JP3237465B2 - Method for determining required amount of liquid chelating agent for fly ash treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for adding a liquid chelating agent to fly ash and treating the amount of the liquid chelating agent necessary for preventing the elution of heavy metals from the fly ash. How to decide.

[0002]

2. Description of the Related Art Fly ash (dust) may degrade the working environment and cause health problems for workers. Therefore, the following waste treatment specified by law (Waste Disposal Law) It is obliged to process according to law.

Chemical treatment method Melt solidification method Cement solidification method Stabilization method with acid and other solvents Among the treatment methods described above, in the treatment by the chemical treatment method,
Liquid chelating agents may be used for the purpose of preventing the elution of heavy metals in fly ash.

Examples of the liquid chelating agent include diethyldithiocarbamic acid and salts thereof, aliphatic polydithiocarbamic acids such as ethylenebisdithiocarbamic acid and salts thereof, polyamine derivatives obtained by introducing a dithiocarboxyl group into a polyamine as an N substituent, and polyethyleneimine. Sulfur compounds such as polyethyleneimine derivatives and thiols having a dithiocarboxyl group introduced as an N substituent are known.

[0005] In order to determine the required amount of the liquid chelating agent, a fly ash is pretreated by adding a liquid chelating agent to the fly ash in a desk test, and further, a method specified by law (Notification 1 of the Environment Agency).
In general, the effect is determined by performing a dissolution test (measurement of dissolution concentration) of heavy metals according to No. 3 method).

On the other hand, the components or properties of fly ash vary greatly depending on its incineration system, dust collection system, harmful gas removal system, and the type of incineration.

[0007]

However, in the above-mentioned conventional method of analyzing the elution amount of heavy metals according to the Environment Agency Notification No. 13 method, it takes a long time to evaluate, and the above-mentioned test is performed every time the properties of fly ash change. It is not easy to do. For this reason, conventionally, it has been difficult to perform appropriate chemical treatment in accordance with fluctuations in the properties of fly ash at the site.

The present invention solves the above-mentioned conventional problems, and enables the required amount of a liquid chelating agent to be added easily and quickly in a chemical treatment of fly ash by a simple operation, thereby performing an appropriate chemical treatment. It is an object of the present invention to provide a method for determining a required addition amount of a liquid chelating agent for fly ash treatment that enables the above.

[0009]

According to a first aspect of the present invention, there is provided a method for determining a required amount of a liquid chelating agent for treating fly ash, the method comprising: mixing a fly ash and a liquid chelating agent with water; ) Is measured, and the required addition amount of the liquid chelating agent is determined from the measured value.

According to a second aspect of the present invention, there is provided a method for determining a required amount of a liquid chelating agent for treating fly ash, comprising measuring the ORP and pH of a solution obtained by mixing the fly ash and the liquid chelating agent with water, and measuring these measured values. The required amount of the liquid chelating agent to be added is determined from the above formula.

The method for determining the required amount of the liquid chelating agent for fly ash treatment according to claim 3 is the method according to claim 1 or 2,
The mixing ratio of water and fly ash is 10 to 10 in solid-liquid ratio (L / S).
00 is set.

The method for determining the required amount of the liquid chelating agent for fly ash treatment of the present invention will be described in detail below.

The method of the present invention can be specifically carried out by the following method.

[I] A fly ash treated with a chelating agent is used to prepare a test solution in accordance with the test method of the Environment Agency Notification No. 13, and the ORP or OR of the solution (slurry) before the filtration is performed.
P and pH are measured, and the effect of the chelating agent is quickly determined by comparing with the value of the condition under which the chelating agent stabilizes the heavy metal.
Determine the required amount of chelating agent to be added.

[II] Fly ash raw ash solid-liquid ratio (L / S) = 1
Dissolve in water (preferably pure water) at 0 to 1000, measure the ORP of the solution, or the ORP and pH, and add the chelating agent dropwise until the value reaches the value of the condition under which the chelating agent stabilizes heavy metals. The required amount of the chelating agent is determined promptly.

Here, the conditions under which the chelating agent stabilizes the heavy metal can be the following conditions, as apparent from the operation section described later and Examples 1 and 2.

[0017]

[Table 1]

As a simple and reliable method, ORP is-
There is a method of determining the necessary amount of the chelating agent to be 120 to -150 mV or less.

[0019]

According to the present invention, as shown in Examples 1 and 2 below, the conditions for the liquid chelating agent to stabilize the heavy metal in the fly ash are as follows: the fly ash to be treated and the liquid chelating agent are dissolved in water. It was found that it depends on the ORP, or pH and ORP.

That is, as is clear from the results of Example 1, for example, the pH at the time of dissolving the fly ash to be treated in water and adding a chelating agent, or the fly ash treated with the chelating agent is added to water. PH when added is 12.4 and ORP is-
ORP at 120 to -150 mV or lower, or when the pH is 8.0, or when the pH is 4.0
Is 120 to 150 mV or less, Pb which is a heavy metal can be stabilized.

The pH when the fly ash to be treated is dissolved in water and a chelating agent is added, or when the fly ash to be treated with the chelating agent is added to water, the pH is 12.4 or 8.0. Or the pH is 4.0 and the ORP is 1
In the case of 20 to 150 mV or less, Cd which is a heavy metal can be stabilized.

Furthermore, the notification 1 of the Environment Agency of various fly ash of Example 2
From the analysis of the eluate in the No. 3 test, the pH was 11.7 for various fly ash irrespective of the type and amount of the chelating agent.
It can be seen that Pb can be stabilized when the ORP is -120 to -150 mV or lower at ~ 12.5. In other words, the ORP of the eluate is -120 to -150.
Pb can be stabilized by adding a chelating agent so as to have a mV or less.

[0023]

The present invention will be described more specifically with reference to the following examples.

In the liquid chelating agents used in the following examples, chelating agents A and B are dithiocarbamic acid compounds, and chelating agent C is an imine compound.

Example 1 Analysis of test fly ash Refuse type: municipal waste, furnace type: stoker furnace, exhaust gas treatment method: dry type, dust collection method: analysis of components of fly ash generated by EP (electric dust collection) and Environment Agency Test No. 13 was conducted, and the results are shown in Tables 2 and 3.

[0026]

[Table 2]

[0027]

[Table 3]

Treatment of Fly Ash 70 g of the test fly ash, 21 g of pure water (solid-liquid ratio (L / S): 0.3) and liquid chelating agent A were put into a 500 ml polybeaker at 4% by weight based on the fly ash. The mixture was kneaded with a spatula for about 5 minutes to prepare a treated ash.

Confirmation of Stabilization (Prevention of Elution) Effect of Heavy Metals 700 g of pure water and 70 g of the above treated ash were put into a 1-liter glass beaker, and the lid was closed (solid-liquid ratio (L / S): 1).
3.3). While stirring the solution in the beaker and simultaneously aerating the solution with air (0.7 L / min),
30% by weight nitric acid or 48% by weight by pH controller
The pH was adjusted to a predetermined value by adding an aqueous sodium hydroxide solution.

After the stirring was started, 50 ml of the solution in the beaker was sampled together with the solid matter over time, and immediately
ORP was measured with an RP meter. Then, 0.45μ
Suction filtration with a membrane filter of m
b, Cd concentrations were measured with an atomic absorption spectrophotometer.

Results FIG. 1 shows the relationship among the pH, ORP, and Pb elution concentration of the solution.
FIG. 2 shows the relationship among the pH, ORP, and Cd elution concentration of the solution.

Discussion From FIGS. 1 and 2, the following can be concluded.

Regarding Pb (a) When the solution has a pH of 12.4, the ORP is from -120 to
Stable at -150 mV or less (b) Stable when the solution is at pH 8.0 (c) ORP is 150 to 20 when the solution is at pH 4.0
Stable Cd at 0 mV or less (d) Stable when the solution is at pH 12.4 and pH 8.0 (e) When the solution is at pH 4.0, the ORP is 120 to 15
Stable at 0 mV or less From these results, the necessary amount of the chelating agent to be added is determined for Pb so as to satisfy the above conditions (a) to (c). It can be understood that the necessary amount of the chelating agent should be determined so as to satisfy the condition (1).

Example 2 Chelating agents A to C were added to fly ash A to K discharged in the incineration process of municipal waste A to K at the ratios shown in Tables 4 and 5, and Pb in a test of method No. 13 notified by the Environment Agency. The relationship between the concentration, ORP and pH was examined, and the results are shown in Tables 4 and 5.

Also, from the results of Tables 4 and 5, ORP and Pb
Fig. 3 shows a graph of the relationship with the concentration (logarithmic conversion value).
Shown in

According to Tables 4 and 5 and FIG. 3, the stabilizing effect of Pb (when the Pb elution concentration is 0.3 mg / l or less) is exhibited regardless of the type and amount of the chelating agent. ORP of eluate (pH 11.0 to 12.5) is -12
This is the time when it becomes 0 to -150 mV or less, and therefore, it can be seen that the addition amount of the chelating agent should be determined so that the ORP becomes -120 to -150 mV or less.

[0037]

[Table 4]

[0038]

[Table 5]

[0039]

As described above in detail, according to the method for determining the required amount of the liquid chelating agent for fly ash treatment according to the present invention, the OR of the solution obtained by mixing the fly ash and the liquid chelating agent with water is obtained.
By an extremely simple operation of measuring P, or pH and ORP, the amount of the chelating agent necessary for stabilizing heavy metals in fly ash can be determined. Therefore, according to the present invention, it is possible to easily perform appropriate chemical treatment that quickly responds to fluctuations in the properties of fly ash.

[Brief description of the drawings]

FIG. 1 is a graph showing the results (Pd elution concentration) of Example 1.

FIG. 2 is a graph showing the results (Cd elution concentration) of Example 1.

FIG. 3 is a graph showing the results of Example 2.

Claims (3)

(57) [Claims] 1. A fly ash characterized by measuring the oxidation-reduction potential of a solution obtained by mixing a fly ash and a liquid chelating agent with water, and determining the required addition amount of the liquid chelating agent from the measured value. A method for determining the required amount of a liquid chelating agent for treatment. 2. The method according to claim 1, wherein the redox potential and the pH of a solution obtained by mixing the fly ash and the liquid chelating agent with water are measured, and the required addition amount of the liquid chelating agent is determined from the measured values. To determine the required amount of added liquid chelating agent for fly ash treatment. 3. The method according to claim 1, wherein the mixing ratio of water and fly ash is 10 to 1000 in terms of a solid-liquid ratio (L / S). How to determine the required amount.