JPH0218289B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for separating mercury by solvent extraction. In particular, it concerns methods for separating mercury contained in wastewater and solid waste.

(Prior art) Mercury is contained in wastewater discharged from mercury-method electrolytic soda plants, chemical plants that use mercury catalysts, and manufacturing plants for pharmaceuticals and disinfectants containing mercury, which causes a great deal of environmental pollution. It is a well-known fact that this has happened. For this reason, various measures have been taken up to now to separate and remove mercury ions contained in wastewater, particularly mercuric ions that have an adverse effect on the human body.

On the other hand, in recent years, environmental pollution caused by mercury contained in solid materials such as used mercury batteries and silver oxide batteries has attracted serious social concern, and complete separation and recovery of mercury from these solid wastes has become a major concern. desired.

Conventionally, wastewater containing mercury has been treated using sedimentation methods, adsorption methods, ion exchange methods, etc. Among these methods, the sedimentation method has the drawbacks of consuming a large amount of chemical solution and being difficult to operate continuously. In addition, the adsorption method using activated carbon or chelate resin, and the ion exchange method have the disadvantage that, when continuous operation is performed, a large amount of adsorbent or ion exchange resin is required in relation to the throughput.

In contrast to these techniques, in recent years, from the viewpoint of energy saving, techniques for selectively and efficiently separating trace metal ions using solvent extraction methods and liquid membrane methods have attracted attention. As the component which acts as an extractant in the case of solvent extraction or a carrier in the case of the liquid membrane method, various high molecular weight amines, neutral phosphorus compound extractants such as trioctylphosphine oxide and tributyl phosphate, etc. can be considered. However, these components cannot necessarily be said to be suitable extractants in terms of selectivity to mercury.

Recently, a method for separating and removing mercury using a liquid membrane using dicyclohexyl-24-crown-8 as a carrier has been developed (Publication of Patent Publication No. 153786/1986 (Patent No. 1257206). 24-Crown-8 is very expensive, so there are problems in actual use.
Moreover, this publication does not mention anything regarding selectivity to mercury.

According to Pearson's concept of “hard acids, soft acids and hard bases, soft bases” (see:
RGPearson; J.Amer.Chem.Soc., 3533
(1963)), mercury is classified as a typical soft acid. Therefore, when selectively extracting mercury, it is more efficient to use a sulfur compound extractant that acts as a soft base than to use the aforementioned high molecular weight amine or neutral phosphorus compound extractant that acts as a hard base. be.

Dialkyl sulfides, petroleum sulfides contained in crude oil, and sulfoxides obtained by oxidizing these are known as sulfur compound extractants, and research on their extraction characteristics is being conducted in the Soviet Union and other countries. It is being said.

(Problems to be Solved by the Invention) The aforementioned dialkyl sulfides and petroleum sulfides are excellent extractants with high selectivity for mercury, but their extraction ability is still insufficient from a practical point of view. It's not something I can be satisfied with.

The object of the present invention is to develop an extractant with a much better extraction ability than the above-mentioned sulfides and to find advantageous operating conditions therefor. On the other hand, the excellent extraction performance of the extractant means that back extraction is sometimes very difficult. It is also an object of the present invention to find an effective back extraction solution to overcome this point.

(Means for solving the problems) In order to solve these problems, the present invention has the following features:
A method for separating mercury using a sulfur-containing carboxylic acid as an extractant is provided. As mentioned above, dialkyl sulfides and petroleum sulfides are excellent extractants with high selectivity for mercury, but α-, a type of sulfur-containing carboxylic acid,
It has been found that alkylthiolauric acids have a much better extraction ability for mercury than sulfides.

The α-alkylthiolauric acids used as extractants in the present invention have the general formula (R in the formula represents an alkyl group).

In addition, R in the formula is preferably an alkyl group having 4 to 8 carbon atoms, and when R is an alkyl group having 3 or less carbon atoms, it is preferable that R is an alkyl group having 3 or less carbon atoms. Synthesis problems arise due to the use of alkyl groups with 9 or more carbon atoms, such as increased surface activity and poor oil/water separation, or the incorporation of minute water droplets into the organic phase. This is not desirable because it causes problems.

The α-alkylthiolauric acids used in the present invention are α-
The following reaction formula is formed using bromurauric acid, the corresponding alkanethiol, which is also obtained at low cost as an industrial chemical, and potassium hydroxide. Accordingly, it can be easily synthesized in methanol in high yield.

The obtained compound can be easily purified by distillation under reduced pressure. These α-alkylthiolauric acids can be used alone or in a mixture of two or more.

Prior to solvent extraction, an aqueous solution of hydrochloric acid, chloride, nitric acid or nitrates can be used as the aqueous medium to dissolve the mercury; however, as will be discussed later, an aqueous solution of nitric acid or nitrates is preferred for better extraction. .

FIG. 1 shows α-butylthiolauric acid, which is one of the extractants used in the present invention, as an extractant.
The extraction percentage (%) ^of mercury and the nitrate ion concentration (mol/ The relationship with the logarithm of dm) is shown in dotted form.

In both cases, toluene was used as a diluent,
A toluene solution of α-butylthiolauric acid with a concentration of 0.052 mol/dm ³ was used.

For comparison, we have shown the results of extraction of dihexyl sulfide, a type of sulfide conventionally known as an efficient extractant for mercury, from nitric acid with a 0.051 mol/dm ³ toluene solution ( △
mark).

Comparing the two, the nitrate ion concentration is 1mol/
It is clear that in the region below dm ³ , the α-alkylthiolauric acid used in the present invention has superior extraction performance to dihexyl sulfide. In addition, in a high concentration region where the nitrate ion concentration is 1 mol/dm ³ or more, a phenomenon was observed in which the α-alkylthiolauric acid used in the present invention was oxidized and decomposed by nitric acid, and the organic phase became cloudy. However, since such a high concentration of nitric acid is not actually used, this poses almost no problem in practice.

In addition, the □ mark in the figure indicates that in the case of the aforementioned sodium nitrate aqueous solution (〇 mark), additional water is added to the aqueous phase.
These are the results when 0.01 mol/dm ³ of hydrochloric acid is included.
Therefore, if anions such as chloride ions that form stable complexes with mercury are present in the aqueous phase, the extraction amount will be extremely reduced, so the use of such anions must be avoided.

The extractant used in the present invention can be used alone or in combination with a diluent, a modifier, etc.

An aqueous solution containing an anion that forms a stable complex ion with mercury is used as a back-extraction solution for extracting and concentrating mercury back into the aqueous phase from the extraction solvent from which mercury has been extracted. In the present invention, a thiocyanate (for example, ammonium thiocyanate) aqueous solution was used as the back extraction solution, and mercury could be completely back extracted even at a concentration of about 1 mol/dm ³ .

Hereinafter, the present invention will be specifically explained with reference to Examples.

(Example) Example 1 Nitric acid aqueous solutions of various concentrations shown below containing mercuric ions at a concentration of 0.0050 mol/dm ³ were used as the aqueous phase.
When 0.015 dm ³ was taken and mixed with 0.015 dm ³ of a toluene solution of α-butylthiolauric acid having a concentration of 0.052 mol/dm ³ , the mercury in the aqueous phase was extracted into the organic phase at the following ratio.

Nitric acid concentration [mol/dm ³ ] Mercury extraction percentage [%] 0.01 84.5 0.03 92.0 0.1 95.2 0.2 93.6 0.5 84.1 1.0 84.1 90% when the nitric acid concentration is in the range of 0.03 to 0.2 mol/dm ³
The above extraction rate was obtained.

When the mercury extracted into the organic phase was shaken and mixed with an aqueous solution of ammonium thiocyanate of about 1 mol/dm ³ , 100% of the mercury was back-extracted into the aqueous phase.

Example 2 0.0015 dm ³ of a sodium nitrate aqueous solution containing mercuric ions at a concentration of 0.0050 mol/dm 3 and hydrogen ions at a concentration of 0.01 mol/dm ³ as shown below was taken as an aqueous phase, and 0.052 mol/dm ³ was taken. α− of concentration in dm ³
When the mixture was shaken and mixed with 0.015 dm ³ of a toluene solution of butylthiolauric acid, mercury in the aqueous phase was extracted into the organic phase at the following ratio.

Sodium nitrate concentration Mercury extraction percentage (mol/dm ³ ) [%] 0.03 96.2 0.1 95.0 0.2 96.2 0.5 94.7 In all cases, an extraction percentage of 90% or more was obtained.

Again, the mercury extracted into the organic phase is approximately
When the mixture was shaken and mixed with a 1 mol/dm ³ ammonium thiocyanate aqueous solution, 100% was back extracted into the aqueous phase.

Example 3 Nitric acid aqueous solutions with the concentrations shown below containing mercuric ions at a concentration of 0.0050 mol/dm ³ were used as the aqueous phase.
When 0.015 dm ³ of the solution was taken and mixed with 0.015 dm ³ of a toluene solution of α-hexylthiolauric acid having a concentration of 0.051 mol/dm ³ , the mercury in the aqueous phase was extracted into the organic phase at the following ratio.

Nitric acid concentration [mol/dm ³ ] Mercury extraction percentage [%] 0.01 84.4 0.03 88.4 0.1 90.4 0.2 89.9 0.5 78.9 1.0 78.1 The mercury extracted into the organic phase was shaken and mixed with an aqueous ammonium thiocyanate solution of about 1 mol/dm ³ However, 100% was back extracted into the aqueous phase.

Example 4 Nitric acid aqueous solutions with the concentrations shown below containing mercuric ions at a concentration of 0.0050 mol/dm ³ were used as the aqueous phase.
When 0.015 dm ³ of the solution was taken and mixed with 0.015 dm ³ of a toluene solution of α-octylthiolauric acid having a concentration of 0.050 mol/dm ³ , the mercury in the aqueous phase was extracted into the organic phase at the following ratio.

Nitric acid concentration [mol/dm ³ ] Mercury extraction percentage [%] 0.01 84.4 0.03 86.7 0.1 87.7 0.2 86.0 0.5 81.6 1.0 78.9 Compared with the case of α-butylthiolauric acid shown in Example 1, the results of Examples 3 and 4 were In this case, the extraction ability will decrease slightly.

When the mercury extracted into the organic phase was shaken and mixed with an aqueous solution of ammonium thiocyanate of about 1 mol/dm ³ , 100% of the mercury was back-extracted into the aqueous phase.

(Effects of the Invention) According to the present invention, mercury contained in wastewater and solid waste can be almost completely separated. Furthermore, back extraction can be easily performed. Also,
According to the present invention, as shown in FIG. 1, it is possible to provide a separation method that has a higher extraction ability than dialkyl sulfides, which have conventionally been excellent as extractants for mercury.

[Brief explanation of drawings]

FIG. 1 is a graph comparing the mercury extraction performance according to the conventional method and the mercury extraction performance according to the present invention.
〓 mark indicates the method of the present invention in which mercury contained in nitric acid aqueous solution, 〇 mark indicates extraction of mercury contained in sodium nitrate aqueous solution with α-butylthiolauric acid, and △ mark indicates extraction of mercury in nitric acid with dihexyl sulfide. A conventional method is shown. The □ mark indicates that the sodium nitrate aqueous solution (○ mark) contains hydrochloric acid.

Claims (1)

[Claims] 1. The following formula as an extractant: α- represented by (R in the formula represents an alkyl group)
A method for separating mercury by solvent extraction, characterized by using one or more types of alkylthiolauric acids. 2. The separation method according to claim 1, wherein R has 4 to 8 carbon atoms. 3 As an extractant, use the following formula α- represented by (R in the formula represents an alkyl group)
A method for separating mercury by solvent extraction, which comprises using one or more alkylthiolauric acids, extracting mercury with a solvent, and further back-extracting the extracted mercury into an aqueous solution of thiocyanate.