Natural pyrite rich in sulfur vacancies as well as preparation method and application of natural pyrite

Abstract

The invention discloses natural pyrite rich in sulfur vacancies and a preparation method and application thereof, and belongs to the technical field of novel environment-friendly materials. The natural pyrite rich in sulfur vacancies is prepared by mixing and ball-milling trivalent iron salt and natural pyrite, wherein the molar ratio of Fe < 3 + > in the trivalent iron salt to the natural pyrite (based on FeS2) is (3-5): 100. When the obtained modified natural pyrite rich in sulfur vacancies is used for treating ClO2 <->-containing wastewater, ClO2 <-> can be efficiently converted into Cl <-> in a wide pH range, and no other chlorine species are generated; meanwhile, the obtained modified natural pyrite is high in stability, can be recycled for multiple times, is simple in preparation process and low in cost, and has important application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of environmentally friendly new materials, and particularly relates to natural pyrite rich in sulfur vacancies and a preparation method and application thereof. Background Art

[0002] Natural pyrite (FexSy) has attracted widespread attention not only in the field of geochemistry, but also in the environmental remediation of groundwater, industrial wastewater, domestic sewage and contaminated soil due to its abundant reserves, low cost and environmental friendliness. Of particular importance is that FexSy can spontaneously produce an acid effect in redox reactions, showing excellent pH adaptability. In addition, its surface Fe(II) and polysulfides show significant reduction activity and can be used as a reducing agent to reduce environmental pollutants. However, due to the presence of a passivation layer on the surface of natural pyrite, a small specific surface area and complex composition, it faces challenges in practical applications such as slow dissolution rate, insufficient surface reactivity, limited solid-liquid interface reaction rate and low electron transfer efficiency. Therefore, modifying natural pyrite to improve its reactivity has become a key research direction.

[0003] Surface vacancies, as a key structural defect in catalytic materials, significantly affect the electron distribution on the surface of the material. It constructs an electronically non-equilibrium surface on the catalyst, greatly promoting the electron transfer process between the metal sites inside the catalyst and the electron-rich pollutants, thus having an important impact on the reaction selectivity. In addition, the abundant local electrons around the vacancies can be used to activate hydrogen peroxide, persulfate, etc., and then generate active free radicals to achieve rapid redox and degradation of pollutants. There are many methods to construct catalyst surface vacancies, including solvothermal synthesis, high-temperature calcination, and vapor deposition. However, these techniques usually rely on a large amount of chemical solvents / reagents, and the operation process is relatively complicated. In contrast, mechanical ball milling has become an ideal choice for inducing the generation of surface defects and significantly improving the reaction activity of catalysts due to its many advantages such as simple operation, wide range of applications, and the ability to reduce particle size and destroy the oxide layer. The modified pyrite prepared by this method can show excellent reaction activity in a short time. However, with the extension of oxidation time, the increase in the number of secondary iron species (such as iron hydroxide, iron oxide, etc.) on the surface of pyrite will have a negative impact on the reaction activity. Therefore, in order to ensure the good reactivity of pyrite, the key is to regulate its surface structure and increase active sites to promote the generation of reducing species on its surface.

[0004] Chemical additives can be used to improve the surface structure and physicochemical properties of iron-based materials and natural minerals modified by mechanical ball milling. For example, oxalic acid-modified zero-valent iron prepared by mechanical ball milling showed the ability to efficiently activate persulfate (PDS) to degrade 2,4-dinitrotoluene, while phosphoric acid-modified kaolin can enhance its ability to degrade K + In addition, sulfuric acid-modified kaolin significantly improves its efficiency in removing As(V) and humic acid by generating highly active aluminum-based coagulants. Although exogenous small molecules can increase the active sites on the catalyst surface through chemical corrosion, additional chemical reactions may have an adverse effect on the activity of the modified catalyst. For example, the solubility of oxalic acid molecules may cause them to complex with divalent iron ions in the solution, thereby reducing their efficiency in activating persulfate. Similarly, incompletely ball-milled phosphoric acid may release H + , affecting the surface charge of kaolin, thus interfering with its exchange adsorption process, while excessive phosphoric acid addition will lead to phosphorus pollution. Excessive sulfuric acid modification will cause kaolin to agglomerate and may produce acidic waste liquid or acid mist. Summary of the invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a natural pyrite rich in sulfur vacancies and a preparation method and application thereof. The method has a simple preparation process and low cost. The obtained natural pyrite rich in sulfur vacancies has high stability and significantly improved redox performance, and can be effectively used for residual ClO2 in the process of domestic sewage disinfection. - removal.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: Provided is a method for preparing natural pyrite rich in sulfur vacancies, comprising the following steps: The trivalent iron salt and natural pyrite are mixed and ball-milled to obtain natural pyrite rich in sulfur vacancies; wherein: The Fe 3+ The molar ratio to natural pyrite (calculated as FeS2) is 3-5:100.

[0007] According to the above scheme, the trivalent iron salt is nitrate or sulfate.

[0008] According to the above scheme, the ball milling time is 2-6 h.

[0009] According to the above scheme, the ball milling speed is 500-600 r / min.

[0010] Provided is a natural pyrite rich in sulfur vacancies prepared by the preparation method.

[0011] Provide a method for treating a natural pyrite rich in sulfur vacancies containing ClO2 - Application in wastewater.

[0012] According to the above scheme, the application is: adding natural pyrite rich in sulfur vacancies to a ClO2 - The reaction time is 50-60 min, and the natural pyrite rich in sulfur vacancies and the wastewater solution are separated, and the ClO2 - Preferably, a magnet is used to separate the natural pyrite rich in sulfur vacancies from the wastewater solution.

[0013] According to the above scheme, containing ClO2 - The wastewater is domestic sewage.

[0014] According to the above scheme, the ClO2 - The pH value of the wastewater is 2.7-8.7; preferably 2.7-6.8.

[0015] According to the above scheme, the ClO2 - ClO2 in wastewater - The concentration is no greater than 0.15 mmol / L; preferably 0.04-0.10 mmol / L.

[0016] According to the above scheme, the natural sulfide iron rich in sulfur vacancies is in the presence of ClO2 - The concentration in wastewater is 1.0-3.0 g / L; preferably 2.0-3.0 g / L.

[0017] The present invention provides a method for preparing natural pyrite rich in sulfur vacancies, which adopts trivalent iron salt and pyrite to perform ball milling. During the ball milling process, the acidic effect of the iron salt continuously providing an acidic microenvironment can corrode the passivation layer on the surface of the pyrite, thereby promoting the active phase FeS x The formation of (Formula 1-7), FeS x It can promote electron transfer. x In the process, the original lattice S2 2- is destroyed, defects are generated on the surface of pyrite, resulting in the generation of sulfur vacancies, which helps to improve the efficiency of electron transfer, thereby enhancing the adsorption and redox properties of natural pyrite for specific molecules.

[0018]

[0019] The beneficial effects of the present invention are as follows: 1. The present invention provides a method for preparing natural pyrite rich in sulfur vacancies, wherein trivalent metal iron salts with specific acidity are used to assist ball milling. The acidic metal iron salts can continuously provide an acidic microenvironment during the ball milling process, which is conducive to more complex chemical reactions with matrix materials or other components, enhances the interaction between particles, more effectively regulates the surface structure of the catalyst, enhances the reconstruction of the natural mineral surface by ball milling, generates more active species, and improves its redox performance; the modified natural pyrite rich in sulfur vacancies is used to treat ClO2 - When treating wastewater, ClO2 can be achieved in a wide pH range - Efficient conversion to Cl - , and no other chlorine species are produced; at the same time, the modified natural pyrite has high stability and can be recycled many times, which has important application prospects.

[0020] 2. The raw material metal iron salt in the present invention is abundant in source, low in price, and has good biocompatibility. The performance improvement and modification of natural pyrite can be achieved by auxiliary ball milling. The preparation process is simple and the cost is low, which is conducive to industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0022] Figure 1 It is the XRD characterization diagram of the natural pyrite modified by ferric nitrate nonahydrate in Example 1 of the present invention and Comparative Examples 1-2.

[0023] Figure 2 It is the EPR characterization diagram of natural pyrite modified by ferric nitrate nonahydrate in Example 1 of the present invention and Comparative Examples 1-2.

[0024] Figure 3 The removal of ClO2 from natural pyrite modified by ferric nitrate nonahydrate in Examples 4-5 and Comparative Examples 6-7 of the present invention - 's effect diagram.

[0025] Figure 4 The conversion of ClO2 into natural pyrite modified by iron nitrate nonahydrate in Example 6 of the present invention - Cl - Efficiency diagram.

[0026] Figure 5 The present invention is to modify the natural pyrite with ferrous sulfate heptahydrate in comparative example 8 to remove ClO2 - 's effect diagram.

[0027] Figure 6 The removal of ClO2 from natural pyrite modified by hydrated iron sulfate in Example 7 and Comparative Example 9 of the present invention- 's effect diagram.

[0028] Figure 7 The present invention is to modify the natural pyrite with ferric nitrate nonahydrate to treat ClO2 with different initial pH in Examples 4 and 8 - 's effect diagram.

[0029] Figure 8 The present invention is to modify the natural pyrite with different doses of ferric nitrate nonahydrate to remove ClO2 in Example 4 and Example 9 - 's effect diagram.

[0030] Fig. 9 The figures are the effects of removing chlorite of different concentrations by pyrite modified with iron nitrate nonahydrate in Examples 4 and 10 of the present invention.

[0031] Fig.10 The modification of natural ferric sulfide by ferric nitrate nonahydrate in Example 11 of the present invention to remove ClO2 - Circulation effect diagram. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] Example 1 Provided is a method for preparing natural pyrite rich in sulfur vacancies, comprising the following steps: 2.0 g natural pyrite and 0.2082 g ferric nitrate nonahydrate (pyrite (in terms of FeS2) / ferric nitrate nonahydrate molar ratio of 1:0.03) were added to the ball mill, and the ball mill speed was set to 500 r / min. The forward and reverse rotations were alternately operated for 1 h each time, and the process was repeated once for a total of 4 h. After the ball milling was completed, the product was washed and dried to obtain the modified natural pyrite rich in sulfur vacancies, which was named FF3.

[0034] Example 2 The specific operation is the same as that of Implementation Example 1, except that the molar ratios of pyrite and ferric nitrate nonahydrate are 1:0.04 and 1:0.05, respectively, and the obtained modified natural pyrite is recorded as FF4 and FF5.

[0035] Comparative Example 1 The specific operation is the same as that of Implementation Example 1, except that ferric nitrate nonahydrate is not added (i.e., the molar ratio of pyrite to ferric nitrate nonahydrate is 1:0), and the resulting modified natural pyrite is recorded as FF0.

[0036] Comparative Example 2 The specific operation is the same as that of Example 1, except that the molar ratios of pyrite and ferric nitrate nonahydrate are 1:0.02 and 1:0.01, respectively, and the obtained modified natural pyrite is recorded as FF2 and FF1.

[0037] Comparative Example 3 The specific operation is the same as that of Example 1, except that the molar ratio of pyrite to ferric nitrate nonahydrate is 1:0.025, and the obtained modified natural pyrite is recorded as FF2.5.

[0038] The crystal structures and surface vacancies of the FF3, FF0, FF2 and FF1 samples prepared in Example 1, Comparative Example 1 and Comparative Example 2 were characterized by X-ray powder diffractometer and electron paramagnetic resonance spectrometer, as shown in Figure 1 and Figure 2 . Figure 1 It shows that the main components of the above samples are FeS2 and Fe3O4, and they also contain SiO2 and S. Figure 2 It shows that the signal peak at g = 2.0029 is the signal peak of sulfur vacancies. Fe(III)-assisted mechanical ball milling generates sulfur vacancies on the surface of natural pyrite. With the increase of Fe(III) addition, the signal peak intensity of sulfur vacancies also increases.

[0039] Comparative Example 4 The specific operation was the same as in Example 1, except that the molar ratios of pyrite and ferrous sulfate heptahydrate were 1:0.03, 1:0.02 and 1:0.01, respectively, and the obtained modified natural pyrite was recorded as FF-3%, FF-2% and FF-1%.

[0040] Example 3 The specific operation is the same as that of implementation case 1, except that the ball milling aid ferric nitrate nonahydrate is replaced by hydrated ferric sulfate. The Fe in natural pyrite and hydrated ferric sulfate is 3+ The molar ratio is 1:0.03, recorded as FF-3.

[0041] Comparative Example 5 The specific operation is the same as in Example 3, except that the Fe in natural pyrite and hydrated ferric sulfate 3+ The molar ratios are 1:0.02 and 1:0.01 respectively, denoted as FF-2 and FF-1.

[0042] Example 4 Provided is a use of the above-mentioned natural pyrite rich in sulfur vacancies in treating chlorite-containing wastewater, comprising the following steps: Weigh 0.20 g of the natural pyrite (FF3) rich in sulfur vacancies obtained in Example 1 and add it to a conical flask containing 100 mL of a 0.1 mmol / L NaClO2 solution with an initial pH of 6.7±0.1. Then, place the conical flask in an oscillator and conduct the experiment at room temperature for 50 min. After the experiment is completed, a magnet is used to separate the modified natural pyrite powder and the wastewater solution, thereby completing the ClO2 - removal.

[0043] Example 5 The specific operation is the same as that in Example 4, except that the natural pyrite rich in sulfur vacancies used is FF4 and FF5 obtained in Example 2.

[0044] Comparative Example 6 The specific operation is the same as that of Example 4, except that the natural pyrite rich in sulfur vacancies used is FF0, FF1 and FF2 obtained in Comparative Examples 1-2, and is compared with Example 4.

[0045] Comparative Example 7 The specific operation is the same as that of Example 4, except that the natural pyrite rich in sulfur vacancies used is FF2.5 obtained in Comparative Example 3, and is compared with Example 4.

[0046] In Example 4, Example 5, Comparative Example 6 and Comparative Example 7, the efficiency of natural pyrite rich in sulfur vacancies (FF0, FF1, FF2, FF2.5, FF3, FF4 and FF5) in removing chlorite is shown in Figure 3 , respectively 41.3%, 45.8%, 56.4%, 66.5%, 100.0%, 100.0%, 100.0%. This indicates that with the increase of Fe(III) loading, the defects on the surface of natural pyrite increase, which is conducive to the formation of ClO2 - Remove.

[0047] Example 6 The ClO2 in Example 4 and Comparative Example 6 was chromatographed by ion chromatography - Analysis of the transformation products: The specific operation is the same as that in Example 4. Every 10 minutes, 2.5 mL of sample is extracted from the conical flask with a syringe. The sample is filtered through a 0.22 µm Teflon filter and then injected into a 5 mL centrifuge tube. 0.2 g of ion exchange resin is added to 2.5 mL of the sample and mixed thoroughly. After the ion exchange resin is allowed to settle, it is filtered again using a 0.22 µm Teflon filter. After the filtration is completed, 2.0 mL of the sample is accurately transferred into an ion chromatograph tube with a volume of 6 mL. 4 mL of ultrapure water is transferred into the ion chromatograph tube. The bubbles in the ion chromatograph tube are exhausted. After the bubbles are exhausted, the prepared test sample tube is placed in the ion chromatograph automatic sampler for testing. Use an ion chromatograph to analyze ClO2 - The conversion products were analyzed, and the detection conditions were set as follows: the eluent was 4.5 mmol / L Na2CO3, 0.8 mmol / L NaHCO3, the eluent flow rate was 1 mL / min, the column oven temperature was 30℃, and the injection volume was 25 μL.

[0048] like Figure 4 As shown, modified natural pyrite removes ClO2 - During the process, ClO2 - Almost completely converted into stable Cl - , no other chlorine species are produced. The specific conversion rates are as follows: FF0, FF1, FF2 and FF3 convert ClO2 - Cl - The efficiencies are 100.0%, 92.9%, 96.4% and 99.1% respectively.

[0049] Comparative Example 8 The specific operation is the same as that of Example 4, except that the modified natural pyrite used is the modified natural pyrite (FF-3%, FF-2% and FF-1%) obtained in Comparative Example 4 and the pyrite (FF0) obtained in Comparative Example 1.

[0050] 0.20 g of modified pyrite powder FF-3%, FF-2%, FF-1% and FF0 were weighed and added into a conical flask containing 100 mL of NaClO2 solution with a concentration of 0.1 mmol / L and an initial pH of 6.7±0.1. The conical flask was then placed in an oscillator and reacted at room temperature for 50 min.

[0051] like Figure 5 As shown in the figure, the removal efficiency of chlorite by modified natural pyrite (FF0, FF-1%, FF-2%, FF-3%) is 41.3%, 49.8%, 55.5%, 65.7%, respectively, indicating that the removal effect of chlorite by pyrite modified by ferrous salt is worse than that by pyrite modified by ferric salt.

[0052] Example 7 The specific operation is the same as that of Example 4, except that the natural pyrite rich in sulfur vacancies used is FF-3 obtained in Example 3.

[0053] Comparative Example 9 The specific operation is the same as that of Example 7, except that the natural pyrite rich in sulfur vacancies used are FF0 of Comparative Example 1 and FF-2 and FF-1 obtained in Comparative Example 5, which are compared with Example 7.

[0054] like Figure 6 As shown in Example 7 and Comparative Example 9, the chlorite removal efficiencies of the modified natural pyrite (FF0, FF-1, FF-2 and FF-3) obtained in Example 3, Comparative Example 1 and Comparative Example 4 are 41.3%, 59.9%, 91.8% and 100.0%, respectively. This indicates that different iron salts can be used to modify natural pyrite to efficiently treat ClO2 - Wastewater.

[0055] Example 8 Treatment of ClO2 in chlorite-containing wastewater using natural pyrite rich in sulfur vacancies obtained in Example 1 - The specific operation is the same as in Example 4, except that ClO2 - The solution pH were 2.7, 4.7 and 8.7 respectively.

[0056] ClO2 of Example 4 and Example 8 - The comparison results of solution removal rate are as follows Figure 7 As shown in the figure, natural pyrite (FF3) rich in sulfur vacancies reacts with ClO2 at initial pH of 2.7, 4.7, 6.7, and 8.7 in 50 min. - The removal rates of the solutions were 100.0%, 100.0%, 100.0% and 63.1%, respectively. It can be seen that natural pyrite rich in sulfur vacancies has a wide pH range for removing chlorite. Under neutral or even alkaline conditions, the removal rate remains above 50.0%. Based on this, the modified natural pyrite prepared by this method can effectively treat ClO2 in a wide pH range. - Wastewater.

[0057] Example 9 Treatment of ClO2 in chlorite-containing wastewater using natural pyrite rich in sulfur vacancies obtained in Example 1 - The specific operation is the same as that of Example 4, except that 0.30 g, 0.25 g, 0.15 g and 0.10 g of the natural pyrite rich in sulfur vacancies obtained in Example 1 are weighed respectively.

[0058] ClO2 of Example 4 and Example 9 -The comparison results of solution removal rate are as follows Figure 8 As shown in the figure, different doses (3.0 g / L, 2.5 g / L, 2.0 g / L, 1.5 g / L and 1.0 g / L) of natural pyrite rich in sulfur vacancies have an effect on ClO2 - The removal efficiencies of pyrite and pyrite were 100.0%, 100.0%, 100.0%, 89.4% and 75.5% respectively. This result shows that natural pyrite rich in sulfur vacancies is very effective in removing ClO2 - The efficiency of ClO2 is significantly dependent on its addition dosage, and when the dosage is in the range of 1.5-3.0 g / L, - Efficient removal.

[0059] Example 10 Treatment of ClO2 in chlorite-containing wastewater using natural pyrite rich in sulfur vacancies obtained in Example 1 - The specific operation is the same as that of Example 4, except that the concentrations of the NaClO2 solutions are 0.15 mmol / L, 0.08 mmol / L, 0.06 mmol / L and 0.04 mmol / L, respectively.

[0060] ClO2 of Example 4 and Example 10 - The comparison results of solution removal rate are as follows Fig. 9 As shown in the figure, the addition of 2.0 g / L of natural pyrite rich in sulfur vacancies resulted in the removal rates of 81.0%, 100.0%, 100.0%, 100.0% and 100.0% for different concentrations of chlorite (0.15 mmol / L, 0.1 mmol / L, 0.08 mmol / L, 0.06 mmol / L and 0.04 mmol / L), respectively. This result shows that natural pyrite rich in sulfur vacancies has a good removal effect on different concentrations of chlorite.

[0061] Embodiment 11 Provided is a cyclic application of the above-mentioned natural pyrite rich in sulfur vacancies for efficiently removing chlorite, comprising the following steps: Weigh 0.2 g of natural pyrite (FF3) rich in sulfur vacancies obtained in Example 1 and add it to 100 mL of ClO2 with a concentration of 0.1 mmol / L. - Then, place the conical flask in an oscillator and perform the experiment at room temperature. After the reaction continues for 50 minutes, measure the ClO2 in the reaction solution. - concentration and calculated its removal rate.

[0062] The natural pyrite rich in sulfur vacancies was separated from the reaction solution by a magnet, and then the separated natural pyrite rich in sulfur vacancies was added with 100 mL of ClO2 with a concentration of 0.1 mmol / L. - solution, continue to evaluate its removal of ClO2 - Efficiency: The above steps are completed once, which is considered as one cycle.

[0063] The experimental results are as follows Fig.10 As shown, after 4 consecutive cycles, natural pyrite rich in sulfur vacancies removes ClO2 - The efficiency is still as high as 95.3%. This shows that the natural pyrite rich in sulfur vacancies prepared by this method has stable and efficient removal of ClO2 - active.

[0064] The above contents are only some embodiments of the present invention and do not constitute any form of limitation thereto. In addition, the scope of application of the present invention is not limited to the treatment of wastewater containing chlorite, but is also applicable to the treatment of other types of oxidative pollutants. Any equivalent changes, modifications or improvements made to the above embodiments / comparative examples based on the core technical principles of the present invention are deemed to fall within the scope of protection covered by the technical solution of the present invention.

Claims

1. A method for preparing natural pyrite rich in sulfur vacancies, characterized in that: The following steps are involved: The trivalent iron salt and natural pyrite are mixed and ball-milled to obtain natural pyrite rich in sulfur vacancies; wherein: Fe 3+ The molar ratio with natural pyrite is 3-5:

100.

2. The preparation method according to claim 1, characterized in that: The trivalent iron salt is nitrate or sulfate.

3. The preparation method according to claim 1, characterized in that: The ball milling time is 2-6 h.

4. The preparation method according to claim 1, characterized in that: The ball mill speed is 500-600 r / min.

5. A natural pyrite rich in sulfur vacancies prepared by the preparation method according to any one of claims 1 to 4.

6. A natural pyrite rich in sulfur vacancies according to claim 5 for treating ClO2 - Application in wastewater.

7. The use according to claim 6, characterized in that: The application is: adding natural pyrite rich in sulfur vacancies to a ClO2 - The reaction time is 50-60 min, and the natural pyrite rich in sulfur vacancies and the wastewater solution are separated, and the ClO2 - removal.

8. The use according to claim 6 or 7, characterized in that: The ClO2 - The pH value of the wastewater is 2.7-8.

7.

9. The use according to claim 6 or 7, characterized in that: The ClO2 - ClO2 in wastewater - Concentration no greater than 0.15 mmol / L.

10. The use according to claim 7, characterized in that: The natural sulfur iron rich in sulfur vacancies is contained in ClO2 - The concentration in wastewater is 1.0-3.0 g / L.

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