JP6573117B2 - Aggregate elemental analysis method - Google Patents

Description

  The present invention relates to an elemental analysis method for aggregates.

  2. Description of the Related Art Conventionally, in a facility that handles radioactive substances such as a nuclear power plant, a structural frame is constructed of concrete because it has sufficient strength and excellent radiation shielding properties. Since concrete exposed to radiation for a long time is activated, it must be disposed and managed as radioactive waste when dismantling the facility.

  The radionuclide contained in the activated concrete varies greatly depending on the kind and concentration of the trace elements contained in the aggregate of the concrete material. In order to systematically dispose and manage the activated concrete, it is desirable to analyze in advance the trace elements contained in the aggregate.

  Usually, after performing the pre-process which melt | dissolves an aggregate chemically, the element contained in an aggregate is analyzed by measuring using apparatuses, such as ICP-MS (for example, nonpatent literature 1). However, when the conventional pretreatment is performed, there is a problem that the detection accuracy of rare earth elements such as europium that can be activated is poor, and the measured value is about one digit lower than the actual content.

“Rapid determination of trace elements in standard rock samples by inductively coupled plasma mass spectrometry” by Takashi Okai, Analytical Chemistry, Vol. 39 (1990) No. 4, T55-T59

  The present invention has been made in view of the above circumstances, and provides an aggregate element analysis method capable of analyzing the contents of various trace elements including rare earth elements in the aggregate with high accuracy. .

The present inventor examined the pretreatment of the aggregate in the conventional method, and the detection accuracy of rare earth elements, alkaline earth metal elements, silver and lead was insufficient because of the insufficient dissolution of the rare earth elements contained in the aggregate. I found that it was falling. That is, when the aggregate is dissolved in hydrofluoric acid, these elements cause precipitation of fluoride, and therefore, a problem that cannot be detected by ICP-MS was found.
The inventor has solved the above problems and completed the present invention described below.

[1] The aggregate and the first mixed acid containing hydrofluoric acid and nitric acid are mixed, the aggregate is decomposed, and then at least a part of the first mixed acid is evaporated, thereby decomposing the aggregate. And obtaining a concentrate of the mixed solution by mixing the decomposed product and perchloric acid, heating the obtained mixed solution, and evaporating at least a part of volatile components from the mixed solution. A concentration step, a dissolution step of mixing the concentrate with a second mixed acid containing boric acid and nitric acid to obtain a solution in which the concentrate is dissolved, and an analysis step of analyzing elements contained in the solution. The elemental analysis method of the aggregate characterized by having.
[2] The aggregate elemental analysis method according to [1], wherein the fluoride contained in the concentrate is dissolved in the dissolution step.
[3] The aggregate elemental analysis method according to [2], wherein the fluoride is a solid component in the concentrate.
[4] The above [2] or [3], wherein the fluoride is one or more fluorides selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, and transition metal elements. ] The elemental analysis method of the aggregate as described in any one of the above.
[5] The aggregate elemental analysis method according to any one of [1] to [4], wherein the aggregate to be mixed with the first mixed acid is pulverized in advance.
[6] The aggregate elemental analysis method according to any one of [1] to [5], wherein in the concentration step, the mixture is concentrated until white smoke is emitted from the mixed solution.
[7] The aggregate elemental analysis method according to any one of [1] to [6], wherein the solution is measured by ICP-MS and elemental analysis is performed.

  According to the elemental analysis method of the present invention, the contents of various trace elements including rare earth elements in the aggregate can be analyzed with high accuracy.

It is a flowchart which shows an example of the elemental analysis method concerning this invention. It is an example of the result of having analyzed using standard rock with known element content as a sample.

  1st embodiment of the elemental analysis method of the aggregate of this invention has at least 4 process steps, a decomposition step, a concentration step, a dissolution step, and an analysis step. Details of each step will be described below, but steps or processes other than these steps may be included.

<Disassembly process>
In the decomposition step of the present embodiment, the aggregate is mixed with a first mixed acid containing hydrofluoric acid and nitric acid, and after the aggregate is decomposed, at least a part of the mixed acid is evaporated, This is a step of obtaining a decomposition product.

  The kind of aggregate is not specifically limited, For example, the earth and sand, rocks, etc. which are used as a conventional concrete material are mentioned. The aggregate is preferably pulverized in advance in order to smoothly proceed with the subsequent processing.

  The mixing ratio of hydrofluoric acid and nitric acid contained in the first mixed acid is, for example, preferably hydrofluoric acid: nitric acid = 1: 10 to 1: 1 by mass ratio, and hydrofluoric acid: nitric acid = 1: 5 to 1: 1. Is more preferable, and hydrofluoric acid: nitric acid = 1: 3 to 1: 1 is more preferable. When the mixing ratio is in the above range, the aggregate can be decomposed in a short time.

  The hydrofluoric acid concentration in the first mixed acid can be adjusted with dilution water so that it can be easily handled. The hydrofluoric acid concentration is, for example, preferably 4 to 24% by mass, more preferably 8 to 24% by mass, and still more preferably 12 to 24% by mass with respect to the total mass of the first mixed acid.

  The concentration of nitric acid in the first mixed acid can be adjusted with dilution water so that it can be easily handled. The nitric acid concentration is, for example, preferably 10 to 45% by mass, more preferably 20 to 45% by mass, and still more preferably 30 to 45% by mass with respect to the total mass of the first mixed acid.

  Examples of the method of mixing the aggregate and the first mixed acid include a method of pouring an appropriate amount of the first mixed acid into the aggregate in an acid-resistant resin container. It is preferable to expedite the decomposition of the aggregate by heating a mixed solution obtained by mixing the aggregate and the first mixed acid. After visually confirming that most of the solid content of the aggregate is decomposed and most of the aggregate is dissolved, at least a part, preferably all, of the first mixed acid remaining in the container is evaporated.

  As a method of evaporating the first mixed acid, for example, a known method such as heating or decompressing is applied. All of the first mixed acid may be evaporated, or a part thereof may be left without being evaporated. When all is evaporated, powder which is a decomposition product of aggregate remains in the container. When a part is left without being evaporated, an aggregate decomposition product is present in the first mixed acid in a precipitated, dispersed or dissolved state.

<Concentration process>
The concentration step of the present embodiment is performed by mixing the decomposition product and perchloric acid (HClO ₄ ), heating the obtained mixed solution, and evaporating at least a part of volatile components from the mixed solution, thereby mixing the mixture. In this step, a liquid concentrate is obtained.

  The concentration of perchloric acid mixed with the decomposition product is preferably adjusted with dilution water, and is preferably 40 to 70% by mass, for example, 50 to 70% by mass with respect to the total mass of the perchloric acid aqueous solution. More preferably, 60-70 mass% is further more preferable. When the concentration is within the above range, perchloric acid can be sufficiently reacted with the decomposition product.

  Examples of the method of mixing the decomposition product and perchloric acid include a method of pouring an appropriate amount of an aqueous solution of perchloric acid into the decomposition product in an acid-resistant resin container. Even when a small amount of the first mixed acid remains in the decomposition product, an aqueous perchloric acid solution may be poured.

A mixed solution obtained by mixing the decomposition product and perchloric acid aqueous solution is heated to evaporate at least a part, preferably all, of volatile components such as moisture and perchloric acid to obtain a concentrate of the mixed solution.
As a standard of concentration, it is preferable to concentrate until white smoke is emitted from the mixed solution. The appearance of white smoke of perchloric acid indicates that the mixture containing perchloric acid has been concentrated to a high concentration. In the process of concentration, it can be visually confirmed that most of the solid content of the decomposition product is decomposed and most of the decomposition is dissolved.

  When all of the volatile components in the liquid mixture are evaporated, the powder as the concentrate remains in the container. When a part of the volatile component is left without being evaporated, the concentrate is present in the mixed solution in a precipitated, dispersed or dissolved state.

<Dissolution process>
The dissolution step of the present embodiment is a step of mixing the concentrate and a second mixed acid containing boric acid and nitric acid to dissolve the concentrate.

  As a mixing ratio of boric acid and nitric acid contained in the second mixed acid, for example, boric acid: nitric acid = 1: 100 to 1: 6 is preferable in terms of mass ratio, and boric acid: nitric acid = 1: 20 to 1: 6. Is more preferable, and boric acid: nitric acid = 1: 10 to 1: 6 is more preferable. When the mixing ratio is in the above range, the precipitated fluoride contained in the concentrate can be sufficiently dissolved in a short time.

  The concentration of nitric acid in the second mixed acid can be adjusted with dilution water so that it can be easily handled. The nitric acid concentration is, for example, preferably 1 to 10% by mass, more preferably 3 to 10% by mass, and still more preferably 5 to 10% by mass with respect to the total mass of the second mixed acid.

  The boric acid concentration in the second mixed acid is preferably, for example, 3 to 15% by mass with respect to the total mass of the second mixed acid, from the viewpoint of sufficiently dissolving the precipitated fluoride contained in the concentrate. 5 to 15% by mass is more preferable, and 10 to 15% by mass is more preferable.

  Examples of the method of mixing the concentrate and the second mixed acid include a method of pouring an appropriate amount of the second mixed acid into the concentrate in an acid-resistant resin container. Even when a small amount of perchloric acid aqueous solution remains in the concentrate, the second mixed acid may be poured. After mixing, it can be visually confirmed that the concentrate has dissolved in about 5 to 60 minutes. In order to accelerate dissolution of the concentrate, the second mixed acid may be heated.

The concentrate obtained in the concentration step includes fluoride. Examples of the fluoride include one or more fluorides selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, and transition metal elements.
These fluorides are hardly soluble solid components in hydrofluoric acid and nitric acid not containing boric acid, and are easily precipitated, and thus could not be detected by ICP-MS analysis using a solution sample as an analysis target.
In the present invention, since these fluorides are dissolved by using the second mixed acid containing boric acid in the dissolving step, the above elements can be analyzed with high accuracy by ICP-MS analysis. .

<Analysis process>
A solution obtained by dissolving the concentrate with the second mixed acid contains various elements contained in the aggregate. Elements in this solution can be analyzed by a known method using ICP-MS. Moreover, you may apply well-known elemental analysis methods other than ICP-MS measurement.

  A flow chart of the analysis method of this embodiment is shown in FIG. The previously crushed aggregate sample is decomposed with a mixed acid of hydrofluoric acid and nitric acid (decomposition step 2). Subsequently, perchloric acid is added to the resulting decomposition product and concentrated until white smoke is produced (concentration step 4). Subsequently, a mixed solution containing boric acid and nitric acid is added to the obtained concentrate to dissolve the fluoride precipitate contained in the concentrate (dissolution step 6). The volume of the obtained solution is adjusted with distilled water, nitric acid or the like, and the concentration of the element is measured by ICP-MS (analysis step 8).

[Comparative Example 1]
Standard rock JA-1 whose element concentration was previously known by various elemental analysis methods was used. 0.5 g of crushed standard rock was heated at 120 ° C for 3 hours in a mixed acid of 5 mL of concentrated hydrofluoric acid and 5 mL of concentrated nitric acid to obtain a decomposition product of standard rock. Most of the mixed acid evaporated by the above heating.
Concentrated perchloric acid (5 mL) was added to the decomposition product, and the mixture was heated at 230 ° C. until white smoke was emitted to obtain a concentrate. Most of the perchloric acid was evaporated by the above heating.
The above concentrate was put into a small amount of 5% nitric acid and mixed, then 5% nitric acid was added to adjust to 100 mL, and elemental analysis was performed by ICP-MS.

[Example 1]
A concentrate was obtained in the same manner as in Comparative Example 1.
The concentrate and 0.5 g of boric acid were added to 10 mL of 5% nitric acid, mixed for 10 minutes, adjusted to 100 mL by adding an appropriate amount of 5% nitric acid, and subjected to elemental analysis by ICP-MS.

The results of elemental analysis of Comparative Example 1 and Example 1 are shown in the graph of FIG.
The horizontal axis of the graph represents various elements, and the vertical axis of the graph represents the ratio of the measured value to the true value of each element concentration (measured value / true value). The closer the true value of the standard rock is to the measured value, the closer the ratio is to 1.
As is clear from the results of FIG. 2, the analysis method of Example 1 according to the present invention has more elements than the analysis method of Comparative Example 1, for example, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Se, Rb, Sr, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, etc. We were able to.

  The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications of known configurations are possible without departing from the spirit of the present invention.

  The present invention can be widely applied to the field of handling activated concrete.

  2 ... Decomposition process, 4 ... Concentration process, 6 ... Dissolution process, 8 ... Analysis process

Claims (7)

Decomposing the aggregate by mixing the aggregate with a first mixed acid containing hydrofluoric acid and nitric acid, decomposing the aggregate, and evaporating at least a portion of the first mixed acid. Process,
A concentration step of mixing the decomposition product and perchloric acid, heating the obtained mixed solution, and evaporating at least a part of volatile components from the mixed solution to obtain a concentrate of the mixed solution;
Mixing the concentrate and a second mixed acid containing boric acid and nitric acid to obtain a solution in which the concentrate is dissolved;
An analysis step of analyzing elements contained in the solution;
An elemental analysis method for an aggregate characterized by comprising:   The aggregate elemental analysis method according to claim 1, wherein in the dissolving step, the fluoride contained in the concentrate is dissolved.   3. The aggregate elemental analysis method according to claim 2, wherein the fluoride is a solid component in the concentrate.   The aggregate according to claim 2 or 3, wherein the fluoride is one or more fluorides selected from the group consisting of alkali metal elements, alkaline earth metal elements, rare earth elements, and transition metal elements. Elemental analysis method.   The aggregate elemental analysis method according to any one of claims 1 to 4, wherein the aggregate to be mixed with the first mixed acid is pulverized in advance.   In the said concentration process, it concentrates until white smoke comes out from the said liquid mixture, The elemental analysis method of the aggregate as described in any one of Claims 1-5 characterized by the above-mentioned.   The elemental analysis method for aggregates according to any one of claims 1 to 6, wherein the solution is measured by ICP-MS and elemental analysis is performed.

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