JPS60105945A - Measurement for concentration of hexavalent chromium ion in solution - Google Patents

Abstract

PURPOSE:To enable a continuous and accurate measurement by a method wherein a measuring light with a specified wavelength is made incident into a solution to be measured flowing through a flowcell and the intensity of the transmission light to determine the ion concentration by absorptiometry. CONSTITUTION:A part of a waste liquid to a reducing tank 20 is shunted to a shunt tube 22 with a pump 24 to be accumulated at a liquid tank 26. Then, it is withdrawn from the liquid tank 26 at a specified speed with a pump 28 and flows into a flowcell 30 continuously. Then, a measuring light with the wavelength of 335-345nm is made incident into the waste liquid and the intensity of the transmission light is measured with an absorptiometer 32 to be recorded on a recorder 34. Thus, the concentration of hexachromium ion can be measured continuously online by absorptiometry from the intensity ratio between the incident light and the transmission light.

Description

[Detailed Description of the Invention] The present invention is based on '? This method relates to a method for measuring the 61Illi chromium ion concentration in an FJ solution, and in particular, it is possible to continuously measure the hexavalent chromium ion depth in a solution online by spectrophotometry. Regarding measurement methods.

Conventionally, waste liquid containing C r6 + used for so-called chromate treatment in continuous chromium plating, electrolytic tin plating, zinc plating, etc. of steel sheets, etc., is reduced by reducing agent.
Reduction processing is performed on r3+. Reduction methods for this purpose include the known method using F62+, Na 2
Although there are methods using SO3, etc., these reduction methods utilize the equivalence relationship between the oxidizing agent and the reducing agent, as is well known. Therefore, in order to know the amount of reducing agent to be added, it is necessary to know the Cr6+ concentration in the waste liquid.

Conventionally, Or"flfI in this waste liquid has been measured by methods such as collecting the waste liquid and then measuring it by chemical analysis or by measuring it with a conductivity meter.

However, in an environment where a large amount of waste liquid is released every moment, and where the C1゛6+ concentration fluctuates over time depending on the operating conditions at the site, chemical analysis methods can provide accurate measurements, but the amount of time required for analysis is There is a problem in that it takes a long time and changes in Cr6 and concentration cannot be accurately captured. On the other hand, the method using a conductivity meter has problems such as poor reliability because it is affected by other components in principle. Therefore, in the actual reduction process, these CrS+
The actual situation was that an excessive amount of reducing agent was added in an amount that was considered to be far safer than the measured value, resulting in an increase in the amount of sludge and an increase in the cost of the reducing agent reagent.

The present invention has been made in view of these conventional problems, and is capable of continuously and accurately measuring the Cr6+ concentration in a solution, and therefore enables efficient and efficient reduction treatment. CrS+ in solution that can be done economically
The purpose is to provide a concentration measurement method.

The present invention allows the solution to be measured to flow continuously through a flow cell, and also allows the solution to be measured to flow through the 70-cell to have wavelengths of 335
The intensity of the transmitted light is measured by using a measuring light of ~345 nm, and the Cr"iR degree in the solution to be measured is continuously measured online using the absorption photometry method based on the intensity ratio of the incident light and the transmitted light. In this way, the above objective was achieved.

The present invention will be explained in detail below.

The present invention employs a so-called spectrophotometric method to continuously determine the CrG+ concentration in a solution.

Absorption photometry is a method in which the logarithm of the ratio of the intensity In of incident light to the intensity I of transmitted light in the absorption of light is Abs! 4 Of course, Lambert's law i1 is proportional to the thickness of the mass layer, and the absorption of light by a gas or solution is determined by the number of molecules in it. It calculates the concentration of the solution based on the so-called Lanno\-1-Beer's law, which is a combination of (1u/(-Le's law), which is unrelated. In other words, the intensity of the incident light is
1. Bow m degree of transmitted light is 1. If the thickness of the solution to be measured is X and the concentration of the solution is C (moles), then the concentration C is not very high.

I=■o10−F−0′ ・・・・・・・・・(1)−
log (1/Io)−ε C× ・・・・・・・・・
(2) Here, ε is called the molar extinction coefficient, and εcl is called the extinction coefficient. This extinction coefficient εC (is a constant determined only by the substance and the wavelength. Also, εC× is called the absorbance, and by measuring this absorbance εCX, the concentration of a substance with a known molar extinction coefficient ε in a solution can be determined. You can get C.

By the way, the waste liquid discharged from chromate treatment etc. changes variously depending on the operating conditions of the equipment, and especially the pH (
hydrogen ion concentration) varies widely from 1 to 8. The present invention attempts to measure the C6+ concentration based on the spectrophotometric method, but as a result of inspection with a real scissors, for example, the wavelength of the measurement light is 3751101, and the Cr6+ concentration is 7m/ρ.
In the case of , the absorbance of CH-6+ is l) as shown in Figure 1.
It has been found that it is difficult to measure using this spectrophotometric method as it is because it changes markedly due to H.

However, when we further investigated these absorption curves in detail, we found that the wavelength of the measurement light was 335 to 345 nm, which is part of the near ultraviolet region (see Figure 2).
(acceptable range), the transmittance 1/io is always equal regardless of the variation of t+l-1, and therefore,
It was found that measurement can be performed without being affected by ++H by measuring using measurement light with a wavelength of 335 to 345 ram. The present invention is based on this knowledge, and Cr”
Absorption photometry was adopted as a means of measuring il1 degrees. As is clear from the figure, the error can be minimized by selecting a wavelength of 340 nm within this range.

FIG. 3 shows the measurement principle of the method of the present invention.

That is, in the present invention, a part of the solution to be measured containing Cr6+ headed for a reduction tank or the like is diverted in a branch direction using a pump 10 or the like, and the solution to be measured that has been branched out is kept at a constant solution layer thickness of 10! The sample solution flowing through the flow cell 12 is continuously supplied with a wavelength of 335~
Measure the measurement light 1o of 345 nm with a long sword, measure the intensity of the transmitted light I, and calculate the intensity ratio I of the incident light 1o and the transmitted light 2.
/Io, that is, the common logarithm of the transmittance 1/Io, determines the absorbance εaX of the solution to be measured, and based on the absorbance εCX, the previously known molar extinction coefficient ε of Cr6 +, the thickness of the solution x Therefore, the Cr 6”m degree C is reduced.

Conventionally, the method of actually measuring the above absorbance εCx is to measure the solution to be measured at a thickness of 5 to 15 I[
A static measurement method was used in which the sample was fractionated into cells designated as II. In contrast, the present invention employs a flow cell system as shown in FIG.
The structure is such that the solution to be measured can continuously pass through the flow cell 12, which can be maintained at a constant temperature. As a result, it is now possible to continuously obtain changes in absorbance corresponding to changes in concentration of the solution to be measured.

The flow cell 12 may be made of quartz and have a solution layer thickness x 5, for example. The reason why the 70-cell 12 with the solution layer thickness X of 5 mm is good is as follows. That is, Fig. 4 shows the Cr
The calibration curve for 6s is shown.

As is clear from the figure, in the case of 5 nons, 1 to 220 + 1
1! It can be measured against the Cl-6 output concentration of +/'J2.

In general, the size of the flow cell can be selected depending on the degree of solution to be measured; for example, if a flow cell of 1 mm or less is used, in principle, the size of the flow cell should be selected according to the temperature of the solution to be measured.

mg/f! Although it is possible to measure concentrations higher than ,
On the other hand, since the amount of liquid to be sent is limited, there is a disadvantage that the delay in measurement increases when a large amount of wastewater is treated. Therefore, it is preferable to adopt a cell size that matches the required 1lt11 constant range and to ensure both the responsiveness of Cr 6" and 11 degree change, and in that sense, a flow cell with a solution layer thickness of 5 cm is better. .

Next, in order to confirm the effectiveness of the present invention, we measured the Or'' concentration of actual waste liquid using the device shown in Figure 5, and compared the results with the values measured by chemical analysis. , a diversion pipe 22 for diverting a part of the waste liquid headed for the reduction tank 20, a pump 24 for drawing the waste liquid into the separation pipe 22, and a liquid tank 26 for storing the drawn waste liquid for sample collection. Then, the waste liquid is 8001β from this liquid tank 26.
/m t n, a quartz flow cell 30 to maintain the drawn waste liquid at a thickness of 5 mm, and a measurement light having a wavelength of 340 r+m to continuously measure the CrG+ concentration. Absorption photometer 3 for
2 and a recorder 34 for recording the measurement results. Note that 3G is a conductive skewer recorder,
38 is a pH lesson.

FIG. 6 shows an actual measurement chart measured by the method of the present invention based on the above-mentioned absorptiometric method using such an apparatus. Further, Table 1 below shows a comparison between the results measured by the method of the present invention and the results obtained by taking samples at the same time and analyzing Crg÷ by chemical analysis.

Table 1 From these results, it is possible to continuously measure Cr6+ using the method of the present invention, and to measure fluctuations in Cr6+11 degrees in fine waste liquid that change from moment to moment with an accuracy that is almost the same as chemical analysis values. It was confirmed that it is possible to reliably capture the In addition, in Figure 6, time 10 and verse 46
The reason why the absorbance appears to change rapidly around the minute is because the measurement range was switched from 0-2 to 0-4 at that point.

As described above, according to the present invention, it is possible to obtain the effect that the concentration of hexavalent ROM ions in a solution can be measured continuously, online, and extremely accurately. As a result, for example, in chromate treatment (reducing waste liquid, etc.), it becomes possible to add only the amount of reducing agent commensurate with the amount of residual hexavalent chromium ions, which prevents increases in costs due to excessive addition, and This has the effect of preventing the generation of sludge and reducing processing costs.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between pH and absorbance, Figure 2 is a diagram showing the relationship between wavelength and transmittance with 1 output as a parameter, and Figure 3 is a diagram showing the 1111 constant of the method of the present invention. The principle diagram, Figure 4, is
A diagram showing the relationship between Cp 6 + concentration and absorbance when the solution layer thickness is 5 μm. FIG. 5 is a partial block diagram of the apparatus configured to confirm the effectiveness of the method of the present invention. FIG. 6 is an actual measurement chart diagram using an absorption photometer in the above-mentioned apparatus. Agent Takaya Ron (and 1 other person) P H Figure 2 Figure 3 ↓ Figure 4

Claims (1)

[Scope of Claims] <1) A solution to be measured is continuously caused to flow through a flow cell, and a wavelength of 335 to 34 is applied to the solution to be measured flowing through the flow cell.
A measurement light of 5 nm is incident, the intensity of the transmitted light is measured, and the 61a [i chromium ion concentration in the solution to be measured is continuously measured online using the absorption photometry method based on the intensity ratio of the incident light and the transmitted light. A method for measuring the concentration of hexavalent ROM ions in a solution, characterized in that: