Method for recovering phosphorus in excess sludge by using carbide slag

Abstract

The invention provides a method for recycling phosphorus in excess sludge by using carbide slag, and belongs to the technical field of solid waste recycling. The method specifically comprises the following steps: S1, pretreating urban excess sludge; s2, carrying out acid leaching reaction on the urban residual sludge to obtain an acid leaching solution; s3, preparing a carbide slag solution; and S4, mixing the acid leaching solution obtained in the step S2 with the carbide slag solution obtained in the step S3 to extract phosphorus. In the step S4, the supernatant of the carbide slag solution is mixed with the acid leaching solution to generate aluminum phosphate precipitate, and the aluminum phosphate precipitate is filtered and recycled; or aluminum removal resin can be used for removing aluminum in the acid leaching solution, then the acid leaching solution and the carbide slag supernate are mixed and react to generate calcium hydrogen phosphate, and the calcium hydrogen phosphate is filtered and recycled. The method provided by the invention has good phosphorus recovery efficiency and low recovery cost, adopts the excess sludge of a sewage treatment plant and the waste carbide slag of a chemical plant as raw materials, realizes resource utilization of the sludge and the carbide slag, and achieves the purpose of treating waste with waste.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization, and in particular to a method for recovering phosphorus in excess sludge by utilizing carbide slag. Background Art

[0002] Phosphorus is a non-renewable resource. Studies have shown that the current global phosphate reserves are only enough for human use for about a hundred years. In the process of urban sewage treatment, a large amount of phosphorus is enriched in the residual sludge, of which inorganic phosphorus accounts for more than 60% and organic phosphorus accounts for only 10% to 35%. Exploring new technologies for efficient recovery of phosphorus from sludge and sewage is the basis for practicing the strategic concept of sustainable development and realizing the recycling of phosphorus resources.

[0003] There are many methods for phosphorus recovery from sludge, but no matter which phosphorus recovery method is used, phosphorus is transferred from the solid phase to the liquid phase, and then some methods are used to enrich and separate it in large quantities to achieve the purpose of phosphorus recovery. Chemical precipitation method: refers to a method that combines physical and chemical processes to achieve phosphorus recovery. Metal salts such as calcium, iron, magnesium, and aluminum are added to phosphorus-containing wastewater, and phosphate ions react with metal salts to form water-insoluble substances, and then solid-liquid separation is used to obtain phosphorus-rich precipitated sludge. The above-mentioned precipitation method is the most commonly used method for industrial phosphorus recovery and can be applied to high-concentration industrial wastewater. Crystallization method: Adding seeds that can crystallize quickly to the reaction device to reduce the interfacial energy, so that phosphate conjugates will produce a large number of crystals on the surface of the seeds. Adsorption method: This method has good selectivity and is easy to use, so this method is also suitable for phosphorus removal and recovery. The adsorption method for phosphorus recovery uses some materials with large specific surface area or porous materials. This material must also have a good adsorption affinity for phosphate ions in the solution to achieve phosphorus recovery from wastewater.

[0004] Carbide slag is the waste residue with calcium hydroxide as the main component after acetylene gas is obtained by hydrolysis of calcium carbide. After drying, the main component is CaO. In the present invention, it is reused together with the remaining sludge to recover the remaining sludge phosphorus and achieve the purpose of waste treatment, which is also of great significance to the sustainable development of the coal chemical industry.

[0005] The main goal of sludge treatment is to achieve resource utilization, volume reduction and safe treatment of sludge, reduce treatment costs, and prevent secondary pollution. Resource utilization can recover nutrients and organic matter in sludge. In the formulation of sludge treatment and resource utilization, attention should be paid to the actual local economic development, the surrounding environment, and the mud quality of sludge. Under the premise that the landfill and agricultural paths are becoming increasingly narrow, direct incineration after sludge drying seems to have become the ultimate choice. The phosphorus in sewage ultimately has only one channel, which is to enter the sludge, and almost all of it remains in the sludge incineration ash. Therefore, recovering phosphorus from sludge incineration ash has gradually become a new phosphorus recovery method advocated internationally. Summary of the invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and propose a method for recovering phosphorus from excess sludge using carbide slag, which can achieve the purpose of efficiently recovering phosphorus from excess sludge. The method specifically comprises the following steps:

[0007] S1. Pretreatment of urban waste sludge;

[0008] S2, acid leaching reaction of urban surplus sludge to obtain acid leaching solution;

[0009] S3, preparation of carbide slag solution;

[0010] S4, mixing the acid leaching solution obtained in step S2 with the carbide slag solution obtained in step S3 to extract phosphorus.

[0011] Preferably, the step S1 specifically comprises: drying the residual sludge in an oven at 105°C and coarsely grinding it into fine particles. The residual sludge is placed in a quartz boat and placed in a tube furnace, and incinerated at 800°C for 1 hour. After cooling to room temperature, the residual sludge incineration ash (SSA) is taken out, and characterized and analyzed by X-ray fluorescence spectrometry (XRF) to determine its elemental composition. The obtained sludge incineration ash is stored in a sealed bag and placed in a dryer for subsequent use.

[0012] Preferably, step S2 is specifically as follows: taking an appropriate amount of the prepared sludge incineration ash and placing it in a container, adding an appropriate amount of hydrochloric acid for reaction, setting the temperature to 25°C, and continuously oscillating at 180r / min for 6h, then centrifuging the mixed solution, taking the supernatant to obtain a phosphoric acid-rich leaching solution sample, the solid-liquid ratio of hydrochloric acid to sludge incineration ash during the acid leaching process is 5g / L, and the concentration of hydrochloric acid is 0.100mol / L to 0.125mol / L; diluting ten times with 5% dilute nitric acid solution, and then using ICP-MS to determine the element content in the diluted sample. It is finally determined that at a concentration of 0.100mol / L to 0.125mol / L, the phosphorus leaching efficiency can reach more than 90%. The prepared acid leaching solution is filtered to obtain a clarified acid leaching solution for subsequent use.

[0013] Preferably, step S3 is specifically as follows: the carbide slag is dried by natural sedimentation, ground with a ball mill at 4000r / min for 10min, passed through a 200-mesh sieve, and carbide slag powder is obtained. The carbide slag powder is added to water at a ratio of 3g:1000mL, stirred for 10min, and then allowed to stand for 30min to obtain a carbide slag solution. Carbide slag is a slightly soluble strong alkaline substance. Theoretically, the saturated concentration of carbide slag at 20°C is 0.165g per 100mL aqueous solution, and the main component of the aqueous solution is Ca(OH)2. In order to reduce the influence of the concentration of carbide slag solution on the P recovery process, an oversaturated carbide slag solution is configured for experiment. Take 1.5g carbide slag and put it into a 500mL beaker, add 500mL distilled water, stir for 10min, and then stand for 30min to prepare for subsequent use.

[0014] Preferably, in step S4, the acid leaching solution and the carbide slag solution are mixed in a ratio of 1:3-5, stirred and reacted at 50° C. for 30 minutes, and after the reaction is completed, the aluminum phosphate precipitate generated in the reaction solution is collected by suction filtration.

[0015] After the reaction is completed, the aluminum phosphate precipitate generated in the reaction solution is collected by filtration using a sand core Büchner funnel, dried in an oven at 60°C for three hours, and then analyzed by X-ray photoelectron spectroscopy (XPS) to determine the elemental composition of the generated substance and judge the properties of the product.

[0016] At the same time, the supernatant of the reaction solution was taken and diluted ten times with 5% dilute nitric acid solution. The phosphorus content in the diluted sample was determined by I CP-MS, and the phosphorus leaching efficiency (P) in the sludge incineration ash was calculated. e ), relative recovery rate (P r ) and final recovery rate (P u ) to obtain the best experimental conditions. The calculation formula is as follows:

[0017]

[0018] Where:

[0019] M1 is the mass of phosphorus in the leaching solution of unit sludge incineration ash;

[0020] M2 is the mass of phosphorus in the solution after the reaction between carbide slag solution and acid leaching solution;

[0021] M S It is the mass of phosphorus per unit of sludge incineration ash.

[0022] A further preferred technical solution is that in step S4, the aluminum element is removed from the acid leaching solution by adding aluminum removal resin, the amount of the aluminum removal resin added is one tenth of the mass of the acid leaching solution, and the solution is stirred at a constant speed of 220r / min for 30min, and the aluminum element in the solution can be completely removed. The treated acid leaching solution is mixed with the carbide slag solution in a ratio of 1:3-5, and the reaction is stirred at 50°C for 30min. After the reaction is completed, the CaHPO4 precipitate generated in the reaction solution is collected by suction.

[0023] The product was dried in an oven at 60°C for three hours, and then analyzed by X-ray photoelectron spectroscopy (XPS) to determine the elemental composition of the product and the properties of the product.

[0024] After the experiment, the relative recovery rate of phosphorus in the sludge incineration ash (P r ) and final recovery rate (P u ) to obtain the best experimental conditions.

[0025] Table 1. Element analysis of carbide slag

[0026]

[0027] Compared with the prior art, the present invention achieves the following technical effects:

[0028] The present invention reuses the excess sludge and carbide slag, and recycles the phosphorus in the excess sludge. Compared with other excess sludge phosphorus recovery technologies, this technology reduces the addition of reagents in the recovery process, and can provide two recovery routes according to the sludge conditions, realizing waste resource reuse to a greater extent, reducing recovery costs, and having higher practical application feasibility.

[0029] The advantages of using carbide slag in the present invention are: as shown in Table 1, the main element of carbide slag is Ca when analyzed by XRF, and no foreign impurities are introduced in the recovery reaction. Carbide slag is a strong alkaline substance. Carbide slag and distilled water are used to make a carbide slag solution, and the pH of the solution is greater than 10. The supernatant is mixed with the acid leaching supernatant of sludge incineration ash. At room temperature, the reaction process is extremely rapid and the reaction can be completed in a short time. At the same time, in the process of recovering calcium hydrogen phosphate, pH has a greater influence on the reaction products. In a weak acid environment (pH 6.5-6.8), CaHPO4 is more stable than Ca3(PO4)2, and in high Ca 2+ At low concentrations, CaHPO4 crystals can even form under lower pH conditions. This is because the carbide slag solution itself is strongly alkaline and contains a large amount of Ca 2+ Adding a certain amount of carbide slag solution can simultaneously adjust the pH and provide excess Ca 2+ to complete the recovery of phosphorus in the acid leaching solution.

[0030] The first recovery route of the present invention is to use carbide slag solution prepared from waste carbide slag as a phosphorus recovery agent, and recover the phosphorus element in the acid leaching solution in the form of AIPO4. Most urban sewage treatment plants use aluminum-containing coagulants (PAC) in the coagulation and sedimentation and sludge dehydration stages. The remaining sludge contains more aluminum elements, so there is also a large amount of aluminum elements in the acid leaching solution. By adding carbide slag solution to adjust the pH, AIPO4 precipitation is generated in the solution by reaction, and the relative recovery rate of phosphorus can reach 99%, and the final recovery rate can reach up to 95%. The purity of the final recovered product AIPO4 can reach 98.2%, which has a high industrial application value.

[0031] The second recovery route of the present invention is to use carbide slag solution prepared from waste carbide slag as a phosphorus recovery agent, and recover the phosphorus element in the acid leaching solution in the form of CaHPO4. When the municipal sewage treatment plant does not use aluminum-containing coagulants, there is still a small amount of aluminum in the sludge, and AIPO4 will be produced in the recovery stage to affect the purity of other recovered products. Therefore, aluminum removal resin is used to remove the aluminum element from the acid leaching solution, and then the pH is adjusted by adding carbide slag solution and excessive Ca elements are provided. CaHPO4 precipitation is generated in the solution by reaction, and the relative recovery rate of phosphorus can reach 99%, and the final recovery rate can reach up to 95%. The purity of the final recovered product CaHPO4 can reach 94.2%, which can be used in agricultural fertilizers and industry, and has a high application value.

[0032] The present invention uses hydrochloric acid to acid-leach the sludge incineration ash. The current mainstream acid-leaching method is a wet chemical method, which uses a strong acid or a strong alkaline solution to leach the phosphorus element in the sludge incineration ash, and the phosphorus leaching efficiency (>90%) of two inorganic strong acids (HCl, H2SO4) is significantly higher than that of weak acids and organic acids. Because the acid-leaching solution and carbide slag contain a large amount of Ca, if the sulfuric acid acid-leaching method is used, there will be excessive SO4 in the subsequent recovery reaction solution. 2- With Ca 2+ , CaSO4 will inevitably be generated during the recovery process. Therefore, in order to avoid the generation of impurities in the recovery stage, H2SO4 acid leaching is not recommended. At the same time, the difference between HCl acid leaching efficiency and H2SO4 is small, and HCl is cheaper and easier to obtain, and is safer than H2SO4 in actual operation. Therefore, the present invention adopts hydrochloric acid acid leaching. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] For ease of explanation, the present invention is described in detail with reference to the following specific embodiments and the accompanying drawings.

[0034] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0035] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments; in the following description, specific details such as specific configurations are provided only to help fully understand the embodiments of the present invention. Therefore, it should be clear to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0037] Example 1

[0038] Step 1: Pretreatment of urban excess sludge;

[0039] The residual sludge was placed in a 105°C oven for drying and coarsely ground into fine particles. The residual sludge was placed in a quartz boat and placed in a tube furnace, incinerated at 800°C for 1 hour, and the residual sludge incineration ash (SSA) was taken out after it cooled to room temperature, and characterized and analyzed by X-ray fluorescence spectrometry (XRF) to determine its elemental composition. The obtained sludge incineration ash was stored in a sealed bag and placed in a dryer for subsequent use.

[0040] Step 2: Acid leaching reaction of urban waste sludge;

[0041] Take 0.5g of each prepared sludge incineration ash and place it in a 150mL conical flask, and add 100ml of 0.100mol / L hydrochloric acid for reaction. Place the conical flask in a constant temperature oscillator, set the temperature to 25℃, and oscillate continuously at 180r / min for 6h; then take the mixed solution and centrifuge it at 8000r / min for 15min, take the supernatant and filter it through a 0.22μm filter membrane to obtain a sample; dilute it ten times with 5% dilute nitric acid solution, and then use I CP-MS to determine the element content in the diluted sample.

[0042] Step 3: preparation of carbide slag solution;

[0043] After natural sedimentation and drying, the carbide slag was ground in a ball mill at 4000r / min for 10min and passed through a 200-mesh sieve to obtain carbide slag powder. Carbide slag is a slightly soluble strong alkaline substance. Theoretically, the saturated concentration of carbide slag at 20°C is 0.165g per 100mL aqueous solution, and the main component of its aqueous solution is Ca(OH)2. In order to reduce the effect of carbide slag solution concentration on the P recovery process, an oversaturated carbide slag solution was prepared for the experiment. Take 1.5g of carbide slag and put it in a 500mL beaker, add 500mL of distilled water, stir for 10min, let it stand for 30min, and take the supernatant for subsequent use.

[0044] Step 4: AIPO4 Recycling

[0045] The acid leaching solution and the carbide slag solution were mixed in a ratio of 1:3, and stirred in a water bath at 50°C for 30 minutes. After the reaction was completed, the aluminum phosphate precipitate generated in the reaction solution was collected by suction filtration using a sand core Buchner funnel, and dried in an oven at 60°C for three hours. The recovered product was then analyzed using X-ray photoelectron spectroscopy (XPS) to determine the elemental composition of the generated substance and determine the properties of the product.

[0046] Step 5: Analyze the data

[0047] Through the above steps, the acid leaching efficiency of phosphorus in sludge incineration ash can reach 90.3%; adding carbide slag solution for recovery, the relative recovery rate of phosphorus can reach 91.3%, and the absolute recovery rate is 77.9%; the purity of the recovered AIPO4 is 97.9%.

[0048] Example 2

[0049] Step 1: Pretreatment of urban excess sludge;

[0050] The residual sludge was placed in a 105°C oven for drying and coarsely ground into fine particles. The residual sludge was placed in a quartz boat and placed in a tube furnace, incinerated at 800°C for 1 hour, and the residual sludge incineration ash (SSA) was taken out after it cooled to room temperature, and characterized and analyzed by X-ray fluorescence spectrometry (XRF) to determine its elemental composition. The obtained sludge incineration ash was stored in a sealed bag and placed in a dryer for subsequent use.

[0051] Step 2: Acid leaching reaction of urban waste sludge;

[0052] Take 0.5g of each of the prepared sludge incineration ash and place it in a 150mL conical flask, and add 100ml of 0.125mol / L hydrochloric acid for reaction. Place the conical flask in a constant temperature oscillator, set the temperature to 25℃, and oscillate continuously at 180r / min for 6h; then take the mixed solution and centrifuge it at 8000r / min for 15min, take the supernatant and filter it through a 0.22μm filter membrane to obtain a sample; dilute it ten times with 5% dilute nitric acid solution, and then use I CP-MS to determine the element content in the diluted sample.

[0053] Step 3: preparation of carbide slag solution;

[0054] After natural sedimentation and drying, the carbide slag was ground in a ball mill at 4000r / min for 10min and passed through a 200-mesh sieve to obtain carbide slag powder. Carbide slag is a slightly soluble strong alkaline substance. Theoretically, the saturated concentration of carbide slag at 20°C is 0.165g per 100mL aqueous solution, and the main component of its aqueous solution is Ca(OH)2. In order to reduce the effect of carbide slag solution concentration on the P recovery process, an oversaturated carbide slag solution was prepared for the experiment. Take 1.5g of carbide slag and put it in a 500mL beaker, add 500mL of distilled water, stir for 10min, let it stand for 30min, and take the supernatant for subsequent use.

[0055] Step 4: AIPO4 Recycling

[0056] The acid leaching solution and the carbide slag solution were mixed in a ratio of 1:4, and stirred in a water bath at 50°C for 30 minutes. After the reaction was completed, the aluminum phosphate precipitate generated in the reaction solution was collected by suction filtration using a sand core Buchner funnel, and dried in an oven at 60°C for three hours. The recovered product was then analyzed using X-ray photoelectron spectroscopy (XPS) to determine the elemental composition of the generated substance and determine the properties of the product.

[0057] Step 5: Analyze the data

[0058] Through the above steps, the acid leaching efficiency of phosphorus in sludge incineration ash can reach 91.8%; by adding carbide slag solution for recovery, the relative recovery rate of phosphorus can reach 99%, and the absolute recovery rate is 91.2%; the purity of the recovered AIPO4 is 98.2%.

[0059] Example 3

[0060] Step 1: Pretreatment of urban excess sludge;

[0061] The residual sludge was placed in a 105°C oven for drying and coarsely ground into fine particles. The residual sludge was placed in a quartz boat and placed in a tube furnace, incinerated at 800°C for 1 hour, and the residual sludge incineration ash (SSA) was taken out after it cooled to room temperature, and characterized and analyzed by X-ray fluorescence spectrometry (XRF) to determine its elemental composition. The obtained sludge incineration ash was stored in a sealed bag and placed in a dryer for subsequent use.

[0062] Step 2: Acid leaching reaction of urban waste sludge;

[0063] Take 0.5g of each prepared sludge incineration ash and place it in a 150mL conical flask, and add 100ml of 0.100mol / L hydrochloric acid for reaction. Place the conical flask in a constant temperature oscillator, set the temperature to 25℃, and oscillate continuously at 180r / min for 6h; then take the mixed solution and centrifuge it at 8000r / min for 15min, take the supernatant and filter it through a 0.22μm filter membrane to obtain a sample; dilute it ten times with 5% dilute nitric acid solution, and then use I CP-MS to determine the element content in the diluted sample.

[0064] Step 3: preparation of carbide slag solution;

[0065] After natural sedimentation and drying, the carbide slag was ground in a ball mill at 4000r / min for 10min and passed through a 200-mesh sieve to obtain carbide slag powder. Carbide slag is a slightly soluble strong alkaline substance. Theoretically, the saturated concentration of carbide slag at 20°C is 0.165g per 100mL aqueous solution, and the main component of its aqueous solution is Ca(OH)2. In order to reduce the effect of carbide slag solution concentration on the P recovery process, an oversaturated carbide slag solution was prepared for the experiment. Take 1.5g of carbide slag and put it in a 500mL beaker, add 500mL of distilled water, stir for 10min, let it stand for 30min, and take the supernatant for subsequent use.

[0066] Step 4: CaHPO4 recovery

[0067] The aluminum element is removed by adding aluminum removal resin to the acid leaching solution. The amount of resin added is one tenth of the mass of the acid leaching solution, and the solution is stirred at a constant speed of 220r / min for 30min, and the aluminum element in the solution can be completely removed.

[0068] The treated acid leaching solution was mixed with the carbide slag solution in a ratio of 1:4, and stirred in a water bath at 50°C for 30 minutes. After the reaction was completed, the CaHPO4 precipitate generated in the reaction solution was collected by suction filtration using a sand core Buchner funnel, and dried in an oven at 60°C for three hours. The recovered product was then analyzed using X-ray photoelectron spectroscopy (XPS) to determine the elemental composition of the generated substance and determine the properties of the product.

[0069] Step 5: Analyze the data

[0070] Through the above steps, the acid leaching efficiency of phosphorus in sludge incineration ash can reach 90.3%; by adding calcium carbide slag solution for recovery, the relative recovery rate of phosphorus can reach 99.3%, and the absolute recovery rate is 90.9%; the purity of the recovered CaHPO4 is 94.2%.

[0071] Example 4

[0072] Step 1: Pretreatment of urban excess sludge;

[0073] The residual sludge was placed in a 105°C oven for drying and coarsely ground into fine particles. The residual sludge was placed in a quartz boat and placed in a tube furnace, incinerated at 800°C for 1 hour, and the residual sludge incineration ash (SSA) was taken out after it cooled to room temperature, and characterized and analyzed by X-ray fluorescence spectrometry (XRF) to determine its elemental composition. The obtained sludge incineration ash was stored in a sealed bag and placed in a dryer for subsequent use.

[0074] Step 2: Acid leaching reaction of urban waste sludge;

[0075] Take 0.5g of each of the prepared sludge incineration ash and place it in a 150mL conical flask, and add 100ml of 0.125mol / L hydrochloric acid for reaction. Place the conical flask in a constant temperature oscillator, set the temperature to 25℃, and oscillate continuously at 180r / min for 6h; then take the mixed solution and centrifuge it at 8000r / min for 15min, take the supernatant and filter it through a 0.22μm filter membrane to obtain a sample; dilute it ten times with 5% dilute nitric acid solution, and then use I CP-MS to determine the element content in the diluted sample.

[0076] Step 3: preparation of carbide slag solution;

[0077] After natural sedimentation and drying, the carbide slag was ground in a ball mill at 4000r / min for 10min and passed through a 200-mesh sieve to obtain carbide slag powder. Carbide slag is a slightly soluble strong alkaline substance. Theoretically, the saturated concentration of carbide slag at 20°C is 0.165g per 100mL aqueous solution, and the main component of its aqueous solution is Ca(OH)2. In order to reduce the effect of carbide slag solution concentration on the P recovery process, an oversaturated carbide slag solution was prepared for the experiment. Take 1.5g of carbide slag and put it in a 500mL beaker, add 500mL of distilled water, stir for 10min, let it stand for 30min, and take the supernatant for subsequent use.

[0078] Step 4: CaHPO4 recovery

[0079] The aluminum element is removed by adding aluminum removal resin to the acid leaching solution. The amount of resin added is one tenth of the mass of the acid leaching solution, and the solution is stirred at a constant speed of 220r / min for 30min, and the aluminum element in the solution can be completely removed.

[0080] The treated acid leaching solution was mixed with the carbide slag solution in a ratio of 1:5, and stirred in a water bath at 50°C for 30 minutes. After the reaction was completed, the CaHPO4 precipitate generated in the reaction solution was collected by suction filtration using a sand core Buchner funnel, and dried in an oven at 60°C for three hours. The recovered product was then analyzed using X-ray photoelectron spectroscopy (XPS) to determine the elemental composition of the generated substance and determine the properties of the product.

[0081] Step 5: Analyze the data

[0082] Through the above steps, the acid leaching efficiency of phosphorus in sludge incineration ash can reach 91.2%; by adding calcium carbide slag solution for recovery, the relative recovery rate of phosphorus can reach 99.9%, and the absolute recovery rate is 91.1%; the purity of the recovered CaHPO4 is 90.2%.

[0083] Those skilled in the art to which the present application belongs may make various modifications or additions to the specific embodiments described or replace them in a similar manner, but they will not deviate from the inventive concept of the present application or exceed the scope defined by the attached claims.

Claims

1. A method for recovering phosphorus from excess sludge using carbide slag, characterized in that: The specific steps include: S1. Pretreatment of urban waste sludge; S2, acid leaching reaction of urban surplus sludge to obtain acid leaching solution; S3, preparation of carbide slag solution; S4, mixing the acid leaching solution obtained in step S2 with the carbide slag solution obtained in step S3 to extract phosphorus.

2. A method for recovering phosphorus from excess sludge using carbide slag according to claim 1, characterized in that: The step S1 specifically comprises crushing the urban surplus sludge, performing high-temperature incineration treatment, and grinding it into powder to obtain surplus sludge incineration ash.

3. A method for recovering phosphorus from excess sludge using carbide slag according to claim 1, characterized in that: The step S2 specifically includes placing an appropriate amount of the prepared sludge incineration ash in a container, adding an appropriate amount of hydrochloric acid for reaction and oscillation, then centrifuging the mixed solution, and taking the supernatant to obtain a phosphoric acid-rich leaching solution sample.

4. A method for recovering phosphorus from excess sludge using carbide slag according to claim 1, characterized in that: The step S3 specifically comprises drying the carbide slag by natural sedimentation, grinding it with a ball mill, and sieving it to obtain carbide slag powder; putting an appropriate amount of the carbide slag powder into a container, adding an appropriate amount of water, stirring it for 10 minutes, and then letting it stand and settle for 30 minutes to obtain a carbide slag solution.

5. The method for recovering phosphorus from excess sludge by using carbide slag according to claim 1, characterized in that: The step S4 specifically comprises mixing the acid leaching solution and the carbide slag solution in a ratio of 1:3-5, stirring and reacting at 50° C. for 30 minutes, and collecting the aluminum phosphate precipitate generated in the reaction solution by suction filtration after the reaction is completed.

6. The method for recovering phosphorus from excess sludge by using carbide slag according to claim 1, characterized in that: The step S4 specifically comprises removing aluminum from the acid leaching solution by adding aluminum removal resin, mixing the treated acid leaching solution with the carbide slag solution at a ratio of 1:3-5, stirring the reaction at 50°C for 30 minutes, and collecting the CaHPO4 precipitate generated in the reaction solution by suction filtration after the reaction is completed.

7. The method for recovering phosphorus from excess sludge by using carbide slag according to claim 4, characterized in that: In the step S3, the carbide slag powder is passed through a 200-mesh sieve and added into water at a ratio of 3 g:1000 mL, and the concentration of the carbide slag solution is 3 g / L.

8. A method for recovering phosphorus from excess sludge using carbide slag according to claim 1 or 3, characterized in that: In the step S2, the solid-liquid ratio of hydrochloric acid to sludge incineration ash during the acid leaching process is 5 g / L, and the concentration of hydrochloric acid is 0.100 mol / L to 0.125 mol / L.

9. The method for recovering phosphorus from excess sludge by using carbide slag according to claim 8, characterized in that: In step S2, the temperature is set at 25° C. and the mixture is continuously oscillated at 180 rpm for 6 hours.

10. The method for recovering phosphorus from excess sludge by using carbide slag according to claim 6, characterized in that: In step S4, the amount of the aluminum-removing resin added is one tenth of the mass of the acid leaching solution, and the mixture is stirred at a constant speed of 220 r / min for 30 min.

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