A method for efficiently oxidizing trivalent arsenic by strengthening electron transfer

Abstract

The application belongs to the field of heavy metal water pollution treatment, and relates to a method for rapidly and efficiently oxidizing trivalent arsenic through enhanced electron transfer, which comprises multifunctional biochar preparation and efficient oxidation process design. The method uses sludge as a biochar precursor, obtains multifunctional biochar with strong alkalinity, high specific surface area and super electron conduction through high-temperature pyrolysis, directly introduces oxygen into an As(III) solution, adds the biochar into the system after the aeration is completed, and fully stirs. The method is simple, economically feasible, has extremely high oxidation efficiency, does not require additional chemical reagents, has no reagent residues, and does not require external light or electricity. The non-free radical oxidation path dominated by electron transfer and singlet oxygen is not easily affected by inorganic ions and humic acid in actual water bodies, has strong anti-interference ability, and has a wide application range. The application not only helps to enrich the catalytic oxidation theoretical system, but also greatly improves the practical feasibility of biochar application, and has good environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology and relates to a process for the efficient oxidation of trivalent arsenic by pre-oxygen-enriched coupled superconducting biochar to enhance electron transfer. Background Technology

[0002] Arsenic is one of the most widely distributed carcinogenic heavy metals in the natural environment, and currently, more than 150 million people in over 70 countries worldwide are affected by arsenic pollution. In water, arsenic exists primarily in two valence states: trivalent arsenic (As(III)) and pentavalent arsenic (As(V)). As(III) is 25-60 times more toxic than As(V) and exhibits higher solubility and mobility. In traditional water treatment processes, As(III) is more difficult to adsorb and stabilize than As(V), resulting in lower treatment efficiency and greater treatment difficulty. Therefore, pre-oxidation methods are commonly used for As(III) removal, oxidizing As(III) to As(V) before further removal to improve the overall arsenic removal rate. Currently, common methods for As(III) oxidation include microbial oxidation, photocatalytic oxidation, electrocatalytic oxidation, and chemical oxidation methods such as ozone / Fenton oxidation. The main mechanism involved is the activation of the oxidant by a catalyst to generate ·OH and SO42-. ·- and O2 ·- Equally strong oxidizing free radicals oxidize As(III) to As(V), i.e., the free radical pathway. Common oxidants include Fenton's reagent, chlorine, chlorine dioxide, persulfate, ferric acid, and permanganate. The use of these chemical reagents can result in the residue of ineffective chemicals and the formation of toxic byproducts, affecting the final water quality. Furthermore, actual water bodies contain abundant humic acid and Cl-. -1 CO3 2- PO4 3- Anions can react with ·OH and SO4. ·- and O2 ·- Free radicals react to generate other free radicals with lower redox potentials, severely reducing oxidation efficiency. Therefore, it is essential to research and develop low-cost, high-efficiency, and universally applicable As(III) oxidation processes based on practical applications.

[0003] Biochar is a stabilized carbonaceous material obtained by pyrolyzing solid waste raw materials under anaerobic or oxygen-deficient conditions. Biochar is a commonly used passivating agent for heavy metal pollution, but traditional processes mainly utilize its adsorption mechanism. However, biochar possesses abundant surface oxygen-containing functional groups, persistent free radicals, and a delocalized π-electron graphitic microcrystalline structure, endowing it with excellent redox properties. Patent document CN115611405A discloses a method for oxidizing As(III) by biochar catalytically generating H2O2 under alkaline and visible light conditions. Patent document CN110204030A discloses a method for oxidizing As(III) using agricultural and forestry waste-based biochar under acidic conditions, with a maximum oxidation amount of only about 0.34 mg / g. Patent document CN114890492A discloses a method for oxidizing As(III) in groundwater using crab shell powder biochar, with a maximum oxidation amount of only about 2 mg / g. Patent document CN110143661B discloses a method for removing As(III) from alkaline calcium-rich water bodies using biochar, with a maximum oxidation amount of only about 3.75 mg / g.

[0004] In summary, the existing As(III) oxidation process has the following problems that need to be solved: (1) It requires the addition of strong chemical oxidants, which can easily cause secondary pollution; (2) The oxidation capacity and efficiency are too low; (3) It requires external light or microwave, which is costly and complicated to operate; (4) It requires the addition of a large amount of modifiers to carry out complex modification treatment of biochar, which is too costly and complicated to operate, and has low practical applicability. Summary of the Invention

[0005] To address the above issues, this invention provides a process for the efficient oxidation of trivalent arsenic by pre-oxygen-enriched coupled sludge-based superconducting biochar to enhance electron transfer.

[0006] The technical solution of the present invention:

[0007] A method for enhancing electron transfer and efficiently oxidizing trivalent arsenic includes the following steps:

[0008] (1) After the water-containing sludge is naturally dried, it is crushed and ready for use;

[0009] (2) The sludge in step (1) is pyrolyzed at high temperature. The overall pyrolysis process does not require the introduction of inert gases such as nitrogen and argon. It only requires filling the pyrolysis reactor and sealing it to obtain biochar.

[0010] (3) After cooling the biochar in step (2), it is packaged directly for use without any water washing or acid washing;

[0011] (4) Pure oxygen is directly introduced into a high-concentration As(III) solution, and no biochar is added to the reaction system at this time;

[0012] (5) After the aeration is completed, add the biochar to the system quickly and mix thoroughly to ensure oxidation.

[0013] Preferably, the sludge mentioned in step (1) of this invention can be anaerobic sludge, aerobic sludge, iron-containing sludge or industrial organic sludge, etc.

[0014] Preferably, in step (1) of this invention, the particle size of the crushed material is 100-200 mesh;

[0015] Preferably, in step (2) of this invention, the pyrolysis temperature is 800-1000℃ and the high-temperature pyrolysis time is 5-60 min;

[0016] Preferably, the oxygen introduction time in step (4) of this invention is 1 to 30 minutes, and more preferably 3 to 5 minutes;

[0017] Preferably, the concentration of As(Ⅲ) in step (4) of this invention is 50–200 mg / L;

[0018] Preferably, in step (4), the biochar has a pH of 11-12 and an addition amount of 0.1-2 g / L, more preferably 1 g / L.

[0019] The beneficial effects of this invention are:

[0020] (1) Fully utilize the high alkalinity of sludge-based biochar to adjust the pH and Eh values ​​of the solution in situ, thereby adjusting the As(III) morphology throughout the process to facilitate oxidation. Fully utilize the surface functional groups and metal salts of sludge-based biochar to form pseudocapacitance and improve electron transport characteristics. Maximize the specific surface area and graphitization degree of biochar to ensure the electron transport characteristics of delocalized π electrons. Pre-oxygen enrichment provides a large oxygen concentration gradient; upon the addition of biochar, the original micro-electric field balance is instantly altered, enabling rapid electron shuttle and thus achieving efficient As(III) oxidation. Furthermore, the optimization of electron transport performance also contributes to singlet oxygen (… 1 The generation of O2 further enhances the non-radical oxidation pathway. The updating and exploration of these mechanisms not only improves the efficiency of arsenic pollution treatment but also enriches the theoretical system of catalytic oxidation and significantly improves the practical feasibility and cost-effectiveness of biochar applications.

[0021] (2) Compared with the existing technology, this process is simple, economically feasible and has extremely high oxidation efficiency and does not produce residual reagents. It does not require additional chemical oxidizing agents, external light or electricity, etc.

[0022] (3) The non-radical oxidation pathway dominated by electron transfer and singlet oxygen is not easily affected by background components such as inorganic ions and humic acid in actual water bodies, has strong anti-interference ability, and has a wide range of applications. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process method of the present invention.

[0024] Figure 2 These are the oxidation effect diagrams of As(Ⅲ) in Examples 1-3.

[0025] Figure 3 These are quenching experiment diagrams from Examples 1-3.

[0026] Figure 4 These are the oxidation effects of As(Ⅲ) in Examples 1-3 and Comparative Examples 1-3.

[0027] Figure 5 The graphs show the oxidation effects of As(Ⅲ) in Example 1 and Comparative Examples 4-7 for the same oxygen-enriched time.

[0028] Figure 6 These are the oxidation effects of As(Ⅲ) in Examples 1-3 and Comparative Examples 8-9 under the same oxygen-enriched time.

[0029] Figure 7 These are the nitrogen adsorption-desorption curves of the biochar prepared in Examples 1-3. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0031] The present invention provides a method for enhancing electron transfer and efficiently oxidizing trivalent arsenic, as follows: Figure 1 As shown, experiments were conducted according to the method of the present invention, and specific embodiments are as follows:

[0032] Example 1

[0033] After the aerobic sludge was naturally dried, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a heating rate of 10℃ / min to 800℃, and maintained for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution at different induction times (1 min, 3 min, 7 min, 12 min, 18 min, and 30 min), without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L and thoroughly stirred to react. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0034] Example 2

[0035] After the anaerobic sludge was naturally air-dried, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a heating rate of 10℃ / min to 800℃, and maintained for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution at different induction times (1 min, 3 min, 7 min, 12 min, 18 min, and 30 min), without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L and thoroughly stirred to react. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0036] Example 3

[0037] After the iron-containing sludge was naturally dried, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a heating rate of 10℃ / min to 800℃, and maintained for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution at different induction times (1 min, 3 min, 7 min, 12 min, 18 min, and 30 min), without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L and thoroughly stirred to react. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0038] Comparative Example 1

[0039] After the aerobic sludge was naturally air-dried, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a heating rate of 10℃ / min to 800℃, and maintained for 60 min. After cooling, the sludge was removed. A certain amount of nitrogen gas was passed into a 50 mg / L As(III) solution to remove oxygen molecules from the solution. No biochar was added to the reaction system at this time. After the aeration was completed, biochar was quickly added to the system at a dosage of 1 g / L and thoroughly stirred to react. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0040] Comparative Example 2

[0041] After the anaerobic sludge was naturally air-dried, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a heating rate of 10℃ / min to 800℃, and maintained for 60 min. After cooling, the sludge was removed. A certain amount of nitrogen gas was passed into a 50 mg / L As(III) solution to remove oxygen molecules from the solution. No biochar was added to the reaction system at this time. After the aeration was completed, biochar was quickly added to the system at a dosage of 1 g / L and thoroughly stirred to react. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0042] Comparative Example 3

[0043] After naturally drying the iron-containing sludge, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a rate of 10℃ / min to 800℃, and maintained at this temperature for 60 min. After cooling, the sludge was removed. A certain amount of nitrogen gas was passed into a 50 mg / L As(III) solution to remove oxygen molecules. No biochar was added to the reaction system at this stage. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred and reacted. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0044] Comparative Example 4

[0045] After naturally drying the iron-containing sludge, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a rate of 10℃ / min to 400℃, and maintained at this temperature for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L LAs(III) solution for 7 min, without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred and reacted. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0046] Comparative Example 5

[0047] After naturally drying the iron-containing sludge, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a rate of 10℃ / min to 500℃, and maintained at this temperature for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution for 7 min, without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred and reacted. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0048] Comparative Example 6

[0049] After naturally drying the iron-containing sludge, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a rate of 10℃ / min to 600℃, and maintained for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution for 7 min, without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred and reacted. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0050] Comparative Example 7

[0051] After naturally drying the iron-containing sludge, it was crushed and passed through a 100-mesh sieve. The sludge powder was then pyrolyzed in a pyrolysis furnace at a rate of 10℃ / min to 700℃, and maintained at this temperature for 60 min. After cooling, the sludge was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution for 7 min, without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred and reacted. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0052] Comparative Example 8

[0053] After naturally drying the corn cobs, they were crushed and passed through a 100-mesh sieve. The corn cob powder was then pyrolyzed in a pyrolysis furnace at a heating rate of 10℃ / min to 800℃, and maintained for 60 min. After cooling, the powder was removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution for 7 min, without adding biochar to the reaction system. After the aeration was completed, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred and reacted. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0054] Comparative Example 9

[0055] After naturally drying the corn stalks, they were crushed and passed through a 100-mesh sieve. The stalks were then pyrolyzed in a pyrolysis furnace at a rate of 10℃ / min to 800℃, and maintained at this temperature for 60 minutes. After cooling, the stalks were removed. Pure oxygen was directly introduced into a 50 mg / L As(III) solution for 7 minutes, without adding biochar. After the aeration was complete, biochar was rapidly added to the system at a dosage of 1 g / L, and the mixture was thoroughly stirred before reacting. The contents of trivalent arsenic and total arsenic were determined using atomic fluorescence spectrometry.

[0056] Results analysis: Through Figure 2 and Figure 4 Data shows that pre-oxygen enrichment is crucial for improving the overall oxidation efficiency of the system; through Figure 3 The data shows that when singlet oxygen is added to the system ( 1 After the O2 quencher, the oxidation efficiency of As(III) in the three systems of Examples 1-3 decreased by about 80%, indicating that the dominant mechanism of As(III) oxidation is the singlet oxygen non-radical pathway; Figure 5 The data shows that the pyrolysis temperature of sludge is very important for the oxidation effect of As(III). High-temperature pyrolysis promotes the electrical conductivity of biochar, thereby improving the electron transfer capacity. Figure 6 The data shows that the unique characteristics of sludge compared to conventional biomass precursors are also one of the factors contributing to the high oxidation rate of As(III); Figure 7This indicates that the biochar prepared by the present invention has a rich pore size, which helps to adsorb As(III) and thus improves its oxidation performance, since adsorption is an important prerequisite for oxidation reaction.

Claims

1. A method of enhancing electron transfer for efficient oxidation of trivalent arsenic, characterized by, The steps are as follows: (1) The aqueous sludge is naturally dried and crushed for use; (2) The sludge in step (1) is pyrolyzed at high temperature, and the whole pyrolysis process does not need to pass inert gas, only needs to fill the pyrolysis reactor and is closed, to obtain treated biochar; (3) The biochar obtained in step (2) is cooled without any water washing or acid washing, and is directly packaged for use; (4) Pure oxygen is directly passed into a high-concentration As(Ⅲ) solution, and no biochar is added in the reaction system at this time; (5) After the aeration is completed, the biochar obtained in step (2) is quickly added to the system, and is fully stirred and mixed to ensure oxidation. The pyrolysis temperature is 800-1000℃. The pH of the biochar is 11-12.

2. The method of claim 1, wherein, In step (1), the aqueous sludge is anaerobic sludge, aerobic sludge, iron-containing sludge or industrial organic sludge.

3. The method of claim 1, wherein, In step (1), the crushing particle size is 100-200 mesh.

4. The method of claim 1, wherein, In step (2), the pyrolysis time is 5-60 min.

5. The method of claim 1, wherein, In step (4), the pure oxygen passing-in time is 1-30 min.

6. The method of claim 1, wherein, In step (4), the As(Ⅲ) concentration is 50-200 mg / L.

7. The method of claim 1, wherein, In step (4), the biochar dosage is 0.1-2 g / L.

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