JP2962207B2 - Lead smelting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead smelting method which has a much higher lead recovery rate than conventional smelting methods and is suitable for reducing the α of the obtained lead. Low α-ray lead obtained by the smelting method of the present invention is particularly useful in the electronics industry, such as in the manufacture of semiconductor devices.

[0002]

2. Description of the Related Art Lead is used not only as a solder material for assembling circuits of electronic equipment, but also for its alloy as a brazing material for die bonding of various LSIs and bonding of device members. It is also used as a glass component as a sealing material for packages. By the way, in these electronic devices, a soft error has become a problem with the high integration of the semiconductor element, which is mainly caused by α rays emitted from a package material of the element. There is a demand for low α lead with as small an α dose (the number of counts of radioactive α particles) as possible. For example, lead with an α dose of 0.02 CPH / cm ² or less is required for semiconductor device materials.

[0003] As a method of obtaining such a lead having a small α dose, a method of electrolyzing a sulfamic acid solution as an electrolytic solution (Japanese Patent Publication No. 62-47955) or a method of separating the weight of lead ore to a source of α rays is used. A method of removing host rocks and gangues and subjecting them to alkali reduction in an oxygen atmosphere (Japanese Patent Laid-Open No. 1-132725) and the like are conventionally known.

[0004]

According to the former electrolytic refining method, metallic lead having a much smaller α dose can be obtained as compared with a normal electrolytic method using hydrofluoric acid as an electrolytic bath. It is greatly affected by the alpha dose of lead metal. If the α dose of the lead metal used for electrolysis is high, there is a limit to the reduction of α by the electrolysis method. Conventionally, lead ingots are obtained by roasting lead ore mainly composed of galena and converting it to lead oxide for smelting reduction or air reduction simultaneously with oxidation. It is difficult to obtain lead with low yield of crude lead and low α dose at low cost.

[0005] In the above-described alkali reduction method, host rocks and gangues which are sources of α-rays are removed by weight separation.
Further, lead ore dispersed as coarsely as possible is used, but the smelting method after beneficiation follows the above-mentioned general reduction method, and therefore, there is a problem that the yield of coarse lead is low and the production cost increases.

The present invention solves the above-mentioned problems in the conventional lead smelting method, and has a significantly higher recovery rate of metallic lead and a lower amount of α-rays than conventional smelting methods. It is an object of the present invention to provide a smelting method that can be manufactured efficiently.

[0007]

The smelting method of the present invention is different from the conventional roasting reduction method in which lead sulfide is roasted, converted into lead oxide and then reduced, or alternatively, sodium carbonate alone is used as a reducing agent. Unlike alkaline reducing agents, lead sulfide is heated and melted together with sodium hydroxide or potassium hydroxide and carbon, and is directly subjected to reductive desulfurization without oxidizing and roasting. It promotes the recovery rate of metallic lead, and makes it possible to obtain a high yield of lead ingot with much lower α-dose than conventional smelting methods.

That is, according to the present invention, there is provided a lead smelting method having the following constitution. (1) By heating and melting sodium hydroxide or potassium hydroxide and carbon together with lead sulfide in a non-oxidizing atmosphere, lead sulfide is desulfurized and reduced to obtain an α dose of 0.01 CHP / cm ^2.
A lead smelting method characterized by producing the following low α-ray lead. (2) The lead smelting method according to claim 1, wherein sodium or potassium hydroxide and carbon having an α dose of 1 CHP / cm ² or less are used.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The smelting method of the present invention will be described below in detail with reference to examples. The raw material lead sulfide (galena) may contain a small amount of copper or zinc. The lead sulfide of the raw ore is heated and melted together with sodium hydroxide or potassium hydroxide and carbon, and sodium hydroxide or the like is reductively decomposed to desulfurize and reduce the lead sulfide.

In sodium hydroxide or potassium hydroxide, an alkali metal generated by its decomposition reduces lead sulfide and combines with sulfur to desulfurize lead sulfide. The use of an alkaline earth metal salt is not preferred because the recovery rate of metallic lead is lower than that of the alkali metal salt. In order to obtain low α lead, it is necessary to use sodium hydroxide or potassium hydroxide having a small α dose, and more specifically, preferably having an α dose of 1 CPH / cm ² or less. As an easily available low α product, sodium hydroxide is the best in terms of temperature conditions and economy.

The reducing agent is for reducing and decomposing the above alkali metal salt, and is preferably carbon such as graphite, coal and coke from the viewpoint of reducing power and reaction products. The carbon used reacts with an alkali metal salt such as sodium hydroxide, which is reduced and decomposed to carbon monoxide, carbon dioxide gas, etc., and goes out of the system. In order to obtain low α lead, it is necessary to use a reducing agent with a small α ray source, but carbon is also preferable from this point because a low α product with an α dose of 1 CPH / cm ² or less is easily available. .

When sodium hydroxide is added to lead sulfide as an alkali metal salt and is heated and melted together with carbon as a reducing agent in a non-oxidizing atmosphere, sodium hydroxide is decomposed by carbon according to the following formula, and sodium reacts with lead sulfide. Lead sulfide is reductively desulfurized to obtain lead ingot. The carbon becomes carbon monoxide and escapes out of the system. The generated sodium sulfide becomes slag. The heating temperature is 800 ° C
In the following, hydrogen gas and carbon dioxide gas are generated instead of H ₂ O and CO in the following formula. PbS + 2NaOH + C → Pb + Na ₂ S + H ₂ O + CO ↑ --- (1)

Although the amounts of the respective raw materials generally follow the equivalent ratio in the above reaction formula, it is preferable that the amounts of sodium hydroxide and carbon are used in slightly larger amounts than the equivalent ratio. Specifically, lead sulfide 10
It is appropriate to use 35 to 60 parts by weight of sodium hydroxide and 5 to 9 parts by weight of carbon with respect to 0 parts by weight. These raw materials are charged into a melting furnace or crucible, and are heated and melted in a non-oxidizing atmosphere at a temperature of 700 to 1200 ° C. By this reaction, lead metal accumulates at the bottom of the melting furnace or crucible, and slag of sodium sulfide is deposited thereon. This slag of sodium sulfide also absorbs other impurity elements in the raw material lead sulfide and silica in the ore, and is removed from the lead metal.

The recovery rate of metallic lead in the above smelting method is as follows:
As shown in the examples described later, it is 90% or more, and a remarkably high recovery rate is achieved as compared with the recovery rate of the conventional smelting method. Further, in the above smelting method, by using low-alpha sodium hydroxide, potassium hydroxide, and carbon, as shown in Example 1, the α-dose of 0.01 CPH / cm ² or less was used. Lead is obtained.

[0015]

Examples and Comparative Examples Examples of the present invention are shown below together with comparative examples. EXAMPLE 1 40 g of sodium hydroxide (purity: 97%, α dose: 0.1 CPH / cm ² ) was added to 1000 g of a raw material lead ore (galena) having a grade shown in Table 1.
0g and graphite powder (99% purity, α dose 0.3 CPH /
cm ² ) 70 g was mixed in a graphite crucible, and the whole crucible was charged into a heating furnace under a nitrogen atmosphere, heated to 200 ° C. to remove moisture and oxygen, and further cooled at 1000 ° C.
The material was melted by heating for an hour. After slow cooling, the slag and the metal were separated to obtain a lead metal. The recovery rate of this crude lead is 93%
The quality was as shown in Table 1 and the α dose was low.

Reference Example Sodium carbonate (purity 98%) in place of sodium hydroxide
A lead metal was obtained in the same manner as in Example 1 except that 500 g was used. The recovery rate of the crude lead was 92%, and the quality was as shown in Table 1.

Comparative Example 1 (Oxidative Desulfurization) In place of sodium hydroxide and graphite powder of Example 1, 500 g of sodium carbonate and 200 g of sodium chloride were used according to the method of JP-A-1-127725, while blowing air. The lead metal was obtained by heating at a temperature of 800 to 1000 ° C. for 6 hours. The recovery rate of this crude lead is 70%, α
The dose was 0.1 CHP / cm ² .

Comparative Example 2 (Iron nailing method) In place of sodium hydroxide and graphite powder of Example 1, iron powder was used as a reducing agent. Obtained. The recovery rate of this crude lead was as low as 65%, and the α dose was 0.2 CHP / cm ² .

[0019]

[Table 1]

[0020]

According to the smelting method of the present invention, metallic lead can be recovered at a high rate of 90% or more. A remarkably high recovery rate is achieved as compared with the recovery rate of crude lead in the conventional smelting method of about 65 to 70%. In addition, in the above-mentioned smelting method, by using a low-α product such as sodium hydroxide, lead having an α dose of 0.01 CPH / cm ² or less and an extremely low α dose can be obtained. In addition, since smelting can be performed at a relatively low temperature, energy costs can be reduced and the working environment is advantageous.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C22B 13/04

Claims (2)

(57) [Claims] 1. Sodium hydroxide or potassium hydroxide
And carbon are heated and melted together with lead sulfide in a non-oxidizing atmosphere, so that lead sulfide is desulfurized and reduced to obtain an α dose of 0.01C.
A lead smelting method characterized by producing low α-ray lead of HP / cm ² or less . ^2. A sodium hydroxide having an α dose of 1 CHP / cm ² or less.
2. The method according to claim 1, wherein said metal or potassium hydroxide and carbon are used.
Lead smelting method described in the above.