JPH0416232B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for separating mercury using solvent extraction and a liquid film, and is particularly useful for recovering mercury contained in wastewater and solid waste. Conventional technology Mercury is contained in wastewater discharged from mercury-method electrolytic soda factories, chemical factories that use mercury catalysts, manufacturing factories for pharmaceuticals and disinfectants that contain mercury, and is a cause of environmental pollution. To date, various measures have been taken to separate and remove mercury ions contained in wastewater, particularly mercuric ions that have an adverse effect on the human body. In addition, 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, the sedimentation method has the drawbacks of consuming a large amount of chemical solution and being difficult to operate continuously. Furthermore, the adsorption method using activated carbon or chelate resin, and the ion exchange method have a disadvantage in that when continuous operation is performed, a large amount of adsorbent or ion exchange resin is required in relation to the throughput. On the other hand, in recent years, from the viewpoint of energy saving, techniques for selectively and efficiently separating trace metals using solvent extraction methods and liquid film methods have been attracting attention. For example, JP-A-59-136435 discloses a method for extracting silver and palladium metals from aqueous solutions using tertiary phosphine sulfide. However, the extraction of mercury from the aqueous phase has not been reported, and the extraction of trace metals in such solvent extraction methods has also been shown to be highly unpredictable (Publication (3), upper left column 14- 15 lines). Also, recently dicyclohexyl-24-crown-8
A method for separating and removing mercury using a liquid film as a carrier was developed (Japanese Patent Application Laid-Open No. 153786, 1983). However, this method is of limited practical use because the carrier dicyclohexyl-24-crown-8 is very expensive. Furthermore, recently, East German chemists have been able to recover 92.5% of mercury from wastewater containing 10 g/ ^m3 of mercury using an emulsifying liquid membrane using dibutylbenzoylthiourea, a type of thiourea compound, as a carrier. has been successful in (East German Patent No. 200230). In addition, the mercury concentration of an aqueous solution containing 100 ppm of mercury can be determined in one extraction using an emulsifying liquid membrane using 1,2-bis(hexylthio)ethane as a carrier.
A method for reducing the amount to 0.5 ppm is also disclosed. (Chemical Engineering Society, 50th Annual Meeting Research Presentation Proceedings, p. 56, B-
110, 1985). Problems to be Solved by the Invention As mentioned above, there is a demand in industry for advances in mercury separation and recovery technology, and solvent extraction methods are energy-saving, effective, and have excellent selectivity. , which is highly unpredictable, and the invention of a superior extractant combination and its advantageous operating conditions has been desired. The present invention meets this need by discovering an extractant that has an excellent ability to extract particularly from aqueous solutions containing chloride ions, and by finding advantageous operating conditions for this purpose. On the other hand, the superior extraction ability of an 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. Furthermore, it is an object of the present invention to reduce the mercury content in wastewater to the minimum by using an emulsion-type liquid membrane in which the extractant obtained for the above purpose is used as a carrier and the reverse extraction liquid is used as an internal aqueous phase. Means for Solving the Problems The present invention provides a method for separating mercury from an aqueous phase by contacting an aqueous phase containing mercury with a tertiary phosphine sulfide compound represented by formula (1) as an extractant; (wherein R ¹ , R ² and R ³ are each independently selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl, substituted aryl and substituted aralkyl having at least 2 carbon atoms. ), and mercury in the aqueous phase is extracted with a solvent using triisobutylphosphine sulfide or trioctylphosphine sulfide as an extractant, and the mercury in the extracted solvent is further extracted with an aqueous solution of thiocyanates or thiosulfate salts. A method for separating mercury characterized by back extraction using triisobutylphosphine sulfide or trioctylphosphine sulfide as a carrier and an aqueous solution of thiocyanates or thiosulfate salts as the internal aqueous phase. This is a method for separating mercury using an emulsion-type liquid film method. The present invention utilizes a solvent extraction method. The mercury to be separated and recovered is that contained in the aqueous phase as mercuric ions. The aqueous phase containing such mercury is typically the various industrial wastewaters mentioned in the prior art section. In addition, mercury contained in solid waste can be dissolved by appropriate means, such as a method that takes advantage of the volatility of mercury and absorbs it into an aqueous solution of an oxidizing agent such as potassium permanganate to form mercuric ions. Therefore, if it is trapped in an aqueous solution, it can be separated by the present invention. If the extractant used in the present invention is a liquid, it can be used alone or dissolved in a diluent, but if it is a powder, it can be used after being dissolved in a suitable diluent. Possible diluents for industrial use include aliphatic diluents such as kerosene and aromatic diluents such as benzene and toluene; however, when the former diluent is used, mercury and extraction The complex with the agent is not sufficiently dissolved and forms precipitates and solids. Such precipitates and solids sometimes impair oil-water separation, and in such cases the use of aliphatic diluents should be avoided. An aqueous solution containing an anion that forms a stable complex ion with mercury may be used as a back-extractant for extracting and concentrating mercury back into the aqueous phase from the extraction solvent from which mercury has been extracted. Such aqueous solutions include aqueous solutions of thiocyanate or thiosulfate salts such as ammonium thiocyanate and sodium thiocyanate.
That is, by using these, almost 100% back extraction is possible even at a dilute concentration of about 1 mol/dm ³ . By using this extractant not only as an extraction solvent but also as a carrier in a liquid film method, it is possible to significantly reduce the concentration of mercury contained in wastewater and the like. The liquid film method is a separation technology developed by Mr. NNLi in the United States in 1938 (U.S. Patent No. 3410794), and its purpose is to simultaneously perform extraction and suction extraction, which were previously performed separately. That is. There are two types of liquid membranes: impregnated liquid membranes and emulsified liquid membranes.In the former, a porous membrane such as a Teflon membrane is impregnated with an extractant, and one side is filled with the extraction liquid and the other side is subjected to back extraction. It is brought into contact with liquid. The latter is achieved by vigorously mixing the back extraction solution and the extraction solvent to which a small amount of surfactant has been added.
An internal aqueous phase, that is, an emulsified phase in which an aqueous solution of thiocyanate salts or thiosulfate salts is incorporated into the back extraction solution as minute water droplets, is prepared and brought into contact with the extraction solution. As a result, the extractant in the oil film selectively extracts the target metal (metal to be separated) present in the external extract into the oil film, and transports it to the internal aqueous phase. Here the metal is extracted back into the internal aqueous phase. Thus, the metal of interest in the external aqueous phase can be selectively separated and concentrated in the internal aqueous phase. When the extractant used in the present invention is used as an aliphatic solution, it may generate precipitates in the organic phase, and when an impregnated liquid membrane is used, there is a risk of clogging the porous membrane. It is recommended to use By using a kerosene solution of the present extractant as a carrier and an emulsified liquid film using sorbitan fatty acid monoester or polyamine as a surfactant, the concentration of mercury contained in the nitrate aqueous solution was reduced to about 100 ppm. We succeeded in reducing the amount of mercury contained in the hydrochloride solution to below 0.6 ppm, and the mercury contained in the hydrochloride aqueous solution to below 5 ppm. When using an emulsified liquid film, it is important to use a strong surfactant that can produce a stable film. Effects Next, the results of measuring the extraction percentage by bringing various extractants into contact with nitric acid and hydrochloric acid aqueous solutions containing mercury are shown. FIG. 1 shows the case of a nitric acid aqueous solution, and FIG. 2 shows the case of a hydrochloric acid aqueous solution. The horizontal axis shows the acid concentration expressed in logarithm, and the vertical axis shows the extraction percentage of mercury. Extraction percentage means that the substance initially present in the aqueous phase (here, mercury) is removed from the organic phase (here, toluene).
It refers to the proportion extracted in In addition, the mercury analysis method is based on the mercury concentration.
In the case of 100 ppm or more, a chelate titration method using Eriochrome and Black T was adopted. Atomic absorption spectrometry was used when the mercury concentration was below 100 ppm. The following extractants were used. (1) Triisobutylphosphine sulfide concentration
0.04 mol/dm ³ toluene solution (black circle in the figure) (2) α-Butylthiolauric acid (C ₁₀ H ₂₁
(SC ₄ H ₉ ) CHCOOH) Toluene solution with a concentration of 0.05 mol/dm ³ (white circle in the figure) (3) Dihexyl sulfide concentration 0.05 mol/dm ³
(marked △ in the figure) (4) Toluene solution of 1,2-bis(hexylthio)ethane (C ₆ H ₁₃ SC ₂ H ₄ SC ₆ H ₁₃ ) with a concentration of 0.05 mol/dm ³ (marked □ in the figure) (5) Trioctylphosphine sulfide concentration
0.04 mol/dm ³ toluene solution (x mark in the figure) The initial mercury concentration in the aqueous phase is approximately 1000 ppm. Figure 1 shows the relationship between nitric acid concentration and extraction percentage in extraction from nitric acid that does not form complexes with mercury. Although the triisobutylphosphine sulfide used in the present invention has a slightly lower concentration, it provides extraction percentages comparable to or higher than other extractants except when the nitric acid concentration is very low. Trioctylphosphine sulfide gives high extraction percentages regardless of nitric acid concentration. When extracting from nitric acid, contact with high-concentration nitric acid should be avoided, as high-concentration nitric acid has strong oxidizing power, and this extractant is relatively susceptible to oxidation, and when oxidized, the extraction ability decreases. , contact should be limited to a short period of time. In reality, the extraction of mercury proceeds very quickly, so it only takes a few tens of seconds of shaking to complete the extraction. Moreover, if the contact time is of this level, oxidation of the extractant will not be a problem. Figure 2 shows the relationship between chloride ion concentration and extraction percentage in extraction from hydrochloric acid that forms a stable complex with mercury. Chloride ions form stable complexes with mercury, which significantly inhibits extraction. However, the extractants used in the present invention, triisobutylphosphine sulfide and trioctylphosphine sulfide, are capable of efficiently extracting mercury even from considerably highly concentrated hydrochloric acid. That is, the other three extractants shown in Figure 1 are 1N
Although it gives an extraction percentage of less than 5% from hydrochloric acid, this extractant gives an extraction percentage of more than 80% even though its concentration is slightly lower. This Figure 2 clearly shows how strong this extractant is against mercury. The present invention will be specifically explained below using Examples. Example 1 Take 15 dm ³ of a nitric acid aqueous solution containing approximately 1000 ppm of mercuric ion at each concentration shown below as the aqueous phase,
When the mixture was shaken for about 30 minutes with 15 dm ³ of a toluene solution of triisobutylphosphine sulfide having a concentration of 0.04 mol/dm ³ , mercury in the aqueous phase was extracted into the organic phase at the ratio shown in Table 1.

[Table] Example 2 Take 30 dm ³ of an aqueous solution of hydrochloric acid at each concentration shown below containing about 1000 ppm mercuric ion as the aqueous phase, and mix it with the same amount of 0.04 mol/dm ³ of a toluene solution of triisobutylphosphine sulfide. After shaking and mixing for about 180 minutes, the mercury in the aqueous phase was extracted into the organic phase in the proportions shown in Table 2.

[Table] Example 3 Equal amounts of an aqueous ammonium thiocyanate solution containing 1030 ppm of mercuric ion at each concentration shown below and a toluene solution of 0.04 mol/dm ³ of triisobutylphosphine sulfide were taken as the aqueous phase.
After shaking for 180 minutes, mercury in the aqueous phase was
It was extracted into the organic phase in the proportions shown in the table.

[Table] From the above results, it can be seen that if an ammonium thiocyanate aqueous solution with a concentration of 2 mol/dm ³ or more is used, the mercury extracted into the organic phase can be back-extracted back into the 100% aqueous phase. Example 4 An organic phase prepared by adding 4% by weight of Span 80 (sorbitan fatty acid monoester) to a kerosene solution of triisobutylphosphine sulfide at a concentration of 0.04 mol/dm ³ and the same volume of ammonium thiocyanate at 1 mol/dm ³ The emulsified phase obtained by vigorously mixing the aqueous solution for about 30 minutes at a rotation speed of 1600 rpm with a 6-blade turbine type stirring blade was mixed with 1N nitric acid and 1N ammonium nitrate containing 101 ppm of mercury ions. It was contacted with an aqueous phase containing a ratio of 1:9. At this time, the volume ratio of the emulsified phase and the aqueous solution containing mercury was 1:10, and the stirring speed was 300 rpm using the same stirring blade as described above.
Stir at a speed of . After the stirring started, the mercury concentration in the aqueous phase changed with time as shown in Table 4.

[Table] After 6 minutes of stirring time, the mercury concentration in the aqueous phase gradually increases. This is because the mercury that was taken into the minute water droplets inside the liquid film came out again into the aqueous phase due to the destruction of the liquid film. Therefore, it is desirable to keep the stirring time as short as possible. Example 5 The same emulsion phase prepared in Example 4 was
Contains 100ppm mercuric ion and is combined with 1N hydrochloric acid.
When contacted with an aqueous phase containing 1N ammonium chloride in a ratio of 1:9 in a manner similar to that of Example 4, the mercury concentration in the aqueous phase changed as shown in Table 5.

[Table] In this case as well, leakage of mercury incorporated into the emulsion phase is observed due to membrane destruction, so it is desirable to keep the stirring time as short as possible. Example 6 An aqueous hydrochloric acid solution containing 995 ppm of mercuric ion at each concentration shown below and a toluene solution of trioctylphosphine sulfide at a concentration of 0.04 mol/dm ³ were prepared in the same manner as in Example 2 as the aqueous phase. When the mixture was shaken and mixed, mercury in the aqueous phase was extracted into the organic phase in the proportions shown in Table 6. Here, in the hydrochloric acid concentration range of 0.5 to 3 mol/dm ³ , formation of a yellow film-like precipitate was observed at the two-phase interface.

【table】

[Table] Example 7 A nitric acid aqueous solution containing 990 ppm mercuric ion at each concentration shown below and a toluene solution of trioctylphosphine sulfide at 0.04 mol/dm ³ were prepared in the same manner as in Example 1 as the aqueous phase. When the mixture was shaken and mixed, mercury in the aqueous phase was extracted into the organic phase in the proportions shown in Table 7. However, in the nitric acid concentration range of 0.5 mol/dm ³ or less, a stable emulsion was formed at the two-phase interface, resulting in poor phase separation, and furthermore, the formation of precipitates adhering to this emulsion was observed.

【table】 [Brief explanation of drawings]

FIGS. 1 and 2 are graphs explaining the effects of the present invention.

Claims (1)

[Scope of Claims] 1. A method for separating mercury from an aqueous phase by contacting a mercury-containing aqueous phase with a tertiary phosphine sulfide compound represented by formula (1) as an extractant. (wherein R ¹ , R ² and R ³ are each independently selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl, substituted aryl and substituted aralkyl having at least 2 carbon atoms. 2. The method for separating mercury according to claim 1, wherein the tertiary phosphine sulfide compound is triisobutylphosphine sulfide or trioctylphosphine sulfide. 3. The method for separating mercury according to claim 1 or 2, wherein the aqueous phase containing mercury contains chloride ions. 4 Solvent extraction of mercury in the aqueous phase using triisobutylphosphine sulfide or trioctylphosphine sulfide as an extractant, and further extracting mercury in the extracted solvent with an aqueous solution of thiocyanates or thiosulfate salts. A method for separating mercury characterized by back extraction. 5. A method for separating mercury by an emulsion-type liquid film method, characterized in that triisobutylphosphine sulfide or trioctylphosphine sulfide is used as a carrier and an aqueous solution of thiocyanates or thiosulfate salts is used as the internal aqueous phase.