Method for recovering heavy metals from electrolytic reduction electroplating wastewater coupled with electrooxidation of organic matter

Abstract

The application discloses a method for recovering heavy metals from electrolytic reduction electroplating wastewater coupled with electro-oxidation of organic matters. The method uses an H-shaped electrolytic cell, which is separated by a diaphragm. One side is an anode cell for electro-oxidation of organic matters, and the other side is a cathode cell for recovering heavy metals from electrolytic reduction electroplating wastewater. By developing an oxidation system of high-value-added chemicals matched with the cathode end at the anode end of the electro-reduction recovery of heavy metals, the overpotential of electrolytic water can be significantly reduced, the recovered metal elements have smooth and high-quality surfaces, and the power consumption is saved by about 40%, and the cathode reduction efficiency is improved. For the tail liquid of the electro-reduction reaction, the calcium-based hydrotalcite can be used to treat it to the discharge standard, realizing complete treatment of heavy metal pollution. The amount of sludge generated is reduced by more than 80% compared with the traditional treatment method, and the discharge of hazardous waste is reduced. The method is simple to operate, simple in process, and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to a method for recovering heavy metals coupled with the electro-oxidation of organic matter from electrolytic reduction of electroplating wastewater. Background Technology

[0002] Currently, methods for treating heavy metal-containing wastewater typically include chemical, adsorption, electrochemical, ion exchange, and biological methods. Among these, chemical precipitation is the most commonly used method in the market. However, it consumes large amounts of chemical raw materials, corrodes equipment, generates significant amounts of hazardous waste, and is prone to secondary pollution, resulting in substantial resource waste. Other methods, such as ion exchange, are limited in practical application due to high costs and low efficiency. Compared to the above technologies, electroreduction technology is a widely used method, particularly suitable for reducing and recovering heavy metal ions from high-concentration heavy metal-containing wastewater into elemental metals. By controlling the cathode reduction potential, metal ions such as Cu, Pb, Sn, and Ag can be recovered and reused, with a recovery rate of up to 98%. However, during electrolysis, the competitive reaction of water reduction to generate hydrogen gas due to the high applied cathode reduction potential produces a large number of bubbles, causing the elemental metal deposited on the electrode plate to become loose and porous, easily flaking off and of low quality. The electrolysis process also suffers from the problem of anolyte oxidation releasing oxygen, exacerbating the high power consumption issue, and the final treated wastewater concentration cannot meet emission standards (e.g., the emission standard for Cu wastewater is 0.1 ppm). Therefore, developing low-energy electrochemical reduction methods to reduce the cathode reduction potential and obtain high-quality elemental metals with smooth and flat surfaces, while simultaneously solving the problem that heavy metal waste liquid still fails to meet standards after reduction, is a key challenge in the current electrochemical treatment of high-concentration heavy metal waste liquid. Summary of the Invention

[0003] To address the problems existing in current technologies, this invention provides a method for recovering heavy metals from electroplating wastewater via electrolytic reduction coupled with organic electrooxidation, used for the pollution treatment of high-concentration electroplating wastewater (copper or nickel wastewater). By developing an oxidation system with high-value-added chemicals matched to the cathode at the anode of the electrolytic reduction heavy metal recovery process, the overpotential of the electrolyzed water can be significantly reduced. This avoids problems such as the generation of numerous bubbles due to hydrogen evolution side reactions at higher cathode potentials, leading to porous and easily detached metal elements. The recovered metal elements have a smooth and high-quality surface, and the process saves approximately 40% of power consumption while improving cathode reduction efficiency. For the tail liquid from the electrolytic reduction reaction, calcium-based hydrotalcite can be used to treat it to meet discharge standards, achieving complete treatment of heavy metal pollution. The amount of sludge generated is reduced by more than 80% compared to traditional treatment methods, reducing hazardous waste emissions.

[0004] The aforementioned electrolytic reduction system for recovering heavy metals from electroplating wastewater coupled with organic electro-oxidation employs an H-type electrolytic cell, separated by a membrane. One side is the anode cell for organic electro-oxidation, and the other side is the cathode cell for electrolytic reduction of electroplating wastewater for recovering heavy metals.

[0005] The membrane in question is a Nafion 117 proton exchange membrane.

[0006] The voltage of the reaction system is 0.3-0.5V vs Ag / AgCl, and the current is 20-50mA / cm. -2 .

[0007] The electrolyte in the anode cell is a KOH solution. Organic compounds such as 5-hydroxymethylfurfural, methanol, glycerol, or benzyl alcohol are added to the anode cell. The oxidation product of 5-hydroxymethylfurfural is 2,5-furandicarboxylic acid; the oxidation product of methanol is formic acid; the oxidation product of benzyl alcohol is benzoic acid; and the oxidation product of glycerol is acrylic acid.

[0008] The cathode tank contains electroplating wastewater of copper or nickel, with stainless steel or copper sheets used as cathodes. The concentration of the electroplating wastewater of copper or nickel is 3000-100000 ppm.

[0009] The tail liquid of electroplating wastewater from the cathode cell electrolytic reduction is mixed with calcium-based hydrotalcite and stirred at room temperature for 10-60 minutes to remove residual heavy metal ions.

[0010] The electrode used in the anode cell is prepared by dispersing the anode catalyst in ethanol, ultrasonically dispersing it, and then coating it on hydrophilic carbon paper.

[0011] The anode catalyst is prepared by dissolving soluble nickel salt, soluble cobalt salt or soluble iron salt and boric acid in decarbonated and deionized water to obtain a mixed salt solution; adding the mixed solution and alkaline solution to a rotating liquid film reactor for mixing; centrifuging, washing and drying the resulting slurry to obtain the anode catalyst.

[0012] The soluble nickel salt is one or more of nickel nitrate, nickel chloride, and nickel sulfate.

[0013] The soluble cobalt salt is one or more of cobalt nitrate, cobalt chloride, and cobalt sulfate.

[0014] The alkaline solution is a sodium hydroxide solution, a potassium hydroxide solution, or ammonia.

[0015] The electroreduction recovery potential of heavy metal ions varies depending on the element, and different organic compounds have different suitable oxidation potentials and reaction currents. This invention selects appropriate oxidation potentials for matching the anode and cathode within the reaction oxidation potential range of 0.3-0.5 V vs Ag / AgCl. The matched coupling system not only improves the reduction efficiency of heavy metals (copper, nickel), yielding high-quality elemental metals with smooth and flat surfaces, achieving a recovery rate of over 95% and realizing resource recovery of heavy metals; but also uses the oxidation of organic matter at the anode instead of the kineticly slow OER process, reducing the overall reaction potential and overall energy consumption by 40%. It also avoids the occurrence of hydrogen evolution and oxygen evolution side reactions, eliminating the need for additional oxidants. Utilizing the active oxygen generated from water electrolysis for highly selective oxidation of organic matter, it achieves the oxidation of high-value-added fine chemicals (5-hydroxymethylfurfural, glycerol, methanol, etc.), with a Faraday efficiency exceeding 90% within the 0.3-0.5 V vs Ag / AgCl range. For the tail liquid from the electroreduction reaction, treatment with calcium-based hydrotalcite can bring it up to emission standards (<0.5 ppm). The method of this invention is simple to operate and has good economic benefits, with broad prospects for industrial application. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the reaction system for recovering heavy metals from electroplating wastewater coupled with the electro-oxidation of organic matter, as described in Example 1.

[0017] Figure 2 This is a diagram of the reaction apparatus for the electrolytic reduction of electroplating wastewater to recover heavy metals coupled with the electro-oxidation of organic matter, as shown in Example 1.

[0018] Figure 3 This is a photograph of elemental copper, the cathode reduction product in Example 1.

[0019] Figure 4 The image shows the XRD pattern of elemental copper, the cathode reduction product in Example 1.

[0020] Figure 5 The image shows the XRD pattern of the anode catalyst prepared in Example 1.

[0021] Figure 6 This is an HRTEM image of the anode catalyst in Example 1.

[0022] Figure 7 This is a photograph of elemental nickel, the cathode reduction product in Example 2.

[0023] Figure 8 The image shows the XRD pattern of elemental nickel, the cathode reduction product in Example 2.

[0024] Figure 9This is an LSV diagram showing the reaction before and after the cathodic electroplating coupled anodic oxidation. Detailed Implementation

[0025]

Example 1

[0026] Preparation of nickel-cobalt layered double hydroxide (LCD) anode catalyst: Nickel nitrate and cobalt nitrate were dissolved in decarbonated water with boric acid and labeled as solution A, wherein the molar ratio of nickel, cobalt, and boron was 3:1:1 and the concentration of nickel ions was 0.1 mol / L; Sodium hydroxide was dissolved in decarbonated water and labeled as solution B, wherein the concentration of sodium hydroxide was 1.5 times the sum of the solubilities of nickel and cobalt ions; Equal volumes of solutions A and B were simultaneously poured into a rotating liquid film reactor for backmixing for 2 min, followed by centrifugation, washing, and drying to obtain the anode catalyst material, single-layer nickel-cobalt LCD.

[0027] Anode electrode preparation: The anode catalyst material nickel cobalt hydrotalcite was dispersed in ethanol, sonicated for 30 min to ensure complete dispersion, and then coated onto hydrophilic carbon paper.

[0028] Electrolytic reduction of electroplating wastewater for heavy metal recovery coupled with organic electrooxidation reaction: An H-type electrolytic cell is used, separated by a 100μm thick Nafion 117 proton exchange membrane. One side is the anode cell, into which a 2cm*1.5cm anode electrode prepared above is inserted, and 25mL of 1M KOH solution is added, along with the reactant 5-hydroxymethylfurfural (5-hydroxymethylfurfural) at a concentration of 10mM. The other side is the cathode cell, into which 25mL of 6000ppm copper plating wastewater is added, with a 2cm*1.5cm stainless steel sheet used as the cathode. A voltage of 0.3 V vs Ag / AgCl is applied, and after 2 hours of reaction, the high-concentration copper plating wastewater becomes clear and transparent after electrolytic treatment. At the cathode, copper ions undergo a reduction reaction, enriching on the stainless steel sheet to form high-quality elemental copper with a smooth and flat surface (e.g., copper ions). Figure 3 (As shown). The copper ion concentration in the solution decreased from 6000 ppm to 60 ppm, with a metal recovery rate as high as 99.0%, and 150 mg of elemental copper was reduced. After the reaction was completed, calcium-based hydrotalcite was added to the tail liquid in the cathode tank, and the mixture was stirred at room temperature for 10 minutes, reducing the copper ion concentration to below 0.5 ppm, meeting the discharge standards for industrial wastewater. In the anode tank, 5-hydroxymethylfurfural was oxidized to generate high-value chemicals to replace the slow-kinetic water oxidation process, matching the cathode reduction efficiency. The Faraday efficiency (FE) of the 2,5-furandicarboxylic acid product generated at the anode was ≥90%.

[0029]

Example 2

[0030] The H-type electrolytic cell is separated by a 100μm thick Nafion 117 proton exchange membrane. One side is the anode cell, into which a 2cm*1.5cm anode electrode prepared in Example 1 is inserted, and 25mL of 1M KOH solution is added, along with benzyl alcohol (10mM). The other side is the cathode cell, into which 25mL of 4000ppm nickel plating wastewater is added, and a 2cm*1.5cm copper sheet serves as the cathode. A voltage of 0.5V vs. Ag / AgCl is applied, and after 2 hours of reaction, the high-concentration nickel plating wastewater becomes clear and transparent after electrolytic treatment. At the cathode, nickel ions undergo a reduction reaction, enriching on the copper sheet to form high-quality elemental nickel with a smooth and flat surface (e.g., nickel ions). Figure 7 (As shown). The nickel ion concentration in the solution decreased from 4000 ppm to 390 ppm, with a metal recovery rate as high as 90.3%, and 90 mg of elemental nickel was reduced. After the reaction was completed, calcium-based hydrotalcite was added to the tail liquid of the cathode tank, and stirred for 10 minutes at room temperature. The nickel ion concentration therein could be reduced to below 0.5 ppm, meeting the discharge standards for industrial wastewater. At the anode, benzyl alcohol was oxidized to produce high-value chemicals to replace the slow water oxidation process, matching the cathode reduction efficiency. The Faraday efficiency (FE) of the benzoic acid product generated at the anode was ≥90%.

[0031]

Example 3

[0032] Preparation of nickel-iron layered double hydroxide anode catalyst: Nickel nitrate and iron nitrate were dissolved in decarbonated water with boric acid and labeled as solution A, wherein the molar ratio of nickel, iron, and boron was 3:1:1 and the concentration of nickel ions was 0.1 mol / L; Sodium hydroxide was dissolved in decarbonated water and labeled as solution B, wherein the concentration of sodium hydroxide was 1.5 times the sum of the solubilities of nickel and iron ions; Equal volumes of solutions A and B were simultaneously poured into a rotating liquid film reactor for backmixing for 2 min, and then centrifuged, washed, and dried to obtain the anode catalyst material, single-layer nickel-iron layered double hydroxide.

[0033] Anode electrode preparation: The anode catalyst material, nickel-iron hydrotalcite, was dispersed in ethanol and sonicated for 30 minutes to ensure complete dispersion. Then, it was coated onto hydrophilic carbon paper.

[0034] Electrolytic reduction of electroplating wastewater for heavy metal recovery coupled with organic electrooxidation reaction: An H-type electrolytic cell was used, separated by a 100 μm thick Nafion 117 proton exchange membrane. One side was the anode cell, into which a 2 cm * 1.5 cm anode electrode prepared above was inserted, and 25 mL of 1 M KOH solution was added, along with the reactant 5-hydroxymethylfurfural (5-hydroxymethylfurfural) at a concentration of 10 mM. The other side was the cathode cell, into which 25 mL of nickel plating wastewater with a concentration of 4000 ppm was added, and a 2 cm * 1.5 cm copper sheet served as the cathode. A voltage of 0.4 V vsAg / AgCl was applied, and after 2 hours of reaction, nickel ions underwent a reduction reaction at the cathode, enriching on the copper sheet to form high-quality elemental nickel with a smooth and flat surface. The nickel ion concentration in the solution decreased from 4000 ppm to 400 ppm, with a metal recovery rate as high as 90.0%, and 90 mg of elemental nickel was reduced. After the reaction is complete, calcium-based hydrotalcite is added to the tailings of the cathode tank, and the mixture is stirred for 10 minutes at room temperature. This reduces the nickel ion concentration to below 0.5 ppm, meeting the discharge standards for industrial wastewater. At the anode, 5-hydroxymethylfurfural is oxidized to produce high-value chemicals, replacing the slow-kinetic water oxidation process. This matches the cathode reduction efficiency, resulting in a Faraday efficiency (FE) ≥ 85% for the 2,5-furandicarboxylic acid product generated at the anode.

[0035]

Example 4

[0036] The H-type electrolytic cell is separated by a 100μm thick Nafion 117 proton exchange membrane. One side is the anode cell, into which a 2cm*1.5cm anode electrode prepared in Example 3 is inserted, and 25mL of 1M KOH solution and methanol (10mM) are added. The other side is the cathode cell, into which 25mL of 6000ppm copper plating wastewater is added, and a 2cm*1.5cm stainless steel sheet is used as the cathode. A voltage of 0.3 V vs Ag / AgCl is applied. After 2 hours of reaction, the high-concentration copper plating wastewater becomes clear and transparent after electrolytic treatment. Copper ions at the cathode undergo a reduction reaction, enriching on the stainless steel sheet to form high-quality elemental copper with a smooth and flat surface. The copper ion concentration in the solution is reduced from 6000 ppm to 50 ppm, with a metal recovery rate as high as 99.2%, and 150mg of elemental copper is reduced. After the reaction is complete, calcium-based hydrotalcite is added to the tailings of the cathode tank, and the mixture is stirred for 10 minutes at room temperature. The copper ion concentration in the solution drops below 0.5 ppm, meeting the discharge standards for industrial wastewater. At the anode, methanol oxidation to generate high-value chemicals replaces the slow-kinetic water oxidation process, matching the cathode reduction efficiency. The formic acid product generated at the anode achieves a Faraday efficiency (FE) ≥ 85%.

Claims

1. A reaction system for recovering heavy metals from electrolytic reduction of electroplating wastewater coupled with the electro-oxidation of organic matter, characterized in that, The reaction system uses an H-type electrolytic cell, which is separated by a membrane in the middle. One side is the anode cell for the electro-oxidation of organic matter, and the other side is the cathode cell for the electrolytic reduction of electroplating wastewater to recover heavy metals. The electrode used in the anode cell is prepared by dispersing the anode catalyst in ethanol, ultrasonically dispersing it, and then coating it on hydrophilic carbon paper. The anode catalyst is prepared by dissolving soluble nickel salt, soluble cobalt salt or soluble iron salt and boric acid in decarbonated and deionized water to obtain a mixed salt solution; adding the mixed solution and alkaline solution to a rotating liquid film reactor simultaneously and mixing them; centrifuging, washing and drying the resulting slurry to obtain the anode catalyst. The voltage of the reaction system is 0.3-0.5V vs Ag / AgCl, and the current is 20-50mA / cm. -2 ; The cathode pool is filled with copper plating wastewater or nickel plating wastewater, and stainless steel or copper sheets are used as cathodes. The concentration of the electroplating copper wastewater or electroplating nickel wastewater is 3000-100000ppm.

2. The reaction system according to claim 1, characterized in that, The membrane in question is a Nafion 117 proton exchange membrane.

3. The reaction system according to claim 1, characterized in that, The electrolyte in the anode cell is a KOH solution.

4. The reaction system according to claim 1, characterized in that, Organic compounds such as 5-hydroxymethylfurfural, methanol, glycerol, or benzyl alcohol are added to the anode pool.

5. The reaction system according to claim 1, characterized in that, The tail liquid of electroplating wastewater from the cathode cell electrolytic reduction is mixed with calcium-based hydrotalcite and stirred at room temperature for 10-60 minutes to remove residual heavy metal ions.

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