CN1277755C - Irradiation method of degrading hexachlorobenzene in water - Google Patents

Abstract

The invention provides a method for degrading hexachlorobenzene in water by means of irradiation, which is a high-efficiency and energy-saving water treatment technology. In the method, electron beams or gamma rays emitted when radioactive atoms decay are used to treat the water body containing hexachlorobenzene to degrade the hexachlorobenzene in the water body.

Description

Method for degrading hexachlorobenzene in water by irradiation

technical field

The invention relates to a method for degrading hexachlorobenzene in water, in particular to a method for degrading hexachlorobenzene in water by irradiation.

Background technique

In 2001, organized by the United Nations Environment Program (UNEP), an international legally binding treaty on the control of 12 typical persistent organic compounds (POPs) was signed at the Swedish Ministerial Conference. my country is one of the signatories.

In 2000, the United Nations Environment Program (UNEP) carried out an assessment of the Global Environment Facility project on PTS. Experts agreed that persistent toxic substances cannot be defined in simple words, although these substances do share the following commonality: organic (including metal-organic) substances ; Slowly degrades in the environment; Bioaccumulates; Toxic.

Hexachlorobenzene is not only one of the 12 POPs listed in the above convention, but also a typical PTS. Hexachlorobenzene has been recognized as a carcinogen and has serious hazards to human health and the environment. It is listed on the "blacklist" of priority pollutants in both the United States and the European Union. Hexachlorobenzene has been widely used in various industrial production and pesticide production, as an intermediate in organic synthesis, as a seed fungicide and wood preservative for organic synthesis, and can also be used in the production of pentachlorophenol, fluorocarbons and The impregnation of paper, and the use of pesticides make hexachlorobenzene form non-point source pollution. Pathways for HCB to enter the environment include releases of wastewater containing these products, air, and flue gases and fly ash from waste incineration, and HCB is thus widely distributed in the environment.

HCB is chemically stable, difficult to biodegrade and persistent in the environment. After being released into the atmosphere, it will mainly exist in the vapor phase, degrade very slowly (the half-life of the reaction with hydroxyl radicals is estimated to be 2 years), and can undergo long-distance global transport. Wet and dry deposition can physically remove HCB from the atmosphere. After entering the water body, hexachlorobenzene will obviously partition into the sediment and suspended solids. It volatilizes quickly from the water, but its strong adsorption with the bottom mud makes it very persistent. Hexachlorobenzene bioaccumulates in fish and enters the food chain (vegetable market surveys found that it can be detected in food). Humans can be exposed to HCB through ambient air, contaminated drinking water and food, contaminated soil, and occupational settings.

The World Health Organization (WHO) recommends that the standard value of hexachlorobenzene in drinking water should not exceed 0.01 μg/L. Hexachlorobenzene is still produced in China and is still used as a chemical intermediate.

Since the research on 12 typical POPs at home and abroad has been carried out for decades, many research results can be cautiously extended to the research and treatment of other persistent toxic substances, but at the same time, specific substances need specific analysis. Compared with aromatic hydrocarbons, the biodegradability of chlorobenzene compounds is greatly reduced. With the increase of chlorine substituents, the activity of chlorobenzene compounds decreases gradually, and the activity of hexachlorobenzene is the lowest. The main reason is that the highly electronegative chlorine atoms make The benzene ring becomes an electron-phobic ring that is difficult to be oxidized, so hexachlorobenzene is hardly biochemical. Some scholars have found that microorganisms in specific sludge have a certain removal effect on hexachlorobenzene, but it is greatly affected by environmental conditions. Hexachlorobenzene is very insensitive to light, and light has almost no degradation effect on hexachlorobenzene. Polychlorobenzene, especially hexachlorobenzene has very high thermal stability and is difficult to be destroyed. Not only that, but another highly toxic pollutant, dioxin, will be produced during the incineration of municipal solid waste containing hexachlorobenzene. It can be seen that the chemical properties of hexachlorobenzene are very stable, and it is extremely difficult to handle. At present, a lot of research has been done on the degradation and removal of hexachlorobenzene at home and abroad, but there is no particularly ideal method.

To sum up, it is extremely urgent to research and develop an ideal and effective treatment method for hexachlorobenzene, which is one of the 12 POPs recognized as a serious threat to human health and the environment and a typical PTS.

Contents of the invention

The object of the present invention is to solve the problems in the above-mentioned prior art and provide a method for degrading hexachlorobenzene in water by irradiation, which is a high-efficiency and energy-saving water treatment technology.

Technical scheme of the present invention:

The invention discloses a method for degrading hexachlorobenzene in water by irradiation, which uses electron beams or gamma rays emitted when radioactive atoms decay to treat the water containing hexachlorobenzene to degrade the hexachlorobenzene in the water.

Among them, γ-rays are produced by the decay of radionuclide ⁶⁰ Co or ¹³⁷ Cs, and the higher the irradiation dose, the higher the degradation rate;

The electron beam is produced by a high-energy electron accelerator; the water body is drinking water;

Higher PH value can promote the effect of irradiation. Under other conditions being the same, the higher the pH value, the higher the degradation rate and the better the treatment effect.

Among them, the higher concentration of CO ₃ ^2- in the water body will promote the irradiation effect. Under other conditions being the same, the higher the carbonate concentration, the higher the degradation rate and the better the treatment effect.

As countries around the world pay more attention to refractory persistent organic pollutants (POPs) and persistent toxic substances (PTS) entering the environment, it is becoming more and more urgent to develop a new technology to degrade toxic organic substances, It is in this situation that the treatment of radiation applied to such substances arises.

The gamma rays emitted by the decay of radioactive atoms have quite strong penetrating power. The most common radiation sources in industry are radionuclides ⁶⁰ Co and ¹³⁷ Cs, which are used for water and sludge treatment. The high-energy electron beam has good controllability, fast reaction rate and strong penetrating power, and has realized industrial application at home and abroad. Previous studies have shown that there is no significant difference between high-energy electron beams and γ-rays on compounds in water. Both high-energy electron beams and gamma rays can produce similar reactive intermediates, the main difference being the relatively low dose release rate of cobalt source gamma rays. The use of radiation technology to treat wastewater has been studied abroad for a long time. The research shows that gamma rays and electron beams have good effects on wastewater containing heavy metals, wastewater containing phenol, wastewater containing cyanide, industrial anthracene, and quinone dyes. processing effect. There are very few relevant reports at home and abroad on the application of γ-ray and electron beam irradiation to the treatment of drinking water.

The reactions of high-energy electron beams and gamma rays entering water are basically the same. When high-energy electron beams or gamma rays enter water bodies, they react with water molecules within 10 ^-7 seconds to generate various active substances:

The numbers in parentheses indicate the number of various free radicals generated in water per 100eV of energy absorbed. Table 1-1 lists the main active substances produced during irradiation and their concentrations at different irradiation doses. Irradiation is to use high-energy electrons or gamma rays to react with water molecules to produce active free radicals e _aq ^- , OH·, H·, etc. when they enter the water body to treat wastewater. These free radicals OH·, H·, e _aq ^- are all highly active substances, which can quickly react with the organic matter in the water body, so as to achieve the purpose of degrading and transforming the organic matter. Since the amount of OH· and e _aq ^- produced by the reaction is basically the same, the removal of pollutants can be either oxidation or reduction, which mainly depends on the concentration, chemical structure and water quality conditions of pollutants. OH is a typical oxidant, its standard redox position is as high as 2.80V, second only to fluorine (2.87V), and it is the strongest oxidant known to be applied in water treatment. The latter chain reaction, and the reaction rate constants of OH· with most organic substances in water are in the range of 10 ⁸ to 10 ¹⁰ M ^-1 ·s ^-1 , and the reactions with organic substances are mainly addition and hydrogen extraction reactions. Addition is mainly with organic compounds containing unsaturated bonds, such as organic compounds containing ethylenic bonds and aromatic rings. The hydrogen extraction reaction mainly reacts with saturated aliphatic compounds and many unsaturated compounds, such as aldehydes and ketones.

The advantages of the present invention are:

At present, a lot of research has been done on the degradation and removal of hexachlorobenzene at home and abroad, but there is no particularly ideal method. Irradiation is the only technology that can simultaneously produce strong oxidants and strong reductants with high and nearly equal concentrations in water systems.

Compared with other traditional treatment methods, irradiation technology has the following advantages: the standard redox site of the free radical OH generated in the reaction is as high as 2.80V, second only to fluorine (2.87V), and is currently known to be used in water treatment. The strongest oxidant used, and the reaction rate constants of OH· with most organic substances in water are in the range of 10 ⁸ ～10 ¹⁰ M ^-1 ·s ^{-1 [46]} ; as an intermediate product of the reaction, it can induce the following chain reaction; OH directly reacts with the pollutants in the wastewater to degrade them into carbon dioxide, water and mineral salts without selection, and will not produce secondary pollution; because it is a physical-chemical process, it is easy to control, To meet the treatment needs, it can even degrade pollutants at the level of 10 ^-9 M ^-1 ·s ^-1 ; it can be used as a separate treatment, but also can be matched with other treatment processes to reduce costs and meet treatment requirements; reaction conditions Mild, is a highly efficient and energy-saving water treatment technology. Degradation of hexachlorobenzene in water by irradiation can achieve a removal rate of over 80%.

Detailed ways

Embodiment 1: the conventional water body containing the hexachlorobenzene of 0.4mg/L, through 1.5MeV, the high-energy electron beam that the high-energy electron accelerator of 50mA produces, under the irradiation dose of 2kGy, hexachlorobenzene can reach the degradation of more than 80% rate, and the degradation products basically do not contain other harmful chlorobenzene compounds. Higher PH value can promote the effect of irradiation. Therefore, in the case of high PH value in the water body, it can be considered to reduce the irradiation dose to reduce the treatment cost.

Example 2: When the irradiation dose in Example 1 is changed to 10kGy, p-hexachlorobenzene can achieve a degradation rate of more than 90%. However, the cost of irradiation is greatly increased, and the irradiation dose should be selected according to the requirements of drinking water treatment in various places.

Example 3: The irradiation in Example 1 was irradiated with a source intensity of 500,000Ci ⁶⁰ Co rays, and other conditions remained unchanged, and the degradation effect was basically unchanged.

Example 4: The irradiation in Example 2 is irradiated with a source intensity of 500,000Ci ⁶⁰ Co rays, and other conditions remain unchanged, and the degradation effect is basically unchanged

Example 5: In Example 1 and Example 2, when the concentration of CO ₃ ^2- in the water body is high, the radiation effect will be promoted, and the radiation dose can be properly degraded.

Claims (4)

1, a kind of method of utilizing Perchlorobenzene in the irradiation-induced degradation water body, its gamma-rays that radiates when adopting electron beam or radioactive atom decay is handled the water body that contains Perchlorobenzene, and the Perchlorobenzene in the water body is degraded.

2, the method for utilizing Perchlorobenzene in the irradiation-induced degradation water body according to claim 1, wherein gamma-rays is by radionuclide ⁶⁰Co or ¹³⁷The Cs generation that decays.

3, the method for utilizing Perchlorobenzene in the irradiation-induced degradation water body according to claim 1, wherein electron beam is produced by high-energy electron accelerator.

4, the method for utilizing Perchlorobenzene in the irradiation-induced degradation water body according to claim 1, wherein water body is the tap water water body.