Method for extracting sulfur element from domestic sewage containing sulfate

Abstract

The invention discloses a method for extracting a sulfur element from sulfate-containing domestic sewage. The method comprises the following steps: S1, adding a molybdate solution at the source of a pipeline for conveying the sulfate-containing domestic sewage; s2, arranging an electrolysis device at the downstream of the molybdate solution adding point; s3, the electrolyzer electrolyzes the passing domestic sewage, two electrodes are adopted for electrolysis, an anode is a graphite electrode, and a cathode is stainless steel. According to the method, the molybdate solution is added into the pipeline for discharging the sulfate-containing domestic sewage, firstly, generation of S2-is inhibited, secondly, MoSxO4-x2-is formed by combining MoO4 < 2-> and S2-for S2-generated without being influenced by molybdate, and MoSxO4-x2-is migrated to an anode for discharging by adopting a heating and dual-electrode electrolysis method, so that the sulfate-containing domestic sewage is discharged, and the sulfate-containing domestic sewage is discharged. According to the method, MoSm is taken as an anode, so that an amorphous MoSm dark brown solid is generated and deposited on the anode, MoSm is calcined and decomposed to obtain a grey black MoS2 solid, and the MoS2 solid can be used as an anode material for producing oxygen through water electrolysis and a cathode material for catalyzing oxygen reduction.

Description

Technical Field

[0001] The invention relates to the technical field of domestic sewage treatment, and in particular to a method for extracting sulfur from domestic sewage containing sulfate. Background Art

[0002] Domestic sewage contains a variety of anions, among which sulfate is the most common. Especially in the areas around sulfide factories, there is a risk of excessive sulfate concentration in sewage discharged into municipal pipes. National standards stipulate that the sulfate concentration in discharged sewage should be controlled within 250 mg / L. Although sulfate in domestic sewage itself is not toxic, under anaerobic conditions, sulfate-reducing bacteria (SRB) can convert sulfate into S 2- , and eventually generate H2S gas. H2S will corrode municipal drainage pipes and facilities, affect the stable operation of urban drainage systems, and cause economic losses; in addition, H2S is a pungent odor that will pollute the surrounding environment after overflow. Therefore, it is of great significance to effectively manage the sulfide problem caused by SRB.

[0003] At present, there are two main strategies for the management of sulfide in wastewater: one is to prevent and control the generation of sulfide from the source, and the other is to treat the wastewater that has accumulated sulfide. The former mainly restricts the activity of microorganisms or prevents S 2- The formation of sulfide is reduced by reducing the production of sulfide. The addition of inhibitors is the main means to achieve this goal, and it has attracted much attention due to its reliable effect and high safety. However, in actual operations, in order to ensure the inhibition effect, it is sometimes necessary to use a large amount of inhibitors, which on the one hand leads to increased costs, and on the other hand, residual substances may also affect the microbial community in subsequent sewage treatment processes. Commonly used substances that inhibit sulfide formation include inhibitors for SRB (such as alkaline substances, molybdates, etc.), substances that promote the denitrification process (such as nitrate ions) and specific metal ions. When using inhibitors, it is necessary to consider the economic cost and the impact on the entire sewage treatment process.

[0004] Previous studies have shown that molybdate can be used to control the growth of SRB groups in sewage. Only a small amount of addition (3-5 mmol / L) is needed to effectively reduce the activity of SRB mixed colonies. Although molybdenum is an essential trace element for the human body, excessive exposure to a molybdenum environment may have adverse effects on human health, such as causing myocardial hypoxia, kidney stones, iron deficiency anemia, and even inducing serious diseases such as esophageal cancer. Therefore, the treatment and discharge of molybdate-containing wastewater also need to strictly ensure that its discharge does not pose a hazard to the environment and public health. The development and application of new resource recovery sewage treatment technologies are not only an effective means to solve environmental problems, but also a necessary measure to achieve efficient resource utilization. Summary of the invention

[0005] The object of the present invention is to solve the above-mentioned shortcomings and provide a method for extracting sulfur from sulfate-containing domestic sewage.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for extracting sulfur from sulfate-containing domestic sewage, comprising the following steps:

[0007] S1. Add molybdate solution at the source of the pipeline for transporting sulfate-containing domestic sewage;

[0008] S2. An electrolysis device is arranged downstream of the molybdate solution addition point;

[0009] S3, the electrolysis device electrolyzes the domestic sewage passing through, and the electrolysis adopts two-electrode electrolysis, the anode is a graphite electrode, and the cathode is stainless steel;

[0010] S4. After continuous electrolysis, the graphite anode is taken out, and the dark brown solid deposited on the anode is peeled off and collected;

[0011] S5. calcining the dark brown solid obtained in step S4 to obtain a gray-black MoS2 solid.

[0012] Furthermore, in S1, the dosage of the molybdate solution is related to the sewage flow rate, and the dosage range is 0.5-5mmolL -1 h -1 .

[0013] Furthermore, the molybdate solution is a sodium molybdate solution or a potassium molybdate solution.

[0014] Furthermore, an electrolysis device is set up 2.5 km or more behind the molybdate solution addition point; if the distance between the addition point and the sewage pipe transmission distance is less than 2.5 km and greater than 0.9 km, an electrolysis device is set up in front of the sewage treatment plant; if the distance between the addition point and the sewage treatment plant is less than 0.9 km, this method is not applicable.

[0015] Furthermore, in S2, the electrolysis device includes an electrolytic cell with a sewage inlet at the bottom and a sewage outlet at the top, an anode rod inserted in the electrolytic cell, a guide plate wound around the outside of the anode rod, and a spiral cathode plate arranged in the guide plate spacing area.

[0016] Further, in the S1, the molybdate solution inhibits S 2- The generation of S 2- , using MoO4 2- and S 2- Combined to form MoS x O 4-x 2- , 0≤x≤4;

[0017] MoO4 2- +xS 2- →MoS x O 4-x 2- +xO 2- .

[0018] Furthermore, in S4, after the domestic sewage enters the electrolysis device, the heating device performs auxiliary heating on the electrolysis device, and MoS x O 4-x 2- Migrate to the anode to discharge and generate amorphous MoS m Dark brown solid, m≥3, the discharge process is as follows:

[0019] MoS x O 4-x 2- +(4-x)S 2- -(6-x)e - →MoS m +(4-x)O 2- (l)+(4-m) / 8S8(s).

[0020] Furthermore, in S3, the electrolytic cell voltage is 2.1-2.7V, and the sewage hydraulic retention time in the electrolytic cell is 5-20min.

[0021] Furthermore, in S4, the continuous electrolysis time is 24-240h.

[0022] Furthermore, in S5, the calcination temperature is 220° C.-350° C., and the calcination time is 0.5-4 h.

[0023] Compared with the prior art, the present invention has the following beneficial effects: the present invention firstly inhibits the S 2- The generation of S 2- hydrolysis, and secondly, for the S produced without the influence of molybdate 2- , using MoO4 2- and S 2- Combined to form MoS x O 4-x 2- , and adopt heating and double-electrode electrolysis method to make MoS x O 4-x 2- Migrate to the anode for discharge, thereby generating amorphous MoS m Dark brown solid is deposited on the anode and is mThe MoS2 solid is calcined and decomposed to obtain gray-black MoS2 solid, which can be used as an anode material for water electrolysis to produce oxygen and a cathode material for catalytic oxygen reduction, showing good electrocatalytic effect.

[0024] This method reduces the generation of sulfides in the pipeline and reduces the risk of sewage pipeline corrosion. On the other hand, the residual MoO4 in domestic sewage 2- With the generated S 2- They are deposited together at the anode, reducing the molybdenum content in domestic sewage and promoting the discharge of domestic sewage in compliance with standards. In addition, the sulfur element on the sulfate in domestic sewage and the molybdenum element in the molybdate are deposited at the anode to obtain MoS2 solid material with good electrocatalytic performance, realizing high added value resource utilization, which has positive significance for environmental protection and wastewater resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 It is a schematic diagram of the present invention.

[0027] Figure 2 Schematic diagram of the electrolysis device of the present invention.

[0028] Figure 3 This is a performance diagram of the MoS2 solid prepared in Example 1 of the present invention used as a catalytic oxygen reduction cathode material.

[0029] Figure 4 This is a performance diagram of the MoS2 solid prepared in Example 2 of the present invention used as an anode material for oxygen production in water electrolysis.

[0030] Figure 5 This is a SEM morphology image of the MoS2 solid prepared in Example 3 of the present invention.

[0031] Figure 6 This is a graph of UV-Vis test results of comparative example 1 of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0033] Because the low sulfate concentration in sewage affects the sulfide generation rate and thus affects the sulfur extraction effect, this plan only treats sewage with a sulfate concentration higher than 250ml / L.

[0034] See also Figure 1-6 .

[0035] Embodiment 1:

[0036] A method for extracting sulfur from domestic sewage containing sulfate, wherein the initial sulfate content in the sewage is 280 mg / L and the sewage flow rate is constant at 1000 L / h, comprising the following steps:

[0037] S1. Add sodium molybdate solution through a dosing device at the source of the pipeline transporting sulfate-containing domestic sewage, adding 1mmolL every hour. -1 h -1 Sodium molybdate was added dropwise in the form of 1L aqueous solution over 30 minutes. The molybdate solution inhibited S 2- The generation of S 2- , will gradually react with MoO4 during pipeline transmission 2- Combined to form MoS x O 4-x 2- , 0≤x≤4, and migrates downstream with the water flow;

[0038] MoO4 2- +xS 2- →MoS x O 4-x 2- +xO 2- ;

[0039] S2. An electrolysis device is installed downstream of the molybdate solution addition point. An electrolysis device is installed 2.5 km or more after the molybdate solution addition point. The S of sulfide not combined with molybdate 2- It will also migrate with the water flow to the electrolysis device;

[0040] S3, the electrolysis device electrolyzes the domestic sewage passing through, the electrolysis adopts two-electrode electrolysis, the anode is a graphite electrode, the cathode is stainless steel, the electrolysis device includes an electrolytic cell with a sewage inlet at the bottom and a sewage outlet at the top, an anode rod inserted in the electrolytic cell, a guide plate wound around the outside of the anode rod, and a spiral cathode plate arranged in the guide plate interval area, the electrolytic cell voltage is 2.1V, and the sewage hydraulic retention time in the electrolytic cell is 5min;

[0041] S4. After the domestic sewage enters the electrolysis device, the heating device performs auxiliary heating on the electrolysis device. MoS x O 4-x2- Migrate to the anode to discharge and generate amorphous MoS m Dark brown solid, m≥3, after 24h of continuous electrolysis, the graphite anode is taken out, and the dark brown solid deposited on the anode is peeled off and collected. The discharge process is as follows:

[0042] MoS x O 4-x 2- +(4-x)S 2- -(6-x)e - →MoS m +(4-x)O 2- (l)+(4-m) / 8S8(s);

[0043] S5. The dark brown solid obtained in step S4 is calcined at 220°C for 0.5h to obtain a gray-black MoS2 solid. When the MoS2 material is used as a cathode material for catalytic oxygen reduction (ORR), the initial potential in a 0.1M HClO4 solution is 0.8056V (vs.RHE), which is close to 0.8701V (vs.RHE) of the Pt / C catalytic material. The current density of the MoS2 material at a potential of 0.4V is 3.25mAcm -1 ,like Figure 3 As shown, the number of electron transfer in the catalytic process is 3.87.

[0044] Preferably, the heating device may use a geothermal heat pump or a solar heating system.

[0045] Embodiment 2:

[0046] A method for extracting sulfur from domestic sewage containing sulfate, wherein the initial sulfate content in the sewage is 350 mg / L and the sewage flow rate is constant at 2500 L / h, comprising the following steps:

[0047] S1. Add sodium molybdate solution through the dosing device at the source of the pipeline transporting sulfate-containing domestic sewage, adding 1.5mmolL every 0.5h. -1 h -1 Sodium molybdate was added dropwise in the form of 1.875L aqueous solution over 20 minutes. The molybdate solution inhibited S 2- The generation of S 2- , will gradually react with MoO4 during pipeline transmission 2- Combined to form MoS x O 4-x 2- , 0≤x≤4, and migrates downstream with the water flow;

[0048] MoO4 2- +xS2- →MoS x O 4-x 2- +xO 2- ;

[0049] S2. An electrolysis device is installed downstream of the molybdate solution addition point. An electrolysis device is installed 2.5 km or more after the molybdate solution addition point. The S of sulfide not combined with molybdate 2- It will also migrate with the water flow to the electrolysis device;

[0050] S3, the electrolysis device electrolyzes the domestic sewage passing through, the electrolysis adopts two-electrode electrolysis, the anode is a graphite electrode, the cathode is stainless steel, the electrolysis device includes an electrolytic cell with a sewage inlet at the bottom and a sewage outlet at the top, an anode rod inserted in the electrolytic cell, a guide plate wound around the outside of the anode rod, and a spiral cathode plate arranged in the guide plate interval area, the electrolytic cell voltage is 2.4V, and the sewage hydraulic retention time in the electrolytic cell is 12min;

[0051] S4. After the domestic sewage enters the electrolysis device, the heating device performs auxiliary heating on the electrolysis device. MoS x O 4-x 2- Migrate to the anode to discharge and generate amorphous MoS m Dark brown solid, m≥3, after 120h of continuous electrolysis, the graphite anode is taken out, and the dark brown solid deposited on the anode is peeled off and collected. The discharge process is as follows:

[0052] MoS x O 4-x 2- +(4-x)S 2- -(6-x)e - →MoS m +(4-x)O 2- (l)+(4-m) / 8S8(s);

[0053] S5. The dark brown solid obtained in step S4 is calcined at a temperature of 285° C. for 2 h to obtain a gray-black MoS2 solid. When the MoS2 material is used as an anode material for water electrolysis oxygen production (OER), the starting potential in a 0.1 mol / L KOH solution is 1.545 V (vs. RHE) and the current density is 10 mA cm -2 When the electrode potential is 1.617V (vs.RHE), it is close to the 1.594V (vs.RHE) of RuO2 electrode. At higher current density, the water electrolysis oxygen production (OER) effect of MoS2 electrode is even better than that of RuO2. Figure 4 shown.

[0054] Embodiment 3:

[0055] A method for extracting sulfur from domestic sewage containing sulfate, wherein the initial sulfate content in the sewage is 400 mg / L and the sewage flow rate is constant at 2900 L / h, comprising the following steps:

[0056] S1. Add potassium molybdate solution through the dosing device at the source of the pipeline transporting sulfate-containing domestic sewage, adding 1.6mmolL every 0.5h. -1 h -1 Potassium molybdate was added dropwise in the form of 2.32L aqueous solution over 20 minutes. The molybdate solution inhibited S 2- The generation of S 2- , will gradually react with MoO4 during pipeline transmission 2- Combined to form MoS x O 4-x 2- , 0≤x≤4, and migrates downstream with the water flow;

[0057] MoO4 2- +xS 2- →MoS x O 4-x 2- +xO 2- ;

[0058] S2. An electrolysis device is set up downstream of the molybdate solution addition point. The distance between the addition point and the sewage pipeline is less than 2.5km and greater than 0.9km. An electrolysis device is set up in front of the sewage treatment plant. The S of sulfide not combined with molybdate 2- It will also migrate with the water flow to the electrolysis device;

[0059] S3, the electrolysis device electrolyzes the domestic sewage passing through, the electrolysis adopts two-electrode electrolysis, the anode is a graphite electrode, the cathode is stainless steel, the electrolysis device includes an electrolytic cell with a sewage inlet at the bottom and a sewage outlet at the top, an anode rod inserted in the electrolytic cell, a guide plate wound around the outside of the anode rod, and a spiral cathode plate arranged in the guide plate interval area, the electrolytic cell voltage is 2.7V, and the sewage hydraulic retention time in the electrolytic cell is 20min;

[0060] S4. After the domestic sewage enters the electrolysis device, the heating device performs auxiliary heating on the electrolysis device. MoS x O 4-x 2- Migrate to the anode to discharge and generate amorphous MoS m Dark brown solid, m≥3; after 240h of continuous electrolysis, the graphite anode is taken out, and the dark brown solid deposited on the anode is peeled off and collected. The discharge process is as follows:

[0061] MoSx O 4-x 2- +(4-x)S 2- -(6-x)e - →MoS m +(4-x)O 2- (l)+(4-m) / 8S8(s);

[0062] S5. The dark brown solid obtained in step S4 is calcined at a temperature of 350° C. for 2 h to obtain a gray-black MoS2 solid. The SEM morphology of the material is as follows: Figure 5 As shown. It can be used as an anode material for water electrolysis to produce oxygen (OER) and a cathode material for electrocatalytic oxygen reduction (ORR), showing good electrocatalytic effect.

[0063] Comparative Example 1:

[0064] Considering that there may be specific impurities in municipal sewage that affect the spectral detection results, simulated domestic sewage (containing 0.05 mol / L sodium sulfide and 0.1 mol / L sodium molybdate) was prepared, and a laboratory-level electrolysis device was used to electrolyze for 20 minutes at 2.3V tank voltage. The UV-Vis test results after the simulated sewage after electrolysis was diluted 10 times are as follows Figure 6 As shown in the figure, it can be seen that there are a series of transition states of MoS in water. x O 4-x 2- , 0≤x≤4,MoS x O 4-x 2- Participate in electrolysis to generate amorphous MoS m Dark brown solid, MoS m The dark brown solid is calcined to obtain MoS2 which can be used as a resource.

[0065] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for extracting sulfur from sulfate-containing domestic sewage, characterized in that: The steps include: S1. Add molybdate solution at the source of the pipeline for transporting sulfate-containing domestic sewage; S2. An electrolysis device is arranged downstream of the molybdate solution addition point; S3. A heating device is arranged at the bottom of the electrolysis device. The electrolysis device electrolyzes the domestic sewage passing through. The electrolysis adopts two-electrode electrolysis, the anode is a graphite electrode, and the cathode is stainless steel; S4. After continuous electrolysis, the graphite anode is taken out, and the dark brown solid deposited on the anode is peeled off and collected; S5. calcining the dark brown solid obtained in step S4 to obtain a gray-black MoS2 solid.

2. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 1, characterized in that: In S1, the dosage of the molybdate solution is related to the sewage flow rate, and the dosage range is 0.5-5mmolL -1 h -1 .

3. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 1, characterized in that: The molybdate solution is a sodium molybdate solution or a potassium molybdate solution.

4. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 1, characterized in that: An electrolysis device is installed in the pipeline 2.5 km or more behind the molybdate solution addition point; if the transmission distance from the addition point to the sewage pipeline is less than 2.5 km and greater than 0.9 km, an electrolysis device is installed in front of the sewage treatment plant.

5. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 1, characterized in that: In S2, the electrolysis device includes an electrolytic cell with a sewage inlet at the bottom and a sewage outlet at the top, an anode rod inserted in the electrolytic cell, a guide plate wound around the outside of the anode rod, and a spiral cathode plate arranged in the guide plate spacing area.

6. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 5, characterized in that: In S1, the molybdate solution inhibits S 2- The generation of S 2- , using MoO4 2- and S 2- Combined to form MoS x O 4-x 2- , 0≤x≤4; MoO4 2- +xS 2- →MoS x O 4-x 2- +xO 2- 。 7. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 6, characterized in that: In S4, after the domestic sewage enters the electrolysis device, the heating device performs auxiliary heating on the electrolysis device, and MoS x O 4-x 2- Migrate to the anode to discharge and generate amorphous MoS m Dark brown solid, m≥3, the discharge process is as follows: MoS x THE 4-x 2- +(4-x)S 2- -(6-x)e - →MoS m +(4-x)O 2- (l)+(4-m) / 8S8(s)。 8. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 6, characterized in that: In S3, the electrolytic cell voltage is 2.1-2.7V, and the sewage hydraulic retention time in the electrolytic cell is 5-20min.

9. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 1, characterized in that: In said S4, the continuous electrolysis time is 24-240h.

10. The method for extracting sulfur from sulfate-containing domestic sewage according to claim 1, characterized in that: In the S5, the calcination temperature is 220°C-350°C, and the calcination time is 0.5-4h.

Images