JP2019132702A - Analytical method for water-soluble selenium and wastewater treatment system for selenium-containing wastewater using the same - Google Patents

Abstract

To enable analyzing a concentration of 6-valence selenium by using a hydrogen selenide gas detector and analyzing a selenium concentration in wastewater by a chemical form using a selenide gas detector accurately.SOLUTION: A method includes step 1 for adding sodium borohydride and hydrochloric acid to wastewater to make them react at room temperature to generate hydrogen selenide gas and hydrogen sulfide gas, a hydrochloric acid reduction step 2 for reducing the 6-valence selenium to a 4-valence selenium remaining in the wastewater, and further a step 3 for adding the sodium borohydride to the wastewater reduced to 4-valence selenium and generating the hydrogen selenide gas, and an equivalent 6-valence selenium concentration is determined on the basis of a signal values detected by the hydrogen selenide gas detector after lead the selenide gas to the hydrogen selenide gas detector. In addition, if the selenium concentration in a chemical form of the equivalent 6-valent selenium concentration and the total selenium concentration is determined, it is possible to operate a wastewater treatment facility for 6-valent selenium by bypassing the wastewater treatment system of the selenium-containing wastewater.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for quantitative analysis of water-soluble selenium using a hydrogen selenide gas detector and a wastewater treatment system for selenium-containing wastewater using the same. More specifically, the present invention relates to a method for analyzing water-soluble selenium useful for quantitative analysis of hexavalent selenium contained in wastewater containing sulfur compounds, for example, desulfurization wastewater discharged from a coal-fired power plant, and the like. The present invention relates to a wastewater treatment system for selenium-containing wastewater.

The selenium content in the wastewater is strictly regulated by the wastewater standards, and continuous monitoring and management of the selenium concentration in the wastewater is required to comply with the wastewater standard values. For example, in the electric power business, the flue gas desulfurization effluent of a coal-fired power plant has water-soluble selenium (tetravalent selenium: SeO ₃ ²⁻ , hexavalent selenium: SeO ₄ ²⁻ due to a small amount of selenium contained in the coal. ) And the water-soluble selenium concentration varies depending on the type of coal used, etc., so it is appropriate to continuously monitor and manage the water-soluble selenium concentration on site and to reduce the water-soluble selenium concentration. It is necessary to take measures, and a process monitor that automatically monitors the selenium concentration on site is required.

  In general, analysis of water-soluble selenium is stipulated by the official method, but analysis by the official method takes too much time and requires large-scale equipment, so the selenium concentration in the wastewater at the site continues. There is a problem that it is not suitable for proper monitoring and management. In order to realize an automatic measuring machine (process monitor) that monitors the selenium concentration on site, it has detection sensitivity that can cover the wastewater standard value, easy management of chemicals used, low running cost, measurement There is an urgent need to establish a method that enables the quantitative analysis of selenium to be performed quickly and easily, as well as having a large and expensive instrument and utility.

  Therefore, as a simple measurement method that replaces the official method, the applicant of the present invention reacts tetravalent selenium in the wastewater with sodium borohydride to reduce it to hydrogen selenide, which is a commercially available gas sensor / hydrogen selenide gas detection. We propose a simple analysis method for quantitative analysis of tetravalent selenium concentration dissolved in an analytical sample based on a calibration curve obtained from a known selenium concentration in advance (Patent Document) 1).

However, desulfurization waste water may contain not only tetravalent selenium but also hexavalent selenium, and may contain sulfur compounds. When such wastewater (collected sample for inspection) is subjected to hydrogenation treatment under the acidic condition by adding sodium borohydride (NaBH ₄ ), tetravalent selenium becomes hydrogen selenide and at the same time becomes a sulfur compound. The derived hydrogen sulfide will also be generated. Since the hydrogen selenide gas detector has the same sensitivity to hydrogen sulfide as hydrogen selenide, hydrogen sulfide becomes a disturbing component (interfering substance), resulting in a problem that only hydrogen selenide cannot be measured. That is, in a selenium monitor using a hydrogen selenide gas detector, if there is a sulfur compound in the wastewater, hydrogen selenide cannot be measured accurately due to the interference with hydrogen sulfide, and accurate analytical values may not be obtained. . Moreover, even if hexavalent selenium is contained in the waste water, the concentration cannot be obtained.

Therefore, the applicant of the present invention added potassium permanganate (KMnO ₄ ) and sulfuric acid to the wastewater and heated them to oxidatively decompose the sulfur compounds in the wastewater into stable sulfate ions, and tetravalent selenium. Is oxidized to hexavalent selenium, then added with hydrochloric acid and heated to reduce all hexavalent selenium to tetravalent selenium by reducing the hexavalent selenium to tetravalent selenium, and then hydrogenate the tetravalent selenium contained in the waste water. It reacts with sodium boron to generate hydrogen selenide gas, which is then introduced to a hydrogen selenide gas detector, and based on the signal value detected by the hydrogen selenide gas detector, Proposed to quantitatively analyze the concentration (see Patent Document 2).

JP 2009-8668 A JP2013-96876A

  However, the selenium monitor using the hydrogen selenide gas detector described in Patent Document 2 can quantitatively analyze the concentration of all selenium (a sum of tetravalent selenium and hexavalent selenium) in the waste water. Only tetravalent selenium or hexavalent selenium cannot be quantitatively analyzed.

  However, while tetravalent selenium can be removed by ordinary wastewater treatment (coagulation sedimentation treatment), hexavalent selenium is difficult to treat, and it is necessary to reduce hexavalent selenium to tetravalent selenium or metal selenium in a dedicated wastewater treatment facility. There is. Nevertheless, the proportion of hexavalent and tetravalent selenium contained in the flue gas desulfurization effluent of coal-fired power plants is not fixed, and in some cases the valence of selenium in six and four valences is halved. In some cases, selenium occupies the majority. Therefore, in order to efficiently operate the selenium treatment facility, accurate monitoring (quantitative analysis) of the concentration of hexavalent selenium to be treated is effective, and the selenium concentration of wastewater is automatically measured by chemical form. Technology (selenium monitor by chemical form) is required.

  Then, an object of this invention is to provide the analysis method of the water-soluble selenium which can carry out the quantitative analysis of the hexavalent selenium density | concentration in waste water easily using a hydrogen selenide gas detector. Another object of the present invention is to provide a wastewater treatment system for selenium-containing wastewater that can efficiently operate selenium treatment equipment.

  In order to solve such a problem, the water-soluble selenium analysis method of the present invention is based on tetravalent selenium in an analysis sample by adding sodium borohydride and hydrochloric acid to an analysis sample collected from desulfurization effluent and reacting at room temperature. Is removed from the sample for analysis as hydrogen selenide gas, and at the same time the sulfur compound in the sample for analysis is also separated from the sample for analysis as hydrogen sulfide gas, and the hydrogen selenide gas and hydrogen sulfide gas are removed. Further, hydrochloric acid is added to the analyzed sample and heated to reduce the hexavalent selenium remaining in the analyzed sample to tetravalent selenium, and the hexavalent selenium is further reduced to tetravalent selenium. Selenide water generated in the selenium hydrogenation process, comprising adding sodium borohydride to the sample for analysis and reacting at room temperature to generate hydrogen selenide gas. So that quantitative analysis of the equivalent hexavalent selenium concentrations lead gas to a hydrogen selenide gas detectors.

  The selenium-containing wastewater treatment system of the present invention quantifies the concentration of hexavalent selenium in a wastewater treatment line equipped with a wastewater treatment facility exclusively for hexavalent selenium and a coagulation sedimentation wastewater treatment facility for treating tetravalent selenium. Equipped with two selenium monitors, a selenium concentration quantification line and a total selenium concentration quantification line that quantifies the total selenium concentration, and a control unit that switches the drainage flow path. To the collected sample for analysis, sodium borohydride and hydrochloric acid are added and reacted to release tetravalent selenium in the sample for analysis from the wastewater as hydrogen selenide gas and at the same time sulfur compounds in the sample for analysis Hydrochloric acid is also added to the hydrogenation removal section that separates from the analysis sample as hydrogen sulfide gas, and the analysis sample from which hydrogen selenide gas and hydrogen sulfide gas have been removed. Heating and reducing the 6-valent selenium remaining in the sample for analysis to hydrochloric acid reducing part, and further adding sodium borohydride to the sample for analysis obtained by reducing 6-valent selenium to tetravalent selenium It has a selenium hydrogenation section that reacts at room temperature to generate hydrogen selenide gas, and a hydrogen selenide gas detector that detects hydrogen selenide gas and obtains equivalent hexavalent selenium concentration. , An oxidation treatment part for adding potassium permanganate and sulfuric acid to the sample for analysis collected from waste water and heating, and a reduction treatment part for adding and heating hydrochloric acid to reduce hexavalent selenium to tetravalent selenium A selenium hydrogenation unit that reacts tetravalent selenium contained in the analysis sample with sodium borohydride to generate hydrogen selenide gas, and detects the hydrogen selenide gas to determine the total selenium concentration in the analysis sample. When the control unit determines that the total selenium concentration detected by the total selenium concentration quantification line meets the effluent standards, the selenium wastewater treatment facility is bypassed to If the total selenium concentration does not meet the wastewater standard and the equivalent hexavalent selenium concentration detected by the hexavalent selenium concentration quantification line does not meet the wastewater standard, the wastewater treatment facility exclusively for hexavalent selenium and the coagulation sedimentation wastewater treatment facility The selenium removal treatment is performed and then drained, and the total selenium concentration does not meet the drainage standard, but when the equivalent hexavalent selenium concentration has not been detected or when the detected equivalent hexavalent selenium concentration satisfies the drainage standard, 6 The wastewater treatment equipment dedicated to selenium is bypassed and the selenium is drained after the tetravalent selenium is removed by the coagulation sedimentation wastewater treatment equipment.

  According to the first aspect of the invention, sodium borohydride and hydrochloric acid are added to the analytical sample and reacted at room temperature, whereby the tetravalent selenium in the analytical sample is analyzed as hydrogen selenide gas. At the same time, the unstable sulfur compound in the analytical sample that becomes a measurement disturbing factor of the hydrogen selenide gas detector is also separated from the analytical sample as hydrogen sulfide (gas). As a result, since only hexavalent selenium remains in the sample for analysis, this is reduced to tetravalent selenium in the hydrochloric acid reduction step, and sodium borohydride is added again to react to generate hydrogen selenide gas. The hydrogen selenide gas is introduced into a hydrogen selenide gas detector, and an equivalent hexavalent selenium concentration can be obtained based on the signal value detected by the hydrogen selenide gas detector. That is, according to the method of the present invention, the hexavalent selenium concentration can be directly quantitatively analyzed.

  According to the second aspect of the present invention, the hexavalent selenium concentration is directly and quantitatively analyzed using a part of the analytical sample collected from the analytical sample, while the whole part of the analytical sample is used for the quantitative analysis. Since the selenium concentration can be directly quantitatively analyzed, it is possible to appropriately operate the selenium treatment facility of the desulfurization drainage system. That is, when the hexavalent selenium treatment is unnecessary, the wastewater treatment cost can be reduced by bypassing the hexavalent selenium dedicated wastewater treatment facility.

It is a principle figure which shows one Embodiment of the process of the analysis method classified by chemical form of water-soluble selenium which carries out quantitative analysis of the hexavalent selenium in the waste_water | drain concerning this invention. It is a block diagram which shows one Embodiment of the selenium monitor (hexavalent selenium quantification line) which implements the analysis method of water-soluble selenium which quantitatively analyzes hexavalent selenium. It is a block diagram which shows one Embodiment of the selenium monitor (total selenium quantification line) which implements the water-soluble selenium analysis method which carries out the quantitative analysis of all selenium. It is explanatory drawing which shows the measurement location of the water-soluble selenium in the desulfurization waste water treatment facility of a thermal power plant. It is a block diagram which shows one Embodiment of the waste water treatment system of the selenium containing waste water of this invention. It is a graph which shows an example of the calibration curve of a selenium monitor (repetition number n = 5, correlation coefficient r ² = 0.990, sensor # 16, diaphragm having a film thickness of 200 μm). It is a graph which shows the time-dependent change of the waste_water | drain selenium density | concentration during the test by an official method. It is a graph which shows a time-dependent change of the selenium density | concentration (ICP-OES) according to chemical form during a test. It is a graph which shows the time-dependent change of the calibration value signal output (upper) and selenium concentration (lower) of the selenium monitor during the test. It is a graph which shows the correlation with the selenium concentration by a selenium monitor, and the selenium concentration by an official method (ICP-OES).

  Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 shows an embodiment of a process of a water-soluble selenium analysis method for quantitatively analyzing hexavalent selenium in waste water according to the present invention. In the water-soluble selenium analysis method according to this embodiment, sodium borohydride and hydrochloric acid are added to a sample A for analysis collected from desulfurization effluent and reacted at room temperature, whereby tetravalent in the sample for analysis is added. Selenium is separated from the sample for analysis as hydrogen selenide gas, and at the same time, unstable sulfur compounds in the sample for analysis that interfere with the measurement of the hydrogen selenide gas detector are also separated from the sample for analysis as hydrogen sulfide gas. Hydrochloric acid is added to the hydrogenation removing step S1 and the analytical sample from which tetravalent selenium and sulfur compounds have been removed (hereinafter referred to as hydrogenated and removed analytical sample B) and heated to convert the remaining hexavalent selenium to 4 Hydrochloric acid reduction step S2 for reducing to selenium valent, and further, the sodium borohydride is added to the analytical sample after the hydrochloric acid reduction treatment (hereinafter referred to as analytical sample C after the reduction treatment) and reacted. Selenium hydrogenation step S3 for generating hydrogen selenide gas, and the hydrogen selenide gas obtained in the hydrogen selenide step S3 are guided to a hydrogen selenide gas detector (not shown) and detected by the hydrogen selenide gas detector. And an analysis step (not shown) for quantitatively analyzing the equivalent hexavalent selenium concentration based on the obtained signal value. An analytical sample in which sodium borohydride is added to the analytical sample C after reduction treatment to generate hydrogen selenide gas is referred to as a hydrogenated analytical sample D.

Desulfurization wastewater, for example, sample A for flue gas desulfurization analysis of coal-fired power plant, water-soluble selenium (tetravalent selenium: SeO ₃ ²⁻ , hexavalent selenium: SeO ₄ ²⁻ ) due to a small amount of selenium contained in coal. As a result of hydrogenation and removal of tetravalent selenium and sulfur compounds as hydrogen selenide gas and hydrogen sulfide gas in the hydrogenation removal treatment of tetravalent selenium and sulfur compounds. Only hexavalent selenium remains in the analytical sample B which has been converted to be removed. At the same time, it is possible to remove the influence by removing in advance an unstable sulfur compound that becomes an interfering substance when measuring the selenization gas with a hydrogen selenide gas detector as hydrogen sulfide. Therefore, hydrochloric acid is added to the hydrogenated analytical sample B and heated to reduce hexavalent selenium remaining in the analytical sample to tetravalent selenium in the hydrochloric acid reduction step (reduced analytical sample C). ), Again, sodium borohydride is added and reacted to generate hydrogen selenide gas. Then, the hydrogen selenide gas is guided to the hydrogen selenide gas detector, and a calibration curve (see, for example, FIG. 6) obtained in advance based on the signal value detected by the hydrogen selenide gas detector is used. Thus, the equivalent hexavalent selenium concentration can be obtained. That is, according to the method for analyzing water-soluble selenium according to the present invention, the hexavalent selenium concentration can be directly quantitatively analyzed.

  This makes it possible to measure selenium in desulfurized effluent by chemical form by using it together with a selenium monitor (Patent Document 2) that can quantitatively analyze the total selenium concentration already established by the applicant of the present application. That is, an analysis system for water-soluble selenium by chemical form using a hydrogen selenide gas detector (referred to as a gas sensor) includes a processing step for quantifying hexavalent selenium concentration, and a processing step for quantifying total selenium concentration. If it comprises, the equivalent hexavalent selenium density | concentration calculated | required at the hexavalent selenium quantification process process and the total selenium density | concentration calculated | required at the total selenium quantification process process can be calculated | required. Therefore, it is possible to appropriately operate the selenium treatment facility of the desulfurization drainage system using these two selenium monitors.

  Here, the total selenium quantitative analysis line consists of an oxidation treatment process in which potassium permanganate and sulfuric acid are added to an analytical sample collected from desulfurization effluent and heated to convert unstable sulfur compounds into sulfate ions, A hydrochloric acid is added to the treated analytical sample and heated to reduce the hexavalent selenium to tetravalent selenium to prepare the tetravalent selenium, and the sodium borohydride is added to the reduced analytical sample for reaction. A selenium hydrogenation step in which tetravalent selenium is converted to hydrogen selenide gas, and a calibration curve obtained in advance based on a detection signal value obtained by introducing the generated hydrogen selenide gas to a hydrogen selenide gas detector. And a quantitative analysis step for determining the total selenium concentration using hexagonal selenium, and quantifying the total selenium after aligning hexavalent selenium with tetravalent selenium.

  2 and 3 show an embodiment of an analysis system for water-soluble selenium according to chemical form using a hydrogen selenide gas detector. The water-soluble selenium analysis system according to the present embodiment has a hexavalent selenium concentration with respect to an analytical sample collected from water-soluble selenium-containing wastewater containing sulfur compounds that may interfere with gas sensors. The line for quantifying the amount of selenium (see Fig. 2) and the line for quantifying the total selenium concentration (see Fig. 3) are operated sequentially or in parallel, and the hexavalent selenium concentration and the total selenium concentration in the sample for analysis Is to ask for.

(Hexavalent selenium monitor)
The hexavalent selenium quantification line 1 shown in FIG. 2 is roughly composed of a drainage collection unit 3, a hydrogenation removal processing unit 4, a hydrochloric acid reduction processing unit 5, a selenium hydrogenation processing unit 6, and an analysis unit 7. Yes. Reference numerals 50 and 51 in the figure are waste liquid pumps, 52 is a low concentration waste liquid line, and 53 is a high concentration waste liquid line.

<Drainage collection unit>
The wastewater collection unit 3 includes, for example, an adjustment tank 11 and a standard sample storage tank 12, and an analysis sample A or standard sample collected from the desulfurization wastewater includes a drainage liquid feeding device 14 by opening and closing a valve. A predetermined amount is fed to the first processing tank 16 via the line 13 and the sample meter 15. In this embodiment, by providing the two adjustment tanks 11 and the standard sample storage tank 12, the state of selenium removal treatment is examined by collecting waste water having different conditions and continuously measuring these analytical samples. Although there is an advantage which becomes easy, providing two adjustment tanks etc. is not an essential condition. A part of the collected sample for analysis is supplied to the whole selenium analysis line 2 through the branch pipe 8.

<Hydrogen removal processing unit>
The hydrogenation removal processing unit 4 adds the solution 18 containing sodium borohydride and hydrochloric acid 20 to the sample A for analysis in the first processing tank 16 and agitates the mixture (hereinafter referred to as the first mixture and the first mixture). The hydrogen selenide gas and the hydrogen sulfide gas are generated and taken out of the bath to remove tetravalent selenium and sulfur compounds from the sample for analysis. Only the hexavalent selenium remains in the hydrogenated and removed analytical sample B obtained by this treatment. Here, the addition amount of sodium borohydride 18 and hydrochloric acid 20 is an amount capable of hydrogenating and discharging tetravalent selenium and sulfur compound of sample A for analysis, and does not inhibit the reduction in hydrochloric acid reduction treatment unit 5. Amount. In the figure, reference numeral 16 denotes a first processing tank for storing a sample for analysis, 17 denotes a tank for storing sodium borohydride, 19 denotes a tank for storing hydrochloric acid, and 21 and 22 denote hydrogen in the first processing tank 16. Syringe pump for supplying sodium borohydride 18 and hydrochloric acid 20 in predetermined amounts, 24 and 25 are a first liquid feeding device and a first feed for feeding the hydrogenated and removed analytical sample B toward the hydrochloric acid reduction treatment unit 5. The liquid line 55 is a refrigerator for storing the sodium borohydride 18 at a low temperature. In the case of the present embodiment, stirring of the sample A for analysis, the sodium borohydride 18 and the hydrochloric acid 20 in the first treatment tank 16 is carried out by a carrier gas (air) supplied from the air compressor 54 via the blast tube 23. However, the present invention is not limited to this, and mechanical stirring with a stirring blade or stirring with a stirrer may be used.

  The solution 18 containing sodium borohydride may be an alkaline solution containing only sodium borohydride, but may contain, for example, ethylenediaminetetraacetic acid and sodium hydroxide. Sodium borohydride is an inexpensive and readily available material that is widely used as a reducing agent, but has the property of being easily decomposed. Therefore, it is known that ethylenediaminetetraacetic acid can be dissolved in a 0.1 mol / L sodium hydroxide solution and stably stored at room temperature for 30 days (ADIdowu, PK Dasgupta, Z. Genfa, and K Toda: “A Gas-Phase Chemiluminescence -Based Analyzer for Waterborne Arsenic”, Anal. Chem., 78, 7088-7097 (2006)). That is, it is a reagent having both ease of use and stability, and is very suitable as a reagent used for on-site analysis. When a solution containing sodium borohydride is stored and used in a certain place for a long time, it is stored in a refrigerator 55 that can be cooled to 0 ° C. to 25 ° C., preferably 0 ° C. to 10 ° C. It is preferable to do. As a result, the solution 20 containing sodium borohydride can be stored without being affected by the analysis environment, and stable sodium borohydride that is not decomposed and deteriorated can be added over a long period of time.

<Hydrochloric acid reduction treatment section>
The hydrochloric acid reduction treatment unit 5 performs a process of reducing hexavalent selenium (hexavalent selenium originally contained in the desulfurization waste water A) remaining in the hydrogenation-removed analysis sample B to tetravalent selenium. A sodium borohydride aqueous solution (NaBH ₄ ) can react with tetravalent selenium to produce hydrogen selenide gas, but does not react with hexavalent selenium. Therefore, by adding hydrochloric acid as a reducing agent, the hexavalent selenium contained in the analytical sample B subjected to the hydrogenation removal treatment is reduced to tetravalent selenium, thereby allowing reaction with sodium borohydride.

  The amount of hydrochloric acid added in the reduction treatment is preferably such that the concentration of hydrochloric acid in the analytical sample subjected to the hydrogenation removal treatment is 4 mol / L to 6.7 mol / L, and the amount to be 6.7 mol / L. More preferably. If the hydrochloric acid concentration is too low, the total amount of hexavalent selenium may not be reduced to tetravalent selenium. If the concentration of hydrochloric acid is excessively increased, the amount of hydrochloric acid added is excessively increased, and the total amount of the analysis sample subjected to the hydrogenation removal treatment is increased, resulting in a longer analysis time. As a specific example, when 5 mL of desulfurization waste water is used as an analysis sample, it is preferable to add about 5 mL of concentrated hydrochloric acid (12 mol / L).

  Moreover, it is preferable that the heating temperature of the hydrogenation-removed analytical sample after addition of hydrochloric acid is 100 ° C. or higher. If the temperature is lower than this, hexavalent selenium that is not reduced to tetravalent selenium remains, and the analysis accuracy may be lowered. If the heating temperature is too high, the analytical sample will boil vigorously, so the heating temperature is preferably 100-120 ° C. Furthermore, the heating time is preferably 10 minutes or more at the above temperature. If it is shorter than this, hexavalent selenium that is not reduced to tetravalent selenium remains, and the analysis accuracy may be lowered. Note that even if the time for reducing hexavalent selenium to tetravalent selenium is too long, no particularly advantageous effect is seen, but rather the analysis time is prolonged. Therefore, the time for reducing hexavalent selenium to tetravalent selenium may be about 10 to 15 minutes at the above temperature.

  The hydrochloric acid reduction treatment unit 5 of the present embodiment includes a second treatment tank 26 that stores the hydrogenation-removed analysis sample, a syringe pump 30 that adds hydrochloric acid 28 as a reducing agent in the second treatment tank 26, The tank 27 for storing the hydrochloric acid 28, the hydrogenation-removed analytical sample B and the hydrochloric acid 28 in the second processing tank 26 are agitated by bubbling with a carrier gas (air) supplied through the blast tube 29. The second liquid feeding device 31 and the second liquid feeding device 31 for feeding a liquid mixture (hereinafter referred to as a second liquid mixture) of the agitation means, the hydrogenation-removed analytical sample B and the hydrochloric acid 28 toward the third treatment tank 34. A second liquid feed line 33, and a heating device 32 that heats the second liquid mixture passing through the second liquid feed line 33 to a temperature at which the reduction reaction of hexavalent selenium to tetravalent selenium proceeds, and hydrogenation The hexavalent cell remaining in the sample B for analysis after removal And supplies as reducing the processed analytical sample C after reduction of emissions to the tetravalent selenium selenium hydrotreating unit 6. In this embodiment, the heating reactor 32 controls the reduction treatment time for reducing the hexavalent selenium contained in the hydrogenation-removed analytical sample B to tetravalent selenium. For example, a PTFE capillary with an inner diameter of 1 mm and a length of 6 m is used as the capillary, the flow rate is set to 1.5 mL / min, the heating temperature of the heater is 100 ° C., and the second mixture is heated at 100 ° C. for 10 minutes. It was to so.

<Selenium hydrogenation processing unit>
The selenium hydrogenation processing unit 6 generates hydrogen selenide gas by hydrogenating tetravalent selenium contained in the reduction-treated analysis sample C with sodium borohydride, and the reduction-treated analysis sample C is sent. A sealed reaction tank 34 that is stored in a liquid state, a gas introduction pipe 42 for sending hydrogen selenide gas accumulated in the head space 41 in the reaction tank 34 to the hydrogen selenide gas detector 43, and a gas introduction pipe 42 A carrier gas supply means 45 for supplying the carrier gas to the gas flow path to the hydrogen selenide gas detector 43 with a carrier gas, and a solution 38 containing sodium borohydride as a hydrogen selenide gas generator is reduced. And a hydrogen selenide gas generator addition means 55 to be added to the processed analysis sample C. The hydrogen selenide gas generator addition means 55 includes a tank 36 for storing a solution 38 containing sodium borohydride, a refrigerator 37 for storing the solution 38 together with the tank 36 after cooling to 0 ° C. to 10 ° C., and sodium borohydride. And a pump 39 for supplying a solution 38 containing Here, the addition of sodium borohydride by the hydrogen selenide gas generator addition means 55 is performed after replacing the gas flow path in the reaction vessel 34 and the gas introduction pipe 42 with the carrier gas. In order to hydrogenate selenium or sulfur compounds with NaBH ₄ , it is necessary to add NaBH ₄ under acidic conditions (acid solution). In the pretreatment (hydrogenation removal of tetravalent selenium and hydrogenation removal of sulfur compounds other than sulfuric acid), hydrochloric acid is added in order to achieve acidic conditions. On the other hand, in the hydrogenation of tetravalent selenium in the last step, hydrochloric acid is added in the reduction step of hexavalent selenium (to tetravalent selenium) before the hydrogenation step. Therefore, since the sample after the reduction step is already an acidic solution (since hydrochloric acid is added in excess), it is not necessary to add additional hydrochloric acid.

  The carrier gas supply means 45 includes two water tanks 46 through which the carrier gas is humidified, a pipe 44 for supplying the humidified carrier gas to the gas introduction pipe 42, and a flow rate of the carrier gas supplied from the air compressor 54. It is composed of a mass controller 49 and a pipe 48 for adjusting the above. By substituting with the carrier gas, the baseline of the signal of the hydrogen selenide gas detector 43 is stabilized, and the analysis is performed with high accuracy based on the stable signal value. In addition, the heating line 47 heats the inner wall of the gas introduction pipe 42 to a temperature at which dew condensation does not occur (70 to 80 ° C.), and the temperature at which the electrolyte in the sensor portion of the hydrogen selenide gas detector 43 does not evaporate and dry. It is preferable to provide a heating device (not shown) for heating to (50 ° C.). Although not shown in the figure, the generation of hydrogen chloride gas is suppressed by supplying the cell 35 with an amount of water that can suppress the generation of hydrogen chloride gas from the analytical sample subjected to the reduction treatment if necessary. It is preferable to eliminate interference in the analysis due to the occurrence of abnormal peaks in the hydrogen selenide gas detector.

Regarding the addition amount of each sodium borohydride in the hydrogenation removal processing unit 4 and the selenium hydrogenation processing unit 6, the total amount of tetravalent selenium considered to be present in the sample for analysis is reduced to hydrogen selenide. An amount larger than the amount that can be used is appropriately selected. In order to reduce 1 mol of H ₂ SeO ₃ (SeO ₃ ²⁻ ) to generate hydrogen selenide, _3/4 mol of NaBH ₄ (BH ₄ ⁻ ) is required. Therefore, a minimum of 0.38 mg NaBH ₄ is required for 1 mg of tetravalent selenium. Here, with respect to the amount of sodium borohydride added in the selenium hydrogenation treatment unit 6, in order to reliably reduce the total amount of tetravalent selenium present in the sample for analysis to hydrogen selenide, pretreated analysis It is preferable to add an excessive amount of sodium borohydride with respect to the total amount of tetravalent selenium considered to be contained in the sample for use. That is, assuming that the tetravalent selenium concentration of the analytical sample subjected to hydrochloric acid reduction treatment is 1 mg / L or less, 0.38 mg to 6.7 g of borohydride with respect to 1 liter of analytical sample subjected to hydrochloric acid reduction treatment. Sodium is preferably added, more preferably 3.8 mg to 3.4 g, and even more preferably 38 mg to 2.0 g. Even if sodium borohydride in an amount exceeding 6.7 g is added, it does not affect the measurement of hydrogen selenide, but it is useless because it does not participate in the hydrogen selenide generation reaction.

  Moreover, it is preferable to continue stirring the analysis sample from the start of the addition of sodium borohydride to the analysis sample until the measurement by the hydrogen selenide gas detector is completed. If stirring is not sufficiently performed, sodium borohydride added to the sample for analysis cannot be sufficiently diffused, and tetravalent selenium and sulfur compounds in the sample for analysis are converted into hydrogen selenide gas and hydrogen sulfide gas. There is a possibility that the removal will be incomplete, or the reaction with the reduction-treated analytical sample will be non-uniform, and the signal intensity of hydrogen selenide by the hydrogen selenide gas detector will decrease. Therefore, the reaction tank 34 is provided with a third stirring device (stirring blade) 35 that stirs the reduction-treated analytical sample C and the sodium borohydride 38 in the reaction tank 34.

<Analysis Department>
The analysis unit 7 sends the hydrogen selenide gas in the head space 41 in the reaction tank 34 to the hydrogen selenide gas detector 43 through the gas introduction pipe 42, and the measurement value ( Based on the signal value), the water-soluble selenium concentration of the analysis sample is analyzed by the calibration curve method.

  As the hydrogen selenide gas detector 43, various types of detectors capable of detecting hydrogen selenide gas can be used. In particular, hydrogen selenide gas having a diaphragm galvanic or concentration cell type sensor unit. The use of a detector is preferred. This type of detector has the advantage that since the sensor itself constitutes a battery, there is very little residual current when there is no gas to be detected, so that zero point stability is high and running cost is low. doing. An example of such a detector is 1GWA / V70 manufactured by Bionics, but is not limited thereto. For example, a new Cosmos Electric PS-7 (dedicated hydrogen selenide sensor unit CDS-7) having a constant potential electrolysis method may be used.

  The hydrogen selenide gas is measured at any time by a hydrogen selenide gas detector, and a measured value is output. Here, it is preferable to supply a carrier gas to the generated hydrogen selenide gas, and guide the hydrogen selenide gas to the hydrogen selenide gas detector along with the carrier gas. Furthermore, it is preferable to suck the hydrogen selenide gas alone or together with the carrier gas using the gas suction function of the hydrogen selenide gas detector. As the carrier gas, not only an inert gas such as nitrogen or argon but also air can be used. Further, it is preferable to humidify the carrier gas as a measure for suppressing the decrease in sensor sensitivity.

The calibration curve used for the calibration curve method was created based on the correlation between the water-soluble selenium concentration obtained in advance from a plurality of standard samples with known water-soluble selenium concentrations and the signal value detected by the hydrogen selenide gas detector. Is. More specifically, each of a plurality of standard samples with known water-soluble selenium concentrations is analyzed under the same conditions as when actually analyzing the sample for analysis, and the water-soluble selenium concentration and hydrogen selenide gas detector are analyzed. By fitting the correlation with the signal value detected by the known method such as the least square method to obtain a calibration curve, from the signal value when analyzing the sample for analysis, using this calibration curve, The water-soluble selenium concentration of the sample for analysis can be determined. For example, when a selenium standard sample, excellent calibration curve linearity is obtained in the concentration range of 0.01 to ^{0.5-SeL -1,} lower detection limit was 0.003 ^{mg-SeL -1} ( The drainage standard value is 0.1 mg-SeL ⁻¹ ).

(All selenium monitors)
FIG. 3 shows an embodiment of the total selenium analysis system 2. In the present embodiment, the total selenium analysis system 2 is supplied with the analysis sample A branched by the waste water collection unit 3 on the upstream side of the hexavalent selenium analysis line 1 shown in FIG. Quantitative analysis of the total selenium concentration, an oxidation treatment unit 57 for adding potassium permanganate 68 and sulfuric acid 70 to the sample A for analysis and heating to convert unstable sulfur compounds into sulfate ions, and oxidation treatment Hydrochloric acid 79 is added to the already analyzed sample E and heated to reduce hexavalent selenium to tetravalent selenium to prepare tetravalent selenium, and sodium borohydride is added to the reduced analysis sample F Based on the detection signal value obtained by introducing the hydrogen selenide gas to the hydrogen selenide gas detector 93 and the selenium hydrogenation treatment part 59 that converts tetravalent selenium into hydrogen selenide gas by reaction. Sought after That by using a calibration curve is constructed by the analyzer 60 to determine the total selenium concentration is to quantify the total selenium and align hexavalent selenium tetravalent selenium. Note that the sample A for analysis is fed to the first processing tank 66 through the drainage feeding line 8 including the drainage feeding device 64 and the sample meter 65 to the total selenium analysis line 2.

<Drainage collection unit>
The wastewater collecting unit 56 includes a wastewater feeding device 64 and a sample meter 65 for feeding the analytical sample A branched from the hexavalent selenium quantification line 1 to the first treatment tank 66 via the wastewater feeding line 8. With. In addition, the drainage collection unit 56 is provided with a standard sample storage tank 63 as necessary.

<Oxidation treatment section>
The oxidation processing unit 57 includes, for example, a first processing tank 66 that stores an analysis sample, and an amount that can decompose the sulfur compound into sulfate ions in the first processing tank 66 and that does not inhibit the reduction in the reduction processing unit 58. The sulfur compound decomposing agent adding means for supplying and adding potassium permanganate 68 and sulfuric acid 70 from the tanks 67 and 69, the waste water in the first treatment tank 66, and the sulfur compound decomposing agent are stirred and mixed. Passing through the first liquid feeding line 76 including the first stirring means as the liquid mixture, the first liquid feeding device 74 that feeds the first liquid mixture toward the reduction processing unit 58, and the first liquid feeding line 76. And a first heating device 75 that heats the first mixed liquid to a temperature at which the sulfur compound is decomposed, and converts the sulfur compound in the sample A for analysis into stable sulfate ions and oxidizes them to the reduction processing unit 58. Sent out as processed sample E for analysis A. A mixed liquid (first mixed liquid E) of the sample A for analysis, potassium permanganate 68, and sulfuric acid 70 is heated in the process of being sent toward the second processing tank 77 of the reduction processing unit 58 to be a sulfur compound. Is decomposed into stable sulfate ions. For example, when the flow rate of the first mixed liquid E is set to 0.5 mL / min, the heating in the heating reactor 75 is performed for about 20 minutes at a heating temperature of the heater of 100 ° C. In addition, manganese dioxide etc. resulting from the potassium permanganate 68 are deposited on the first liquid feeding line 76 after the first mixed solution E of the sample A for analysis, potassium permanganate 68 and sulfuric acid 70 passes. Since the inner diameter is narrowed or closed, hydrochloric acid is supplied as a cleaning agent by a cleaning agent supply means (not shown). The addition amounts of potassium permanganate 68 and sulfuric acid 70 are controlled by syringe pumps 71 and 72. In the present embodiment, the analysis sample A, potassium manganate 68 and sulfuric acid 70 in the first processing tank 66 are agitated by bubbling the compressed air supplied from the compressor 54 through the blast tube 73.

Potassium permanganate (KMnO4) and sulfuric acid are added to the sample for analysis and heated to increase the oxidizing power of potassium permanganate and oxidatively decompose the sulfur compounds contained in the wastewater into stable sulfate ions. At the same time, it has been clarified by the present inventors that tetravalent selenium contained in the analytical sample is oxidized to hexavalent selenium. That is, in the total selenium quantitative process of the present embodiment, the precursor (unstable sulfur compound) in the waste water that generates hydrogen sulfide, which is a disturbing component of the gas sensor, is eliminated by converting it into stable sulfate ions. . The tetravalent selenium is oxidized to hexavalent selenium, and all the water-soluble selenium (tetravalent selenium: SeO ₃ ²⁻ , hexavalent selenium: SeO ₄ ²⁻ ) existing in the waste water is aligned with the hexavalent selenium. .

  The decomposition of the sulfur compound will be described in more detail. Sulfur compounds such as dithionic acid and hydroxylamine sulfonic acid compound (NS compound) are oxidized and decomposed by potassium permanganate whose oxidizing power is enhanced by sulfuric acid, and finally sulfuric acid Become an ion. Sulfate ions are chemically stable, and hydrogen sulfide gas is not generated even when sodium borohydride is added. Accordingly, a sulfur compound that can generate hydrogen sulfide gas by reaction with sodium borohydride by potassium permanganate whose oxidizing power is enhanced by sulfuric acid, that is, a stable sulfur compound that does not react with sodium borohydride (sulfuric acid It is possible to eliminate the interference of the measurement of hydrogen selenide gas by a sulfur compound other than (such as peroxodisulfuric acid), and so on, and to perform accurate analysis.

  The added amount of potassium permanganate and sulfuric acid is an amount that can oxidatively decompose the sulfur compound contained in the sample for analysis into stable sulfate ions, and the excessive amount does not inhibit the reduction in the reduction treatment. If the amount of potassium permanganate added is too large, the excess will react with hydrochloric acid, which is the reducing agent, in the reduction treatment, and the amount of hydrochloric acid will be consumed, thereby inhibiting the reduction reaction of hexavalent selenium to tetravalent selenium. It will be.

  The specific amount of potassium permanganate added is preferably, for example, 100 to 1000 times the amount required to oxidize the sulfur compound expected to be contained in the analytical sample. It is more preferable that the amount is 500 to 5000 times.

  The amount of sulfuric acid added is preferably such that the sulfuric acid concentration of the analytical sample after adding sulfuric acid and potassium permanganate (aqueous solution) is adjusted to 1.3 to 3 mol / L. More preferably, the amount is adjusted to 3 mol / L. If the sulfuric acid concentration is too low, the effect of increasing the oxidizing power of potassium permanganate by sulfuric acid is reduced, so that the sulfur compound cannot be sufficiently decomposed and the analysis accuracy can be lowered. If the sulfuric acid concentration is too high, the amount of sulfuric acid added becomes too large, increasing the total amount of the sample for analysis, leading to an increase in reaction time. As a specific example, when 5 mL of an analytical sample containing a sulfur compound is used as drainage, 1 to 2 mL of 6 to 18 mol / L sulfuric acid may be added to obtain the above concentration, and 1 to 9 to 12 mol / L sulfuric acid may be added. It is preferable to add ˜2 mL to the above concentration, and it is more preferable to add 2 mL of 9 mol / L sulfuric acid to the above concentration.

  Here, potassium permanganate and sulfuric acid can be added by thoroughly stirring and mixing the analytical sample and sulfuric acid before adding potassium permanganate, or by thoroughly stirring and mixing the analytical sample and potassium permanganate. It is preferable to add sulfuric acid after that. Thereby, it is possible to suppress the boiling of the analytical sample due to the neutralization reaction of sulfuric acid, and it is possible to prevent a reduction in the resolution of the sulfur compound due to the direct contact between potassium permanganate and sulfuric acid to generate solids.

  The heating temperature of the analytical sample to which potassium permanganate and sulfuric acid have been added in the oxidation treatment is preferably 100 ° C. or higher. If the temperature is lower than this, the sulfur compound cannot be completely decomposed, and the analysis accuracy can be lowered. If the heating temperature is too high, the analytical sample will boil vigorously, so the heating temperature is preferably 100-120 ° C.

  The heating time in the oxidation treatment is preferably 15 minutes or more at the above temperature. When shorter than this, a sulfur compound cannot be decomposed | disassembled and an analysis precision may fall. It should be noted that even if the decomposition processing time is too long, no particularly advantageous effect is seen, but rather the analysis time is lengthened. Therefore, the decomposition treatment time may be approximately 15 to 30 minutes at the above temperature, preferably 15 minutes to 20 minutes, and considering the certainty of the decomposition treatment, it may be approximately 20 minutes. More preferred.

<Reduction processing unit>
The reduction processing unit 58 has the same configuration as the reduction processing unit 5 of the hexavalent selenium analysis system 1 of FIG. 2, and is different from the hexavalent selenium analysis line 1 of FIG. The sample E for analysis in the previous stage contains a stable sulfate ion obtained by decomposing a sulfur compound, hexavalent selenium originally present, and one obtained by oxidation from tetravalent selenium to hexavalent selenium. is there. Therefore, by reducing the oxidized analytical sample E, all selenium (hexavalent selenium and tetravalent selenium) contained in the analytical sample is all converted to tetravalent selenium. In the figure, reference numeral 78 is a tank for storing hydrochloric acid 79, 80 is a syringe pump for supplying a predetermined amount of hydrochloric acid 79 to the second processing tank 77, and 81 is an oxidized analytical sample E in the second processing tank 77. Are blown tubes constituting stirring means for stirring by stirring bubbling and hydrochloric acid 79, and 82 and 84 are the second for feeding the mixed solution F of the oxidized analytical sample E and hydrochloric acid 79 toward the third processing tank 85. The liquid feeding device and the second liquid feeding line 83 are tetravalent hexavalent selenium of a mixed liquid (second mixed liquid F) of the oxidized analysis sample E and hydrochloric acid 79 passing through the second liquid feeding line 84. It is a heating device that heats to a temperature at which the reduction reaction to selenium proceeds.

<Selenium hydrogenation processing unit>
The selenium hydrogenation processing unit 59 has the same configuration as the hydrogen selenization processing unit in the hexavalent selenium analysis system of FIG. In the figure, reference numeral 85 denotes a sealed reaction tank in which a reduction-processed analytical sample is accommodated, 92 is a gas introduction pipe, 95 is a carrier gas supply means, 86 is a stirring blade (third stirring device), and 61 is selenized. This is a hydrogen gas generator addition means. The hydrogen selenide gas generator addition means 61 detects a tank 87 and a refrigerator 88 that store a solution 89 containing sodium borohydride, and a solution 89 containing sodium borohydride by a hydrogen selenide gas detector 93. The pump 90 is supplied at a speed less than the speed at which the peak of the signal value splits. The carrier gas supply means 95 includes two water tanks 96 for humidifying the carrier gas, a pipe 94 for supplying the humidified carrier gas to the gas introduction pipe 42, and a flow rate of the carrier gas supplied from the air compressor 54. It is composed of a mass controller 49 and a pipe 98 for adjusting the above. Further, the heating line 97 heats the inner wall of the gas introduction pipe 42 to a temperature at which no dew condensation occurs, and also heats the electrolyte of the sensor part of the hydrogen selenide gas detector 43 to a temperature at which the electrolyte does not evaporate to dryness. Equipped with equipment.

<Analysis Department>
Since the analysis unit has the same configuration as the hydrogen selenide gas generation unit in the hexavalent selenium analysis system of FIG. 2, detailed description thereof is omitted.

(Wastewater treatment system for selenium-containing wastewater)
The equivalent hexavalent selenium concentration determined in the above-described hexavalent selenium quantification line 1 and the total selenium concentration determined in the total selenium quantitative analysis line 2 are, for example, operations of the selenium treatment facility in the selenium-containing wastewater treatment system shown in FIG. Can be used.

  The selenium-containing wastewater treatment system is a wastewater treatment line 100 that includes a hexavalent selenium wastewater treatment facility 101 and a coagulation sedimentation wastewater treatment facility 102. A detour 105 for bypassing the monovalent selenium wastewater treatment facility 101, a line drained via the hexavalent selenium wastewater treatment facility 101 and the coagulation sedimentation wastewater treatment facility 102, and a hexavalent selenium wastewater treatment It is possible to switch to a line that bypasses the facility 101 and drains only through the coagulation sedimentation wastewater treatment facility 102. Note that the control unit 103 is, for example, a programmable logic controller (PLC), a central processing unit (CPU) that reads a program on a storage device and executes the following comparison calculation, determination, and control processing of a control target. Consists of.

  Here, in general, there is no wastewater treatment facility dedicated to tetravalent selenium in the wastewater treatment facility, and tetravalent selenium is treated by a normal coagulating sedimentation apparatus for treating heavy metal ions. On the other hand, since hexavalent selenium cannot be treated with a normal coagulation sedimentation apparatus, a dedicated wastewater treatment facility for reducing hexavalent selenium to tetravalent selenium (which may be further reduced to zero-valent selenium) is required. . Therefore, when hexavalent selenium is contained in the wastewater, the hexavalent selenium is converted into tetravalent selenium by the exclusive wastewater treatment facility for hexavalent selenium, and then the tetravalent selenium originally present in the wastewater and the 6 to 4 All selenium including tetravalent selenium converted to valence is treated with a normal coagulating sedimentation apparatus (already installed in a power plant) that treats heavy metal ions.

  Therefore, the control unit 103 uses the selenium drainage standard as a threshold value, and compares the respective output values of the equivalent hexavalent selenium concentration and the total selenium concentration from the selenium monitors 1 and 2 with, for example, a comparison operation element or a central operation element When it is determined that the total selenium concentration detected by the total selenium concentration quantification line 2 satisfies the drainage standard, the wastewater treatment equipment 101 dedicated to hexavalent selenium is bypassed and drained, and the total selenium concentration satisfies the drainage standard. If the equivalent hexavalent selenium concentration detected by the hexavalent selenium concentration quantification line does not satisfy the drainage standard, the selenium removal treatment is performed by the hexavalent selenium dedicated wastewater treatment facility 101 and the coagulation sedimentation wastewater treatment facility 102. The total selenium concentration does not meet the effluent standard, but the equivalent hexavalent selenium concentration is detected when the equivalent hexavalent selenium concentration is not detected or detected. There is controlled so as to waste water after removing the tetravalent selenium hexavalent selenium dedicated wastewater treatment facility 102 with coagulation-sedimentation waste water treatment facility 102 is bypassed when meeting the effluent standard. As a result, when the hexavalent selenium dedicated wastewater treatment facility 102 and the coagulation sedimentation wastewater treatment facility 102 are used in combination, the operation of each wastewater treatment facility can be optimized.

  Of course, in order to efficiently operate the selenium treatment facility, it is necessary to reduce the hexavalent selenium to tetravalent selenium or metal selenium in the wastewater treatment facility 102 dedicated to hexavalent selenium. Accurate monitoring (quantitative analysis) is effective. On the other hand, the concentration of tetravalent selenium that can be removed by ordinary wastewater treatment (coagulation sedimentation treatment) was reduced from what was originally hexavalent selenium present in the wastewater, even if it was not uniquely determined separately from hexavalent selenium. A quantitative analysis of the total selenium concentration including the minute is sufficient. In normal agglomeration and precipitation, other high-concentration metal ions are removed at the same time as tetravalent selenium, so the drug is excessively added (addition amount is fixed) with a margin, so it has a lower concentration than other metal ions. There is no change in the amount of drug added according to the tetravalent selenium concentration. Therefore, the selenium monitor classified by chemical form that automatically measures the selenium concentration of wastewater by chemical form has two systems, a line that quantifies at least hexavalent selenium concentration and a line that quantifies the total selenium concentration. It's enough.

  Instead of the automatic control by the control unit described above, the equivalent hexavalent selenium concentration and the total selenium concentration are displayed on the selenium type monitor, and the operator himself who reads the values switches the flow path. Also good. Even in this case, wastewater treatment costs can be reduced by bypassing the hexavalent selenium wastewater treatment facility 101.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  The water-soluble selenium analysis system (referred to as selenium monitor) that implements the water-soluble selenium analysis method according to the present invention was used to determine the selenium concentration by chemical form of all selenium contained in the desulfurization effluent.

First, a test for quantitative analysis of total selenium in waste water was performed using a selenium monitor having the configuration shown in FIG. It is known from experience so far that hydrogen sulfide is produced when a sulfur compound (other than sulfate ions) is hydrogenated without oxidation to sulfate ions. Therefore, no experiment was conducted in which a sulfur compound was added.
The total selenium quantitative analysis measurement flow by this selenium monitor is
(1) Collecting and weighing samples for analysis,
(2) Addition of oxidative degradation reagents (potassium permanganate (KMnO ₄ ) solution and sulfuric acid (H ₂ SO ₄ ) solution),
(3) Oxidative decomposition (105 ° C),
(4) Addition of Se reducing reagent (hydrochloric acid (HCl) solution),
(5) Reduction of Se (105 ° C),
(6) Hydrogenation of Se (addition of sodium borohydride (NaBH ₄ ) solution),
(7) Se detection / quantification,
It consists of each process.
For detection and quantification of H ₂ Se generated by Se hydrogenation, a diaphragm galvanic cell type electrochemical sensor GT-3260H manufactured by Bionics Instruments Co., Ltd. was used. The sensor electrolyte used was a commercial product (E-3260-1) provided by bionics equipment. The gas sensor made of Teflon (registered trademark) having a film thickness of 200 μm was used.

  A selenium monitor was installed at a domestic coal-fired power plant for three months, and the selenium concentration in the reduction tower supply tank wastewater (drainage before selenium treatment) in the chemical wastewater treatment process for selenium was measured (see Fig. 4). The selenium monitor was installed in a container house equipped with air conditioning equipment.

The specifications of the test are shown below.
Test period: September 26, 2016-December 26, 2016 Sample for analysis: Reduction tower supply tank wastewater in the wastewater treatment process for selenium (Selenium treatment inlet)
Measurement frequency: Every 3 hours Sample volume: 5.0 mL
Carrier gas humidification: Yes (Bubbling at room temperature)
Quantitative calculation: Based on the maximum output value of the sensor signal during measurement (peak height calculation)
Calibration: Two-point calibration with blank sample and selenium standard sample.
Calibration frequency: Every 24 hours Selenium standard sample: SeO ₃ ^2- solution 0.200 mg-Se / L
Sample pretreatment temperature: 105 ° C
Reagents used and amount used per measurement: 9.0 mol / LH ₂ SO ₄ solution 2 mL
6.0 g / L KMnO ₄ solution 1 mL
12 mol / L HCl solution 5 mL
3.0 g / L NaBH ₄ solution 10 mL

  In order to verify the measured value of the selenium monitor, 250 mL of waste water supplied to the selenium monitor was collected once a day from the sampling reservoir on the side of the selenium monitor. The selenium concentration of the sample for analysis was determined by ICP emission spectroscopy (ICP-OES) according to the official method (factory drainage test method JIS K0102). Regular maintenance of the selenium monitor was performed once a month. The gas sensor used two sensors (# 17 and # 18) alternately and was replaced during maintenance. After use, the sensor exchanged the electrolyte solution and the diaphragm, and then waited for the battery to be charged (aging) to prepare for the next use.

(Results and discussion)
(Quantitative with standard sample)
Using a selenium monitor shown in FIG. 3, a SeO ₃ ^2- standard sample was measured and its quantitative property was evaluated. The Se concentration of the standard sample was 0.00, 0.05, 0.10, 0.20 mg / L. The results are shown in FIG. A calibration curve with high linearity (see Fig. 6) was obtained in the selenium concentration range of 0 to 0.2 mg / L (repetition number n = 5, correlation coefficient r ² = 0.990), and the relative standard deviation of each concentration was 3 to 9%.
A calibration curve with high linearity in the range of 0.00 to 0.50 mg / L (0.00, 0.05, 0.10, 0.20, 0.40, 0.50 mg / L) (repetition number n = 3, correlation coefficient r ² = 0.992) was obtained. The relative standard deviation of each concentration was 3-14%. It is the film thickness of the gas sensor diaphragm (200 μm).

(Change in selenium concentration over time)
FIG. 7 shows the change with time of the selenium concentration by the official method. The selenium concentration in the selenium treatment wastewater supplied to the selenium monitor generally fluctuated gradually in the range of 0.02 to 0.16 mg / L. The dark gray color in the graph indicates the period when the wastewater supply to the selenium monitor was stopped. There were places where the selenium concentration changed discontinuously during the test, but this reflected the operating status of the wastewater treatment equipment, such as switching the reduction tower supply tank (drainage system 1, drainage system 2) to be supplied to the selenium monitor. It was thought that As a result of quantifying selenium in wastewater by ICP-OES by chemical form, the chemical form of selenium was almost hexavalent (Fig. 8).

(Monitoring with selenium monitor)
FIG. 8 shows the results of monitoring the selenium concentration with a selenium monitor. The graph shows the signal output of the gas sensor at the time of calibration (FIG. 9, upper graph) and the measured selenium concentration by the monitor (FIG. 9, lower graph). The concentration graph also shows the measured values by the official method.
Incidentally, during the test period, the selenium monitor intermittently suffered measurement failures for 16 days (lightly shaded portion in FIG. 9) due to malfunction of the component parts and sensor life. The dark shaded area indicates the period when the selenium monitor drainage supply was stopped.
The troubles that occurred during this test are as follows.
(1) On October 23-25, 2016, a measurement failure (no addition of hydrochloric acid) occurred due to a solenoid valve failure.
(2) From October 31 to November 2, 2016, measurement failure occurred due to the stop of the agitator in the reaction tank.
(3) Since dawn on December 15, 2016, the signal output (baseline) drop and the two signal output excess (scale over) occurred at the time of switching one flow path due to a failure estimated to be the sensor life.
Note that the decrease in signal output at the time of switching the channel was not resolved after December 20, and measurement failures continued. Examination after completion of the test confirmed that the decrease in signal output at the time of switching the flow path was due to insufficient replacement of HCl gas in the reaction tank. On the other hand, in response to the trouble on December 20, we also confirmed the malfunction of three solenoid valves and one drainage diaphragm pump.

  The selenium monitor measurement value, as well as the official method measurement value, sometimes caused the selenium concentration to change discontinuously during the test. In addition to the effect of switching the reduction tower supply tank (drainage system 1 and drainage system 2) supplied to the selenium monitor, the effect of the stop (and activation) of the feed pump that supplies wastewater from the supply tank to the selenium monitor It was thought to reflect. This is because when the liquid feed pump is stopped, it becomes impossible to collect a drainage sample due to a drop in the liquid level of the sample supply tank on the side of the monitor.

FIG. 10 shows the correlation between the measured value of the selenium monitor and the measured value by the official method. Excluding measurement failure data, a correlation (data number 69) with a slope of 0.949 and a coefficient of determination r ² = 0.978 was obtained. By the way, the selenium monitor measured value (0.075 mg / L) on November 11 was significantly different from the official method concentration (0.016 mg / L) (outlier). When the official method sample for concentration verification was measured again on the monitor after the test was completed, the concentration was 0.026 mg / L, and the correlation with the official method was confirmed. It was considered that the difference in concentration during the test of the sample was caused by the monitor not measuring the same sample as the official method.

  As a result of this experiment, it was found that the selenium concentration of the waste water can be monitored with the same accuracy as the official method using the selenium monitor that performs the water-soluble selenium analysis method according to the present invention.

Moreover, it experimented about the quantitative analysis of hexavalent selenium. In order to make this experiment simple, it was made simple using a Teflon beaker or the like without using the selenium monitor shown in FIG. First, an experiment was conducted on hydrogenation removal of tetravalent selenium.
By adding sodium borohydride aqueous solution (NaBH ₄ ) and hydrochloric acid to a selenium-containing aqueous solution (containing tetravalent selenium and hexavalent selenium) and reacting at room temperature, the tetravalent selenium in the sample is converted to hydrogen selenide (H ₂ Converted to Se) (hydrogenated) and removed from the solution. When NaBH ₄ is added to the selenium-containing acidic solution, only tetravalent selenium is hydrogenated, and the phenomenon that hexavalent selenium is not hydrogenated is utilized.
It was assumed that only hexavalent selenium remained in the sample after this hydrogenation removal, and the total selenium concentration of the sample after removal determined by the official method (JIS K0102) was regarded as the hexavalent selenium concentration (FIG. 1).
As the measurement sample, two types of desulfurization waste water (Table 2, desulfurization waste water A and B) and a standard concentration of hexavalent selenium of a predetermined concentration, or both tetravalent selenium and hexavalent selenium were used.

The hydrogenation removal was carried out by the following procedure.
(1) 25 mL of a sample for analysis was dispensed into a 100 mL Teflon beaker (solution A).
(2) 25 mL of hydrochloric acid (HCl, 12 mol / L) was collected and added to Solution A (Solution B).
(3) A predetermined amount of NaBH ₄ solution (containing 0.1 mol / L NaOH and 1 mmol / L EDTA) with a predetermined concentration (3.0, 6.0, 12.0 g / L) while stirring the solution B with a stirrer (3.0g / L NaBH ₄ is 50mL, 6.0g / L NaBH ₄ is 25mL, 12.0g / L NaBH ₄ is 12.5 mL) was added and stirred for 5 minutes.
(4) The recovery rate was calculated from the following equation.
Recovery rate (%) = (C ₀ -C ₁ ) / C ₀ × 100
C ₀ : Set concentration of selenium in the sample
(Mg / L, measured value of drainage selenium concentration plus standard addition concentration)
C ₁ : selenium concentration measured value of sample (mg / L)
The set concentration of all selenium and hexavalent selenium in the analytical sample removed by hydrogenation was set to the hexavalent selenium concentration set value of the sample before hydrogenation removal.

( Results and discussion)
HCl and NaBH ₄ solution were added to the analysis sample, and tetravalent selenium in the analysis sample was hydrogenated to H ₂ Se to be vaporized and removed. It was assumed that all tetravalent selenium in the analytical sample was removed by hydrogenation removal, and all selenium remaining in the sample after hydrogenation removal was hexavalent selenium. For this reason, the total selenium concentration of the analytical sample after hydrogenation removal was read as the hexavalent selenium concentration.

Table 3 shows the results of hydrogenating and removing tetravalent selenium from Sample A for analysis with a 3.0 g / L NaBH ₄ solution. The measured value is 0.07 to 0.31 mg / L and the recovery rate is 100 to 120% with respect to the hexavalent selenium set concentration of 0.06 to 0.26 mg / L of the sample after hydrogenation removal. The tendency to evaluate was shown. As a factor for overestimating the hexavalent selenium recovery rate, it is considered that a part of the tetravalent selenium remains without being hydrogenated when the tetravalent selenium is removed by hydrogenation.

Table 4 shows the result of hydrogenating and removing tetravalent selenium from the analytical sample B with a 3.0 g / L NaBH ₄ solution. The measured value was 0.04 to 0.28 mg / L and the recovery rate was 100 to 112% with respect to the hexavalent selenium set concentration of 0.04 to 0.24 mg / L of the analysis sample after hydrogenation removal. .

Table 5 shows the results of hydrogenating and removing tetravalent selenium from analytical sample A and analytical sample B with a 6.0 g / L NaBH ₄ solution. The hexavalent selenium concentration recovery rate of the analysis sample after hydrogenation removal was 105 to 114%.

Table 6 shows the results obtained by hydrogenating and removing tetravalent selenium from analytical sample A with 6.0 g / L and 12.0 g / L NaBH ₄ solutions. The recovery rate of the hexavalent selenium concentration of the sample after hydrogenation removal is 106 to 110% when a 6.0 g / L NaBH ₄ solution is used, and 104 to 10 when a 12.0 g / L NaBH ₄ solution is used. It was 112%. The recovery rate when using 6.0 g / L NaBH ₄ solution was the same as when using 12.0 g / L NaBH ₄ solution.

From the above, if tetravalent selenium in a measurement sample is hydrogenated and removed using a 6.0 g / L or 12.0 g / L NaBH ₄ solution, the recovery rate is 100 to 110% in the analysis sample. The hexavalent selenium concentration was obtained. Further, since the tetravalent selenium concentration is obtained from the difference between the total selenium concentration and the hexavalent selenium concentration, the selenium concentration of the analysis sample can be separated into tetravalent selenium and hexavalent selenium. It was found that the concentration of tetravalent selenium and hexavalent selenium can be measured with an error of about 10% at maximum under conditions that maximize the fractionation performance.

  From this, it was proved that the online selenium monitor that implements the selenium analysis method according to the present embodiment can provide concentration data necessary for wastewater selenium management in real time and can be used as a process monitor.

S1 Hydrogenation removal process of tetravalent selenium and sulfur compound S2 Hydrochloric acid reduction process S3 Selenium hydrogenation process A Sample for analysis B Sample for analysis after dehydration C Sample for analysis after reduction treatment D Sample for analysis after hydrogenation 1 Hexavalent Selenium monitor (hexavalent selenium quantification line)
2 Total selenium monitor (total selenium quantitative analysis line)
DESCRIPTION OF SYMBOLS 100 Waste water treatment line 101 Waste water treatment equipment only for hexavalent selenium 102 Coagulation sedimentation waste water treatment equipment 103 Control part 104 Switching valve 105 Detour

Claims (2)

  At the same time that sodium borohydride and hydrochloric acid are added to the analytical sample collected from the desulfurization effluent and reacted at room temperature to release tetravalent selenium in the analytical sample as hydrogen selenide gas from the analytical sample. The sulfur compound in the analytical sample is also removed from the analytical sample as hydrogen sulfide gas, and further, hydrochloric acid is added to the analytical sample from which the hydrogen selenide gas and hydrogen sulfide gas have been removed. A hydrochloric acid reduction step of heating and reducing the hexavalent selenium remaining in the analytical sample to tetravalent selenium, and adding sodium borohydride to the analytical sample further reducing hexavalent selenium to tetravalent selenium And a selenide hydrogenation step for generating hydrogen selenide gas by reacting at room temperature, and the hydrogen selenide gas generated in the selenide hydrogenation step is converted to hydrogen selenide gas. Soluble selenium analysis method characterized by determining the equivalent hexavalent selenium concentration led to knowledge unit. A hexavalent selenium concentration quantification line for quantifying the hexavalent selenium concentration and a total selenium concentration in a wastewater treatment line equipped with a hexavalent selenium dedicated wastewater treatment facility and a coagulation sedimentation wastewater treatment facility for treating tetravalent selenium. Two selenium monitors with a total selenium concentration quantification line and a controller that switches the drainage flow path,
In the hexavalent selenium concentration quantification line, sodium borohydride and hydrochloric acid are added to and reacted with an analytical sample collected from wastewater, and tetravalent selenium in the analytical sample is used as hydrogen selenide gas in the wastewater. At the same time, the sulfur compound in the sample for analysis is separated from the sample for analysis as hydrogen sulfide gas, and hydrochloric acid is further added to the sample for analysis from which the hydrogen selenide gas and hydrogen sulfide gas have been removed. A hydrochloric acid reducing part that reduces the hexavalent selenium remaining in the analytical sample to tetravalent selenium by adding and heating, and the analytical sample further reducing hexavalent selenium to tetravalent selenium. Hydrogen selenide gas detector that detects hydrogen selenide gas and obtains equivalent hexavalent selenium concentration by adding sodium and reacting at room temperature to generate hydrogen selenide gas It has a door,
The total selenium concentration quantification line includes an oxidation treatment section for adding and heating potassium permanganate and sulfuric acid to an analytical sample collected from waste water, and adding and heating hydrochloric acid to heat 4 hexavalent selenium. A reduction treatment unit for reducing to selenium valence, a selenium hydrogenation unit for reacting tetravalent selenium contained in the analytical sample with sodium borohydride to generate hydrogen selenide gas, and detecting the hydrogen selenide gas. And a hydrogen selenide gas detector for determining the total selenium concentration of the analytical sample,
When the control unit determines that the total selenium concentration detected in the total selenium concentration quantification line satisfies a drainage standard, the control unit bypasses the selenium dedicated wastewater treatment facility and drains the drainage, and the total selenium concentration satisfies the drainage standard. When the equivalent hexavalent selenium concentration detected by the hexavalent selenium concentration quantification line does not satisfy the effluent standard, selenium removal treatment is performed by the hexavalent selenium dedicated wastewater treatment facility and the coagulation sedimentation wastewater treatment facility. When the total selenium concentration does not meet the drainage standard, but the equivalent hexavalent selenium concentration is not detected or the detected equivalent hexavalent selenium concentration satisfies the drainage standard, the hexavalent selenium dedicated drainage Drainage of selenium-containing wastewater, characterized in that the treatment facility is bypassed and tetravalent selenium is removed by the coagulation sedimentation wastewater treatment facility and then drained. Management systems.