A method for treating sulfides in wastewater using modified stainless steel

Abstract

This invention discloses a method for treating sulfides in wastewater using modified stainless steel, belonging to the field of water treatment technology. The method includes: (1) polishing and cleaning the stainless steel; the stainless steel includes iron and nickel, with a nickel content of 4-7%; (2) placing the stainless steel treated in step (1) in a sodium hydroxide electrolyte to form a dual-electrode system, using constant current technology to corrode the anode, and using the corroded anode as the working electrode; (3) placing the working electrode in wastewater containing sulfides, using an Ag / AgCl electrode as a reference electrode, and the stainless steel treated in step (1) as the counter electrode to form a three-electrode system, using constant potential technology to remove sulfides from the wastewater. This invention has simple steps, is easy to implement, has good desulfurization effect, and the modified stainless steel can be reused after in-situ regeneration, exhibiting good operational stability.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a method for treating sulfides in wastewater using modified stainless steel. Background Technology

[0002] Hydrogen sulfide is a colorless, toxic gas with a rotten egg smell, produced by sulfate-reducing bacteria (SRB) during wastewater treatment in biological or industrial processes, such as anaerobic fermentation, pig manure storage, and municipal sewage collection. Due to the activity of SRB, sulfates are rapidly reduced to sulfides, which are then released into the air as hydrogen sulfide, posing a health and life threat to exposed humans and animals. Furthermore, in the presence of aerobic bacteria, hydrogen sulfide can be oxidized to sulfuric acid (H₂SO₄), leading to sewer corrosion. Traditional methods for removing sulfides often employ physicochemical or biological techniques, but these methods consume large amounts of chemicals, have high operating and storage costs, and generate large quantities of toxic sludge. Therefore, there is a need to develop a more economical and environmentally friendly method for treating hydrogen sulfide in wastewater.

[0003] Electrochemical oxidation is effective because it can remove sulfides in situ and selectively oxidize sulfides to elemental sulfur (S). 0 With its lower treatment costs and avoidance of sulfide reforming and the formation of toxic sludge, it is attracting increasing attention from researchers.

[0004] Chinese patent document CN116083938A discloses a high-temperature electrochemical method for the complete decomposition of hydrogen sulfide to produce hydrogen and sulfur. This method includes the following steps: a gas containing hydrogen sulfide undergoes an electrochemical oxidation reaction at the anode of an electrolytic cell to produce sulfur and protons. Sulfur is collected as a gaseous stream from the anode chamber of the electrolytic cell under high-temperature conditions. Protons pass through a solid electrolyte membrane in the electrolytic cell to reach the cathode, where they are reduced to produce hydrogen. The solid electrolyte membrane is a high-temperature proton conductor, allowing protons to travel from the anode to the cathode under high-temperature conditions. However, this method is for the complete decomposition of hydrogen sulfide in a mixed gas and requires the assistance of an anode catalyst.

[0005] Chinese patent document CN108529714A discloses a photoelectrochemical reaction cell and its method for treating hydrogen sulfide waste gas and wastewater. This invention involves adding redox-active substances (such as iodide ions and ferric ions) to the anode and cathode chambers. Holes generated at the photocatalytic anode indirectly oxidize sulfur ions to generate high-purity, recyclable elemental sulfur particles. Simultaneously, catalytically active ions (such as ferrous ions) generated at the cathode are used to activate persulfate to generate free radicals, thereby achieving efficient removal of pollutants from wastewater. This method is suitable for treating anaerobic digestion waste gas, sulfur-containing wastewater / waste gas, and water environment remediation. However, the photocatalysis involved in this method requires addressing the issue of light transmittance in practical applications. Some suspended solids and deep colors in certain wastewaters (such as dyeing wastewater) hinder light transmission, affecting the photocatalytic effect.

[0006] The efficiency and products of electrochemical sulfide oxidation largely depend on the type of electrode material. Furthermore, the final product of sulfide oxidation, elemental sulfur, is non-conductive and its deposition on the electrode surface can passivate it and cause it to gradually fail over time. Therefore, there is a need to develop a simple method for treating hydrogen sulfide in wastewater with reusable electrodes. Summary of the Invention

[0007] This invention provides a method for treating sulfides in wastewater using modified stainless steel. The method is simple, easy to implement, and has a good desulfurization effect. The desulfurization efficiency can be changed by adjusting the Ni content in the stainless steel oxide film. Furthermore, the modified stainless steel can be reused after in-situ regeneration and has good operational stability.

[0008] The specific technical solution adopted is as follows:

[0009] A method for treating sulfides in wastewater using modified stainless steel includes the following steps:

[0010] (1) Polishing and cleaning the stainless steel; the stainless steel includes iron and nickel, with the nickel content being 4-7%;

[0011] (2) The stainless steel treated in step (1) is placed in sodium hydroxide electrolyte to form a dual electrode system as anode and cathode respectively. The anode is corroded using constant current technology and the corroded anode is used as the working electrode.

[0012] (3) The working electrode is placed in the wastewater containing sulfides, the Ag / AgCl electrode is used as the reference electrode, and the stainless steel treated in step (1) is used as the counter electrode to form a three-electrode system. The sulfides in the wastewater are removed by constant potential technology.

[0013] The sulfur in the sulfides is in the negative divalent state, including hydrogen sulfide.

[0014] This invention utilizes inexpensive stainless steel as raw material, transforming it into a high-performance electrocatalytic sulfide oxidation electrode material (catalytically active component includes NiOOH) through simple electro-corrosion modification. A three-electrode system is further constructed to treat hydrogen sulfide in wastewater, achieving a hydrogen sulfide removal rate exceeding 90% within 48 hours, demonstrating excellent desulfurization performance. At a lower anodic potential (1.62V), sulfides are desulfurized through direct electro-oxidation. At a higher anodic potential (≥1.82V), sulfides are removed not only through direct electro-oxidation but also through indirect oxidation by the generated O2. Furthermore, NiOOH indirectly catalyzes desulfurization by promoting the oxygen evolution reaction.

[0015] Preferably, the stainless steel is AISI 304 stainless steel, which includes iron, nickel and chromium, with the iron content being 72-78%, the nickel content being 4-7%, and the chromium content being 17-19%.

[0016] Preferably, the stainless steel is polished with silicon carbide sandpaper, and then ultrasonically cleaned with acetone, ethanol and deionized water respectively.

[0017] Preferably, the concentration of the sodium hydroxide electrolyte is 1-10M. If the concentration of the sodium hydroxide electrolyte is too low, the corrosion degree will be insufficient, and a higher current density or a longer corrosion time is required to control the nickel content of the oxide film. If the concentration of the sodium hydroxide electrolyte is too high, it will easily cause excessive corrosion, directly melting away the stainless steel and preventing the formation of an oxide film.

[0018] Preferably, in step (2), when using constant current technology, the current density is 0.1–3 A cm⁻¹. -2 The etching time ranges from 1 to 600 seconds, and under these parameters, the Ni content in the oxide film can be effectively controlled. As the etching time increases (gradually from 0 to 30 seconds), the Ni content in the oxide film gradually increases, reaching its highest level (approximately 69%) after 150 seconds of etching.

[0019] Preferably, the initial pH value of the sulfide-containing wastewater is 6 to 8.

[0020] Preferably, in step (3), based on the voltammetric method, a constant voltage technique is used to conduct an anodic desulfurization experiment within the voltage range where sulfides are oxidized, with a voltage of 1.62–2.22 V vs. RHE. The oxidation products of hydrogen sulfide, etc., are mainly elemental sulfur, and the generated elemental sulfur is partially deposited on the surface of the working electrode.

[0021] The method for treating sulfides in wastewater using modified stainless steel further includes step (4): placing the working electrode after treating the wastewater in step (3) in a phosphate buffer solution, using an Ag / AgCl electrode as a reference electrode, and using the stainless steel after treatment in step (1) as a counter electrode to form a three-electrode system, and using constant potential technology to regenerate the working electrode.

[0022] The method of this invention employs a cathodic polarization strategy to remove elemental sulfur from the electrode surface, enabling in-situ regeneration of the working electrode, solving the problem of reduced desulfurization efficiency caused by sulfur deposition on the working electrode surface, and improving the reusability of the working electrode.

[0023] Preferably, in step (4), when constant voltage technology is used, the voltage is -0.1 to -0.5V vs. RHE.

[0024] Preferably, in step (4), the regeneration time is 1 to 6 hours.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The method of the present invention uses inexpensive stainless steel as raw material and obtains modified stainless steel electrode material with oxide film for efficient desulfurization through electro-corrosion. Furthermore, the Ni content in the stainless steel oxide film is controlled to improve the electrochemical activity and desulfurization efficiency of the electrode material. In addition, the elemental sulfur deposited on the electrode surface is removed by the cathode recovery strategy to achieve in-situ regeneration of the working electrode, thereby optimizing the regeneration performance and operational stability of the modified stainless steel electrode material and increasing the reusability of the electrode.

[0027] (2) The method of the present invention has simple steps, small equipment footprint, low cost, and industrialization potential. Attached Figure Description

[0028] Figure 1 The graph shows the Fe, Ni, and Cr content on the surface of the working electrode (modified stainless steel) in Comparative Example 1 and Examples 1-8.

[0029] Figure 2 The graph shows the desulfurization rate and desulfurization efficiency of the methods in Comparative Example 1 and Examples 1-8.

[0030] Figure 3 This study aims to investigate the desulfurization products of the methods in Comparative Example 1 and Examples 1-8.

[0031] Figure 4 The images shown are SEM, EDS, XRD and XPS images of the desulfurization products in Example 6. Among them, (a) to (c) are SEM images at different magnifications, (d) is an EDS elemental distribution map, (e) is an EDS elemental distribution statistical map, (f) is an XRD image, and (g) is an XPS image.

[0032] Figure 5 This is a statistical graph showing the desulfurization rate of the working electrode in Example 6 after four desulfurization cycles and one regeneration treatment. Detailed Implementation

[0033] The present invention will be further illustrated below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0034] In the comparative examples and embodiments of the present invention, the AISI 304 stainless steel used was purchased from Dongguan Ruipu Metal Materials Factory. AISI 304 stainless steel includes iron, nickel and chromium elements, with the iron content being 72-78%, the nickel content being 4-7%, and the chromium content being 17-19%.

[0035] In the comparative examples and embodiments of this invention, wastewater containing sulfides is simulated using a 10 mM Na2S solution. The Na2S solution is prepared as follows: First, 90 mL of phosphate buffer solution (PB, 0.1 M Na2HPO4 / NaH2PO4·2H2O, pH 7.0, N2 purging for 10 min) is added to the electrochemical reactor. Then, the reactor is sealed and purged with N2 for 5 min to remove air from the headspace. Subsequently, 10 mL of Na2S·9H2O-PB solution is added to the reactor to prepare 100 mL of 10 mM Na2S solution (containing 10 mM sulfides and 0.1 M PB solution, pH 7.2). Na2S undergoes hydrolysis in water to produce H2S: Na2S + H2O → NaHS + H2S.

[0036] Comparative Example 1

[0037] (1) Using a single piece of stainless steel AISI 304 (SS) with a length of 45mm, a width of 10mm, and a thickness of 0.3mm as the substrate, the surface of the SS was polished with silicon carbide sandpaper (2000 grit), and then ultrasonically cleaned with acetone, ethanol, and deionized water for 15 minutes each; each electrode was coated with silicone to control the thickness of one side to 1cm. 2 2cm on both sides 2 The effective area is named SS.

[0038] (2) SS is used as the working electrode and placed in wastewater containing sulfides. Another piece of SS of the same size is placed 30 mm away from the working electrode as the counter electrode. The Ag / AgCl electrode is placed near the working electrode 25 mm away as the reference electrode, forming a three-electrode system. Hydrogen sulfide in the wastewater is removed under a constant potential of 2.02V vs. RHE (based on the potential of the reference electrode).

[0039] Example 1

[0040] (1) Using a single piece of stainless steel AISI 304 (SS) with a length of 45mm, a width of 10mm, and a thickness of 0.3mm as the substrate, the surface of the SS was polished with silicon carbide sandpaper (2000 grit), and then ultrasonically cleaned with acetone, ethanol, and deionized water for 15 minutes each; each electrode was coated with silicone to control the thickness of one side to 1cm. 2 2cm on both sides 2 The effective area.

[0041] (2) The stainless steel treated in step (1) is placed in a 7.5M sodium hydroxide electrolyte as the anode, and another stainless steel sheet without silicone coating is used as the cathode to form a dual-electrode system. The anode is then corroded using a constant current technique with a current density of 1A cm⁻¹. -2 Stir (480 r / min) -1 After 1 second of corrosion, the corroded anode is used as the working electrode and named SS-1.

[0042] (2) SS-1 is used as the working electrode and placed in wastewater containing sulfides. Another SS of the same size is placed 30 mm away from the working electrode as the counter electrode. The Ag / AgCl electrode is placed near the working electrode 25 mm away as the reference electrode, forming a three-electrode system to remove hydrogen sulfide from the wastewater at a constant potential of 2.02 V vs. RHE.

[0043] Examples 2-8

[0044] The only difference between the methods for treating sulfides in wastewater using modified stainless steel in Examples 2-8 and those in Example 1 is the corrosion treatment time, which is set to 5s, 10s, 30s, 60s, 150s, 300s, and 600s, respectively. The etched anode is used as the working electrode and is named SS-5, SS-10, SS-30, SS-60, SS-150, SS-300, and SS-600, respectively.

[0045] Example 9

[0046] (1) The working electrode SS-300 prepared in Example 6 was subjected to four desulfurization cycles to obtain a working electrode with surface sulfur deposition. The working electrode with surface sulfur deposition was placed in phosphate buffer (PB solution, 0.1M Na2HPO4 / NaH2PO4·2H2O, pH 7.0). An Ag / AgCl electrode was placed about 25 mm away from the working electrode as a reference electrode. Another SS electrode of the same size was placed 30 mm away from the working electrode as a counter electrode to form a three-electrode system. The working electrode was regenerated for 5 h at a constant potential of -0.38V vs. RHE (based on the potential of the reference electrode).

[0047] (2) The regenerated working electrode is placed in the wastewater containing sulfides. Another SS of the same size is placed 30 mm away from the working electrode as the counter electrode. The Ag / AgCl electrode is placed near the working electrode 25 mm away as the reference electrode, forming a three-electrode system. Hydrogen sulfide in the wastewater is removed under a constant potential of 2.02 V vs. RHE (based on the potential of the reference electrode).

[0048] Example 10

[0049] The method of treating sulfides in wastewater using modified stainless steel in Example 10 differs from that in Example 1 only in that the concentration of sodium hydroxide electrolyte is 5M, the current density in step (2) is 1.5A, and the corrosion time is 20s.

[0050] Sample Analysis

[0051] Analysis of the Fe, Ni, and Cr content on the surface of the working electrode (modified stainless steel) in Comparative Example 1 and Examples 1-8 is shown in the following figures. Figure 1 As shown, at 1A / cm 2 Surface corrosion treatment of stainless steel was carried out under corrosion conditions of current density within 150s, resulting in modified stainless steel with different Ni contents. As the corrosion time increased (gradually increasing from 0 to 30s), the Ni content in the oxide film also gradually increased, reaching the highest level (approximately 69%) at 150s of corrosion treatment. This indicates that the Ni content of the surface oxide film of stainless steel can be controlled through surface corrosion.

[0052] The desulfurization time for Comparative Example 1 and Examples 1-8 was uniformly set to 48 hours. The corresponding desulfurization rates and efficiencies were statistically analyzed, and the results are as follows: Figure 2As shown, the Ni content in the oxide film on the modified stainless steel surface affects the removal of hydrogen sulfide. Corrosion treatment significantly promotes the removal of hydrogen sulfide. The working electrodes in Examples 1 to 8 all showed significant catalytic activity for sulfide oxidation. In particular, the working electrodes with a corrosion time of not less than 30 seconds achieved a hydrogen sulfide removal rate of over 90% within 48 hours. Among them, the working electrode SS-150 had the highest removal rate, approximately 97%, which was about 20% higher than that of the untreated SS. Furthermore, when the corrosion time did not exceed 150 seconds, the desulfurization efficiency was directly proportional to the Ni content.

[0053] The desulfurization product distributions of Comparative Example 1 and Examples 1-8 are as follows: Figure 3 As shown, the main product of desulfurization is elemental sulfur.

[0054] Figure 4 The images shown are SEM, EDS, XRD and XPS images of the desulfurization products in Example 6. (a) to (c) are SEM images at different magnifications, (d) is an EDS elemental distribution map, (e) is an EDS elemental distribution statistical map, (f) is an XRD image, and (g) is an XPS image. This shows that the elemental sulfur in the desulfurization product will be deposited on the surface of the working electrode.

[0055] In Example 9, the statistical graphs of the desulfurization rate of the working electrode SS-150 during each desulfurization cycle (each desulfurization cycle is 48 hours) and after regeneration treatment are shown below. Figure 5 As shown, the first-order reaction rate in the sulfide removal experiment decreased significantly in each cycle, from (58.9±2.4)×10 -3 h -1 It decreased to (8.6±0.7)×10 in the fourth cycle. -3 h -1 This is because the accumulation of elemental sulfur deposits passivates the electrode, reducing the electrocatalytic activity and thus partially lowering the performance. When the elemental sulfur on the electrode surface is removed using a cathodic polarization strategy, and the electrode is regenerated, the sulfide removal experiment is continued. The first-order rate of sulfide removal is partially recovered, from (8.6±0.7)×10 -3 h -1 It rose to (45.0±0.8)×10 -3 h -1 This achieved partial recovery of the electrode's catalytic performance, indicating that cathode regeneration can improve the electrode's reusability.

[0056] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating sulfides in wastewater using modified stainless steel, characterized in that, Includes the following steps: (1) Polishing and cleaning stainless steel; the stainless steel includes iron and nickel elements; (2) The stainless steel treated in step (1) is placed in sodium hydroxide electrolyte to form a dual electrode system as anode and cathode respectively. The anode is corroded using constant current technology and the corroded anode is used as the working electrode. (3) The working electrode is placed in the wastewater containing sulfides, the Ag / AgCl electrode is used as the reference electrode, and the stainless steel treated in step (1) is used as the counter electrode to form a three-electrode system. The sulfides in the wastewater are removed by constant potential technology. Step (4): The working electrode after the wastewater treatment in step (3) is placed in phosphate buffer solution, the Ag / AgCl electrode is used as the reference electrode, and the stainless steel after the treatment in step (1) is used as the counter electrode to form a three-electrode system. The working electrode is regenerated using constant potential technology. The sulfur in the sulfides is in the negative divalent state, including hydrogen sulfide; The stainless steel mentioned is AISI 304 stainless steel, which includes iron, nickel and chromium. The iron content is 72-78%, the nickel content is 4-7%, and the chromium content is 17-19%. In step (2), when using constant current technology, the current density is 0.1–3 A cm⁻¹. -2 The corrosion time is 150–600 seconds; The initial pH value of the sulfide-containing wastewater is 6-8; In step (3), when using constant voltage technology, the voltage is 1.62–2.22V vs. RHE; In step (4), when constant voltage technology is used, the voltage is -0.1 to -0.5V vs. RHE, and the regeneration time is 1 to 6 hours.

2. The method for treating sulfides in wastewater using modified stainless steel according to claim 1, characterized in that, The stainless steel was polished with silicon carbide sandpaper, and then ultrasonically cleaned with acetone, ethanol and deionized water respectively.

3. The method for treating sulfides in wastewater using modified stainless steel according to claim 1, characterized in that, The concentration of the sodium hydroxide electrolyte is 1–10 M.

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