JPS5813633B2 - How to recover thallium from lead electrolyte - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering thallium from a lead electrolyte containing thallium by electrolytic operation, and particularly relates to an improvement in the above-mentioned thallium electrowinning process by using a diaphragm anode. There is something.

The lead electrolyte generally contains thallium from several g/l to about 20 g/l, and it is possible to avoid accumulation of thallium in the electrolyte that is recycled and to recover metallic thallium as a resource. As is well known, attempts have been made recently to recover metallic thallium from lead electrolytes.

All conventional methods have been chemical methods, requiring multiple steps and laborious operations, and have not always been industrially satisfactory.

Therefore, the present applicant previously proposed a method of directly recovering thallium by electrolytic operation instead of the conventional chemical method (Japanese Patent Application No. 169306/1982).

This method uses an insoluble anode to electrodeposit thallium on the cathode from the deleaded solution after removing lead from the lead electrolyte, and it is easy and efficient to produce high-purity thallium on the order of 99%. This is an excellent method in that it can be used to collect samples.

As a result of continuing research on this thallium electrowinning method, it was found that there was room for consideration of the aging of the electrolyte during the electrolytic process and the anode material.

That is, the lead electrolyte usually contains several kinds of additives in order to improve the electrodeposition state of electrodeposited lead during the lead electrolysis process, such as glue 0.3 to 8. 0 g/l and Sunextract (trade name of sodium lignonate) 0.1-4
09/l, and these additives remain in the electrolyte even after the lead electrolysis step.

In the thallium electrowinning process, these additives decompose in a strongly oxidizing atmosphere and gradually reduce the conductivity of the electrolyte.

This is the problem of electrolyte aging.

Furthermore, since the electrolyte is a silicofluoric acid solution, it is impossible to use lead as an anode material when performing electrowinning of thallium.
It was necessary to use carbon electrodes, platinum electrodes, etc. that are not affected by silicofluoric acid.

However, carbon electrodes have a short lifespan due to oxidation, and contamination of electrodeposited thallium poses a problem.

Platinum electrodes are extremely expensive and have practical problems.

As described above, there is room for improvement regarding the anode as well in relation to corrosion or oxidation caused by the electrolyte.

The inventor of the present invention recognized that the above two problems have a commonality in that they are essentially caused by contact between the anode and the electrolyte, and aimed to solve these problems all at once by adopting a diaphragm-type anode structure. I measured it and got good results.

By using a diaphragm-type anode, the electrolyte containing additives such as glue does not come into direct contact with the anode, which prevents aging of the electrolyte due to oxidation of the anode and eliminates the need to use carbon electrodes or platinum electrodes. Therefore, even if lead is used as an anode material, corrosion problems will not occur.

Thus, the present invention provides a method for recovering thallium by electrowinning from a deleaded solution obtained by removing lead from a lead electrolytic solution, which is characterized in that a diaphragm-type anode is used as an anode during electrowinning. provide a method.

Referring to the drawings, FIG. 1 shows a flow sheet of a thallium recovery process related to the present invention.

The lead electrolyte generally contains thallium in an amount of several g/l to about 20 g/l, and when thallium is electrolytically extracted from it, the lead contained in the electrolyte becomes an obstacle to the electrolytic operation. First, delead treatment is carried out.

In addition to lead, the lead electrolyte contains small amounts of bismuth, indium, tin, copper, etc., but only trace amounts of these are mixed into the electrodeposited thallium during the subsequent electrolytic operation.

Deleading treatment is easily carried out by adding sulfuric acid depending on the amount of lead contained to precipitate the lead as lead sulfate.

The lead sulfate precipitate is recycled into the lead smelting process.

The deleaded solution after removing the precipitate is sent to the electrowinning process.

In the electrowinning step, an electrolytic operation using a diaphragm anode according to the invention is carried out, and equipment suitable for carrying it out is shown in FIG.

A cathode 2 and an anode structure 3 are suspended in an electrolytic cell 1 at intervals.

The anode structure 3 includes an anode 5, a diaphragm 6, and an anolyte 7 filled inside the diaphragm.

The anode and cathode are connected to a suitable power source in the usual manner.

The electrolyte 9 is circulated by a pump. The electrolytic conditions themselves are the same as the previously proposed method and are as follows: Electrolyte solution silicofluoric acid (H2SiF3) concentration 100-200
g/l current density 350 A/m" or less Bath temperature Room temperature cathode material Stainless steel plate As described above, the feature of the present invention lies in the use of a diaphragm type anode structure in place of the conventional carbon electrode.

The diaphragm electrode itself is already known, and the installation of a partition wall to separate the cathode chamber and the anode chamber has been practiced for a long time in electrolysis in order to improve current efficiency and prevent dangers such as explosions. .

The present invention is significant in that it provides a solution to the above-mentioned special problems associated with electrowinning of thallium from a lead electrolyte by applying this diaphragm type anode.

In the anode structure, the diaphragm preferably has a structure with as many micropores as possible since the purpose is to separate the electrolyte, but from the viewpoint of reducing electrical resistance, it is required to be as thin as possible and porous. Ru.

In the present invention, it is important that the electrolyte is not attacked by silicofluoric acid in the electrolyte.

Any material that satisfies the above conditions may be used, such as wood, synthetic resin, synthetic fiber, ceramic, etc., but wood is particularly preferred because of its resistance to silicofluoric acid.

As the wood, pine, cypress, lauan, etc. can be used.

The anolyte that is stored surrounding the anode in the diaphragm may be of any material as long as it has good electrical conductivity and does not attack lead.
Usually a sulfuric acid solution is used.

Generally 50-400 g/l, preferably 20
The sulfuric acid concentration is around 0 g/l.

As an anode, the use of this diaphragm structure allows the use of lead, thereby ensuring that the inexpensively available anode material can be used for more than a year.

In the electrowinning process described above, the electrodeposited thallium produced on the cathode is on the order of 90%, and bismuth,
Contains trace amounts of indium, lead, etc.

If necessary, this electrodeposited thallium is sent to a purification process.

The purification of electrodeposited thallium is described, for example, in the aforementioned Japanese Patent Application No. 54-169.
As described in No. 306, electrolysis is carried out by casting electrodeposited thallium as an anode and using it in an electrolytic solution with a sulfuric acid concentration of 10 to 35 g/l and a current density of 20 to 100 A/m. High purity thallium of 99.99% can be obtained.

EXAMPLE An experiment was conducted to recover thallium from a lead-deleaded solution obtained by adding sulfuric acid to a lead electrolytic solution using the electrolytic apparatus shown in FIG. 2.

The composition of the test electrolyte was as follows (unit: g/l)
:Cathode Stainless steel plate anode
Lead diaphragm Pine board anolyte 200 g/l sulfuric acid solution reflux 200 cc/min Electrodeposited thallium obtained after 28 hours of electricity was analyzed and found to be 99%
Tl, 0.07%Pb, 0.006%Ri 5~
A result of 10 ppm Cu was obtained.

The conductivity of the electrolyte during thallium collection was measured.

The results are shown as curve A in Figure 3.

In FIG. 3, curve B shows the change in electrical conductivity when a carbon plate is used as an anode without using a diaphragm type anode.

In the case of a carbon plate anode, it can be seen that the conductivity decreases due to decomposition of glue and oxidation of the anode, as explained above.

By using a diaphragm type anode according to the present method, aging of the liquid conductivity is effectively suppressed.

In curve A, a slight increase in conductivity is observed, which is due to an increase in the concentration of free silicofluoric acid.

Incidentally, in FIG. 3, the aspect of decrease in thallium concentration is shown as a curve C for reference.

The same curve C can be obtained in both the case of the diaphragm type anode and the case of the carbon plate anode.

After the test, the appearance of the lead anode was inspected, but no trace of corrosion was observed.

The leakage loss of the anolyte into the electrolyte is 1. 5 cc
It was also found that the following is true and can be almost ignored.

As can be seen from the above description, the present invention is a thallium electrowinning method from a lead electrolyte proposed as an alternative to the conventional multi-step and troublesome chemical method. This is an extremely useful industrial improvement, as it prevents the aging of the anode and ensures the long-term use of inexpensively available lead material as an anode.

In this specification, "lead material" refers not only to pure lead, but also to
It also includes lead alloys that are conventionally used as anode materials and contain small amounts of antimony, silver, etc.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet for recovering thallium from a lead electrolyte according to the improvement of the present invention, Fig. 2 is a schematic diagram of an apparatus used for electrowinning thallium, and Fig. 3 is a diagram showing the energization time and time. It is a graph showing the relationship between the conductivity of an electrolytic solution and the thallium concentration. 1... Electrolytic cell, 2... Cathode, 3...
...Anode structure, 5...Anode, 6...
・Diaphragm, I...Anolyte, 9...Electrolyte.

Claims (1)

[Claims] 1. In a method of recovering thallium by electrowinning from a deleaded solution obtained by removing lead from a lead electrolyte, a diaphragm-type anode covered with lead material is used as the anode during electrowinning, and the lead material is used as the anolyte. A method for recovering thallium characterized by using a solution that does not corrode and has good electrical conductivity.