CN112174288A

CN112174288A - Method for degrading organic pollutants by iron salt-zero-valent iron concerted catalysis

Info

Publication number: CN112174288A
Application number: CN202011071401.8A
Authority: CN
Inventors: 殷旭东; 毛玉凤; 王儒珍; 刘志森; 朱越平; 刘正辉; 李长刚; 叶芳芳; 张帅
Original assignee: Guangdong University of Petrochemical Technology
Current assignee: Guangdong University of Petrochemical Technology
Priority date: 2020-10-09
Filing date: 2020-10-09
Publication date: 2021-01-05

Abstract

The invention discloses a method for degrading organic pollutants by iron salt-zero-valent iron concerted catalytic degradation, which comprises the following steps of 1) adding iron powder, water-soluble iron salt and persulfate into organic wastewater for ultrasonic treatment; 2) and after the reaction is completed, obtaining the treated organic wastewater. In some embodiments of the invention, the iron salt and the iron powder have good synergistic effect, the reaction efficiency is higher compared with that of the method of simply adding the iron powder, the organic pollutant degradation effect is better under both acidic and alkaline conditions, the application range is wider, meanwhile, a large amount of iron mud is not generated, and the method is particularly suitable for treating printing and dyeing wastewater.

Description

Method for degrading organic pollutants by iron salt-zero-valent iron concerted catalysis

Technical Field

The invention relates to the field of environmental protection, in particular to a treatment process of organic wastewater, and particularly relates to a method for degrading organic pollutants by iron salt-zero-valent iron through synergetic catalytic degradation.

Background

Environmental pollution and treatment are inevitable challenges and problems in the development process of the world at present, the environmental pollution causes severe influence and harm to animals and plants in the ecological environment, and the unpredictable influence on the ecological environment is caused by the improper treatment of dye wastewater. Dyes are often used in the textile, paper, food, pharmaceutical and other industries. Dyes have a complex structure, many are variants, the sources of which are wide, most of the dyes are made of carcinogens, and if discharged into water without treatment, studies have shown that some dyes accumulate continuously through the food chain. Although possibly at a low concentration, it can still adversely affect the human body if it enters the body through the food chain. For this reason, the dye waste water must be properly treated. The treatment method of the dye wastewater can be classified into a physical method, a chemical method, a physicochemical method, a biochemical method, acoustics, radiation and the like. These methods have various advantages and disadvantages, and have various characteristics.

The dye wastewater is complex, variable, stubborn and difficult to realize the rapid, economic and efficient treatment of the dye wastewater by a single method. In recent years, some advanced oxidation technologies have been receiving wide attention from researchers, and there is much room for development and application thereof to the treatment of dye wastewater. The art of advanced oxidation was initially OH-based and has been widely used in the treatment of dye wastewater, and at present, SO₄ ^-The more students are concerned and studied. In comparison with OH (E)_k=2.7 V)，SO₄ ^-The redox potential of the catalyst is 2.5V-3.1V, compared with the acid environment, the redox potential of the catalyst is higher under the alkaline or neutral condition,SO₄ ^-the survival time is longer than that of OH and better contact with the target pollutant is achieved. In the usual case, SO₄ ^-It may be generated from Peroxymonosulfate (PMS) or Persulfate (PS), and may be activated by heat, light, transition metal, ultrasonic waves, alkali, or the like.

Common PS comprises sodium persulfate, potassium persulfate and ammonium persulfate, and ammonium persulfate is not stable in an aqueous solution and is not suitable for treating actual wastewater or theoretical research. Potassium persulfate and sodium persulfate can exist stably in water solution. Potassium persulfate is a highly efficient oxidant that activates and produces HO and SO₄ ^-Has great application prospect in treating dye wastewater.

For activating persulfates to produce SO₄ ^-The modes of (1) include ultraviolet activation, thermal activation, ultrasonic activation, alkali activation, transition metal ion activation, and the like. The common method for activating the persulfate easily converts the treatment condition into acidity, which is not beneficial to direct discharge, and the alkali activation technology can effectively avoid the transition of the treatment environment into the acidity condition, but the reaction condition at the beginning is alkaline, and the equipment is easy to corrode under the alkaline condition, so the application of the equipment is limited, and the alkali activation technology is usually used in alkaline wastewater. The repair research of degrading chlorobenzene by using alkali-heat activated persulfate is researched by the Zhuger et al, and experiments show that the removal rate of chlorobenzene can reach more than 99.9% after 5 hours of reaction by using the method for activating persulfate by using alkali heat, the pH value of the solution after the reaction meets the limit of the pH value in the standard (the pH value is between 6 and 9), and the result shows that when the pH value is 10.28, the reaction constant of alkali-heat activation is (0.069 min)^-1) Higher than single alkali activation (0.061 min)^-1). The related research of alkali-activated persulfate is less at home, and the method is developed to a certain extent at foreign countries. M.A Lominchar et al have studied the repairing and treating effect of diesel oil polluted soil after alkali activation PS treatment, the soil contains TPH, aliphatic compounds and aromatic compounds, the aromatic compounds are mainly naphthalene, phenanthrene and the like, the experiment is carried out in an intermittent operation mode by using NaOH as an activating agent, and the experiment shows that after the operation is carried out for a period of timeAnd under the condition that the concentrations of PS and an activating agent are high, TPH is completely converted and removed, wherein the conversion rate of the aromatic compounds is faster than that of the aliphatic compounds, and meanwhile, the products after reaction are detected, and the intermediate products of the aromatic compounds are not detected, so that the alkali activation technology has a good repairing effect on the polluted soil.

Transition metal activated persulfate systems are one of the most common methods for treating organic wastewater. Transition metals such as Fe, Co, Cu and the like have wide general sources, simple manufacturing method and lower cost, can show powerful catalytic activity at normal temperature and normal pressure, and particularly, iron material is widely adopted to activate persulfate or peroxymonosulfuric acid oxygen, Fe²⁺The metal ions can well activate persulfate or peroxymonosulfate under the acidic condition by means of electron transfer to generate sulfate radicals to react with target pollutants, however, the single transition metal Fe activated persulfate or peroxymonosulfate oxygen has certain problems and disadvantages, such as generation of iron sludge, and the optimal pH value range of solution reaction is in the acidic condition, so further research and solution are needed. The Sungzhujiao and the like take Sulfamethoxazole (SMZ) as target pollutants, the effect and the principle of Hydroxylamine (HA) on activating persulfate by oxides containing different types of transition metal elements are researched, the influence of different influence factors such as hydroxylamine concentration, transition metal oxide concentration, persulfate concentration and SMZ concentration on the SMZ degradation rate is simultaneously researched, and the result shows that the Hydroxylamine (HA) can enhance the effect of degrading the Sulfamethoxazole (SMZ) by different systems, and Co can enhance the effect of degrading the Sulfamethoxazole (SMZ) by using different systems under respective optimal conditions (the SMZ concentration is 9.4 mg/L), wherein Co and Co are in a concentration range of 9.4 mg/L)₂O₃HA, PDS, Co consumed by the/HA/PDS system for degrading SMZ₂O₃In an amount significantly less than alpha-Fe₂O₃Amounts of the/HA/PDS system and the CuO/HA/PDS system.

The existing persulfate activation method has relatively high cost. The method has very practical significance in reducing the activation cost while ensuring the activity effect.

Disclosure of Invention

The invention aims to overcome at least one defect of the prior art and provide a method for effectively activating persulfate and degrading organic pollutants by using iron salt-zero-valent iron as a synergetic catalyst.

The technical scheme adopted by the invention is as follows:

a method for degrading organic wastewater by using iron salt-zero-valent iron as a synergetic catalyst comprises the following steps:

1) adding iron powder, water-soluble ferric salt and persulfate into the organic wastewater, and carrying out ultrasonic treatment, wherein the water-soluble ferric salt is at least one of ferrous salt or ferric salt;

2) and after the reaction is completed, obtaining the treated organic wastewater.

In some examples, the initial concentration of the iron salt in the organic wastewater is 0.5-2 mM Fe calculated on Fe³⁺：Fe² ⁺In a molar ratio of 1: (1-2).

In some examples, the water soluble iron salts are ferric sulfate and ferrous sulfate.

In some examples, the iron powder is added in an amount of not less than 0.1 mg/L, preferably 0.1 to 0.5 mg/L.

In some examples, the iron powder has a particle size of no greater than 5mm, preferably 0.1 to 3 mm.

In some examples, the persulfate is initially added to the organic wastewater at a concentration of 0.5 to 2.0 mM.

In some examples, the pH of the organic wastewater is adjusted to 3 to 9, preferably 5 to 7.

In some examples, the sonication time is not less than 10 min.

In some examples, the sonication time is 10-30 min.

In some examples, the organic wastewater is printing wastewater.

In some examples, the printing and dyeing wastewater has a pH of 5 to 7.

The invention has the beneficial effects that:

in some embodiments of the invention, the iron salt and the iron powder have good synergistic effect, the reaction efficiency is higher compared with that of the method of simply adding the iron powder, the organic pollutant degradation effect is better under both acidic and alkaline conditions, the application range is wider, meanwhile, a large amount of iron mud is not generated, and the method is particularly suitable for treating printing and dyeing wastewater.

In some embodiments of the present invention, iron powder may be more fully utilized.

Some embodiments of the present invention significantly improve the reaction efficiency by using ferric and ferrous salts in conjunction with iron powder to catalyze the reaction.

Drawings

FIG. 1 is a standard curve for an aqueous solution of RhB;

FIG. 2 is US/Fe⁰/Fe²⁺/Fe³⁺/PS、US/Fe⁰/Fe²⁺/PS、US/Fe⁰/Fe³⁺/PS、US/Fe⁰/PS、US/ Fe⁰、US/ PS、Fe⁰/Fe²⁺/Fe³⁺/PS、Fe⁰/Fe²⁺/PS、Fe³⁺/PS、Fe²⁺/PS、Fe⁰Comparison of/PS (under different systems);

FIG. 3 is the effect of initial pH on the degradation rate of RhB;

FIG. 4 is the effect of initial RhB concentration on RhB degradation rate;

FIG. 5 is a graph of the effect of initial potassium persulfate concentration on the rate of degradation of RhB;

FIG. 6 is the effect of zero valent iron addition on RhB degradation rate;

FIG. 7 is the effect of zero valent iron particle size on RhB degradation rate;

FIG. 8 is the effect of iron salt addition on RhB degradation rate;

FIG. 9 is the effect of molar ratio of iron salts on the degradation rate of RhB;

FIG. 10 is the effect of ultrasonic power on RhB degradation rate;

FIG. 11 is NaHCO₃Influence on RhB degradation rate;

FIG. 12 is the effect of NaCl on the degradation rate of RhB;

FIG. 13 is KNO₃Influence on RhB degradation rate;

FIG. 14 is the effect of free radical inhibitors on the degradation of RhB;

FIG. 15 is an analysis of mineralization rate during the reaction.

Detailed Description

The inventor previously passed through US/Fe⁰Research on treatment of rhodamine B by a PS system shows that the RhB degradation rate can reach 98.5% after 18min of reaction, wherein the initial concentration of RhB is 40 mg/L, the initial pH value of a solution is 5, the using amount of potassium persulfate is 1.5 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and the ultrasonic power is 420W. Common anion pair US/Fe in water⁰The influence of degrading rhodamine B by a PS system has inhibition effect on the system, and HCO is sequentially used from large to small in inhibition effect₃ ^->Cl^->NO₃ ^-. Meanwhile, in order to increase the reaction rate, iron powder with a relatively small particle size needs to be used, but the addition amount is often difficult to accurately control, which causes a certain waste. Using US/Fe⁰the/PS system, although having a better positive effect, has the potential for further improvement.

In some examples, the initial concentration of the iron salt in the organic wastewater is 0.5-2 mM Fe calculated on Fe³⁺：Fe² ⁺In a molar ratio of 1: (1-2). Experimental data show that the iron salt with the concentration and the proportion has better synergistic catalytic effect.

In some examples, the water soluble iron salts are ferric sulfate and ferrous sulfate. Experimental data show that the sulfate has a better synergistic catalytic effect.

In some examples, the iron powder has a particle size of no greater than 5mm, preferably 0.1 to 3 mm. In some embodiments of the present invention, the requirement on the particle size of the iron powder is looser, the iron powder with larger particles can be used, which is beneficial to saving cost, and is also beneficial to recycling redundant iron powder or secondarily utilizing the iron powder, so that the utilization rate of the iron powder is more sufficient.

In some examples, the pH of the organic wastewater is adjusted to 3 to 9, preferably 5 to 7. When the initial pH of the organic wastewater is within the defined range, no further pH adjustment is necessary.

In some examples, the sonication time is not less than 10 min.

In some examples, the sonication time is 10-30 min.

The specific ultrasonic treatment time can be adjusted correspondingly according to the specific organic pollutant degradation condition. The ultrasonic power may also be similarly adjusted.

In some examples, the organic wastewater is printing wastewater.

In some examples, the printing and dyeing wastewater has a pH of 5 to 7.

The technical scheme of the invention is further explained by combining experiments.

Experimental methods

Preparation of test reagent

Deionized water was used as the experimental process water, except as specified.

(1) Preparing a rhodamine B stock solution: accurately weighing 1 g of rhodamine B by using an electronic balance, dissolving the rhodamine B in a small beaker with a proper amount of water, fully stirring the rhodamine B by using a glass rod, and then fixing the volume in a volumetric flask of 1000 mL to prepare a RhB stock solution of 1 g/L, and storing the RhB stock solution in a dark place.

(2) Preparing a rhodamine B standard solution: and (3) taking 40 mL of rhodamine B stock solution, fixing the volume in a 1000 mL volumetric flask, and preparing into 40 mg/L RhB standard experimental solution which is used as the original solution.

(3) Preparing a sodium nitrite solution: accurately weighing 3.45 g of sodium nitrite by an electronic balance, adding a proper amount of water to dissolve the sodium nitrite, continuously stirring the sodium nitrite by a glass rod, and then placing the sodium nitrite into a 50 mL volumetric flaskConstant volume is prepared into 1 mol/L NaNO₂And (3) solution.

(4) Respectively weighing K required by the experimental process by using an electronic balance₂S₂O₈、Fe⁰、NaHCO₃NaCl and KNO₃Dosage, directly adding in the experiment.

Determination of rhodamine B aqueous solution concentration

Through UV-Vis spectrum (measuring wavelength range is 200 nm-800 nm), the rhodamine B (RhB) aqueous solution has a characteristic peak of a conjugated structure at the wavelength of 553nm, and the rhodamine B (RhB) aqueous solution is not influenced by other miscellaneous peaks. The absorbance of RhB can thus be measured at a wavelength of 553nm and converted to RhB concentration according to a standard curve, according to lambert-beer's law.

And drawing a rhodamine B water solution standard curve, and the steps are as follows. RhB standard solutions (prepared by using deionized water) with concentrations of 1, 2, 4, 6, 8 and 10 mg/L are prepared, absorbances of the RhB standard solutions with different concentrations are measured at 553nm by using a 752N ultraviolet-visible spectrophotometer, and a RhB standard curve is drawn by taking the RhB concentration as an abscissa and the absorbance as an ordinate, as shown in fig. 1.

The linear regression equation of the concentration and absorbance of the RhB simulated wastewater is as follows:

y = 0.0225x - 0.0002，R² = 0.9996

as can be seen from FIG. 1, the concentration of RhB solution is linearly related to the absorbance. Thus, the removal rate of RhB can be expressed as:

removal rate (%) = (C)₀-Ct）/C₀

In the formula (I), the compound is shown in the specification,

C₀-initial concentration of RhB, mg/L;

concentration of Ct-RhB at time t, mg/L.

⁰²⁺³⁺Experimental method for degrading rhodamine B

The experiment was carried out in an ultrasonic cleaner, maintaining the temperature at 30 ℃ and the ultrasonic frequency at 80 kHz. Preparing 1 g/L RhB stock solution, diluting to 40 mg/L RhB aqueous solution during experiment, measuring 200 mL of 40 mg/L RhB aqueous solution (pH is approximately equal to 5 due to error in preparation process) by using a measuring cylinderPoor, the pH value is controlled to be between 4.94 and 5.09) and poured into a conical flask. The erlenmeyer flask was placed in an ultrasonic cleaner while the accurately weighed potassium persulfate, reduced iron powder and water soluble iron salt required for the experiment were added. Starting an ultrasonic device to start reaction, starting timing at the same time, sampling at different time points by using an injector, dripping 10 drops of methanol by using a rubber head dropper to inhibit reaction, centrifuging, taking supernate to measure absorbance at the wavelength of 553nm (if the absorbance exceeds a standard curve, diluting by a plurality of times and then measuring), and recording data. In the experiment, the default ultrasonic power is 420W, the use amount of potassium persulfate is 1.0 mmol/L, the addition amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amount of (b) is 0.5 mmol/L, and NaOH and H are used for pH₂SO₄And (6) adjusting.

The influence of different systems, different initial pH values, different initial RhB concentrations, different initial potassium persulfate concentrations, different zero-valent iron adding amounts, different zero-valent iron particle sizes, different iron salt adding amounts, different molar ratios of iron salts, different ultrasonic power, different anions, different free radical inhibitors and the like on RhB degradation is researched.

Characteristic study on degrading rhodamine B by ultrasonic-enhanced iron salt-zero-valent iron/potassium persulfate system

US/Fe⁰/Fe²⁺/Fe³⁺/PS、US/Fe⁰/Fe²⁺/PS、US/Fe⁰/Fe³⁺/PS、US/Fe⁰/PS、US/ Fe⁰、US/ PS、Fe⁰/Fe²⁺/Fe³⁺/PS、Fe⁰/Fe²⁺/PS、Fe³⁺/PS、Fe²⁺/PS、Fe⁰Comparison of/PS (in different systems)

In different systems, the degradation rate of RhB is compared, and the effect of potassium persulfate, zero-valent iron, iron salt and ultrasonic waves in the system is researched. The results of the experiment are shown in FIG. 2. Comparative US/Fe⁰US/PS and US/Fe⁰The degradation rates of rhodamine B after 18min reaction are respectively 4.0%, 10.42% and 87.78% according to the PS system, so that Fe can be seen⁰And PS can significantly improve the reaction efficiency because the ultrasonic wave can stimulate the production of zero-valent ironMore ferrous ions and potassium persulfate generate more sulfate radicals to promote the degradation of RhB; in the same way, compare US/Fe⁰/Fe²⁺/Fe³⁺(ii) PS and Fe⁰/Fe²⁺/Fe³⁺the/PS system, US/Fe⁰/Fe²⁺(ii) PS and Fe⁰/Fe²⁺the/PS system, US/Fe⁰(ii) PS and Fe⁰the/PS system shows that the degradation efficiency of RhB can be greatly improved by ultrasonic waves because the ultrasonic waves can form chemical effects to promote H₂O produces HO. Comparative US/Fe⁰/Fe²⁺/Fe³⁺/PS、US/Fe⁰/Fe²⁺/PS、US/Fe⁰/Fe³⁺Per PS and US/Fe⁰It is known that iron salts can also increase the RhB degradation efficiency, among which US/Fe⁰/Fe²⁺/Fe³⁺The maximum degradation efficiency of the/PS reaches 99.56 percent, because the ultrasonic wave is favorable for Fe²⁺And Fe³⁺The circulation between the two promotes the high-efficiency operation of the reaction. From the above, US/Fe in all systems⁰/Fe²⁺/Fe³⁺The degradation efficiency of the/PS is highest, only 18min is needed for degrading RhB, and the method has good application prospect, and therefore the method is applied to US/Fe⁰/Fe²⁺/Fe³⁺The RhB is degraded under the PS system to carry out characteristic study.

Effect of initial pH of solution on RhB degradation Rate

The pH value influences the running cost, so the influence of the initial pH value of the solution on the degradation rate of RhB is researched. The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amount of (A) was 0.5 mmol/L, the ultrasonic power was 420W, and the initial pH values of the solutions were adjusted to 3, 5, 7, and 9, respectively, to investigate the effect of the initial pH values on the degradation rate of RhB, as shown in FIG. 3. As can be seen from the figure, under different pH values, after reacting for 18 minutes, the degradation rate of RhB reaches more than 99%, the treatment effect is good, compared with the pH value in a single zero-valent iron activated persulfate system, the U.S. Pat. No. 4,000,⁰/Fe²⁺/Fe³⁺the PS widens the application range of the pH value, so that the RhB can obtain better treatment effect under both acidic and alkaline conditions, but under the acidic conditionThe degradation effect is still more remarkable. The initial RhB concentration of 40 mg/L had a pH of about 5, so that subsequent experiments did not require a pH change unless otherwise specified.

Effect of initial RhB concentration on RhB degradation Rate

The initial RhB concentration directly affects the rate of RhB degradation and the reaction time. The using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amount of (A) was 0.5 mmol/L, the ultrasonic power was 420W, the initial RhB concentrations were sequentially changed to 10 mg/L, 20 mg/L, 30 mg/L, and 40 mg/L, respectively, and the pH value was adjusted to 5 to investigate the effect of the initial RhB concentration on the degradation rate of RhB, as shown in FIG. 4. As can be seen, at low concentrations, US/Fe⁰/Fe²⁺/Fe³ ⁺The degradation effect of the/PS system on RhB is very obvious, and after 6 min of reaction, the degradation rate of more than 94% is achieved. The higher the initial RhB concentration, the less efficient the degradation in the same time of the reaction, and the longer it takes for complete degradation. Because potassium persulfate has limited oxidizing ability under the same conditions, the degradation efficiency is lower for higher concentrations of target pollutant RhB. In combination with the actual conditions, the initial RhB standard concentration used in this experiment was 40 mg/L.

Effect of initial Potassium persulfate concentration on RhB degradation Rate

The sulfate radical is a main substance degrading the target pollutant, and potassium persulfate can be activated by some method to generate the sulfate radical, so that the initial potassium persulfate concentration is US/Fe⁰/Fe²⁺/Fe³⁺The important influencing factor for degrading RhB by the PS system. The initial RhB concentration is 40 mg/L, the zero-valent iron dosage is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amounts of (A) and (B) were all 0.5 mmol/L, the initial pH value of the solution was 5, the ultrasonic power was 420W, and the initial potassium persulfate concentrations were sequentially changed to 0.5 mmol/L, 1 mmol/L, 1.5 mmol/L, and 2 mmol/L, respectively, to investigate the effect of the initial potassium persulfate on the degradation rate of RhB, as shown in FIG. 5. As can be seen, the degradation rate of RhB increases from 90.32% to 99.54% when the PS concentration increases from 0.5 mmol/L to 1.0 mmol/L at 18 min. However, when the PS concentration was further increased to 2 mmol/L, the degradation rate of RhB decreasedTo 90.21%. When the amount of the oxidant is increased within a moderate range, the system can be promoted to have more sulfate radicals, and the degradation efficiency is improved, but the excessive amount of the oxidant can relatively reduce the number of the radicals in the system, so that the reaction is not facilitated. According to the literature, the use of Fe²⁺Too much persulfate is not beneficial to removing target pollutants when the activated persulfate degrades the decabromodiphenyl oxide in the soil. When the concentration of the oxidizing agent is too high, part of the radicals in the solution is consumed by the following reactions 3-1, 3-2, 3-3.

SO₄ ^-·+S₂O₈ ^2-→SO₄ ^2-+ S₂O₈ ^-· (3-1)

SO₄ ^-·+ SO₄ ^-·→S₂O₈ ^2- (3-2)

HO·+HO·→H₂O₂ (3-3)

Therefore, 1.0 mmol/L is the optimal initial PS concentration for this experiment, which is used subsequently.

Influence of zero-valent iron addition on RhB degradation rate

At an initial RhB concentration of 40 mg/L, a potassium persulfate concentration of 1.0 mmol/L, Fe³⁺And Fe²⁺The addition amounts of (A) and (B) are all 0.5 mmol/L, the initial pH value of the solution is 5, the ultrasonic power is 420W, and the addition amounts of the zero-valent iron are sequentially changed to be 0 mg/L, 0.2 mg/L, 0.4 mg/L and 0.6 mg/L respectively so as to study the influence of the addition amounts of the zero-valent iron on the degradation rate of RhB, as shown in FIG. 6. As can be seen from the figure, the zero-valent iron has certain activation effect on potassium persulfate. When Fe⁰When the addition amount of (2) is increased from 0 mg/L to 0.4 mg/L, the degradation rate of RhB shows a gradual increase trend, but Fe is continuously increased⁰When the addition amount of (2) is 0.6 mg/L, the degradation rate of RhB is reduced. Fe⁰When the adding amount of the Fe-B-Fe alloy is increased in a proper range, the system can be promoted to have more sulfate radicals, the degradation efficiency is improved, but the excessive Fe⁰The number of free radicals in the system is relatively reduced, which is not favorable for the reaction. Fe⁰The more the addition amount of the raw materials is,produced Fe²⁺And more so, as mentioned above, Fe²⁺And the degradation efficiency of RhB is reduced by competing reaction with free radicals and consuming partial sulfate free radicals in water, and the reactions are shown as the following 3-4, 3-5 and 3-6.

Fe²⁺+S₂O₈ ^2-→SO₄ ^2-+ S₂O₈ ^-·+Fe³⁺ (3-4)

SO₄ ^-·+Fe²⁺→SO₄ ^2-+Fe³⁺ (3-5)

Fe³⁺+Fe⁰→Fe²⁺ (3-6)

Therefore, 0.4 mg/L was used as Fe in this experiment⁰The optimum dosage of (2) is adopted in the following steps.

Influence of zero-valent iron particle size on RhB degradation rate

The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amount of (A) was 0.5 mmol/L, the initial pH value of the solution was 5, the ultrasonic power was 420W, and the influence of the average particle size of zero-valent iron of 2mm, 5mm and 10mm on the degradation rate of RhB was investigated, as shown in FIG. 7. From the figure, Fe⁰Too large and too small particle size of RhB will decrease the degradation rate. The catalyst with too small particle size is easy to agglomerate, and the RhB degradation efficiency is influenced by too large particle size and too small surface area. Therefore, the experiment adopts Fe with the grain diameter of 2mm⁰。

Effect of iron salt addition on RhB degradation Rate

Fe was studied in the initial RhB concentration of 40 mg/L, the amount of potassium persulfate used of 1.0 mmol/L, the amount of zero-valent iron added of 0.4 mg/L, the initial pH of the solution of 5, and the ultrasonic power of 420W, respectively³⁺And Fe²⁺The effect of the addition of (b) on the degradation rate of RhB is 0.0125 mmol/L, 0.5 mmol/L and 2 mmol/L, as shown in FIG. 8. As can be seen, Fe³⁺And Fe²⁺When the addition amount of the compound is 0.0125 mmol/L, the degradation rate of RhB is only 79.2 percent, because the reaction efficiency is reduced due to insufficient amount of ferric salt; fe³⁺And Fe²⁺When the adding amount of the compound is 0.5 mmol/L and 2 mmol/L, the degradation rate of RhB reaches more than 99 percent. From the economic cost perspective, therefore, Fe in this experiment³⁺And Fe²⁺The dosage of (A) is 0.5 mmol/L.

Effect of molar ratio of iron salt on degradation Rate of RhB

Respectively researching Fe when the initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, the initial pH value of the solution is 5, the ultrasonic power is 420W, and keeping the adding amount of iron salt to be 1 mmol/L³⁺And Fe²⁺The effect of molar ratios of 2:1, 1:3 on RhB degradation rate is shown in fig. 9. As can be seen, Fe³⁺And Fe²⁺At a molar ratio of 2:1, the degradation rate of RhB was only 84.5%, since Fe³⁺The occupied proportion is high, so that the reaction efficiency is reduced; fe³⁺And Fe²⁺The molar ratio of (1: 1) to (1: 3) is such that the degradation rate of RhB is 99% or more. From the economic cost perspective, therefore, Fe in this experiment³⁺And Fe²⁺The molar ratio of (A) to (B) is 1: 1.

Influence of ultrasonic power on RhB degradation rate

The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amount of (A) was 0.5 mmol/L, the initial pH value of the solution was 5, and the ultrasonic power was studied at 350W, 420W and 560W, respectively, to investigate the effect of the ultrasonic power on the degradation rate of RhB, as shown in FIG. 10. As can be seen from the figure, the higher the ultrasonic power is, the better the degradation effect of RhB is, and when the power is increased from 350W to 560W, the degradation rate of RhB is increased from 93% to more than 99%. This is because the higher the power, the more the energy generated is, the more the material on the surface of the zero-valent iron can be cleaned, so that the zero-valent iron, the iron salt, the potassium persulfate and the target pollutant can be contacted more fully, more ferrous ions can be generated by stimulation, the reaction effect can be enhanced, and the ultrasonic wave can increase the reaction heat and can activate the potassium persulfate to generate sulfate radicals. From the economic cost point of view, the ultrasonic power of the experiment is 420W.

Effect of common anions in Water on the System

HCO₃ ^-Influence of (2)

The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The addition amount of (b) is 0.5 mmol/L, the initial pH value of the solution is 5, the ultrasonic power is 420W, 200 mL of RhB solution is put into a conical flask, a certain amount of sodium bicarbonate is respectively added to ensure that the concentration of the sodium bicarbonate in the aqueous solution is 0 mmol/L, 1 mmol/L and 5 mmol/L respectively, and the HCO is researched₃ ^-The effect on RhB degradation rate is shown in fig. 11. The results show that HCO is present in aqueous solution₃ ^-The degradation rates of RhB were 99.52%, 37.81%, and 29.32% at concentrations of 0 mmol/L, 1 mmol/L, and 5 mmol/L, respectively (after 18min of reaction). Analytically, HCO₃ ^-Has strong inhibiting effect on degradation rate of RhB, HCO₃ ^-The higher the concentration, the more obvious the inhibition effect, but with HCO₃ ^-The degradation rate of RhB is reduced less obviously in the same reaction time due to the increase of the concentration. It has been shown that this is due to HCO₃ ^-Is a free radical scavenger capable of reacting with SO₄ ^-A substance which reacts with HO to form other adverse reactions, the reaction formulae are shown as 3-7 and 3-8, although CO having a certain oxidizing ability is formed₃ ^-·（E_k= 1.78V), but it is a transient and selective radical, which is detrimental to RhB degradation.

HCO₃ ⁺+ SO₄ ^-·→SO₄ ^2-+ CO₃ ^-·+H⁺ (3-7)

HO·+HCO₃ ^-→OH^-+ CO₃ ^-·+H⁺ (3-8)。

Influence of (2)

The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The adding amount of the solution is 0.5 mmol/L, the initial pH value of the solution is 5, the ultrasonic power is 420W, and 200 mLRhB solution is taken out and put inIn the Erlenmeyer flask, a certain amount of sodium chloride was added to make the concentration of sodium chloride in the aqueous solution 0 mmol/L, 1 mmol/L, 5 mmol/L, respectively, and Cl was investigated^-The effect on RhB degradation rate is shown in fig. 12. The results show that Cl is present in an aqueous solution^-The degradation rates of RhB were 99.49%, 88.25%, and 55.72% at concentrations of 0 mmol/L, 1 mmol/L, and 5 mmol/L, respectively (after 18min of reaction). According to analysis, Cl in water^-Has strong inhibiting effect on the degradation of RhB, and the cause of the degradation may be Cl^-Capable of competing with RhB for sulfate radicals, the reaction of which is shown in 3-9.

Cl^-+ SO₄ ^-·→SO₄ ^2-+Cl· (3-9)

As can be seen from the above reaction formula, Cl.is generated in the reaction, and the oxidation-reduction potential of the generated Cl.is obviously higher than that of SO₄ ^-Low to SO₄ ^-Thereby reducing the rate of RhB degradation.

₃ ^-Influence of (2)

The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The adding amount of the potassium nitrate is 0.5 mmol/L, the initial pH value of the solution is 5, the ultrasonic power is 420W, 200 ml of the LRhB solution is put into a conical flask, a certain amount of potassium nitrate is respectively added, so that the concentrations of the potassium nitrate in the aqueous solution are respectively 0 mmol/L, 1 mmol/L and 10 mmol/L, and the HCO is researched₃ ^-The effect on RhB degradation rate is shown in fig. 13. The results show that NO is present in aqueous solution₃ ^-The degradation rates of RhB were all 90% or more (after 18min of reaction) at concentrations of 0 mmol/L, 1 mmol/L, and 10 mmol/L, respectively. Analytically, NO₃ ^-The concentration has less effect on the degradation of RhB, which may be due to NO although₃ ^-Can react with free radicals to form other less reactive free radicals, but the rate constant of this reaction is higher than that of SO₄ ^-·The rate constant with RhB is very small, with little effect, and the equations are shown in 3-10.

NO₃ ^-+ SO₄ ^-·→SO₄ ^2-+NO₃· (3-10)。

Identification of free radicals

To explore US/Fe⁰/Fe²⁺/Fe³⁺the/PS system degrades the type of free radicals generated by potassium persulfate during RhB, using methanol and t-butanol as radical quenchers. The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The adding amount of the compound is 0.5 mmol/L, the initial pH value of the solution is 5, the ultrasonic power is 420W, a certain amount of methanol and a certain amount of tert-butyl alcohol are respectively added at the beginning to search the type of the free radicals, and the experimental result is shown in figure 14. As a result, the degradation rates of RhB without addition of a quencher, and with addition of t-butanol and methanol were 99.35%, 72.58% and 24.74%, respectively (after 18min of reaction). Because methanol contains a-H, the quenching effect on sulfate radicals and hydroxyl radicals is good; tert-butyl alcohol has a good quenching effect on hydroxyl radicals, but has a poor quenching effect on sulfate radicals, and the reaction rate constant is very small relative to that of the hydroxyl radicals. Therefore, it is known that sulfate radicals play a major role in the reaction system, and hydroxyl radicals play an auxiliary role.

Mineralization rate analysis

In the treatment of organic wastewater, TOC in solution is an important parameter for evaluating practical engineering application, and for this reason, US/Fe needs to be explored⁰/Fe²⁺/Fe³⁺Mineralization rate during degradation of RhB in PS system. The initial RhB concentration is 40 mg/L, the using amount of potassium persulfate is 1.0 mmol/L, the adding amount of zero-valent iron is 0.4 mg/L, and Fe³⁺And Fe²⁺The adding amount of the solution is 0.5 mmol/L, the initial pH value of the solution is 5, and the ultrasonic power is 420W, the mineralization rate of the reaction system is researched. The results of the experiment are shown in FIG. 15. Analysis shows that the TOC degradation rate gradually increases, and the TOC degradation rate reaches 48.92% after 18 min. This indicates that a large amount of RhB is mineralized to CO during the reaction₂。

To summarize:

by US/Fe⁰/Fe²⁺/Fe³⁺The characteristic study of the PS system for treating rhodamine B leads to the following conclusion:

1)US/Fe⁰/Fe²⁺/Fe³⁺the degradation efficiency of the/PS is highest, only 18min is needed for degrading the RhB, and the method has a good application prospect;

2) the degradation rate of RhB reaches more than 99% after the reaction is carried out for 18 minutes at the pH value of 3-9, the treatment effect is good, compared with the pH value in a single zero-valent iron activated persulfate system, the U.S. Pat. No. 4,000,⁰/Fe²⁺/Fe³⁺the application range of the pH value is widened by PS, so that the RhB can obtain better treatment effect under both acidic and alkaline conditions;

3) the degradation rate of RhB increased from 90.32% to 99.54% at 18min as the PS concentration increased from 0.5 mmol/L to 1.0 mmol/L. However, when the PS concentration was further increased to 2 mmol/L, the degradation rate of RhB decreased to 90.21%. When the using amount of the oxidant is increased within a proper range, the system can be promoted to have more sulfate radicals, the degradation efficiency is improved, but the excessive oxidant can relatively reduce the number of the radicals in the system and is not beneficial to the reaction;

4) the zero-valent iron has certain activation effect on potassium persulfate. When Fe⁰When the addition amount of (2) is increased from 0 mg/L to 0.4 mg/L, the degradation rate of RhB shows a gradual increase trend, but Fe is continuously increased⁰When the adding amount of (2) is up to 0.6 mg/L, the degradation rate of RhB is reduced;

5)Fe⁰too large and too small particle size of RhB will decrease the degradation rate. The catalyst with too small particle size is easy to agglomerate, and the RhB degradation efficiency is influenced by too large particle size and too small surface area;

6)Fe³⁺and Fe²⁺When the addition amount of the compound is 0.0125 mmol/L, the degradation rate of RhB is only 79.2 percent, because the reaction efficiency is reduced due to insufficient amount of ferric salt; fe³⁺And Fe²⁺When the adding amount of the compound is 0.5 mmol/L and 2 mmol/L, the degradation rate of RhB reaches more than 99 percent;

7)Fe³⁺and Fe²⁺At a molar ratio of 2:1, the degradation rate of RhB is only 84.5%, Fe³⁺And Fe²⁺At a molar ratio of 1:1 and 1:3, RhBThe degradation rate of the composite material reaches more than 99 percent.

Claims

1. A method for degrading organic wastewater by using iron salt-zero-valent iron as a synergetic catalyst comprises the following steps:

2. The method of claim 1, wherein: the initial concentration of the ferric salt in the organic wastewater is 0.5-2 mM in terms of Fe, and Fe³⁺：Fe²⁺In a molar ratio of 1: (1-2); preferably, the water-soluble iron salt is ferric sulfate and ferrous sulfate.

3. The method of claim 1, wherein: the addition amount of the iron powder is not less than 0.1 mg/L, and preferably 0.1-0.5 mg/L.

4. The method of claim 1, wherein: the particle size of the iron powder is not more than 5mm, and preferably 0.1-3 mm.

5. The method according to any one of claims 1 to 4, wherein: the initial adding concentration of the persulfate in the organic wastewater is 0.5-2.0 mM.

6. The method according to any one of claims 1 to 4, wherein: the pH value of the organic wastewater is adjusted to 3-9, preferably 5-7.

7. The method according to any one of claims 1 to 4, wherein: the ultrasonic treatment time is not less than 10 min.

8. The method of claim 7, wherein: the ultrasonic treatment time is 10-30 min.

9. The method according to any one of claims 1 to 4, wherein: the organic wastewater is printing and dyeing wastewater.

10. The method of claim 9, wherein: the pH value of the printing and dyeing wastewater is 5-7.