h at room temperature, centrifuged at 3500r / min for 10min, and the concentration of Cd 2+ and Pb 2+ in the solution was measured after passing through a 0.22μm water filter membrane.

[0039] The results are shown in a of Figure 1 . With the increase of the mass ratio of K2HPO4 to oyster shell powder, the removal rates of Pb 2+ and Cd 2+ increased continuously, reached the peak at the mass ratio of 0.2, and remained stable after reaching the peak. It can be seen that the modified oyster shell powder at the mass ratio of 0.2 has good adsorption effect on Pb 2+ and Cd 2+ . This may be due to the increase of phosphate, the oyster shell surface can adsorb more Pb 2+ and Cd 2+ sites, but with the increase of the mass ratio, the adsorption rate is limited by the specific surface area of oyster shell, and potassium hydrogen phosphate cannot be combined with oyster shell powder, so the optimal mass ratio of K2HPO4 to oyster shell powder is 0.2.

[0040] The experimental results of the effect of calcination temperature on the removal rates of Pb 2+ and Cd 2+ are shown in b of Figure 1 . With the increase of calcination temperature, the removal rates of Pb 2+ and Cd 2+ increased gradually, and reached equilibrium at 400℃-600℃. This is mainly because the organic components of oyster shell are lost at high temperature, more pores are formed in the material, the specific surface area increases, and the adsorption sites increase. However, when the temperature reaches 800℃, the microporous and mesoporous structures are destroyed, the specific surface area decreases sharply, and calcium silicate or calcium aluminate with layered structure is generated at 800℃, which significantly enhances the ion exchange capacity between layers, Pb 2+ always maintains a high removal rate because it is easier to be fixed by displacement precipitation, and the reaction has low dependence on pore structure. The removal of Cd 2+ is more dependent on specific surface area, so it is more sensitive to structural changes. Until the new phase is generated at high temperature, it provides a more efficient adsorption path for Cd 2+ . Considering economic benefits, 400℃ is selected as the optimal calcination temperature.

[0041] The experimental results of the effect of calcination time on the removal rates of Pb 2+ and Cd 2+ are shown in c of Figure 1 . With the increase of calcination time from 30min to 120min, the removal rates of Pb 2+ and Cd2+ The removal rate of phosphorus remained stable, and the internal pore shaping of oyster shells and the generation of each adsorption site were completed within 30 min of high-temperature calcination time. Therefore, 30 min was selected as the optimal calcination time.

[0042] Example 5, this example is to prepare the phosphorus modified calcium-based biomimetic mineral material of example 1 for each characterization, specifically: An environmental scanning electron microscope (ESEM, model: Quattro S, manufacturer: Thermo Fisher) was used for observation and analysis. All samples were analyzed by Fourier transform infrared spectroscopy (FTIR, model: IRPvestige-21, manufacturer: Shimadzu, Japan) to infer the range of KBr particles from 7800 to 350 cm-1. X-ray diffraction (XRD, model: PANalytical X'pert, manufacturer: Spectris Pte. Ltd) was used for determination and analysis, test conditions: Cu-Kα ray source, voltage 45KV, current 40mA, diffraction angle 2θ=5°~90°.

[0043] The SEM images of the oyster shells before and after modification are shown in Figure 2 The original oyster shell presents a typical "brick-mud" structure, which is alternately stacked by regular arranged sheet aragonite and a small amount of organic matrix layer. The surface flatness is high, the sheet edge is clear, and the ladder-shaped growth marks can be seen at the arrow position, which is consistent with the directional crystallization characteristics of biological mineralization. The high magnification image shows that there are nanoscale pores (diameter about 50nm~100nm) on the surface of the sheet layer, which may be the channels left after the degradation of biological organic matter. The original sheet structure is completely destroyed, forming a nanoscale particle aggregate with a particle size of about 200nm~500nm, showing a "coral-like" porous morphology. This may be due to the preferential dissolution of grain boundaries caused by phosphoric acid corrosion and the particle fusion phenomenon caused by high-temperature sintering. The surface roughness increases significantly, and there are a large number of mesopores between the particles.

[0044] EDS spectrum analysis of the oyster shells before and after modification, the results are shown in Figure 3As shown. Both samples exhibit strong peaks at ~0.5 keV (O-Kα) and ~3.7 keV (Ca-Kα), consistent with the characteristics of CaCO3 (the main component of oyster shells). The modified sample shows more pronounced peaks at ~2.0 keV (P-Kα) and ~3.3 keV (K-Kα), confirming the introduction of P and K. Oxygen (O) and calcium (Ca): Both are major components, but their proportions differ significantly. In the modified oyster shell, O accounts for 57.39% by mass and Ca for 29.85% by mass, while in the natural oyster shell, Ow accounts for 62.81% by atomic number and Caw for 22.40% by mass. The higher calcium content after modification may be due to calcium salt enrichment or impurity removal during the processing. The natural sample has higher Na (3.26% by mass) and Mg (1.74% by mass), which decrease to 1.03% and 0.12% respectively after modification. This indicates that the modification process may have removed some soluble salts (such as NaCl) or magnesium impurities. Silicon (Si) and chlorine (Cl): their contents decreased after modification (Si 0.74%→0.39%, Cl 0.19%→0.15%), possibly related to the high-temperature treatment. The modified sample had a slightly higher background, possibly due to increased surface roughness or enhanced X-ray scattering caused by amorphization treatment.

[0045] FTIR spectra of oyster shells before and after modification are as follows: Figure 4 As shown, the carbonate characteristic region (400cm) - ¹~1500cm - ¹), after modification ν(CO²) - (566cm) - ¹~873cm - ¹) Sharpened peak shape and increased transmittance indicate improved crystallinity but preserved crystal structure, suggesting that the main structure of the oyster shell has not changed; in the organic component region (1000 cm⁻¹) -1 ~1641cm -1 ): 1039cm -¹ (CO) and 1641cm -1 The weakening of the (amide I) peak indicates partial degradation of organic matter, suggesting that the organic components in the oyster shell were decomposed during high-temperature calcination; the hydroxyl region (3000 cm⁻¹) -1 ~4000cm -1 ): Newborn 3642cm -1 The appearance of free hydroxyl peaks reflects an increase in surface active sites. Combined with the nanoporous structure revealed by SEM, it is confirmed that the modification significantly improves the specific surface area and surface reactivity of the material by removing the organic matrix and reconstructing the hydroxyl network, providing more adsorption sites for heavy metal immobilization.

[0046] XRD patterns of oyster shells before and after modification are as follows: Figure 5The results show that the main components of both are CaCO3, and the main component is calcite type CaCO3. Previous studies have shown that the main component of oyster shell is about 95% CaCO3 crystal and 5% organic matter. Some peaks of CaO and Ca(OH)2 were found in the modified oyster shell, mainly due to the conversion of CaCO3 during high temperature calcination, and some peaks of CaH2PO4 appeared, indicating the introduction of phosphate, which is consistent with the data of EDS and infrared.

[0047] Example 6, this embodiment is the detection of phosphorus modified calcium-based biomimetic material on the stabilization of heavy metals in fly ash, specifically: The fly ash obtained from a certain waste incineration plant in Haikou was determined by pH to have a pH of 12.23, which was alkaline, consistent with the characteristics of general incineration fly ash. In the flue gas purification system, lime semi-dry flue gas desulfurization was used, which mainly through the injection of lime slurry and flue gas mixed with neutralization reaction, easy to produce lime excessive phenomenon, therefore fly ash is alkaline. The moisture content of fly ash was determined, and the moisture content of fly ash was 24.32%, which was lower than the limit value (30%) specified in "Standard for Pollution Control on Domestic Waste Landfill Sites" (GB 16889-2008).

[0048] The total content of 7 kinds of heavy metals in fly ash was extracted by microwave digestion, and the content of heavy metals in fly ash was finally obtained as shown in Table 1, in which the concentration of Zn was the highest, reaching 4394.01 ppm, and the concentration of Pb was the second, reaching 1540.53 ppm. The potential sources of these two metals are galvanized materials, batteries, rubber additives, paints and other industries, which have high content in domestic waste. In addition, Zn, Pb and other low boiling point metal elements are easy to combine with chlorine to form volatile chlorides during the incineration process, and are condensed and enriched on the surface of fly ash during the cooling process in the flue gas purification system. Compared with the other, Ni, Cr and other high melting point metals are not easy to migrate by gasification, so their concentration in the fly ash phase is relatively low. As for other metals, they are at a medium level.

[0049] Table 1 Total amount of metal in original fly ash

[0050] The simulation experiment of heavy metal leaching of MSWI fly ash needs to simulate the landfill leachate environment by acetic acid buffer solution method. The specific operation process is as follows: first, prepare the leaching agent 2# with pH value of 2.64±0.05 (dilute 17.25 mL glacial acetic acid to 1 L ultrapure water), and add fly ash sample and leaching agent in a 50 mL centrifuge tube with liquid-solid ratio of 20:1. The mixed system is placed in a constant temperature shaker (23±2℃) for 16 hours with a rotation speed of 50 r / min to simulate the dynamic leaching process of leachate. Then, the solid-liquid separation is realized by centrifugation at 3000 r / min for 10 minutes, and the clear leaching liquid is obtained by filtering through a 0.45 μm water microporous filter membrane. Finally, the ICP-OES spectrometer is used for quantitative analysis of 7 kinds of heavy metals (Zn, Pb, Cu, Cd, Cr, Ni and As) in the filtrate.

[0051] The leaching concentration of 7 kinds of heavy metals in fly ash is shown in Table 2 by leaching experiment of heavy metals in fly ash by leaching liquid. Among them, the highest leaching concentration is Zn, mainly because Zn has the highest concentration in fly ash. In addition, Pb and Cd also have high leaching concentration, and Pb has the highest leaching rate, nearly 28.34% leaching, which may be because Pb and Cd are not tightly combined in the mineral phase of fly ash and can be easily released in acidic leaching solution. The leaching concentration of As and Cr is low, which may be mainly due to the fact that the two metals are fixed in the crystal lattice of fly ash and are difficult to be released. In addition, the leaching concentrations of Cd and Pb are 1.20 mg / L and 18.5 mg / L respectively, which exceed the concentration limit value of GB 16889-2008 "Standard for Pollution Control on Domestic Waste Landfill"; the concentrations of the remaining elements are below the limit value of landfill control standard.

[0052] Table 2 Leaching concentration of metals in fly ash

[0053] Take 5 grams of fly ash sample, respectively, and use dry or wet modified oyster shell powder, according to the ratio of modified oyster shell powder / fly ash of 0.01, 0.05, 0.1 to configure the sample. Then add 30 milliliters of ultrapure water and mix thoroughly. The mixed system is placed at room temperature for 24 hours to complete the stabilization process, and then transferred to a 65℃ oven for drying to constant weight (for 24 hours), and finally the solidified product is sealed and stored in a desiccator for subsequent physical and chemical analysis.

[0054] 1%, 5% and 10% oyster shell and modified oyster shell are used respectively for stabilization treatment of fly ash, and 7 kinds of heavy metals in the stabilized fly ash are extracted by leaching liquid, and the results are as follows Figure 6As shown, the leaching concentrations of several heavy metals gradually decreased with increasing amounts of oyster shells and modified oyster shells. Compared with the concentration limits in GB16889-2008 "Standard for Pollution Control of Municipal Solid Waste Landfill," the heavy metals in fly ash met landfill standards under the stabilizing effect of oyster shell materials. Overall, phosphate-modified oyster shells showed better heavy metal fixation than unmodified oyster shells.

[0055] Comparative Example 1 differs from Example 6 in that it uses a traditional lime stabilizer to stabilize heavy metals in fly ash. In addition to lime, traditional lime stabilizers also require the addition of other chelating agents to prevent the leaching of heavy metals under low pH conditions. The best effect is achieved when the dosage of lime stabilizer is 5-8%. However, the modified oyster shell prepared by this invention can fix the heavy metals in fly ash to the landfill standard when the dosage is 1%.

[0056] Example 7 summarizes the changes in heavy metal speciation during the stabilization of fly ash using phosphorus-modified calcium-based biomineral materials. Specifically: The speciation of seven heavy metals (Zn, Pb, Cu, Cd, Cr, Ni, and As) in different fly ash samples was analyzed using a five-step extraction method. The specific procedures are as follows.

[0057] 1. Water-soluble (F1) (1) Take 1.00 g of fly ash sample, suspend it in 30 mL of deionized water, shake for 16 hours, centrifuge at 3000 r / min for 10 min, and filter the supernatant through 0.45 μm filter paper.

[0058] 2. Surface adsorbed state (F2) (2) The fly ash residue from step (1) was washed with 30 mL of water and centrifuged, and then the washing liquid was discarded by vacuum filtration. The residue was resuspended in 30 mL of 0.05 M sodium bicarbonate solution and shaken for 16 hours. Then, it was centrifuged again as in step (1), and the supernatant was filtered through 0.45 μm filter paper.

[0059] 3. Iron-aluminum oxide bonded state (F3) (3) The fly ash residue from step (2) was washed with 30 mL of water and centrifuged, and then the washing liquid was discarded by vacuum filtration. The residue was resuspended in 30 mL of 0.1 M sodium hydroxide solution and shaken for 16 hours. Then, it was centrifuged again as in step (1), and the supernatant was filtered through 0.45 μm filter paper.

[0060] 4. Acid-extractable state (F4) (4) The fly ash residue of step (3) was washed with 30 mL of water, centrifuged, and the wash liquid was discarded by suction filtration. The residue was resuspended in 30 mL of 1 M nitric acid and shaken for 16 hours. It was then centrifuged again (as in step 1) and the supernatant was filtered through a 0.45 μm filter paper. The soil residue was oven dried at 60 degrees Celsius for 48 hours and then finely ground in a marble mortar.

[0061] 5. Residual form (F5) (5) The remaining residue was weighed into a Teflon digestion tube, 10 mL of aqua regia (V hydrochloric acid:V nitric acid = 3:1) was added, and the fly ash sample was digested using a microwave digestion instrument. The maximum temperature of the digestion system was 200°C. After the digestion program was completed and the fly ash sample in the digestion tank was completely digested, the digestion liquid was filtered through a 0.45 μm microporous filter membrane for testing.

[0062] Figure 6 As shown in the figure, different fly ash treatment methods (original fly ash, oyster shell fixed fly ash, modified oyster shell fixed fly ash) have a significant effect on the distribution of heavy metals (Cr, Ni, Cu, Zn, As, Cd, Pb). In the original fly ash, heavy metals mainly exist in the residual form (F5) and the acid extractable form (F4), and the water-soluble form (F1) and the surface adsorption form (F2) account for a low proportion. In the oyster shell fixed fly ash, the proportion of F4 and F5 forms of some heavy metals increases, and the proportion of F1 and F2 forms of some heavy metals increases slightly, indicating that the oyster shell has a certain fixing effect on some heavy metals, but can cause the release of some heavy metals. In the modified oyster shell fixed fly ash, the proportion of F4 and F5 forms further increases, and the proportion of F1 and F2 forms significantly decreases, indicating that the modified oyster shell has a more significant effect on heavy metal fixation.

[0063] Heavy metal Cr mainly exists in F4, F5 and F2 in the original fly ash, and is relatively stable, mainly because Cr mainly exists in the form of chromate in fly ash. After oyster shell treatment, the proportion of F5 decreases and most of it is converted to F4, mainly because the introduction of new substances may damage the stable chromium acid salt in the crystal lattice, causing it to be converted to F4 form. After the addition of phosphoric acid modified oyster shell, the F5 form of Cr in fly ash increases, which may be due to the introduction of PO4 3- in fly ash, generating some stable mineral phases to fix Cr, thereby forming F5 form. Similar to Cr, As also shows the same situation after oyster shell treatment.

[0064] For Ni, Cu, Pb, Cd and Zn, they mainly exist in F4 in fly ash, mainly because fly ash is alkaline, and most of these metal cations exist in the form of hydroxide precipitate, which can only be released under acid extraction. In addition, after the modification of oyster shell, CO3 2-The heavy metals in fly ash can be further fixed, and converted to F4-type metals. In the fly ash stabilized by modified oyster shell, due to the introduction of PO4 3- , not only more adsorption sites are brought, but also more stable phosphates are formed, which are finally converted into F5 form, which also leads to an increase in F5 form of heavy metals in fly ash after treatment by modified oyster shell.

[0065] Example 8, this embodiment is the ecological risk assessment of phosphorus modified calcium-based biomineral stabilized fly ash, specifically: The environmental risk index RAC (Risk Assessment Code) is used to evaluate the ecological risk of heavy metals in fly ash. The toxicity of metal elements to the environment is mainly determined by the proportion of active form in total form, and the higher the proportion, the greater the threat to the environment. The RAC result is calculated according to formula (1).

[0066] Formula (1).

[0067] The risk level corresponding to RAC is: RAC> 50%, very high risk, 50%> RAC> 30%, high risk, 30%> RAC> 11%, medium risk, 10%> RAC> 1%, low risk RAC<1%, no risk.

[0068] Individual Contamination Factor (ICF) is a key indicator for assessing the environmental risk of heavy metals, and its core is to quantify the correlation between the dynamic stability of metal forms and environmental risk. The index is calculated by formula (2). The increase of ICF value reflects the decrease of stable state proportion of heavy metals and the increase of active state proportion, which will lead to the extension of the residence time of metals in the environment, and thus aggravate the potential harm to the ecological system.

[0069] Formula (2).

[0070] As shown in Figure 6 , the As in the original fly ash is at a high risk level, and its RAC value is reduced to 3.69 after treatment by oyster shell, but its RAC value rises to 20.49 after treatment by modified oyster shell, which should be due to the introduction of PO4 3- , both of which are unified main group elements with similar properties, and some lattice substitution reactions occur, which reduces the stable state form and increases the RAC value. In addition, Cr and Pb are medium risk metals, which are converted to low risk or no risk after treatment by oyster shell. Overall, the RAC values of metals in fly ash after treatment by oyster shell are reduced, and the modified oyster shell has better risk control effect on metals.

[0071] Figure 7As shown, the ICF values of Cu, Zn, As, Cd and Pb in the original fly ash are all about 30, indicating that these metals are likely to be released into the environment as the fly ash migrates in the environment over time and as environmental conditions change. After treatment with oyster shells, especially modified oyster shells, the ICF values of several metals in the fly ash are all reduced to below 5, significantly reducing the ecological risk.

[0072] The data of RAC and ICF in Table 2 show that the phosphate-modified calcium-based biomimetic mineral has a stabilizing effect on the heavy metals in the fly ash, significantly reducing the ecological risk of the fly ash. Figure 8 9 The data of RAC and ICF in Table 2 show that the phosphate-modified calcium-based biomimetic mineral has a stabilizing effect on the heavy metals in the fly ash, significantly reducing the ecological risk of the fly ash.

[0073] The present application provides a phosphate-modified calcium-based biomimetic mineral material for inhibiting the leaching of heavy metals in fly ash and an application thereof, which improves the fixation efficiency and stability of heavy metals such as arsenic, cadmium, chromium, copper, lead, nickel and zinc in fly ash, and reduces the ecological risk in the disposal process of fly ash.

[0074] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, and all should be included in the scope of the present application.​

Claims

1. A method for the preparation of a phosphorus-modified calcium-based biomineral material for inhibiting the leaching of heavy metals in fly ash, characterized by: The application relates to a modified calcium-based biomaterial and a preparation method thereof. Raw material pretreatment: oyster shell is ground and sieved to obtain oyster shell powder; Phosphate modification: the oyster shell powder is uniformly mixed with dipotassium hydrogen phosphate, and ultrapure water is added, and the mixture is modified for 8-12 hours and then dried; Pyrolysis treatment: the dried mixture is pyrolyzed at 400-600 DEG C; Grinding and sieving: the pyrolysis product is ground and sieved to obtain a phosphate-modified calcium-based biomaterial.

2. A method of preparing a phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash according to claim 1, characterized in that: The mass-volume ratio of K2HPO4 to water is 8-9 g: 1 mL.

3. A method of preparing a phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash according to claim 1, characterized by: The mass ratio of the oyster shell powder to dipotassium hydrogen phosphate K2HPO4 is 1: 0.01-0.

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4. A method of preparing a phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash according to claim 1, characterized by: The drying temperature is 30-50 DEG C.

5. A method of preparing a phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash according to claim 1, characterized by: The pyrolysis time is 0.5-2 hours.

6. A method of preparing a phosphorus-modified calcium-based biomineral material for inhibiting leaching of heavy metals in fly ash according to claim 1, characterized by: The pyrolysis product is ground and sieved, and the mesh size is 0.15-0.22 mm.

7. The phosphorus-modified calcium-based biomineral material prepared by the method of any one of claims 1 to 6, wherein the phosphorus-modified calcium-based biomineral material is characterized by, The pH value of the material is 10.2-11.3, the total calcium mass percentage is 20%-30%, and the phosphorus element content is 6%-8%.

8. Use of the phosphorus-modified calcium-based biomineral material according to claim 7 for inhibiting the leaching of heavy metals from fly ash, characterized in that, The material is mixed with fly ash at a mass ratio of 0.01-0.1, ultrapure water is added and uniformly mixed, and then the mixture is maintained at room temperature for 24 hours, and then dried at 65 DEG C until the weight is constant.

9. Use of the phosphorus-modified calcium-based biomineral material according to claim 8 for inhibiting the leaching of heavy metals from fly ash, characterized in that, The heavy metals include arsenic, cadmium, chromium, copper, lead, nickel and zinc.

10. Use of the phosphorus-modified calcium-based biomineral material according to claim 8 for inhibiting the leaching of heavy metals from fly ash, characterized in that: The fly ash is waste incineration fly ash, the pH value of the fly ash is 12.0-12.5, and the water content is less than or equal to 25%.

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