Process for the preparation of hydroxyapatite and its use in sludge treatment

Abstract

The application discloses a preparation method of hydroxyapatite and application of the hydroxyapatite in sludge treatment. First, the hydroxyapatite is prepared by taking marble waste material with a calcium carbonate content of more than 90% as a calcium source and diammonium hydrogen phosphate as a phosphorus source, so that marble waste material resource utilization is realized, cost is reduced, and the environmental protection concept of 'waste treatment with waste' is met; subsequently, the hydroxyapatite is used as a catalyst to generate more high-activity hydroxyl radicals by catalyzing ozone, so that the sludge floc structure can be destroyed to reduce the water content, efficient dewatering is realized, polycyclic aromatic hydrocarbons can be adsorbed and catalytically degraded by ozone, harmless treatment of pollutants is achieved, and the problems of high energy consumption in traditional sludge treatment, incomplete degradation of polycyclic aromatic hydrocarbons and easy generation of secondary pollution are effectively solved. In addition, the hydroxyapatite can be used as a skeleton support body to promote water release, greatly improve sludge dewatering performance, simplify the process, and be suitable for advanced treatment of municipal sludge, industrial sludge and various types of sludge.

Description

Technical Field

[0001] This invention relates to the field of environmental protection and sludge treatment technology, specifically to a method for preparing hydroxyapatite and a method for enhancing sludge detoxification and dewatering by hydroxyapatite-catalyzed ozone, which is particularly suitable for the dewatering treatment of residual sludge generated by municipal sewage treatment plants and industrial wastewater treatment stations, as well as the degradation and removal of polycyclic aromatic hydrocarbon pollutants therein. Background Technology

[0002] With the acceleration of urbanization and the expansion of industrial production, the amount of residual sludge generated during wastewater treatment has increased dramatically. Sludge has a complex composition, containing not only a large amount of water (often as high as 95%-99%), but also enriched with hydrophilic colloidal substances (such as polysaccharides, proteins, humic acids, etc.). The stable colloidal structure formed by these substances makes sludge dewatering extremely difficult. Traditional mechanical dewatering technologies are unable to reduce the sludge moisture content to below 60%, resulting in high subsequent transportation and disposal costs. Meanwhile, sludge often contains persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs), which are highly carcinogenic, teratogenic, and mutagenic. If improperly treated and released into the environment, they can harm ecosystems and human health through soil, water bodies, and the food chain. In existing sludge treatment technologies, dewatering and detoxification often need to be carried out separately. The dewatering process largely relies on the addition of chemical agents such as polyaluminum chloride and polyacrylamide, posing a risk of agent residue. The detoxification process requires technologies such as high-temperature incineration and advanced oxidation, which are energy-intensive, complex to operate, and difficult to optimize in a synergistic manner between dewatering and detoxification. Hydroxyapatite, with its unique crystal structure, abundant surface hydroxyl sites, and good chemical stability, shows potential application value in the field of catalysis. However, current research on the use of hydroxyapatite for catalytic ozone oxidation is limited, especially lacking technical solutions for its application in the synergistic treatment of sludge dewatering and polycyclic aromatic hydrocarbon (PAH) degradation. Furthermore, existing hydroxyapatite preparation processes often employ expensive raw materials or complex synthetic routes, making them difficult to meet the demands of industrial applications. Therefore, developing a hydroxyapatite catalyst that uses inexpensive raw materials and is easy to prepare, and applying it to catalyze ozone oxidation for integrated deep detoxification and efficient dewatering of sludge, has become an urgent problem to be solved in the field of sludge treatment. Summary of the Invention

[0003] One of the objectives of this invention is to provide a method for preparing hydroxyapatite that uses readily available raw materials, is low in cost, and involves simple steps.

[0004] The second objective of this invention is to provide the application of hydroxyapatite prepared by the above method in sludge treatment. Through the catalytic effect of hydroxyapatite, the ozone oxidation efficiency is improved, and the efficient degradation of polycyclic aromatic hydrocarbons and the reduction of sludge moisture content are achieved simultaneously, without the risk of secondary pollution and with low treatment cost.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing hydroxyapatite, wherein marble waste is used as a calcium source, diammonium hydrogen phosphate is used as a phosphorus source, and sodium hydroxide is used as a pH adjuster. The specific preparation steps are as follows: (1) Preparation of precursor: Prepare calcium carbonate suspension with a concentration of 0.5-1.5 mol / L and diammonium hydrogen phosphate aqueous solution with a concentration of 0.4-1.2 mol / L respectively, control the molar ratio of calcium carbonate to diammonium hydrogen phosphate to be 5:3, and use ultrasonic-assisted mixing to form hydroxyapatite liquid precursor; (2) Microwave-assisted hydrothermal crystallization: The prepared liquid precursor was transferred to a multi-throughput microwave reactor and subjected to microwave-assisted hydrothermal treatment at 180°C for 1 hour to promote the formation of Ca in the liquid. 2+ With PO4 3- The reaction proceeds fully and crystallizes to form crude hydroxyapatite; (3) Post-treatment and purification: After the hydrothermal reaction, the solid product was collected by centrifugation. It was then washed dropwise with a 1% ammonium chloride solution while being filtered until the pH of the filtrate reached 9 to remove residual impurities. The washed solid was dried, ground, and sieved to finally obtain hydroxyapatite (Ca). 10 (PO4)6(OH)2) powder.

[0006] Preferably, the calcium carbonate in step (1) is obtained by removing impurities, ball milling, precipitation and purification from marble waste with a calcium carbonate content of >90%.

[0007] Preferably, the power of the microwave in step (2) is 300-500 W.

[0008] Preferably, the centrifugation speed in step (3) is 10000 r / min and the centrifugation time is 5 min.

[0009] Secondly, this invention provides a method for enhancing sludge detoxification and dewatering using hydroxyapatite-catalyzed ozone. This method uses the hydroxyapatite prepared above as a catalyst, combined with ozone oxidation technology, to achieve synergistic treatment of sludge detoxification and dewatering. The specific steps are as follows: (1) Sludge pretreatment: Take the sludge to be treated, place it in the reaction vessel, stir it evenly, and adjust the sludge temperature to 25-40℃; (2) Catalyst addition: Add the above-mentioned hydroxyapatite catalyst to the pretreated sludge. The catalyst addition amount is 20-60 mg / gTS. Stir and mix for 10-20 min to ensure that the catalyst is in full contact with the sludge. (3) Ozone oxidation reaction: Turn on the ozone generator and introduce ozone into the sludge system at a rate of 20-80 mg / gTS, while continuously stirring at a rate of 200-300 r / min, and control the ozone reaction time to 30-60 min. (4) Sludge dewatering: After the ozone oxidation reaction is completed, stop stirring and mechanically dewater the treated sludge to finally obtain dewatered sludge.

[0010] Preferably, the dosage of the hydroxyapatite catalyst is 40 mg / gTS, and the dosage of ozone introduced is 60 mg / gTS.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. Hydroxyapatite can stably fix polycyclic aromatic hydrocarbons (PAHs) on its surface through adsorption, effectively improving the degradation efficiency of PAHs. Simultaneously, it can catalyze the decomposition of ozone to generate strong oxidizing free radicals, which can attack PAHs, promoting their gradual ring-opening and hydroxylation, ultimately oxidizing them into smaller molecules or mineralizing them into CO2 and H2O, without generating toxic intermediate products. 2. The hydroxyl sites on the surface of hydroxyapatite can catalyze the decomposition of ozone to generate highly active hydroxyl radicals, which efficiently degrade extracellular polymers (EPS) composed of polysaccharides and proteins in sludge, destroying their network structure and releasing bound water and interstitial water; in addition, it contains Ca... 2+ It can neutralize the negative charge on the surface of sludge colloidal particles, reduce the electrostatic repulsion between particles, and promote the aggregation of colloids to form loose, large flocs, creating favorable conditions for water removal. Furthermore, hydroxyapatite can act as a skeletal support, further promoting water release and significantly improving sludge dewatering performance.

[0012] 3. Environmentally friendly with no secondary pollution: Hydroxyapatite is chemically stable and will not release heavy metals or toxic substances after reaction. In addition, some of it can be disposed of together with the dewatered sludge, with no risk of catalyst loss. The filtrate has low pollutant content, which meets the requirements of green environmental protection. 4. The preparation process of hydroxyapatite is simple, the raw materials are readily available, the processing does not require complex equipment, it is compatible with existing sludge treatment systems, and it is easy to promote industrialization. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating the method of this application.

[0014] Figure 2 This is the XRD pattern of the hydroxyapatite prepared in Example 1.

[0015] Figure 3 (a) is a SEM image of the untreated sludge in Example 9. Figure 3 (b) is a SEM image of the sludge after ozone treatment alone in Example 3. Figure 3 (c) is a SEM image of the sludge after catalytic ozone treatment in Example 9.

[0016] Figure 4 (a) is the hydroxyl radical signal spectrum of the untreated, ozone-treated alone, and catalytically treated systems in Comparative Example 3 and Example 9. Figure 4 (b) is a graph showing the concentration of hydroxyl radicals in the ozone treatment and catalytic ozone treatment systems in Comparative Example 3 and Example 9. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0018] Example 1: Preparation of hydroxyapatite like Figure 1 The process shown involves selecting marble waste from stone processing, removing surface-attached mud, sand, and metallic impurities, crushing it into 5-10mm pieces, and then grinding it into 150-mesh powder. 1.8mol / L dilute hydrochloric acid is added at a solid-liquid ratio of 1:6 (g:mL), and the mixture is stirred in a 45℃ constant temperature water bath for 50 minutes (reaction equation: CaCO3 + 2HCl = CaCl2 + CO2↑ + H2O). After filtering to remove insoluble impurities (such as SiO2), 2mol / L ammonia is added dropwise to the filtrate to adjust the pH to 8.8, thus reducing the Fe content in the solution. 3+ Mg 2+ After the metal ions form a hydroxide precipitate, let it stand for 1.5 hours and then filter again. Add 1.5 mol / L sodium carbonate solution dropwise to the pure CaCl2 solution while stirring (250 r / min) until no more white precipitate forms (reaction equation: CaCl2 + Na2CO3 = CaCO3↓ + 2NaCl). Wash the precipitate with deionized water until no Cl is visible. - After drying at 75°C for 9 hours, calcium carbonate powder was obtained.

[0019] Weigh 5.0 g of calcium carbonate powder and add 50 mL of deionized water. Stir ultrasonically to form a 1.0 mol / L suspension. Weigh 5.3 g of diammonium hydrogen phosphate and dissolve it in 50 mL of deionized water to prepare a 0.8 mol / L aqueous solution. Control the molar ratio of calcium carbonate to diammonium hydrogen phosphate to be 5:3. Mix under 100 W ultrasonic assistance for 15 min to obtain the liquid precursor.

[0020] The precursor was transferred to a microwave reactor, and the microwave power was set to 400 W, the heating rate to 8 °C / min, and the reaction was maintained at 180 °C for 1 h. After the reaction, the mixture was allowed to cool naturally. The product was centrifuged at 10000 r / min for 5 min to separate the solid phase. The solid phase was washed with 1% ammonium chloride solution until the pH of the filtrate was 9. After drying at 100 °C for 24 h, the product was ground and sieved to obtain hydroxyapatite powder. The product was characterized by XRD, as shown in the figure. Figure 2 As shown, Ca 10 The presence of (PO4)6(OH)2 as the main phase indicates the successful preparation of hydroxyapatite.

[0021] The following section examines the application of hydroxyapatite in sludge treatment, particularly in ozone treatment of sludge.

[0022] In the following embodiments, the sludge was taken from the same municipal wastewater treatment plant and had a moisture content of (97.2±0.5)%, with an allowable deviation of 0.5%. The sludge, after gravity settling, was conditioned and then filtered using a plate and frame filter press at a pressure of 0.5 MPa for 45 minutes.

[0023] Example 2: At room temperature, hydroxyapatite at a concentration of 20 mg / g TS was added to 200 mL of sludge with a moisture content of 97.5% and stirred thoroughly. Ozone at a concentration of 20 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 68.9% according to the gravimetric method in CJ / T221.

[0024] Example 3: At room temperature, 40 mg / g TS of hydroxyapatite was added to 200 mL of sludge with a moisture content of 97.5% and stirred thoroughly. Ozone at a dosage of 20 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 65.1% according to the gravimetric method in CJ / T221.

[0025] Example 4: At room temperature, hydroxyapatite at a concentration of 60 mg / g TS was added to 200 mL of sludge with a moisture content of 97.5% and stirred thoroughly. Ozone at a concentration of 20 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 61.4% according to the gravimetric method in CJ / T221.

[0026] Example 5: At room temperature, 20 mg / g TS of hydroxyapatite was added to 200 mL of sludge with a moisture content of 96.8%, and the mixture was stirred thoroughly. Ozone at a dosage of 40 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 70.5% according to the gravimetric method in CJ / T221.

[0027] Example 6: At room temperature, hydroxyapatite at a concentration of 40 mg / g TS was added to 200 mL of sludge with a moisture content of 96.8% and stirred thoroughly. Ozone at a concentration of 40 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 60.1% according to the gravimetric method in CJ / T221.

[0028] Example 7: At room temperature, hydroxyapatite at a concentration of 60 mg / g TS was added to 200 mL of sludge with a moisture content of 96.8%, and the mixture was stirred thoroughly. Ozone at a concentration of 40 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 58.9% according to the gravimetric method in CJ / T221.

[0029] Example 8: At room temperature, 20 mg / g TS of hydroxyapatite was added to 200 mL of sludge with a moisture content of 97.3%, and the mixture was stirred thoroughly. Ozone at a dosage of 60 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 66.7% according to the gravimetric method in CJ / T221.

[0030] Example 9: At room temperature, 40 mg / g TS of hydroxyapatite was added to 200 mL of sludge with a moisture content of 97.3%, and the mixture was stirred thoroughly. Ozone at a dosage of 60 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain a dewatered sludge cake. The moisture content of the sludge cake was determined to be 56.4% according to the gravimetric method in CJ / T221.

[0031] Example 10: At room temperature, hydroxyapatite at a concentration of 60 mg / g TS was added to 200 mL of sludge with a moisture content of 97.3%, and the mixture was stirred thoroughly. Ozone at a concentration of 60 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 61.3% according to the gravimetric method in CJ / T221.

[0032] Example 11: At room temperature, 20 mg / g TS of hydroxyapatite was added to 200 mL of sludge with a moisture content of 96.9%, and the mixture was stirred thoroughly. Ozone at a dosage of 80 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 66.3% according to the gravimetric method in CJ / T221.

[0033] Example 12: At room temperature, 40 mg / g TS of hydroxyapatite was added to 200 mL of sludge with a moisture content of 96.9%, and the mixture was stirred thoroughly. Ozone at a dosage of 80 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 64.6% according to the gravimetric method in CJ / T221.

[0034] Example 13: At room temperature, hydroxyapatite at a concentration of 60 mg / g TS was added to 200 mL of sludge with a moisture content of 96.9%, and the mixture was stirred thoroughly. Ozone at a concentration of 80 mg / g TS was then introduced. After the reaction was complete, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 62.8% according to the gravimetric method in CJ / T221.

[0035] Comparative Example 1: At room temperature, ozone at a dosage of 20 mg / g TS was introduced alone into 200 mL of sludge with a moisture content of 97.5%. After the reaction was completed, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 87.8% according to the gravimetric method of CJ / T221.

[0036] Comparative Example 2: At room temperature, ozone at a dosage of 40 mg / g TS was introduced alone into 200 mL of sludge with a moisture content of 96.8%. After the reaction was completed, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. The moisture content of the sludge cake was determined to be 88.4% according to the gravimetric method of CJ / T221.

[0037] Comparative Example 3: At room temperature, ozone at a dosage of 60 mg / g TS was introduced alone into 200 mL of sludge with a moisture content of 97.3%. After the reaction was completed, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. According to the gravimetric method of CJ / T221, the moisture content of the sludge cake was determined to be 89.1%.

[0038] Comparative Example 4: At room temperature, ozone at a dosage of 80 mg / g TS was introduced alone into 200 mL of sludge with a moisture content of 96.9%. After the reaction was completed, the product was filtered using a plate and frame filter press to obtain dewatered sludge cake. According to the gravimetric method of CJ / T221, the moisture content of the sludge cake was determined to be 89.7%.

[0039] Figure 3 (a) is a SEM image of the untreated sludge in Example 9. The untreated sludge exhibits a dense, agglomerated block structure with a relatively compact surface, few small pores, and a stable structure, but it is difficult to degrade and dewater. Figure 3 (c) is a SEM image of the sludge after ozone treatment with hydroxyapatite in Example 9. After ozone treatment with hydroxyapatite, the sludge structure is looser, with more and larger pores, exhibiting a porous and fragmented morphology. This indicates that the catalyst enhances the oxidation capacity of ozone, generates more hydroxyl radicals, more thoroughly destroys the sludge's aggregate structure, decomposes organic matter, significantly improves the sludge's dispersibility and porosity, and improves the sludge's dewatering performance. Figure 3 (b) is a SEM image of the sludge treated with ozone alone in Comparative Example 3. After ozone treatment, the aggregated structure of the sludge was initially destroyed, and more pores and fragmented structures appeared. This indicates that the oxidation effect of ozone can break down microbial cells and decompose some organic matter, causing the sludge structure to change from a compact state to a loose state. However, compared with the sludge treated with hydroxyapatite-catalyzed ozone in Example 9, the overall uniformity and size of the pores were limited.

[0040] The measurement results of Examples 2-13 and Comparative Examples 1-4 are shown in Table 1.

[0041] Table 1. Moisture content of sludge dewatering cake after treatment with different ozone and hydroxyapatite dosages.

[0042] Table 1 shows that hydroxyapatite-catalyzed ozone effectively improves sludge dewatering performance. Example 9 showed the best dewatering effect under the conditions of 60 mg / g TS ozone and 40 mg / g TS hydroxyapatite, reducing the sludge moisture content to 56.4%. Comparative Examples 1-4, however, indicate that ozone treatment alone worsens sludge dewatering performance. Hydroxyapatite can catalyze the generation of more hydroxyl radicals from ozone. These highly oxidizing reactive species can more thoroughly destroy the structure of microbial cells in the sludge, decompose organic matter, and break down the dense aggregate state of the sludge, significantly increasing its porosity and dispersibility, thereby improving the sludge dewatering performance from a structural perspective.

[0043] Example 14: Under optimal process conditions, using the process parameters determined in Example 9, namely, a hydroxyapatite dosage of 40 mg / gTS and an ozone dosage of 60 mg / gTS, a hydroxyapatite-catalyzed ozone system was constructed and used to treat sludge. The dewatered filter cake from the treated sludge was taken, and the content of 16 polycyclic aromatic hydrocarbons (∑16PAHs) in the sludge was quantitatively detected using gas chromatography-mass spectrometry (GC-MS) according to the standard "Determination of Polycyclic Aromatic Hydrocarbons in Soil and Sediments" (HJ805-2016). The results are shown in Table 2.

[0044] Comparative Example 5: Ozone treatment alone was used as the experimental group, with the ozone dosage controlled at 60 mg / gTS. The sludge was subjected to single ozone oxidation treatment. The dewatered filter cake of the treated sludge was collected, and the content of ∑16PAHs in the sludge was determined using the same GC-MS detection method and quantitative analysis standards as in Example 14. The results are shown in Table 2.

[0045] Comparative Example 6: The experimental group was treated with hydroxyapatite alone, with the dosage of hydroxyapatite controlled at 40 mg / gTS. The sludge was treated with a single chemical conditioner. The dewatered filter cake of the treated sludge was taken, and the content of ∑16PAHs in the sludge was determined by GC-MS detection method and quantitative standard consistent with Example 14. The results are shown in Table 2.

[0046] Table 2. Polycyclic aromatic hydrocarbon content (mg / kgTS) in raw sludge, sludge treated with ozone alone, sludge treated with hydroxyapatite alone, and sludge dewatering cake after hydroxyapatite-catalyzed ozone treatment.

[0047] Table 2 shows that ozone treatment alone (Comparative Example 5) and hydroxyapatite treatment alone (Comparative Example 6) can both reduce the content of polycyclic aromatic hydrocarbons (PAHs) in sludge to a certain extent, but the overall removal rate of both is limited. However, hydroxyapatite-catalyzed ozone treatment (Example 14) has a significantly better removal effect on PAHs of all ring numbers than the previous two single treatment methods. For example, 2-ring naphthalene (Nap) decreased from 3.88 mg / kgTS in the original sludge to 0.70 mg / kgTS, 3-ring acenaphthene (Ace) decreased from 0.081 mg / kgTS to 0.022 mg / kgTS, 4-ring benzo[a]anthracene (BaA) decreased from 1.61 mg / kgTS to 0.82 mg / kgTS, 5-ring benzo[a]pyrene (Bap) decreased from 2.42 mg / kgTS to 0.95 mg / kgTS, and 6-ring dibenzo[a,h]anthracene (DahA) decreased from 0.53 mg / kgTS to 0.19 mg / kgTS.

[0048] Ozone, with its strong oxidizing properties, directly disrupts the conjugated π bonds and cyclic structures of polycyclic aromatic hydrocarbons (PAHs), achieving pollutant degradation and mineralization through ring-opening and hydroxylation reactions. Hydroxyapatite can efficiently catalyze ozone activation, generating a large number of more reactive hydroxyl radicals, further enhancing the breaking of organic chemical bonds, promoting PAH degradation, and ultimately significantly improving its removal efficiency. Electron paramagnetic resonance (EPR) technology combined with DMPO capture agent was used to detect the generation of hydroxyl radicals in the original sludge, ozone alone, and hydroxyapatite-catalyzed ozone systems in Comparative Example 3 and Example 9, respectively. Figure 4(a) It can be seen that the 1:2:2:1 characteristic signal peak appears in the spectrum, which proves that hydroxyl radicals can be generated in both ozone treatment alone and hydroxyapatite-catalyzed ozone system, and the introduction of hydroxyapatite can enhance the signal intensity of this characteristic peak. Figure 4 (b) Further analysis of hydroxyl radical concentration shows that, compared to ozone systems alone, hydroxyapatite-catalyzed ozone systems can effectively increase the concentration of hydroxyl radicals.

[0049] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing hydroxyapatite, characterized in that, Includes the following steps: (1) Preparation of precursor: Prepare calcium carbonate suspension with a concentration of 0.5-1.5 mol / L and diammonium hydrogen phosphate aqueous solution with a concentration of 0.4-1.2 mol / L respectively, control the molar ratio of calcium carbonate to diammonium hydrogen phosphate to be 5:3, and mix them ultrasonically to form hydroxyapatite liquid precursor; (2) Microwave-assisted hydrothermal crystallization: The prepared liquid precursor was transferred to a multi-throughput microwave reactor and subjected to microwave-assisted hydrothermal treatment at 180°C for 1 hour to form crude hydroxyapatite product. (3) Post-treatment and purification: After the hydrothermal reaction is completed, the solid product is collected by centrifugation. The solid product is washed dropwise with 1wt% ammonium chloride solution and filtered until the pH value of the filtrate reaches 9. The washed solid is dried, ground and sieved to finally obtain hydroxyapatite powder.

2. The method for preparing hydroxyapatite according to claim 1, characterized in that, The calcium carbonate mentioned in step (1) is obtained by removing impurities, ball milling, precipitation and purification from marble waste with a calcium carbonate content of >90%.

3. The method for preparing hydroxyapatite according to claim 1, characterized in that, The power of the microwave in step (2) is 300-500 W.

4. The method for preparing hydroxyapatite according to claim 1, characterized in that, The centrifugation speed in step (3) is 10000 r / min, and the centrifugation time is 5 min.

5. A method for enhancing sludge detoxification and dewatering with ozone catalyzed by hydroxyapatite, characterized in that, Includes the following steps: (1) Sludge pretreatment: Take the sludge to be treated, place it in the reaction vessel, stir it evenly, and adjust the sludge temperature to 25-40℃; (2) Catalyst addition: Add the hydroxyapatite catalyst prepared by any one of claims 1 to 4 to the pretreated sludge, the catalyst addition amount is 20-60 mg / gTS, stir and mix for 10-20 min to make the catalyst fully contact the sludge; (3) Ozone oxidation reaction: Turn on the ozone generator and introduce ozone into the sludge system at a rate of 20-80 mg / gTS, while continuously stirring at a rate of 200-300 r / min, and control the ozone reaction time to 30-60 min. (4) Sludge dewatering: After the ozone oxidation reaction is completed, stop stirring and mechanically dewater the treated sludge to finally obtain dewatered sludge.

6. The method according to claim 5, characterized in that, The dosage of the hydroxyapatite catalyst is 40 mg / gTS, and the dosage of ozone introduced is 60 mg / gTS.

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