Method for removing arsenic in water by sacrificial iron anode electrocoagulation

Abstract

The invention provides a method for removing arsenic in water through sacrificial iron anode electrocoagulation, and belongs to the technical field of feed water treatment. According to the method for removing arsenic in water through sacrificial iron anode electrocoagulation, arsenic-containing underground water is electrolyzed through electrocoagulation treatment, an iron sheet serves as an anode in the electrocoagulation treatment, a sodium sulfate solution serves as electrolyte, and arsenic in water is removed after electrolysis is finished. The current of the electrocoagulation treatment is 5-10 mA, the treatment time is 8-15 min, and the concentration of the sodium sulfate solution is 5-20 mM. According to the invention, an electric coagulation technology is adopted, ferrous iron is generated by electrolysis of an iron anode to promote oxidation of arsenite and adsorption of arsenic on iron precipitates, so that the purpose of separating arsenic from water is achieved, and the method has the advantages of high treatment efficiency, environmental friendliness, flexibility, controllability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and particularly relates to a method for removing arsenic in water by sacrificial iron anode electrocoagulation. Background Art

[0002] Arsenic is one of the top ten water quality-related pollutants. More than 70 countries have reported varying degrees of groundwater arsenic pollution, affecting a population of 150 million. Due to hydrogeological movements and industrial activities, regions such as Inner Mongolia, Shanxi, Xinjiang, Ningxia, and Yunnan in China have serious over-standard groundwater arsenic content. In addition, about 70% of the population in China mainly uses groundwater as the drinking water source. Long-term drinking of water with high arsenic content causes great harm to human health. Therefore, it is urgent to develop new technologies to solve the problem of arsenic pollution in groundwater.

[0003] In groundwater, arsenic mainly exists in the forms of arsenite (uncharged) and arsenate (negatively charged), with arsenite accounting for the main part. The toxicity of arsenite (As(III)) is much higher than that of arsenate (As(V)), and it is difficult to separate by forms such as adsorption precipitation, which brings great difficulties to the removal of arsenic in groundwater. Traditional methods for removing arsenic from groundwater include chemical oxidation precipitation, adsorption, membrane filtration, and ion exchange. In the process of removing arsenite by chemical oxidation precipitation, in addition to adding strong oxidants such as ozone, in existing research, it has been found that under air conditions, the coexistence of divalent iron and arsenite will cause a chemical process of arsenite oxidation to arsenate, and produce reactive species such as hydrogen peroxide, which will greatly reduce the difficulty of removing arsenic from groundwater. Moreover, the method of aeration and adding divalent iron has advantages such as low price, relatively simple process, and combining oxidation and adsorption removal to improve the arsenic removal efficiency compared with other methods (membrane filtration, ion exchange, etc.). However, the above existing technologies still have disadvantages such as large dosage of added drugs, a large amount of sludge generated, and uncontrollable reaction process. Therefore, the present invention proposes a method for removing arsenic in water by sacrificial iron anode electrocoagulation. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a method for removing arsenic in water by sacrificial iron anode electrocoagulation (Fe-EC). The present invention adopts electrocoagulation technology, uses the iron anode to electrolyze to generate divalent iron, to promote the oxidation of arsenite and the adsorption of arsenic on iron precipitates, so as to achieve the purpose of separating arsenic from the water body, and has the advantages of high treatment efficiency, environmental friendliness, and flexible controllability.

[0005] To achieve the above object, the present invention provides a method for removing arsenic in water by sacrificial iron anode electrocoagulation. The electrocoagulation treatment is used to electrolyze arsenic-containing groundwater. The electrocoagulation treatment uses an iron sheet as the anode and a sodium sulfate solution as the electrolyte, and the removal of arsenic in water is achieved after the electrolysis ends.

[0006] Further, the current for the electrocoagulation treatment is 5 - 10 mA, the treatment time is 8 - 15 min, and the initial pH value is 7.5.

[0007] Further, the concentration of sodium sulfate in the arsenic-containing groundwater is 5 - 20 mM.

[0008] Further, the cathode for the electrocoagulation treatment is made of stainless steel or graphite, and the electrode spacing between the cathode and the anode is 4 cm.

[0009] Further, the effective area of the cathode or the anode is 7.48 cm 2 .

[0010] Further, the arsenic concentration in the arsenic-containing groundwater is 10 μM.

[0011] Further, the arsenic-containing groundwater is groundwater containing arsenite.

[0012] Further, before the electrocoagulation treatment, the iron sheet is activated.

[0013] Further, the activation is to soak the iron sheet in a sulfuric acid solution with a concentration of 2 wt.% for 1 min.

[0014] Further, the electrocoagulation treatment process is carried out under stirring, and the rotation speed of the stirring is 300 r / min.

[0015] More specifically, a method for removing arsenic from water by sacrificial iron anode electrocoagulation includes the following steps:

[0016] Soak the iron sheet in a sulfuric acid solution with a concentration of 2 wt.% for 1 min to obtain an iron sheet anode, use stainless steel as the cathode, install the two electrode sheets on the electrode rod, and the effective area of both electrode sheets is 7.48 cm 2 , set the distance between the two electrode sheets to 4 cm. After assembly, add arsenic-containing groundwater and sodium sulfate (Na2SO4, as an electrolyte) to the electrolytic cell to make the concentration of sodium sulfate in the arsenic-containing groundwater 20 mM, and adjust the initial pH value to 7.5 with 0.01 - 1.0 mM of NaOH or 0.005 - 0.5 mM of H2SO4. Then, use the electrocoagulation treatment technology to electrolyze the arsenic-containing groundwater, turn on the power supply to supply power to the two electrodes, and at the same time turn on the stirring treatment device to stir at 300 r / min. The current is 5 - 10 mA, and the electrolysis reaction time is 15 min to achieve the removal of arsenic in the arsenic-containing groundwater.

[0017] During the electrocoagulation treatment process, a current of 5 - 10 mA can ensure the supply of Fe(II) and O2, thereby improving the oxidation and adsorption effects of arsenite (As(III)), converting arsenite (As(III)) into arsenate (As(V)) which is easily adsorbed and removed. At the same time, Fe(II) is oxidized to Fe(III), forming positively charged hydroxide flocs, which further adsorb and remove arsenic in the water body. The current magnitude can be adjusted according to the different water bodies to be treated, so as to achieve the expected effect in a short time.

[0018] During the electrocoagulation treatment process, the electrode distance between the cathode and the anode is set to 4 cm. The distance between the anode and the cathode of the electrode should not be too large. If the distance is too large, it will cause the voltage to increase, waste electric energy, or other side reactions will occur, which will reduce the oxidation efficiency of arsenite.

[0019] During the electrocoagulation treatment process, the expected oxidation effect can be achieved within 15 minutes of the electrolysis treatment time, which is efficient and fast. Subsequently, the flocs can be separated from the water body by precipitation or centrifugal filtration.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] (1) Compared with the traditional technology of adding divalent iron to remove arsenic, in the present invention, zero-valent iron is electrolyzed to produce Fe(II) at a constant current using an iron anode in the air. During the self-oxidation process of iron, (Fe III ·O2 2- ·Fe III ) ligands are generated under the action of Coulomb force, and H2O2 is decomposed. Fe(II) undergoes a coordination complexation reaction with As(III) in the wastewater. Fe(IV) is generated under the action of H2O2, and a part of arsenite (As(III)) is oxidized. Fe(IV) is reduced to Fe(II), and then immediately oxidized to Fe(III); another part of As(III) coordinates with Fe(III) and is oxidized to arsenate (As(V)) by H2O2. Then, it is adsorbed by the formed trivalent iron oxide colloid, greatly enhancing the removal of arsenic from the water body.

[0022] (2) During the operation of the present invention, the current magnitude can be flexibly adjusted according to the required treatment effect, thereby controlling the generation amount of trivalent iron hydroxide and the arsenic removal effect. While ensuring the treatment effect, it reduces the iron consumption, sludge generation, and energy consumption, and is easy to combine with automatic control.

[0023] (3) The present invention generates Fe(II) by electrolyzing an anodic zero-valent iron. During the auto-oxidation process of Fe(II), reactive species such as H2O2 are generated. During the coordination complexation process of Fe(II) and As(III), co-oxidation occurs, oxidizing arsenite (As(III)) to arsenate (As(V)), Fe(II) to Fe(III), and forming a precipitate floc to adsorb and remove arsenic in water. The removal rate can reach over 95% in a short time.

[0024] (4) The method of the present invention can treat groundwater with high arsenic content. Under the condition of sufficient oxygen, it can spontaneously generate reactive species, and the coordination of iron with trivalent arsenic (As(III)) more easily oxidizes arsenite to arsenate. At the same time, the generated flocculant can remove arsenic in water by methods such as electrostatic adsorption, net capture, and sweeping.

[0025] (5) The present invention is used in the pretreatment scenario of groundwater with high arsenic content. After reducing the arsenic content in the water body to the required value, subsequent water treatment work in the waterworks is carried out. Moreover, the present invention has higher treatment efficiency and lower energy consumption, which is beneficial to treating groundwater with high arsenic content in the water source. Description of the Drawings

[0026] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic 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:

[0027] Figure 1 is the mechanism diagram of the sacrificial iron anode electrocoagulation for removing arsenite arsenic of the present invention;

[0028] Figure 2 are the measurement results of the oxidation rate (a) of arsenite and the total arsenic removal rate (b) in Example 1 and Comparative Examples 1-4. Among them, the electrolytic iron anode is Example 1, the one-time addition of Fe(III) is Comparative Example 1, the per-minute addition of Fe(III) is Comparative Example 2, the one-time addition of Fe(II) is Comparative Example 3, and the per-minute addition of Fe(II) is Comparative Example 4;

[0029] Figure 3 are the measurement results of the oxidation rate (a) of arsenite and the total arsenic removal rate (b) in Examples 1-3. Among them, 5 mA represents Example 1, 10 mA represents Example 2, and 20 mA represents Example 3;

[0030] Figure 4Determination results of the oxidation rate (a) and total arsenic removal rate (b) of arsenite in Example 1, Examples 4-5, and Comparative Examples 5-6, where 5 mM Na2SO4 represents Example 4, 10 mM Na2SO4 represents Example 5, 20 mM Na2SO4 represents Example 1, 30 mM Na2SO4 represents Comparative Example 5, and 40 mM Na2SO4 represents Comparative Example 6;

[0031] Figure 5 In (a), it is a diagram showing the influence of adding different concentrations of BPY on the oxidation of arsenite in the Fe-EC system of Example 1, and in (b), it is a diagram showing the change in the concentrations of Fe(II) and Fe(III) in the Fe-EC system of Example 1 with or without adding 1 nM BPY;

[0032] Figure 6 In (a), it is a diagram showing the influence of adding different concentrations of Tiron reagent on the oxidation of arsenite in the Fe-EC system of Example 1, and in (b), it is a diagram showing the change in the concentrations of Fe(II) and Fe(III) in the Fe-EC system of Example 1 with or without adding 1 nM Tiron;

[0033] Figure 7 In (a), it is a diagram showing the influence of adding different concentrations of TBA on the oxidation of arsenite in the Fe-EC system of Example 1, and in (b), it is a diagram showing the influence of different concentrations of DMSO on the oxidation of arsenite;

[0034] Figure 8 It is a diagram showing the influence of different concentrations of CAT on the oxidation of arsenite in the Fe-EC system of Example 1. Detailed implementation manners

[0035] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0036] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0037] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0038] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which will be obvious to those skilled in the art. Other embodiments obtained from the specification of this invention will be obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0039] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0040] An embodiment of this invention provides a method for removing arsenic in water by sacrificial iron anode electrocoagulation (Fe-EC). The electrocoagulation treatment is used to electrolyze arsenic-containing groundwater. The electrocoagulation treatment uses an iron sheet as the anode and sodium sulfate as the electrolyte. After the electrolysis is completed, arsenic in water is removed.

[0041] In a preferred embodiment of this invention, the current of the electrocoagulation treatment is 5 - 10 mA, the treatment time is 15 min, and the initial pH value is 7.5. During the electrocoagulation treatment, a current of 5 - 10 mA can ensure the supply of Fe(II) and O2, so as to improve the oxidation and adsorption effects of arsenite (As(III)), convert arsenite (As(III)) into arsenate (As(V)) which is easily adsorbed and removed, and oxidize Fe(II) to Fe(III) to form positively charged hydroxide flocs, thereby adsorbing and removing arsenic in the water body. The current magnitude can be adjusted according to the different water bodies to be treated so as to achieve the expected effect in a short time.

[0042] In a preferred embodiment of this invention, the concentration of sodium sulfate in the arsenic-containing groundwater is 5 - 20 mM.

[0043] In a preferred embodiment of this invention, the electrocoagulation treatment uses stainless steel or graphite as the cathode, and the electrode spacing between the cathode and the anode is 4 cm. During the electrocoagulation treatment, the electrode spacing between the cathode and the anode is set to 4 cm. The distance between the anode and the cathode cannot be too large. If the distance is too large, it will cause the voltage to increase, waste electric energy, or other side reactions will occur, which will reduce the oxidation efficiency of arsenite.

[0044] In a preferred embodiment of the present invention, the effective area of the cathode or anode is 7.48 cm 2 .

[0045] In a preferred embodiment of the present invention, the arsenic concentration in the arsenic-containing groundwater is 10 μM.

[0046] In a preferred embodiment of the present invention, the arsenic-containing groundwater is groundwater containing arsenite.

[0047] In a preferred embodiment of the present invention, the iron sheet is activated before electrocoagulation treatment.

[0048] In a preferred embodiment of the present invention, the activation is to soak the iron sheet in a sulfuric acid solution with a concentration of 2 wt.% for 1 min.

[0049] In a preferred embodiment of the present invention, the electrocoagulation treatment process is carried out under stirring, and the rotation speed of the stirring is 300 r / min.

[0050] In a preferred embodiment of the present invention, the iron sheet used is a zero-valent iron electrode synthesized by the reduction-calcination method of industrial iron scraps. The present invention has no limitation on its specific preparation method. The purpose is to use industrial iron scraps as raw materials to achieve resource recycling, energy conservation and environmental protection.

[0051] More specifically, in a preferred embodiment of the present invention, a method for removing arsenic from water by sacrificial iron anode electrocoagulation includes the following steps:

[0052] Soak the iron sheet in a sulfuric acid solution with a concentration of 2 wt.% for 1 min to obtain an iron sheet anode, use stainless steel as the cathode, install the two electrode sheets on the electrode rod, and the effective area of the two electrode sheets is 7.48 cm 2 , set the distance between the two electrode sheets to 4 cm. After assembly, add arsenic-containing groundwater and sodium sulfate (Na2SO4, as an electrolyte) to the electrolytic cell, so that the concentration of sodium sulfate in the arsenic-containing groundwater is 20 mM, and use 0.01 - 1.0 mM of NaOH (such as 1 mM, 0.1 mM and 0.01 mM NaOH) or 0.005 - 0.5 mM of H2SO4 (such as 0.5 mM, 0.05 mM and 0.005 mM of H2SO4) to adjust the initial pH value to 7.5. Then, use electrocoagulation treatment technology to electrolyze the arsenic-containing groundwater, turn on the power supply to supply power to the two electrodes, and at the same time turn on the stirring treatment device to stir at 300 r / min. The current is set to a constant value of 5 mA, and the electrolysis reaction time is 15 min to achieve the removal of arsenic in the arsenic-containing groundwater.

[0053] In the method of the embodiment of the present invention, Fe(Ⅱ) is generated by electrolyzing zero-valent iron with an iron anode under a constant current. During the self-oxidation process of iron, (Fe III ·O22- ·Fe III ) The ligand decomposes to produce H2O2. Fe(II) undergoes coordination complexation with As(III) in the wastewater. Under the action of H2O2, Fe(IV) is generated, which oxidizes a part of arsenite (As(III)). Fe(IV) is reduced to Fe(II) and then immediately oxidized to Fe(III). Another part of As(III) coordinates with Fe(III) and is oxidized to arsenate (As(V)) by H2O2. Then, it is adsorbed by the formed ferric oxide colloid, greatly enhancing the removal of arsenic from the water body. The schematic diagram of the mechanism is shown in Figure 1 .

[0054] In the embodiments of the present invention, power is supplied to the electrodes through a DC power supply.

[0055] The embodiments of the present invention are all carried out under the condition of room temperature (25 ± 3 °C).

[0056] The technical solutions of the present invention are further described below through examples.

[0057] In the following examples, sodium arsenite was used to prepare simulated arsenic-containing groundwater. The concentration of sodium arsenite in the arsenic-containing groundwater was 10 μM. Each time, 1 mL of the sodium arsenite stock solution was taken and fixed in a 250 mL volumetric flask, and finally placed in a reactor to participate in electrocoagulation treatment.

[0058] Example 1

[0059] The iron sheet was soaked in a sulfuric acid solution with a concentration of 2 wt.% for 1 min to obtain an iron sheet anode, and stainless steel was used as the cathode. The two electrode sheets were installed on the electrode rod, and the effective area was 7.48 cm 2 , the distance between the two electrode sheets was set to 4 cm. After assembly, arsenic-containing groundwater and sodium sulfate (Na2SO4, as an electrolyte) were added to the electrolytic cell, so that the concentration of sodium sulfate in the arsenic-containing groundwater was 20 mM, and the initial pH value was adjusted to 7.5. Then, electrocoagulation treatment technology was used to electrolyze the arsenic-containing groundwater. The power supply was turned on to supply power to the two electrodes, and at the same time, the stirring treatment device was turned on to stir at 300 r / min. The current was set to a constant value of 5 mA. Samples were taken at 0, 1, 2, 3, 5, 7, 9, 12, and 15 min, and immediately added to a colorimetric tube containing 2% dilute hydrochloric acid. The role of dilute hydrochloric acid was a reaction terminator to terminate the oxidation of arsenite. Then, an atomic fluorescence spectrophotometer was used to measure the concentration of arsenic to detect the oxidation and removal effects of arsenite at different reaction times. A 0.22 μm filter head was required for sampling.

[0060] The amount of Fe(II) electrolytically generated by electrocoagulation treatment technology within 15 min in Example 1:

[0061] According to Faraday's law: nFe(II) =It / nF(mol)(I is the current; t is the power-on time; n is the number of transferred electrons, in this embodiment n=2; F is the Faraday constant, F=96485C / mol). In the system of Example 1, under the conditions of 5mA and 15min reaction time, the amount of Fe(II) generated by electrolysis is n Fe(II) =23.25 μmol.

[0062] Comparative Example 1

[0063] Sodium sulfate is added to the arsenic-containing groundwater to make the concentration of sodium sulfate in the arsenic-containing groundwater 20mM, and 23.25μmol of ferrous sulfate (FeSO4·7H2O) is added to the arsenic-containing groundwater at one time so that the initial pH value of the water body is adjusted to 7.5. At the same time, the stirring treatment device is turned on and stirred at 300r / min. Samples are taken at 0, 1, 2, 3, 5, 7, 9, 12, and 15min, respectively, and immediately added to a colorimetric tube containing 2% dilute hydrochloric acid. The dilute hydrochloric acid acts as a reaction terminator to terminate the oxidation of arsenite. Then, an atomic fluorescence spectrophotometer is used to measure the arsenic concentration, and the oxidation and removal effects of arsenite at different reaction times are detected. A 0.22μm filter head is used for filtration when sampling.

[0064] Comparative Example 2

[0065] Sodium sulfate is added to arsenic-containing groundwater to make the concentration of sodium sulfate in the arsenic-containing groundwater 20mM, and 1.55μmol of ferrous sulfate (FeSO4·7H2O) is added to the electrolytic cell every minute, that is, 23.25μmol is added in 15 minutes, and then the initial pH value is adjusted to 7.5, and the stirring treatment device is turned on to stir at 300r / min. Samples are taken at 0, 1, 2, 3, 5, 7, 9, 12, and 15 minutes, respectively, and immediately added to a colorimetric tube containing 2% dilute hydrochloric acid. The role of dilute hydrochloric acid is a reaction terminator to terminate the oxidation of arsenite. Then, the concentration of arsenic is measured using an atomic fluorescence spectrophotometer to detect the oxidation and removal effects of arsenite at different reaction times. When sampling, a 0.22μm filter head is required.

[0066] Comparative Example 3

[0067] Sodium sulfate was added to the arsenic-containing groundwater to make the concentration of sodium sulfate in the arsenic-containing groundwater 20 mM, and 11.625 μmol of ferric sulfate (Fe2(SO4)3, i.e., the amount of Fe(II) added was 23.25 μmol) was added to the arsenic-containing groundwater at one time. Then, the initial pH value was adjusted to 7.5. At the same time, the stirring treatment device was turned on and stirred at 300 r / min. Samples were taken at 0, 1, 2, 3, 5, 7, 9, 12, and 15 min respectively, and immediately added to a colorimetric tube containing 2% dilute hydrochloric acid. The role of the dilute hydrochloric acid was a reaction terminator to terminate the oxidation of arsenite. Then, an atomic fluorescence spectrophotometer was used to measure the concentration of arsenic to detect the oxidation and removal effects of arsenite at different reaction times. When sampling, a 0.22 μm filter head was required for filtration.

[0068] Comparative Example 4

[0069] Sodium sulfate was added to the arsenic-containing groundwater to make the concentration of sodium sulfate in the arsenic-containing groundwater 20 mM. 0.775 μmol of ferric sulfate (Fe2(SO4)3) was added to the electrolytic cell per minute, i.e., the total amount of Fe(II) added within 15 min was 23.25 μmol. Then, the initial pH value was adjusted to 7.5. At the same time, the stirring treatment device was turned on and stirred at 300 r / min. Samples were taken at 0, 1, 2, 3, 5, 7, 9, 12, and 15 min respectively, and immediately added to a colorimetric tube containing 2% dilute hydrochloric acid. The role of the dilute hydrochloric acid was a reaction terminator to terminate the oxidation of arsenite. Then, an atomic fluorescence spectrophotometer was used to measure the concentration of arsenic to detect the oxidation and removal effects of arsenite at different reaction times. When sampling, a 0.22 μm filter head was required for filtration.

[0070] The measurement results of the oxidation rate (a) of arsenite and the total arsenic removal rate (b) in Example 1 and Comparative Examples 1-4 are shown in Figure 2 , where the electrolytic iron anode was Example 1, the one-time addition of Fe(II) was Comparative Example 1, the addition of Fe(II) per minute was Comparative Example 2, the one-time addition of Fe(III) was Comparative Example 3, and the addition of Fe(III) per minute was Comparative Example 4. It can be seen from Figure 2 that in Comparative Examples 1 and 2, although the addition of Fe(III) reagent had a certain removal effect on total arsenic (As(T)), the oxidation of arsenite did not occur significantly, so the removal effect on arsenic was not ideal. In Comparative Examples 3 and 4, the oxidation of arsenite occurred, and the removal effect of total arsenic was significantly improved. Compared with the systems of other comparative examples, the oxidation effect and removal effect of arsenic in Example 1 were the best. Therefore, the sacrificial iron anode electrocoagulation (Fe-EC) system of the present invention can effectively oxidize arsenite and form efficient flocs to adsorb and remove arsenic.

[0071] Example 2

[0072] Same as Example 1, except that the current is a constant value of 10 mA.

[0073] Example 3

[0074] Same as Example 1, except that the current is a constant value of 20 mA.

[0075] The measurement results of the oxidation rate (a) of arsenite and the total arsenic removal rate (b) in Examples 1 - 3 are shown in Figure 3 (5 mA represents Example 1, 10 mA represents Example 2, 20 mA represents Example 3). It can be seen that under the current condition of 5 - 10 mA, with the increase of the current, both the oxidation effect of As(III) and the removal effect of total arsenic As(T) increase. This is because according to Faraday's law C Fe(II) = It / nFV, it can be known that with the increase of the current I, the Fe(II) generated per unit time increases, thus accelerating the oxidation of As(III) and the formation of iron flocs, and promoting the removal of total arsenic As(T).

[0076] Example 4

[0077] Same as Example 1, except that after assembly, arsenic-containing groundwater and sodium sulfate (Na2SO4, as the electrolyte) are added to the electrolytic cell, so that the concentration of sodium sulfate in the arsenic-containing groundwater is 5 mM.

[0078] Example 5

[0079] Same as Example 1, except that after assembly, arsenic-containing groundwater and sodium sulfate (Na2SO4, as the electrolyte) are added to the electrolytic cell, so that the concentration of sodium sulfate in the arsenic-containing groundwater is 10 mM.

[0080] Comparative Example 5

[0081] Same as Example 1, except that after assembly, arsenic-containing groundwater and sodium sulfate (Na2SO4, as the electrolyte) are added to the electrolytic cell, so that the concentration of sodium sulfate in the arsenic-containing groundwater is 30 mM.

[0082] Comparative Example 6

[0083] Same as Example 1, except that after assembly, arsenic-containing groundwater and sodium sulfate (Na2SO4, as the electrolyte) are added to the electrolytic cell, so that the concentration of sodium sulfate in the arsenic-containing groundwater is 40 mM.

[0084] The measurement results of the oxidation rate (a) of arsenite and the total arsenic removal rate (b) in Example 1, Examples 4 - 5 and Comparative Examples 5 - 6 are shown in Figure 4(Example 4 is represented by 5 mM Na2SO4, Example 5 is represented by 10 mM Na2SO4, Example 1 is represented by 20 mM Na2SO4, Comparative Example 5 is represented by 30 mM Na2SO4, and Comparative Example 6 is represented by 40 mM Na2SO4). It can be seen that in the reactions with Na2SO4 concentrations of 5 mM, 10 mM, and 20 mM, as the electrolyte concentration increases, the oxidation rate of As(III) accelerates. However, in the reactions with 20 mM, 30 mM, and 40 mM, the oxidation rate of As(III) shows a downward trend. This is because the change in sodium sulfate concentration from 5 mM, 10 mM, to 20 mM is from a low concentration to a moderate concentration. As the concentration increases, the conductivity increases, and the electrolysis reaction rate accelerates. The change in sodium sulfate concentration from 20 mM, 30 mM, to 40 mM is from a moderate concentration to an excessive concentration. The ionic strength increases, the interaction between ions enhances, the conductivity and the ion migration rate decrease, and the electrolysis reaction rate shows a downward trend.)

[0085] Study on the action principle of arsenic removal in Example 1:

[0086] 2,2-Bipyridine (BPY) is a commonly used Fe(II) complexing agent that selectively coordinates with Fe(II) and inhibits the oxidation of Fe(II). Different amounts of BPY were added to the Fe-EC system in Example 1 to obtain arsenic-containing wastewater with different BPY concentrations, verifying that the complexation between Fe(II) generated by the anode iron sheet in electrocoagulation treatment and As(III) in the wastewater will cause the oxidation of As(III). Figure 5 In (a) is the oxidation effect diagram of arsenite with different concentrations of BPY added to the Fe-EC system in Example 1; (b) is the change diagram of the concentrations of Fe(II) and Fe(III) in the Fe-EC system of Example 1 with or without the addition of 1 nM BPY. The ordinate represents the concentration of Fe(II) or Fe(III). It can be seen that as the BPY concentration increases, the oxidation of As(III) and Fe(II) is completely inhibited; the addition of BPY inhibits the oxidation of Fe(II), interrupts the occurrence of reaction formulas (1), (2), and (3), and thus significantly reduces the generation of H2O2.

[0087]

[0088] In the electrolytic cell of Example 1, different amounts of Tiron reagent were added to detect the coordination complex reaction between Fe(III) and As(III). Tiron reagent is a commonly used Fe(III) complexing agent that can selectively coordinate with Fe(III). Figure 6(a) in Example 1 of the Fe-EC system shows the effect of adding different concentrations of Tiron reagent on the oxidation of arsenite; (b) shows the change in the concentrations of Fe(II) and Fe(III) in the Fe-EC system of Example 1 with or without the addition of 1 nM Tiron. The ordinate represents the concentration of Fe(II) or Fe(III). As the concentration of Tiron increases, the oxidation of As(III) is completely inhibited. Although the addition of H2O2 alone does not oxidize As(III), in the coexistence of Fe(III) and As(III), the addition of H2O2 will oxidize As(III), that is, when Fe(III) coordinates with As(III), As(III) is more easily oxidized. The specific reaction is shown in Equation (4).

[0089] Fe(Ⅲ)-As(IⅢ)complex+H2O2→Fe(Ⅲ)-As(V)complex (4)

[0090] Determination of the active species acting in the co-oxidation process of Fe(II) and As(III) in the present invention:

[0091] The oxidation of As(III) may be caused by the reactive oxygen species formed during the oxidation of Fe(II) (such as H2O2, ·OH, etc.). Using tert-butanol (TBA) as a specific scavenger for ·OH radicals (k ·OH / TBA =(3.8 - 7.6)×10 8 M -1 s -1 ), different amounts of tert-butanol (TBA) were added to the electrolytic cell in Example 1. As shown in Figure 7 (a), when an excessive amount of tert-butanol was added, the oxidation of As(III) was not inhibited, indicating that ·OH radicals are not the reactive oxygen species acting.

[0092] Fe(IV) is also an active species causing the oxidation of As(III). Dimethyl sulfoxide (DMSO) can be used as a quencher for Fe(IV). Different amounts of dimethyl sulfoxide (DMSO) were added to the electrolytic cell in Example 1. As shown in Figure 7 (b), when an excessive amount of DMSO was added to the reaction system, only a small part of the oxidation of As(III) was inhibited, indicating that Fe(IV) is not the main reactive oxygen species.

[0093] Catalase (CAT) can degrade H2O2 under neutral conditions, and its chemical reaction rate constant is 7.9×10 6 M - 1 s -1Different amounts of catalase (CAT) were added to the electrolytic cell of Example 1, such as Figure 8 As shown, after adding 5000U / mL of CAT, the oxidation of As(III) was completely inhibited. Therefore, it can be confirmed that H2O2 is the main oxidative active species and the generation of Fe(IV) is also the result of hydrogen peroxide oxidation. The specific reaction is shown in formula (5).

[0094] Fe(II)-As(III)complex+H2O2→Fe(IV)-As(III)complex (5)

[0095] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for removing arsenic from water by electrocoagulation using a sacrificial iron anode, characterized in that: The arsenic-containing groundwater is electrolyzed by electrocoagulation, wherein the electrocoagulation uses an iron sheet as an anode and sodium sulfate as an electrolyte, and the arsenic in the water is removed after the electrolysis is completed.

2. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 1, characterized in that: The current of the electrocoagulation treatment is 5-10 mA, the treatment time is 8-15 min, and the initial pH value is 7.

5.

3. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 1, characterized in that: The concentration of sodium sulfate in the arsenic-containing groundwater is 5-20 mM.

4. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 1, characterized in that: The electrocoagulation treatment uses stainless steel or graphite as the cathode, and the electrode distance between the cathode and the anode is 2-4 cm.

5. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 4, characterized in that: The effective area of ​​the cathode or anode is 7.48 cm 2 .

6. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 1, characterized in that: The arsenic concentration in the arsenic-containing groundwater is 10 μM.

7. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 6, characterized in that: The arsenic-containing groundwater is groundwater containing arsenite.

8. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 1, characterized in that: Before the electrocoagulation treatment, the method further includes a step of activating the iron sheet.

9. The method for removing arsenic from water by sacrificial iron anode electrocoagulation according to claim 8, characterized in that: The activation is performed by immersing the iron sheet in a sulfuric acid solution with a concentration of 2 wt.% for 1 minute.

10. The method for removing arsenic from water by using sacrificial iron anode electrocoagulation according to claim 1, characterized in that: The electrocoagulation treatment process is carried out under stirring, and the stirring speed is 300r / min.

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