JP2955648B2 - Removal method of trivalent arsenic ion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing arsenic from an aqueous solution containing trivalent arsenic ions at particularly low concentrations, and more particularly to a method for removing arsenic ions from an aqueous solution. By contacting the ion-containing aqueous solution with an organic solvent containing a compound having a specific structure or a porous resin carrying the compound, a dilute arsenic ion having a dilute concentration, which has conventionally been considered difficult to recover, is removed from the ion-containing aqueous solution. The present invention relates to a method for efficiently separating and recovering. The method of the present invention is useful, for example, as a method of separating and removing trivalent arsenic ions contained in a trace amount in industrial wastewater or an etching solution for electronic substrates by a simple operation.

[0002]

2. Description of the Related Art Arsenic is an element widely used as a raw material for alloys and semiconductors, but its toxic nature has been pointed out, and arsenic is contained in trace amounts in industrial wastewater and etching solutions for electronic substrates. Removal has been an important issue. In the ordinary wastewater treatment process, precipitation separation with ferric ion has been generally performed.However, this method, which is effective for pentavalent arsenic ion, is also effective for trivalent arsenic ion, especially in the low concentration region. It had the disadvantage that it was difficult to form a precipitate.

On the other hand, in the solvent extraction method using an organic reagent, compounds such as diethyldithiocarbamate and pyrrolidinedithiocarbamate are known, but these compounds have low solubility in non-polar solvents such as kerosene. Further, it has a disadvantage that it is easily desorbed into the aqueous phase.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to separate and remove arsenic from a dilute aqueous solution of trivalent arsenic ion by a simple operation.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the separation and recovery of trivalent arsenic ions from an aqueous solution, and as a result, it has been found that a compound having a specific structure is favorable for trivalent arsenic ions. The present invention has been found to have excellent reactivity and can be applied to a solvent extraction method and a resin-supporting method, and has accomplished the present invention.

That is, according to the present invention, when removing trivalent arsenic ions from an aqueous solution containing trivalent arsenic ions, the aqueous solution is loaded with an organic solvent containing a compound represented by the chemical formula (1) or a compound represented by the chemical formula (1). The present invention provides a method for transferring and removing trivalent arsenic ions from an aqueous solution into an organic solvent phase or into a porous resin by contact with the porous resin.

According to the present invention for solving the above-mentioned problems, in removing trivalent arsenic ions from an aqueous solution containing trivalent arsenic ions, the aqueous solution is brought into contact with an organic solvent containing a compound represented by the chemical formula (1). A method for removing trivalent arsenic ions, which comprises transferring valent arsenic ions from an aqueous phase to an organic phase. In another embodiment of the present invention, in removing trivalent arsenic ions from an aqueous solution containing trivalent arsenic ions, the aqueous solution is brought into contact with a porous resin supporting a compound represented by the chemical formula (1) to form a trivalent arsenic ion. A method for removing trivalent arsenic ions, characterized in that ions are transferred from an aqueous phase into a resin. Further, another aspect of the present invention is characterized in that the trivalent arsenic ion is transferred from the resin to the aqueous phase by contacting the resin supporting the trivalent arsenic ion by the above method with an alkaline aqueous solution having a pH of 10 or more. A method for recovering trivalent arsenic ions. Further, the present invention provides the method for removing trivalent arsenic ions, wherein the pH of the aqueous solution containing trivalent arsenic ions is in the range of 0 to 7, and the method for removing trivalent arsenic ions and pentavalent arsenic ions together. The method for removing trivalent arsenic ions described above, wherein only the trivalent arsenic ions are removed from the contained aqueous solution, wherein the porous resin supporting the compound represented by the chemical formula (1) is used as a cylindrical column. The above-described method for removing trivalent arsenic ions, which is characterized by the following, is a preferred embodiment.

[0008]

Next, the present invention will be described in more detail. In the present invention, a compound represented by the following chemical formula (1) is used. Here, specific examples of R ₁ and R ₂ include, for example, hexyl, heptyl, octyl, decyl, dodecyl, isooctyl, phenyl, 2-ethylhexyl, tosyl, naphthyl, cyclohexyl, and the like. Examples include bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate, dihexylammonium dihexyldithiocarbamate, dioctylammonium dioctyldithiocarbamate, and the like.

[0009]

Embedded image

The compound represented by the formula (1) used in the present invention is a compound represented by the corresponding dialkylamine (R _1-
NH-R ₂ ) to one-half equivalent of carbon disulfide (C
It can be synthesized by mixing with S ₂ ) at room temperature. When the amine is a solid, the reaction can be carried out by dissolving the amine in an appropriate organic solvent, but care must be taken in that case, since the yield may be reduced.

[0011] Among the compounds represented by the chemical formula (1),
Bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate where R ₁ = R ₂ = 2-ethylhexyl is liquid even at room temperature and has high solubility in organic solvents. Can be used well.

In the present invention, it is necessary that the compound represented by the chemical formula (1) is dissolved in an organic solvent or supported on a porous resin and brought into contact with a trivalent arsenic ion solution.

The organic solvent used at this time is not particularly limited as long as it can dissolve the above-mentioned compound and is not miscible with water, and is not particularly limited, but can be easily obtained and handled. Hydrocarbons such as hexane, heptane, octane, benzene, toluene, xylene and kerosene, and halogenated hydrocarbons such as chloroform, carbon tetrachloride and trichloroethane are preferred.

On the other hand, as the porous resin for supporting the above compound, a resin insoluble in water or an organic solvent used in the process of supporting the reagent is used. Examples of such resins include expanded polyethylene, expanded polypropylene, expanded polystyrene, expanded polyvinyl chloride, expanded polyurethane,
Phenolic resin foams or cross-linked compounds thereof can be mentioned, and cross-linked polyacrylic acid ester and cross-linked polymethacrylic acid ester foams are particularly preferable. These porous resins have a specific surface area of 50 to 800 m.
^It is advantageously used as granules having a mass of ² / g, an average pore diameter of 5 to 40 nm and a particle size of 20 to 200 mesh. It is desirable to use the resin after removing impurities by washing and drying it sufficiently to remove the water content.

In order to carry the compound represented by the chemical formula (1) on a porous resin, for example, the compound is dissolved in a low-boiling organic solvent such as acetone or hexane, and the porous resin is added thereto, followed by several hours. After stirring, the solvent may be distilled off under reduced pressure. In this manner, usually 1 to 100 parts by weight, preferably 10 to 100 parts by weight,
It is used by supporting up to 70 parts by weight of the compound.

The trivalent arsenic ion-containing aqueous solution in the present invention is based on the premise that arsenic is contained in the form of free arsenite (H ₃ AsO ₃ ), and includes alkali metal ions, halide ions, nitrate ions, Sulfate ions and the like may coexist. But iron, copper, zinc, cadmium, lead,
The extraction of arsenic may be hindered by the coexistence of ions such as cobalt and precious metals, and care must be taken especially when these ions are contained in high concentrations.

In addition, when the pH of the aqueous solution containing trivalent arsenic ions is large at the time of solvent extraction, foaming may occur upon contact with an organic solvent, making phase separation difficult. It is preferable to adjust the pH to 11 or less. When the reagent is carried in the resin, there is no problem of foaming.

In the method of the present invention, when an organic solvent is used, it can be directly applied to an aqueous solution containing a high concentration of trivalent arsenic ion.
Since it is disadvantageous in terms of resin volume and reaction rate, it is suitable for use with dilute solutions.

It should be noted that if the amount of the reagent in the organic solvent is not sufficient compared to the amount of the trivalent arsenic ion to be removed, the extraction rate will decrease, so care must be taken. At least three times the amount of reagent to arsenic is required. On the other hand, when the amount of the reagent is excessively increased, the extraction rate reaching a certain value tends to reach a plateau.

The reagent used in the present invention has the ability to react and extract many types of metal ions. For example, iron, manganese, nickel, cadmium, copper,
When ions of lead, mercury, tin, zinc, noble metal, etc. coexist with trivalent arsenic ions, they have the ability to extract these ions well. Therefore, it is necessary to pay attention to the possibility that the extraction of these ions consumes the reagent in the organic solvent or the porous resin, thereby lowering the arsenic extraction ability.

The reagents used in the present invention do not have the ability to extract pentavalent arsenic ions under most conditions. That is, when trivalent and pentavalent arsenic ions coexist, only trivalent arsenic ions can be extracted and separated.

In order to carry out the method of the present invention particularly preferably, a trivalent arsenic ion solution is passed through an apparatus in which a porous resin carrying the compound represented by the chemical formula (1) is packed in a column.
The ions are adsorbed. In this way, a large amount of an aqueous solution containing trivalent arsenic ions can be continuously treated. However, since a certain time is required for the reaction between the trivalent arsenic ion and the resin, the residence time of the solution in the resin column is preferably set to about 30 minutes or more.

In the present invention, it is effective to use an alkaline aqueous solution to back-extract the trivalent arsenic ion from the porous resin to which the trivalent arsenic ion has been adsorbed into the aqueous phase again. For example, 0.01 mol /
An aqueous solution containing at least liter is preferably used.

Next, an example in which the resin column is used to test the capture and elution of trivalent arsenic ions will be described. Test Example 1 Bis (2-ethylhexyl) ammonium
8 g of (ethylhexyl) dithiocarbamate was supported on 20 g of a porous polyacrylate resin to prepare an impregnated resin. 9 g of the resin was packed in a cylindrical column having an inner diameter of 1.5 cm and a length of 27 cm, and trivalent arsenic ion
0 ^-5 mol / liter aqueous solution containing (pH 6.8, buffer 0.001 mole / l and sodium chloride 0.1 mol / l containing) were were passed through the column at 24 ml / time of speed.
The effluent from the column was collected over time and the arsenic concentration was measured. The results are shown in FIG. 1 as a graph in which the horizontal axis represents the volume of the eluent and the vertical axis represents the arsenic concentration. About 2500
The ml eluate showed an arsenic concentration of 10 ⁻⁶ mol / l or less, indicating that arsenic was successfully removed. However, after that, trapping became insufficient, and an increase in the concentration of arsenic was observed.

Test Example 2 In Test Example 1, a 0.1 mol / L sodium hydroxide aqueous solution was passed through the column supporting trivalent arsenic ion at a rate of 24 ml / hour. The effluent from the column was collected over time and the arsenic concentration was measured. The result is
FIG. 2 is a graph showing the volume of the eluent on the horizontal axis and the arsenic concentration on the vertical axis. Arsenic eluted quickly from the column, indicating that arsenic in the resin could be easily recovered. The arsenic carried is eluted quantitatively and as a concentrated solution, which is effective for arsenic post-treatment or reuse.

The trivalent arsenic ion carried on the resin eluted quantitatively and was recovered in the eluate.

[0027]

EXAMPLES Next, the present invention will be described more specifically based on examples, but the present invention is not limited to the examples. Example 1 It was confirmed that the organic reagent bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate was synthesized by the following procedure. 48.3 g of bis (2-ethylhexyl) amine was placed in a flask, and 7.61 g of carbon disulfide was added dropwise with stirring at room temperature. When the mixture began to exotherm, the flask was immersed in a water bath at room temperature and stirred overnight to obtain the desired compound.

Example 2 10 m aqueous solution of pH 5.8 containing trivalent arsenic ion at a concentration of 10 ^-4 mol / l (buffer 0.001 mol / l, sodium chloride 0.1 mol / l)
to 0.01 l of bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate
10 ml of heptane containing mol / l are added and 15
For 16 minutes to remove arsenic remaining in the aqueous solution.
It was measured by CP emission spectroscopy. As a result, the arsenic concentration was reduced to 2 × 10 ⁻⁶ mol / l after 1 hour of shaking, and was maintained until after 16 hours of shaking.

Example 3 Bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) ammonium
8 g of (ethylhexyl) dithiocarbamate was supported on 20 g of a porous polyacrylate resin to prepare a granular impregnated resin. Aqueous solution of pH2.5 containing trivalent arsenic ions at a concentration of 10 ^-4 mol / l (hydrochloride 0.01
M, coexistence of sodium chloride 0.09 mol / l) 10
0.1 g of the impregnated resin was added to each ml, and the mixture was shaken for 15 minutes to 20 hours, and arsenic remaining in the aqueous solution was measured by ICP emission spectroscopy. As a result, the concentration decreased to 9 × 10 ⁻⁷ mol / liter after shaking for 1 hour, and the concentration was maintained until 20 hours after shaking.

Example 4 Aqueous solution of pH 0 to 11 containing trivalent arsenic ion at a concentration of 10 ^-4 mol / l (buffer 0.001 mol / l, sodium chloride 0.1 mol / l) 1
0 ml of bis (2-ethylhexyl) ammonium
Bis (2-ethylhexyl) dithiocarbamate was added to 0.1.
3 ml of a heptane solution containing 01 mol / l was added,
After shaking for 6 hours, the concentration of arsenic remaining in the aqueous phase was measured, and the distribution ratio of arsenic between the organic phase and the aqueous phase was determined. The results are shown in a graph in which the horizontal axis is the pH of the aqueous phase and the vertical axis is the logarithm of the distribution ratio, and is shown in FIG. Arsenic is acidic to neutral (pH 0
7) Extracted into the organic phase from the wide range, indicating that it is applicable to the aqueous phase in a wide acid concentration range. The removal of arsenic is preferably carried out on the acidic side, as the distribution ratio gradually decreases as it becomes neutral to alkaline.

Example 5 Aqueous solutions of pH 2.3 and 6.3 containing trivalent arsenic ions at a concentration of 10 ^-4 mol / l (both 0.1 mol / l of sodium chloride and coexistence with a solution of pH 2.3) Is 0.01 mol / l hydrochloric acid, pH 6.3 solution contains 0.001 mol / l buffer) 10 ml
Bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate is added with 3 ml of a heptane solution containing 10 ^-4 to 10 ^-2 mol / l, shaken for 6 hours, and the concentration of arsenic remaining in the aqueous phase is measured. Then, the distribution ratio of arsenic between the organic phase and the aqueous phase was determined. The results are shown in a graph in which the horizontal axis represents the logarithm of the reagent concentration and the vertical axis represents the logarithm of the arsenic distribution ratio. In the region where the reagent concentration is high, the distribution ratio of arsenic levels off, indicating that arsenic extraction is independent of the reagent concentration. On the other hand, a decrease in partition was observed in the region where the reagent was diluted, which is considered to be due to the fact that the amount of the reagent was not sufficient to extract arsenic. If the amount of the reagent (the number of moles) is less than three times the amount of arsenic, attention must be paid to the decrease in distribution.

Example 6 An aqueous solution of pH 0 to 8 containing pentavalent arsenic ion at a concentration of 10 ^-4 mol / l (containing 0.001 mol / l of a buffer and 0.1 mol / l of sodium chloride) 1
0.0 ml of bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate is added to 0 ml.
After adding 3 ml of a heptane solution containing 1 mol / l and shaking for 6 hours, the concentration of arsenic remaining in the aqueous phase was measured. As a result, no arsenic extraction was observed in the pH range.

Example 7 Divalent zinc ion, divalent manganese ion, divalent nickel ion, and trivalent arsenic ion were added together with 10 ^-4 mol / l.
An aqueous solution containing 10 ^-4 mol / L of one of divalent copper ions, ferric iron ions, divalent cadmium ions and divalent lead ions (0.01 mol / L of hydrochloric acid and 0.1 mol / L of sodium chloride) 10ml
And bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate
After adding 3 ml of a heptane solution containing mol / liter and shaking for 6 hours, the concentration of arsenic remaining in the aqueous phase and the concentration of coexisting metals were measured. The resulting arsenic and metal extraction rates are shown in Table 1. Trivalent iron ions and divalent copper ions have a particularly large decrease in extraction rate, and the presence of these metals requires attention. On the other hand, the extraction rates of the coexisting metals showed high extraction rates except for the divalent manganese ion and the divalent nickel ion, except that the distribution was low, indicating that these metal ions can be removed simultaneously with arsenic.

[0034]

[Table 1]

[0035] Example 8 trivalent arsenic ions with 10 ^-4 mol / liter divalent zinc ion, ^10-5 divalent copper ions or trivalent iron ions
Aqueous solution coexisting with 10 to 10 ^-2 mol / liter (hydrochloric acid 0.01
3 ml of heptane containing 0.01 mol / l of bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) dithiocarbamate was added to 10 ml of mol / l and containing 0.1 mol / l of sodium chloride, and the mixture was shaken for 6 hours. Thereafter, the concentration of arsenic remaining in the aqueous phase was measured, and the distribution ratio of arsenic between the organic phase and the aqueous phase was determined. The results are shown in FIG. 5 as a graph in which the horizontal axis represents the initial concentration of coexisting metal ions and the vertical axis represents the logarithm of the arsenic distribution ratio. No significant decrease in the distribution ratio was observed with increasing concentration of divalent zinc ions, but a clear decrease was observed with divalent copper ions and ferric iron ions. This result indicates that the distribution ratio of arsenic depends on the coexisting concentration of these metal ions, and that attention must be paid especially when the arsenic is present at a high concentration.

Example 9 0.1 g of the same granular material used in Example 3 contains trivalent arsenic ion at a concentration of 10 ^-4 mol / L, pH
0-14 aqueous solution (buffer 0.001 mol / l,
10 ml of sodium chloride (coexisting with 0.1 mol / liter of sodium chloride) was added, and the mixture was shaken for 3 hours. After that, the concentration of arsenic remaining in the aqueous phase was measured, and the distribution ratio of trivalent arsenic between the resin and the aqueous phase was determined. The results are shown in a graph in which the horizontal axis represents pH and the vertical axis represents the logarithm of the distribution ratio, and is shown in FIG. The distribution ratio of arsenic shows a high value in a wide range of acidity from neutral to neutral (pH 0 to 7), indicating that the resin can effectively extract arsenic in this region.
On the other hand, a decrease in the distribution ratio was observed in the pH range of 8 or more. Therefore, it was considered that arsenic supported in the resin could be recovered by using an alkaline solution.

Example 10 Trivalent arsenic ion was added to 0.1 g of the same granular material as used in Example 3 together with ^10-4 mol / l of trivalent arsenic ion, divalent manganese ion, divalent nickel ion, Aqueous solution containing 10 ^-4 mol / L of one of valence copper ion, ferric iron ion, divalent cadmium ion and divalent lead ion (0.01 mol / L of hydrochloric acid and 0.1 mol / L of sodium chloride ) Add 10ml and add 3
After shaking for a time, the concentration of arsenic remaining in the aqueous phase and the concentration of coexisting metals were measured. Table 2 shows the extraction rates of the arsenic and each metal obtained as a result. As with the solvent extraction system, relatively large interference was observed with divalent copper ions and ferric iron ions. Extraction of coexisting ions was observed in any of the metals, and showed a high value of 97% or more except for divalent manganese ions. Therefore, it is considered that the concentration of these metal ions requires attention from the viewpoint of hindering the extraction of arsenic or consuming reagents.

[0038]

[Table 2]

[0039]

According to the present invention, arsenic present in an aqueous solution as trivalent arsenic ions, particularly, arsenic can be efficiently separated and removed from a dilute arsenic ion-containing aqueous solution having a dilute concentration which has been conventionally difficult to recover. Can be. The method of the present invention is useful, for example, as a method of separating and removing trivalent arsenic ions contained in a trace amount in industrial wastewater or an etching solution for electronic substrates by a simple operation.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an eluent volume and an arsenic concentration in an eluate when trivalent arsenic ions are captured using a resin column in the present invention.

FIG. 2 is a graph showing a relationship between an eluent volume and an arsenic concentration in an eluate when arsenic is eluted from a column supporting trivalent arsenic ions in the present invention.

FIG. 3 is a graph showing the relationship between the pH of an aqueous solution containing trivalent arsenic ions and the distribution ratio of arsenic in solvent extraction in the present invention.

FIG. 4 shows bis (2-ethylhexyl) ammonium bis (2-ethylhexyl) in an organic phase according to the present invention.
4 is a graph showing the relationship between the concentration of dithiocarbamate and the distribution ratio of arsenic in solvent extraction.

FIG. 5 is a graph showing the relationship between the coexisting metal ion concentration and the distribution ratio of arsenic between an organic phase and an aqueous phase when another metal ion coexists with trivalent arsenic ion in the present invention.

FIG. 6 is a graph showing the relationship between the pH of an aqueous phase and the distribution ratio of arsenic when trivalent arsenic ions are adsorbed to a resin supporting a reagent in the present invention.

Claims (6)

(57) [Claims] When removing trivalent arsenic ions from an aqueous solution containing trivalent arsenic ions, the aqueous solution is converted to a chemical formula (1). A trivalent arsenic ion is transferred from an aqueous phase to an organic phase by bringing the organic solvent into contact with an organic solvent containing the compound described in (1). 2. In removing trivalent arsenic ions from an aqueous solution containing trivalent arsenic ions, the aqueous solution is brought into contact with a porous resin supporting a compound represented by the chemical formula (1) to convert trivalent arsenic ions from the aqueous phase. A method for removing trivalent arsenic ions, characterized in that the ions are transferred into a resin. 3. The pH of an aqueous solution containing trivalent arsenic ions.
Is in the range of 0 to 7.
3. The method for removing trivalent arsenic ions according to item 1. 4. The method for removing trivalent arsenic ions according to claim 1, wherein only trivalent arsenic ions are removed from an aqueous solution containing both trivalent arsenic ions and pentavalent arsenic ions. 5. The method according to claim 2, wherein the trivalent arsenic ion-supported resin is brought into contact with an aqueous alkaline solution having a pH of 10 or more to transfer the trivalent arsenic ion from the resin to an aqueous phase. To recover trivalent arsenic ions. 6. The method for removing trivalent arsenic ions according to claim 2, wherein the porous resin supporting the compound represented by the chemical formula (1) is used as a cylindrical column.