JP2016049481A - Device and method for determining additive amount of chelate agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate an additive amount of chemicals necessary for insolubilization of heavy metal in waste such as fly ash.SOLUTION: A device 1 related to the present invention includes: absorbance measurement means 2 for measuring absorbance of a sample with a wavelength allowing for measurement of a content of a chelated metal which is a reaction product between a metal compound and an unreacted chelate agent remaining unreacted in reaction of heavy metal in waste with the chelate agent; and a chelate agent amount calculation means 3 which calculates the amount of the chelate agent necessary for treatment based on the measurement result. A method related to the present invention includes: a chelate agent addition step S1 of adding an excessive amount of a chelate agent to heavy metal-containing waste thereby insolubilizing heavy metal; a metal compound addition step S4 of adding the metal compound to the sample thereby chelating the metal compound with the unreacted chelate agent; an absorbance measurement step S5 of measuring absorbance of the sample with wavelength allowing for measurement of the content of the chelated metal obtained in the step S4; and a chelate agent amount calculation step S6 of calculating the amount of the chelate agent necessary for treatment of the waste based on the measurement result.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a chelating agent addition amount determining device and a chelating agent addition amount determining method, and more specifically, an apparatus for determining the amount of a chelating agent necessary for insolubilizing heavy metals contained in solid waste such as waste incineration fly ash. And a method.

  When waste is incinerated, ash containing heavy metals (hereinafter also referred to as “fly ash”) is generated. Fly ash is designated as specially managed general waste by the Waste Disposal Law, and it is obliged to dispose of it by landfill after intermediate treatment.

  As one method of intermediate treatment, it is known to mix a chelate heavy metal fixing agent with fly ash to insolubilize heavy metals contained in fly ash. If the addition amount of the chelating agent is insufficient, there will be a problem in terms of processing stability, and if the addition amount of the chelating agent is excessive, there will be a problem in terms of economy. It is extremely important to determine

  As a method for determining the appropriate amount of chelating agent, the oxidation-reduction potential of the slurry when a certain amount of the chelating heavy metal immobilizing agent is added to the slurry of heavy metal-containing ash and water is measured over time. It has been proposed to obtain a positive change amount of the oxidation-reduction potential after addition of the chelate heavy metal immobilizing agent and determine the required addition amount based on the positive change amount (for example, Patent Document 1). reference).

  Also, take a sample from waste, add a liquid chelating agent to a predetermined amount of the sample, react the heavy metal in the sample with the liquid chelating agent, and add the liquid chelating agent. The absorbance IB at a specific wavelength is determined, the amount B of the unreacted liquid chelating agent in the sample is determined from the absorbance IB, and the absorbance IA at the wavelength corresponding to the total amount of the liquid chelating agent added by the blank test is determined. The total amount A of the liquid chelating agent added from IA is determined, the amount C of the liquid chelating agent reacted with the heavy metal is determined from the difference between the total amount A and the amount B, and based on the ratio between the amount C and a predetermined amount of the sample. It has been proposed to determine the amount of liquid chelating agent added to treat waste (see, for example, Patent Document 2). Patent Document 2 also describes that when the chelating agent is dithiocarbamic acid, the chelating agent has maximum absorption at 286 nm, 257 nm, and 215 nm.

  Incidentally, heavy metals have an absorption peak in the ultraviolet region (200 nm to 250 nm). In the method described in Patent Document 2, since the absorbance at 286 nm, 257 nm, or 215 nm is obtained, there is a possibility of being disturbed by unreacted heavy metal. Therefore, after adding an excessive amount of a chelating agent to a solid waste containing heavy metal and reacting it, the amount of the unreacted chelating agent is 330 nm or more, and the absorbance is measured by the absorbance at a wavelength having a peak of 1 ABS to 3 ABS. It has been proposed to determine the addition amount of a chelating agent necessary for insolubilizing heavy metals in solid waste from the measured values (see, for example, Patent Document 3).

JP 2002-126585 A JP-A-10-337550 JP 2010-260010 A

  However, in the method described in Patent Document 1, the pH of the slurry and the unreacted metal contained in the slurry can affect the redox potential. Therefore, there is still room for improvement in terms of increasing measurement accuracy.

  Fly ash contains not only heavy metals and other metals, but also a number of components that are difficult to identify. In the methods described in Patent Documents 2 and 3, when these components affect the absorbance and the required amount of liquid chelating agent is calculated, there is a possibility that it may be calculated higher than the minimum required amount. is there. Therefore, there is still room for improvement in terms of increasing the measurement accuracy even by the methods described in Patent Documents 2 and 3.

  The present invention has been made in view of the above circumstances, and is to provide a method for more accurately estimating the amount of chemicals necessary for insolubilization of heavy metals contained in waste such as waste incineration fly ash. .

  As a result of intensive studies to achieve the above object, the present inventors have insolubilized the heavy metal contained in the waste with a chelating agent, and then added a metal compound to the sample so that it has not reacted with the heavy metal. The above problem is solved by generating a chelated metal, which is a reaction product of the unreacted chelating agent and the metal compound, and measuring the absorbance of the sample at a wavelength that allows the content of the chelated metal to be measured. The present inventors have found that this can be done and have completed the present invention. Specifically, the present invention provides the following.

  (1) The present invention is a wavelength capable of measuring the content of a chelated metal that is a reaction product of an unreacted unreacted chelating agent and a metal compound in the reaction of a heavy metal and a chelating agent contained in waste, Absorbance measuring means for measuring the absorbance of the chelated metal-containing sample containing the chelating metal, and a chelating agent for calculating the amount of the chelating agent necessary for the treatment of the waste based on the measurement result by the absorbance measuring means A chelating agent addition amount determination device comprising an amount calculation means.

  (2) Moreover, this invention is a chelating agent addition amount determination apparatus as described in (1) whose said chelating metal containing sample is a sample which does not contain the reaction product of the said heavy metal and the said chelating agent substantially. is there.

  (3) Moreover, this invention is a chelating agent addition amount determination apparatus as described in (1) or (2) in which the said chelating metal containing sample contains a pH buffer.

  (4) Moreover, this invention is a chelating agent addition amount determination apparatus in any one of (1) to (3) in which the said chelating agent contains a dithiocarbamic acid type chelating agent.

  (5) Further, in the present invention, the metal compound includes one or more metal salts selected from divalent iron salts, trivalent iron salts, copper salts, nickel salts, cadmium salts, and magnesium salts. ) To the chelating agent addition amount determination device according to any one of (4).

  (6) Moreover, the present invention provides the chelate according to any one of (1) to (5), wherein the absorbance measurement unit measures the absorbance of the chelated metal-containing sample at a wavelength of 400 nm to 700 nm. It is an agent addition amount determination apparatus.

  (7) The present invention also includes a chelating agent addition step of adding an excessive amount of a chelating agent to a waste containing heavy metal to insolubilize the heavy metal, adding a metal compound to the sample after the addition of the chelating agent, and the chelating agent. A metal compound addition step of chelating the metal compound with an unreacted chelating agent that has not reacted with the heavy metal in the adding step, and a content of a chelated metal that is a reaction product of the unreacted chelating agent and the metal compound. An absorbance measurement step for measuring the absorbance of the chelated metal-containing sample containing the chelated metal at a measurable wavelength, and a chelating agent necessary for the treatment of the waste based on the measurement result in the absorbance measurement step A chelating agent addition amount determination method including a chelating agent amount calculation step.

  (8) Moreover, this invention is the solid-liquid mixing which contains the reaction product of the said heavy metal and the said chelating agent after the said chelating agent addition process, and the said heavy metal, and a liquid unreacted chelating agent. The chelating agent addition amount determination method according to (7), further including a solid-liquid separation step of solid-liquid separation of the sample, wherein the metal compound addition step is a step performed after the solid-liquid separation step.

  (9) Moreover, this invention further includes the pH buffer agent addition process of adding a pH buffer agent to a sample before the said metal compound addition process, The chelating agent addition amount as described in (7) or (8) It is a decision method.

  The present invention is not a wavelength suitable for measuring an unreacted chelating agent itself unreacted with a heavy metal, but an absorbance method of a sample at a wavelength suitable for a chelated metal that is a reaction product of an unreacted chelating agent and a metal compound. taking measurement. According to the present invention, in addition to various metals contained in fly ash, it is possible to suppress the influence of numerous difficult-to-specify components on absorbance, resulting in insolubilization of heavy metals contained in waste such as garbage incineration fly ash. It is possible to estimate the required amount of drug addition more accurately.

It is a block diagram for demonstrating schematic structure of the chelating agent addition amount determination apparatus 1 which concerns on this embodiment. It is a flowchart for demonstrating the chelating agent addition amount determination method which concerns on this embodiment. It is a figure which shows the relationship between the chelating agent addition rate with respect to fly ash, and the lead concentration in an eluate. It is a figure which shows the light absorbency in the measurement wavelength of 200-700 nm of the sample which concerns on Example 2 and Comparative Examples 3-5.

  Hereinafter, although embodiment of this invention is described, these do not limit this invention.

<Chelating agent addition amount determination device 1>
FIG. 1 is a block diagram for explaining a schematic configuration of a chelating agent addition amount determining apparatus 1 according to the present embodiment. The chelating agent addition amount determination device 1 is a wavelength capable of measuring the content of a chelating metal that is a reaction product of an unreacted unreacted chelating agent and a metal compound in the reaction of a heavy metal and a chelating agent contained in waste. Then, based on the absorbance measurement unit 2 for measuring the absorbance of the chelated metal-containing sample containing the chelated metal and the measurement result by the absorbance measuring means 2, the amount of the chelating agent necessary for the treatment of the waste is calculated. A chelating agent amount calculation unit 3.

[Absorbance measurement unit 2]
The absorbance measurement unit 2 is a chelate having a wavelength capable of measuring the content of a chelated metal that is a reaction product of an unreacted unreacted chelating agent and a metal compound in the reaction of a heavy metal and a chelating agent contained in waste. It has a function of measuring the absorbance of a chelated metal-containing sample containing a metal halide.

[waste]
The waste is not particularly limited as long as it contains heavy metals. The present embodiment is characterized in that, in addition to various metals contained in the waste, the influence of many difficult-to-specify components on the absorbance can be suppressed. Therefore, the waste contains many hard-to-specify components. For example, waste incineration fly ash, electric furnace dust, biomass incineration ash and the like are preferable.

  Examples of heavy metals contained in the waste include lead, mercury, cadmium, hexavalent chromium, arsenic, selenium, nickel, molybdenum, antimony, copper, zinc, manganese, and the like.

[Chelating agent]
The type of the chelating agent is not particularly limited, but the chelating agent is preferably a dithiocarbamic acid-based chelating agent in that it can react favorably with heavy metals and suitably insolubilize heavy metals, and is a dithiocarbamate, dialkyldithiocarbamine. More preferred are acid salts, cycloalkyldithiocarbamates, piperazine dithiocarbamates, tetraethylenepentamine dithiocarbamates, and polyamine dithiocarbamates. A chelating agent may be used individually by 1 type, and may use 2 or more types together.

[Unreacted chelating agent]
In the present specification, the “unreacted chelating agent” refers to an unreacted chelating agent in the reaction between the heavy metal and the chelating agent. The sample after the addition of the chelating agent is not particularly limited as long as it contains the unreacted chelating agent, but in order to improve the measurement accuracy, the sample substantially contains the reaction product of the heavy metal and the chelating agent. It is preferable that the sample does not contain.

  The reaction product produced by the reaction between the heavy metal and the chelating agent is insoluble in water, and precipitates and precipitates in the sample. Therefore, the method for removing the reaction product is not particularly limited as long as it can solid-liquid separate the reaction product that is solid and the unreacted chelating agent that is liquid. Examples include centrifugation and membrane separation.

  In addition, when the sample is alkaline, when a metal compound is added to the sample, the metal ions in the metal compound react with hydroxide ions to form insoluble hydroxides. May affect the accuracy of calculating the amount of agent. Therefore, the sample after adding the chelating agent preferably contains a pH buffer.

  The pH buffering agent preferably has a pH in the buffer region of 6 or more and 7 or less. For example, tris (hydroxymethyl) aminomethane, piperazine-1,4-diethanesulfonic acid or 2- [4- (2-hydroxy Ethyl) -1-piperazinyl] ethanesulfonic acid. More preferably, the pH buffer is piperazine-1,4-diethanesulfonic acid. A pH buffer may be used individually by 1 type, and may use 2 or more types together.

[Metal compounds]
The type of the metal compound to be reacted with the unreacted chelating agent is not particularly limited, but the metal compound is a divalent iron salt in that it can react with the unreacted chelating agent to suitably generate a chelated metal precipitate. It is preferably one or more metal salts selected from trivalent iron salts, copper salts, nickel salts, cadmium salts and magnesium salts. Moreover, it is preferable that a metal compound is a sulfate or hydrochloride. Since no special treatment is required at the time of discharge after the completion of analytical work or the degree of color development, metal compounds are divalent iron salts or trivalent iron salts such as ferrous chloride, ferrous sulfate, ferric chloride. Or it is more preferable that it is ferric sulfate.

[Measurement of absorbance of chelated metal-containing samples]
The wavelength for measuring the absorbance of the chelated metal-containing sample containing the chelated metal only needs to be a wavelength capable of measuring the content of the chelated metal. Specifically, the measurement wavelength is preferably 400 nm or more and 700 nm or less, and more preferably 500 nm or more and 700 nm or less. If the wavelength is within this range, it can be said that the influence of pH buffer and unreacted metal compound contained in the eluate on the absorbance is extremely small.

  In this embodiment, since a suitable measurement wavelength is 400 nm or more and 700 nm or less, the spectrophotometer generally used widely is enough for the apparatus for measuring absorbance. Therefore, there is no problem in safety or the like even in automatic driving. If the measurement wavelength is 400 nm or more, the absorption peak due to the glass cell is on the shorter wavelength side than the main wavelength, so that an ordinary glass cell can be used instead of an expensive quartz cell, which is highly convenient.

[Chelating agent amount calculation unit 3]
The chelating agent amount calculation unit 3 has a function of calculating the amount of the chelating agent necessary for waste treatment based on the measurement result by the absorbance measurement unit 2.

  The calculation method is not particularly limited, for example, using a calibration curve indicating the relationship between the concentration of the chelated metal that is a reaction product of the chelating agent and the metal compound and the absorbance at the measurement wavelength, Calculate the concentration of chelating metal contained in the chelated metal-containing sample from the absorbance of the chelated metal-containing sample minus the absorbance of the blank test, and calculate the amount of chelating agent required for waste treatment from this concentration To do.

  In this case, the sample for the blank test is not a sample containing neither waste nor a chelating agent, but is preferably a sample containing waste but not containing a chelating agent. A sample from which only the agent has been removed, that is, a sample containing waste, a pH buffering agent and a metal compound, but not containing a chelating agent is more preferred. By doing so, it is possible to suppress the influence of many difficult-to-specify components contained in the waste on the absorbance, and it is possible to more accurately estimate the amount of drug added necessary for the insolubilization of heavy metals contained in the waste. it can.

<Method for determining the amount of chelating agent added>
FIG. 2 is a flowchart for explaining the chelating agent addition amount determining method according to the present embodiment. The chelating agent addition amount determination method includes at least a chelating agent addition step S1, a metal compound addition step S4, an absorbance measurement step S5, and a chelating agent amount calculation step S6. Moreover, although not essential, it is preferable that the chelating agent addition amount determination method further includes a solid-liquid separation step S2 and a pH buffer addition step S3. Hereinafter, the chelating agent addition amount determining method according to the present embodiment will be described in order.

[Chelating agent addition step S1]
The chelating agent addition step S1 is a step of adding an excessive amount of the chelating agent to the waste containing the heavy metal to insolubilize the heavy metal.

  The method of adding a chelating agent to waste and insolubilizing the heavy metals contained in the waste is not particularly limited, and contains waste by adding a small amount of water to the waste and the chelating agent and mixing this with a spatula etc. You may add a lot of water to the sample and shake it horizontally, or add a small amount of water to the waste and mix it with a spatula etc. to add a chelating agent and a lot of water. You may make it shake horizontally. Moreover, after adding much water with respect to a waste material and a chelating agent, you may make it stir with a magnetic stirrer.

  The reason why a small amount of water is added to the waste before mixing with a spatula or the like is to avoid scattering of ash by mixing. Therefore, the amount of water added is not particularly limited as long as it is an amount that can prevent the ash from scattering.

  On the other hand, after mixing with a spatula or the like, a large amount of water is added to the waste in order to appropriately dilute the concentration of the measurement object, and this dilution increases the measurement accuracy when measuring the absorbance of the sample. Rise. By the way, there is an idea that impurities contained in water affect the absorbance by diluting the concentration of the measurement object. Therefore, there is an idea that the measurement wavelength is deliberately excluded from the wavelength having the maximum absorption of the measurement object, and the concentration of the measurement object is not intentionally diluted (for example, Patent Document 3). However, in the present embodiment, the influence of impurities contained in water on the absorbance is negligible (Example 2 below). Rather, by removing the measurement wavelength from the wavelength having the maximum absorption of the measurement object. The effect is greater (Example 1 below). Therefore, in this embodiment, after mixing with a spatula or the like, it is preferable to add water to the waste to appropriately dilute the concentration of the measurement object.

  In the present embodiment, a parameter called a liquid-solid ratio defined by the mass of water / the mass of waste is employed as a parameter representing the degree of dilution. The liquid-solid ratio of the sample is not particularly limited, but the liquid-solid ratio is preferably 10 or more and 1000 or less, more preferably 50 or more and 500 or less, and further preferably 100 or more and 300 or less. If the liquid-solid ratio is too small, the degree of dilution is not sufficient, and the absorbance may exceed the measurement upper limit of the measuring instrument when measuring the absorbance of the sample. Moreover, insolubilization of heavy metals may not proceed sufficiently, and subsequent solid-liquid separation may not proceed properly. If the liquid-solid ratio is too large, the absorbance may be too small and the accuracy of the absorbance of the sample may be lacking. In addition, a large apparatus is required to promote insolubilization, which is inefficient.

  Further, the type of water is not particularly limited, but the water is preferably distilled water or pure water in order to minimize the influence of impurities contained in the water on the absorbance.

  In the present embodiment, the content of the chelated metal that is a reaction product of the unreacted unreacted chelating agent and the metal compound in the reaction of the heavy metal and the chelating agent contained in the waste is measured. Therefore, in the reaction between the heavy metal and the chelating agent, the addition amount of the chelating agent needs to be excessive, that is, more than the chemical equivalent required for the reaction with the heavy metal contained in the waste. If the amount of the chelating agent added is less than the above chemical equivalent, it is not preferable in that the unreacted chelating agent is not produced in the first place.

  The reaction time between the heavy metal and the chelating agent is not particularly limited, but is preferably 5 minutes or more and 60 minutes or less, more preferably 10 minutes or more and 30 minutes or less, and further preferably 10 minutes or more and 20 minutes or less. preferable. If the reaction time is too short, the chelation reaction may not reach equilibrium. If the reaction time is too long, the reaction between the heavy metal and the chelating agent continues even though the chelation reaction has already reached equilibrium, which is inefficient.

[Solid-liquid separation step S2]
In the solid-liquid separation step S2, after the chelating agent addition step S2, the reaction product of the heavy metal and the chelating agent and the solid-liquid mixed sample that has not reacted with the heavy metal and contains the liquid unreacted chelating agent are subjected to solid-liquid separation. It is a process to do.

  The method of solid-liquid separation is not particularly limited, and examples thereof include sedimentation separation, filtration, centrifugation, and membrane separation. Among them, it is preferable to employ filtration as a technique for removing the reaction product because it is excellent in separability between a solid and a liquid and is simple. Filtration is preferably performed using glass fiber filter paper or a membrane filter.

  The pore size of the filter is not particularly limited, but considering the separability between the reaction product that is a solid and the unreacted chelating agent that is a liquid, the filtration time, etc., the pore size of the filter is 0.45 μm or more and 1 It is preferably 0.0 μm or less, and more preferably 0.80 μm or more and 1 μm or less.

[PH buffer addition step S3]
The pH buffering agent adding step S3 is a step of adding a pH buffering agent to the sample before the metal compound adding step S4 described later. As mentioned above, when the sample is alkaline, when adding a metal compound to the sample, the metal ions in the metal compound react with the hydroxide ions to form insoluble hydroxides, which is necessary for the disposal of waste. May affect the accuracy of calculating the amount of a chelating agent. Therefore, it is preferable to adjust the pH of the sample by performing a pH buffering agent adding step S3.

[Metal compound addition step S4]
The metal compound addition step S4 is a step of adding a metal compound to the sample after the addition of the chelating agent and chelating the metal compound with the heavy metal and the unreacted unreacted chelating agent in the chelating agent addition step S1.

[Absorbance measurement step S5]
The absorbance measurement step S5 is a step of measuring the absorbance of the chelated metal-containing sample containing the chelated metal at a wavelength capable of measuring the content of the chelated metal that is a reaction product of the unreacted chelating agent and the metal compound. It is.

[Chelating agent amount calculation step S6]
The chelating agent amount calculating step S6 is a step of calculating the amount of chelating agent necessary for the treatment of the waste based on the measurement result in the absorbance measuring step S5. The calculation method is not particularly limited, for example, using a calibration curve indicating the relationship between the concentration of the chelated metal that is a reaction product of the chelating agent and the metal compound and the absorbance at the measurement wavelength, Calculate the concentration of chelating metal contained in the chelated metal-containing sample from the absorbance of the chelated metal-containing sample minus the absorbance of the blank test, and calculate the amount of chelating agent required for waste treatment from this concentration To do.

  By the way, the blank test is to minimize the influence of many difficult-to-specify components contained in waste on the absorbance and estimate the amount of chemicals required for insolubilization of heavy metals contained in waste more accurately. Do. Therefore, the blank test is the same for all samples except that no chelating agent is added, that is, from the solid-liquid separation step S2 to the absorbance measurement step S5 except that no chelating agent is added in the above-described chelating agent addition step S1. It is preferable to measure the absorbance by going through the same steps all the way.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these.

  In all the following experiments, municipal waste incineration fly ash was used as waste, and the same sample was used for all. In addition, dithiocarbamate (product name: K-8122, manufactured by Kurita Kogyo Co., Ltd.) was used as the chelating agent.

<Preliminary experiment>
First, in order to ascertain the appropriate amount of chelate added to reliably meet the lead reclamation standard value (less than 0.3 mg / L), the amount of chelate added that satisfies the lead analysis lower limit (less than 0.05 mg / L) is appropriate. Preliminary experiments were conducted with a moderate addition amount.

  After adding 30 wt% of distilled water to 50 g of fly ash, 0 wt% (no addition), 1.5 wt%, 2.0 wt%, 2.5 wt% of chelating agent with respect to flyash % And then mixed with a spatula to prepare four samples. Next, 50 g of sample and 500 ml of distilled water are added to a 500 mL container so that the liquid-solid ratio defined by the mass of water / the mass of fly ash is 10, and the mixture is shaken horizontally for 6 hours. Obtained. Thereafter, the obtained eluate was filtered using a membrane filter having a pore diameter of 1 μm, and the lead concentration in the liquid was measured by an atomic absorption method.

  FIG. 3 shows the relationship between the chelating agent addition rate for fly ash and the lead concentration in the eluate obtained as described above. From FIG. 3, it was found that the appropriate amount of chelating agent added satisfying the lower limit of analysis of lead (less than 0.05 mg / L) was 2.5% by weight with respect to fly ash.

<Experiment 1> Comparison of measurement accuracy of chelating agent addition amount

[Example 1] Color reagent: chelating metal, measurement wavelength: 525 nm
[Create calibration curve]
The calibration curve in Example 1 (not shown) was obtained by linearly approximating the relationship between the content of the chelated metal that is a reaction product of the chelating agent and iron (II) chloride tetrahydrate and the absorbance at a wavelength of 525 nm. ).

[Calculation of appropriate addition rate]
In order to dilute the concentration of the measurement object contained in the sample in a 500 mL capacity container, 500 mL of distilled water is added so that the liquid-solid ratio becomes 200, and then a rotor is inserted and magnetic. While stirring with a stirrer, 5 parts by weight of a chelating agent was further added to fly ash and stirred for 20 minutes to obtain an eluate. Subsequently, this eluate was filtered using a membrane filter having a pore diameter of 1 μm. To 10 mL of this filtrate, 1 mL of a mixed solution containing 500 mg / L each of piperazine-1,4-dietansulfonic acid, which is a pH buffering agent, and iron (II) chloride tetrahydrate, which is a metal compound, is added. Absorbance (a) at 525 nm was measured. Further, the same operation was performed except that no chelating agent was added, and the measured absorbance was defined as the absorbance (b) of the blank test. The difference (ab) between the absorbance of the chelating agent-containing sample and the absorbance of the blank test obtained as described above was taken as the absorbance of the actual chelated metal in the chelating agent-containing sample.

  Subsequently, the chelated metal concentration corresponding to this absorbance was calculated from a calibration curve prepared in advance. The chelated metal concentration calculated in this manner corresponds to the residual chelating agent concentration in the solution. From the concentration of the residual chelating agent and the solid-liquid ratio of the eluate, the addition rate of the residual chelating agent to fly ash was determined. Subsequently, the difference between the addition rate of the chelating agent and the residual chelating agent was determined as the appropriate addition rate. Table 1 shows the measured values and calculated values.

[Comparative Example 1] Coloring reagent: chelating agent, measurement wavelength: 286 nm
[Create calibration curve]
The relationship between the content of the chelating agent and the absorbance at a wavelength of 286 nm was linearly approximated to obtain a calibration curve (not shown) in Comparative Example 1.

[Calculation of appropriate addition rate]
Add 2.5 g of fly ash into a 500 mL container, add 500 mL of distilled water to a liquid-solid ratio of 200, add a rotor and stir with a magnetic stirrer to further add chelating agent to fly ash. 5 wt% of the mixture was added and stirred for 20 minutes to obtain an eluate. Subsequently, this eluate was filtered using a membrane filter having a pore diameter of 1 μm. The absorbance of the chelating agent-containing sample at a wavelength of 286 nm of this filtrate was measured. Further, the same operation was performed except that no chelating agent was added, and the measured absorbance was taken as the absorbance in the blank test. The difference between the absorbance (a) of the chelating agent-containing sample and the absorbance (b) of the blank test obtained as described above was taken as the absorbance of the residual chelating agent contained in the chelating agent-containing sample.

  Subsequently, the chelating agent concentration corresponding to this absorbance was calculated from a calibration curve prepared in advance. From the concentration of the residual chelating agent and the solid-liquid ratio of the eluate, the addition rate of the residual chelating agent to fly ash was determined. Subsequently, the difference between the addition rate of the chelating agent and the residual chelating agent was determined as the appropriate addition rate. Table 1 shows the measured values and calculated values.

[Comparative Example 2] Color reagent: chelating agent, measurement wavelength: 350 nm
Except for setting the wavelength at the time of measuring absorbance to 350 nm, the same operation as in Comparative Example 1 was performed to calculate the appropriate addition rate. Table 1 shows the measured values and calculated values.

〔result〕
The optimum addition rate determined according to Example 1 is 2.4% by weight, and it is appropriate to satisfy the addition rate of the chelate additive determined by the preliminary experiment, that is, the lower limit of analysis of lead (less than 0.05 mg / L). It almost coincided with the chelate addition rate (2.5% by weight).

  On the other hand, the appropriate addition rate calculated | required by the comparative example 1 was 2.8 weight%, and was a little excessive compared with the addition rate of the chelate additive calculated | required by the preliminary experiment. Moreover, in the comparative example 2, the calculated residual chelating agent addition rate exceeded the original chelating agent addition rate, and an appropriate addition rate was not able to be calculated | required. When determining the appropriate addition rate by measuring the absorbance when the chelating agent itself is a color reagent and the measurement wavelength is 286 nm or 350 nm, a number of difficultly specified components contained in fly ash affected the absorbance. It seems to be.

<Experiment 2> Effect of pH buffer, metal compound and components in eluate on absorbance

[Example 2] Color reagent: chelating metal Absorbance (a) was measured by the same operation as in Example 1 except that the measurement wavelength of absorbance was a continuous range of 200 nm to 700 nm. The results are shown in FIG.

[Comparative Example 3] Color Reagent: Chelating Agent Absorbance (a) was measured by the same operation as Comparative Example 1 except that the measurement wavelength of absorbance was a continuous range of 200 nm to 700 nm. The results are shown in FIG.

[Comparative Example 4] Color reagent: None, pH buffer and metal compound: None Absorbance (a) was measured in the same manner as in Comparative Example 3 except that no chelating agent was added. The results are shown in FIG.

[Comparative Example 5] Color reagent: None, pH buffer and metal compound: Existence Absorbance (a) was measured in the same manner as in Example 2 except that no chelating agent was added. The results are shown in FIG.

〔result〕
From Comparative Example 4 and Comparative Example 5 in FIG. 4, when the measurement wavelength is 400 nm or more and 700 nm or less, piperazine-1,4-dietansulfonic acid that is a pH buffering agent and iron (II) chloride that is a metal compound It can be said that the effect of tetrahydrate on the absorbance is extremely small. Moreover, when a chelating metal is used as a color reagent as in Example 2, it can be said that the appropriate addition rate of the chelating agent can be accurately estimated because it has a sufficiently high absorbance in the range of the measurement wavelength.

  On the other hand, it can be said from Comparative Examples 3 and 4 that when the measurement wavelength is 215 nm or more and 350 nm or less, the influence of components other than the chelating agent in the eluate on the absorbance cannot be ignored. Therefore, when a chelating agent is used as a color reagent and a wavelength of 215 nm or more and 350 nm or less is used as a measurement wavelength, components other than the chelating agent in the eluate may affect the absorbance and cause measurement errors.

  According to the chelating agent addition amount determination apparatus or the chelating agent addition amount determination method of the present invention, fly ash, incineration ash, and soot generated at a garbage incineration site; mineral waste discharged from a mine, activated sludge generated at the time of wastewater treatment, It is possible to determine the amount of chelating agent necessary for preventing heavy metals from eluting from contaminated soil such as a chemical factory site, etc., simply, quickly, inexpensively and accurately.

DESCRIPTION OF SYMBOLS 1 Chelating agent addition amount determination apparatus 2 Absorbance measuring part 3 Chelating agent calculation part S1 Chelating agent addition process S2 Solid-liquid separation process S3 pH buffer addition process S4 Metal compound addition process S5 Absorbance measuring process S6 Chelating agent quantity calculation process

[Metal compounds]
The kind of metal compound to be reacted with the unreacted chelating agent is not particularly limited, it reacts with unreacted chelating agent, in that it can suitably generate chelate gold genus, metal compounds, divalent iron salt, tri- One or more metal salts selected from ferrous salts, copper salts, nickel salts, cadmium salts and magnesium salts are preferred. Moreover, it is preferable that a metal compound is a sulfate or hydrochloride. Since no special treatment is required at the time of discharge after the completion of analytical work or the degree of color development, metal compounds are divalent iron salts or trivalent iron salts such as ferrous chloride, ferrous sulfate, ferric chloride. Or it is more preferable that it is ferric sulfate.

Claims (9)

In the reaction of heavy metal and chelating agent contained in waste, the chelating metal is contained at a wavelength capable of measuring the content of the chelating metal that is a reaction product of the unreacted unreacted chelating agent and the metal compound. Absorbance measuring means for measuring the absorbance of the chelated metal-containing sample,
A chelating agent addition amount determining device, comprising: a chelating agent amount calculating unit that calculates an amount of a chelating agent necessary for the treatment of the waste based on a measurement result by the absorbance measuring unit.   The chelating agent addition amount determination device according to claim 1, wherein the chelating metal-containing sample is a sample that substantially does not contain a reaction product of the heavy metal and the chelating agent.   The chelating agent addition amount determination device according to claim 1 or 2, wherein the chelating metal-containing sample contains a pH buffer.   The chelating agent addition amount determining apparatus according to any one of claims 1 to 3, wherein the chelating agent includes a dithiocarbamic acid-based chelating agent.   5. The metal compound according to claim 1, wherein the metal compound includes one or more metal salts selected from divalent iron salts, trivalent iron salts, copper salts, nickel salts, cadmium salts, and magnesium salts. The chelating agent addition amount determination device described.   6. The chelating agent addition amount determination device according to claim 1, wherein the absorbance measurement unit measures the absorbance of the chelated metal-containing sample at a wavelength of 400 nm to 700 nm. A chelating agent addition step of adding an excessive amount of a chelating agent to waste containing heavy metal and insolubilizing the heavy metal;
A metal compound addition step of chelating the metal compound with an unreacted chelating agent unreacted with the heavy metal in the chelating agent addition step, adding a metal compound to the sample after addition of the chelating agent;
An absorbance measurement step of measuring the absorbance of the chelated metal-containing sample containing the chelated metal at a wavelength capable of measuring the content of the chelated metal that is a reaction product of the unreacted chelating agent and the metal compound; ,
A chelating agent addition amount determining method including a chelating agent amount calculating step of calculating an amount of a chelating agent necessary for the treatment of the waste based on a measurement result in the absorbance measuring step. After the chelating agent addition step, the reaction product of the heavy metal and the chelating agent, and the solid-liquid separation for solid-liquid separation of the solid-liquid mixed sample that is unreacted with the heavy metal and contains the liquid unreacted chelating agent Further comprising a step,
The chelating agent addition amount determination method according to claim 7, wherein the metal compound addition step is a step performed after the solid-liquid separation step.   The chelating agent addition amount determination method according to claim 7 or 8, further comprising a pH buffering agent adding step of adding a pH buffering agent to the sample before the metal compound adding step.

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