JP2009294002A - In situ x-ray absorption fine structure analyzer of very small amount of substance in solution and method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an in-situ XAFS analyzer of a very small amount of a substance in a solution capable of analyzing the reaction process of a very small amount of the substance in the solution by in-situ analysis. <P>SOLUTION: The in-situ XAFS analyzer is equipped with a stirrer 1 with a heater for uniformly stirring the solution 11 containing a very small amount of the substance and advancing the specific reaction in the solution 11, a measuring cell 3 having not only the inflow port and outflow port of the solution 11 but also the storage part 3A of the solution 11 between the inflow port and the outflow port to keep the uniformity of the solution 11 and having a light receiving window 3B for irradiating the solution 11 in the storage part 3A with incident X rays 12 radiated from an X-ray source, a 7 element SDD8 capable of detecting a very small amount of the substance in the solution 11 on the spot by detecting the fluorescent X rays 13 radiated from the solution 11 irradiated with X rays through the light receiving window 3B, the flow channels 4 and 5 for allowing the stirrer with the heater and the measuring cell 3 to communicate with each other, and a liquid sending pump 2 for circulating the solution 11 between the stirrer with the heater and the measuring cell 3 both of which are interposed on the way of the flow channels 4 and 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an in-situ X-ray absorption edge fine structure analysis (hereinafter referred to as in-situ XAFS (X-ray Absorption Fine Structure) analysis) apparatus and method for a trace substance in a solution, and more particularly to a trace substance in a solution. It is useful when applied to analysis of reaction processes.

ICP emission analysis is known as a method for analyzing trace substances in a solution. ICP emission analysis can also be applied to quantitative analysis for each form by performing necessary pretreatment when trace substances to be analyzed exist in a plurality of forms. For example, when measuring a trace amount of Se (IV) and Se (VI) concentration in a solution sample for each form, as shown in the flow charts of FIGS. 14 (a) and 14 (b), organic matter decomposition and reduction Is described in the JIS method (JIS-K0102 67.3), in which Se in the sample is hydrogenated (generates selenium hydride H ₂ Se) and measured with an ICP emission spectrometer. In this way, the total Se (Se ^Total ) in the sample can be quantified (see step ST1 to step ST3). For the analysis method for quantifying Se for each form, a method in which the form is separated by ion chromatography and then measured by ICP-MS (mass spectrometer), a method using coprecipitation separation by tellurium (Te), etc. Various studies have been made, but there is no clear provision in JIS.

Therefore, Se (IV) is hydrogenated but Se (VI) is not hydrogenated, and Se (IV) is quantified by analyzing with hydrogenation ICP, omitting the pretreatment operation of JIS method. The difference between the Se (IV) concentration and the total Se (Se ^Total ) concentration obtained by the normal JIS method is calculated as the Se (VI) concentration (see step ST5). ).

However, in such ICP spectroscopic analysis, as shown in FIG. 14, the pretreatment (see step ST1) is performed to quantify the total Se (Se ^Total ) in the sample (see step ST3), while the pretreatment is not performed. The Se (IV) concentration is detected, and then the Se (VI) concentration is calculated based on the difference from the total Se (Se ^Total ) concentration. As a result, the analysis takes a lot of time. In particular, the pretreatment requires many complicated treatments such as addition of sulfuric acid and nitric acid, heating, cooling, addition of hydrochloric acid, heating, etc. The treatment itself is not only troublesome, but the number of treatments is also large. There is a high possibility that a large analysis error due to the large number will occur, and there is a limit to improving the analysis accuracy.

  In particular, a small amount of sample must be extracted from the solution to be analyzed each time it is analyzed, which has a fatal defect in improving the accuracy of analysis because the state of the sample must be changed. ing.

  Moreover, since it is necessary to extract a sample and perform a predetermined analysis every time it is analyzed, it is possible to obtain only an analysis result on a discrete time axis and detect a reaction process of a specific reaction in a sample. It also has the problem that it is difficult. In particular, it is impossible to follow a reaction process that is continuous in time in real time.

  On the other hand, all elements have a characteristic of absorbing X-rays having a specific wavelength. The X-ray absorption rate calculated from the ratio of the intensity of X-rays irradiated to the sample (incident X-rays) and X-rays transmitted through the sample (transmitted X-rays) or fluorescent X-rays generated from the sample is the energy of the incident X-rays ( When plotted against (wavelength), a spectrum (XAFS spectrum) reflecting the chemical form of the absorbing atom is obtained. Analysis of the chemical form of a trace substance in a sample using such properties has been performed. This is called XAFS analysis. If such XAFS analysis is used, it will be possible to easily identify the form of a trace substance in a solution.

  However, simply using the XAFS analysis according to the prior art cannot detect the reaction process occurring in a solution containing a trace amount of substance over time.

  If such a reaction process can be observed over time, it is possible to obtain information on a reaction process that is continuous in time, whereas conventional information can only be obtained in a timely manner. It is considered that unknown and useful information can be obtained by applying it to an extremely wide range of analysis such as the reaction process of No. 1.

  Patent Document 1 can be cited as a publicly known document related to XAFS analysis.

JP 2005-262063 A

  An object of the present invention is to provide an in-situ XAFS analyzer and method for a trace substance in a solution, which can analyze a reaction process of the trace substance in a solution by in-situ analysis in view of the above-described conventional technology.

The first aspect of the present invention for achieving the above object is as follows:
A reaction means for uniformly stirring a solution containing a trace substance and causing a specific reaction in the solution to proceed;
The solution storing portion is provided between the inlet and the outlet together with the solution inlet and outlet, so that the uniformity of the solution can be maintained and X-rays radiated from the X-ray source are stored in the reservoir. A measuring cell having a light receiving window for irradiating a solution of
Detecting means capable of detecting the trace substance in the solution in situ by receiving fluorescent X-rays emitted from the solution irradiated with the X-rays through the light receiving window;
A flow path communicating between the reaction means and the measurement cell;
An in-situ XAFS analyzer for trace substances in a solution, comprising a liquid feed pump interposed in the middle of the flow path and circulating the solution between the reaction means and the measurement means is there.

  According to this aspect, each function can be performed in a state in which a reaction field that must be a dynamic field and a measurement field that is required to replace the solution without causing a field disturbance as much as possible are separated. In addition, since a single integrated system can be formed as a reaction system, by irradiating the measurement cell with X-rays, the reaction in the reaction system is not disturbed. -Situ XAFS analysis is possible. As a result, the reaction proceeding in the solution can be continuously analyzed with high accuracy and in real time without disturbing the reaction system. As a result, it is possible to clarify the reaction process of trace substances in a solution, which was impossible in the prior art, and an extremely wide range of applications can be considered.

The second aspect of the present invention is:
In the in-situ XAFS analyzer for trace substances in a solution according to the first aspect,
The inflow port of the measurement cell opens at the lower part of the storage unit, the outflow port opens at the upper part of the storage unit, and the light receiving window faces the central part of the storage unit. It is in the in-situ XAFS analyzer for trace substances in the solution.

  According to this aspect, since the solution is filled from the lower part of the storage part and is discharged from the upper part, it can be set as the solution storage part which does not have a solution flow substantially in the center part used as a measurement field. Moreover, since the solution in the reservoir is continuously changed, the reaction occurring in the solution can be accurately followed.

The third aspect of the present invention is:
In the in-situ XAFS analyzer for trace substances in a solution according to the second aspect,
The inflow port and the outflow port are in an in-situ XAFS analyzer for trace substances in a solution, wherein the inflow port and the outflow port are opened on a center line in a vertical direction of the reservoir.

  According to this aspect, it is possible to suppress as much as possible the influence of the solution entering and exiting the storage unit, and it is possible to configure the most static measurement field, thereby contributing to highly accurate measurement.

The fourth aspect of the present invention is:
In the in-situ XAFS analyzer for trace substances in a solution according to any one of the first to third aspects,
In the in-situ XAFS analyzer for trace substances in a solution, the surface of the reservoir is a plane parallel to the light receiving window.

  According to this aspect, X-rays can be incident on the surface of the solution at a shallow angle, and fluorescent X-rays can be generated from the solution in the reservoir most efficiently.

According to a fifth aspect of the present invention,
In the in-situ XAFS analyzer for trace substances in the solution according to any one of the first to fourth aspects,
The reaction means is in an in-situ XAFS analyzer for trace substances in a solution, characterized by having a heating means for the solution.

  According to this aspect, the predetermined reaction in the reaction field can be favorably promoted.

The sixth aspect of the present invention is:
The solution containing a trace amount of substance is uniformly stirred and the solution is allowed to flow from a reaction field that causes a specific reaction in the solution to proceed to a storage part in a measurement field, and the solution is allowed to flow out from the storage part. The solution is circulated between the reaction field and the measurement field so that the solution is exchanged while maintaining the uniformity of the solution in the storage part, while the solution in the storage part is irradiated with X-rays. An in-situ XAFS analysis method for a trace substance in a solution, wherein the trace substance in the solution is detected in situ by detecting fluorescent X-rays emitted from the irradiated solution as a result It is in.

  According to this aspect, the reaction field that must be a dynamic field to promote the reaction by stirring or the like is separated from the measurement field that is required to cause as little disturbance of the field as possible. In-situ XAFS analysis of trace substances in a solution can be performed by one integrated system that performs each function and is closed as a reaction system. As a result, it is possible to provide an in-situ XAFS analysis technique capable of analyzing a reaction process of a trace substance in a solution.

  According to a seventh aspect of the present invention, in the in-situ X-ray absorption edge fine structure analysis method for a trace substance in a solution according to the sixth aspect, the solution includes an oxidant and a trace substance in a form capable of being oxidized. In-situ X-ray absorption of a trace substance in a solution characterized in that the oxidation process of the trace substance in the solution is analyzed in situ by detecting the fluorescent X-ray It is in the edge fine structure analysis method.

  According to this aspect, as a result of applying the in situ XAFS analysis to selenium (Se (IV)) in a solution in the oxidation reaction process as one of trace substances that can be oxidized, Se ( The morphological change from IV) to Se (VI) could be captured. Here, the change in the concentration of Se (IV) and Se (VI) obtained by the linear fitting analysis of the XAFS spectrum almost coincided with the result of quantitative analysis by form by ICP emission analysis. From this, it was found that the result of in-situ XAFS analysis according to this embodiment has high quantitativeness.

The eighth aspect of the present invention is
In the in-situ XAFS analysis method of the trace amount substance in the solution according to claim 6,
The solution is a solution containing an oxidizing agent and a trace substance in a form capable of being oxidized, to which an additive capable of suppressing oxidation of the trace substance is added, and the fluorescent X-ray is detected. The in-situ XAFS analysis method for trace substances in a solution is characterized in that the effect of suppressing oxidation of the trace substances by the additive in the solution is analyzed in situ.

As a result of examining the mechanism of suppressing the oxidation of Se (IV) by Mn (II) as one of the additives that may suppress the oxidation of Se (IV) using the in situ XAFS analysis technique according to this embodiment, The oxidizing agent (S ₂ O ₈ ²⁻ ) in the solution oxidizes Mn (II) instead of Se (IV) to form a precipitate of Mn (IV) O ₂ , and a part of Se (IV) is Mn (IV) It was found that the oxidation of Se (IV) was suppressed by being incorporated into the precipitate of O ₂ .

  According to the present invention, since a uniform solution circulation system containing a trace amount of substance that forms one closed system as a reaction system is formed, by irradiating the measurement cell with X-rays, In-situ XAFS analysis can be performed on a reaction caused by a trace amount of substance proceeding in the reaction system without disturbing the reaction system. As a result, the reaction proceeding in the solution can be continuously analyzed with high accuracy and in real time without disturbing the reaction system. As a result, it is possible to clarify the reaction process of trace substances in the solution, which is impossible in the prior art.

  As a result, it is possible to obtain information on reaction processes that are continuous in time, whereas only information that is discrete in time can be obtained in the past. It is thought that unknown useful information can be obtained by applying.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing the entire in-situ XAFS analyzer according to the embodiment of the present invention, FIG. 2 is an exploded perspective view showing the measurement cell portion extracted, and FIG. 3 is an enlarged view of the measurement cell portion. It is a figure shown, (a) is the front view, (b) is the AA sectional view taken on the line.

  As shown in FIG. 1, the in-situ XAFS analyzer according to the present embodiment includes a stirrer 1 with a heater as a reaction means, a liquid feed pump 2, a measurement cell 3, pipes 4 and 5, a 7-element SDD8, and an X-ray source. (Not shown). Here, the stirrer 1 with a heater is a device that has a heater as a heating means and uniformly stirs a solution 11 containing a trace amount substance that is a sample stored in a reaction vessel 1A. That is, it constitutes a reaction field that promotes a specific reaction.

  The liquid feed pump 2 circulates a solution 11 in which a predetermined reaction is proceeding in the reaction vessel 1 </ b> A between the stirrer 1 with a heater and the measurement cell 3 through a pipeline 4 serving as a forward path and a pipeline 5 serving as a return path. Let

  The measurement cell 3 has a storage portion 3A for temporarily storing the inflowing solution 11 and then outflowing it to maintain the uniformity of the inflowing solution 11 and radiate incident X-rays 12 emitted from an X-ray source (not shown). Has a light receiving window 3B for irradiating the solution 11 in the reservoir 3A.

  The 7-element SDD 8 is a detecting means for analyzing a trace amount substance in the solution 11 by receiving the fluorescent X-ray 13 emitted from the solution 11 by X-ray irradiation through the light receiving window 3B, and is a conventional semiconductor element detector. Compared to (SSD), the silicon drift detector (SDD), which enables X-ray measurement of higher flux, is geometrically arranged in 7 elements, so that the trace amount of 10 mg / kg or less contained in the solution 11 can be reduced. The XAFS analysis can also be applied to this.

  Among these, as shown in more detail in FIGS. 2 and 3, the measurement cell 3 is made of acrylic in order to prevent interference with X-rays, and is connected to the cell body 3 </ b> C so as to communicate with the conduit 4 integrally. The solution 11 injected from the upper part through the formed inflow path 3G flows from the bottom to the top of the cell body 3C in the reservoir 3A, and is formed in the cell body 3C so as to communicate with the conduit 5 integrally. The structure is such that the pipe 5 is again released from the upper part through the outflow passage 3H. Here, an O-ring 3D and a Mylar film 3E made of polyester with high X-ray transparency are sandwiched, and an acrylic cell cover 3F having a light receiving window 3B at the center is attached to the cell body 3C with acrylic screws 9 and nuts 10. By fixing, leakage of the solution 11 is prevented. Here, the storage portion 3A is formed as a circular recess at the center of the cell body 3C, and the inflow port 3I that is an end portion of the inflow passage 3G opens to the lower portion of the storage portion 3A, and the end portion of the outflow passage 3H. The outlet 3J is an opening in the upper part of the storage part 3A, and the light receiving window 3B faces the central part of the storage part 3A. In particular, in this embodiment, the inflow port 3I and the outflow port 3J are open on the vertical center line of the storage portion 3A. Here, the arrangement of the inflow port 3I and the outflow port 3J is optimal in this embodiment. The solution 11 that has flowed into the reservoir 3A via the inlet 3I moves to the upper part without causing field disturbance in the reservoir 3A, and the uniformity of the solution 11 is best maintained via the outlet 3J. While being discharged, incident X-rays 12 are irradiated through the light receiving window 3B to the central solution 11 which is the most static field between the inlet 3I and the outlet 3J.

  However, as long as the solution 11 in the reservoir 3A is in a static field that is not affected by the solution 11 in the reaction vessel 1A that is a dynamic field due to stirring or the like, the configuration is limited to the above. Not what you want. This is because the uniformity of the solution 11 in the reaction vessel 1A only needs to be maintained in the reservoir 3A.

  Moreover, it is optimal to form the surface of the storage portion 3A as a plane parallel to the light receiving window 3B. This is because the incident X-rays 12 can be incident on the surface of the solution 11 in the storage unit 3A at a shallow angle, and the fluorescent X-rays 13 can be emitted from the solution 11 in the storage unit 3A most efficiently.

  Thus, the specific reaction proceeds satisfactorily in the reaction vessel 1A of the stirrer 1 with a heater, and the solution 11 circulates between the reaction vessel 1A and the measurement cell 3 by the liquid feed pump 2, so The solution 11 is constantly changed, and the reaction process proceeding in the reaction vessel 1A can be reproduced in the reservoir 3A which is a static field. That is, since the measurement cell 3 can replace the solution 11 while maintaining the uniformity of the solution 11 that has flowed into the storage unit 3A, the incident X-rays 12 emitted from an X-ray source (not shown) are stored in the storage unit. In-situ XAFS analysis of trace substances in the solution 11 can be performed by receiving and analyzing the fluorescent X-rays 13 obtained by irradiating the solution 11 in 3A with the 7-element SDD8.

  This time, the present inventors applied in-situ XAFS analysis to selenium (Se), which is a trace substance in the solution in the reaction process, using the in-situ XAFS analyzer as described above. In addition, using the same apparatus, the mechanism of suppressing the oxidation of Se (IV) by Mn was examined based on in-situ XAFS analysis. Therefore, an in-situ XAFS analysis method according to the present invention using these as the first to second embodiments will be described. Table 1 shows the measurement conditions in this case.

In Table 1, Se (IV) was prepared by dissolving the reagent SeO ₂ in water. Also, the form in solution Se _(IV) ^{O 3} is ^2, the value in the table is the concentration of the Se.

In Table 1, S ₂ O ₈ ²⁻ used was prepared by dissolving K ₂ S ₂ O ₈ as a reagent in water. The value in the table is the concentration of the ^2- _S ² _O ^8.

  In Table 1, Mn (II) used was a reagent Mn standard solution diluted with water.

  Furthermore, Table 2 shows the measurement conditions for each XAFS analysis in this case.

  In the XAFS analysis in this case, the X-ray energy incident around the Se-K absorption edge (12.655 keV) and the Mn-K absorption edge (6.538 keV) is continuously changed, and the intensity of the incident X-ray 12 is determined. The analysis time per time was adjusted to about 60 minutes by changing the sensitivity of the 7-element SDD8 and the distance to the measurement cell 3. Further, in this example, for comparison, XAFS analysis was also performed on various standard substances containing Se and Mn as measurement target elements and precipitates generated during the reaction.

  Further, the XAFS analysis in the present example was performed at SPring-8 industrial dedicated beam line BL16B2. In BL16B2, which can use a radiation source from a polarized electromagnet, white X-rays in a wide wavelength region (equivalent to 3.5 to 130 keV) can be used, so that stable and highly accurate ZAFS measurement is possible for a wide range of elements. It has characteristics.

  In the XAFS measurement by a general transmission method, the X-ray absorption rate of the measurement sample is measured in the vicinity of the X-ray absorption edge energy specific to the element. If the target element has a low concentration, IO (incident X-ray intensity) And I (transmission X-ray intensity) are small, and it is impossible to measure the absorbance with high accuracy. Therefore, in this experiment, a fluorescence method was adopted in which the fluorescent X-ray generated with the X-ray irradiated to the sample was measured instead of the transmitted X-ray. Since the intensity of the generated fluorescent X-rays is proportional to the absorbed X-ray intensity, the XAFS spectrum similar to the transmission method can be obtained by plotting this against the incident X-ray energy. Therefore, all in-situ XAFS analyzes according to this example were performed by the fluorescence method.

<In-situ XAFS analysis method for selenium (Se) in the solution in the reaction process>
The Se concentration in the solution 11 was 100 mg / l, and the powder of the reagent selenium dioxide (Se (IV) O ₂ ) was dissolved in water. To this solution 11, S ₂ O ₈ ²⁻ which is an oxidizing agent was added so as to be 5,000 mg / l (condition [1] in Table 1). The XAFS measurement conditions relate to the Se-K absorption edge (12.655 keV) in Table 2.

  FIG. 4 shows an XAFS spectrum obtained by in-situ XAFS analysis under such conditions. As shown in the figure, the XAFS spectrum of the Se-K absorption edge obtained by the in-situ XAFS analysis of the solution 11 containing Se as a trace substance shows the local electronic structure and atomic structure of the absorbing atom appearing near the absorption edge. X-ray absorption near edge structure (XANES) reflected, and wide-area X-ray absorption fine structure (EXAFS) reflecting quantitative local structure around absorbing atoms appearing on the higher energy side than the XANES region : Extended X-ray Absorption Fine Structure), and by analyzing these, it becomes possible to specify the chemical form of the absorbing atom.

FIG. 5 shows a change with time of the XAFS spectrum of the Se-K absorption edge obtained by in-situ XAFS analysis of the solution 11 containing Se as a trace substance. In the figure, XAFS spectra of Se (IV) O ₃ ²⁻ (corresponding to 0 min) and Se (VI) O ₄ ²⁻ (standard solution (std)) are also shown for comparison.

As shown in FIG. 5, the energy value taking the peak top differs depending on the valence. Further, in the spectrum of Se (VI) O ₄ ²⁻ , a gentle peak is observed around 12.68 keV. Further, in the XAFS spectrum obtained by such in-situ analysis, the energy value taking the peak top shifts from Se (IV) (12.662 keV) to Se (VI) (12.665 keV) with the passage of time. It was confirmed that Moreover, a peak around 12.68 keV, which is a characteristic of Se (VI), gradually appeared with the passage of reaction time. These results indicate that the XAFS spectrum obtained by the in-situ XAFS analysis captured the morphological change from Se (IV) to Se (VI). Incidentally, the rising edge of the sharp absorption edge as shown in FIG. 5 is called a white line and appears when the absorbing atom is bonded to oxygen, and Se in the solution 11 is Se (IV) O ₃ ^{2. -} which means that it is and Se _(VI) form bound to ^{O 4 2-oxygen} like.

  The EXAFS spectrum is obtained by performing a Fourier transform to obtain a radial distribution function and information on the local structure of the absorbing atom.

FIG. 6 shows the Fourier transform of the EXAFS spectrum of the solution 11 containing Se as a trace substance obtained by the in-situ XAFS analysis method according to this example, and the horizontal axis is coordinated to Se atoms and Se atoms. The distance from the atom in question and the vertical axis represent the coordination number. Here, Se (IV) O ₃ ²⁻ is coordinated with 3 O atoms, and Se (VI) O ₄ ²⁻ is coordinated with 4 O atoms, respectively. It is known to be 5 to 1.8 mm.

In FIG. 6, the result that the inter-atomic distance of Se—O was about 1.1 to 1.4 mm was obtained. However, the XAFS analysis includes the phase shift term, and is displayed about 0.4 mm shorter than the actual distance. Taking this into account, the measurement results of this time were in good agreement with the actual interatomic distance. Further, the oxygen coordination number represented by the vertical axis tended to gradually increase with the lapse of the reaction time. From this, the EXAFS spectrum obtained by the in-situ XAFS analysis according to the present example captures the progress of the oxidation reaction from Se (IV) O ₃ ²⁻ to Se (VI) O ₄ ²⁻ . It became clear that there was.

  Furthermore, when a plurality of chemical species constituting the XAFS spectrum of the mixed material can be specified to some extent, the contribution of each chemical species can be quantified based on the XAFS spectrum of the standard material. In the case of the in-situ XAFS analysis performed in this example, since the solution 11 contains Se (IV) and Se (VI), linear fitting analysis is performed based on the XAFS spectrum of each standard sample. The ratio of Se (IV) and Se (VI) in the solution during the oxidation reaction process was calculated. In the analysis, the same background correction and normalization processing were performed for the standard sample and the spectrum (data point: 607 points) in the energy range of 12.6 to 12.8 keV obtained by in-situ XAFS analysis.

  FIG. 7 shows an example of analysis by linear fitting (360 min). In this case, the existence ratio of Se by valence is 41.719% for Se (IV) and 58.281% for Se (VI). Obtained.

  In order to examine the quantitativeness of in-situ XAFS analysis, the analysis results by linear fitting and the concentrations of Se (IV) and Se (VI) in the solution in the oxidation reaction process under the same conditions were quantified by ICP emission spectrometry. Compared with the results. As a result, as shown in FIG. 8, the temporal changes in the existence ratios of Se (IV) and Se (VI) calculated and analyzed by the two methods almost coincided. That is, it has been clarified that the XAFS spectrum obtained by the in-situ XAFS analysis according to the present example reflects the quantitative progress of the oxidation reaction of Se.

  In addition, in the quantitative analysis of Se by ICP emission analysis performed as a comparison, as shown in FIG. 14, all Se and Se (IV) were analyzed according to the presence or absence of the reduction step, and the difference between them was defined as Se (VI). . That is, the ICP emission analysis is an analysis method based on the premise that Se (VI) is completely reduced to Se (IV) in the reduction step and all Se (IV) is hydrogenated in the hydrogenation step. In addition, since it takes time and troublesome operations such as heating by adding an acid, there is a possibility that the form of Se may change during that time, and even if it is assumed that reduction or hydrogenation occurs completely, the analyst's It seems that it contains many factors that cause analysis errors including skill level. Therefore, in-situ XAFS analysis is considered to be more advantageous than quantitative analysis for each form using ICP emission analysis in that morphological changes can be directly analyzed without requiring pretreatment.

  As shown in FIG. 8, the results of both analysis methods matched to demonstrate the quantitativeness of in-situ XAFS analysis, and at the same time, reliability of quantitative analysis by form using ICP with complicated preprocessing operations. It is thought that was also supported.

  As described above in detail, according to this example, in-situ XAFS analysis was applied to Se (100 mg / l in terms of Se) in the solution 11 in the oxidation reaction process, and the obtained XAFS spectrum was obtained. As a result of analysis, an XAFS spectrum reflecting a change in form from Se (IV) to Se (VI) was obtained despite the dilute concentration of 100 mg / l. Furthermore, the EXAFS Fourier transform succeeded in capturing changes in the number of oxygen coordinated to Se. Moreover, it became clear from the result of the linear fitting of the XAFS spectrum that the progress degree of quantitative reaction was reflected.

  Thus, the in-situ XAFS analysis method according to the present example has information that leads to the elucidation of various reaction mechanisms such as oxidation and reduction reactions of minute amounts of metals in the order of ppm in solution, material synthesis reactions, and elution behavior from solid samples. It is thought that there is a possibility to be obtained.

<In-situ XAFS analysis on mechanism of inhibiting oxidation of Se (IV) by Mn>
In some cases, wastewater from a wet desulfurization apparatus, which is one of the treatment facilities for combustion exhaust gas, contains Se derived from fuel. In general, Se in wastewater exists in the form of Se (IV) O ₃ ^2- and Se (VI) O ₄ ^2- . This is because Se (IV) O ₂ (g) in the combustion exhaust gas is dissolved in the absorption liquid of the wet desulfurization apparatus to become Se (IV) O ₃ ²⁻ , and in the desulfurization apparatus having a strong oxidizing atmosphere, Se (VI ) O ₄ ²⁻ is considered to be generated.

  Of Se in the desulfurization effluent, Se (IV) can be treated by a technique such as coagulation precipitation using iron or ion exchange. On the other hand, since Se (VI) cannot be processed by such a method, it is necessary to reduce to Se (IV) or insoluble metal Se (Se (0)) as a pretreatment, such as using microorganisms or granulated iron. Various techniques have been developed. Among them, the effect of the reduction and removal apparatus for Se using granulated iron has been demonstrated, but it requires iron more than tens of times the reduction equivalent of Se, and a large amount of sludge (iron hydroxide) is required. Therefore, development of sludge generation suppression technology and reduction of processing costs are issues.

When treating Se in wastewater, in addition to reducing Se (VI) and removing it, Se (IV) is not oxidized, that is, suppressing generation of Se (VI) also reduces removal costs. It is considered as one of the means to make it. In this regard, the present inventors have proposed a method for quantifying Se (Se (IV), Se (VI), Se (0)) in a liquid sample according to form, and oxidizing such as S ₂ O ₈ ^2−. It has been found that an oxidation reaction from Se (IV) to Se (VI) is likely to occur in an aqueous solution containing an active substance. Furthermore, it has also been found that by adding Mn, oxidation of Se is suppressed and a part of Se is taken into the generated Mn precipitate.

  In this example, an in-situ XAFS analysis was performed using the analyzer shown in FIG. 1 in order to examine the mechanism of suppressing the oxidation of Se (IV) by Mn based on such knowledge.

FIG. 9 shows a change in the concentration of Se (IV) and Se (VI) when the Se solution 11 containing S ₂ O ₈ ²⁻ is held at 50 ° C. corresponding to the actual temperature of the desulfurization waste water. . Referring to the figure, when Mn was not added, Se (VI) was completely oxidized after 20 hours, while Se (IV) was present after 48 hours when Mn was added. In addition, it can be seen that a decrease in the concentration of all Se due to the incorporation of a part of Se into the precipitate containing Mn as a main component at the same time. This result is a new discovery showing that Mn has an effect of suppressing oxidation of Se (IV), that is, Se (VI). However, the reaction mechanism of Mn involved in such oxidation inhibition of Se, the form of Se incorporated into the precipitate, etc. are still unclear. In-situ XAFS analysis is considered to be an extremely effective analytical method for elucidating the oxidation inhibition mechanism of Se.

Therefore, in this example, S ₂ O ₈ ²⁻ , which is an oxidizing agent, is added to the solution 11 containing 100 mg / l Se so as to be 5,000 mg / l, and Mn having an oxidation inhibiting effect is further added to 500 mg. In-situ XAFS analysis was performed (see condition [2] in Table 1). Here, Mn is a commercially available standard solution (Kanto Chemical), and the valence of dissolved Mn is bivalent. The measurement conditions for in-situ XAFS analysis are as shown in Table 2 for the Mn—K absorption edge (6.538 keV).

  FIG. 10 is a diagram showing the change over time of the XANES spectrum obtained by in-situ XAFS analysis of the Se solution with Mn added, where (a) shows the Se-K absorption edge and (b) shows the Mn-K absorption edge. FIG.

  As is clear from FIG. 10 (a), in this example, in-situ XAFS analysis was performed until 600 minutes after the start of the reaction, as in the case where Mn was not added (see FIG. 4). A significant peak top energy value shift and a peak near 12.68 keV, which is a characteristic of Se (VI), are not observed.

  Further, FIG. 11 shows a comparison between the results of separating the XAFS spectrum during the reaction into Se (IV) and Se (VI) by linear fitting analysis, and the results of quantitative analysis by form using ICP emission analysis. FIG. The characteristics shown in the figure show that both of them hardly oxidized to Se (VI) over time. From this, it was confirmed that the oxidation of Se was suppressed by the addition of Mn, and the result showed again that the in-situ XAFS analysis has high quantitativeness.

As described above, the oxidation suppression effect of Se is due to the addition of Mn. Here, FIG. 10 (b) shows the result of in-situ XAFS analysis for Mn, and the initial Mn (II) took the peak top around 6.551 keV. Attenuated and a new peak appeared at 6.551 keV. Comparison with a standard sample (Mn (IV) O ₂ (std)) revealed that this was a shift from Mn (II) to Mn (IV). That is, according to the present example, it became clear that Mn (II) itself having an effect of suppressing oxidation of Se was oxidized to Mn (IV).

FIG. 12 is a diagram showing an XANES spectrum of a precipitate formed when Mn is added, and (a) is a characteristic diagram showing a Se-K absorption edge and (b) is a Mn-K absorption edge. Among these, as shown in FIG. 12 (a), the precipitation sample has a peak top at 12.662 keV, and from the comparison with the XANES spectrum of Se (IV) O ₃ ²⁻ which is a standard sample, It turned out to be a form. From this result, it was found that although the specific form of the compound is unknown, Se (IV) in the solution 11 remains tetravalent and is taken into the precipitate.

On the other hand, FIG. 12B is an XANES spectrum at the Mn-K absorption edge of the same precipitation sample and the initial Mn aqueous solution. For comparison, the measurement results of four types of standard samples containing Mn having different valences are also shown. Described. Mn (II) O, Mn (III) ₂ O ₃ , and Mn (IV) O ₂ are all Mn oxides and peaked at energy values of 6.651 keV, 6.655 keV, and 6.659 keV, respectively. . The 7-valent KMn (VII) O ₄ is characterized in that a sharp pre-edge appears in the vicinity of 6.54 keV before the absorption edge. Since the spectrum of precipitation was 6.6659 keV and peaked at the top, the valence of Mn in the precipitation was considered to be tetravalent. Furthermore, not only the energy value of the absorption edge but also a gentle peak and absorption around 6.54 keV. such as spectral shape of high-energy side of the edge, since it matches the standard of Mn (IV) O _2, the precipitate was found to be a Mn (IV) O _2.

As described above in detail, as a result of examining the oxidation inhibition mechanism of Se through in-situ XAFS analysis using the SPring-8 industrial dedicated beam line BL16B2, the following has been clarified.
1) The oxidation reaction from Se (IV) to Se (VI) by an oxidizing substance (for example, S ₂ O ₈ ²⁻ ) is suppressed by the presence of Mn (II).
2) Eventually Mn (II) is gradually oxidized and precipitates as Mn (IV) O ₂ .
3) A part of Se in the solution is incorporated into this precipitate and exists as Se (IV).

FIG. 13 shows an image of the mechanism of inhibiting oxidation of Se by Mn estimated from the results of XAFS analysis. When Mn does not coexist as shown in FIG. 4A, Se (IV) is oxidized to Se (VI) by the action of the oxidizing agent (S ₂ O ₈ ²⁻ ), but Mn coexists as shown in FIG. At the time (when Mn is added), since the oxidizing agent acts preferentially on Mn, not Se, Mn (II) is oxidized and Mn (IV) O ₂ precipitates are formed. As a result, Se (VI) becomes It is thought that it becomes difficult to generate. For this reason, it is presumed that Se exists as Se (IV) for a long time and is taken into the generated Mn (IV) O ₂ precipitate.

In general, Mn in wastewater often exists in the form of divalent ions (Mn ²⁺ ) and is hardly oxidized in an air atmosphere, so hypochlorous acid or potassium permanganate as shown in the following formula: It is processed as a precipitate of MnO ₂ by adding an oxidizing agent such as.

Mn ²⁺ + NaClO + H ₂ O → MnO ₂ ↓ + NaCl + 2H ⁺
3Mn ²⁺ + 2KMnO ₄ → 5MnO ₂ ↓ + 2K ⁺ + 4H ⁺

That is, in the present embodiment is considered ^{that Mn 2+} in _S ² _O ^{8 2-} by solution 11 was added as an oxidizing agent is precipitated as MnO _2. By applying in-situ XAFS analysis, it was possible to clarify reaction mechanisms that have been unknown so far, such as identification of valence and existence form of Mn and Se involved in the reaction.

In order to fully elucidate the oxidation inhibition mechanism of Se (IV), various other experiments and analyzes are required, but in-situ XAFS analysis can be applied to Se in solution in the oxidation reaction process. By doing so, the following results were obtained.
1) As a result of applying in-situ XAFS analysis to Se in a solution in the course of oxidation reaction, we succeeded in capturing the morphological change from Se (IV) to Se (VI) as the reaction time progressed.
2) Since the concentration change of Se (IV) and Se (VI) obtained by the linear fitting analysis of the XAFS spectrum almost coincided with the result of quantitative analysis by form by ICP emission analysis, the result of in-situ XAFS analysis Was found to have high quantitativeness.
3) As a result of examining the oxidation inhibition mechanism of Se by Mn using in-situ XAFS analysis, S ₂ O ₈ ^{2− in} solution 11 oxidizes Mn (II) instead of Se (IV), and Mn with precipitation of (IV) _{O 2} is produced, a part of Se (IV) was found to be incorporated in the precipitation of Mn (IV) _{O 2.}

  As mentioned above, according to the present Example, the reaction process of the trace substance in a solution was able to be clarified by in-situ XAFS analysis. It was also possible to elucidate the reaction mechanism of Mn involved in the oxidation inhibition of Se (IV).

  The present invention can be effectively used in the industrial field in which trace substances contained in a solution are analyzed.

It is explanatory drawing which shows the whole in-situ XAFS analyzer which concerns on embodiment of this invention. It is a disassembled perspective view which extracts and shows the measurement cell part of the in-situ XAFS analyzer shown in FIG. It is a figure which expands and shows the measurement cell part of the in-situ XAFS analyzer shown in FIG. 1, (a) is the front view, (b) is the AA sectional view. It is a characteristic view which shows the XAFS spectrum of the Se-K absorption edge obtained by the in-situ XAFS analysis of the solution containing Se as a trace substance. It is a characteristic view which shows the time-dependent change of the XAFS spectrum of the Se-K absorption edge obtained by the in-situ XAFS analysis of the solution containing Se as a trace substance. This is an EXAFS spectrum of a solution containing Se as a trace substance and is a Fourier transform, and is a characteristic diagram showing the distance between Se atoms and atoms coordinated to Se atoms on the horizontal axis and the coordination number on the vertical axis. is there. It is a characteristic view which shows the analysis result of the XANES area | region by linear fitting analysis in the in-situ XAFS analysis of the solution which contains Se as a trace amount substance. It is a characteristic diagram compared with the analysis result by the linear fitting in the in-situ XAFS analysis of the solution containing Se as a trace substance, and the result quantified by the ICP emission analysis in the solution in the oxidation reaction process on the same conditions. Is a characteristic diagram showing the change in concentration of S ₂ O ₈ ^2-a containing the Se solution when held at 50 ° C., which corresponds to the actual temperature of the desulfurization waste water Se (IV) and Se (VI). The figure which shows the time-dependent change of the XANES spectrum obtained by the in-situ XAFS analysis of the Se solution which added Mn, (a) is a Se-K absorption edge, (b) is a characteristic view which shows a Mn-K absorption edge, respectively. It is. The XAFS spectrum during the reaction of the Se solution to which Mn was added was separated into Se (IV) and Se (VI) by linear fitting analysis, and the quantitative analysis results by form using ICP emission analysis were compared. FIG. It is a figure which shows the XANES spectrum of the precipitation produced | generated when Mn is added, (a) is a Se-K absorption edge, (b) is a characteristic view which respectively shows a Mn-K absorption edge. It is a figure which shows the image of the oxidation suppression mechanism of Se by Mn estimated from the result of a XAFS analysis, (a) is a schematic diagram which respectively shows the time of Mn non-coexistence, and (b) the time of Mn coexistence (at the time of Mn addition). . It is a flowchart which shows the procedure of ICP emission analysis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stirrer with heater 2 Liquid feed pump 3 Measurement cell 3A Reservoir 3B Light receiving window 3I Inlet 3J Outlet 4,5 Pipe 11 Solution
12 Incident X-ray 13 Fluorescent X-ray

Claims (8)

A reaction means for uniformly stirring a solution containing a trace substance and causing a specific reaction in the solution to proceed;
In addition to the solution inlet and outlet, the solution reservoir is provided between the inlet and outlet, so that the uniformity of the solution can be maintained and X-rays emitted from the X-ray source are contained in the reservoir. A measuring cell having a light receiving window for irradiating a solution of
Detecting means capable of detecting the trace substance in the solution in situ by receiving fluorescent X-rays emitted from the solution irradiated with the X-rays through the light receiving window;
A flow path communicating between the reaction means and the measurement cell;
An in-situ X-ray absorption edge fine of a trace substance in the solution, comprising a liquid feed pump interposed in the middle of the flow path and circulating the solution between the reaction means and the measurement means Structural analysis device. In the in-situ X-ray absorption edge fine structure analyzer of trace substances in the solution according to claim 1,
The inflow port of the measurement cell opens at the lower part of the storage unit, the outflow port opens at the upper part of the storage unit, and the light receiving window faces the central part of the storage unit. In-situ X-ray absorption edge fine structure analyzer for trace substances in solution. In the in-situ X-ray absorption edge fine structure analyzer of trace substances in the solution according to claim 2,
The in-situ X-ray absorption edge fine structure analyzer for trace substances in a solution, wherein the inflow port and the outflow port are opened on a center line in a vertical direction of the reservoir. In the in-situ X-ray absorption edge fine structure analyzer for trace substances in the solution according to any one of claims 1 to 3,
An in-situ X-ray absorption edge fine structure analysis apparatus for trace substances in a solution, wherein a surface of the reservoir is a plane parallel to the light receiving window. In the in-situ X-ray absorption edge fine structure analyzer of trace substances in the solution according to claim 1,
The in-situ X-ray absorption edge fine structure analyzing apparatus for trace substances in a solution, wherein the reaction means includes a heating means for the solution.   The solution containing a trace amount of substance is uniformly stirred and the solution is allowed to flow from a reaction field that causes a specific reaction in the solution to proceed to a storage part in a measurement field, and the solution is allowed to flow out from the storage part. The solution is circulated between the reaction field and the measurement field so that the solution is exchanged while maintaining the uniformity of the solution in the storage part, while the solution in the storage part is irradiated with X-rays. In-situ X-ray absorption edge of the trace substance in the solution, wherein the trace substance in the solution is detected in situ by detecting fluorescent X-rays emitted from the irradiated solution as a result Fine structure analysis method. In the in-situ X-ray absorption edge fine structure analysis method of the trace substance in the solution according to claim 6,
The solution is a solution containing an oxidizing agent and a trace substance in a form capable of being oxidized, and the oxidation process of the trace substance in the solution is analyzed in situ by detecting the fluorescent X-ray. An in-situ X-ray absorption edge fine structure analysis method for trace substances in a solution. In the in-situ X-ray absorption edge fine structure analysis method of the trace substance in the solution according to claim 6,
The solution is a solution containing an oxidizing agent and a trace substance in a form capable of being oxidized, to which an additive capable of suppressing oxidation of the trace substance is added, and the fluorescent X-ray is detected. The in-situ X-ray absorption edge fine structure analysis method for trace substances in a solution is characterized in that the effect of suppressing oxidation of the trace substances by the additive in the solution is analyzed in situ.