Method for preparing iron-based catalyst by using iron-oxidizing microorganisms and application of iron-based catalyst

Abstract

The invention discloses a method for preparing an iron-based catalyst by using iron-oxidizing microorganisms and application of the iron-based catalyst. The preparation method of the iron-based catalyst comprises the following steps: adding CaO into animal waste, adjusting the pH value, drying and sieving; the method comprises the following steps: preparing an impregnation liquid, inoculating iron-oxidizing microorganisms with a volume ratio of 3%-5% into the impregnation liquid, culturing until the content of ferrous ions in the impregnation liquid is lower than 0.1 g / L, namely culturing completely, and then adding lanthanum nitrate into the impregnation liquid; adding the animal waste into the steeping liquor, enabling the steeping liquor to submerge the animal waste, stirring for a period of time, and fixing the iron-based catalyst on a carrier of the animal waste; and carrying out solid-liquid separation on the fixed iron-based catalyst, and drying the separated precipitate to obtain an iron-based catalyst finished product. According to the preparation method, the preparation process is simplified, the production cost is reduced, and the preparation method is an environment-friendly preparation method for preparing the catalyst and has remarkable industrial application value and wide popularization prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and more particularly to a method for preparing an iron-based catalyst by utilizing iron-oxidizing microorganisms and its application. Background Art

[0002] Traditional methods for preparing iron-based catalysts primarily include chemical precipitation, impregnation, and co-precipitation. Chemical precipitation typically uses soluble iron salts such as ferric nitrate and ferric chloride as precursors. A precipitant such as ammonia or sodium carbonate is added to form a precursor of iron hydroxide or iron carbonate. The final catalyst is then filtered, washed, dried, calcined, and reduced. While this method is simple to operate and easily scaled up industrially, the calcination process can lead to sintering of iron species, resulting in a reduction in active sites. Furthermore, the washing process generates a large amount of saline wastewater.

[0003] The impregnation method involves immersing a porous carrier such as alumina or silica in an iron salt solution, allowing the active component to be loaded onto the carrier surface through capillary action. While this method can achieve a high degree of dispersion of the active component and a controllable loading amount, it can easily cause iron species to migrate and aggregate during the drying and calcination stages. Furthermore, the interaction between the carrier and the active component is weak, making it prone to active component shedding during long-term use. The coprecipitation method involves mixing iron salts with other metal salts, producing a composite oxide through a precipitation reaction, which is then subsequently processed.

[0004] These traditional preparation methods have the following problems: active components are prone to sintering and aggregation during preparation and use, resulting in a decrease in specific surface area and active sites. The catalysts have poor thermal stability and are prone to phase change or carbonization of iron species under high-temperature reaction conditions, leading to inactivation. Auxiliary elements such as potassium and copper are easily lost during the reaction due to volatilization or combination with poisons. The pore structure lacks precise control, which not only affects the mass transfer efficiency of the reactants but also easily leads to inactivation due to carbon deposition or blockage. The preparation process usually requires high-temperature reduction treatment, which is not only energy-intensive but also may generate inactive iron oxide intermediates.

[0005] In addition, traditional methods also face environmental pollution problems, especially the precipitation method produces a large amount of salt-containing wastewater, and the high energy consumption is contrary to the development concept of green chemistry. Summary of the Invention

[0006] In view of this, the present invention provides a method and application for preparing an iron-based catalyst using iron-oxidizing microorganisms. This invention addresses the high energy consumption and complex process conditions of traditional preparation methods by adopting a microbial synthesis method to prepare an iron-based catalyst, and employs a carrier to improve the stability and catalytic efficiency of the iron-based catalyst. Furthermore, the carrier is agricultural waste, which not only reduces the pressure caused by agricultural waste but also effectively improves the catalytic ability. Furthermore, by adding rare earth ions as additives, the catalytic ability of the catalyst is further enhanced, resulting in an iron-based catalyst with higher activity and good dispersibility, while also reducing environmental pollution and energy consumption.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing an iron-based catalyst using iron-oxidizing microorganisms comprises the following steps:

[0009] Step 1: Prepare the carrier

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

[0011] Adding calcium oxide can adjust the pH of animal manure and absorb moisture from it during the mixing process, facilitating drying. Furthermore, calcium oxide increases the porosity of the manure, facilitating its fixation and adsorption of catalysts, thereby enhancing its effectiveness as a carrier. Natural air drying is typically used to reduce energy consumption. Heat drying is also an option. Manure can be cow manure, chicken manure, or a mixture. Sieving is used to increase carrier uniformity.

[0012] The advantage of using animal manure as a carrier is that animal manure is a cheap and readily available agricultural waste. Converting it into a catalyst carrier can achieve resource recycling, reduce waste pollution to the environment, and comply with the concept of sustainable development. Secondly, animal manure is rich in organic matter, which can form a rich pore structure and surface functional groups, providing a large number of active sites for the catalyst and enhancing adsorption and catalytic performance. In addition, its organic components have good biocompatibility and will not have a negative impact on soil microorganisms and plant growth. It can also provide a habitat, carbon source and nitrogen source for microorganisms, promote microbial activity, further promote humus production, and improve soil fertility. In short, this catalyst performs well in cost-effectiveness, environmental friendliness, catalytic performance and soil improvement, and has broad applications.

[0013] Step 2: Prepare the dipping solution

[0014] Nitrogen source, phosphorus source, metal ions and FeSO4·7H2O are added to the impregnation liquid, and iron oxidizing microorganisms are inoculated into the impregnation liquid at a volume ratio of 3%-5%, wherein the number of iron oxidizing microorganisms in the liquid is 5-50×107 The culture temperature, culture time, initial pH and other conditions are adjusted according to the growth characteristics of the selected iron-oxidizing microorganisms, and the culture is completed when the ferrous ion content in the immersion liquid is less than 0.1 g / L.

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

[0016] Add the animal feces from step 1 to the impregnation liquid until the impregnation liquid is higher than the animal feces, and stir for a period of time to fix the iron-based catalyst on 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 a 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 is adjusted according to actual conditions such as the type of animal feces.

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

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

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

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

[0024] These microorganisms can oxidize ferrous ions to produce trivalent ferrous ions and have high biological activity. The reaction takes place at room temperature and pressure without the addition of strong oxidants, reducing treatment costs and causing no secondary pollution. It is an environmentally friendly and low-cost treatment method that does not require external energy supply, complies with the principles of green chemistry, and is suitable for large-scale engineering applications.

[0025] Preferably, the microorganism culture conditions are 30-45° C. and a rotation speed of 120-200 rpm. Under these conditions, the growth activity of the microorganisms is high, which is convenient for the growth of the microorganisms and the oxidation of divalent iron ions.

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

[0027] After adding lanthanum nitrate, the lanthanum ions can increase the chain structure of the iron-based oxidant, thereby enhancing its adsorption capacity. In addition, the lanthanum ions can increase the number of active sites on the catalyst, promoting the adsorption and activation of reactants, thereby improving catalytic efficiency.

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

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

[0030] Another object of the present invention is to provide the use of the iron-based catalyst prepared by the above-mentioned method of preparing an iron-based catalyst using iron-oxidizing microorganisms in the preparation of a seedling medium.

[0031] An iron-based catalyst is added to a compost substrate at a mass ratio of 1:200-300. The compost substrate includes a carbon source (rice husk or plant straw) and a nitrogen source (nitrogen fertilizer, such as urea, soybean meal, or peptone). The carbon source to nitrogen source ratio is 25-30:1.

[0032] The present invention applies iron-oxidizing microorganisms to the preparation of seedling substrates. The conversion of ferrous ions into ferric ions by the iron-oxidizing microorganisms can reduce the use of chemical reagents such as strong oxidants, while also reducing energy consumption. This is an environmentally friendly preparation method. Furthermore, the addition of rare earth ions can enhance the active sites of the iron-based catalyst and the catalytic effect of the iron-based catalyst. Furthermore, the effective immobilization of the iron-based catalyst on the carrier not only improves the dispersibility and stability of the catalyst, but also improves the efficiency and product quality of humus production in the seedling substrate by regulating surface properties and adsorption activation of reactants.

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

[0034] The present invention uses iron-oxidizing bacteria to prepare an iron-based catalyst, which is an environmentally friendly preparation method. Compared with traditional chemical synthesis, it does not require the use of large amounts of chemical reagents and high-temperature and high-pressure conditions, reducing energy consumption and environmental pollution. When using iron-oxidizing and reducing bacteria to synthesize the catalyst, the iron-oxidizing bacteria can fix iron ions in their biofilm during the oxidation of ferrous sulfate, thereby reducing the migration and loss of iron ions.

[0035] In addition, the present invention also adds rare earth ions during the preparation of the iron-based oxidant, which can further improve the catalytic effect of the iron-based oxidant by increasing the active sites of the iron-based oxidant. In addition, using animal feces as a carrier, the iron-based catalyst is further fixed and the catalytic activity is further increased. The preparation method of the present invention simplifies the preparation process, reduces production costs, is an environmentally friendly preparation method for preparing a catalyst, and has significant industrial application value and broad promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

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

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

[0039] Figure 3 Photo of the finished product of mature compost. DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0041] Example 1:

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

[0043] An impregnation solution is prepared, and a nitrogen source, a phosphorus source, metal ions, and FeSO4·7H2O are added to the solution. In this example, 1 L of impregnation solution is prepared, containing 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. The concentration of ferrous ions is approximately 0.903 g / L.

[0044] Acidithiobacillus ferrooxidans was inoculated at a 3% inoculum size and cultured at 30°C and 180 rpm. The ferrous ion content of the immersion solution was measured using o-phenanthroline spectrophotometry. When the ferrous ion concentration was less than 0.1 g / L, lanthanum nitrate was added to the immersion solution and stirred evenly. Alternatively, the lanthanum nitrate and immersion solution were further mixed in a shaker. In this embodiment, the lanthanum nitrate was added and mixed evenly in a shaker for 1 hour.

[0045] In the present embodiment, the molar ratio of lanthanum to iron is 1:115, and the final ferrous ion concentration measured is 0.09 g / L, so 0.041 g of lanthanum nitrate is added. Subsequently, the air-dried cow dung mixture is added to the prepared impregnation solution and slowly stirred (using a glass rod or a 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 is 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 minutes. In this embodiment, centrifugation at 3000 rpm for 20 minutes is used.

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

[0048] The iron-based oxidant in this example was added to the compost raw material at a ratio of 1:200. The compost raw material used was rice husk and urea, with a mass ratio of 25:1. Specifically, the mass of the iron-based oxidant in this example was 0.1 kg, and the mass of the compost raw material was 20 kg. After mixing evenly, the compost was treated and designated as 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, and the control group did not add a catalyst. After 42 days of fermentation, the humification index of the different treatments was measured. Using the catalyst obtained in this scheme, the humification index of Treatment 1 increased by 246.67% compared to the control group, and Treatment 2 increased by 133.33% compared to the control group. The conventional catalyst increased the humification index by 93.33% compared to the control group. In addition, the physical and chemical indicators of the finished seedling medium in this example were measured, and the prepared seedling medium complied with the "Tobacco Floating Seedling Medium" (YC / T 310-2024).

[0049] Process 1 Process 2 Process 3 comparison Humification index 5.2 3.5 2.9 1.5

[0050] Example 2:

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

[0052] Prepare 1 L of impregnation solution: weigh 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. The ferrous ion concentration is approximately 0.903 g / L.

[0053] Acidithiobacillus ferrooxidans was inoculated at a 3% inoculum size and cultured at 30°C and 180 rpm. The ferrous ion content of the immersion solution was measured using o-phenanthroline spectrophotometry. When the ferrous ion concentration was less than 0.1 g / L, lanthanum nitrate was added to the immersion solution and stirred evenly. Alternatively, the lanthanum nitrate and the immersion solution were mixed in a shaker. In this embodiment, the lanthanum nitrate was added and mixed in a shaker for 0.5 h.

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

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

[0056] The iron-based oxidant in this example was added to the compost raw material at a ratio of 1:230. The compost raw material used was rice husk and urea, with a mass ratio of 28:1. Specifically, the mass of the iron-based oxidant in this example was 0.1 kg, and the mass of the compost raw material was 23 kg. After being mixed evenly, the compost was treated and designated as 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, and the control group did not add a catalyst. After 42 days of fermentation, the humification index of the different treatments was measured. Using the catalyst obtained in this scheme, the humification index of Treatment 1 increased by 292.31% compared to the control group, and Treatment 2 increased by 153.85% compared to the control group. The conventional catalyst increased the humification index by 92.31% compared to the control group. In addition, the physical and chemical indicators of the finished seedling medium in this example were measured, and the prepared seedling medium complied with the "Tobacco Floating Seedling Medium" (YC / T 310-2024).

[0057] Process 1 Process 2 Process 3 comparison Humification index 5.1 3.3 2.5 1.3

[0058] Example 3:

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

[0060] Prepare 1 L of impregnation solution: weigh 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. The ferrous ion concentration is approximately 0.903 g / L.

[0061] Inoculate Leptospirillumferriphilum, inoculum size is 3%, after inoculation, cultivate under the condition of 37 ℃, 180rpm, and measure the content of ferrous ion in the immersion solution, the content of ferrous ion adopts o-phenanthroline-spectrophotometry to measure.When measuring the concentration of ferrous ion lower than 0.1g / L, add lanthanum nitrate in the immersion solution, and stir, also can continue in shaking table to mix lanthanum nitrate and immersion solution.In the present embodiment, after adding lanthanum nitrate, mix 1h in shaking table.In the present embodiment, the mol ratio of lanthanum to iron is 1:120, and the concentration of the final ferrous ion measured is 0.08g / L, therefore, add 0.040g lanthanum nitrate.Subsequently, the cow dung mixture after air-drying is added in the immersion solution prepared, slowly stir (adopting glass rod to stir or stirring in magnetic stirring apparatus), stir 1.5h, make iron-based catalyst fully attached in the cow dung carrier. The iron-based catalyst attached to the carrier is filtered to collect the precipitate, the precipitate is air-dried, and after drying, the final iron-based catalyst product is obtained by grinding.

[0062] The iron-based oxidant in this example was added to the compost raw material at a ratio of 1:300. The compost raw material used was rice husk and urea, with a mass ratio of 30:1. Specifically, the mass of the iron-based oxidant in this example was 0.1 kg, and the mass of the compost raw material was 30 kg. After mixing evenly, the composting process was carried out. This was designated as Treatment Group 1. Treatment Group 2 adopted the method of Treatment Group 1, but without the addition of lanthanum nitrate. Treatment Group 3 used ferric sulfate as a catalyst. The control group did not add a catalyst. After 42 days of fermentation, the humification index of the different treatments was measured. Using the catalyst obtained in this scheme, the humification index of Treatment 1 increased by 336.36% relative to the control group, and Treatment 2 increased by 209.09% relative to the control group, while the conventional catalyst increased by 100% relative to the control group. In addition, the physical and chemical indicators of the finished seedling substrate in this example were measured, and the prepared seedling substrate complied with the "Tobacco Floating Seedling Substrate" (YC / T 310-2024).

[0063] Process 1 Process 2 Process 3 comparison Humification 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 the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0065] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one 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 present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an iron-based catalyst using iron-oxidizing microorganisms, characterized in that: The following steps are involved: Step 1: Prepare the carrier Add CaO to animal manure, adjust pH, dry, and sieve; Step 2: Prepare the dipping solution A nitrogen source, a phosphorus source, metal ions and FeSO4·7H2O are added to the impregnation solution, and 3% to 5% by volume of iron-oxidizing microorganisms are inoculated into the impregnation solution, and the culture is carried out until the content of ferrous ions in the impregnation solution is less than 0.1 g / L, which means the culture is complete; Step 3: Preparation of iron-based catalyst Add the animal feces from step 1 to the impregnation liquid until the impregnation liquid is higher than the animal feces, and stir for a period of time to fix the iron-based catalyst on 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 a finished iron-based catalyst.

2. The method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to claim 1, characterized in that: The mass ratio of animal feces to CaO in step 1 is 2.5%-4%.

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

4. The method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to claim 1, wherein: In step 2, the nitrogen source is (NH4)2SO4, the phosphorus source is KH2PO4, and the metal ions include KCl, MgSO4·7H2O and Ca(NO3)2·4H2O; Among them, the concentrations of (NH4)2SO4, KH2PO4, KCl, MgSO4·7H2O, Ca(NO3)2·4H2O and FeSO4·7H2O are 3g / L, 0.5g / L, 0.1g / L, 0.5g / L, 0.01g / L and 4.5g / L, respectively.

5. The method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to claim 1, wherein: The iron oxidizing microorganisms include a mixture of one or more of Thiobacillus ferrooxidans, Acidithiobacillus ferrooxidans, Gallionella ferruginea, and Leptospirillum ferrooxidans.

6. The method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to claim 1, characterized in that: The microorganism culture conditions are 30-45° C. and a rotation speed of 120-200 rpm.

7. The method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to claim 1, characterized in that: After the culture is complete in step 2, lanthanum nitrate is added to the impregnation solution, and the molar ratio of lanthanum to trivalent iron is 1:(115-120).

8. The method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to claim 1, wherein: The solid-liquid separation in step 4 is performed by filtering with filter paper or centrifuging at 3000 rpm for 10-20 min; The drying is air drying or drying at 55° C. for 2 h.

9. Use of an iron-based catalyst prepared by the method for preparing an iron-based catalyst using iron-oxidizing microorganisms according to any one of claims 1 to 8 in the preparation of a seedling culture medium.

10. The use according to claim 9, characterized in that Add the iron-based catalyst to the compost substrate at a mass ratio of 1:200-300.

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