JP2006316183A - Heavy metal treating agent and treating method of heavy metal using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piperazinedithiocarbamate superior as a heavy metal treating agent without precipitation of solid contents at a low temperature even at a high concentration. <P>SOLUTION: This heavy metal treating agent comprises the piperazinedithiocarbamate having 0.7 wt.% or less of alkali hydroxide concentration. The agent does not precipitate the solid contents at a low temperature even when at a high concentration of 36-44 wt.% and does not generate gaseous substances such as hydrogen sulfide and carbon sulfide, so that it can be employed effectively and safely. <P>COPYRIGHT: (C)2007,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 is related to a heavy metal treatment agent that makes it possible to easily fix and elute harmful heavy metals such as zinc and copper, and has excellent storage stability especially at high concentrations and without crystal precipitation at low temperatures. The present invention relates to a heavy metal treating agent.

  Fly ash discharged from municipal waste incineration plants has a high heavy metal content and needs to be treated to prevent elution of heavy metals. As such a heavy metal treatment method, there is a chemical treatment method, and a method of insolubilizing heavy metal by adding a chelate heavy metal treatment agent is known.

As a heavy metal treating agent, an amine derivative dithiocarbamate has high performance, and piperazine dithiocarbamate is particularly widely used because it generates less harmful gases such as hydrogen sulfide and carbon disulfide. (See Patent Document 1)
However, the aqueous solution of piperazine dithiocarbamate can be increased to a certain degree at room temperature or higher, but there is a problem that the stability at a high concentration is poor at a low temperature, and crystals of dithiocarbamate precipitate. Since the heavy metal treating agent is used in an aqueous solution, it is necessary to have a high concentration from the viewpoint of economy and handling, from transportation to use for heavy metals. However, with a conventional heavy metal treating agent comprising an aqueous solution of piperazine dithiocarbamate, an aqueous solution of about 40% by weight can be obtained immediately after synthesis, but it is necessary to lower the concentration in order to maintain stability at low temperatures. However, the problem of crystal precipitation at low temperature is inevitable if the concentration remains high.

  One or more kinds selected from the group consisting of carboxylic acid groups, sulfonic acid groups, hydroxyl groups, phosphoric acid groups, phosphonic acid groups and their alkali metal salts as a method for improving the low temperature stability of the heavy metal treating agent There has been proposed a method of adding an oligomer having a functional group of and a number average molecular weight of 1,000 to 30,000. However, depending on the type of oligomer to be added, there is a possibility that the performance and physical properties of the heavy metal treating agent may change, and it is necessary to conduct a detailed examination in advance. Further, a method has been proposed in which 0.1 to 5% by weight of one kind selected from the group consisting of piperazine and polyamine is contained in diethyldithiocarbamate. However, this method is effective for diethyldithiocarbamate but not for piperazine dithiocarbamate. Furthermore, in these methods, it is necessary to add a specific additive other than the raw material to the heavy metal treating agent, and there is a problem that the number of steps during production increases and the basic unit decreases.

Patent No. 3391173 (Specification, Item 2, Item 0005, Columns 1 to 6) Japanese Patent No. 3532798 (Claim 1) JP 2003-105318 A (Claim 1)

  An aqueous solution containing piperazine dithiocarbamate is excellent as a heavy metal treating agent, but there is a problem that crystals are precipitated at a low temperature when the concentration is high. In the present invention, there is provided a heavy metal treating agent comprising piperazine dithiocarbamate having a high concentration and which is safe and free from generation of crystals at low temperatures and does not generate harmful gases during storage and use.

  As a result of intensive investigations to solve the above-mentioned problems, the present invention provides a heavy metal treating agent mainly composed of a high concentration of piperazine dithiocarbamate, with an alkali hydroxide content in a specific concentration range. The inventors have found that the stability at low temperature can be remarkably improved, and have completed the present invention.

  Hereinafter, the heavy metal treating agent of the present invention and the method for treating heavy metal contaminants using the heavy metal treating agent will be described in detail.

  The heavy metal treating agent of the present invention comprises piperazine dithiocarbamate. As the piperazine dithiocarbamate of the present invention, an alkali salt of piperazine dithiocarbamate can be used, and it is preferably a sodium salt or potassium salt having high solubility and being thermally stable. Piperazine dithiocarbamate has a bis form and a mono form, and any salt can be used in the present invention, but a bis form is particularly preferred.

  The alkali hydroxide used in the present invention is not particularly limited, and examples thereof include sodium hydroxide and potassium hydroxide, and it is particularly preferable to use potassium hydroxide having high solubility.

  The alkali hydroxide in the heavy metal treating agent of the present invention is 0.7% by weight or less, particularly in the range of 0.3 to 0.7% by weight, more preferably in the range of 0.4 to 0.5% by weight. It is preferable. If it is less than 0.3% by weight, harmful gases such as carbon disulfide may be generated during heavy metal treatment. On the other hand, when it exceeds 0.7% by weight, there is no problem at room temperature or higher, but the low-temperature stability is remarkably lowered, which causes a problem in use in a cold region.

  The concentration of the alkali hydroxide in the heavy metal treating agent of the present invention can be confirmed by acid-base titration or the like.

  Conventionally, a heavy metal treating agent mainly composed of piperazine dithiocarbamate is synthesized with an alkali hydroxide concentration of 1.0% by weight or more for the purpose of suppressing gas generation such as carbon disulfide as a decomposition product. It was. The heavy metal treating agent of the present invention is stable at a low temperature even at a high concentration of 36 to 44% by weight by controlling the alkali hydroxide to 0.7% by weight or less, particularly 0.3 to 0.7% by weight. Is high and generates a low amount of harmful gases. In the present invention, the alkali hydroxide that imparts low-temperature stability is a raw material used for the production of piperazine dithiocarbamate and does not require a new compound, so the load on the production process is small.

  The piperazine dithiocarbamate concentration of the present invention is preferably in the high concentration range of 36 to 44% by weight, and preferably in the range of 38 to 42% by weight. In the range exceeding 44% by weight, it is difficult to completely suppress the precipitation of crystals at a low temperature, and when the concentration is less than 36% by weight, the addition amount required for the treatment increases.

  Since the heavy metal treating agent of the present invention is an aqueous solution, the remaining component is water. It does not preclude the inclusion of other components (additives, organic solvents, etc.) as long as the performance as a heavy metal treating agent of the present invention is not adversely affected.

  Next, this invention demonstrates the processing method of the heavy metal contaminant which uses the above-mentioned heavy metal processing agent.

  As a method for treating heavy metal contaminants according to the method of the present invention, a general method can be generally applied except that the heavy metal treating agent of the present invention is used.

  For example, when the heavy metal pollutant is fly ash, it varies depending on the heavy metal content in the fly ash, but the heavy metal treatment agent is 0.01 to 30% by weight, most of which is 0.01 to 5% by weight. Add in range. Since the concentration of piperazine dithiocarbamate, which is an active ingredient, is high, the amount of the heavy metal treating agent of the present invention can be reduced as compared with the usual method.

  Further, when mixing the heavy metal treating agent and the heavy metal contaminant, humidified water may be added during kneading in order to facilitate disposal of the treated fly ash.

  The heavy metal treatment agent of the present invention has high stability at low temperatures and high concentration of heavy metal treatment components, so that it can be used stably in winter and in cold regions, and can be used stably, and waste with a low addition rate. Can be processed. In addition, the amount of harmful gas generated during storage and use is small and can be used safely.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

Example 1
Piperazine dithiocarbamate potassium was dissolved in pure water so as to be 40 wt% potassium hydroxide and 0.3 wt% potassium to prepare a mixed aqueous solution of piperazine potassium dithiocarbamate and potassium hydroxide. 150 g of the aqueous solution, α-alumina 0.5 μm (Wako Pure Chemical Industries, Ltd.) 10 mg, and a Teflon (registered trademark) rotor were placed in a 150 ml glass bottle. Next, it is installed in a constant temperature and high humidity tank LH41-13P (Nagano Science Co., Ltd.) and stirred at 400 to 500 rpm using a stirrer, and the temperature range from 5 ° C. to −5 ° C. is set to −0. After cooling at 5 ° C./hour, the temperature at which crystals were precipitated was investigated. The results are shown in Table 1. In the solution, no precipitation of crystals was observed in the solution up to −5 ° C., and it was confirmed that the solution had high low temperature stability.

  3 ml of the aqueous solution was taken in a 40 ml glass vial, and the carbon disulfide concentration of the gas in the vial after standing at 25 ° C. for 1 day was measured by gas chromatography. The results are shown in Table 1. The concentration was 1 ppm or less, and it was confirmed that the amount of gas generated was low.

  Using the piperazine potassium dithiocarbamate aqueous solution, a treatment test for heavy metal-containing fly ash A was conducted. A predetermined amount (1% by weight, 2% by weight with respect to fly ash) of the aqueous solution and 30% by weight of humidified water with respect to fly ash were added and kneaded for 5 minutes. The ash after kneading was subjected to the Environmental Agency Notification No. 13 test. The composition of fly ash A used in the test is shown in Table 2, and the Environmental Agency Notification No. 13 test results are shown in Table 3. By adding 2% by weight of the aqueous solution with respect to fly ash, the elution of heavy metals could be treated to a standard value or less, and the heavy metal treatment performance was high.

Example 2
Piperazine dithiocarbamate potassium was dissolved in pure water so as to be 40 wt% potassium hydroxide and 0.7 wt% potassium to prepare a mixed aqueous solution of potassium piperazine dithiocarbamate and potassium hydroxide. The crystal precipitation temperature was examined in the same manner as in Example 1. The results are shown in Table 1. Crystal precipitation was not observed even at -5 ° C, and it was confirmed that there was high low-temperature stability.

  Further, the carbon disulfide concentration was measured in the same manner as in Example 1. The results are shown in Table 1. The measured concentration was 1 ppm or less, and it was confirmed that the amount of gas generated was low.

  A treatment test of heavy metal-containing fly ash A was conducted in the same manner as in Example 1. Table 4 shows the results of the Environmental Agency Notification No. 13 test. By adding 2% by weight of the aqueous solution with respect to fly ash, the elution of heavy metals could be treated to a standard value or less, and the heavy metal treatment performance was high.

Comparative Example 1
Piperazine dithiocarbamate potassium was dissolved in pure water to a concentration of 40% by weight and potassium hydroxide to 1.5% by weight to prepare a mixed aqueous solution of piperazine dithiocarbamate potassium and potassium hydroxide. The crystal precipitation temperature was examined in the same manner as in Example 1. The results are shown in Table 1. Crystal precipitation was confirmed at 0 ° C. Crystal precipitation was observed at a higher temperature than in the Examples. A treatment test of heavy metal-containing fly ash A was conducted in the same manner as in Example 1. Table 5 shows the results of the Environmental Agency Notification No. 13 test.

Comparative Example 2
Piperazine dithiocarbamate potassium was dissolved in pure water so as to be 40% by weight and potassium hydroxide was 0.8% by weight to prepare a mixed aqueous solution of piperazine dithiocarbamate potassium and potassium hydroxide. The crystal precipitation temperature was examined in the same manner as in Example 1. The results are shown in Table 1. Crystal precipitation was confirmed at -3 ° C. It was confirmed that crystal precipitation occurred at a higher temperature than in the examples.

Comparative Example 3
Piperazine dithiocarbamate potassium was dissolved in pure water so as to be 40 wt% potassium hydroxide and 0.2 wt% to prepare a mixed aqueous solution of potassium piperazine dithiocarbamate and potassium hydroxide. The carbon disulfide concentration was measured in the same manner as in Example 1. The results are shown in Table 1. The measured concentration was 2.4 ppm, which was a higher value than that of the example, and the stability of the agent was lower than that of the example.

Comparative Example 4
Piperazine dithiocarbamate potassium was dissolved in pure water so as to be 40 wt% potassium hydroxide and 0.1 wt% potassium to prepare a mixed aqueous solution of potassium piperazine dithiocarbamate and potassium hydroxide. The carbon disulfide concentration was measured in the same manner as in Example 1. The results are shown in Table 1. The measured concentration was 7.5 ppm, which was a higher value than that of the example, and the stability of the agent was lower than that of the example.

The heavy metal treating agent of the present invention is effective for treating heavy metal pollutants particularly in cold regions because crystal precipitation hardly occurs at low temperatures and the amount of gas generation is small.

Claims (6)

A heavy metal treating agent comprising 0.7% by weight or less of alkali hydroxide, 36 to 44% by weight of piperazine dithiocarbamate, and water. The heavy metal treating agent according to claim 1, wherein the alkali hydroxide concentration is 0.3 to 0.7% by weight. The heavy metal treating agent according to claim 1, wherein the piperazine dithiocarbamate is potassium piperazine dithiocarbamate. A method for treating a heavy metal pollutant, comprising mixing the heavy metal treating agent according to claim 1 with a heavy metal pollutant. The heavy metal contaminant treatment method according to claim 4, wherein the heavy metal contaminant is fly ash, soil, or sludge. 6. The method for treating heavy metal contaminants according to claim 4, wherein the heavy metal contaminant is a substance containing any one of lead, cadmium, chromium and mercury.