JP2005118617A - Method for fixing heavy metal in fly ash - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detoxifying a heavy metal in fly ash by which the heavy metal can be fixed satisfactorily even in such a case where the heavy metal cannot be fixed satisfactorily owing to the heavy metal content or moisture content of the fly ash the properties of which vary from place to place. <P>SOLUTION: This method for fixing the heavy metal in the fly ash comprises a step of heating at ≥80°C a mixture of the heavy metal-containing fly ash, water and piperazine-N,N'-biscarbodithionic acid or its salt. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to ash discharged together with exhaust gas from incineration plants such as municipal waste and industrial waste, such as EP ash collected by an electric dust collector, ash collected by a bag filter, etc. (in this specification, “ The present invention relates to a technology for detoxifying a fly fly ash).

  Fly ash discharged from incineration of municipal waste and industrial waste contains a large amount of heavy metals that are harmful to the human body, especially lead, cadmium, mercury, etc. due to rainwater etc. in the fly ash treatment area Dissolution is a problem. As a countermeasure for that, for example, water and piperazine-N-carbodithioic acid or piperazine-N, N′-biscarbodithioic acid, or a mixture or salt thereof are added and kneaded. A characteristic method for immobilizing heavy metals in fly ash is known. (See Patent Document 1)

In addition, a compound (1) having a molecular weight of 100 to 500 having one functional group containing a sulfur atom and being salt-forming or complex-forming, and a functional group containing a sulfur atom and being salt-forming or complex-forming A heavy metal immobilizing agent comprising a compound (2) having a molecular weight of 200 to 5,000 in the molecule and a water-soluble polymer compound (3) having a number average molecular weight of 5,000 to 10,000,000 as necessary. In particular, a heavy metal immobilizing agent in which (2) is piperazine bisdithiocarbamic acid potassium salt and / or dialkylamine salt is known. (See Patent Document 2)
JP-A-8-224560 JP-A-8-269434

However, there are various types of fly ash depending on the location, and there are cases where sufficient heavy metal immobilization effect cannot be obtained depending on the heavy metal content, moisture content, and the like.
An object of this invention is to provide the detoxification processing method of the heavy metal in fly ash from which the sufficient heavy metal fixation effect is acquired even in such a case.

  As a result of intensive studies to solve the above problems, the present inventors have used piperazine-N, N′-biscarbodithioic acid or a salt thereof as a heavy metal fixing agent and heat-treated at 80 ° C. or higher in the fly ash treatment. As a result, the inventors have found that the ability to immobilize heavy metals can be dramatically improved, and the present invention has been completed.

That is, the present invention
(1) A heavy metal-containing fly ash, water, and piperazine-N, N′-biscarbodithioic acid or a salt thereof is heated to 80 ° C. or higher, and a heavy metal immobilization method in fly ash,
(2) A heavy metal-containing fly ash, water, and piperazine-N, N′-biscarbodithioic acid or a salt thereof are heated to 100 ° C. or more, and the present invention relates to a heavy metal immobilization method in fly ash.
(3) Water and piperazine-N, N′-biscarbodithioic acid or a salt thereof are added to heavy metal-containing fly ash, heated to 80 ° C. or higher, and kneaded or mixed. Regarding heavy metal immobilization method,
(4) Water and piperazine-N, N′-biscarbodithioic acid or a salt thereof are added to heavy metal-containing fly ash, heated to 100 ° C. or higher, and kneaded or mixed. The present invention relates to a heavy metal immobilization method.
(5) The salt of piperazine-N, N′-biscarbodithioic acid is an alkali metal salt, alkaline earth metal salt or ammonium salt, according to any one of (1) to (4) Regarding the method for fixing heavy metals in fly ash,
(6) The heavy metal is one or more selected from the group consisting of lead, mercury, chromium, cadmium, zinc, and copper. The fly ash according to any one of (1) to (5), The present invention relates to a heavy metal immobilization method.

  By using the method of the present invention, it has become possible to immobilize heavy metals contained in fly ash more effectively than in the past. Considering that leakage of heavy metals into the environment must be prevented, it can be said that the industrial applicability of the present invention is great.

  In the method for immobilizing heavy metals contained in the fly ash of the present invention, the heavy metal-containing fly ash, water, and piperazine-N, N′-biscarbodithioic acid or a salt thereof are 80 ° C. or higher, preferably 100 ° C. or higher. It is characterized by heating.

  The heavy metal-containing fly ash used in the method of the present invention is not particularly limited, and examples thereof include fly ash discharged from incineration plants such as municipal waste and industrial waste. Moreover, in the treatment process of heavy metal-containing fly ash, alkali such as slaked lime may be added first, and it is preferable to use the method of the present invention for these fly ash. The heavy metal contained is not particularly limited as long as it is a heavy metal that can be insolubilized from an aqueous solution by chelating a carbodithioic acid group, and specifically, lead, mercury, chromium, cadmium, zinc, copper, nickel, arsenic, selenium. In particular, lead, mercury, chromium, cadmium, zinc, and copper are preferable because of their high chelating effect.

  Piperazine-N, N′-biscarbodithioic acid or a salt thereof used in the present invention can be obtained by reacting piperazine with carbon disulfide in the presence of a base, if necessary. These can be used after being separated as a salt, but can also be used as they are after the reaction without performing separation and purification. When water is used as a reaction solvent, it can be added to fly ash as an aqueous solution. When the reaction is carried out using 2 mol or more of carbon disulfide with respect to 1 mol of piperazine, piperazine-N, N′-biscarbodithioic acid is obtained, and the reaction is carried out at 2 mol or less. Is a mixture of piperazine-N-carbodithioic acid and piperazine-N, N′-biscarbodithioic acid, both of which can be used.

  The piperazine-N, N′-biscarbodithioate of the present invention is preferably an alkali metal, alkaline earth metal or ammonium salt. Of these, lithium, sodium, potassium, magnesium, calcium, and ammonium salts that are soluble in water are preferred. Furthermore, a thermally stable and inexpensive sodium salt or potassium salt is particularly preferred.

  The amount of piperazine-N, N′-biscarbodithioic acid or a salt thereof used in the present invention varies depending on the content of heavy metal in the fly ash to be treated and the form of heavy metal, but is not particularly limited. The range of 0.1 to 40% by weight can be preferably exemplified.

  In the present invention, a heavy metal fixing agent other than piperazine-N, N′-biscarbodithioic acid or a salt thereof can be used in combination as the heavy metal fixing agent. Examples of such heavy metal fixing agents include sodium sulfide and potassium sulfide. Inorganic sulfides such as sodium hydrosulfide, potassium hydrosulfide, sodium polysulfide, potassium polysulfide, ammonium polysulfide, dialkyldithiocarbamate such as sodium dialkyldithiocarbamate, potassium dialkyldithiocarbamate, dithiocarboxyl group or its salt -Ethylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine (molecular weight 1000 or more), diethylenetriamine, triethylenetetramine, 1,3-diaminopropane, hexamethylenedi as substituents Min, can be mentioned polyamine derivatives such as octamethylene diamine, it may be used one kind of them or a mixture of two or more thereof.

In addition, in the present invention, in the fly ash treatment, gluconate polyoxyalkylene condensate, lignin sulfonic acid or its salt, oxycarboxylic acid or its salt, naphthalene sulfonate formalin condensate, phenol sulfonate formalin condensate Various dispersions such as phenol sulfanilate formalin condensate, phenol melamine methylolated sulfonate bridge cocondensate, melamine sulfonate formalin condensate, polyoxyethylene aryl ethers, dialkyl sulfosuccinate, polyoxyalkylene copolymer A compound having a surface activity such as wetting or penetration can be added as appropriate.
Moreover, a cement can be added as needed, and specific examples of such cement include Portland cement. The amount of cement to be used is not particularly limited, but is in the range of 1 to 50 parts by weight, preferably in the range of 5 to 25 parts by weight with respect to 100 parts by weight of fly ash.

  The amount of water used in the method of the present invention is not particularly limited, but in order to facilitate disposal of the treated fly ash, it is usually used in the range of 5 to 400% by weight with respect to the fly ash to be treated. Preferably, it is used in the range of 5 to 50% by weight. If it is 5% by weight or less, the kneading state with the drug may not be sufficient, and if it is used 400% by weight or more, there is a problem that it takes time to treat water. Considering that it may be difficult to dispose of fly ash in a liquid state, etc., 50% by weight or less is preferable. When an aqueous solution of piperazine-N, N′-biscarbodithioic acid or a salt thereof is used, the water in the aqueous solution can be all or part of the added water.

  In the method of the present invention, the method for adding water and piperazine-N, N′-biscarbodithioic acid or a salt thereof is not particularly limited. For example, a method in which fly ash is kneaded or mixed within the range of the amount of water described above and then treated by adding piperazine-N, N′-biscarbodithioic acid or a salt thereof or an aqueous solution in which they are dissolved, or A method of dissolving and adding a predetermined amount of piperazine-N, N′-biscarbodithioic acid or a salt thereof to the total amount of water to be used can be employed.

  The method of the present invention is further characterized by heating to 80 ° C. or higher, preferably 100 ° C. or higher. The method for heating is not particularly limited, but for example, the method of heating the outer periphery or the inside of the reaction vessel with a heat source, the method of heating the heat medium through the blades of the stirrer, the method of passing the mixture through the heat medium, etc. , A method of adding water previously heated to 80 ° C. or higher, or an aqueous solution of piperazine-N, N′-biscarbodithioic acid or a salt thereof, adding water to high-temperature fly ash immediately after collecting the filter, and the remaining heat It is preferable to heat while mixing or kneading.

  In the method of the present invention, a mixture of heavy metal-containing fly ash, water, and piperazine-N, N′-biscarbodithioic acid or a salt thereof is finally mixed at 80 ° C. or higher, preferably 100 ° C. or higher for a predetermined time. If it can be kneaded, the heating time is not particularly limited, but in order to prevent the fly ash from scattering, etc., water and piperazine-N, N′-biscarbodithioic acid or a salt thereof are added to the fly ash. After the addition, a method of heating to 80 ° C. or higher and mixing or kneading is preferable. The temperature at which water or the like is added is not particularly limited, but it is preferably added at a temperature of 80 ° C. or lower so that fly ash and water are sufficiently mixed. The heating can be performed under normal pressure or under pressure.

In the method of the present invention, the heating time largely depends on the nature and type of fly ash, but is generally about 0.01 hour to 24 hours, and 0.05 hours to the handling property etc. One hour is preferred.
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples.

  Water of the amount shown in Table 1 and piperazine at room temperature with respect to 100 parts by weight of alkaline lead-containing waste incineration fly ash (Pb content: 9.6 mg / L) pretreated with slaked lime and having a pH of 12 or more 1 part by weight of an aqueous solution of —N, N′-biscarbodithioic acid potassium salt (solid content: 40%) was added, and the mixture was sufficiently kneaded with a Hope mixer. In Example 1-3, 10 parts by weight of Portland cement was further added and kneaded. In Example 1-1 and Example 1-3, the kneaded product is put in a 200 ml polycup and the mouth is sealed with Saran wrap. In Example 1-2, the kneaded product is put in a glass petri dish and covered. Then, each was heated to the temperature shown in Table 1 for 1 hour and then allowed to stand at 25 ° C. for 1 day, and then a heavy metal dissolution test was conducted according to Notification No. 13 of the Environment Agency. The results are summarized in Table 1.

  400 parts by weight of water and piperazine-N, at room temperature, with respect to 100 parts by weight of alkaline lead-containing waste incineration fly ash (Pb content: 9.6 mg / L) pretreated with slaked lime and having a pH of 12 or more 1 part by weight of an N′-biscarbodithioic acid potassium salt aqueous solution (solid content: 40%) was added, and the mixture was heated and mixed at 80 ° C. for 1 hour. Thereafter, water was distilled off under reduced pressure and left at 25 ° C. for 1 day, and then a heavy metal elution test was performed according to Notification No. 13 of the Environment Agency. The results are summarized in Table 1.

Comparative Example 1
The same procedure as in Example 1 was performed except that kneading was performed at room temperature without performing a heat treatment at 80 ° C. The results are shown in Table 1.

  From Table 1, it was found that the amount of lead elution was reduced by heat treatment at 80 ° C. or higher. Moreover, it turned out that lead can be insolubilized more effectively by heat-processing 100 degreeC or more.

  To 2L tetraback, add 100g of stoker furnace fly ash, 5g of heavy metal fixing agent shown in Table 2 and 30g of water, mix well, heat to each temperature shown in Table 2 for 30 minutes, and then use gas detector tube The amount of amine and carbon disulfide generated was measured. The results are summarized in Table 2.

  From Table 2, when piperazine-N, N′-biscarbodithioate is used, it is possible to work in a safe environment under heating conditions with little generation of carbon disulfide and amine by heating. I knew it was possible.

Claims (6)

A method for immobilizing heavy metals in fly ash, comprising heating heavy metal-containing fly ash, water, and piperazine-N, N′-biscarbodithioic acid or a salt thereof to 80 ° C. or higher. A method for immobilizing heavy metals in fly ash, comprising heating heavy metal-containing fly ash, water, and piperazine-N, N′-biscarbodithioic acid or a salt thereof to 100 ° C. or higher. Water and piperazine-N, N′-biscarbodithioic acid or a salt thereof are added to heavy metal-containing fly ash, heated to 80 ° C. or higher, kneaded or mixed, and fixed to heavy metal in fly ash Method. Water and piperazine-N, N′-biscarbodithioic acid or a salt thereof are added to heavy metal-containing fly ash, heated to 100 ° C. or higher, kneaded or mixed, and fixed to heavy metal in fly ash Method. The heavy metal in fly ash according to any one of claims 1 to 4, wherein the salt of piperazine-N, N'-biscarbodithioic acid is an alkali metal salt, an alkaline earth metal salt or an ammonium salt. Immobilization method. The heavy metal immobilization method in fly ash according to any one of claims 1 to 5, wherein the heavy metal is at least one selected from the group consisting of lead, mercury, chromium, cadmium, zinc and copper.