JP2011194248A - Heavy metal treatment agent and stable treatment method for heavy metal pollutant using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method for heavy metal pollutant which solves the problem that heavy metal elutes with pH fluctuation of a processed object in the conventional disposal method which sets the pH of eluate to 8-11 in the Environment Agency notification No.13 test for heavy metal pollutant in the year 1973.SOLUTION: When heavy metal pollutant is processed using a carbodithioate salt of an amine, the heavy metal can be processed with high efficiency and yet can be immobilized without the eluate of heavy metal with pH fluctuation of a processed object by using a metal hydroxide and a carbodithioate salt of an amine and by setting the pH of eluate to higher than 12 in the Environment Agency notification No.13 test for processed objects in the year 1973.

Description

  The present invention relates to solid waste containing heavy metals, for example, incineration ash and fly ash discharged from a garbage incineration plant, soil contaminated with heavy metals, lead contained in sludge generated after wastewater treatment, cadmium, chromium, The present invention relates to a heavy metal treating agent that can easily, efficiently and stably fix harmful heavy metals such as mercury and that does not re-elute heavy metals from a once treated object, and a treatment method using the same.

  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 chemical treatment method, and a method of insolubilizing heavy metals by adding a heavy metal treatment agent such as a chelate-based chemical or an inorganic chemical is used.

  As chelating agents, carbodithioates of amine derivatives are mainly used. In particular, piperazine carbodithioate produces less harmful gases such as hydrogen sulfide and carbon disulfide than other amine derivatives, and is widely used as a heavy metal treating agent. (See Patent Document 1) In recent years, there has been a tendency for molten fly ash and the like containing a high concentration of heavy metal to increase, and the amount of heavy metal treating agent used is increasing, and there is a need for a more efficient treatment method for fly ash. Is growing.

  On the other hand, a fly ash treatment method using a chelating agent, a metal hydroxide, a metal carbonate and the like in combination has been proposed. (For example, refer to Patent Documents 2 and 3) In addition, a fly ash formulation in which an inorganic drug and a pH adjuster are used in combination has been proposed. (For example, refer to Patent Document 4) In these conventional methods, the pH of the treated product is 8 to 11 where the solubility of lead is lowered. However, when the pH is 8 to 11, the lead salt is insolubilized without eluting, but in an environment where the treated product is disposed of in landfill, when it comes into contact with other strongly alkaline treated ash, etc., or acidic substances such as acidic sludge There was concern about the re-elution of heavy metals due to contact with or exposure to acid rain.

Japanese Patent No. 3391173 JP 2006-130438 A JP-A-8-52446 JP 10-113641 A

  The object of the present invention is to be able to easily, efficiently and stably treat heavy metal pollutants contaminated with heavy metals such as lead, cadmium, chromium and mercury. It is an object of the present invention to provide a heavy metal treating agent and a method for treating heavy metal pollutants that do not re-elute heavy metals even in contact with substances.

  As a result of intensive investigations to solve the above-mentioned problems, the present invention is composed mainly of heavy metal contaminants whose pH of the eluate of the Environmental Agency Notification No. 13 test is 1 to 12, and carbodithioate of amine. When a heavy metal treatment agent containing a metal hydroxide exceeding 5 wt% is added and kneaded and the pH of the eluate in the same test of the treated product is more than 12 and 14 or less, the treated product pH after treatment is large. Even if it fluctuates, it has been found that there is no re-elution of heavy metals, and in particular when the chelating agent uses piperazine carbodithioate, it has been found that its performance is excellent, and the present invention has been completed.

  Hereinafter, the heavy metal treating agent and the heavy metal contaminant treatment method of the present invention will be described in detail.

  The heavy metal treating agent of the present invention comprises more than 1.5% by weight of metal hydroxide and amine carbodithioate. By making the hydroxide concentration more than 1.5% by weight, the alkalinity of the heavy metal treating agent is increased. By increasing the alkalinity of the heavy metal treatment agent, re-elution of heavy metal from the treated product after heavy metal treatment can be suppressed.

  The amine carbodithioate in the present invention is not particularly limited as long as it is a carbodithioate derived from an amine compound, but a piperazine carbodithioate having very high stability is preferable. Piperazine carbodithioate is superior to other amine carbodithioates in terms of heat resistance and acid resistance, does not generate harmful gases such as carbon disulfide and hydrogen sulfide, and is treated with piperazine carbodithioate. By setting the pH of the eluate of the product to more than 12, it is possible to immobilize heavy metals as chelate complexes and prevent re-elution of heavy metals due to decomposition of chelate complexes when they come into contact with acidic or alkaline substances at the final disposal site. it can.

  Examples of the piperazine carbodithioate 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 piperazine carbodithioate in the heavy metal treating agent of the present invention is preferably high, and is preferably in the range of 10 to 60% by weight, particularly 20 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 metal hydroxide used in the present invention is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth metals such as magnesium hydroxide and calcium hydroxide. Examples thereof include hydroxides and transition metal hydroxides. Particularly preferred are sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide which are inexpensive and easily available.

  The concentration of the metal hydroxide in the heavy metal treating agent of the present invention depends on the acidity of the heavy metal contaminant and the concentration of the carbodithioate of the amine, but it must be over 1.5% by weight, preferably 3 to 30%. % By weight, more preferably in the range of 4.5-30. When the concentration is low, the pH of the treated product cannot be controlled within the target range, and when it is too high, there is a problem in terms of the solubility and viscosity of the heavy metal treating agent.

  The reason why the re-elution of heavy metal is suppressed by using the heavy metal treatment agent of the present invention is not necessarily clear, but by setting the pH to more than 12, the heavy metal in the heavy metal contaminant is first eluted once before the heavy metal treatment. Therefore, it is considered that the treatment with the heavy metal treating agent of the present invention is reliably performed.

  The heavy metal treating agent of the present invention may contain other components as long as the effects of the present invention are not hindered. Examples of other components include inorganic heavy metal treating agents and organic solvents.

  The heavy metal treatment method using the heavy metal treatment agent of the present invention is a mixture of a heavy metal pollutant whose pH of the eluate of the Environmental Agency Notification No. 13 test is 1 to 12 and the heavy metal treatment agent of the present invention. The pH of the eluate in the same test is adjusted to more than 12 and 14 or less. By setting the pH of the eluate in the same test of the treated product to be more than 12, heavy metals are stably insolubilized and will not be eluted again even when the pH fluctuates. Moreover, heavy metals can be insolubilized with high efficiency.

  At the eluate pH 12 or less of the Environmental Agency Notification No. 13 test of treated products, a part of heavy metals are not insolubilized by the amine carbodithioate, but are present in the form of hydroxide or the like, and hydroxylated when the pH changes. There is a possibility that substances will dissolve and re-elute.

  In the present invention, the amount of heavy metal treatment agent added varies depending on the concentration of heavy metal treatment agent, the state of heavy metal contaminants, the content of heavy metal and the form of heavy metal. Used in the range of 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.

  In the method for treating heavy metal contaminants of the present invention, depending on the state of heavy metal contaminants, the content of heavy metals and the form of heavy metals, the acidity of the heavy metal contaminants, the amine carbodithioate and the metal hydroxide are added separately, It can be processed by mixing. For example, when the acidity of heavy metal pollutants is high, the amount of metal hydroxide required increases, so adding them separately can increase the pH of the treated product more efficiently and improve the efficiency of heavy metal treatment To do.

  When the amine carbodithioate and the metal hydroxide are added separately, the order of addition is not particularly limited, but it is preferable to add the metal hydride first or simultaneously. In particular, when the acidity of the heavy metal contaminant is high, it is preferable to add the metal hydroxide first. By adding the metal hydroxide first, the heavy metal contaminant is made alkaline in advance, and the heavy metal is easily eluted, and the treatment efficiency with the carbodithioate of the amine is improved.

  Examples of heavy metal contaminants in the method for treating heavy metal contaminants of the present invention include fly ash, soil, sludge and the like.

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

  In the treatment of heavy metal contaminants using the heavy metal treatment agent of the present invention, heavy metal can be treated with high efficiency, and there is no problem that heavy metal is re-eluted due to the change in pH after the treatment, thereby improving the reliability of heavy metal treatment. Can be increased.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
(Heavy metal processing ability test)
Example 1
Fly ash (Ca = 12.0%, Mg = 0.4%, Na = 3.3%, K = 1.8%, Pb = 10400ppm, Zn = 39300ppm, Cu = 17700ppm, Environment Agency Notification No. 13 10 parts by weight of water (20% by weight with respect to fly ash) and 50 parts by weight of the eluate of the test and a heavy metal treating agent (piperazine-N, N′-biscarbodithioate potassium 35) 7.5 parts by weight (15% by weight with respect to fly ash) was added and kneaded. This treated product was designated as treated product A.

  When the processed product A was subjected to a dissolution test in accordance with the Environmental Agency Notification No. 13 test of 1973, the pH of the eluate was 12.5, and lead and cadmium were less than 0.05 mg / L and were insolubilized.

  9 parts by weight of a 48% aqueous sodium hydroxide solution was added to the treated product A, and an elution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The results are shown in Table 1. At pH 13, the elution amounts of lead and cadmium were lower than the standard values, and there was no re-elution.

Example 2
15 parts by weight of 60% nitric acid was added to the processed product A, and an elution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The results are shown in Table 1. At pH 5.5, the elution amounts of lead and cadmium were lower than the standard values, and there was no re-elution.

Comparative Example 1
50 parts by weight of ash similar to Example 1, 5 parts by weight of water (10% by weight with respect to fly ash), 15 parts by weight of sulfuric acid band (30% by weight with respect to fly ash), 75% phosphoric acid 2.5 parts by weight (5% by weight based on fly ash) was added and kneaded. This treated product was designated as treated product B.

  Dissolution test was performed on treated product B according to the Environmental Agency Notification No. 13 test in 1973. The pH of the eluate was 10.3, and the elution amount of lead and cadmium was less than 0.05 mg / L, which was insolubilized. It was.

  10 parts by weight of a 48% aqueous sodium hydroxide solution was added to the treated product B, and a dissolution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The results are shown in Table 1. At pH 13, the elution amount of lead exceeded the reference value and was eluted again.

Comparative Example 2
14 parts by weight of 60% nitric acid was added to the treated product B, and an elution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. The results are shown in Table 1. At pH 5.7, the elution amounts of lead and cadmium exceeded the standard values and were eluted again.

実施例３
飛灰（Ｃａ＝０．７８％、Ｍｇ＝０．２％、Ｎａ＝１４．６％、Ｋ＝１３．５％、Ｐｂ＝１４７００ｐｐｍ、Ｚｎ＝９４０００ｐｐｍ、Ｃｕ＝３７００ｐｐｍ、Ｃｄ＝７２２ｐｐｍを含み、環境庁告示１３号試験の溶出液のｐＨが６．１）５０重量部に対し、水酸化カルシウム５重量部（飛灰に対して１０重量％）、水７．５重量部（飛灰に対して１５重量％）と、ピペラジン−Ｎ，Ｎ’−ビスカルボジチオ酸カリウム（４０重量％含有する水溶液）を５．５重量部（飛灰に対して１１重量％）加え、混練した。

Example 3
Fly ash (Ca = 0.78%, Mg = 0.2%, Na = 14.6%, K = 13.5%, Pb = 14700 ppm, Zn = 94000 ppm, Cu = 3700 ppm, Cd = 722 ppm, environment The pH of the eluate of the Agency Notification No. 13 test is 6.1) 50 parts by weight, 5 parts by weight of calcium hydroxide (10% by weight with respect to fly ash), 7.5 parts by weight of water (with respect to fly ash) 15% by weight) and 5.5 parts by weight (11% by weight based on fly ash) of piperazine-N, N′-biscarbodithioate (40% by weight aqueous solution) were added and kneaded.

  After the treatment, a dissolution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. Table 2 shows the pH of the eluate and the results of elution of lead. The pH was 12.2, the elution amount of lead and cadmium was below the standard value, and it was insolubilized. By adding potassium hydroxide, the pH became more than 12, and it was thought that heavy metals eluted and became easy to process.

Comparative Example 3
Using the same ash as in Example 3, 5 parts by weight of water (10% by weight with respect to fly ash) and 50% by weight of fly ash, tetraethylenepentamine-N1, N2, N3, N4, N5-penta 9 parts by weight (18% by weight based on fly ash) of sodium carbodithioate (40% by weight aqueous solution) was added and kneaded.

  After the treatment, a dissolution test was conducted according to the Environmental Agency Notification No. 13 test in 1973. Table 2 shows the pH of the eluate and the results of elution of lead. The pH was 11.8, lead elution exceeded the standard value, and treatment was insufficient despite the use of a larger amount of heavy metal treatment agent than Example 3, and hydrogen sulfide gas and carbon disulfide gas were generated. did.

  12.5 parts by weight (25% by weight based on fly ash) of tetraethylenepentamine-N1, N2, N3, N4, N5-pentacarbodithioic acid sodium (an aqueous solution containing 40% by weight) in the same ash as above When added, it could be processed.

  It was confirmed that the treatment efficiency was lowered and harmful gases were generated when the strongly acidic ash was treated without adding alkali hydroxide.

（重金属錯体の耐酸性）
鉛５０ｍｇ／Ｌの水溶液にピペラジン−Ｎ，Ｎ’−ビスカルボジチオ酸カリウム、ジエチルカルボジチオ酸カリウム、エチレンジアミン−Ｎ，Ｎ’−ビスカルボジチオ酸ナトリウム、ジエチレントリアミン−Ｎ１、Ｎ２、Ｎ３−トリスカルボジチオ酸ナトリウム、テトラエチレンペンタミン−Ｎ１，Ｎ２，Ｎ３，Ｎ４，Ｎ５−ペンタカルボジチオ酸ナトリウムをそれぞれ、ＣＳ_２／Ｐｂのモル比が１．５となるよう添加し、得られた重金属キレート錯体をろ過し、採取した。採取した重金属キレート錯体を十分に洗浄した後、ｐＨ２の塩酸溶液１００ｍＬ中に移し、１時間攪拌した。その後、ろ過を行い、ろ液中の鉛の濃度をＩＣＰにて分析を行った。結果を表３に示す。

(Acid resistance of heavy metal complexes)
Piperazine-N, N'-biscarbodithioate potassium, diethyl carbodithioate potassium, ethylenediamine-N, N'-biscarbodithioate sodium, diethylenetriamine-N1, N2, N3-triscarbodithio Sodium nitrate, tetraethylenepentamine-N1, N2, N3, N4, sodium N5-pentacarbodithioate were added so that the molar ratio of CS ₂ / Pb was 1.5, respectively, and the resulting heavy metal chelate complex Filtered and collected. The collected heavy metal chelate complex was thoroughly washed, then transferred into 100 mL of pH 2 hydrochloric acid solution, and stirred for 1 hour. Thereafter, filtration was performed, and the concentration of lead in the filtrate was analyzed by ICP. The results are shown in Table 3.

  Piperazine carbodithioate showed no elution of lead, and the stability of the heavy metal chelate complex to pH fluctuations was superior to carbodithioate of other amines.

Claims (4)

The carbodithioate of amine and metal hydroxide were separately added to the heavy metal pollutant whose pH of the eluate of the Environmental Agency Notification No. 13 test is 1 to 12, and the eluate of the eluate in the same test after kneading was mixed. A method for treating heavy metal contaminants, characterized in that the pH is between 12 and 14 or less. The method for treating heavy metal contaminants according to claim 1, wherein the amine carbodithioate is a piperazine carbodithioate. The method for treating heavy metal contaminants according to claim 1 or 2, wherein the heavy metal contaminants are fly ash, soil, and sludge. The processing method of the heavy metal pollutant in any one of Claims 1-3 in which a heavy metal pollutant contains either lead, cadmium, chromium, and mercury.