Method for reactivating passivated and inactivated zero-valent iron and application of method in wastewater treatment

Abstract

The invention provides a method for reactivating passivated and inactivated zero-valent iron and application in wastewater treatment.The method comprises the following specific steps that S1, zero-valent iron powder is added into wastewater to be stirred till the zero-valent iron is passivated and inactivated, a magnet is used for separating the passivated and inactivated zero-valent iron powder from the wastewater, and the zero-valent iron powder is obtained; washing the passivated and inactivated zero-valent iron powder with deionized water, and drying the zero-valent iron powder under nitrogen flow; s2, a wet ball mill is filled with grinding beads, passivated zero-valent iron powder and pure ethyl alcohol are added into the wet ball mill, a circulating water cooling system is used for controlling the temperature of a ball milling chamber of the wet ball mill to be 8-12 DEG C, the ball milling rotating speed is 1900-2100 rpm, the ball milling time is 9-11 min, the particle size of the ball milling beads is 0.3-0.5 mm, and the mass of the ball milling beads is 0.7-0.8 kg; and S3, the activated zero-valent iron powder is added into the wastewater to be stirred.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for reactivating passivated and deactivated zero-valent iron and an application thereof in wastewater treatment. Background Art

[0002] Zero-valent iron is a highly efficient reducing agent and has been widely used in sewage treatment. However, after use, the surface of zero-valent iron will be passivated and deactivated, resulting in its low utilization rate.

[0003] In the prior art, wet ball milling technology is mainly used in the preparation of nanomaterials and composite materials, aiming to improve the physical and chemical properties of materials. However, previous studies have focused on material preparation and performance optimization, and have not conducted in-depth research on the surface depassivation of passivated materials. The defects of these technologies are mainly reflected in the following aspects:

[0004] Research limitations: Traditional wet ball milling is mostly used to prepare composite materials and improve material properties, such as enhancing material strength, corrosion resistance or conductivity. However, these studies have ignored the solution to the problem of surface passivation of metal materials, especially in materials such as zero-valent iron that require high surface reactivity, and have failed to effectively restore their reactivity after passivation and deactivation.

[0005] Lack of targeted depassivation methods: Wet ball milling for composite material preparation usually enhances material properties by changing the microstructure of the material, but lacks a targeted depassivation mechanism. For passivated zero-valent iron materials, these methods are difficult to effectively remove the passivation layer on the surface through physical and mechanical means, which limits their application in environmental remediation.

[0006] Failure to solve the obstacle of the passivation layer: The wet ball milling of the previous composite material preparation failed to deeply solve the problem of the passivation layer in hindering the reaction between the material and the pollutant. This passivation layer hinders the electron transfer process, greatly limits the ability of zero-valent iron to reduce pollutants, and cannot meet the actual environmental remediation needs.

[0007] Therefore, the technical problem that needs to be solved urgently is: how to specifically solve the problem of zero-valent iron passivation layer hindering the reaction, while improving the re-reaction ability of zero-valent iron materials. Summary of the invention

[0008] The present invention is made to solve the above-mentioned problem, and aims to provide a method for reactivating passivated and deactivated zero-valent iron and its application in wastewater treatment.

[0009] The present invention provides a method for reactivating passivated and deactivated zero-valent iron, which has the following characteristics and comprises the following steps: loading grinding beads into a wet ball mill, adding passivated zero-valent iron powder and pure ethanol into the wet ball mill, using a circulating water cooling system to control the ball milling chamber temperature of the wet ball mill to 8-12°C, the ball milling speed to 1900-2100rpm, the ball milling time to 9-11min, the particle size of the ball milling beads to 0.3-0.5mm, and the mass of the ball milling beads to 0.7-0.8kg.

[0010] The method for reactivating passivated and deactivated zero-valent iron provided by the present invention may also have the following feature: the grinding beads are made of zirconium oxide.

[0011] The present invention also provides a wastewater treatment method having the following characteristics, comprising the following steps: S1, adding zero-valent iron powder into wastewater and stirring until the zero-valent iron is passivated and inactivated, using a magnet to separate the passivated and inactivated zero-valent iron powder from the wastewater, washing the passivated and inactivated zero-valent iron powder with deionized water and drying it under a nitrogen flow; S2, reactivating the dried passivated and inactivated zero-valent iron; S3, adding the activated zero-valent iron powder into wastewater and stirring, wherein step S2 adopts the method for reactivating the passivated and inactivated zero-valent iron as claimed in claim 1.

[0012] The wastewater treatment method provided by the present invention may also have the following characteristics: wherein the wastewater in step S1 contains potassium dichromate solution, nickel chloride solution and / or trichloroethylene solution.

[0013] The wastewater treatment method provided by the present invention may also have the following characteristics: wherein the wastewater is a 28-32 mg / L potassium dichromate solution and / or a 2.5-3.5 mg / L nickel chloride solution, and the decontamination time in step S1 is 280-320 min.

[0014] The wastewater treatment method provided by the present invention may also have the following characteristics: wherein the wastewater is a trichloroethylene solution of 8-12 mg / L, and the decontamination time in step S1 is 100-140 min.

[0015] The wastewater treatment method provided by the present invention may also have the following characteristics: wherein the stirring speed in step S1 and step S3 is 450-550 rpm, and the stirring is carried out in a constant temperature water bath at 24-26°C.

[0016] Functions and Effects of the Invention

[0017] According to the method for reactivating passivated and deactivated zero-valent iron and its application in wastewater treatment, not only can the problem of the passivation layer hindering the reaction be solved and the passivation layer be effectively removed, but also the regeneration reaction ability of the material can be significantly improved.

[0018] Through the high-energy impact and shearing action of mechanical ball milling, the oxide and passivation layer on the surface of passivated zero-valent iron can be efficiently removed, and its surface reaction activity can be restored, breaking through the limitations of existing composite material preparation and realizing the reactivation of passivated metal materials; compared with traditional chemical depassivation methods, the mechanical depassivation process of the present invention does not rely on acidic or alkaline chemical reagents, avoiding excessive consumption of materials and environmental pollution problems, making the depassivation process more environmentally friendly; the wet ball milling depassivation technology of the present invention shows excellent removal ability in treating complex wastewater containing multiple pollutants (such as Cr(VI), Ni(II) and TCE, etc.), and can be widely used in various actual environmental remediation scenarios; by removing the passivation layer, the reaction sites of zero-valent iron are fully exposed, the reaction efficiency is significantly improved, and the service life and economic value of the material are greatly extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a wet ball mill of the present invention;

[0020] Figure 2 It is a schematic diagram of ball milling depassivation of the present invention;

[0021] Figure 3 is the change in removal efficiency of zero-valent iron of different concentrations in the process of removing Cr(VI) in Example 1 of the present invention;

[0022] Figure 4 is the variation trend of pH value and oxidation-reduction potential (ORP) during the depassivation process in Example 1 of the present invention;

[0023] Figure 5 is the effect of the number of ball milling times on the content of Cr(VI) and zero-valent iron in Example 1 of the present invention;

[0024] Figure 6 is the removal effect of different concentrations of zero-valent iron on Ni(II) in Example 2 of the present invention;

[0025] Figure 7 is the removal efficiency of TCE by zero-valent iron at different concentrations in Example 3 of the present invention;

[0026] Figure 8 is the specific surface area of ​​zero-valent iron in the original, reacted, ball-milled depassivated and re-reacted states in Examples 1-3 of the present invention;

[0027] Fig. 9 are scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) element distribution diagrams of zero-valent iron before and after ball milling in Examples 1-3 of the present invention;

[0028] Fig.10 is the analysis result of X-ray photoelectron spectroscopy (XPS) in Examples 1-3 of the present invention;

[0029] Fig.11 is the X-ray diffraction (XRD) spectrum of Examples 1-3 of the present invention;

[0030] Fig.12 A graph showing the relative intensity variation of iron oxides under different treatment conditions in Examples 1-3 of the present invention;

[0031] Fig.13 are the electrochemical polarization curves of zero-valent iron in different treatment states in Examples 1-3 of the present invention;

[0032] Fig.14 are scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDS) element distribution diagrams of zero-valent iron under different treatment methods (after reaction, ball milling, pickling, and ultrasonic treatment) in Examples 1-3 of the present invention;

[0033] Fig.15 The removal effect of the zero-valent iron treated in Examples 1-3 of the present invention on Cr(VI), Ni(II) and TCE in complex wastewater;

[0034] Fig.16 is an element content analysis bar chart comparing the molar fractions of surface oxygen, chromium and nickel of zero-valent iron after different depassivation treatments in Examples 1-3 of the present invention; and

[0035] Fig.17 The effects of the three depassivation treatment methods (ball milling, pickling, and ultrasound) in Examples 1-3 of the present invention on the total mass loss of zero-valent iron (ZVI) and the loss of metallic iron (Fe(0)). DETAILED DESCRIPTION

[0036] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0037] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments and the accompanying drawings specifically illustrate the method of reactivating passivated and deactivated zero-valent iron and its application in wastewater treatment.

[0038] Figure 1 Schematic diagram of the structure of the wet ball mill 100 of the present invention.

[0039] like Figure 1 As shown, the wet ball mill used in the above method of the present invention comprises a reactor housing 10, a rotor 20, an end cover 30 and a driving mechanism 40. The driving mechanism 40 is used to drive the rotor 20 to rotate, and comprises a main shaft 42, a bearing seat 41, and a pulley 45.

[0040] The reactor shell 10 is generally cylindrical, and has a cavity formed inside, which is the reaction chamber 11. The reactor shell 10 is provided with a feed port 12 and a discharge port 13 connected to the reaction chamber 11, which are used to allow the slurry to enter and flow out of the reaction chamber 11, respectively.

[0041] In the reactor shell 10, a cooling water chamber 14 is formed around the reaction chamber 11 and is not connected to the reaction chamber 11, and is used to contain cooling water for cooling the reaction chamber 11. The cooling water can enter the cooling water chamber through the cooling water inlet 15 and flow out of the cooling water chamber from the cooling water outlet 16.

[0042] The rotor 20 is disposed in the reaction chamber 11 and is columnar with a plurality of annular sheets disposed on the circumference. The surface of the rotor is covered with a layer of polyurethane material to reduce the wear of the ball milling beads and the like on the rotor body.

[0043] The end cover 30 is disposed at one end of the reactor housing 10 , and a middle end cover 31 is installed on the end of the end cover 30 away from the reactor housing 10 .

[0044] The bearing seat 41 is disposed on the other side of the middle end cover 31 relative to the end cover 30 .

[0045] The main shaft 42 is installed in the bearing seat 41 through the bearing 43, and one end of the main shaft 42 passes through the middle end cover 31 and the end cover 30 in sequence and extends into the reaction chamber 11. This end is connected to the rotor 20, so that the main shaft 42 can drive the rotor 20 to rotate.

[0046] A mechanical seal assembly 44 is also provided in the end cover 30 . The mechanical seal assembly 44 is sleeved on the main shaft 42 and is located close to the reaction chamber 11 . The mechanical seal assembly 44 is used to form a seal on the main shaft 42 to prevent the liquid in the reaction chamber 11 from leaking to the bearing seat 41 and other parts.

[0047] The other end of the main shaft 42 extends to the outside of the bearing seat 41, and is fixed by a locking nut 46 and a bearing cover plate 47, and a main pulley 45 is fixed on this end. The driving mechanism 40 drives the pulley 45 to rotate through the belt transmission mechanism, so that the main shaft 42 rotates and drives the rotor 20 to rotate in the reaction chamber 11. When there is slurry containing ball milling beads in the reaction chamber 11, the high-speed rotation of the rotor 20 can strongly stir the slurry, so that the slurry can undergo a mechanochemical reaction under the action of the ball milling beads; a large amount of heat will be generated in the process, and the heat can be taken away by cooling water.

[0048] Figure 2 It is a schematic diagram of ball milling depassivation of the present invention.

[0049] like Figure 2 As shown, the wastewater treatment method of the present invention specifically comprises the following steps:

[0050] S1, adding zero-valent iron powder into wastewater and stirring until the zero-valent iron is passivated and inactivated, using a magnet to separate the passivated and inactivated zero-valent iron powder from the wastewater, washing the passivated and inactivated zero-valent iron powder with deionized water and drying it under a nitrogen flow.

[0051] S2, loading zirconium oxide grinding beads into a wet ball mill, adding passivated and deactivated zero-valent iron powder and pure ethanol into the wet ball mill, using a circulating water cooling system to control the temperature of the ball milling chamber of the wet ball mill to 8-12°C, the ball milling speed to 1900-2100 rpm, the ball milling time to 9-11 min, the particle size of the ball milling beads to 0.3-0.5 mm, and the mass of the ball milling beads to 0.7-0.8 kg.

[0052] S3, adding the activated zero-valent iron powder into the wastewater and stirring.

[0053] Example 1

[0054] The wastewater treatment method specifically includes the following steps:

[0055] S1. Weigh 100 g of zero-valent iron powder with a purity of ≥98.5%, place it in a 1000 mL four-necked flask, add 500 mL of a 30 mg / L potassium dichromate solution, stir in a 25° C. constant temperature water bath for 300 min at a stirring speed of 500 rpm, and introduce nitrogen with a purity of >99.0% throughout the stirring process. Use a magnet to separate the passivated and deactivated zero-valent iron powder from the wastewater, wash the passivated and deactivated zero-valent iron powder with deionized water, and dry it under a nitrogen flow.

[0056] S2. Load zirconium oxide grinding beads into a wet ball mill, add the passivated and deactivated zero-valent iron powder and 100 ml of pure ethanol into the wet ball mill, use a circulating water cooling system to control the temperature of the ball milling chamber of the wet ball mill to 10°C, the ball milling speed to 2000 rpm, the ball milling time to 10 min, the particle size of the ball milling beads to 0.4 mm, and the mass of the ball milling beads to 0.75 kg.

[0057] S3, adding the activated zero-valent iron powder to 500 mL of a 30 mg / L potassium dichromate solution, stirring in a 25° C. constant temperature water bath for 300 min at a stirring speed of 500 rpm, and introducing nitrogen with a purity of >99.0% throughout the stirring process.

[0058] Figure 3 The removal efficiency of zero-valent iron at different concentrations in the process of removing Cr(VI) in Example 1 of the present invention is changed.

[0059] like Figure 3 As shown, the removal efficiency changes of zero-valent iron with concentrations of 10.0 g / L, 5.0 g / L, 2.0 g / L, 1.0 g / L and 0.5 g / L in the process of removing Cr(VI). It can be seen that the higher the concentration of zero-valent iron, the higher the removal efficiency.

[0060] Figure 4 It is the variation trend of pH value and oxidation-reduction potential (ORP) during the depassivation process in Example 1 of the present invention.

[0061] like Figure 4 As shown in the figure, with the increase of time, the pH gradually increased and the ORP decreased, indicating that the surface activity of zero-valent iron was enhanced after ball milling treatment.

[0062] Figure 5 The figure shows the influence of the number of ball milling times on the contents of Cr(VI) and zero-valent iron in Example 1 of the present invention.

[0063] like Figure 5 As shown in the figure, the Cr(VI) content decreased significantly with the increase of ball milling times.

[0064] Example 2

[0065] The wastewater treatment method specifically includes the following steps:

[0066] S1. Weigh 100 g of zero-valent iron powder with a purity of ≥98.5%, place it in a 1000 mL four-necked flask, add 500 mL of a nickel chloride solution with a concentration of 3 mg / L, stir in a constant temperature water bath at 25° C. for 300 min at a stirring speed of 500 rpm, and introduce nitrogen with a purity of >99.0% throughout the stirring process. Use a magnet to separate the passivated and deactivated zero-valent iron powder from the wastewater, wash the passivated and deactivated zero-valent iron powder with deionized water, and dry it under a nitrogen flow.

[0067] S2. Load zirconium oxide grinding beads into a wet ball mill, add the passivated and deactivated zero-valent iron powder and 100 ml of pure ethanol into the wet ball mill, use a circulating water cooling system to control the temperature of the ball milling chamber of the wet ball mill to 10°C, the ball milling speed to 2000 rpm, the ball milling time to 10 min, the particle size of the ball milling beads to 0.4 mm, and the mass of the ball milling beads to 0.75 kg.

[0068] S3, adding the activated zero-valent iron powder to 500 mL of a nickel chloride solution with a concentration of 3 mg / L, stirring in a constant temperature water bath at 25° C. for 300 min at a stirring speed of 500 rpm, and introducing nitrogen with a purity of >99.0% throughout the stirring process.

[0069] Figure 6 This is the removal effect of different concentrations of zero-valent iron on Ni(II) in Example 2 of the present invention.

[0070] like Figure 6 As shown, there is a positive correlation between the concentration of zero-valent iron and the removal efficiency.

[0071] Example 3

[0072] The wastewater treatment method specifically includes the following steps:

[0073] S1. Weigh 100 g of zero-valent iron powder with a purity of ≥98.5%, place it in a 1000 mL four-necked flask, add 500 mL of a trichloroethylene solution with a concentration of 10 mg / L, stir in a constant temperature water bath at 25° C. for 120 min at a stirring speed of 500 rpm, and introduce nitrogen with a purity of >99.0% throughout the stirring process. Use a magnet to separate the passivated and deactivated zero-valent iron powder from the wastewater, wash the passivated and deactivated zero-valent iron powder with deionized water, and dry it under a nitrogen flow.

[0074] S2. Load zirconium oxide grinding beads into a wet ball mill, add the passivated and deactivated zero-valent iron powder and 100 ml of pure ethanol into the wet ball mill, use a circulating water cooling system to control the temperature of the ball milling chamber of the wet ball mill to 10°C, the ball milling speed to 2000 rpm, the ball milling time to 10 min, the particle size of the ball milling beads to 0.4 mm, and the mass of the ball milling beads to 0.75 kg.

[0075] S3, adding the activated zero-valent iron powder to 500 mL of a 10 mg / L trichloroethylene solution, stirring in a 25° C. constant temperature water bath for 120 min at a stirring speed of 500 rpm, and introducing nitrogen with a purity of >99.0% throughout the stirring process.

[0076] Figure 7 It is the removal efficiency of TCE by zero-valent iron of different concentrations in Example 3 of the present invention.

[0077] like Figure 7 As shown in Figure 2, the reactivity of zero-valent iron in TCE removal is significantly improved after ball milling depassivation.

[0078] Figure 8 It is the specific surface area of ​​zero-valent iron in Examples 1-3 of the present invention in the original, reacted, ball-milled depassivated and re-reacted states.

[0079] like Figure 8 As shown, ball milling can effectively maintain the specific surface area of ​​zero-valent iron and help improve its reaction activity.

[0080] Fig. 9 1 is a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) element distribution diagram of zero-valent iron before and after ball milling in Examples 1-3 of the present invention.

[0081] like Fig. 9 As shown, the surface morphology of zero-valent iron after reaction with Cr(VI), Ni(II) and TCE and the distribution of oxygen, iron and pollutant elements are respectively shown. The ball milling treatment significantly reduces the content of oxygen and pollutants in the passivation layer.

[0082] Fig.10 These are the analysis results of X-ray photoelectron spectroscopy (XPS) in Examples 1-3 of the present invention.

[0083] like Fig.10 As shown in the figure, the relative contents of Fe(0), Fe(II) and Fe(III) in different states reflect the increase of Fe(0) active sites after ball milling treatment.

[0084] Fig.11 It is the X-ray diffraction (XRD) spectrum in Example 1-3 of the present invention.

[0085] like Fig.11 As shown, the crystal structure changes of zero-valent iron at different treatment stages indicate that ball milling treatment did not change the crystal phase structure of zero-valent iron.

[0086] Fig.12 A graph showing the relative intensity variation of iron oxides under different treatment conditions in Examples 1-3 of the present invention. Fig.131 is the electrochemical polarization curve of zero-valent iron in different treatment states in Examples 1-3 of the present invention.

[0087] like Figure 12-13 As shown, ball milling depassivation significantly improves the electrochemical activity and reduction performance of zero-valent iron.

[0088] In order to simulate the interfering factors in actual wastewater treatment, common suspended solids (such as silica SiO2, aluminum oxide Al2O3 and kaolin Al2Si2O5(OH)4), as well as impurities such as coagulants (such as polyacrylamide PAM) were also added.

[0089] In summary, wet ball milling treatment significantly improved the reactivity of passivated zero-valent iron (ZVI), and the removal ability of various pollutants was significantly restored and enhanced.

[0090] Cr(VI) removal effect: The removal rate of the passivated zero-valent iron before ball milling was low for the Cr(VI) solution with an initial concentration of 30 mg / L. After 10 minutes of wet ball milling, the removal rate of ZVI was significantly improved, indicating that ball milling depassivation significantly restored the reactivity of ZVI. Surface characterization results showed that after ball milling, the oxygen content on the ZVI surface decreased from 5.98% to 2.00%, while the chromium content decreased from 0.50% to 0.05%, verifying the effectiveness of the ball milling depassivation process ( Fig. 9 A1, A2 and Fig.10 A3 in the table).

[0091] Ni(II) removal effect: For the Ni(II) solution with an initial concentration of 3 mg / L, the removal efficiency of passivated ZVI is low. After 10 minutes of wet ball milling, the removal rate of Ni(II) by ZVI is improved. Surface element analysis shows that after ball milling, the oxygen content on the surface of ZVI is reduced from 4.96% to 2.49%, while the nickel content is reduced from 0.12% to 0.05% ( Fig. 9 B1, B2 and Fig.10 XPS analysis further showed that ball milling increased the Fe(0) content on the ZVI surface from 7.84% to 10.11%, indicating that more active iron sites were exposed on the ZVI surface after mechanical depassivation.

[0092] TCE removal effect: The passivated ZVI has limited removal capacity for TCE solution with an initial concentration of 10 mg / L. After ball milling, the removal rate of ZVI was greatly improved, indicating that ball milling depassivation significantly enhanced the removal effect of ZVI on TCE. Surface characterization results showed that the surface oxygen content of ZVI after treatment decreased from 6.05% to 2.36%, while the iron content increased to 97.64% ( Fig. 9 C1, C2 and Fig.10This result indicates that ball milling not only removes the passivation layer but also significantly increases the number of surface active sites.

[0093] Electrochemical performance analysis: The electrochemical test results show that ball milling significantly improves the electrochemical reaction activity of ZVI. Taking Cr(VI) solution as an example, the corrosion potential of passivated ZVI before ball milling is -116mV and the current density is 27.98μA / cm 2 After ball milling, the corrosion potential shifted significantly to -286 mV, and the current density increased to 83.18 μA / cm 2 These data indicate that the ball milling treatment not only removes the passivation layer but also improves the electrochemical reaction rate and surface reactivity of ZVI.

[0094] Fig.14 These are scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDS) element distribution diagrams of zero-valent iron under different treatment methods (after reaction, ball milling, pickling, and ultrasonic treatment) in Examples 1-3 of the present invention.

[0095] like Fig.14 As shown in the figure, the oxygen, chromium and nickel content on the surface of zero-valent iron decreased significantly after ball milling, indicating that ball milling effectively removed the passivation layer and restored the surface active sites of zero-valent iron. In contrast, although pickling had a certain removal effect on Cr and Ni, its oxygen content was high and new passivation components may have been introduced; ultrasonic treatment had the worst effect on removing the passivation layer, with obvious residues of Cr and Ni and insufficient recovery of surface activity.

[0096] Fig.15 The results are as follows: The removal effect of the zero-valent iron treated in Examples 1-3 of the present invention on Cr(VI), Ni(II) and TCE in complex wastewater.

[0097] like Fig.15 As shown in the figure, the results show that the ball milling treatment group (orange) has the highest removal rate for Cr(VI), far exceeding the acid washing (purple) and ultrasonic (green) treatment groups; in the Ni(II) and TCE removal experiments, the zero-valent iron treated with ball milling also showed a higher removal efficiency, significantly improving the reactivity of zero-valent iron. These experimental results show that ball milling can not only remove the passivation layer on the surface of zero-valent iron, but also restore or even enhance its reactivity.

[0098] Fig.16 It is an element content analysis bar chart comparing the molar fractions of surface oxygen, chromium and nickel of zero-valent iron after different depassivation treatments in Examples 1-3 of the present invention.

[0099] like Fig.16As shown in the figure, the effects of different treatment methods on the surface elements of zero-valent iron are shown. The molar fractions of oxygen, Cr and Ni on the surface of zero-valent iron treated by ball milling are the lowest, which verifies the effectiveness of its depassivation effect and surface activity recovery. Although pickling treatment can remove some Cr and Ni, the oxygen content is high, indicating that chemical treatment may cause new surface passivation problems; while ultrasonic treatment is weak in removing the passivation layer and fails to significantly improve the reactivity of zero-valent iron.

[0100] In summary, ball milling as a mechanical depassivation method can not only remove the passivation layer more effectively than traditional pickling and ultrasonic treatment, but also greatly enhance the environmental remediation performance of zero-valent iron.

[0101] Fig.17 The effects of the three depassivation treatment methods (ball milling, pickling, and ultrasound) in Examples 1-3 of the present invention on the total mass loss of zero-valent iron (ZVI) and the loss of metallic iron (Fe(0)).

[0102] like Fig.17 As shown, it is an important indicator for evaluating the material consumption during the depassivation process. Ball milling: The total mass loss and metal iron loss of ZVI after ball milling are both low, about 80% of the total mass, among which the proportion of metal iron is high, indicating that the ball milling process effectively removes the passivation layer with little loss of metal iron. This shows that the ball milling process removes the surface passivation layer with mechanical force, which can significantly restore the activity of ZVI while retaining more iron core structure, ensuring the reuse rate and economy of the material.

[0103] Pickling: The total mass loss of ZVI after pickling is large, and the loss of metallic iron is significantly lower than the total mass loss, indicating that during the pickling process, the acidic environment not only removes the passivation layer, but also causes a large amount of dissolution of the iron body. Although pickling can remove the surface passivation layer, it is accompanied by a large amount of loss of metallic iron. This loss significantly weakens the subsequent reuse performance of ZVI, which is not conducive to long-term practical application.

[0104] Ultrasonication: The total mass and metallic iron loss of the ultrasonically treated ZVI were both small, close to 100%, but the depassivation effect was poor, indicating that the ultrasonic treatment had limited effect on the removal of the passivation layer and had little effect on the ZVI metallic iron body. This treatment method was not efficient enough in removing the passivation layer, resulting in unsatisfactory recovery of ZVI activity.

[0105] In summary, ball milling can effectively retain the metallic iron core of zero-valent iron while removing the passivation layer, showing good economy and sustainability. In contrast, although pickling can remove the passivation layer, the accompanying loss of metallic iron is large, which weakens the activity and regeneration ability of zero-valent iron; ultrasonic treatment has no significant effect on the removal of the passivation layer, and retains the metallic iron well, but fails to significantly restore the activity of the material. Therefore, ball milling achieves the best balance between depassivation effect and material loss, and is currently the best depassivation method.

[0106] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for reactivating passivated and deactivated zero-valent iron, characterized in that: The specific steps are as follows: Grinding beads are loaded into a wet ball mill, passivated zero-valent iron powder and pure ethanol are added into the wet ball mill, and a circulating water cooling system is used to control the temperature of the ball milling chamber of the wet ball mill to 8-12°C, the ball milling speed is 1900-2100 rpm, the ball milling time is 9-11 min, the particle size of the ball milling beads is 0.3-0.5 mm, and the mass of the ball milling beads is 0.7-0.8 kg.

2. The method for reactivating the passivated and deactivated zero-valent iron according to claim 1, characterized in that: in, The grinding beads are made of zirconium oxide.

3. A wastewater treatment method, characterized in that: The specific steps are as follows: S1, adding zero-valent iron powder into wastewater and stirring until the zero-valent iron is passivated and inactivated, separating the passivated and inactivated zero-valent iron powder from the wastewater using a magnet, washing the passivated and inactivated zero-valent iron powder with deionized water and drying it under a nitrogen flow; S2, reactivating the passivated and inactivated zero-valent iron after drying; S3, adding the activated zero-valent iron powder into the wastewater and stirring, Wherein, the step S2 adopts the method for reactivating the passivated and deactivated zero-valent iron as described in claim 1.

4. The wastewater treatment method according to claim 3, characterized in that: in, The wastewater in step S1 contains potassium dichromate solution, nickel chloride solution and / or trichloroethylene solution.

5. The wastewater treatment method according to claim 4, characterized in that: in, The wastewater is a 28-32 mg / L potassium dichromate solution and / or a 2.5-3.5 mg / L nickel chloride solution, and the decontamination time in step S1 is 280-320 min.

6. The wastewater treatment method according to claim 4, characterized in that: in, The wastewater is a trichloroethylene solution at a concentration of 8-12 mg / L, and the decontamination time in step S1 is 100-140 min.

7. The wastewater treatment method according to claim 3, characterized in that: in, The stirring speed in step S1 and step S3 is 450-550 rpm, and the stirring is performed in a constant temperature water bath at 24-26°C.

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