An electrochemical method for rapid removal of scale-forming ions from water

Abstract

This invention proposes an electrochemical method for rapidly removing scale-forming ions from water, belonging to the field of electrochemical technology. The method includes the following steps: A pulsed power supply is used; at least one anode plate is located inside the reactor; at least one cathode plate is located inside the reactor; and a dosing device is used; the pulsed power supply provides a pulsed voltage to the anode plate; after an appropriate time for the electrocoagulation reaction, the power supply is turned off, and an appropriate amount of sodium carbonate is added to the reactor. This invention utilizes an intermittent pulsed discharge mode, stopping the power supply after a suitable amount of metal flocs is generated, and cleverly utilizes the heterogeneous nucleation characteristics of calcium and magnesium ions on the floc surface, significantly reducing energy consumption and total reaction time, demonstrating significant advantages in the field of high-hardness water softening.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, and in particular relates to an electrochemical method for rapidly removing scale-forming ions from water. Background Technology

[0002] With the rapid development of urbanization and industrialization, industrial water consumption has increased significantly, accounting for approximately 20% of total water consumption, and 80% of industrial water is used for cooling operating equipment. To fully and effectively utilize water resources, cooling water must be recycled, a process known as circulating cooling water. Circulating cooling water involves large volumes and high energy consumption, significantly impacting enterprise operating costs and making it a key concern for energy and environmental protection departments. During the cooling water recycling process, the water temperature continuously rises and is in prolonged contact with air, causing evaporation and leading to the enrichment and concentration of various inorganic and organic substances in the water. This results in a continuous increase in hardness ions (Ca). 2+ Mg 2+ Scale easily forms precipitates such as CaCO3 and Mg(OH)2, which have low heat transfer coefficients, during operation. These precipitates adhere to the surfaces of operating equipment or cooling towers, reducing heat transfer efficiency, exacerbating equipment corrosion, and promoting the proliferation of microorganisms. Furthermore, scale adhering to the return water pipes can clog filters and condensers, affecting unit safety. Therefore, removing or reducing the hardness (scale-forming substances) of circulating cooling water is crucial for increasing the circulating water concentration ratio, effectively conserving water resources, reducing wastewater discharge, and ensuring the stable operation of the circulating cooling water system.

[0003] Traditional water softening methods include ion exchange, chemical precipitation, and reverse osmosis. Ion exchange works by exchanging calcium and magnesium ions with sodium or hydrogen ions on a saturated resin to reduce hardness; however, the saturated resin requires frequent acid or alkali leaching for regeneration. Chemical precipitation involves adding chemical reagents to precipitate calcium and magnesium ions, but requires large dosages, is complex to operate, has high maintenance costs per ton of water, and can cause secondary pollution, leading to excessive total dissolved solids (TDS) levels over time. Reverse osmosis uses system pressure differences and the selective permeability of membranes to separate liquids, removing dissolved salts and impurities, but requires regular membrane material replacement. While optimizing traditional hardness removal methods, researchers are also actively seeking new, efficient, low-consumption, and clean water softening technologies.

[0004] Electrochemical water softening technology, as an emerging active scale removal and inhibition technology, has attracted attention in recent years. Driven by clean electrical energy, this technology offers advantages over traditional chemical softening methods, including less chemicals, less sludge, less secondary pollution, and greater flexibility and control. It is playing an increasingly important role in industrial wastewater treatment and resource utilization. With the rapid development of green energy industries such as wind and nuclear power, the advantages of electrochemical technology are becoming more prominent, and it has a broad market in the harmless treatment and resource recovery of industrial wastewater. The electrochemical process is highly controllable; by precisely adjusting parameters such as current, voltage, and electrolysis time, it can flexibly adapt to different water quality conditions, achieving precise control over the removal of scale-forming ions in water. Furthermore, electrochemical water softening technology often integrates multiple processes. For example, while removing hardness ions, it can simultaneously remove some organic matter, ammonia nitrogen, heavy metal ions, and other pollutants from the water, and it also has bactericidal and algae-removing functions, effectively improving the overall treatment effect of water purification.

[0005] Currently, electrodeposition is a widely studied method in the field of electrochemical water softening. The key advantage of electrodeposition is its ability to directly reduce and deposit scale-forming ions in the water onto the electrode surface, thus removing these ions. However, it also has significant drawbacks. Firstly, scaling easily occurs on the electrode surface, and over time, the scale layer thickens, reducing the electrode's conductivity and affecting treatment efficiency. This necessitates frequent scraping and cleaning, increasing the difficulty and frequency of electrode maintenance. Secondly, the electrodeposition process requires a large specific surface area of ​​the cathode, limiting the large-scale application of this method.

[0006] In addition, electrocoagulation can be achieved through an applied electric field, causing an electrochemical reaction at the electrodes, where the metal anode produces cations with flocculation properties (such as Fe). 2+ And Al 3+ Electrocoagulation (e.g., hydrolysis and polymerization) occurs in water, forming a series of hydroxides or polynuclear hydroxyl complexes. These complexes adsorb pollutants in the water, causing them to aggregate and be removed through sedimentation or flotation. However, electrocoagulation also has its drawbacks. When used alone, its removal efficiency for hardness ions in water is limited, especially when treating high-hardness water. It requires a large amount of electrical energy to maintain the electrolysis process and produces a significant amount of sludge. Improper handling can easily lead to secondary pollution and increase treatment costs. Summary of the Invention

[0007] This invention proposes a reaction method for rapidly removing scale-forming ions from water through pulsed anodic electrocoagulation coupled with alkaline softening. Addressing the problem of scale buildup on electrodeposition electrodes, this method employs indirect pulsed discharge technology to generate a suitable amount of flocs (such as iron flocs) on the anode (e.g., an iron anode) within a short time, rather than directly depositing large amounts of metal ions on the cathode surface. This effectively reduces electrode scaling and ensures efficient and continuous electrode operation. Simultaneously, the pulsed electrocoagulation coupled with alkaline softening process involves stopping the current after a short pulsed electrocoagulation reaction and adding an alkaline agent, sodium carbonate. Sodium carbonate provides carbonate ions, promoting rapid and non-uniform nucleation of calcium carbonate and magnesium hydroxide on the surface of the iron flocs. The large specific surface area and abundant active sites of the iron flocs accelerate the precipitation of scale-forming ions, improving softening efficiency and effectively solving the drawbacks of low hardness removal efficiency, high energy consumption, and large sludge production associated with electrocoagulation alone.

[0008] This invention proposes an electrochemical method for rapidly removing scale-forming ions from water, comprising: The method uses a reactor containing at least one anode and at least one cathode, and a pulse power supply is used to provide a pulse voltage to the anode; First, an electrocoagulation reaction is carried out. After the reaction, the pulse power supply is turned off, and sodium carbonate is added to the reactor. The reaction then removes scale-forming ions from the water. Furthermore, the anode is an iron plate or an aluminum plate; preferably, the anode is an iron plate. Preferably, the cathode is a stainless steel mesh.

[0009] Furthermore, the pulse voltage is a square wave pulse voltage.

[0010] Furthermore, the square wave pulse voltage ranges from 0 to 3 V; Preferably, the square wave pulse voltage ranges from 0 to 0.5 V.

[0011] Furthermore, the duty cycle of the square wave pulse voltage is 10-90%; Preferably, the duty cycle of the square wave pulse voltage is 30% to 50%.

[0012] Furthermore, the pulse frequency of the square wave pulse voltage is 0.05 Hz ~ 100 Hz; Preferably, the pulse frequency of the square wave pulse voltage is 0.1 Hz to 10 Hz.

[0013] Furthermore, the electrocoagulation reaction time is 0.5 to 30 minutes; Preferably, the electrocoagulation reaction takes 3 to 10 minutes. Furthermore, the reaction time after adding sodium carbonate is 2 to 35 minutes; Preferably, the reaction time after adding sodium carbonate is 5 to 10 minutes. Furthermore, the molar ratio of sodium carbonate to total hardness in water is (0.2 ~ 2):1, wherein the total hardness in water is expressed as calcium carbonate; Preferably, the molar ratio of sodium carbonate to total hardness in water is (0.75 ~ 1.5):1. Furthermore, the scale-forming ions include at least one of calcium ions and magnesium ions.

[0014] This invention has the following advantages: The proposed method for rapidly removing scale-forming ions from water utilizes a pulsed power supply to provide a pulsed voltage to the anode. When the pulsed power supply is activated, an oxidation reaction occurs on the anode surface, causing the dissolved metal ions, such as ferrous ions, to rapidly hydrolyze, generating a series of flocculating iron hydroxide colloids, i.e., iron flocs. By adjusting appropriate pulse parameters (pulse voltage, pulse frequency, duty cycle, etc.), the release rate and mass transfer efficiency of iron ions are optimized, improving the spatiotemporal matching of electron transfer and reactant mass transfer at the electrode / solution interface under traditional steady-state power supply mode. This enhances the electrochemical reaction kinetics and system energy efficiency, giving the iron flocs a larger specific surface area and more active sites. These flocs can not only serve as carriers for physical adsorption but also as seed crystals for scale-forming ions, promoting the heterogeneous nucleation of CaCO3 and Mg(OH)2 crystals. Once a suitable amount of iron flocs has formed in the solution, the pulse power supply is turned off. Sodium carbonate, an alkaline agent, is then added to the water to provide carbonate ions. These carbonate ions react with scale-forming ions such as calcium and iron to form calcium carbonate and magnesium carbonate precipitates. Simultaneously, the alkaline environment generated by carbonate hydrolysis induces heterogeneous nucleation of calcium and magnesium ions on the floc surface, significantly improving the removal rate of scale-forming ions. The total hardness removal rate can reach 99.6%. This method not only significantly reduces energy consumption and sludge production but also effectively shortens the total reaction time, demonstrating significant advantages in the field of high-hardness water softening. Attached Figure Description

[0015] 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: Figure 1 This is a schematic diagram of the structure of the pulse electrocoagulation coupled alkaline softening electrochemical reaction device in an embodiment of the present invention; 1-Anode; 2-Cathode; 3-Dosing device; Figure 2 This is a schematic diagram of the applied square wave pulse voltage in Embodiment 1 of the present invention; Figure 3To compare the average particle size of flocs in different processes of constant voltage electrocoagulation in Comparative Example 1 and pulse electrocoagulation coupled with alkaline softening in Example 14 (pulse electrocoagulation coupled with alkaline softening: pulse voltage 0-0.1 V, pulse frequency 0.4 Hz, duty cycle 30%, molar ratio of sodium carbonate to total hardness in water is 1.25:1; constant voltage electrocoagulation: voltage 0.05 V); Figure 4 To compare the Zeta potential of flocs in different processes of constant voltage electrocoagulation in Comparative Example 1 and pulse electrocoagulation coupled with alkaline softening in Example 14 (pulse electrocoagulation coupled with alkaline softening: pulse voltage 0-0.1 V, pulse frequency 0.4 Hz, duty cycle 30%, molar ratio of sodium carbonate to total hardness in water is 1.25:1; constant voltage electrocoagulation: voltage 0.05 V). Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0017] One embodiment of the present invention proposes an electrochemical method for rapidly removing scale-forming ions from water, comprising: The method uses a reactor containing at least one anode and at least one cathode, and a pulse power supply is used to provide a pulse voltage to the anode; First, an electrocoagulation reaction is carried out. After the reaction, the pulse power supply is turned off, and sodium carbonate is added to the reactor. The reaction then removes scale-forming ions from the water.

[0018] The method for rapidly removing scale-forming ions from water by pulsed anodic electrocoagulation coupled with alkaline softening, as proposed in this invention, firstly utilizes indirect pulsed discharge technology. By adjusting appropriate pulse parameters, metal ions, such as iron ions, are pulsedly deposited at the anode. These iron ions then react with OH- ions deposited at the cathode. - Through combination and self-hydrolysis, iron flocs are generated. These iron flocs have a large specific surface area and are rich in more active sites, enabling them to efficiently adsorb calcium and magnesium ions in water. They can also act as seed crystals for scale-forming ions, promoting the heterogeneous nucleation of CaCO3 and Mg(OH)2 crystals. After the short-term electrocoagulation reaction, a small amount of sodium carbonate is added to replenish carbonate ions and alkalinity. The abundant active sites on the floc surface provide nucleation sites for CaCO3 and Mg(OH)2, reducing the nucleation energy and thus greatly improving the speed of scale-forming ion removal.

[0019] Specifically, in this embodiment of the invention, the square wave pulse voltage mode provides a pulsed voltage during electrolysis, and the current and charge will change differently depending on the specific pulse conditions, such as... Figure 2As shown, under the drive of a pulsed potential, the iron anode undergoes an oxidation reaction, releasing Fe ions into the solution. These Fe ions hydrolyze or react with hydroxide ions released from the cathode to form iron flocs. The resulting iron hydroxide colloids possess extremely strong flocculation activity, efficiently adsorbing various suspended impurities and scale-forming ions in the water.

[0020] Hydrogen evolution occurs on the cathode surface, reducing the hydrogen ion concentration in the solution near the cathode. Based on the ion product constant of water, the water ionizes to produce more hydroxide ions to maintain equilibrium. Due to the strong pull of the electric field, scale-forming ions migrate directionally to the alkaline zone near the cathode.

[0021] When sodium carbonate is added to the reaction system, carbonate ions (CO3-) 2- The scale-forming ions adsorbed on the floc surface rapidly and heterogeneously nucleate on the floc surface. This process benefits from the large number of active sites on the floc surface, greatly promoting the rapid formation and sedimentation of precipitates. Another portion of carbonate ions (CO3-) 2- The iron hydroxide colloids formed during the pulsed electrocoagulation process rapidly react with scale-forming ions in the water that have not yet been adsorbed and removed, resulting in precipitation. These colloids possess a large specific surface area, providing numerous attachment sites for the precipitate and greatly promoting its rapid formation. Furthermore, the addition of sodium carbonate steadily increases the pH of the solution, and this enhanced alkaline environment further promotes the precipitation of remaining scale-forming ions in the form of hydroxides.

[0022] In one embodiment of the present invention, the anode is an iron plate or an aluminum plate. More preferably, the cathode is a stainless steel mesh. In this embodiment of the invention, the chemical reaction that occurs during the electrocoagulation coupled with alkaline softening to remove scale-forming ions (calcium and magnesium) by the pulse anode (taking iron anode and stainless steel mesh cathode as examples) is as follows: Anode: Driven by a pulsed potential, the iron anode undergoes an oxidation reaction and gradually dissolves. The key reaction formula is: Fe – 2e - → Fe 2+ (1) The ferrous ions (Fe) generated by dissolution 2+ It then rapidly undergoes hydrolysis with water, the specific reaction formula is as follows: Fe 2+ + 2H2 Fe(OH)2+ 2H + (2) The generated ferrous hydroxide (Fe(OH)2) is unstable and will undergo further oxidation in the presence of oxygen: 4Fe(OH)2+ O2+ 2H2O → 4Fe(OH)3(3) The resulting iron hydroxide colloids possess extremely strong flocculation activity, enabling them to efficiently adsorb scale-forming ions and other impurities in the water. Cathode: During the pulsed electrocoagulation stage, an important hydrogen evolution reaction occurs on the surface of the stainless steel mesh cathode: 2H + + 2e - → H2↑(4) This hydrogen evolution reaction will decrease the concentration of hydrogen ions in the solution near the cathode. According to the ion product constant of water, water will ionize to produce more hydroxide ions to maintain equilibrium. The reaction equation is as follows: H2O H + + OH - (5) As the hydrogen evolution reaction proceeds, the equilibrium shifts to the right, leading to an increase in the concentration of hydroxide ions.

[0023] The alkaline softening stage after adding sodium carbonate: When sodium carbonate is precisely added to the reaction system, carbonate ions (CO3-) 2- It quickly reacts with scale-forming ions in the water that have not yet been removed, resulting in precipitation. Ca 2+ + CO3 2- → CaCO3↓(6) Mg 2+ + CO3 2- → MgCO3↓(7) The iron hydroxide colloids formed during the pulsed anodic electrocoagulation process have a large specific surface area. These colloids adsorb calcium and magnesium ions on the floc surface, and with the addition of CO3... 2- With the addition of calcium carbonate and magnesium hydroxide, calcium carbonate and magnesium hydroxide rapidly form heterogeneous nuclei on the surface of the flocs.

[0024] The addition of sodium carbonate leads to an increase in the pH of the carbonate hydrolysis solution system, further promoting the precipitation of remaining scale-forming ions in the water as hydroxides. Mg 2+ + 2OH - → Mg(OH)2↓(8).

[0025] In one embodiment of the present invention, the reactor contains one anode and one cathode, or two anodes and two cathodes, or three anodes and two cathodes, or three anodes and three cathodes, etc. The number of cathodes and anodes can be adjusted as needed.

[0026] In one embodiment of the present invention, the anode and cathode have the same shape and are arranged parallel to each other. Further, the distance between adjacent electrodes of the anode and cathode is 0.5-2 cm. In one embodiment of the present invention, the pulse voltage is a square wave pulse voltage. It should be noted that, from a waveform perspective, a square wave pulse voltage exhibits a rectangular shape, with the voltage value rapidly switching between high and low voltages, and the duration of holding these high and low voltages being relatively fixed. This periodic abrupt change distinguishes it from traditional DC or sinusoidal AC voltages. When applied to a pulsed anode-coupled alkaline softening system, it brings unique advantages to the entire reaction process.

[0027] In this embodiment of the invention, the square wave pulse voltage causes the oxidation and dissolution process of the anode metal, such as iron, to be intermittent. The anode pulse voltage promotes the efficient removal of scale-forming ions in the entire system mainly in the following ways: (1) ion mass transfer during the iron anode dissolution process is enhanced; (2) the iron hydroxide colloid generated at the anode can diffuse more efficiently into the bulk solution. Specifically, when a pulse voltage is applied to the anode, Fe - 2e⁻ occurs rapidly. - → Fe 2+ The oxidation reaction generates a large amount of ferrous ions. When the anode is de-energized or at a lower potential, it enters the diffusion stage. Anions in the solution diffuse to the anode surface, balancing the excessively high local ion concentration. At the same time, the generated iron hydroxide colloids have the opportunity to be more evenly dispersed throughout the solution, keeping the ion concentration relatively stable. The anode surface is also given a brief "rest," reducing the accumulation of excessive polarization. This helps the electrode maintain good activity and extend its service life. It also allows the generated ferrous ions time to fully hydrolyze, forming highly efficient flocculated iron hydroxide colloids. This effectively improves the spatiotemporal matching of electron transfer and reactant mass transfer at the electrode / solution interface under the traditional steady-state power supply mode, thereby improving the electrochemical reaction kinetics and system energy efficiency. In one embodiment of the present invention, the square wave pulse voltage ranges from 0 to 3 V. Preferably, the square wave pulse voltage ranges from 0 to 0.5 V.

[0028] In one embodiment of the present invention, the duty cycle of the square wave pulse voltage is 10-90%. Preferably, the duty cycle of the square wave pulse voltage is 30% to 50%. It should be noted that the duty cycle refers to the ratio of the energizing time to the total time in one square wave pulse cycle.

[0029] In one embodiment of the present invention, the pulse frequency of the square wave pulse voltage is 0.05 Hz to 100 Hz. Preferably, the pulse frequency of the square wave pulse voltage is 0.1 Hz to 10 Hz. In one embodiment of the present invention, the electrocoagulation reaction time is 0.5 to 30 minutes. In a preferred embodiment of the present invention, the electrocoagulation reaction time is 3 to 10 minutes. In one embodiment of the present invention, the molar ratio of sodium carbonate to total hardness in water is (0.2 ~ 2):1. The total hardness in water is expressed as calcium carbonate. In a preferred embodiment of the present invention, the molar ratio of sodium carbonate to total hardness in water is (0.75 ~ 1.5):1. It should be noted that expressing total hardness in water as calcium carbonate means that the total amount of calcium and magnesium ions in the water is expressed as calcium carbonate. For example, if the initial hardness in water is 850 mg / L, then the total amount of calcium and magnesium ions is equivalent to 850 mg / L, expressed as calcium carbonate. In this embodiment of the invention, after a period of electrocoagulation reaction at the pulsed anode, the pulsed power supply is turned off, and sodium carbonate is added as an alkaline agent. If the amount of sodium carbonate added is insufficient, the scale-forming ions cannot be completely removed. If the amount added is excessive, it will not only waste the agent, but may also lead to excessive alkalinity of the water and cause secondary pollution.

[0030] In one embodiment of the present invention, the reaction time after adding sodium carbonate is 2 to 35 minutes. In a preferred embodiment of the present invention, the reaction time after adding sodium carbonate is 5 to 10 minutes. For example, the reaction time after adding sodium carbonate is 10 minutes.

[0031] In this embodiment of the invention, after the addition of the alkaline agent sodium carbonate, on the one hand, CO3 2- It reacts chemically with residual calcium and magnesium ions in the water to form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitates. Because the iron hydroxide colloids formed in the previous electrocoagulation reaction have a large specific surface area, they can serve as good active attachment sites for the precipitates, promoting rapid formation and sedimentation. On the other hand, the addition of sodium carbonate increases the pH of the solution system from neutral (around 7.5) to weakly alkaline (9-9.5), further promoting the precipitation of scale-forming ions in the water as hydroxides, which are then adsorbed by the flocs, such as magnesium hydroxide (Mg(OH)2). The reaction method proposed in this invention requires no external flocculant, is mild, and has low energy consumption. The applied pulse voltage mode is as follows: Figure 2 As shown, the electrodes are intermittently in a non-working or low-voltage state. The iron flocs are formed by the hydrolysis of iron ions precipitated in situ from the anode. While adsorbing scale-forming ions, they also provide nucleation sites for them, and work together with alkaline softening to quickly and efficiently remove scale-forming ions from the water.

[0032] In one embodiment of the present invention, the concentration of total hardness in the water is 100-2000 mg / L. Preferably, the concentration of total hardness in the water is 300-1300 mg / L. In this embodiment of the present invention, the method for rapidly removing scale-forming ions from water by pulsed anodic electrocoagulation coupled with alkaline softening is suitable for wastewater containing high hardness. Anodic pulsed voltage electrocoagulation is used, utilizing the flocs generated by anodic hydrolysis to adsorb scale-forming ions. Subsequently, sodium carbonate is added to promote the nucleation of calcium and magnesium ions, which are removed after sedimentation with the flocs, significantly improving the rate of scale-forming ion removal; the total hardness removal rate can reach 99.6%.

[0033] The present invention will now be described in detail with reference to embodiments.

[0034] Example 1 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 0.75:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min.

[0035] After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 187 mg / L, and the total hardness removal rate was 78%.

[0036] Example 2 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the distance between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode using a pulsed power supply, with the voltage set to 0-0.1 V, the pulse frequency to 0.4 Hz, the duty cycle to 30%, the initial hardness to be 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate to total hardness in the water (calculated as calcium carbonate) to be 1:1. Using the pulsed power supply with the above pulsed voltage, the electrolysis time was 3 min, and the reaction time was 10 min after the addition of sodium carbonate. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the hardness was 119 mg / L, and the total hardness removal rate was 86%.

[0037] Example 3 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode using a pulsed power supply, with the voltage set to 0~0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Using the pulsed power supply with the above pulsed voltage, the electrolysis time was 3 min, and the reaction time was 10 min after the addition of sodium carbonate. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the hardness was 85 mg / L, and the total hardness removal rate was 90%.

[0038] Example 4 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.5:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min.

[0039] After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 51 mg / L, and the total hardness removal rate was 94%.

[0040] Example 5 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.05 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anode electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 119 mg / L, and the total hardness removal rate was 86%.

[0041] Example 6 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.5 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min.

[0042] After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 102 mg / L, and the total hardness removal rate was 88%.

[0043] Example 7 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.1 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min.

[0044] After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the hardness was 136 mg / L, and the total hardness removal rate was 84%.

[0045] Example 8 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.02 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min.

[0046] After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the hardness was 171.7 mg / L, and the total hardness removal rate was 79.8%.

[0047] Example 9 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0~0.1 V, the pulse frequency 1 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anode electrocoagulation coupled with alkaline softening treatment, the total hardness in the water was 85 mg / L, and the total hardness removal rate was 90%.

[0048] Example 10 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 10%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 157.25 mg / L, and the total hardness removal rate was 81.5%.

[0049] Example 11 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 50%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 110.5 mg / L, and the total hardness removal rate was 87%.

[0050] Example 12 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 75%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 3 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness in the water was 131.75 mg / L, and the total hardness removal rate was 84.5%.

[0051] Example 13 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 5 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 12.75 mg / L, and the total hardness removal rate was 98.5%.

[0052] Example 14 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 850 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 10 min, and the reaction was allowed to proceed for another 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 3.4 mg / L, and the total hardness removal rate was 99.6%.

[0053] Example 15 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 1000 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 5 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 13.6 mg / L, and the total hardness removal rate was 98.4%.

[0054] Example 16 An electrochemical method for rapidly removing scale-forming ions from water In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrode spacing between adjacent electrodes was 0.7 cm, placed parallel to each other. A pulsed voltage was applied to the iron anode via a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 0.4 Hz, the duty cycle 30%, the initial hardness 1250 mg / L (calculated as calcium carbonate), and the molar ratio of sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) 1.25:1. Sodium carbonate was added immediately after the pulsed electrocoagulation reaction for 5 min, and the reaction was allowed to proceed for 10 min. After pulsed iron anodic electrocoagulation coupled with alkaline softening treatment, the total hardness of the water was 31.45 mg / L, and the total hardness removal rate was 96.3%.

[0055] Comparative Example 1 An electrochemical method for rapidly removing scale-forming ions from water (using only constant voltage) In the electrochemical reactor, the anode was an iron plate, the cathode was a stainless steel mesh, and the electrodes were placed parallel to each other with a spacing of 0.7 cm between adjacent electrodes. A constant voltage of 0.05 V was applied to the iron anode using a constant power supply, and the initial water hardness was 850 mg / L (calculated as calcium carbonate). The constant voltage electrocoagulation reaction was carried out for 20 min.

[0056] After constant voltage electrocoagulation treatment, the hardness was 459 mg / L, and the total hardness removal rate was 23%.

[0057] Comparative Example 1 used a constant voltage instead of a pulsed voltage for electrocoagulation, and the effect was significantly lower than that of Example 1. Compared with a constant voltage, a pulsed voltage can dynamically disturb the electrode-liquid interface to promote the diffusion of ions and substances, reduce the concentration polarization of the electrochemical reaction, and facilitate the generation, diffusion, and hydrolysis of Fe ions during the electrochemical reaction.

[0058] In Comparative Example 1, when a constant potential is applied to the anode, iron atoms on the anode surface dissolve rapidly and continuously, leading to an excessively high local concentration of ferrous ions in the solution. This easily triggers side reactions, reducing the activity of the generated iron hydroxide colloid and hindering the adsorption of scale-forming ions. Furthermore, prolonged exposure to a high potential results in severe electrode polarization, consuming excessive electrical energy and causing the anode to wear out too quickly. However, when a pulsed voltage is applied to the anode, the reaction and diffusion processes alternate. When the anode is energized or a high potential is applied, the Fe - 2e⁻ reaction occurs rapidly. - → Fe 2+ The oxidation reaction generates a large amount of ferrous ions, which hydrolyze to form ferric hydroxide colloids. When the anode is de-energized or at a lower potential, the diffusion stage begins. Anions in the solution diffuse to the anode surface, balancing the locally excessively high ion concentration. Simultaneously, the generated ferric hydroxide colloids have the opportunity to disperse more evenly throughout the solution. This process is completed rapidly within a short timeframe. Therefore, applying a pulsed voltage to the anode maintains a relatively stable ion concentration on the electrode surface, while the ferric hydroxide colloids continuously diffuse into the bulk solution, improving the spatiotemporal matching of electron transfer and reactant mass transfer at the electrode / solution interface, thereby accelerating the entire electrocoagulation and subsequent scale-forming ion removal process.

[0059] In Comparative Example 1, such as Figure 3 As shown, using constant voltage electrocoagulation, the average particle size of the flocs was 300 μm after 10 min of reaction. In contrast, compared to pulsed electrocoagulation coupled with alkaline softening at the same reaction time, the latter achieved an average particle size of 1200 μm. The larger average particle size implies a larger specific surface area and more active sites for Ca adsorption. 2+ / Mg 2+ This improves hardness removal capabilities.

[0060] In Comparative Example 1, the closer the absolute value of the Zeta potential of the flocs is to 0 mV, the more unstable the flocs are, and the easier they are to aggregate and form larger flocs. The flocs promote Ca2+ aggregation through the double-layer compression effect. 2+ / Mg 2+ Adsorption removes calcium and magnesium ions. For example... Figure 4 As shown, the Zeta potential on the floc surface during constant voltage electrocoagulation after 20 min of reaction is -12.5 mV, which is much smaller than the Zeta potential (-6.8 mV) on the floc surface generated by pulse electrocoagulation coupled with alkaline softening at the same reaction time. Therefore, pulse electrocoagulation coupled with alkaline softening can more rapidly adsorb and remove calcium and magnesium ions. Comparative Example 2 An electrochemical method for rapidly removing scale-forming ions from water (using only pulsed voltage for electrocoagulation) In the electrochemical reactor, the anode was an iron plate, and the cathode was a stainless steel mesh, with adjacent electrodes placed parallel to each other and spaced 0.7 cm apart. A pulsed voltage was applied to the iron anode using a pulsed power supply, with the voltage set to 0 ~ 0.1 V, the pulse frequency 1 Hz, and the duty cycle 40%. The pulsed electrocoagulation reaction was carried out for 20 min, and the initial hardness was 850 mg / L (calculated as calcium carbonate).

[0061] After pulsed iron anodic electrocoagulation treatment, the hardness was 255 mg / L, and the total hardness removal rate was 54%.

[0062] In Comparative Example 2, the method of removing scale-forming ions using pulsed electrocoagulation technology alone has low removal efficiency due to relying solely on electrocoagulation, and requires a longer electrolysis time. This not only leads to a large consumption of electrical energy but also generates a high amount of sludge during the electrolysis process. If this sludge is not properly treated, it can cause secondary pollution problems and have a negative impact on the environment.

[0063] Comparative Example 3 An electrochemical method for rapidly removing scale-forming ions from water (using only alkaline softening) In a chemical reactor, a separate alkaline softening process was used, with a sodium carbonate dosage to total hardness in water (calculated as calcium carbonate) molar ratio of 1:1. The reaction time was 20 min, and the initial hardness was 850 mg / L.

[0064] After alkaline softening treatment, the hardness was 323 mg / L, and the total hardness removal rate was 62%.

[0065] In Comparative Example 3, when alkaline softening was used alone—that is, sodium carbonate was directly added to hard water to remove scale-forming ions—calcium carbonate and magnesium hydroxide mainly underwent homogeneous nucleation in the solution. This homogeneous nucleation process was significantly slower than the heterogeneous nucleation process, and the resulting crystal nuclei were smaller, which was not conducive to subsequent sedimentation and separation. This resulted in relatively low softening efficiency, making it difficult to meet the actual requirements for efficient hardness removal. Furthermore, using alkaline softening alone required the addition of a large amount of reagents, increasing treatment costs.

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrochemical method for rapidly removing scale-forming ions from water, characterized in that, include: The method uses a reactor containing at least one anode and at least one cathode, and a pulse power supply is used to provide a pulse voltage to the anode; First, an electrocoagulation reaction is carried out. After the reaction, the pulse power supply is turned off, and sodium carbonate is added to the reactor. The reaction then removes scale-forming ions from the water.

2. The electrochemical method according to claim 1, characterized in that, The anode is an iron plate or an aluminum plate; preferably, the anode is an iron plate. Preferably, the cathode is a stainless steel mesh.

3. The electrochemical method according to claim 1, characterized in that, The pulse voltage is a square wave pulse voltage.

4. The electrochemical method according to claim 3, characterized in that, The range of the square wave pulse voltage is: 0 ~ 3 V; Preferably, the square wave pulse voltage ranges from 0 to 0.5 V.

5. The electrochemical method according to claim 3, characterized in that, The duty cycle of the square wave pulse voltage is 10-90%; Preferably, the duty cycle of the square wave pulse voltage is 30% to 50%.

6. The electrochemical method according to claim 3, characterized in that, The pulse frequency of the square wave pulse voltage is 0.05 Hz ~ 100 Hz; Preferably, the pulse frequency of the square wave pulse voltage is 0.1 Hz to 10 Hz.

7. The electrochemical method according to claim 1, characterized in that, The electrocoagulation reaction time is 0.5 to 30 minutes; Preferably, the electrocoagulation reaction takes 3 to 10 minutes.

8. The electrochemical method according to claim 1, characterized in that, The reaction time after adding sodium carbonate is 2 to 35 minutes. Preferably, the reaction time after adding sodium carbonate is 5 to 10 minutes.

9. The electrochemical method according to claim 1, characterized in that, The molar ratio of sodium carbonate to total hardness in water is (0.2 ~ 2):1, wherein the total hardness in water is expressed as calcium carbonate. Preferably, the molar ratio of sodium carbonate to total hardness in water is (0.75 ~ 1.5):

1.

10. The electrochemical method according to claim 1, characterized in that, The scale-forming ions include at least one of calcium ions and magnesium ions.

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