Method for treating organic-inorganic composite pollutants by electrically assisted ferric phosphide activated persulfate

Abstract

The application discloses a method for treating organic-inorganic composite pollutants by electrically-assisted phosphatized iron activated persulfate, and the electrically-assisted phosphatized iron is used to generate SO4 ·‑ ·2-6 by synergistically activating persulfate (PDS), so as to strengthen the synchronous removal effect of organic-inorganic composite pollutants in oxidized wastewater. In addition, the added substances (for example, PDS and Fe3P) will not produce additional treated pollutants in water, and the cost of the Fe-based catalyst is lower than that of other catalysts.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, and particularly relates to a method for treating organic-inorganic composite pollutants by using electrically assisted phosphatized iron activated persulfate. BACKGROUND

[0002] Activated persulfate (APS) is a kind of advanced oxidation technology, which can generate highly reactive sulfate radicals (SO4 ·- ) by activating persulfate through thermal activation, photoactivation, electrochemical activation and the use of transition metals, so as to effectively degrade organic pollutants in water and soil. However, some activation technologies require precise control of reaction conditions such as temperature, pH value and light intensity or expensive equipment, or produce some residues during the treatment process due to limited treatment efficiency, which need further treatment.

[0003] In order to improve the efficiency and application range of APS technology, researchers have developed various improved technologies. Using nanomaterials such as nano-iron, nano-titanium dioxide, etc. as catalysts can improve the activation efficiency of persulfate. The development of composite catalysts, such as the combination of biochar and montmorillonite, can enhance the electronic interaction and thus improve the activation efficiency of persulfate. By optimizing the structure of the catalyst, such as preparing crown-shaped MnCeOx hollow nanospheres, the exposure of active sites can be increased, and the specific surface area of the catalyst can be improved, thus enhancing the catalytic performance. In addition, in the APS process, in addition to the free radical pathway, non-radical pathways (such as active oxygen species generated by electron transfer) have also been found to contribute to the degradation of pollutants in some cases.

[0004] Activated persulfate technology is a powerful water treatment technology, and its efficiency and application range have been significantly improved through continuous research and improvement. With the development of new materials and new methods, APS technology is expected to play a greater role in future environmental governance. However, in order to achieve wider application, challenges such as cost, operation complexity and free radical control still need to be addressed. Further improvement of the efficiency and environmental compatibility of APS technology can provide more effective solutions for pollution control. SUMMARY

[0005] The purpose of the present application is to provide a method for treating organic-inorganic composite pollutants by using electrically assisted phosphatized iron activated persulfate, which can generate SO4 ·- and strengthen the simultaneous removal effect of organic-inorganic composite pollutants in oxidized wastewater.

[0006] The present application is realized by the following technical solutions:

[0007] The application discloses a method for treating organic-inorganic composite pollutants by using electrically-aided phosphatized iron activated persulfate, and the method comprises the following steps: adding persulfate (PDS) and Fe3P into wastewater containing organic-inorganic composite pollutants of phenol and inorganic As (III), and then effectively removing the phenol and inorganic As (III) in the water by applying a small amount of electric current.

[0008] The specific steps of applying a small amount of electric current are as follows: using a DSA electrode as an anode and a carbon felt as a cathode, under the action of an electric field, the transition metal elements Fe and P in the Fe3P are activated to enhance the activation effect of PDS, and SO4 ·- and · OH with high oxidizability are efficiently generated, so that the composite pollutants (such as phenol and inorganic As (III)) in the water can be rapidly oxidized.

[0009] The content of the persulfate (PDS) in the system is 1-8 mM, the content of the Fe3P is 0.025-0.20 g / L, the current density is 0.9-14.4 mA / cm 2 , and the initial pH of the solution is 3-9.

[0010] Preferably, in the system, the content of the persulfate (PDS) is 4 mM-8 mM, the content of the Fe3P is 0.1 g / L-0.2 g / L, the current density is 7.2 mA / cm 2 -14.4 mA / cm 2 , and the initial pH of the solution is 3-5.

[0011] Most preferably, in the system, the content of the persulfate (PDS) is 4 mM, the content of the Fe3P is 0.1 g / L, the current density is 7.2 mA / cm 2 , and the initial pH of the solution is 3, and the removal rate of total organic carbon (TOC) in the solution within 6 h can be up to 92.32%. The low content of As (III) in the water can be rapidly oxidized at a lower current, and the Fe3P in the solution can form a substance with a Fe-As bond, thereby also having the function of adsorbing part of As (V) (an oxidation product of As (III)) in the water body.

[0012] The application has the following beneficial effects:

[0013] 1) The application realizes the coupling of the iron, phosphorus elements and electric field in the Fe3P to activate the PDS, so that the PDS is changed into SO4 ·- and ·OH, thus effectively oxidizing toxic organic compounds (e.g. phenol) and inorganic salts (e.g. As(III)) in wastewater, rapidly oxidizing low content of As(III) salts in water to less toxic As(V), and Fe3P has a certain adsorption effect on the oxidation product of inorganic salts of Fe3P in water (i.e. As(V)). Under the optimal conditions, the removal rate of phenol can reach 100% in 1 hour, and the oxidation rate of As(III) can reach 100% in 2 minutes.

[0014] 2) The added substances (e.g. PDS and Fe3P) do not produce additional pollutants in water for treatment, and the cost of Fe-based catalyst is lower than that of other catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the schematic diagram of the electrolytic device for activating persulfate to oxidize wastewater containing phenol and arsenic in water in Example 2 of the present application.

[0016] Figure 2 is the removal effect diagram of phenol in Example 3 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0017] The following is a further description of the present application, but not a limitation of the present application.

[0018] Example 1: Synthesis of iron phosphide

[0019] 0.01 mol of iron nitrate nonahydrate (Fe(NO3)2·9H2O) was added to a mixed solution containing 11 mL of n-butanol, 1.32 mL of concentrated nitric acid and 1.16 g of triblock copolymer P123 (molecular weight = 5800), and stirred for 30 minutes under magnetic stirring to completely dissolve the iron nitrate. The mixed solution was transferred to an oven at 80°C and heated for 3 hours. After taking out, it was washed with ethanol for 4 times and separated by centrifugation, and the obtained solid product was dried in a vacuum oven at 40°C overnight. The obtained material was placed in a muffle furnace, heated to 150°C at a heating rate of 5°C / min, and calcined at this temperature for 12 hours. Then cooled to room temperature to obtain iron oxide.

[0020] 20 mg of the above prepared iron oxide and sodium hypophosphite were mixed according to the mass ratio of 2:3 and ground into fine powder. Placed in a porcelain square canister and transferred to a tube furnace with continuous N2inlet, and the tube furnace program was set to heat to 320°C at a heating rate of 2°C / min. Calcined at 320°C for 2 hours, and then cooled to room temperature to obtain Fe3P material. The product was ground, dispersed in 500 mL of ultrapure water, ultrasonicated for 30 minutes, filtered, washed, and dried in a vacuum oven at 60°C for 12 hours to obtain the purified Fe3P material.

[0021] Example 2:

[0022] Initial pollutant concentration in wastewater: phenol 30 mg / L, As 3+ 5 mg / L.

[0023] The organic-inorganic complex pollutants containing phenol and inorganic As(III) were added with PDS and Fe3P prepared in Example 1. The DSA electrode was used as anode and carbon felt as cathode. Under the effect of electric field, the transition metal elements Fe and P in Fe3P were activated to enhance the activation of PDS, and SO4 ·- and · OH were generated, so that the phenol and inorganic As(III) in water could be quickly oxidized.

[0024] In the process of designing the experiment to treat simulated wastewater, when the current density was 1.8 mA / cm 2 , the dosage of Fe3P was 0.05 g / L, and the content of PDS was 2 mM, the first variable investigated was the initial pH value of the solution system. Under the conditions of initial pH values of 3, 5, 7, and 9, it was finally found that the optimal range of the initial pH value of the solution was 3-5, and the optimal condition was 3. Under the optimal condition, the removal rate of phenol in the simulated water sample reached 99.44% within 120 min, As(III) with a concentration of 5 mg / L could be completely oxidized within 2 min, 23.28% of As(V) in the water body could be removed, and the TOC removal rate could reach 83.96% within 6 h.

[0025] Subsequently, under the conditions of an initial pH value of 3, a dosage of Fe3P of 0.05 g / L, and a content of PDS of 2 mM, the current density to the wastewater was investigated. From the minimum current density of 0.9 mA / cm 2 to the maximum current density of 14.4 mA / cm 2 (the current density variables were 0.9 mA / cm 2 , 1.8 mA / cm 2 , 3.6 mA / cm 2 , 7.2 mA / cm 2 , and 14.4 mA / cm 2 ), according to the experiment, the optimal current density was 7.2 mA / cm 2 -14.4 mA / cm 2 , and the optimal current density was 7.2 mA / cm 2 . When the current density was 7.2 mA / cm 2 , As(III) in the water was completely removed within 2 min, 47.87% of As(V) in the water sample was removed, phenol in the water could be completely removed within 90 min of reaction time, and the TOC removal rate could reach 90.23% within 6 h.

[0026] After the initial pH of the solution is 3, the current density is 7.2 mA / cm 2 , the dosage of ferrophosphorus is 0.05 g / L, and the concentration of PDS added in the wastewater is investigated from 1 mM to 8 mM (the PDS concentration variables are 1 mM, 2 mM, 4 mM and 8 mM), it is obtained from the experiment that the concentration of PDS is preferably 4 mM-8 mM, the optimal condition is that when the concentration of PDS is 4 mM, As (III) in the water can be rapidly oxidized in 5 min, 53.96% of As (V) in the water can be removed, the removal rate of phenol is obviously increased, and the phenol in the water can be completely removed in 60 min. The TOC removal rate can reach 91.64% in 6 h.

[0027] Finally, the initial pH of the solution is 3, the current density is 7.2 mA / cm 2 , the concentration of PDS is 2 mM, and the content of Fe3P added in the wastewater is investigated, the content of Fe3P is expanded from 0.025 g / L to 0.20 g / L (the content of Fe3P variables is 0.025 g / L, 0.05 g / L, 0.10 g / L and 0.20 g / L), according to the experiment, the content of Fe3P added in the wastewater is preferably 0.1 g / L-0.2 g / L, the optimal is 0.1 g / L, when the content of ferrophosphorus added in the water reaches 0.1 g / L, As (III) in the water sample can be completely removed in 2 min, 82.85% of As (V) can be removed in 2 h, the phenol in the water can also be completely removed in 40 min, and the TOC removal rate can reach 92.32% in 6 h. Therefore, it is most suitable to add 0.1 g / L of ferrophosphorus.

[0028] It is obtained from the above that the optimal condition is that the concentration of PDS is 4 mM, the content of Fe3P is 0.1 g / L, the current density is 7.2 mA / cm 2 , the initial pH of the solution is 3, the TOC removal efficiency in the solution is the highest, up to 92.32%, and the effects of removing As (III) and As (V) in the water are the best.

[0029] The experimental results show that:

[0030] 1) The optimal technical scheme for oxidizing As (III) and phenol in the water is that the content of PDS is 4 mM, the amount of Fe3P in the system is 0.10 g / L, the current density is 7.2 mA / cm 2 , the initial pH of the solution is 3, and the removal of pollutants is that As (III) can be completely removed in 2 min, and the phenol in the water can be completely removed in 90 min.

[0031] 2) The optimal conditions for adsorbing As(Ⅴ) in water are: PDS content of 2 mM, Fe3P content of 0.20 g / L, current density of 1.8 mA / cm 2 , and initial pH of solution of 7.0. The As(Ⅴ) in water can be completely adsorbed within 120 min.

[0032] Example 3

[0033] The initial contaminant concentration in the wastewater is: phenol of 30 mg / L, and As 3+ of 5 mg / L.

[0034] The wastewater containing organic-inorganic combined pollutants of phenol and inorganic As(Ⅲ) is added with PDS and Fe3P prepared in Example 1, so that the PDS content is 4 mM, the Fe3P content is 0.40 g / L, the DSA electrode is used as anode, and the carbon felt is used as cathode, and the current density is 7.4 mA / cm 2 . The removal rate of phenol can reach 100% within one hour.

[0035] Comparative Example 1

[0036] According to Reference Example 3, the difference is that the phenol is removed by using only the phosphide-activated PDS without using electric field. The removal rate of phenol is only 21% within one hour.

[0037] Comparative Example 2

[0038] According to Reference Example 3, the difference is that the phenol is removed by using only the electric field-activated PDS without adding the Fe3P prepared in Example 1. The removal rate of phenol can reach 55% within one hour.

[0039] It can be known from the comparison between Example 3 and Comparative Examples 1-2 that the phenol is removed by using the phosphide-activated PDS under the assistance of electric field in Example 3. The removal rate of phenol can reach 100% within one hour, which is higher than the sum of the removal rates of Comparative Examples 1 and 2. It is proved that the phosphide and electric field have coupling effect in activating PDS.

Claims

1. A method for treating organic-inorganic composite pollutants by electrically assisted ferric phosphide activated persulfate, characterized in that, The method comprises the following steps: adding PDS and Fe3P to wastewater containing organic-inorganic composite pollutants of phenol and inorganic arsenic, and effectively removing phenol and inorganic arsenic in water by applying a current with a current density of 0.9-14.4 mA / cm 2 .

2. The method of claim 1, wherein, The specific steps of applying current are as follows: using DSA electrode as anode, carbon felt as cathode, and under the action of electric field, the organic-inorganic composite pollutants in water are rapidly oxidized.

3. The method of claim 1, wherein, In the system, the content of peroxodisulfate PDS is 1-8 mM, the content of Fe3P is 0.025-0.20 g / L, and the initial pH of the solution is 3-9.

4. The method of claim 3, wherein, In the system, the content of peroxodisulfate PDS is 4 mM-8 mM.

5. The method of claim 3, wherein, In the system, the content of Fe3P is 0.1 g / L-0.2 g / L.

6. The method of claim 3, wherein, In the system, the current density is 7.2 mA / cm 2 -14.4 mA / cm 2 .

7. The method of claim 3, wherein, In the system, the initial pH of the solution is 3-5.

8. The method of claim 3, wherein, In the system, the content of peroxodisulfate PDS is 4 mM, the content of Fe3P is 0.1 g / L, the current density is 7.2 mA / cm 2 , and the initial pH of the solution is 3.

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