JP2002282836A - Treatment agent and treatment method for heavy metal in the heavy metal contaminated soil or in the waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove heavy metal in the heavy metal contaminated soil or in the waste by eluting it in a short time and efficiently. SOLUTION: This invention relates to a treatment agent to remove heavy metal in the heavy metal contaminated soil or that in the waste including a chelate agent and a non-ionic surface active agent. By making the heavy metal treatment agent contact with the heavy metal contaminated soil or the waste, and thereafter separating them from the soil or the waste, heavy metal can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a method for treating heavy metals in soil or waste contaminated with heavy metals, and more particularly to a heavy metal treatment agent for eluting and removing heavy metals from soil or waste contaminated with heavy metals. And a method for purifying heavy metal contaminated soil or waste using the heavy metal treating agent.

[0002]

2. Description of the Related Art In recent years, soil pollution and waste pollution due to heavy metals such as lead and cadmium have been found in various places, mainly in former factory sites, and therefore, a method of purifying soil and waste contaminated with heavy metals has been found. Research on is being promoted.

[0003] Since heavy metals cannot be decomposed like organic matter, in order to treat heavy metal contaminated soil, the contaminated soil is excavated and transported to a disposal site, and insoluble heavy metal salts are formed and insolubilized. And a method of solidifying the soil by adding a solidifying agent such as cement to the soil, or energizing the soil to generate heat and solidifying it into a glassy state. However, all of these methods leave heavy metals in the soil, and thus lack reliability in terms of long-term stability.

Therefore, as a method for removing heavy metals from soil, an electroosmosis method has been proposed (Japanese Patent Laid-Open No. 6-2183).
No. 55, "Method of on-site restoration of contaminated soil",
No. 59716, “Method and apparatus for treating contaminated soil”). Also, a method of removing heavy metals from contaminated soil using a chelating agent has been proposed (JP-A-4-2638).
No. 74, "Method of Purifying Soil Contaminated with Heavy Metals",
r, Air, and Soil Pollutio
n, 45, 361 (1989)), chelating agents such as ethylenediaminetetraacetate (EDTA), nitrilotriacetate (NTA), and citric acid have been studied (Japanese Patent Application Laid-Open No. H11 (1999)).
156338, "Method of repairing contaminated soil").

[0005]

However, the electroosmosis method has low efficiency and requires a large amount of cost, so that it is not practical. Further, in the method using a chelating agent, heavy metals are eluted after coming into contact with soil. It takes time to process, and the processing efficiency is poor.

The present invention solves the above-mentioned conventional problems and provides a heavy metal-treating agent in heavy metal-contaminated soil or waste that can efficiently elute and remove heavy metal from heavy metal-contaminated soil or waste in a short time. It is another object of the present invention to provide a method for treating heavy metal contaminated soil or waste using the heavy metal treating agent.

[0007]

The agent for treating heavy metals in soil or waste contaminated with heavy metals according to the present invention is a treatment agent for removing heavy metals in soil or waste contaminated with heavy metals, comprising a chelating agent. And a nonionic surfactant.

[0008] The surfactant has a hydrophilic group and a hydrophobic group in the molecule and lowers the interfacial tension between soil or waste and water, so that the hydrophobic part in soil or waste and the fine particles inside soil or waste are reduced. Easy to penetrate into the structure. For this reason, when a chelating agent that generates a stable water-soluble chelate with a heavy metal is used in combination with a nonionic surfactant, the effect of increasing the permeability of the surfactant is shorter than when elution is performed using only the chelating agent, thereby shortening the time. Thus, heavy metals such as lead, cadmium and mercury can be efficiently made water-soluble and eluted from soil or waste into water.

The nonionic surfactant used in the present invention preferably has a hydrophilic-lipophilic balance (HLB) value of 15 or less in order to effectively obtain the above-mentioned effect of improving permeability.

[0010] The HLB value is one of indexes indicating the effect of a surfactant, and the higher the HLB value, the higher the hydrophilicity.

In the method for treating heavy metal-contaminated soil or waste according to the present invention, such a heavy metal treating agent of the present invention is brought into contact with soil or waste contaminated with heavy metal, and the treating agent after contact is contacted with the soil. Alternatively, it is separated from waste.

[0012]

Embodiments of the present invention will be described below in detail.

In the present invention, the chelating agent is preferably a substance having a carboxyl group and / or an amino group in the molecule and capable of forming a stable water-soluble chelate with heavy metals.
For example, EDTA, NTA, citric acid, L-aspartic acid-N, N-diacetate (ASDA) and the like can be used.

As the nonionic surfactant, among nonionic surfactants such as polyoxyethylene monoalkyl ether, the HLB value is 15 or less, particularly, the HLB value is 10 or less.
Those having a range of ~ 15 are preferably used. HLB value is 1
If the nonionic surfactant exceeds 5, the effect of the aforementioned permeability is low, and the effect of promoting the elution of heavy metals according to the present invention cannot be sufficiently obtained. However, non-ionic surfactants having an HLB value of less than 10 have low solubility in water.
Those having a value of 10 to 15 are preferred. Such nonionic surfactants include, for example, ethylene oxide adducts of polyoxyethylene cetyl ether with an addition mole number of 6 to 15.

[0015] These chelating agents and nonionic surfactants are practically used as an aqueous solution in which the chelating agent and nonionic surfactant are dissolved for treating heavy metal contaminated soil or waste.

If the concentration of the chelating agent in the aqueous solution is low, the elution effect of heavy metals decreases, and if the concentration is high, the cost increases and waste occurs.
0.01 to 10% by weight, especially 0.1 to
Preferably it is 3% by weight.

On the other hand, if the concentration of the nonionic surfactant in the aqueous solution is low, the elution effect of heavy metals is reduced, and if the concentration is high, the foaming property is increased and the work becomes difficult.
The cost is high. For this reason, the concentration of the nonionic surfactant in the aqueous solution is preferably 0.01 to 10% by weight, particularly 0.05 to 1% by weight as a solid concentration, and the chelating agent and the nonionic surfactant The ratio of the chelating agent and the non-ionic surfactant is 1: 0.01 to 0.5.
(Weight ratio).

In the present invention, the method of contacting an aqueous solution in which such a chelating agent and a nonionic surfactant are dissolved with heavy metal-contaminated soil or waste is not particularly limited. Can be adopted. First, a contaminated part of the soil is specified, and this part is surrounded by a seepage barrier such as a sheet pile, and an injection well and a pumping well are dug. An aqueous solution of the chelating agent and the nonionic surfactant is injected from the injection well to bring the contaminated soil into contact with the aqueous solution. After the injection of the aqueous solution or while the aqueous solution is being injected, the solution is pumped up from the pumping well to recover the aqueous solution in which the heavy metal is dissolved. The excavated contaminated soil is put into a washing tank and stirred together with the above-mentioned chelating agent and the aqueous solution of the nonionic surfactant. Thereafter, solid-liquid separation is performed to separate the purified soil and water from which the heavy metal has eluted, and the purified soil is backfilled.

Heavy metal contaminated waste can be treated in the same manner as described above. The treated waste may be disposed of by landfill.

The heavy metal elution water discharged by such treatment is subjected to heavy metal removal treatment by ion exchange, electrolysis, insolubilized coagulation sedimentation and the like.

[0021]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1-3, Comparative Example 1 Lead-contaminated soil collected from the site of a battery manufacturer was air-dried,
The particles were sieved to a particle size of 2 mm or less.

Separately, L-aspartic acid-N, N-diacetate (ASDA) and a nonionic surfactant shown in Table 1 were combined with an ASDA molar concentration of 0.005 mol / L (1.3% by weight). ), And an aqueous solution dissolved in water was prepared so as to have a nonionic surfactant concentration of 0.1% by weight (Comparative Example 1).
Does not use nonionic surfactants, only ASDA),
500 mL of this aqueous solution and 5 g of the above soil sample were placed in a 1 L plastic container with a lid, and were shaken under the condition of 200 rpm. After the shaking treatment for 2 hours and the shaking treatment for 5 hours, 20 mL of the treatment solution was collected and filtered through a 0.45 μm filter, and the lead concentration of the filtrate was measured by ICP emission spectrometry.

The lead content in the contaminated soil was measured in advance, and the dissolution effect was shown by the removal rate with respect to this value. The pH of the aqueous solution containing the chelating agent was adjusted to 7.0 ± 0.5 before mixing with the contaminated soil.

The results are as shown in Table 1. According to the present invention in which a chelating agent and a nonionic surfactant are used in combination,
It can be seen that the heavy metals in the heavy metal contaminated soil can be eluted and removed efficiently in a short time as compared with the case of using only the chelating agent.

[0026]

[Table 1]

[0027]

As described in detail above, according to the agent for treating heavy metals in heavy metal-contaminated soil or waste and the method for treating heavy metals of the present invention, heavy metals in soil or waste contaminated with heavy metals can be removed in a short time. It can be efficiently eluted and removed.

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Claims (3)

[Claims] 1. A treatment agent for removing heavy metal in soil or waste contaminated with heavy metal, comprising: a chelating agent and a nonionic surfactant; Heavy metal treatment agent in waste. 2. The heavy metal treating agent according to claim 1, wherein the nonionic surfactant has a hydrophilic-lipophilic balance (HLB) value of 15 or less. 3. The heavy metal treating agent according to claim 1 or 2 is brought into contact with soil or waste contaminated with heavy metal, and the treated agent after contact is separated from the soil or waste. To treat heavy metal contaminated soil or waste.