JP2019070581A - Contamination water processing method, contamination water processing system and sodium compound addition device used therefor - Google Patents

Abstract

To provide a contamination water processing method of various kinds of contaminated water capable of facilitating adsorption removal of radioactive nuclide while suppressing effects of coexisting substances other than radioactive substances.SOLUTION: The contamination water processing method comprises: a pH buffer process for making contaminated water slightly alkaline; an adsorption step for adsorption removing radioactive nuclide contained in the contaminated water after the pH buffer process; and controlling the water quality of the contaminated water so that sodium contained in contaminated water is excessive to calcium before the adsorption step of the radioactive nuclide.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polluted water treatment method, a polluted water treatment system, and a sodium compound addition apparatus used therefor.

  As a method of removing radioactive materials from water (contaminated water) containing radioactive materials generated in nuclear related facilities, for example, nuclear power plants, a method using an ion exchange resin, adsorption of radioactive materials by an inorganic or organic adsorbent And the like are known. Here, radioactive substances include substances derived from fuel (U, actinides such as Pu), substances generated by activation (Fe, Co, Ni, etc.), and fission products (Cs, Sr, I, etc.) included.

  In the in-use plant, even if fuel failure occurs, the concentration of fission products and substances derived from fuel is low, and is well controlled including substances generated by activation. On the other hand, if the fuel is greatly damaged as in the case of an accident, reprocessing facilities or waste treatment facilities have a high proportion of fission products and substances derived from the fuel, and the concentration of these radioactive substances in the contaminated water is high.

  Various properties (components, pH, etc.) are assumed for the contaminated water generated in nuclear related facilities. For example, acidic and alkaline contaminated water can be considered. In addition, some adsorbents have an appropriate pH range to exhibit adsorption performance, and when selecting such adsorbents, the pH of the contaminated water is adjusted to acidic or alkaline depending on the adsorbent, and then In some cases, radionuclides contained in contaminated water may be adsorbed onto the adsorbent.

  The treatment method and the treatment apparatus for adsorbing and removing the radionuclide from the radioactive waste liquid are described in Patent Document 1, Patent Document 2 and Patent Document 3.

  Patent documents 1 to 3 generally include a filtration device for removing particulate matter contained in radioactive waste liquid, a colloid removal device for removing colloidal material, and an adsorption tower for adsorbing and removing radionuclides. It is described that it is desirable to be packed with oxine-impregnated activated carbon, which is a water treatment apparatus, in an adsorption column.

  Patent Document 4 discloses a pH adjustment tank which adjusts the pH of a radioactive waste solution containing salt to be weakly alkaline in order to improve the removal efficiency of strontium etc., and an adsorption tower which adsorbs radionuclides from the waste solution after pH adjustment; A radioactive waste liquid treatment system is described.

  Patent Document 5 describes a method of obtaining an adsorbent in which the adsorption performance of cesium and strontium is improved by subjecting crystallized silicotitanate (CST), which is a titanium silicate compound, to caustic treatment.

JP, 2015-40826, A JP, 2015-59852, A JP, 2015-59870, A JP, 2013-108818, A JP 2014-122806 A

  Contaminated water produced at nuclear facilities may vary in nature, and may include, among others, seawater, freshwater from rivers, groundwater, water in contact with concrete used in construction, and the like. Therefore, in addition to the radioactive substance to be removed, a substance to be adsorbed by the adsorbent coexists. Therefore, the contaminated water may contain salt (such as calcium or magnesium) derived from seawater or groundwater.

  In such a case, even if the radioactive waste liquid treatment system described in Patent Document 4 is used, due to the influence of the coexisting substance, it may be difficult to sufficiently adsorb and remove the radioactive substance.

  An object of the present invention is to suppress the influence of coexisting substances other than radioactive substances and promote adsorption and removal of radionuclides in the treatment of various types of polluted water.

  The contaminated water treatment method of the present invention comprises a pH buffering step for making the contaminated water weakly alkaline, and a radionuclide adsorption step for adsorbing and removing radionuclides contained in the contaminated water after the pH buffering step, Before the process, control the quality of the contaminated water so that the sodium contained in the contaminated water is excessive to calcium.

  According to the present invention, in the treatment of various polluted waters, the influence of coexisting substances other than radioactive substances can be suppressed, and adsorption and removal of radionuclides can be promoted.

FIG. 1 is a schematic configuration view showing a contaminated water treatment system of a first embodiment. It is a graph which shows the result of having calculated the state of the sodium ion couple | bonded with silicotitanate. FIG. 7 is a schematic configuration view showing a contaminated water treatment system of Example 2; FIG. 8 is a schematic configuration view showing a contaminated water treatment system of Example 3;

  The present invention relates to a method of treating contaminated water containing a radionuclide, a contaminated water treatment system, and a sodium compound addition device used therefor.

  The present invention is characterized in that the ratio of sodium to calcium contained in the contaminated water is adjusted to an excess state of a predetermined value or more.

  Contaminated water (raw water) usually contains 0.1 to several ppm of strontium. Similarly, several tens ppm to several hundreds ppm of calcium and magnesium are contained. Here, most of the strontium is derived from seawater and is a non-radioactive isotope. In a radionuclide adsorption apparatus (radionuclide adsorption step) described later, strontium containing a radioactive isotope is adsorbed and removed, but calcium and magnesium are hardly adsorbed.

  Below, the case where the adsorption material used for a contaminated water treatment apparatus performs a caustic process to crystallized silicotitanate (CST) or this is demonstrated to an example. In addition, when the compound whose adsorption | suction characteristic is similar to CST is used, it can think similarly.

The adsorptive removal of radioactive substances by CST utilizes a phenomenon in which Na ^{+ on} the surface of CST and Cs ⁺ or Sr ²⁺ which are radioactive substances contained in contaminated water are exchanged.

FIG. 2 is a graph showing the results of calculation of the state of sodium ion bound to CST. The horizontal axis represents pH, and the vertical axis represents the ratio (presence ratio) of CST adsorbed with Na ⁺ and H ⁺ . The case where the concentration of sodium ion is 200 ppm is shown. The long broken line represents H ₃ CST, the alternate long and short dash line represents H ₂ NaCST, the short broken line represents HNa ₂ CST, and the solid line represents Na ₃ CST.

As shown in the figure, up to three Na ⁺ can be bound to the surface of one CST molecule. Here, as a representation of the compound, Na ₃ CST (a combination of three Na ⁺ ), HNa ₂ CST (Na in a form corresponding to the number of Na ⁺ and H ⁺ ions adsorbed to CST. ^{It is described that +} represents two ⁺ one proton bonded), H ₂ NaCST (a combination of Na ⁺ one proton and two protons), and H ₃ CST (three protons combined).

The state of these CSTs is in equilibrium with Na ⁺ concentration and pH. Therefore, the higher the pH and the higher the Na concentration in water, the higher the abundance ratio of Na on the surface of CST.

Near neutral (pH 4 to 8), the CST surface has a high abundance ratio of H ₂ NaCST in which one Na is bound. And by making it alkaline (pH 8 or more), the ratio of HNa ₂ CST or Na ₃ CST increases. Since two adsorbed Na ^{+ ions} are replaced with one Sr ^{2+ ion} , in this state, CST becomes easy to adsorb a radionuclide such as Sr ^{2+ ion} by the substitution with Na ^{+ ions} . Therefore, the adsorption performance can be improved by controlling the liquid property to the weakly alkaline side as in Patent Document 4.

The pH of the contaminated water is approximately 3 to 7. In order to enhance the adsorption performance, it is desirable to set the pH to 8 to 10. When the pH is in this range, the abundance ratio of HNa ₂ CST to H ₂ NaCST antagonizes. When the pH exceeds 10 and the alkalinity is strong, Sr ^{2+ and the} like tend to precipitate, so that it is difficult to remove the radionuclide Sr ^{2+ and the} like by adsorption.

  When the effect of weak alkalinization was experimentally examined according to various water quality conditions, it was found that the Sr adsorption amount is largely influenced by the concentration ratio of Ca to Na (Ca / Na ratio).

  Table 1 shows how the amount of Sr adsorbed in the weakly alkaline state (pH 8 to 10) changes relative to the Ca / Na ratio.

  As shown in the table, when the Ca / Na ratio is 0.3 as in the water quality 1, the amount of Sr adsorption increases due to weak alkalization. On the other hand, when the Ca / Na ratio is 1.2 as in the case of water quality 2, the amount of Sr adsorption does not change even if it is weakly alkalized.

  The charge of Ca ion and Na ion is +2, +1, respectively. Therefore, considering the charge ratio, when the Ca / Na ratio is 1.2, the Ca charge is 2.4 times the Na charge, and the Ca charge is excessive. On the other hand, when the Ca / Na ratio is 0.3, the Ca charge is 0.6 times the Na charge, and the Na charge is excessive.

As described above, the ion exchange capacity at the surface of CST is determined by the abundance ratio of Na ^{+ on} the surface, but since Ca has a slightly larger selection coefficient than Na, when Ca coexists, Ca is exchanged with Na. As a result, it is considered that the exchange between Sr and Na decreased, and the increase in Sr adsorption amount due to weak alkalinization did not appear significantly.

As described above, by making the contaminated water moderately weakly alkaline (pH 8 to 10) and adding Na ⁺ so that the ratio of the Ca charge to the Na charge becomes small, the radioactivity such as Sr ^{2+ on} the surface of CST It turned out that the adsorption performance of the nuclide can be improved. And it turned out that it is desirable to control the concentration of Na ⁺ so that the ratio of Ca charge to Na charge is 1.0 or less on the Na excess side, that is, the Ca / Na ratio is 0.5 or less. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the contaminated water treatment system of the first embodiment.

As shown in the figure, the contaminated water treatment system 1 comprises a filter device 2 for removing particulate matter contained in the contaminated water, a colloid removal device 3 for removing colloidal matter, a pH buffer device 5, and a radionuclide And a heavy metal removing device 7 using an oxine-impregnated activated carbon. These devices are connected by pipes 8, 9, 10, 11, 12, 13 and are configured to pass contaminated water sequentially. The pH buffer 5 is a container filled with particles of magnesium oxide (MgO). Since the solubility of MgO is low and buffer action by anions (for example, CO ₃ ^2- etc.) contained in the contaminated water, the pH of the contaminated water can be made into a desired range of weak alkalinity.

  A sodium compound addition device 4 is connected to a pipe 10 between the colloid removal device 3 and the pH buffer device 5. Thereby, the concentration ratio (Ca / Na ratio) of calcium (Ca) to sodium (Na) on the basis of the number of moles in the contaminated water can be reduced. In other words, the metal ion in the contaminated water can be in excess of sodium.

  Although the example which connected the sodium compound addition apparatus 4 to the piping 10 of the upstream side of the pH buffer apparatus 5 was shown in this figure, this invention is not limited to this, The sodium compound addition apparatus 4 is radioactive It may be connected to any of the pipes 8, 9, 10 and 11 on the upstream side of the nuclide adsorption device 6. By installing the sodium compound addition device 4, the polluted water can be brought into a state of excess of sodium, so that the amount of adsorption of radionuclides in the weakly alkaline state can be increased regardless of the quality of polluted water .

  Patent Document 4 exemplifies addition of sodium hydroxide (NaOH) for weak alkalinization. However, in the case of NaOH, the amount required for weak alkalization is at a concentration level of several ppm or less. On the other hand, the amount of Ca contained in the contaminated water is about 400 ppm in the case of seawater, and is also contained at a high concentration when in contact with concrete. For this reason, the water quality which needs to add more Na compound than the amount required for weak alkalinization is also assumed.

If the sodium compound changes the pH significantly, the overall performance of the contaminated water treatment system 1 may be affected by the formation of complexes, precipitation, and the like. Therefore, as the sodium compound to be added, NaCl having little influence on pH is preferable, and a weakly alkaline substance such as NaHCO ₃ is suitably used. Since the addition of NaHCO ₃ often contains CO _{3 2} ⁺ in the polluted water (raw water), the buffer action usually works and hardly affects the pH.

  The water quality of the water source (reservoir, pumped water) supplied to the contaminated water treatment system 1 is analyzed in advance or immediately before, and the sodium compound addition device so that the Ca / Na ratio becomes less than a predetermined value (Na charge is excessive) Control the amount of Na compound supplied from 4. If the water quality is constant, the set value is supplied, and if the water quality fluctuates, the supply amount is controlled in conjunction with the measured value of the Na concentration. In addition, control is performed by the control apparatus installed in centralized control rooms etc., such as a nuclear power plant. Alternatively, it may be performed by a mobile control device.

  In addition, each element which comprises the contaminated water treatment system 1 can be regarded as each process of the contaminated water treatment method of this invention, respectively.

  Therefore, the method for treating contaminated water according to this embodiment includes a filtration step for removing particulate matter contained in the contaminated water, a colloid removal step for removing a colloidal substance, a pH buffering step, and a radioactive removal for adsorbing and removing a radionuclide. It includes a nuclide adsorption step and a heavy metal removal step by an oxine-impregnated activated carbon. And a sodium compound addition process is performed before any process among a filtration process, a colloid removal process, a pH buffer process, and a radionuclide adsorption process.

  Examples 2 and 3 shown below are examples in which the influence on the radionuclide adsorption amount is reduced by switching the water sources having different Na concentrations so that the Ca / Na ratio is equal to or less than a predetermined value.

  FIG. 3 shows an embodiment in which the contaminated water treatment system is not provided with a sodium compound addition device.

  In this figure, the point which does not have the sodium compound addition apparatus 4 of FIG. 1, and the point which provided the contaminated water storage tanks 15, 16, 17 and the flow control devices 21, 22, 23 on the upstream side of the piping 8.

  Contaminated water storage tanks 15, 16 and 17 store contaminated water having different water quality and different Na concentration. The contaminated water storage tanks 15, 16 and 17 are connected to the pipe 14 via the pipe 18 and the flow control device 21, the pipe 19 and the flow control device 22, the pipe 20 and the flow control device 23, respectively. The pipe 14 is connected to the pipe 8 and sends the contaminated water to the filtration device 2 of the contaminated water treatment system 1. When the polluted water is supplied from the polluted water storage tank 15, 16 or 17 to the polluted water treatment system 1, the flow rate adjusting devices 21, 22 are controlled so that the stored polluted water becomes equal to or less than a predetermined value. , Mix according to 23.

  In this case, data of the water quality (Na concentration and / or Ca concentration) of the contaminated water storage tank 15, 16, 17 measured in advance, or a water quality sensor (Na concentration meter attached to the piping 18, 19, 20) The amount of contaminated water supplied from the contaminated water reservoirs 15, 16, 17 is adjusted using data obtained by the (or Ca concentration meter).

  However, even if the stored contaminated water is mixed, the Ca / Na ratio may not fall below the predetermined value. In order to prepare for that case, it is desirable to install the sodium compound addition device 4 of the first embodiment. If the Ca / Na ratio is less than or equal to the predetermined value only by mixing the stored contaminated water, the sodium compound addition device 4 is stopped, and if the Ca / Na ratio is not less than or equal to the predetermined value, the sodium compound addition device Run 4

  FIG. 4 shows another embodiment of the contaminated water treatment system of the present invention. In the figure, the details of the contaminated water treatment system 1 are omitted because they are the same as in the case of the first embodiment or the second embodiment.

  In this figure, polluted seawater, fresh water from rivers and lakes (hereinafter simply referred to as "fresh water"), underground water, or stagnant water from nuclear facilities are pumped up by the polluted water pumping devices 24, 25, 26. Contaminated water sent from the contaminated water pumping devices 24, 25, 26 is joined by a pipe 14 and sent to the contaminated water treatment system 1. When the contaminated water is supplied to the contaminated water treatment system 1, the Ca / Na ratio can be reduced to a predetermined value or less by adjusting the ratio of the contaminated water pumped by the contaminated water pumping devices 24, 25 and 26. Mix. Here, as in the second embodiment, the mixing ratio may be adjusted using the water quality data of the contaminated water.

  In the above embodiment, the contaminated water storage tank, the flow rate control device, the contaminated water pumping device and the like are described in a form not included in the contaminated water treatment system, but these peripheral devices are contaminated by the present invention. It may be interpreted as being included in a water treatment system.

  1: Contaminated water treatment system, 2: Filter, 3: Colloid remover, 4: Sodium compound addition, 5: pH buffer, 6: Radionuclide adsorber, 7: Heavy metal remover, 8, 9, 10 11, 12, 13, 14, 18, 19, 20: Piping, 15, 16, 17: Contaminated water storage tank, 21, 22, 23: Flow control device, 24, 25, 26: Contaminated water pumping device.

Claims (15)

PH buffering process to make contaminated water weakly alkaline;
After the pH buffering step, a radionuclide adsorption step of adsorbing and removing a radionuclide contained in the contaminated water;
A contaminated water treatment method, comprising controlling the quality of the contaminated water such that sodium contained in the contaminated water is excessive to calcium prior to the radionuclide adsorption step.   The contaminated water treatment method according to claim 1, wherein the control is performed by adding a sodium compound to the contaminated water prior to the pH buffering step or the radionuclide adsorption step.   The contaminated water treatment method according to claim 1 or 2, wherein the concentration ratio of calcium to sodium based on the number of moles of the contaminated water is set to 0.5 or less by the control.   The contaminated water treatment method according to any one of claims 1 to 3, wherein the radionuclide contains at least strontium.   The said control is a contaminated water treatment method of Claim 1 performed by mixing two or more types of contaminated water in which water quality differs before the said pH buffer process or the said radionuclide adsorption process.   The contaminated water treatment method according to claim 5, wherein the two or more types of the polluted water are a combination of two or more types selected from the group consisting of a polluted water storage tank, seawater, fresh water, ground water, and stagnant water of a nuclear facility. . PH buffer that makes polluted water weakly alkaline;
A radionuclide adsorption device for adsorbing and removing a radionuclide contained in the contaminated water that has passed through the pH buffer device;
The contaminated water treatment system which controls the water quality of the said contaminated water so that the sodium contained in the said contaminated water which flows in into the said radionuclide adsorption apparatus may become excess with respect to calcium.   The contaminated water treatment system according to claim 7, wherein a sodium compound addition device for adding a sodium compound to the contaminated water is provided upstream of the pH buffer device or the radionuclide adsorption device.   The contaminated water treatment system according to claim 7 or 8, wherein the concentration ratio of calcium to sodium based on the number of moles of the contaminated water is set to 0.5 or less by the control.   The contaminated water treatment system according to any one of claims 7 to 9, wherein the radionuclide contains at least strontium.   The said control is a contaminated water treatment system of Claim 7 performed by mixing two or more types of contaminated water in which water quality differs in the upstream from the said pH buffer apparatus or the said radionuclide adsorption apparatus.   The contaminated water treatment system according to claim 11, wherein the two or more types of polluted water are a combination of two or more types selected from the group consisting of a polluted water storage tank, seawater, fresh water, groundwater, and stagnant water of a nuclear facility. . An apparatus used for a contaminated water treatment system, comprising: a pH buffer device which makes the contaminated water weakly alkaline; and a radionuclide adsorption device which adsorbs and removes radionuclides contained in the contaminated water which has passed through the pH buffer device ,
It is installed upstream of the pH buffer or the radionuclide adsorption device,
A sodium compound addition device, wherein a sodium compound is added to the polluted water such that sodium contained in the polluted water flowing into the radionuclide adsorption device is excessive to calcium.   The sodium compound addition device according to claim 13, wherein the sodium compound is added such that the concentration ratio of calcium to sodium on the basis of the number of moles of the contaminated water is 0.5 or less. The sodium compound addition device according to claim 13, wherein the sodium compound is NaCl or NaHCO ₃ .

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