What Is Fenton's Reagent?

In 1894, the British HJHFenton first research showed that H ₂ O ₂ has the ability to oxidize a variety of organic compounds under the catalysis of Fe ²⁺ ions. The combination of hydrogen peroxide and ferrous ions is the Fenton reagent. Among them, Fe ^{2+ is} mainly used as a homogeneous catalyst, and H ₂ O ₂ is used for oxidation. Fenton reagent has extremely strong oxidizing ability, and is especially suitable for the treatment of some industrial waste water that is difficult to biodegrade or biologically toxic. Therefore, the Fenton oxidation method has attracted widespread attention.

Fenton reagent

In 1894, the British HJHFenton first research showed that H ₂ O ₂ has the ability to oxidize a variety of organic compounds under the catalysis of Fe ²⁺ ions. The combination of hydrogen peroxide and ferrous ions is the Fenton reagent. Among them, Fe ^{2+ is} mainly used as a homogeneous catalyst, and H ₂ O ₂ is used for oxidation. Fenton reagent has extremely strong oxidizing ability, and is especially suitable for the treatment of some industrial waste water that is difficult to biodegrade or biologically toxic. Therefore, the Fenton oxidation method has attracted widespread attention.

Chinese name

Fenton reagent

Time

1894

Nature

Oxidation system

Range

Chemistry

The oxidation system composed of hydrogen peroxide and catalyst Fe2 + is often called Fenton reagent. Under the action of a catalyst, hydrogen peroxide can produce two active hydroxides

pH value

Because the form of Fe in solution is limited by the pH value of the solution, Fenton reagent only works under acidic conditions. In neutral and alkaline environments, Fe cannot catalyze the production of H ₂ O ₂ · OH. Researchers generally believe that when the pH value is in the range of 2 to 4, the treatment effect of oxidation wastewater is better, and the best effect appears when pH = 3. Lin and Peng [10] found that when using Fenton reagent to treat textile waste water, when the pH value increased and exceeded 3, the COD in the waste water rose rapidly, so as to obtain the most advantageous pH = 3. Under these conditions, the COD removal rate reached 80%.
Casero applied Fenton's reagent to the treatment of aromatic amine wastewater and found that the conversion of O-dianisidine into ring-opened organics was independent of the initial pH. After the reaction is completed, the pH value of the wastewater is lower than the initial pH value, which may be due to the hydrolysis of the Fenton reaction product Fe to reduce the pH value. At the same time, Fenton reagent can degrade organic matter in a wide pH range, which avoids buffering of wastewater.

Reagent ratio

In the Fenton reaction, Fe acts as a catalyst and is a necessary condition for catalyzing the generation of free radicals from H ₂ 0 ₂ . In the absence of Fe, H ₂ 0 _{2 is} difficult to decompose to generate free radicals. When the Fe concentration is low, the reaction (1) is slow, the amount of free radicals generated is small, and the rate of production is slow, and the entire process is limited. When the Fe concentration is too high, H ₂ 0 _{2 will be} reduced and oxidized to Fe, resulting in an increase in chromaticity.

J. Yoon studied the effect of different [Fe] / [H ₂ 0 ₂ ] ratios on the reaction. In the [Fe] / [H ₂ 0 ₂ ] = 2 environment, when no organic matter is present, Fe is consumed in a few seconds. In the presence of organic matter, Fe consumption is greatly limited. But regardless of the presence or absence of organics, H ₂ 0 ₂ is completely consumed within a few seconds of the start of the reaction. This shows that under the condition of high [Fe] / [H ₂ 0 ₂ ] ratio, the process of consuming H ₂ 0 _{2 to} generate · OH radicals is completed in a few seconds. In the [Fe2 +] / [H ₂ 0 ₂ ] = 1 environment, when organic matter is absent, the consumption of H ₂ 0 ₂ is consumed quickly at the beginning of the reaction, and then consumed slowly. In the presence of organics, the consumption of H ₂ 0 ₂ is very rapid at the beginning of the reaction and then completely ceases. Regardless of the presence or absence of organic matter, Fe was completely consumed shortly after the reaction began. Therefore, Fe added at the beginning of the reaction cannot consume H ₂ 0 ₂ in 90 min. Under the conditions of [Fe] / [H ₂ 0 ₂ ] 1, as in the case of [Fe] / [H ₂ 0 ₂ ] = 1, Fe is completely consumed shortly after the reaction starts, but H ₂ 0 ₂ is It takes longer.

temperature reflex

According to the principle of reaction kinetics, as the temperature increases, the reaction speed increases. However, for a complex reflection system such as Fenton's reagent, the increase in temperature not only accelerates the progress of positive reactions, but also accelerates side reactions. Therefore, the effect of temperature on the treatment of wastewater by Fenton reagent is complicated. Appropriate temperature can activate the · OH radical. Excessively high temperature will decompose H ₂ O ₂ into H ₂ O and O ₂ . Sheng [8] found that when the desizing wastewater was treated with Fenton reagent, the optimal reaction temperature appeared at 30 , and the COD of the effluent below this temperature increased rapidly. This may be caused by the slow reaction of FeSO4 / H ₂ 0 ₂ . When the temperature is higher than 30 , the COD removal rate increases slowly due to the adverse effects caused by the decomposition of H ₂ 0 ₂ . When Basu and Somnath treated trichlorophenol with Fenton's reagent, they found that when the temperature was lower than 60 , the low temperature reaction had a positive effect, and when it was higher than 60 , it was not conducive to the reaction. The above researchers have obtained different results, which may be caused by the different components of the wastewater.

Dosing method

As mentioned earlier, Fenton reagent has different processing functions under different Fe / H ₂ 0 ₂ ratios. When FeSO _{4 is} larger than H ₂ 0 ₂ , Fenton reagent has chemical flocculation. When the latter is larger than the former, the Fenton reagent has a chemical oxidation function. Therefore, it may be of practical significance to divide the entire reaction process into two steps. Relevant experiments comparing the first dose of Fenton reagent (FeSO ₄ / H ₂ 0 ₂ ratio is 400/1000) and the second dose (FeSO ₄ / H ₂ 0 ₂ ratio of 300/100, 100/900), the results are compared It was found that although the reaction proceeded to the second step, the removal rate of COD still had a cumulative effect. However, the overall removal rate did not increase significantly.

Dynamic effect

The chemical oxidation process of Fenton reagent can be represented by m-level reaction kinetic model;
Sheng H. Lin's research found that the experimental results can be well expressed in a first-order reaction kinetic model. The reaction rate constant is related to temperature, the initial concentrations of FeSO ₄ and H ₂ 0 ₂ , and Fenton oxidation is more dependent on FeSO ₄ than H ₂ 0 ₂ .

In addition, factors that affect the degree of Fenton reagent treatment include organic concentration, residence time, pressure, etc. Therefore, in engineering practice, multiple factors need to be comprehensively considered to determine the best treatment process in order to achieve good economic operation.

Treatment of dye wastewater

The composition of textile printing and dyeing wastewater is complex, and it is a kind of difficult-to-degrade organic wastewater. How to harmlessly treat it has been the focus of researchers. Using Fenton oxidation technology to treat printing and dyeing wastewater has the advantages of high efficiency, low consumption and no secondary pollution.

Ye Zhaolian and Chen Yuhong used Fenton oxidation to treat acidic scarlet dye simulated wastewater. The study found that the degradation rate of COD was highest when the ratio of H ₂ O ₂ to FeSO ₄ was between 3 and 6 (mass ratio).

Gu Pingping studied the treatment of reactive black KBR dye wastewater by Fenton reagent. The results show that when the dye concentration is 400mg / L, the dosage of hydrogen peroxide is 0.4ml / L, and the dosage of ferrous sulfate is 300mg / L, the decolorization rate can reach 96%, and the COD removal rate is 70%. The optimal initial pH is The value is 3.

Treatment of benzene and phenol wastewater

Phenol wastewater is widely present in a variety of industrial wastewater. This wastewater is difficult to degrade and has toxic effects on microorganisms. In the treatment process, chemical oxidation is generally used to pre-treat phenol-containing wastewater to degrade its toxicity, and then use biological treatment. In all oxidation processes, Fenton requires the shortest time to oxidize benzene and phenols. Therefore, it is expected to be widely used in the treatment of such wastewater.

Lou.J.C et al. Conducted a Fenton reaction test using a mixture of benzene, toluene and xylene (BTX) as a simulated compound. The results show that xylene can be treated with the Fenton method. At 60, the dissolved BTX can disappear completely within 10min.

Liu Yongdi and others treated the phenol-containing wastewater with Fenton reagent to obtain a pH value of about 3 to 4, and the treatment effect was better when the amount of H ₂ 0 ₂ was 115 times the theoretical amount of COD. Many literature reports [8, 9, 10] have suggested that the oxidation of chlorophenols by Fenton reagents is carried out by a free radical reaction process.

Treatment of landfill leachate

With the continuous generation of municipal waste, the treatment of landfill leachate has attracted more and more attention. Municipal landfill leachate is a kind of difficult-to-treat wastewater with complex components, poor biochemical properties, and high water quality changes. Because it contains highly refractory organic matter, it is not conducive to the operation of the activated sludge process. The Fenton oxidation method can solve the above problems. It can oxidize and decompose organic compounds with benzene rings, hydroxyl groups, COOHSO ₃ H, NO ₂ and other substituents, thereby improving the biodegradability of wastewater and reducing the toxicity of wastewater Improve its solubility and precipitation, which is conducive to the subsequent biochemical or coagulation treatment. In addition, Fenton reagent is widely used because it has the advantages of rapid oxidation, mild temperature and pressure, and no secondary pollution. It has been found through research that the Fenton oxidation process mainly oxidizes large organic molecules into small molecules, thereby reducing the COD of landfill leachate. Therefore, the removal rate of organic matter with relatively small molecular weight in landfill leachate by Fenton oxidation method is not high.

Treatment of engineering water

Tianjin Port Oil Sewage Treatment and Reconstruction Project (mainly treating oil-containing ballast water, tank washing water and oil-containing production wastewater discharged from petrochemical complexes discharged from ships arriving in the port of Nanjiang Port), the Fenton method is used for coagulation sedimentation desalination and removal COD. China Academy of Engineering Physics uses Fenton oxidation method to pretreat radioactive waste ion exchange resin (uranium) to completely decompose 3 kinds of common uranium-containing radioactive waste resins of type 717, 201 × 4 and 201 × 7, COD in the residual liquid The removal rate is over 97%, which provides a new idea for the pretreatment of radioactive waste ion exchange resin curing treatment. The study found that the bipolar electric Fenton method was used to treat oily wastewater from ships, and it was found to have a high degradation effect. Removal of anion and non-ionic surfactant foam from Fenton refinery wastewater is also effective.

Application in drinking water

With the deterioration of drinking water raw water quality and the improvement of drinking water standards, the Fenton oxidation method has also been widely used in drinking water treatment, mainly focusing on the removal of halogenated compounds. Watter Z Tang et al. Carried out an in-depth study of the kinetics of the four trihaloalkanes in drinking water treated by the Fenton method, and found that: for different concentrations of bromoform, when pH = 3.5, When the molar ratio is 1.9 3.7, the degradation rate of bromoform at 3min can reach 85%. The degradation mechanism conforms to the quasi-first-order kinetic equation, but chloroform does not degrade during this process. This shows that Fenton reagent is more susceptible to degradation of tribromomethane.

In addition, many studies have shown that Fenton reagent can effectively degrade THMs in drinking water, even in small amounts, and studies have found that Fenton reagent can also oxidize THMs precursors to carbon dioxide and water, thereby solving the drinking water treatment process Difficulties in the problem.