A method and application for the resource utilization of sulfur-containing wastewater based on the tandem oxidation of electrochemistry and chemistry

Abstract

The present invention provides a method for the resource utilization of sulfur-containing wastewater based on the tandem oxidation of electrochemistry and chemistry, belonging to the technical fields of sulfur-containing wastewater treatment and resource utilization, as well as electrochemically hydrogen evolution technology. This method uses wastewater rich in high-concentration sulfide ions as a substrate, and adopts an electrochemical oxidation method to electrocatalytically oxidize it to polysulfide at the anodic end, coupling with the hydrogen evolution reaction to produce high-purity hydrogen at the cathode; at the same time, a sodium ion exchange membrane is used to achieve alkali recovery at the cathode, and a two-electrode system for low-energy-consuming sulfur ion oxidation-assisted electrolytic hydrogen production is constructed. Further, the sodium polysulfide solution obtained at the anode is catalytically oxidized and filtered and crystallized by using a metal sulfide powder catalytic material to prepare sodium thiosulfate, obtaining a high-value-added product. The present invention adopts the electrochemistry + chemistry tandem method to simultaneously realize the treatment of sulfur-containing waste liquid and the production of high-value-added substances, which is a new solution combining environmental governance and clean energy hydrogen production, and has important significance and application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of sulfur-containing wastewater treatment and resource utilization and electrochemical hydrogen evolution technology, and specifically relates to a method and application for realizing resource utilization of sulfur-containing wastewater based on electrochemical and chemical tandem oxidation. Background Art

[0002] Sulfur-containing waste liquid rich in high-concentration sulfur ions comes from the toxic acidic hydrogen sulfide gas formed by alkali adsorption during industrial production. It is widely present in heavy industrial fields such as petroleum refining, metallurgy, and natural gas extraction. It has large emissions and high chemical oxygen demand (COD). Direct discharge of waste liquid and sewage will seriously affect the ecological environment. Therefore, it is very important to remove it and utilize it as a resource.

[0003] Traditional methods for treating wastewater containing sulfur ions include precipitation, chemical oxidation, and biological treatment for desulfurization. The precipitation method precipitates metal salts and sulfur ions to form metal sulfides and fix the sulfur element; the chemical oxidation method is to oxidize and reduce sulfur ions with strong oxidants such as Cl2, H2O2, KMnO4, and O3 to convert them into sulfate ions and reduce COD. Both methods require irreversible consumption of chemical reagents, and the added value of the output metal sulfides (such as cuprous sulfide) or sodium sulfate is low. Biological methods often rely on biological metabolism to convert sulfur ions into products such as sulfur elements. They are sensitive to conditions such as sulfur ion concentration and ambient temperature in the wastewater and are difficult to treat on a large scale.

[0004] Electrochemical treatment of sulfur-containing wastewater is a novel and potential solution. The reaction can be driven by applying voltage at room temperature and pressure, and new energy power technology can be integrated. It is a green zero-carbon emission technical means. In this process, the anode is a sulfur ion oxidation reaction, which can oxidize the sulfur-containing waste liquid to reduce the COD value of the waste liquid; the cathode can couple the hydrogen evolution reaction to produce high-value-added hydrogen, and construct a sulfur ion oxidation-assisted water electrolysis hydrogen production system. Since the electrode potential of the sulfur ion oxidation reaction (SOR, 0.17 V) is lower than the anode oxygen evolution reaction (OER, 1.23 V) in traditional water electrolysis, the system can not only treat sulfur-containing wastewater under mild conditions, but also reduce the two-electrode voltage in the water electrolysis hydrogen production process to reduce energy consumption. It is a solution that kills two birds with one stone.

[0005] However, the current treatment of polysulfides generated by the electrolytic sulfur ion oxidation reaction requires a large amount of acid to neutralize the highly alkaline polysulfide solution, precipitate the sulfur element and recover the sulfur; in addition, since sulfur element is relatively cheap and of low value, and the cost of acidic reagents is high, H2S poisonous gas is easily produced after acidification, so the electrochemical oxidation scheme is difficult to apply on a large scale.

[0006] Based on this, there is an urgent need to develop new methods and design new reaction systems to simultaneously treat wastewater rich in sulfide ions on a large scale at low cost, while taking into account green hydrogen production and alkali recovery, and converting the electrolysis product polysulfide into high-value-added products under low-cost conditions to achieve the resource utilization of sulfur-containing wastewater. Summary of the Invention

[0007] One of the objectives of the present invention is to provide a method based on electrochemical and chemical tandem oxidation to realize the resource utilization of sulfur-containing wastewater and produce high-value-added products while achieving the treatment of sulfur-containing wastewater, green hydrogen production, and alkali recovery.

[0008] Another objective of the present invention is to provide an application of the method based on electrochemical and chemical tandem oxidation in the resource utilization of sulfur-containing wastewater to achieve large-scale, low-cost treatment and high-value-added utilization of wastewater rich in sulfide ions.

[0009] The technical solution adopted by the present invention to achieve the first objective is as follows: providing a method for realizing the resource utilization of sulfur-containing wastewater based on electrochemical and chemical tandem oxidation, including the following steps:

[0010] S1. Add a sulfide ion solution as the anolyte to a two-electrode electrolysis system; in the two-electrode electrolysis system, the anode uses a catalytic electrode with in-situ growth of metal sulfide, the cathode uses a catalytic electrode for hydrogen evolution reaction, and the catholyte uses an alkaline solution containing sodium ions; a sodium ion exchange membrane is provided between the cathode and the anode.

[0011] S2. Perform an electrolysis reaction on the two-electrode electrolysis system to obtain a sodium polysulfide solution at the anode, and a concentrated alkaline electrolyte and high-purity hydrogen at the cathode.

[0012] S3. Add a metal sulfide powder catalytic material to the sodium polysulfide solution and perform a chemical wet oxidation reaction under the condition of introducing air or oxygen, and separate the product into solid and liquid components.

[0013] S4. Concentrate, filter, and crystallize the liquid component to obtain sodium thiosulfate pentahydrate.

[0014] The general idea of the present invention is as follows:

[0015] In view of the problems of high treatment cost of oxidation products and low added value of products existing in the electrochemical treatment of sulfur-containing waste liquid, the present invention provides an electrochemical + chemical tandem catalytic system. In the electrochemical part, based on the constructed two-electrode electrolysis system, the anodic sulfur ion oxidation reaction can reduce the COD of sulfur-containing wastewater and be coupled with the cathodic hydrogen evolution reaction, enabling the simultaneous production of high-value-added hydrogen and the realization of alkali recovery; in the subsequent chemical oxidation step, the anolyte after the electrochemical reaction is used as a substrate, and a metal sulfide powder catalytic material is added for chemical wet oxidation reaction to wet-oxidize the polysulfide ions obtained from the electrochemical reaction into thiosulfate ions, and finally, through impurity removal and crystallization, sodium thiosulfate pentahydrate crystals are obtained. This product can be used in industries such as medicine, agriculture, and metallurgy, with wide applications and high added value, thereby realizing the treatment and resource utilization of sulfur-containing wastewater.

[0016] Further, in step S1, the sulfur ion-containing solution is an aqueous solution of sodium sulfide or a mixed solution of sodium sulfide and sodium hydroxide, with a pH of 13 - 14 and a sulfur ion concentration of 1 - 4 mol L -1 , and the sulfur ion exists in the solution in the form of HS - .

[0017] Further, in step S1, in the catalytic electrode with in-situ growth of metal sulfide, the metal sulfide includes one or a combination of more of nickel sulfide, copper sulfide, and cobalt sulfide; the substrate material of the catalytic electrode includes one of nickel foam, carbon paper, and carbon cloth.

[0018] Preferably, the preparation method of the catalytic electrode with in-situ growth of metal sulfide includes: growing hydroxides of transition metals such as nickel, copper, and cobalt on the substrate material by electrodeposition, and then soaking the substrate material with the grown transition metal hydroxides in a sodium sulfide solution for sulfidation treatment.

[0019] Further, the catalytic electrode with in-situ growth of metal sulfide can also be obtained by spraying commercial powder materials such as nickel sulfide, copper sulfide, and cobalt sulfide on a carbon paper substrate.

[0020] In some preferred embodiments, the catalytic electrode with in-situ growth of metal sulfide uses a copper sulfide / nickel foam anode catalytic electrode or a cobalt sulfide / nickel foam anode catalytic electrode, which is paired with a Pt / C electrode to catalyze the cathodic hydrogen evolution reaction, and the working potential of the formed two-electrode system can be as low as 0.6 V to drive an industrial-grade current density of 200 mA cm -2 , reducing the energy consumption by more than 60% compared with traditional electrolyzed water.

[0021] Preferably, the catalytic electrode with in-situ growth of metal sulfide is in the shape of a sheet of 2 × 2 cm 2 , with a thickness of 0.05 - 1 cm.

[0022] Further, in step S1, the hydrogen evolution reaction catalytic electrode of the cathode uses a Pt / C electrode, which is prepared by coating Pt / C powder on substrate materials such as carbon paper, nickel foam, and carbon cloth.

[0023] Further, the cathode electrolyte is selected from one of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution, and its concentration is 0.1 - 4 mol L -1 . Preferably, the cathode electrolyte uses sodium hydroxide solution. Compared with sodium carbonate solution and sodium bicarbonate solution, sodium hydroxide solution has stronger alkalinity, can improve the hydrogen evolution effect, and has a positive impact on the reaction system of efficient electrolysis.

[0024] Further, in step S1, the sodium ion exchange membrane uses a carbon-modified sodium ion exchange membrane, and its preparation method includes the following steps: Immerse the Nafion membrane in 1 wt% - 20 wt% hydrogen peroxide and 0.1 - 6 mol L -1 sodium hydroxide solution and heat it to 60 - 90 °C for soaking treatment, then wash it with deionized water and dry it under vacuum; Coat the double-layer surface of the dried ion exchange membrane with an aqueous dispersion slurry of activated carbon and polytetrafluoroethylene, and after drying treatment, a sodium ion exchange membrane with a uniform and stable carbon layer covering its surface is obtained.

[0025] In the electrochemical reaction stage of the present invention, by optimizing the selection of the cathode electrode material and the anode electrode material, the energy consumption of the electrochemical step can be reduced and the efficiency of electrochemical treatment can be improved; by carbon-modifying and modifying the surface of the ion exchange membrane, anion shuttling can be effectively prevented, and the reaction efficiency and product purity can be further improved.

[0026] Preferably, in step S1, a flow-through electrolytic cell is used, the window of the cathode and anode chambers is 1×1 cm 2 , the containers filled with the cathode electrolyte and the anode electrolyte are placed in an oil bath for heating, the flow rate of the electrolyte is controlled at 5 - 100 sccm, and the hydrogen gas generated at the cathode end is collected through the gas outlet.

[0027] Further, in step S2, the electrolysis reaction adopts a constant voltage electrolysis mode or a constant current electrolysis mode; when adopting the constant voltage electrolysis mode, the voltage is 0.4 - 1.5 V. It has been found through research that when it is lower than 0.4 V, it is difficult to drive the cathode and anode reactions to occur, and when it is higher than 1.5 V, anodic oxygen evolution side reactions are likely to be triggered. When adopting the constant current electrolysis mode, the current is 10 mAcm -2 - 1 A cm -2 , preferably 200 - 500 mA cm -2 .

[0028] Furthermore, the temperature of the electrolysis reaction is from room temperature to 80 °C. The time of the electrolysis reaction is calculated and determined according to the concentration and volume of the anolyte. The electrolysis time is determined to ensure the oxidation of Na2S to Na2S2. Preferably, during the electrolysis process, a small amount of the anolyte is taken out at intervals of 1 - 3 hours, diluted 500 times, and then the inductively coupled plasma atomic emission spectrometry is tested. The electrolysis ends when the molar ratio of Na:S in the solution is close to 1:1. The anolyte after the reaction is a Na2S2 solution.

[0029] Furthermore, in step S3, the metal sulfide powder catalytic material is prepared by co-precipitation of a transition metal salt solution and a sodium disulfide solution, followed by filtration, washing, and drying.

[0030] Preferably, the transition metal salt solution includes one or a combination of a nitrate solution, a sulfate solution, and a chloride solution of a transition metal; the transition metal includes one or a combination of nickel, iron, and cobalt.

[0031] Preferably, the addition amount of the metal sulfide powder catalytic material in the sodium polysulfide solution is 10 - 20 mg / mL.

[0032] Furthermore, in step S3, the chemical wet oxidation reaction is carried out under stirring conditions at 20 - 80 °C, the stirring speed is 1 - 1000 rpm, and air or oxygen is introduced at a flow rate of 1 - 500 sccm during the reaction process.

[0033] Furthermore, in step S3, the solid powder obtained after the reaction is the metal sulfide powder catalytic material, which can be recycled after washing and drying. The main component of the liquid component obtained in step S3 is sodium thiosulfate, and there are also a small amount of over-oxidation products such as sodium sulfate and sodium sulfite, as well as impurities such as sodium carbonate formed after CO2 in the air is absorbed by the alkaline solution.

[0034] Furthermore, in step S4, the concentration is carried out by vacuum evaporation, and the temperature of the vacuum evaporation is 60 - 80 °C. During the vacuum evaporation process, after the white powder (impurities such as sodium sulfate, sodium sulfite, and sodium carbonate) is formed, it is filtered while it is hot; the filtrate is retained and cooled to below 40 °C, and sodium thiosulfate starts to crystallize. After the surface moisture is evaporated dry at room temperature, transparent crystals of sodium thiosulfate pentahydrate are obtained.

[0035] The technical solution adopted to achieve the second object of the present invention is: to provide an application of the method according to the first object of the present invention in treating sulfur-containing wastewater, and the sulfur-containing ion solution is sulfur-containing ion wastewater generated after absorbing hydrogen sulfide gas with a sodium hydroxide solution in industrial production.

[0036] The above-mentioned sulfur-ion-containing wastewater is widely present in production processes such as propane dehydrogenation, natural gas wells, and the petroleum industry, with large discharge and high chemical oxygen demand (COD), which has an adverse impact on the ecological environment. The method provided by the present invention is applied to the treatment process of the above-mentioned sulfur-ion-containing wastewater, which can not only simultaneously achieve sulfur-containing wastewater treatment, green hydrogen production and alkali recovery, but also resource utilization of sulfur-containing wastewater and produce high value-added products, which is of great significance for the treatment and resource utilization of sulfur-containing industrial wastewater.

[0037] Preferably, the sulfur ion-containing wastewater is filtered before the reaction to remove insoluble impurities.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention provides a method for realizing resource utilization of sulfur-containing wastewater based on electrochemical and chemical tandem oxidation. Through the electrochemical + chemical tandem oxidation method, the waste liquid rich in sulfur ions is catalytically converted into high-value-added sodium thiosulfate, and green hydrogen production and alkali recovery are achieved simultaneously. Different from the existing method of treating polysulfide, a product of electrochemical oxidation (i.e., consuming a large amount of acid neutralization to recover sulfur), the present invention develops electrochemical + chemical tandem conversion of sulfur ions, and further catalytically oxidizes the sodium polysulfide obtained by the electrochemical reaction with air to obtain industrial raw material thiosulfate with higher added value. In addition, compared with the current industrial production process of sodium thiosulfate, which requires sodium sulfite, sulfur, sodium sulfide and other chemicals as raw materials to be heated and reacted to obtain the product, the present invention uses sulfur-containing wastewater as raw material for production, which is low-cost, and obtains hydrogen and concentrated alkali in the tandem oxidation process under mild conditions, further improving the overall benefits and facilitating large-scale production.

[0040] (2) The present invention provides a method for realizing resource utilization of sulfur-containing wastewater based on electrochemical and chemical tandem oxidation. In the electrochemical part, only a voltage of about 0.6 V is required to drive 200 mA cm -2 The industrial-grade current density is significantly lower than the voltage of about 1.8 V required for traditional water electrolysis to produce hydrogen; the electrochemical + chemical tandem catalysis can convert sulfur ions into thiosulfate ions with a conversion rate of 90%; in the chemical oxidation part, metal sulfide powder catalytic materials such as nickel and cobalt are preferred as wet oxidation materials for sodium polysulfide to sodium thiosulfate, which can significantly promote the catalytic conversion of polysulfides under room temperature air oxidation conditions and increase the yield of high value-added product sodium thiosulfate.

[0041] (3)The method for resource utilization of sulfur-containing wastewater based on the tandem oxidation of electrochemistry and chemistry provided by the present invention solves the problems in the current process for treating sulfur-containing wastewater, such as high consumption cost of chemical reagents and low added value of resource recovery. While treating wastewater rich in sulfide ions on a large scale and at low cost, the present invention also takes into account the production of green hydrogen and alkali recovery, and converts the electrolysis product polysulfide into high-value-added products under low-cost conditions, realizing the resource utilization of sulfur-containing wastewater, and having broad prospects for popularization and application. Description of the Drawings

[0042] Figure 1 It is a schematic structural diagram of a two-electrode electrolysis device for hydrogen production by electrolysis assisted by sulfide ion oxidation in Example 1 of the present invention;

[0043] Figure 2 It is a physical diagram of the construction of a two-electrode system for hydrogen production by electrolysis assisted by sulfide ion oxidation in Example 1 of the present invention;

[0044] Figure 3 It is the stability test of the two-electrode sulfide ion oxidation-assisted electrolysis hydrogen production system in Step 2 of Example 1 of the present invention;

[0045] Figure 4 It is the ion chromatogram (diluted 500 times) of the filtered and clarified liquid after the chemical wet oxidation process in Step 3 of Example 1 of the present invention;

[0046] Figure 5 It is the XRD pattern of the sodium thiosulfate pentahydrate crystals prepared in Step 4 of Example 1 of the present invention;

[0047] Figure 6 It is a schematic diagram of the reaction principle and process for treating and resource-utilizing industrial wastewater containing sulfide ions based on the method of tandem oxidation of electrochemistry and chemistry in Example 5 of the present invention. Detailed Embodiments

[0048] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0050] The present invention will be further described below in conjunction with specific embodiments, but it is not limited to the present invention.

[0051] Example 1

[0052] A method for the resource utilization of sulfur-containing wastewater based on electrochemistry and chemical tandem oxidation, comprising the following steps:

[0053] Step 1: Construct a two-electrode electrolysis system: The anode uses a catalytic electrode with in-situ growth of metal sulfide, the cathode uses a Pt / C electrode, and a carbon-modified sodium ion exchange membrane is provided between the cathode and the anode; The cathode electrolyte uses an aqueous sodium hydroxide solution with a concentration of 1 mol / L, and the anode electrolyte uses a 3 mol / L Na2S aqueous solution. 75 mL of each of the cathode and anode electrolytes is prepared and placed in a storage bottle. A flow-through electrolytic cell is used, and the structure of the electrolytic cell is as shown in Figure 1 and 2 . During the reaction process, the flow rate of the electrolyte is controlled at about 50 sccm. The reaction module is made of corrosion-resistant polytetrafluoroethylene, and the exposed area of the cathode and anode chamber openings is 1×1 cm. The cathode electrode sheet substrate is carbon paper, which is led out by sticking with copper conductive adhesive tabs; The anode electrode sheet substrate is nickel foam, which is led out by ultrasonic spot welding with nickel tabs. -1 of -1 Na2S aqueous solution. During the reaction process, the flow rate of the electrolyte is controlled at about 50 sccm. The reaction module is made of corrosion-resistant polytetrafluoroethylene, and the exposed area of the cathode and anode chamber openings is 1×1 cm. The cathode electrode sheet substrate is carbon paper, which is led out by sticking with copper conductive adhesive tabs; The anode electrode sheet substrate is nickel foam, which is led out by ultrasonic spot welding with nickel tabs. Figure 1 and 2 shown. During the reaction process, the flow rate of the electrolyte is controlled at about 50 sccm. The reaction module is made of corrosion-resistant polytetrafluoroethylene, and the exposed area of the cathode and anode chamber openings is 1×1 cm². The cathode electrode sheet substrate is carbon paper, which is led out by sticking with copper conductive adhesive tabs; The anode electrode sheet substrate is nickel foam, which is led out by ultrasonic spot welding with nickel tabs. 2 ². The cathode electrode sheet substrate is carbon paper, which is led out by sticking with copper conductive adhesive tabs; The anode electrode sheet substrate is nickel foam, which is led out by ultrasonic spot welding with nickel tabs.

[0054] Among them, the catalytic electrode with in-situ growth of anode metal sulfide uses a copper sulfide / nickel foam anode catalytic electrode, and its preparation method is as follows:

[0055] (1) Immerse nickel foam (with a thickness of 1 mm) in HCl solution, deionized water, and absolute ethanol in sequence and ultrasonically clean to remove impurities, and then dry.

[0056] (2) Dissolve 1.25 mol of metal copper nitrate in 50 mL of water and stir until the solution is evenly mixed. Use the solution as the electrolyte, the nickel foam treated in the first step as the working electrode, the saturated calomel electrode as the reference electrode, and the Pt sheet as the counter electrode to perform electrodeposition in a three-electrode system. The deposition time is 1200 s, and the potential is -1 V vs. SCE. After the electrodeposition is completed, take out the electrode, rinse it with clean water and dry it at room temperature.

[0057] (3) Immerse the above electrode material precursor into a 1 mol / L Na2S2 solution (prepared by co-placing equimolar proportions of Na2S and sulfur in water and heating to 60 °C and stirring) and keep it for 12 h. After complete sulfidation, take it out, wash it with deionized water and absolute ethanol, and dry it to obtain a metal sulfide electrode. -1 Na2S2 solution (prepared by co-placing equimolar proportions of Na2S and sulfur in water and heating to 60 °C and stirring) and keep it for 12 h. After complete sulfidation, take it out, wash it with deionized water and absolute ethanol, and dry it to obtain a metal sulfide electrode.

[0058] The preparation method of the cathode Pt / C / carbon paper cathode electrode is as follows: Disperse 5 mg of Pt / C (20 wt%) powder ultrasonically in 950 μL of isopropanol and 50 μL of Nafion (5 wt%) solution, and drop-coat or spray it onto the surface of the carbon paper, with a loading of about 0.5 mg / cm². -2, leave it to dry at room temperature overnight for later use.

[0059] The preparation method of the carbon-modified sodium ion exchange membrane is as follows: Immerse the Nafion membrane (DuPont) in aqueous solutions of H2O2 (5wt%) and NaOH (1 mol L -1 ) respectively and heat them to 80 °C for 1 hour each. Then wash with deionized water and dry in a vacuum oven overnight. Coat the double-layer surface of the dried ion exchange membrane with an aqueous dispersion slurry of activated carbon and polytetrafluoroethylene (mass ratio of 8:1), and dry it to make the membrane surface covered with a uniform and stable carbon layer. The single-layer loading is approximately 1 mg cm -2 .

[0060] Step 2: Under the condition of constant current, carry out an electrolysis reaction on the two-electrode electrolysis system, and the reaction temperature is 80 °C. Adopt the constant current electrolysis mode, and set the current value to 0.5 A (current density of 500 mA cm -2 ). During the electrolysis process, place the cathode and anode electrolyte storage bottles in an oil bath for heating, set the temperature to 80 °C, and collect the hydrogen generated at the cathode through the gas outlet. The stability test of the two-electrode electrolysis system under the condition of constant current (current density of 500 mA cm -2 ) is as Figure 3 shown. During the total reaction time of 60 h, the voltage is stably maintained at 1.2 V.

[0061] During the electrolysis reaction, take out a small amount of the anode electrolyte at two-hour intervals, dilute it 500 times, and then test the inductively coupled plasma atomic emission spectrum to determine that the electrolysis ends when the molar ratio of Na:S in the solution is close to 1:1. The anode electrolyte after the reaction is Na2S2 solution, showing a dark red-brown state, and the cathode electrolyte remains colorless and transparent. Take it out after the electrolyte temperature drops to room temperature. At this time, the cathode is the purified alkali liquor after concentration and recovery for recycling absorption; the polysulfide solution obtained at the anode end is stored for further air wet oxidation conversion.

[0062] Step 3: Take 20 mL of the polysulfide solution, which is the product of the sulfur ion-oxidized anode electrolyte obtained in Step 2, as the substrate, and add 300 mg of the metal sulfide powder catalyst material nickel sulfide (NiS x), under the conditions of introducing air and stirring, a chemical wet oxidation reaction is carried out. A small part of the reaction solution is taken out every two hours of reaction. After filtration, a clear solution is obtained and diluted 500 times to test the ion chromatography. Quantify the thiosulfate ions in the ion chromatography. When the calculated conversion rate of sulfide ions to thiosulfate ions approaches 90%, the wet oxidation step ends; the product is filtered or centrifuged to separate, and the solid product, the black metal sulfide catalytic powder, is washed and dried for recycling; the clear liquid component is bottled for subsequent crystallization treatment. Among them, the liquid component is diluted and then the ion chromatography is tested, and the results are as Figure 4 shown.

[0063] Among them, the preparation method of nickel sulfide (NiS x ) is as follows: Mix 18 g of solid Na2S·9H2O and 2.4 g of elemental sulfur powder into a beaker containing 50 mL of deionized water, heat to 70 °C and stir vigorously for 30 min to form a red-brown sodium disulfide (Na2S2) solution; add 50 mL of an aqueous solution dissolving 5 g of NiSO4 to the above solution, and a dark precipitate is quickly formed. Continue to stir for 30 min until the precipitate crystals grow completely, separate, wash, dry the solid precipitate, and store it in a vacuum oven.

[0064] Step 4: Concentrate, filter, and crystallize the liquid component obtained in Step 3 to obtain sodium thiosulfate pentahydrate. Specifically, the concentration is carried out by means of vacuum evaporation, and the temperature of the vacuum evaporation is 60 - 80 °C. In the above steps, impurity crystals are precipitated from the clear solution and filtered while it is hot; the container containing the filtrate is quickly placed in an ice-water bath for cooling, so that sodium thiosulfate crystals can be precipitated, and a small amount of water is continuously filtered and dried under normal temperature and pressure to obtain sodium thiosulfate pentahydrate crystals, and its XRD pattern is as Figure 5 shown.

[0065] Example 2

[0066] The difference between this example and Example 1 is that in Step 1, the catalytic electrode with in-situ growth of anode metal sulfide is a cobalt sulfide / nickel foam anode catalytic electrode, and its preparation method is as follows:

[0067] (1) Immerse the nickel foam (with a thickness of 1 mm) in HCl solution, deionized water, and anhydrous ethanol in sequence and ultrasonically clean to remove impurities, and then dry.

[0068] (2) Dissolve 1.25 mol of cobalt nitrate in 50 mL of water and stir until the solution is well mixed. Use the solution as the electrolyte, the nickel foam treated in the first step as the working electrode, the saturated calomel electrode as the reference electrode, and the Pt sheet as the counter electrode to perform electrodeposition under a three-electrode system. The deposition time is 1200 s and the potential is -1 V vs. SCE. After the electrodeposition is completed, take out the electrode, rinse it with clean water and dry it at room temperature.

[0069] (3) Immerse the above electrode material precursor into a 1 mol / L -1 Na2S2 solution (mix equimolar proportions of Na2S and sulfur in water, heat to 60 °C and stir) and keep it for 12 h. After complete sulfidation, take it out, wash it with deionized water and absolute ethanol, and dry it to obtain the metal sulfide electrode.

[0070] Keep the remaining steps and operations unchanged. In step 2, a concentrated alkaline electrolyte and high-purity hydrogen are obtained at the cathode, and the sodium polysulfide solution obtained at the anode undergoes chemical wet oxidation reaction and purification operations in steps 3 and 4, and finally the high-value-added product sodium thiosulfate pentahydrate is obtained.

[0071] Example 3

[0072] The difference between this example and Example 1 is that in step 2, under a constant voltage condition, an electrolysis reaction is carried out on the two-electrode electrolysis system. The electrolysis voltage is 0.4 - 1.5 V. During the electrolysis process, the cathode and anode electrolyte storage bottles are placed in an oil bath for heating, and the temperature is set at 80 °C. The hydrogen generated at the cathode is collected through the gas outlet. During the electrolysis reaction, take out a small amount of the anode electrolyte every two hours, dilute it 500 times, and then test the inductively coupled plasma atomic emission spectrum to determine the electrolysis end when the Na:S molar ratio in the solution is close to 1:1. The anode electrolyte after the reaction is a Na2S2 solution, showing a dark red-brown state, and the cathode electrolyte remains colorless and transparent. After the electrolyte temperature drops to room temperature, take it out. At this time, the cathode is the pure concentrated recovered alkali solution for cyclic absorption use; the sodium polysulfide solution obtained at the anode end is saved for further air wet oxidation conversion.

[0073] Keep the remaining steps and operations unchanged. The sodium polysulfide solution obtained at the anode in step 2 undergoes chemical wet oxidation reaction and purification operations in steps 3 and 4, and finally the high-value-added product sodium thiosulfate pentahydrate is obtained.

[0074] Example 4

[0075] The difference between this example and Example 1 is that in step 3, the added metal sulfide powder catalytic material is cobalt sulfide.

[0076] Among them, the preparation method of cobalt sulfide is as follows: 18 g of solid Na2S·9H2O and 2.4 g of elemental sulfur powder are mixed into a beaker containing 50 mL of deionized water, heated to 70 °C and stirred vigorously for 30 min to form a red-brown sodium disulfide (Na2S2) solution; 50 mL of an aqueous solution dissolving 5 g of CoSO4 is added to the above solution, and a dark precipitate is rapidly formed. Stir for another 30 min until the precipitate crystals grow completely, separate, wash, dry the solid precipitate, and store it in a vacuum oven.

[0077] For the remaining steps and operations, they remain unchanged. The liquid component obtained in step 3 is processed through step 4, and finally, the high-value-added product sodium thiosulfate pentahydrate is obtained.

[0078] Example 5

[0079] The difference between this example and Example 1 is that in step 1, the anolyte uses the sulfur ion-containing wastewater (sulfur ion concentration is 1.02 mol L -1 , pH is 13.5) generated after absorbing hydrogen sulfide gas with sodium hydroxide solution in industrial production. Before the reaction, the sulfur ion-containing wastewater is filtered to remove insoluble impurities. The remaining steps and operations are the same as those in Example 1.

[0080] As Figure 6 shown, the sulfur ion-containing wastewater is used as the anolyte and flows into the anode chamber of the two-electrode system, and the sodium hydroxide solution is used as the catholyte and introduced into the cathode chamber. A carbon-modified sodium ion exchange membrane is used in the middle to block and transfer ions. During electrolysis, sodium ions continuously transfer from the anode to the cathode, and a hydrogen evolution reaction occurs at the cathode to generate high-purity hydrogen. And due to the continuous consumption of hydrogen ions, the pH increases, realizing alkali concentration and recovery. At the same time, the sulfur ions in the anolyte are continuously oxidized to polysulfides. After electrolysis is completed, the polysodium sulfide solution obtained from the oxidation reaction of sulfur ions at the anode is catalytically oxidized with a metal sulfide powder catalytic material in the air and filtered and crystallized to prepare sodium thiosulfate, converting the sulfur-containing wastewater into a high-value-added product.

[0081] In summary, the present invention adopts an electrochemical and chemical tandem method to simultaneously realize the treatment of sulfur-containing waste liquid and the production of high-value-added substances, which is a new solution combining environmental governance and clean energy hydrogen production, and has important significance and application prospects.

[0082] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention accordingly. For those skilled in the art, it should be able to realize that all the equivalent replacements and obvious changes made by using the content of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A method for resource utilization of sulfur-containing wastewater based on electrochemistry and chemical tandem oxidation, characterized in that, It includes the following steps: S1. Add a sulfur ion-containing solution as the anolyte to a two-electrode electrolysis system; In the two-electrode electrolysis system, the anode uses a catalytic electrode for in-situ growth of metal sulfide, the cathode uses a catalytic electrode for hydrogen evolution reaction, the catholyte uses an alkaline solution containing sodium ions, and a carbon-modified sodium ion exchange membrane is provided between the cathode and the anode; in the catalytic electrode for in-situ growth of metal sulfide, the metal sulfide includes one or a combination of more of nickel sulfide, copper sulfide, and cobalt sulfide; The preparation method of the carbon-modified sodium ion exchange membrane includes: soaking a Nafion membrane in hydrogen peroxide and sodium hydroxide solution successively, washing and drying it, then coating a mixed aqueous dispersion slurry of activated carbon and polytetrafluoroethylene on the double layer surface, and performing a drying treatment to obtain a sodium ion exchange membrane with a carbon layer covered on the surface; S2. Perform an electrolysis reaction on the two-electrode electrolysis system to obtain a sodium polysulfide solution at the anode, and a concentrated alkaline electrolyte and high-purity hydrogen at the cathode. The electrolysis reaction adopts a constant voltage electrolysis mode or a constant current electrolysis mode. When the constant voltage electrolysis mode is adopted, the voltage is 0.4 - 1.5 V. When the constant current electrolysis mode is adopted, the current is 10 mA cm -2 - 1 A cm -2 ; S3. Add a metal sulfide powder catalytic material to the sodium polysulfide solution, and carry out a chemical wet oxidation reaction under the condition of introducing air or oxygen, separate the product into solid and liquid phases to obtain a solid powder and a liquid component; the metal sulfide powder catalytic material is prepared by co-precipitation of a salt solution of a transition metal and a sodium disulfide solution, followed by filtration, washing, and drying; the transition metal includes one or a combination of more of nickel, iron, and cobalt; the addition amount of the metal sulfide powder catalytic material in the sodium polysulfide solution is 10 - 20 mg / mL; the chemical wet oxidation reaction is carried out under stirring conditions at 20 - 80 °C, the stirring speed is 1 - 1000 rpm, and air or oxygen is introduced at a flow rate of 1 - 500 sccm during the reaction process; S4. Concentrate, filter, and crystallize the liquid component to obtain sodium thiosulfate pentahydrate.

2. The method according to claim 1, wherein In step S1, the sulfur ion-containing solution is an aqueous solution of sodium sulfide or a mixed solution of sodium sulfide and sodium hydroxide, and the sulfur ion concentration is 1-4 mol / L -1 .

3. The method according to claim 1, characterized in that In step S1, in the catalytic electrode for in-situ growth of metal sulfide, the substrate material of the catalytic electrode includes one of nickel foam, carbon paper, and carbon cloth.

4. The method according to claim 1, characterized in that In step S1, the cathode uses a Pt / C electrode; the cathode electrolyte is selected from one or a combination of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution, and the concentration of the cathode electrolyte is 0.1 - 4 mol L -1 .

5. The method according to claim 1, wherein In step S4, concentration is carried out by means of vacuum evaporation, and the temperature of vacuum evaporation is 60 - 80 °C.

6. Use of the method according to any one of claims 1, 3, 4 or 5 in treating sulfur-containing wastewater, characterized in that, The sulfur ion-containing solution is the sulfur ion-containing wastewater generated after using sodium hydroxide solution to absorb hydrogen sulfide gas in industrial production.

Images