JP2001000959A - Method and apparatus for cleaning heavy metal polluted soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regenerate polluted soil into soil containing no heavy metals to reutilize the same as clean soil. SOLUTION: A cleaning apparatus of heavy metal polluted soil is equipped with a soil dissolving tank 1, an electric separation tank 2 for separating heavy metal ions from soil electrically, a chemical treatment and sedimentation tank 3 gathering an aq.soln. containing heavy metal ions to chemically treat the same and a pump 4 for transferring cleaned water to the soil dissolving tank 1. When DC voltage is applied to the electric separation tank, heavy metal ions are easily moved in an electrode direction by electrical force to be separated and removed from heavy metal polluted soil certainly, safely and efficiently for a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for remediating heavy metal contaminated soil by electrically and chemically separating and removing heavy metals from contaminated soil.

[0002]

2. Description of the Related Art In a conventional general in situ soil purification method, water is poured into contaminated soil at a contaminated site, an electrode is inserted into the ground, a DC voltage is applied, and heavy metals are electrically moved and lifted from the periphery of the electrode. In this case, a means for performing chelation treatment, precipitation filtration, and treatment as sludge is employed.

[0003]

The above-mentioned conventional method requires a sufficient amount of water when the contaminated site is poorly permeable or impermeable, or in an unsaturated zone where the water cannot be kept in a saturated state. Since water cannot penetrate into the soil and water cannot be retained, the electricity cannot be supplied or the power supply becomes unstable. As a result, heavy metals cannot be separated from the soil, and the soil purification varies depending on the location.

Further, since chromate ions (hexavalent chromium), cyanide, and the like have very high solubility in water, when water is injected into the ground, the chromate ions easily move to the deep part of the ground, There was a problem of contaminating the deep part.

When an electrode is installed in the ground and a DC voltage is applied, the working voltage and the potential gradient are regulated in terms of human safety due to stray current. For this reason, it takes a long time for the treatment, and furthermore, it is considered that the stray current may have a corrosive effect on the existing buried pipe, and there is a problem that the cost for safety measures at the construction site is inevitably increased.

The present invention has been made in view of the above-mentioned problems of the conventional method, and it is a technique for separating and removing heavy metals from heavy metal-contaminated soil in a safe and efficient manner in a short time and efficiently. The purpose of the present invention is to enable recycling and reuse of purified water, and to systematically separate and remove all removed heavy metals from waste liquid.

[0007]

In order to achieve the above-mentioned object, the present invention firstly puts a heavy metal-contaminated soil into a soil dissolving tank to allow water to penetrate into the soil, and releases a contaminated soil aqueous solution in which heavy metal ions are eluted. Transfer to an electric separation tank and apply DC voltage. Then, heavy metal ions existing as cations and anions are moved to the negative electrode and the positive electrode to separate and remove metal ions from the soil, and the harmless soil is returned to its original position,
The aqueous solution containing cations and anions transferred to the vicinity of the electrodes is transferred to the chemical treatment precipitation tank through pipes installed around both electrodes, and metal ions and the like are captured and removed in the precipitation tank, and the purified water is pumped using a pump. It is a heavy metal-contaminated soil purification method comprising a step of returning to the soil dissolving tank and reusing it.

Further, the present invention provides a soil dissolving tank in which stirring rotating blades are provided inside to dissolve the soil by stirring and mixing, and a DC voltage power supply connected to apply a DC voltage to electrically move and separate heavy metal ions from the soil. Heavy metal-contaminated soil consisting of an electrical separation tank, a chemical treatment sedimentation tank for collecting and chemically treating an aqueous solution containing heavy metal ions separated from soil, and a pump for transferring purified water to a soil dissolution tank and circulating it It is a purification device.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. Heavy metal-contaminated soil excavated from underground A is dissolved while being stirred and mixed in a soil dissolving tank 1 having stirring stirring blades.
Heavy metals in soil have a high solubility in water, and are easily eluted. The heavy metal-contaminated soil aqueous solution is transferred to the electric separation tank 2 by a pump, a direct current voltage is applied thereto, heavy metal ions are moved to the anode side and the cathode side, and the aqueous solution containing the heavy metal is pumped from the periphery of the electrode to the chemical treatment precipitation tank 3. To collect.

The soil remaining in the electric separation tank 2 is separated and removed of heavy metals, converted into detoxified soil and returned to the original ground A, and the aqueous solution containing heavy metals is treated systematically. Those existing in the form of anions such as chromate ions are trapped and removed by, for example, an anion exchange resin tower (not shown), and the cations pass through the anion exchange resin tower. Chemically forms sulfides and hydroxides of heavy metals and insolubilizes them.

The heavy metal sulfides and hydroxides are aggregated with an aggregating agent or the like, filtered and recovered. The water from which heavy metals have been removed in the chemical treatment sedimentation tank 3 is returned to the soil dissolution tank 1 by the pump 4 and reused. Chromate ions and the like captured by the anion exchange resin are eluted with an eluent and used as a raw material of a chromium compound.

That is, in the present invention, a soil dissolving tank 1 for dissolving heavy metal-contaminated soil with water, an electric separation tank 2 having an electrode for applying a DC voltage to separate and remove heavy metals from the heavy metal-contaminated soil, and an injection pipe / water collecting pipe. A chemical treatment sedimentation tank 3 for storing waste liquid containing heavy metals collected from the electric separation tank 2 and removing metal compounds, and a pump 4 for returning the purified water to the soil dissolving tank 1 by a pump 4. And

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment relating to a treatment for purifying soil contaminated with hexavalent chromium will be described below. 1. Chromic acid (CrO4) (CrO3 equivalent 4
2.5 m of contaminated soil containing 1.75 g) is put into a soil dissolution tank (dimension 184 (DIA) × 150 mm), water is injected, and the mixture is stirred and mixed for 30 minutes. 2. The contaminated soil aqueous solution is transferred to an electric separation tank by a mud pump. 3. The electrodes are placed at 1 m intervals, and a DC voltage of DC 80 V is applied. 4. An aqueous solution containing chromate ions is pumped into the chemical treatment precipitation tank by a pump for pumping (flow rate: 6 L / min). 5. Filtration tower (1u) by pumping aqueous solution of chemical treatment settling tank
Through the anion exchange resin tower (A-C1 type) to return to the chemical treatment precipitation tank. 6. A solution of iron sulfate and sodium sulfide is added to the aqueous solution returned to the chemical treatment precipitation tank, and a precipitate is formed. Filtered precipitate (heavy metal sulfide)
Collect. 7. Water is added to the soil remaining in the electric separation tank, transferred to a dehydrator by a mud pump, and dewatered. The soil regenerated by removing heavy metals and rendering it harmless is returned to the original position and reused. 8. For the quantitative analysis of chromium (Cr), diphenylcarbazide absorption spectrophotometry is applied.

[0014]

The present invention described above has the following unique effects different from the conventional ones.

Since the contaminated soil is dissolved in water in the soil dissolving tank, heavy metal ions having high solubility in water are easily eluted from the soil. When a DC voltage is applied to the heavy metal contaminated soil in an electric separation tank, the heavy metal ions easily move in the direction of the electrodes due to electric force. At this time, heavy metal ions are reliably and safely separated from the heavy metal contaminated soil in a short time and efficiently. The soil from which heavy metals have been removed is rendered harmless and reused as clean soil.

The heavy metal ions separated from the contaminated soil are collected in a chemical treatment sedimentation tank, and systematically separate and recover heavy metals. The aqueous solution from which heavy metal ions have been removed is reused, and the recovered heavy metal ions become a raw material for the metal compound. Further, by burning the sulfide, it becomes an insoluble oxide.

Chromate ions and cyan ions have high solubility in water. Electrodes are installed in the ground like conventional heavy metal-contaminated soil purification systems, and when water is injected into the ground, the energization time is long, during which the aqueous solution containing chromate ions and cyanine penetrates deep into the ground. However, the present invention purifies contaminated soil in a soil dissolution tank and an electric separation tank installed on the ground in the original position, so that harmful polluting heavy metals do not pollute the soil environment.

Since the apparatus for purifying the contaminated soil is performed on the ground at the original position, there is no need to consider the danger caused by the stray current. No extra action costs are required,
Since the safety is extremely high and a higher DC voltage can be used, it is possible to reduce the processing time required for purification of soil contaminated with heavy metals.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an apparatus for implementing the present invention.

[Explanation of symbols]

 1 Soil dissolution tank 2 Electric separation tank 3 Chemical treatment sedimentation tank 4 Pump

Claims (2)

[Claims] 1. A heavy metal-contaminated soil is put into a soil dissolution tank to allow water to penetrate into the soil, and the contaminated soil aqueous solution in which heavy metal ions are eluted is transferred to an electric separation tank, and a direct current voltage is applied to the soil. The heavy metal ions that are present as a negative electrode and positive electrode are transferred to the negative and positive electrodes to separate and remove the metal ions from the soil. Transfer to a chemical treatment sedimentation tank through a pipe installed around the electrode,
A heavy metal-contaminated soil remediation method comprising the steps of capturing and removing heavy metal ions and the like in the sedimentation tank, returning purified water to the soil dissolution tank using a pump, and reusing the water. 2. A soil dissolving tank in which stirring rotating blades are provided inside to dissolve the soil by stirring and mixing, and an electric separation for connecting a DC voltage power supply to apply a DC voltage to electrically move and separate heavy metal ions from the soil. A heavy metal-contaminated soil purification device comprising a tank, a chemical treatment settling tank for collecting and chemically treating an aqueous solution containing heavy metal ions separated from soil, and a pump for transferring purified water to a soil dissolving tank for circulation.