JPH03150321A - How to recover thallium - Google Patents

Abstract

PURPOSE:To efficiently recover high-purity Tl by executing respective stages for adding an alkali carbonate to the caustic alkaline leaching liquid of Tl raw materials to settle and remove lead and executing the pH adjustment and two-stage reduction of the deleaded liquid under specified conditions. CONSTITUTION:The Tl raw material essentially contg. Pb, Zn, Cd, As, and Fe as impurities and the caustic alkaline soln. (NaOH, etc.) are brought into reaction at 40 to 70 deg.C liquid temp. and 9.5 to 10pH to obtain the leaching liquid. The alkali carbonate (Na2CO3, etc.,) is added to this leaching liquid to adjust the pH to 9.0 to 9.5 and to settle and separate the Pb. An acid is added to this deleaded liquid to adjust the pH to 1.5 to 2.5. A reducing agent (Zn, etc.) of 0.8 to 1.2 quiv. of the amt. of the Tl ions existing in this liquid is added to the liquid to form sponge Tl. The reducing agent of 1.8 to 2.2 equiv. of the amt. of the Tl ions contained in the final liquid of the prereducing stage is added to the liquid and the Tl is taken out as precipitate. This precipitate is further subjected repeatedly to the above-mentioned leaching stage or pH adjusting stage, by which the reducing agent, etc., contained therein are removed and the Tl is recovered.

Description

[Detailed description of the invention] [Industrial application field] The present invention contains Pb, Zn, Cd, as main impurities.
As.

The present invention relates to a method for recovering thallium from a thallium-containing compound containing Fe.

[Prior art] In the lead and zinc smelting process, each process contains 10 to 60% by weight (hereinafter referred to as %) of TI, and 1 to 20% of Pb%.
Residues and waste containing CL ZnlFe and 0.01 to several percent As are generated. A method for recovering TI using these residues and wastes as raw materials is disclosed in Japanese Patent Publication No. 61-54847, but this method involves dissolving the above TI raw materials in sulfuric acid in the coexistence of a reducing agent, and adding carbonic acid to the resulting leachate. Add an alkali such as sodium or lime to adjust the pH to 9 or higher, separate the formed precipitate, and remove Yes Pbs As from the liquid.
Next, the pH of the filtrate is adjusted to 2.5 or less using sulfuric acid, and Zn powder is added to precipitate the TI ions in the solution as sponge TI.

[Problem to be solved by the invention] However, in the above method, 1 to 2 g of TI is contained in the final solution after recovery.
1 of 1 is contained, and it cannot be discharged outside the factory as it is, and if it is combined with other wastewater in the wastewater treatment process, a large amount of sediment will be generated, and TI will be unrecoverable and discarded. This has no choice but to result in a low recovery rate.

Furthermore, the above method cannot be said to be sufficient for treating TI raw materials with a high As content. That is, the above method is
When applied to TI raw materials with high content, A
This is because there is a problem in that s is not completely precipitated and remains in the filtrate, generating harmful Ashs during reduction using Zn powder. As a way to prevent this, if you try to completely precipitate and remove A3 during neutralization by adding re etc. to the leachate, depending on the reducing agent used, the impurity concentration in the obtained TI will increase, and the quality of the product TI will deteriorate. There is a problem in that not only is the TI loss reduced, but the TI loss is increased, leading to an increase in cost.

An object of the present invention is to provide a method for recovering TI that has high TI recovery efficiency and does not cause the above-mentioned problems even when a raw material with a high As content is used.

[Means for Solving the Problems] The method of the present invention for solving the above problems mainly involves P.
b. TI raw material containing Cds Zns Ass Fe as an impurity and an alkaline solution at a liquid temperature of 40 to 70''
C, a leaching step in which a leachate is obtained by reacting at pH 9.5-10, and an alkali carbonate is added to the leachate to pH 9.0-9.
．． 5, a neutralization step in which lead is precipitated and separated to obtain a deleaded solution, a pH adjustment step in which acid is added to the deleaded solution to adjust pn to 1.5 to 2.5, and from the pH adjustment step. In the resulting neutralized final solution, the amount of TI ions present in the solution is 0.8 to 1.
．． Adding 2 equivalents of reducing agent to obtain sponge TI Nol
In the reduction process and the Not reduction final solution obtained from the Nol reduction process, t, with respect to the amount of T1 ions contained in the final solution,
It consists of a No2 reduction step in which TI in the final solution is removed by adding a to 2.2 equivalents of reducing agent, and the precipitate obtained in the No2 reduction step is repeated to the leaching step or pH adjustment step. That is.

The alkaline solution used in the leaching process of the present invention is a solution of caustic alkali such as caustic soda.

[Function] In the method of the present invention, alkali carbonate is not used because the solubility of the produced thallium carbonate is relatively lower than that of thallium hydroxide.

If the pH during leaching is too low, As and Cd will be leached out, and if the pH is too high, Pb will be leached out. Therefore, p during leaching
H is required to be 9.5 to 1 (LO).Although leaching can be performed at room temperature, it is preferable to increase the leaching temperature in order to speed up the leaching rate and perform leaching economically. The leaching temperature is desirably 40"C or higher. Furthermore, since an alkaline solution is handled, considering the danger of handling, the leaching temperature is preferably 70"C or lower.

Since Pb is present in the leachate thus obtained, it is necessary to remove it before entering the reduction step. It is possible to use sulfuric acid as a method for removing Pb, but in this case, in order to completely precipitate Pb, a large amount of sulfuric acid must be used (and in this case, it may lead to precipitation of thallium sulfate). Therefore, in order to completely precipitate and remove Pb in the leachate, the pH of the liquid must be 9.0 to 9.0 as in the present invention.
It is necessary to add alkali carbonate to make it 9.5. Examples of the alkali carbonate that can be used in the present invention include sodium carbonate.

The leachate thus obtained contains Pb and Cd.

Impurities such as Zn and AslFe are hardly included in C↓,
There is no need to use high-cost recovery methods such as electrolysis or evaporation, and TI ions can be easily recovered from sponge T through a reduction reaction.
It can be recovered as I.

The reducing agent used in the reduction step may be anything less noble than TI, but metals less noble than TI, such as Zn powder, are preferred from the viewpoint of cost and the like. In order to precipitate TI ions in the liquid as sponge TI through a reduction reaction, it is necessary to make the liquid acidic and then add a metal less noble than TI. If the pH of the solution is too low, the metal added as a reducing agent will dissolve too rapidly, resulting in poor reduction efficiency; if the pH is too high, it will not dissolve, prolonging the reduction time, and entraining air, etc., resulting in the sponge T.
Problems such as re-dissolution of I occur. Therefore, the liquid pt
It is necessary that t be 1-5 to 2.5. This pH
Any acid that can be used for g adjustment may be used as long as it can lower the pH to 1.5 or less, and for example, mineral acids such as hydrochloric acid and sulfuric acid may be used.

The amount of the reducing agent used in the Nol reduction step is 0.8 to 1.2 equivalents relative to the amount of TI ions in the final neutralized solution. This is because if the amount is less than 0.8 equivalents, the recovery of TI ions will not be sufficient and the amount of reducing agent to be used in the next process will increase, which will impair economic efficiency. This is because the amount of unreacted reducing agent present as an impurity in TI increases.

Since the sponge TI obtained in this manner has a high purity, it can be subjected to a conventional dry purification treatment after solid-liquid separation to obtain high-purity TI.

On the other hand, in order to recover and remove TI ions remaining in the No1 reduction final solution obtained by solid-liquid separation, a reducing agent is added in the No2 reduction step. The reducing agent at this time is most preferably a metal less noble than TI, such as Zn, for the same reason as mentioned above. The purpose of this No2 reduction step is to almost completely remove the TI ions in the solution, and for that purpose, the amount of reducing agent added must be at least 1.8 equivalents relative to the amount of TI ions in the final solution. It is necessary to do so. However, if it is added in excess, the effect will not increase, and on the contrary, it will impair economic efficiency, so 2.2
It may be less than the equivalent amount. Since the precipitate thus obtained contains a large amount of unreacted reducing agent and the like, it will not become a product even if it is dry purified as it is. Therefore, the pH
Repeat step E to collect TI in the precipitate.

In addition, when using raw materials containing only a small amount of ^S, conventionally leaching with phosphoric acid and deleading are performed before TI.
It is sufficient to reduce the ions, but it can be easily deduced from the present invention that the reduction step is performed in two or more stages.

[Example-1] T1. Pb, Cd, Zn, Cu, As, F
e, respectively, 45.7.15, l, L64.2,
Contains at a rate of 20.0.54.2.32.0.31%,
100 g of TI raw material with a moisture content of 37.3% (dry basis)
was mixed with 51 water and stirred at 50"C for 2 hours while maintaining the pH at IO using a NaOH solution with a concentration of 500 g/l. After solid-liquid separation, TI, Pb, and Cd were mixed.
, Zn%Cu%As%Fe, respectively, 6.2.0.
08, <O,QOl, <O,QOl, <O,
QQ1. <0.002, (4.41 leachate containing pH 10 at a ratio of 0,002 g/1 was obtained.

Note that the amount of NaOH solution used was 21 if.

Next, while stirring the leachate, 250 g/l of soda carbonate slurry was added until the pH reached 9.4, and the generated precipitate was removed. The carbonated soda slurry added was 78 ml.

The Pb concentration in the obtained delead solution was <O-ool g/l.

Next, this deleading solution 4. While stirring Ol, Zn
Add 6.4 g (1 equivalent), stir for 1 hour,
I got 16 g of sponge rt. The impurity quality in this sponge TI was as follows.

Cu6, PbTO, Fe<5,
Cd Is, Ni <5, Mnku5, Z
n 450 each ppI In addition, the amount of Not reduced final solution obtained was 3.81, and the TI concentration in the solution was 1.0
g/1.

Next, while stirring this Nol reduced final solution 3.81,
1.3 g of Zn powder was added in an amount of 2 equivalents to the amount of TI. After stirring for 4 hours, solid-liquid separation was performed to obtain 3.7 g of precipitate and 3.51 g of NO,2 reduced final solution. This precipitate mainly contains TI and Cu.

Pb, Fe, Cd%Kn, respectively <5.36,
<5.9.35000 ppm, and the TI concentration in the treated waste liquid was 0.02 g/l.

Next, the precipitate was suspended in water and stirred for 2 hours while adjusting the pH to 1.5 using sulfuric acid to dissolve it, and 90% of the TI in the precipitate was dissolved.

From the above, it can be said that the usefulness of the method of the present invention is clear.

[Example-2] 2.3 g of sodium hydroxide was added to 15 g of sponge thallium obtained in Example-1, and the mixture was heated and dissolved at 400"C. After cooling, the generated garami and metallic thallium were separated. The amount of metal thallium obtained was 14.1 g, and the quality of the impurities Gus Pb% Fes CdsZn was (5, lO, (5, (5, <5pp), respectively.

This shows that metallic thallium of 9L 99% or more can be easily obtained using sponge thallium obtained by the method of the present invention.

[Effects of the Invention] According to the method of the present invention, TI can be selectively leached, high As raw materials can be treated, and since cementation is performed in two stages, the T1 concentration in the waste liquid can be reduced. can be lowered. As a result, by using the method of the present invention, it is possible not only to prevent the occurrence of pollution problems, but also to
Economic efficiency can also be improved by increasing the recovery rate.

Moreover, metallic thallium of 99.99% or more can be easily obtained using the sponge thallium obtained by the method of the present invention.

Claims (1)

[Claims] In a method for recovering thallium from a thallium raw material containing mainly lead, cadmium, zinc, arsenic, and iron as impurities, (1) the raw material and an alkaline solution are mixed at a liquid temperature of 40 to 70°C;
Leaching step (2) to obtain a leachate by reacting at pH 9.5 to 10. Add alkali carbonate to the leachate and adjust to pH 9.0 to 9.
5. Neutralization step in which lead is precipitated and separated to obtain a deleaded solution (3) A pH adjustment step in which acid is added to the deleaded solution to adjust the pH to 1.5 to 2.5 (4) From the pH adjustment step No. 1 reduction step (5) Obtained from No. 1 reduction step to obtain sponge thallium by adding a reducing agent of 0.8 to 1.2 equivalents to the amount of thallium ions present in the solution to the resulting neutralized final solution. For the No1 reduced final solution,
1.8 to 1.8 to the amount of thallium ions contained in the final solution
It is characterized by comprising a No2 reduction step of adding 2.2 equivalents of reducing agent to remove thallium in the final solution, and repeating the precipitate obtained in the No2 reduction step to the leaching step or pH adjustment step. How to recover thallium.