An electrochemically regulated phosphate adsorption-desorption method

Abstract

This invention provides an electrochemically regulated phosphate adsorption-desorption method, comprising: 1) Phosphate adsorption: a first electrolytic cell using a tetravalent cerium electrode as the cathode and phosphorus-containing wastewater as the electrolyte for a first electrolytic treatment; after the first electrolytic treatment is completed, the circuit is disconnected; and after the phosphorus concentration in the phosphorus-containing wastewater remains constant, phosphorus-free purified water and a trivalent cerium-phosphorus enriched electrode are obtained; 2) Phosphate desorption: a second electrolytic cell using a trivalent cerium-phosphorus enriched electrode as the anode for a second electrolytic treatment; after the second electrolytic treatment is completed, the circuit is disconnected; and after the phosphorus concentration in the electrolyte of the second electrolytic cell remains constant, a tetravalent cerium electrode and a phosphorus-rich recovery solution are obtained; the time for both the first and second electrolytic treatments is greater than 900 s. This method offers high process flexibility, a wide range of desorption solutions, and can achieve phosphate desorption in low-concentration desorption solutions, exhibiting high phosphate removal and recovery rates, as well as excellent cyclic adsorption-desorption performance.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to an electrochemically regulated phosphate adsorption-desorption method. Background Technology

[0002] To alleviate the water demand pressure on landscape water use, reclaimed water is gradually replacing clean water as the replenishment water for urban rivers and lakes. However, residual phosphorus in reclaimed water may exacerbate eutrophication of landscape water, causing serious ecological imbalance. Therefore, how to remove phosphorus from water bodies is an urgent problem to be solved.

[0003] Currently, some researchers have utilized the aerobic properties of polyphosphate-accumulating bacteria to adsorb phosphorus from wastewater. However, the process of using polyphosphate-accumulating bacteria to adsorb and remove phosphorus requires strict control over pH, temperature, dissolved oxygen levels, and the content of impurities in the phosphorus-containing wastewater, resulting in poor process flexibility.

[0004] The adsorption of phosphate using porous materials or porous materials loaded with active components has attracted widespread attention due to its simplicity and stable performance. Currently, the desorption and recovery of adsorbed phosphate typically involves adding an alkaline solution (desorption solution). However, this method has strict requirements on the type and concentration of the alkaline solution, and the recovery rate after desorption is low. Generally, a strong base such as sodium hydroxide or potassium hydroxide is required; specifically, a 4000 mg / L sodium hydroxide solution requires at least 6 hours to complete desorption, and the phosphate recovery rate is only 76%. Therefore, this method suffers from high desorption costs. Furthermore, the adsorbent desorbed using this method is difficult to reuse for adsorbing phosphate, resulting in poor recycling performance.

[0005] Therefore, it is of great significance to develop an adsorption and desorption method for phosphorus-containing wastewater that combines process flexibility, adsorption and desorption efficiency, and adsorption-desorption cycle performance. Summary of the Invention

[0006] This invention provides an electrochemically regulated phosphate adsorption-desorption method, which solves the problem of strict requirements on pH, temperature, dissolved oxygen levels, and impurity element content in phosphorus-containing wastewater when adsorbing and desorbing phosphate in existing technologies. At the same time, this method allows for the selection of diverse desorption solution types and can desorb phosphate in low-concentration desorption solutions. Furthermore, this method has high phosphate removal and recovery rates, as well as excellent adsorption-desorption cycle performance.

[0007] This invention provides an electrochemically regulated phosphate adsorption-desorption method, comprising:

[0008] 1) Phosphate adsorption: The first electrolytic cell is used as a first electrolytic cell with a tetravalent cerium electrode as the cathode and phosphorus-containing wastewater as the electrolyte for the first electrolytic treatment. After the first electrolytic treatment is completed, the circuit is disconnected. After the phosphate concentration in the phosphorus-containing wastewater remains unchanged, phosphorus-removed purified water and a trivalent cerium-phosphorus enrichment electrode are obtained.

[0009] 2) Phosphate desorption: A second electrolytic cell is used with the trivalent cerium-phosphorus enrichment electrode as the anode for a second electrolytic treatment. After the second electrolytic treatment is completed, the circuit is disconnected. After the phosphate concentration in the electrolyte of the second electrolytic cell remains unchanged, a tetravalent cerium electrode and a phosphorus-rich recovery solution are obtained.

[0010] The duration of both the first and second electrolytic treatments is greater than 900 seconds.

[0011] According to one embodiment of the present invention, the electrolyte concentration of the second electrolytic cell is 10-5000 mg / L.

[0012] According to one embodiment of the present invention, the electrolyte of the second electrolytic cell includes at least one of sodium chloride solution, sodium sulfate solution, sodium hydroxide solution, sulfuric acid solution, and ammonia solution.

[0013] According to one embodiment of the present invention, the voltage of the first electrolytic treatment is less than 0.32V vs. RHE.

[0014] According to one embodiment of the present invention, the time for the first electrolysis treatment is 900-1200s.

[0015] According to one embodiment of the present invention, after the first electrolysis treatment is completed, the circuit is disconnected, and the phosphorus-containing wastewater is stirred to obtain the phosphorus-removed purified water and the trivalent cerium-phosphorus enrichment electrode.

[0016] The stirring rate is 400-600 r / min, and the time is 1-6 h.

[0017] According to one embodiment of the present invention, the voltage of the second electrolysis treatment is higher than 0.43V vs. RHE.

[0018] According to one embodiment of the present invention, the second electrolysis treatment time is 900-1200s.

[0019] According to one embodiment of the present invention, after the second electrolysis treatment is completed, the solution is allowed to stand for 0.5-2 hours to obtain a phosphorus-rich recovery solution.

[0020] According to one embodiment of the present invention, before step 1), the method further includes: pretreating the phosphorus-containing wastewater;

[0021] The pretreatment includes sequentially performing flocculation and filtration treatments on the phosphorus-containing wastewater.

[0022] This invention achieves the adsorption and removal of phosphate from phosphorus-containing wastewater and its desorption and recovery by utilizing the adsorption and desorption properties of trivalent and tetravalent cerium to control the valence state of the cerium electrode to trivalent or tetravalent cerium through electrochemical regulation. The adsorption and desorption of phosphate using this method is virtually unaffected by pH, temperature, or impurities in the phosphorus-containing wastewater, offering high process flexibility. This method allows for a wide range of desorption solutions and can remove phosphate even in low-concentration solutions. Furthermore, it exhibits high phosphate removal and recovery rates and enables cyclic adsorption and desorption of phosphate. Attached Figure Description

[0023] Figure 1 These are the results of cyclic voltammetry tests on the CeO2 electrode;

[0024] Figure 2 The desorption capacity of Examples 1, 17, and Comparative Examples 2-4 varies with desorption treatment time.

[0025] Figure 3 The adsorption and desorption capacities of Example 1 after 10 cycles are shown. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides an electrochemically regulated phosphate adsorption-desorption method, comprising:

[0028] 1) Phosphate adsorption: The first electrolytic cell is used as the cathode and phosphorus-containing wastewater as the electrolyte for the first electrolytic treatment. After the first electrolytic treatment is completed, the circuit is disconnected. After the phosphate concentration in the phosphorus-containing wastewater remains unchanged, phosphorus-removed purified water and trivalent cerium-phosphorus enrichment electrode are obtained.

[0029] 2) Phosphate desorption: A second electrolytic cell is used with a trivalent cerium-phosphorus enrichment electrode as the anode for the second electrolytic treatment. After the second electrolytic treatment is completed, the circuit is disconnected. After the phosphate concentration in the electrolyte of the second electrolytic cell remains unchanged, a tetravalent cerium electrode and a phosphorus-rich recovery solution are obtained.

[0030] The time for both the first and second electrolytic treatments is greater than 900 seconds.

[0031] The aforementioned tetravalent cerium electrode refers to an electrode in which the active material includes tetravalent cerium. This invention does not limit the source of the tetravalent cerium electrode; it can be commercially available or prepared in-house. This invention also does not limit the specific type of tetravalent cerium in the tetravalent cerium electrode; for example, it can be CeO2, Ce(OH)4, CeF4, etc.

[0032] This invention does not limit the specific type of phosphorus-containing wastewater, which can be one or more of domestic sewage, electroplating wastewater, phosphating wastewater, and coal chemical wastewater.

[0033] It is understood that the second electrolytic cell includes an electrolyte, which is a desorption solution for desorbing phosphate. This invention does not limit the type of electrolyte in the second electrolytic cell, as long as it can convert trivalent cerium into tetravalent cerium.

[0034] In step 1) above, a trivalent cerium electrode is obtained after the first electrolysis treatment. During and after the first electrolysis treatment, the trivalent cerium electrode continuously adsorbs phosphates in the electrolyte.

[0035] Similarly, in step 2), after the second electrolysis treatment, the trivalent cerium electrode is transformed into a tetravalent cerium electrode again. During and after the second electrolysis treatment, the tetravalent cerium electrode continuously desorbs phosphate from the electrolyte.

[0036] Studies have shown that the above method is almost unaffected by pH, temperature, and impurities in phosphorus-containing wastewater during phosphate adsorption and desorption, and avoids the dependence on dissolved oxygen found in existing technologies, offering high process flexibility. Furthermore, this method has a wide range of desorption solutions, enabling phosphate desorption in electrolytes of the second electrolytic cell with concentrations as low as 10 mg / L. In addition, this method exhibits high phosphate removal and recovery rates for phosphorus-containing wastewater with phosphate concentrations of 10-200 mg / L. After the tetravalent cerium electrode from step 2) is reduced to a trivalent cerium electrode through the first electrolytic treatment, the trivalent cerium electrode can continue to be used for phosphate adsorption, thus allowing for further phosphate desorption. Therefore, this method also possesses excellent cyclic adsorption-desorption performance.

[0037] The inventors analyzed the reasons and believed that the method is based on electrochemical regulation. It uses a trivalent cerium electrode to adsorb phosphate ions through electrostatic adsorption and internal spherical complexation, and uses the poor adsorption performance of tetravalent cerium on phosphate to desorb phosphate. Therefore, this method can avoid dependence on the above-mentioned pH and other processes, reduce the requirements for desorption solutions, and has excellent adsorption-desorption performance and adsorption-desorption cycle performance.

[0038] It should be noted that in steps 1) and 2) above, the electrolysis time and whether the phosphate concentration changes after the circuit is disconnected are important factors affecting the phosphate adsorption and desorption effects. If the electrolysis time is too short, the adsorption and desorption effects will be poor. If the phosphate concentration changes continuously after the circuit is disconnected, it indicates that the cerium electrode is continuously undergoing adsorption and desorption, while a constant phosphate concentration indicates that the adsorption and desorption process is complete. Therefore, this invention controls the first and second electrolysis times to be greater than 900 seconds, ensuring that the phosphorus concentration in the phosphorus-containing wastewater and the electrolyte of the second electrolytic cell remains constant after the circuit is disconnected, thus achieving a phosphate removal rate and recovery rate of no less than 80%. In specific implementation, this invention determines whether adsorption or desorption is complete by monitoring the phosphorus concentration in the phosphorus-containing wastewater and the electrolyte of the second electrolytic cell.

[0039] It is understood that, in addition to the cerium electrode and electrolyte, the first and second electrolytic cells also include a counter electrode forming the circuit. This invention does not limit the type of counter electrode. The counter electrode can be a graphite sheet, Pt sheet, etc. The structure of the first and second electrolytic cells, the area of ​​the cerium electrode, the area of ​​the counter electrode, the electrode spacing, and the electrochemical testing process can all adopt conventional methods in the art. For example, the volume of both the first and second electrolytic cells can be 50 mL, and the area of ​​both the cerium electrode and the counter electrode can be 4 cm². 2 The electrode spacing is 2cm.

[0040] In the specific implementation process, the present invention obtained tetravalent cerium electrodes with electrode structure and filled three-dimensional electrode structure by self-preparation.

[0041] Taking CeO2 as an example, the tetravalent cerium electrode with an electrode structure of the present invention is prepared by the following method: a mixture of CeO2, conductive agent and binder is placed in a dispersant to form a uniform film-forming liquid, a film-forming treatment is performed to form a film sheet, and then the film sheet is pressed onto a current collector; the mass ratio of CeO2, conductive agent and binder can be (82-88):(7-13):5; the above-mentioned conductive agent, binder, dispersant and current collector can all be selected from conventional materials in the art, and can be obtained by commercial purchase or self-production. For example: the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), LA132, and LA133; the conductive agent may include at least one of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and conductive silver powder; the dispersant may include at least one of ethanol, water, N-methylpyrrolidone (NMP), dimethylformamide, acetone, and carbon dichloride; the current collector may be selected from at least one of stainless steel mesh, stainless steel sheet, nickel mesh, nickel foam, nickel sheet, titanium mesh, titanium foil, carbon felt, and carbon paper.

[0042] The tetravalent cerium electrode with a filled three-dimensional electrode structure is prepared by the following method: CeO2, activated carbon and deionized water are mixed in a mass ratio of (3-5):(4-8):20, mechanically stirred at 200-400 rpm for 8-12 min, and then placed in a reaction vessel at 160-200℃ and allowed to stand for 12-24 h. The precipitate is then separated and washed with deionized water and ethanol in sequence, and then dried and calcined in air at 300-450℃ for 2-5 h to obtain CeO2 loaded onto activated carbon. The CeO2 loaded onto activated carbon is then filled into a container to form a filled three-dimensional electrode. The container can be a stainless steel cage or conductive carbon felt, or other conventional containers in the art. For example, it can be a stainless steel cage with a width of 0.1-5 m.

[0043] When preparing the two types of tetravalent cerium electrodes mentioned above, CeO2 can be used by dissolving Ce(NO3)3·6H2O and urea separately in deionized water at a ratio of 8-12 mM / 20 mL and 1.2-1.8 g / 20 mL, respectively. After mixing at a volume ratio of 1:1, the mixture is mechanically stirred at 200-400 rpm for 8-12 min at room temperature to obtain a clear solution. The clear solution is placed in a reaction vessel and allowed to stand at 160-200℃ for 24-48 h. The precipitate is then separated, washed successively with deionized water, ethanol, and acetone, dried, and calcined in air at 300-450℃. Alternatively, Ce(NO3)3·6H2O can be dissolved in deionized water at a ratio of 5-8 mM / 100 mL, and mechanically stirred at 200-400 rpm for 8-12 min at room temperature to obtain a mixed solution. 20 mL of 0.24 M sodium oxalate solution is slowly added to the mixed solution, and mechanical stirring is continued at 200-400 rpm for 30-40 min at room temperature to obtain a suspension. The precipitate is separated and washed successively with deionized water and ethanol to obtain the final product. The final product is dried at room temperature and then calcined in air at 300-450℃ for 2-5 h to obtain the final product.

[0044] In the specific implementation process, when the concentration of the inorganic solution is controlled at 10-5000 mg / L, efficient desorption of phosphate can be achieved at low concentrations, avoiding complex post-treatment problems and secondary pollution problems caused by excessively high inorganic solution concentrations, which has certain environmental and economic significance.

[0045] In this invention, the electrolyte of the second electrolytic cell includes at least one of sodium chloride solution, sodium sulfate solution, sodium hydroxide solution, sulfuric acid solution, and ammonia solution. When the above electrolytes are used as desorption solutions, they have excellent desorption effects on phosphates, which is beneficial to improving the cycle performance of the cerium-based electrode.

[0046] Through the inventor's research, it was found that by controlling the voltage of the first electrolysis treatment to be lower than 0.32V vs. RHE, effective adsorption of phosphates can be achieved.

[0047] It is understandable that when the reduction voltage of the tetravalent cerium electrode is lower than a certain value (the upper limit of the reduction voltage), tetravalent cerium gains electrons and is gradually reduced to trivalent cerium. Therefore, the upper limit of the voltage for the first electrolytic treatment can be determined by testing the upper limit of the reduction voltage of the tetravalent cerium electrode.

[0048] This invention does not limit the method for determining the upper limit of the voltage for the first electrolytic treatment. It can be tested using conventional methods in the art. For example, it can be tested using a traditional three-electrode reaction (reaction electrode, reference electrode, counter electrode) system, where the reaction electrode is a tetravalent cerium electrode, and the reference and counter electrodes can be any commonly used electrodes. The upper limit of the reduction voltage of the tetravalent cerium electrode is obtained by subtracting the standard potential of the reference electrode from the reduction voltage.

[0049] Specifically, the above-mentioned three-electrode reaction system can be tested in a three-electrode reactor with KOH solution as the electrolyte. A CeO2 electrode is used as the reaction electrode, a Hg / HgO electrode (standard electrode potential 0.098V vs. RHE) as the reference electrode, and a platinum electrode as the counter electrode. The potential window is set to 0.3V-0.6V vs. Hg / HgO. Connected to an electrochemical workstation, the reduction voltage of the CeO2 electrode is tested using cyclic voltammetry. In the obtained cyclic voltammetric curve, the peak scanned at the cathode is the reduction peak. The voltage value corresponding to this peak minus the standard electrode potential of Hg / HgO is the upper limit of the reduction voltage of the CeO2 electrode. The area of ​​the CeO2 electrode is 1 cm². 2 The area of ​​the platinum electrode is 4 cm². 2 The electrode spacing is 2 cm, the electrolyte concentration is 3 M, and the electrolyte volume is 50 mL. The reaction equation for this process is: CeO₂ + e⁻ - +H₂O→Ce 3+ OOH+OH-.

[0050] Furthermore, when the first electrolysis treatment lasts for 900-1200 seconds, tetravalent cerium can be fully converted into trivalent cerium, which is beneficial for the efficient removal of phosphates from phosphorus-containing wastewater.

[0051] In this invention, after the first electrolysis treatment is completed, the circuit is disconnected, and the phosphorus-containing wastewater is stirred to obtain phosphorus-removed purified water and a trivalent cerium-phosphorus enrichment electrode. The stirring rate is 400-600 r / min, and the time is 5-7 h. When the stirring rate and stirring time are controlled within the above range, the phosphate in the phosphorus-containing wastewater can be rapidly and fully adsorbed by the trivalent cerium electrode, thereby obtaining phosphorus-removed purified water and a trivalent cerium-phosphorus enrichment electrode.

[0052] In specific implementation, the present invention uses ammonium molybdate spectrophotometry to monitor the concentration of phosphate in phosphorus-containing wastewater to determine the stirring time. When the concentration of phosphate no longer changes, it indicates that the trivalent cerium electrode has reached adsorption saturation.

[0053] According to the inventors' research, when the voltage of the second electrolysis treatment is greater than 0.43V vs. RHE, effective desorption of phosphate can be achieved.

[0054] When the oxidation voltage of the trivalent cerium electrode exceeds a certain value (the lower limit of the oxidation voltage), trivalent cerium loses electrons and is gradually oxidized to tetravalent cerium. Therefore, the lower limit of the second electrolytic treatment voltage can be determined by testing the oxidation voltage of the trivalent cerium electrode. This invention does not limit the method for determining the lower limit of the second electrolytic treatment voltage. Preferably, the method is the same as the method for determining the upper limit of the reduction voltage described above. Specifically, in the cyclic voltammetry curve, the peak scanned at the anode is the oxidation peak, and the voltage value corresponding to this peak plus the standard electrode potential of Hg / HgO is the lower limit of the oxidation voltage of the CeO2 electrode. When using the above method to test the lower limit of the oxidation voltage, the reaction formula is: Ce... 3+ OOH-e - +OH - →CeO2+H2O.

[0055] Further research revealed that the second electrolytic treatment time is 900-1200 s. Within this time range, trivalent cerium can be fully converted to tetravalent cerium, thereby enabling the desorption of phosphate.

[0056] In the specific implementation process, after the second electrolysis treatment is completed, the solution is allowed to stand for 0.5-2 hours to obtain a phosphorus-rich recovery solution. The tetravalent cerium-phosphorus enrichment electrode is then placed in the electrolyte of the second electrolytic cell, and the desorption time is controlled to be 0.5-2 hours to ensure that the phosphate is fully desorbed.

[0057] Before step 1), the present invention further includes: pretreatment of phosphorus-containing wastewater; the pretreatment includes sequential flocculation treatment and filtration treatment of phosphorus-containing wastewater.

[0058] Flocculation and filtration can remove solid impurities from phosphorus-containing wastewater, thus avoiding mechanical impact on the cerium electrode during adsorption or desorption processes, which would otherwise lead to electrode wear. This improves the cycling performance of the cerium electrode.

[0059] In specific implementation, flocculation treatment includes: adding flocculant to phosphorus-containing wastewater and letting it stand for 0.5 to 2 hours; the mass-to-volume ratio of flocculant to phosphorus-containing wastewater can be 0.01 to 1 g: 1 L; the flocculant includes at least one of polyaluminum chloride, polyferric chloride, polyaluminum silicate, activated silica, chitosan violet, and polyacrylamide.

[0060] The present invention will now be described in more detail through specific embodiments.

[0061] Example 1

[0062] 1) Preparation of CeO2

[0063] 10 mM Ce(NO3)3·6H2O and 1.5 g urea were dissolved in 20 mL of deionized water, then mixed and stirred at 400 rpm for 10 minutes before being transferred to a reaction vessel. The reaction vessel was placed in an oven at 160 °C for 24 h. The precipitate was then separated and washed with deionized water, ethanol and acetone in sequence. After drying and calcination in air at 300 °C for 3 h, CeO2 was obtained.

[0064] 2) Preparation of CeO2 electrode

[0065] The CeO2, conductive carbon black and PTFE emulsion (10wt%) prepared above were mixed in a mass ratio of 8:1:1. After adding 3mL of anhydrous ethanol, the mixture was ultrasonically stirred for 15min, and then 2mL of anhydrous ethanol was added and ultrasonically stirred again for 60min to make the PTFE and CeO2 evenly dispersed. The mixture was stirred continuously until it fibrousized and formed a lumpy paste. The paste was rolled into a 1mm thick film at 80℃ using a film press and rolled onto a titanium mesh (80-120 mesh) current collector. After drying in an oven at 80℃ for 2h, the CeO2 electrode (CeO2 electrode sheet) was obtained.

[0066] 3) Determination of redox potential

[0067] Using a CeO2 electrode as the reaction electrode, the reaction electrode area is 1 cm². 2 The Hg / HgO electrode serves as the reference electrode, and the platinum electrode as the counter electrode, with a counter electrode area of ​​4 cm². 2 The electrode spacing was 2 cm, and 3M KOH solution was used as the electrolyte. The electrolyte volume was 50 mL, and the potential window was 0.3 V–0.6 V vs. Hg / HgO. The redox voltage of the CeO2 electrode was measured using an electrochemical workstation (CHI660E). The cyclic voltammetry (CV) results are shown below. Figure 1 .

[0068] according to Figure 1 It can be seen that the reduction voltage of CeO2 is 0.42V vs. Hg / HgO, and the oxidation voltage of trivalent cerium is 0.52V vs. Hg / HgO. Through potential conversion, the upper limit of the reduction voltage for tetravalent cerium to be reduced to trivalent cerium is 0.32V vs. RHE, and the lower limit of the oxidation voltage for trivalent cerium to be oxidized to tetravalent cerium is 0.43V vs. RHE.

[0069] 4) Adsorption of phosphates in phosphorus-containing wastewater

[0070] A phosphate solution with a concentration of 30 mg / L was prepared to represent phosphorus-containing wastewater (pH 6.5) with a COD of 12 mg / L;

[0071] At 25℃, in an 80mL first electrolytic cell, a CeO2 electrode was used as the cathode, and phosphorus-containing wastewater was used as the electrolyte. The electrode area was 4cm². 2 The counter electrode is a graphite sheet electrode with a counter electrode area of ​​4 cm². 2 The electrode spacing is 2 cm; the electrolyte is 50 mL of phosphorus-containing wastewater; the first electrolysis treatment is performed by connecting to a power source.

[0072] The voltage for the first electrolysis treatment is -0.6V, and the treatment time is 900s.

[0073] After the first electrolysis treatment is completed, the circuit is disconnected and the phosphorus-containing wastewater is stirred at a speed of 400 r / min for 6 hours. The phosphorus concentration in the phosphorus-containing wastewater remains unchanged, and phosphorus-removed purified water and trivalent cerium-phosphorus enrichment electrode are obtained.

[0074] 5) Desorption of phosphates from phosphorus-containing wastewater

[0075] At 25℃, in an 80mL second electrolytic cell, a trivalent cerium-phosphorus enriched electrode was used as the anode, and 50mL of a 100mg / L sodium chloride solution (pH 7.1) was used as the electrolyte. The electrode area was 4cm². 2 The counter electrode is a graphite sheet electrode with a counter electrode area of ​​4 cm². 2 The electrode spacing is 2 cm; a second electrolytic treatment is performed by connecting a power source to obtain a tetravalent cerium-phosphorus enriched electrode.

[0076] The voltage for the second electrolysis treatment is +0.6V, and the treatment time is 900s.

[0077] After the second electrolysis process is completed, the circuit is disconnected and the solution is left to stand for 1 hour to keep the phosphorus concentration in the sodium chloride solution constant, thus obtaining a tetravalent cerium electrode and a phosphorus-rich recovery solution.

[0078] Example 2

[0079] The difference between this embodiment and Embodiment 1 is that:

[0080] CeO2 in step 1) is prepared by the following method

[0081] Ce(NO3)3·6H2O was dissolved in deionized water at a ratio of 6 mM / 100 mL. The mixture was mechanically stirred at 400 rpm for 10 min to obtain a mixed solution. 20 mL of 0.24 M sodium oxalate solution was slowly added to the mixed solution, and the mixture was mechanically stirred at 400 rpm for 30 min at room temperature to obtain a suspension. The precipitate was separated and washed with deionized water and ethanol in sequence to obtain the final product. The final product was dried at room temperature and then calcined in air at 400 °C for 3 h to obtain CeO2.

[0082] The CeO2 electrode in step 2) is prepared by the following method.

[0083] CeO2, activated carbon, and deionized water were mixed in a mass ratio of 5:5:20 and mechanically stirred at 400 rpm for 10 min. The mixture was then placed in a reactor at 160 °C and allowed to stand for 24 h. The precipitate was then separated and washed with deionized water and ethanol in sequence. After drying, the mixture was calcined in air at 350 °C for 2 h to obtain CeO2 loaded onto activated carbon. The CeO2 loaded onto activated carbon was then filled into a stainless steel cage to form a CeO2 electrode (filled three-dimensional electrode).

[0084] In step 4), a phosphate solution with a concentration of 180 mg / L is prepared to represent phosphorus-containing wastewater (pH 5.2);

[0085] The voltage for the first electrolysis treatment was 0.32V, and the time for the first electrolysis treatment was 1200s;

[0086] After the first electrolysis treatment is completed, the circuit is disconnected and the phosphorus-containing wastewater is stirred at a speed of 400 r / min for 6 hours. The phosphorus concentration in the phosphorus-containing wastewater remains unchanged, and phosphorus-removed purified water and trivalent cerium-phosphorus enrichment electrode are obtained.

[0087] In step 5), the electrolyte for the second electrolysis treatment is a sodium sulfate solution (pH 7.3) with a concentration of 100 mg / L, the voltage for the second electrolysis treatment is +0.6 V, and the time for the second electrolysis treatment is 900 s.

[0088] After the second electrolysis process is completed, the circuit is disconnected and the solution is left to stand for 1 hour to keep the phosphorus concentration in the sodium sulfate solution constant, thus obtaining a tetravalent cerium electrode and a phosphorus-rich recovery solution.

[0089] Example 3

[0090] The difference between this embodiment and Embodiment 1 is that: flocculant is added to the landscape wastewater to treat the landscape water body by flocculation, and the mixture is left to stand for 0.5 to 2 hours; the mass-volume ratio of flocculant to phosphorus-containing wastewater is 0.05 g: 1 L; and the flocculant is polyaluminum chloride.

[0091] Replace the phosphate solution in step 1) with a phosphorus-containing landscape water body. The phosphorus-containing landscape water body has a phosphate concentration of 27.7 mg / L, a nitrate concentration of 19.1 mg / L, a sulfate concentration of 79.5 mg / L, a pH of 6.9, and a COD of 179.6.

[0092] Example 4

[0093] The difference between this embodiment and Embodiment 1 is that the pH of the phosphorus-containing wastewater is adjusted to 2 by adding 1M HCl solution.

[0094] Example 5

[0095] The difference between this embodiment and Embodiment 1 is that the pH of the phosphorus-containing wastewater is adjusted to 11 by adding 1M NaOH solution.

[0096] Example 6

[0097] The difference between this embodiment and Embodiment 1 is that: at 10°C, the phosphorus-containing wastewater is stirred at a speed of 400 r / min for 6 hours to keep the phosphorus concentration in the wastewater constant, thereby obtaining phosphorus-removed purified water and a trivalent cerium-phosphorus enrichment electrode.

[0098] Example 7

[0099] The difference between this embodiment and Embodiment 1 is that: at 37°C, the phosphorus-containing wastewater is stirred at a speed of 400 r / min for 6 hours to keep the phosphorus concentration in the wastewater constant, thereby obtaining phosphorus-removed purified water and a trivalent cerium-phosphorus enrichment electrode.

[0100] Example 8

[0101] The difference between this embodiment and Embodiment 1 is that the voltage of the first electrolysis treatment is -2.0V vs. RHE.

[0102] Example 9

[0103] The difference between this embodiment and Embodiment 1 is that the electrolyte used in the second electrolysis treatment is a sodium hydroxide solution (pH 11.4).

[0104] Example 10

[0105] The difference between this embodiment and Embodiment 1 is that the electrolyte used in the second electrolysis treatment is an ammonia solution (pH 9.3).

[0106] Example 11

[0107] The difference between this embodiment and Embodiment 1 is that the electrolyte used in the second electrolysis treatment is a sulfuric acid solution (pH 3.9).

[0108] Example 12

[0109] The difference between this Example 1 and Example 1 is that the pH of the sodium chloride solution is adjusted to 3 by adding 1M HCl.

[0110] Example 13

[0111] The difference between this Example 1 and Example 1 is that the pH of the sodium chloride solution is adjusted to 5 by adding 1M HCl.

[0112] Example 14

[0113] The difference between this Example 1 and Example 1 is that the pH of the sodium chloride solution is adjusted to 7 by adding 1M NaOH.

[0114] Example 15

[0115] The difference between this Example 1 and Example 1 is that the pH of the sodium chloride solution is adjusted to 9 by adding 1M NaOH.

[0116] Example 16

[0117] The difference between this Example 1 and Example 1 is that the pH of the sodium chloride solution is adjusted to 11 by adding 1M NaOH.

[0118] Example 17

[0119] The difference between this embodiment and Embodiment 1 is that the second electrolysis treatment time is 1200s.

[0120] Example 18

[0121] The difference between this embodiment and Embodiment 1 is that 50 mL of a sodium chloride solution with a concentration of 10 mg / L (pH 7.6) is used as the electrolyte.

[0122] Comparative Example 1

[0123] The difference between this comparative example and Example 1 is that the first electrolysis treatment is not performed; instead, the phosphate in the phosphorus-containing wastewater is directly adsorbed using a cerium dioxide electrode.

[0124] Comparative Example 2

[0125] The difference between this comparative example and Example 1 is that the second electrolysis treatment time is 300s.

[0126] Comparative Example 3

[0127] The difference between this comparative example and Example 1 is that the second electrolysis treatment time is 600s.

[0128] Comparative Example 4

[0129] The difference between this comparative example and Example 1 is that: no second electrolysis treatment is performed (the second electrolysis treatment time is 0s), and the trivalent cerium-phosphorus enrichment electrode is directly placed in 50mL of sodium chloride solution with a concentration of 100mg / L for phosphate desorption. The desorption treatment (the phosphorus concentration in the sodium chloride solution remains unchanged) takes 1h.

[0130] Comparative Example 5

[0131] The difference between this comparative example and Example 11 is that: no second electrolysis treatment is performed, and the trivalent cerium-phosphorus enrichment electrode is directly placed in 50 mL of sodium hydroxide solution with a concentration of 100 mg / L for phosphate desorption. The desorption treatment (with the phosphorus concentration in the sodium hydroxide solution remaining unchanged) takes 6 hours.

[0132] Comparative Example 6

[0133] The difference between this comparative example and Example 11 is that: no second electrolysis treatment is performed, and the trivalent cerium-phosphorus enrichment electrode is directly placed in 50 mL of sodium hydroxide solution with a concentration of 4000 mg / L for phosphate desorption. The desorption treatment (with the phosphorus concentration in the sodium hydroxide solution remaining unchanged) takes 3 hours.

[0134] Experimental Example 1

[0135] The phosphate concentration in phosphorus-containing wastewater during the adsorption and desorption of phosphate in Examples 1-18 and Comparative Examples 1-6 of this invention was determined using an ammonium molybdate spectrophotometer. The phosphate removal rate, phosphate adsorption capacity of the trivalent cerium electrode, phosphate desorption capacity of the tetravalent cerium-phosphorus enrichment electrode, and phosphate recovery rate in the phosphorus-containing wastewater were calculated using the following formulas. The results are shown in Table 1. The desorption capacity of Examples 1 (second electrolysis treatment time 900s), 17 (second electrolysis treatment time 1200s), 2 (second electrolysis treatment time 300s), 3 (second electrolysis treatment time 600s), and 4 (second electrolysis treatment time 0s) as a function of desorption treatment time is shown in Table 1. Figure 2 As shown.

[0136]

[0137]

[0138]

[0139] W2(%) = Q2 / Q1;

[0140] In the formula, Q1 is the adsorption capacity of phosphate per gram of cerium-based electrode, in mg / g; C0 is the initial concentration of phosphate in the phosphorus-containing wastewater, in mg / L; C1 is the concentration of phosphate in the phosphorus-containing wastewater after adsorption, in mg / L; V1 is the volume of the phosphorus-containing wastewater, in L; and m is the mass of the cerium dioxide electrode, in g.

[0141] Q2 is the phosphate desorption capacity per gram of cerium-based electrode, in mg / g; C2 is the phosphate concentration in the phosphorus-rich recovery solution after phosphate desorption, in mg / L; V2 is the volume of the inorganic solution, in L.

[0142] W1 represents the phosphate removal rate in phosphorus-containing wastewater; W2 represents the phosphate recovery rate.

[0143] Table 1

[0144]

[0145]

[0146] As shown in Table 1, compared with Comparative Examples 1-6, all embodiments of the present invention exhibit superior adsorption-desorption effects. This indicates that the cerium-based electrode based on electrochemical regulation has significant advantages in adsorbing phosphates, and that efficient adsorption and desorption of phosphates can be achieved by controlling the electrolysis time.

[0147] Examples 1, 3-7, and 12-16 all exhibit high adsorption capacity, desorption capacity, phosphate removal rate, and recovery rate. This indicates that even when there are impurities in the phosphorus-containing wastewater, pH changes, temperature changes, or changes in the pH of the inorganic solution, the cerium-based electrode still has excellent adsorption and desorption effects on phosphate. Therefore, the method of the present invention is almost unaffected by impurities, pH, and temperature, and has high process flexibility.

[0148] Compared to Examples 1 and 17, Comparative Examples 2 and 3 showed poorer desorption effects. This indicates that the voltage of the first electrolysis treatment, the voltage of the second electrolysis treatment, and the time are important factors affecting the adsorption and desorption effects.

[0149] Based on Examples 1, 9, and Comparative Examples 4-6, it is evident that the trivalent cerium-phosphorus enrichment electrode without a second electrolytic treatment requires a high concentration of inorganic solution, has a long desorption time, and a small desorption capacity during desorption (Comparative Examples 4-6). However, by electrochemically controlling the desorption of phosphate (Examples 1 and 9), the process can be carried out at a lower concentration, with a high phosphate recovery rate and a short desorption time. This helps reduce costs and minimizes secondary pollution caused by high inorganic solution concentrations.

[0150] Furthermore, Example 18 demonstrates that the present invention can achieve efficient desorption of phosphates when the electrolyte (desorption solution) concentration is as low as 10 mg / L, which helps to reduce desorption costs and reduce secondary pollution.

[0151] according to Figure 2 It can be seen that the recovery rate of phosphate in sodium chloride solution by the trivalent cerium-phosphorus enrichment electrode without the second electrolysis treatment is extremely low and can be ignored; however, after the second electrolysis treatment, the desorption capacity is significantly improved, and the desorption capacity shows a trend of first increasing and then stabilizing as the second electrolysis treatment time is extended.

[0152] Experimental Example 2

[0153] The tetravalent cerium electrode obtained after the second electrolytic treatment was subjected to a first electrolytic treatment again to obtain a trivalent cerium electrode; the adsorption-desorption cycle was considered as one cycle; the adsorption and desorption cycle performance of Example 1 was characterized by testing the adsorption and desorption capacities after 10 cycles. The results are shown below. Figure 3 .

[0154] The results show that, after 10 cycles, the adsorption capacity of the cerium-based electrode is more than 79% of the first adsorption capacity, and the desorption capacity is still more than 80% of the first desorption capacity. This indicates that the cerium-based electrode of the present invention has excellent adsorption-desorption cycle stability for phosphate in phosphorus-containing wastewater.

[0155] Experimental Example 3

[0156] The cerium-based electrodes of Examples 1, 3, 9 and Comparative Example 6 were tested for phosphate removal rate, adsorption capacity, desorption capacity and phosphate recovery rate in phosphorus-containing wastewater after 3 cycles. The results are shown in Table 2.

[0157] Table 2

[0158]

[0159]

[0160] As shown in Table 2, the methods of Examples 1, 3, and 9 of the present invention still have a high adsorption capacity for phosphate in phosphorus-containing wastewater after three cycles. This indicates that the selection of different inorganic solutions for phosphate desorption, the presence or absence of impurities in the phosphorus-containing wastewater, and the type of electrolyte used in the desorption process do not affect the stability of the adsorption and desorption effects.

[0161] Compared to Example 9, the desorption capacity and phosphate adsorption capacity of the cerium-based electrode in Comparative Example 6 decreased sharply after three cycles, rapidly dropping from 61.5 mg / g to 44.7 mg / g. The corresponding desorption capacity decreased from 46.8 mg / g to 20.1 mg / g, and the recovery rate also decreased significantly. This is likely because the high concentration of hydroxide ions occupied the adsorption sites of cerium oxide, leading to a rapid decline in the adsorption capacity of the cerium-based electrode when it cyclically adsorbed phosphate from phosphorus-containing wastewater. In contrast, the method in Example 9 showed a phosphate adsorption capacity decline rate of less than 5% after three cycles, and the phosphate recovery rate remained almost unchanged (98.1%, 97.7%, and 97.1%, respectively). This indicates that a second electrolytic treatment is an effective way to achieve efficient desorption and is key to the excellent cycling performance of the cerium-based electrode of this invention.

[0162] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention have been clearly and completely described above in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

Claims

1. A phosphate adsorption-desorption method based on electrochemical regulation, characterized in that, include: 1) Phosphate adsorption: The first electrolytic cell is used as a first electrolytic cell with a tetravalent cerium electrode as the cathode and phosphorus-containing wastewater as the electrolyte for the first electrolytic treatment. After the first electrolytic treatment is completed, the circuit is disconnected. After the phosphate concentration in the phosphorus-containing wastewater remains unchanged, phosphorus-removed purified water and a trivalent cerium-phosphorus enrichment electrode are obtained. 2) Phosphate desorption: A second electrolytic cell is used with the trivalent cerium-phosphorus enrichment electrode as the anode for a second electrolytic treatment. After the second electrolytic treatment is completed, the circuit is disconnected. After the phosphate concentration in the electrolyte of the second electrolytic cell remains unchanged, a tetravalent cerium electrode and a phosphorus-rich recovery solution are obtained. The voltage of the first electrolytic treatment is less than 0.32V vs. RHE; The voltage of the second electrolysis treatment is greater than 0.43V vs. RHE; the time of the first electrolysis treatment and the time of the second electrolysis treatment are both 900-1200s.

2. The method according to claim 1, characterized in that, The electrolyte concentration in the second electrolytic cell is 10-5000 mg / L.

3. The method according to claim 1, characterized in that, The electrolyte in the second electrolytic cell includes any one of sodium chloride solution, sodium sulfate solution, sodium hydroxide solution, sulfuric acid solution, and ammonia solution.

4. The method according to claim 1, characterized in that, After the first electrolysis treatment is completed, the circuit is disconnected, and the phosphorus-containing wastewater is stirred to obtain the phosphorus-removed purified water and the trivalent cerium-phosphorus enrichment electrode. The stirring rate is 400-600 r / min, and the time is 1-6 h.

5. The method according to claim 1, characterized in that, After the second electrolysis treatment is completed, let it stand for 0.5-2 hours to obtain a phosphorus-rich recovery solution.

6. The method according to claim 1, characterized in that, Before step 1), the process also includes: pretreatment of the phosphorus-containing wastewater; The pretreatment includes sequentially performing flocculation and filtration treatments on the phosphorus-containing wastewater.

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