Electrodialysis phosphorus extraction method based on biomass porous carbon electrode

Abstract

The invention provides an electrodialysis phosphorus extraction method based on a biomass porous carbon electrode. The method comprises the following steps: dividing an electrolytic tank into a cathode tank and an anode tank by adopting an anion exchange membrane; phosphorus-containing wet sludge is subjected to acid leaching to obtain a phosphorus-releasing solution, the phosphorus-releasing solution is introduced into the cathode pool, and a sulfate solution is introduced into the anode pool; and inserting a carbon cloth containing biomass porous carbon as a cathode into the anode tank, inserting a blank carbon cloth as an anode into the cathode tank, electrifying for electrodialysis, and obtaining a pure phosphorus-rich solution in the anode tank. According to the method, an electrolytic tank is separated by adopting an anion exchange membrane, biomass porous carbon from a plant source is combined as an electrode material, and an electrodialysis technology is adopted, so that the dialysis efficiency of phosphorus is greatly improved, and selective migration of phosphorus is also realized, so that a pure phosphorus solution is enriched in an anode tank; the method has the advantages of simple process, convenience in operation, low cost and the like, and is convenient for large-scale industrial recovery operation.

Description

Technical Field

[0001] The present invention relates to a method for extracting phosphorus by electrodialysis, specifically to a method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode, belonging to the technical field of phosphorus resource treatment. Background Art

[0002] Phosphorus is one of the main pollutants in wastewater. Excessive phosphorus may cause excessive growth of algae and plants in rivers and lakes, leading to eutrophication problems. Eutrophication will directly lead to a decline in water quality, damage the ecological structure, and increase the treatment difficulty and water supply cost. Phosphorus is also a key component of fertilizers in the current food production and consumption system, and phosphorus is a non-renewable resource, which is rapidly depleted due to the increase in sedimentation caused by the natural phosphorus cycle and the intensification of phosphate utilization. Because the most easily accessible and high-quality phosphate rocks are being depleted, low-grade minerals with high impurity levels, low phosphorus content, and poor synergy ratios are being increasingly exploited. However, compared with the use of high-quality minerals, the mining and production costs are higher. Therefore, there is an urgent need for alternative and renewable phosphorus sources, and wastewater containing a large amount of phosphorus is such a potential source.

[0003] Many physical, biological, and chemical methods for recovering phosphorus from wastewater have been developed, including chemical precipitation, crystallization, adsorption and ion exchange, membrane and biological methods, etc. However, these methods have different defects. The phosphorus concentration in some industrial wastewater is relatively high, exceeding the limit of phosphorus storage by microorganisms. Sometimes, there are coexisting substances such as more salts and metals, which are not suitable for the growth of microorganisms. Traditional biological methods are difficult to be used to remove and recover phosphorus from high-phosphorus wastewater. The adsorption method can effectively remove low-concentration phosphates in water. Due to the limited capacity of the adsorbent, it is not suitable for treating wastewater with a high phosphorus concentration. The chemical precipitation method can effectively remove phosphorus in wastewater, but the formed phosphorus-containing sludge still needs subsequent treatment, and it is also difficult to realize the recovery of phosphorus resources. The crystallization method has become the mainstream method for wastewater phosphorus recovery because it can realize the recovery and reuse of phosphorus resources. The main crystallization recovery products are struvite (MgNH4PO4·6H2O), hydroxyapatite [Ca5(PO4)3OH], etc. Although there are some engineering cases for the struvite crystallization phosphorus recovery technology, due to problems such as a relatively high crystallization suitable pH and high costs of adding alkali liquor and magnesium salts, it cannot be more widely promoted and applied. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode. This method uses an anion exchange membrane to separate the electrolytic cell, combines a biomass porous carbon derived from plants as the electrode material, and then not only greatly improves the dialysis efficiency of phosphorus but also realizes the selective migration of phosphorus through electrodialysis technology, thereby enriching a pure phosphorus solution in the anode cell.

[0005] To achieve the above technical objectives, the present invention provides an electro-dialysis phosphorus extraction method based on a biomass porous carbon electrode, which includes: separating an electrolytic cell into a cathode chamber and an anode chamber by an anion exchange membrane; acid-leaching phosphorus-containing wet sludge to obtain a phosphorus-releasing solution, introducing it into the cathode chamber, and introducing a sulfate solution into the anode chamber; using a carbon cloth containing biomass porous carbon as the cathode, inserting it into the anode chamber, using a blank carbon cloth as the anode, inserting it into the cathode chamber, and energizing for electro-dialysis to obtain a pure phosphorus-rich solution in the anode chamber; the biomass porous carbon is obtained by two-step carbonization using plants as the carbon source.

[0006] The technical solution provided by the present invention uses biomass porous carbon as the electrode material. Utilizing its porous structure and good electrical conductivity, in electro-dialysis, it not only greatly increases the electrode adsorption capacity, provides more active sites, but also effectively promotes phosphorus migration, improves the current efficiency, and thus realizes the high-efficiency and selective enrichment and recovery of phosphorus.

[0007] As a preferred solution, the process of acid leaching is as follows: Add 8 - 12 ml / L of concentrated sulfuric acid to the phosphorus-containing wet sludge, stir well and then let it stand. The obtained acidolysis solution is the phosphorus-releasing solution. The dosage of sulfuric acid must be strictly implemented according to the above requirements. When the sulfuric acid content is too low, due to insufficient acidolysis, the concentration of the phosphorus-releasing solution decreases, resulting in a decrease in electro-dialysis efficiency; while when the sulfuric acid content is too high, it may corrode the equipment, damage the performance of the anion exchange membrane, and when excessive sulfuric acid reacts with the sludge, it will release multiple competitive anions, thereby interfering with the migration selectivity of phosphorus.

[0008] As a preferred solution, the water content of the phosphorus-containing wet sludge is ≥90%.

[0009] As a preferred solution, the sulfate solution is at least one of potassium sulfate, sodium sulfate, zinc sulfate, and iron sulfate.

[0010] As a preferred solution, the concentration of the sulfate solution is 0.05 - 0.15 M. The concentration of the sulfate solution must be strictly implemented according to the above requirements. When the concentration of the sulfate solution is too low, the solution conductivity is low, the current intensity is insufficient, the electro-dialysis time is prolonged, and the efficiency is reduced; while when the concentration of the sulfate solution is too high, on the one hand, the high ionic strength leads to concentration polarization, the surface resistance of the electrode increases, and the energy consumption rises. On the other hand, as electro-dialysis proceeds, sulfates may crystallize and precipitate, clogging the membrane pores or the electrode surface, thereby hindering phosphorus migration.

[0011] As a preferred solution, sulfates also need to be added to the cathode chamber to increase the current intensity. Calculated as anhydrous sodium sulfate, the addition amount is 3 - 6 g / L.

[0012] As a preferred solution, the pH of the phosphorus-releasing solution is 1 - 1.5.

[0013] As a preferred scheme, the preparation process of the porous carbon containing biomass is as follows: the preparation process of the porous carbon containing biomass is as follows: the plant carbon source is ground through 100 mesh, subjected to a stage of low-temperature carbonization, and then fully mixed with a solid strong base in a mass ratio of 1:3~7 and subjected to a second stage of high-temperature carbonization. After the carbonization is completed, the carbon is acid-washed to neutrality and dried to obtain the product.

[0014] As a preferred solution, the solid strong base is sodium peroxide and / or potassium peroxide. Further preferably, the solid strong base is potassium peroxide.

[0015] As a preferred solution, the condition of the one-stage low-temperature carbonization is: carbonization at 400-500° C. for 3-5 hours under a protective atmosphere.

[0016] As a preferred solution, the conditions of the second-stage high-temperature carbonization are: carbonization at 800-1000° C. for 1-4 hours under a protective atmosphere.

[0017] As a preferred solution, the preparation process of the cathode is: evenly coating the cathode slurry containing biomass porous carbon on the carbon cloth, and drying to a constant weight without cracks on the surface of the carbon cloth.

[0018] As a preferred solution, the drying method is one of vacuum drying, freeze drying and oven drying.

[0019] As a preferred solution, when the drying method is oven drying, the conditions are: temperature is 60-90° C., and time is 1-3 hours.

[0020] As a preferred solution, the cathode slurry includes the following mass parts: 5-9 parts of biomass porous carbon, 1-2 parts of carbon black, and 1-2 parts of binder. The biomass porous carbon in the cathode slurry is the core active material, which mainly provides adsorption sites and active surfaces to promote phosphorus ion migration; the main function of carbon black is to enhance the conductivity of the electrode, reduce contact resistance, and ensure uniform current distribution; and the binder is to fix each component to the carbon cloth, improve the mechanical strength of the electrode, prevent the electrode from falling off and cracking, and ensure the stability of the electrode structure.

[0021] As a preferred solution, the binder is one of polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid and polytetrafluoroethylene.

[0022] As a preferred solution, the cathode slurry further contains a binder auxiliary.

[0023] As a preferred solution, the binder auxiliary agent is N-methylpyrrolidone, and the mass ratio of N-methylpyrrolidone to the binder is 120-180:1.

[0024] As a preferred solution, the process conditions of the electrodialysis process are as follows: the rated voltage is 1 - 10 V, and the running time is 20 - 30 h.

[0025] Compared with the prior art, the beneficial technical effects of the technical solution provided by the present invention are as follows:

[0026] 1) The method provided by the present invention uses an anion exchange membrane to separate the electrolytic cell, combines a biomass porous carbon derived from plants as the electrode material, and not only greatly improves the dialysis efficiency of phosphorus but also realizes the selective migration of phosphorus through the electrodialysis technology, thereby enriching a pure phosphorus solution in the anode cell.

[0027] 2) In the technical solution provided by the present invention, compared with the traditional electrode, the use of the biomass porous carbon electrode material improves the phosphorus migration efficiency by more than 4 times, significantly optimizing the phosphorus migration kinetics; in addition, based on the porous structure of the biomass porous carbon, the competitive adsorption of other ions, such as metal impurities, can be effectively inhibited, thereby further improving the selectivity of phosphorus. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the device used in the electrodialysis phosphorus extraction method in Example 1 of the present invention;

[0029] Figure 2 It is a graph showing the change of phosphorus concentration in the anode cell during the operation of Example 1 of the present invention;

[0030] Figure 3 It is a graph showing the change of phosphorus concentration in the anode cell during the operation of Comparative Example 1 of the present invention;

[0031] Figure 4 It is a schematic diagram of the phosphorus release rate of Example 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0032] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and in detail in conjunction with the accompanying drawings of the specification and preferred embodiments. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1

[0034] This example provides an electrodialysis phosphorus extraction method based on a biomass porous carbon electrode, using municipal wet sludge from a certain place in Hunan. The specific process is as follows:

[0035] 1) By a two-step carbonization method, biomass porous carbon with high electrochemical performance was prepared using corncob as the raw material. The process was as follows: First, the corncob was ground into fine powder and sieved through 100-mesh. Subsequently, the obtained powder was placed in a tube furnace and pre-carbonized at 450 °C under N2 atmosphere for 4 hours. The obtained powder was mixed with KOH solid in a mass ratio of 1:5 and thoroughly ground. It was then placed in the tube furnace again and activated at 900 °C under N2 atmosphere for 3 hours. After being taken out, it was washed thoroughly with 1M hydrochloric acid solution, and then washed with pure water until neutral. It was placed in an oven at 80 °C until completely dry, thus obtaining the product. The obtained biomass porous carbon, carbon black, and PVDF were mixed in a mass ratio of 7:1.5:1.5, and an appropriate amount of NMP was added and stirred thoroughly until the liquid became viscous. It was evenly coated on a carbon cloth electrode with an area of about 16 cm 2 , and placed in an oven at 80 °C to dry for 2 h, obtaining the cathode electrode coated with the material.

[0036] 2) 10 ml / L of concentrated sulfuric acid was added to the as-received wet sludge and stirred evenly. It was left standing for 2 h, and then the acidolysis solution was taken and filtered to obtain a phosphorus-release solution (with a concentration of 155.98 mg / L). 100 ml of the above phosphorus-release solution was added to the cathode cell, and 4 g / L of anhydrous sodium sulfate was added thereto. The cathode electrode was placed into the phosphorus-release solution so that the part coated with the bio-based porous carbon material was completely immersed in the phosphorus-release solution. A 0.1M sodium sulfate solution was prepared, and 130 ml of a 0.1M sodium sulfate solution was added to the anode chamber. The anode electrode (blank carbon cloth) was placed into the anode chamber with the same area as the cathode chamber and immersed in the phosphorus-release solution.

[0037] 3) The distance between the anode electrode and the cathode electrode was 4 cm. The negative and positive poles of the power supply were respectively connected to the cathode area and the anode area. The power supply was turned on. In this embodiment, the power supply was a constant-voltage DC power supply with the model of adjustable DC regulated power supply MS152D. Its current was set to 10 mA, and the rated voltage was set to 10 V.

[0038] 4) An electrodialysis experiment was carried out on the phosphorus-release solution by energization, and the experiment was stopped after running for 24 h. Samples of the phosphorus solution in the anode chamber after the electrodialysis reaction were taken, once every 2 h. The change in the phosphorus concentration before and after the reaction was measured with reference to the ammonium molybdate spectrophotometric colorimetric method;

[0039] The electrodialysis experiment on the wet sludge phosphorus-release solution was carried out according to the above steps. Its device schematic diagram is as shown in Figure 1 , and the change in the phosphorus concentration in the anode cell during the running process is as shown in Figure 2 . It can be seen from Figure 2 that the inorganic phosphorus content reached a maximum of 37.95 mg / L after 24 h.

[0040] Comparative Example 1

[0041] This comparative example is exactly the same as Example 1, except that: a blank carbon cloth electrode without coated porous carbon material is used as the electrode in the cathode chamber and the anode chamber.

[0042] After testing, the change of phosphorus concentration in the anode cell during the operation of this comparative example is as Figure 3 shown, and it can be known through Figure 3 that the content of inorganic phosphorus is only 7.9 mg / L after 24 h.

[0043] From the results of the phosphorus concentration in the anode chamber in Example 1 and Comparative Example 1, it can be seen that when the electro-dialysis treatment is carried out on the sludge phosphorus release solution using a carbon cloth electrode containing biomass porous carbon, the dialysis efficiency can reach 31.62%, while when the electro-dialysis treatment is carried out on the sludge phosphorus release solution using a blank carbon cloth, the dialysis efficiency is only 7.27%. This shows that the method provided by the present invention can not only achieve the selective transfer of phosphorus elements to the anode, but also effectively improve its dialysis efficiency.

Claims

1. A method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode, characterized in that, include: An anion exchange membrane is used to separate the electrolytic cell into a cathode cell and an anode cell; The phosphorus-releasing liquid is obtained after acid leaching of phosphorus-containing wet sludge and introduced into the cathode tank, and the sulfate solution is introduced into the anode tank; The carbon cloth containing biomass porous carbon is used as cathode and inserted into the anode pool, and the blank carbon cloth is used as anode and inserted into the cathode pool, and the electricity is turned on for electrodialysis to obtain pure phosphorus-rich liquid in the anode pool; The biomass porous carbon is obtained by carbonizing plants as carbon sources in two steps.

2. The electro-dialysis phosphorus extraction method based on a biomass porous carbon electrode according to claim 1, characterized in that: The acid leaching process is: adding 8-12 ml / L of concentrated sulfuric acid to the phosphorus-containing wet sludge, stirring it fully and then letting it stand, and the obtained acid solution is the phosphorus-releasing solution; the water content of the phosphorus-containing wet sludge is ≥90%.

3. The electro-dialysis phosphorus extraction method based on a biomass porous carbon electrode according to claim 1, wherein: The sulfate solution is at least one of potassium sulfate, sodium sulfate, zinc sulfate and iron sulfate; the concentration of the sulfate solution is 0.05-0.15M.

4. The electro-dialysis phosphorus extraction method based on a biomass porous carbon electrode according to claim 1, wherein: Sulfate needs to be added to the cathode cell to increase the current intensity. The amount added is 3-6 g / L in terms of anhydrous sodium sulfate. The pH of the phosphorus-releasing liquid is 1-1.

5.

5. A method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode according to claim 1, characterized in that: The preparation process of the porous carbon containing biomass is as follows: grinding the plant carbon source through 100 meshes, performing a low-temperature carbonization, and then fully mixing with a solid strong base at a mass ratio of 1:3-7 and performing a second high-temperature carbonization, and after the carbonization is completed, acid washing to neutrality, and drying to obtain; The solid strong base is sodium peroxide and / or potassium peroxide; The conditions for the first stage low-temperature carbonization are: carbonization at 400-500° C. for 3-5 hours under a protective atmosphere; the conditions for the second stage high-temperature carbonization are: carbonization at 800-1000° C. for 1-4 hours under a protective atmosphere.

6. The electro-dialysis phosphorus extraction method based on a biomass porous carbon electrode according to claim 1, wherein: The preparation process of the cathode is as follows: the cathode slurry containing biomass porous carbon is evenly coated on the carbon cloth, and then dried until the weight is constant and there is no crack on the surface of the carbon cloth.

7. A method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode according to claim 6, characterized in that: The drying method is one of vacuum drying, freeze drying and drying; when the drying method is drying, the conditions are: temperature is 60-90° C., and time is 1-3 hours.

8. The electro-dialysis phosphorus extraction method based on a biomass porous carbon electrode according to claim 6, characterized in that: The cathode slurry comprises the following components in parts by weight: 5-9 parts of biomass porous carbon, 1-2 parts of carbon black, and 1-2 parts of a binder; the binder is one of polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid and polytetrafluoroethylene.

9. A method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode according to claim 8, characterized in that: The cathode slurry also contains a binder auxiliary; the binder auxiliary is N-methyl pyrrolidone, and the mass ratio of the binder auxiliary to the binder is 120-180:

1.

10. A method for extracting phosphorus by electrodialysis based on a biomass porous carbon electrode according to claim 1, characterized in that: The process conditions of the electrodialysis process are: rated voltage of 1-10V, and operating time of 20-30h.

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