JP2013147686A - Method of producing bismuth anode for use in electrolytic refining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a bismuth anode for use in electrolytic refining, capable of decreasing the concentration of impurities having a risk of influencing eventual bismuth quality upon carrying out electrolytic refining, and a bismuth anode.SOLUTION: A method of producing an anode, includes adding elemental tellurium into crude bismuth prior to casting the crude bismuth to form an anode for use in electrolytic refining, melting the crude bismuth, and subsequently carrying out casting to obtain a bismuth anode. The crude bismuth contains silver and lead as impurities, and the amount of the elemental tellurium to be added is 0.5 to 4 times as much as the amount of the silver present in the crude bismuth. The crude bismuth is heated at least to 590°C and melted subsequent to adding tellurium thereinto, subsequently solid matters coagulating on the surface of the molten bismuth is removed, and subsequently the anode is cast. The anode for use in electrolytic refining of bismuth contains, by weight ratio, bismuth at least 90%, and tellurium and silver in a ratio of Te/Ag=0.5-4.

Description

  The present invention relates to a method for producing a crude bismuth anode for use in electrolytic purification of bismuth.

  In the smelting of bismuth, a method of smelting from sulfide ore by a dry method is known. However, the most bismuth-producing method is the bismuth-rich method, such as the ion-exchange method that dissolves in solution as a by-product of copper and lead, and the melt is flocculated and concentrated and recovered as an impurity mass. This is a method of obtaining a high-purity bismuth by electrolytic purification after obtaining a liquid and reducing it to a crude bismuth metal. (Non-Patent Document 1, Patent Documents 1 and 2)

  In the electrolytic purification of bismuth, the impurity concentration in the electrolytic solution, particularly lead (Pb), copper (Cu), and silver (Ag), has a great influence on the purity of the final purified bismuth.

  For example, in Patent Document 1, when melting bismuth bean paste in an electric furnace, FeS is charged in addition to calami and coke to obtain bismuth metal from which Ag is removed, and this is further added to the anode furnace along with sulfur. The technology of casting into the shape of an anode plate is described except for the residue (PbS, CuS) obtained by reacting sulfur with Pb and Cu. Patent Document 2 describes a general method for reducing and recovering bismuth.

  In recent years, recycling raw materials such as electronic materials have attracted attention as raw materials for non-ferrous metals and rare metals, but even when this recycled raw material is used, bismuth is recovered as a by-product of lead smelting. In this case as well, the presence of impurities becomes a problem, but as a feature of the impurities when using recycled raw materials, there is a large amount of silver as well as lead and copper.

JP2000-045087 JP2010-196140

Akira Tanaka "Basics and Mechanism of the Latest Rare Metals That Can Be Understood" Hidekazu System

  By the way, in the past, bismuth anodes are often produced from bismuth recovered as impurities of lead ore or lead smelting, and even if components other than bismuth are included, the quality is low, and bismuth anodes were used. It was possible to suppress the impurity grade of refined bismuth by adjusting the conditions for electrolytic purification of bismuth. However, due to the recent situation where it is required to use recycled raw materials that contain more components than bismuth than ores, even the bismuth anodes made from such raw materials suppress the impurity grade of electrolytically refined bismuth. It is necessary.

Many impurities precipitate as slime during electrolytic refining, but particularly when silver is eluted from the anode, it becomes a stable complex ion, for example, a silver chloro complex ion AgCl ₂ ^{− in} the case of a chlorination bath. Will remain. In addition, lead precipitates during electrolytic purification, but lead chloride, for example, is somewhat soluble in water and therefore dissolves in the electrolyte to some extent.

  On the other hand, it is possible to remove a considerable amount of impurities such as silver and lead if repeated removal is performed even using a removal technique such as silver and lead using sulfur as described in Patent Document 1. However, care must be taken when handling sulfur, and there remains a problem in terms of cost, so there is room for study from the viewpoint of commercialization of refined bismuth.

  Therefore, returning to the viewpoint that impurities that may affect the quality of the purified bismuth are eluted during electrolytic purification or dissolved in the electrolytic solution after precipitation, such impurities are electrolyzed. If a bismuth anode for purification that does not remain in the electrolytic solution after purification is realized, high-purity bismuth that has been electrolytically purified can be obtained.

  As a result of intensive studies to solve the above problems, the inventors of the present invention melted at about 600 ° C. when casting a Bi anode, added simple Te to silver and lead to silver telluride and lead telluride. Since it can be insolubilized in water by changing to, elution into the electrolytic solution is suppressed when electrolytic purification is performed using the obtained Bi anode, and high-purity bismuth that is electrolytically purified can be obtained. I found out.

That is, the present invention includes the following inventions.
(1) A method for producing an anode in which a crude bismuth anode is obtained by adding simple tellurium and casting after melting before casting the crude bismuth on an electrolytic purification anode.
(2) The method according to (1), wherein the crude bismuth contains silver and lead as impurities.
(3) The method according to (1) or (2), wherein the amount of the simple tellurium added is 0.5 to 4 times the amount of silver in the crude bismuth.
(4) The method according to any one of (1) to (3), wherein tellurium is added to the crude bismuth and then heated to 590 ° C or higher.
(5) The method according to any one of (1) to (4), wherein after the melting, the solid is aggregated on the surface of the bismuth melt, and then the anode is cast.
(6) An anode for bismuth electrolytic purification containing 90% or more of bismuth and tellurium and silver in a ratio of Te / Ag = 0.5 to 4 by weight ratio.

  According to the present invention, the final content of electrolytic bismuth can be obtained by insolubilizing silver and lead, which are conventionally contained in a crude bismuth anode and may affect the final bismuth quality upon electrolytic purification, as telluride during casting of the anode. Impurity concentration affecting quality can be lowered.

From one aspect, the present invention provides a method for manufacturing an anode for electrolytic purification of bismuth.
This method is characterized in that elemental tellurium is added when casting an anode in which crude bismuth is used for electrolytic purification. When simple tellurium is melted together with crude bismuth, and preferably further mixed, for example, silver (Ag), which is an impurity, becomes Ag ₂ Te and is insolubilized.

  The method of the present invention can be applied to the production of a bismuth anode used in an electrolytic purification process in bismuth smelting, but in particular, recovery of crude bismuth produced from a raw material rich in silver as an impurity, for example, lead in a recycling plant -Even if bismuth produced as a by-product of smelting is used, a bismuth anode suitable for the electrolytic purification process of bismuth can be obtained.

In the smelting of bismuth, intermediate emissions from the copper smelting process and intermediate products of lead smelting are often used as raw materials. Compared to smelting from bismuth concentrate (Bi ₂ S ₃ ), silver, Lead and copper are mixed as impurities, and it is difficult to completely separate them through various purification processes. Therefore, the crude bismuth anode before electrolytic purification, which is the final step, contains about 1% by weight of silver and about 0.1% by weight of copper.

When electrolytic purification is performed using such a crude bismuth anode, silver elutes in the electrolytic solution (in the case of a chloride bath, it becomes complex ion AgCl ₂ ⁻ ) and is contained as an impurity in electrolytic bismuth. Therefore, in the present invention, when tellurizing the anode, simple tellurium is added to make silver insoluble Ag ₂ Te.

Therefore, the melting temperature of the crude bismuth when casting the anode from the melting point 590 ° C. of Bi ₂ Te ₃ to the melting point 960 ° C. of Ag ₂ Te, efficiently silver and more preferably be 600 to 700 ° C. Ag ₂ Instead of Te, silver can be in a form that does not elute when electrolytic purification of bismuth is performed. This silver telluride is recovered as electrolytic slime and can be used for silver recycling.

  In addition, when simple tellurium is added to crude bismuth, impurities such as lead and copper also float as casting solids on the bismuth molten metal surface at the time of casting, and agglomerate and agglomerate. Lead quality can be reduced. Since this cast residue can be separated and used as a raw material, it is advantageous from the viewpoint of metal recycling. Further, even if it remains on the anode, it is in a telluride state and is insoluble in water, so it does not affect the quality of the electrolytically purified bismuth.

If the amount of the simple tellurium is too small, it is not preferable to form Ag ₂ Te, and silver is eluted into the electrolyte when used as an anode for bismuth electrolytic purification. On the other hand, if the amount of simple tellurium added is too large, the voltage becomes unstable during electrolytic purification, which may cause a decrease in current efficiency. From this viewpoint, the amount of the simple tellurium added is preferably about 0.5 to 4 times the weight of silver in the crude bismuth, more preferably about 1 to 2 times the weight.

  High-purity bismuth with few impurities can be obtained by subjecting the bismuth anode produced according to the present invention to electrolytic purification.

From another point of view, the present invention provides an anode suitable for bismuth electrolytic purification thus obtained.
This anode for bismuth electrolytic purification contains bismuth in a ratio of 90% or more, preferably 98% or more, and tellurium and silver in a ratio of Te / Ag = 0.5-4, preferably 1-2.
In the past, it was difficult to completely remove silver during casting of the anode for refining, so silver was eluted in the electrolytic solution after electrolytic refining, and the quality of bismuth was reduced. By performing electrolytic purification of bismuth using, the elution of silver into the electrolytic solution after electrolytic purification can be suppressed even if the anode contains silver to some extent, and as a result, the quality of the purified bismuth can be improved. .

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these.

Example 1
100 g of crude bismuth was weighed into a graphite crucible, and simple tellurium in an amount equivalent to silver was added. It heated to 600 degreeC with the electric heating furnace in the air atmosphere. The crucible was shaken and the contents were mixed. After 15 minutes, the cast residue was removed from the furnace and suspended on the surface, and then transferred to a mold to cast the anode. Each component is shown in Table 1.

  It can be seen that lead is concentrated in the removed cast residue, and by removing this from the surface of the molten metal before casting, elution of lead from the bismuth anode to the electrolyte during bismuth electrolytic purification can be suppressed.

The Te-added anode is immersed in an electrolytic solution (Bi: 40 g / L, HCl: 60 g / L), and the electrodeposited bismuth is peeled off with a titanium plate as a cathode at a current density of 80 A / m ² and a liquid temperature of 25 ° C. for 96 hours. did.

Electrodeposited bismuth after electrolytic purification and components in the electrolyte were subjected to quantitative analysis. Electrodeposited bismuth was dissolved in nitric acid, and the concentration was determined by ICP-AES. The electrolyte solution was diluted appropriately and the concentration was determined by ICP-AES.
Table 2 shows the electrodeposited Bi quality and the silver concentration in the electrolyte after purification.

  As will be described later, when no tellurium is added, the silver grade usually contained in electrodeposited bismuth is 100 ppm or more, and the silver concentration in the electrolyte is about 6 mg / L. It can be seen that pure bismuth was obtained.

(Example 2)
100 g of crude bismuth was weighed in a graphite crucible, and simple tellurium twice the amount of silver was added. In the same manner as in Example 1, it was heated to 600 ° C. in an electric heating furnace in the air atmosphere. After 15 minutes, the mixture was confirmed to be well mixed and removed from the furnace to remove the cast residue floating on the surface. Then, the cast residue was transferred to a mold to cast the anode.

As in Example 1, bismuth was electrodeposited by immersing in an electrolytic solution (Bi: 40 g / L, HCl: 60 g / L), with a current density of 80 A / m ² and a liquid temperature of 25 ° C. for 96 hours using a titanium plate as a cathode. Was peeled off. Electrodeposited bismuth was dissolved in nitric acid, and the concentration was determined by ICP-AES. The electrolyte solution was diluted appropriately and the concentration was determined by ICP-AES.
Table 3 shows the electrodeposited Bi quality and the silver concentration in the electrolyte after purification.

  Although the electrolytic bismuth content is kept low, it can be seen that it is higher than the silver quality of Example 1 shown in Table 2 and the silver concentration of the electrolytic solution after electrolysis. It can be seen that the effect diminishes if too much is added.

(Comparative Example 1)
Table 4 shows the anode quality and electrolytic bismuth quality when electrolytically purified in the same manner as in Example 1 except that an anode not containing tellurium was prepared.

  According to Table 4, it can be seen that when a bismuth anode is prepared without adding Te and electrolytically refined, the quality of silver and lead is remarkably increased.

Claims (6)

  A method for producing an anode in which a crude bismuth anode is obtained by adding simple tellurium and casting it after melting before casting the crude bismuth on an electrolytic purification anode.   The method of claim 1, wherein the crude bismuth contains silver and lead as impurities.   The method according to claim 1 or 2, wherein the amount of the simple tellurium added is 0.5 to 4 times the amount of silver in the crude bismuth.   The method according to any one of claims 1 to 3, wherein after the tellurium is added to the crude bismuth, the mixture is heated to 590 ° C or higher.   5. The method according to claim 1, wherein after the melting, the anode is cast after removing solids aggregated on the surface of the bismuth melt.   An anode for electrolytic purification of bismuth containing 90% or more of bismuth and tellurium and silver at a ratio of Te / Ag = 0.5-4 by weight.