JP6532077B2 - Method and system for separating radioactive strontium - Google Patents

Description

  The present invention relates to a separation method and separation system for radioactive strontium, and more particularly to a separation method and separation system for low level radioactive strontium-contaminated water.

Conventionally, as a method of separating radioactive substances from radioactively contaminated water, phosphoric acid or phosphate is added and a magnesium salt is added, and the pH is adjusted to alkali to adjust the pH to an alkali so that the poorly soluble phosphate MgCsPO ₄ or Sr A method of precipitating ₃ (PO ₄ ) ₂ and performing solid-liquid separation thereof has been proposed (see, for example, Patent Documents 1 and 2). For high-level radioactive contaminated water, add iron chloride and aluminum chloride together with phosphate solution, add alkaline solution to precipitate poorly soluble phosphate SrPO ₄ etc. A method is also proposed (see, for example, Patent Document 3).

JP, 2013-152218, A JP, 2013-217686, A JP 2012-247407 A

However, the conventional examples described in Patent Documents 1 to 3 are particularly directed to low-level radioactively contaminated water because the strontium component of the phosphate is derived only from radioactive strontium ( ⁹⁰ Sr). It was difficult to increase the concentration of phosphate ( ⁹⁰ SrPO ₄ ) to reach solubility, and it was not possible to separate strontium so as to satisfy a predetermined removal rate. Even if it was possible to precipitate phosphates, such precipitates would be micronized, and recovery of such colloidal fine particles required a significant increase in cost and process complexity.

  In view of the above-described prior art, the present invention provides a separation method and separation system for radioactive strontium that can efficiently separate radioactive strontium and satisfy a predetermined removal rate even with a low level radioactive strontium treated solution. To aim.

The embodiment of the present invention for achieving the above object determines the target removal rate of the radioactive strontium based on the strontium concentration of the radioactive strontium-contaminated water, and the non-radioactive strontium and calcium in an amount according to the target removal rate A first step of preparing a solution to be treated as seawater mixed in water , and adding a phosphorus compound containing calcium phosphate to the solution to form a precipitate containing radioactive strontium and non-radioactive strontium, and And a second step of solid-liquid separation, which is a method of separating radioactive strontium.

According to this aspect, the solution to be treated to which the phosphorus compound is added contains at least non-radioactive strontium (eg, ⁸⁴ Sr), which is an isotope of radioactive strontium ( ⁹⁰ Sr) to be removed. Even if radioactive contamination water is at a high level, the concentration of phosphate ( ⁹⁰ Sr ⁸⁴ SrPO ₄ ) can be increased to reach solubility and be suitably precipitated, thereby suppressing micronization of the precipitate in the solution to be treated Solid-liquid separation can be performed efficiently in a simple process. Furthermore, since the amount of non-radioactive strontium contained at least in the solution to be treated is determined according to the target removal rate, excess or deficiency of radioactive strontium will not occur. Accordingly, excessive residual strontium can be avoided in the solid solution obtained by precipitating radioactive strontium and non-radioactive strontium as described above and solid-liquid separation can be avoided, so additional processes such as further column adsorption treatment of the supernatant are also applied. It becomes easy to do.

  Here, in the first step, it is preferable to prepare a solution to which calcium is further mixed as the solution to be treated. According to this, the radioactive strontium can be efficiently separated in a simple process by solid-liquid separation using the fact that calcium has a high coprecipitation effect with strontium. In addition, the amount of non-radioactive strontium contained in the solution to be treated can be reduced as much as calcium which is easy to obtain and handle is further mixed.

In the second step, it is preferable to produce coprecipitated CaSrPO ₄ containing the radioactive strontium, the nonradiative strontium and the calcium. According to this, the concentration of phosphate co-precipitation (Ca ⁹⁰ Sr ⁸⁴ SrPO ₄ ) can be increased to reach solubility and be preferably precipitated, and solid-liquid separation can be performed more efficiently in a simple process.

Another embodiment of the present invention for achieving the above object is a solution to be treated as seawater , wherein at least non-radioactive strontium and calcium are mixed with low level radioactive strontium-contaminated water according to the target removal rate of radioactive strontium And storage means for storing a phosphorus compound, addition means for adding a phosphorus compound to the solution to be treated, and solid-liquid separation means for solid-liquid separation of the precipitate containing radioactive strontium and non-radioactive strontium formed by addition of a phosphorus compound. It is in the separation system of radioactive strontium characterized by According to this aspect, the solution to be treated to which the phosphorus compound containing calcium phosphate is added contains at least non-radioactive strontium (eg, ⁸⁴ Sr) which is an isotope of radioactive strontium ( ⁹⁰ Sr) to be removed. Even in low-level radioactive contaminated water, the concentration of phosphate ( ⁹⁰ Sr ⁸⁴ SrPO ₄ ) can be increased to reach solubility and be suitably precipitated, and the precipitation of precipitates in the solution to be treated can be finely divided Can be efficiently separated in a simple process.

According to the separation method and separation system of radioactive strontium of the present invention, the solution to be treated to which the phosphorus compound is added contains at least non-radioactive strontium (eg, ⁸⁴ Sr) which is an isotope of radioactive strontium ( ⁹⁰ Sr) to be removed. Even if it is low-level radioactive contaminated water, the concentration of phosphate can be increased to reach solubility and precipitation can be suitably performed, and micronization of the precipitate in the solution to be treated can be achieved. The solid-liquid separation can be efficiently performed in a simple process by suppressing

FIG. 2 is a schematic view showing an example of a separation method according to Embodiment 1. The figure which shows the change of the strontium concentration according to addition of a phosphorus compound. FIG. 8 is a schematic view showing an example of a separation method according to Embodiment 2. The figure explaining the coprecipitation effect of calcium and strontium. FIG. 8 is a schematic view showing an example of a separation method according to Embodiment 3. The figure which shows the density | concentration of Sr, Ca, and Mg according to the addition of the phosphorus compound to sea water. The figure which compares the isolation | separation method which concerns on Embodiment 3, and the prior art example which uses a precipitation agent. FIG. 10 is a schematic view showing an example of a separation system according to a third embodiment. The figure which shows the ratio change of the precipitate by centrifugation, drying, and solidification.

  Embodiments of the present invention will be described in detail based on the drawings.

(Embodiment 1)
FIG. 1 is a schematic view showing an example of a separation method of radioactive strontium according to Embodiment 1 of the present invention. The separation method of the present embodiment determines the target removal rate of radioactive strontium based on the strontium concentration of radioactive strontium-contaminated water, and the solution to be treated in which non-radioactive strontium in an amount according to the target removal rate is mixed with contaminated water The first step (steps S1 to S4) to prepare, and the second step (steps S5 to S6) in which a phosphorus compound is added to the solution to form a precipitate containing radioactive strontium and non-radioactive strontium, and solid-liquid separation of the precipitate And. Hereinafter, each step will be described in detail, but as long as the scope of the present invention is not changed, the order of these steps may be changed as appropriate, and may be performed simultaneously.

  In step S1, a target removal rate of radioactive strontium is determined based on the concentration of strontium in the radioactive strontium-contaminated water. Here, the decontamination factor represented by the ratio of the concentration of radioactive strontium before treatment to the concentration of radioactive strontium after treatment (the concentration before treatment / the concentration after treatment) was calculated and used. The format is not limited to the above example. If the strontium concentration or target removal rate can be used as the strontium concentration or target removal rate can be used, such as when the radioactive strontium concentration before treatment can not be fluctuated and the target removal rate calculated in the past can be applied, It is not necessary to measure the strontium concentration or calculate the target removal rate, and these measurements and calculations may be omitted, and may be performed at predetermined intervals.

  Here, the present embodiment is particularly directed to low-level radioactive strontium-contaminated water (eg, several hundred Bq / L). That is, according to the present embodiment, solid-liquid separation can be efficiently performed by a simple process, even for low-level radioactive strontium-contaminated water, in which separation of radioactive strontium is particularly difficult in the conventional method. The present embodiment is not limited to the low level radioactive strontium-contaminated water, and it is of course possible to target high level radioactive strontium-contaminated water.

  In step S2, low-level radioactive strontium-contaminated water is prepared. In step S3, non-radioactive strontium in an amount corresponding to the target removal rate determined in step S1 is newly added to the low-level radioactive strontium-contaminated water prepared in step S2. Mix in Then, in step S4, the liquid mixture is appropriately stirred to form a solution to be treated. As long as the gist of the present invention is not changed, it is sufficient if non-radiative strontium can be blended in the low level radioactive strontium-contaminated water, a solution containing non-radiative strontium ions may be blended as it is, or non-radiative strontium ions are included. The solution may be diluted with a predetermined solvent to formulate such diluted solution.

Thus, the present embodiment adds strontium to the contaminated water from which strontium is to be removed, specifically, the solution to be treated to which a phosphorus compound is added is an isotope of radioactive strontium ( ⁹⁰ Sr) to be removed. It is based on the finding that certain non-radiative strontium (for example, ⁸⁴ Sr) should be contained, according to which phosphate ( ⁹⁰ Sr ⁸⁴ The concentration of SrPO ₄ ) can be increased to reach solubility and be suitably precipitated. Such reasons will be specifically described.

The solubility of phosphate (SrPO ₄ ) in the solution is S, and the concentration of radioactive strontium ( ⁹⁰ Sr) is W ₀ . In addition, the radioactivity by the radioactive strontium contamination water which is an initial state will become _W0 * R, when R is made a constant. Here, in the present embodiment, for example, nonradiative strontium (for example, ⁸⁴ Sr), which is X times the strontium concentration that gives the solubility S, is newly mixed. Radioactive strontium concentrations before and after the addition of non-radioactive strontium is not changed, while there is no change in radioactivity W ₀ · R, the concentration of phosphate radioactive strontium and nonradioactive strontium ^{(90 Sr} 84 ^SrPO ₄₎ solubility By far exceeding S, a precipitate corresponding to X times the strontium concentration giving the solubility S is obtained. By removing this phosphate ( ⁹⁰ Sr ⁸⁴ SrPO ₄ ), the radioactive strontium concentration in the solution to be treated can be made W ₀ / X, ie, the decontamination factor X can be achieved. As an example, if the solubility of phosphate (Sr ₃ (PO ₄ ) ₂ ) in the solution is 0.11 ppm, 0.2 ppm of non-radioactive strontium which is 10 times the strontium concentration of 0.02 ppm which gives the solubility is newly added A decontamination factor of 10 can be achieved by mixing.

And according to this embodiment, since it is possible to precipitate the phosphate (Sr ₃ (PO ₄ ) ₂ ) corresponding to X times the strontium concentration giving the solubility S, precipitation in the solution to be treated Can be efficiently separated in a simple process. Moreover, since the amount of non-radioactive strontium newly added to the solution to be treated in step S3 corresponds to the target removal rate determined in step S1, excess or deficiency of radioactive strontium will not occur. Therefore, it is possible to avoid excessive residual strontium in the supernatant obtained by precipitation of radioactive strontium and nonradioactive strontium as described above and solid-liquid separation, so that the supernatant is further subjected to column adsorption treatment in a later step. Additional processes are also easier to apply.

  Therefore, in the subsequent step S5, a phosphorus compound is added to the solution to be treated prepared in step S4 to precipitate a phosphate containing radioactive strontium and non-radioactive strontium, and in step S6, the precipitate obtained in step S5 is Solid-liquid separation. Phosphorus compounds that can be used include phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, calcium hydrogen phosphate, Examples thereof include tricalcium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, barium hydrogen phosphate, magnesium phosphate, magnesium hydrogen phosphate, metaphosphoric acid and polyphosphoric acid, etc. It is not limited to. The phosphorus compounds may be used alone or in combination. However, depending on the type of phosphorus compound to be used, a phosphorus compound is added while using a strong base such as sodium hydroxide and adjusting the pH of the solution to be treated or after adjusting the pH of the solution to be treated. Is preferred.

FIG. 2 is a graph showing a change in strontium concentration with respect to the amount of phosphorus compound added when the types of phosphorus compounds are different. On the vertical axis, the strontium concentration (strontium concentration C / strontium initial concentration C ₀ ) in the solution to be treated is represented, and on the horizontal axis, the amount of added phosphorus compound is represented.

As shown in the figure, when sodium dihydrogen phosphate (weak acidity) is used, the decrease of the strontium concentration C / C ₀ according to the addition amount of the phosphorus compound is not seen, but changes near the initial concentration. , when using trisodium phosphate (weakly basic), the strontium concentration C / C ₀ in accordance with the amount of the phosphorus compound is lowered. On the other hand, even when sodium dihydrogen phosphate (weakly acidic) is used, the strontium concentration C as in the case of using trisodium phosphate (weakly basic) by using sodium hydroxide (strongly basic) in combination / C ₀ drops. That is, depending on the type of phosphorus compound, it becomes possible to suitably precipitate strontium by the use of a so-called pH adjuster, and a phosphorus compound represented by trisodium phosphate, which can make a solution to be treated from neutral to alkaline region Therefore, strontium can be suitably precipitated without using a pH adjuster.

  As solid-liquid separation in step S6, for example, a centrifugal separation method including a liquid cyclone can be used. According to the present embodiment, a large amount of precipitation can be obtained even with a low level radioactive strontium treated solution, and since the formation of phosphate in the treated solution is suppressed, a simple procedure such as centrifugation is possible. Solid-liquid separation can be performed efficiently in the process.

  After step S6, the precipitate can be dried and reduced in volume as required, and then discarded as a low level radioactive material. In addition, the supernatant liquid of the solution to be treated, which has been solid-liquid separated, may be temporarily stored and subjected to aggregation treatment so as to satisfy the discharge standard of the phosphorus compound. Furthermore, the supernatant may be passed through a column for strontium adsorption. As described above, since the amount of non-radioactive strontium contained at least in the solution to be treated is determined according to the target removal rate, excess or deficiency with respect to radioactive strontium will not occur, and after solid-liquid separation Excessive non-radioactive strontium in the supernatant is avoided. Therefore, it is possible to prevent the column waste from being significantly increased when the process of additionally carrying out the column adsorption treatment of the supernatant is also added.

As described above, according to the present embodiment, the target solution to be treated contains at least non-radioactive strontium (for example, ⁸⁴ Sr), which is an isotope of radioactive strontium ( ⁹⁰ Sr), in which strontium is daringly mixed with the contaminated water from which strontium is to be removed. By doing this, even in low-level radioactive contaminated water, the concentration of phosphate ( ⁹⁰ Sr ⁸⁴ SrPO ₄ ) can be increased to reach solubility and preferably be precipitated, and precipitation in the solution to be treated Can be efficiently separated in a simple process.

Second Embodiment
FIG. 3 is a flow chart showing an example of the method for separating radioactive strontium according to Embodiment 2 of the present invention. In this embodiment, in the first step, a solution to which calcium is further mixed is prepared in the first step as compared with the above-described embodiment 1, and in the second step, a radioactive strontium, non-radioactive strontium and calcium are contained together. It points to cause precipitation CaSrPO ₄ are different. The following description will focus on the different parts.

  Steps S1 to S2 are the same as in the first embodiment. Here, as step S3, step S3a of mixing non-radiative strontium and step S3b of mixing calcium are performed. The order of step S3a and step S3b may be reversed, or may be performed simultaneously. As long as the gist of the present invention is not changed, it is sufficient if non-radioactive strontium and calcium can be mixed in low-level radioactive strontium-contaminated water, and a solution containing non-radioactive strontium and calcium ions may be mixed as it is. Alternatively, a solution containing calcium ions may be diluted with a predetermined solvent to mix the diluted solution. When using a calcium compound such as calcium phosphate as the phosphorus compound, non-radioactive strontium or calcium is mixed according to the target removal rate determined in step S1 in consideration of the calcium ion contained in the phosphorus compound. can do.

  In step S4a, the mixed solution is appropriately stirred to obtain a treated solution in which non-radioactive strontium and calcium in amounts according to the target removal rate are mixed with the contaminated water. FIG. 4 is a diagram for explaining the coprecipitation effect of calcium and strontium. As shown in the figure, calcium has a high coprecipitation effect with strontium, and the decontamination factor can be improved by several times when the condition other than the presence of calcium is the same condition.

By addition of the phosphorus compound in the same manner as in step S5 in the first embodiment, in step S6a, it is possible to produce a co-precipitate CaSrPO ₄ containing radioactive strontium, nonradioactive strontium and calcium. The concentration of phosphate co-precipitation (Ca ⁹⁰ Sr ⁸⁴ SrPO ₄ ) can be increased to reach solubility and be preferably precipitated, and strontium phosphate is extremely difficult to be micronized, and more efficient in a simple process Solid-liquid separation is possible.

  As described above, according to the second embodiment, radioactive strontium can be efficiently solid-liquid separated in a simple process by utilizing the fact that calcium has a high coprecipitation effect with strontium. In addition, the amount of non-radioactive strontium contained in the solution to be treated can be reduced as much as calcium which is easy to obtain and handle is further mixed.

(Embodiment 3)
FIG. 5 is a schematic view showing an example of a separation method of radioactive strontium according to Embodiment 3 of the present invention. The present embodiment is different from the above-described Embodiment 1 in that seawater including radioactive strontium is prepared as a solution to be treated in the first step. The following description will focus on the different parts.

  First, seawater contains several ppm of natural strontium ions and several hundred ppm of calcium ions including sodium, magnesium and potassium. The present embodiment focuses on making the natural strontium ion and calcium ion function as the above non-radioactive strontium and calcium.

According to this, the amount of non-radioactive strontium and calcium added to radioactive strontium-contaminated water can be reduced, and low level radioactive pollution water equivalent to the above-mentioned step 2 is prepared depending on the target removal rate as in this embodiment. It is possible to omit the step and the step of adding non-radioactive strontium and calcium corresponding to the step S3 and the like. Nevertheless, even low-level radioactive strontium treated solutions can produce co-precipitated CaSrPO ₄ containing radioactive strontium, non-radiative strontium and calcium, and this co-precipitation is more efficient in a simple step at step S6a Solid-liquid separation is possible.

FIG. 6 is a graph showing concentrations of strontium, calcium and magnesium (concentration C / initial concentration C ₀ ) according to the addition of a phosphorus compound (eg, Na ₃ PO ₄ ) to seawater. Magnesium has a weak coprecipitation effect with strontium, while it can be seen from the fact that the strontium concentration and the calcium concentration decrease with the same tendency according to the addition of a phosphorus compound, utilizing calcium having a high coprecipitation effect with strontium. Thus, co-precipitation (Ca ⁹⁰ Sr ⁸⁴ SrPO ₄ ) can be suitably generated by the addition of the phosphorus compound.

In the conventional example, in order to accelerate the precipitation of phosphate, a precipitant such as polyaluminum chloride (PAC) or a sulfate band (FeSO ₄ ) which is known per se may be used in combination. As shown in the figure, when a precipitant made of aluminum, iron or the like is used in combination in the present embodiment, the phosphorus component precipitates alone before forming the phosphate of strontium, and the removal rate of the strontium concentration decreases. As described above, the present embodiment is fundamentally different from the conventional example in which the precipitating agent made of aluminum, iron or the like can be used in combination.

  The amount of natural strontium in seawater is almost constant. In addition, when radioactive strontium is widely drained into seawater in ports and the like, it can be assumed that the concentration of radioactive strontium in seawater as the solution to be treated is almost constant, whereby the total concentration of strontium in seawater is converted. It becomes possible to easily determine the radioactive strontium concentration by measuring the, and the management of the radioactive strontium concentration becomes extremely easy.

  Here, an example of a separation system for realizing the separation method of the present embodiment will be described. FIG. 8 is a view showing a schematic configuration of the separation system of the present embodiment.

The separation system 1 of the present embodiment includes an oil-water separator 12 into which seawater from the water channel 11 is introduced, a pump 13 for feeding seawater that has passed through the oil-water separator 12, and storage means (in which seawater is introduced by the pump 13 The settling tank 14), addition means (phosphorus compound tank 15 and pump 16) for adding a phosphorus compound to the settling tank 14, and the target removal rate are determined according to the target removal rate while the target removal rate is determined. The control means 17 for controlling the operation, the centrifugal separator 18 into which the seawater passed through the settling tank 14 is introduced, and the coprecipitate (Ca ⁹⁰ Sr ⁸⁴ SrPO ₄ ) separated by centrifugation are dried and used as a low level radioactive material The drying / solidification device 19 to be discharged, the adsorption column 20 into which the supernatant liquid by centrifugation is introduced, and the management tank 21 to store the seawater passing through the adsorption column 20 It is. In addition, although the pump is arrange | positioned suitably between these each apparatuses, illustration of such a pump is abbreviate | omitted.

  Thus, the separation system 1 is configured by combining strontium separation by so-called precipitation method and strontium separation with the adsorption column 20. As described above, since the operation of the pumps 13, 16 etc. is controlled according to the target removal rate, excessive radioactive radioactive strontium etc. can be prevented from remaining in the supernatant after centrifugation, and the adsorption column can be The arrangement can ensure complete separation of strontium and can also prevent significant increase in column waste. Although a plurality (two in FIG. 8) of adsorption columns 20 are used in the present embodiment, the present invention is not limited to the above example. As the adsorbent, known ones such as silica and zeolite are used.

As the addition of phosphorus compounds (eg Na ₃ PO ₄ ) to the precipitation tank 14 increases, the phosphorus concentration in seawater tends to increase, but with the target discharge standard of phosphorus concentration (eg 8 ppm or less) as a target, A temporarily stored known flocculant is added. In addition, the seawater that has passed through the management tank 21 is returned to the water channel 11.

The centrifugation in the centrifuge 18 can be performed, for example, at 6000 ppm for 10 minutes. Thus, as shown in FIG. 9 (a), in either case using various phosphorus compounds, several% to several tens wt% of the coprecipitate respect supernatant ^{(Ca 90} Sr 84 SrPO ₄₎ is It is separated. The drying temperature in the drying / solidifying apparatus 19 can be set, for example, to 60 ° C., whereby the precipitate can be reduced to about 1/10 as shown in FIG. 9 (b) and discarded as a low level radioactive material it can.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used in a separation method and separation system of radioactive strontium, particularly in an industrial field implementing a separation method and separation system of radioactive strontium for low level radioactive strontium-contaminated water.

DESCRIPTION OF SYMBOLS 1 separation system 11 water channel 12 oil-water separator 13, 16 pump 14 sedimentation tank 15 phosphorus compound tank 17 control means 18 centrifugal separator 19 drying / solidification apparatus 20 adsorption column 21 management tank

Claims (2)

A target solution as seawater which determines the target removal rate of the radioactive strontium based on the strontium concentration of radioactive strontium-contaminated water, and an amount of non-radioactive strontium and calcium mixed with the target removal rate according to the target removal rate The first step of preparing
A second step of adding a phosphorus compound containing calcium phosphate to the solution to be treated to form a precipitate containing the radioactive strontium and the non-radioactive strontium, and solid-liquid separating the precipitate;
A method of separating radioactive strontium, comprising: A storage means for storing a treated solution as seawater mixed with at least non-radioactive strontium and calcium according to the target removal rate of radioactive strontium for low-level radioactive strontium-contaminated water;
Addition means for adding a phosphorus compound to the solution to be treated;
Solid-liquid separation means for solid-liquid separation of the precipitate containing radioactive strontium and non-radioactive strontium which is generated by the addition of a phosphorus compound containing calcium phosphate;
A radioactive strontium separation system comprising: