JP4867700B2 - Heavy metal treatment agent and method for treating heavy metal contaminants using the same - Google Patents

Description

  The present invention relates to solid waste containing heavy metals, for example, incineration ash and fly ash discharged from garbage incineration sites, soil contaminated with heavy metals, lead contained in sludge generated after wastewater treatment, cadmium, mercury, Regarding heavy metal treatment agents and heavy metal contaminant treatment methods that can easily and efficiently fix harmful heavy metals such as arsenic, selenium, chromium, etc., especially cationic heavy metals such as lead, arsenic, etc. The present invention relates to an agent and method capable of simultaneously treating anionic species.

  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 insolubilizing heavy metals by adding a heavy metal treatment agent such as a chelate-based drug is used.

As chelating agents, amine derivative carbodithioate is mainly used. Especially piperazine carbodithioate has less harmful gas generation such as hydrogen sulfide and carbon disulfide compared with other amine derivatives. Widely used as an agent. (For example, see Patent Document 1)
However, among the harmful elements contained in heavy metal contaminants, those present in oxygenate anions such as arsenic have been difficult to treat with chelating agents such as amine carbodithioates.

On the other hand, the method of using powdery slaked lime together is proposed. (Patent Document 2)
According to the method using powdered slaked lime, it is said that arsenic can be removed because it becomes an insoluble calcium arsenate, etc., and elution is prevented, and powdered slaked lime also has the effect of adsorbing and collecting heavy metals. ing. However, the use of powdered slaked lime alone has not yet sufficiently fixed arsenic.

Furthermore , in order to use powdered slaked lime or powdered chemicals, powder supply equipment is necessary, and the operability is poor, and when these are made into a single slurry, solid content settles and performance varies. There was a problem that occurred.

Japanese Patent No. 3391173 JP 2003-181411 A

The object of the present invention is to be able to easily and stably treat heavy metal pollutants complex-contaminated with harmful cationic species such as lead, cadmium and mercury and harmful anionic species such as arsenic, selenium and chromium. An object of the present invention is to provide a heavy metal treating agent and a treatment method using the same.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention used an amine carbodithioate to remove heavy metal contaminants containing arsenic and containing any of lead, cadmium, chromium, mercury, and selenium. During processing, it was found that phosphorus in heavy metal pollutants affected the elution of arsenic, and by using alkaline earth metal compounds, especially water-soluble alkaline earth metal compounds and amine carbodithioates. As a result, it was found that phosphorus was immobilized and the performance of immobilizing heavy metals of anionic species such as arsenic was stabilized, and the present invention was completed.

  Hereinafter, the heavy metal treating agent and the treating method according to the present invention will be described in detail.

  The heavy metal treating agent of the present invention comprises an amine carbodithioate, an alkaline earth metal salt, and water.

  Amine carbodithioates immobilize harmful cationic species such as lead, cadmium and mercury, and alkaline earth metal salts immobilize phosphorus in heavy metal pollutants that inhibit the immobilization of anionic species such as arsenic Use.

  The amine carbodithioate in the present invention is not particularly limited, and examples thereof include carbodithioates obtained from amines such as diethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and piperazine. . In particular, piperazine carbodithioate is preferable because of its high stability.

  Here, when the alkaline earth metal water-soluble salt is alkaline, a hydroxide is likely to precipitate, a scale is generated during storage, and the calcium concentration in the aqueous solution may change over time.

  With normal amine dithiocarbamate, dithiocarbamate may be decomposed when it is lowered to a pH at which calcium salt does not precipitate, and harmful gases such as carbon disulfide and hydrogen sulfide may be generated. It is necessary to adjust according to the stability (acid resistance, alkali resistance, etc.).

On the other hand, piperazine carbodithioate has excellent acid resistance and is difficult to be decomposed even when the pH is lowered. Examples include piperazine-N-carbodithioate, piperazine-N, N′-biscarbodithioate, or a mixture thereof. In particular, piperazine-N, N′-biscarbodithioate or a compound having a high ratio thereof is preferable. As these salts, alkali metal salts, alkaline earth metal salts, and ammonium salts are used, and sodium salts and potassium salts are preferable from the viewpoint of thermal stability and solubility.

  The concentration of the amine carbodithioate in the heavy metal treating agent of the present invention is preferably high, and is preferably in the range of 1 to 60% by weight, particularly 3 to 45% by weight. When the concentration is too low, the effect is reduced, and when it is too high, there is a problem in terms of solubility and viscosity.

  The alkaline earth metal salt in the present invention is not particularly limited, and examples thereof include hydroxide, chloride, nitrate, nitrite and carbonate. Water-soluble alkaline earth metal salts are particularly preferable. When water-soluble alkaline earth metal salts are used, the phosphorous immobilization effect that inhibits the immobilization of anionic species is higher than that of powdered or slurry alkaline earth metal salts. It can be used as an aqueous solution containing no solid content, and has high operability and storage stability.

  The water-soluble alkaline earth metal salt is not particularly limited, but an alkaline earth metal salt having high solubility is preferable, and hydroxide, chloride, nitrate, and nitrite are preferably used. Of these, chlorides having high solubility, low cost, and neutrality that do not affect pH are preferable.

  Further, as the alkaline earth metal of the alkaline earth metal salt, magnesium and calcium are preferable because they are inexpensive and easily available.

  The concentration of the alkaline earth metal salt in the present invention is preferably 0.1 to 50% by weight, although it depends on the phosphorus content in the heavy metal contaminant. Among the phosphorus components contained in heavy metal contaminants, the amount of alkaline earth metal salt required is high when there is a large amount of soluble phosphoric acid, and the alkaline earth material that is required when there is a low amount of soluble phosphoric acid. Since the amount of the metal salt is reduced, it is preferable that phosphorus in the heavy metal contaminant to be treated is converted to phosphoric acid so that the phosphoric acid is equal to or more than the equivalent amount for forming the alkaline earth metal salt.

In the heavy metal treatment of the present invention, other components may be added as long as the effects of the present invention are not hindered.
Examples thereof include organic solvents, amines, alkali metal hydroxides, and the like.

  The method for treating heavy metal contaminants using the heavy metal treating agent of the present invention is not particularly limited, and includes the heavy metal treating agent of the present invention (or the case where each component thereof is added separately) and the heavy metal contaminant. What is necessary is just to mix.

  The amount of the heavy metal treating agent of the present invention varies depending on the state of heavy metal contaminants, the content of heavy metals and the form of heavy metals, but is usually used in the range of 0.01 to 30% by weight with respect to fly ash. 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.

  Further, the method for treating heavy metal contaminants of the present invention is not particularly limited, but depending on the state of heavy metal contaminants, the content of heavy metals and the form of heavy metals, the content of phosphorus and the form of phosphorus, alkaline earth The metal salt and amine carbodithioate can be added and mixed.

  With respect to the phosphorus content that adversely affects arsenic treatment, the addition amount of alkaline earth metal salt is 0.1 to 10 times equivalent, more preferably 0.3 to 3 with respect to phosphorus contained in the heavy metal contaminant. It is preferable to add so that it may become a double equivalent. Of the phosphorus contained in heavy metal contaminants, the amount of alkaline earth metal salt required is high when there is a large amount of soluble phosphoric acid, and the alkaline earth metal salt required when there is a small amount of soluble phosphoric acid. The amount of can be small. If the amount of phosphorus in the heavy metal contaminant is greater than that of the heavy metal, the amine carbodithioate and the alkaline earth metal salt may be added separately.

  Although the heavy metal contaminant in this invention will not be specifically limited if it is a substance containing a heavy metal, Fly ash, soil, sludge, etc. are illustrated.

  Examples of harmful heavy metals in these heavy metal contaminants include substances containing any of lead, cadmium, mercury, arsenic, selenium, and hexavalent chromium.

  The heavy metal treating agent of the present invention can simultaneously treat cationic species such as lead, cadmium and mercury and anionic species such as arsenic, selenium and chromium with respect to heavy metal pollutants containing phosphorus, and can reliably treat heavy metal contaminants. Can increase the sex.

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

Example 1
Fly ash (Ca = 2.5%, Mg = 0.7%, Na = 1.2%, Fe = 13.8%, Pb = 3100 ppm, Cu = 2900 ppm, Cd = 77 ppm, As = 240 ppm, Se = 2 ppm , P = including 5000 ppm), 5 parts by weight of water (10% by weight with respect to fly ash), heavy metal treating agent (piperazine-N, N′-biscarbodithioate potassium 4% by weight, chloride) 7 parts by weight (aqueous solution containing 15% by weight of calcium) (14% by weight with respect to fly ash and 1.2 equivalents of calcium with respect to phosphorus) was added and kneaded. Although the pH of the heavy metal treating agent was 10.5, there was no generation of harmful gases such as carbon disulfide and hydrogen sulfide, and there was no generation of scales of hardly soluble calcium salts.

  After the treatment, a dissolution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. Table 1 shows the elution results of heavy metals. The elution of arsenic, selenium, lead and cadmium was below the standard value and was insolubilized.

Example 2
Fly ash (Ca = 1.19%, Mg = 0.07, Na = 14.6%, Fe = 0.2%, Pb = 4600 ppm, Cu = 3700 ppm, Cd = 133 ppm, As = 44 ppm, Se = 6 ppm, 50 parts by weight of P (including P = 25500 ppm), 2.5 parts by weight of water (5% by weight with respect to fly ash), and a heavy metal treating agent (piperazine-N, N′-biscarbodithioate potassium 40% by weight) 3 parts by weight (6% by weight with respect to fly ash) and 5 parts by weight of 35% calcium chloride aqueous solution (10% by weight with respect to fly ash and 0.38 equivalents of calcium with respect to phosphorus) did.

  After the treatment, a dissolution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The elution results of heavy metals are also shown in Table 1. The elution of arsenic, selenium, lead and cadmium was below the standard value and was insolubilized.

Comparative Example 1
The same operation as in Example 1 was performed except that calcium chloride was not included. The results are shown in Table 1. Although harmful cation species lead and cadmium were below the standard values, harmful anion species arsenic and selenium exceeded the standard values.

Comparative Example 2
The same operation as in Example 2 was performed except that calcium chloride was not used. The results are shown in Table 1. Although harmful cation species lead and cadmium were below the standard value, harmful anion species arsenic and selenium were above the standard value.

Reference example 1
The same operation as in Example 1 was performed using tetraethylenepentamine carbodithioate as the carbodithioic acid of the amine. The carbodithioate of tetraethylenepentamine had a pH of 11.0, and the carbodithioate was decomposed as the pH decreased, and generation of carbon disulfide and hydrogen sulfide was observed. On the other hand, when pH was not lowered, calcium chloride formed hydroxides and scales were generated in the heavy metal treating agent.

  After the treatment, a dissolution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The elution results of heavy metals are also shown in Table 1. Despite the generation of toxic gases accompanying the decomposition of carbodithioate, the elution of arsenic, selenium, lead and cadmium was below the standard value and was insolubilized.

Claims (7)

A heavy metal treating agent comprising piperazine carbodithioate, an alkaline earth metal salt, and water. The heavy metal treating agent according to claim 1, wherein the alkaline earth metal salt is a water-soluble compound. The heavy metal treating agent according to claim 2, wherein the water-soluble alkaline earth metal salt is a chloride. A method for treating a heavy metal pollutant, comprising mixing the heavy metal treating agent according to any one of claims 1 to 3 and a heavy metal pollutant containing phosphorus. A method of heavy metal contaminants in a mixture of heavy metals treatment agent according to claim 1 to process the heavy metals, 0.1 in a phosphoric alkaline earth metal compound contained in the heavy metal contaminants A method for treating heavy metal contaminants, characterized in that the equivalent amount is 10 times. The method for treating heavy metal contaminants according to any one of claims 4 to 5, wherein the heavy metal contaminant is fly ash, soil, or sludge. The method for treating a heavy metal pollutant according to any one of claims 4 to 6, wherein the heavy metal pollutant contains arsenic and contains any one of lead, cadmium, chromium, mercury, and selenium.