JP2018194307A - Necessary addition quantity determination method of hexavalent chromium reductant - Google Patents

Abstract

To provide a determination method that is drastically simple and rapid compared with a method for determining necessary quantity of a reductant using an official method when a reductant is added to a treated substance containing hexavalent chromium so as to perform a reduction treatment of hexavalent chromium.SOLUTION: An eluate of hexavalent chromium is obtained by allowing a treated substance containing hexavalent chromium to have contact with water. A reductant is added to the eluate so as to perform a reduction treatment of hexavalent chromium. An optical density derived from hexavalent chromium of the eluate, where a reduction treatment is performed, is measured. The concentration of hexavalent chromium in the measured optical density is calculated by using a previously generated calibration curve. Then, a necessary addition quantity of the reductant with respect to a treated substance is determined based on an addition quantity of the reductant where calculated concentration of hexavalent chromium becomes equal to or less than 0.10 ppm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for determining a necessary addition amount of a hexavalent chromium reducing agent when a hexavalent chromium reducing agent is added to a hexavalent chromium-containing substance to treat the hexavalent chromium.

  Dust (fly ash) generated when burning municipal waste, industrial waste, coal, biomass, etc., incineration residues such as incineration ash, or dust generated when these are melted are disposed of in landfills. Is common. These fly ash, incineration residue, dust, and the like frequently contain heavy metals (Pb, Cd, Hg, etc.), and those that further contain hexavalent chromium (in the present invention, These are also referred to as “hexavalent chromium-containing substances.”) When landfilling, disposal of hexavalent chromium is made harmless and other heavy metals are not eluted.

  Conventionally, as a method of detoxifying hexavalent chromium, a method of reducing to harmless trivalent chromium by a reduction treatment using chemicals is generally used. For example, it is used in metal plating and contains hexavalent chromium. A method of adding a hexavalent chromium reducing agent to waste liquids, fly ash from which hexavalent chromium is eluted, sludge, soil, and the like has been disclosed (for example, see Patent Documents 1 and 2).

  In addition to hexavalent chromium, a hexavalent chromium-containing substance containing Pb, Cd, Hg, etc. should be used in combination with a heavy metal treating agent (amine carbodithioate chelating agent) and a hexavalent chromium reducing agent. There are many (for example, refer patent documents 3-5).

  In such chemical treatment methods, in order to ensure the detoxification of hexavalent chromium and insolubilization of heavy metals in the hexavalent chromium-containing ash, the required amounts of the hexavalent chromium reducing agent and heavy metal treatment agent are ascertained. It is important to.

  As a method to determine the required amount of hexavalent chromium reducing agent and heavy metal treating agent so far, adding hexavalent chromium reducing agent and heavy metal treating agent to hexavalent chromium-containing ash by desktop test, adding humidified water, kneading, etc. In addition, the eluate obtained by performing the elution test by the method prescribed in the Environmental Agency Notification No. 13 Law on February 17, 1973 (hereinafter referred to as “No. 13 Test”) is described in the JIS method. There is a method (so-called official method) for measuring the concentration of hexavalent chromium and the concentration of heavy metals such as Pb, Cd, and Hg based on the test method. However, since this official method requires a long time of about 48 hours, it has been difficult to respond in the field where continuous processing is required like fly ash.

  For this reason, for a method for simply determining the required amount of a heavy metal treating agent (for example, a chelating agent for amine carbodithioate) for heavy metal-containing ash (for example, ash containing Pb, Cd, Hg, etc.) Various studies and proposals have been made, and quick response is possible (for example, see Patent Documents 6 to 10). However, for hexavalent chromium-containing ash, it is difficult to determine the required amount of hexavalent chromium reducing agent even by using the simple determination method using the amine carbodithioate chelating agent described above. there were.

JP 2008-149309 A JP 2006-274321 A JP 2011-0662620 A JP 2001-121133 A JP 2011-74350 A JP-A-10-337550 JP 2006-000829 A JP 2010-260010 A JP, 2014-028342, A JP 2006-049481 A

  The object of the present invention is significantly simpler than the method for determining the required amount of reducing agent using the official method when reducing the hexavalent chromium by adding a reducing agent to the substance to be treated containing hexavalent chromium. It is to provide a quick decision method.

  As a result of intensive studies on a method for determining a necessary addition amount of a reducing agent for a substance to be treated containing hexavalent chromium, the present inventors have completed the present invention.

  That is, the present invention includes the following embodiments.

[1] A method for determining a necessary addition amount of the reducing agent in a treatment method for reducing hexavalent chromium by adding a reducing agent to a substance to be treated containing hexavalent chromium,
A step of obtaining a hexavalent chromium eluate by contacting a substance to be treated containing hexavalent chromium with water;
Adding the reducing agent to the eluate to reduce hexavalent chromium;
Measuring the absorbance derived from hexavalent chromium in the reduced eluate,
A step of calculating the hexavalent chromium concentration at the measured absorbance using a calibration curve prepared in advance, and the amount of the reducing agent added so that the calculated hexavalent chromium concentration is 0.10 ppm or less. A method for determining a required addition amount of a hexavalent chromium reducing agent, comprising a step of determining a required addition amount of a reducing agent.

  [2] The method according to [1], wherein the substance to be treated containing hexavalent chromium is fly ash, sludge, or soil.

  [3] The above-mentioned feature, wherein the reducing agent is at least one selected from the group consisting of ferrous sulfate (II), ferrous chloride (II), a sulfur compound, an organic acid, and an organic acid salt. [1] or [2].

  [4] The sulfur compound is carbon disulfide, sodium sulfate, sodium sulfide, sodium hydrogen sulfide, potassium sulfate, potassium sulfide, sodium thiosulfate, sodium sulfite, sulfur monochloride, sulfur dichloride, ammonium peroxodisulfate, sodium peroxodisulfate The method according to [3] above, which is at least one selected from the group consisting of sodium hydrogensulfite, hydroxylamine sulfate, and sodium hyposulfite.

  [5] The organic acid or organic acid salt is at least one selected from the group consisting of citric acid, malic acid, ascorbic acid, erythorbic acid, and salts thereof, as described in [3] above Method.

  [6] The method according to any one of [1] to [5] above, wherein the absorbance derived from hexavalent chromium is an absorbance measured in the range of 325 nm to 425 nm.

  [7] Any one of [1] to [6] above, wherein the hexavalent chromium eluate is an aqueous solution obtained by contacting and filtering a substance to be treated containing hexavalent chromium and water. The method of crab.

  [8] The method according to any one of [1] to [7], wherein the treatment method for reducing hexavalent chromium is a detoxification method for hexavalent chromium.

  According to the present invention, in a treatment method for reducing hexavalent chromium by adding a reducing agent to a substance to be treated containing hexavalent chromium, the hexavalent chromium reducing agent capable of insolubilizing hexavalent chromium in the substance to be treated is provided. The required amount can be determined easily, quickly and accurately compared to the official method.

The test result which measured the density | concentration and the light absorbency of hexavalent chromium standard solution (pH = 12.5) is shown. It is a figure which shows the calibration curve calculated | required from the test result of the density | concentration of a hexavalent chromium standard solution (pH = 12.5), and the light absorbency of wavelength 372nm, and its relational expression. The test result which measured the light absorbency in each density | concentration of hexavalent chromium standard solution (pH = 7) is shown. It is a figure which shows the calibration curve calculated | required from the test result of the density | concentration of a hexavalent chromium standard solution (pH = 7), and the light absorbency of wavelength 372nm, and its relational expression. The test result which measured the light absorbency in each density | concentration of hexavalent chromium standard solution (pH = 3) is shown. It is a figure which shows the analytical curve calculated | required from the test result of the density | concentration of hexavalent chromium standard solution (pH = 3), and the light absorbency of wavelength 350nm, and its relational expression. The test result of the light absorbency of 372 nm of a fly ash sample 1 eluate is shown. The test result of the light absorbency of 372 nm of a fly ash sample 2 eluate is shown.

  Hereinafter, the present invention will be described in more detail.

The present invention is a method for determining a necessary addition amount of the reducing agent in a processing method for reducing hexavalent chromium by adding a reducing agent to a substance to be treated containing hexavalent chromium,
A step of obtaining a hexavalent chromium eluate by contacting a substance to be treated containing hexavalent chromium with water;
Adding the reducing agent to the eluate to reduce hexavalent chromium;
Measuring the absorbance derived from hexavalent chromium in the reduced eluate,
The step of calculating the hexavalent chromium concentration at the measured absorbance using a calibration curve prepared in advance, and the amount of the reducing agent added so that the calculated hexavalent chromium concentration is 0.10 ppm or less. It is characterized by including a step of determining a necessary addition amount of the reducing agent.

  The substance containing hexavalent chromium in the present invention is not particularly limited as long as it contains hexavalent chromium, and examples thereof include fly ash containing hexavalent chromium, incineration residue, sludge, or soil. Among these, fly ash containing hexavalent chromium or incineration residue is preferable because it can be easily applied to the method of the present invention.

  The reducing agent in the present invention is not particularly limited as long as it has a reducing power capable of reducing hexavalent chromium. For example, ferrous sulfate (II), ferrous chloride (II), sulfur compounds , Organic acids or organic acid salts.

  The sulfur compound is not particularly limited, and examples thereof include carbon disulfide, sodium sulfate, sodium sulfide, sodium hydrogen sulfide, sodium thiosulfate, sodium sulfite, sulfur monochloride, sulfur dichloride, ammonium peroxodisulfate, peroxo Examples thereof include sodium disulfate, sodium bisulfite, hydroxylamine sulfate, and sodium hyposulfite.

  Although it does not specifically limit as an organic acid or organic acid salt, For example, oxalic acid, a citric acid, malic acid, gluconic acid, ascorbic acid, erythorbic acid etc., or those salts can be mentioned.

  Although it does not specifically limit as water in this invention, For example, a pure water, distilled water, ion-exchange water, or ultrafiltration water etc. can be used.

  In the present invention, the method for bringing the substance to be treated containing hexavalent chromium into contact with water is not particularly limited, but for example, a method for bringing it into contact with a closed container such as a plastic bag, a plastic bottle, or a glass container, Further, there can be mentioned a method in which water is passed through a fixed bed or moving bed filled with a substance to be treated containing hexavalent chromium and continuously contacted. Although there is no particular limitation after contacting the substance to be treated containing hexavalent chromium with water, for example, it is preferable to separate the aqueous solution by, for example, a sedimentation method or a filtration method, and the accuracy of this method is improved. In terms of improvement, it is preferable to remove tangible substances from the aqueous solution using filter paper or the like.

  The amount of water used in the present invention is not particularly limited. For example, it is preferable to use a range of 50 to 1000 times by weight with respect to 1 part by weight of the substance to be treated containing hexavalent chromium.

  In the method of contacting the material to be treated containing hexavalent chromium and water in the present invention, although not particularly limited, for example, by adding the amount of water to the material to be treated containing hexavalent chromium, It is preferable to perform stirring or shaking for 1 to 30 minutes.

  The eluate of hexavalent chromium obtained by bringing the material to be treated containing hexavalent chromium obtained by the above operation into contact with water contains hexavalent chromium and is derived from hexavalent chromium at 300 nm to 500 nm. Having an ultraviolet-visible absorption spectrum of About the said eluate, the amount of hexavalent chromium to contain can be quantified from the light absorbency of the absorption spectrum using the analytical curve mentioned later.

  Further, the eluate contains hexavalent chromium, but by adding the reducing agent, the hexavalent chromium in the eluate is reduced to trivalent chromium, and accordingly, derived from the hexavalent chromium. UV-visible absorbance decreases. By measuring the absorbance at this time, the amount of hexavalent chromium remaining without being reduced by the reducing agent can be quantified.

  The method of adding the reducing agent to the eluate is not particularly limited, but there are a method of directly adding and stirring the reducing agent, a method of adding and stirring after dissolving or diluting the reducing agent in water, and the like. Can be mentioned. Moreover, the addition method of the hexavalent chromium reducing agent used in the determination method of the present invention is not particularly limited, and examples include addition using a pump and addition using a pipette.

  Further, the time from the addition of the hexavalent chromium reducing agent to the measurement of the UV-visible absorption spectrum is not particularly limited, but in order to reduce the variation due to the measurement, the time is within 30 minutes immediately after the addition / stirring. In particular, it is more preferably within 15 minutes immediately after the addition and stirring.

  The calibration curve in the present invention can be prepared by measuring an ultraviolet-visible absorption spectrum of an aqueous solution in which a hexavalent chromium standard substance is dissolved in water. Although it does not specifically limit as a hexavalent chromium standard substance, For example, the high purity hexavalent chromium of a commercial item can be used. Further, the water used for preparing the calibration curve is not particularly limited, but it is preferable to use the same water as that used for adjusting the eluate.

  In addition, although it does not specifically limit about the fixed_quantity | quantitative_assay of the hexavalent chromium by the ultraviolet visible absorption spectrum of hexavalent chromium aqueous solution, It is preferable to use the absorption in 325 nm-425 nm. However, for the hexavalent chromium aqueous solution, since the absorption maximum wavelength varies depending on the pH, it is preferable that the pH of the eluate and the pH of the aqueous solution used for preparing the calibration curve are the same.

  In the present invention, the required addition amount of the target reducing agent is the addition amount of the reducing agent when the hexavalent chromium concentration in the eluate obtained from the calibration curve becomes 0.10 ppm or less (hereinafter referred to as “end point”). May be referred to as “addition amount”).

  The required addition amount X (reducing agent g / fly ash g) of the target reducing agent can be calculated using the following formula (1) by using the end point addition amount of the reducing agent.

  In formula (1), A represents the weight (g) of the hexavalent chromium-containing substance used for simple elution, B represents the weight (g) of water used for elution of hexavalent chromium, and C represents absorbance measurement. Represents the weight (g) of the hexavalent chromium eluate used in the above, D represents the dilution ratio of the reducing agent used in the method for determining the reducing agent addition amount, and E represents the end point addition weight (g) of the reducing agent.

  For example, when hexavalent chromium is eluted from x gram of a hexavalent chromium-containing substance with water and the hexavalent chromium reducing agent is gradually added to the eluate, the hexavalent chromium reducing agent [here, undiluted (D = If the hexavalent chromium concentration in the eluate becomes 0.10 ppm based on the calibration curve when y gram is added], that is the end point, and the hexavalent chromium-containing substance x The required amount of hexavalent chromium reducing agent per gram can be determined as y gram.

  Moreover, in the actual hexavalent chromium treatment, the hexavalent chromium treatment varies depending on the form of the hexavalent chromium-containing substance, the variation in the hexavalent chromium content (concentration unevenness), the mixing method of the hexavalent chromium reducing agent, etc. It is preferable to use an amount further added to the necessary amount of the hexavalent chromium reducing agent determined by the determination method of the present invention. In this case, the amount of addition is not particularly limited, but is preferably 0.1% by weight to 3.0% by weight with respect to the weight of the hexavalent chromium-containing substance, and particularly 0.5% by weight to 2.% by weight. 0% by weight is preferred.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited to these Examples.

Reference Example 1 Preparation of a hexavalent chromium calibration curve (pH 12.5).
A 1000 ppm hexavalent chromium standard solution (reagent: manufactured by Kanto Chemical Co., Inc.) was diluted to adjust samples with concentrations of 0.1 ppm, 1 ppm, 2 ppm, and 10 ppm under the conditions of pH 12.5, and a spectrophotometer (instrument: Absorbance was measured with an ultraviolet-visible spectrophotometer UV-3100 (manufactured by Shimadzu Corporation). Absorption due to hexavalent chromium was confirmed at 372 nm. Moreover, the light absorbency in each density | concentration of hexavalent chromium was measured (refer FIG. 1, Table 1).

  A calibration curve was prepared from the hexavalent chromium concentration and absorbance in Table 1 (see FIG. 2).

Reference Example 2 Preparation of a hexavalent chromium calibration curve (pH 7).
A 1000 ppm hexavalent chromium standard solution was diluted, and samples with concentrations of 1 ppm, 5 ppm, and 10 ppm were prepared under the condition of pH 7, and absorbance was measured with a spectrophotometer. Absorption due to hexavalent chromium was confirmed at 372 nm. Moreover, the light absorbency in each density | concentration of hexavalent chromium was measured (refer FIG. 3, Table 2).

  A calibration curve was prepared from the hexavalent chromium concentration and absorbance in Table 2 (see FIG. 4).

Reference Example 3 Preparation of a hexavalent chromium calibration curve (pH 3).
A 1000 ppm hexavalent chromium standard solution was diluted, and samples with concentrations of 1 ppm, 5 ppm, and 10 ppm were prepared under the condition of pH 3, and absorbance was measured with a spectrophotometer. Absorption due to hexavalent chromium was confirmed at 350 nm. Moreover, the light absorbency of each density | concentration of hexavalent chromium was measured (refer FIG. 5, Table 3).

  A calibration curve was prepared from the hexavalent chromium concentration and absorbance in Table 3 (see FIG. 6).

Reference Example 4 Confirmation of the quantitativeness of hexavalent chromium by absorbance.
Test No. 13 was conducted on fly ash (fly ash sample 1) containing 47 mg / kg of hexavalent chromium, and eluate 1 was obtained. It was 2.0 mg / L when the hexavalent chromium density | concentration was measured about the said eluate 1 based on the test method described in JIS method.

  Moreover, No. 13 test was done about the fly ash (fly ash sample 2) containing 160 mg / kg of hexavalent chromium, and the eluate 2 was obtained. When the hexavalent chromium concentration of the eluate 2 was measured based on the test method described in the JIS method, it was 6.1 mg / L.

  Next, the absorbance of each of the eluates 1 and 2 was measured (see FIGS. 7 and 8). At this time, since the pH of the eluate was 12.5, the absorbance at 372 nm was measured, and the hexavalent chromium concentration was calculated from the value using the calibration curve shown in FIG.

  The absorbance of the eluate 1 was 0.175 Abs, and the hexavalent chromium concentration was 1.93 ppm. The eluate 2 had an absorbance of 0.541 Abs and a hexavalent chromium concentration of 5.96 ppm.

  These results are also shown in Table 4.

  As apparent from Table 4, since there was no difference in the hexavalent chromium concentration between the JIS method and the absorbance measurement method, it was confirmed that the hexavalent chromium in fly ash could be quantified by the absorbance measurement method.

Example 1
[Simple elution method]
Place 1.0 g of fly ash sample 1 and 100 g of pure water in a 250 mL polyethylene container, attach the inner lid and outer lid firmly, shake for 1 minute, and perform elution treatment to elute hexavalent chromium. I got it. Next, the eluate was filtered through 1 μ filter paper (GS-25, manufactured by Advantech), and then the pH was measured to prepare a sample.

[Reducing agent addition amount determination method]
About 20 g of the specimen obtained by the simple elution method was placed in a 30 ml sample bottle to prepare an evaluation sample. A reducing agent obtained by diluting a hexavalent chromium reducing agent (heavy metal treatment agent TF-20, manufactured by Tosoh Corporation) 100 times with pure water is added to the evaluation sample, stirred, and absorbance (derived from hexavalent chromium) using a spectrophotometer. Absorbance 300 to 500 nm) was measured. The absorbance decreased as the amount of the reducing agent added increased, but the amount of decrease in absorbance gradually decreased, and finally there was almost no change in absorbance. The hexavalent chromium concentration in the sample at the absorbance was determined from the calibration curve, and the amount of reducing agent added (referred to as “end point added amount”) that was 0.10 ppm or less was determined. The required addition amount of the hexavalent chromium reducing agent to the fly ash was determined using the end point addition amount. The required addition amount was 1 g / 100 g of fly ash.

  The required addition amount was calculated using the above-described calculation formula (1).

[Addition amount test]
30 g of fly ash sample 1 is put into a polyethylene bag (Unipack H-4, manufactured by Nippon Nihonsha) and the amount of reducing agent and humidifying water shown in Table 5 is added. Then, the ash that was collected to some extent was spread and homogenized with a stick or wooden mallet. In order to make it uniform, the kneaded ash was unwound and further homogenized with a stick or wooden mallet. This operation was repeated 3 to 5 times to finish the kneading operation. The kneaded ash was cured for 16 hours or more, and an elution test was conducted in the No. 13 test, and the hexavalent chromium concentration of the obtained eluate was measured based on the test method described in the JIS method. The hexavalent chromium eluted from the fly ash was 1.5 mg / L.

  These results are shown in Table 5.

  As is clear from Table 5, it was confirmed that hexavalent chromium could be treated to the elution standard value or less with the amount of reducing agent estimated by the method for determining the amount of reducing agent added. The working time from simple elution to estimation of the required amount of reducing agent was 1 hour.

Example 2
[Simple elution method]
Put 1.0g of fly ash sample 2 and 100g of pure water into a 250mL polyethylene container, attach the inner lid and outer lid firmly, shake for 1 minute, and perform elution treatment to elute hexavalent chromium. I got it. Next, the eluate was filtered through 1 μ filter paper (GS-25, manufactured by Advantech), and then the pH was measured to prepare a sample.

[Reducing agent addition amount determination method]
About 20 g of the specimen obtained by the simple elution method was placed in a 30 ml sample bottle to prepare an evaluation sample. A reducing agent obtained by diluting a hexavalent chromium reducing agent (heavy metal treatment agent TF-20, manufactured by Tosoh Corporation) 100 times with pure water is added to the evaluation sample, stirred, and absorbance (derived from hexavalent chromium) using a spectrophotometer. Absorbance 300 to 500 nm) was measured. The absorbance decreased as the amount of the reducing agent added increased, but the amount of decrease in absorbance gradually decreased, and finally there was almost no change in absorbance. From the calibration curve, the hexavalent chromium concentration in the sample at the absorbance was determined, and the end point addition amount was determined. The required addition amount of the hexavalent chromium reducing agent to the fly ash was determined using the end point addition amount. The required addition amount was 6 g / 100 g of fly ash.

  The required addition amount was calculated using the above-described calculation formula (1).

[Addition amount test]
30 g of fly ash sample 1 is put into a polyethylene bag (Unipack H-4, produced by Production Japan Co., Ltd.), the reducing agent and humidifying water in the amounts shown in Table 6 are added, and the reducing agent and humidifying water are quickly dispersed in the ash. Then, the ash that was collected to some extent was spread and homogenized with a stick or wooden mallet. In order to make it uniform, the kneaded ash was unwound and further homogenized with a stick or wooden mallet. This operation was repeated 3 to 5 times to finish the kneading operation. The kneaded ash was cured for 16 hours or more, and an elution test was conducted in the No. 13 test, and the hexavalent chromium concentration of the obtained eluate was measured based on the test method described in the JIS method. The hexavalent chromium eluted from the fly ash was 1.5 mg / L.

  These results are shown in Table 6.

  As is clear from Table 6, it was confirmed that hexavalent chromium could be treated to the elution standard value or less with the amount of reducing agent estimated by the method for determining the amount of reducing agent added. The working time from simple elution to estimation of the required amount of reducing agent was 1 hour.

Synthesis Example Synthesis of sodium tetraethylenepentamine-N1, N2, N3, N4, N5-pentacarbodithioate (Compound No. 1).
In a glass container under a nitrogen atmosphere, tetraethylenepentamine (manufactured by Tosoh Corporation, triethylenetetramine content 1% or less, diethylenetriamine content 0.1% or less) 53 parts by weight, 48% NaOH 91 parts by weight, water 821 parts by weight Into this mixed solution, 82 parts by weight of carbon disulfide was added dropwise over 4 hours at 40 ° C. or lower with stirring. After completion of the dropping, aging was performed at the same temperature for about 1 hour. Nitrogen was blown into the reaction solution, and unreacted carbon disulfide was distilled off to obtain a yellowish brown transparent liquid. As a result of iodometric titration, the amine carbodithioate concentration in this aqueous solution was 15% by weight.

Comparative Example 1
Using a 1000 ppm hexavalent chromium standard solution, an aqueous solution having a hexavalent chromium concentration of 10 ppm was prepared, and 20 g was placed in a 30 ml sample bottle to prepare the required number of samples. Next, the amine carbodithioate chelating agent obtained in Synthesis Example 1 (Compound No. 1) was diluted 33-fold with pure water, added arbitrarily in a certain amount, and the absorbance (derived from hexavalent chromium) was measured with a spectrophotometer. The absorbance was 300 to 500 nm. The results are shown in Table 7.

  As is clear from Table 7, compound no. No increase in absorbance was observed even when the amount of compound No. 1 was increased. 1 shows that hexavalent chromium is not treated.

Comparative Example 2
Using a 1000 ppm hexavalent chromium standard solution, an aqueous solution having a hexavalent chromium concentration of 10 ppm was prepared, and 20 g was placed in a 30 ml sample bottle to prepare the required number of samples. Next, a 40% aqueous solution of sodium diethylthiocarbamate (Compound No. 2, manufactured by Wako Pure Chemical Industries, Ltd.) was prepared, further diluted 100-fold with pure water, arbitrarily added in portions, and the absorbance was measured with a spectrophotometer. ((Absorbance 300 to 500 nm derived from hexavalent chromium) was measured. The results are shown in Table 8.

  As is apparent from Table 8, compound no. No increase in absorbance was observed even when the amount of No. 2 was increased. 2 shows that hexavalent chromium is not treated.

  The method for determining the required amount of the hexavalent chromium reducing agent of the present invention can determine the required amount of the hexavalent chromium reducing agent capable of insolubilizing the hexavalent chromium in the hexavalent chromium-containing ash in a simple, rapid and accurate manner. Therefore, it is particularly useful for continuously treating hexavalent chromium-containing ash such as fly ash discharged continuously at the incineration plant.

Claims (8)

A method for determining a required addition amount of the reducing agent in a processing method for reducing hexavalent chromium by adding a reducing agent to a substance to be treated containing hexavalent chromium,
A step of obtaining a hexavalent chromium eluate by contacting a substance to be treated containing hexavalent chromium with water;
Adding the reducing agent to the eluate to reduce hexavalent chromium;
Measuring the absorbance derived from hexavalent chromium in the reduced eluate,
A step of calculating the hexavalent chromium concentration at the measured absorbance using a calibration curve prepared in advance, and the amount of the reducing agent added so that the calculated hexavalent chromium concentration is 0.10 ppm or less. A method for determining a required addition amount of a hexavalent chromium reducing agent, comprising a step of determining a required addition amount of a reducing agent. The method according to claim 1, wherein the substance to be treated containing hexavalent chromium is fly ash, sludge, or soil. The reducing agent is at least one selected from the group consisting of ferrous sulfate (II), ferrous chloride (II), sulfur compounds, organic acids, and organic acid salts. The method described in 1. Sulfur compounds are carbon disulfide, sodium sulfate, sodium sulfide, sodium hydrogen sulfide, potassium sulfate, potassium sulfide, sodium thiosulfate, sodium sulfite, sulfur monochloride, sulfur dichloride, ammonium peroxodisulfate, sodium peroxodisulfate, hydrogen sulfite. The method according to claim 3, wherein the method is at least one selected from the group consisting of sodium, hydroxylamine sulfate, and sodium hyposulfite. The method according to claim 3, wherein the organic acid or the organic acid salt is at least one selected from the group consisting of citric acid, malic acid, ascorbic acid, erythorbic acid, and salts thereof. 6. The method according to claim 1, wherein the absorbance derived from hexavalent chromium is an absorbance measured in a range of 325 nm to 425 nm. The method according to any one of claims 1 to 6, wherein the hexavalent chromium eluate is an aqueous solution obtained by filtering a substance to be treated containing hexavalent chromium in contact with water. The method according to any one of claims 1 to 7, wherein the treatment method of reducing hexavalent chromium is a detoxifying method of hexavalent chromium.

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