JP5072684B2 - Cyanide concentration measurement method - Google Patents

Description

The present invention relates to a method for measuring the concentration of a cyanide compound in a sample containing a compound having a manganese ion and an NS bond while preventing erroneous detection of the cyanide compound .

  Cyanide is a general term for cyanide ions in water, cyano complexes, and the like, and is contained in industrial wastewater from plating factories, metal refining, photographic industries, and city gas manufacturing factories. Cyanide compounds are extremely toxic and have a fast impact on the human body. Depending on their intake, symptoms of poisoning may occur in seconds or minutes, causing headache, dizziness, disturbance of consciousness, and paralysis. Cyan is designated as a specified chemical substance in the Industrial Safety and Health Law and as a poisonous substance in the Poisonous and Deleterious Substances Control Law, and the wastewater standard value stated by the Ministry of the Environment is 1 mg / L or less.

  About the method of measuring the density | concentration of the cyanide in waste water, the factory waste water test method JIS-K0102 is prescribed | regulated. In this method, phosphoric acid is added to the waste water which is a sample to bring the pH to 2 or less, and then an EDTA (disodium ethylenediaminetetraacetate) solution is added and distilled by heating, and the generated hydrogen cyanide is collected by a sodium hydroxide solution. Next, the absorbance of the cyanide compound is measured for the collected sample by pyridine-pyrazolone absorptiometry, 4-pyridinecarboxylic acid-pyrazolone absorptiometry, or ion electrode method, and the concentration of the cyanide is determined.

In addition, since cyanide compounds are easy to change, it is desirable to perform the test immediately after sampling, but if this is not possible, add 4-5 grains of sodium hydroxide per liter of sample, store it, and test as soon as possible. .
JIS-K0102 “Examples of cyanide detection from offices that do not use cyanide compounds and cyan analysis methods (Part 2) —Effects of organic compounds and nitrogen compounds in the production of hydrogen cyanide” Makoto Nonomura, Environment and Measurement Technology vol. 17 (1990) no. 2

  However, the present inventors have found that, depending on the sample, cyan may be detected by the JIS-K0102 method even though the sample itself does not contain a cyanide compound. This is considered to be caused by components other than the cyanide compound in the sample. It seems that components other than the cyanide compound in this sample react with the reagent added in the operation for measuring the concentration of the cyanide compound to produce a cyanide compound. For this reason, there exists a possibility that the situation where the exact measurement of the cyanide compound which actually exists in a sample is not performed may occur.

  The present invention has been made in view of such points, and the object thereof is not affected by the reagent added when measuring the concentration of the cyanide compound in the waste water in the JIS-K0102 method. The purpose is to enable accurate measurement of cyanide concentration.

In order to achieve the above object, the invention of claim 1 of the present application is a method for measuring the concentration of a cyanide compound in a sample containing a compound having an NS bond while preventing erroneous detection of the cyanide compound. a step a you decompose the compound having a N-S bond nitrite was added to the sample, a step B of applying an EDTA to the sample, obtaining a distilled to distillate the sample, wherein The step of measuring the absorbance of the cyanide compound in the distillate and the step of determining the concentration of the cyanide compound in the sample from the absorbance were included.

According to this configuration, by adding nitrite in Step A, the compound having an NS bond in the sample is decomposed, so that the reaction between EDTA and the compound having an NS bond added later in Step D is performed. Thus, the formation of a cyanide can be prevented in advance.

The invention of claim 2 of the present application is a method for measuring the concentration of a cyanide compound in a sample containing manganese ions while preventing erroneous detection of the cyanide compound, and manganese oxide is added to the sample by adding sodium hydroxide. Generated step C, step D in which the manganese oxide disappears by adding a reducing agent to the sample, step B in which EDTA is added to the sample, step of distilling the sample to obtain a distillate, The step of measuring the absorbance due to the cyanide compound in the distillate and the step of determining the concentration of the cyanide compound in the sample from the absorbance were included.

According to this configuration, sodium hydroxide is added to the sample for long-term storage and pH adjustment, followed by a reducing agent. As a result, the sample can be stored for a long time, and manganese oxide produced by adding sodium hydroxide is eliminated from the manganese ions in the sample, and manganese oxide acts as an oxidizing agent for EDTA added later. Can be prevented in advance.

  The invention according to claim 3 of the present application further includes step C of adding nitrite to the sample after step B in claim 2.

According to this configuration, sodium hydroxide is added to store the sample for a long time, followed by the reducing agent. As a result, the sample can be stored for a long time, and manganese oxide produced by adding sodium hydroxide is eliminated from the manganese ions in the sample, and manganese oxide acts as an oxidizing agent for EDTA added later. Can be prevented in advance. Moreover, subsequent addition of nitrite is in process, the compounds having a N-S bonds are degraded, a compound having a N-S bonds in the sample, the cyanide is produced by the reaction of EDTA added after Can be prevented in advance.

  The invention of claim 4 of the present application is that in claim 1 or 3, the nitrite is added in an amount of 0.1 mmol / L or more and 5.2 mmol / L or less.

  According to this configuration, by adding nitrite in the above range, the false detection concentration of the cyanide compound can be suppressed to 1 mg / L or less, which is the wastewater standard value described by the Ministry of the Environment.

  The invention of claim 5 of the present application is that in claim 2 or 3, the reducing agent is sodium thiosulfate.

  According to this configuration, sodium thiosulfate serves as a reducing agent for manganese oxide produced by adding sodium hydroxide to the sample.

  The invention of claim 6 of the present application is that in claim 5, the sodium thiosulfate is added in an amount of 1 mmol / L to 10 mmol / L.

  According to this configuration, by adding sodium thiosulfate in the above range, the false detection concentration of the cyanide compound can be suppressed to 1 mg / L or less which is the wastewater standard value described by the Ministry of the Environment.

  The invention of claim 7 of the present application is the exhaust gas desulfurization waste water discharged from the flue gas desulfurization apparatus according to any one of claims 1 to 6.

According to this configuration, since the sample is the flue gas desulfurization waste water discharged from the flue gas desulfurization apparatus, NO ₂ ⁻ and HSO ₃ ⁻ caused by NO _X and SO _X in the exhaust gas react with each other, and NS Although a compound having a bond is generated, the concentration of the cyanide compound can be measured without being affected by the present invention even if a compound having an NS bond is contained in the sample.

According to the invention of claim 1, nitrite is added before EDTA is added. By doing so, the compound having an NS bond contained in the sample is decomposed by the nitrite, so that a cyanide compound is generated by a reaction between EDTA added later and the compound having an NS bond. Can be prevented in advance. This prevents the generation of cyanide and prevents the influence of the compound having an NS bond on the false detection of the cyanide in the sample.

  According to the invention of claim 2, the reducing agent is added after adding sodium hydroxide for preserving the sample for a long time. By adding sodium hydroxide to the sample, manganese ions contained in the sample react with sodium hydroxide and oxygen dissolved in the sample to produce manganese oxide. Here, the manganese oxide produced | generated by adding a reducing agent lose | disappears. This can prevent the reaction between manganese oxide and EDTA, which is one factor that acts as an EDTA oxidant and generates cyanide. As a result, the sample can be stored for a long time, and the influence of manganese ions on the erroneous detection of the cyanide compound in the sample can be prevented.

  According to the invention of claim 3, by adding the step C of adding nitrite to the sample, the influence of the compound having an NS bond in addition to the manganese ion can be prevented against the false detection of the cyanide compound. Can do.

  According to the invention of claim 4, by adding nitrite 0.1 mmol / L or more and 5.2 mmol / L or less, the false detection concentration of cyanide is 1 mg / L or less which is the wastewater standard value described by the Ministry of the Environment. Can be suppressed.

  According to the invention of claim 5, sodium thiosulfate acts as a reducing agent for manganese oxide generated by adding sodium hydroxide to the sample, and manganese oxide that is an oxidizing agent disappears. By the action of this sodium thiosulfate, it is possible to prevent adverse effects due to sodium hydroxide added to preserve the sample for a long time.

  According to the invention of claim 6, by adding sodium thiosulfate in an amount of 1 mmol / L to 10 mmol / L, the false detection concentration of the cyanide compound is suppressed to 1 mg / L or less which is the wastewater standard value described by the Ministry of the Environment. Can do.

According to the invention of claim 7, since the sample is the flue gas desulfurization waste water discharged from the flue gas desulfurization device, NO ₂ ⁻ and HSO ₃ ⁻ caused by NO _X and SO _X in the exhaust gas react, Although a compound having an NS bond is generated, even if a compound having an NS bond is included in the sample, it is not affected by the compound and is originally included in the sample. The concentration of the cyanide compound can be measured.

  Hereinafter, before explaining the embodiments of the present invention, it was decided to elucidate the cause of the false detection of cyanide compounds.

  The present inventor has not used any cyanide in the process until the concentration of cyanide in the wastewater is measured in order to treat the wastewater, that is, although there is no cyanide in the wastewater. Discovered that cyanide would be detected in some cases. As a result of intensive studies in the process of accurately measuring the cyanide concentration in the flue gas desulfurization waste water, the inventors of the present application have come up with the following two causes of this problem.

  The first is the influence of manganese ions contained in the sample and sodium hydroxide added to preserve the sample for a long time.

  In the said nonpatent literature 1, although it is supposed that sodium hydroxide is added as a preservation | save method of a sample, when this process is performed, when manganese ion which is a metal is contained in waste water, sodium hydroxide and in a sample Manganese oxide is produced by the dissolved oxygen. This manganese oxide worked as an oxidant of EDTA to promote the generation of cyanide from EDTA, which led to false detection of cyanide and thought to significantly increase its concentration.

  The second is that a cyanide compound may be erroneously detected by a compound having an NS bond contained in the sample.

In the wastewater discharged from the flue gas desulfurization apparatus, NO ₂ ⁻ and HSO ₃ ⁻ caused by NO _X and SO _X in the exhaust gas react to generate a compound having an N—S bond. The compound having NS bond in the waste water and EDTA added in the operation for measuring the concentration may react during the operation to generate a cyanide compound. For this reason, cyan which is actually dissolved in the waste water. More than the amount of compound is detected. For this reason, accurate concentration measurement was not performed, and it was considered that erroneous detection occurred.

  Hereinafter, the two views will be described in detail based on the drawings.

  First, in order to confirm the above two considerations that are considered to be the cause of false detection of cyanide compounds, the following tests were conducted to find a solution to the problem.

  The cyan compound concentration measuring method in this test is JIS-K0102, and this method includes the following steps.

  The steps include step A in which sodium hydroxide is added to the sample, step B in which EDTA is added to the sample, a step in which the sample is distilled to obtain a distillate, and the absorbance by the cyanide compound in the distillate. And a step of determining the concentration of the cyanide compound in the sample from the absorbance.

  Moreover, the sample used here is the flue gas desulfurization waste water discharged | emitted from a flue gas desulfurization apparatus, and 4-pyridinecarboxylic acid-pyrazolone absorption photometry was used for the measurement of light absorbency.

-Confirmation of the effect of sodium hydroxide on the false detection of cyanide compounds-
First, it was confirmed that manganese ions and sodium hydroxide had an effect on the false detection of cyanide compounds.

  FIG. 1 shows a comparison of the JIS-K0102 method, the method in which step A is removed from the JIS-K0102 method, and the density of the cyanide compound detected in each case. According to JIS-K0102, sodium hydroxide is added in an amount of 4 to 5 particles per liter of sample (about 0.5 g / L when 5 particles are added) in order to preserve the sample for a long time. However, in the JIS-K0102 method, it was confirmed that the concentration of the detected cyanide compound was several times higher than in the method obtained by removing the step A from the JIS-K0102 method.

  This confirmed that sodium hydroxide added in step A was one of the causes of erroneous detection of cyanide compounds.

  Therefore, the following two experiments were conducted on the effect of sodium hydroxide on the false detection concentration of cyanide.

  First, a test was conducted on the influence of the amount of sodium hydroxide added in Step A and the sample standing time on the false detection concentration of the cyanide compound.

  FIG. 2 shows the results of the test. As a result, it was found that the higher the amount of sodium hydroxide added and the longer the sample was left, the higher the false detection concentration of the cyanide compound. However, the influence of the standing time causes a false detection of the cyanide compound caused by the addition of sodium hydroxide, since 50% or more of the false detection concentration of the cyanide compound increases in 5 minutes after the addition of sodium hydroxide. The component formation reaction is considered to be relatively fast.

  Secondly, since the precipitate produced by the step A in the sample subjected to the step A is used to verify whether the precipitate produced in the step A has an influence on the false detection of the cyanide compound. The sample subjected to Step A was separated into a precipitate and a filtrate, and the detected concentration of the cyanide compound was determined for each by the JIS-K0102 method.

  Furthermore, the SS (Suspended Solid: suspended matter suspended in water) concentration of the sample that has undergone Step A is measured, and the concentration of the cyanide compound is adjusted by adjusting the sample in which the mixing ratio of the filtrate and the precipitate is changed. Asked.

  FIG. 3 shows the results of the test. According to this result, although the cyanide compound was not contained in the filtered precipitate itself, it was confirmed that the false detection concentration of the cyanide compound was increased due to the presence of the precipitate. Moreover, as shown in FIG. 4, it was confirmed that the false detection density | concentration of a cyanide compound increases, so that the density | concentration of a precipitate, ie, SS density | concentration, becomes high. This suggests that the precipitate generated in step A contains a component that causes the cyan compound to be erroneously detected in the JIS-K0102 method.

-Identification of substances that react with sodium hydroxide to increase the false detection concentration of cyanide compounds-
From the result of the test, since the false detection concentration of the cyanide compound is increased due to the presence of the precipitate generated in the step A, it is investigated which component in the precipitate is involved in the false detection of the cyanide compound. It was.

  Then, the component analysis of the said precipitate was performed and the component which has caused the false detection of the cyanide compound was identified.

  What is the result of the component analysis? As shown in FIG.

  Regarding the generation of cyan, Non-Patent Document 2 describes the following.

The presence of an oxidant significantly increases the cyan detection rate of hydroxylamine (NH ₂ OH), which is a hydrolysis product of a compound having an NS bond. This hydroxylamine and active oxygen generated by the oxide react to generate NO ₂ ⁻ , and this NO ₂ ⁻ reacts with EDTA added by the JIS-K0102 method to generate cyan.

From the description of FIG. 5 and Non-Patent Document 2, the oxide that may generate active oxygen in the precipitate generated in Step A is manganese oxide represented by MnOOH or MnOx. It was thought that manganese ions contained in the desulfurization effluent generated Mn (OH) ₂ by the addition of sodium hydroxide and were oxidized by dissolved oxygen in the desulfurization effluent to generate manganese oxide.

FIG. 6 shows the influence test result of the false detection of cyan by the JIS-K0102 method by the addition test of manganese oxide (MnOOH), manganese sulfate (manganese ion: Mn ²⁺ ) and iron oxide (Fe ₂ O ₃ ). According to this result, it was confirmed that a significant amount of cyanide was detected with a small amount of manganese oxide. It was also found that cyanide was hardly detected with manganese ions and iron oxide.

  From the above results, by adding sodium hydroxide to the sample flue gas desulfurization effluent, manganese ions in the sample generate MnOOH by sodium hydroxide and dissolved oxygen in the sample, and this MnOOH is converted into JIS- Acts as an oxidant of EDTA added in the cyan analysis of the K0102 method and promotes the formation of cyanide. This was confirmed as one of the causes of the false detection that cyan was detected from flue gas desulfurization wastewater even though cyan was not used at all.

-Solution for problems caused by samples containing manganese ions and sodium hydroxide-
Therefore, a method for measuring the concentration of cyanide when sodium hydroxide is added to a sample containing manganese ions will be considered.

  From the results of the above test, it is considered that MnOOH works as an oxidizing agent for EDTA to promote the formation of cyanide compound. Therefore, sodium thiosulfate, which is a reducing agent, is added to the sample subjected to step A to add manganese oxide. A test was conducted to determine whether the concentration would be the same as the detected concentration of the cyanide when Step A was not performed.

  The result is shown in FIG. According to this result, by adding sodium thiosulfate as a reducing agent, the detected concentration of the cyanide compound in the JIS-K0102 method was remarkably lowered as compared with the sample not added. This value is almost the same value as that of the sample not subjected to the process A, and it was confirmed that the adverse effect of the process A can be prevented by adding a reducing agent.

  Moreover, the addition width | variety of the sodium thiosulfate added as a reducing agent is 1 mmol / L or more and 10 mmol / L or less. The reason for this is that in the JIS method, when it is erroneously detected that the cyanide compound is present at a concentration of about 1 mg / L, if 1 mmol / L of sodium thiosulfate is added, the false detection concentration of the cyanide compound is about 0.1 mg / L. In the JIS method, when it is erroneously detected that the cyanide compound is present at a concentration of about 10 mg / L, the addition of sodium thiosulfate at 10 mmol / L results in a cyanide compound having a false detection concentration of about 0.1 mg / L. By adding sodium in this range, even if there are manganese ions in the sample, the false detection concentration of the cyanide compound in the JIS-K0102 method is suppressed to 1 mg / L or less, which is the wastewater standard value described by the Ministry of the Environment. Because you can.

  In this way, a numerical value substantially equivalent to the detected concentration of the cyanide when step A is not performed can be obtained.

-Confirmation of the effect of compounds with NS bond on false detection of cyanide compounds-
Next, it was confirmed that the compound having an NS bond dissolved in the waste water had an influence on the erroneous detection of the cyanide compound.

In the absorption liquid of the flue gas desulfurization apparatus, NO ₂ ⁻ and HSO ₃ ⁻ caused by NOx and SOx in the exhaust gas react to produce a compound having an NS bond (hereinafter referred to as an NS compound). To do. It is considered that this NS compound and EDTA (disodium ethylenediaminetetraacetate) added during the distillation operation of JIS-K0102 react to form a cyanide compound.

  From this, first, the following three tests were carried out in order to confirm the influence of interfering substances in the analysis of cyanide compounds of JIS-K0102 and to prove that the main factor of the interfering substances is NS compounds. .

First, in order to identify the cause of cyanide compound detection in the JIS-K0102 method, the cyanide detection density was measured in (1) to (3).
(1) Analysis of the cyanide according to JIS-K0102 method (2) JIS-K0102 method in sodium nitrite (NaNO ₂₎ nitrite addition method of adding (3) EDTA-free addition method without addition of EDTA in JIS-K0102 method In addition, flue gas desulfurization waste water and general waste water were used as samples, and sodium nitrite was used as nitrites.

  FIG. 8 shows the results of the above test. According to this result, in (3), the cyanide compound detection density decreased compared to (1) in which EDTA was added.

  In (2), the concentration of the cyanide compound was measured in each case by changing the concentration of sodium nitrite in four stages. As a result, by adding 1.0 mmol / L of sodium nitrite, the detected concentration of cyanide was significantly lowered in both the flue gas desulfurization effluent and the general effluent.

  Secondly, the nitrite addition test proved that the NS compound was the main cause of the interfering substance.

  Sodium nitrite is added to the flue gas desulfurization wastewater sample A used in FIG. 8, and the NS compound concentration is measured before the distillation operation in JIS-K0102, and the operation is further continued to measure the detected cyanide compound concentration. did.

  The results are shown in FIG. 9 and FIG. According to this result, when sodium nitrite is added at 1 mmol / L, the NS compound becomes 0 mmol / L, and no cyanide compound is detected in the JIS-K0102 method. Prove that there is.

  Third, a test was conducted on the relationship between the concentration of NS compound and the cyanide compound detection concentration.

  FIG. 11 shows the result. For the NS compound, the detected concentration of the cyanide compound was measured by the JIS-K0102 method using hydroxylamine / trisulfate ion standard solution, and the relationship with the NS compound concentration was shown. According to this result, the NS compound is actually detected within the NS compound concentration range corresponding to the cyanide compound concentration (0.4 to 1.2 mg / L) detected from the flue gas desulfurization effluent. From this, it was confirmed that the main factor of cyanide compound detection was NS compound.

From the above, it is proved that the main factor of cyanide compound detection in the JIS-K0102 method is due to the NS compound, and the NS compound reacts with EDTA added during the distillation operation in the JIS-K0102 method. It was demonstrated that a cyanide was formed.
That is, it was confirmed that the NS compound has an influence on the false detection of the cyanide compound.

-Solutions to problems caused by compounds with NS bond-
From the results of the first and second tests, by adding nitrite (sodium nitrite in this test) before Step C, the concentration of the erroneously detected cyanide compound is lowered. From this, it became clear that the bad influence by NS compound can be prevented by adding nitrite. Moreover, the addition width of nitrite is 0.1 mmol / L or more and 5.2 mmol / L or less. The reason for this is that in the test (1), nitrite is added so that the false detection concentration of the cyan compound is less than the minimum false detection concentration of all the cyan compounds used in the test (1). For example, the effect of nitrite was demonstrated for any sample, and it was considered that the effluent standard value described by the Ministry of the Environment was 1 mg / L or less. Therefore, FIG. 10 is a graph of the sample with the highest false detection concentration of the cyanide in the test of (1), and 0.81 mg / kg which is the minimum value of the false detection concentration of the cyanide in the test result of (1). From L, the addition width of nitrite became 0.1 mmol / L or more and 5.2 mmol / L or less.

  In addition, when N-S compound concentration is in the range of 0.2 to 0.4 mmol / L, when 1 mmol / L of nitrite is added, the effect on the false detection concentration of cyanide is most exerted, and erroneously detected cyanide. The concentration of the compound is lowest.

  Hereinafter, embodiments will be described in detail.

Embodiment 1
1) Take 50 ml of sample into 500 ml of distillation flask and add water to make about 250 ml. Put about 10 boiling stones (particle size 2-3mm). Add 1 drop of phenolphthalein solution (5 g / L) as indicator.

  2) If alkaline, add phosphoric acid dropwise until the red color of the solution disappears.

  3) The distillation flask 1 is connected as shown in FIG. 12, and 100 ml of a graduated cylinder (plugged type) is used as the receiver 8, and 20 ml of sodium hydroxide solution is put into it and connected as shown in FIG.

  4) Add 1 mmol / L of sodium nitrite from the addition funnel 4 to the distillation flask 1.

  5) Then add 10 ml of phosphoric acid.

  6) Next, add 10 ml of the EDTA solution, wash the injection funnel 4 with a small amount of water, and add the washing to the distillation flask 1.

  7) After being allowed to stand for several minutes (about 2 to 5 minutes), the distillation flask 1 is heated and distilled at a distillation rate of 2 to 3 ml / min until the liquid volume in the receiver 8 reaches about 90 ml.

  8) Remove the cooler 6 and the backflow stopper 7, wash the inner tube of the cooler 6 and the back and forth of the backflow stopper 7 with a small amount of water, add the washing liquid to the receiver 8, and then add water to the 100 ml mark. Add.

  9) Take 10 ml from the resulting solution into a 50 ml volumetric flask.

  10) Add 1 drop of phenolphthalein solution (5 g / L) as an indicator and neutralize by adding acetic acid (1 + 8) dropwise until the red color of the solution disappears while gently shaking, then phosphate buffer ( pH 7.2) Add 10 ml.

  11) Add 0.5 ml of chloramine T solution (10 g / L) to this and leave it in a water bath at about 25 ° C. for about 5 minutes.

  12) Add 10 ml of 4-pyridinecarboxylic acid-pyrazolone solution, add water to the marked line, seal tightly and shake gently, then leave in a water bath at about 25 ° C. for 30 minutes.

  13) Transfer a portion of this to an absorption cell and measure the absorbance around a wavelength of 638 nm.

  14) As a blank test, take 10 ml of water in a 50-ml volumetric flask, add 10 ml of phosphate buffer solution (pH 7.2), perform the operations of 12) to 14), measure the absorbance, and obtain the absorbance obtained for the sample. Correct.

15) Obtain the amount of cyanide ions from the calibration curve, and calculate the concentration of cyanide ions (mgCN ⁻ / L).

  As a result of this method, as shown in FIG. 8, the detected concentration of the cyanide compound was suppressed to 0.1 or less by adding 1 mmol / L of sodium nitrite in 5). In addition, the false detection concentration of the cyanide compound was significantly reduced as compared with the test (1) in which nitrite was not added.

<< Embodiment 2 >>
1) Adjust pH to about 12 by adding sodium hydroxide solution (200 g / L) per liter of sample.

  2) Add 5 mmol / L sodium thiosulfate.

  3) Take 50 ml of sample into 500 ml 1 of distillation flask and add water to make about 250 ml. Put about 10 boiling stones (particle size 2-3mm). Add 1 drop of phenolphthalein solution (5 g / L) as indicator.

  4) If alkaline, add phosphoric acid dropwise until the red color of the solution disappears.

  5) Next, 1 ml of ammonium amidosulfate solution (100 g / L) is added.

  6) The distillation flask 1 is connected as shown in FIG. 12, and 100 ml of graduated cylinder (plugged type) is used for the receiver 8, and 20 ml of sodium hydroxide solution is put into this and connected as shown in FIG.

  7) Add 10 ml of phosphoric acid from the injection funnel 4 to the distillation flask 1.

  8) Next, add 10 ml of EDTA solution, wash the injection funnel 4 with a small amount of water, and add the washing to the distillation flask 1.

  9) After standing for several minutes (about 2 to 5 minutes), the distillation flask 1 is heated and distilled at a distillation rate of 2 to 3 ml / min until the liquid volume in the receiver is about 90 ml.

  10) Remove the cooler 6 and the backflow stopper 7, wash the inner pipe of the cooler 6 and the back and forth of the backflow stopper 7 with a small amount of water, add the washing liquid to the receiver 8, and then add water to the 100 ml mark. Add.

  11) Take 10 ml from the resulting solution into a 50 ml volumetric flask.

  12) Add 1 drop of phenolphthalein solution (5 g / L) as an indicator, neutralize by adding acetic acid (1 + 8) dropwise until the red color of the solution disappears while gently shaking, then phosphate buffer ( pH 7.2) Add 10 ml.

  13) Add 0.5 ml of chloramine T solution (10 g / L) to this and leave it in a water bath at about 25 ° C. for about 5 minutes.

  14) Add 10 ml of 4-pyridinecarboxylic acid-pyrazolone solution, add water to the marked line, seal tightly and shake gently, then leave in a water bath at about 25 ° C. for 30 minutes.

  15) Transfer a portion of this to an absorption cell and measure the absorbance around a wavelength of 638 nm.

  16) As a blank test, take 10 ml of water in a 50-ml volumetric flask, add 10 ml of phosphate buffer (pH 7.2), perform the operations of 13) to 15), measure the absorbance, and obtain the absorbance obtained for the sample. Correct.

17) Obtain the amount of cyanide ions from the calibration curve, and calculate the concentration of cyanide ions (mgCN ⁻ / L).

  The result of this method is shown in FIG. Step A in FIG. 7 is 1) of the second embodiment. By adding sodium thiosulfate to the sample, the detected concentration of the cyanide compound was significantly reduced as compared with the sample not added.

<< Embodiment 3 >>
In the third embodiment, 7 mmol of sodium nitrite is added from the injection funnel 4 to the distillation flask 1 before adding 10 ml of phosphoric acid to the distillation flask 1 from 7) the injection funnel 4 of the second embodiment. This is a form in which a process is added.

  Since this method is a method in which the first embodiment and the second embodiment are combined, it is considered to have a function of preventing an increase in the false detection density of the cyan compound, equivalent to or higher than those in the first and second embodiments.

  From the above, the false detection concentration of the cyan compound in the JIS-K0102 method includes the reaction between the NS compound in the sample and EDTA as a main factor. Furthermore, the manganese oxide produced by the reaction of sodium hydroxide added for long-term storage of the sample and the manganese ions in the sample promotes the reaction between the NS compound and EDTA, thereby further increasing the cyanide compound. It was found that the false detection concentration was increased.

  Therefore, the present invention adds a reducing agent to the conventional JIS-K0102 by adding 1 mmol / L or more and 10 mmol / L or less, and adding nitrite 0.1 mmol / L or more and 5.2 mmol / L or less, respectively. We found a way to prevent false detection. In particular, when a reducing agent is added at 5 mmol / L and nitrite is added at 1 mmol / L, the erroneous detection of cyanide can be almost completely prevented.

  Further, as an advantage of the present invention, the conventional JIS-K0102 method is not significantly changed or a complicated reagent is not used, but a reducing agent and nitrite, and these two types of reagents are used in the above amounts and reducing agents. There is a point that a great effect can be obtained by adding nitrite after adding sodium hydroxide and before adding EDTA.

  Furthermore, when sodium hydroxide is not added to the sample, the false detection concentration of cyanide can be suppressed to 1 mg / L or less, which is the wastewater standard value described by the Ministry of the Environment, by simply adding nitrite. And the density | concentration of the cyanide compound originally contained in the sample can be measured rapidly.

  In this embodiment, sodium thiosulfate is used as the reducing agent, sodium nitrite is used as the nitrite, and the flue gas desulfurization effluent discharged from the flue gas desulfurization apparatus is used. However, the reducing agent, the nitrite, the sample are used. This is not the case.

  Further, in this embodiment, 5 mmol / L of sodium thiosulfate as a reducing agent and 1 mmol / L of sodium nitrite as a nitrite are added, but the addition amount is not limited to this. For sodium thiosulfate, the addition width may be 1 mmol / L or more and 10 mmol / L or less, and for nitrite, the addition width may be 0.1 mmol / L or more and 5 mmol / L or less.

  Further, 4-pyridinecarboxylic acid-pyrazolone absorptiometry is used for measuring the concentration of cyanide, and the apparatus shown in FIG. 12 is used as the distillation apparatus. However, this is not the case.

As described above, the present invention is useful in a method for measuring the cyanide concentration of a sample containing a compound having a manganese ion and an NS bond while preventing erroneous detection of the cyanide compound .

Comparison of cyan density detected by JIS-K0102 method with and without sodium hydroxide addition (step A) It is a table | surface and a graph which show the influence which the addition amount of sodium hydroxide (NaOH) and standing time have on the detection density | concentration of a cyanide compound. It is a table | surface which shows the influence of the deposit produced | generated by sodium hydroxide addition (process A). It is a graph which shows the influence of the deposit density | concentration produced | generated by sodium hydroxide addition. It is a table | surface which shows the fluorescent X ray analysis result of the deposit produced | generated by sodium hydroxide addition. It is a table | surface which shows the influence confirmation result of an oxide. (The meaning of as in the table is the meaning of) It is a table | surface which shows the effect confirmation at the time of adding sodium thiosulfate to a sample with sodium hydroxide addition (process A). It is a table | surface which shows the detection density | concentration measurement result of cyan by various conditions. It is a table | surface which shows the relationship between the addition amount of nitrite, the detection density | concentration of cyan | cyanogen, and NS compound density | concentration. It is a graph which shows the relationship between the addition amount of nitrite, the detection density | concentration of cyan | cyanogen, and NS compound density | concentration. It is a graph which shows the relationship between NS compound density | concentration and cyanide compound density | concentration. It is a figure of a distillation apparatus.

1 Distillation flask 500ml
2 Connecting pipe 3 Grinding cock 4 Injection funnel 5 Trap ball (kildal type)
6 Liebig cooler 300mm
7 Backflow stop (about 50ml)
8 Receiver [Measuring cylinder (plug type) 250ml (or 100ml)]
9 Common alignment 10 Common spherical alignment 11 Holding spring

Claims (7)

A method for measuring the concentration of a cyanide compound in a sample containing a compound having an NS bond while preventing erroneous detection of the cyanide compound ,
A step A you decompose the compound having a N-S bond nitrite was added to the sample,
Step B of adding EDTA to the sample;
Distilling the sample to obtain a distillate;
Measuring the absorbance due to cyanide in the distillate;
A method for measuring the concentration of cyanide which comprises the step of determining the concentration of cyanide in said sample from said absorbance. A method for measuring the concentration of cyanide in a sample containing manganese ions while preventing false detection of cyanide ,
Step C in which manganese oxide is produced by adding sodium hydroxide to the sample;
Step D for eliminating the manganese oxide by adding a reducing agent to the sample;
Step B of adding EDTA to the sample;
Distilling the sample to obtain a distillate;
Measuring the absorbance due to cyanide in the distillate;
A method for measuring the concentration of cyanide which comprises the step of determining the concentration of cyanide in said sample from said absorbance. The method for measuring a concentration of a cyanide compound according to claim 2,
The sample includes a compound having an NS bond;
Wherein after step D, A method for measuring the concentration of cyanide, characterized by further comprising the step A decompose the compound having a N-S bond nitrite added to the sample. The method for measuring a concentration of a cyanide compound according to claim 1 or 3,
The cyanate concentration measurement method , wherein the nitrite is added in an amount of 0.1 mmol / L to 5.2 mmol / L. The method for measuring a concentration of a cyanide compound according to claim 2 or 3,
The method for measuring a concentration of a cyanide compound, wherein the reducing agent is sodium thiosulfate. The method for measuring a concentration of a cyanide compound according to claim 5,
The method for measuring the concentration of a cyanide compound, wherein the sodium thiosulfate is added in an amount of 1 mmol / L to 10 mmol / L. In the method for measuring the concentration of the cyanide compound according to any one of claims 1 to 6,
The cyanide concentration measuring method , wherein the sample is flue gas desulfurization waste water discharged from the flue gas desulfurization apparatus.

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