JPH10332672A - Measuring method for hexavalent chromium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method in which hexavalent chromium can be measured precisely without generating a white precipitate by a method wherein, before the hexavalent chromium is adjusted to be sufurically acidic, a hexametaphosphate aqueous solution is added to sample water. SOLUTION: About 5 ml of a hexametaphosphate aqueous solution (about 500 mg/l) is added to about 25 ml of sample water, and water is added additionally so as to obtain the total amount of 40 to 45 ml. Then, about 2.5 ml of sulfuric acid (1+9) is added, about 1 ml of a diphenylcarbazide solution (about 10 g/l) is added, and water is added, and the total amount is set at about 50 ml so as to be stirred. After about five minutes, an absorbance A is measured at a wavelength of about 540 nm by a spectrophotometer or the like. When the hexametaphosphate aqueous solution is added, it is possible to prevent the generation of the precipitate of calcium sulfate due to the addition of the sulfuric acid (1+9). As a reference solution for a blank test, about 0.5 ml of acetone is added instead of the diphenylcarbazide solution, it is treated in the same manner, and an absorbence B is measured at a wavelength of about 540 nm. When the absorbance B is subtracted from the absorbance A, an absorbance which is based on hexavalent chromium in the sample water is obtained, and the concentration of the hexavalent chromium in the sample water can be found on the basis of a working curve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for measuring hexavalent chromium. More specifically, the present invention provides a method for determining the concentration of hexavalent chromium in a sample water containing a large amount of calcium ions,
The present invention relates to a method for measuring hexavalent chromium, which can be accurately measured by diphenylcarbazide absorption spectrophotometry and is particularly useful for analysis of fly ash-related eluate or ash wastewater.

[0002]

2. Description of the Related Art Hexavalent chromium is formed by adding diphenylcarbazide (1,5-diphenylcarbonohydrazide) to a sample water and forming a red-purple complex to form a color.
It is quantified by measuring the absorbance near m. JI
According to SK0102, an appropriate amount of sample water is neutralized and then transferred to a 50 ml volumetric flask, and sulfuric acid (1 + 9)
2.5 ml was added, and a diphenylcarbazide solution (1
(0 g / liter), add 1 ml, shake immediately, add water to the marked line, leave for about 5 minutes, and measure the absorbance at a wavelength of about 540 nm. When garbage is incinerated, exhaust gas including fly ash such as dust and dust and incinerated ash are generated. Fly ash in the exhaust gas is captured by an electric dust collector and a filter.
The ash is hot and cools with water. Usually, water is used in circulation, and this water is called ash wastewater. This ash wastewater is discharged as it is or after wastewater treatment. In this case, effluent standards are legally applied. Fly ash,
The incinerated ash is left as it is, or if it does not meet the criteria, it is disposed of by chemical treatment, concrete solidification and landfill disposal. At this time, the possibility of dumping is determined by adding water 10 (weight-volume ratio 10%) to the sample 1 of fly ash and incinerated ash,
Shaking for a period of time, determined by the content of metal in the filtrate or eluate. Since the hexavalent chromium may be contained in the fly ash-related eluate or ash wastewater, it is necessary to analyze it. However, if sulfuric acid is added to the sample water of fly ash-related eluate or ash sewage, a white precipitate is formed, which makes it impossible to measure the absorbance of the liquid developed by adding diphenylcarbazide. Often occurs.
In such a case, re-collect the sample water again and
The measurement was repeated with a dilution of 0 to 20 to avoid the effect of the white precipitate. The lower limit of the quantitative range of hexavalent chromium is 0.04 mg / liter according to the JIS method, but such dilution increases the lower limit to 0.4 to 0.8 mg / liter. In the criteria for industrial waste containing metals, etc., the standard for hexavalent chromium in the eluate is 0.5 mg at sea.
Per liter, 1.5 mg / liter on land, and the standard for hexavalent chromium in ash sewage is 0.5 mg / liter. By diluting the sample water, the lower limit of the quantitative range is determined. Value and the effluent standard value will be close to or exceed the standard value, and the measurement accuracy will also decrease. In addition, since the operation of collecting the sample water again, diluting it and reanalyzing it is also complicated, there is no formation of a white precipitate due to the addition of sulfuric acid, and the reproducibility and reliability are always high by a constant operation. The development of a measurement method capable of quantifying chromium (VI) has been strongly desired. As a method of suppressing the precipitation of calcium sulfate, the use of a chelating agent such as EDTA or NTA, which forms a complex salt with calcium ions, was examined. However, the complex salt was effectively formed at an acid concentration of about 0.2 N in hexavalent chromium measurement. No chelating agent was found. Further, although calcium ions can be removed by a Na ⁺ type cation exchange resin, the operation is complicated and not suitable for practical use.

[0003]

SUMMARY OF THE INVENTION According to the present invention, in the measurement of the hexavalent chromium concentration in a sample water by diphenylcarbazide absorption spectrophotometry, a white precipitate is not formed when sulfuric acid is added. The purpose of the present invention is to provide a method for measuring hexavalent chromium, which can be measured, and is particularly useful for analysis of fly ash-related eluate or ash wastewater.

[0004]

Means for Solving the Problems As a result of diligent studies to solve the above-mentioned problems, the present inventor found that, in the determination of hexavalent chromium by diphenylcarbazide absorption spectrophotometry, a white precipitate formed upon addition of sulfuric acid was determined. The substance was found to be calcium sulfate, and furthermore, it was found that the addition of hexametaphosphate to the sample water before adjusting the acidity to sulfuric acid could prevent the formation of calcium sulfate precipitate.
Based on this finding, the present invention has been completed. That is, the present invention relates to (1) a method of measuring hexavalent chromium in water in which a sample water is made acidic with sulfuric acid, color is added by adding diphenylcarbazide, and then absorbance is measured. And a method for measuring hexavalent chromium, characterized in that hexametaphosphate is added thereto. Further, as a preferred embodiment of the present invention, (2) Measurement of hexavalent chromium according to (1), wherein a liquid obtained by adding hexametaphosphate, sulfuric acid and acetone in this order to a sample water is used as a control liquid for a blank test. Method.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention can be applied to the determination of hexavalent chromium in a sample water in which a large amount of calcium ions are dissolved. It can be suitably applied to the determination of hexavalent chromium in sample water containing several thousand mg / liter. FIG. 1 is a flow sheet of one embodiment of the method of the present invention. 25 ml of sample water is placed in a 50 ml color tube with a stopper and a hexametaphosphoric acid aqueous solution (500 mg / l)
Add 5 ml and add water to bring the total volume to about 40-45 ml. Then, after adding 2.5 ml of sulfuric acid (1 + 9),
1 ml of a diphenylcarbazide solution (10 g / l) is added, water is added to make up the total volume to 50 ml, and the mixture is immediately stirred.
After 5 minutes, use a spectrophotometer or a photoelectric photometer to measure the wavelength of 5
The absorbance A at 40 nm is measured. In addition, the sodium hexametaphosphate aqueous solution (500 mg / liter)
It is prepared by dissolving 1 g of sodium hexametaphosphate prescribed in the official food additive standard in water to make a total volume of 100 ml, further taking 10 ml of this solution, and adding water to make a total volume of 200 ml. Further, the diphenylcarbazide solution (10 g / liter) is prepared by adding diphenylcarbazide (1, 1
0.5 g of 5-diphenylcarbonohydrazine) is dissolved in 25 ml of acetone, and water is added to make 50 ml.

In the method of the present invention, before the addition of sulfuric acid (1 + 9), hexametaphosphate is added to prevent the formation of calcium sulfate precipitation due to the addition of sulfuric acid (1 + 9), and to prevent the formation of Cr (VI) and Cr (VI). The absorbance based on the magenta color generated by the reaction of diphenylcarbazide can be measured at a wavelength of around 540 nm without being hindered by precipitation. The addition amount of hexametaphosphate can be appropriately selected according to the amount of calcium ions in the sample water, but is usually 20 mg / l or more, preferably 50 to 100 mg / l. The mechanism by which the precipitation of calcium sulfate is suppressed by the presence of hexametaphosphate is not clear, but is thought to be due to the threshold effect of hexametaphosphate. In the method of the present invention, the control solution for the blank test was a solution treated in the same manner as above except that 0.5 ml of acetone was added instead of the diphenylcarbazide solution. Measure absorbance B. Absorbance A
(AB) is the absorbance based on Cr (VI) in the sample water, and the Cr (VI) concentration in the sample water can be determined using a calibration curve created in advance.

[0007] Fly ash-related eluates and ash wastewater often contain yellow-brown colored substances and turbid components in addition to hexavalent chromium ions. According to the method specified in JIS K 0102, a solution obtained by adding sulfuric acid (1 + 9) and ethanol to a sample water and boiling to reduce Cr (VI) to Cr (III) and then adding a diphenylcarbazide solution. Is used as a control solution. However, in the fly ash-related eluate and ash sewage having a large content of coloring components and turbid components, the turbid components are aggregated and flocculated by the boiling operation, and the properties are changed. It is difficult to obtain a control solution. By adding only acetone used to dissolve the diphenylcarbazide reagent to the sample water instead of the diphenylcarbazide solution, and treating it as a control solution for the blank test, coloring and turbid components It is possible to measure the concentration of Cr (VI) even in a sample water having a high content of. Even if Cr (VI) ions are present in the blank test control solution and exhibit yellow, the yellow color of Cr (VI)
Since the light of 0 nm is not absorbed, the measurement of hexavalent chromium by the method of the present invention is not affected. In the method of the present invention, if the turbidity of the sample water is remarkable, it is desirable to perform filtration using a filter paper or the like in advance. If no color or turbidity is observed in the sample water, the blank test can be omitted. However, if the sample water is colored, always perform the blank test to correct the absorbance value. The method of the present invention can be applied not only to fly ash-related eluate and ash wastewater, but also to general wastewater.

[0008]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In the examples, the absorbance was measured using a spectrophotometer [U-1100, Hitachi, Ltd.]. Reference Example 1 (identification of white precipitate) Water quality was pH 12.3, electric conductivity 5,050 mS / m, P
Fly ash having an alkalinity of 2,060 mg CaCO ₃ / l, an M-alkalinity of 2,310 mg CaCO ₃ / l, a calcium hardness of 10,300 mg CaCO ₃ / l, a chloride ion of 15,300 mg / l and a sulfate ion of 2,690 mg / l Sulfuric acid was added to the relevant eluate, and the resulting white precipitate crystals were filtered, washed with water, and air-dried at room temperature until a constant weight was reached. To 20.0 mg of these crystals was added hydrochloric acid (1
+1) 4 ml was added and dissolved by heating, and water was added to make a total amount of 10 ml.
0 ml. For this solution, the calcium concentration was quantified by an atomic absorption method, barium chloride was added, and the sulfate ion concentration was quantified by a turbidimetric method. The calcium concentration is 49.2m
Since g / l, the sulfuric acid ion concentration is 113 mg / liter, respectively crystal coincides with the theoretical value 46.5 mg / l and 112 mg / liter when as a CaSO ₄ · 2H ₂ O, a white precipitate sulfate It was confirmed to be calcium dihydrate. Reference Example 2 (suppression of precipitation of calcium sulfate by addition of sodium hexametaphosphate) To 25 ml of the fly ash-related eluate used in Reference Example 1, an aqueous solution of sodium hexametaphosphate (500 mg / liter) was added.
Sodium hexametaphosphate was added to a concentration of 2 mg / liter when the total amount was 50 ml. Then, water was added to make up the volume to about 45 ml, 2.5 ml of sulfuric acid (1 + 9) was added, water was further added to make the total volume 50 ml, and the mixture was stirred immediately.
The absorbance at nm was measured. The absorbance is 0.311
Met. When the same operation was repeated without adding sodium hexametaphosphate, the absorbance was found to be 0.48.
It was 5. When the concentration of sodium hexametaphosphate is 50 ml in total, 4, 8, 20, 50 and 100 mg /
The absorbances when added to liters are 0.304, 0.112, 0.003, 0.001 and 0.001, respectively.
001. The results are shown in Table 1.

[0009]

[Table 1]

Since the absorbance at a wavelength of 660 nm indicates the turbidity of the liquid, it can be seen from the results that the precipitation of calcium sulfate can be suppressed if the concentration of sodium hexametaphosphate is 20 mg / liter or more. Reference Example 3 (Effect of sodium hexametaphosphate on coloring by diphenylcarbazide) The effect of sodium hexametaphosphate on coloring of hexavalent chromium by diphenylcarbazide was examined. The diphenylcarbazide solution (10 g / liter) was prepared by dissolving 0.5 g of diphenylcarbazide in 25 ml of acetone.
It was prepared by adding water to 50 ml. A Cr (VI) standard solution containing 0.375 mg / liter of hexavalent chromium was prepared, 25 ml of this standard solution was placed in a 50 ml-capacity colorimetric tube with a stopper, and an aqueous sodium hexametaphosphate solution (500 mg
/ Liter) was added so that the concentration of sodium hexametaphosphate was 20 mg / liter when the total amount was 50 ml. After adding water to a volume of about 45 ml, sulfuric acid (1+
9) 2.5 ml, then diphenylcarbazide solution (10
g / liter), add 1 ml, and add water to make the total amount 5
The mixture was immediately stirred at 0 ml and placed in a cell having an optical path length of 50 mm after 5 minutes, and the absorbance at a wavelength of 540 nm was measured.
The absorbance was 0.807. When the same operation was repeated without adding sodium hexametaphosphate, the absorbance was 0.806. When the total concentration of sodium hexametaphosphate is 50 ml, 40, 10
The absorbances when added to 0 and 200 mg / l were 0.807, 0.810 and 0.810, respectively.
Met. In addition, as a blank test, Cr (VI) standard solution 25 ml
Was placed in a 50 ml color tube with a stopper and a sodium hexametaphosphate aqueous solution (500 mg / liter) was added when the total concentration of sodium hexametaphosphate was 50 ml.
It was added so as to be 00 mg / liter. After adding water to a volume of about 45 ml, 2.5 ml of sulfuric acid (1 + 9) and then 0.5 ml of acetone were added, and further water was added to make a total volume of 50 ml.
After 5 minutes, the mixture was placed in a cell having an optical path length of 50 mm, and the absorbance at a wavelength of 540 nm was measured. The absorbance was 0.001. When the same operation was repeated without adding sodium hexametaphosphate,
The absorbance was 0.000. The results are shown in Table 2.

[0011]

[Table 2]

From the results shown in Table 2, it can be seen that the presence of sodium hexametaphosphate does not affect the coloration of hexavalent chromium by diphenylcarbazide. Reference Example 4 (absorbance of hexavalent chromium) The relationship between the wavelength of coloring with hexavalent chromium and the absorbance was examined.
Potassium dichromate in deionized water with a Cr (VI) concentration of 1
A solution dissolved to a concentration of 0 mg / liter was added to an optical path length of 50
The absorbance was measured in a mm cell. At a wavelength of 420 nm, the absorbance was 0.219, and at a wavelength of 480 nm, the absorbance was 0.089, but at a wavelength of 540 nm, the absorbance was 0.0.
00, indicating no absorption. Table 3 shows the measurement results including the absorbances at other wavelengths.

[0013]

[Table 3]

From the results in Table 3, the yellow color of hexavalent chromium is
The measured value of the method of the present invention for measuring the absorbance at a wavelength of 540 nm has no effect, and it can be seen that hexavalent chromium can be used as a blank test control solution in the presence of hexavalent chromium. Reference Example 5 (Preparation of Calibration Curve) A potassium dichromate standard solution was added to deionized water, and Cr was added.
(VI) A solution having a concentration of 0.020 mg / liter was prepared. 25 ml of this solution was placed in a 50 ml color tube with a stopper, and 5 ml of an aqueous solution of sodium hexametaphosphate (500 mg / l) was added. After adding water to a volume of about 45 ml, 2.5 ml of sulfuric acid (1 + 9) and then 1 ml of a diphenylcarbazide solution (10 g / l) were added, and further water was added to bring the total amount to 50 ml. The cell was placed in a 50 mm long cell, and the absorbance at a wavelength of 540 nm was measured. The absorbance was 0.043. Similarly, the Cr (VI) concentrations are 0.050 and 0.10, respectively.
Prepare solutions at 0, 0.250 and 0.500 mg / l, color with diphenylcarbazide,
The absorbance at 40 nm was measured. The absorbances were 0.106, 0.213, 0.520 and 1.060, respectively. The relationship between the Cr (VI) concentration and the absorbance is shown in Table 4 and FIG.

[0015]

[Table 4]

As can be seen from FIG. 2, within the measured range, the absorbance and the linearity of the Cr (VI) concentration are good.
By measuring the absorbance at a wavelength of 540 nm,
It can be seen that the concentration of Cr (VI) in the sample water can be determined using this straight line as a calibration curve. Example 1 A volume of 25 ml of the fly ash-related eluate used in Reference Example 1 was used.
And a 5 ml aqueous solution of sodium hexametaphosphate (500 mg / liter) was added. After adding water to a volume of about 45 ml, 2.5 ml of sulfuric acid (1 + 9), and then diphenylcarbazide solution (10 g / l) 1
ml, and then water was added to bring the total volume to 50 ml. The mixture was immediately stirred. After 5 minutes, the mixture was placed in a cell having an optical path length of 50 mm.
The absorbance at 40 nm was measured. The absorbance is 0.0
92. As a blank test, 25 ml of the same eluate was placed in a 50 ml volumetric color tube with a stopper, and 5 ml of an aqueous solution of sodium hexametaphosphate (500 mg / l) was added. After adding water to a volume of about 45 ml, sulfuric acid (1 + 9) 2.5 m
l, then add acetone (0.5 ml), add water to make the total volume 50 ml and immediately stir. After 5 minutes, the optical path length is 50 mm
And the absorbance at a wavelength of 540 nm was measured. The absorbance was 0.007. From the difference between the absorbance of the color-developed sample water and the absorbance of the control solution in the blank test, 0.085, the concentration of Cr (VI) in the fly ash-related eluate was determined to be 0.040 mg / liter using a calibration curve. Was done. Example 2 Water quality is pH 12.5, electric conductivity 9,160 mS / m, P
-The Cr (VI) concentration of fly ash-related sewage having an alkalinity of 1,900 mg CaCO ₃ / liter and a calcium hardness of 15,500 mg CaCO ₃ / liter was measured. This ash sewage 2
5 ml was placed in a 50 ml color tube with a stopper and a 5 ml aqueous sodium hexametaphosphate solution (500 mg / l) was added. After adding water to a volume of about 45 ml, sulfuric acid (1+
9) 2.5 ml, then diphenylcarbazide solution (10
g / liter), add 1 ml, and add water to make the total amount 5
The mixture was immediately stirred at 0 ml and placed in a cell having an optical path length of 50 mm after 5 minutes, and the absorbance at a wavelength of 540 nm was measured.
The absorbance was 0.164. As a blank test, 25 ml of the same ash sewage was placed in a 50 ml-capacity color tube with a stopper, and an aqueous solution of sodium hexametaphosphate (500 mg / l) was added.
ml was added. After adding water to a volume of about 45 ml, 2.5 ml of sulfuric acid (1 + 9) and then 0.5 ml of acetone were added, and further water was added to bring the total volume to 50 ml, and the mixture was immediately stirred. The absorbance at a wavelength of 540 nm was measured. The absorbance was 0.015. From the difference of 0.149 between the absorbance of the color-developed sample water and the absorbance of the control solution in the blank test, the Cr in the fly ash-related eluate was determined.
(VI) The concentration was determined to be 0.070 mg / liter using a calibration curve. Comparative Example 1 J of Cr (VI) concentration of fly ash-related sewage used in Example 2
Quantitative determination by IS standard diphenylcarbazide absorption spectrophotometry was attempted. 25 ml of ash wastewater into two beakers (A) and (B)
The solution in the beaker (A) was transferred to the total volume flask (A), and 2.5 ml of sulfuric acid (1 + 9) was added. Further, to the solution in the beaker (B), 2.5 ml of sulfuric acid (1 + 9) was added. At this stage, both the beakers (A) and (B) produced a large amount of white precipitate, and no further measurement operation was possible.

[0017]

According to the method of the present invention, hexavalent chromium can be accurately measured by the diphenylcarbazide absorptiometry even for the fly ash-related eluate and ash wastewater containing a large amount of calcium ions. .

[Brief description of the drawings]

FIG. 1 is a flow sheet of one embodiment of the method of the present invention.

FIG. 2 is a calibration curve showing the relationship between absorbance and Cr (VI) concentration.

Claims (1)

[Claims] 1. A method for measuring hexavalent chromium in water, wherein a sample water is made acidic with sulfuric acid, color is added by adding diphenylcarbazide, and absorbance is measured. A method for measuring hexavalent chromium, comprising adding a salt.