Iron-based gel particle catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and relates to an iron-based gel particle catalyst and a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing sodium alginate, a photocatalyst medium and deionized water, and uniformly stirring to obtain a mixed solution; (2) dropwise adding the mixed solution obtained in the step (1) into a ferrite solution, enabling sodium alginate and ferrous ions to be subjected to a cross-linking reaction to form spherical gel particles, coating a gel network with a photocatalyst medium, and then carrying out curing treatment; and (3) collecting the spherical gel particles obtained in the step (2), and sequentially washing and drying to obtain the iron-based gel particle catalyst. The preparation method provided by the invention is simple in process, the carrier is cheap and easy to obtain, the obtained catalyst is high in catalytic efficiency, efficient in iron circulation and easy to separate and recover, the dosage of required chemicals in the wastewater treatment process is small, the amount of generated sludge is small, and the process compatibility and economic benefits are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to an iron-based gel particle catalyst, its preparation method and application. Background Technology

[0002] Nickel complexation wastewater is a typical and difficult-to-treat industrial wastewater generated during the production processes of industries such as electroplating, electronics manufacturing, and chemical synthesis. Its core pollution characteristic lies in the formation of stable coordination compounds by nickel ions with complexing agents such as ethylenediaminetetraacetic acid (EDTA), citric acid, and tartaric acid. These complexes have high stability constants, and conventional chemical precipitation methods cannot break down the complex structure, making it difficult to separate nickel ions from water bodies. Direct discharge can lead to the accumulation of heavy metals in aquatic waters, threatening ecosystems and human health. Therefore, efficient complex breaking and nickel removal is a core technical challenge in the field of industrial wastewater treatment.

[0003] Currently, the mainstream treatment technology in the industry is advanced oxidation process. Its core principle is to generate strong oxidizing free radicals in the reaction system through catalysis. The strong oxidizing power of the free radicals breaks the coordination bonds between the complexing agent and nickel ions, allowing the nickel ions to be released and removed by precipitation. This process is further divided into homogeneous catalysis and heterogeneous catalysis. However, both of these technologies have significant technical bottlenecks and cannot meet the industrial requirements of low cost, high efficiency, and low secondary pollution.

[0004] In homogeneous catalytic systems, the traditional Fenton reaction is the most widely used technology, but it has three major problems: First, ferric ions are easily deactivated and difficult to recover. After ferrous ions are oxidized to ferric ions in the reaction, if there is no effective reduction mechanism, a large amount of iron sludge will be generated in the form of ferric hydroxide. This not only leads to catalyst loss, but also requires additional investment in sludge disposal costs. At the same time, the residual nickel complex in the iron sludge can easily cause secondary pollution. Second, the reaction conditions are harsh. Homogeneous Fenton reactions need to be carried out under strongly acidic conditions. After treatment, the wastewater needs to be adjusted to neutral pH, increasing the consumption of acid and alkali reagents. Third, the oxidant has poor stability. Hydrogen peroxide, which is commonly used in the system, is easily decomposed and needs to be stored at low temperatures and added on-site. This results in high transportation and operating costs, and excessive hydrogen peroxide remains in the water, which has a toxic inhibitory effect on subsequent biological treatment units.

[0005] To overcome the shortcomings of homogeneous catalysis, the industry is gradually shifting towards heterogeneous catalysis, achieving the separation of catalysts from water by synthesizing iron-based catalysts with specific morphologies or functions. However, the preparation and application of existing heterogeneous catalysts still have significant drawbacks: Firstly, the preparation processes are complex and energy-intensive. For example, CN119500134A uses spray drying and high-temperature calcination to synthesize copper-iron bimetallic Fenton catalysts, resulting in high energy costs and the high temperature easily leads to sintering of catalyst active sites, reducing catalytic efficiency. CN119215892A uses alternating current or direct current as triggering conditions to prepare iron-based catalysts, requiring customized electrode equipment. During operation, the electrodes are prone to corrosion, resulting in high maintenance costs. CN115703077A uses a hydrothermal reactor for co-precipitation, requiring the reaction to be carried out under high pressure, resulting in a long reaction cycle and making it difficult to achieve large-scale continuous production. Secondly, catalyst separation is challenging. Existing heterogeneous catalysts are mostly nano- or micron-sized particles. Although they can be separated by filtration, high-precision membrane filtration equipment is required, resulting in high equipment costs and a high risk of membrane clogging, leading to low separation efficiency. Some processes employ centrifugal separation, which is energy-intensive and unsuitable for large-volume water treatment scenarios. Thirdly, catalytic stability is insufficient. Most heterogeneous iron-based catalysts lack an in-situ iron ion recycling mechanism, making it difficult to efficiently reduce iron ions to ferrous ions. This leads to a gradual decrease in the generation of active free radicals during the reaction, a significant drop in complex-breaking efficiency with repeated use, short catalyst lifespan, and the need for frequent replacement, increasing operating costs.

[0006] Furthermore, the selection of oxidants in existing advanced oxidation processes is also limited. In addition to hydrogen peroxide, persulfates (such as potassium persulfate and sodium persulfate) are another commonly used oxidant, but they require activation under alkaline conditions or high temperatures, and the activation conditions are harsh. Excessive persulfates can remain in the water, damaging the microbial activity of subsequent biological treatment systems.

[0007] In summary, current technologies for treating complex nickel wastewater generally face multiple challenges, including complex processes, high costs, difficult separation, and poor stability. There is an urgent need to develop a heterogeneous catalytic material that is simple to prepare, has inexpensive and readily available carriers, high catalytic activity, efficient iron recycling, and is easy to separate and recover. At the same time, the oxidant system should be optimized to improve process compatibility and economic benefits. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide an iron-based gel particle catalyst, its preparation method, and its application, which simplifies the process flow, reduces raw material costs, improves catalytic activity, achieves efficient iron recycling, facilitates separation and recovery, and enhances process compatibility and economic benefits.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing an iron-based gel particle catalyst, comprising the following steps:

[0011] (1) Mix sodium alginate, photocatalyst and deionized water, and stir until homogeneous to obtain a mixed solution;

[0012] (2) The mixed solution obtained in step (1) is dropped into the ferrous salt solution, so that sodium alginate and ferrous ions undergo cross-linking reaction to form spherical gel particles, and the photocatalyst is coated in the gel network, and then solidification treatment is performed.

[0013] (3) Collect the spherical gel particles obtained in step (2), and after washing and drying, obtain the iron-based gel particle catalyst.

[0014] The preparation method provided by this invention uses natural and inexpensive sodium alginate as a carrier. By leveraging its cross-linking reaction with ferrous ions, a sodium alginate-iron gel structure is synthesized in an aqueous solution in one step, thereby effectively immobilizing ferrous ions. At the same time, in order to achieve the reuse of the catalyst, a photocatalyst that can complex with iron ions and dissipate electrons under light is introduced on the basis of the cross-linked structure. Subsequently, in-situ reduction of ferric iron in the catalyst can be achieved by light irradiation, thereby accelerating the iron cycle, significantly improving the catalytic efficiency and catalyst stability, and ultimately achieving convenient recovery and reuse of the catalyst.

[0015] Preferably, the photocatalyst in step (1) includes carbon nitride and / or terephthalic acid.

[0016] Preferably, the mass ratio of sodium alginate to photocatalyst in step (1) is (2-3):1.

[0017] Preferably, in the mixed solution of step (1), the concentration of sodium alginate is 10-30 g / L.

[0018] Preferably, the ferrous salt solution in step (2) includes ferrous sulfate and ferrous chloride solutions.

[0019] Preferably, the concentration of ferrous ions in the ferrous sulfate solution is 5-15 wt%.

[0020] Preferably, the dripping process in step (2) is accompanied by stirring, and the stirring speed is 40-60 rpm.

[0021] Preferably, the curing time in step (2) is 1-3 hours.

[0022] Preferably, the washing liquid used in step (3) includes deionized water.

[0023] Preferably, the drying method in step (3) includes freeze drying and / or oven drying.

[0024] In a second aspect, the present invention provides an iron-based gel particle catalyst, prepared by the method described in the first aspect, comprising spherical gel particles formed by a crosslinking reaction of sodium alginate and ferrous ions, and a photocatalyst in a gel network encapsulating the spherical gel particles, wherein the particle size of the iron-based gel particle catalyst is on the millimeter scale.

[0025] The catalyst provided by this invention uses sodium alginate instead of the traditional framework structure. Because the gel can crosslink into larger catalysts, forming iron-based gel particle catalysts with millimeter-sized particles, it is easy to separate from wastewater through simple physical methods, which is beneficial for the reuse of the catalyst and significantly reduces operating costs.

[0026] Thirdly, the present invention provides an application of the iron-based gel particle catalyst as described in the second aspect, wherein the iron-based gel particle catalyst is used to treat wastewater containing complexed nickel, comprising the following steps:

[0027] (a) The pH of the wastewater containing nickel complex was adjusted to 2.0-6.0 to obtain acidic wastewater;

[0028] (b) Add iron-based gel particle catalyst and sodium hypochlorite solution sequentially to the acidic wastewater obtained in step (a), and maintain the pH value of the acidic wastewater during the feeding process;

[0029] (c) The acidic wastewater obtained in step (b) is stirred to carry out a catalytic oxidation reaction, thereby breaking down the complexed nickel in the acidic wastewater;

[0030] (d) After the reaction is completed, the iron-based gel particle catalyst is separated into solid and liquid phases, and the pH of the separated wastewater is adjusted to above 12 to precipitate the dissociated nickel ions.

[0031] This invention treats wastewater under acidic conditions, promoting the conversion of hypochlorite ions into more potent oxidizing agents, hypochlorous acid and chlorine gas. This simultaneously accelerates the release of iron from the iron catalyst and the catalytic process, while the efficient catalytic cycle reduces the dosage of sodium hypochlorite. Furthermore, because iron ions are fixed and recycled, the amount of iron sludge generated subsequently is significantly reduced.

[0032] Preferably, the available chlorine content of the sodium hypochlorite solution in step (b) is 8%-12%.

[0033] Preferably, the amount of sodium hypochlorite solution fed in step (b) is 40-60 g / L.

[0034] Preferably, the mass ratio of the iron-based gel particle catalyst to the sodium hypochlorite solution in step (b) is 1:(2.5-10).

[0035] Preferably, the difference between the pH value of the acidic wastewater in step (b) and the pH value of the initial wastewater is ≤1.

[0036] Preferably, the catalytic oxidation reaction in step (c) takes 6-12 hours.

[0037] Preferably, the solid-liquid separation method in step (d) includes any one of sedimentation, filtration, or sieve separation.

[0038] Preferably, the pH adjustment in step (d) includes adding lime slurry to the separated wastewater.

[0039] Preferably, the iron-based gel particle catalyst obtained in step (d) is regenerated.

[0040] Preferably, the regeneration process includes irradiating the iron-based gel particle catalyst with visible or ultraviolet light.

[0041] Preferably, the wavelength of the visible or ultraviolet light is ≤400nm.

[0042] Preferably, the irradiation time is ≥8h.

[0043] This invention utilizes light to achieve in-situ regeneration of ferric iron in a catalyst. Because the photocatalyst in the catalyst can release electrons under light conditions, it promotes the in-situ circulation of iron ions, enabling the catalyst to continuously generate active free radicals, resulting in high complex breaking efficiency and long catalytic life, significantly improving process compatibility and economic benefits.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The preparation method provided by the present invention uses natural and inexpensive sodium alginate as a carrier. By means of its cross-linking reaction with ferrous ions, a sodium alginate-iron gel structure is synthesized in an aqueous solution in one step, thereby effectively fixing ferrous ions. At the same time, in order to realize the reuse of the catalyst, a photocatalyst that can complex with iron ions and can dissipate electrons under light is introduced on the basis of the cross-linking structure. Subsequently, the in-situ reduction of ferric iron in the catalyst can be realized by light irradiation, thereby accelerating the iron cycle, greatly improving the catalytic efficiency and the stability of the catalyst, and finally realizing the convenient recovery and reuse of the catalyst.

[0046] (2) The catalyst provided by the present invention uses sodium alginate instead of the traditional framework structure. Because the gel can cross-link into a larger catalyst, forming iron-based gel particle catalyst with a size of millimeters, it is easy to separate from wastewater by simple physical methods, which is conducive to the reuse of the catalyst and significantly reduces the operating cost.

[0047] (3) The present invention treats wastewater under acidic conditions, which promotes the conversion of hypochlorite ions into hypochlorous acid and chlorine gas, which have stronger oxidizing power, and simultaneously promotes the release of iron from the iron catalyst and the catalytic process. Moreover, the efficient catalytic cycle reduces the amount of sodium hypochlorite to be added. At the same time, because iron ions are fixed and recycled, the amount of iron sludge generated subsequently is significantly reduced. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0049] One embodiment of the present invention provides a method for preparing an iron-based gel particle catalyst, comprising the following steps:

[0050] (1) Mix sodium alginate, photocatalyst and deionized water, and stir until homogeneous to obtain a mixed solution;

[0051] (2) The mixed solution obtained in step (1) is dropped into the ferrous salt solution, so that sodium alginate and ferrous ions undergo cross-linking reaction to form spherical gel particles, and the photocatalyst is coated in the gel network, and then solidification treatment is performed.

[0052] (3) Collect the spherical gel particles obtained in step (2), and after washing and drying, obtain the iron-based gel particle catalyst.

[0053] The preparation method provided by this invention uses natural and inexpensive sodium alginate as a carrier. By leveraging its cross-linking reaction with ferrous ions, a sodium alginate-iron gel structure is synthesized in an aqueous solution in one step, thereby effectively immobilizing ferrous ions. At the same time, in order to achieve the reuse of the catalyst, a photocatalyst that can complex with iron ions and dissipate electrons under light is introduced on the basis of the cross-linked structure. Subsequently, in-situ reduction of ferric iron in the catalyst can be achieved by light irradiation, thereby accelerating the iron cycle, significantly improving the catalytic efficiency and catalyst stability, and ultimately achieving convenient recovery and reuse of the catalyst.

[0054] In some embodiments, the photocatalyst in step (1) includes carbon nitride and / or terephthalic acid.

[0055] In some embodiments, the mass ratio of sodium alginate to photocatalyst in step (1) is (2-3):1, for example, it can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] In some embodiments, the concentration of sodium alginate in the mixed solution of step (1) is 10-30 g / L, for example, it can be 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L, 20 g / L, 22 g / L, 24 g / L, 26 g / L, 28 g / L or 30 g / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0057] In some embodiments, the ferrous salt solution in step (2) includes ferrous sulfate and ferrous chloride solutions.

[0058] In some embodiments, the concentration of ferrous ions in the ferrous sulfate solution is 5-15 wt%, for example, it can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0059] In some embodiments, the dripping process described in step (2) is accompanied by stirring, and the stirring speed is 40-60 rpm, for example, it can be 40 rpm, 42 rpm, 44 rpm, 46 rpm, 48 rpm, 50 rpm, 52 rpm, 54 rpm, 56 rpm, 58 rpm or 60 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0060] In some embodiments, the curing time in step (2) is 1-3 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] In some embodiments, the washing liquid used in step (3) includes deionized water.

[0062] In some embodiments, the drying method described in step (3) includes freeze drying and / or oven drying.

[0063] One embodiment of the present invention also provides an iron-based gel particle catalyst, which is prepared by the preparation method described in any of the above embodiments. It includes spherical gel particles formed by the cross-linking reaction of sodium alginate and ferrous ions, and a photocatalyst in a gel network coated with the spherical gel particles, wherein the particle size of the iron-based gel particle catalyst is on the millimeter scale.

[0064] The catalyst provided by this invention uses sodium alginate instead of the traditional framework structure. Because the gel can crosslink into larger catalysts, forming iron-based gel particle catalysts with millimeter-sized particles, it is easy to separate from wastewater through simple physical methods, which is beneficial for the reuse of the catalyst and significantly reduces operating costs.

[0065] One embodiment of the present invention also provides an application of the iron-based gel particle catalyst described in any of the above embodiments, wherein the iron-based gel particle catalyst is used to treat wastewater containing complexed nickel, comprising the following steps:

[0066] (a) The pH of the wastewater containing nickel complex was adjusted to 2.0-6.0 to obtain acidic wastewater;

[0067] (b) Add iron-based gel particle catalyst and sodium hypochlorite solution sequentially to the acidic wastewater obtained in step (a), and maintain the pH value of the acidic wastewater during the feeding process;

[0068] (c) The acidic wastewater obtained in step (b) is stirred to carry out a catalytic oxidation reaction, thereby breaking down the complexed nickel in the acidic wastewater;

[0069] (d) After the reaction is completed, the iron-based gel particle catalyst is separated into solid and liquid phases, and the pH of the separated wastewater is adjusted to above 12 to precipitate the dissociated nickel ions.

[0070] This invention treats wastewater under acidic conditions, promoting the conversion of hypochlorite ions into more potent oxidizing agents, hypochlorous acid and chlorine gas. This simultaneously accelerates the release of iron from the iron catalyst and the catalytic process, while the efficient catalytic cycle reduces the dosage of sodium hypochlorite. Furthermore, because iron ions are fixed and recycled, the amount of iron sludge generated subsequently is significantly reduced.

[0071] In some embodiments, the available chlorine content of the sodium hypochlorite solution in step (b) is 8%-12%, for example, it can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% or 12%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0072] In some embodiments, the amount of sodium hypochlorite solution added in step (b) is 40-60 g / L, for example, it can be 40 g / L, 42 g / L, 44 g / L, 46 g / L, 48 g / L, 50 g / L, 52 g / L, 54 g / L, 56 g / L, 58 g / L or 60 g / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0073] In some embodiments, the mass ratio of the iron-based gel particle catalyst to the sodium hypochlorite solution in step (b) is 1:(2.5-10), for example, it can be 1:2.5, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0074] In some embodiments, the difference between the pH value of the acidic wastewater in step (b) and the pH value of the initial wastewater is ≤1, for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0075] In some embodiments, the catalytic oxidation reaction in step (c) takes 6-12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0076] In some embodiments, the solid-liquid separation method in step (d) includes any one of sedimentation, filtration, or sieve separation.

[0077] In some embodiments, the pH adjustment in step (d) includes adding lime slurry to the separated wastewater.

[0078] In some embodiments, the iron-based gel particle catalyst obtained in step (d) is regenerated.

[0079] In some embodiments, the regeneration process includes irradiating the iron-based gel particle catalyst with visible or ultraviolet light.

[0080] In some embodiments, the wavelength of the visible or ultraviolet light is ≤400nm, for example, it can be 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm or 400nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0081] In some embodiments, the irradiation time is ≥8h, for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0082] This invention utilizes light to achieve in-situ regeneration of ferric iron in a catalyst. Because the photocatalyst in the catalyst can release electrons under light conditions, it promotes the in-situ circulation of iron ions, enabling the catalyst to continuously generate active free radicals, resulting in high complex breaking efficiency and long catalytic life, significantly improving process compatibility and economic benefits.

[0083] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0084] Example 1

[0085] This embodiment provides an iron-based gel particle catalyst and its preparation method, the preparation method comprising the following steps:

[0086] (1) Dissolve 50 mg sodium alginate and 20 mg carbon nitride in 2.5 mL of deionized water and stir until homogeneous to obtain a mixed solution; wherein the carbon nitride is synthesized by thermal polymerization of melamine;

[0087] (2) The mixed solution obtained in step (1) was slowly dripped into a 10wt% ferrous sulfate solution using a syringe, and the solution was stirred at 50rpm during the dripping process, so that sodium alginate and ferrous ions would undergo a cross-linking reaction to form spherical gel particles, and the photocatalyst would be coated in the gel network. Then, the solution was cured for 2 hours.

[0088] (3) Collect the spherical gel particles obtained in step (2), wash them thoroughly with deionized water, and then freeze-dry them to obtain the iron-based gel particle catalyst, denoted as Fe-SAL.

[0089] Comparative Example 1

[0090] This comparative example provides an iron-based gel particle catalyst and its preparation method, the preparation method comprising the following steps:

[0091] (1) Dissolve 50 mg of sodium alginate in 2.5 mL of deionized water and stir until homogeneous to obtain a mixed solution;

[0092] (2) The mixed solution obtained in step (1) is slowly dripped into a 10wt% ferrous sulfate solution using a syringe, and the solution is stirred at 50rpm during the dripping process, so that sodium alginate and ferrous ions undergo cross-linking reaction to form spherical gel particles, and then solidified for 2h.

[0093] (3) Collect the spherical gel particles obtained in step (2), wash them thoroughly with deionized water, and then freeze-dry them to obtain the iron-based gel particle catalyst, denoted as Fe-SA.

[0094] Application Example 1

[0095] This application example uses the iron-based gel particle catalyst Fe-SAL provided in Example 1 to treat wastewater containing complexed nickel. The wastewater is prepared using ultrapure water, and the heavy metal and complexing agent are Ni and EDTA, respectively, with a molar ratio of 1:1. 2+ The concentration was 20 ppm.

[0096] The wastewater treatment method provided in this application example includes the following steps:

[0097] (a) The pH of the wastewater containing nickel complex was adjusted to 4.0 to obtain acidic wastewater;

[0098] (b) Add 10 g / L iron-based gel particle catalyst and 50 g / L sodium hypochlorite solution (with an effective chlorine content of 10%) sequentially to the acidic wastewater obtained in step (a), and maintain the pH of the acidic wastewater at 4.0 ± 0.1 during the feeding process;

[0099] (c) The acidic wastewater obtained in step (b) is stirred and treated to carry out a catalytic oxidation reaction for 8 hours, so that the complexed nickel in the acidic wastewater is broken down.

[0100] (d) After the reaction is complete, the iron-based gel particle catalyst is filtered out, and lime milk is added to adjust the pH of the separated wastewater to above 12, so that the dissociated nickel ions are precipitated, and the Ni content is determined by taking the filtrate.

[0101] (e) Repeat the above steps for 3 sets of experiments. The Ni content in the filtrate each time is recorded as Ni①, Ni② and Ni③, respectively. Then, the iron-based gel particle catalyst is irradiated with ultraviolet light for 8 hours. After regeneration treatment, the above experiments are repeated for verification. The Ni content in the filtrate is recorded as Ni④.

[0102] Comparative Application Example 1

[0103] This comparative application example uses the iron-based gel particle catalyst Fe-SA provided in Comparative Example 1 to treat wastewater containing complexed nickel. The composition of the wastewater and the wastewater treatment method are the same as in Application Example 1, so they will not be described again here.

[0104] Comparative Application Example 2

[0105] This comparative application example provides a method for treating wastewater containing nickel complex, wherein the composition of the wastewater is the same as in Application Example 1, and the wastewater treatment method includes the following steps:

[0106] (a) The pH of the wastewater containing nickel complex was adjusted to 4.0 to obtain acidic wastewater;

[0107] (b) Add 50 g / L sodium hypochlorite solution (with an available chlorine content of 10%) to the acidic wastewater obtained in step (a), and maintain the pH of the acidic wastewater at 4.0 ± 0.1 during the addition process;

[0108] (c) The acidic wastewater obtained in step (b) was stirred for 8 hours, and then lime milk was added to adjust the pH value of the wastewater to above 12. The Ni content of the filtrate was then determined.

[0109] Comparative Application Example 3

[0110] This comparative application example provides a method for treating wastewater containing nickel complex, wherein the composition of the wastewater is the same as in Application Example 1, and the wastewater treatment method includes the following steps:

[0111] (a) The pH of the wastewater containing nickel complex was adjusted to 4.0 to obtain acidic wastewater;

[0112] (b) Add 5 g / L ferrous sulfate solution (concentration of 10 wt%) and 50 g / L sodium hypochlorite solution (available chlorine content of 10%) sequentially to the acidic wastewater obtained in step (a), and maintain the pH of the acidic wastewater at 4.0 ± 0.1 during the feeding process;

[0113] (c) The acidic wastewater obtained in step (b) was stirred for 8 hours, and then lime milk was added to adjust the pH value of the wastewater to above 12. The Ni content of the filtrate was then determined.

[0114] Comparative Application Example 4

[0115] This comparative application example provides a method for treating wastewater containing nickel complex, wherein the composition of the wastewater is the same as in Application Example 1, and the wastewater treatment method includes the following steps:

[0116] (a) The pH of the wastewater containing nickel complex was adjusted to 4.0 to obtain acidic wastewater;

[0117] (b) First, add 50 g / L sodium hypochlorite solution (with an available chlorine content of 10%) to the acidic wastewater obtained in step (a), and then add 5 g / L ferrous sulfate solution (with a concentration of 10 wt%) in two separate additions, while maintaining the pH of the acidic wastewater at 4.0 ± 0.1 during the addition process;

[0118] (c) The acidic wastewater obtained in step (b) was stirred for 8 hours, and then lime milk was added to adjust the pH value of the wastewater to above 12. The Ni content of the filtrate was then determined.

[0119] Comparative Application Example 5

[0120] This comparative application example provides a method for treating wastewater containing nickel complex, wherein the composition of the wastewater is the same as in Application Example 1, and the wastewater treatment method includes the following steps:

[0121] (a) The pH of the wastewater containing nickel complex was adjusted to 4.0 to obtain acidic wastewater;

[0122] (b) First, add 50 g / L sodium hypochlorite solution (with an available chlorine content of 10%) to the acidic wastewater obtained in step (a), and then add 5 g / L ferrous sulfate solution (with a concentration of 10 wt%) in three separate additions, while maintaining the pH of the acidic wastewater at 4.0 ± 0.1 during the addition process;

[0123] (c) The acidic wastewater obtained in step (b) was stirred for 8 hours, and then lime milk was added to adjust the pH value of the wastewater to above 12. The Ni content of the filtrate was then determined.

[0124] The Ni content in the filtrate obtained from Application Example 1 and Comparative Application Examples 1-5 is shown in Table 1 below.

[0125] Table 1

[0126]

[0127] Therefore, the preparation method provided by this invention uses natural and inexpensive sodium alginate as a carrier. By leveraging its cross-linking reaction with ferrous ions, a sodium alginate-iron gel structure is synthesized in an aqueous solution in one step, thereby effectively immobilizing ferrous ions. At the same time, in order to achieve the reuse of the catalyst, a photocatalyst that can complex with iron ions and dissipate electrons under light is introduced on the basis of the cross-linked structure. Subsequently, in-situ reduction of ferric iron in the catalyst can be achieved by light irradiation, thereby accelerating the iron cycle, significantly improving the catalytic efficiency and catalyst stability, and ultimately achieving convenient recovery and reuse of the catalyst.

[0128] Furthermore, the catalyst provided by this invention uses sodium alginate instead of the traditional framework structure. Because the gel can crosslink into larger catalysts, forming iron-based gel particle catalysts with millimeter-sized particles, it is easy to separate from wastewater through simple physical methods, which is beneficial for the reuse of the catalyst and significantly reduces operating costs.

[0129] Furthermore, this invention treats wastewater under acidic conditions, promoting the conversion of hypochlorite ions into more potent oxidizing agents, hypochlorous acid and chlorine gas. This simultaneously accelerates the release of iron from the iron catalyst and the catalytic process, while the efficient catalytic cycle reduces the dosage of sodium hypochlorite. At the same time, because iron ions are fixed and recycled, the amount of iron sludge generated subsequently is significantly reduced.

[0130] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an iron-based gel particle catalyst, characterized in that, The preparation method includes the following steps: (1) Mix sodium alginate, photocatalyst and deionized water, and stir until homogeneous to obtain a mixed solution; (2) The mixed solution obtained in step (1) is dropped into the ferrous salt solution, so that sodium alginate and ferrous ions undergo cross-linking reaction to form spherical gel particles, and the photocatalyst is coated in the gel network, and then solidification treatment is performed. (3) Collect the spherical gel particles obtained in step (2), and after washing and drying, obtain the iron-based gel particle catalyst.

2. The method for preparing the iron-based gel particle catalyst according to claim 1, characterized in that, The photocatalyst in step (1) includes carbon nitride and / or terephthalic acid; And / or, the mass ratio of sodium alginate to photocatalyst in step (1) is (2-3):1; And / or, in the mixed solution described in step (1), the concentration of sodium alginate is 10-30 g / L.

3. The method for preparing the iron-based gel particle catalyst according to claim 1, characterized in that, The ferrous salt solution in step (2) includes ferrous sulfate and ferrous chloride solutions; The concentration of ferrous ions in the ferrous sulfate solution is 5-15 wt%. And / or, the dripping process described in step (2) is accompanied by stirring, and the stirring speed is 40-60 rpm; And / or, the curing time in step (2) is 1-3 hours.

4. The method for preparing the iron-based gel particle catalyst according to claim 1, characterized in that, The washing solution used in step (3) includes deionized water; And / or, the drying method described in step (3) includes freeze drying and / or baking.

5. An iron-based gel particle catalyst, characterized in that, The iron-based gel particle catalyst is prepared by the preparation method described in any one of claims 1-4, comprising spherical gel particles formed by crosslinking sodium alginate and ferrous ions, and a photocatalyst in a gel network encapsulating the spherical gel particles, wherein the particle size of the iron-based gel particle catalyst is on the millimeter scale.

6. An application of the iron-based gel particle catalyst as described in claim 5, characterized in that, The iron-based gel particle catalyst is used to treat wastewater containing complexed nickel, comprising the following steps: (a) The pH of the wastewater containing nickel complex was adjusted to 2.0-6.0 to obtain acidic wastewater; (b) Add iron-based gel particle catalyst and sodium hypochlorite solution sequentially to the acidic wastewater obtained in step (a), and maintain the pH value of the acidic wastewater during the feeding process; (c) The acidic wastewater obtained in step (b) is stirred to carry out a catalytic oxidation reaction, thereby breaking down the complexed nickel in the acidic wastewater; (d) After the reaction is completed, the iron-based gel particle catalyst is separated into solid and liquid phases, and the pH of the separated wastewater is adjusted to above 12 to precipitate the dissociated nickel ions.

7. The application of the iron-based gel particle catalyst according to claim 6, characterized in that, The available chlorine content of the sodium hypochlorite solution in step (b) is 8%-12%; And / or, the amount of sodium hypochlorite solution fed in step (b) is 40-60 g / L; And / or, the mass ratio of the iron-based gel particle catalyst to the sodium hypochlorite solution in step (b) is 1:(2.5-10); And / or, the difference between the pH value of the acidic wastewater in step (b) and the initial pH value of the wastewater is ≤1.

8. The application of the iron-based gel particle catalyst according to claim 6, characterized in that, The catalytic oxidation reaction in step (c) takes 6-12 hours; And / or, the solid-liquid separation method described in step (d) includes any one of sedimentation, filtration or sieve separation; And / or, the pH adjustment method described in step (d) includes adding lime slurry to the separated wastewater.

9. The application of the iron-based gel particle catalyst according to any one of claims 6-8, characterized in that, The iron-based gel particle catalyst obtained in step (d) is regenerated.

10. The application of the iron-based gel particle catalyst according to claim 9, characterized in that, The regeneration process includes irradiating the iron-based gel particle catalyst with visible or ultraviolet light. Wherein, the wavelength of the visible light or ultraviolet light is ≤400nm; And / or, the irradiation time is ≥8h.

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