JP2019147110A - Method of treating contaminated water - Google Patents

Abstract

To provide a method of treating contaminated water capable of immobilizing and sealing contaminants such as radioactive nuclides and heavy metals contained in the contaminated water, stably for a long period.SOLUTION: A method of treating contaminated water of this invention includes mixing papermaking sludge incinerated ash, an alkaline activator, chlorine, and contaminated water into a solidified geopolymer.SELECTED DRAWING: None

Description

  The present invention relates to a method for treating contaminated water such as radioactively contaminated water.

As a result of the Tohoku-Pacific Ocean Earthquake that occurred on March 11, 2011, the Fukushima Daiichi Nuclear Power Station suffered enormous damage. . Major radionuclides in the radioactive contaminated water, cesium ^{(137 Cs,} 134 ^Cs), strontium ⁽⁸⁵ Sr) and tritium.

  Currently, this radioactively contaminated water is treated by a so-called adsorption method including pretreatment, intermediate treatment and adsorption treatment. However, the treatment system using the adsorption method has a complicated equipment configuration, and requires a large amount of money for operation and maintenance of the equipment. Furthermore, in the adsorption method, an adsorbent such as zeolite or activated carbon is used for the treatment of radioactively contaminated water, so that a difficult problem of disposal of the adsorbent after use contaminated at a high level newly arises.

  Therefore, the present inventors mixed paper sludge incineration ash, alkali activator, and contaminated water so that the liquid-solid ratio is 1.0 or more as a method for treating contaminated water such as radioactively contaminated water. Invented a method for treating contaminated water as a geopolymer solidified body (see Patent Document 1). According to this treatment method, contaminants such as radionuclides contained in the contaminated water can be fixed and confined in the geopolymer solidified body.

  However, the present inventors simulated radioactive radioactive water and converted the contaminated water containing non-radioactive strontium (Sr) and cesium (Cs) into a geopolymer solidified body by the above treatment method. When the elution test of Sr and Cs was continued, it was found that the composition of the solid geopolymer was destabilized in the long-term age, and as a result, the fixing ratio of strontium and cesium was also destabilized.

Japanese Patent No. 5669120

  The problem to be solved by the present invention is to provide a method for treating contaminated water that can stably fix and confine contaminants such as radionuclides and heavy metals contained in the contaminated water over a long period of time.

  In the early stage of the accident at the Fukushima Daiichi NPS, emergency fresh water used for cooling water was difficult to procure, so seawater was substituted. Therefore, radioactively contaminated water including seawater (seawater-containing radioactively contaminated water) remains in tank storage. Thus, as a result of research on the seawater-containing radioactively contaminated water, the present inventors have found that the conventionally unstable strontium and cesium fixation rates can be stabilized for a long time when seawater is added. In other words, we invented a chlorine addition method that stabilizes the fixation of pollutants such as radionuclides by solidified geopolymers, triggered by research and development for seawater-containing radioactively contaminated water.

  That is, the method for treating contaminated water according to the present invention is characterized in that a papermaking sludge incineration ash, an alkali activator, chlorine, and contaminated water are mixed to obtain a solid polymer.

  According to the present invention, pollutants such as radionuclides contained in contaminated water can be stably fixed and confined over a long period of time.

  The method for treating contaminated water according to the present invention is basically an application of geopolymer technology. Geopolymer technology is known per se, and the active filler containing soluble silicon and aluminum and the alkali solution containing the alkali activator for activating this are mixed to promote the formation of siloxane bonds by the condensation polymerization reaction. This is a technique for obtaining a solid geopolymer.

  Conventionally, as the active filler, fly ash (pulverized coal boiler coal ash, fluidized bed boiler coal ash), blast furnace slag powder, metakaolin, municipal waste incineration ash molten slag powder, sewage sludge incineration ash molten slag powder, and the like are known. However, in the present invention, paper sludge incineration ash is used as an active filler. Papermaking sludge incineration ash is incineration ash generated when papermaking sludge (paper sludge) generated from a pulp manufacturing process, a paper manufacturing process, a used paper processing process, and the like is incinerated.

As disclosed in the above-mentioned Patent Document 1, the present inventors investigated the properties of paper sludge incineration ash (hereinafter referred to as “PS ash”). As a result, PS ash contains SiO ₂ and Al ₂ O ₃ and is a geopolymer. It was found that it can be used as an active filler. Furthermore, since PS ash has a nest-like porous structure and high water absorption, a larger amount of liquid is required to produce a solidified geopolymer using PS ash as an active filler than when using a conventional active filler. I also found it necessary. That is, the liquid-solid ratio (mass of alkali solution / mass of active filler) when using a conventional active filler is about 0.5 at most. However, when PS ash is used as the active filler, the liquid-solid ratio is It was found that 1.0 or more is appropriate.

  As described above, the present invention is characterized in that PS ash is used as an active filler. However, other active fillers can be used in combination as long as the water absorption characteristics of PS ash as an active filler are not lost. It is. An adsorption modifier that can adsorb contaminants such as radionuclides may be used in combination with PS ash. As this adsorption modifier, for example, zeolite, titanium oxide, bentonite and the like are preferably used in combination. By this combined use, the adsorptivity of the radionuclide of the PS ash geopolymer solidified body can be further improved.

  On the other hand, the alkali activator in the alkaline solution is a component that accelerates the polymerization of the silicon component eluted from the active filler and the metal component (mainly aluminum). Examples of the alkali activator include potassium hydroxide, sodium hydroxide, sodium silicate, and potassium silicate. From the test results described below, it was found that sodium silicate is preferably used alone. Typically, powdered or granular sodium silicate is mixed at a predetermined ratio using contaminated water as a solvent to form an alkaline solution.

  And in this invention, as mentioned above, the said contaminated water is processed by mixing PS ash, an alkali activator, chlorine, and contaminated water to make a geopolymer solidified body. At this time, the liquid-solid ratio can be 1.5 or more. In the treatment method of Patent Document 1 in which chlorine is not added, the liquid-solid ratio is about 1.0 to 1.2. However, in the treatment method of the present invention in which chlorine is added, the liquid-solid ratio is 1.5. It has been found that it can be further increased (approximately 1.5 to 2.0). That is, according to the treatment method of the present invention, a larger amount of contaminated water can be treated as compared with the treatment method of Patent Document 1.

Contaminated water to be treated mainly by the present invention is radioactive contaminated water containing radionuclides, typically cesium ( ¹³⁷ Cs, ¹³⁴ Cs) and strontium ( ⁹⁰ Sr) generated at the Fukushima Daiichi Nuclear Power Station. ), And seawater-containing radioactively contaminated water including seawater. That is, in the present invention, chlorine can be derived from seawater or saltwater originally containing contaminated water (hereinafter collectively referred to as “seawater or the like”) without special addition and mixing. However, in this invention, chlorine is not limited to seawater etc., Inorganic salts, such as sodium chloride, can also be added and mixed with contaminated water. The chlorine content is preferably 0.1 to 2% by mass when the total amount of the alkali activator and the contaminated water is 100% by mass.

  The scope of application of the present invention is not limited to radioactively contaminated water. The geopolymer solidified material has the property that it can fix pollutants such as heavy metal ions in addition to radionuclides, so it can be applied to the treatment of contaminated water containing heavy metal ions such as plating waste liquid and mine waste liquid. . Further, it can be applied to solidification treatment of muddy or solid waste such as contaminated soil other than water, contaminated mud, contaminated ash, contaminated sludge, and used nuclide adsorbent. That is, in the treatment method of the present invention, mud or solid waste can be further mixed to obtain a geopolymer solidified body.

  The test which made the contaminated water which simulated seawater containing radioactively contaminated water as follows was made into a geopolymer solidified body (GP solidified body) was conducted.

1. Preparation of alkaline solution (GP solution) As a seawater mixed alkaline solution (GP solution), a commercial product called JIS No. 1 water glass (sodium silicate aqueous solution Na ₂ O · 2SiO ₂ · aq, standard composition) was purchased and purified water was used. Seawater was mixed with a diluted sodium silicate stock solution having a specific gravity of 1.54, and a specific gravity of 1.27 (hereinafter referred to as “No. 1 GP solution”) and this No. 1 GP solution Furthermore, two kinds of alkaline solutions (GP solutions) prepared by mixing 1 part of 10M caustic soda aqueous solution with 3 parts of No. 1 GP solution by volume ratio (hereinafter referred to as “No. 0 GP solution”) were prepared. did. The details are shown in Table 1. In practice, seawater-containing radioactively contaminated water is mixed.

  On the other hand, as a seawater-unmixed alkaline solution (GP solution), seawater-mixed No. 1 GP solution and No. 0 GP solution equivalent No. 1 GP solution and No. 0 GP solution were prepared.

2. Chemical composition and physical properties of active filler (PS ash) Table 2 shows the chemical analysis values and physical properties of PS ash used as the active filler.

3. Production method of geopolymer solidified body (GP solidified body) A GP solidified body was produced using each of the two types of active fillers (PS ash) shown in Table 2.
Specifically, 100 g of the active filler was weighed, the seawater-mixed GP solution was mixed up to the limit where no breathing occurred, and well mixed by hand kneading and poured into a mold. As shown in Tables 3a and 3b, the liquid-solid ratio (L / F) = “GP liquid (alkali solution) / active filler (PS ash)” (weight ratio) varied depending on the type of active filler.

  The mold used was made of 3 square pillars, and the size was 20 × 20 × 80 mm. Grease was previously applied to the inner surface of the mold as a release agent. After pouring into the mold, in order to prevent cracks and shrinkage, it was transferred into a 100% saturated humidity plastic container with water on the bottom, and was cured in air overnight in a constant temperature chamber at 20 ° C. . After demolding, it was further cured under the same conditions until the age of 4 weeks. At the time of the age of 4 weeks, the bulk density of the GP solidified body was measured from the mold size and the weight of the GP solidified body. Further, a three-point bending test was performed, and bending strength was obtained with an average value of three pieces. In the three-point bending test, the span distance of the lower fulcrum was 50 mm, and the loading speed was 0.2 mm / min.

  Thereafter, the GP solidified body was left in the room and kept in an air-dried state until it reached the age of 6 (4 + 2), 12, 24, 52 weeks. The bulk density was measured at each age and used to calculate the element elution rate. The initial dimension of the GP solidified body was used as a formwork dimension for convenience.

Since nuclides that mainly form radioactively contaminated water are ¹³⁷ Cs, ¹³⁴ Cs, ⁹⁰ Sr, 1% of non-radioactive nitrate reagent (Sr (NO ₃ ) ₂ , CsNO ₃ ) is applied to the active filler weight as an external factor. Added. Since these are soluble and small amounts, they are excluded from the calculation of the liquid-solid ratio for convenience. The radiation dose of contaminated water at Fukushima Daiichi NPS is estimated to be 10 ⁸ to 10 ⁹ Bq / L. On the other hand, the added nitrate is equivalent to 10 ¹² Bq / L, which is a sufficient addition amount.

  For comparison, a similar GP solidified body was prepared using a seawater-unmixed GP solution.

4). Bulk density and strength test results of GP solidified body Table 3a shows the test results of the bulk density and bending strength of the GP solidified body using the seawater mixed GP liquid. For comparison, Table 3b shows the test results of the bulk density and bending strength of the GP solidified body using the seawater-unmixed GP solution.

  As can be seen from Table 3a and Table 3b, one of the characteristics of the GP solidified body using the seawater-mixed GP liquid is that the liquid-solid ratio can be made larger than that of the GP solidified body using the seawater-unmixed GP liquid. . This is very effective in that the contaminated water can be taken in larger and solidified.

  The bending strength is lower when the seawater-mixed GP solution is used than when the seawater-unmixed GP solution is used. However, the GP solidification using the seawater-mixed No.1 GP solution is exceptionally low. Some parts of the body were slightly higher (the reason is not clear at this time).

  Regarding the bulk density, when seawater-mixed GP liquid is used, there is no significant difference from the case where seawater-unmixed GP liquid is used over all ages, although the liquid-solid ratio is high. However, exceptionally, the bulk density of the OTo3 GP solidified body using the seawater mixed solution No. 0 tends to be low, and foaming is remarkable and porous, which is considered to be a result of promoting moisture evaporation. Foaming was also observed in the solidified GP of OTo3 using No. 1 GP liquid regardless of seawater mixing or non-seawater mixing, but foaming was slight and no effect was observed. The cause of foaming is that some PS ash may use waste paper as the raw material, and the ultrafine particles left unoxidized by evaporation of the aluminum foil in the furnace are the GP solution (alkaline solution). It is thought that this is because it reacts in this to generate hydrogen.

5. Result of dissolution test of GP solidified body Table 4a shows the result of the dissolution test of the GP solidified body using the seawater mixed GP solution. For comparison, Table 4b shows the results of the dissolution test of the GP solidified body using the seawater-unmixed GP solution.

The dissolution test method is based on the method developed by the present inventors. Specifically, the GP solidified body is pulverized to 4 mm or less, and 12.5 g is weighed. Transfer the sample to a 250 mL wide-mouth plastic bottle, add 10 volumes of exudate, and seal. As the leachate, a pH 4.01 standard solution containing phthalate as a main ingredient is used. This is applied to a ball mill rotating machine for 6 hours under a rotation condition of 60 rpm, filtered through qualitative filter paper No. 131, and diluted 10 times with pure water to obtain a test solution. The concentration of the test solution is measured by ICP-AES.
The element fixation rate (%) is calculated from the concentration measurement result of the test solution. That is, the fixation rate (%) = (100−elution rate). In the calculation of the dissolution rate, the bulk density at each age was compared with the 4-week bulk density, and the remaining solid weight (active filler weight) was recalculated using the weight loss value as the water evaporation amount. The content of the added nitrate is obtained from the result, and the converted content weight of Sr ²⁺ and Cs ⁺ is obtained. On the other hand, the elution weight is obtained from the result of ICP-AES, and the elution rate is finally calculated from the ratio with the converted content.

As can be seen from Table 4a and Table 4b, when using the seawater mixed GP liquid, compared to the case of using the seawater unmixed GP liquid, Sr ²⁺ , Cs over all ages regardless of the type of GP liquid and PS ash. The fixing rate of ⁺ was stable, and no scale over (SO) was observed.
However, at the age of 52 weeks, a slight decrease in the fixation rate was observed when the No. 0 GP solution was used. When judging comprehensively, when using No. 1 GP solution, a result of a high fixation rate is obtained, the material strength is high, and since no caustic soda is added, it is inexpensive. That is, as the GP solution (alkali activator), it is preferable to use a solution containing sodium silicate and not additionally mixed with sodium hydroxide.

Claims (7)

  A method for treating contaminated water by mixing paper sludge incineration ash, an alkali activator, chlorine, and contaminated water to obtain a solidified geopolymer.   The method for treating contaminated water according to claim 1, wherein the chlorine content is 0.1 to 2 mass% when the total amount of the alkali activator and the contaminated water is 100 mass%.   The method for treating contaminated water according to claim 1 or 2, wherein the chlorine is derived from any of river water containing seawater and salinity.   The method for treating contaminated water according to any one of claims 1 to 3, wherein a muddy or solid waste is further mixed.   The method for treating contaminated water according to any one of claims 1 to 4, wherein the alkali activator contains sodium silicate and is not further mixed with sodium hydroxide.   The method for treating contaminated water according to any one of claims 1 to 5, wherein the contaminated water is radioactively contaminated water including seawater.   The method for treating contaminated water according to any one of claims 1 to 5, wherein the contaminated water is contaminated water containing heavy metals.