CN106829873B - The method that ferrous iron-silicic acid complex activate molecular oxygen generates hydrogen peroxide in situ - Google Patents

Abstract

The invention discloses a method for generating hydrogen peroxide in situ by activating molecular oxygen with a complex of ferrous-silicic acid. Silicate in the system forms a complex with ferrous ions to form ferrous-silicon with stronger reducing ability. Acidic substances make O ₂ undergo one-electron reduction to generate superoxide anion radicals (·O ₂ ^‑ ), and the superoxide anion radicals are further reduced to H ₂ O ₂ . At the same time, due to the simultaneous presence of H ₂ O ₂ and ferrous complexes, the Fenton effect can be generated, and a large number of hydroxyl radicals ( OH) are generated. As a strong oxidant, hydroxyl radicals can almost non-selectively degrade and mineralize organic pollutants. The use of silicate will not cause secondary pollution, nor will it compete with organic matter for hydroxyl radicals. Ferrous ions can be derived from natural water bodies, or produced by ferrous salts artificially added to the solution, or produced by the reaction of zero-valent iron and aqueous solution, and can also be produced by electrolysis of iron anodes. The invention has wide application prospects in the fields of environment restoration, water treatment and the like.

Description

A method for generating hydrogen peroxide in situ by activating molecular oxygen with ferrous-silicic acid complex

technical field

The invention belongs to the field of environmental protection, and in particular relates to a water treatment method for activating molecular oxygen to generate hydrogen peroxide in situ by a ferrous-silicic acid complex.

Background technique

Hydrogen peroxide is a compound with both oxidation and reduction properties. When it encounters oxidizing substances, it shows reducing properties; when it encounters reducing substances, it shows certain oxidizing properties. At the same time, since the oxidation product of hydrogen peroxide is oxygen and the reduction product is water, it is considered as a green, non-secondary pollution chemical, and is widely used in production and life. In the field of chemical industry, hydrogen peroxide can be used as a synthetic raw material for chemicals; in the field of environmental protection, hydrogen peroxide can produce disinfection effect, oxidation effect, and can produce Fenton effect with ferrous ion at the same time (the hydroxyl free radical formed can produce strong advanced oxidation effect); in the field of social life, the dilute solution of hydrogen peroxide is used for disinfection and decolorization and so on.

The industrial production method of hydrogen peroxide is mainly the ethylanthraquinone method, through which hydrogen peroxide with a mass concentration of 30% can be produced. In practical applications, the use of high concentrations of hydrogen peroxide presents a safety risk of corrosion and explosion. Therefore, in-situ synthesis or generation of hydrogen peroxide is safer and more reliable, and has become the first choice for various environmental protection applications. The so-called in-situ synthesis refers to the direct generation of hydrogen peroxide through physical, chemical or biological reactions at the application site, rather than through the addition of hydrogen peroxide. In-situ synthesis of low-concentration hydrogen peroxide will not cause safety risks. At the same time, in the presence of iron ions or other transition metal catalysts, it can produce Fenton’s advanced oxidation effect, which is used for sewage treatment, oxidation disinfection, sludge dehydration, Environmental restoration and more. Therefore, it has always been a hot spot in the field of environmental protection to seek a cost-saving, simple and easy method for in-situ generation of hydrogen peroxide.

At present, there are many kinds of hydrogen peroxide generation in situ, which can be roughly divided into electrochemical process and non-electrochemical process. The basic principle is to reduce molecular oxygen (O ₂ ) to generate hydrogen peroxide. Among them, the electrochemical process mainly adopts the cathode reduction process (gas diffusion electrode, graphite and carbon cathode, metal foam cathode, etc.), and the electrons in the cathode are directly transferred to O ₂ to generate hydrogen peroxide. Non-electrochemical methods mainly include chemical reduction of oxygen molecules, enzymatic reduction of oxygen molecules and microbial reduction of oxygen molecules to produce hydrogen peroxide. Among them, the use of chemical reducing substances to reduce oxygen molecules to produce hydrogen peroxide is a new phenomenon discovered in recent years, also known as the oxygen molecule activation method. At present, it has been found that the chemically reducing substances with the activation effect of oxygen molecules mainly include zero-valent iron metals, iron sulfides, and ferrous complexes. Among them, the concentration of hydrogen peroxide produced by zero-valent iron and iron sulfide is not high, and because zero-valent iron and iron sulfide are strongly reducing heterogeneous catalysts, the produced hydrogen peroxide lacks environmental protection application value. Zero-valent iron ferrous complexes mainly include ferrous-ethylenediaminetetraacetic acid complex (Fe(II)-EDTA) and ferrous-tetrapolyphosphoric acid, etc. These complexes have stronger reducing ability ( i.e. lower oxidation-reduction potential), and at the same time, because they are in a dissolved state in water, they can further interact with the hydrogen peroxide produced to produce a strong homogeneous Fenton effect, so these two complexes can be in the presence of molecular oxygen Under these conditions, organic pollutants can be degraded. However, because EDTA and tetrapolyphosphoric acid will cause secondary pollution in water bodies, the existing method of reducing iron complexes to generate hydrogen peroxide cannot be applied in environmental protection fields such as sewage treatment.

Contents of the invention

In order to overcome the deficiencies of the prior art methods, the present invention proposes a method for activating molecular oxygen with a ferrous-silicic acid complex to generate hydrogen peroxide. Silicic acid and layered disilicate can form soluble complexes (expressed as SIL-Fe ²⁺ ) with ferrous ions in the pH range of 5-9. This complex has a lower redox potential, It can directly reduce oxygen molecules dissolved in water to produce hydrogen peroxide.

A kind of water treatment method that ferrous-silicic acid complex activates molecular oxygen to generate hydrogen peroxide in situ, as shown in Figure 1, comprising the following steps: adding soluble silicate to organic waste water, adjusting the pH value of the solution to 5 -9, then add ferrous ions, silicate and ferrous ions to form a ferrous-silicate complex (SIL-Fe ²⁺ complex); continue to feed oxygen or air, and the ferrous-silicate complex will react to O ₂ One-electron reduction is performed to generate superoxide anion radical·O ₂ -, and the superoxide anion radical is further reduced to H ₂ O ₂ , so that the homogeneous Fenton oxidation effect is generated in situ in organic wastewater.

The soluble silicate is sodium metasilicate or sodium disilicate.

The ferrous ions are added in the following ways: (i) directly adding divalent iron salt; (ii) produced by electrolysis of iron anode or (iii) produced by corrosion of zero-valent iron.

The ferrous salts include ferrous sulfate, ferrous chloride, ammonium ferrous sulfate and the like.

The zero valent iron is micron zero valent iron or nanometer zero valent iron.

When the ferrous ions are produced by the electrolysis of the iron anode, current is continuously passed through the whole water treatment process, and the anode adopts a cast iron electrode.

The concentration of soluble silicate in the system is 2-50mmol/L.

The concentration of ferrous ions in the system is 1-10mmol/L.

The chemical principle of the present invention is as follows:

[SIL-Fe ²⁺ ]+O ₂ →[SIL-Fe ³⁺ ]+·O ₂ ^-

[SIL-Fe ²⁺ ]+ O ₂ ^- +2H ₂ O→[SIL-Fe ³⁺ ]+H ₂ O ₂ +2OH ^-

[SIL-Fe ²⁺ ]+H ₂ O ₂ →[SIL-Fe ³⁺ ]+·OH+OH ^-

Figure 2 shows the comparison of SIL-Fe ²⁺ with the Fe ³⁺ /Fe ²⁺ pair in acidic solution, confirming that the redox potential of this complex is indeed higher than that of ferrous ion/iron ion at pH=3 The potential is lower by nearly 1.1V vs. SCE. Due to the existence of the SIL-Fe ²⁺ complex, the dissolved oxygen in the water undergoes one-electron reduction, and the generated hydrogen peroxide finally reacts with the ferrous complex to generate a large number of hydroxyl radicals. It can efficiently degrade and mineralize pollutants. Compared with the existing ferrous complex system, as a non-toxic and harmless inorganic complexing agent, silicate will not decompose itself, nor will it compete with the carbon-containing organic pollutants to be degraded The use of hydroxyl radicals in water treatment fully complies with the country's various existing sewage discharge standards (silicon content is not an indicator for the detection of drainage water quality).

In the present invention, the silicate capable of forming a complex with ferrous iron includes sodium metasilicate and sodium disilicate, and the concentration of the silicate in the system is 2-50 mmol/L. At the same time, the pH range of the solution is required to be 5 to 9. Outside this range, if the pH is too low, the ferrous ions mainly exist in free non-coordinated forms. If the pH is too high, the ferrous ions will combine with hydroxide to form hydrogen Iron oxide, also cannot form good SIL-Fe ²⁺ complexes.

When the initial ferrous ion concentration is 1-10mmol/L, the equilibrium concentration of hydrogen peroxide that can be generated in the aqueous solution is 0.1mM-2mM. The hydrogen peroxide produced can produce a homogeneous Fenton effect through the following reactions:

[SIL-Fe ²⁺ ]+H ₂ O ₂ →[SIL-Fe ³⁺ ]+·OH+OH ^-

Fenton reaction can further oxidize dyes, pesticides, antibiotics and other organic substances to achieve the goal of wastewater treatment. In this method, ferrous ions can come from natural water bodies, can be produced by ferric salts artificially added to the solution, can be produced by the reaction of zero-valent iron and aqueous solution, and can also be produced by electrolysis of iron anodes. The invention has wide application prospects in the fields of environment restoration, water treatment and the like.

Description of drawings

Fig. 1 is the water treatment method schematic diagram that ferrous-silicic acid complex activates molecular oxygen in situ and produces hydrogen peroxide;

Figure 2 is the cyclic voltammogram (redox potential comparison) of SIL-Fe ²⁺ and Fe ³⁺ /Fe ²⁺ couple in acidic solution under different conditions.

Fig. 3 is a comparison chart of the change of H ₂ O ₂ concentration with time under the condition of presence or absence of sodium disilicate.

Figure 4 is a comparison chart of the change of chlorophenol residual rate with time under the condition of presence or absence of ferrous-disilicate complex.

Fig. 5 is a comparison diagram of the change of H ₂ O ₂ concentration with time under different current densities.

Figure 6 is a comparison chart of the residual rate of chlorophenols changing with time under different current densities.

Detailed ways

The technical solutions of the present invention will be further described through specific examples below, but the protection scope of the present invention is not limited to the following examples.

Example 1

Adopt additional ferrous sulfate as ferrous source. Add 250mL of 20mg/L aqueous solution of chlorophenol into a 500mL beaker, and add 20mmol/L sodium disilicate, use sulfuric acid to adjust the initial pH value to 7.5, then add 5mmol/L ferrous sulfate, and pass pure oxygen (Rate is 2mL/s). At a specific sampling time, measure the concentration of chlorophenol and hydrogen peroxide in the system. Wherein the concentration of chlorophenol is determined by liquid chromatography, hydrogen peroxide is determined by titanium salt method. As a control, another group of experiments did not add sodium disilicate, but adjusted the pH of the solution to 7.5, and added 5 mmol/L ferrous sulfate, and took samples at the same reaction time to measure the concentration of chlorophenol and hydrogen peroxide. As can be seen from Figure 3, in the solution where sodium disilicate exists, a hydrogen peroxide concentration peak of 0.2mmol/L is produced, and the hydrogen peroxide of this concentration is gradually consumed along with the decomposition of pollutant chlorophenol. As can be seen from Fig. 4, in the solution that has ferrous-disilicate complex to exist, the concentration of chlorophenol has dropped by 40%, and the hydrogen peroxide that illustrates generation and ferrous-disilicate complex effect, produces The homogeneous Fenton effect was achieved, and the chlorophenol pollutants were effectively degraded.

Example 2

Electrolysis is used to generate ferrous ions as a source of ferrous iron. The electrolysis system is composed of cast iron anode and ruthenium-titanium cathode. The electrolytic cell is filled with 175mL chlorophenol solution, the concentration of chlorophenol is 20mg/L, the temperature of the external circulating water is 25°C, sodium disilicate is used as the chelating agent, disilicate The concentration of sodium is 5mmol/L, the initial pH of the system is 7.5, the current is 5mA (or 10mA, or 20mA), and oxygen is fed. Measure the concentration of hydrogen peroxide and chlorophenol in the system at a specific point in time, and the test method is the same as in Example 2. The results are shown in Figure 5 and Figure 6. It can be seen that when sodium disilicate is used as the electrolyte, the cumulative concentration of hydrogen peroxide in the solution increases continuously. After three hours of electrolytic reaction, under 20mA conditions, the hydrogen peroxide The concentration rose to 0.85mmol/L. At the same time, more than 95% of chlorophenols were degraded (20mA condition), indicating that the method was very effective for the degradation of chlorophenols.

Example 3

Ferrous ions are generated by means of micron-sized zero-valent iron. In a 500mL beaker, add 250mL of an aqueous solution containing 20mg/L of phenol, and add 10mmol/L of sodium disilicate, use sulfuric acid to adjust the initial pH value to 7.5, then add 5g of zero-valent iron with a micron particle size, and pass Pure oxygen (2mL/s), and stir the solution, so that the zero-valent iron particles in the solution are in a suspended state. At a specific sampling time, the concentration of phenol in the system was determined by liquid chromatography. As a control, the other group did not add sodium disilicate, only added zero-valent iron, and other conditions were the same. The results showed that after 2 hours of reaction, in the solution containing 10mmol/L sodium disilicate, the removal rate of phenol exceeded 80%, while in the control group, the removal rate of phenol was only 20%. This result indicates that in the solution containing sodium disilicate, there is a strong oxidative degradation process of phenol, that is, the Fenton oxidation process induced by the in situ generation of hydrogen peroxide.

Claims (8)

1. a kind of ferrous-silicic acid complex activation molecular oxygen in situ produces the water treatment method of hydrogen peroxide, it is characterized in that, comprises the following steps: in organic waste water, add soluble silicate, the pH value of adjusting solution is 5 -9, then add ferrous ions, silicate and ferrous ions to form a ferrous-silicate complex; continuously feed oxygen or air, and the ferrous-silicate complex will perform one-electron reduction of _O2 to generate superoxide anion Free radical·O ₂ ^- , superoxide anion radicals are further reduced to H ₂ O ₂ , so that the homogeneous Fenton oxidation effect occurs in situ in organic wastewater. 2. The water treatment method according to claim 1, characterized in that: the soluble silicate is sodium metasilicate or sodium disilicate. 3. The water treatment method according to claim 1, characterized in that: said ferrous ions are added in the following manner: (i) directly adding ferrous salt; (ii) produced by electrolysis of iron anode or (iii) Produced by zero valent iron corrosion. 4. The water treatment method according to claim 3, characterized in that: ferrous salts include ferrous sulfate, ferrous chloride, ammonium ferrous sulfate and the like. 5. The water treatment method according to claim 3, characterized in that: when the ferrous ions are produced by electrolysis of the iron anode, the entire water treatment process continues to pass current, and the anode is a cast iron anode. 6. The water treatment method according to claim 3, characterized in that: said zero-valent iron is micron zero-valent iron or nano-zero-valent iron. 7. The water treatment method according to claim 1, characterized in that: the concentration of soluble silicate in the system is 2-50mmol/L. 8. The water treatment method according to claim 1, characterized in that: the concentration of ferrous ions in the system is 1-10mmol/L.