JPH0995659A - Production of metal scavenger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a metal scavenger for mercury, lead, etc., capable of effectively removing residual hydrogen sulfide, thiocarbonate, etc., as hydrogen sulfide gas without leaving precipitate after the treatment. SOLUTION: An aqueous solution of a metal scavenger having a dithioic acid (salt) group as a functional group bonded to N of an amine such as ethylenediamine and/or O of hydroxyl group of a hydroxy compound such as ethanol is incorporated with an acid (preferably a mineral acid) to keep the aqueous solution in neutral or weakly alkaline state (especially preferably to pH7.5-9). Preferably, an inert gas such as N2 gas is introduced into the aqueous solution of the metal scavenger and the solution is heated at about 20-100 deg.C usually for about 30min to 6hr to remove hydrogen sulfide in high efficiency.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to a method for producing a metal collecting agent.

[0002]

2. Description of the Related Art There are strict regulations on metals contained in wastewater, especially mercury, cadmium, zinc, lead, copper, chromium, etc., which are harmful to the human body. Various methods for removal have been investigated.

[0003] Conventional methods for removing metals contained in wastewater and the like include, for example, neutralization coagulation sedimentation, ion flotation, ion exchange, electrolytic flotation, electrodialysis, adsorption, and reverse osmosis. Are known. However, in the neutralization coagulation sedimentation method, there is a problem in working that a large amount of the generated metal hydroxide sludge must be treated, and metal ions are re-eluted from the discarded sludge into rivers, seawater, etc. There are problems such as causing pollution and it is not easy to reduce the metal ion concentration in the wastewater to below the standard value established by the government.Ion flotation method, ion exchange method, electrolytic flotation method, electrodialysis method, adsorption Method, reverse osmosis method, etc., had problems in metal removal rate, operability, running cost, etc.

Therefore, a method of collecting and removing the metal in the waste water by using a metal collector has been widely used in place of these methods, and as the metal collector, mercury, lead, etc. are used. A compound having a dithio acid group or a salt thereof as a functional group, which exhibits an excellent adsorptivity, is widely used. As such a compound, for example, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine or the like is reacted with carbon disulfide, or a hydroxy compound such as an alcohol is reacted with carbon disulfide. Then, a compound in which a dithio acid group or a salt thereof is introduced as a functional group is known.

[0005]

However, the metal scavenger in which the above-mentioned dithio acid group or a salt thereof is introduced as a functional group is
It has been found that toxic hydrogen sulfide gas may be generated when added to wastewater having a low pH. When treating wastewater with a metal scavenger, the scavenger is treating at a pH (usually around pH = 7) at which the metal scavenger can easily collect metals in the wastewater, but in recent years the diversification of wastewater types Accordingly, the amount of low pH wastewater containing a large amount of acidic substances is increasing. When treating wastewater with such a low pH, add an alkali to adjust the pH.
It is common to add the metal scavenger after adjusting the pH value. However, if the metal scavenger is mistakenly added before adjusting the pH of the wastewater, there is a risk that hydrogen sulfide gas is generated.

The metal scavenger is not only used for treating wastewater,
It is also used for the treatment of metals in fly ash generated in garbage incinerators, the treatment of metals contained in slag discharged from mines, sludge containing metals, and soil contaminated with metals.
By the way, since fly ash is a residue of incineration of refuse, various substances are contained in fly ash, and with the recent increase in the number of types of dust, fly ash may contain a large amount of acidic substances. .
Also, many of the slag, sludge, contaminated soil, etc. contain acidic substances. Hydrogen sulfide may also be generated when the above metal scavenger is added to fly ash, slag, sludge, soil, etc. containing such acidic substances. Further, when treating fly ash, various additives are used in combination, and acidic substances are also contained therein. It has been found that when a metal scavenger is added together with such an acidic additive, the fly ash itself becomes locally acidic and hydrogen sulfide gas is generated even if the fly ash itself does not contain an acidic substance.

The reason why hydrogen sulfide gas is generated when the metal scavenger is used under acidic conditions is that hydrogen sulfide or thiocarbonate as a by-product when carbon disulfide is reacted with polyamines or hydroxy compounds. Is believed to remain in the metal scavenger, which reacts with the acid and is released as hydrogen sulfide gas. In order to prevent hydrogen sulfide gas generation accidents at the treatment site with the metal scavenger, the present inventors have previously treated the aqueous solution of the metal scavenger with an acid to remove the hydrogen sulfide remaining in the metal scavenger. It was studied to remove thiocarbonate as hydrogen sulfide gas. However, when the aqueous solution of the metal scavenger is made acidic, the metal scavenger often precipitates, and there is a problem that a complicated work is required to redissolve the precipitated metal scavenger. .

The present inventors have conducted further studies in view of the above points, and as a result, by adding an acid to an aqueous solution of a metal scavenger to maintain the aqueous solution in a neutral to weakly alkaline state for treatment,
The inventors have found that hydrogen sulfide, thiocarbonate, etc. remaining in the metal scavenger can be effectively removed as hydrogen sulfide gas without causing precipitation of the metal scavenger, and have completed the present invention. .

[0009]

That is, the method for producing a metal scavenger of the present invention is directed to a dithioacid group and / or a salt thereof bonded to a nitrogen atom of an amine and / or an oxygen atom of a hydroxy compound as a functional group. An acid is added to the aqueous solution of the metal scavenger, which maintains the aqueous solution to be neutral to weakly alkaline.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as the metal scavenger, a compound having a dithioacid group bonded to the nitrogen atom of amines or a salt thereof as a functional group, or a hydroxy group, is used which is obtained by reacting amines with carbon disulfide. Examples thereof include a compound having a dithioacid group bonded to an oxygen atom of a hydroxyl group or a salt thereof as a functional group, which is obtained by reacting a compound with carbon disulfide.

Examples of the amines include ethylamine, propylamine, aminoethylethanolamine,
Monoethanolamine, piperidine, ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenediamine, dibutylenetriamine, triethylenetetramine, tripropylenetetramine, tributylenetetramine, tetraethylenepentamine, tetrapropylenepentamine, Aliphatic amines such as tetrabutylene pentamine, pentaethylenehexamine, iminobispropylamine, monomethylaminopropylamine, methyliminobispropylamine and the like can be mentioned.

Aromatic amines such as phenylenediamine, o-, m-, p-xylylenediamine and 3,5-diaminochlorobenzene; cycloalkane amines such as 1,3-bis (aminomethyl) cyclohexane A piperazine such as 1-aminoethylpiperazine or piperazine, or a polymer of cyclic imine such as polyethyleneimine, polypropyleneimine, poly-3-methylpropylimine or poly-2-ethylpropylimine can be used.

Further, polymers of unsaturated amines such as polyvinylamine and polyallylamine, unsaturated amines such as vinylamine and allylamine, and dimethylacrylamide,
Copolymers with other monomers having a copolymerizable unsaturated bond, such as styrene, methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, styrene sulfonic acid and the like, and the like can also be mentioned. In the case of the above cyclic imine polymer, unsaturated amine polymer and copolymer thereof,
An average molecular weight of 300 to 2,000,000 is preferable, and 100
The thing of 0-500,000 is more preferable.

The above amines may have a branched chain such as an N-alkyl substituent, an N-hydroxyalkyl substituent and an N-acyl substituent. The N-hydroxyalkyl substituent is introduced by reacting the amine with an epoxyalkane, and the N-acyl substituent is introduced by reacting the amine with a fatty acid. The N-alkyl substituent is introduced by reacting an amine with an alkyl halide. The N-hydroxyalkyl substituent preferably has 2 to 28 carbon atoms in the alkyl group, and the N-acyl substituent preferably has 2 to 24 carbon atoms. The N-alkyl substituent preferably has 2 to 18 carbon atoms. Further, among the above amines, those obtained by reacting one or more polyalkylenepolyamines having two or more amino groups with epihalohydrin and crosslinking the same can also be used as the amines. However, amines having N-alkyl substituents, N-hydroxyalkyl substituents, N-acyl substituents or the like introduced, or amines crosslinked by reacting with epihalohydrin have at least one amino group remaining. Need to be

On the other hand, examples of the hydroxy compound include monohydric or polyhydric alcohols, cellulose, starch, polyvinyl alcohol, polyvinyl alcohol and ethylene, propylene, styrene, acrylic acid, methacrylic acid, allylamine, vinylamine, vinyl acetate, etc. Polymeric hydroxy compounds such as coalesce, chitin and chitosan, and compounds obtained by introducing an alkyl group, a β-hydroxyalkyl group, an acyl group, an alkylphenyl group, an alkyl-substituted hydroxyalkyl group or the like as a substituent, and the like can be mentioned.

Examples of the monohydric alcohol include methyl alcohol, ethyl alcohol, butyl alcohol,
Propylene alcohol, isopropyl alcohol, amyl alcohol, hexyl alcohol, octyl alcohol, nonyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, aliphatic saturated alcohols such as behenyl alcohol, allyl alcohol, crotyl alcohol, propargyl alcohol, etc. Alicyclic alcohols such as aliphatic unsaturated alcohols, cyclopentyl alcohol and cyclohexyl alcohol, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, and heterocyclic alcohols such as furfuryl alcohol. Monohydric alcohol has 1 carbon
~ 28 are preferred.

Examples of the polyhydric alcohol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,
5-pentanediol, diethylene glycol, triethylene glycol, diethylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, polyethylene glycol, glycerin, pentaglycerin, sorbitan, mannitan, traits, erythritol, pentaerythritol, arabite, rebit,
Examples thereof include xylit, lamb knit, sorbit, mannite, idit, talit, galactit, alit, and allit. 2 carbon atoms as polyhydric alcohol
~ 28 are preferred.

Examples of the hydroxy compound include those obtained by treating the hydroxy compound with nitric acid or the like, those obtained by partially reducing the carbonyl group, and those obtained by reacting a polyalkylene polyamine with an epoxy compound such as an alkylene oxide to introduce a hydroxyl group. Can be used. Further, a product obtained by reacting the hydroxy compound with an epoxy compound can also be used. Examples of the epoxy compound include alkylene oxides having 1 to 60 carbon atoms such as ethylene oxide, propylene oxide, butylene oxide, and 1,2-epoxyalkane, and aromatic oxides such as styrene oxide. These epoxy compound adducts may be the ones to which only one type has been added or the two or more types to which they have been added in a random or block form.

The metal scavenger used in the present invention is obtained by reacting an amine or a hydroxy compound with carbon disulfide as described above, whereby the nitrogen atom of the amine or the oxygen atom of the hydroxyl group of the hydroxy compound is converted into a dithio acid group. And a salt thereof is introduced. Carbon disulfide is reacted with a compound having an amino group and a hydroxyl group at the same time (for example, a compound in which an N-hydroxyalkyl substituent is introduced into polyalkylene polyamine) to react with nitrogen of the amino group. A dithio acid group or a salt thereof may be introduced into either or both of the atom and the oxygen atom of the hydroxyl group. Whether the reaction of amines or hydroxy compounds with carbon disulfide is carried out in the presence of alkali,
By treating with an alkali after completion of the reaction, a metal scavenger having a salt of a dithioacid group as a functional group can be obtained, and by adjusting the amount of addition of alkali, etc., both the dithioacid group and the salt of the dithioacid group can be obtained. It is possible to obtain a metal scavenger having In the present invention, those having only a dithio acid group as a functional group, those having only a salt of a dithio acid group as a functional group,
Alternatively, any of those having both a dithio acid group and a salt of a dithio acid group as a functional group can be used.

Sodium hydroxide is used as the alkali.
Alkali metal hydroxides such as potassium hydroxide and alkaline earth metal hydroxides such as calcium hydroxide can be used, but sodium hydroxide is preferred.

The functional group is preferably introduced by substituting it with 5 to 100% of the active hydrogen atom bonded to the nitrogen atom of the amine or the hydrogen atom of the hydroxyl group of the hydroxy compound, and with 30 to 100%. It is more preferable to introduce. Further, it is preferable that the amount of carbon disulfide to be added is gradually added over 30 minutes to 20 hours while maintaining the liquid temperature at 10 to 100 ° C. After adding carbon disulfide, 30 ~
It is preferable that the added carbon disulfide is caused to react substantially completely by stirring and holding at 100 ° C. for 1 to 15 hours.

The method of the present invention removes hydrogen sulfide gas from the aqueous solution by adding an acid to the aqueous solution of the metal scavenger obtained as described above and keeping the aqueous solution neutral to weakly alkaline. A metal scavenger as a final product is obtained. In the present invention, the range of neutrality to weak alkalinity of an aqueous solution to which an acid is added refers to about pH = 7 to 10, but a range of pH = 7.5 to 9 is particularly preferable. When treating wastewater, it is a common practice to add a metal scavenger after adjusting the pH of the wastewater to around pH 7, but hydrogen sulfide gas is not normally generated. On the other hand, according to the method of the present invention, hydrogen sulfide gas can be generated and removed even when the pH is around 7. The reason why such a difference occurs is not clear, but various metals are contained in the wastewater to be treated by the metal scavenger, and the cause of these metals and hydrogen sulfide (or hydrogen sulfide gas) is generated. It is considered that hydrogen sulfide gas is not substantially generated even if the metal scavenger is added to the wastewater having a pH of about 7 because some interaction occurs with the sulfur compound).

Examples of the acid added to the aqueous solution of the metal scavenger include mineral acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, malonic acid, succinic acid and gluconic acid. Examples thereof include acids, and it is preferable to use mineral acids in order to suppress BOD components and COD components in water or the eluate after treatment. You may use these acids in mixture of 2 or more types.

In the method of the present invention, when an acid is added to an aqueous solution of a metal scavenger to adjust the aqueous solution to be neutral to weakly alkaline, hydrogen sulfide gas is generated. It is necessary to have equipment capable of exhausting hydrogen gas. Further, in order to remove the hydrogen sulfide gas efficiently, it is preferable to blow an inert gas such as nitrogen gas into the aqueous solution of the metal scavenger and perform the treatment while heating at about 20 to 100 ° C. The treatment time required to remove hydrogen sulfide gas almost completely depends on the type of metal scavenger, the pH value adjusted by adding acid, the presence or absence of inert gas blowing, the heating temperature, the stirring speed, etc. It is usually about 30 minutes to 6 hours, although it varies depending on the situation.

The metal scavenger obtained by the method of the present invention is
The product may be in the form of an aqueous solution, or may be a solid product obtained by removing water.However, since the metal scavenger is usually added to wastewater as an aqueous solution, the product in the form of the aqueous solution should be used. Is preferred. The metal scavenger obtained by the method of the present invention is, in addition to the treatment of waste water containing metal, the treatment of gaseous metal contained in flue gas, or is discharged from incinerator ash such as a refuse incinerator or mine. For the purpose of immobilization of metals in solid waste such as sludge as industrial waste generated by slag, neutralization coagulation sedimentation treatment in wastewater treatment or sedimentation treatment with coagulant, soil with advanced pollution, etc. Can be used.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

The metal scavengers used in the following Examples and Comparative Examples are as follows, and all were used as an aqueous solution. Metal scavenger A: a metal scavenger having sodium dithioate as a functional group, obtained by reacting 2 mol of carbon disulfide with 1 mol of ethylenediamine in the presence of sodium hydroxide (bonded to a nitrogen atom of ethylenediamine). Substitution ratio of functional group to active hydrogen is 50%, 5% aqueous solution, pH = 11.
5)

Metal scavenger B: carbon disulfide 2 per mol of diethylenetriamine in the presence of potassium hydroxide.
A metal scavenger containing potassium dithioate as a functional group obtained by reacting moles (substitution ratio of functional group to active hydrogen bonded to nitrogen atom of diethylenetriamine is 40%. 40% aqueous solution, pH = 11.2)

Metal scavenger C: 1 carbon disulfide per 1 mol of metaxylenediamine in the presence of sodium hydroxide.
A metal scavenger containing sodium dithioate as a functional group, obtained by reacting moles (the substitution ratio of the functional group with respect to the active hydrogen bonded to the nitrogen atom of meta-xylenediamine is 25%. 5% aqueous solution, pH = 12.0). )

Metal scavenger D: A metal scavenger containing calcium dithioate as a functional group, obtained by reacting 1 mol of carbon disulfide with 1 mol of propylamine in the presence of calcium hydroxide (of propylamine). Substitution ratio of functional group to active hydrogen bonded to nitrogen atom is 50%, 10% aqueous solution, pH
= 12.2)

Metal scavenger E: Sodium dithioate as a functional group obtained by reacting 1 mol of carbon disulfide per monomer unit of polyethyleneimine having an average molecular weight of 100,000 in the presence of sodium hydroxide. Metal scavenger (100% substitution rate of functional groups for active hydrogen bonded to nitrogen atom of polyethyleneimine. 5% aqueous solution, pH = 11.8)

Metal scavenger F: Sodium dithioate as a functional group obtained by reacting 1 mol of carbon disulfide per monomer unit of polyvinylamine having an average molecular weight of 10,000 in the presence of sodium hydroxide. Metal scavenger (substitution ratio of functional group to active hydrogen bonded to nitrogen atom of polyvinylamine is 50%. 20% aqueous solution, pH = 12.5)

Metal scavenger G: Obtained by reacting 0.8 mol of carbon disulfide per monomer unit of polyallylamine having an average molecular weight of 3000 in the presence of sodium hydroxide.
Metal scavenger having sodium dithioate as a functional group (substitution rate of functional group to active hydrogen bonded to nitrogen atom of polyallylamine is 40%, 30% aqueous solution, pH = 12.7)

Metal scavenger H: Metal scavenger containing sodium dithioate as a functional group, obtained by reacting 1 mol of carbon disulfide with 1 mol of ethyl alcohol (dithio acid for hydrogen atom of hydroxyl group of ethyl alcohol). Sodium substitution rate 100%, pH of 20% aqueous solution = 10.5)

Examples 1 to 8 To 1 liter of the aqueous metal scavenger solution shown in Table 1, the acid shown in Table 1 was added to adjust the pH shown in the same table, and the mixture was kept under stirring. The holding time and temperature at this time are also shown in Table 1. To the treated metal scavenger aqueous solution containing 5 g of the metal scavenger as a solid component, 100 ml of 50% sulfuric acid was added under a nitrogen stream, and the generated gas was passed through a 5% zinc acetate aqueous solution. Whether or not hydrogen sulfide gas was generated was determined by whether or not the zinc acetate aqueous solution became cloudy. Table 2 shows the results.

[0036]

[Table 1]

[0037]

[Table 2]

Comparative Examples 1 to 8 1 liter of metal scavenger aqueous solution shown in Table 3 (aqueous solution containing 5 g of solid content) was used without adding acid and treated with 100 ml of 50% sulfuric acid under nitrogen stream. In addition, the generated gas was passed through a 5% zinc acetate aqueous solution, and it was confirmed whether hydrogen sulfide gas was generated. The results are also shown in Table 3.

[0039]

[Table 3]

[0040]

INDUSTRIAL APPLICABILITY As described above, the metal scavenger obtained by the method of the present invention is toxic even when it is added to acidic wastewater or when treating fly ash, slag, sludge, soil, etc. containing acidic substances. Since there is no possibility of generation of a large amount of hydrogen sulfide gas, the range of use of the metal scavenger is expanded, and the safety of the treatment operation of wastewater and the like can be dramatically improved.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C02F 1/62 C02F 1/62 Z

Claims (1)

[Claims] 1. An aqueous solution obtained by adding an acid to an aqueous solution of a metal scavenger having a dithioacid group and / or a salt thereof as a functional group, which is bonded to a nitrogen atom of an amine and / or an oxygen atom of a hydroxyl group of a hydroxy compound. A method for producing a metal scavenger, which comprises maintaining the neutrality to weak alkalinity.