JP4844906B2 - Method and system for removing contaminants from solid materials - Google Patents

Description

  The present invention relates to a contaminant removal method and a removal system for quickly removing contaminants contained in a solid substance placed in a liquid.

Conventionally, waste sand discharged from a foundry and containing solid spilled sand and dust collection dust has been reused as a cement raw material and a roadbed material. However, due to the recent tightening of environmental purification regulations including soil including waste sand, it has become necessary to prevent pollutants such as heavy metals and halogens shown in Ministry of the Environment Notification No. 46 from exceeding the elution standard value. It was.
As a technique for preventing the elution of the pollutant from the solid substance, there are a method for insolubilizing the pollutant and a method for removing the pollutant (see Patent Document 1).

JP 2009-039664 A

Conventionally, as a technique for preventing the elution of contaminants from a solid substance, as disclosed in Patent Document 1, there is a method of dissolving heavy metals in soil using mineral acid and removing heavy metals.
As a problem of this processing method, it is necessary to use an expensive member that is resistant to acid in the construction of the equipment because it handles acid, and the initial cost may be high.

Conventionally, as a technique for preventing the elution of contaminants from a solid substance, as shown in FIG. 2, a method is used in which particles are collided with each other in water in a rotating drum to exfoliate contaminant particles, and then adsorb and remove. There is.
As a problem of this processing method, since the acid is handled, it is necessary to make the structure of the equipment an expensive member resistant to the acid, and the initial cost is high. In addition, a large amount of power is required such as rotating the rotating drum.

An object of the present invention is to provide a contaminant removal method and a removal system that remove contaminants contained in a solid substance at a low cost.
Conventionally, there is a method of insolubilizing contaminants as a technique for preventing the elution of contaminants from solid substances. However, this technique does not remove contaminants from solid substances, but is attached to solid substances. Therefore, it is not a subject of the present invention.

  In order to achieve the above object, a method for removing contaminants from a solid substance according to the present invention includes a step of immersing a solid substance containing a contaminant in a liquid filled in a reaction tank, and the solid substance is immersed in the process. A step of supplying bubbles into the liquid, a step of separating the solid content of the contaminant eluted in the liquid from the liquid by solid-liquid filtration, and fluorine and boron contained in the contaminant eluted in the liquid And a further separating step.

  Moreover, the pollutant removal method from the solid substance of the present invention is characterized in that the bubbles are microbubbles.

  Furthermore, the contaminant removal method from the solid substance of the present invention is characterized in that carbon dioxide is dissolved in the liquid by the bubbles.

Moreover, the contaminant removal method from the solid substance of the present invention is characterized by returning the liquid after the solid-liquid filtration and the separation of fluorine and boron to the reaction tank again.

In order to achieve the above object, a system for removing contaminants from a solid substance according to the present invention includes a means for eluting a contaminant from the solid substance by immersing the solid substance containing the contaminant in a liquid, Means for separating the pollutants from the liquid by solid-liquid filtration, means for separating fluorine and boron from the liquid after the solid-liquid filtration, and liquid after the solid-liquid filtration and separation of fluorine and boron are performed. It is characterized by comprising means for re-use.

According to the present invention, a solid substance containing a contaminant is immersed in a liquid filled in a reaction tank, air bubbles are supplied into the liquid, and the contaminant is extracted and removed from the solid substance. In the method for removing a substance, a step of immersing a solid substance containing the contaminant in a liquid filled in a reaction vessel, a step of supplying bubbles into the liquid in which the solid substance is immersed, and a liquid in the liquid Because it consists of a step of separating the solid content of the pollutant eluted from the liquid by solid-liquid filtration and a step of separating fluorine and boron contained in the pollutant eluted in the liquid from the liquid. Material removal processing can be performed, less equipment is required, and initial cost is low. Also, the running cost is low because there are few places that require power. Furthermore, since the pollutants are concentrated in the solid-liquid separation tank or adsorption tank, the volume and weight of the waste are small and the disposal cost is low. In addition, the life of the landfill site can be extended. In addition, toxic substances are removed from the washed casting sand and are not present in the sand. Therefore, there is an effect that safety is ensured when landfilling or reuse.

It is a flowchart of one Example of the contaminant removal method of this invention. It is a flowchart of one Example of a prior art.

Hereinafter, modes for carrying out the present invention will be described.
The present invention is a contaminant removal method for quickly removing contaminants contained in a solid substance placed in a liquid, and a step of immersing a solid substance containing a contaminant in a liquid filled in a reaction vessel Supplying air bubbles into the liquid in which the solid substance is immersed, separating the solid content of the contaminant eluted in the liquid from the liquid by solid-liquid filtration, and the contaminant eluted in the liquid Separating fluorine and boron contained in the liquid from the liquid.

  The solid substance is intended for soil and waste, and among them, waste sand, dust collection dust and slag, which are waste generated from a foundry.

The contaminants include fluorine and boron contained in the solid material and heavy metals (arsenic, lead, cadmium, hexavalent chromium, mercury, etc.) listed as the second specified harmful substances in the Soil Contamination Countermeasures Law.

The reaction tank is a container that causes a reaction to dissolve contaminants out of the solid substance into the solution using bubbles, and water is usually used as the solution filled in the reaction tank. The bubbles are produced by a separately installed generator and supplied into the reaction vessel.

The purpose of the solid-liquid filtration is to filter and remove fine foreign matters including contaminants separated and suspended from the solid substance in the reaction tank in the reaction tank. If these foreign substances are not removed, the adsorbent removal in the next step may cause problems such as blocking between adsorbents, reducing the adsorbent performance, shortening the adsorbent life, and clogging. Leading to a decline.

The method for separating fluorine and boron contained in the contaminants eluted in the liquid from the liquid is to remove the fluorine and boron present in the liquid by an adsorption tank and to remove the solution (water) from which fluorine and boron have been removed. Below groundwater environmental standards. As the adsorbent, an adsorption resin that selects fluorine and boron is used. In the case of fluorine, a fluorine selective adsorption resin such as selenium or zirconium is used. In the case of boron, a strongly basic ion exchange resin such as magnesium oxide is used.

In the pollutant removing method according to the present invention, an embodiment for removing fluorine, which is a pollutant, from green waste sand generated from a green mold line of a foundry is shown below.
Raw waste sand such as spilled sand and used sand generated from the casting molding line of a foundry is collected, and fluorine, which is a pollutant, is removed from the raw waste sand through the process shown in FIG.

First, the green waste sand is put into a reaction tank filled with water (PH = about 7-8). Air bubbles generated by a separate generator are blown into the water. By blowing the bubbles, the opportunity for contact between the green waste sand and the bubbles is increased, and elution of fluorine in the green waste sand into water can be promoted by the bubbles.

In this embodiment, micro bubbles which are fine bubbles are used as the bubbles to be supplied. Microbubbles are bubbles with a diameter of 50 μm or less, and because they are fine, they have a long residence time in water and are excellent in gas dissolving ability. It has the characteristic of disappearing (complete dissolution).

Due to the above characteristics, the microbubbles have a larger surface area per unit volume than ordinary bubbles and have a greater chance of contact with the green waste sand, so that the elution of fluorine into water can be further promoted.
Specifically, when the microbubbles generated by the microbubble generator are blown into the water, the fluorine compound in the green waste sand becomes fluoride ions and moves into the water. At that time, some of the solid substances such as bentonite, coal powder, and starch covering the silica sand which is the main component of green waste sand are also peeled off from the green waste sand and dispersed in water (hereinafter referred to as solid foreign matter). ).

Next, fluoride ions and solid foreign matters eluted in water in the reaction tank are sent to the solid-liquid separation tank. In the solid-liquid separation tank, the solid foreign matter is separated by filtration from water and removed. In addition, fluoride ion is sent to the next adsorption tank.

As the adsorbent in the adsorption tank, selenium or zirconium-based selective fluoride adsorption resin is used. This selectively removes fluoride ions in the water.
The water that has passed through the adsorption tank is returned to the reaction tank by a pump that circulates the water. Since fluoride ions cannot be completely removed in the adsorption tank, the circulated water contains a small amount of fluoride ions, but does not reduce the elution rate in the reaction tank.
The fluorine elution amount of the green waste sand discharged from the reaction tank after a predetermined time has passed through the process of this example can be set to an environmental standard value of 0.8 mg / L or less.

Further, by blowing carbon dioxide into the microbubbles, the pH of water in the reaction vessel can be reduced, that is, changed to the acidic side. In general, inorganic elements exhibit high solubility under acidic conditions. For example, in steel slag, the elution amount of fluorine shows a minimum value in the neutral range of PH = 7 to 8, and the solubility rapidly increases as the acidity and alkalinity increase. A strong PH dependence with increasing is observed. Therefore, elution of fluorine into water can be further promoted by changing the water in the reaction tank to the acidic side.

Although this embodiment is intended for green waste sand, it is possible to remove contaminants from self-hardening waste sand.

It can be used as a method for reclaiming foundry sand, such as removing coal powder, combustible substances, and volatile components from used foundry sand. It can also be used as a method for removing fluorine, boron and other heavy metals from crushed steel slag. Furthermore, it can be used as a method for removing harmful substances such as heavy metals in the soil.

Claims (4)

1. In the method of immersing a solid substance containing contaminants in a liquid filled in a reaction vessel, supplying bubbles into the liquid, and extracting and removing the contaminants from the solid substance,
   Immersing the solid substance containing the contaminant in a liquid filled in a reaction vessel;
   Supplying microbubbles having a diameter of 50 μm or less as the bubbles in the liquid in which the solid substance is immersed;
   Separating the solid content of the contaminants eluted in the liquid from the liquid by solid-liquid filtration;
   Separating fluorine and boron contained in contaminants eluted in the liquid from the liquid;
   Returning the liquid after the solid-liquid filtration and the separation of fluorine and boron to the reaction tank again;
   A method for removing contaminants from a solid substance having
2. 2. The method for removing contaminants from a solid substance according to claim 1, wherein the liquid filled in the reaction tank is changed to the acidic side.
3. The method for removing contaminants from a solid substance according to claim 1 or 2, wherein carbon dioxide is dissolved in the liquid filled in the reaction tank by the bubbles.
4. In a pollutant removal system that immerses a solid substance containing a pollutant in a liquid filled in a reaction tank, supplies bubbles into the liquid, and extracts and removes the pollutant from the solid substance.
   The solid substance containing the contaminant is immersed in the liquid, and the contaminant is eluted from the solid substance by supplying microbubbles having a diameter of 50 μm or less as the bubbles in the liquid in which the solid substance is immersed. Means,
   Means for separating the eluted contaminants from the liquid by solid-liquid filtration;
   Means for separating fluorine and boron from the liquid after the solid-liquid filtration;
   Means for circulating the liquid after the solid-liquid filtration and the separation of fluorine and boron;
   Contaminant removal system from solid material having