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

Abstract

The application discloses application of a pre-oxidized zero-valent iron / peroxyacetic acid system in removal of chlorophenol organic pollutants, and specifically comprises the following operation process: adding the peroxyacetic acid as an oxidant in an organic pollutant solution containing the chlorophenol, adjusting pH, and adding the pre-oxidized zero-valent iron to activate the peroxyacetic acid to generate hydroxyl radicals and high-valence iron to remove the chlorophenol organic pollutants; and the pre-oxidized zero-valent iron is prepared by mixing and grinding the zero-valent iron and peroxydisulfate. The pre-oxidized zero-valent iron is used for activating the peroxyacetic acid to remove the chlorophenol organic pollutants, and has higher reaction activity and longer service life compared with the heterogeneous zero-valent iron.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic pollutant treatment, and particularly relates to application of a pre-oxidized zero-valent iron / peroxyacetic acid system in removal of chlorophenol organic pollutants. BACKGROUND

[0002] Chlorophenol organic pollutants are a typical kind of chlorinated organic pollutants, which are widely used in pesticide, herbicide, pharmaceutical, bactericide and papermaking industries, are difficult to be biodegraded, can exist in the environment for a long time, and can adhere to cell membranes and accumulate in organisms due to lipophilicity. Many studies have shown that chlorophenol substances have potential risks of “carcinogenic, teratogenic and mutagenic”.

[0003] Zero-valent iron has been widely used in removal of various pollutants due to advantages of reduction activity, environmental friendliness and low cost. However, after the zero-valent iron is in contact with air and water, a natural iron (hydroxyl) oxide layer is formed on the surface of the zero-valent iron, which hinders the zero-valent iron from delivering electrons to pollutants, and finally leads to passivation of the surface of the zero-valent iron. The formation of the passivation layer greatly reduces the reaction activity of the zero-valent iron.

[0004] Peroxyacetic acid (PAA) is an organic peroxy acid, which is synthesized from 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 has poor oxidation effect on most refractory organic matters due to high selectivity. Meanwhile, the bond energy of the peroxy bond 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 difficulty of activating PAA can be indicated by the low energy of its empty molecular orbital, and the energy of the empty molecular orbital of PAA (-0.25 eV) is lower than that of H2O2 (0.57 eV), which indicates that the ability of PAA to accept electrons is stronger than that of H2O2, and then PAA is easier to be activated. Therefore, PAA-AOPs (Advanced Oxidation Processes) have attracted more and more attention from researchers. At present, there are many applications of iron-based catalysts for activating peroxyacetic acid, but the passivation of zero-valent iron in the activation of peroxyacetic acid has not been solved, and the zero-valent iron is only suitable for use in a slightly acidic environment, and a high content of zero-valent iron is usually required for the activation of peroxyacetic acid by zero-valent iron. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide application of a pre-oxidized zero-valent iron / peroxyacetic acid system in removal of chlorophenol organic pollutants.

[0006] The specific technical solutions are as follows:

[0007] An application of a pre-oxidized zero-valent iron / peracetic acid system in the removal of chlorophenol organic pollutants includes the following steps: adding peracetic acid as an oxidant to a solution containing chlorophenol organic pollutants, adjusting the pH, adding pre-oxidized zero-valent iron to activate the peracetic 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 persulfate.

[0008] Furthermore, pre-oxidized zero-valent iron is added to achieve a concentration of 0.02-0.05 g / L in the solution containing chlorophenols and other organic pollutants.

[0009] Further adjust the pH to 3-9.

[0010] Furthermore, the molar ratio of persulfate to zero-valent iron is 0.050-0.125.

[0011] The principle of this invention is as follows: both hydroxyl radicals and ferric iron (Fe3+) possess high oxidizing properties. Hydroxyl radicals can react rapidly with most organic compounds except for chlorinated alkanes. While ferric iron has a relatively weaker oxidizing ability compared to hydroxyl radicals, it can still oxidize most chlorophenol pollutants. The reaction system primarily utilizes the in-situ generated, highly oxidizing hydroxyl radicals and ferric iron for catalytic oxidation to oxidize chlorophenol pollutants. Therefore, pre-oxidation of zero-valent iron to activate peracetic acid produces two active substances: hydroxyl radicals and ferric iron. These two active substances can oxidize chlorophenol pollutants to remove them.

[0012] The beneficial effects of this invention are as follows:

[0013] This invention uses pre-oxidized zero-valent iron to activate peracetic acid to remove chlorophenolic organic pollutants. Compared with heterogeneous zero-valent iron, it has higher reactivity and a longer service life. Even after multiple uses, it still has reactivity to activate oxidants to remove chlorophenolic pollutants. Pre-oxidized zero-valent iron and peracetic acid can effectively produce active substances (hydroxyl groups and high-valent iron) that can remove chlorophenolic pollutants. Attached Figure Description

[0014] Figure 1 Graphs showing the effects of pre-oxidation of zero-valent iron and activation of peracetic acid to remove p-chlorophenol using different heterogeneous catalysts;

[0015] Figure 2 Graphs showing the effects of pre-oxidation of zero-valent iron and activation of peracetic acid with different homogeneous catalysts on the removal of p-chlorophenol;

[0016] Figure 3 The effect of pre-oxidation of zero-valent iron to activate different oxidants for the removal of p-chlorophenol is illustrated in the figure.

[0017] Figure 4 Graphs showing the effect of pre-oxidation of zero-valent iron to activate peracetic acid for the removal of p-chlorophenol at different pH values;

[0018] Figure 5 Graphs showing the effect of pre-oxidation of zero-valent iron to activate peracetic acid for the removal of p-chlorophenol under different water conditions;

[0019] Figure 6 A cyclic test diagram showing the effect of removing chlorophenol using pre-oxidized zero-valent iron activated peracetic acid;

[0020] Figure 7 For pH indicator experiments;

[0021] Figure 8 For pH test paper experiments;

[0022] Figure 9 For EPR testing;

[0023] Figure 10 For PMSO experiments;

[0024] Figure 11 PMSO experiment in the presence of TBA;

[0025] Figure 12 A schematic diagram showing the results of removing chlorophenol pollutants by activated peracetic acid under different PDS / Fe molar ratios. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] Example 1: Preparation of pre-oxidized zero-valent iron for experimental use

[0028] The synthesis of pre-oxidized zero-valent iron was carried out using a vibratory ball mill (PBMS-200), equipped with a stainless steel jar (200 mL) and zirconia balls of different sizes (75 balls with a diameter of 6 mm and 75 balls with a diameter of 8 mm). 2.656 g of PDS (persulfate) was mixed with 10 g of mZVI (zero-valent iron) solid (PDS to Fe molar ratio of 0.125), and the mixture was ground at a vibration frequency of 20.5 Hz in headspace for 6 hours. The resulting particles were pre-oxidized zero-valent iron, which were collected and stored in vacuum bags for further use.

[0029] Example 2: Removal of p-chlorophenol by peracetic acid after pre-oxidation of zero-valent iron and activation with different heterogeneous catalysts

[0030] The reaction vessel was set as a 500ml beaker, and 100ml of a 10mg / L p-chlorophenol solution was added as a contaminant. Five beakers were taken, and 0.002g of pre-oxidized zero-valent iron, 0.002g of ball-milled zero-valent iron, and 0.002g of commercial micron-sized zero-valent iron were added to three of them respectively; 0.001g and 0.005g of pre-oxidized zero-valent iron were added to the other two respectively. 20μmol of peracetic acid was added to each beaker as an oxidant to bring the peracetic acid concentration in the solution to 200μM. After adding both the catalyst and oxidant, a certain amount of water was taken at regular intervals to measure the p-chlorophenol content. The reaction time was one hour. Figure 1 As 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. Furthermore, even if the concentration of pre-oxidized zero-valent iron is reduced to 0.01 g / L, p-chlorophenol cannot be completely removed within 1 hour. Increasing the concentration of pre-oxidized zero-valent iron to 0.05 g / L will result in a higher removal rate.

[0031] Example 3: Removal of p-chlorophenol by pre-oxidation of zero-valent iron and activation of peracetic acid with different homogeneous catalysts

[0032] First, 0.001 g of pre-oxidized zero-valent iron was prepared into a saline solution using hydrochloric acid and water at a volume ratio of 1:9. This solution was then completely dissolved in a 50 ml cuvette. The iron content in the pre-oxidized zero-valent iron was then determined using the Linfellowen method. Calculations showed that the iron content in 0.02 g / L of pre-oxidized zero-valent iron is equivalent to the iron content in 0.069 g / L homogeneous FeSO4·7H2O. Simultaneously, assuming the iron content of the pre-oxidized zero-valent iron is 100%, this iron content is equivalent to the iron content in 0.099 g / L FeSO4·7H2O.

[0033] The reaction vessel was set as a 500ml beaker, and 100ml of a 10mg / L p-chlorophenol solution was added as a contaminant. Three beakers were taken, and 20μmol of peracetic acid was added to each beaker as an oxidant to bring the peracetic acid concentration in the solution to 200μM. Then, 0.02g / L of pre-oxidized zero-valent iron and 0.069g / L and 0.099g / L of FeSO4·7H2O were added to the three beakers respectively. A certain amount of water was taken at regular intervals to measure the p-chlorophenol content. The reaction time was one hour. Figure 2 As shown, although the initial rate of homogeneous divalent iron is very fast, it cannot achieve complete removal of chlorophenol.

[0034] Example 4: Removal of p-chlorophenol by pre-oxidation of zero-valent iron to activate different oxidants

[0035] The reaction vessel was set as a 500ml beaker, and 100ml of a 10 mg / L p-chlorophenol solution was added as a contaminant. Four beakers were prepared, and 0.02g / L of pre-oxidized zero-valent iron was added to each beaker. Then, 20μmol of peracetic acid, hydrogen peroxide, persulfate, and perdisulfate were added to the four beakers respectively, maintaining the oxidant concentration at 200μM. A certain amount of water was taken at regular intervals, and the p-chlorophenol content was measured. The reaction time was one hour. Figure 3 As shown, only peracetic acid has a high removal rate when used as an oxidant, while other different oxidants have poor oxidation effects.

[0036] Example 5: Effect of pH on the removal of chlorophenol by pre-oxidized zero-valent iron-activated peracetic acid

[0037] Take six beakers and add 100 ml of a 10 mg / L p-chlorophenol solution as a contaminant. Leave one beaker unadjusted for pH, and adjust the pH of the remaining beakers to 3, 5, 7, 9, and 11 respectively. Then, add 0.02 g / L of pre-oxidized zero-valent iron and 20 μmol of peracetic acid to each beaker to initiate the reaction. Take water samples at regular intervals and measure the p-chlorophenol content. 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 weakly alkaline conditions.

[0038] Example 6: Removal of chlorophenol compounds from different water bodies by pre-oxidation of zero-valent iron-activated peracetic acid

[0039] The actual water used was tap water and water from a local lake. Simulated wastewater was prepared by mixing four beakers, adding different solutions of p-chlorophenol prepared with different amounts of water, followed by the sequential addition of 0.02 g / L of pre-oxidized zero-valent iron and 20 μmol of peracetic acid. Water samples were taken at regular intervals to measure the p-chlorophenol content. The reaction time was one hour. Figure 5 As shown, the reaction between pre-oxidized zero-valent iron and peracetic acid can still maintain high activity under different water conditions.

[0040] Example 7: Stability of pre-oxidized zero-valent iron

[0041] Take a beaker and add 100 ml of a 10 mg / L p-chlorophenol solution as the contaminant. Then, add 0.02 g / L of pre-oxidized zero-valent iron and 20 μmol of peracetic acid sequentially to initiate the reaction. Take a water sample at regular intervals and measure the p-chlorophenol content. The reaction time is one hour. After one hour, add peracetic acid and p-chlorophenol again to maintain the p-chlorophenol concentration at 10 mg / L and the peracetic acid concentration at 200 μM. Repeat the reaction for another hour, taking a water sample at regular intervals and measuring the p-chlorophenol content. Repeat this process eight times. Figure 6 As shown, the removal rate of p-chlorophenol can still be achieved after eight cycles, while when other heterogeneous catalysts are used directly (Example 2), the reaction cannot achieve 100% removal in the first cycle.

[0042] Example 8: Observing pH Changes in Solution Using a pH Colorimetric Reagent

[0043] Take two beakers and add pre-oxidized ferric iron to them. Prepare two different colorimetric reagents: bromocresol green-methyl red (5.0~5.2) and methyl red (4.4~6.2). The left beaker contains bromocresol green-methyl red, and the right beaker contains methyl red. Use a large magnet to attract the pre-oxidized ferric iron to the beaker wall, ensuring it remains on the beaker wall. Observe the color of the solution after 2 minutes, 1 hour, and 2 hours. Figure 7 As shown, over time, the color of the left beaker gradually changes from blue to purple, and the purple color deepens until the entire beaker is purple; simultaneously, the color of the right beaker gradually changes from orange to red, and the red color deepens until the entire beaker is red. This phenomenon proves that pre-oxidation of zero-valent iron gradually releases ferrous iron over time, eventually causing the solution to gradually become acidic. Therefore, it can be concluded that pre-oxidation of zero-valent iron itself causes the solution to gradually become acidic, lowering the pH to provide better reaction conditions, as the reaction of peracetic acid is more likely to occur under acidic conditions.

[0044] Example 9: Observing pH changes in a solution using pH test paper

[0045] Take a beaker, add pre-oxidized zero-valent iron to the bottom of the beaker, and fix it to the bottom using a magnet. At 5 minutes, 30 minutes, 60 minutes, and 120 minutes, if... Figure 8 A water sample was taken from the indicated location and measured using pH test paper. It can be concluded that the pH value at the top of the solution did not change over time and remained neutral, while the pH at the bottom of the solution gradually became acidic over time.

[0046] Example 10: EPR Detection

[0047] EPR capture experiments utilize various capture agents to capture different free radicals, simultaneously forming capture agent-radical complexes. These complexes are detectable by the instrument and exhibit peak shapes with specific area ratios. In this EPR capture experiment, 5,5-dimethyl-1-pyrrolino-N-oxide (DMPO) was used as the capture agent. This agent can capture hydroxyl radicals and form DMPO−OH. DMPO−OH is detectable by the instrument, forming peaks with a 1:2:2:1 ratio. The presence of a 1:2:2:1 peak in the EPR chromatogram indicates the formation of hydroxyl radicals in the system (OH + DMPO → DMPO−OH). Figure 9 As shown, there are obvious DMPO−OH peaks at 10 minutes and 30 minutes, proving that a large number of hydroxyl radicals are generated in the system.

[0048] Example 11: Methylphenyl sulfoxide experiment

[0049] Methylphenyl sulfoxide (PMSO) can be oxidized to methylphenyl sulfone (PMSO2) by ferric iron (Fe). PMSO2 cannot be further oxidized by ferric iron, but it can be oxidized by hydroxyl radicals. Therefore, the presence or absence of ferric iron or hydroxyl radicals can be determined by whether PMSO2 is generated and the conversion rate of PMSO to PMSO2. If PMSO2 is generated and the conversion rate is high, it indicates the generation of ferric iron. However, if PMSO decreases again over time and the conversion rate decreases, it indicates that the generated ferric iron is oxidized again by hydroxyl radicals. Take a beaker and add 1 mmol / L PMSO as the substrate. Add 0.02 g / L of pre-oxidized zero-valent iron and 20 μmol peracetic acid as the oxidant to bring the peracetic acid concentration in the solution to 200 μM. After adding both the catalyst and the oxidant, take a certain amount of water sample at regular intervals and measure the content of p-chlorophenol. The reaction time is one hour. Figure 10 As shown, initially, PMSO gradually decreases while PMSO2 is gradually generated, with a conversion rate close to 100%. As time progresses, PMSO2 ceases to be generated, but PMSO continues to decrease, resulting in a lower conversion rate. This demonstrates that a large amount of high-valent iron is generated in the initial stage of the reaction, thus PMSO is converted to PMSO2 with a high conversion rate. As the reaction proceeds, high-valent iron ceases to be generated, but hydroxyl radicals continue to be produced, causing PMSO to continuously decrease while PMSO2 no longer increases, leading to a gradual decrease in the conversion rate. Therefore, it can be concluded that pre-oxidation of zero-valent iron will produce high-valent iron.

[0050] Example 12: Methylphenyl sulfoxide experiment in the presence of tert-butanol

[0051] tert-Butanol (TBA) is a known hydroxyl radical quencher, which can be used to quench hydroxyl radicals during reactions, making the effect of hydroxyl groups negligible in the reaction system. Example 11 was repeated in the presence of TBA.Figure 11 As shown, initially PMSO gradually decreases while PMSO2 is gradually generated, with a conversion rate close to 100%. As time progresses, PMSO2 ceases to be generated, and PMSO no longer decreases. This demonstrates that a large amount of high-valent iron is generated in the initial stage of the reaction, thus PMSO is converted to PMSO2 with a high conversion rate. As the reaction continues, high-valent iron is no longer generated, and the generated hydroxyl radicals are quenched by TBA. Therefore, the contents of PMSO and PMSO2 no longer change, and the conversion rate remains close to 100%.

[0052] Example 13: Removal of chlorophenol contaminants by activated peracetic acid under different PDS / Fe molar ratios

[0053] Example 1 was repeated, with five different PDS / Fe ratios of 0.025, 0.050, 0.075, 0.100, and 0.150, including the pre-oxidized zero-valent iron obtained in Example 1. This resulted in six different materials with six different PDS / Fe ratios.

[0054] The reaction vessel was set as a 500ml beaker, and 100ml of a 10mg / L p-chlorophenol solution was added as a contaminant. Six beakers were prepared, and 20μmol peracetic acid was added to each beaker as an oxidant to achieve a peracetic acid concentration of 200μM. Then, 0.02g / L of the obtained material was added to each of the six beakers at different proportions. Water samples were taken at regular intervals, and the p-chlorophenol content was measured. The reaction time was one hour. The final result was as follows: Figure 12 As shown, when the PDS / Fe ratio is low, the material cannot effectively activate peracetic acid due to insufficient pre-oxidation; when the PDS / Fe ratio reaches 0.150, the catalyst content is insufficient due to the small Fe ratio, thus peracetic acid cannot be effectively activated either.

Claims

1. Use of a pre-oxidized zero-valent iron / peroxyacetic acid system for the removal of chlorophenolic organic pollutants, characterized in that, The method comprises the following steps: adding peracetic acid as an oxidant in a solution of organic pollutants containing chlorophenols, adjusting pH, adding pre-oxidized zero-valent iron to activate peracetic 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 peroxodisulfate and zero-valent iron; the pre-oxidized zero-valent iron is added to make its concentration in the solution of organic pollutants containing chlorophenols be 0.02-0.05 g / L.

2. Use of a pre-oxidized zero-valent iron / peroxyacetic acid system for the removal of chlorophenol organic pollutants according to claim 1, characterized in that, The pH is adjusted to 3-9.

3. Use of a pre-oxidized zero-valent iron / peroxyacetic acid system for the removal of chlorophenol organic pollutants according to claim 1, characterized in that, The molar ratio of peroxodisulfate to zero-valent iron is 0.050-0.125.

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