JPH0123192B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a treatment method for effectively purifying acid digestion waste liquid. It is well known that nuclear energy is currently regarded as an important alternative to fossil fuels, and nuclear power plants and plutonium fuel manufacturing facilities are in operation in various places. These facilities generate radioactively contaminated ion exchange resin, vinyl chloride neoprene rubber, and other organic waste (hereinafter referred to as radioactive waste). Although some of these wastes are treated by various methods to reduce their volume, the majority of them are currently stored under strict control. The amount of radioactive waste stored is increasing year by year, and therefore, the development and industrialization of treatment processes primarily aimed at reducing the volume of this waste has become the most important issue in the development of the nuclear industry. Furthermore, with the diversification of waste types in recent years, the amount of waste that is not suitable for incineration is increasing, and there is a tendency to recommend landfilling. Currently, it is difficult to secure new landfill sites and to prolong the life of such materials, so reducing the volume of such flame-retardant or non-combustible materials as pre-treatment for landfill disposal has become as important as radioactive waste. There is. Under these circumstances, one of the methods adopted to reduce the volume of waste is the acid digestion process, in which the waste is placed in a strong acid solution to decompose and oxidize the organic matter. It is also well known that waste treatment methods have been developed and are being put into practical use, albeit on a small scale. The acid digestion process allows easy control of process operating conditions for waste volume reduction, and unlike the incineration volume reduction method, it does not allow uranium, plutonium, etc. to penetrate into refractories during the treatment of radioactive waste. It has the advantage that it can be recovered in the form of a highly concentrated aqueous solution without having to run. However, it has the disadvantage of producing organic matter-containing wastewater (hereinafter referred to as acid digestion wastewater), which is subject to drainage regulations, and therefore this acid digestion wastewater needs to be purified several times before being discharged into a natural watershed. Acid digestion waste liquid contains around 10% of mineral acids such as hydrochloric acid and sulfuric acid, or their salts, and contains hundreds to thousands of ppm (as total organic carbon) of various organic compounds. It is a characteristic. As methods for purifying acid digestion waste liquid, electrolytic oxidation, sodium hypochlorite treatment, ozone oxidation, hydrogen peroxide oxidation, ultraviolet irradiation, activated carbon adsorption, and the like have already been proposed. The electrification oxidation method involves passing a half-wave direct current or direct current through the waste liquid to be treated in the presence of an electrolyte (usually common salt) to oxidize organic matter with oxygen generated at the anode and convert carboxylic acid into hydrocarbons through the Kolbe reaction. This method purifies the waste liquid by conversion, electrolytic levitation, decomposition and oxidation by halogen generated at the anode, but as a result of investigating the purification effect using actual waste liquid from the acid digestion process, we found that the oxidation and oxidation by the above-mentioned generated oxygen The reaction rate of decomposition and oxidation by halogen is extremely slow, and the reduction rate in terms of TOC (total organic carbon) in a short period of time is only a few percent, so this electrolytic oxidation method cannot be practically applied to the purification of actual acid digestion waste fluid. It turned out to be impossible. The inventors also used actual acid digestion waste liquid for the sodium hypochlorite method to determine the treatment temperature and the purification efficiency.
We investigated the effects of the amount of sodium hypochlorite added, the PH value, etc., and found that purification efficiency could be improved by keeping the PH value during treatment on the weakly alkaline side.
Even if this effect is utilized, the purification efficiency is only about 20% at most if the treatment time is only a few hours, and it has become clear that it is extremely difficult to obtain treated water that does not violate wastewater regulations. The inventors also conducted reaction engineering research on the treatment of acid digestion waste liquid by ozone oxidation, and investigated the possibility of applying this treatment to the acid digestion waste liquid. As a result, it was confirmed in the laboratory that the purification efficiency was significantly higher than that of the above two treatment methods, reaching a TOC reduction rate of over 80%. However, even if an activated carbon adsorption device is attached before and after this treatment, although the purification efficiency increases to some extent, treated water of sufficiently good quality cannot be obtained. Furthermore, the inventors investigated and researched the purification effect of hydrogen peroxide oxidation in the same way as ozone oxidation, but they treated it at a high temperature of 250°C in the presence of a catalyst (e.g. copper ions), and further performed hydrogen peroxide oxidation. Even with activated carbon adsorption or ozone oxidation before and after the treatment, sufficient purification efficiency cannot be obtained, and the TOC reduction rate is only about 90% at most, and the resulting treated water quality far exceeds the wastewater regulation value. It was hot. The ultraviolet irradiation treatment method is also called the photooxidation treatment method.
This method aims to purify wastewater by oxidizing COD substances in the wastewater with sodium hypochlorite while irradiating it with normal ultraviolet rays. Although this treatment method has the characteristic of increasing purification efficiency compared to the above-mentioned sodium hypochlorite method, the COD reduction rate or TOC reduction rate per unit time is extremely low, and therefore the acid digestion waste liquid is not drained. In order to improve the water quality to a level that does not violate regulations, a long treatment time of several tens of hours is required, and the treatment equipment becomes excessively large, which is not desirable from an economic standpoint. As mentioned above, the inventors conducted various investigations and research on the above-mentioned conventional methods and clarified the problems faced by these methods. The purpose of this invention is to solve the problems of the above-mentioned conventional methods and to provide a new method for treating acid digestion waste liquid that can efficiently treat acid digestion waste liquid in a short time unlike those methods. be. The gist of the method of the present invention is that the acid digestion waste liquid is first purified as much as possible by treating it with activated carbon in a strongly acidic environment, preferably on the acidic side with a pH value of 2 or less, and then the activated carbon-treated waste liquid is purified as much as possible. using an alkali metal hydroxide etc. to reduce the pH value to 8-11, preferably 9.
-11 by ozone and hydrogen peroxide.
This is a method for treating acid digestion wastewater, in which the wastewater is treated at a temperature of 70°C to 100°C to oxidize and reduce COD and TOC components contained in the wastewater. Next, this invention will be explained in detail. As mentioned above, acid digestion waste fluid contains different types of organic compounds, which makes theoretical research and consideration regarding purification difficult. The application of activated carbon adsorption method is considered to be effective for purifying wastewater and waste liquids containing a large number of different organic compounds, but the knowledge reported so far suggests that the optimal adsorption method that can obtain the highest purification efficiency is The conditions were unclear. Therefore, the inventors conducted experimental research on a method for purifying acid digestion waste fluid using more than ten types of commercially available activated carbon. As a result, the processing temperature
Virtually no effect of temperature on purification efficiency was observed between 10°C and 60°C. On the other hand, during adsorption
The influence of PH value on purification efficiency was observed. In other words, in strong acidity with a PH value of 2 or less, the PH value for purification efficiency is
Although there was virtually no change in the effect of the pH value, when the pH value exceeded 2, a decrease in purification efficiency was observed as the pH value increased, and in particular, from around neutral to alkaline, the cleaning efficiency in the acid digestion waste liquid decreased. Almost no adsorption of soluble organic matter onto activated carbon occurred. It has also been found that the type of activated carbon, that is, the difference in the raw material such as coal-based, coconut shell-based, petroleum-based, etc., and the pore size distribution, etc., affect the purification efficiency. Coal-based coals generally show good purification efficiency, and among them, the maximum value of the pore size distribution curve is about 4000 Å, and the average pore size is about 20 Å.
The results were particularly good. Next, the effect of simultaneous treatment of ozone and hydrogen peroxide in the presence of an alkali on activated carbon-treated acid digestion waste fluid will be explained. As mentioned above, even if the acid digestion waste liquid is treated with activated carbon before and after the ozone oxidation treatment, a certain degree of waste liquid purification can be expected, but treated water that satisfies wastewater regulations cannot be obtained. Therefore, the inventors carried out oxidation treatment of acid digestion waste liquid,
In particular, comparative tests were conducted on hydrogen peroxide oxidation, ozone oxidation, and simultaneous oxidation of hydrogen peroxide and ozone. As a result, when activated carbon-treated acid digestion waste liquid is treated simultaneously with hydrogen peroxide and ozone, the purification efficiency is significantly improved compared to sequential treatment with ozone and peracid hydrogen or sequential treatment with hydrogen peroxide and ozone. It turned out to be. That is, if the acid digestion waste liquid treated with activated carbon on the strongly acidic side is simultaneously treated with hydrogen peroxide and ozone while maintaining the pH value at 8-11 with caustic soda, soda carbonate, or a mixture thereof, the purification efficiency will be improved. In addition, its purification efficiency improves as the processing temperature increases, especially by 70%.
Above 100%, the purification efficiency becomes significantly better.
% or higher, almost no improvement in purification efficiency was observed due to temperature rise. We also investigated the effects of PH value and catalytic effects (e.g. copper ions) on purification efficiency. From acidity to neutrality, the lower the PH value, the worse the purification efficiency;
Stable purification efficiency was obtained when the value was 8 or higher. Even in strongly alkaline conditions with a PH value exceeding 11, the PH
The purification efficiency was virtually the same as when the value was 8 to 11. Therefore, it is not necessary to make the PH value particularly strong alkalinity exceeding 11. It was also found that the catalytic effect was negligible on the alkaline side, while it was only slightly noticeable on the acidic side. Next, the type of alkali used will be explained. It is difficult to apply inorganic bases such as slaked lime and ammonia and organic bases such as methylamine as alkaline agents for the following reasons. That is, ammonia and organic amines consume a large amount of these oxidizing agents during the ozone-hydrogen peroxide simultaneous treatment, and in addition, the alkali itself is liberated, and furthermore, other types of compounds are produced, making them unfavorable for purification of acid digestion waste fluid. ,
On the other hand, slaked lime reacts with carbon dioxide generated during the oxidation process of acid digestion waste liquid, lowers the pH value and reduces purification efficiency, and produces calcium carbonate, which is insoluble in clean water, as a by-product, which is not desirable for process operation. That's because there isn't. On the other hand, alkali metal alkalis such as caustic soda, caustic potash, and soda carbonate do not consume the oxidizing agent, have high solubility, and are non-volatile, so they are most suitable as alkalis for use in the present invention. Here, the significance of activated carbon adsorption for simultaneous treatment with ozone and hydrogen peroxide will be explained. The inventors conducted various studies on the simultaneous treatment of acid digestion waste fluid with ozone and hydrogen peroxide without treating it with activated carbon, and further conducted experimental research on activated carbon treatment of acid digestion waste fluid that had been treated with ozone and hydrogen peroxide. carried out. As a result, we found conditions that provide the best purification efficiency by directly treating the acid digestion waste liquid with ozone and hydrogen peroxide. However, in that case, compared to the case of simultaneous treatment of acid digestion waste liquid treated with activated carbon,
The PH value retention conditions are almost the same, but the treatment temperature is slightly higher, and even after long treatment,
The removal rate of COD and TOC was 90%. Further, even if the acid digestion waste liquid after direct simultaneous treatment with ozone and hydrogen peroxide was subjected to activated carbon adsorption treatment without first being treated with activated carbon, the purification efficiency was not improved and favorable results were not obtained. This means that the acid digestion waste liquid contains organic substances that cannot be oxidized and decomposed by simultaneous treatment with ozone and hydrogen peroxide, and that these organic substances are converted into compounds that are difficult to adsorb with activated carbon during the simultaneous treatment process. do. In other words, when treating the acid digestion waste liquid from the acid digestion process, first treating the digestion waste liquid with strong acidity and activated carbon plays a complementary role to the simultaneous treatment with ozone and hydrogen peroxide. . Next, the amounts of ozone and hydrogen peroxide required for purification of acid digestion waste liquid in the present invention will be explained. As mentioned above, acid digestion waste liquid contains many types of organic compounds, some of which have unknown chemical formulas, so it is virtually impossible to calculate the amounts of ozone and hydrogen peroxide required based on the stoichiometric formula. It is possible. Therefore, the amount used should be determined based on the amount of acid digestion waste liquid to be treated.
Calculated based on TOD (total oxygen demand) value.
The inventors conducted reaction engineering research on the simultaneous oxidation of acid digestion waste liquid with ozone and hydrogen peroxide, and found that salts contained in acid digestion waste liquid cause the self-decomposition of ozone, that is, the combination of ozone and organic matter. In addition to influencing the reaction, it was revealed that hydrogen peroxide acts as an oxidizing agent, suppresses the self-decomposition of ozone, and has a type of catalytic action that increases the reactivity of ozone toward organic substances. Although the required amounts of ozone and hydrogen peroxide vary somewhat depending on the type and concentration of coexisting salts in the acid digestion waste, ozone and The amount of hydrogen peroxide is equal to or more than the TOD value, and if this amount is supplied, it is possible to efficiently purify the activated carbon-treated acid digestion waste liquid without being affected by the concentration and type of salts. Here, the larger the amount of ozone and hydrogen peroxide, the more effective it is, but if the amount is too large, the purification effect will not increase that much and it will be uneconomical. Next, the present invention will be explained in more detail with reference to the drawings. In the figure, after confirming that the acid digestion waste liquid 1 has a pH value of 2 or less, it is transferred to the activated carbon adsorption tower as shown by the arrow.
is loaded into the If the PH value of this acid digestion waste liquid exceeds 2, sulfuric acid or hydrochloric acid 3 is introduced in the PH adjustment tank 12 to adjust the PH value of the acid digestion waste liquid to 2 or less. is charged into the activated carbon adsorption tower 2. In the activated carbon adsorption tower 2,
After the organic matter in the acid digestion waste liquid is selectively removed by ozone and hydrogen peroxide treatment and other organic matters are removed as much as possible, the acid digestion waste liquid that has been treated with activated carbon is transferred to an oxidation treatment tank. 4 and charged with an alkali 5 such as caustic soda, the acid digestion waste liquid is adjusted to have a pH value of 8-11 in the oxidation treatment tank 4 and heated by a heat source 6 to 70°C or more.
Maintained at 100℃. After confirming these treatment conditions, ozone 15 from the ozone generator 7 and hydrogen peroxide 8 are simultaneously charged into the oxidation treatment tank 4 to adjust the internal pH.
Contact with adjusted activated carbon treated acid digestion waste liquid. In these processes, the acid digestion waste liquid in the PH adjustment tank 12 and the oxidation treatment tank 4 is mixed with a stirrer 2 as needed.
1,22 to promote its PH adjustment and oxidation effect. The organic matter in the acid digestion waste liquid is decomposed into water and carbon dioxide in the oxidation treatment tank 4 at a temperature of 70° C. or higher for 1 to 11/2 hours. In the simultaneous treatment with ozone and hydrogen peroxide in the oxidation treatment tank 4, it is also possible to charge the activated carbon-treated acid digestion waste liquid into the oxidation treatment tank 4 after adjusting the pH with alkali and treat it with ozone and hydrogen peroxide simultaneously. However, carbon dioxide is generated during the oxidation process and is partially absorbed by the alkali used to adjust the pH.
Care must be taken as this may lower the value and deviate from the optimum PH conditions. The acid digestion waste liquid treated in the oxidation treatment tank 4 is cooled in the cooler 9, and then transferred to another PH adjustment tank 1 as necessary.
After being neutralized with an acid 3' such as sulfuric acid in step 3, it is sent out of the system as clean treated water 10. The gas from the oxidation treatment tank 4 is cooled by a gas cooler 11 and then released into the atmosphere. The oxidation treatment tank 4 used in this invention does not require a special type, and a general-purpose jacketed treatment tank, internal heating type treatment tank, or other treatment tank is sufficient. It is preferable to use a treatment tank that is equipped with 22 or can be expected to have a mixing effect. As explained above, according to the present invention, it has become possible to completely purify the acid digestion waste liquid from the acid digestion process in a short time. This has been extremely difficult with conventional methods. Next, embodiments of the invention will be described. This invention is not limited to these embodiments unless it goes beyond the scope of the claims. Example Acid digestion waste liquid with a pH value of 0.01 and a temperature of 18℃ (TOC 1670mg/, TOD 8900mg/, COD (Mn)
650mg/) was subjected to batch treatment in the same manner as explained in the drawings, and the results shown in the following table were obtained.

[Table] The acid digestion waste liquid treated with activated carbon is as follows. TOC915mg/, TOD4900mg/, COD (Mn)
530mg/A 20% by weight aqueous caustic soda solution was used to adjust the pH of this acid digestion waste liquid. Heating is done by electric heating, ozone is produced using an ozone generator using air 14 as raw material, and hydrogen peroxide is produced using a commercially available 35% aqueous solution.
Four equivalents (as oxygen atoms) of the TOD value (4900 mg/) were used. In addition to this, regarding acid digestion waste liquid treated with activated carbon.
Treated with ozone alone for 3 hours under the condition of PH value 9.
Treated water with a COD of 80 mg/was obtained. As is clear from the above examples, according to the present invention, it is possible to obtain treated water from acid digestion wastewater that satisfies the wastewater regulation value COD (Mn) of 10 mg/or less in a shorter time than with conventional methods. It became. This is extremely useful for pollution prevention.

[Brief explanation of drawings]

The figure is a process explanatory diagram of the method of this invention. 1: Acid digestion waste liquid, 2: Activated carbon adsorption tower, 3,
3': acid, 4: oxidation treatment tank, 5: alkali, 6:
Heat source, 7: Ozone generator, 8: Hydrogen peroxide, 9:
Cooler, 10: Treated water, 11: Gas cooler, 1
2, 13: PH adjustment tank, 14: Air, 15: Ozone, 21, 22: Stirrer.

Claims (1)

[Claims] 1. A method for treating acid-digested waste fluid generated from the process of acid-digesting waste containing organic matter, which purifies the acid-digestion waste fluid by treating it with activated carbon under strong acidity with a pH value of 2 or less. Then, this activated carbon-treated acid digestion waste liquid is simultaneously treated with ozone and hydrogen peroxide in the presence of an alkali at a pH value of 8 to 11 and a temperature range of 70°C to 100°C. A method for treating acid digestion waste liquid. 2. Using an alkali metal hydroxide, carbonate, or a mixture of the hydroxide and carbonate as the alkali, the activated carbon-treated acid digestion waste liquid is adjusted to a pH value of 8 to 11.
A method for treating acid digestion waste liquid according to claim 1, which maintains the following.