JPH0871597A - Separation of harmful metal in sludge - Google Patents

Abstract

PURPOSE: To simply separate and remove a heavy metal contained in sludge. CONSTITUTION: An acid such as sulfuric acid 7 is added to sludge containing a heavy metal to lower the pH of the sludge to elute the heavy metal and this sludge is electrolyzed in an electrolytic cell 3 having an anode and a cathode both of which are constituted of iron. Subsequently, the polarities of both electrodes are converted to peel the ferrite bonded to the electrode plates and this ferrite is separated from sludge by a magnetic separator 4. A harmful nonferrous metal is separated as an iron compd. by the use of magnetism.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating metals contained in sewage sludge and the like, which are harmful to the human body and the like.

[0002]

2. Description of the Related Art It is well known that mercury and cadmium contained in sewage sludge are harmful to humans.
The large amount of sewage sludge, which contains fertilizer and is known to be effective for agricultural crops, cannot be used at present. Then, as a means for separating the harmful metal from the sludge, the sludge containing the metal is solidified and discarded so that the harmful metal is not eluted.

[0003]

The amount of sludge containing harmful metals as described above increases year by year, requires a large amount of solidifying material to solidify, and has a limit to the dumping site. There is. Further, as described above, there is a problem in processing harmful metals in that it can be used by composting.

[0004]

The present invention can solve the above-mentioned problems, and the gist of the present invention is to add sulfuric acid or the like to sludge containing harmful metals such as cadmium to remove PH. After reducing and ionizing the harmful metal to elute it, and then electrolyzing this sludge with iron electrodes with both positive and negative poles, this electrolytic solution is polarity-converted in the same electrolytic cell and electrolyzed, and the electrolytic solution is magnetically separated. It is designed to be processed by a vessel.

[0005]

That is, according to the present invention, sludge containing harmful metals is treated with an acid to dissolve the harmful metals in the liquid, and the sludge is electrolyzed by an iron electrode, whereby a compound of the harmful metal and iron ( Ferrite) is deposited, and the ferrite is peeled from the electrode by changing the polarity, and the peeled iron compound is separated from other contaminants by using magnetic force. The present invention will be specifically described below with reference to the drawings.

[0006]

1 is a block diagram of a method for removing harmful metals according to the present invention. Reference numeral 1 is a sludge tank, 2 is a harmful metal elution tank, 3 is an electrolytic tank, 4 is a magnetic separation tank, 5 Indicates a separation ferrite tank, 6 indicates a treated sludge tank, and 7 indicates a sulfuric acid tank to be added. In the illustrated example, sulfuric acid is used to reduce PH.

FIG. 2 is a schematic perspective view of the electrolytic cell 3 in which the electrode plate 3a is made of iron for both the anode and the cathode.
Reference numeral 8 is a polarity switching device, 9 is a power source, 10 is an electrolysis sludge supply port, and 11 is an electrolysis-treated sludge removal port.

Next, a method for removing harmful metals from sludge using the above-mentioned apparatus will be described. First, the sulfuric acid in the sulfuric acid tank 7 is added to the sludge introduced into the elution tank 2 to reduce the pH of the sludge, and the harmful metals contained therein are ionized and eluted.

Then, the treated sludge is introduced into the electrolytic cell 3 and is energized for electrolysis. By doing so, iron ions are eluted from the anode, part of which produces iron hydroxide by the hydration reaction, and raises the pH of sludge. On the other hand, other part of iron ions moves to the cathode together with harmful metal ions, is oxidized by oxygen generated by electrolysis, and adsorbs the harmful metal ions, and performs ferrite (iron compound) which undergoes oxidative growth ferrite reaction. To form.

The formed ferrite adheres to the cathode and is separated from the sludge. Since the ferrite attached to the cathode does not redissolve, it is peeled from the electrode plate (which has been converted to the anode) by changing the electrode pole.

In this way, since the peeled ferrite is a magnetic substance, it can be separated from the sludge by the magnetic separation means in the next stage. That is, the method according to the present invention converts harmful metal scattered in sludge into insoluble ferrite by electrolyzing with an iron electrode, peels from the electrode by converting the electrode pole, and collects with a magnet. The collection operation is simple, and
Only harmful metals can be reliably separated from sludge.

[0012] In this way, the sludge from which harmful metals have been separated and removed is not only safe as it contains organic substances and is used in agriculture, but it is also modified by the action of iron hydroxide produced by electrolysis. Therefore, the dehydration property is improved and the dehydration work in the latter stage of the treatment can be facilitated.

The results of a test operation on the sludge containing Zn by the above treatment operation were as follows. When sludge containing 8.7 mg of Zn per liter was treated by the above means, the amount of Zn contained in the treated sludge was 2.22.
It was mg. That is, the amount of removed Zn was 6.48.
mg, 74.5% of the amount of Zn contained in the original sludge
Could be separated and removed.

[0014]

As described above, the present invention can easily and reliably remove harmful metals contained in sewage sludge and the like, which were conventionally difficult to separate and remove, and can be reused as agricultural compost or the like. In addition to being made available, the sludge treated according to the present invention has an improved post-process dehydration treatment property, and can completely solve the conventional problems in treating and disposing of this type of sludge.

[Brief description of drawings]

FIG. 1 is a block diagram showing steps of a sludge treatment method according to the present invention.

FIG. 2 is a perspective view of an electrolysis device used for treating sludge according to the present invention.

[Explanation of symbols]

 3 Electrolyzer 3a Electrode

Claims (1)

[Claims] 1. Sulfuric acid is added to sludge containing harmful metals to obtain P.
H is lowered to ionize and elute the harmful metal, and then the sludge is electrolyzed with the positive and negative electrodes 3a together with the iron electrode 3a, and then the electrolytic solution is subjected to polarity conversion in the same electrolytic cell 3 to be electrolyzed, A method for separating harmful metals in sludge, which is characterized by treating the electrolytic solution with a magnetic separator.