JP2008106348A - Method of separating and recovering zinc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To separate zinc from a zinc-containing cadmium solution and to recover it in the form of high-purity metal zinc. <P>SOLUTION: The method of separating and recovering zinc comprises: a first step where a solution containing at least zinc and cadmium is subjected to pH adjustment using an alkali agent; a second step where zinc is extracted from the resultant cadmium solution into an organic phase by solvent extraction using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester; a third step where the resultant zinc-containing organic phase is washed to remove impurities such as cadmium; a fourth step where the zinc-containing organic phase after the washing is subjected to back extraction of zinc using a zinc electrolytic solution; and a fifth step where metal zinc is obtained by electrowinning from the solution after the back extraction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for separating and recovering zinc from a solution produced in a process of recovering valuable materials from a smelting intermediate treatment product. The present invention relates to a method for separating zinc accumulated in a cadmium solution in a system in a manufacturing process and recovering the separated zinc as high-purity metallic zinc.

Generally, cadmium accompanies zinc concentrate, and as can be seen from the fact that cadmium is produced in conjunction with zinc smelting, zinc and cadmium are likely to coexist. For this reason, cadmium becomes a main impurity in the process of manufacturing zinc, and zinc becomes a main impurity in the process of manufacturing cadmium.
One method for producing cadmium is disclosed in Japanese Patent Application No. 2006-097724 (Patent Document 1). In this method, the cadmium is used in a system that repeatedly uses the electrolytic solution after electrolytic collection, so that impurity components that could not be removed in the purification process accumulate in the cadmium solution in the system. The main impurity components that accumulate are zinc, sodium, chlorine, etc. contained in the sulfide of the raw material.
If zinc accumulates during the manufacturing process of cadmium, the electrodeposition state of cadmium deteriorates, which hinders operation. Zinc is one of the impurities that must be removed during the cadmium production process.

As a method for separating zinc from a solution of zinc and cadmium, there is a separation method using a precipitation pH difference as disclosed in JP-A-2006-89807 (Patent Document 2). This method is a method in which zinc is preferentially precipitated and separated from the cadmium solution by utilizing the fact that zinc precipitates at a lower pH than cadmium. Although this method is a simple method, cadmium is likely to precipitate simultaneously with zinc, and it cannot be said that the separation efficiency of zinc and cadmium is high.

On the other hand, there is a method in which cadmium is precipitated and separated from a solution of zinc and cadmium. As disclosed in JP-A-11-12667 (Patent Document 3), a cadmium solution is generally purified by a cementation method using zinc powder. As a result, cadmium in the solution becomes a spongy precipitate and is separated from the solution.
When this method is applied to a solution having a high cadmium concentration, which is the subject of the present invention, the consumption of zinc powder increases and the amount of spongy cadmium produced increases, which requires a great deal of labor for the treatment.
Furthermore, it is easy to procure zinc powder if it is associated with zinc smelting, but in other cases it is necessary to purchase it from outside.

In general solvent extraction of zinc, a solution in which a large amount of cadmium coexists is not assumed, and there is a point that cannot cope with the situation where zinc is separated from a high concentration cadmium solution as in the present invention.

Japanese Patent Application No. 2006-097724 “Cadmium production method” JP 2006-89807 “Method of treating cadmium leachate” Japanese Patent Application Laid-Open No. 11-12667 “Method for treating and recovering liquid containing cadmium and zinc”

The present invention solves the above-mentioned drawbacks and provides a method for separating zinc from a high-concentration cadmium solution containing zinc with high separation efficiency and recovering the separated zinc as metallic zinc having a purity of 99.99% by weight or more.

The present invention solves the above problems,
(1) The pH of a zinc solution containing cadmium is adjusted with an alkaline agent as the first step,
Zinc is extracted from the cadmium solution obtained as the second step by solvent extraction with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester into the organic phase,
After washing the organic phase containing zinc obtained as the third step and removing cadmium,
As a fourth step, the organic phase containing zinc after washing is back-extracted with a zinc electrolyte,
A method for separating and recovering zinc to obtain metallic zinc in the fifth step.
(2) A method for separating and recovering zinc, wherein the pH when adjusting the pH of the cadmium solution with an alkaline agent after the third step of (1) is 2 or less.
(3) In any one of the above (1) to (2), zinc as a cadmium solution containing zinc is a cadmium electrolytic tail solution or a solution after copper removal from a cadmium solution. Separation and recovery method.
(4) The method for separating and recovering zinc according to any one of (1) to (3) above, wherein the pH of the solution when extracting zinc with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is 2 or less.
(5) The method for separating and recovering zinc according to any one of the above (1) to (4), wherein the pH of the cleaning liquid used for cleaning the zinc extraction solvent is 1.5-2.
(6) A method for separating and recovering zinc according to any one of (1) to (5) above, wherein the zinc extraction solvent is washed in two stages to wash away impurities such as cadmium in the organic phase.
(7) The method for separating and recovering zinc according to any one of (1) to (6) above, wherein the back extract used when back extracting the obtained zinc extraction solvent is a zinc electrolytic tail solution .
(8) In any one of the above (1) to (7), when electrolytically collecting zinc from the zinc solution obtained by back extraction, an insoluble anode coated with iridium oxide is used to elute the metal from the anode. A method for separating and recovering zinc, characterized by preventing contamination of cathode electrodeposits.
It is.

By carrying out the above zinc separation and recovery method,
(1) Zinc can be efficiently separated from a high concentration cadmium solution by solvent extraction.
(2) Impurities in the organic phase can be easily removed by washing the separated organic phase containing zinc.
(3) A high-purity zinc solution can be obtained by back extraction using an electrolytic tail solution of zinc.
(4) Zinc can be recovered as high-purity metallic zinc by electrolytic extraction from a zinc solution obtained by back extraction.
(5) In the above (4), by using an insoluble anode from which the metal does not elute instead of the Pb anode at the time of electrowinning, it is possible to obtain metallic zinc of higher purity.
The effect is obtained.

The present invention will be described in detail below.
The solution to be treated of the present invention is a cadmium solution in the process of producing metal cadmium by a wet treatment from a sulfide generated in a treatment process such as dust generated in non-ferrous dry smelting. In this cadmium solution, zinc, sodium, chlorine, etc. contained in the raw material sulfide accumulate as operation continues. If these impurities accumulate above a certain concentration, the metal cadmium production process will be adversely affected, so a mechanism for discharging it out of the system is necessary.
FIG. 1 shows an embodiment of a process for producing zinc metal by separating zinc from the cadmium solution as described above and discharging sodium and chlorine out of the system.

First step (pH adjustment step)
When the acid concentration of the cadmium solution containing zinc is high (for example, cadmium electrolytic tail solution in the metal cadmium production process), an alkali agent (for example, sodium hydroxide solution) is first added to the cadmium solution before solvent extraction. The pH of the solution is adjusted to about 2. This is because the pH of the solution at the time of solvent extraction must be 1.5-2 in the next step.
In this pH adjusting step, when the pH is set to 2 or more, precipitation of zinc or cadmium hydroxide occurs. Since this precipitate is hardly dissolved, it is not preferable to set the pH to 2 or more.
Any alkaline agent can be used as long as it is easily soluble in water. Sodium hydroxide solution is readily available and suitable.
When the acid concentration of the cadmium solution is low (for example, after the copper removal in the metal cadmium production process of FIG. 1), this pH adjustment step is not necessary. When this solution is used, it can be directly introduced into the zinc solvent extraction step without pretreatment.

Second step (zinc solvent extraction step)
2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is used as an extractant for zinc. A solvent prepared by diluting this extractant with kerosene and a cadmium solution containing zinc adjusted in pH in the first step are mixed to perform solvent extraction of zinc. Alternatively, it is mixed with a cadmium solution having a low acid concentration (for example, a solution after copper removal in the metal cadmium production process of FIG. 1), and zinc is subjected to solvent extraction.
Di (2-ethylhexyl) phosphoric acid or the like can be used as an extractant for zinc, but 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester has higher separability between cadmium and zinc.
Although diluents other than kerosene can be used as a diluent for the extractant, kerosene is inexpensive and easily available.
The pH of the solution during zinc extraction is preferably about 1.5-2. If the pH is higher than this, the amount of cadmium extracted into the organic phase simultaneously with zinc increases. Further, if the pH is lower than this, the extraction of cadmium into the organic phase can be suppressed to a low level, but the extraction amount of zinc also decreases.
During extraction of zinc, protons are released from the extractant, and the pH of the solution decreases. Therefore, zinc extraction is performed while adding an alkaline agent such as sodium hydroxide solution and maintaining the pH.

Third step (cleaning step)
The organic phase after extraction of zinc contains a trace amount of impurities, and these must be washed away from the organic phase. The aqueous solution adjusted to pH with sulfuric acid is stirred together with the organic phase to remove impurities in the organic phase to the aqueous phase. The pH of the cleaning solution used at this time is preferably 1.5-2. If the pH is lower than this, the amount of zinc in the organic phase lost into the aqueous phase along with impurities increases. Moreover, when pH is high, the removal efficiency of impurities falls. In practice, it is convenient to use a solution obtained by diluting a zinc electrolytic tail solution with water as a cleaning solution.
This washing is preferably repeated twice. This is because the electrodeposited zinc equivalent to the cadmium quality of the zinc bullion generally sold cannot be obtained by one washing.
When cleaning is performed in two stages, the amount of cleaning liquid can be reduced by using the cleaning liquid countercurrently.

Fourth step (back extraction step)
In this step, the organic phase containing zinc after washing is back-extracted with a sulfuric acid solution, and zinc is back-extracted from the organic phase into the aqueous phase. At this time, it is convenient to use a zinc electrolytic tail solution as a back extract. The organic phase after back-extracting zinc is returned to the second step (zinc solvent extraction step) and used repeatedly.

5th process (zinc electrowinning process)
In this step, metallic zinc is obtained from the zinc solution obtained by back extraction by electrowinning. At this time, by using an insoluble anode, it is possible to prevent contamination of the electrodeposited zinc by the effluent from the anode. In the fourth step of the present invention, the electrolytic tail solution produced by zinc electrowinning is used as a zinc back-extraction solution from the organic phase containing zinc.

  The washed solution used in the third step of the present invention contains cadmium mixed in the organic phase. This cadmium is removed by a substitution reaction by dipping a self-produced electrodeposited zinc plate into the solution and stirring. Use the cleaning solution after removing cadmium repeatedly.

In the second step of the present invention, the solution after zinc extraction is the zinc solution remaining without being extracted with cadmium. This solution contains sodium and chlorine accumulated in the metal cadmium production process. An alkaline agent is added to this solution, and cadmium and zinc remaining without extraction are precipitated and recovered as hydroxides. The recovered hydroxide is supplied as a cadmium raw material to the metal cadmium production process.
Since the solution after recovering cadmium contains sodium ions and chloride ions, it is possible to discharge sodium and chlorine while recovering zinc accumulated in the metal cadmium production process if these are discharged out of the system. Become.
If the concentration of sodium and chlorine in the solution after zinc extraction is not high, it is possible to return to the metal cadmium production process without adding an alkali agent.

(Example 1)
Table 1 shows the compositions of the cadmium electrolytic tail solution and the post-decopperization solution in the metal cadmium production process, which is one of the treatment target solutions. Since this solution has already been purified by the metal cadmium production process shown in FIG. 1, most of the impurities have been removed. In Table 1, the post-copper removal solution is a solution after the copper removal step in the metal cadmium production process shown in FIG. 1, and this solution is supplied to the Cd electrowinning step during electrolysis. Therefore, the solution has a high Cd concentration.

After adjusting the cadmium electrolytic tail solution having the composition shown in Table 1 to pH around 2 with sodium hydroxide, it was mixed with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester solvent diluted to 33 vol% with kerosene. Under the conditions, zinc was extracted at each equilibrium pH.
A sodium hydroxide solution was used to adjust the equilibrium pH. FIG. 2 shows the extraction rates of zinc and cadmium extracted into the organic phase at each equilibrium pH. From this result, it can be seen that it is appropriate to perform the equilibrium pH at the time of extraction at 2 or less in order to obtain a high zinc extraction rate while suppressing the extraction of cadmium.

(Example 2)
An aqueous solution adjusted to pH 1-5 with sulfuric acid was mixed with the organic phase after zinc extraction, and the cleaning effect of the organic phase with each pH cleaning solution was investigated. The organic phase tested was equilibrated pH under the conditions of Example 1.
The organic phase extracted with zinc at 2.5 was used. Other cleaning conditions are shown in Table 2.
The graph of FIG. 3 represents the concentrations of zinc and cadmium in the cleaning solution when the unwashed organic phase is washed once with the cleaning solution of each pH. From this result, pH
In the cleaning solution higher than 2, the effect of removing cadmium in the organic phase was not obtained so much. The cleaning solution with a pH lower than 1.5 has a high cadmium removal effect, but at the same time, the amount of the target component zinc back-extracted into the cleaning solution aqueous phase increased.
From the above results, it is understood that the pH of the cleaning liquid is 1.5-2 in order to obtain the effect of removing cadmium while suppressing the amount of zinc extracted into the aqueous phase of the cleaning liquid.

(Example 3)
The results of the effect of removing impurities in the organic phase depending on the number of washings are shown in FIG. Here, the number of cleaning times of 0 means uncleaned.
An aqueous solution adjusted to pH 1.5 with sulfuric acid was mixed with the organic phase after zinc extraction, and the number of washings required to make the Cd concentration in the organic phase lower than 0.1 mg / L was investigated. The organic phase used was an extractant concentration of 25 vol% and an equilibrium pH.
The organic phase from which zinc was extracted was used under the conditions of 2.0 and the liquid volume ratio (organic phase / aqueous phase) = 1/2. Other cleaning conditions are shown in Table 2. As a result, when washed twice or more, the Cd concentration in the organic phase became lower than 0.1 mg / L.
The Cd grade contained in zinc ingots with a purity of 99.99% by weight generally sold is about 1 ppm. To obtain zinc equivalent to these, the Cd concentration in the organic phase after zinc extraction is 0.1 mg / L. Lowering is required.
From the above results, it can be seen that the number of times of cleaning needs to be two or more.

Example 4
Zinc was recovered as plate-like electrodeposited zinc from the zinc solution obtained in the zinc solvent extraction step of FIG. 1 by electrowinning. The impurity composition in this electrodeposited zinc is shown in Table 3. The type of Zn extraction stock solution in Table 3 means which step the zinc was recovered from among the metal cadmium production steps in FIG. The composition of each solution is as shown in Table 1.
Electrodeposition with Cd content of about 3-5ppm from Cd electrolytic tail solution or post-copper removal solution with higher Cd concentration than Cd electrolytic tail solution (solution after the copper removal step in the metal Cd production process of Fig. 1) Zinc could be obtained. As described above, in this patent, electrodeposited zinc having a low Cd content can be obtained from a solution having a very high cadmium concentration.
Table 3 below was performed under the following conditions.
Current density: 500A / m ² Electrolysis time: 24 hours
Anode used: Insoluble anode coated with iridium oxide

(Comparative Example 1)
When zinc electrowinning is performed using a Pb anode under the same conditions as in Example 4, the electrodeposited zinc is contaminated by lead eluted from the Pb anode, and the lead content in the electrodeposited zinc is usually 10-20 ppm. . If an insoluble anode coated with iridium oxide is used, the electrodeposited zinc is not contaminated by lead, and as shown in Table 3, Pb
<1 ppm of electrodeposited zinc can be obtained.

Flow of zinc separation and recovery process and cadmium production process Extraction curves of Zn and Cd with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester. The effect of removing impurities in the organic phase after zinc extraction with each pH cleaning solution and the amount of zinc lost in the cleaning solution at that time. The effect of removing impurities in the organic phase after zinc extraction by the number of washings.

Claims (8)

The pH of the cadmium solution containing at least zinc is adjusted with an alkaline agent as the first step,
Zinc is extracted from the cadmium solution obtained as the second step by solvent extraction with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester into the organic phase,
After washing the organic phase containing zinc obtained in the third step and removing impurities such as cadmium,
As a fourth step, the organic phase containing zinc after washing is back-extracted with zinc electrolyte,
A method for separating and recovering zinc, wherein metal zinc is obtained by electrolytic extraction from the solution after back extraction in the fifth step. 2. The method for separating and recovering zinc according to claim 1, wherein the pH when adjusting the pH of the cadmium solution containing zinc with an alkaline agent is 2 or less. 3. The method for separating and recovering zinc according to claim 1, wherein the zinc-containing cadmium solution is a cadmium electrolytic tail solution or a solution after copper removal from the cadmium solution. The method for separating and recovering zinc according to any one of claims 1 to 3, wherein the equilibrium pH of the solution when zinc is extracted with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is 2 or less. The method for separating and recovering zinc according to any one of claims 1 to 4, wherein the pH of the cleaning liquid used for cleaning the zinc extraction solvent is 1.5-2. 6. The method for separating and recovering zinc according to any one of claims 1 to 5, wherein the zinc extraction solvent is washed in two countercurrent stages to remove impurities in the organic phase. The method for separating and recovering zinc according to any one of claims 1 to 6, wherein the back-extracted solution used for back-extracting the obtained zinc-extracting solvent is a zinc electrolytic tail solution. 8. The electrocatalyst of a cathode electrodeposit by elution of metal from an anode using an insoluble anode coated with iridium oxide when electrolytically collecting zinc from a zinc solution obtained by back extraction according to any one of claims 1 to 7. A method for separating and collecting zinc, characterized by preventing contamination.