Method for preparing an alkaline fenton-like catalyst using sludge and red mud and method for its application in the recovery of phosphorus from sludge

Abstract

The application discloses a method for preparing an alkaline Fenton-like catalyst by using sludge and red mud, the alkaline Fenton-like catalyst and a method for recycling phosphorus in sludge, and the method is prepared according to the following method: centrifugal dewatering is carried out on sludge in a concentration tank, then the sludge is dried in an oven, after drying, the sludge is ground into powder, sieved and reserved; the red mud is dried, ground into powder and sieved and reserved; the sludge powder and the red mud powder are mixed uniformly at a mass ratio of 1:0.8-1.2, put into a tube furnace, sintered at 900 DEG C for 1.5-2h under nitrogen protection, and cooled to room temperature, so that a black powder is obtained, which is the alkaline Fenton-like catalyst. The preparation process is simple, and any external reagent does not need to be added. The catalyst is applied to wall breaking of sludge, acid does not need to be added, and release of phosphorus and dewatering of original sludge can be realized under alkaline conditions. After use, the catalyst can be directly recycled and utilized by magnetic recovery. The application provides a new idea for resource utilization of red mud and sludge, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge treatment, in particular to a method for preparing an alkaline Fenton-like catalyst from sludge and red mud, an alkaline Fenton-like catalyst and a method for recovering phosphorus from sludge. BACKGROUND

[0002] Phosphate is a valuable crop nutrient that regulates protein synthesis and promotes cell division and development of new tissue. Therefore, phosphate is a key component of most crop fertilizers, and the consistent provision of sufficient phosphate is critical to ensure agricultural growth to feed the ever-increasing world population. Currently, phosphate for fertilizers is derived mainly from inorganic sources, such as phosphate rock, and organic sources, such as urine and animal bone ash. Phosphate rock is currently the main commercial source of phosphate used in fertilizers, but the extraction rate exceeds the regeneration rate and can be considered a non-renewable resource. Current sources of organic phosphate (such as bone meal and animal manure) are insufficient, so new technologies need to be developed to sustainably recover phosphate from other organic waste sources, such as sewage sludge.

[0003] In wastewater treatment systems, more than 90% of phosphorus in the influent will be transferred to excess sludge. Therefore, excess sludge can be considered a potential resource of phosphorus. An effective method for recovering phosphorus from excess sludge is to form struvite by adding a magnesium source with economic cost-effectiveness for magnesium ammonium phosphate (MAP) precipitation. The product obtained by struvite crystallization can be used as an effective slow-release fertilizer in agriculture, so using struvite as a fertilizer not only recovers but also reuses nutrients, thereby improving the sustainable management of wastewater treatment plants. Although research on struvite crystallization for recovering phosphorus from excess sludge is ongoing, further research is needed on methods for effectively releasing phosphorus from excess sludge. So far, many sludge wall-breaking phosphorus release processes have been developed. Sludge pretreatment methods can be divided into physical treatment, chemical treatment, and biological treatment according to technical characteristics. Among them, physical treatment generally involves high temperature, biological treatment has a long cycle, and the heterogeneous catalytic Fenton technology in chemical treatment can avoid the disadvantages of Fe 2+ loss, non-reusability, and easy secondary metal pollution of traditional Fenton technology. The electrode potential E 0 of Fe 0 (Fe 2+ / Fe 0 )=-0.44 V is large. It has strong reducing power and can oxidize on one hand and reduce heavy metals on the other. It has the advantages of simple method, wide pH range of sludge, fast reaction rate, magnetic recovery, and no harmful residues. The development trend of zero-valent iron Fenton oxidation technology is still to develop high-performance and inexpensive Fenton catalysts. This process mainly involves the following reactions:

[0004] Fe 0 + H2O2 + 2H + → Fe 2+ + 2H2O

[0005] Fe 2+ + H2O2→ Fe 3+ + ·OH + OH -

[0006] 2Fe 3+ + Fe 0 → 3Fe 2+

[0007] Red mud (RM) is an industrial solid hazardous waste containing abundant iron and aluminum, which is produced by the Bayer process for alumina production. About 1-2.5 tons of RM are generated per ton of alumina produced. In recent years, the global annual production of red mud has exceeded 13.05 billion tons. Red mud with high yield, high alkalinity and complex composition is defined as a harmful substance, which is a serious environmental problem. However, due to the fact that the Fe species in RM is mainly composed of low-activity Fe2O3, the oxidation effect is low when directly applying RM as a catalyst for heterogeneous Fenton reaction. Most of the existing red mud-based catalysts use biochar as the substrate, and red mud is only used as an iron source. In the preparation process, a large amount of acid method and hydrothermal method are used to extract iron from red mud, which is harmful to the environment or has high energy consumption.

[0008] Wang J, Shen M, Wang H, et al. Red mud modified sludge biochar for the activation of peroxymonosulfate: singlet oxygen dominated mechanism and toxicity prediction[J]. Science of The Total Environment, 2020, 740: 140388. discloses the use of persulfate catalyst, sludge is vacuum dried at 60 °C, then pyrolyzed in a tube furnace at 700 °C for 2 h to become biochar; the above process is repeated with a mass ratio of red mud: sludge of 3:1, and finally an iron oxide persulfate catalyst is obtained. It is used for the degradation of sulfamethoxazole.

[0009] Liang L, Chen G, Li N, et al. Active sites decoration on sewage sludge-red mud complex biochar for persulfate activation to degrade sulfanilamide [J]. Journal of Colloid and Interface Science, 2022, 608: 1983-1998 discloses drying sewage sludge and red mud at 105 °C for 24 hours, followed by grinding and sieving with a 200 mesh sieve. After that, sewage sludge (1.0 g) and red mud (1.0 g) powders were mixed together. Subsequently, different amounts of urea (0, 1.0, 2.0, and 4.0 g) were added to the above mixture. Then, four precursors were prepared. Finally, the obtained precursors were transferred to a tube furnace and kept at 700 °C for 2 hours under a nitrogen atmosphere (300 mL / min). All the obtained products were washed with deionized water and ethanol several times and then dried at 60 °C overnight. Iron oxide form of persulfate catalyst was obtained. Used for degrading sulfanilamide.

[0010] Song C, Li C, Zhu D, et al. Waste utilization of sewage sludge and red mud based on chemical looping catalytic oxidation [J]. Fuel, 2023, 332: 125990. discloses that first, the raw materials were dried in an oven at 105 °C for two hours. Then, the dry samples were crushed and sieved to obtain fine particles with a particle size of less than 150 pm. Then, the fine material was stirred with deionized water at a mass ratio of 1:1 at a speed of 450 revolutions per minute for 2 hours. The viscous liquid was dried in an oven at 105 °C for two hours. Finally, the samples were calcined in a muffle furnace at 1250 °C and sieved to 180-355 pm. These particles were obtained in preparation for future experiments. The calcination procedure was as follows: the sample was heated from room temperature to 950 °C at a rate of 5 °C / min, and then heated to 1250 °C at a rate of 2 °C / min. After 6 hours at a constant temperature of 1250 °C, the sample was cooled to room temperature at the same rate. The final catalyst was obtained in the form of iron oxide, red mud was used as an oxygen carrier, sewage sludge was used as fuel, and catalytic oxidation of methane was carried out in a fluidized bed to generate heat for catalytic oxidation of methane.

[0011] We want to modify the red mud with sewage sludge to prepare a catalyst that can effectively catalyze the Fenton-like reaction of hydrogen peroxide, achieve the release of phosphorus and dewatering of the original sludge. SUMMARY

[0012] To solve the above technical problems, the first object of the present application is to provide a method for preparing an alkaline Fenton-like catalyst using sludge and red mud and an alkaline Fenton-like catalyst, and the second object is to provide a method for recovering phosphorus from sludge.

[0013] The first object of the present application is achieved by the following technical solution: a method for preparing an alkaline Fenton-like catalyst using sludge and red mud, characterized in that the method is prepared as follows:

[0014] The sludge in the concentration tank is centrifuged and dewatered, and then dried in an oven. After drying, the sludge is ground into powder, sieved, and prepared for use;

[0015] The red mud is dried, ground into powder, and sieved for use;

[0016] The sludge powder and the red mud powder are mixed uniformly at a mass ratio of 1:0.8-1.2, placed in a tube furnace, sintered at 900 DEG C for 1.5-2 h under nitrogen protection, and cooled to room temperature to obtain a black powder, which is the alkaline Fenton-like catalyst.

[0017] In the above scheme, the sieving is performed through a 100-mesh sieve.

[0018] In the above scheme, the flow rate of nitrogen is 10-20 ml / min.

[0019] The method for preparing an alkaline Fenton-like catalyst using sludge and red mud.

[0020] The present application uses centrifugal dewatering and drying of sludge powder and solid waste RM as raw materials, and uses co-pyrolysis process to prepare a high-efficiency and stable zero-valent iron Fenton-like catalyst under alkaline conditions. Iron exists in the form of zero-valent iron and triiron tetroxide, without iron oxide. The catalyst uses red mud as a base material, and the preparation process is simple without adding any external reagent. The catalyst is applied to break the wall of sludge without adding acid, and can release phosphorus and dewater the original sludge under alkaline conditions. After use, the catalyst can be directly recovered from the broken sludge, and after simple cleaning, it can be reused. The present application provides a new idea for the resource utilization of red mud and sludge, and has good application prospect.

[0021] The second object of the present application is achieved by the following technical solution: a method for recovering phosphorus from sludge, characterized in that the method is performed as follows:

[0022] (1) Adjust the pH of the sludge to 9-10 by adding alkali, add the alkaline Fenton-like catalyst, stir uniformly, add H2O2, and react until the reaction is complete. Then, the alkaline Fenton-like catalyst is recovered by a magnet, and the supernatant and the sludge are separated by centrifugation;

[0023] (2) After centrifugation, magnesium chloride is added to the supernatant, stirred and reacted, and struvite precipitate is obtained by centrifugation and drying.

[0024] (3) PAC and PAM are added to the sludge of step (1), and the sludge filter cake is obtained by pressure filtration.

[0025] In the above scheme: in step (1), the alkali is sodium hydroxide solution with a concentration of 1-3 mol / L.

[0026] In the above scheme: 0.7-1 g of basic Fenton catalyst is added to every 100 ml of sludge.

[0027] In the above scheme: the molar ratio of the amount of magnesium chloride added to phosphorus is 1.6-3.5:1.

[0028] In the above scheme: in step (2), the stirring reaction time is 2-3 h.

[0029] The present application proposes a co-pyrolysis reaction of industrial waste residual sludge and red mud, which can prepare a high-efficiency Fenton-like catalyst that can be magnetically recovered and used in an alkaline environment without any additives, and can be used for wall breaking and phosphorus release of concentrated residual sludge to precipitate struvite and recover phosphorus, which has the following advantages:

[0030] (1) The raw material is industrial waste, which not only protects the environment but also realizes resource utilization.

[0031] (2) The preparation process does not require any additives, and a Fenton-like catalyst can be directly prepared for use in a pH 9-10 environment. Only a small amount of alkali needs to be added to the reaction to achieve the dual effects of Fenton oxidation and alkaline corrosion on the wall breaking of residual sludge, reducing the amount of catalyst used.

[0032] (3) The alkaline catalyst prepared by the present application exists in the form of zero-valent iron and magnetite, and the catalyst after reaction can be directly recovered by magnetism, and can be reused after simple cleaning.

[0033] (4) After wall breaking, centrifugation is performed, the pH of the supernatant is between 8.7 and 8.8, and magnesium source is directly added to form struvite. The pH of the supernatant after struvite precipitation is about 8.1, and after mixing uniformly with the wall-broken centrifuged sludge, a flocculating agent is directly added for pressing to achieve deep dewatering. The whole process does not require the addition of extra alkali, compared with the traditional Fenton, greatly reducing the use of alkali and avoiding the use of acid, and 100% of the phosphorus is released. The recovery rate of phosphorus in the supernatant is greater than 87%.

[0034] (5) Under alkaline conditions, heavy metals will not be dissolved into the solution, improving the purity of struvite, and the recovered struvite can be directly used as phosphorus fertilizer. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Appearance of the alkaline Fenton-like catalyst prepared for Example 1 of the present application.

[0036] Figure 2 Color change of the centrifugal supernatant before (left) and after (right) the Fenton-like reaction when the catalyst of the present application is used for recovering phosphorus from sludge.

[0037] Figure 3 Cleaning effect of the alkaline Fenton-like catalyst, (a) direct magnet recovery of the catalyst; (b) cleaned and recovered catalyst; (c) catalyst after cleaning.

[0038] Figure 4 FT-IR spectrum of the modified red mud of sludge.

[0039] Figure 5 XRD pattern of the modified red mud of sludge.

[0040] Figure 6 Phosphorus in the supernatant under the reaction conditions as a percentage of total phosphorus.

[0041] Figure 7 SCOD in the supernatant under the reaction conditions.

[0042] Figure 8 Struvite after recovery, grinding and drying.

[0043] Figure 9 XRD pattern of the recovered struvite.

[0044] Figure 10 Growth effect of the cardoon before adding phosphorus fertilizer, only adding tap water, adding sludge recovered phosphorus and commercially available dicalcium phosphate. DETAILED DESCRIPTION

[0045] The present application will be further described below in conjunction with the drawings and examples.

[0046] Example 1:

[0047] The method for preparing the alkaline Fenton-like catalyst using sludge and red mud is prepared according to the following method:

[0048] The sludge in the concentration tank is centrifuged and dewatered, and then dried in an oven at 60°C. After drying, it is ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0049] Dry the red mud, grind it into powder, sieve it through a 100-mesh sieve, and put it in a 60℃ oven for later use.

[0050] Sludge powder and red mud powder were mixed evenly at a mass ratio of 1:1 and placed into a ceramic boat. The ceramic boat was then placed in a tube furnace under nitrogen protection at a flow rate of 10-20 ml / min. Sintering was carried out at 900℃ for 1.5-2 h, and then cooled to room temperature to obtain a black powder, which is the basic Fenton catalyst. Figure 4 The image shows the FT-IR spectrum of sludge-modified red mud. Figure 5 The image shows the XRD pattern of sludge-modified red mud.

[0051] FT-IR analysis was performed on red mud and modified red mud to study the chemical bonds and identify potentially present chemical substances. Figure 4 It can be seen that at a wavelength of 3463 cm -1 and 164l cm -1 The absorption bands that appear correspond to the stretching and bending vibrations of the hydroxyl groups in the adsorbed water, respectively, at 1461 cm⁻¹. -1 The band appearing at 600-1300 cm⁻¹ corresponds to the asymmetric stretching vibration of OCO and may originate from carboxylic acids in the sludge. -1 The corresponding fingerprint spectral region mainly reflects the stretching vibrations of single bonds, and the group vibrations of inorganic compounds also mainly appear in this region. The stretching vibration of the Si-O-Al bond corresponds to the region at 997 cm⁻¹. -1 The spectral peak appears at 471 cm⁻¹ -1 The band at that location corresponds to the asymmetric stretching vibration of the Fe-O bond. Combined with the XRD pattern of the sludge-modified red mud, as shown... Figure 5 As shown, the spectrum only contains peaks for zero-valent iron and magnetite (Fe3O4), and no ferric oxide (Fe2O3). This indicates that the sintering temperature of this invention yields a zero-valent iron-based Fenton catalyst.

[0052] Example 2: A method for preparing an alkaline Fenton-like catalyst using sludge and red mud, prepared according to the following method:

[0053] The sludge from the thickening tank is centrifuged and dewatered, then dried in an oven at 60°C. After drying, it is ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for later use.

[0054] Dry the red mud, grind it into powder, sieve it through a 100-mesh sieve, and put it in a 60℃ oven for later use.

[0055] Sludge powder and red mud powder were mixed evenly in a 1:1 mass ratio and placed into a ceramic boat. The ceramic boat was then placed in a tube furnace under nitrogen protection at a flow rate of 10-20 ml / min. Sintering was carried out at 700 ℃ for 1.5-2 h, and then cooled to room temperature to obtain a black powder, which is the basic Fenton catalyst.

[0056] Example 3, a method for preparing a basic Fenton-like catalyst using sludge and red mud, was prepared according to the following method:

[0057] The sludge in the concentration tank was centrifuged and dewatered, then dried in an oven at 60°C. After drying, it was ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0058] The red mud was dried, ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0059] The sludge powder and red mud powder were mixed in a mass ratio of 1:1, then placed in a porcelain boat, and the porcelain boat was placed in a tube furnace under nitrogen protection. The nitrogen flow rate was 10-20 ml / min. Sintering was carried out at 1100°C for 1.5-2 h, and then cooled to room temperature to obtain a black powder, which was the basic Fenton-like catalyst.

[0060] A method for recovering phosphorus from sludge was carried out according to the following method:

[0061] (1) In three 100ml sludge (sludge from the sludge tank after wastewater treatment, containing water), 2mol / L sodium hydroxide solution was added to adjust the pH to 9, and 0.8g of the Fenton-like catalyst obtained in Example 1, Example 2 and Example 3 was added respectively. After stirring uniformly, 1.3ml of H2O2 (mass concentration 30%) was added, and the reaction was carried out. Every 6 minutes, 5mL of reaction solution was taken as a sample, and potassium iodide (to stop the Fenton reaction) and 1 drop of sulfuric acid solution (to make the pH of the sludge neutral again, to prevent the alkali from breaking the wall) were added. Centrifugation was carried out to obtain the supernatant, which was filtered with a 0.45 μm water filter membrane, and the SCOD and phosphorus content were measured with a water quality detector.

[0062] As Figure 6 and Figure 7 showed the reaction effect of the catalyst of Example 1. The figure shows that the wall breaking effect of the sludge is very obvious, and most of the phosphorus in the sludge has been released into the liquid phase within the first six minutes. After 60 minutes of reaction, the phosphorus was completely released. The SCOD change in the picture shows that mineralization occurred during the oxidation process, indicating that the Fenton-like reaction effect is good, and the wall breaking effect of the sludge is good. The highest SCOD can reach 2028 mg / L, and the SCOD is still as high as 1118 mg / L at the 60th minute. After 1h of reaction, the basic Fenton-like catalyst was recovered with a magnet, and the supernatant and sludge were separated by centrifugation.

[0063] (2) Magnesium chloride was added to the supernatant after centrifugation, and the molar ratio of magnesium chloride to phosphorus was 1.6:1. After stirring for 2h, struvite precipitate was obtained by centrifugation, and was dried to obtain struvite. The recovered struvite (ammonium magnesium phosphate hexahydrate) was subjected to XRD detection and compared with the standard cardFigure 9 It can be seen that the recovered struvite has good purity. Figure 10 The growth effect diagrams of adding tap water, adding sludge to recover phosphorus, and adding commercial dicalcium phosphate to the gallbladder before adding phosphorus fertilizer to gallbladder are shown in the figures. It is illustrated that the struvite prepared by the application has good fertilizer effect when used as phosphorus fertilizer.

[0064] (3) 1ml PAC (10% w) + 4ml PAM (0.5% w) is added to the sludge of step (1), and the flocculated sludge is squeezed by a belt filter under a pressure of 0.2 MPa for 10 min, and the moisture content of the filter cake is 65.33%, and the moisture content of the filter cake under the same squeezing and flocculating conditions of the original sludge is 89.56%.

[0065] The reaction effect of the catalyst prepared in Example 2:

[0066] The reaction and catalytic effect method of the basic Fenton catalyst is as follows:

[0067] The SCOD result is 28 mg / L, the phosphorus content in the liquid phase accounts for 39.25% of the total phosphorus, and the sludge wall breaking and phosphorus release effect is poor.

[0068] The reaction effect of the catalyst prepared in Example 3:

[0069] The SCOD result is 884 mg / L, the phosphorus content in the liquid phase accounts for 66.85% of the total phosphorus, and the sludge wall breaking and phosphorus release effect is general.

[0070] Example 4

[0071] The method for recovering phosphorus from sludge is carried out according to the following method:

[0072] (1) 3mol / L of sodium hydroxide solution is added to 100ml of sludge (concentrated sludge in the sludge pool after wastewater treatment, containing water) to adjust the pH to 10, 1g of the Fenton-like catalyst obtained in Example 1 is added, and after stirring uniformly, 1.3ml of H2O2 (mass concentration 30%) is added, and the reaction is carried out. Every 6 minutes, 5mL of reaction solution is taken as a sample, potassium iodide (to stop the Fenton reaction) and 1 drop of sulfuric acid solution (to make the pH of the sludge neutral again, to prevent alkaline wall breaking) are added. Centrifugation is performed to obtain the supernatant, which is filtered by a 0.45μm water filter membrane, and the COD and phosphorus content are measured by a water quality detector.

[0073] After 1h of reaction, the phosphorus is completely released, and then the basic Fenton catalyst is recovered by a magnet, and the supernatant and the sludge are separated by centrifugation.

[0074] (2) Magnesium chloride is added to the supernatant after centrifugation, and the molar ratio of the added amount of magnesium chloride to phosphorus is 3.5:1, and the mixture is stirred for 2h, struvite precipitate is obtained by centrifugation, and struvite is obtained by drying.

[0075] (3) The sludge of step (1) is added with 1 ml of PAC (10% w) + 4 ml of PAM (0.5% w), and the flocculated sludge is squeezed under a pressure of 0.2 MPa for 10 min by using a belt filter cloth, and the moisture content of the filter cake is 65.35%, and the moisture content of the filter cake of the original sludge under the same squeezing and flocculating conditions is 89.56%.

[0076] Example 5

[0077] The method for preparing the alkaline Fenton-like catalyst from sludge and red mud is prepared according to the following method:

[0078] The sludge in the concentration tank is centrifuged and dewatered, and then dried in an oven at 60°C. After drying, it is ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0079] The red mud is dried, ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0080] The sludge powder and red mud powder with a mass ratio of 1:1.2 are mixed uniformly and placed in a porcelain boat, and then the porcelain boat is placed in a tube furnace under nitrogen protection, and the flow rate of nitrogen is 10-20 ml / min. Sintering is carried out at 900°C for 1.5-2 h, and then cooled to room temperature to obtain black powder, which is the alkaline Fenton-like catalyst.

[0081] (1) In 100 ml of sludge (concentrated sludge from the sludge tank after wastewater treatment, containing water), 2 mol / L of sodium hydroxide solution is added to adjust the pH to 10, 0.7 g of the Fenton-like catalyst obtained in the example is added, and then stirred uniformly. 1.3 ml of H2O2 (mass concentration 30%) is added, and the reaction is carried out. Every 6 min, 5 mL of reaction solution is taken as a sample, and potassium iodide (to stop the Fenton reaction) and 1 drop of sulfuric acid solution (to make the pH of the sludge neutral, to prevent alkali from breaking the wall). Centrifugation is performed to obtain the supernatant, which is filtered through a 0.45 μm water filter membrane, and the COD and phosphorus content are measured by a water quality detector.

[0082] After 1 h of reaction, the phosphorus is completely released, and then the alkaline Fenton-like catalyst is recovered by a magnet, and the supernatant and sludge are separated by centrifugation.

[0083] (2) The supernatant after centrifugation is added with magnesium chloride, and the molar ratio of the added amount of magnesium chloride to phosphorus is 2:1. Stirring is carried out for 2 h, and struvite precipitate is obtained by centrifugation, and then dried to obtain struvite.

[0084] (3) The sludge of step (1) is added with 1 ml of PAC (10% w) + 4 ml of PAM (0.5% w), and the flocculated sludge is squeezed under a pressure of 0.2 MPa for 10 min by using a belt filter cloth, and the moisture content of the filter cake is 65.78%, and the moisture content of the filter cake of the original sludge under the same squeezing and flocculating conditions is 89.56%.

[0085] Example 6

[0086] The method for preparing the basic Fenton-like catalyst using sludge and red mud was prepared according to the following method:

[0087] The sludge in the concentration tank was centrifuged and dewatered, and then dried in an oven at 60°C. After drying, it was ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0088] The red mud was dried, ground into powder, sieved through a 100-mesh sieve, and placed in a 60°C oven for standby.

[0089] The sludge powder and red mud powder with a mass ratio of 1:0.8 were mixed uniformly and placed in a porcelain boat. The porcelain boat was then placed in a tube furnace under nitrogen protection, and the nitrogen flow rate was 10-20 ml / min. Sintering was carried out at 900°C for 1.5-2 h, and the temperature was cooled to room temperature to obtain a black powder, which was the basic Fenton-like catalyst.

[0090] (1) In 100 ml of sludge (concentrated sludge from the sludge tank after wastewater treatment, containing water), 2 mol / L of sodium hydroxide solution was added to adjust the pH to 10, 1 g of the Fenton-like catalyst obtained in the example was added, and the mixture was stirred uniformly. Then, 1.3 ml of H2O2 (mass concentration 30%) was added, and the reaction was carried out. Every 6 min, 5 mL of reaction solution was taken as a sample, and potassium iodide (to stop the Fenton reaction) and 1 drop of sulfuric acid solution (to make the pH of the sludge neutral again, to prevent the alkali from breaking the wall) were added. Centrifugation was performed to obtain the supernatant, which was filtered through a 0.45 μm water filter membrane. The COD and phosphorus content were measured using a water quality detector.

[0091] After 1 h of reaction, the phosphorus was completely released, and then the basic Fenton-like catalyst was recovered using a magnet. The supernatant and sludge were separated by centrifugation.

[0092] (2) Magnesium chloride was added to the supernatant after centrifugation, and the molar ratio of magnesium chloride to phosphorus was 2:1. The mixture was stirred and reacted for 2 h, and struvite precipitate was obtained by centrifugation. After drying, struvite was obtained.

[0093] (3) In the sludge of step (1), 1 ml of PAC (10% w) and 4 ml of PAM (0.5% w) were added, and the flocculated sludge was pressed using a belt filter under a pressure of 0.2 MPa for 10 min. The moisture content of the filter cake was 66.28%, and the moisture content of the original sludge under the same pressing and flocculation conditions was 89.56%.

[0094] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recovering phosphorus from sludge, characterized by, The method is as follows: (1) adjust pH 9-10 by adding alkali solution to the sludge, add basic Fenton-like catalyst, stir uniformly, then add H2O2, react until the reaction is complete, then recover the basic Fenton-like catalyst with a magnet, and centrifuge the supernatant and the sludge; (2) add magnesium chloride to the supernatant after centrifugation, stir and react, centrifuge to obtain struvite precipitate, and dry to obtain struvite; (3) add PAC and PAM to the sludge of step (1), filter-press, and obtain sludge filter cake; The basic Fenton-like catalyst is prepared as follows: Centrifuge the sludge in the concentration tank, then dry in an oven, grind into powder after drying, sieve, and reserve; Dry the red mud, grind into powder, sieve, and reserve; Mix the sludge powder and the red mud powder in a mass ratio of 1:0.8-1.2, put into a tube furnace, sinter at 900℃ for 1.5-2h under nitrogen protection, cool to room temperature, and obtain black powder, which is the basic Fenton-like catalyst.

2. The method according to claim 1, c h a r a c t e r i z e d in that: Sieve through a 100-mesh sieve.

3. The method according to claim 1 or 2, c h a r a c t e r i z e d in that: The flow rate of nitrogen is 10-20 ml / min.

4. The method of recovering phosphorus from sludge according to claim 1, characterized by: In step (1), the alkali solution is sodium hydroxide solution with a concentration of 1-3 mol / L.

5. The method of recovering phosphorus from sludge according to claim 1, characterized by: Add 0.7-1 g of basic Fenton-like catalyst per 100 ml of sludge.

6. The method according to claim 5, wherein: The molar ratio of the amount of magnesium chloride added to phosphorus is 1.6-3.5:

1.

7. The method according to claim 6, wherein: In step (2), the stirring and reaction time is 2-3 h.

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