JPS63278589A - Method for making fly ash harmless - Google Patents

Abstract

PURPOSE:To make fly ash harmless by adding requisite amts. of a chelating agent and an iron salt while adding a requisite amt. of water to fly ash to humidity the ash and kneading the ash. CONSTITUTION:Fly ash is supplied into the main body 1 of a vibrating mixer 7 from a supply port 5. The ash is mixed by a mixing medium 4. Water and a pH regulator, if necessary, are then added to the ash. A chelating agent and an aq. soln. of an iron salt such as ferric chloride are added to the ash, and mixed. By this method, the cost of chemicals can be reduced, and the operation, maintenance, and control can be remarkably simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention is applicable to ash discharged together with exhaust gas from incineration plants for municipal waste, industrial waste, etc., such as EP ash, which is ash collected by electrostatic precipitators, and bag filters. The present invention relates to a processing method for rendering harmless ash, etc. (this type of ash is referred to as "fly ash" throughout this specification) collected in the field.

Prior art and its problems This type of fly ash contains large amounts of chlorides of heavy metals that are harmful to the human body, and in particular, the contents of cadmium, lead, and mercury are classified as ``hazardous industrial waste.'' There is a tendency to exceed the elution standard value stipulated in the Prime Minister's Office Ordinance Establishing Such Judgment Standards.

Therefore, recently, as shown in attached Figure 3 (a) and (b), methods have been developed to solidify EP ash by adding and mixing cement and water, and to extract heavy metals contained in EP ash using acid. Increasingly, EP ash is being treated to make it harmless.

However, in these treatment methods, the cost of adding cement and chemicals for fixing the extracted heavy metals is considerable, and furthermore, the operation and maintenance of this treatment equipment is extremely troublesome.

In view of the above-mentioned circumstances, it is an object of the present invention to provide a method for detoxifying fly ash that can be carried out with the minimum necessary chemical cost and simple operation and maintenance.

Means for Solving the Problems The fly ash detoxification treatment method according to the present invention involves adding a required amount of water and, if necessary, a required amount of a pH adjuster to the fly ash, and humidifying the fly ash using a vibrating mixer. The method is characterized in that the chelating agent and iron salt are added in required amounts during kneading.

In a preferred embodiment of the invention, the moisture content of the final sludge is between 15 and 50% on a wet basis.

In general, fly ash often exhibits alkalinity with a pH of about 12, so if necessary, an acid such as hydrochloric acid is added to it to adjust its I)H. In the humidification and kneading of fly ash, the pH before the addition of the chelating agent is set to 3 to 10, and the pH after the completion of this treatment is set to 9 to 10.

The amount of the pH adjuster added during humidification and kneading of fly ash can be set in advance by automatic titration using a sample of fly ash.

The amounts of the chelating agent and iron salt added are appropriately set depending on the properties of the fly ash. As the chelating agent, a commercially available heavy metal fixing agent is used.

A vibrating mixer is preferably used as the fly ash kneading means.

By using a vibrating mixer, the following effects are achieved.

■ The excitation force applied to the fly ash during humidification and kneading allows moisture to spread homogeneously through the fly ash.

Therefore, the amount of water to be added can be suppressed to the necessary minimum, and the reaction can be carried out homogeneously throughout.

■ Since the amount of water can be suppressed as described above, the moisture content of the finally obtained detoxified sludge can also be kept low. Therefore, there is no need to subject the sludge to post-treatment such as dehydration, and therefore no wastewater is generated.

■ Due to the mechanism of the vibratory mixer, the relative speed difference between the fly ash and the internal structure of the mixer is very small. Therefore, wear on internal structural parts is extremely low.

An example of a vibratory mixer is shown in FIGS. 1 and 2. That is, the mixer main body (1) in the shape of a horizontally cylindrical body is supported by a spring (2).
) is supported on the floor (3) by the same body (1)
is made to vibrate by means such as a vibration motor. A large number of mixed media (4) are contained inside the main body (1). A supply port (5) is provided at the top of one end of the main body (1), and a discharge port (6) is provided at the bottom of the other end. In this way, a vibratory mixer (7) is constructed.

The fly ash supplied from the supply port (5) into the vibrating main body (1) is well mixed by the mixing medium (4). When water and chemicals are added here, the fly ash is effectively humidified and kneaded and reacts well with them.

Effects of the Invention Since the method according to the present invention is configured as described above, the cost of the chemicals used can be kept to the necessary minimum and operation and maintenance management can be greatly simplified compared to methods according to the prior art. can be converted into

Embodiments Next, embodiments of the present invention will be specifically described based on the drawings.

In FIGS. 1 and 2, the vibratory mixer (7) is vibrated at an acceleration of about 6G. From the hopper (8) through the feeder (9) to the supply port (5) of the vibratory mixer (7)
::6 kg of EP ash was supplied. Next, supply port (5)
1,160 ml of water and 240 ml of 35% hydrochloric acid were added to the mixture, and 60 ml of a 10% chelate aqueous solution (heavy metal fixative manufactured by Miyoshi Oil Co., Ltd., trade name "Epofloc L'-IJ") was added to remove crosstalk. This continued for 10 minutes.Next, 170 ml of 1% ferric chloride aqueous solution was added and mixing continued for 15 minutes.The thus finally obtained detoxified sludge was taken out from the outlet (6).

During kneading, it was observed that the EP ash was homogeneously distributed with moisture, forming a slurry and obtaining good reaction conditions.

The final sludge was clay-like. When the bulk specific gravity of this was measured, it was 1.67, which was reduced to about 115 compared to the bulk specific gravity of 0.33 before treatment.

In addition, the pH and moisture content of this sludge were measured, and further, as shown below, according to the method specified in the "Method for testing metals, etc. contained in industrial waste (February 17, 1970, Announcement 13)", When we conducted an elution test for heavy metals, all of the measured values obtained were as shown in Table 1. The results sufficiently passed the standard values set forth in the General Assembly 5).

Elution test method for heavy metals Mix solid sludge and pure water (pH -6°3) at a weight/volume ratio of 10%, and mix the resulting mixture (500ml or more) at room temperature and pressure for 6 hours. Shake continuously. The sample liquid thus obtained was filtered through a glass fiber filter paper with a pore size of 1 micron, and the total mercury, cadmium, and lead in this filtrate were all quantitatively analyzed by atomic absorption spectrophotometry.

(Margin below)

[Brief explanation of the drawing]

Fig. 1 is a side view of a vibratory mixer showing an embodiment of the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 (
A) (B) is a flow sheet showing a method using conventional technology;
Figure (c) is a flow sheet showing the method according to the present invention. Figure 1 1 Figure 2

Claims (4)

[Claims] (1) Fly ash with the required amount of water and, if necessary, the required amount of p.
A method for detoxifying fly ash, which comprises adding a chelating agent and iron salt in required amounts while humidifying and kneading the fly ash using a vibratory mixer with the addition of an H adjuster. (2) The method according to claim 1, wherein the moisture content of the finally obtained sludge is set to 15 to 50% on a wet basis. (3) The method according to claim 1 or 2, wherein the fly ash has a pH of 3 to 10 during kneading. (4) The method according to any one of claims 1 to 3, wherein the amount of the pH adjuster is preset by automatic titration of a sample of fly ash.