A method for preparing iron-based catalysts using iron-oxidizing microorganisms and applications thereof

Abstract

The application discloses a method for preparing an iron-based catalyst by using iron-oxidizing microorganisms and application of the iron-based catalyst. The method for preparing the iron-based catalyst comprises the following steps: adding CaO into animal manure, adjusting pH, drying, and sieving; configuring an impregnation liquid, inoculating iron-oxidizing microorganisms with a volume ratio of 3%-5% into the impregnation liquid, and culturing until the content of ferrous ions in the impregnation liquid is lower than 0.1 g / L, that is, the culture is complete, and then adding lanthanum nitrate into the impregnation liquid; adding the animal manure into the impregnation liquid, the height of the impregnation liquid being higher than that of the animal manure, stirring for a period of time, and fixing the iron-based catalyst on the carrier of the animal manure; and performing solid-liquid separation on the fixed iron-based catalyst, drying the separated precipitate, and obtaining the finished iron-based catalyst. The preparation method simplifies the preparation process, reduces the production cost, is an environment-friendly preparation method of the catalyst, and has remarkable industrial application value and wide popularization prospect.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically to a method and application for preparing iron-based catalysts using iron-oxidizing microorganisms. Background Technology

[0002] Traditional methods for preparing iron-based catalysts mainly include chemical precipitation, impregnation, and co-precipitation. Chemical precipitation typically uses soluble iron salts such as ferric nitrate and ferric chloride as precursors, adding precipitants such as ammonia or sodium carbonate to form ferric hydroxide or ferric carbonate precursors. The final catalyst is then obtained through steps such as filtration, washing, drying, calcination, and reduction. While this method is simple to operate and easy to scale up industrially, the iron species are prone to sintering during calcination, leading to a reduction in active sites. Simultaneously, the washing process generates a large amount of saline wastewater.

[0003] The impregnation method involves immersing porous supports such as alumina and silica in an iron-containing salt solution. Capillary action allows the active component to be loaded onto the support surface. While this method achieves high dispersion and controllable loading of the active component, it is prone to iron species migration and aggregation during drying and calcination. Furthermore, the interaction between the support and the active component is weak, leading to potential detachment of the active component during long-term use. The co-precipitation method involves mixing iron salts with other metal salts, obtaining a composite oxide through a precipitation reaction, followed by further processing.

[0004] These traditional preparation methods suffer from several drawbacks. Active components are prone to sintering and aggregation during preparation and use, leading to a decrease in specific surface area and active sites. The catalysts also exhibit poor thermal stability, with iron species easily undergoing phase transitions or carbonization and deactivating under high-temperature reaction conditions. Additive elements such as potassium and copper are easily lost during the reaction due to volatilization or binding with poisons. Furthermore, the lack of precise control over pore structure affects mass transfer efficiency and can lead to deactivation due to carbon buildup or blockage. Finally, the preparation process typically requires high-temperature reduction treatment, which is not only energy-intensive but may also generate inactive iron oxide intermediates.

[0005] In addition, traditional methods also face environmental pollution problems, especially the large amount of saline wastewater generated by precipitation methods, and high energy consumption, which are contrary to the development concept of green chemistry. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing iron-based catalysts using iron-oxidizing microorganisms and its application. Addressing the high energy consumption and complex process conditions of traditional preparation methods, this invention employs a microbial synthesis method to prepare iron-based catalysts and utilizes a support to improve the stability and catalytic efficiency of the iron-based catalysts. Furthermore, the support is made from agricultural waste, which reduces the pressure from agricultural waste while effectively improving catalytic activity. The addition of rare earth ions as promoters further enhances the catalytic activity of the catalyst, resulting in iron-based catalysts with higher activity and better dispersibility, while simultaneously reducing environmental pollution and energy consumption.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing iron-based catalysts using iron-oxidizing microorganisms includes the following steps:

[0009] Step 1: Preparation of the carrier

[0010] Add CaO to animal feces, adjust the pH, dry, and sieve;

[0011] Adding calcium oxide can adjust the pH of animal manure, absorb moisture during mixing, and facilitate drying. Furthermore, calcium oxide increases the porosity of the animal manure, facilitating the fixation and adsorption of catalysts and enhancing its effectiveness as a carrier. Natural air drying is typically used to reduce energy consumption. Heating drying can also be employed. Animal manure can be cow dung, chicken manure, or a mixture of both. Sieving increases the uniformity of the carrier.

[0012] The advantages of using animal manure as a catalyst carrier are twofold: firstly, it is a cheap and readily available agricultural waste, and converting it into a catalyst carrier enables resource recycling, reduces environmental pollution from waste, and aligns with the concept of sustainable development. Secondly, animal manure is rich in organic matter, forming abundant porous structures and surface functional groups, providing numerous active sites for the catalyst and enhancing its adsorption and catalytic performance. Furthermore, its organic components exhibit good biocompatibility, do not negatively impact soil microorganisms and plant growth, and can provide habitats, carbon sources, and nitrogen sources for microorganisms, promoting microbial activity, further driving humus formation, and improving soil fertility. In summary, this catalyst demonstrates excellent performance in terms of cost-effectiveness, environmental friendliness, catalytic performance, and soil improvement, and has broad application prospects.

[0013] Step 2: Prepare the impregnation solution

[0014] Nitrogen source, phosphorus source, metal ions, and FeSO4·7H2O were added to the impregnation solution, and iron-oxidizing microorganisms were inoculated into the impregnation solution at a volume ratio of 3%-5%, wherein the number of iron-oxidizing microorganisms in the liquid was 5-50 × 10⁻⁶.7 The culture temperature, culture time, initial pH and other conditions are adjusted according to the growth characteristics of the selected iron-oxidizing microorganisms. Culture is carried out until the content of ferrous ions in the impregnation solution is lower than 0.1 g / L, which is considered as complete culture.

[0015] Step 3: Preparation of iron-based catalyst

[0016] Add the animal feces from step 1 to the impregnation solution, ensuring the impregnation solution covers the height of the animal feces, and stir for a period of time to fix the iron-based catalyst onto the animal feces carrier.

[0017] Step 4: Prepare the finished iron-based catalyst

[0018] The iron-based catalyst fixed in step 3 is subjected to solid-liquid separation, and the separated precipitate is dried to obtain the finished iron-based catalyst.

[0019] Preferably, the mass ratio of animal feces to CaO in step 1 is 2.5%-4%. The specific mass ratio can be adjusted according to actual conditions such as the type of animal feces.

[0020] Preferably, in step 1, the pH is adjusted to 7-8, and the sieve is passed through a 2mm sieve.

[0021] Preferably, the nitrogen source in step 2 is (NH4)2SO4, the phosphorus source is KH2PO4, and the metal ions include KCl, MgSO4·7H2O and Ca(NO3)2·4H2O;

[0022] The concentrations of (NH4)2SO4, KH2PO4, KCl, MgSO4·7H2O, Ca(NO3)2·4H2O and FeSO4·7H2O were 3 g / L, 0.5 g / L, 0.1 g / L, 0.5 g / L, 0.01 g / L and 4.5 g / L, respectively.

[0023] Preferably, the iron-oxidizing microorganisms include one or more of Thiobacillus ferrooxidans, Acidithiobacillus ferrooxidans, Gallionella ferruginea, and Leptospirillum ferrooxidans.

[0024] These microorganisms can oxidize ferrous ions to ferric ions, exhibiting high biological activity. The reaction takes place at room temperature and pressure, eliminating the need for strong oxidants, thus reducing treatment costs and causing no secondary pollution. It is an environmentally friendly and cost-effective treatment method that requires no external energy supply, conforms to green chemistry principles, and is suitable for large-scale engineering applications.

[0025] Preferably, the microbial culture conditions are 30-45℃ and a rotation speed of 120-200 rpm. Under these conditions, the microorganisms exhibit high growth activity, which facilitates their growth and oxidation of ferrous ions.

[0026] Preferably, after the cultivation is complete in step 2, lanthanum nitrate is added to the impregnation solution, with a molar ratio of lanthanum to ferric iron of 1:(115-120). Under this ratio, the iron catalyst exhibits the strongest activity.

[0027] The addition of lanthanum nitrate increases the chain structure of iron-based oxidants, thereby enhancing their adsorption capacity. Furthermore, lanthanum ions increase the number of active sites on the catalyst, promoting the adsorption and activation of reactants and thus improving catalytic efficiency.

[0028] Preferably, the solid-liquid separation in step 4 is performed by filtration with filter paper or by centrifugation at 3000 rpm for 10-20 min.

[0029] Preferably, the drying in step 4 is air drying or drying at 55°C for 2 hours.

[0030] Another object of the present invention is to provide the application of the iron-based catalyst prepared by the above-described method of preparing iron-based catalyst using iron-oxidizing microorganisms in the preparation of seedling substrate.

[0031] Iron-based catalysts are added to the compost substrate at a mass ratio of 1:200-300. The compost substrate includes a carbon source and a nitrogen source. The carbon source is rice husks or plant straw, and the nitrogen source can be nitrogen fertilizer (such as urea), soybean meal, peptone, etc. The ratio of carbon source to nitrogen source is 25-30:1.

[0032] This invention applies iron-oxidizing microorganisms to the preparation of seedling substrates. By converting ferrous ions into ferric ions using these microorganisms, the use of strong oxidizing agents and other chemical reagents can be reduced, while also decreasing energy consumption—making it an environmentally friendly preparation method. Furthermore, the addition of rare earth ions enhances the active sites of the iron-based catalyst, thereby improving its catalytic effect. In addition, effectively immobilizing the iron-based catalyst on the support not only improves the catalyst's dispersibility and stability but also enhances the efficiency and quality of humus generation in the seedling substrate by regulating surface properties and reactant adsorption and activation.

[0033] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention presents an environmentally friendly method for preparing iron-based catalysts using iron-oxidizing bacteria. Compared to traditional chemical synthesis, it eliminates the need for large quantities of chemical reagents and high-temperature, high-pressure conditions, thus reducing energy consumption and environmental pollution. When synthesizing catalysts using iron-oxidizing bacteria, the bacteria can fix iron ions in their biofilm during the oxidation of ferrous sulfate, thereby reducing the migration and loss of iron ions.

[0035] Furthermore, this invention incorporates rare earth ions during the preparation of the iron-based oxidant. By increasing the active sites of the iron-based oxidant, its catalytic effect can be further enhanced. Additionally, using animal feces as a carrier further immobilizes the iron-based catalyst and further increases its catalytic activity. The preparation method of this invention simplifies the process, reduces production costs, and is an environmentally friendly method for catalyst preparation, possessing significant industrial application value and broad prospects for promotion. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0037] Figure 1 SEM image of the precipitate from the impregnation solution.

[0038] Figure 2 Photographs showing the application of iron-based catalysts in composting.

[0039] Figure 3 Photo of the finished product of composting. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1:

[0042] Weigh 200g of cow dung and 5.6g of calcium oxide, mix them evenly, air dry them, pass them through a 2mm sieve, and measure the pH of the mixture to be 7.5.

[0043] An impregnation solution was prepared, in which a nitrogen source, a phosphorus source, metal ions, and FeSO4·7H2O were added. In this embodiment, 1 L of impregnation solution was prepared, wherein 3 g of (NH4)2SO4, 0.5 g of KH2PO4, 0.1 g of KCl, 0.5 g of MgSO4·7H2O, 0.01 g of Ca(NO3)2·4H2O, and 4.5 g of FeSO4·7H2O were weighed. The concentration of ferrous ions was approximately 0.903 g / L.

[0044] The *Acidithiobacillus ferrooxidans* was inoculated at a rate of 3% and cultured at 30°C and 180 rpm. The ferrous ion content in the impregnation solution was measured using the o-phenanthroline spectrophotometric method. When the ferrous ion concentration was found to be below 0.1 g / L, lanthanum nitrate was added to the impregnation solution and stirred until homogeneous. Alternatively, the mixture could be further stirred in a shaker to ensure thorough mixing of the lanthanum nitrate with the impregnation solution. In this example, the mixture was stirred in a shaker for 1 hour after the addition of lanthanum nitrate.

[0045] In this embodiment, the molar ratio of lanthanum to iron was 1:115, and the final concentration of ferrous ions was measured to be 0.09 g / L. Therefore, 0.041 g of lanthanum nitrate was added. Subsequently, the air-dried cow dung mixture was added to the prepared impregnation solution and stirred slowly (using a glass rod or magnetic stirrer) for 1 hour to allow the iron-based catalyst to fully adhere to the cow dung carrier.

[0046] The iron-based catalyst attached to the carrier can be filtered or centrifuged to collect the precipitate. Filter paper can be used for filtration, or the precipitate can be collected after centrifugation at 3000 rpm for 10-20 min. In this embodiment, centrifugation at 3000 rpm for 20 min is used.

[0047] The precipitate is air-dried or dried in an oven at 55°C for 2 hours. In this embodiment, an oven is used for drying. After drying, the precipitate is ground to obtain the final iron-based catalyst product.

[0048] The iron-based oxidant in this embodiment was added to the composting raw materials at a ratio of 1:200. The composting raw materials consisted of rice husks and urea in a mass ratio of 25:1. Specifically, the mass of the iron-based oxidant in this embodiment was 0.1 kg, and the mass of the composting raw materials was 20 kg. After being mixed evenly, the mixture was composted and named Treatment Group 1. Treatment Group 2 followed the method of Treatment Group 1 but without the addition of lanthanum nitrate. Treatment Group 3 used ferric sulfate as a catalyst, while the control group did not add any catalyst. After 42 days of fermentation, the humification index of each treatment was measured. Using the catalyst obtained in this scheme, the humification index of Treatment 1 increased by 246.67% compared to the control group, Treatment 2 increased by 133.33% compared to the control group, while the ordinary catalyst increased by 93.33% compared to the control group. In addition, the physicochemical properties of the seedling substrate product in this embodiment were measured, and the prepared seedling substrate met the requirements of "Tobacco Floating Seedling Substrate" (YC / T 310-2024).

[0049] Process 1 Process 2 Process 3 Comparison Humus Index 5.2 3.5 2.9 1.5

[0050] Example 2:

[0051] Weigh out 200g of cow dung and chicken dung, including 130g of cow dung, 70g of chicken dung, and 6.5g of calcium oxide. Mix them evenly, air dry, pass through a 2mm sieve, and measure the pH of the mixture to be 7.3.

[0052] Prepare a 1L impregnation solution, comprising: 3g of (NH4)2SO4, 0.5g of KH2PO4, 0.1g of KCl, 0.5g of MgSO4·7H2O, 0.01g of Ca(NO3)2·4H2O, and 4.5g of FeSO4·7H2O. The concentration of ferrous ions is approximately 0.903g / L.

[0053] The *Acidithiobacillus ferrooxidans* was inoculated at a rate of 3% and cultured at 30°C and 180 rpm. The ferrous ion content in the impregnation solution was measured using the o-phenanthroline spectrophotometric method. When the ferrous ion concentration was found to be below 0.1 g / L, lanthanum nitrate was added to the impregnation solution and stirred until homogeneous. Alternatively, the mixture could be further stirred in a shaker to ensure thorough mixing of the lanthanum nitrate with the impregnation solution. In this example, the mixture was stirred in a shaker for 0.5 h after adding lanthanum nitrate.

[0054] In this embodiment, the molar ratio of lanthanum to iron was 1:118, and the final concentration of ferrous ions was measured to be 0.1 g / L. Therefore, 0.040 g of lanthanum nitrate was added. Subsequently, the air-dried mixture of cow dung and chicken manure was added to the prepared impregnation solution and stirred slowly (using a glass rod or magnetic stirrer) for 1.5 h to allow the iron-based catalyst to fully adhere to the cow dung and chicken manure carrier.

[0055] The iron-based catalyst attached to the support was collected by filtration and the precipitate was dried in an oven at 55°C for 2 hours. After drying, it was ground to obtain the final iron-based catalyst product.

[0056] The iron-based oxidant in this embodiment was added to the composting raw materials at a ratio of 1:230. The composting raw materials consisted of rice husks and urea in a mass ratio of 28:1. Specifically, the mass of the iron-based oxidant in this embodiment was 0.1 kg, and the mass of the composting raw materials was 23 kg. After being mixed evenly, the mixture was composted and named Treatment Group 1. Treatment Group 2 followed the method of Treatment Group 1 but without the addition of lanthanum nitrate. Treatment Group 3 used ferric sulfate as a catalyst, while the control group did not add any catalyst. After 42 days of fermentation, the humification index of each treatment was measured. Using the catalyst obtained in this scheme, the humification index of Treatment 1 increased by 292.31% compared to the control group, Treatment 2 increased by 153.85% compared to the control group, while the ordinary catalyst increased by 92.31% compared to the control group. In addition, the physicochemical properties of the seedling substrate product in this embodiment were measured, and the prepared seedling substrate met the requirements of "Tobacco Floating Seedling Substrate" (YC / T 310-2024).

[0057] Process 1 Process 2 Process 3 Comparison Humus Index 5.1 3.3 2.5 1.3

[0058] Example 3:

[0059] Weigh out 200g of cow dung and 5.7g of calcium oxide, mix them evenly, air dry them, pass them through a 2mm sieve, and measure the pH of the mixture to be 7.3.

[0060] Prepare a 1L impregnation solution, comprising: 3g of (NH4)2SO4, 0.5g of KH2PO4, 0.1g of KCl, 0.5g of MgSO4·7H2O, 0.01g of Ca(NO3)2·4H2O, and 4.5g of FeSO4·7H2O. The concentration of ferrous ions is approximately 0.903g / L.

[0061] Leptospirillum ferriphilum was inoculated at a rate of 3%, and cultured at 37°C and 180 rpm. The ferrous ion content in the impregnation solution was measured using the o-phenanthroline-spectrophotometric method. When the ferrous ion concentration was found to be below 0.1 g / L, lanthanum nitrate was added to the impregnation solution and stirred until homogeneous. Alternatively, the mixture could be further stirred in a shaker to ensure thorough mixing. In this example, the mixture was stirred in a shaker for 1 hour after adding lanthanum nitrate. In this example, the molar ratio of lanthanum to iron was 1:120, and the final ferrous ion concentration was measured to be 0.08 g / L; therefore, 0.040 g of lanthanum nitrate was added. Subsequently, the air-dried cow dung mixture was added to the prepared impregnation solution and stirred slowly (using a glass rod or magnetic stirrer) for 1.5 hours to ensure that the iron-based catalyst was fully attached to the cow dung carrier. The iron-based catalyst attached to the carrier is collected by filtration and the precipitate is dried by air drying. After drying, it is ground to obtain the final iron-based catalyst product.

[0062] The iron-based oxidant in this embodiment was added to the composting raw materials at a ratio of 1:300. The composting raw materials consisted of rice husks and urea in a mass ratio of 30:1. Specifically, the mass of the iron-based oxidant in this embodiment was 0.1 kg, and the mass of the composting raw materials was 30 kg. After being mixed evenly, the mixture was composted and named Treatment Group 1. Treatment Group 2 followed the method of Treatment Group 1 but without the addition of lanthanum nitrate. Treatment Group 3 used ferric sulfate as a catalyst, while the control group did not add any catalyst. After 42 days of fermentation, the humification index of each treatment was measured. Using the catalyst obtained in this scheme, the humification index of Treatment 1 increased by 336.36% compared to the control group, Treatment 2 increased by 209.09% compared to the control group, while the ordinary catalyst increased by 100% compared to the control group. In addition, the physicochemical properties of the seedling substrate product in this embodiment were measured, and the prepared seedling substrate met the requirements of "Tobacco Floating Seedling Substrate" (YC / T 310-2024).

[0063] Process 1 Process 2 Process 3 Comparison Humus Index 4.8 3.4 2.2 1.1

[0064] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0065] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing iron-based catalysts using iron-oxidizing microorganisms, characterized in that, Includes the following steps: Step 1: Preparation of the carrier Add CaO to animal feces, adjust the pH, dry, and sieve; Step 2: Prepare the impregnation solution Nitrogen source, phosphorus source, metal ions, and FeSO4·7H2O are added to the impregnation solution, and iron-oxidizing microorganisms are inoculated into the impregnation solution at a volume ratio of 3%-5%. The solution is cultured until the ferrous ion content in the impregnation solution is below 0.1 g / L, indicating complete culture. After complete culture, lanthanum nitrate is added to the impregnation solution, with a molar ratio of lanthanum to ferric iron of 1:(115-120). The iron-oxidizing microorganisms are... Acidithiobacillus ferrooxidans ; Metal ions include KCl, MgSO4·7H2O and Ca(NO3)2·4H2O; Step 3: Preparation of iron-based catalyst Add the animal feces from step 1 to the impregnation solution, ensuring the impregnation solution covers the height of the animal feces, and stir for a period of time to fix the iron-based catalyst onto the animal feces carrier. Step 4: Prepare the finished iron-based catalyst The iron-based catalyst fixed in step 3 is subjected to solid-liquid separation, and the separated precipitate is dried to obtain the finished iron-based catalyst.

2. The method for preparing iron-based catalysts using iron-oxidizing microorganisms according to claim 1, characterized in that, The mass ratio of animal feces to CaO in step 1 is 200:(5.6-6.5).

3. The method for preparing iron-based catalysts using iron-oxidizing microorganisms according to claim 1, characterized in that, In step 1, the pH is adjusted to 7-8, and the sieve is passed through a 2mm sieve.

4. The method for preparing iron-based catalysts using iron-oxidizing microorganisms according to claim 1, characterized in that, The nitrogen source mentioned in step 2 is (NH4)2SO4 and the phosphorus source is KH2PO4; The concentrations of (NH4)2SO4, KH2PO4, KCl, MgSO4·7H2O, Ca(NO3)2·4H2O and FeSO4·7H2O were 3 g / L, 0.5 g / L, 0.1 g / L, 0.5 g / L, 0.01 g / L and 4.5 g / L, respectively.

5. The method for preparing iron-based catalysts using iron-oxidizing microorganisms according to claim 1, characterized in that, The conditions for microbial culture are 30-45℃ and a rotation speed of 120-200 rpm.

6. The method for preparing iron-based catalysts using iron-oxidizing microorganisms according to claim 1, characterized in that, The solid-liquid separation in step 4 is achieved by filtration with filter paper or centrifugation at 3000 rpm for 10-20 min. The drying process described in step 4 involves air drying or drying at 55°C for 2 hours.

7. The application of an iron-based catalyst prepared by the method of preparing iron-based catalyst using iron-oxidizing microorganisms as described in any one of claims 1-6 in the preparation of seedling substrate.

8. The application according to claim 7, characterized in that, Iron-based catalysts are added to compost substrates at a mass ratio of 1:200-300.

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