Method and device for recycling heavy metals in wastewater based on sulfur dioxide membrane electrolysis

Abstract

The invention provides a method and a device for recycling heavy metals in wastewater based on sulfur dioxide membrane electrolysis. The method comprises the following steps: placing a membrane electrode in initial wastewater for electrochemical reduction, reacting with the initial wastewater to generate hydrogen sulfide gas, and precipitating heavy metal ions in the initial wastewater by the hydrogen sulfide gas. Wherein the initial wastewater comprises heavy metal ions and sulfur dioxide, and the initial wastewater is heavy metal wastewater or a mixture of the heavy metal wastewater and a substance containing sulfur dioxide. The membrane electrode is provided with hydrophobic membrane holes which are uniformly distributed, and the membrane electrode can catalyze reduction of sulfur dioxide to generate hydrogen sulfide gas. In the treatment method of the heavy metal wastewater, the membrane electrode reacts with sulfur dioxide in the initial wastewater to generate hydrogen sulfide gas. The hydrogen sulfide gas can realize micro-nano-scale dispersion through the membrane pores, so that the hydrogen sulfide gas is in full contact with the heavy metal ions, the utilization rate of the hydrogen sulfide gas is high, and different heavy metal ions can be recovered through fractional precipitation.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment, and in particular to a method and a device for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis. Background Art

[0002] Wastewater containing heavy metal ions and sulfur dioxide, because both heavy metal ions and sulfur dioxide are elements harmful to the environment, both need to be treated, resulting in a relatively complicated entire treatment process. For example, waste acid from non-ferrous smelting, specifically waste acid from non-ferrous smelting flue gas acid production, contains a large amount of heavy metals such as arsenic, lead, copper, and includes free SO2 (molecular form) and / or dissolved SO2 (hydrated form), which is a typical wastewater containing heavy metal ions and sulfur dioxide. The commonly used waste acid treatment method for non-ferrous smelting waste acid is to react it with hydrogen sulfide to remove most of the heavy metals. However, this treatment process requires additional digestion of hydrogen sulfide gas, and the heavy metal ion residues are relatively high. Summary of the invention

[0003] The main purpose of the present invention is to provide a method and device for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis, so as to solve the technical problems that the commonly used treatment method requires the purchase of dangerous hydrogen sulfide gas and has a high level of heavy metal ion residues.

[0004] To achieve the above object, the present application provides a method for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis, wherein the heavy metal wastewater includes heavy metal ions, comprising the following steps:

[0005] Placing the membrane electrode in the initial wastewater for electrochemical reduction, reacting with the initial wastewater to generate hydrogen sulfide gas, and the hydrogen sulfide gas precipitates heavy metal ions in the initial wastewater; wherein the initial wastewater includes heavy metal ions and sulfur dioxide, and the initial wastewater is heavy metal wastewater, or a mixture of heavy metal wastewater and a substance containing sulfur dioxide;

[0006] The membrane electrode has uniformly distributed hydrophobic membrane pores, and the membrane electrode can catalyze the reduction of sulfur dioxide to generate hydrogen sulfide gas.

[0007] According to an embodiment of the present application, the method further includes adjusting the operating current of the membrane electrode to adjust the hydrogen sulfide gas generation rate and control the hydrogen sulfide partial pressure at the initial wastewater-membrane electrode interface during the electrochemical reduction process.

[0008] According to the embodiment of the present application, the adjusting the working current of the membrane electrode comprises adjusting stepwise in multiple reaction stages based on the solubility product of the heavy metal ions corresponding to the heavy metal sulfides in the initial wastewater from small to large;

[0009] In any two adjacent reaction stages of the working current, the working current of the previous reaction stage is smaller than the working current of the next reaction stage, and the concentration of hydrogen sulfide gas generated by the working current of any reaction stage avoids the precipitation of heavy metal ions in the subsequent stage.

[0010] According to an embodiment of the present application, in the working current of each reaction stage, the initial working current is smaller than the terminal working current.

[0011] According to an embodiment of the present application, the step of energizing the membrane electrode in the initial wastewater to react with the initial wastewater to generate hydrogen sulfide gas also includes maintaining the pH of the initial wastewater <2.

[0012] According to an embodiment of the present application, the heavy metal ions are at least one of arsenic ions, lead ions, and copper ions.

[0013] According to an embodiment of the present application, the initial wastewater is heavy metal wastewater, the heavy metal wastewater is non-ferrous smelting waste acid, and the non-ferrous smelting waste acid includes arsenic ions, lead ions, copper ions and sulfur dioxide.

[0014] According to an embodiment of the present application, the membrane electrode comprises a membrane substrate and a load layer loaded on at least one surface of the membrane substrate, the material of the load layer comprises at least one of a metal element with catalytic properties, a heavy metal sulfide, and a metal selenide, the membrane substrate has the hydrophobic membrane pores, or:

[0015] The membrane electrode is a single-layer membrane structure, and the material of the membrane structure is a material with catalytic function and surface hydrophobicity.

[0016] According to an embodiment of the present application, the material of the membrane substrate is a hydrophobic porous material or a porous material subjected to a surface hydrophobic treatment;

[0017] The metal element is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium; the heavy metal sulfide is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium sulfide; the metal selenide is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium selenide; or;

[0018] The material having catalytic function and surface hydrophobicity is carbon cloth or porous carbon paper, or a porous metal material with surface hydrophobicity treatment.

[0019] The present application also provides a device for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis, which is used to implement the above method. The wastewater treatment device includes an electrolytic cell, a working electrode and a counter electrode. The electrolytic cell includes a cathode chamber and an anode chamber. The electrolyte in the cathode chamber is initial wastewater, and the working electrode is a membrane electrode.

[0020] In the above-mentioned method for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis, hydrogen sulfide gas is generated by the reaction of the membrane electrode with sulfur dioxide in the initial wastewater. Hydrogen sulfide gas can be dispersed at the micro-nano level through the membrane pores, so that hydrogen sulfide gas is fully in contact with heavy metal ions, so that the utilization rate of hydrogen sulfide gas is high and the removal efficiency of heavy metal ions is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0022] Figure 1 This is a schematic diagram of the principle of graded recovery of waste acid heavy metals based on sulfur dioxide membrane electrolysis according to one embodiment of the present application;

[0023] Figure 2 This is a diagram showing the selectivity results of different metal ion precipitation regulated by membrane electrode current density according to one embodiment of the present application;

[0024] Figure 3 This is a schematic diagram of a device and its principle for recovering heavy metals from wastewater based on sulfur dioxide membrane electrolysis according to one embodiment of the present application.

[0025] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with the implementation methods and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be noted that all directional indications (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0028] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0029] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0030] The present application provides a method for treating heavy metal wastewater, wherein the heavy metal wastewater includes heavy metal ions, comprising the following steps:

[0031] The membrane electrode is placed in the initial wastewater for electrochemical reduction, reacting with the initial wastewater to generate hydrogen sulfide gas, and the hydrogen sulfide gas precipitates the heavy metal ions in the initial wastewater. The initial wastewater includes heavy metal ions and sulfur dioxide, and the initial wastewater is heavy metal wastewater, or a mixture of heavy metal wastewater and sulfur dioxide-containing substances. The membrane electrode has a plurality of hydrophobic membrane pores, and the membrane electrode can catalyze the reduction of sulfur dioxide to generate hydrogen sulfide gas.

[0032] The heavy metal wastewater treatment method of the present application may target heavy metal wastewater including gold ions, silver ions, copper ions, iron ions, mercury ions, lead ions, cadmium ions, arsenic ions, and the like.

[0033] The initial wastewater is the direct treatment object of this treatment method. The initial wastewater is required to include heavy metal ions and sulfur dioxide at the same time, wherein the sulfur dioxide can be free SO2 (molecular form) and / or dissolved SO2 (hydrated form).

[0034] Therefore, for example, if the heavy metal-containing wastewater itself includes sulfur dioxide, such as non-ferrous smelting waste acid and sulfurous acid production wastewater, the heavy metal wastewater can be directly used as the initial wastewater, or some sulfur dioxide-containing substances (such as sulfur dioxide absorption liquid) can be added to adjust the sulfur dioxide in the initial wastewater to the target concentration, such as 1mmol / L~2mol / L.

[0035] For example, if the heavy metal wastewater itself does not include sulfur dioxide, such as electroplating wastewater, metal processing wastewater, etc., some sulfur dioxide-containing substances (such as sulfur dioxide absorption liquid) can be added to the heavy metal wastewater to adjust the sulfur dioxide in the initial wastewater to the target concentration.

[0036] In some embodiments, the sulfur dioxide absorption liquid is obtained by absorbing sulfur dioxide gas with an alkali solution or water, or by injecting sulfur dioxide microbubbles into an acidic electrolyte (pH <7). Common alkali solutions include ammonia water, sodium hydroxide solution, potassium hydroxide solution, etc., the water absorption liquid of sulfur dioxide is mainly H2SO3 solution, and the alkali absorption liquid of sulfur dioxide such as ammonium bisulfite solution, potassium bisulfite solution, sodium bisulfite solution, etc. are all suitable for the technical solution of the present invention. The concentration of the sulfur dioxide absorption liquid is not limited, and it can be a sulfur dioxide-containing solution formed by the dissolution of sulfur dioxide during the flue gas scrubbing process. The sulfur dioxide gas can be an enriched high-concentration sulfur dioxide gas, or it can be sulfur dioxide flue gas, etc.

[0037] The membrane electrode is placed in the initial wastewater for electrochemical reduction, and reacts with the initial wastewater to generate hydrogen sulfide gas. The membrane electrode has a hydrophobic porous structure and has the function of catalytic reduction of sulfur dioxide to generate hydrogen sulfide and uniform distribution of hydrogen sulfide gas.

[0038] The membrane electrode can highly selectively reduce the sulfur dioxide absorption liquid into hydrogen sulfide gas and separate it in situ, and it enters the heavy metal precipitation reaction side under the driving force of concentration difference.

[0039] The membrane electrode has a porous structure. The intermediate state of hydrogen sulfide produced during the electrochemical reduction of the sulfur dioxide absorbent can be quickly and highly selectively separated by the membrane electrode, thereby prompting the chemical reaction equilibrium of the entire electrochemical reduction reaction to move in a direction that is favorable for the generation of hydrogen sulfide, thereby improving the Faraday efficiency of hydrogen sulfide. The entire electrochemical reduction process avoids the secondary reaction of hydrogen sulfide and sulfur dioxide, and almost no elemental sulfur is produced on the electrode surface. The membrane electrode with a porous structure has a higher specific surface area, and after the dispersed loaded catalyst, more catalytic active sites can be exposed, which has higher catalytic activity than general block electrodes. Hydrogen sulfide gas comes into contact with heavy metal ions to generate heavy metal sulfides and precipitate.

[0040] Moreover, using membrane electrodes to generate hydrogen sulfide H2S gas and then treating heavy metal ions also has the following beneficial effects.

[0041] 1. H2S does not require any storage link, it can be used immediately after being produced in milliseconds, and it is easy to realize automation and continuous operation.

[0042] 2. The membrane interface can provide nucleation sites for the crystallization of heavy metal sulfides.

[0043] 3. H2S can be dispersed at the micro-nano level through the membrane pores, and the concentration distribution on the membrane surface is very uniform. There is no side reaction caused by excessive local H2S, which is conducive to the highly selective and uniform conduct of the specified sulfidation reaction;

[0044] 4. Overcome the disadvantage of insufficient H2S utilization in traditional gas-liquid sulfidation.

[0045] In some embodiments, the method further includes adjusting the operating current of the membrane electrode to adjust the hydrogen sulfide gas generation rate, thereby controlling the hydrogen sulfide gas partial pressure at the reaction interface.

[0046] Since H2S is transmitted through the membrane pores, its flux can be precisely controlled without delay by the current density. The working current of the membrane electrode is positively correlated with the partial pressure of hydrogen sulfide gas. When the working current of the membrane electrode is small, the partial pressure of hydrogen sulfide gas is small and the local concentration of the reaction is low. Therefore, it can preferentially react with heavy metal ions with smaller solubility product constants.

[0047] In the above-mentioned embodiments, the heavy metal sulfides generated by the heavy metal ions in the heavy metal wastewater are not separated. In some embodiments, the heavy metal sulfides can be separated by gradient. Exemplarily, adjusting the working current of the membrane electrode includes adjusting the working current in corresponding reaction stages based on the solubility product of the heavy metal ions corresponding to the heavy metal sulfides in the initial wastewater from small to large.

[0048] In any two adjacent reaction stages of the working current, the working current of the previous reaction stage is smaller than the working current of the subsequent reaction stage, and the concentration of hydrogen sulfide gas generated by the working current of any reaction stage will not cause precipitation of heavy metal ions corresponding to the working current of the subsequent reaction stage.

[0049] In this embodiment, the difference in solubility products of different heavy metal sulfides is utilized to achieve the sequential occurrence and step-by-step separation of different heavy metal sulfidation reactions.

[0050] Specifically, the entire treatment process is divided into different reaction stages according to the order of the solubility products of heavy metal sulfides from small to large. The order of the solubility products of heavy metal sulfides from small to large is consistent with the time sequence of the corresponding reaction stages in the treatment process, and is also consistent with the order of the magnitude of the working currents of the corresponding reaction stages in the treatment process. The corresponding working current in the previous reaction stage is less than the corresponding working current in the subsequent reaction stage. The corresponding working current in the previous reaction stage can only precipitate the heavy metal ions in the corresponding working reaction stage, but is not enough to precipitate the heavy metal ions in the subsequent working reaction stage.

[0051] The solubility product of heavy metal sulfide is small, which means that the heavy metal sulfide is easy to precipitate, and the corresponding heavy metal ion can be precipitated by reacting with a smaller concentration of H2S. On the contrary, it means that the heavy metal sulfide is not easy to precipitate, and the corresponding heavy metal ion can only precipitate after reacting with a larger concentration of H2S. Therefore, by controlling the appropriate working current, only the heavy metal sulfide with the smallest solubility product is precipitated, while the heavy metal sulfides with other solubility products are not precipitated, thereby separating the heavy metal sulfide with the smallest solubility product. Based on the same principle, the heavy metal sulfide with the second smallest solubility product is separated. Repeat the above steps until all heavy metal sulfides are separated. In this way, the effect of graded recovery of heavy metal ions is achieved.

[0052] Take heavy metal ions including lead ions, mercury ions, and copper ions as examples. Figure 1 , the Ksp of PbS is 9.3×10 -28 , the Ksp of CuS is 9.3×10 -33 , the Ksp of HgS is 1×10 -47 . Ksp of PbS>Ksp of CuS>Ksp of HgS.

[0053] Therefore, the reaction stage is divided into three stages, namely the first reaction stage, the second reaction stage and the third reaction stage. The working current of the first reaction stage is less than the working current of the second reaction stage and less than the working current of the third reaction stage. In some embodiments, 0.1 mA / cm 2 ≤Working current in the first reaction stage<1.6mA / cm 2 , 1.6mA / cm 2 ≤The working current of the second reaction stage<3.2mA / cm 2 , 3.2mA / cm 2 ≤Working current of the third reaction stage≤16mA / cm 2 The current of the working current in the first reaction stage only precipitates HgS, but is insufficient to precipitate CuS and PbS; the current of the working current in the second reaction stage only precipitates CuS, but is insufficient to precipitate PbS. The current of the working current in the third reaction stage only precipitates PbS. In this way, the first reaction stage only precipitates and separates HgS, the second reaction stage only precipitates and separates CuS, and the third reaction stage only precipitates and separates PbS.

[0054] In some embodiments, the duration of the current flow in each reaction stage (ie, the duration of the electrochemical reduction) is determined by the concentration and total amount of heavy metal ions in the wastewater and the applied current density.

[0055] In this embodiment, by adjusting the working current on the membrane electrode to accurately control the H2S concentration, different metal sulfidation reactions can be sequentially occurred and separated in stages based on the difference in Ksp of heavy metal sulfidation.

[0056] In some embodiments, in the working current of each reaction stage, the initial working current is smaller than the terminal working current.

[0057] In each reaction stage, as the reaction proceeds, the corresponding heavy metal ions are gradually precipitated, and the concentration of heavy metal ions gradually decreases. Therefore, in this reaction stage, the later working current (i.e., the terminal working current) can increase and be greater than the initial working current (i.e., the initial working current). Specifically, in each reaction stage, the magnitude of the working current can gradually increase, or the magnitude of the working current can be increased after a fixed period of time. For example, still taking heavy metal ions including lead ions, mercury ions, and copper ions as an example. A lower working current density (range 0.1~1.6mA / cm 2 mA / cm 2 ), the second reaction stage increases the working current density (range 1.6~3.2mA / cm 2 ), the third reaction stage sets a higher working current density (range 3.2~16mA / cm 2 ). The local partial pressure of hydrogen sulfide at the reaction interface can be linearly adjusted by the current density, and different types of metal ions can be selectively precipitated in sequence to achieve graded recovery.

[0058] In some embodiments, the step of applying electricity to the membrane electrode in the initial wastewater to react with the initial wastewater to generate hydrogen sulfide gas also includes maintaining the pH of the initial wastewater < 2. This can maintain the electrolyte in a slightly acidic environment that is conducive to the generation of hydrogen sulfide.

[0059] In some embodiments, the heavy metal ion is at least one of arsenic ion, lead ion, and copper ion.

[0060] In some embodiments, the initial wastewater is heavy metal wastewater, the heavy metal wastewater is non-ferrous smelting waste acid, and the non-ferrous smelting waste acid includes arsenic ions, lead ions, copper ions and sulfur dioxide. The non-ferrous smelting waste acid basically meets the composition requirements of the initial wastewater, so that the step of preparing the initial wastewater from the heavy metal wastewater can be omitted or the operation in the step of preparing the initial wastewater from the heavy metal wastewater can be simplified. In addition, the non-ferrous smelting waste acid is acidic, which is also conducive to the generation of hydrogen sulfide.

[0061] In addition, arsenic ions, lead ions, copper ions and sulfur dioxide in non-ferrous smelting waste acid are all pollutants and need to be treated. Although conventional methods for treating non-ferrous smelting waste acid can treat non-ferrous smelting waste acid, it is difficult to selectively precipitate and recover heavy metal resources. In the above treatment method, sulfur dioxide dissolved in waste acid is directly used to treat heavy metal ions, achieving the effect of treating waste with waste.

[0062] In some embodiments, the membrane electrode comprises a membrane substrate and a supporting layer loaded on at least one surface of the membrane substrate, the material of the supporting layer comprises at least one of a metal element with catalytic properties, a heavy metal sulfide, and a metal selenide, and the membrane substrate has membrane pores.

[0063] In this embodiment, the membrane electrode is a composite membrane layer structure, which includes a membrane substrate and a support layer supported on at least one surface of the membrane substrate. In some optional embodiments, the material of the membrane substrate is a hydrophobic porous material or a porous material with a surface hydrophobic treatment. The metal element is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium; the heavy metal sulfide is selected from at least one sulfide of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium; the metal selenide is selected from at least one selenide of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium.

[0064] There are many options for the material of the membrane substrate. For example, the hydrophobic porous material can be composed of a hydrophobic polymer material or a hydrophobic inorganic non-metallic material.

[0065] Exemplarily, the porous material with surface hydrophobic treatment is a porous material with surface modification by hydrophobic polymers or hydrophobic small molecules (such as PTFE, biowax, octadecyl mercaptan, etc.), for example: a foam copper with a pore size of 0.1 mm is immersed in an ethyl acetate solution containing 1% octadecyl mercaptan for 1 to 5 minutes and then naturally air-dried.

[0066] Another example is a porous material that has been processed at the micro-nano scale to make its surface hydrophobic. Specifically, for example, a copper foam with a pore size of 0.1 mm is anodized in a 3 mol / L potassium hydroxide solution to in-situ construct a nanoarray with a needle length of about 2 microns, making its surface hydrophobic.

[0067] The hydrophobic material has a good affinity for hydrogen sulfide and can prevent the electrolyte from penetrating. Therefore, the hydrophobic material is selected as the porous membrane matrix to allow hydrogen sulfide gas to pass through with high selectivity, thereby strengthening the separation of electrolyte and hydrogen sulfide gas. In some embodiments, the hydrophobic polymer material is selected from PTFE, PEEK, PP or PE; in other embodiments, the hydrophobic inorganic non-metallic material is a carbon material.

[0068] More specifically, the common PTFE porous membrane, PEEK porous membrane, PP porous membrane, PE porous membrane, carbon cloth or porous carbon paper, etc. on the market can be used as the porous membrane substrate. The porous structure on the surface of the porous membrane substrate allows hydrogen sulfide gas to pass through, but does not allow the electrolyte to pass through. The porous material substrate in the porous material after surface hydrophobic treatment can be a metal material, a polymer material, or an inorganic non-metallic material. Such as foam copper, foam nickel, PEEK, etc.

[0069] In some other embodiments, the membrane electrode is a single-layer membrane structure, and the material of the membrane structure is a material with catalytic function and surface hydrophobicity.

[0070] As a preferred solution, the material having catalytic function and surface hydrophobicity is carbon cloth or porous carbon paper, or a metal porous material with surface hydrophobic treatment. Materials such as carbon cloth or porous carbon paper have catalytic function and certain hydrophobicity, and can be used as membrane electrodes. The metal porous material with surface hydrophobic treatment is a porous material with surface modification by hydrophobic polymers or hydrophobic small molecules, such as PTFE, biowax, octadecyl mercaptan, etc., or a porous material with surface micro-nanoscale processing to make its surface have hydrophobic properties; and the metal porous material is composed of materials such as lead, copper, cobalt, iron, nickel, gold, silver, platinum or palladium.

[0071] The present application also provides a device for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis, which is used to implement the above method. The wastewater treatment device includes an electrolytic cell, a working electrode and a counter electrode. The electrolytic cell includes a cathode chamber and an anode chamber. The electrolyte in the cathode chamber is initial wastewater, and the working electrode is a membrane electrode.

[0072] In some embodiments, the cathode chamber includes two regions, one of which is heavy metal wastewater and the other is sulfur dioxide-containing material. The two regions are separated by a membrane electrode. The side of the membrane electrode bearing the catalyst faces the electrolyte containing sulfur dioxide.

[0073] As a preferred solution, an electrode system is used for electrochemical reduction of sulfur dioxide absorption liquid, with initial wastewater as the electrolyte in the cathode chamber and a membrane electrode as the working electrode. As a further preferred solution, sulfur dioxide absorption liquid is used as the electrolyte in the cathode chamber, a membrane electrode is used as the working electrode, and a metal-based or carbon electrode is used as a counter electrode. Electrodes composed of materials such as metal platinum, graphite, nickel, and iridium oxide can be used as counter electrodes. The electrolyte contained in the electrolyte in the anode chamber is not limited, and common electrolytes in the industry basically meet the requirements, such as a Na2SO4 / H2SO4 mixed solution.

[0074] The technical solution of the present application is described below in conjunction with specific embodiments.

[0075] The sulfur dioxide absorption liquid in the following embodiments is electrochemically reduced using an electrode system. The cathode chamber and the anode chamber of the electrode system are separated by a DuPont N117 proton membrane. The electrolyte in the cathode chamber is a sodium hydroxide absorption liquid of sulfur dioxide, and the electrolyte in the anode chamber is a mixed solution of Na2SO4 / H2SO4. The membrane electrode is used as the working electrode, and Pt is used as the counter electrode. The reduction voltage can be selected from -1.2V to -1.8V (vs SCE).

[0076] The preparation process of Au / PTFE membrane electrode in the following examples is as follows: Au catalyst is loaded on a PTFE porous membrane (commercial raw material purchased directly) substrate by magnetron sputtering coating. The specific magnetron sputtering parameters are as follows: vacuum degree 1.3×10 -4 Pa or less, sputtering rate: substrate temperature: 150℃; cathode voltage: 420V; current: 13A; sputtering vacuum: 1Pa; sputtering time: 6min / piece.

[0077] The preparation method of CoS2 / PTFE membrane electrode in the following embodiment is as follows: CoS2 is directly dispersed in ethanol solvent to form a mixed solution with a concentration of 10%, and CoS2 is coated on the surface of the PTFE porous membrane substrate at 1 mg / g by spraying, and dried to obtain a CoS2 / PTFE membrane electrode.

[0078] The preparation method of the hydrophobic carbon paper in the following example is as follows: the carbon paper is immersed in an ethyl acetate solution containing 1% octadecyl mercaptan for 4 minutes, and then naturally air-dried.

[0079] Unless otherwise specified in the following examples, the chemical reagents used are conventional commercially available products and are of analytical grade.

[0080] Example

[0081] The sulfur dioxide absorption liquid (wherein the concentration of sulfur dioxide is 0.1 mol / L) is taken into the cathode chamber and the pH is adjusted to 0.5. 10 mL of anhydrous sodium sulfate aqueous solution (0.1 mol / L) is used as the anolyte. The Au / PTFE membrane electrode is used as the working electrode. The side of the working electrode with the catalyst faces the sulfur dioxide-containing cathode liquid, and the other side faces the simulated heavy metal wastewater containing heavy metals to be precipitated and separated (Hg 2+ , Pb 2+ , Cu 2+ The concentration of each was 1000ppm), the cathode liquid and the simulated heavy metal wastewater circulated at a rate of 3ml / min; a constant current electrolysis mode was set, and heavy metal selective precipitation was performed at different current densities in each embodiment.

[0082] After electrolysis according to different electrolysis procedures, ICP-OES was used to measure the change in metal ion concentration in the simulated heavy metal wastewater, and the selectivity of metal precipitation was calculated based on the change in metal ion concentration. The calculation formula for mercury precipitation selectivity is: η = ΔHg / ΔHg + ΔCu + ΔPb; the calculation formula for copper precipitation selectivity is: η = ΔCu / ΔHg + ΔCu + ΔPb; the calculation formula for lead precipitation selectivity is: η = ΔPb / ΔHg + ΔCu + ΔPb.

[0083] The results are as follows Figure 2 And as shown in Table 1.

[0084] Table 1 Selectivity of metal precipitation obtained in each embodiment

[0085] Example Electrolysis Procedure Hg(%) Cu(%) Pb(%) Example 1 <![CDATA[1.59mA / cm 2 ,30min]]> 94.2 5.1 0.7 Example 2 <![CDATA[3.18mA / cm 2 ,30min]]> 92.1 6.6 1.3 Example 3 <![CDATA[4.78mA / cm 2 ,30min]]> 87.2 9.5 3.3 Example 4 <![CDATA[6.39mA / cm 2 ,30min]]> 76.6 20.1 3.3 Example 5 <![CDATA[15.92mA / cm 2 ,30min]]> 53.3 41 5.7

[0086] From the above examples, it can be seen that the method for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis of the present application has reaction selectivity for different metal ions at different current densities, that is, under the same conditions, different current densities have a tendency to selectively precipitate different ions.

[0087] Embodiment 6:

[0088] Referring to Examples 1 to 5, except for the difference in the electrolysis procedure, the other steps are the same. In Example 6, different heavy metals are continuously precipitated in stages according to the current density, which is specifically divided into 3 stages. The electrolysis conditions of each stage and the metal element composition in the precipitate are shown in Table 2.

[0089] Table 2 Selectivity of metal precipitation in the staged electrolysis process

[0090]

[0091] In the first stage, the current is mainly small. At this time, due to the difference in Ksp, mercury is precipitated first, and a small amount of copper is carried at the same time, indicating that mercury is selectively precipitated and separated in this stage; in the second stage, the current density is doubled, and the mercury ions in the first stage are exhausted. At this time, copper is mainly precipitated, accompanied by a small amount of lead precipitation, indicating that copper is preferentially precipitated when copper and lead are present at the same time; in the third stage, the current density is increased five times. Since the mercury ions and copper ions in the first and second stages are exhausted, lead is mainly precipitated at this time. It can be seen from this that the method for recovering heavy metals in wastewater based on sulfur dioxide membrane electrolysis in this application can achieve staged graded precipitation of different heavy metal ions.

[0092] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for recovering heavy metals from wastewater based on sulfur dioxide membrane electrolysis, characterized in that: The heavy metal wastewater contains heavy metal ions, and the steps include: Placing the membrane electrode in the initial wastewater for electrochemical reduction, reacting with the initial wastewater to generate hydrogen sulfide gas, and the hydrogen sulfide gas precipitates heavy metal ions in the initial wastewater; wherein the initial wastewater includes heavy metal ions and sulfur dioxide, and the initial wastewater is heavy metal wastewater, or a mixture of heavy metal wastewater and a substance containing sulfur dioxide; The membrane electrode has uniformly distributed hydrophobic membrane pores, and the membrane electrode can catalyze the reduction of sulfur dioxide to generate hydrogen sulfide gas.

2. The method according to claim 1, characterized in that The method also includes adjusting the working current of the membrane electrode to adjust the generation rate of the hydrogen sulfide gas and control the hydrogen sulfide partial pressure at the initial wastewater-membrane electrode interface during the electrochemical reduction process.

3. The method according to claim 2, characterized in that The adjusting of the working current of the membrane electrode comprises adjusting stepwise in multiple reaction stages based on the solubility product of the heavy metal ions corresponding to the heavy metal sulfides in the initial wastewater from small to large; In any two adjacent reaction stages of the working current, the working current of the previous reaction stage is smaller than the working current of the next reaction stage, and the concentration of hydrogen sulfide gas generated by the working current of any reaction stage avoids the precipitation of heavy metal ions in the subsequent stage.

4. The method according to claim 3, characterized in that In the working current of each reaction stage, the initial working current is smaller than the terminal working current.

5. The method according to claim 1, characterized in that The method further includes maintaining the pH of the initial wastewater less than 2 during the step of energizing the membrane electrode in the initial wastewater to react with the initial wastewater to generate hydrogen sulfide gas.

6. The method according to claim 1, characterized in that The heavy metal ions are at least one of arsenic ions, lead ions and copper ions.

7. The method according to claim 1, characterized in that The initial wastewater is heavy metal wastewater, the heavy metal wastewater is non-ferrous smelting waste acid, and the non-ferrous smelting waste acid includes arsenic ions, lead ions, copper ions and sulfur dioxide.

8. The method according to any one of claims 1 to 7, characterized in that: The membrane electrode comprises a membrane substrate and a support layer supported on at least one surface of the membrane substrate, the material of the support layer comprises at least one of a metal element with catalytic properties, a heavy metal sulfide, and a metal selenide, the membrane substrate has the hydrophobic membrane pores, or: The membrane electrode is a single-layer membrane structure, and the material of the membrane structure is a material with catalytic function and surface hydrophobicity.

9. The method according to claim 8, characterized in that The material of the membrane substrate is a hydrophobic porous material or a porous material with a surface hydrophobic treatment; The metal element is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium; the heavy metal sulfide is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium sulfide; the metal selenide is selected from at least one of lead, copper, cobalt, iron, nickel, gold, silver, platinum and palladium selenide; or; The material having catalytic function and surface hydrophobicity is carbon cloth or porous carbon paper, or a porous metal material with surface hydrophobicity treatment.

10. A device for recovering heavy metals from wastewater based on sulfur dioxide membrane electrolysis, used for implementing the method according to any one of claims 1 to 9, characterized in that: The device comprises an electrolytic cell, a working electrode and a counter electrode. The electrolytic cell comprises a cathode chamber and an anode chamber. The electrolyte in the cathode chamber is initial wastewater. The working electrode is a membrane electrode.

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