A method for recovering potassium dihydrogen phosphate by using a capacitive deionization technique

Abstract

This invention belongs to the field of wastewater treatment and recycling technology, and more specifically relates to a method for recovering potassium dihydrogen phosphate using capacitive deionization technology. The invention prepares a potassium ion selective electrode using a mixture of 18-crown ether-6, tetraethyl orthosilicate, silane coupling agent, and activated carbon powder as active ingredients, and a dihydrogen phosphate ion selective electrode using a mixture of polyacrylic acid, polyaniline, and activated carbon powder as active ingredients. The potassium ion selective electrode serves as the cathode, and the dihydrogen phosphate ion selective electrode serves as the anode. Capacitive deionization technology is used to recover dihydrogen phosphate and potassium ions from urinary wastewater. Solid potassium dihydrogen phosphate is recovered through evaporation concentration followed by cooling crystallization, achieving a purity of 94.93% (±0.16%), which meets the standards for fertilizer-grade potassium dihydrogen phosphate.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and recycling technology, and more specifically relates to a method for recovering potassium dihydrogen phosphate using capacitive deionization technology. Background Technology

[0002] Urine wastewater is a typical high-salt, high-nitrogen wastewater, characterized by large quantities and complex composition, exhibiting significant variations depending on the population and region. As a significant component of sewage, it is typically treated directly at wastewater treatment plants. Although urine only accounts for about 1% of the total wastewater in treatment plants, it contains approximately 80% of the nitrogen, 50% of the phosphorus, and 60% of the potassium. Furthermore, urine, as a potential fertilizer with high nutritional value, is usually discharged directly into sewers, where it hydrolyzes and precipitates, causing significant problems for wastewater treatment and wasting resources. Modern public facilities widely incorporate waterless toilets and source separation devices. Therefore, utilizing technologies to recover nitrogen and phosphorus from urine in these facilities can not only reduce the load on end-of-pipe wastewater treatment plants but also facilitate the timely recovery of fertilizer resources.

[0003] Common technologies for the resource recovery of urine wastewater include concentration and dewatering, membrane technology, and electrochemical technology. For phosphorus treatment, wastewater treatment plants typically combine chemical precipitation and biological phosphorus removal; however, traditional treatment technologies may be insufficient for future phosphorus resource recovery. Current phosphorus recovery technologies include adsorption, electrochemical technology, and struvite precipitation. For potassium treatment, commercial potash fertilizer production technologies generally include shaft mining and solution mining of salt deposits, as well as extraction from brine / seawater, primarily employing membrane technology, stripping absorption, and chemical precipitation.

[0004] Electrodeionization (CDI) is a novel technology for seawater desalination and wastewater treatment. It removes ions from water under atmospheric pressure by applying a low voltage between the anode and cathode using a power source. The CDI principle primarily relies on the formation of an electrical double layer (EDL). There are two common CDI cell structures: a flow-through mode where the solution flows between parallel electrodes and a cross-flow mode where the solution flows through the electrodes. Therefore, as ions in the solution are absorbed by both electrodes, the ion concentration in the wastewater gradually decreases. After the electroadsorption process, ion desorption is achieved by reversing the electrode polarity or short-circuiting the DC power supply, while simultaneously allowing the solution to flow between the electrodes. Current research on capacitive deionization technology mainly includes classical capacitive deionization (CDI), hybrid capacitive deionization (HCDI), flow capacitive deionization (FCDI), and membrane capacitive deionization (MCDI).

[0005] Classical capacitive deionization (CDI) technology has a relatively simple structure, requiring only cathode and cation electrodes in the adsorption cell. Traditional CDI systems typically include end plates, gaskets, a pair of porous electrodes, adsorbent material, and a separator. The adsorbent material is usually carbon-based, such as activated carbon. Due to the inherent electrical resistance of carbon materials, current CDI technology is mainly used for low-concentration salt solutions, and it is difficult to handle high-concentration salt solutions. Furthermore, activated carbon generally lacks ion selectivity, requiring material modification or coupling with other technologies. HCDI combines the principles of capacitive deionization with other ion exchange processes. Compared to traditional seawater desalination technologies such as reverse osmosis and distillation, HCDI's main advantages are lower energy consumption, less fouling, and lower maintenance costs. However, the probability of electrode corrosion is higher during charging and discharging in HCDI systems, significantly shortening their lifespan and necessitating timely electrode material replacement. Therefore, the stability of HCDI systems is generally lower than that of traditional carbon-based CDI systems. The reduced stability of the capacitive electrodes and the higher cost of the electrode materials themselves both lead to increased operating costs. FCDI uses a flowing electrode slurry instead of a conventional solid carbon electrode, primarily to overcome the limitations of low adsorption capacity in traditional fixed-electrode CDI systems. Flowing electrodes have different operating modes, such as isolated closed-loop circulation, short-circuit closed-loop circulation, and single-loop circulation. While FCDI technology overcomes the adsorption saturation limitation of fixed electrodes, this type of electrode has higher energy consumption and may experience problems such as electrode slurry blockage and decreased selectivity under long-term operation. MCDI is a seawater desalination technology that combines the principles of CDI and membrane technology. Selective ion exchange membranes are placed on two porous electrodes. Compared to traditional CDI, MCDI systems improve charging efficiency by preventing the repulsion of co-ions near the electrodes. The membrane prevents ions with opposite charges from reaching the electrodes, eliminating concerns about additional adsorption on the electrodes. It is less affected by organic pollutants and reduces corrosion of the electrodes by fouling, so its performance is not as easily affected or degraded as that of traditional CDI systems. However, compared to single carbon electrode materials, ion exchange membranes are more expensive, and their inherent resistance is higher. When attached to the electrodes, this resistance increases further, thus affecting the desalination efficiency of MCDI. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recovering potassium dihydrogen phosphate using capacitive deionization technology, and more specifically, to provide a capacitive deionization electrode for selectively recovering potassium ions and a capacitive deionization electrode for selectively recovering dihydrogen phosphate ions, so as to solve the problems existing in the prior art and realize the recovery of potassium dihydrogen phosphate from high-salt and high-nitrogen wastewater.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] One of the technical solutions of the present invention is to provide a capacitive deionization electrode modification material for selectively recovering potassium dihydrogen phosphate, wherein the capacitive deionization electrode modification material comprises an ion-selective functional material and activated carbon;

[0009] The ion-selective functional material includes 18-crown ether-6 and a crosslinking agent, or polyacrylic acid (PAA) and polyaniline (PANI);

[0010] The crosslinking agents include silane coupling agent KH550 (APTES) and tetraethyl orthosilicate (TEOS).

[0011] Furthermore, the volume ratio of the silane coupling agent KH550 to tetraethyl orthosilicate is 1:4.

[0012] Furthermore, when the ion-selective functional material is 18-crown ether-6 and a crosslinking agent, the volume ratio of 18-crown ether-6 to the crosslinking agent is 2:1; and the mass ratio of the ion-selective functional material to activated carbon is 1:(3-4).

[0013] Furthermore, when the ion-selective functional material is polyacrylic acid and polyaniline, the mass ratio of polyacrylic acid, polyaniline and activated carbon is 2:1:(3-4).

[0014] The second technical solution of this invention provides a method for preparing the above-mentioned capacitive deionization electrode modification material for selective recovery of potassium dihydrogen phosphate. When the ion-selective functional material is 18-crown ether-6 and a crosslinking agent, the preparation steps include:

[0015] Silane coupling agent KH550 and tetraethyl orthosilicate were dissolved in ethanol as crosslinking agents, and then 18-crown ether-6 and potassium chloride were added. After stirring and elution, ion-selective functional materials (imprinted polymers) were obtained.

[0016] The ion-selective functional material and activated carbon were mixed evenly to obtain a capacitor deionization electrode modification material that selectively recovers potassium ions.

[0017] When the ion-selective functional material is polyacrylic acid and polyaniline, the preparation steps include:

[0018] Polyacrylic acid and polyaniline were dispersed in water and stirred. Activated carbon was then added, stirred evenly, and dried to obtain a capacitor deionization electrode modification material that selectively recovers dihydrogen phosphate ions.

[0019] Furthermore, the volume ratio of ethanol to crosslinking agent is 40:1.

[0020] Furthermore, the ratio of 18-crown ether-6 to potassium chloride is 2 mL: 8 mg.

[0021] Furthermore, the elution is performed at least once using 1M hydrochloric acid.

[0022] Furthermore, the mass ratio of the polyacrylic acid, polyaniline, and water is 2:1:200.

[0023] The third technical solution of the present invention provides a capacitive deionization electrode for selectively recovering potassium ions, wherein the active component of the capacitive deionization electrode includes the above-mentioned capacitive deionization electrode modification material for selectively recovering potassium dihydrogen phosphate.

[0024] The ion-selective functional material in the capacitive deion electrode modification material for selective recovery of potassium dihydrogen phosphate is 18-crown ether-6 and a crosslinking agent;

[0025] The crosslinking agent includes silane coupling agent KH550 and tetraethyl orthosilicate.

[0026] Crown ethers can form stable complexes by coordinating with alkali metal ions, thereby creating specific cavity sizes within the crown ether and enabling selective separation of different ions. 18-crown ether-6 is mixed with potassium ions, and after elution, imprint sites are left. The crown ether is then loaded onto activated carbon using the crosslinking agent tetraethyl orthosilicate (TEOS) and the silane coupling agent KH550 (APTES).

[0027] The fourth technical solution of the present invention provides a capacitive deionization electrode for selectively recovering potassium dihydrogen phosphate ions, wherein the active component of the capacitive deionization electrode includes the above-mentioned capacitive deionization electrode modification material for selectively recovering potassium dihydrogen phosphate.

[0028] The ion-selective functional materials in the capacitive deionization electrode modification material for selective recovery of potassium dihydrogen phosphate are polyacrylic acid (PAA) and polyaniline (PANI).

[0029] In a neutral pH environment, phosphates in water generally exist in the form of dihydrogen phosphate ions. Under the influence of an electric field, dihydrogen phosphate ions move to the electrode surface, and the carboxyl functional groups on the electrode surface selectively bind to dihydrogen phosphate ions through hydrogen bonds at the neutral pH of the solution.

[0030] The fifth technical solution of the present invention provides an application of the above-mentioned capacitive deionization electrode for selectively recovering potassium ions or the above-mentioned capacitive deionization electrode for selectively recovering dihydrogen phosphate ions in the recovery of potassium dihydrogen phosphate from high-salt and high-nitrogen wastewater.

[0031] The sixth technical solution of the present invention provides an electrochemical device for selectively recovering potassium dihydrogen phosphate, wherein the cathode of the electrochemical device is the above-mentioned capacitive deionization electrode for selectively recovering potassium ions, and the anode is the above-mentioned capacitive deionization electrode for selectively recovering dihydrogen phosphate ions.

[0032] The seventh technical solution of the present invention provides a method for recovering potassium dihydrogen phosphate using capacitive deionization technology. The method uses the electrochemical device for selective recovery of potassium dihydrogen phosphate as a capacitive deionization device to selectively adsorb potassium ions and dihydrogen phosphate ions. Then, after desorption, evaporation and concentration, and cooling and crystallization, potassium dihydrogen phosphate is recovered.

[0033] Furthermore, the positive and negative electrode voltages of the capacitor deionization device are 0.8-2.0V, the influent flow rate is 10mL / min, the electrode spacing is 1.5mm, the electro-adsorption time is 60min, and the desorption time is 40min.

[0034] Optionally, the desorption is performed by simultaneously introducing pure water through reverse polarity, releasing potassium ions and dihydrogen phosphate ions into the pure water.

[0035] Furthermore, the evaporation and concentration temperature is 100°C.

[0036] Furthermore, the cooling crystallization temperature is 30°C.

[0037] The present invention discloses the following technical effects:

[0038] This invention prepares a potassium ion selective electrode by mixing 18-crown ether-6, tetraethyl orthosilicate, silane coupling agent, and activated carbon powder as active ingredients, and a dihydrogen phosphate ion selective electrode by mixing polyacrylic acid, polyaniline, and activated carbon powder as active ingredients. The potassium ion selective electrode serves as the cathode, and the dihydrogen phosphate ion selective electrode serves as the anode. Capacitive deionization technology is used to recover dihydrogen phosphate and potassium ions from urinary wastewater. Solid potassium dihydrogen phosphate is recovered through evaporation concentration-cooling crystallization, with a purity of 94.93% (±0.16%), meeting the qualified product standard for fertilizer-grade potassium dihydrogen phosphate. Attached Figure Description

[0039] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0040] Figure 1 The images show the FTIR spectra of the K-IIP electrode and the C electrode.

[0041] Figure 2 The images show the FTIR spectra of the PPC electrode and the C electrode.

[0042] Figure 3 The CV curve is for the K-IIP electrode.

[0043] Figure 4 The CV curve is for the PPC electrode.

[0044] Figure 5 The CV curve is for the C electrode.

[0045] Figure 6 The changes in the electroadsorption of potassium ions by the K-IIP electrode and the C electrode under different voltage conditions are shown.

[0046] Figure 7 The electroadsorption changes of dihydrogen phosphate ions on the PPC and C electrodes under different voltage conditions are shown.

[0047] Figure 8 The graph shows the selectivity results of the K-IIP electrode and the C electrode for potassium ions.

[0048] Figure 9 The results show the selectivity of the PPC electrode and the C electrode for dihydrogen phosphate ions.

[0049] Figure 10 The recovery amount of potassium dihydrogen phosphate at different electroadsorption times is shown.

[0050] Figure 11 The purity of potassium dihydrogen phosphate solid recovered under different electroadsorption times is shown. Detailed Implementation

[0051] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0052] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0053] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0054] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0055] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0056] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0057] Unless otherwise specified, the room temperature and ambient temperature involved in the specific embodiments of the present invention are 25±2℃.

[0058] In the specific embodiments of this invention, all raw materials and reagents used are commercially available products. Among them, polyacrylic acid is analytical grade, polyaniline is analytical grade, and activated carbon has a particle size of 200 mesh.

[0059] Example 1

[0060] The preparation steps of the capacitive deionization electrode modification material for selective potassium ion recovery include:

[0061] 0.8 mL of tetraethyl orthosilicate (TEOS) and 0.2 mL of silane coupling agent KH550 (APTES) were uniformly mixed in 40 mL of anhydrous ethanol. Then, 2 mL of 18-crown ether-6 and 8 mg of potassium chloride were added. The resulting mixture was stirred for 9 hours at room temperature in a sealed environment. Potassium chloride was removed by elution three times with 1 M hydrochloric acid to obtain an ion-selective functional material. The obtained ion-selective functional material was then mixed with activated carbon powder at a mass ratio of 1:3 and stirred for 2 hours to obtain a capacitor deionization electrode modification material that selectively recovers potassium ions.

[0062] Example 2

[0063] The preparation steps of the capacitive deionization electrode modification material for selectively recovering dihydrogen phosphate ions include:

[0064] 0.2 g of polyacrylic acid (PAA) and 0.1 g of polyaniline (PANI) were mixed in 20 mL of distilled water and stirred at 55 °C for 4 hours. Then, 0.3 g of activated carbon powder was added and the mixture was stirred for another 2 hours. After drying, a capacitor deionization electrode modification material that selectively recovers dihydrogen phosphate ions was obtained.

[0065] Example 3

[0066] The preparation steps of the capacitive deionization electrode for selective potassium ion recovery include:

[0067] Weigh 0.8 g of the selective potassium ion recovery capacitive deionization electrode modification material prepared in Example 1, along with 0.1 g of conductive agent (graphite powder) and 0.1 g of binder (polyvinylidene fluoride PVDF). Dissolve the binder in 5 mL of dimethylacetamide (DMAC) solution, then add the selective potassium ion recovery capacitive deionization electrode modification material and conductive agent. Stir and mix on a magnetic stirrer for 2 hours, then uniformly coat the mixture onto the surface of a titanium electrode (coating amount is 8 mg / cm² based on the capacitive deionization electrode modification material). 2 The electrode is placed in a constant temperature oven at 60℃ and dried for 6 hours to obtain a capacitive deionization electrode (potassium ion imprinted polymer coating working electrode) that selectively recovers potassium ions, denoted as K-IIP electrode.

[0068] Example 4

[0069] The preparation steps of the capacitive deionization electrode for selectively recovering dihydrogen phosphate ions include:

[0070] Weigh 0.8 g of the selectively recoverable dihydrogen phosphate (DH2) ion-recycling capacitive deionization electrode modification material prepared in Example 2, along with 0.1 g of conductive agent (graphite powder) and 0.1 g of binder (polyvinylidene fluoride PVDF). Dissolve the binder in 5 mL of dimethylacetamide (DMAC) solution, then add the selectively recoverable DH2 ion-recycling capacitive deionization electrode modification material and conductive agent. Stir and mix on a magnetic stirrer for 2 hours, then uniformly coat the mixture onto the surface of a titanium electrode (coating amount is 8 mg / cm³ based on the capacitive deionization electrode modification material). 2 The electrode was placed in a constant temperature oven at 60°C and dried for 6 hours to obtain a capacitive deionization electrode (PAA-PANI polymer-coated working electrode) that selectively recovers dihydrogen phosphate ions, denoted as PPC electrode.

[0071] Comparative Example 1

[0072] Compared with Example 3, the only difference is that the selective potassium ion recovery capacitor deionization electrode modification material is replaced with an equal amount of activated carbon powder, and the prepared electrode is denoted as electrode C.

[0073] Test case

[0074] Figure 1 The images show the FTIR spectra of the K-IIP electrode and the C electrode. As can be seen from the figures, the wavenumber is 1100 cm⁻¹. -1 955cm -1 and 832cm -1 The nearby peak is attributed to the stretching vibration of the -COC group on 18-crown ether-6, with a wavenumber of 881 cm⁻¹. -1The characteristic peak at that point is attributed to the Si-O-Si stretching of TEOS and APTES, while the characteristic peak of the same wavenumber was not clearly observed on the blank C electrode.

[0075] Figure 2 The images show the FTIR spectra of the PPC and C electrodes. As can be seen from the figures, the wavenumber is 1705 cm⁻¹. -1 The peak at this location is a typical peak of the C=O group in PAA, with a wavenumber of 1578 cm⁻¹. -1 and 1447cm -1 The peaks at these locations are characteristic peaks of the PANI polymer, corresponding to the stretching vibrations of the quinone and benzene rings, respectively. Therefore, it can be inferred that the K-IIP and PPC electrodes were successfully fabricated.

[0076] Figure 3 The CV curve is for the K-IIP electrode.

[0077] Figure 4 The CV curve is for the PPC electrode.

[0078] Figure 5 The CV curve is for the C electrode.

[0079] Depend on Figures 3-5 It can be seen that no characteristic peaks related to redox reactions appeared in the CV curves, indicating that the electrode has almost no pseudocapacitance and exhibits typical double-layer capacitance characteristics. The CV curve areas of both the K-IIP electrode and the PPC electrode are larger than those of the C electrode, indicating that the K-IIP electrode and the PPC electrode have superior specific capacitance performance.

[0080] Using a K-IIP electrode as the cathode, the changes in the electroadsorption of potassium ions under different voltage conditions were studied. Specifically:

[0081] The initial concentration of potassium chloride solution was 500 mg / L, with a conductivity of 1102 ± 6 μs / cm. The influent flow rate was 10 mL / min, the electrode spacing was 1.5 mm, and the environment was room temperature. The K-IIP electrode was used as the cathode, and the C electrode was used as the anode (in the comparative experiment, both the anode and cathode were C electrodes). The applied voltage was provided by a regulated DC power supply. Under different gradient working voltages of 0.8 V, 1.0 V, 1.2 V, 1.4 V, 1.6 V, 1.8 V, and 2.0 V, the solution conductivity value was recorded every minute. The experiment ended after the conductivity reached an equilibrium state to determine the optimal voltage parameters.

[0082] Figure 6 The changes in the electroadsorption of potassium ions by the K-IIP electrode and the C electrode under different voltage conditions are shown.

[0083] As shown in the figure, the adsorption capacity of the electrode first increases and then tends to stabilize with the increase of voltage. When the voltage reaches 1.4V, the desalination capacity approaches equilibrium. Therefore, 1.4V is selected as the optimal voltage parameter. Under this voltage condition, the K-IIP electrode of the example has an electroadsorption capacity of approximately 15.91 mg / g for potassium ions, while the C electrode of Comparative Example 1 has an electroadsorption capacity of approximately 10.51 mg / g for potassium ions. The K-IIP electrode improves the capacity by approximately 52.04% compared to the C electrode.

[0084] Using a PPC electrode as the anode, the changes in the electroadsorption of dihydrogen phosphate ions under different voltage conditions were studied. Specifically:

[0085] The initial concentration of potassium dihydrogen phosphate solution was 500 mg / L, with an initial conductivity of 311 ± 6 μs / cm. The influent flow rate was 10 mL / min, the electrode spacing was 1.5 mm, and the environment was room temperature. The working electrode was the anode, and the C electrode was the cathode (in the comparative experiment, both the anode and cathode were C electrodes). The applied voltage was provided by a regulated DC power supply. Different gradient working voltages were set: 0.8 V, 1.0 V, 1.2 V, 1.4 V, 1.6 V, 1.8 V, and 2.0 V. The conductivity value of the solution was recorded every minute. The experiment ended after the conductivity reached an equilibrium state, and the optimal voltage parameters were determined.

[0086] Figure 7 The electroadsorption changes of dihydrogen phosphate ions on the PPC and C electrodes under different voltage conditions are shown.

[0087] As shown in the figure, the adsorption capacity of the electrode initially increases and then tends to stabilize with increasing voltage. When the voltage reaches 1.6V, the desalination capacity approaches equilibrium. Therefore, 1.6V is selected as the optimal voltage parameter. Under this voltage condition, the electroadsorption capacity of the PPC electrode in Example 2 for dihydrogen phosphate ions is approximately 48.41 mg / g, while the electroadsorption capacity of the C electrode in Comparative Example 1 for dihydrogen phosphate ions is approximately 29.97 mg / g. The PPC electrode shows an improvement of approximately 61.9% compared to the C electrode.

[0088] Selectivity experiments of potassium ions using K-IIP and C electrodes:

[0089] Table 1 Simulated Urine Wastewater Configuration Table

[0090]

[0091] Using 100 mL of simulated urine (as shown in Table 1) as the influent sample, and under the conditions of a voltage of 1.4 V, an influent flow rate of 10 mL / min, and an electrode spacing of 1.5 mm, ammonium ions, sodium ions, calcium ions, and magnesium ions were used as interfering ions to conduct an anti-interference experiment on capacitive deionization.

[0092] Figure 8The graph shows the selectivity results of the K-IIP electrode and the C electrode for potassium ions.

[0093] As shown in the figure, the K-IIP electrode exhibits an adsorption capacity of 15.33 mg / g for potassium ions, and electroadsorption capacities of 3.32 mg / g for ammonium ions, 2.14 mg / g for sodium ions, 1.22 mg / g for calcium ions, and 1.05 mg / g for magnesium ions, respectively. The target ion shows the highest adsorption capacity. The selectivity for interfering ions is related to the hydration radius of the ions; the larger the hydration radius, the smaller the adsorption capacity. Therefore, the adsorption order of the K-IIP electrode at the cathode is potassium ions, ammonium ions, sodium ions, calcium ions, and magnesium ions.

[0094] Selectivity experiments of PPC and C electrodes for dihydrogen phosphate ions:

[0095] Using 100 mL of simulated urine (as shown in Table 1) as the influent sample, and under the conditions of a voltage of 1.6 V, an influent flow rate of 10 mL / min, and an electrode spacing of 1.5 mm, an anti-interference experiment was conducted using chloride ions, sulfate ions, and nitrate ions as interfering ions.

[0096] Figure 9 The results show the selectivity of the PPC electrode and the C electrode for dihydrogen phosphate ions.

[0097] As shown in the figure, the PPC electrode exhibits an adsorption capacity of 34.74 mg / g for dihydrogen phosphate ions, and electroadsorption capacities of 8.67 mg / g, 5.11 mg / g, and 2.39 mg / g for chloride, sulfate, and nitrate ions, respectively. The target ion shows the highest adsorption capacity, while the selectivity for interfering ions is related to the ion's hydration radius; the larger the hydration radius, the smaller the adsorption capacity. Therefore, the adsorption order of the PPC electrode at the anode is dihydrogen phosphate ions, chloride ions, sulfate ions, and nitrate ions.

[0098] This study investigates the practical application value of capacitive deionization recovery technology using a combination of K-IIP electrode as cathode and PPC electrode as anode. Specifically, this combination selectively adsorbs potassium and dihydrogen phosphate ions from urinary wastewater and recovers solid potassium dihydrogen phosphate.

[0099] The experimental parameters were: voltage 1.6V, influent flow rate 10mL / min, and electrode spacing 1.5mm. In the capacitive deionization device, a K-IIP electrode was used as the cathode and a PPC electrode as the anode, with gradient treatment times of 20, 30, 40, 50, 60, 70, and 80 minutes. After reaching equilibrium, the electrodes were reversed, and 50mL of distilled water was introduced for desorption. The recovered solution was then added to 50mL of saturated potassium dihydrogen phosphate solution and evaporated and concentrated to 50mL at 100℃. Subsequently, the solution was cooled and crystallized in a 30℃ water bath.

[0100] Figure 10 The recovery amount of potassium dihydrogen phosphate at different electroadsorption times is shown.

[0101] As shown in the figure, the recovery amount first increases and then stabilizes with time. When the electroadsorption stage lasts for 60 minutes, the recovery amount tends to stabilize. At this time, the recovery amount is about 42.98 mg / g (the ratio of the recovery amount of potassium dihydrogen phosphate to the mass of the active material in the electrode). Therefore, 60 minutes is selected as the optimal time for the adsorption stage of the combined electrode.

[0102] Figure 11 The purity of potassium dihydrogen phosphate solid recovered under different electroadsorption times is shown.

[0103] Because the concentration of the target product in the recovery solution was far from saturation, a method similar to spiking recovery was chosen, involving evaporation concentration followed by cooling crystallization to recover potassium dihydrogen phosphate. As shown in the figure, the purity of the recovered potassium dihydrogen phosphate solid was high at different electroadsorption times, approximately 94.93% (±0.16%), indicating that the recovery method has good stability, and the recovered product meets the standards for qualified fertilizer-grade potassium dihydrogen phosphate.

[0104] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0105] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A capacitive deionization electrode-modified material for selective recovery of potassium dihydrogen phosphate, characterized by, The capacitor deionization electrode modification material includes ion-selective functional materials and activated carbon; The ion-selective functional material includes 18-crown ether-6 and a crosslinking agent, or polyacrylic acid and polyaniline; The crosslinking agent includes silane coupling agent KH550 and tetraethyl orthosilicate; The volume ratio of the silane coupling agent KH550 to tetraethyl orthosilicate is 1:4; When the ion-selective functional material is 18-crown ether-6 and a crosslinking agent, the volume ratio of 18-crown ether-6 to the crosslinking agent is 2:1; the mass ratio of the ion-selective functional material to activated carbon is 1:(3-4); the preparation steps of the capacitor deionization electrode modification material for selectively recovering potassium dihydrogen phosphate include: dissolving silane coupling agent KH550 and tetraethyl orthosilicate as crosslinking agents in ethanol, then adding 18-crown ether-6 and potassium chloride, stirring, eluting, and obtaining the ion-selective functional material; mixing the ion-selective functional material and activated carbon evenly to obtain the capacitor deionization electrode modification material for selectively recovering potassium ions; When the ion-selective functional material is polyacrylic acid and polyaniline, the mass ratio of polyacrylic acid, polyaniline and activated carbon is 2:1:(3-4); the preparation steps of the capacitor deionization electrode modification material for selectively recovering potassium dihydrogen phosphate include: dispersing polyacrylic acid and polyaniline in water, stirring, then adding activated carbon, stirring evenly and drying to obtain the capacitor deionization electrode modification material for selectively recovering potassium dihydrogen phosphate ions.

2. A method for preparing the capacitive deionization electrode modification material for selective recovery of potassium dihydrogen phosphate as described in claim 1, characterized in that, When the ion-selective functional material is 18-crown ether-6 and a crosslinking agent, the preparation steps include: Silane coupling agent KH550 and tetraethyl orthosilicate were dissolved in ethanol as crosslinking agents, and then 18-crown ether-6 and potassium chloride were added. After stirring and elution, ion-selective functional material was obtained. The ion-selective functional material was mixed with activated carbon to obtain a capacitor deionization electrode modification material that selectively recovers potassium ions. When the ion-selective functional material is polyacrylic acid and polyaniline, the preparation steps include: Polyacrylic acid and polyaniline were dispersed in water and stirred. Activated carbon was then added, stirred evenly, and dried to obtain a capacitor deionization electrode modification material that selectively recovers dihydrogen phosphate ions.

3. The preparation method according to claim 2, characterized in that, The volume ratio of ethanol to crosslinking agent is 40:1; and / or the volume ratio of 18-crown ether-6 to potassium chloride is 2 mL:8 mg; and / or the elution is performed at least once with 1 M hydrochloric acid; and / or the mass ratio of polyacrylic acid, polyaniline, and water is 2:1:

200.

4. A capacitive deionization electrode for selectively recovering potassium ions, characterized in that, The active component of the capacitive deion electrode includes the capacitive deion electrode modification material for selective recovery of potassium dihydrogen phosphate as described in claim 1. The ion-selective functional material in the capacitive deion electrode modification material for selective recovery of potassium dihydrogen phosphate is 18-crown ether-6 and a crosslinking agent; The crosslinking agent includes silane coupling agent KH550 and tetraethyl orthosilicate.

5. A capacitive deionization electrode for selective recovery of dihydrogen phosphate ions, characterized by, The active component of the capacitive deion electrode includes the capacitive deion electrode modification material for selective recovery of potassium dihydrogen phosphate as described in claim 1. The ion-selective functional materials in the capacitive deionization electrode modification material for selective recovery of potassium dihydrogen phosphate are polyacrylic acid and polyaniline.

6. The application of the capacitive deionization electrode for selectively recovering potassium ions as described in claim 4 or the capacitive deionization electrode for selectively recovering dihydrogen phosphate ions as described in claim 5 in the recovery of potassium dihydrogen phosphate from high-salt and high-nitrogen wastewater.

7. An electrochemical device for the selective recovery of potassium dihydrogen phosphate, characterized in that, The cathode in the electrochemical device is the capacitive deionization electrode for selectively recovering potassium ions as described in claim 4, and the anode is the capacitive deionization electrode for selectively recovering dihydrogen phosphate ions as described in claim 5.

8. A method for recovering potassium dihydrogen phosphate using capacitive deionization technology, characterized in that, The method utilizes the electrochemical device for selective recovery of potassium dihydrogen phosphate as described in claim 7 as a capacitor deionization device to selectively adsorb potassium ions and dihydrogen phosphate ions, and then recovers potassium dihydrogen phosphate through desorption, evaporation and concentration, and cooling and crystallization.

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