Method for degrading organic pollutants in water by activating percarbonate with zero-valent iron

Abstract

The invention relates to a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which comprises the following steps: injecting to-be-treated water containing trace organic pollutants into a device containing zero-valent iron, adding percarbonate after adsorption saturation, and keeping the treatment time for 10-60 minutes after the adding amounts of the zero-valent iron and the percarbonate are 0.1-1.0 g / L and 5-30 mM respectively, the treatment of the trace organic pollutants in the water is completed. The zero-valent iron provided by the invention activates percarbonate to degrade trace organic pollutants in water, the zero-valent iron not only serves as an activator of the percarbonate, but also serves as a catalyst generated in situ to further catalyze decomposition of the percarbonate to generate free radicals and oxidize the pollutants; extra additives are not needed. According to the method, the treatment efficiency of micropollutants in water is improved, reaction products are non-toxic and harmless, secondary pollution risks are avoided, the treatment cost is reduced, and the potential application value is achieved.

Description

Technical Field

[0001] The invention relates to a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, and belongs to the technical field of water treatment oxidation. Background Art

[0002] In recent years, with the acceleration of industrialization and the widespread use of chemicals, the problem of micro-pollutants in water bodies has become increasingly serious. Micro-organic pollutants refer to pollutants with small contents, toxic and harmful properties that are difficult to degrade, including linear aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), organic pesticides, persistent organic pollutants (POPs), endocrine disruptors (EDCs), antibiotics, etc. Although they exist in the environment at low concentrations, they are potentially toxic and bioaccumulative. They can also enter water bodies through industrial wastewater discharge, surface runoff, groundwater infiltration, and discharge from sewage treatment plants, posing a serious threat to the water environment and human health. Micro-pollutants have been detected in water bodies around the world, including rivers, lakes, oceans, and even drinking water sources. The migration and transformation pathways of micro-pollutants in water bodies are complex and difficult to effectively control. They can accumulate and amplify through the food chain, posing a threat to biodiversity and may cause a series of ecological and health problems. Long-term exposure to an environment contaminated by micro-organic pollutants may also lead to chronic diseases such as cancer, endocrine disorders, and reproductive system diseases. However, it is difficult for current conventional water treatment processes to effectively reduce micropollutants in water bodies. Therefore, it is urgent to develop green and efficient methods to treat micropollutants in water bodies.

[0003] Percarbonate advanced oxidation technology (AOPs) is an optional and efficient water treatment method for trace organic pollutants in water. As a strong oxidant, percarbonate has been widely used in the field of water treatment. However, when percarbonate is used alone, there are problems such as slow self-decomposition rate, low oxidation rate and interference from various substrates in water. It is urgent to develop a new type of percarbonate enhanced oxidation water treatment technology that is efficient, economical and environmentally friendly. Invention patent CN 116477746 A discloses a method for removing organic pollutants in water by activating percarbonate with copper ions. 2+The initial concentration of 15 μM to 120 μM can complete the removal of micropollutants in water, but there is secondary pollution of copper ions in the effluent; the invention patent CN 118289924 A discloses a method for degrading naproxen in water using a divalent manganese / percarbonate / tetraacetylethylenediamine system. The addition of divalent manganese and tetraacetylethylenediamine significantly accelerates the oxidation rate of naproxen by percarbonate, but ultimately fails to achieve complete removal of naproxen, and the residual tetraacetylethylenediamine and manganese ions after the reaction increase the subsequent treatment cost; zero-valent iron is a green reductant and activator. On the one hand, it can be used as a reductant to activate oxidation, and on the other hand, the oxidation product acts as a potential electron donor / acceptor to accelerate the reaction rate. In addition, the residual iron ions in the reaction can be removed by a simple aeration sedimentation process to avoid secondary pollution and reduce post-processing costs. The invention patent CN 118894591 A discloses a method for treating phenol and nitrate composite wastewater with zero-valent iron catalyzed ozone, in which zero-valent iron significantly accelerates the removal efficiency of ozone for phenol and nitrate composite wastewater. Therefore, zero-valent iron also plays an important promoting role in the percarbonate advanced oxidation system. Using zero-valent iron to enhance the percarbonate oxidation degradation of trace organic pollutants in water has important research significance and application prospects. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of slow self-decomposition rate, low oxidation rate and interference from various substrates in water of existing percarbonate, give full play to the role of zero-valent iron in the percarbonate advanced oxidation system, and disclose a method for activating percarbonate with zero-valent iron to degrade organic pollutants in water.

[0005] The technical solution implemented by the present invention is as follows: a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron. The method first places water containing trace organic pollutants to be treated into a device containing zero-valent iron, and after adsorption-desorption equilibrium is reached, percarbonate is added into the reaction device. When the addition amounts of zero-valent iron and percarbonate are 0.1-1.0 g / L and 5-30 mM respectively, the treatment time is maintained at 10 min-60 min, and the treatment of organic pollutants in water is completed.

[0006] The zero-valent iron is prepared by a chemical reduction method, the iron source is one or more of ferric sulfate, ferric chloride, ferric nitrate, and ferric carbonate, and the reducing agent is one or more of sodium borohydride, sodium citrate, hydrogen, hydroxylamine hydrochloride, sulfite, and hydroxyethyl mercaptan.

[0007] The particle size of the zero-valent iron powder is 5 nm to 100 μm.

[0008] The dosage of the zero-valent iron powder is 0.1 g / L to 1.0 g / L.

[0009] The percarbonate is added in the form of solid or aqueous solution.

[0010] The concentration of the percarbonate is 5-30 mM.

[0011] The working principle of the present invention is as follows: First, water containing trace organic pollutants is fully mixed with zero-valent iron, and the potential difference between the pollutants and the zero-valent iron is used to accelerate the hydrolysis of the zero-valent iron and increase the distribution ratio of high-valent iron on the surface of the zero-valent iron shell. Then, percarbonate is added to the mixed solution. On the one hand, the high-valent iron species on the surface of the zero-valent iron will accelerate the decomposition rate of percarbonate and quickly generate hydrogen peroxide and carbonate. On the other hand, the hydrolysis products of zero-valent iron will also accelerate the decomposition products of hydrogen peroxide of percarbonate, resulting in a Fenton-like reaction to produce hydroxyl radicals (HO • , E 0 = 1.89–2.72 V vs. NHE), accelerating the oxidative removal of pollutants.

[0012] In addition, zero-valent iron can also reduce high-valent iron, effectively overcoming the rate-limiting step (Fe 3+ →Fe 2 + ), accelerating the generation of highly reactive free radicals.

[0013] The reaction process is as follows: ; The beneficial effect of the present invention is that the zero-valent iron proposed in the present invention activates percarbonate to degrade organic pollutants in water. The zero-valent iron not only acts as an accelerator for the hydrolysis of percarbonate, but also acts as a catalyst to accelerate the generation of active species such as carbonate free radicals and hydroxyl free radicals. In addition, the zero-valent iron also acts as an electron donor to accelerate the cyclic conversion of iron. No additional additives are required during the reaction of the present invention. After the reaction, only simple aeration precipitation and removal of residual iron ions are required, which effectively avoids secondary pollution. Zero-valent iron and percarbonate complement each other, rather than simply superimposed. A method for degrading organic pollutants in water by activating percarbonate with zero-valent iron proposed in the present invention has high reaction efficiency and a new reaction mechanism, and has outstanding substantive characteristics and significant progress.

[0014] In the present invention, zero-valent iron and percarbonate can be prepared and used immediately, thus avoiding transportation and storage costs. In addition, the iron salt has a low cost, thus avoiding the use of heterogeneous catalysts with high costs and complicated preparation, thereby effectively reducing costs. At the same time, due to the effective iron cycle, the generation of active free radicals is accelerated, the removal efficiency of micropollutants is significantly improved, the complete mineralization of pollutants is achieved, and the generation of disinfection by-products is effectively avoided. In addition, compared with the use of copper ion homogeneous catalysts proposed in the invention patent CN 116477746 A, the present invention effectively avoids secondary pollutants, and the hydrolysis product of zero-valent iron also acts as a homogeneous catalyst to achieve a homogeneous reaction rate. The iron in the water is separated in the form of precipitation, thus avoiding secondary pollution of metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the zero-valent iron-activated percarbonate degradation of organic pollutants in water according to the present invention; Figure 2 (a) to Figure 2 (b) are schematic representations of zero-valent iron prepared by the present invention (iron sulfate and sodium borohydride reduction method); Figure 2 (a) is a SEM image of zero-valent iron prepared by the reduction method of ferric sulfate and sodium borohydride. It can be seen from the figure that the particle diameter of the synthesized zero-valent iron is ~60 nm; Figure 2 (b) is an XRD image of the synthesized zero-valent iron, where ~45° is the characteristic peak of zero-valent iron and ~35° is the characteristic peak of ferric oxide, which is caused by the partial oxidation of zero-valent iron in the air; Figure 2 (c) is an XPS image of the synthesized zero-valent iron. From the peak separation in the figure, it can be seen that the surface of the synthesized zero-valent iron (Fe(0)) is rich in Fe(II) and Fe(III), which provides abundant sites for the activation and activation of percarbonate; FIG3 (a) is a diagram showing the removal effect of a typical organic matter (sulfamethazine) by simple zero-valent iron adsorption, percarbonate oxidation, and a two-by-two combination system in a method for degrading organic pollutants in water by zero-valent iron-activated percarbonate provided in an embodiment of the present invention; FIG3 ( b ) is a diagram showing the removal effect of typical organic matter (sulfamethazine) at different percarbonate dosages in a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, and the steps are as follows: (1) Injecting water containing organic pollutants to be treated into a reaction device containing zero-valent iron to conduct an adsorption equilibrium experiment; (2) After adsorption equilibrium has been reached, percarbonate is added into the reaction device, wherein the dosages of zero-valent iron and percarbonate are 0.1 g / L to 1.0 g / L and 5 to 30 mM, respectively. The treatment lasts for 10 min to 60 min, thus completing the treatment of organic pollutants in the water.

[0017] The percarbonate in this embodiment is sodium percarbonate, and the addition method is to add it in the form of solid or aqueous solution; Figure 1 The preparation and characterization results of zero-valent iron in the embodiment of the present invention are as follows: in a deoxygenated N,N-dimethylformamide aqueous solution, excess NaBH4 is slowly added dropwise to Fe2(SO4)3 to synthesize zero-valent iron, and the preparation of zero-valent iron is achieved under normal temperature and magnetic stirring conditions. After the reaction, the zero-valent iron stock solution of a certain concentration is collected by centrifugation and washing.

[0018] Figure 3 (a) is a diagram showing the removal effect of a typical organic matter (sulfamethazine) by simple zero-valent iron adsorption, percarbonate oxidation, and a combination of these two systems in a method for degrading organic pollutants in water with zero-valent iron-activated percarbonate provided in an embodiment of the present invention; Figure 3 (b) is a diagram showing the removal effect of a typical organic matter (sulfamethazine) at different percarbonate dosages in a method for degrading organic pollutants in water with zero-valent iron-activated percarbonate provided in an embodiment of the present invention.

[0019] A total of six experimental comparisons were set up: (1) adding only zero-valent iron for adsorption; (2) adding only percarbonate for oxidation; (3) adding zero-valent iron-percarbonate to enhance oxidation; (4)-(6) adding different concentrations of percarbonate to zero-valent iron to enhance oxidation. The above six settings are completed by the following examples.

[0020] Example 1 This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which is specifically carried out in the following steps: First, water containing organic pollutants to be treated is injected into a reaction chamber containing zero-valent iron, wherein the dosage of zero-valent iron is 0.5 g / L; after adsorption equilibrium is reached, percarbonate is added, and after the dosage of percarbonate is 20 mM, the treatment is performed for 30 minutes, thus completing the treatment of organic pollutants in the water. The organic wastewater to be treated contains 20 μM sulfamethazine.

[0021] In this embodiment, the method of adding percarbonate is solution addition, and the percarbonate is sodium percarbonate. The concentration change of sulfadimethoxine in the wastewater to be treated in this verification example is recorded, and a time-concentration ratio curve is drawn. The time-concentration ratio curve is shown in the zero-valent iron / percarbonate curve in Figure 3 (a).

[0022] Example 2 This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which is specifically carried out in the following steps: First, the water containing organic pollutants to be treated is injected into the reaction chamber containing zero-valent iron to conduct an adsorption equilibrium experiment, wherein the amount of zero-valent iron added is 0.5 g / L, and the treatment of organic pollutants in the water is completed after adsorption equilibrium is reached. The organic wastewater to be treated contains 20 μM sulfamethazine.

[0023] In this embodiment, no percarbonate was added, and only zero-valent iron was added.

[0024] The concentration change of sulfadimethoxine in the wastewater to be treated in this verification example was recorded, and a time-concentration ratio curve was drawn. The time-concentration ratio curve is shown in the zero-valent iron curve in Figure 3 (a).

[0025] Example 3 This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which is specifically carried out in the following steps: First, water containing organic pollutants to be treated is injected into the reaction chamber, and then percarbonate is added. When the percarbonate dosage is 20 mM, the treatment is carried out for 30 minutes to complete the treatment of organic pollutants in the water. The organic wastewater to be treated contains 20 μM sulfamethazine.

[0026] In this example, zero-valent iron was not added, and only percarbonate was added; in this example, the percarbonate was added in the form of solution, and the percarbonate was sodium percarbonate. The concentration change of sulfadimethoxine in the wastewater to be treated in this verification example was recorded, and a time-concentration ratio curve was drawn. The time-concentration ratio curve is shown in the percarbonate curve in Figure 3 (a).

[0027] Example 4 This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which is specifically carried out in the following steps: First, water containing organic pollutants to be treated is injected into a reaction chamber containing zero-valent iron, wherein the amount of zero-valent iron added is 0.5 g / L; after adsorption equilibrium is reached, percarbonate is added, and after the percarbonate addition amount reaches 5 mM, the treatment is continued for 30 minutes, thus completing the treatment of organic pollutants in the water. The organic wastewater to be treated contains 20 μM sulfamethazine.

[0028] In this embodiment, the percarbonate is added in the form of solution, and the percarbonate is sodium percarbonate. The concentration change of sulfadimethoxine in the wastewater to be treated in this verification example is recorded, and a time-concentration ratio curve is drawn. The time-concentration ratio curve is shown in the 5 mM percarbonate curve in Figure 3 (b).

[0029] Example 5 This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which is specifically carried out in the following steps: First, water containing organic pollutants to be treated is injected into a reaction chamber containing zero-valent iron, wherein the amount of zero-valent iron added is 0.5 g / L; after adsorption equilibrium is reached, percarbonate is added, and after the percarbonate dosage reaches 10 mM, the treatment is continued for 30 minutes, thus completing the treatment of organic pollutants in the water. The organic wastewater to be treated contains 20 μM sulfamethazine.

[0030] In this embodiment, the percarbonate is added in the form of solution, and the percarbonate is sodium percarbonate. The concentration change of sulfadimethoxine in the wastewater to be treated in this verification example is recorded, and a time-concentration ratio curve is drawn. The time-concentration ratio curve is shown in the 10 mM percarbonate curve in Figure 3 (b).

[0031] Example 6 This embodiment provides a method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, which is specifically carried out in the following steps: First, water containing organic pollutants to be treated is injected into a reaction chamber containing zero-valent iron, wherein the amount of zero-valent iron added is 0.5 g / L; after adsorption equilibrium is reached, percarbonate is added, and after the percarbonate addition amount reaches 15 mM, the treatment is continued for 30 minutes, thus completing the treatment of organic pollutants in the water. The organic wastewater to be treated contains 20 μM sulfamethazine.

[0032] In this embodiment, the percarbonate is added in the form of solution, and the percarbonate is sodium percarbonate. The concentration change of sulfadimethoxine in the wastewater to be treated in this verification example is recorded, and a time-concentration ratio curve is drawn. The time-concentration ratio curve is shown in the 15 mM percarbonate curve in Figure 3 (b).

[0033] Depend on Figure 1 The characterization results show that the prepared zero-valent iron is a diamond-shaped particle with a diameter of 20nm, and the valence state of iron is a mixture of divalent iron, trivalent iron and zero-valent iron. The outer layer is high-valent iron and the inner shell is unoxidized zero-valent iron. The composition meets the conditions for catalysis and Fenton reaction.

[0034] As can be seen from the curve graph of Figure 3 (a), Example 1 has the best effect of zero-valent iron / percarbonate-degrading organic pollutants in water; the effects of Example 2 in which only zero-valent iron is added to adsorb organic pollutants in water and Example 3 in which only percarbonate is added to oxidize trace organic pollutants are both worse than those of Example 1; the effects of other examples are also far inferior to those of Example 1, indicating that the combination of zero-valent iron and percarbonate has a significant coupling effect, and zero-valent iron can significantly accelerate the oxidation efficiency of percarbonate.

Claims

1. A method for degrading organic pollutants in water by activating percarbonate with zero-valent iron, characterized in that: The method first places water containing trace organic pollutants to be treated into a device containing zero-valent iron, and after adsorption-desorption equilibrium is reached, percarbonate is added into the reaction device. When the dosage of zero-valent iron is 0.1 g / L-1.0 g / L and the dosage of percarbonate is 5 mM-30 mM, the treatment time is maintained at 10 min-60 min, thus completing the treatment of organic pollutants in the water.

2. The method for degrading organic pollutants in water by activating percarbonate with zero-valent iron according to claim 1, characterized in that: The zero-valent iron is prepared by a chemical reduction method; the iron source is one or more of ferric sulfate, ferric chloride, ferric nitrate, and ferric carbonate; the reducing agent is one or more of sodium borohydride, sodium citrate, hydrogen, hydroxylamine hydrochloride, sulfite, and hydroxyethyl mercaptan.

3. The method for degrading organic pollutants in water by activating percarbonate with zero-valent iron according to claim 1, characterized in that: The particle size of the zero-valent iron powder is 5 nm to 100 μm.

4. The method for degrading organic pollutants in water by activating percarbonate with zero-valent iron according to claim 1, characterized in that: The percarbonate is added in the form of solid or aqueous solution.

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