A method utilizing Fe 3+ Method for producing ammonium by reducing nitrate with oxidized modified pyrite

Abstract

This invention discloses a method utilizing Fe 3+ This method for reducing nitrate ions in oxidized pyrite to produce ammonium belongs to the field of water treatment and resource recovery technology. The method includes the following steps: S1, reacting acid-washed pyrite with Fe... 3+ The solution is mixed and oxidized to obtain oxidized pyrite; under S2 and anaerobic conditions, the oxidized pyrite is mixed with an alkaline nitrate solution and reacted in the dark. This invention can efficiently and selectively reduce nitrate to ammonium without external energy or precious metal catalysts. The nitrate removal rate can reach up to 99.8%, and the ammonium conversion rate can reach up to 100%, making it suitable for wastewater denitrification and resource recovery.

Description

Technical Field

[0001] This invention relates to the field of water treatment and resource recycling technology, and more specifically, to a method utilizing Fe 3+ A method for producing ammonium by reducing nitrate ions from oxidized pyrite. Background Technology

[0002] Nitrate pollution is one of the main sources of eutrophication and health risks in water bodies. Traditional treatment methods (such as biological denitrification and electrocatalytic reduction) suffer from problems such as low efficiency, numerous byproducts, and reliance on precious metal catalysts.

[0003] Pyrite (FeS2) is the most abundant iron-sulfur mineral in groundwater environments, due to its high Fe content. 2+ The reducing site can be used as a cheap reducing agent to remove nitrates, but the reducing ability of natural pyrite is limited, and the products are mainly nitrite or nitrogen, which are difficult to be directionally converted into ammonium.

[0004] Existing methods for improving nitrate conversion from pyrite include: enhancing the surface activity of pyrite through ball milling activation, but the nitrate removal rate is only 19% and requires ultraviolet light assistance (see patent CN115246666A, "A method for removing nitrate nitrogen from water using pyrite"); introducing denitrifying bacteria to improve denitrification efficiency, but the process is complex and requires strict control of anaerobic conditions (see the paper "Mechanism and Influencing Factors of N2O Generation in Wastewater Denitrification in Constructed Wetlands"), and the conversion of nitrate into useless nitrogen gas results in nitrogen loss; preparing noble metal electrodes (such as NiFe-LDH, Cu / TiO2) for electrocatalysis is costly and the Faraday efficiency is unstable (see patent CN113926456A, "A method for preparing and applying NiFe-LDH catalyst for nitrate reduction to ammonia"). Therefore, in the nitrate removal process, existing methods cannot simultaneously achieve efficient reduction, selective ammonium conversion, and low-cost operation. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method utilizing Fe 3+ The proposed method for reducing nitrates in oxidized pyrite to produce ammonium addresses the problems of low reduction activity of natural pyrite, poor product selectivity, limited efficiency of air oxidation pretreatment, high cost due to reliance on precious metal catalysts (such as Pt and Rh) for electrocatalytic reduction, and the complexity and strict anaerobic condition control required for biological processes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method utilizing Fe 3+ A method for reducing nitrate ions in oxidized pyrite to produce ammonium includes the following steps:

[0008] S1. Acid-washed pyrite and Fe 3+ The solution is mixed and oxidized to obtain oxidized pyrite;

[0009] S2. Under anaerobic conditions, oxidized pyrite is mixed with an alkaline nitrate solution and reacted in the dark.

[0010] The present invention is further configured to grind and sieve natural pyrite, then immerse it in deoxygenated hydrochloric acid solution, followed by washing with deoxygenated water and freeze-drying to obtain acid-washed pyrite.

[0011] The present invention is further configured such that the concentration of the deoxyhydrochloric acid solution is 0.1 mol / L.

[0012] The present invention is further configured such that, in step S1, Fe 3+ The solution is acidic Fe 3+ Solution, Fe 3+ The concentration was 0.1 mol / L, and the pH value was 1-3; after acid washing, pyrite and Fe... 3+ The volume ratio of the solution used is 10g:100mL.

[0013] The present invention is further configured such that, in step S1, Fe 3+ The solution is an acidic FeCl3 solution.

[0014] The present invention is further configured such that, in step S1, the oxidation time is 1 to 10 days.

[0015] The present invention is further configured such that, in step S2, the nitrate concentration of the alkaline nitrate solution is 20 mg / L and the pH value is 6-10.

[0016] The present invention is further configured such that the alkaline nitrate solution is an alkaline sodium nitrate solution or an alkaline potassium nitrate solution.

[0017] The present invention is further configured such that, in step S2, oxidized modified pyrite is mixed with alkaline nitrate solution to form oxidized pyrite-nitrate solution, and the concentration of pyrite in the solution is 2~10 g / L.

[0018] The present invention is further configured such that, in step S2, the reaction time in the dark is 24~48h.

[0019] In summary, the present invention has the following beneficial effects:

[0020] This invention utilizes Fe 3+ Oxidized pyrite produces more adsorbed Fe. 2+ Highly reactive minerals such as rust and magnetite, whose oxidation products themselves possess high reducing activity, and which form abundant Fe-OS bonds on the pyrite surface, enhancing electron transfer capacity and promoting NO3- oxidation.– Directly reduced to NH4 + (Instead of byproducts such as nitrite), this method overcomes the limitations of natural mineral reduction capabilities, achieving highly efficient and selective reduction of nitrate to ammonium under alkaline conditions with a pH ≥ 6.0 (nitrate removal rate up to 99.8%, ammonium conversion rate up to 100%). This method requires no external energy source or precious metal catalyst and offers advantages such as simple operation, low processing cost, and significant economic and environmental benefits. Attached Figure Description

[0021] Figure 1 The graph shows the test results of the changes in nitrate ion content and ammonium ion content in pyrite-sodium nitrate solutions with different pyrite concentrations in Example 1.

[0022] Figure 2 The graph shows the test results of the changes in nitrate and ammonium ion content in oxidized pyrite-sodium nitrate solution after pyrite oxidation for different days in Example 2.

[0023] Figure 3 The graph shows the test results of the changes in nitrate and ammonium ion content in pyrite-sodium nitrate solution after 1 day of oxidation of pyrite at different pH values ​​in Example 3.

[0024] Figure 4 The graph shows the test results of the changes in nitrate and ammonium ion content in pyrite-sodium nitrate solutions at different pH values ​​after pyrite was oxidized for 2 days, as described in Example 3. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0026] This invention involves reacting pyrite, which has been acid-washed with deoxygenated hydrochloric acid, with Fe... 3+ Solution (Fe 3+ Oxidized pyrite is prepared by mixing and oxidizing pyrite with a concentration of 0.1 mol / L and a pH of 1-3. Then, under anaerobic conditions, the oxidized pyrite is mixed with an alkaline nitrate solution (alkaline sodium nitrate solution or alkaline potassium nitrate solution, nitrate concentration of 20 mg / L, pH of 6-10) and carried out a light-protected reaction to achieve the reduction of nitrate to produce ammonium.

[0027] Example 1

[0028] (1) Grind and sieve natural pyrite to obtain pyrite particles with a particle size of 200-300 mesh, and then use freshly prepared 0.1 mol / L deoxygenated hydrochloric acid solution (or similar solution). The pyrite was obtained by removing dissolved oxygen from hydrochloric acid solution with N2 for 20 min. It was then rinsed three times to remove oxides from the surface of natural pyrite, washed three times with deoxygenated water, and freeze-dried at -40 °C for 12 h. The acid-washed pyrite was then placed in a glove box (N2>99.999%, H2O<0.1 ppm, O2<0.1 ppm) for later use.

[0029] (2) At room temperature, the acid-washed pyrite was mixed with acidic FeCl3 solution and oxidized for 2 days in a glove box (the acidic FeCl3 solution contained Fe... 3+ The pyrite was prepared by adding hydrochloric acid dropwise to a FeCl3 solution at a concentration of 0.1 mol / L and a pH of 2.7. After acid washing, the ratio of pyrite to acidic FeCl3 solution was 10 g: 100 mL. The pyrite solid was then removed, washed three times with deoxygenated water, and freeze-dried at -40℃ for 12 h to obtain Fe. 3+ Pyrite oxidized for 2 days;

[0030] (3) Under anaerobic conditions, different masses of pyrite oxide were added to an alkaline sodium nitrate solution (prepared by adding sodium hydroxide dropwise to sodium nitrate solution) with an initial pH of 10.0 and a nitrate concentration of 20 mg / L, respectively, to prepare pyrite oxide-sodium nitrate solutions with pyrite concentrations of 2 g / L, 5 g / L, and 10 g / L. These solutions were then placed in a constant-temperature shaker at 25 ± 0.2 ℃ and 300 rpm for 48 h in the dark. Samples were taken periodically to detect the nitrate and ammonium ion content. The results are as follows: Figure 1 As shown.

[0031] The results showed that pyrite oxide concentrations of 2 g / L, 5 g / L, and 10 g / L had an effect on NO3- oxidization within 48 h. - The removal rates were 37%, 74.5%, and 100% respectively for NH4. + The conversion rates were 67%, 60%, and 85%, respectively.

[0032] Example 2

[0033] (1) Grind and sieve natural pyrite to obtain pyrite particles with a particle size of 200-300 mesh, and then use freshly prepared 0.1 mol / L deoxygenated hydrochloric acid solution (or similar solution). The pyrite was obtained by removing dissolved oxygen from hydrochloric acid solution with N2 for 20 min. It was then rinsed three times to remove oxides from the mineral surface. After washing three times with deoxygenated water, it was freeze-dried at -40 °C for 12 h. The resulting acid-washed pyrite was then placed in a glove box (N2 > 99.999%, H2O < 0.1 ppm, O2 < 0.1 ppm) for later use.

[0034] (2) At room temperature, the acid-washed pyrite was mixed with acidic FeCl3 solution and oxidized for 1, 2, 5, and 10 days in a glove box (the acidic FeCl3 solution contained Fe...). 3+ The pyrite was prepared by adding hydrochloric acid dropwise to FeCl3 solution at a concentration of 0.1 mol / L and pH value of 2.0. After acid washing, the ratio of pyrite to acidic FeCl3 solution was 10 g: 100 mL. The solid pyrite was taken out, washed three times with deoxygenated water, and then freeze-dried at -40 °C for 12 h to obtain pyrite oxidized for 1 day, 2 days, 5 days, and 10 days.

[0035] (3) Under anaerobic conditions, pyrite oxidized for 1 day, 2 days, 5 days, and 10 days was added to an alkaline sodium nitrate solution (prepared by adding sodium hydroxide dropwise to sodium nitrate solution) with an initial pH of 10.0 and a nitrate concentration of 20 mg / L, respectively, to prepare oxidized pyrite-sodium nitrate solutions with a pyrite concentration of 10 g / L but different oxidation days (i.e., pyrite-sodium nitrate solution oxidized for 1 day, pyrite-sodium nitrate solution oxidized for 2 days, pyrite-sodium nitrate solution oxidized for 5 days, and pyrite-sodium nitrate solution oxidized for 10 days). These solutions were then placed in a constant temperature shaker at 25 ± 0.2℃ and 300 rpm for 48 h, protected from light. Samples were taken periodically to detect the nitrate and ammonium ion content. The results are as follows: Figure 2 As shown.

[0036] The results showed that, except for pyrite oxidized for 1 day, 20 mg / L of NO3 could not be completely removed within 48 hours. - In addition (NO3) - The removal rate was 75.5% for NH4. + The conversion rate was 60% for the other three Fe groups. 3+ Oxidized pyrite on NO3 - The removal rate of NH4 was 100%. + The conversion rate was 80% for all of them.

[0037] Example 3

[0038] (1) Grind and sieve natural pyrite to obtain pyrite particles with a particle size of 200-300 mesh. Wash the natural pyrite three times with freshly prepared 0.1 mol / L deoxygenated hydrochloric acid solution (obtained by passing N2 through the solution for 20 min to remove dissolved oxygen) to remove oxides on the surface of the natural pyrite. Wash it three times with deoxygenated water and freeze-dry it at -40℃ for 12 h. Then place the acid-washed pyrite in a glove box (N2>99.999%, H2O<0.1 ppm, O2<0.1 ppm) for later use.

[0039] (2) At room temperature, the acid-washed pyrite was mixed with acidic FeCl3 solution in a glove box and oxidized for 1 and 2 days respectively (the acidic FeCl3 solution contained Fe... 3+ The pyrite solution, with a concentration of 0.1 mol / L and a pH of 2.5, is prepared by adding hydrochloric acid dropwise to a FeCl3 solution. After acid washing, the ratio of pyrite to acidic FeCl3 solution is 10 g: 100 mL. The solid pyrite is then removed, washed three times with deoxygenated water, and freeze-dried at -40°C for 12 h to obtain FeCl3. 3+ Pyrite and Fe oxidized for 1 day 3+ Pyrite oxidized for 2 days;

[0040] (3) Under anaerobic conditions, pyrite oxidized for 1 day was added to alkaline sodium nitrate solutions with initial pH values ​​of 6.0, 7.0, 8.0, 9.0, and 10.0, and nitrate concentrations of 20 mg / L, respectively (i.e., prepared by adding sodium hydroxide dropwise to sodium nitrate solution), to prepare oxidized pyrite-sodium nitrate solutions with pyrite oxidized for 1 day and pyrite concentrations of 10 g / L, but with different pH values; under anaerobic conditions, pyrite oxidized for 2 days was added to alkaline sodium nitrate solutions with initial pH values ​​of 6.0, 7.0, 8.0, 9.0, and 10.0, and nitrate concentrations of 20 mg / L, respectively (i.e., prepared by adding sodium hydroxide dropwise to sodium nitrate solution), to prepare oxidized pyrite-sodium nitrate solutions with pyrite oxidized for 2 days and pyrite concentrations of 10 g / L, but with different pH values. Each pyrite-sodium nitrate solution was placed in a constant temperature shaker at 25 ± 0.2 ℃ and 300 rpm for 48 h, protected from light. Nitrate and ammonium ion contents were measured periodically. The test results of pyrite-sodium nitrate solutions at different pH values ​​after 1 day of pyrite oxidation are shown below. Figure 3 As shown, the detection results of pyrite-sodium nitrate solution oxidized at different pH values ​​after 2 days of oxidation are as follows: Figure 4 As shown.

[0041] The results showed that at pH values ​​of 6.0 and 7.0, pyrite oxidized for 1 day and pyrite oxidized for 2 days had a greater effect on NO3. -While some removal effects were observed, the overall removal efficiency was poor; as the pH value rose to 8.0 and above, NO3... - The removal rate and conversion rate both increased significantly. Specifically, the removal rates of pyrite oxidized for 1 day were 12.5%, 50.6%, and 83.3% at pH values ​​of 8.0, 9.0, and 10.0, respectively, with corresponding NH4+ removal rates... + The conversion rates were 62.5%, 66.3%, and 73.0%, respectively; in contrast, the removal rates of pyrite oxidized for 2 days at pH values ​​of 8.0, 9.0, and 10.0 were 62.5%, 76.9%, and 99.8%, respectively, with corresponding NH4+ removal rates... + The conversion rates were 41.0%, 71.8%, and 87.5%, respectively.

[0042] In this invention, the method for detecting nitrate ion content (ultraviolet spectrophotometry) is as follows:

[0043] Take 1 mL of the reacted sample and place it in a 25 mL colorimetric tube. Add 1 mL of 1 mol / L hydrochloric acid solution and 0.1 mL of 0.8 wt% aminosulfonic acid solution. Dilute with water to the mark and let stand for 15 min. Measure the absorbance of nitrate at a wavelength of 220 nm. Calculate the content of nitrate ions based on the absorbance.

[0044] The method for detecting ammonium ion content (ultraviolet spectrophotometry) is as follows:

[0045] Take 1 mL of the reacted sample and place it in a 25 mL colorimetric tube. Add 1 mL of potassium sodium tartrate and 1 mL of Nessler's reagent, dilute with water to the mark, and let it react at room temperature for 15 min. Detect the absorbance at a wavelength of 420 nm and calculate the ammonium content based on the absorbance.

[0046] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method utilizing Fe 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, Includes the following steps: S1. Acid-washed pyrite and Fe 3+ The solution is mixed and oxidized to obtain oxidized pyrite; S2. Under anaerobic conditions, oxidized pyrite is mixed with an alkaline nitrate solution and reacted in the dark.

2. A method for utilizing Fe according to claim 1 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, Natural pyrite is ground, sieved, and then soaked in deoxygenated hydrochloric acid solution. It is then washed with deoxygenated water and freeze-dried to obtain acid-washed pyrite.

3. A method for utilizing Fe according to claim 2 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, The concentration of the deoxyhydrochloric acid solution is 0.1 mol / L.

4. A method for utilizing Fe according to claim 1 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, In step S1, Fe 3+ The solution is acidic Fe 3+ Solution, Fe 3+ The concentration was 0.1 mol / L, and the pH value was 1-3; after acid washing, pyrite and Fe... 3+ The volume ratio of the solution used is 10g:100mL.

5. A method for utilizing Fe according to claim 4 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, In step S1, Fe 3+ The solution is an acidic FeCl3 solution.

6. A method for utilizing Fe according to claim 1 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, In step S1, the oxidation time is 1 to 10 days.

7. A method for utilizing Fe according to claim 1 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, In step S2, the nitrate concentration of the alkaline nitrate solution is 20 mg / L and the pH value is 6-10.

8. A method for utilizing Fe according to claim 7 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, Alkaline nitrate solutions are either alkaline sodium nitrate solutions or alkaline potassium nitrate solutions.

9. A method for utilizing Fe according to claim 1 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, In step S2, oxidized pyrite is mixed with alkaline nitrate solution to form oxidized pyrite-nitrate solution, and the concentration of pyrite in the solution is 2~10 g / L.

10. A method for utilizing Fe according to claim 1 3+ The method for producing ammonium by reducing nitrate with oxidized modified pyrite is characterized by, In step S2, the reaction time in the dark is 24~48h.

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