A method of electrochemical water softening

Abstract

The application provides a method for electrochemical water softening, which adopts an electrochemical device with a cathode and an anode to treat wastewater, the wastewater is fed into the cathode and discharged from the anode, and the cathode is a corrugated electrode. The corrugated electrode is a sawtooth corrugated electrode with a sawtooth surface or a wave corrugated electrode with a wave surface. In the electrochemical water softening method, the hydrogen bubble generation and release of the cathode are utilized to have a certain mechanical peeling effect on the scale layer, and due to the special structure of the electrode surface, the hydrogen bubble has a certain pushing force outward, so that the scale layer can be taken away from the surface of the substrate, thereby preventing the scale layer from depositing on the cathode, which not only prolongs the service life of the cathode but also enables the cathode to have a certain self-cleaning ability. The corrugated electrode adopted in the application can make the scale not deposit on the surface of the cathode but crystallize and grow in water, relieve the scale deposition speed on the surface of the electrode, and reduce the energy consumption in the reaction process.

Description

Technical Field

[0001] This invention relates to the field of electrochemical hardening technology, specifically to a method for electrochemical hardening using improved electrodes. Background Technology

[0002] Circulating cooling water is widely used in industries such as power generation, petrochemicals, steel, and HVAC, and its stability is a prerequisite for ensuring stable industrial production. However, scaling and corrosion problems in circulating cooling water systems lead to significant economic losses and serious safety issues. Developing effective treatment processes for industrial wastewater hardness has always been a hot research topic in the environmental field.

[0003] Currently, the main methods for treating wastewater hardness both domestically and internationally are scale inhibitor methods, electromagnetic methods, and lime softening methods. Each of these methods has its advantages, but also significant drawbacks. Scale inhibitors are unstable at high temperatures, and the addition of chemical agents leads to high operating costs, difficulty in management, and large amounts of waste salt generated. Electromagnetic methods are only suitable for treating low-hardness wastewater, and their scale removal and prevention mechanisms are currently unclear. Lime softening methods involve cumbersome and complex processes, generating large amounts of sludge and causing environmental pollution. Electrochemical methods can separate scale-forming ions from circulating water in the form of solid CaCO3 and Mg(OH)2, fundamentally preventing scale formation and showing promising application prospects. Compared with traditional methods, they offer advantages such as simple operation, effective scale removal, and no secondary pollution to the environment. Although electrochemical descaling technology has irreplaceable advantages, scale deposition on the cathode surface, once reaching a certain thickness, requires interrupting the reaction for mechanical scraping, electrode reversal, or acid washing for electrode regeneration. This reduces treatment capacity and electrode lifespan, increases operating costs, and limits the large-scale application of electrochemical water treatment descaling technology.

[0004] Patent CN113200615A discloses a method and system for electrochemically reducing wastewater hardness. The method includes the following steps: pretreated wastewater is fed into an electrochemical hardening device for electrolysis, then reacts with dispersed carbon dioxide to obtain de-hardened water, which is then subjected to solid-liquid separation to obtain de-hardened water. However, the scale generated by this invention remains on the cathode plate, requiring cathode regeneration, which reduces processing capacity and electrode lifespan.

[0005] Patent CN109399812A discloses an electrochemical descaling device. The working system consists of parallel, closely spaced, and alternating anodes and cathodes. The cathode is composed of multiple layers of metal wire mesh with varying numbers of components. Cathode regeneration is achieved through ultrasonic cleaning. This method slows down scale deposition to some extent, but ultrasonic cleaning reduces the cathode's lifespan, and multiple cathode layers increase costs.

[0006] Given the above problems, further improvements are still needed in electrochemical hardening technology to improve descaling efficiency and electrode lifespan while effectively reducing hardness. Summary of the Invention

[0007] To address the problem of scale buildup and short lifespan of electrodes in existing hardening technologies, this invention provides an electrochemical hardening method that employs a cathode with improved structural morphology to alleviate scale buildup on the electrode surface and extend the electrode's lifespan.

[0008] To achieve the above-mentioned technical objectives, the present invention provides an electrochemical method for hardening removal, which uses an electrochemical device with a cathode and an anode to treat wastewater. The wastewater enters through the cathode and exits through the anode, wherein the cathode is a pleated electrode.

[0009] Furthermore, the wrinkled electrode is a serrated wrinkled electrode with a serrated surface, or a wavy wrinkled electrode with a wavy surface.

[0010] Furthermore, the folding angle of the serrated corrugated electrode is 20-150°, preferably 40-120°, and most preferably 60-100°. The length of a single side of the serration is 0.2-1.0 cm, preferably 0.5-1.0 cm.

[0011] Furthermore, the diameter of the inscribed circle corresponding to the arc segment of the corrugated electrode is 0.4-1.2 cm, preferably 0.6-1.0 cm. The length of the arc segment is 0.2-2.4 cm, preferably 1.0-2.0 cm.

[0012] Furthermore, the pleated electrode is a plate-shaped or mesh-shaped graphite electrode, carbon felt electrode, copper-nickel alloy electrode, titanium electrode, iron electrode, copper electrode, or stainless steel plate electrode, preferably a mesh-shaped iron electrode, copper electrode, or stainless steel electrode, and most preferably a mesh-shaped stainless steel electrode.

[0013] Furthermore, the pleated electrode is a 10-200 mesh stainless steel mesh electrode, preferably a 50-100 mesh stainless steel mesh electrode.

[0014] Furthermore, the anode is a DSA electrode, a graphite plate electrode, a lead dioxide electrode, a tin dioxide electrode, or other non-satellite electrode.

[0015] Furthermore, the distance between the anode and cathode of the electrochemical device is 2-10 cm, preferably 4-8 cm.

[0016] Furthermore, the current density of the electrochemical device is 5-30 mA / cm². 2 .

[0017] Furthermore, the residence time of the material in the electrochemical device is 10-120 min, preferably 30-90 min.

[0018] Furthermore, the wastewater has calcium and magnesium ion concentrations of 200-1000 mg·L⁻¹. -1 The concentration of bicarbonate is 300-3000 mg·L. -1 Wastewater.

[0019] Furthermore, the hardening removal method also includes the step of flocculating and settling the scale in the hardening removal device after the wastewater descaling reaction.

[0020] The technical solution of the present invention has the following advantages:

[0021] (1) In the electrochemical hardening method of the present invention, the hydrogen bubbles generated and released by the cathode after the change of the cathode structure have a certain mechanical stripping effect on the scale layer. At the same time, due to the special structure of the electrode surface, the hydrogen bubbles form a certain driving force to the outside, which can carry the scale layer away from the substrate surface, thereby preventing the scale layer from depositing on the cathode. This not only extends the service life of the cathode, but also makes the cathode have a certain self-cleaning ability.

[0022] (2) The pleated electrode used in this invention prevents scale from depositing on the cathode surface but instead crystallizes and grows in the water, thus slowing down the scaling rate on the electrode surface and reducing energy consumption during the reaction process. The average energy consumption of the electrochemical device for scale removal in the method of this invention, calculated based on the electrode operating cycle, is generally 6~15 kW·h / kg CaCO3.

[0023] (3) The pleated electrode used in this invention increases the electrode area, provides a large number of active sites, accelerates mass transfer, and improves the descaling speed.

[0024] (4) The scale layer on the cathode is directly flocculated and settled, which further reduces the risk of scale blockage in the chemical hardening device and realizes the efficient and stable operation of the electrochemical hardening process.

[0025] (5) The hardness removal method of the present invention can achieve 40-80% hardness removal and the homogeneous nucleation rate can reach more than 30%. In the preferred technical solution, it can reach more than 70%, and the single operation cycle of the electrode can reach more than 3 months.

[0026] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0027] Figure 1 Schematic diagram of the sawtooth-shaped corrugated electrode used in Examples 1-3; where α is the corrugation angle of the sawtooth-shaped corrugated electrode, and a is the length of one side of the sawtooth.

[0028] Figure 2The schematic diagram of the wave-shaped pleated electrode used in Examples 4-5 shows that b is the diameter of the inscribed circle corresponding to the arc segment of the wave-shaped pleated electrode, and the length of the arc segment from point c to point d is the length of the arc segment. Detailed Implementation

[0029] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0031] In this invention, the pH value was determined by the glass electrode method for determining pH value in water (GB / T6920), the suspended matter was determined by the gravimetric method for determining suspended matter in water (GB / T 11901), and the metal ions were determined by the microwave digestion / inductively coupled plasma mass spectrometry (ICP-MS).

[0032] Homogeneous nucleation rate = Homogeneous nucleation amount / (Homogeneous nucleation amount + Heterogeneous nucleation amount) * 100%

[0033] The heterogeneous nucleation is obtained by the difference subtraction method, and the mass change before and after electrode descaling is the heterogeneous nucleation amount; the homogeneous nucleation amount is obtained by subtracting the heterogeneous nucleation amount from the total hardness removal amount.

[0034] The average energy consumption of the electrochemical device for descaling in this invention is expressed as the amount of electricity consumed to remove a unit mass of hardness, and the energy consumption for removing a unit mass of hardness is calculated according to the following formula.

[0035] E=UIt / VC*1000

[0036] Where E represents the energy consumption per unit mass removed; U represents the voltage (V); I represents the current (A); t represents the electrolysis time (h); V represents the water sample volume (L); and C represents the concentration difference in hardness before and after treatment (mg / L).

[0037] Example 1

[0038] The industrial wastewater treated by electrochemical hardening removal is circulating water from a coal chemical plant. The water quality characteristics are: total hardness 600 mg / L, calcium content 379 mg / L, magnesium content 221 mg / L, and total alkalinity 912 mg / L.

[0039] The anode of the electrochemical hardening device is a DSA electrode, and the cathode is a serrated corrugated electrode, which is a 70-mesh, three-dimensional serrated stainless steel mesh with a corrugation angle α of 80°. The single-side length 'a' of the serrations is 0.8 cm. Figure 1As shown. Adjust the insulating pads of different sizes to make the distance between the cathode and anode plates 5cm.

[0040] The wastewater to be treated is pumped from the cathode into the electrochemical hardening device via an inlet pump and exits from the anode, using a bottom-in, top-out method. During the hardening process, the DC constant current source is adjusted to maintain a current density of 15 mA / cm². 2 Adjust the agitator to a stirring speed of 150-300 rpm / min. After reacting for 30 minutes, add chemicals to the treated wastewater for flocculation and sedimentation for 60 minutes. The effluent is discharged through the outlet, and the scale generated is discharged through the slag outlet.

[0041] After the above reaction treatment, the total hardness of the wastewater is 124 mg / L, the calcium content is 76 mg / L, the magnesium content is 48 mg / L, the total alkalinity is 183 mg / L, the hardness removal rate is 83.1%, the homogeneous nucleation rate is 79.3%, the single operation cycle of the electrode can reach more than 6 months, and the average energy consumption for descaling of the device during 6 months of operation is 6 kW·h / kg CaCO3.

[0042] Example 2

[0043] The industrial wastewater treated was the same as in Example 1, specifically industrial wastewater treated with electrochemical hardening removal. It was circulating water from a coal chemical plant, with the following water quality characteristics: total hardness of 600 mg / L, calcium content of 379 mg / L, magnesium content of 221 mg / L, and total alkalinity of 912 mg / L.

[0044] The anode of the electrochemical hardening device is a DSA electrode, and the cathode is a serrated corrugated electrode, which is a 70-mesh, three-dimensional serrated stainless steel mesh with a corrugation angle α of 30°. The single-side length 'a' of the serrations is 0.8 cm. Figure 1 As shown. Adjust the insulating pads of different sizes to make the distance between the cathode and anode plates 5cm.

[0045] The wastewater to be treated is pumped from the cathode into the electrochemical hardening device via an inlet pump and exits from the anode, using a bottom-in, top-out method. During the hardening process, the DC constant current source is adjusted to maintain a current density of 15 mA / cm². 2 Adjust the agitator to a stirring speed of 150-300 rpm / min. After reacting for 30 minutes, add chemicals to the treated wastewater for flocculation and sedimentation for 60 minutes. The effluent is discharged through the outlet, and the scale generated is discharged through the slag outlet.

[0046] After the above reaction treatment, the total hardness of the wastewater is 302 mg / L, the calcium content is 182 mg / L, the magnesium content is 120 mg / L, the total alkalinity is 179 mg / L, the hardness removal rate is 49.6%, the homogeneous nucleation rate is 33.2%, the single operation cycle of the electrode can reach more than 4 months, and the average energy consumption for descaling of the device during 4 months of operation is 12 kW·h / kg CaCO3.

[0047] Example 3

[0048] The industrial wastewater treated was the same as in Example 1, but was treated with electrochemical hardening removal. It was circulating water from a coal chemical plant, and its water quality characteristics were: total hardness of 600 mg / L, calcium content of 379 mg / L, magnesium content of 221 mg / L, and total alkalinity of 912 mg / L.

[0049] The anode of the electrochemical hardening device is a DSA electrode, and the cathode is a serrated, corrugated electrode, which is a three-dimensional serrated stainless steel mesh with a 5-mesh diameter and a corrugation angle α of 80°. The single-side length 'a' of the serrations is 0.8 cm. Figure 1 As shown. Adjust the insulating pads of different sizes to make the distance between the cathode and anode plates 5cm.

[0050] The wastewater to be treated is pumped from the cathode into the electrochemical hardening device via an inlet pump and exits from the anode, using a bottom-in, top-out method. During the hardening process, the DC constant current source is adjusted to maintain a current density of 15 mA / cm². 2 Adjust the agitator to a stirring speed of 150-300 rpm / min. After reacting for 30 minutes, add chemicals to the treated wastewater for flocculation and sedimentation for 60 minutes. The effluent is discharged through the outlet, and the scale generated is discharged through the slag outlet.

[0051] After the above reaction treatment, the total hardness of the wastewater is 260 mg / L, the calcium content is 145 mg / L, the magnesium content is 115 mg / L, the total alkalinity is 387 mg / L, the hardness removal rate is 56.7%, the homogeneous nucleation rate is 41.9%, the single operation cycle of the electrode can reach more than 4.5 months, and the average energy consumption for descaling after 4 months of operation is 10 kW·h / kg CaCO3.

[0052] Example 4

[0053] The industrial wastewater treated was the same as in Example 1, but was treated with electrochemical hardening removal. It was circulating water from a coal chemical plant, and its water quality characteristics were: total hardness of 600 mg / L, calcium content of 379 mg / L, magnesium content of 221 mg / L, and total alkalinity of 912 mg / L.

[0054] The anode of the electrochemical hardening device is a DSA electrode, and the cathode is a corrugated electrode, which is a 70-mesh three-dimensional corrugated stainless steel mesh. The diameter b of the inscribed circle corresponding to the arc segment of the corrugated electrode is 0.8 cm, and the length of the arc segment is 1.5 cm. Figure 2 As shown. Adjust the insulating pads of different sizes to make the distance between the cathode and anode plates 5cm.

[0055] The wastewater to be treated is pumped from the cathode into the electrochemical hardening device via an inlet pump and exits from the anode, using a bottom-in, top-out method. During the hardening process, the DC constant current source is adjusted to maintain a current density of 15 mA / cm². 2Adjust the agitator to a stirring speed of 150-300 rpm / min. After reacting for 30 minutes, add chemicals to the treated wastewater for flocculation and sedimentation for 60 minutes. The effluent is discharged through the outlet, and the scale generated is discharged through the slag outlet.

[0056] After the above reaction treatment, the total hardness of the wastewater is 159 mg / L, the calcium content is 91 mg / L, the magnesium content is 68 mg / L, the total alkalinity is 234 mg / L, the hardness removal rate is 73.5%, the homogeneous nucleation rate is 70.9%, the single operation cycle of the electrode can reach more than 5 months, and the average energy consumption for descaling of the device in 5 months of operation is 8 kW·h / kg CaCO3.

[0057] Example 5

[0058] The industrial wastewater treated was the same as in Example 1, but was treated with electrochemical hardening removal. It was circulating water from a coal chemical plant, and its water quality characteristics were: total hardness of 600 mg / L, calcium content of 379 mg / L, magnesium content of 221 mg / L, and total alkalinity of 912 mg / L.

[0059] The anode of the electrochemical hardening device is a DSA electrode, and the cathode is a corrugated electrode, which is a 70-mesh three-dimensional corrugated stainless steel mesh. The diameter b of the inscribed circle corresponding to the arc segment of the corrugated electrode is 3 cm, and the length of the arc segment is 1.5 cm. Figure 2 As shown. Adjust the insulating pads of different sizes to make the distance between the cathode and anode plates 5cm.

[0060] The wastewater to be treated is pumped from the cathode into the electrochemical hardening device via an inlet pump and exits from the anode, using a bottom-in, top-out method. During the hardening process, the DC constant current source is adjusted to maintain a current density of 15 mA / cm². 2 Adjust the agitator to a stirring speed of 150-300 rpm / min. After reacting for 30 minutes, add chemicals to the treated wastewater for flocculation and sedimentation for 60 minutes. The effluent is discharged through the outlet, and the scale generated is discharged through the slag outlet.

[0061] After the above reaction treatment, the total hardness of the wastewater is 338 mg / L, the calcium content is 190 mg / L, the magnesium content is 148 mg / L, the total alkalinity is 500 mg / L, the hardness removal rate is 53.8%, the homogeneous nucleation rate is 37.9%, the single operation cycle of the electrode can reach more than 4 months, and the average energy consumption for descaling of the device during 4 months of operation is 13 kW·h / kg CaCO3.

[0062] Comparative Example 1

[0063] Similar to Example 1, except that the cathode uses a two-dimensional stainless steel mesh. After reaction treatment, the total hardness of the wastewater was 385 mg / L, the calcium content was 227 mg / L, the magnesium content was 158 mg / L, the total alkalinity was 210 mg / L, the hardness removal rate was 45.8%, the homogeneous nucleation rate was 18.4%, the single operation cycle of the electrode was only 0.5 months, and the average energy consumption for descaling during the 0.5-month operation was 20 kW·h / kg CaCO3. In addition, two main problems were found during the experiment: (1) Scale deposits on the cathode plate reduce the working surface area, hinder the occurrence of electrochemical reactions, and hinder the mass transfer process; (2) It causes irreparable damage to the electrode and reduces the service life of the electrode.

Claims

1. An electrochemical method for hardening removal, comprising treating wastewater using an electrochemical device having a cathode and an anode, characterized in that, Wastewater enters through the cathode and exits through the anode. The cathode is a pleated electrode, a 50-100 mesh stainless steel mesh electrode. The pleated electrode has a serrated surface or a wavy surface. The pleated angle of the serrated electrode is 60-100°, and the length of a single side of the serration is 0.2-1.0 cm. The diameter of the inscribed circle corresponding to the arc segment of the wavy electrode is 0.4-1.2 cm, and the length of the arc segment is 0.2-2.4 cm. The wastewater has calcium and magnesium ion concentrations of 200-1000 mg·L⁻¹. -1 The concentration of bicarbonate is 300-3000 mg·L. -1 Wastewater.

2. The method according to claim 1, characterized in that, The anode is a DSA electrode, a graphite plate electrode, a lead dioxide electrode, a tin dioxide electrode, or other non-satellite electrode.

3. The method according to claim 1, characterized in that, The distance between the anode and cathode of the electrochemical device is 2-10 cm.

4. The method according to claim 1, characterized in that, The current density of the electrochemical device is 5-30 mA / cm². 2 .

5. The method according to claim 1, characterized in that, The residence time of materials in the electrochemical device is 10-120 min.

6. The method according to claim 1, characterized in that, The hardening removal method also includes the step of flocculating and settling the scale in the hardening removal device after the wastewater descaling reaction.

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