JPH044001B2 - - Google Patents

Description

[Detailed description of the invention]

Technical field: The present invention processes an aqueous solution containing at least one of Cd () and Pb () and Zn () by a solvent extraction method using an acidic monothiophosphoric acid compound as an extractant. and a method of separating at least one kind of Pb from Zn. Conventional technology: Zn() to Cd(), Pb() and Cu()
A typical method for separating zinc is the cementation method, which is a liquid purification method in zinc hydrometallurgy. In this method, zinc powder is added to a Zn ()-containing aqueous solution containing impurity ions such as Cd () and Pb (), and the impurity ions such as Cd () are replaced with metallic zinc by utilizing the difference in ionization tendency. It is removed by precipitation. This substitution reaction requires a long time and has the disadvantage that the resulting precipitate contains a large amount of Zn. Furthermore, since solid-liquid reaction and separation operations are involved, the operations are inevitably complicated and inefficient.
Moreover, a large capital investment is required. In order to eliminate the above drawbacks of cementation method, Zn and Cd, Pb and
Separation methods with one type of Cu are being considered.
For example, there is a solvent extraction method that uses di-2-ethylhexyl phosphoric acid (DEHPA) as an extractant.
In this method, Zn than Cd, Pb and Cu
are preferentially extracted. Therefore, Zn is Cd, Pb
And if it is contained in a larger amount than Cu,
Although the purpose is to separate small amounts of Cd, Pb, and Cu, it is necessary to first extract a large amount of Zn, which requires a large amount of extraction solvent and large extraction equipment. In addition, the extractant DEHPA Cd, Cu
Also, the selective extraction ability for separating Pb and Zn is not sufficient. OBJECT OF THE INVENTION: An object of the present invention is to provide a solvent extraction method using an extractant that has excellent separation and extraction ability for Cd, Pb, and Zn. Another object of the invention is that Cd and
Using an extractant that can extract Pb preferentially over Zn, Cd
and Pb and Zn. Still another object of the present invention is to provide a solvent extraction method that does not require special extraction operations. Summary of the Invention: The method of the present invention provides an extraction solvent containing an acidic monothiophosphoric acid compound represented by the following general formula as an extractant: an aqueous solution containing a metal salt of at least one of lead and cadmium and a zinc salt. Alternatively, the method includes selectively extracting and separating at least one of lead and cadmium from the zinc-containing aqueous solution by bringing it into contact with the impregnated solid, thereby achieving the above object.

[Formula] Here, A is a sulfur atom, B is an oxygen atom; R ₁ and R ₂ are each substituted or unsubstituted alkyl, cycloalkyl, aryl, or alkyl bonded to the P atom directly or via an oxygen atom. Allyl or arylalkyl group; and R ₁ and R ₂
are the same or different, and the sum of the carbon numbers of R ₁ and R ₂ is 9 or more. The total number of carbon atoms in R ₁ and R ₂ is preferably 9 or more and 36 or less. When the total carbon number is less than 9, the extractant becomes soluble in water, and when it exceeds 36, the metal loading capacity of the extractant becomes small. In addition, R ₁ and R ₂ are preferably alkyl groups such as 2-ethylhexyl group, isooctyl group, 1-methylheptyl group, octyl group, and isodecyl group from the viewpoint of easy solubility in the diluted organic solvent of the extractant. preferable. As an extractant that satisfies these conditions, there is an O.O'-dialkylmonothiophosphoric acid compound. In particular, those represented by the chemical formula (RO) ₂ PSOH may be used. Examples include bis(2-ethylhexyl) monothiophosphoric acid, di-isooctylmonothiophosphoric acid, bis(1-methylheptyl)monothiophosphoric acid/di-octylmonothiophosphoric acid, bis(3,5,5-trimethylhexyl) There are monothiophosphoric acid and di-isodecylmonothiophosphoric acid. These compounds are obtained by preparing (RO) ₂ PSCl by reacting phosphorus sulfide (PSCl ₃ ) with alcohols having the corresponding alkyl, and then hydrolyzing this. Alternatively, it can also be obtained by subjecting (RO) ₂ POH to an addition reaction with sulfur in the presence of triethylamine or a polar solvent to prepare an amine salt of the desired product, which is metathesized with an acid. The method of carrying out the present invention is not special, as it is possible to set up a circuit for extraction, washing, and back extraction in the same way as in a normal solvent extraction method. The above general formula used in the present invention

The extraction reaction between the extractant and the metal represented by the formula is mainly an ion exchange reaction between the acidic group H ⁺ of the extractant and a metal ion or complex cation of the metal. Therefore, the basic concept for selecting conditions in the solvent extraction method is to use di-2-ethylhexyl phosphate or mono-2-ethylheosylphosphonic acid as the extractant, except for the difference in the extraction order of metals. It is similar or similar to the conventional solvent extraction method using ethylhexyl ester. In other words, the reactions of metal extraction and back-extraction are controlled by the buffering effect of pH. The extractant of the present invention has a major feature in that the extraction order of various metals is completely reversed compared to the conventional extractant di-2-ethylhexyl phosphate. The extraction order of the conventional extractant di-2-ethylhexyl phosphate is Fe()Al()Zn()>Cu()
While Cd()Pb()>Co()Mg()Ni(), the extraction order on the extraction side of the present invention is Cu
()＞Cd()＞Pb()＞Fe()Zn()Al(
)
Ca()>Co()Mn()Mg()Ni(). The extraction order of metals above indicates that metal ions classified on the left side are more easily extracted than metal ions classified on the right side, and the pH at the time of extraction is
When PH is small (when the H ⁺ concentration is large), the left group is extracted first, and as the PH increases, the right group is extracted sequentially. By the solvent extraction method using the extractant of the present invention, Cu(), Cd() and Pb() and Zn()
The basic method for separating these is as follows: (1) An extraction step in which an aqueous solution containing at least one of Cu (), Cd (), and Pb () and Zn () is brought into contact with an extraction solvent. At least one of Cu, Cd and Pb is extracted almost completely, and extraction conditions (mainly H ⁺ concentration of the aqueous phase at the time of extraction) are selected to extract as little as possible. A purified Zn-containing aqueous solution is obtained as roughinate. The metal-loaded solvent separated from the aqueous phase is then subjected to a washing step, if necessary, to remove the co-extracted Zn.
Aqueous solutions containing relatively concentrated mineral acids and selected PH
(H ⁺ concentration). At this time, Zn moves from the organic phase to the aqueous phase. The resulting Zn-containing aqueous solution can be recycled to the extraction process. Furthermore, the purified metal-loaded solvent is contacted with a relatively high concentration of mineral acid in a back-extraction step under PH (H ⁺ concentration) conditions based on the back reaction during extraction. These metals are then recovered in the back-extraction aqueous phase.
The regenerated extraction solvent is recycled to the extraction process. (2) Also, for reference, to explain a back extraction method different from the present invention, Zn () in the raw material water solution
If the content of Zn is small, or if there is a metal that is more difficult to extract than Zn, a method can be adopted in which most of the Zn is extracted along with at least one of Cu, Cd, and Pb in the extraction process. In this case, Zn is
It is purified and recovered by controlling the PH of the contact. Furthermore, an additional washing step can be provided between the extraction step and the Zn washing step in order to remove metals of lower extraction order than Zn from the organic phase. The extraction solvent used in the present invention can be used alone, but it is generally diluted with an organic diluent to facilitate phase separation between the organic phase and the aqueous phase after liquid-liquid contact operation. It is preferable to use Any organic diluent may be used as long as it dissolves the extractant, is insoluble in water, and does not interfere with the function of the extractant during extraction. Effective diluents include, for example, high flash point paraffinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, and halogen-substituted compounds thereof. Particularly suitable are petroleum fractions such as kerosene or naphtha, toluene, and carbon tetrachloride, but the present invention is not limited thereto. The extractant concentration in the extraction solvent is determined by the concentration of the metal to be extracted in the aqueous solution (undiluted solution) to be extracted, and
It is also determined in relation to the phase ratio of organic phase and aqueous phase,
Generally 1 to 60% by volume of extractant, preferably 1 to 60% by volume
30% capacity is adopted. It is also possible to add modifiers to the extraction solvent to prevent it from forming emulsions and promote phase separation, or to increase the solubility of the extracted metal complexes in the organic phase. . Examples of modifiers include organic phosphorus compounds such as tributyl phosphate, dibutyl butylphosphonate, di-2-ethylhexyl phosphoric acid, and trioctylphosphine oxide; higher alcohols such as isodecanol; higher carboxylic acids; higher ethers; higher ketones. There is. The use of these modifiers has the above-mentioned effect of improving phase separation and the effect of acting as a diluent. At the same time, it has the effect of lowering the extractant's ability to increase the extraction pH range of metals such as Cu, Cd, and Pb, and further lowering the ability to separate them from other metals such as Zn. Therefore, it is not preferable to add a large amount of the modifier. On the other hand, when back-extracting metals,
The favorable effect of being able to use mineral acids at low concentrations can also be expected. Therefore, there is a limit to the amount of modifier added. The amount of modifier used is usually the same as that of the extractant.
It is preferable to use less than twice the molar amount. The reaction of bringing the above extraction solvent used in the present invention into contact with an aqueous solution containing metal ions to extract metal ions is similar to the extraction reaction using conventional extraction solvents, as described above, due to the buffering effect of PH (H ⁺ concentration). Therefore, it is important to select the pH during extraction. Therefore, in order to sufficiently extract Cu and Cd, the hydrochloric acid concentration during extraction is selected to be 3.5N or less, preferably 2.5N or less. For extraction of Pb, the hydrochloric acid concentration during extraction is selected to be 2.5N or less, preferably 2.0N or less. As the hydrochloric acid concentration during extraction is decreased (PH is increased), Cu,
Following the extraction of Cd and Pb, post-extraction metal ions such as Zn are extracted. The upper limit of PH is limited by the formation of precipitates, deterioration of phase separation, etc.
A value of 6.5 or less, preferably 4 or less is appropriate. Cu,
In order to maximize the extraction of Cd and Pb and minimize the extraction of Zn, the concentration of hydrochloric acid at the time of extraction should be 0.5N or more.
Preferably, it is 1.5 normal or more.
On the other hand, in the case of extraction from a sulfate aqueous solution, Cu and Cd are sufficiently extracted not only when the sulfuric acid concentration is 6N or less, but also at 6N or more. For extraction of Pb, the sulfuric acid concentration is selected to be 6N or less. In order to suppress the extraction of Zn, the sulfuric acid concentration should be 1.5N or more, preferably
It is preferable to set it to 3N or more. When performing multi-stage countercurrent extraction, by controlling the mineral acid concentration of the contacting aqueous phase in the aqueous phase (raw material aqueous solution) introduction stage to be greater than the H ⁺ concentration of the contacting aqueous phase in the organic phase introduction stage. In the organic phase introduction step, Cu is removed from the aqueous phase.
It is possible to maximize the extraction of Cd and Pb and at the same time transfer Zn from the organic phase to the aqueous phase in the aqueous phase introduction step. By doing so, it is possible to improve the separation effect and recovery rate of Cu, Cd, and Pb from Zn. The optimum pH or mineral acid concentration at this time is Cu, Cd and Pb in the raw material aqueous solution,
It can be easily determined depending on the ratio and concentration with Zn. The pH or mineral acid concentration during extraction can be controlled by appropriately adding and mixing an alkali or mineral acid to the organic phase (extraction solvent) or aqueous phase (raw material aqueous solution) introduced into the extraction device. Furthermore, if necessary, an alkali or mineral acid can be added when the organic phase and the aqueous phase are brought into contact with each other. Alkali does not need to be special, and includes those containing ammonium ions, alkali metal ions, alkaline earth metal ions, etc., their hydroxides, oxides,
There are carbonates and their aqueous solutions. Specifically, ammonia, caustic soda; soda carbonate, calcium hydroxide, etc. Hydroxides, oxides, and carbonates having metal ions at a later extraction rank than the metal to be extracted may also be used. To control the pH, it is also possible to use an appropriate proportion of the acidic groups (H ⁺ ) of the extractant in the extraction solvent in the form of an alkali or a salt of a metal ion that is later in the extraction order than the metal to be extracted. . Extraction solvent (organic phase) that comes into contact with the extraction process
The volume ratio (o/A) of the raw material aqueous solution (aqueous phase) can vary over a wide range. The most effective volume ratio is related to the concentration of the extractant in the extraction solvent, the concentration of the target metal to be extracted in the raw material aqueous solution, as well as the operating operation and the type of equipment, and is not particularly limited, but is preferably 20 /1 to 1/20, especially 5/
It is 1 to 1/5. This ratio is generally set in such a way that it is possible to incorporate all of the metal to be extracted into the organic phase used. In order to remove and recover Zn in the organic phase obtained in the extraction step, a washing step can be provided between the extraction step and the back extraction step. The cleaning step applies ion exchange reactions and procedures similar to the extraction step to remove mineral acids or/and Cu, Pb and
It is preferable to use an aqueous solution containing at least one type of Cd as the cleaning liquid. Furthermore, if the mineral acid concentration of the contact aqueous phase during cleaning is selected within an appropriate range,
Zn can be removed even if the cleaning solution contains metal ions, such as Zn(), which are in a later extraction order than the metal to be extracted. For example, a part of the aqueous phase obtained in the back extraction step or the raw material aqueous solution (before extraction treatment) can also be used as the cleaning liquid. Even in the cleaning process,
By bringing the organic phase and the aqueous phase into multi-step countercurrent contact, it is possible to increase the Zn removal effect and efficiency, reduce the loss of Pb and Cd to the cleaning solution, and increase the purity of the recovered Zn. The PH (H ⁺ concentration) of the aqueous phase (at the time of contact between the organic phase and the aqueous phase in the washing process) is usually
Mineral acid concentration ranges from 6N to PH4. However, when using a cleaning solution containing hydrochloric acid, it is recommended to use no more than 4N and Pb to prevent loss of Cd to the cleaning aqueous phase.
2.5N or less is preferable to prevent loss. Also,
When a cleaning solution containing sulfuric acid is used, there is less loss of Pb and Cd to the washing water phase (even if the sulfuric acid concentration is 5N or higher), and Zn recovery is faster (than when using a cleaning solution containing hydrochloric acid). The effect increases. Further, the contact ratio (o/A) between the organic phase and the aqueous phase in the washing step can be set over a wide range, but a small range, for example, 0.5 to 5, is preferable because feed back is carried out industrially. The organic phase containing at least one of Pb, Cd, and Cu obtained through the above extraction step or washing step is subjected to back extraction treatment to recover these metals. Back extraction is generally performed with an aqueous solution containing a mineral acid such as hydrochloric acid or sulfuric acid, and the metal ions in the organic phase are ion-exchanged with H ⁺ of the mineral acid to form the salt of the mineral acid used in the back extraction solution. It is recovered as a precipitate or an aqueous solution. Furthermore, even if alkali and/or ammonium hydrogen fluoride etc. are used,
Desorption and recovery of metals from the organic phase is possible. When performing back extraction using mineral acids, the optimal H ⁺ concentration in the aqueous phase at the time of contact between the organic phase and the aqueous phase (mineral acid) is:
It varies depending on the type of mineral acid, the concentration of the extractant in the extraction solvent, the presence or absence of a modifier in the extraction solvent, etc. for example,
Back extraction is possible using hydrochloric acid at a lower normal concentration than when using sulfuric acid. Hydrochloric acid is therefore preferred over sulfuric acid. Hydrochloric acid can also be advantageously used in the back-extraction step if contact with aqueous sulfate solutions takes place in the extraction and washing steps. When hydrochloric acid is used and no modifier is added to the extraction solvent, the concentration of hydrochloric acid in the aqueous phase at the time of contact required for back extraction is usually Cd
3.5 standard or higher for back extraction of Pb,
Selected as 2N or higher. Furthermore, when a modifier is added to the extraction solvent, back extraction is possible even at lower hydrochloric acid concentrations. When using sulfuric acid, Pb can be effectively back-extracted using, for example, 6N or more. Cu and Cd are difficult to back-extract with sulfuric acid. However, it may be possible to do so by adding a modifier. When nitric acid is used for back extraction, it can be carried out at a lower specified concentration than hydrochloric acid. but,
There is a limit to the repeated use of extraction solvents as this involves deterioration of the extractant. In addition, Pb, Cd, and Cu are added to the organic phase.
etc., the back extraction process is divided into several stages, and the mineral acid concentration of the contact aqueous phase of each back extraction stage is adjusted, or the back extraction method, such as the type of mineral acid, is changed. It is also possible to separate and recover each metal. In the extraction, washing, and back extraction steps of the present invention, the temperature at which liquid-liquid contact and phase separation are performed is not critical. Higher temperatures are better in relation to the viscosity of the extraction solvent and phase separation rate, but on the other hand, lower temperatures are better in relation to the flash point of the diluent (organic solvent) and the stability of the extractant. It is. Generally kept at 20-70℃. In addition, (metal) extraction, cleaning,
The operations and methods of each stage of back-extraction can be carried out by any known procedure using any equipment used in liquid-liquid extraction methods. For example, a countercurrent continuous contact method using a multistage extraction device is generally preferred, but cocurrent, batch, or circulating methods are also effective. Furthermore, the present invention provides an emulsion type liquid membrane extraction method or a continuous porous plate in which a W/O/W type emulsion is formed between a raw material aqueous solution, an extraction solvent, and a back extraction liquid (mineral acid), and extraction and back extraction are performed simultaneously. A fixed membrane type liquid membrane extraction method in which an organic or inorganic porous plate with pores is impregnated with an extraction solvent and the raw material aqueous solution and back-extracted mineral acid are brought into contact on both sides, or an inert porous body is impregnated with the extraction solvent. It goes without saying that this can also be carried out by impregnating and supporting the raw material aqueous solution and alternately flowing the back-extracted mineral acid. EXAMPLES The present invention will be described in more detail below based on examples. Example 1 Cu(), Cd(), Pb(),
The following extraction experiment was conducted to clarify the extraction separation ability regarding Zn (), Fe () and Co (). Extractant: (RO) ₂ Di-2-ethylhexylmonothiophosphoric acid, in which R of PSOH is a 2-ethylhexyl group, is diluted with paraffinic hydrocarbon (trade name: Cielzol 71: (manufactured by Ciel Kagaku Co., Ltd.) and brought it into contact with an aqueous solution containing a chloride of each of the metals to perform extraction. Extraction pH: To adjust the pH or hydrochloric acid concentration during extraction, add aqueous ammonia to the organic phase to convert the acidic groups of the extractant into ammonium salt at a certain ratio, or add hydrochloric acid at a certain concentration to the metal salt aqueous solution in advance. This was done by bringing into existence. Ratio of organic phase to aqueous phase: Ratio of organic phase to aqueous phase (o/A)
A ratio of 1:1 was adopted. Metal ion concentration: The initial concentration of metal ions is Cu, Cd,
Zn, Fe and Co 1g/ each; Pb 0.5g/
:Then, the initial total concentration of metal ions is 5.5g/
The organic phase and the aqueous phase were brought into contact so that Extraction procedure: Contacting was carried out by shaking for 20 minutes in an Ellenmeyer flask at 25°C. The relationship between the PH or hydrochloric acid concentration of the aqueous phase at extraction equilibrium and the extraction percentage of each metal is shown in FIGS. 1A and B.
Figure 1A shows the hydrochloric acid concentration of the roughinate aqueous phase and the extraction rate of each metal, and Figure 1B shows the extraction of each metal with respect to the pH of the roughinate aqueous phase for the region of low hydrochloric acid concentration of the roughinate aqueous phase in Figure 1A. Show rate. Figure 1 A and B show that Cu, Cd, Pb, Fe, Zn and
This shows that Co is sequentially extracted into the organic phase.
For example, in the case of roughinate hydrochloric acid concentration 2N,
100% Cu, 98% Cd and 86% Pb are extracted.
On the other hand, Fe, Zn and Co are each extracted at less than 5%. Note that the hydrochloric acid concentration in the roughinate aqueous phase has increased from the initial concentration by approximately the same amount as the equivalent concentration of the extracted metal, but this is due to ion exchange between the extracted metal cation and H ⁺ or NH ₄ ⁺ of the extractant. It shows that you have reacted. Example 2 Using the same extractant as in Example 1, Cd(),
Extraction tests of these metals from aqueous sulfate solutions containing Zn (), Co () and Ni () were carried out. Di-2-ethylhexylmonothiophosphoric acid
It was dissolved in a naphthenic hydrocarbon solvent (trade name: Dispersol, manufactured by Ciel Chemical Co., Ltd.) to a concentration of 0.5 mol/(approximately 18% by volume), and mixed with an aqueous solution containing the sulfate of each metal at 50°C for 20 minutes. Shake contact for minutes. The ratio of organic phase to aqueous phase (o/A) was 1:1; and the initial concentration of metal ions was 2.5 g/each (total concentration 10 g/A). The pH or sulfuric acid concentration during extraction was adjusted in the same manner as in Example 1 by adding concentrated aqueous ammonia and sulfuric acid. Table 1 shows the relationship between the sulfuric acid concentration or PH of the aqueous phase at extraction equilibrium and the extraction rate of each metal. Table 1 shows a comparative example in which DEPA was used in place of the di-2-ethylhexyl monothiophosphoric acid of the present invention as an extractant.

【table】

[Table] As is clear from this table, according to the extractant of the present invention, even if the raw material aqueous solution is a sulfate aqueous solution,
Cd is extracted preferentially over Zn. Also, instead of Cd(), the same amount of Cu()
When attempting to extract from an aqueous solution containing
Almost the same extraction results as Cd in the table were obtained. Example 3 The metal extraction characteristics were investigated using the extractants of the present invention in which the R of (RO) ₂ PSOH was varied. Extractants in which R is an n-octyl group, 1-methylheptyl group, 3,5,5-trimethyl group, and isodecyl group, respectively, were dissolved in dispersol to make a 0.5M solution, and the pH at the time of extraction was
All extraction conditions were the same as in Example 1 except that the sample was adjusted with sulfuric acid. The results showed the same tendency as in Example 2 when di-2-ethylhexyl monothiophosphoric acid was used, regardless of which extractant was used. i.e. Zn(), Co()
and preferentially extracted Cd from Ni(). There was also no significant difference in the relationship between the sulfuric acid concentration or pH of the aqueous phase during extraction and the extraction rate of each metal. As an example, the extraction results when R is an isodecyl group are shown in Table 2.

[Table] Example 4 Crude zinc oxide containing _small amounts of cadmium, lead, copper, etc. is dissolved in sulfuric acid, and the resulting zinc sulfate aqueous solution is used as the extractant (RO) of the present invention.2 PSOH R is 3.5. 5-
Extraction treatment was performed using di-3,5,5-trimethylhexylmonothiophosphoric acid, which is a trimethylhexyl group, and the effect of extracting and removing Pb, Cd, and Cu (from an aqueous zinc sulfate solution) was investigated. Dissolve crude zinc oxide in sulfuric acid and add 100g of Zn/other
Cd28mg/, Pb8.9mg/, Cu1.2mg/, Fe11
A zinc sulfate solution of 0.5 N (equivalent concentration) and 0.5 N (equivalent concentration) of free sulfuric acid was prepared. The extraction solvent obtained by diluting the above extractant with a hydrocarbon solvent (dispersol) to various concentrations and the above zinc sulfate aqueous solution were mixed at various volume ratios (o/A) in an Ellenmeyer flask.
Shaking contact was carried out at 25°C for 25 minutes. The result is the third
Shown in the table.

[Table] As is clear from Table 3, Pb, Cd and Cu are preferentially extracted from Zn even in sulfuric acid solution, and all Pb, Cd and Cu are effectively extracted in one step of extraction process. Extracted and removed. This also indicates that small amounts of Pb, Cd, and Cu can be removed even if the extractant concentration and o/A are set small. Extractant concentration is low and O/A
It goes without saying that the fact that the value is small is extremely advantageous for implementation on an industrial scale. Example 5 The maximum amount of metal extractable by the extraction solvent was measured. Maximum extraction amount of Cd(): When a 0.5M solution of di-2-ethylhexyl monothiophosphoric acid in paraffinic hydrocarbon (Sierzol-71) is contacted with an aqueous solution containing excess cadmium chloride, extractable Cd is extracted into the organic phase. The amount extracted was determined. The pH during extraction was adjusted in the same manner as in Example 1 by adding NaOH or hydrochloric acid. The extraction temperature was 25° C., o/A was 1, and the initial concentration of Cd() in the aqueous phase was 56 g/(1.0 g equivalent/). In addition, the above extractant is 0.3M
Experiments were also conducted in the same manner regarding extraction solvent concentrations. The initial concentration of Cd () in the aqueous phase at that time was 34 g/
(0.6 g equivalent/). The relationship between the Cd concentration in the organic phase after extraction and the extraction pH is shown in Figure 2A. Maximum extraction amount of Pb(): A 0.1 M Schierzol 71 solution of di-2-ethylhexylmonothiophosphoric acid was brought into contact with an aqueous solution containing lead chloride(). At this time, o/A was 1/2, and the initial concentration of Pb () in the aqueous phase was 8.2 g/(0.08 g equivalent/).
Other conditions are the same as for Cd() above. Figure 2B shows the relationship between the Pb concentration in the organic phase after extraction and the extracted pH. Example 6 A washing (back extraction) test was conducted to remove metals such as Zn from the organic phase containing metals such as Zn that were extracted simultaneously with Cu, Cd and Pb. () Cleaning with hydrochloric acid: Cd
Fe() and Zn in addition to () and Pb()
Zn () in the organic phase containing extracted ()
and Fe() removal effects were tested. The metal concentration in the organic phase before washing was Cd() 2.9g/
, Pb () 0.51 g/, Fe () 0.96 g/, and Zn () 0.92 g/. During washing, the volume ratio (o/A) of the organic phase to the aqueous phase was 1, the mixing contact time was 1 hour, and the temperature was 25°C. Figure 3 shows the relationship between the concentration of hydrochloric acid used for cleaning and the cleaning rate (%). However, the cleaning rate (%) is calculated using the following formula. Cleaning rate (%) = C ₁ - C ₂ / C ₁ × 100 C ₁ : Initial concentration of metal in the organic phase before cleaning C ₂ : Concentration of metal in the organic phase after cleaning As is clear from Figure 3, cleaning By appropriately adjusting the hydrochloric acid concentration at
Zn () and Fe () can be removed. for example,
When the hydrochloric acid concentration used for washing was 2N, 97% of Zn () and 87% of Fe () in the organic phase were removed, and 6.8% of Pb () and 0.8% of Cd () were then transferred to the washing aqueous phase. remain. The concentration of hydrochloric acid in the aqueous phase during washing was reduced from the initial concentration of hydrochloric acid by an amount commensurate with the equivalent concentration of metal transferred to the aqueous phase. What can be further understood from Figure 3 is that by dividing the cleaning stage into several stages and adjusting the mineral acid concentration at the time of contact between the organic phase and the aqueous phase in each stage, and increasing the metal concentration sequentially, each metal can be selectively recovered from the organic phase to the aqueous phase. () Washing with sulfuric acid: A paraffinic hydrocarbon solution of 0.5 mol/di-2-ethylhexylmonothiophosphoric acid is brought into contact with an aqueous sulfate solution of Cd (), Zn (), Co () and Ni (),
Cd3.27g/, Zn2.66g/, Co2.34g/,
An organic phase containing 2.00 g of Ni was extracted and prepared. This was mixed and contacted with 5.01N sulfuric acid,
The removal effect of Zn, Co and Ni in the organic phase was investigated. Volume ratio of organic phase to aqueous phase during washing (o/A)
The temperature was 2/1, the time of mixing contact was 20 minutes, and the temperature was 25°C. The organic phase was washed repeatedly with fresh sulfuric acid each time, and the results of the four washes were used as the fourth wash.
Shown in the table.

[Table] As is clear from Table 4, most of the Zn is removed from the organic phase by washing the organic phase four times with 1/2 volume of 5N sulfuric acid. Moreover, Cd
There is little loss of water to the wash aqueous phase. The method of using sulfuric acid for cleaning requires a higher concentration of acid than the case of using hydrochloric acid, but has the advantage of less loss of Cd to the cleaning water phase during cleaning.
It was also confirmed in another experiment that the loss of Pb to the washing water phase was similarly small. The method using sulfuric acid is also industrially advantageous because when the raw material aqueous solution in the extraction step is a sulfuric acid solution and the washed aqueous phase is recycled to the extraction step, foreign anions are not mixed into the extracted ruffinate aqueous phase. () Cleaning with an aqueous solution containing Cu, Cd and Pb salts: The initial concentration of each metal ion was Cu () 1.03g/
, Cd()2.01g/, Pb()0.504g/,
A raw material aqueous solution containing chlorides of Fe () 0.08 g/ and Zn () 1.14 g/ and a paraffinic hydrocarbon solution containing di-2-ethylhexyl monothiophosphoric acid 0.3 mol/ are mixed at pH 1.7 and o/A.
Cu ()1.03g/, mixed contact at =1
Cd()2.01g/, Pb()0.504g/, Fe
An organic phase containing 1.03 g/Zn () was obtained. This is mixed with the above raw material aqueous solution and a chloride aqueous solution containing the same type of metal at the same concentration at o/A=1
and o/A=2 for 30 minutes at 25°C. The cleaning effect was investigated by changing the concentration of hydrochloric acid in the cleaning solution. The results are shown in Figure 4 A and B.
Shown below. FIG. 4A shows the case where o/A is 1 at the time of contact, and FIG. 4B shows the case where o/A is 2. As is clear from Figures 4A and B, Cu,
When using a cleaning solution containing Cd or Pb,
Even if the concentration of hydrochloric acid during washing is small, it is possible to wash Zn from the organic phase. Furthermore, even if the cleaning solution contains Zn, Zn can be removed from the organic phase by appropriately adjusting the hydrochloric acid concentration during cleaning, and the concentrations of Cu, Cd, and Pb in the organic phase can be increased or decreased. can be kept to a minimum. This is industrially advantageous because the extraction process is carried out in multiple steps in countercurrent flow, and an effect of washing and removing Zn from the organic phase can be expected in the contact between the organic phase and the aqueous phase in the step of introducing the raw material aqueous solution. Example 7 A back extraction test of each metal ion from the organic phase from which Pb, Cd and Cu were extracted was conducted. () Reverse extraction of Pb: 5 g of Pb was extracted into a paraffinic hydrocarbon solution containing 0.3 mol of di-2-ethylhexylmonothiophosphoric acid, and the organic phase containing it was brought into contact with hydrochloric acid or sulfuric acid to perform back extraction of Pb. The ratio of organic phase to aqueous phase (o/A) was 1, the contact time was 30 minutes and the contact temperature was 25°C. FIG. 5 shows the relationship between the mineral acid concentration and the back extraction rate at the time of back extraction equilibrium. The back extraction rate is calculated using the following formula. Reverse extraction rate (%) = C ₁ - C ₂ / C ₁ × 100 C ₁ Initial concentration of Pb in organic phase C ₂ Concentration of Pb in organic phase () Reverse extraction of Cd: di-2-ethylhexyl monothiophosphoric acid 0.5 mol Cd was back-extracted by extracting 12.7 g of Cd/ into an aromatic hydrocarbon (Cierzol A) solution and bringing the containing organic phase into contact with hydrochloric acid. o/A was 1, contact time was 5 minutes, and temperature was 25°C.
Back extraction was performed by repeated extraction using 4.5N or 6N hydrochloric acid each time. The results are shown in Table 5.

[Table] () Reverse extraction of Cu (reference example): 7.04 g of Cu was extracted into a paraffinic hydrocarbon solution containing 0.5 mol of di-2-ethylhexyl monothiophosphoric acid and 0.5 mol of tributyl phosphate. Back extraction was carried out by contacting the phase with hydrochloric acid. The contact time was 30 minutes and the temperature was 25°C. Back extraction was performed by repeated contact with 3N or 6N hydrochloric acid each time. The results are shown in Table 6.

[Table] As is clear from Table 6, in the back extraction of Cu, hydrochloric acid can sufficiently achieve the purpose if used in combination with a modifier such as tributyl phosphate. Example 8 The metal extraction characteristics were investigated when R of the extractant R ₂ PSOH of the present invention was directly bonded to a phosphorus (P) atom without intervening oxygen. All conditions were the same as in Example 1 except that di-n-octylmonothiophosphinic acid in which R was an n-octyl group was used. The results are shown in FIGS. 6A and B. As is clear from the figure, this extractant also exhibited the same extraction characteristics as di-2-ethylhexylmonothiophosphoric acid used in Example 1. i.e. from Zn and Fe
It was observed that Cu, Cd and Pb were extracted on priority basis. Effects of the invention: According to the method of the present invention, at least one of lead and cadmium can be efficiently extracted and removed from a zinc-containing aqueous solution, and the concentration of the extractant is relatively low. At least one of lead and cadmium can be preferentially and efficiently extracted from a zinc-containing aqueous solution even if the volume ratio of lead and cadmium to the aqueous solution is small. Since it can be extracted from the aqueous solution containing it and the extraction operation can be performed using a small extraction device, it is extremely advantageous for implementation on an industrial scale.

[Brief explanation of drawings]

Figure 1 A and B show the hydrochloric acid concentration in the aqueous phase and the PH of the aqueous phase at extraction equilibrium when R of the extractant is a 2-ethylhexyl group bonded to P via O, respectively.
Figure 2 A and B show the relationship between the extraction percentage of each metal and the extraction percentage of each metal.
Figure 3 shows the relationship between the maximum extraction amount of Cd and Pb and the extraction pH, and Figure 4 shows the relationship between the hydrochloric acid concentration used for cleaning and the cleaning rate of each metal when the same extractant was used. A and B are the relationships between the hydrochloric acid concentration and the cleaning rate of each metal when cleaning with a cleaning solution containing each metal at o/A = 1 and o / A = 2 when using the same extractant as above, respectively. Figure 5 shows the relationship between the mineral acid concentration at back extraction equilibrium and the back extraction rate of Pb when the same extractant is used, and Figures 6 A and B show the relationship between the extractant R and the Pb back extraction rate. The relationship between the concentration of hydrochloric acid in the aqueous phase at extraction equilibrium and the PH of the aqueous phase and the extraction percentage of each metal when the n-octyl group is directly bonded to is shown.

Claims (1)

[Scope of Claims] 1. An aqueous solution containing a metal salt of at least one of lead and cadmium and a zinc salt is extracted using an extraction solvent containing an acidic monothiophosphoric acid compound represented by the following general formula as an extractant, or an extraction solvent containing this as an extractant. A method of separating zinc from at least one of lead and cadmium, the method comprising selectively extracting and separating at least one of lead and cadmium from the zinc-containing aqueous solution through contact with an impregnated solid. . [Formula] Here, A is a sulfur atom, B is an oxygen atom; R ₁ and R ₂ are each substituted or unsubstituted alkyl, cycloalkyl, aryl, or alkyl bonded to the P atom directly or via an oxygen atom. Allyl or arylalkyl group; and R ₁ and R ₂
are the same or different, and the sum of the carbon numbers of R ₁ and R ₂ is 9 or more. 2. The method according to claim 1, wherein the extractant is o.o'-dialkylmonothiophosphoric acid.