JPH0432717B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides ethylenediaminetetraacetic acid (hereinafter referred to as
Heavy metal ions such as copper, nickel, mercury, manganese, cadmium, zinc, and lead are extracted using a polymeric metal scavenger from wastewater containing heavy metal ions chelated with EDTA (abbreviated as EDTA). This relates to a method for collecting and removing.

It has been said that it is extremely difficult to treat heavy metal ions that have been bound to EDTA due to EDTA's strong chelate-forming ability.

To date, the methods for treating metal ions bound to EDTA include, firstly, oxidative decomposition of EDTA, and then treatment of heavy metal ions by neutralization, coagulation, and precipitation, and secondly, methods for treating heavy metal ions bound to EDTA. A method in which the PH value of wastewater is set to 3 or less, iron salt is added in an equivalent amount or in excess of the equivalent amount of heavy metal ions in the water, and then the PH value is rapidly increased to separate and remove the heavy metal ions as hardly soluble precipitates ( (Japanese Patent Application Laid-Open No. 161056), and thirdly, the wastewater containing heavy metal ions combined with EDTA should be treated with at least about 1.2 reaction equivalents.
Add twice the amount of calcium compound and add at least enough of the heavy metal to form a precipitate of its hydroxide.
In the alkaline region of pH 12.6, a method is known in which the heavy metal components are separated and removed as insoluble precipitates (Japanese Patent Laid-Open No. 10176/1983).

However, since the first method requires oxidative decomposition, it has the disadvantage of using a large amount of oxidizing agent and requiring a large number of processing steps. In addition, the second method requires many steps, such as the step of reducing the pH to 3 or less and the step of increasing the pH to 11 or more, and is therefore uneconomical. In the third method, 1.2 times the amount of calcium compound is added to the wastewater to make it at least alkaline at pH 12.6, which is sufficient to form hydroxide precipitates, which results in a huge amount of chemicals being used. It's the economy.
Furthermore, these first to third methods have the drawback that the lower limit of removal of heavy metal ions is not good.

The present inventors conducted intensive research to solve these drawbacks and found that wastewater containing heavy metal ions combined with EDTA can be treated with dithiocarbamic acid or its salt, dithioic acid or its salt, thiol or its salt as a functional group. , and thiourea, or the above-mentioned polymeric metal trapping agent and at least one selected from sodium sulfide, sodium polysulfide, and sodium hydrogen sulfide. We have discovered that heavy metal ions bound to EDTA can be efficiently collected and removed down to a low concentration by treatment in combination with EDTA. When soda sulfides are added, the collection rate of heavy metals increases compared to not adding them, and wastewater treatment can be performed efficiently in a short time. Furthermore, there is an advantage that the volume of the sludge after filtration is reduced, making it easier to process.

According to the present invention, it is sufficient to simply add a specific polymeric metal scavenger to wastewater containing heavy metal ions combined with EDTA and treat the wastewater, and if the insoluble precipitate formed is then subjected to solid-liquid separation, the heavy metals contained in the wastewater can be treated. Ions are collected and removed while remaining bound to EDTA. Therefore, the treatment process is simple and economically advantageous.

Furthermore, after removing heavy metal ions combined with EDTA, by reducing the pH to 3 or less,
It has the advantage that EDTA is an insoluble substance and can be recovered.

The metal collecting method of the present invention includes a polymeric metal trapping agent alone or a polymeric metal trapping agent combined with at least one selected from sodium sulfide, sodium polysulfide, and sodium hydrogen sulfide. can be added to wastewater and treated by a batch method or the like. The amount of these scavengers to be added depends on the heavy metal content in the wastewater, but the scavenger may be added in an amount of 0.3 to 1.2 times the molar equivalent, preferably 0.5 to 1.0 times the molar equivalent of the heavy metal content. Sodium polysulfide includes sodium disulfide,
Examples include sodium trisulfide, sodium tetrasulfide, and sodium pentasulfide.

When using the above sodium sulfides together, the ratio of the polymeric metal scavenger to the soda sulfides by weight is
Each is used in the range of 99:1 to 20:80, but 90:10
A range of ~40:60 is preferred.

Further, it is also possible to use an aqueous solution of iron ions and aluminum ions in combination for the purpose of adjusting the amount of the scavenger added or increasing the collection efficiency of the scavenger.

The polymeric metal scavenger in the present invention includes dithiocarbamic acid or a salt thereof as a functional group,
It has at least one selected from the group consisting of dithioic acid or its salt, thiol or its salt, and thiourea group, and has at least one selected from polystyrene, polyacrylic acid, vinyl chloride, epoxy resin, and polyethyleneimine in its main chain. It is a polymeric metal scavenger, which can be produced by a conventional method. For example, as a polymeric metal scavenger with polystyrene as the main chain, its aromatic nucleus is chloromethylated, then reacted with monmonium or polyalkylenepoamine, and then reacted with carbon disulfide in the presence of sodium hydroxide. A compound in which a dithiocarbamate group is introduced by chloromethylating polystyrene, a compound in which a thiol group is introduced by reacting with thiourea, and a compound in which a thiol group is introduced and then reacted with thiophosgene, and then treated with sodium hydroxide to form a dithiocarbamate. Examples include compounds into which acid groups have been introduced. In addition, as polymeric metal scavengers with polyacrylic acid as the main chain, there are compounds in which thiourea groups are introduced by reacting lower alcohol esters of polyacrylic acid with thiourea, and compounds in which thiourea groups are introduced into lower alcohol esters of polyacrylic acid. Examples include compounds in which dithiocarbamate groups are introduced by reacting ammonia or polyalkylenepoamine and then reacting with carbon disulfide in the presence of sodium hydroxide. Polymeric metal scavengers with polyvinyl chloride as the main chain include compounds in which thiol groups are introduced by reacting polyvinyl chloride with sodium hydrogen sulfide, and compounds in which thiol groups are introduced by reacting polyvinyl chloride with ammonia or polyalkylenepoamine. Examples include compounds in which a dithiocarbamate group is introduced by reacting carbon disulfide in the presence of sodium hydroxide. As a polymeric metal scavenger with an epoxy resin as the main chain, polyalkylene polyamine is reacted with carbon disulfide in the presence of sodium hydroxide so as to leave two active hydrogen atoms, and then cross-linked with a bisepoxide compound. Examples include compounds having a dithiocarbamic acid group. As a polymeric metal scavenger with a polyethyleneimine main chain, polyethyleneimine in the presence of sodium hydroxide,
Examples include compounds obtained by reacting carbon disulfide.

The present invention will be specifically explained below using examples, but is not limited to the following examples.

Example 1 To aqueous solution 1 of pH 7 containing 1000 ppm of ethylenediaminetetraacetic acid (2Na) and 10 ppm of copper ions, 5 ml of a 1% aqueous solution of a metal scavenger having polyethyleneimine as a base and a dithiocarbamate group as a functional group was added. The mixture was stirred for a minute. After solid-liquid separation,
Measurement of residual ion (Cu ²⁺ ) concentration
It was 0.1 ppm, and the removal rate was 99%.

Example 2 Ethylenediaminetetraacetic acid (2Na) 1%, copper ion 2ppm, nickel ion 2ppm, mercury ion
10 ml of a 1% aqueous solution of a metal scavenger in which thiourea is bonded to polyethyleneimine as a functional group and 2 ml of a 3% aqueous sodium sulfide solution were added to aqueous solution 1 containing 2 ppm and having a pH of 7.5, and the mixture was stirred for 30 minutes. After solid-liquid separation of the generated insoluble matter, the remaining metal ion concentration was measured; Cu ²⁺ : 0.01 ppm, Ni ²⁺ :
0.05ppm, Hg ²⁺ : 0.005ppm.

Example 3 Ethylenediaminetetraacetic acid (2Na) 5000ppm,
To aqueous solution 1 of pH 6.5 containing 3ppm of Cd ²⁺ , 5ppm of Zn ²⁺ , 500ppm of Ca, and 2% of NaCl, 3 ml of a 5% aqueous solution of a metal scavenger having polystyrene with a dithiocarbamate group as a functional group was added and stirred for 20 minutes. Processed. After solid-liquid separation, the remaining metal ion concentrations were measured and found to be 0.05 ppm for Cd ²⁺ and 0.05 ppm for Zn ²⁺ .

Example 4 Ethylenediaminetetraacetic acid (2Na) 1600ppm,
Aqueous solution 1 of PH4.2 containing Cu ²⁺ 4ppm and Zn ²⁺ 6ppm
To the mixture, 2 ml of a 6% aqueous solution of a metal scavenger having polyacrylic acid as a main chain and a thiourea group as a functional group was added, and the mixture was stirred for 30 minutes. After solid-liquid separation, the remaining metal ion concentration was measured and found that Cu ²⁺ :
It was 0.01ppm, Zn ²⁺ : 0.04ppm.

Example 5 Ethylenediaminetetraacetic acid (2Na) 400ppm,
Aqueous solution 1 of PH5.2 containing 10ppm Pb ²⁺ and 2ppm Cd ²⁺
4 ml of a 0.5% aqueous solution of a metal scavenger in which a thiol group was introduced into vinyl chloride was added to the mixture, and the mixture was stirred for 10 minutes. After solid-liquid separation, the remaining metal ion concentrations were measured and found to be 0.01 ppm for Pb ²⁺ and 0.01 ppm for Cd ²⁺ .

Example 6 Ethylenediaminetetraacetic acid (2Na) 6000ppm,
Aqueous solution 1 of PH6.1 containing 3ppm Ni ²⁺ and 5ppm Cu ²⁺
To this was added 0.5 ml of a 2% aqueous solution of a metal scavenger having an epoxy resin main chain and a dithioic acid group as a functional group, and the mixture was stirred for 40 minutes. After solid-liquid separation, the remaining metal ion concentration was measured and found that Ni ²⁺ :
0.1ppm, Cu ²⁺ : 0.01ppm.

Comparative Example 1 To aqueous solution 1 of pH 7 containing 1000 ppm of ethylenediaminetetraacetic acid (2Na) and 10 ppm of copper ions, 5 ml of a 1% aqueous solution of sodium dimethyldithiocarbamate was added and stirred for 10 minutes. After solid-liquid separation, the residual metal ion (Cu ²⁺ ) concentration was measured to be 3 ppm, and the negative removal rate was 70%.

Claims (1)

[Scope of Claims] 1. Has at least one functional group selected from the group consisting of dithiocarbamic acid or its salt, dithioic acid or its salt, thiol or its salt, and thiourea group, and has polystyrene, polyacrylic acid, Wastewater characterized by treating wastewater containing ethylenediaminetetraacetic acid combined with heavy metal ions using a polymeric metal scavenger whose main chain is at least one selected from vinyl chloride, epoxy resin, and polyethyleneimine. processing method. 2 Wastewater containing ethylenediaminetetraacetic acid combined with heavy metal ions by using the metal scavenger according to claim 1 in combination with at least one selected from sodium sulfide, sodium polysulfide, and sodium hydrogen sulfide. A wastewater treatment method characterized by treating.