JP7141302B2 - Method and equipment for processing mineral oil in radioactive controlled areas - Google Patents

Description

The present invention relates to a method and apparatus for on-site treatment of mineral oil held within a radioactive controlled area, and more particularly to a method and apparatus for on-site treatment of mineral oil containing silicone oil.

In the general industrial field, waste oil is collected as waste oil by an industrial waste disposal company and then incinerated if the oil is not toxic. Toxic oils, such as PCBs, are processed in legally specified facilities.

On the other hand, the oil (turbine oil, lubricating oil, etc.) used in the equipment and devices in nuclear facilities has little or no radioactive contamination, but due to the lack of liquid clearance laws and regulations, In many cases, it cannot be carried out of the facility, and is stored in a radiation controlled area. For this reason, used waste oil that has been replaced during periodic inspections is stored in radiation controlled areas, and the amount thereof is increasing. Non-radioactive contaminants in radiation controlled areas are incinerated, but the incineration of waste oil is not progressing. Particularly in the case of oil containing silicone, incineration generates silicon oxide, which clogs the exhaust dust collection system of the incinerator, and therefore incineration is not realistic.

As a decomposition treatment method for waste oil other than incineration, there is an electrolysis treatment method using an amphiphilic solvent (Patent Document 1). However, this treatment method is a technique for electrolyzing VOCs containing volatile oils that are easily dispersed in solvents, and is not suitable for treatment of low-volatility mineral oils such as silicone oils. As a method for decomposing low-volatility mineral oil, there is an electrolytic oxidation treatment method using a diamond electrode (Patent Document 2). However, when the present inventors conducted additional tests on this treatment method, it was found that although low-concentration silicone oil treatment is possible, when trying to treat high-concentration silicone oil of 20 g / L or more, the decomposition of silicone oil As a result, the silicon compound accumulates in the liquid, and the decomposition rate gradually decreases, resulting in stagnation. In addition, the oil remaining in the treated liquid must be removed at the time of drainage in order to meet the wastewater standard values such as the n-hexane extract concentration, but the removal by the usual coagulants or adsorbents is inefficient. There was a problem that the amount of solid waste (secondary waste) increased.

Since the Great East Japan Earthquake, public opinion has been negative about the restart of nuclear power plants, and it is expected that the number of plants whose decommissioning decisions will be accelerated will increase in the future, including those that had been decided to be decommissioned before the earthquake. A large amount of oil is discarded in the decommissioning process. At present, large amounts of waste oil must be stored in a radiation controlled area, resulting in a shortage of storage space. It is necessary to rapidly detoxify and reduce the volume of waste oil that is not contaminated with radiation within a radiation controlled area. Moreover, when treating waste oil in a radiation controlled area, it is required to reduce the generation of secondary treated substances as much as possible.
There is a demand for an efficient method of treating mineral oil containing at least silicone oil in a nuclear facility controlled area.

Japanese Patent Application Laid-Open No. 2010-149069 Patent No. 6084386

The amount of silicone oil stored in radiation-controlled areas is currently on the rise without a treatment method. Since there is an upper limit to the storage space in the radiation controlled area, some sort of processing is required in terms of operation management of nuclear facilities. In addition, volume reduction of the oil is required for decommissioning. An object of the present invention is to provide a processing method and apparatus for solving the above problems.

In order to solve the above problems, the present inventors have made intensive research, and as a result, added mineral oil containing silicone oil to water to maintain an emulsified state to impart conductivity, and use a conductive diamond electrode to provide electricity. We discovered that it is possible to obtain treated water with a reduced oil content by removing the lipophilic silicon compounds generated during decomposition to restore the decomposition rate of silicone oil. The inventors have found that by reusing the liquid after removal and repeatedly using it for silicone oil treatment, it becomes unnecessary to drain the treatment liquid, and have completed the present invention.

That is, according to the present invention, there is provided a method for treating mineral oil in a radiation controlled area, comprising: adding mineral oil containing silicone oil to water; Provided is a treatment method for oxidatively decomposing oil, characterized by filtering an electrolysis treatment liquid containing a lipophilic silicon compound produced by decomposition of silicone oil.

In the treatment method of the present invention, a mineral oil containing silicone oil is added to water to maintain an emulsified state to impart electrical conductivity, and electrolysis is performed using a conductive diamond electrode. In the electrolysis reaction of silicone oil or the electrolysis reaction of partial decomposition products of silicone oil on the electrode surface, the coexistence of a lipophilic silicon compound physically inhibits the reaction and slows the electrolysis rate. In the treatment method of the present invention, the electrolysis rate can be recovered by removing the lipophilic silicon compound from the electrolysis treatment liquid.

In order to maintain an emulsified state by adding mineral oil to water, it is preferable to add an emulsifier at a ratio of 1/6 (weight ratio) or more to mineral oil. If the addition ratio of the mineral oil and the emulsifier is significantly different, the emulsified state cannot be maintained and the electrolysis cannot be performed.

The emulsifier includes two or more hydrocarbons with different viscosities (preferably a combination of kinematic viscosities of 5 to 30 mm ² /s and 1 to 15 mm ² /s at 40° C.), a nonionic surfactant (preferably polyoxyethylene • It is preferably an organic emulsifier containing two or more alkyl (C8-C18) ethers, a higher alcohol (C8-C18) and water, or an inorganic emulsifier containing fine particles.

In the method of the present invention, the temperature of the water in the emulsifying tank, which forms an emulsified state of mineral oil and water, is desirably controlled at about 40° C. from the standpoint of decomposition efficiency. In selecting the emulsifier, it is preferable to confirm the emulsification effect at 40°C in advance.

It is preferable to further add an electrolyte to the water. Electrolytes include sodium hydroxide, sodium sulfate, and sodium bicarbonate. Sodium chloride, which is widely used as an electrolyte, is not preferable because it becomes hypochlorous acid and remains during electrolysis.

Sodium bicarbonate is particularly suitable as the electrolyte, and it is more preferable to add sodium bicarbonate to the solution to be electrolyzed in an amount of 10 g/L or more, preferably 20 g/L or more and 70 g/L or less. If it is less than 10 g/L, the efficiency of electrolysis is not improved, and it is meaningless to add an electrolyte. Even if 70 g/L or more is added, dissolution is difficult and the efficiency of electrolysis is not improved, so there is no point in adding a large amount.

The mineral oil containing silicone oil that can be treated in the present invention is a mineral oil containing a water-insoluble silicone oil containing at least one of dimethylpolysiloxane, dimethylphenylpolysiloxane and methylhydrogenpolysiloxane as a component. Oil is preferred.

In general, in order to maintain the emulsified state in the electrolysis process and to supply the emulsified liquid to the electrolysis tank, mixing is performed using a stirrer, a centrifugal pump, or a rotor. It has been found that the lipophilic silicon compound is dispersed by the shear force generated by the operation, making it difficult to capture with the filter cloth.

It is preferable to further include maintaining the electrolyzed liquid containing the lipophilic silicon compound for 5 minutes or more at a stirring strength per volume of less than 16700 rpm/m ² before filtering the electrolyzed liquid. . In the present invention, "the stirring intensity G per volume" is defined by the following formula.

Before filtering the electrolysis treatment liquid containing the silicon compound, demulsification occurs by placing it under low stirring or static conditions with a stirring strength per volume of less than 16700 rpm / m ² for at least 5 minutes or more, and the silicon compound naturally aggregates and can be captured by the filter cloth. More preferably, by placing the mixture under low stirring or standing conditions for 1 hour or more, spontaneous aggregation of the silicon compound proceeds to increase the size of the aggregates, thereby improving the filtration efficiency.

The lipophilic component and the hydrophilic component contained in the electrolyzed liquid are liquid-liquid separated by maintaining the stirring strength of the electrolyzed liquid within the above range or by allowing the electrolyzed liquid to stand still. As a result, the oil phase containing lipophilic components floats to the top and the aqueous phase containing hydrophilic components settles to the bottom. It is preferable that the electrolyzed liquid containing the lipophilic silicon compound is a liquid obtained by recovering the oil phase that floats to the top of the electrolyzed liquid.

In the present invention, the decomposition rate of the silicone oil can be restored by efficiently removing the silicon compound from the electrolysis treatment liquid. In addition, since the filtrate can be returned to the emulsifying tank and reused, there is no need for drainage. For this reason, the coagulant and adsorbent treatment that is normally performed for oil removal during waste water treatment is almost unnecessary, and the amount of secondary waste such as waste adsorbents generated can be greatly reduced.

According to the present invention, there is also provided a processing apparatus for carrying out the above processing method. The processing apparatus of the present invention is
an emulsifying tank for mixing and stirring mineral oil containing silicone oil and water;
an electrolytic cell comprising diamond electrodes;
a pipe for sending the emulsion prepared in the emulsifying tank to the electrolytic tank;
and a filtering device for filtering the electrolyzed liquid containing the lipophilic silicon compound, and means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsifying tank. and

As the filtration device that can be used in the present invention, pressure filtration devices such as bag filters and filter presses can be preferably mentioned. The filter cloth to be used is preferably made of polypropylene having a capture rate of 1 μm particles of about 70 to 90%, and the silicon compound forms a filter cake layer on the surface of the filter cloth to efficiently filter out the silicon compound. can do.

The means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsification tank is preferably connected to the upper part of the emulsification tank. Since the oil phase floats to the top of the liquid, the recovery means connected to the upper part of the emulsifying tank can efficiently recover the oil phase of the electrolyzed liquid containing the lipophilic silicon compound.

Alternatively, the means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsification tank may be connected to the bottom of the emulsification tank. In this case, since the electrolyzed liquid containing the oil phase and the water phase is recovered from the bottom of the emulsifying tank, the oil phase is separated from the water phase before being introduced into the filtering device.

It is preferable that the means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsifying tank further includes a retention tank for retaining the electrolyzed liquid discharged from the emulsifying tank for a predetermined time. Regardless of whether the electrolyzed liquid recovered from the emulsification tank contains a large amount of oil phase or is a liquid containing both an oil phase and an aqueous phase, the liquid is retained for a predetermined time after being extracted from the emulsification tank. can extract the oil phase containing lipophilic silicon compounds.

Preferably, the processing apparatus of the present invention further comprises a circulation pipe for returning the treated liquid electrolyzed in the electrolysis tank to the emulsification tank.

In the processing method and processing apparatus of the present invention, diamond electrodes are used for electrolysis. The diamond electrode used in the present invention is an electrode obtained by coating the surface of a metal substrate with a thin film of conductive diamond by the hot filament CVD method. A diamond electrode has a large potential difference between oxygen evolution and hydrogen evolution in the electrolysis of water (large thermodynamic window), and oxygen is less likely to occur. Since oxygen is less likely to be generated, electrolytic reactions other than electrolysis of water are likely to proceed, generating OH radicals, which are strong oxidizing agents. Mineral oil has a large molecular weight and is difficult to decompose with ordinary oxidizing agents. Even if ozone, which is a strong oxidizing agent generated from carbon electrodes such as platinum, gold, and graphite, there is concern that multiple intermediate products may remain, making it difficult to completely detoxify mineral oil. On the other hand, the Fenton method, which is a typical OH radical generation method, uses ferrous ions and hydrogen peroxide to act, and neutralizes the liquid when it is discharged, generating iron hydroxide sludge. Unsuitable for handling mineral oil in radiation controlled areas where it is necessary to avoid generation.

According to the present invention, mineral oil containing silicone oil, which has been kept in a radioactive controlled area for which no treatment method has been found, is electrolyzed using a conductive diamond electrode while maintaining an emulsified state to remove silicone oil. By filtering the electrolysis treatment liquid containing the lipophilic silicon compound generated by decomposition, the organic carbon component of the silicone oil is efficiently mineralized, suppressing the amount of oil-derived secondary waste generated, Efficient detoxification and aqueous solution. For this reason, it is possible to avoid an increase in the amount of mineral oil accumulated in the radioactive controlled area, reduce the volume of waste oil, and solve the problems associated with nuclear plant operation and decommissioning.
In addition, according to the present invention, since the oil concentration is reduced and a filtrate from which the generated silicon compound is removed is obtained, the same filtrate can be reused for electrolysis and repeatedly used for electrolysis of silicone oil. can. As a result, almost no waste water is generated, so that no adsorbent or coagulant treatment is required to satisfy waste water standard values such as n-hexane extract concentration, and waste adsorbents and the like are not generated. Therefore, not only the amount of wastewater but also the amount of solid secondary waste can be greatly reduced.

FIG. 1 shows an embodiment of a treatment apparatus for carrying out the treatment of mineral oil in a radioactive controlled area according to the present invention (Method 1 of recovering and filtering the oil phase that floats to the top of the emulsification tank). 1 is a schematic diagram; FIG. FIG. 2 shows an embodiment of the treatment apparatus for carrying out the treatment of mineral oil in the radioactive controlled area of the present invention (Method 2 in which the oil phase that floats to the top of the emulsification tank is recovered and filtered). 1 is a schematic diagram; FIG. FIG. 3 shows one embodiment of the treatment apparatus for carrying out the treatment of mineral oil in a radioactive controlled area according to the present invention (a method of recovering and filtering a mixture of an oil phase and an aqueous phase from the bottom of an emulsification tank). 1) is a schematic diagram showing part 1). FIG. 4 shows one embodiment of the treatment apparatus for carrying out the treatment of mineral oil in a radioactive controlled area according to the present invention (a method of recovering and filtering a mixture of an oil phase and an aqueous phase from the bottom of an emulsifying tank). 2) is a schematic diagram showing part 2); FIG. FIG. 5 is a graph of COD and cumulative cracked oil weight showing the results of treatment in the example. FIG. 6 is a graph of the weight of silicon in liquid showing the results of the treatments in the examples. FIG. 7 is a graph showing the results of processing in Comparative Example 1. FIG. FIG. 8 is a graph showing the results of processing in Comparative Example 2. FIG.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.
An example embodiment of an apparatus for carrying out the treatment method of the invention is shown in FIGS. 1-4.

1 to 4 are prepared by an emulsification tank 10 for mixing and stirring mineral oil containing silicone oil, an emulsifier, and water, an electrolysis tank 20 equipped with a diamond electrode, and an emulsification tank 10. It comprises a pipe 30 for sending the emulsified liquid to the electrolysis tank 20 and a filtering device 50 for filtering the electrolyzed liquid extracted from the emulsification tank. The pipe 30 is connected to the emulsification tank 10 so that the emulsified liquid prepared in the emulsification tank 10 flows out from the bottom of the emulsification tank 10 into the pipe 30 .

The emulsification tank 10 or the pipe 30 is provided with means for maintaining the emulsified state of the emulsion. In the embodiment of FIGS. 1 to 4, the emulsifying tank 10 is provided with stirring means 90 such as a stirrer and rotor, and the piping 30 is provided with a centrifugal pump 95 .

In the embodiment of FIGS. 1-4, a circulation pipe 40 is provided for returning the electrolyzed water from the electrolysis tank 20 to the emulsification tank 10 .

Next, common points of the mineral oil treatment method of the present invention using the treatment apparatus shown in FIGS. 1 to 4 will be described. Features of each embodiment and processing methods specific to each embodiment will be described individually after describing common points.

In the embodiment of FIGS. 1 to 4, the treatment apparatus of the present invention is installed in a radiation controlled area, emulsification tank 10 is filled with water or waste water, and mineral oil containing silicone oil and an emulsifier are added while stirring. do. The emulsified liquid at the bottom of emulsification tank 10 is sent to electrolysis tank 20 via pipe 30 . The emulsified liquid is electrolyzed in the electrolytic bath 20 while maintaining the emulsified state, and is oxidized to reduce the oil content. The treated water from which the oil content has disappeared is returned to the emulsification tank 10 via the circulation pipe 40 and used for preparing the emulsion. The oil content and COD manganese or COD chromium in the treated water are measured and used as indicators of the progress of oil decomposition.

Since electrolysis is an aqueous solution reaction, water-insoluble oil cannot be oxidatively decomposed by itself. In the present invention, an emulsified state is maintained to provide conductivity. Although it varies depending on the type of mineral oil, it is necessary to use a specific emulsifier especially in the case of mineral oil such as silicone oil, which has a short retention time in an emulsified state. Suitable emulsifiers include one or more hydrocarbon and nonionic surfactants and higher alcohols. Specifically, emulsifiers consisting of 60-70 wt.% hydrocarbons, 3-5 wt.% n-paraffins, 10-30 wt.% POE alkyl ethers, 3-5 wt.% higher alcohols and 5-10 wt.% water are particularly suitable. The amount of emulsifier added is preferably 1/6 or more of the weight of mineral oil from the viewpoint of emulsification and decomposition efficiency.

In order to improve the efficiency of electrolysis, it is preferable to further add an electrolyte. Preferred electrolytes are sodium hydroxide, sodium sulfate and sodium bicarbonate.

The electrolyte is particularly preferably sodium bicarbonate, and is more preferably added in an amount of 10 g/L or more, preferably 20 g/L or more and 70 g/L or more.

In addition, when oil-water separation occurs during electrolysis of mineral oil due to the decomposition rate of surfactants and higher alcohols being higher than that of mineral oil, or due to de-emulsification. There is In the former case, the emulsifier can be re-emulsified by re-adding the emulsifier at a rate of 1/6 or more of the remaining amount of mineral oil. In the latter case, the emulsified state can be maintained by continuing to stir the emulsified liquid. Stirring methods include circulation with a pump, stirring with a stirrer, and ultrasonic irradiation. A pump is also essential for supplying the liquid to the electrode section, but a centrifugal pump with a high mixing effect is preferable in order to exhibit a stirring effect. In addition to the stirring effect, ultrasonic irradiation has an additional effect of alleviating foaming caused by generated gas. In particular, it is preferable to use low-frequency ultrasonic waves of 15 to 40 kHz with high mixing force due to cavitation. A stirrer may be installed in the emulsifying tank, and a shear stirrer with a particularly high mixing effect is preferred.

Next, the features of each embodiment of FIGS. 1-4 will be individually described.

[First Embodiment]
FIG. 1 shows an embodiment of an apparatus for filtering the upper layer liquid of an emulsification tank for carrying out the treatment method of the present invention.
In the embodiment of FIG. 1, as a means for recovering the oil phase floating on the upper part of the emulsifying tank and supplying it to the filtering device 50, a pipe 60 for sending the oil phase in the emulsifying tank 10 to the liquid sending pump 70 and a liquid sending pump A pipe 80 for sending the liquid discharged from 70 to the filtering device 50 is provided. Further, a pipe may be provided to return the filtrate generated in the filtering device 50 to the emulsification tank 10 .

Although not shown, a pipe for returning the filtrate generated in the filtering device 50 to the emulsification tank 10 may be provided with a treated water pipe for discharging the treated water. Further, a water supply pipe for supplying water to the emulsification tank may be provided.

Moreover, although not shown, a trough may be provided at a portion of the emulsification tank 10 connected to the pipe 60 . In this case, the upper layer liquid of the emulsifying tank climbs over the weir of the trough, enters the trough, and is supplied to the liquid feed pump 70 via the pipe 60 .

Next, the characteristics of the method for treating mineral oil containing silicone oil according to the present invention using the treatment apparatus shown in FIG. 1 will be described.
When the electrolysis of the silicone oil progresses and the silicon compound accumulates in the liquid and the decomposition rate slows down, the oil phase that floats to the top of the emulsifying tank is collected and filtered.

When recovering the oil phase that floated to the top of the emulsification tank and supplying it to the filtration device 50, the stirring means 90 and the centrifugal pump 95 were stopped or the output was lowered so that the stirring strength per volume inside the emulsification tank 10 was 16700 rpm/m. After maintaining the state of ² or less for 5 minutes or more, the oil phase is recovered from the upper part of the emulsification tank using the liquid sending pump 70 and supplied to the filtering device 50 . Preferably, the liquid inside the emulsification tank is allowed to stand still for one hour or more, and then the oil phase floating above the emulsification tank is recovered using the liquid-sending pump 70 and supplied to the filtering device 50 .

By holding the liquid in the emulsifying tank in a state of being slightly stirred or in a stationary state for a certain period of time, the oil content rises to the top of the emulsifying tank and forms an oil phase. Since the lipophilic silicon compound that inhibits the decomposition of the silicone oil floats along with the oil, the lipophilic silicon compound can be efficiently filtered off by recovering this part of the oil phase.

The filtrate filtered by the filtering device 50 may be directly returned to the emulsification tank 10, or may be temporarily stored in an arbitrary container and then returned to the emulsification tank for reuse.
In addition, by introducing filtrate from the filtering device 50 or water from the water supply pipe, the water level of the emulsification tank can be raised to guide the oil phase floating above the emulsification tank to the pipe 60 or the trough. .

[Second embodiment]
FIG. 2 shows an embodiment of an apparatus for filtering the upper layer liquid of an emulsification tank for carrying out the treatment method of the present invention.

In the embodiment of FIG. 2, as a means for supplying the oil phase floating above the emulsifying tank to the filtering device 50, a pipe 60 for sending the oil phase from the emulsifying tank 10 to the liquid sending pump 70, and discharge from the liquid sending pump 70 A pipe 81 for sending the collected liquid to the retention tank 100 and a pipe 82 for sending the liquid discharged from the retention tank 100 to the filtering device 50 are provided. Further, a pipe may be provided to return the filtrate generated in the filtering device 50 to the emulsification tank 10 .

Although not shown, a pipe for returning the filtrate generated in the filtering device 50 to the emulsification tank 10 may be provided with a treated water pipe for discharging the treated water. Further, a water supply pipe for supplying water to the emulsification tank may be provided.

Moreover, although not shown, a trough may be provided at a portion of the emulsification tank 10 that is connected to the pipe 60 . In this case, the oil phase from the emulsifying tank climbs over the weir of the trough, enters the trough, and is supplied to the liquid transfer pump 70 via the pipe 60 .

Next, the features of the mineral oil processing method of the present invention using the processing apparatus shown in FIG. 2 will be described.
When the electrolysis of the silicone oil progresses and the silicon compound accumulates in the electrolysis treatment liquid and the decomposition rate slows down, the oil phase floating to the top of the emulsification tank is filtered.

When the oil phase from the emulsifying tank is supplied to the filtering device 50, the stirring means 90 and the centrifugal pump 95 are stopped or their outputs are lowered, and the stirring strength per volume inside the emulsifying tank 10 is less than 16700 rpm/m ² for 5 minutes. After holding the above, the oil phase from the emulsifying tank is supplied to the retention tank 100 using the liquid sending pump 70 . Preferably, after the oil phase from the emulsifying tank is retained in the retention tank 100 for one hour or more, the liquid discharged from the retention tank 100 is supplied to the filter device 50 using the liquid feed pump 70 .

By holding the electrolyzed liquid in the emulsifying tank in a slightly stirred state or in a stationary state for a certain period of time, oil floats to the top of the emulsifying tank liquid to form an oil phase. Since the lipophilic silicon compound that inhibits the decomposition of the silicone oil floats together with the oil, the lipophilic silicon compound can be efficiently recovered by collecting the oil phase that has risen to the top of the emulsifying tank.

By retaining the collected oil phase from the emulsifying tank in the retention tank 100 for preferably 1 hour or longer, the lipophilic silicon compound naturally aggregates to increase the size of the aggregate, thereby improving the filtration efficiency. Since the lipophilic silicon compound migrates upward along with the oil component in the retention tank 100, the pipe 82 is used to efficiently guide the electrolyzed liquid containing the lipophilic silicon compound to the filtration device 50. It is preferably installed in the upper part of the tank.

The filtrate filtered by the filtering device 50 may be directly returned to the emulsification tank 10, or may be temporarily stored in an arbitrary container and then returned to the emulsification tank for reuse.
It is also preferable to raise the water level of the emulsifying tank by introducing the filtrate from the filtering device 50 or water from the water supply pipe, thereby leading the oil phase from the emulsifying tank to the pipe 60 or the trough.

[Third Embodiment]
FIG. 3 shows an embodiment of an apparatus for carrying out the treatment method of the present invention, in which an electrolyzed solution containing an oil phase and an aqueous phase is recovered from an emulsifying tank and filtered.

In the embodiment of FIG. 3, as a means for supplying the electrolyzed liquid from the emulsifying tank to the filtering device 50, a pipe 61 for sending the electrolyzed liquid from the emulsifying tank 10 to the liquid sending pump 70, and the liquid discharging pump 70 A pipe 80 for sending the filtered liquid to the filtering device 50 is provided. Further, a pipe may be provided to return the filtrate generated in the filtering device 50 to the emulsification tank 10 .

Although not shown, a pipe for returning the filtrate generated in the filtering device 50 to the emulsifying tank 10 may be provided with a treated water pipe for discharging the treated water. Further, a water supply pipe for supplying water to the emulsification tank may be provided.

Next, the features of the mineral oil processing method of the present invention using the processing apparatus shown in FIG. 3 will be described.
When the electrolysis of the silicone oil progresses and the silicon compound accumulates in the liquid and the decomposition rate decreases, the electrolyzed liquid is recovered from the emulsifying tank and filtered.

In this embodiment, when the electrolyzed liquid is supplied from the emulsifying tank to the filtering device 50, the stirring means 90 and the centrifugal pump 95 are not stopped or their outputs are lowered. Therefore, filtration treatment and electrolysis treatment can be performed in parallel.

In the present embodiment, by controlling the flow rate of the liquid feed pump 70 to be low, the electrolyzed liquid is recovered from the emulsifying tank and the silicon compound is not aggregated until it reaches the filter cloth surface inside the filtering device 50. is preferably generated. For example, it is preferable that it takes 5 minutes or more for the electrolyzed liquid to reach the surface of the filter cloth of the filter from the emulsifying tank.

In this embodiment, since the liquid mixture in which the oil phase and the water phase are completely mixed is filtered, not the oil phase that floats to the top of the emulsifying tank, the lipophilic silicon compound contained in the oil phase as well as the water phase is filtered. Hydrophilic silicon compounds contained in are also subject to filtration.

The filtrate filtered by the filtering device 50 may be directly returned to the emulsification tank 10, or may be temporarily stored in an arbitrary container and then returned to the emulsification tank for reuse.

[Fourth embodiment]
FIG. 4 shows an embodiment of an apparatus for carrying out the treatment method of the present invention, which collects an electrolyzed solution containing an oil phase and an aqueous phase from an emulsifying tank and filters it.

In the embodiment of FIG. 4, as a means for supplying the electrolyzed liquid from the emulsifying tank to the filtering device 50, a pipe 61 for sending the electrolyzed liquid from the emulsifying tank 10 to the liquid feeding pump 70, and A pipe 81 for sending the discharged liquid to the retention tank 100 and a pipe 82 for sending the discharged liquid from the retention tank 100 to the filtering device 50 are provided. Further, a pipe may be provided to return the filtrate generated in the filtering device 50 to the emulsification tank 10 .

Although not shown, a pipe for returning the filtrate generated in the filtering device 50 to the emulsifying tank 10 may be provided with a treated water pipe for discharging the treated water. Further, a water supply pipe for supplying water to the emulsification tank may be provided.

Next, the characteristics of the method for treating mineral oil containing silicone oil according to the present invention using the treatment apparatus shown in FIG. 4 will be described.
When the electrolysis of the silicone oil progresses and the silicon compound accumulates in the liquid and the decomposition rate decreases, the electrolyzed liquid is recovered from the emulsifying tank and filtered.

In this embodiment, when supplying the electrolyzed liquid from the emulsifying tank to the filtering device 50, the operation of stopping or reducing the output of the stirring means 90 and the centrifugal pump 95 is not performed. Therefore, filtration treatment and electrolysis treatment can be performed in parallel.

By recovering the electrolyzed liquid from the emulsification tank and retaining it in the retention tank 100 for preferably 1 hour or more, natural aggregation of the lipophilic silicon compound progresses, the diameter of the aggregation increases, and the filtration efficiency improves. Since the lipophilic silicon compound migrates upward along with the oil component in the retention tank 100, the pipe 82 is installed at the top of the retention tank in order to efficiently guide the floating silicon compound to the filtration device 50. is preferred.

In the present embodiment , since the electrolyzed liquid in which the oil phase and the water phase are completely mixed is filtered, not the oil phase that floats to the top of the emulsifying tank, so that not only the lipophilic silicon compound contained in the oil phase but also the , hydrophilic silicon compounds contained in the aqueous phase are also subject to filtration.

The filtrate filtered by the filtering device 50 may be directly returned to the emulsification tank 10, or may be temporarily stored in an arbitrary container and then returned to the emulsification tank for reuse.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples.
An electrolysis test of silicone oil (KF-50-100CS manufactured by Shin-Etsu Chemical Co., Ltd.) was performed using the treatment apparatus shown in FIG. The silicone oil was treated under the operating conditions shown in Table 1.

The silicon concentration in the electrolyzed liquid in the emulsifying tank was measured by atomic absorption spectrometry.
The organic substance concentration in the liquid phase of the emulsifying tank was measured by the COD chromium concentration analysis method (JIS K0102:2016 spectrophotometric method using a test tube with a lid). COD chromium measurements provide an indication of the concentration of all organic matter, including oil and its decomposition products, in the liquid.
Also, the oil concentration in the liquid phase of the emulsifying tank was measured by infrared absorption spectrometry using a HORIBA oil concentration meter OCMA-305.

[Example 1] Alternating electrolysis and filtration operation by reusing filtrate Using "EBAFOSE-9500" (semi-aqueous cleaning agent manufactured by Ebara Industrial Cleaning Co., Ltd.) as an emulsifier, electrolysis treatment of silicone oil is performed about 48 times. did the time. Thereafter, the treated liquid in the emulsifying tank was allowed to stand still for 1 hour, and the upper 10% of the liquid was collected and filtered under pressure using R-1-PP filter cloth manufactured by Kajika Corporation. The obtained filtrate was returned to the emulsifying tank, the silicone oil and the emulsifier were added again, the electrolysis treatment was performed, and after the completion of the electrolysis treatment, the solution was allowed to stand and the upper 10% of the liquid was filtered. Table 2 shows the test results.

"EBAFOSE-9500" contains hydrocarbons (5 to 30 mm ² /s kinematic viscosity at 40°C), n-paraffin (1 to 15 mm ² /s kinematic viscosity at 40°C), two kinds of POE alkyl ethers, higher alcohol (C8-C18) and water.

As shown in Table 2, about 14 g of silicone oil was added each time up to the 4th time of repeated operation, and from the 5th time onwards, no new oil was added, and only the emulsifier was added to decompose the remaining oil. rice field. The oil concentration after the seventh treatment was 5.2 g/L. While the cumulative electrolysis treatment time was 336 hours, the weight of cracked oil was 50.8 g and the average cracking rate was 151 mg oil/L/hr.

The generated solid secondary waste was 11.3 g of filtered matter. Decomposing 50.8 g of silicone oil generated 11.3 g of waste, and the volume reduction rate was (50.8 - 11.3) / 50.8 x 100 = 77.8%. rice field.

FIG. 5 shows changes in the COD in liquid and the cumulative weight of cracked oil in this example, and FIG. 6 shows changes in the weight of silicon in liquid. As shown in FIGS. 5 and 6, by repeating the operation seven times, the COD concentration and silicon concentration in the liquid once increased, then decreased, and finally decreased to a concentration close to the initial state. It is

In addition, as can be seen from the transition of the accumulated weight of the cracked oil in FIG. 5, the decomposition rate of the silicone oil was almost constant throughout the period.

From these results, it can be concluded that the method of the present invention efficiently decomposes silicone oil to produce waste without lowering the decomposition rate or accumulating decomposition products even when the electrolysis solution is repeatedly used. It was shown that the volume can be reduced.

[Comparative example] Operation in which the treated liquid is discharged for each batch without reusing the filtrate As a comparative example, the electrolytic treatment is performed until the COD concentration decreases, and then the treated liquid is neutralized and de-emulsified. and an oil adsorbent were added, and the oil concentration was adjusted to 10 mg/L or less by filtering, and the oil decomposition rate and the amount of secondary waste generated were evaluated. Refus E manufactured by Nippon Shield Co., Ltd. was used as a demulsifier, and Refus BA manufactured by Nippon Shield Co., Ltd. was used as an oil absorbent.

[Comparative Example 1]
In Comparative Example 1, the electrolysis treatment results were evaluated when 28 g of silicone oil, which was half the amount used in the example, was added. The results are shown in FIG.

Under the conditions of Comparative Example 1, the decomposition rate gradually decreased as the silicone oil decomposed, and the decomposition stagnated at a decomposition rate of about 66%. Even after 215 hours of electrolysis treatment, 9.5 g/L of oil remained in the liquid, and the treatment could not be completed.
From this, it was confirmed that conventional methods cannot treat high-concentration silicone oil.

[Comparative Example 2]
In Comparative Example 2, 14 g of silicone oil, which is 1/4 of the amount used in Example, was added and subjected to electrolysis treatment. We evaluated the oil decomposition rate and the amount of secondary waste generated when The results are shown in FIG.

Under the conditions of Comparative Example 2, although the decomposition rate decreased at a decomposition rate of about 80%, an oil decomposition rate of 93% could be obtained after 197 hours of operation. 0.95 g/L of oil remained in the liquid, and a total of 2.5 g/L of demulsifier and oil adsorbent was added to this, and after reacting for 2 hours, pressure filtration was performed. /L of the treated liquid was obtained.

The oil decomposition rate under the conditions of Comparative Example 2 was 66 mg oil/L/hr, and the oil decomposition rate was reduced to 1/2 or less compared to the Examples.

The solid secondary waste generated was 5.82 g of filtered material such as oil adsorbent (including silicon compound aggregates generated during neutralization and adsorption reaction). 5.82 g of waste was generated by decomposing and adsorbing 14 g of silicone oil, and the volume reduction rate was (14 - 5.82)/14 x 100 = 58.4%.
The volume reduction ratio was lower than 1/1.3 as compared with the examples.

From the above results, it was confirmed that the method of the present invention is superior to the conventional method in terms of both silicone oil decomposition rate and secondary waste volume reduction rate.

[Examples 2 and 3 and Comparative Example 3]
Next, a test was conducted to examine the relationship between the stirring strength per unit volume and the amount of collected solids.
Using the electrolytically treated liquid under the same conditions as after the end of the fifth repeated operation in Example 1, the stirring strength per volume was changed and the solution was allowed to stand or stirred for 1 hour, and then filtered in the same manner as in Example 1. Table 3 shows the test results.

In Examples 2 and 3 in which the stirring strength per volume was lower than 16700 [rpm/m ² ], the weight of the filter cake was almost constant, but the stirring strength per volume was increased to 16700 [rpm/m ² ]. In Comparative Example 3, the weight of the filter cake was reduced to half or less.

From the results in Table 3, when the stirring strength per volume is 16700 [rpm/m ² ] or more, the generated shear force causes the lipophilic silicon compound to disperse, making it difficult to capture with the filter cloth. was confirmed.

The oil treatment method of the present invention can smoothly treat mineral oil that is currently difficult to dispose of in the radioactive controlled area of a nuclear facility, and solves problems in facility operation management such as securing installation space. It can also be a means of solving the problem of residual waste toward decommissioning.

Claims (7)

A method of treating mineral oil in a radiation controlled area, wherein a mineral oil containing silicone oil and an emulsifier are added to water, electrolysis is performed using a conductive diamond electrode, and the mineral oil is oxidatively decomposed. In the treatment method, an electrolyzed solution containing a lipophilic silicon compound generated by decomposition of silicone oil is filtered , and the filtrate obtained by filtering the electrolyzed solution is used for oxidative decomposition of the mineral oil. A treatment method characterized by reusing as water . 2. The treatment method according to claim 1, wherein the electrolyzed liquid containing the lipophilic silicon compound is a liquid obtained by recovering an oil phase that floats to the top of the electrolyzed liquid. The method further comprises maintaining the electrolyzed liquid containing the lipophilic silicon compound at a stirring strength per volume of less than 16700 rpm/m ² for 5 minutes or more before filtering the electrolyzed liquid. The processing method according to claim 1 or 2, wherein an emulsifying tank for mixing and stirring a mineral oil containing silicone oil, an emulsifier, and water;
an electrolytic cell comprising diamond electrodes;
a pipe for sending the emulsion prepared in the emulsifying tank to the electrolytic tank;
a filtering device for filtering the electrolyzed liquid containing the lipophilic silicon compound;
and means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsification tank. 5. The processing apparatus according to claim 4 , wherein the means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsification tank is connected to the upper part of the emulsification tank. 5. The processing apparatus according to claim 4 , wherein the means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsification tank is connected to the bottom of the emulsification tank. 7. The means for recovering the liquid containing the oil phase of the electrolyzed liquid from the emulsifying tank further includes a retention tank for retaining the electrolyzed liquid discharged from the emulsifying tank for a predetermined time. The processing device according to .

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