JP7186123B2 - How to treat decontamination mud - Google Patents

Description

The present invention relates to a method for treating decontaminated mud.

If water areas such as dams, lakes and marshes exist in radioactively contaminated areas, the bottom sediments in those water areas will be decontaminated.
The removed soil dredged for the decontamination work of the bottom of the lake (hereinafter referred to as "decontamination mud") is a mud-like substance containing a large amount of water, so it is difficult to store it as it is. . Regarding the treatment of the decontaminated mud, there is a method of storing the agglomerated decontaminated mud in a storage bag after agglomeration, and further in a concrete container for storage (see, for example, Patent Document 1).
As a flocculant used for flocculating decontamination mud, there is a flocculant containing gypsum powder (see, for example, Patent Documents 2, 3, and 4).

JP 2016-17772 A JP 2010-172883 A JP 2010-172882 A JP-A-2003-94100

By reducing the water content of the mud, transportation, storage, etc. become easier. For this reason, it is desired to quickly separate the solid content such as mud contained in the muddy water from the water, and to achieve the solid-liquid separation at an early stage. However, the aggregating agents described in Patent Documents 1 to 3 require time to agglutinate objects, so it has been difficult to perform rapid solid-liquid separation.
SUMMARY OF THE INVENTION An object of the present invention is to provide a method for treating decontaminated mud that can more quickly separate solids and water to reduce the water content of the mud.

The method for treating decontaminated mud according to the present invention includes a dehydration acceleration step of adding a dehydration accelerator containing anhydride gypsum to mud containing decontamination mud, and a solid-liquid separation of separating solid content and water in the mud. The anhydrite has an average particle diameter D50 of 5 to 100 μm, and among the peak intensities obtained by X-ray diffraction, the peak intensity of the (020) plane (I ₍₀₂₀₎ ) and the peak intensity (I ₍₁₀₂₎ ) of the (102) plane (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) is 5 or more.

ADVANTAGE OF THE INVENTION According to this invention, the solid content and water|moisture content are isolate|separated more rapidly and the processing method of the decontamination mud which can reduce the water|moisture content of mud is provided.

1 is a scanning electron microscope (SEM) photograph of the surface of natural anhydrite. It is a SEM photograph of the surface of industrial anhydrite.

Hereinafter, embodiments of the present invention will be described in detail.
The decontamination mud treatment method of the present invention includes a dehydration acceleration step of adding a dehydration acceleration agent containing anhydrite to mud containing decontamination mud, and a solid-liquid separation step of separating solid content and water in the mud. including. Each step will be described below.

[Dehydration promotion step]
First, a predetermined dehydration accelerator is added to mud containing decontamination mud. Dehydration of the decontaminated mud is promoted by adding a predetermined dewatering accelerator. The dehydration accelerator used in the present invention can be obtained by mixing components such as polymers with anhydrite. Anhydrous gypsum includes, for example, natural anhydrite (produced in Thailand). The physical properties are shown below in comparison with industrial anhydride gypsum (manufactured by Asahi Glass Co., Ltd.).

<Comparison between natural anhydrite and industrial anhydrite>
(Average particle size D50)
The average particle diameter D50 obtained from the wet particle size distribution of each anhydrite is summarized in Table 1 below. Water was used as the dispersion medium, and after pretreatment by ultrasonic dispersion, the particle size distribution was measured using a particle size distribution analyzer (manufactured by Microtrack Bell Co., Ltd.).

It was confirmed that natural anhydrite has a significantly larger average particle size D50 than industrial anhydrite. A large average particle diameter D50 is advantageous in terms of improving dispersibility in muddy water.
If the average particle size D50 of the natural anhydrite is as small as less than 5 µm, it will not disperse well in muddy water, possibly impairing its function as a dehydrating agent. On the other hand, if the average particle size D50 of the natural anhydrite exceeds 100 µm, it is not preferable in that the particle size diverges from that of the other components and segregation may occur. Therefore, in the present invention, natural anhydrite having an average particle size D50 of 5 to 100 μm is used. The average particle size D50 of the natural anhydrite is preferably 10-40 μm, more preferably 15-30 μm.

(dry particle size)
Table 2 below summarizes the dry particle size of each anhydrite. The dry particle size was measured using a 150 μm sieve and a 90 μm sieve.

Natural anhydrite was shown to have a lower percentage of particles on a 150 μm sieve than engineered anhydrite. This result indicates that the particle size of natural anhydrite is more uniform than that of industrial anhydrite. A comparison of the SEM photographs of FIGS. 1 and 2 shows that the natural anhydrite has a larger particle size than the industrial anhydrite.

Table 3 below summarizes the contents of components contained in natural anhydrite and industrial anhydrite. The content of each component was determined by ICP analysis.

The content of CaO can be considered equivalent if it is within the range of 30-50%, and the content of _SO3 can be considered equivalent if it is within the range of 40-60% . Therefore, no clear difference is confirmed between the natural anhydrite and the industrial anhydrite in terms of the components contained. The balance in each anhydrite is impurities and the like.

(crystallite measurement)
Crystallites of natural anhydrite (produced in Thailand) and industrial anhydrite (produced by Asahi Glass Co., Ltd.) were measured using a fully automatic multipurpose X-ray interpretation device (D8 ADVANCE, manufactured by Bruker Aix). The measurement conditions were as follows.
・Tube voltage, tube current: 40 kV, 40 mA
・Scanning range: 20 to 50° ・Step width: 0.02° ・Measurement time: 1 S/step ・Divergence slit, light receiving slit: both 0.3°
The crystallite was calculated from the peak of the (020) plane by Scherrer's formula. Crystallites are calculated automatically by the device.
D=Kλ/(B cos θ)
(D: crystallite size, K: Scherrer constant (0.9), λ: X-ray wavelength B: peak half-width, θ: Bragg angle)
The results obtained are summarized in Table 4 below.

Natural anhydrite was confirmed to have higher peak intensity and crystallite than industrial anhydrite. Therefore, it can be seen that the natural anhydrite has a higher orientation than the industrial anhydrite.
Since natural anhydrite has a higher orientation than industrial anhydrite, it is presumed to have a fibrous shape growing in the length direction. Table 5 below shows the intensity ratio between the (020) plane and the (102) plane.

Based on the results shown in the table above, the peak intensity ratio of the natural anhydrite is, among the peak intensities obtained by X-ray diffraction, the peak intensity of the (020) plane (I ₍₀₂₀₎ ) and the peak intensity of the (102) plane. The ratio (I ₍₀₂₀₎ /I (102 ₎ ) to the peak intensity (I ₍₁₀₂₎ ) was defined to be 5 or more. The ratio (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) is preferably 50 or less, more preferably 10-40, most preferably 15-30.
If the ratio (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) is too small, the orientation is not high and the fiber does not grow in the longitudinal direction, which is considered to have an adverse effect on the dispersibility in muddy water. . It was found that by setting the ratio (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) to 5 or more, the dispersibility in muddy water is improved. Considering the range of intensity ratios that can be easily measured, the upper limit of the ratio (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) can be about 50.

The above results show that natural anhydrite has a significantly larger average particle diameter D50 than industrial anhydrite, as well as high crystallinity and high orientation. Natural anhydrite is produced in nature over a long period of time. In contrast, industrial anhydrite, for example phospho gypsum, is produced in a short period of time when phosphate rock and sulfuric acid are reacted to produce phosphoric acid. Due to the difference in properties between natural anhydrite and industrial anhydrite due to the difference in crystal formation rate, and due to these physical properties, the dehydration accelerator containing natural anhydrite has poor dispersibility in water. It is presumed to be superior to industrial anhydride gypsum and to act effectively as a nucleus when contaminant suspended matter agglomerates.

<Polymer>
Although the polymer imparts the effect of enlarging flocs due to aggregation, the effect is not remarkably improved even if it is excessively blended. If 10 to 15 parts by mass of the polymer is used with respect to 100 parts by mass of the natural anhydrite, the desired effect can be sufficiently obtained.

As the polymer, either a synthetic polymer or a natural polymer may be used. As the synthetic polymer, it is preferable to use a combination of a low anionic low molecular weight polymer having a weight average molecular weight (Mw) of about 6 million to 12 million and a strong anionic high molecular weight polymer having an Mw of about 13 million to 16 million. Low-molecular-weight polymers and high-molecular-weight polymers can be used in any ratio. For example, the mass ratio (low-molecular-weight polymer:high-molecular-weight polymer) can be about 80:20 to 40:60.

Conventionally known synthetic polymers can be used. For example, carboxylate-based polymers such as sodium acrylate, copolymers of carboxylate and acrylamide, copolymers of sulfonate and acrylamide, copolymers of alkylaminoacrylate salt and acrylamide, alkyl Copolymers of amino methacrylate salts and acrylamide and the like are included. Among these, polycarboxylate-based substances, that is, carboxylate polymers and copolymers of carboxylate and acrylamide are preferred.

Examples of the polycarboxylic acid in the copolymer of carboxylate and acrylamide include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and carboxymethylcellulose.
Examples of the sulfonic acid in the copolymer of sulfonate and acrylamide include acrylamide 2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid.

Alkylaminoacrylate salts in copolymers of alkylaminoacrylate salts and acrylamide include dimethylaminoethyl acrylate, dimethylaminopropylacrylamide, acryloyloxyethyltrimethylammonium chloride, acryloylaminopropyltrimethylammonium chloride and acryloyl 2-hydroxypropylide. etc. can be mentioned.

Examples of alkylamino methacrylate salts in copolymers of alkylamino methacrylate salts and acrylamide include dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, methacryloyloxyethyltrimethylammonium chloride, methacryloylaminopropyltrimethylammonium chloride, methacryloyl 2-Hydroxypropylide and the like can be mentioned. The composition of the synthetic polymer can be changed as appropriate within a range that does not deviate from its effects.

Examples of natural polymers include seed polysaccharides such as guar gum, roasted gua gum, and roasted bingham; resin polysaccharides such as arabinogalactan gum and gum arabic; seaweed polysaccharides such as alginic acid and chitosan; and fruit polysaccharides such as pectin and psyllium gum. , starch, rhizome polysaccharides such as konnyaku, fibrous polysaccharides such as cellulose, microbial xanthan gum, xanquat, xanflo, curdlan, succinoglucan, and animal gelatin, casein, albumin, and shellac. Starch derivatives, guar gum derivatives, roasted guar gum derivatives obtained by subjecting starch, guar gum, roasted guar gum, cellulose, alginic acid, etc. to treatments such as oxidation, methylation, carboxymethylation, hydroxyethylation, phosphorylation, cationization, etc. , cellulose derivatives, alginic acid derivatives and the like may also be used. The composition of the natural polymer can be appropriately changed within a range that does not deviate from its effects.

<Other ingredients>
The dehydration accelerator used in the present invention may contain aluminum sulfate, soda ash, powdered polyaluminum chloride (PAC), diatomaceous earth (P1200), and the like. These components are preferably used in the following ratios, respectively, with respect to 100 parts by mass of natural anhydrite.
Aluminum sulfate: 15 to 30 parts by mass
Alginic acid: 1 to 10 parts by mass
Soda ash: 10 to 20 parts by mass
Powder PAC: 0.5 to 10 parts by mass
Diatomaceous earth: 5 to 20 parts by mass

<Dehydration accelerator>
The dehydration accelerator can be produced by blending natural anhydride gypsum with predetermined amounts of polymer and components such as aluminum sulfate, and mixing the mixture using a powder mixer or the like.
A desired effect can be sufficiently obtained by adding 0.01 to 0.1 parts by mass of the dehydration accelerator to 100 parts by mass of the mud containing decontamination mud. A dehydration promoting material is placed together with muddy water in a predetermined container, and stirred at 100 to 400 rpm using, for example, a stirring blade. About 20 seconds to 2 minutes after mixing, flocs are generated and settled. Dehydration promotion of the decontaminated mud can be determined based on floc sedimentation time and floc mass.

[Solid-liquid separation step]
Mud water in which the decontamination mud has been accelerated is separated into solids and water using a water-permeable member. For example, a sieve can be used as the water permeable member. The mesh size of the sieve can be selected as appropriate, but is preferably within the range of 0.25 mm to 1.8 mm, more preferably within the range of 0.4 mm to 1.2 mm. When the muddy water is supplied to a sieve having a predetermined mesh size, the solid content and water content are separated, and flocs with reduced water content are obtained on the sieve.

Solid-liquid separation can also be performed by containing muddy water in a bag, at least a part of which is made of a water-permeable member. In this case, the water-permeable member includes a mesh material with an opening of 0.25 to 1.8 mm, preferably a mesh material of 0.4 mm to 1.2 mm. The mesh material preferably constitutes the bottom of the bag, and more preferably the entire bag is made of the mesh material.
Muddy water is contained in a bag, and the water is discharged by, for example, hanging from above, so that dewatered mud can be obtained. Since the mud is already contained in the bag, it is easy to carry out operations such as transportation and storage after dehydration.
When the bag containing muddy water is pressurized, the discharge of water is accelerated, so that the solid-liquid separation can be performed more quickly. Further, even when the bag containing the muddy water is rotated and subjected to centrifugal separation, the discharge of water can be accelerated.

Specific examples of the present invention are shown below, but they are not intended to limit the present invention.
<Selection of gypsum to be used>
First, the dehydration performance of natural anhydrite and industrial anhydrite was confirmed. Specifically, natural anhydrite and industrial anhydrite were each added to the sediment of the reservoir, and a floc formation test and a sedimentation test were conducted.

(Preparation of sample)
475 g of water was added to 25 g of bottom sediment to prepare 500 g of muddy water. A sample was prepared by adding 0.3 g of natural anhydrite (produced in Thailand) to the obtained muddy water.

(Examination content)
Flock formation test: The prepared sample (mud water to which natural anhydrite was added) was stirred at a mixing speed of 200 rpm using a general-purpose agitator (general-purpose agitator BL300 manufactured by Shinto Kagaku Co., Ltd.). After 1 minute, the muddy water was filtered using a sieve (850 μm mesh) to separate solid and liquid, and the mass of flocs on the sieve was measured.
Further, a flocculation test was conducted in the same manner as described above except that the mesh size of the sieve was changed, and the mass of the flocs on the sieve was measured. The results are shown in Table 6 below. More flocs on the sieve indicates more accelerated dewatering.

For comparison, 0.3 g of industrial anhydride gypsum (manufactured by Asahi Glass Co., Ltd.) was added to the same muddy water (500 g), and the same floc formation test was conducted. A sieve with an opening of 850 μm was used for solid-liquid separation. The mass of floc on the sieve is as shown in the table below.

As shown in the above table, the samples using natural anhydrite are larger than the samples using industrial anhydrite in both the total mass remaining on the sieve and the dry mass after water is removed from the total mass. This is because the sample with the addition of natural anhydrite forms flocs more favorably than the sample with industrial anhydrite, and more of the solid content in the muddy water (the material contained in the dry mass) is taken into the floc, It is based on suppressing solids in the mud from passing through the sieve. That is, compared to industrial anhydrite, natural anhydrite acts effectively as a nucleus when polluted suspended matter agglomerates, and easily forms large flocs. .

Sedimentation test: The same sample prepared in the flocculation test was stirred in the same manner as in the flocculation test, then placed in a 500 ml graduated cylinder and allowed to stand, and the amount of sedimentation was measured. In this test, raw water (muddy water without gypsum) was also measured. The measurement results are shown in Table 8 below.

As shown in the above table, about 70% of the sample using natural anhydrite settled in just over 10 seconds, and 80% settled in 1 minute. On the other hand, the sample using industrial anhydride gypsum took more than 30 seconds for 70% settling and 5 minutes for 80% settling. Samples using natural anhydrite can quickly coagulate and settle solids in muddy water compared to industrial anhydrite, and have high dehydration acceleration performance. This is based on the fact that natural anhydrite has better dispersibility in water than industrial anhydrite and can form large flocs.

As shown by the above results, natural anhydrite is superior to industrial anhydrite in dehydration acceleration performance. Therefore, it is expected that the treatment by the method of the present invention using the dehydration promoting material containing natural anhydrite can more quickly separate the solid content from the water content and reduce the water content of the mud.

In the following, a dewatering accelerator containing natural anhydrite or industrial anhydrite is produced, and decontamination mud is treated using the obtained dewatering accelerator.

<Preparation of dehydration promoting material>
Polymer, aluminum sulfate, alginic acid (coarse powder), soda ash, powdered polyaluminum chloride (PAC), and diatomaceous earth (P1200) are blended in the parts by mass shown in Table 9 below with respect to 100 parts by mass of natural anhydrite, and a sample is prepared. 1 to 10 dehydration accelerators were produced.

For comparison, a dehydration promoting material of sample 11 was produced in the same formulation as sample 3, except that natural anhydrite was changed to industrial anhydrite.

<Treatment of muddy water>
As the object to be treated, 25 g of decontamination mud (bottom soil collected from a predetermined reservoir in Fukushima Prefecture) and 475 g of tap water were mixed to prepare 500 g of mud. Treatments with samples 1-10 containing natural anhydrite are Examples 1-10, and treatments with sample 11 containing engineered anhydrite are comparative examples.

First, each dehydration promoting material was added to muddy water to promote dehydration, and then solid-liquid separation was performed. The floc formation rate, floc size, pH of the tap water, and transparency of the tap water were comprehensively judged to evaluate the treatment performance. Specifically, the muddy water was placed in a 1-liter glass beaker, and 0.3 g (0.06% by mass) of a dehydration accelerator was added. Using a general-purpose stirrer (BL300 manufactured by Shinto Kagaku Co., Ltd.), the dehydration accelerating material and muddy water were mixed by stirring at a rotation speed of 200 rpm while visually observing.
When the state of dispersion of the dehydration accelerator in the muddy water was visually observed, it was confirmed that the dehydration accelerators of Samples 1 to 10 were better dispersed than the dehydration accelerator of Sample 11.

(Flock formation speed)
The time (t _F ) from the start of mixing to the formation of flocs was measured, and the flocculation rate was evaluated as follows.
◎: t _F ≤ 30 sec
○: 30 sec < _tF ≤ 60 sec
△: 60 sec < _tF ≤ 120 sec
×: _tF > 120 sec
The flocculation rate was also marked as "x" when flocculation was not formed.
As for the flocculation rate, "Δ", "○", and "⊚" are acceptable. The shorter the flocculation rate, the better the dehydration promotion performance, which also leads to the shortening of the treatment time.

(flock size)
Muddy water containing flocs was separated into solids (flocs) and moisture using a circular sieve with an opening of 850 μm, and the size of the flocs remaining on the sieve was measured. The size of flocs refers to the size of flocs formed in muddy water, and was obtained by visual observation and measurement from the outside of the beaker. If the size of the floc is 5 mm or more and 10 mm or less, it is defined as "large", and if it is 1 mm or more and less than 5 mm, it is defined as "small". The larger the flocs formed, the faster the solid-liquid separation can be carried out.

(Evaluation of moisture under sieve)
The pH of the moisture under the sieve was measured with a desktop pH meter. The pH is preferably about 5-9, more preferably about 5.8-8.6.
The transparency of the moisture under the sieve was visually examined and evaluated according to the following criteria.
◎: No floating matter is seen, and the water becomes transparent.
○: There are some floating substances, but the water is almost transparent.
△: There are some floating substances, and the water is slightly turbid
x: Suspended matter is present and the water is turbid. Excellent transparency corresponds to sedimentation of contaminant suspended matter in the muddy water, that is, accelerated dehydration.

The floc formation rate, floc size, pH of the tap water, and transparency of the tap water are summarized in Table 10 below together with the overall evaluation of the treatment performance. The overall evaluation was obtained by comprehensively judging mainly the flocculation rate and the size of the flocs, and subordinately the transparency and pH of the tap water.

As shown in Table 10 above, in Examples 1 to 10 using the dehydration accelerating material containing natural anhydrite, the solid content in the mud was higher than the comparative example using the dehydration accelerating material containing industrial anhydrite. and moisture can be rapidly separated, and the dehydration performance is improved.

Claims (4)

A method for treating decontamination mud contaminated with radioactivity,
A dehydration acceleration step of adding a dehydration accelerator containing anhydrite to mud containing decontamination mud, and a solid-liquid separation step of separating solid content and water in the mud,
The anhydrite is a natural anhydrite (produced in Thailand) having an average particle diameter D50 of 5 to 100 μm as determined from the wet particle size distribution. ₍₀₂₀₎ ) and the peak intensity (I ₍₁₀₂₎ ) of the (102) plane (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) is 5 or more, and the result of dry particle size measurement using a sieve A method for treating decontamination mud, wherein less than 0.1% of particles do not pass through a sieve with an opening of 150 μm, and 98.7% or more of particles pass through a sieve with an opening of 90 μm. 2. The method for treating decontamination mud according to claim 1, wherein the ratio (I ₍₀₂₀₎ /I ₍₁₀₂₎ ) is 50 or less. 3. The method for treating decontaminated mud according to claim 1 , wherein the solid-liquid separation step is performed using a bag at least partially made of a water-permeable member . 4. The method for treating contaminated mud according to claim 3 , wherein the permeable member is a mesh material having an opening of 0.25 to 1.8 mm .

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