JP2011126933A - Heavy metal-treating agent and method for treating heavy metal by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein an aqueous solution of sodium carbodithionate of piperazine easily precipitates crystals when the aqueous solution is formed into a high concentration, although the aqueous solution of the carbodithionate of the piperazine has high heavy metal-immobilizing ability and is excellent heavy metal-treating agent hardly causing harmful gas when treating he heavy metal. <P>SOLUTION: The high-concentration aqueous solution exceeding 25 wt.% at room temperature (25°C) is obtained in the aqueous solution of the sodium piperazine-N, N'-biscarbodithionate containing a dissimilar metal cation, and the precipitation of the crystal is not caused. The molar ratio of the sodium cation to the dissimilar cation is preferably from 99:1 to 80:20, and the dissimilar cation is preferably potassium cation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to solid waste containing heavy metals, for example, incineration ash and fly ash discharged from garbage incineration plants, soil contaminated with heavy metals, lead contained in sludge generated after wastewater treatment, mercury, chromium, cadmium It relates to a heavy metal treatment agent that makes it possible to easily fix and elute harmful heavy metals such as zinc and copper, and in particular, precipitation of solids by mixing with other general-purpose heavy metal treatment agents at a high concentration The present invention relates to a heavy metal treating agent comprising an aqueous solution of piperazine di-N, N′-biscarbodithioate without water.

  Fly ash discharged from municipal waste incineration plants and the like has a high heavy metal content and needs to be treated to suppress elution of heavy metals. As one of such treatment methods, there is a drug treatment method, and a method of treating a heavy metal by adding a heavy metal treatment agent such as a chelate-type drug is used.

  As chelating agents, carbodithioates of amine derivatives are mainly used. In particular, carbodithioate of piperazine is widely used as a heavy metal treating agent because it has a feature that less harmful gases such as hydrogen sulfide and carbon disulfide are generated unlike carbodithioate of other amine derivatives (for example, patent documents). 1).

  Currently, potassium salt is used as an aqueous solution of piperazine carbodithioate used as a heavy metal treating agent, but when mixed with other general-purpose heavy metal treating agents, piperazine carbodithioic acid potassium salt aqueous solution contains solids. There was also a problem of precipitation.

  On the other hand, carbodithioic acid sodium salt of piperazine has a high ability to immobilize heavy metals like potassium salt, and has excellent basic performance that is thermally stable and does not generate harmful gases. There was a problem that crystals of sodium salt were precipitated.

  A method of adding an alkali hydroxide in a specific range in order to suppress crystal precipitation from an aqueous solution of piperazine-N, N′-biscarbodithioate, particularly potassium salt (particularly crystal precipitation at low temperature). Has been proposed (see, for example, Patent Documents 2 to 3). However, crystal precipitation from a high-concentration solution of piperazine-N, N′-biscarbodithioate could not be suppressed only by controlling the amount of alkali hydroxide added.

  The solubility of piperazine-N, N′-biscarbodithioate sodium is about 20% by weight at room temperature, and even when heated, it is up to 25% by weight. Crystals at high concentrations exceeding 25% by weight at room temperature (25 ° C.) A high-concentration piperazine-N, N′-biscarbodithioate aqueous solution without precipitation was not obtained.

Japanese Patent No. 3391173 JP 2006-316183 A JP2008-184470

  When the aqueous solution of piperazine-N, N′-biscarbodithioate is a high-concentration aqueous solution, there is a problem that crystals precipitate at room temperature. The present invention provides a high-concentration aqueous solution of piperazine-N, N'-biscarbodithioate, particularly a high-concentration aqueous solution exceeding 25% by weight at room temperature (25 ° C.).

  As a result of intensive studies to solve the above problems, the present inventors have mixed piperazine-N, N′-biscarbodithioic acid with a different cation other than sodium cation, particularly potassium cation, as a counter cation that forms a salt. As a result, it was found that a high-concentration aqueous solution of piperazine-N, N′-biscarbodithioate without crystal precipitation can be obtained, and the present invention has been completed.

  Hereinafter, the present invention will be described in detail.

  The heavy metal treating agent of the present invention comprises an aqueous solution in which the concentration of sodium piperazine-N, N′-biscarbodithioate exceeds 25% by weight at room temperature (25 ° C.). The concentration of piperazine-N, N'-biscarbodithioic acid sodium is preferably higher, and preferably 27% by weight or more.

  On the other hand, since the heavy metal treating agent is diluted with water to be uniformly dispersed in the heavy metal-containing material, the concentration of piperazine-N, N′-biscarbodithioic acid sodium does not exceed 30% by weight. is there.

  The aqueous piperazine-N, N′-biscarbodithioate aqueous solution of the present invention is stabilized without precipitation of crystals at room temperature, and forms a salt with piperazine-N, N′-biscarbodithioic acid. This is achieved by using a mixed cation with a different cation other than sodium as a cation, not sodium alone.

  The reason why the high-concentration aqueous solution is stabilized by using mixed cations is not necessarily clear, but for example, the following mechanism can be considered. Piperazine-N, N'-biscarbodithioic acid is a coordinator between the functional group at both ends of the piperazine-N, N'-biscarbodithioic acid molecule and the metal cation, depending on the counter cation (metal cation species) forming the metal complex. It is said that a polymer structure may be formed through a bond. By analogy that the crystal of piperazine-N, N′-biscarbodithioate sodium is a needle-like crystal, the salt of this salt is also regularly arranged in a certain direction in the piperazine-N, N′-biscarbodithioate molecule ( It is estimated that crystallization is progressing. For this reason, the use of a mixture of different cations that inhibits such a regular arrangement and polymerisation will inhibit molecular association and crystal formation, and a high-concentration aqueous solution cannot be obtained stably. It is thought.

  On the other hand, in the case of piperazine-N, N′-biscarbodithioic acid potassium salt, the solubility is not significantly improved by introduction of different cations.

  The different cation introduced with respect to the sodium cation is 1 to 20 mol% (molar ratio of sodium cation to different cation 99: 1 to 80:20), particularly 3 to 20 mol%, A range of 10 mol% is preferred. If it is less than 1 mol%, the stabilization effect (crystal precipitation inhibiting effect) of the high-concentration aqueous solution is not sufficient. On the other hand, when it exceeds 20 mol%, the ratio of piperazine-N, N′-biscarbodithioic acid potassium salt is increased, and the characteristics as a sodium salt, for example, solid precipitation when mixed with other general-purpose heavy metal treating agents The deterrent effect is easily lost.

  There is no particular limitation on the different cation species to be introduced into piperazine-N, N′-biscarbodithioate sodium as long as it is a cation species other than sodium cation, but itself is insoluble in piperazine-N, N′-biscarbodithioate. A potassium cation that does not form a salt complex is particularly preferred.

  In the heavy metal treating agent of the present invention, carbodithioates of different amines may be further mixed and used.

  The heavy metal treating agent of the present invention may contain other components as long as the effects of the present invention are not impaired. For example, sodium piperazine-N-carbodithioate is likely to be generated as a by-product in the production of sodium piperazine-N, N'-biscarbodithioate. Piperazine-N-carbodithioic acid sodium has only one functional group for immobilizing heavy metals, and its ability to treat heavy metals per unit weight is low, so its content is preferably low, especially less than 1% by weight Is preferred.

  Next, the manufacturing method of the heavy metal processing agent of this invention is demonstrated.

  The heavy metal treating agent of the present invention is not limited as long as it has a different cation in the aqueous solution of piperazine-N, N′-biscarbodithioate, and its production method is not limited. Piperazine-N, N′-biscarbodithioate sodium by mixing sodium hydroxide containing different cations in a method for producing sodium piperazine-N, N′-biscarbodithioate by mixing sodium oxide It is preferable to produce a mixed cationic system from the molecular production stage.

  When piperazine-N, N′-biscarbodithioate in aqueous solution is mixed with carbodithioate of different amines, carbon disulfide and alkali metal are first added to the mixed aqueous solution of piperazine and different amines. It is preferable to add a hydroxide to react.

  Next, the heavy metal processing method using the heavy metal processing agent of this invention is demonstrated.

  The heavy metal treating agent of the present invention can treat heavy metal contaminants by mixing with heavy metal contaminants, that is, insolubilize heavy metals in the heavy metal contaminants.

  Heavy metal pollutants are not limited, but examples include fly ash, soil, sludge, and examples of heavy metals to be treated include lead, cadmium, chromium, and mercury.

  The heavy metal treatment method using the heavy metal treatment agent of the present invention is not particularly limited, and the heavy metal treatment agent of the present invention and the heavy metal contaminant may be sufficiently mixed. The amount of heavy metal treating agent used varies depending on the state of heavy metal contaminants, the content of heavy metals and the form of heavy metals. Moreover, in order to make a process easy, you may add 5-50 weight% humidified water with respect to a processed material at the time of kneading | mixing.

  The piperazine-N, N'-biscarbodithioate aqueous solution of the present invention has a high heavy metal immobilization ability.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Examples 1-2
A piperazine-N, N′-biscarbodithioate aqueous solution was obtained by dropping a mixed aqueous solution of carbonized carbon and sodium hydroxide and potassium hydroxide under stirring in a nitrogen stream to the piperazine aqueous solution. The reaction time was 4 hours, and the aqueous solution was heated to 35 ° C. by the heat of reaction. After the reaction, it was aged for 1 hour, and unreacted carbon disulfide was distilled off with nitrogen gas to obtain a yellow transparent aqueous solution.

  The obtained aqueous solution was allowed to stand overnight, cooled to room temperature (25 ° C.), and the presence or absence of crystal precipitation was confirmed.

  Table 1 shows the concentration of piperazine-N, N′-biscarbodithioate in the aqueous solution (the upper column in the second column in Table 1) and the mixed cation forms piperazine-N, N′-biscarbodithioate. The total piperazine-N, N′-biscarbodithioate concentration assumed in the second column (lower column in Table 1) and the content of each cation (mol / kg) are shown.

Comparative Examples 1-2
Piperazine-N, N′-biscarbodithioate aqueous solution was obtained in the same procedure as in Example 1 using sodium hydroxide not containing potassium hydroxide. The results are shown in Table 1.

  Crystal precipitation was not observed when the piperazine-N, N'-biscarbodithioate sodium concentration was 20% by weight, but at 25% by weight, crystals were precipitated at room temperature.

Comparative Example 3
The ratio of different cations was increased to 0.25 (25 mol%) in the molar ratio of K / (Na + K) to prepare an aqueous solution containing 30% by weight of sodium piperazine-N, N′-biscarbodithioate.

  Crystal precipitation was already observed from the end of the reaction.

Reference Example TS-275 (manufactured by Tosoh Corporation), an aqueous potassium piperazine-N, N′-biscarbodithioate solution currently on the market, has a concentration of 35% by weight and is approximately 1.11 mol / kg in terms of molar concentration. It is.

  Since piperazine-N, N′-biscarbodithioate has a low molecular weight, the molar concentration of the active ingredient of the heavy metal treating agent of the present invention is comparable to that of the conventional product, and the concentration of piperazine-N, It can be seen that the sodium N'-biscarbodithioate aqueous solution has the same ability to treat heavy metals as conventional products.

(Heavy metal treatment test)
30 parts by weight of water was added to 100 parts by weight of fly ash (Pb content = 2100 ppm), and the heavy metal treating agents of the examples and comparative examples were converted to 0 in terms of the solid content of piperazine-N, N′-biscarbodithioate. After adding 5 parts by weight and kneading, the Environmental Agency Notification No. 13 test was conducted.

  The lead concentration in the eluate was 0.05 ppm or less.

  The heavy metal treatment agent of the present invention is used for insolubilization treatment of lead, cadmium, chromium, mercury and the like in heavy metal-containing materials such as fly ash, soil, and sludge.

Claims (9)

  A heavy metal treating agent comprising an aqueous solution having a piperazine-N, N′-biscarbodithioic acid sodium concentration exceeding 25% by weight at room temperature (25 ° C.).   The heavy metal treating agent according to claim 1, comprising a different cation other than a sodium cation.   The heavy metal treating agent according to claim 2, wherein the molar ratio of the sodium cation to the different cation is 99: 1 to 80:20.   The heavy metal treating agent according to claim 2 or 3, wherein the different cation is a potassium cation.   2. A method for producing piperazine-N, N′-biscarbodithioate by mixing carbon disulfide and sodium hydroxide in an aqueous piperazine solution, wherein sodium hydroxide containing a different cation is used. The manufacturing method of the heavy metal processing agent in any one of thru | or 4.   The production method according to claim 5, wherein the molar ratio of the sodium cation to the different cation is 99: 1 to 80:20.   A method for treating a heavy metal pollutant, comprising mixing the heavy metal treating agent according to any one of claims 1 to 4 with a heavy metal pollutant.   The method for treating heavy metal contaminants according to claim 7, wherein the heavy metal contaminants are fly ash, soil, and sludge.   The method for treating a heavy metal contaminant according to claim 7 or 8, wherein the heavy metal contaminant is a substance containing any of lead, cadmium, chromium, and mercury.