Method for simultaneous removal of calcium and phosphorus in industrial circulating cooling water

Abstract

The application discloses a method for synchronously removing calcium and phosphorus in industrial circulating cooling water, which comprises the following steps: adding sodium bicarbonate into a solution containing calcium ions to which a scale inhibitor is added; passing oxygen into the solution so that the solution is in an oxygen saturation state; taking a carbon-based TiO2 electrode as a working electrode, a graphite electrode as a counter electrode, and a silver chloride standard electrode as a reference electrode, applying a voltage through an electrochemical workstation to electrochemically treat the solution, continuously passing oxygen in the whole process, and generating white precipitates in the solution after the reaction is completed; and realizing the synchronous removal of calcium and phosphorus by filtering and drying the white precipitates. The method can induce the release of calcium and phosphorus in the industrial circulating cooling water and induce the generation of calcium phosphate crystals, so that the synchronous Ca removal and P recovery are realized, and phosphorus fertilizer is provided for agricultural production. The method provides an environment-friendly and potentially economically valuable new idea for the repair of the industrial circulating cooling water.

Description

Technical Field

[0001] This invention belongs to the field of industrial circulating cooling water remediation technology, and specifically relates to a method for simultaneous removal of calcium and phosphorus from industrial circulating cooling water. Background Technology

[0002] Industrial circulating cooling water accounts for 70% of industrial water volume. The accumulation of hardness ions such as calcium and magnesium in this water leads to scaling, causing a loss of approximately 0.25% of GDP. Current scale inhibition technologies for industrial circulating cooling water include adding scale inhibitors and removing calcium from the water. Adding scale inhibitors can prevent calcium precipitation and is relatively inexpensive, but it introduces organic matter such as organophosphates, causing secondary pollution of the industrial circulating cooling water. Phosphorus removal technologies mainly include biological, adsorption, and chemical deposition. Chemical deposition is easy to operate and highly efficient, but it relies on adding Fe and Al salts as flocculants, making it difficult to generate bioavailable calcium phosphates (slow-release fertilizers or fertilizer raw materials). Some studies have also introduced multiple calcium and magnesium ion sources to achieve crystallization for phosphorus removal, but the formation of calcium phosphates is significantly affected by pH and reactant concentrations. Due to the high volume of industrial circulating cooling water, pH and reactant concentration adjustments are limited. Furthermore, the scale inhibition effect of scale inhibitors also has an upper limit.

[0003] In comparison, methods for removing calcium from industrial circulating cooling water are cleaner and more sustainable, but they are technically demanding and costly. In industry, a common approach is to create a localized alkaline environment using electrochemical methods to induce calcium ion deposition at the cathode. However, this method is energy-intensive, causes hydrogen evolution at high potentials, and leads to scale formation on the electrode surface, shortening electrode lifespan. These are two reverse approaches. However, in industrial circulating cooling water treatment, these two approaches are often used in parallel. That is, scale inhibitors are used to increase the calcium capacity of the industrial circulating cooling water, combined with calcium removal technologies (chemical and physical methods) to remove calcium brought in by the supplementary industrial circulating cooling water.

[0004] •OH, as a strong oxidizing free radical, is often used to dissolve metal-organic complexes, bind to various ion chelates and gain electrons, thereby releasing metal ions and destroying chelates. Simultaneously, •OH can induce flocculation by increasing the number of ligands. •OH has also been shown to have high activity in organic synthesis; studies have demonstrated that •OH can promote the breaking and formation of valence bonds during the transformation of zeolites from an amorphous state to a crystal state, and reduce its dependence on pH conditions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for simultaneously removing calcium and phosphorus from industrial circulating cooling water, thereby achieving simultaneous calcium removal and phosphorus recovery and providing phosphate fertilizer for agricultural production.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for simultaneous removal of calcium and phosphorus from industrial circulating cooling water includes the following steps:

[0008] S1: Add sodium bicarbonate to a calcium ion-containing solution containing a scale inhibitor;

[0009] S2: Pass oxygen into the solution to make the solution oxygen saturated;

[0010] S3: Using a carbon-based TiO2 electrode as the working electrode, a graphite electrode as the counter electrode, and a silver chloride standard electrode as the reference electrode, voltage is applied through an electrochemical workstation to perform electrochemical treatment on the solution. Oxygen is continuously introduced throughout the treatment process. After the reaction is completed, a white precipitate is generated in the solution, which is then filtered and dried to achieve simultaneous removal of calcium and phosphorus.

[0011] In the above scheme, the scale inhibitor is aminotrimethylenephosphonic acid.

[0012] In the above scheme, the concentration of sodium bicarbonate in the solution after adding sodium bicarbonate is 300 mg / L. Sodium bicarbonate acts as a seed, accelerating crystal formation and shortening crystallization time. The bicarbonate ions in the solution provide nucleation conditions for free calcium ions, preferentially forming calcium carbonate crystals and promoting the growth of calcium phosphate and other calcium complexes. Co-precipitation through heterogeneous nucleation or external crystal nucleation improves calcium removal efficiency. However, while excessive bicarbonate accelerates nucleation, it inhibits the formation of ·OH, resulting in low removal efficiency. To ensure nucleation and the dechelation effect of ·OH, the concentration of sodium bicarbonate is controlled at 300 mg / L.

[0013] In the above scheme, the oxygen supply time in step S2 is 15-30 minutes.

[0014] The generation of ·OH depends on the oxygen reduction process (ORR) that occurs at the cathode in the Fenton-like system, as shown in equations (1)-(3). Therefore, an oxygen-saturated solution environment is required before the reaction begins.

[0015] ≡TiIV+e - →≡TiIII (1)

[0016] 2≡TiIII+O2+2H + →2TiIV-OH (2)

[0017] 2≡TiIV-OH+e - →2≡TiIV+OH - +·OH (3)

[0018] Preferably, in step S2, the oxygen supply time is 20 minutes.

[0019] In the above scheme, in step S3, the voltage of the electrochemical workstation is -0.55V and the processing time is 40-70min.

[0020] Preferably, in step S3, the processing time is 60 minutes.

[0021] In the above scheme, in step S3, a vacuum pump is used for filtration, and the drying conditions are 60°C and vacuum drying.

[0022] In the above scheme, the carbon-based TiO2 electrode is prepared using the sol-gel method, and the specific operation is as follows:

[0023] (1) After ultrasonically cleaning the expanded graphite powder with ultrapure water and anhydrous ethanol for 30 min in sequence, it was placed in a vacuum drying oven and dried at 80℃ for 8 h.

[0024] (2) Place 1g of pretreated expanded graphite powder into an aniline-ethanol solution with a volume ratio of 1:4 and sonicate at 60Hz for 30min.

[0025] (3) The expanded graphite powder that has been washed with ultrapure water is added to 75 mL of a mixed acid solution of HCl and H2SO4 with molar concentrations of 0.5 M and 1 M respectively. While stirring, 7.6325 g of ammonium persulfate is added. After stirring at 6 °C for 10 h, the mixture is filtered and dried at 80 °C for 10 h to obtain EG-PAN powder.

[0026] (4) Mix 1g of EG-PAN powder, 7.5ml of tetrabutyl titanate and 22.5ml of anhydrous ethanol, and stir with a magnetic stirrer for 20min to form mixed solution A;

[0027] (5) Mix 22.5 ml of anhydrous ethanol, 3 ml of deionized water and 0.6 ml of concentrated nitric acid, and stir with a magnetic stirrer for 20 min to form mixed solution B;

[0028] (6) Add mixed solution B dropwise to mixed solution A at a volume ratio of 1:1, mix the two thoroughly and evenly, and then let it stand at 20°C for a period of time until a non-flowing gel system is formed.

[0029] (7) Dry it in an oven at 105℃ for 8 hours to obtain blackish-gray granules;

[0030] (8) Grind it into powder using a glass mortar and place it in a muffle furnace and calcine at 500°C for 2 hours to obtain self-supporting carbon-based TiO2 electrocatalytic material EG-PAN-TiO2 powder;

[0031] (9) Weigh 40mg of carbon-based TiO2 powder and mix it with 160μL of Nafion. After mixing evenly, coat it on the surface of the graphite plate electrode and let it air dry at room temperature to obtain a carbon-based TiO2 electrode.

[0032] In the above scheme, the carbon-based TiO2 electrode has a thickness of 2 mm and a length and width of 4 cm × 4 cm.

[0033] Through the above technical solution, the method for simultaneous removal of calcium and phosphorus from industrial circulating cooling water provided by the present invention has the following characteristics:

[0034] Beneficial effects:

[0035] (1) Compared with calcium removal methods that rely on alkaline precipitation with high pH, ​​the present invention does not require pH adjustment and does not introduce other metal ions;

[0036] (2) Compared with electrochemical scale inhibition technology, the present invention only requires the application of a potential of -0.55V, consumes less power and does not depend on the alkaline environment of the cathode, and has a long electrode life.

[0037] (3) The present invention can achieve simultaneous removal of calcium and phosphorus without the need for additional flocculants to remove phosphorus, thus achieving a clean and environmentally friendly process.

[0038] (4) The present invention can remove 52% of calcium after 60 minutes of power-on, which is similar to the calcium removal rate in a solution with pH adjusted to 12, providing feasibility for the recycling of industrial circulating cooling water.

[0039] (5) The phosphorus-containing crystals recovered by this invention can be used as phosphate fertilizer for plant cultivation, which is conducive to sustainable development.

[0040] In summary, this invention employs heterogeneous electro-Fenton technology to generate ·OH, utilizing the strong oxidizing properties of ·OH to disrupt the CP bonds in scale inhibitors, triggering the release of calcium and phosphorus from industrial circulating cooling water and inducing the formation of calcium phosphate crystals. This achieves simultaneous Ca removal and P recovery, providing phosphate fertilizer for agricultural production. This offers a novel, environmentally friendly, sustainable, and potentially economically valuable approach to the remediation of industrial circulating cooling water. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0042] Figure 1 The following are fluorescence micrographs of ·OH in the crystal of this invention; (A) is the adsorbed hydroxyl group, and (B) is the free hydroxyl group;

[0043] Figure 2This is a comparison of the total calcium removal efficiency of alkaline precipitation in Example 1 and Comparative Example 1 of the present invention.

[0044] Figure 3 This invention provides a comparison of the calcium removal efficiency between Example 1 (carbon-based TiO2 electrode) and Comparative Example 2 (ordinary graphite electrode).

[0045] Figure 4 This invention provides a comparison of the calcium removal efficiency between Example 1 (carbon-based TiO2 electrode) and Comparative Example 2 (ordinary graphite electrode).

[0046] Figure 5 Example 1 shows the effect of recycled crystals and Comparative Example 3 on the growth of Arabidopsis thaliana; (A) Example 1; (B) Comparative Example 3. Detailed Implementation

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0048] This invention provides a method for the simultaneous removal of calcium and phosphorus from industrial circulating cooling water. It generates ·OH through heterogeneous electro-Fenton technology, and utilizes the strong oxidizing properties of ·OH to break the CP bonds in the scale inhibitor, triggering the release of calcium and phosphorus from the industrial circulating cooling water and inducing the formation of calcium phosphate crystals, thereby achieving simultaneous Ca removal and P recovery, and providing phosphate fertilizer for agricultural production.

[0049] Example 1

[0050] Step 1: Preparation of carbon-based TiO2 electrode

[0051] (1) After ultrasonically cleaning the expanded graphite powder with ultrapure water and anhydrous ethanol for 30 min in sequence, it was placed in a vacuum drying oven and dried at 80℃ for 8 h.

[0052] (2) Place 1g of pretreated expanded graphite powder into an aniline-ethanol solution with a volume ratio of 1:4 and sonicate at 60Hz for 30min.

[0053] (3) The expanded graphite powder that has been washed with ultrapure water is added to 75 mL of a mixed acid solution of HCl and H2SO4 with molar concentrations of 0.5 M and 1 M respectively. While stirring, 7.6325 g of ammonium persulfate is added. After stirring at 6 °C for 10 h, the mixture is filtered and dried at 80 °C for 10 h to obtain EG-PAN powder.

[0054] (4) Mix 1g of EG-PAN powder, 7.5ml of tetrabutyl titanate and 22.5ml of anhydrous ethanol, and stir with a magnetic stirrer for 20min to form mixed solution A;

[0055] (5) Mix 22.5 ml of anhydrous ethanol, 3 ml of deionized water and 0.6 ml of concentrated nitric acid, and stir with a magnetic stirrer for 20 min to form mixed solution B;

[0056] (6) Add mixed solution B dropwise to mixed solution A at a volume ratio of 1:1, mix the two thoroughly and evenly, and then let it stand at 20°C for a period of time until a non-flowing gel system is formed.

[0057] (7) Dry it in an oven at 105℃ for 8 hours to obtain blackish-gray granules;

[0058] (8) Grind it into powder using a glass mortar and place it in a muffle furnace and calcine at 500°C for 2 hours to obtain self-supporting carbon-based TiO2 electrocatalytic material EG-PAN-TiO2 powder;

[0059] (9) Weigh 40mg of carbon-based TiO2 powder and mix it with 160μL of Nafion. After mixing evenly, coat it on the surface of the graphite plate electrode and let it air dry at room temperature to obtain a carbon-based TiO2 electrode.

[0060] Step 2: Preparation of calcium-containing solution

[0061] Prepare 150 ml of calcium chloride (CaCl2) solution with a concentration of 300 mg / L, and add 10 mg / L aminotrimethylenephosphonic acid (NTMP) solution.

[0062] Step 3: Add seed solution

[0063] Add 45 mg of sodium bicarbonate (NaHCO3) to the calcium solution to make the concentration of sodium bicarbonate 300 mg / L.

[0064] Step 4: Introduce oxygen

[0065] Expose the solution to oxygen for 20 minutes to bring the solution to oxygen saturation.

[0066] Step 5: Electrochemical reaction

[0067] A carbon-based TiO2 electrode was used as the working electrode, a graphite electrode as the counter electrode, and a silver chloride standard electrode as the reference electrode. A voltage of -0.55V was applied through an electrochemical workstation for 60 minutes. Oxygen was continuously introduced throughout the reaction, and magnetic stirring was performed at a speed of 500 rpm. A white precipitate formed in the solution during the reaction. Every 10 minutes, a water sample was taken from the solution and filtered through a 0.22-micron filter membrane. The concentration changes of total calcium and total phosphorus in the filtered solution were recorded.

[0068] Step Six: Crystal Recovery

[0069] After the reaction was completed, the solution containing calcium and phosphorus crystals was filtered through an oil-free vacuum pump and dried under vacuum at 60°C to obtain solid crystals.

[0070] Step Six: Planting

[0071] Arabidopsis thaliana was cultured using 1 / 2 MS medium prepared with dried crystals as phosphate fertilizer.

[0072] Take an appropriate amount of Arabidopsis thaliana seeds into a 1.5 mL centrifuge tube, treat with 75% ethanol for 3-4 minutes for surface sterilization, then aspirate the 75% ethanol and treat with 95% ethanol for 1-2 minutes. Aspirate the seeds and place them on sterile filter paper. After drying, operate in an ultra-clear workbench and sow them on 3 different solid culture media. Seal with sealing film and place in a 12-hour light / 12-hour dark environment at room temperature.

[0073] 1. Study on electrochemical treatment mechanism:

[0074] The ·OH generated in Example 1 was observed under a fluorescence microscope.

[0075] After the reaction, the solution was allowed to stand for a period of time to allow solid-liquid separation. 15 ml of the precipitate was mixed with 1 ml of 10 mM 3-(bromoacetyl)coumarin. Then, another 15 ml of the precipitate was mixed with 1 ml of 15 mM 7-(diethylamino)coumarin. The mixture was then transferred to a glass slide using a dropper for microscopic observation. The fluorescence micrograph is shown below. Figure 1 (A) and (B).

[0076] 3-(bromoacetyl)coumarin and 7-(diethylamino)coumarin were used to capture adsorbed hydroxyl radicals (i.e., hydroxyl radicals adsorbed on crystals) and free hydroxyl radicals (i.e., hydroxyl radicals free in solution), respectively. Since coumarins can react with hydroxyl radicals to generate fluorescent visible substances, in-situ observation of ·OH can be achieved. Figure 1 As can be seen from (A) and (B), both adsorbed and free hydroxyl groups can be detected in the precipitate, which proves that ·OH was generated in the system and participated in the reaction.

[0077] 2. Comparison of Fenton-like reaction and alkaline precipitation

[0078] To compare the calcium removal rate in Example 1 with the calcium removal rate of alkaline precipitation at pH=12, this invention includes a comparative example 1 of alkaline precipitation, which only includes steps two and three of Example 1: preparing 150 ml of 300 mg / L calcium chloride (CaCl2) solution, adding 10 mg / L aminotrimethylenephosphonic acid (NTMP) solution, adding 300 mg / L sodium bicarbonate (NaHCO3) solution, and adjusting the pH to 12 with 1 M NaOH.

[0079] like Figure 2 As shown, within 60 minutes, the removal rate of the electro-Fenton-like device was comparable to that of calcium removal under a high-alkaline environment, both being approximately 52%, indicating that the electro-Fenton-like device can promote calcium removal without relying on a high pH environment.

[0080] 3. Effect of different working electrodes on total calcium removal rate

[0081] This invention includes Comparative Example 2, in which the working electrode in Example 1 is replaced with a 4cm × 4cm × 0.2cm graphite electrode, while other conditions remain the same as in Example 1. The total calcium removal rates of Comparative Example 2 and Example 1 are compared, and the results are shown in [Figure 1]. Figure 3 .

[0082] like Figure 3 As shown, within 60 minutes, the total calcium removal rate of the graphite electrode in Comparative Example 2 was 10%, while the total calcium removal efficiency of the carbon-based TiO2 used as the working electrode in Example 1 of this invention was 52%. This is because the graphite electrode produces hydrogen peroxide and hardly produces ·OH, so the removal efficiency is not high. This also proves that hydroxyl radicals can promote calcium removal.

[0083] 4. Effect of different working electrodes on total phosphorus removal rate

[0084] The total phosphorus removal rates in Comparative Example 2 and Example 1 were compared, and the results are shown in [Figure Number]. Figure 4 .

[0085] like Figure 4 As shown, within 60 minutes, the total phosphorus removal rate of the graphite electrode in Comparative Example 2 was 30%, while the total calcium removal efficiency was 63% when carbon-based TiO2 was used as the working electrode in Example 1 of this invention. This is because the hydrogen peroxide generated by the graphite electrode can also release phosphate ions to generate calcium phosphate crystals, but the efficiency is far less than that of hydroxyl radicals, so the removal efficiency is not high. This also proves that hydroxyl radicals can promote the simultaneous removal of calcium and phosphorus.

[0086] 5. The impact of phosphorus recovery on plant growth

[0087] This invention includes Comparative Example 3, in which the recovered crystals from Example 1 were replaced with those obtained without the application of any phosphate fertilizer, while other conditions remained the same as in Example 1. The growth status of Arabidopsis thaliana in Comparative Example 3 was compared with that in Example 1 on the ninth day; the results are shown below. Figure 5 .

[0088] like Figure 5As shown, after nine days, Arabidopsis thaliana in the culture medium without added phosphate fertilizer showed almost no growth of roots, stems and leaves, while Arabidopsis thaliana cultured with the crystals in Example 1 as phosphate fertilizer showed better growth. This proves that the recovered crystals can be used as phosphate fertilizer for plant growth.

[0089] 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 method for simultaneous removal of calcium and phosphorus in industrial circulating cooling water, characterized in that, The method comprises the following steps: S1: adding sodium bicarbonate into a solution containing calcium ions with an antifouling agent; S2: passing oxygen into the solution to make the solution oxygen-saturated; S3: taking a carbon-based TiO2 electrode as a working electrode, a graphite electrode as a counter electrode, and a silver chloride standard electrode as a reference electrode, applying a voltage through an electrochemical workstation to electrochemically treat the solution, continuously passing oxygen during the treatment, and generating white precipitate in the solution after the reaction, and realizing the synchronous removal of calcium and phosphorus by filtering and drying the solution; The antifouling agent is aminotri (methylene) phosphonic acid.

2. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, The concentration of sodium bicarbonate in the solution after adding sodium bicarbonate is 300 mg / L.

3. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, In step S2, the oxygen is passed for 15-30 min.

4. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, In step S2, the oxygen is passed for 20 min.

5. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, In step S3, the voltage of the electrochemical workstation is-0.55 V, and the treatment time is 40-70 min.

6. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, In step S3, the treatment time is 60 min.

7. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, In step S3, the solution is filtered by a vacuum pump, and the drying condition is 60℃ and vacuum drying.

8. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, The carbon-based TiO2 electrode is prepared by a sol-gel method, and the specific operation is as follows: (1) after the expanded graphite powder is cleaned with ultrapure water and anhydrous ethanol by ultrasonic cleaning for 30 min, the powder is placed in a vacuum drying box and dried at 80℃ for 8 h; (2) 1g of the pretreated expanded graphite powder is put into a solution of aniline-ethanol with a volume ratio of 1:4, and ultrasonic treatment is performed at 60 Hz for 30 min; (3) the expanded graphite powder cleaned with ultrapure water is added into a mixed acid solution of HCl and H2SO4 with a molar concentration of 0.5M and 1M respectively, 7.6325g of ammonium persulfate is added while stirring, and the solution is continuously stirred at 6℃ for 10 h, then filtered, and dried at 80℃ for 10 h to obtain EG-PAN powder; (4) 1g of EG-PAN powder, 7.5ml of tetrabutyl titanate, and 22.5ml of anhydrous ethanol are mixed, and stirred with a magnetic stirrer for 20 min to form a mixed solution A; (5) 22.5 ml of anhydrous ethanol, 3 ml of deionized water, and 0.6 ml of concentrated nitric acid are mixed, and stirred with a magnetic stirrer for 20 min to form a mixed solution B; (6) the mixed solution B is added dropwise into the mixed solution A at a volume ratio of 1:1, and the two are fully mixed and uniform, then the mixture is placed at 20℃ for a period of time until a gel system that cannot flow is formed; (7) the mixture is placed in a 105℃ oven for drying for 8 h to obtain black and gray particles; (8) the particles are ground into powder with a glass mortar, and calcined in a muffle furnace at 500℃ for 2 h to obtain a self-supporting carbon-based TiO2 electrocatalytic material EG-PAN-TiO2 powder; (9) 40 mg of the EG-PAN-TiO2 powder prepared in step (8) is mixed with 160 μL of Nafion, and the mixture is uniformly coated on the surface of a graphite plate electrode, and naturally dried at room temperature to obtain a carbon-based TiO2 electrode.

9. The method for simultaneously removing calcium and phosphorus in industrial circulating cooling water according to claim 1, characterized in that, The thickness of the carbon-based TiO2 electrode is 2 mm, and the length and width dimensions are 4 cm×4 cm.

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