JPS6224740B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an improvement in an apparatus for continuously measuring cyanide in a liquid. [Prior art] Cyanide compounds are widely used in various factories such as Metsuki factories, gas factories, steel factories, and pharmaceutical factories, but they are toxic substances that act rapidly on living organisms, and the lethal dose is approximately 50 mg. It is an extremely dangerous substance. Therefore, the Water Pollution Control Law requires factory wastewater standards to be
It is strictly regulated to 1ppm, and ``undetectable'' under standards related to human health. Therefore, it is important to constantly monitor cyanide in general public water such as industrial wastewater and rivers.
The emergence of an excellent continuous measurement method for cyan has been desired. To solve this problem, the following method using electrodes is used. The first method uses a so-called silver iodide electrode, which uses a pressure-molded film of silver iodide as the detection element. In this method, this electrode is inserted together with a reference electrode, and the cyanide concentration in the liquid is measured from the electric potential between the two electrodes. Figure 1 shows an example of measuring cyanide in wastewater or rivers using this method. An alkali tank 5 for supplying to the measurement tank 3, a drainage tank 6 for receiving the discharged liquid (strongly alkaline pH 11 or higher) from the measurement tank 3, and a silver iodide type cyanide ion electrode immersed in the measurement tank 3. 7 and comparison electrode 8, both electrodes 7,
It consists of an indicator and alarm meter 9 which is connected to 8. However, this method has the following problems. It is necessary to add the reagent (alkali) at a fixed ratio, and therefore it is necessary to use an expensive constant flow ratio mixing device using pumps (two units), which is not only economically disadvantageous but also mechanically difficult. It is also disadvantageous in terms of maintenance because it has moving parts. Not only is it complicated to regularly prepare and replenish reagents, but it is also dangerous because it is strongly alkaline.
Pump lubrication, piping system, and other cleaning are required, which requires maintenance work and maintenance costs. The effluent after measurement is also strongly alkaline (pH 11 or higher) and is dangerous to handle, and if it is disposed of as it is, it will cause secondary pollution, so treatment such as neutralization is required. When strong reducing substances such as hydroquinone, iodine ions, thiosulfate ions, sulfur ions, etc. coexist, the electrodes are easily affected and the electrodes are easily contaminated. In particular, sulfur ions cause the electrode to lose its ability to detect cyanide. Dirt on the liquid junction of the reference electrode causes measurement errors. As a second method to solve such problems, the present inventors sealed the support tube with a gas-permeable diaphragm (which does not allow water and ions to pass through), and placed a silver ion electrode, a reference electrode, and an alkaline electrode inside the support tube. proposed a method using a so-called diaphragm-type electrode that contained a silver-cyanide complex ion solution as an internal liquid (Japanese Patent Application Laid-Open No. 121391/1983). An example of this diaphragm type electrode is shown in FIG.
The O-ring 13 is held between the diaphragm support 14 and the diaphragm fixing device 1 is screwed onto the support tube 11.
5, the support tube 11 has an internal liquid 16, a detection electrode 17, a counter electrode 18, and a temperature compensation resistor 1.
9th grade is included. This is an electrode that is sensitive to hydrogen cyanide gas (HCN) rather than cyanide ions (CN ^- ), but
When this electrode is immersed in water containing cyanide, dissolved hydrogen cyanide (HCN) enters the inside of the electrode through the diaphragm and changes the potential of the electrode to change the silver ion concentration in the internal solution. Cyan concentration can be determined by measuring potential changes. At this time, unless the aqueous solution of cyanide compound has a pH of 8.5 or below, i.e., is not strongly alkaline, cyanide ions combine with hydrogen ions and almost all of the solution is dissolved in the HCN state. Cyan can be measured simply by dipping the electrode into the sample. Figure 3 shows the relationship between the ratio of cyanide present in the form of HCN in an aqueous solution and pH. Therefore, as shown in FIG. 4, this diaphragm type electrode 20 can be immersed in a flow of wastewater such as factory wastewater or a river 21 to measure cyanide. This second method using a diaphragm type electrode solves all the problems of the first method using a silver iodide type electrode and is a practically excellent method. It is increasingly being used to monitor cyanide concentrations in wastewater from the Metsuki factory. [Problems to be solved by the invention] However, as the present inventors have widely applied the method using this diaphragm type electrode, when the sample water contains a high concentration of residual chlorine, surfactant In the case where the cyanide detection ability of the electrode is rapidly lost, a problem arises in that the electrode must be regenerated each time. As a result of investigating the cause of this problem, we found that if the chlorine concentration in the sample water was less than 10 ppm, the electrode would not deteriorate, but if it exceeded 15 ppm, the electrode's ability to detect cyanide would rapidly deteriorate. If a so-called neutral detergent, which is widely used for washing dishes, etc., gets mixed into the sample water, the diaphragm becomes water-permeable and the internal liquid of the electrode flows out through the diaphragm, causing the electrode to lose its function as a cyan detection electrode. . The fact has become clear. To prevent this, ensure that the residual chlorine concentration in the sample water never exceeds 10 ppm.
It would be better to ensure that no neutral detergent is mixed in, but this is also impossible for the following reasons. However, the commonly used method for detoxifying wastewater containing cyanide is to make the wastewater alkaline and add an excessive amount of chlorine, which is actually impossible. However, in plating factories, it is customary to perform a degreasing process prior to plating, and this is not possible because neutral detergents are widely used for degreasing. Regarding this, it is also possible to pump the sample water at a constant flow rate with a pump, add a certain amount of sodium thiosulfate solution to it to eliminate residual chlorine, and then introduce it to the diaphragm electrode for measurement. The disadvantages of the silver iodide type electrode method will be restored, and the advantages of the diaphragm type electrode will be completely lost. The inventors of the present invention conducted research experiments to solve the problems in cyan concentration measurement using such a diaphragm-type electrode, and as a result, they came to the following findings. That is, the present inventors sealed the tip of a support tube with a gas-permeable diaphragm, and installed a cyanide measuring electrode in which a silver ion electrode, a reference electrode, and an alkaline silver cyanide complex ion electrode solution were housed as an internal solution. The gas-permeable diaphragm of the cyanide measuring electrode is placed in a gas phase that is in equilibrium with the cyanide concentration in the liquid phase of the liquid, without directly immersing the cyanide in the liquid to be measured. We have discovered a method to indirectly measure the cyanide concentration in the liquid phase from the concentration. The principle will be explained below. Cyanide compounds exist in the form of cyanide ions (CN ^- ) in solutions under strong alkalinity, but at pH 8.5 or lower, they combine with hydrogen ions (H ⁺ ) and almost all exist in the form of dissolved hydrogen cyanide (HCN). What to do is as described above. It is said that this dissolved hydrogen cyanide (HCN) is easily volatilized into the air, but the relationship between the concentration of hydrogen cyanide in the gas phase that is in equilibrium with the hydrogen cyanide water is not known. Therefore, the present inventors dissolved potassium cyanide in water to prepare solutions with various concentrations and adjusted the pH to 8.0 or less.Then, the inventors placed this in a sealed container and placed it in a constant temperature bath to reach an equilibrium state, and then dissolved it in the gas phase. The hydrogen cyanide concentration was determined by analysis and the results shown in Figure 5 were obtained. This study clarified the relationship between the concentration in the liquid phase (converted to CN ^- concentration) and the HCN concentration in the gas phase, which is in equilibrium with this. When measuring the concentration, it was found that it was possible to indirectly measure the cyanide concentration in the sample water by placing a diaphragm-type electrode in the gas phase in an equilibrium relationship near the surface of the sample water, without immersing the electrode in the sample water. . According to the above method, the liquid phase cyanide concentration is indirectly measured by gas phase measurement, so even if neutral detergent is mixed into the sample water, the diaphragm electrode is not in contact with the sample water, so it is different from immersion measurement. The phenomenon of loss of cyan detection ability does not occur at all. In addition, as a result of considering the influence of residual chlorine in the sample water (if residual chlorine exists, it will volatilize to some extent into the gas phase), we found that even after 3 hours had passed, the above method could not be used for sample water containing 30 ppm of residual chlorine. It was confirmed that the cyan detection ability of the diaphragm-type electrode did not deteriorate. On the other hand, in the immersion measurement method, as mentioned above,
It deteriorated rapidly with 15 ppm of residual chlorine, demonstrating the remarkable effectiveness of this method. Furthermore, in order to confirm the effectiveness of this method, we conducted parallel measurements using the gas phase measurement method using this method and the conventional immersion measurement method over a long period of time in the drainage ditch of the Metsuki factory, and conducted timely sensitivity tests to compare the two. are shown in Table 1.

[Means for solving problems]

The present invention provides an apparatus for effectively implementing this method, and its gist is that a support tube is sealed with a gas-permeable diaphragm, and a silver ion electrode, a reference electrode, and an alkaline electrode are placed inside the support tube. The cyanide concentration in the liquid is determined by measuring the cyanide concentration in the gas phase, which is in equilibrium with the cyanide concentration in the liquid phase, using a cyanide measuring electrode containing a silver cyanide complex ion electrode solution as an internal solution. In a cyanide concentration measuring device, a hood is attached to the gas-permeable diaphragm part of the cyanide measurement electrode, and the hood is immersed in the surface of the liquid whose cyanide concentration is to be determined, thereby sealing the gas phase in which the cyanide concentration is to be measured with the liquid. A cyanide concentration measuring device is characterized in that it is equipped with an aeration pump that sends aeration gas into the liquid whose cyanide concentration is to be determined into the gas phase in which the cyanide concentration is to be measured, thereby achieving the intended purpose. It is something. [Examples and Effects of the Invention] Examples and comparative examples will be given below to clarify the effects of the present invention. Comparative Example 1 Figure 7 shows a second gas phase near the water surface of sample water 101.
This is an example in which a diaphragm type electrode 102 having the structure shown in the figure is arranged. In this example, where there is movement of air currents such as wind, there is a risk that hydrogen cyanide volatilized from the water may be washed away, so consideration should be given to carrying out the process in a closed structure. Comparative Example 2 FIG. 8 shows an example in which an electrode 102 is attached to the upper part of a pipe 103 of an appropriate thickness, and the lower end of the pipe 103 is inserted into sample water 101 for measurement. According to this example, the problems of Comparative Example 1 are solved and can be effectively applied to river water, etc. as is. Embodiment 1 Figure 9 is an improved version of Figure 8, with pipe 103
In this example, a small hole 104 is provided at an appropriate position in consideration of the position of the electrode 102 in the upper part of the tube, and hydrogen cyanide is forcefully volatilized inside the pipe 103 by aerating the sample water using an aeration pump 105 or the like. In the method of Comparative Example 2, HCN is transferred from the sample water to the gas phase.
However, according to the first embodiment, the response of the diaphragm electrode 102 is significantly improved. The comparison results are shown in FIG. In addition, the ventilation method uses an air pump 105,
If piping equipment for compressed air, air for measurement, etc. is nearby, such as in a factory, this may be used. Embodiment 2 FIG. 11 is a further embodiment of Embodiment 1 shown in FIG. The ventilation flow rate by the ventilation pump 105 mentioned above is several
Since a small flow rate of about 100 ml/min is sufficient and a small device is sufficient, the pump 105 is fixed to the pipe 103 using the pump fitting 106, and at the same time, the air supply pipe 107 connected to the pump discharge side is inserted into the pipe from near the lower end of the pipe 103. This is an example in which the entire structure is integrated, with the opening opening below the surface of the sample water. Power is supplied to the pump 105 via a power cord 108. Furthermore, if a drip-proof cover 109 is applied to the pump 105, it can be installed outdoors. In addition, a battery-powered pump 105 is used,
If it is integrated with a battery, an amplifier, and an indicator, it becomes a portable measuring device that is convenient for measurements at multiple locations.

[Brief explanation of the drawing]

Figure 1 is an illustration of a method for measuring cyanide concentration using a conventional silver iodide type electrode, Figure 2 is a cross-sectional view showing the structure of a diaphragm type electrode, and Figure 3 is a diagram showing the ratio of HCN in an aqueous solution and pH. Figure 4 is an illustration of the cyanide concentration measurement method using the immersion method using a conventional diaphragm electrode, and Figure 5 shows the relationship between the CN ^- concentration in the liquid phase and the gas phase that is in equilibrium with it. Figure 6 is a diagram of the relationship between the generated hydrogen cyanide concentration and temperature, Figures 7 and 8 are explanatory diagrams of Comparative Examples 1 and 2, and Figures 9 and 11 are diagrams of the present invention. Each explanatory diagram showing Examples 1 and 2 of the method, FIG. 10 is Comparative Example 2
3 is a chart comparing the response speeds of instrument indications in Example 1. 101...Sample water, 102...Diaphragm type electrode, 103
...pump, 104...small hole, 105...ventilation pump,
106...Pump fitting, 107...Vent pipe, 108
...power cord, 109...splash-proof cover.

Claims (1)

[Claims] 1 Seal the support tube with a gas-permeable diaphragm, and measure cyanide in the liquid phase using a cyanide measuring electrode containing a silver ion electrode, a reference electrode, and an alkaline silver cyanide complex ion electrode solution as an internal solution. In a cyanide concentration measuring device for determining the cyanide concentration in a liquid by measuring the cyanide concentration in the gas phase, which has an equilibrium relationship with the concentration, a hood is attached to the gas permeable diaphragm portion of the cyanide measurement electrode, and the hood is Measuring the cyanide concentration by immersing it in the surface of the liquid whose cyanide concentration is to be determined.Sealing the gas phase with the liquid and providing a ventilation device to measure the cyanide concentration.Passing the liquid whose cyanide concentration is to be determined into the gas phase. A cyanide concentration measuring device characterized by sending ventilation gas.