Application of pre-oxidized zero-valent iron / peracetic acid system in removal of chlorophenol organic pollutants

Abstract

The invention discloses an application of a pre-oxidized zero-valent iron / peracetic acid system in removal of chlorophenol organic pollutants, and the specific operation process is as follows: adding peracetic acid as an oxidizing agent into an organic pollutant solution containing chlorophenols, adjusting the pH value, filtering, washing, and drying to obtain the pre-oxidized zero-valent iron / peracetic acid system. Pre-oxidized zero-valent iron is added to activate peroxyacetic acid to generate hydroxyl radicals and high-valent iron to remove chlorophenol organic pollutants; the pre-oxidized zero-valent iron is prepared by mixing and grinding zero-valent iron and peroxydisulfate. The pre-oxidized zero-valent iron is used for activating peracetic acid to remove chlorophenol organic pollutants, and compared with heterogeneous zero-valent iron, the pre-oxidized zero-valent iron has higher reaction activity and longer service life.

Description

Technical Field

[0001] The invention belongs to the technical field of organic pollutant treatment, and particularly relates to an application of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants. Background Art

[0002] Chlorophenols are a typical class of chlorinated organic pollutants, widely used in pesticides, herbicides, pharmaceuticals, fungicides and papermaking industries. They are difficult to biodegrade and can exist in the environment for a long time. Because of their lipophilicity, they can adhere to cell membranes and accumulate in organisms. Many studies have shown that chlorophenols have the potential risk of "carcinogenicity, teratogenicity and mutagenicity".

[0003] Zero-valent iron has been widely used to remove various pollutants due to its reducing activity, environmental friendliness and low cost. However, when zero-valent iron comes into contact with air and water, natural iron (hydroxide) oxides will be produced on its surface. The formation of this layer of iron (hydroxide) oxides hinders zero-valent iron from transferring electrons to pollutants, ultimately leading to the passivation of the zero-valent iron surface. The formation of the passivation layer will greatly reduce the reactivity of zero-valent iron.

[0004] Peracetic acid (PAA) is an organic peroxyacid synthesized by the reaction of acetic acid and hydrogen peroxide under the catalysis of concentrated sulfuric acid. PAA can directly oxidize some organic pollutants, such as tetracycline antibiotics and pyrazolone drugs, but due to its high selectivity, it has poor oxidation effect on most refractory organic matter. At the same time, the peroxide bond energy of PAA is 159 kJ / mol, which is lower than that of H2O2 (213 kJ / mol) and PMS (317 kJ / mol), which means that PAA can be activated with less energy. In addition, the ease of activating PAA can be represented by its lower empty molecular orbital energy, and the empty molecular orbital energy of PAA (-0.25 eV) is lower than that of H2O2 (0.57 eV), which indicates that PAA has a stronger ability to accept electrons than H2O2, and is then easier to activate. Therefore, peracetic acid advanced oxidation processes (PAA-AOPs) have received increasing attention from researchers. Currently, there are many applications of using iron-based catalysts to activate peracetic acid, but the phenomenon of passivation of zero-valent iron in the activated peracetic acid has not been solved, and it is only suitable for use in an acidic pH environment. At the same time, using zero-valent iron to activate peracetic acid usually requires a higher content of zero-valent iron. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide an application of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants.

[0006] The specific technical solutions are as follows: The invention discloses an application of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants, comprising the following steps: adding peracetic acid as an oxidant to a solution of organic pollutants containing chlorophenols, adjusting the pH, adding pre-oxidized zero-valent iron to activate the peracetic acid to generate hydroxyl radicals and high-valent iron to remove the chlorophenol organic pollutants; the pre-oxidized zero-valent iron is prepared by mixing and grinding zero-valent iron and peroxydisulfate.

[0007] Furthermore, pre-oxidized zero-valent iron is added so that its concentration in the organic pollutant solution containing chlorophenols is 0.02-0.05 g / L.

[0008] Further, the pH is adjusted to 3-9.

[0009] Furthermore, the molar ratio of peroxodisulfate to zero-valent iron is 0.050-0.125.

[0010] The principle of the present invention is that both hydroxyl radicals and high-valent iron have high oxidation performance, and hydroxyl radicals can react quickly with most organic compounds except chlorinated alkanes. High-valent iron has weaker oxidation ability than hydroxyl radicals, but can still oxidize most chlorophenol pollutants. The reaction system mainly utilizes hydroxyl radicals with strong oxidizing properties generated in situ and high-valent iron for catalytic oxidation to oxidize chlorophenol pollutants. Therefore, pre-oxidation zero-valent iron activates peracetic acid to produce two active substances, hydroxyl radicals and high-valent iron. These two active substances can oxidize chlorophenol pollutants to remove pollutants.

[0011] The beneficial effects of the present invention are: The present invention uses pre-oxidized zero-valent iron to activate peracetic acid to remove chlorophenol organic pollutants. Compared with heterogeneous zero-valent iron, it has higher reactivity and longer service life. After multiple uses, it still has reactivity and can activate oxidants to remove chlorophenol pollutants. Pre-oxidized zero-valent iron and peracetic acid can effectively produce active substances (hydroxyl and high-valent iron) that can remove chlorophenol pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a diagram showing the effect of removing p-chlorophenol by pre-oxidizing zero-valent iron and activating peracetic acid with different heterogeneous catalysts; Figure 2 This is a diagram showing the effect of removing p-chlorophenol by pre-oxidizing zero-valent iron and activating peracetic acid with different homogeneous catalysts; Figure 3 This is a diagram showing the effect of pre-oxidized zero-valent iron activating different oxidants to remove p-chlorophenol; Figure 4 This is a graph showing the effect of zero-valent iron pre-oxidation at different pH levels to activate peracetic acid to remove p-chlorophenol; Figure 5 This is a diagram showing the effect of pre-oxidized zero-valent iron activating peracetic acid in removing p-chlorophenol under different water conditions; Figure 6 This is a cycle test effect diagram of removing chlorophenol by activating peracetic acid with pre-oxidized zero-valent iron; Figure 7 For pH indicator experiment; Figure 8 For pH paper test; Fig. 9 For EPR testing; Fig.10 For PMSO experiments; Fig.11 For PMSO experiments in the presence of TBA; Fig.12 Schematic diagram of the results of removing chlorophenol pollutants by activating peracetic acid under different PDS / Fe molar ratios. DETAILED DESCRIPTION

[0013] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited thereto.

[0014] Example 1: Preparation of pre-oxidized zero-valent iron for experiment The synthesis of pre-oxidized zero-valent iron was performed using a vibrating ball mill (PBMS-200) equipped with a stainless steel tank (200 mL) and zirconia balls of different sizes (75 balls of 6 mm diameter and 75 balls of 8 mm diameter). 2.656 g of PDS (peroxydisulfate) was mixed with 10 g of mZVI (zero-valent iron) solid (PDS to Fe molar ratio of 0.125) and ground at a vibration frequency of 20.5 Hz in air headspace. The running time was 6 h. The particles obtained were pre-oxidized zero-valent iron, which were collected and stored in vacuum bags for further use.

[0015] Example 2: Removal of p-chlorophenol by pre-oxidized zero-valent iron and activation of peracetic acid with different heterogeneous catalysts The reaction container is set as a 500ml beaker, and 100ml of 10mg / L p-chlorophenol solution is added as a pollutant. Take five beakers, add 0.002g of pre-oxidized zero-valent iron, 0.002g of zero-valent iron that has been ball-milled, and 0.002g of commercial micron zero-valent iron to three of them respectively; add 0.001g and 0.005g of pre-oxidized zero-valent iron to the other two, respectively. Add 20μmol of peracetic acid as an oxidant to each beaker to make the peracetic acid concentration in the solution reach 200μM. After the catalyst and oxidant are added, a certain amount of water samples are taken at regular intervals and the p-chlorophenol content is measured. The reaction time is one hour. Figure 1As shown, 0.02 g / L and 0.05 g / L of pre-oxidized zero-valent iron can completely remove p-chlorophenol within 1 hour. The two heterogeneous iron species cannot completely remove p-chlorophenol. At the same time, if the pre-oxidized zero-valent iron concentration is reduced to 0.01 g / L, p-chlorophenol cannot be completely removed within 1 hour. If the pre-oxidized zero-valent iron concentration is increased to 0.05 g / L, a higher rate will be obtained.

[0016] Example 3: Removal of p-chlorophenol by pre-oxidized zero-valent iron and activation of peracetic acid with different homogeneous catalysts First, 0.001g of pre-oxidized zero-valent iron was taken, and a saline solution was prepared with hydrochloric acid and water in a volume ratio of 1:9, and completely dissolved in a 50ml cuvette. Then, the iron content in the pre-oxidized zero-valent iron was measured using the Linfiloline method, and it was calculated that the iron content in the pre-oxidized zero-valent iron of 0.02g / L was equivalent to the iron content in the homogeneous FeSO4·7H2O of 0.069g / L. At the same time, it was assumed that the iron content of the pre-oxidized zero-valent iron was 100%, and the iron content at this time was equivalent to the iron content in FeSO4·7H2O of 0.099 g / L.

[0017] The reaction vessel is set as a 500ml beaker, and 100ml of 10mg / L p-chlorophenol solution is added as a pollutant. Take three beakers, and add 20μmol peracetic acid as an oxidant to each beaker to make the peracetic acid concentration in the solution reach 200μM. Then add 0.02g / L of pre-oxidized zero-valent iron and 0.069g / L and 0.099 g / L of FeSO4·7H2O to the three beakers respectively. Take a certain amount of water sample at regular intervals and measure the content of p-chlorophenol in it. The reaction time is one hour. Figure 2 As shown, although the initial rate of homogeneous divalent iron is very fast, it cannot achieve complete removal of p-chlorophenol.

[0018] Example 4: Pre-oxidation of zero-valent iron to activate different oxidants to remove p-chlorophenol The reaction vessel is set as a 500ml beaker, and 100ml of 10 mg / L p-chlorophenol solution is added as a pollutant. Take four beakers and add 0.02g / L of pre-oxidized zero-valent iron. Then add 20μmol of peracetic acid, hydrogen peroxide, peroxymonosulfate and peroxydisulfate to the four beakers respectively to keep the oxidant concentration at 200μM. Take a certain amount of water sample at regular intervals and measure the content of p-chlorophenol in it. The reaction time is one hour. Figure 3 As shown, only peracetic acid as an oxidant has a high removal rate, while the oxidation effects of other different oxidants are poor.

[0019] Example 5: Effect of pH on the removal of p-chlorophenol by pre-oxidation with zero-valent iron and activation of peracetic acid Take six beakers, add 100ml of 10mg / L p-chlorophenol solution as the pollutant, do not adjust the pH of one beaker, and adjust the pH of the remaining beakers to 3, 5, 7, 9, and 11 respectively. Then, add 0.02g / L of pre-oxidized zero-valent iron and 20μmol of peracetic acid to each beaker for reaction. Take a certain amount of water sample at regular intervals and measure the p-chlorophenol content in it. The reaction time is one hour. Figure 4 It can be seen that although the removal efficiency of pre-oxidized zero-valent iron is not good under strong alkaline conditions, it still has a high removal rate under acidic, neutral and weak alkaline conditions.

[0020] Example 6: Pre-oxidation of zero-valent iron to activate peracetic acid to remove chlorophenol compounds in different water bodies The actual water used was tap water and lake water from a certain place. The simulated wastewater was prepared by ourselves. Four beakers were added with p-chlorophenol solutions prepared with different waters. Then, 0.02g / L of pre-oxidized zero-valent iron and 20μmol of peracetic acid were added in turn for reaction. A certain amount of water samples were taken at regular intervals and the p-chlorophenol content was measured. The reaction lasted for one hour. Figure 5 As shown, the reaction of pre-oxidized zero-valent iron with peracetic acid can still maintain a high activity under different water conditions.

[0021] Example 7: Stability of pre-oxidized zero-valent iron Take a beaker, add 100ml of 10mg / L p-chlorophenol solution as the pollutant, and then add 0.02g / L of pre-oxidized zero-valent iron and 20μmol of peracetic acid in turn for reaction. Take a certain amount of water sample at regular intervals and measure the content of p-chlorophenol therein, and the reaction time is one hour. After the one-hour reaction is completed, re-add peracetic acid and p-chlorophenol to keep the p-chlorophenol in the solution at 10mg / L and the peracetic acid at 200μM, react again for one hour, and take a certain amount of water sample at regular intervals and measure the content of p-chlorophenol therein. Repeat eight times. Figure 6 As shown, after eight cycles, 100% removal rate of p-chlorophenol can still be achieved, while when other heterogeneous catalysts are directly used (Example 2), the reaction cannot achieve 100% removal only in the first cycle.

[0022] Example 8: pH color developer to observe the change of solution pH Take two beakers, add pre-oxidized zero-valent iron into them, and prepare two different color developers, bromocresol green-methyl red (5.0~5.2) and methyl red (4.4~6.2), respectively. The left beaker is bromocresol green-methyl red, and the right beaker is methyl red. Use a large magnet to suck the pre-oxidized zero-valent iron to the wall of the beaker to ensure that the pre-oxidized zero-valent iron remains on the wall of the beaker. Observe the color of the solution at 2 minutes, 1 hour, and 2 hours. Figure 7As shown, it can be seen that as time changes, the color of the left beaker gradually changes from blue to purple, and the purple gradually deepens until the entire beaker is purple; at the same time, the color of the right beaker gradually changes from orange to red, and the red gradually deepens until the entire beaker is red. This phenomenon proves that pre-oxidized zero-valent iron can gradually release divalent iron over time, eventually causing the solution to gradually become acidic. From this, it can be concluded that pre-oxidized zero-valent iron itself will gradually make the solution acidic, lowering the pH of the solution to provide better reaction conditions, because the reaction of peracetic acid is more likely to occur under acidic conditions.

[0023] Example 9: pH test paper to observe the pH change of the solution Take a beaker, add pre-oxidized zero-valent iron to the bottom of the beaker, and fix it to the bottom with a magnet. Figure 8 Water samples were taken at the indicated locations and measured with pH test paper. It can be concluded that at the top of the solution, the pH value did not change over time and remained neutral, while at the bottom of the solution, it gradually became acidic over time.

[0024] Example 10: EPR detection The EPR capture experiment uses various capture agents to capture different free radicals and form capture agent-free radical complexes. The complexes can be detected by the instrument and show peaks with specific area ratios. This EPR capture experiment uses 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a capture agent, which can capture hydroxyl radicals and form DMPO-OH. DMPO-OH can be detected by the instrument and form a peak of 1:2:2:1. If a peak of 1:2:2:1 appears in the EPR graph, it means that hydroxyl radicals are generated in the system (OH+DMPO→DMPO-OH). Fig. 9 As shown in the figure, there are obvious DMPO−OH peaks at 10 minutes and 30 minutes, proving that more hydroxyl radicals are generated in the system.

[0025] Example 11: Methyl phenyl sulfoxide experiment Methyl phenyl sulfoxide (PMSO) can be oxidized by high-valent iron (Fe) to methyl phenyl sulfone (PMSO2). PMSO2 cannot be further oxidized by high-valent iron, but can be oxidized by hydroxyl radicals. Therefore, whether high-valent iron or hydroxyl radicals are generated can be judged based on whether PMSO2 is generated and the conversion rate of PMSO to PMSO2. If PMSO2 is generated and the conversion rate is high, it means that high-valent iron is generated. However, if PMSO decreases again over time and the conversion rate becomes lower, it means that the generated high-valent iron is oxidized by hydroxyl radicals again. Take a beaker and add 1mmol / L PMSO as a substrate. Add 0.02g / L of pre-oxidized zero-valent iron and 20μmol peracetic acid as an oxidant to make the peracetic acid concentration in the solution reach 200μM. After the catalyst and oxidant are added, a certain amount of water samples are taken at regular intervals and the content of para-chlorophenol is measured. The reaction time is one hour. Fig.10 As shown, at first, PMSO gradually decreases while PMSO2 is gradually generated, and the conversion rate is close to 100%. As time goes on, PMSO2 is no longer generated, but PMSO still gradually decreases, and the conversion rate decreases. This proves that a large amount of high-valent iron is generated in the initial stage of the reaction, so PMSO is converted into PMSO2, and the conversion rate is high; as the reaction proceeds, high-valent iron is no longer generated, but hydroxyl radicals continue to be generated, so PMSO continues to decrease and PMSO2 no longer increases, and the conversion rate gradually decreases. From this, it can be concluded that pre-oxidation of zero-valent iron will produce high-valent iron.

[0026] Example 12: Methyl phenyl sulfoxide experiment in the presence of tert-butyl alcohol Tert-butyl alcohol (TBA) is a known quencher of hydroxyl radicals and can be used to quench hydroxyl radicals during the reaction, so that the influence of hydroxyl radicals in the reaction system can be ignored. Example 11 was repeated in the presence of TBA. Fig.11 As shown, at first, PMSO gradually decreased while PMSO2 was gradually generated, and the conversion rate was close to 100%. As time went on, PMSO2 was no longer generated, and PMSO no longer decreased. This proves that a large amount of high-valent iron was generated in the initial stage of the reaction, so PMSO was converted into PMSO2 with a high conversion rate. As the reaction time progressed, high-valent iron was no longer generated, and the hydroxyl radicals generated were quenched by TBA, so the content of PMSO and PMSO2 no longer changed, and the conversion rate remained close to 100%.

[0027] Example 13 Removal of chlorophenol pollutants by activation of peracetic acid at different PDS / Fe molar ratios Example 1 was repeated, with five different ratios of PDS / Fe being 0.025, 0.050, 0.075, 0.100, and 0.150, including the pre-oxidized zero-valent iron obtained in Example 1. Finally, six different materials at six PDS / Fe ratios were obtained.

[0028] The reaction vessel is set as a 500ml beaker, and 100ml of 10mg / L p-chlorophenol solution is added as a pollutant. Take six beakers, and add 20μmol peracetic acid as an oxidant to each beaker to make the peracetic acid concentration in the solution reach 200μM. Then add 0.02g / L of the obtained materials in different proportions to the six beakers respectively. Take a certain amount of water sample at regular intervals and measure the content of p-chlorophenol therein. The reaction time is one hour. Finally, as shown in the figure below: Fig.12 When PDS / Fe is low, the material cannot activate peracetic acid well due to insufficient pre-oxidation; when PDS / Fe reaches 0.150, the Fe ratio is too small and the catalyst content is insufficient, so peracetic acid cannot be activated well.

Claims

1. Application of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants, characterized in that: The method comprises the following steps: adding peracetic acid as an oxidant to a solution of organic pollutants containing chlorophenols, adjusting the pH, adding pre-oxidized zero-valent iron to activate the peracetic acid to generate hydroxyl free radicals and high-valent iron to remove the chlorophenol organic pollutants; The pre-oxidized zero-valent iron is prepared by mixing and grinding zero-valent iron and peroxydisulfate.

2. The use of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants as claimed in claim 1, characterized in that: Pre-oxidized zero-valent iron is added so that its concentration in the organic pollutant solution containing chlorophenols is 0.02-0.05 g / L.

3. The use of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants as claimed in claim 1, characterized in that: Adjust pH to 3-9.

4. The use of a pre-oxidized zero-valent iron / peracetic acid system in removing chlorophenol organic pollutants as claimed in claim 1, characterized in that: The molar ratio of peroxydisulfate to zero-valent iron is 0.050-0.125.

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