JP2006176857A - Slag fuming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slag fuming method where in which, from slag produced from a refining furnace for zinc and/or lead refining, zinc and lead are volatilized and separated, fume comprising zinc and lead and having the low contents of arsenic and antimony and slag capable of stably satisfying soil environmental standards are produced, and further, the fume can be efficiently recovered in a metallic state. <P>SOLUTION: In the slag fuming method, a copper source is added to the above slag, thereafter, the fuming of the slag is performed, and the produced fume comprising zinc and lead is caught into molten lead in a metallic state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a slag fuming method, and more particularly, to a slag fuming method for volatilizing and separating zinc and lead from slag produced from a smelting furnace for zinc and / or lead smelting. The present invention relates to a slag fuming method capable of generating a fume containing a small amount of zinc and lead and a slag that can stably satisfy soil environmental standards and efficiently recovering the fume in a metallic state.

  In zinc and / or lead smelting, a smelting furnace method (hereinafter sometimes abbreviated as ISP) called smelting zinc and lead at the same time, which is referred to as Imperial Melting Process, is widely used. The processing method of the slag generated in the blast furnace by the ISP is as follows. The slag is guided to the front floor of the blast furnace, the copper-containing crude lead and the furnace iron are roughly separated, and then water-granulated to produce a product slag for cement raw materials. It is said that. In general, the slag has a high zinc content and contains lead, arsenic, antimony and other metals as components of spices. And commercialized.

  The slag fuming volatilizes metals such as zinc, lead, arsenic, and antimony contained in the slag by heating and reducing the molten slag. As a result, zinc and lead can be recovered from the slag and the impurity metal can be removed, thereby obtaining a purified slag. Here, the slag fuming process is performed using a gas blowing lance or a heating furnace provided with tuyere at the lower part of the furnace. For example, by using a furnace equipped with a lance for gas blowing, slag is immersed in the slag charged in the furnace, and carbonaceous fuel such as heavy oil and pulverized coal and air are ejected from the tip of the lance. This process reduces and volatilizes the metal inside. The treated slag is extracted from the furnace bottom, and the fumes made of volatilized metal (hereinafter sometimes referred to as “fumes”) are oxidized by adding air during the movement to the furnace top and zinc. And recovered as fuming dust containing lead.

However, in the slag fuming treatment, group 15 elements such as arsenic and antimony having a low boiling point and high vapor pressure are volatilized together with zinc and lead which are main recovery elements, and are concentrated in the recovered zinc and lead dust. These group 15 elements, together with the recovered zinc and lead, for example, are repeated in the sintering process of the blast furnace method, but volatilize in the sintering process to increase the load on the exhaust gas treatment system, or sintering When charged into the blast furnace together with the lumps, there was a problem that spices, which are high melting point metal compounds, were produced, making the blast furnace operation difficult.
In addition, repeating fume dust containing zinc and lead generated by oxidizing fumes to the sintering process will be recovered after passing through the sintering and smelting processes again. There was a problem of being connected.
In addition, when harmful elements such as lead or arsenic remain in the slag due to variations in the slag fuming treatment, there arises a problem that the soil environment standard cannot be satisfied in the elution test of the cleaned slag. Therefore, a method that stably satisfies the soil environmental standards has been desired.

  As a solution to this problem, a slag reforming method has been proposed. As a typical example, after the slag produced in the blast furnace is guided to the front floor to roughly separate copper-containing crude lead and furnace iron, There is a two-stage process (for example, see Patent Document 1) in which the copper-containing crude lead and the furnace iron are precipitated and separated by heating and then processed in a fume furnace. However, this method satisfies the slag zinc, lead and arsenic contents and slag soil environmental standards, but does not provide a fundamental solution for volatilization of arsenic and antimony, and volatilization recovery. There was an efficiency problem of repeating the zinc and lead to the sintering process.

From the above situation, in the fuming method of slag produced from zinc and / or lead smelting furnace, fume containing zinc and lead with low arsenic and antimony content is recovered efficiently and stably There is a need for a slag fuming method capable of obtaining a slag that can satisfy the soil environmental standards (Pb and As elution amounts in an elution test according to Environmental Agency Notification No. 46, each 0.01 mg / L or less). .
JP-A-11-269567 (first page, second page)

  An object of the present invention is to provide a slag fuming method for volatilizing and separating slag zinc and lead produced from a smelting furnace for zinc and / or lead smelting in view of the above problems of the prior art. To provide a slag fuming method capable of generating a fume containing less zinc and lead and slag that can stably satisfy soil environmental standards and efficiently recovering the fume in a metal state It is in.

  In order to achieve the above-mentioned object, the present inventors have earnestly studied on a slag fuming method for slag containing zinc, lead and arsenic produced from a zinc and / or lead smelting furnace. As a result, after adding a copper source to the slag, fuming of the slag was performed, and the fumes produced here were collected in molten lead in a metallic state, and the fumes containing zinc and lead with low arsenic and antimony contents Was able to be efficiently recovered in a metallic state, and it was found that slag capable of stably satisfying soil environmental standards could be generated, and the present invention was completed.

  That is, according to the first aspect of the present invention, in the slag fuming method for volatilizing and separating zinc and lead from slag produced from a smelting furnace for zinc and / or lead, a copper source is added to the slag. Then, slag fuming is performed, and the generated fumes containing zinc and lead are collected in molten lead in a metallic state.

According to a second aspect of the present invention, in the first aspect, the fuming is performed while maintaining the temperature at 1075 to 1500 ° C. and controlling the oxygen partial pressure of the slag within a range represented by the following equation. A slag fuming method is provided.
−8> logPo ₂ > −11.5
(However, in the formula, Po ₂ represents the partial pressure of oxygen in the slag in units of atm and is converted to a temperature reference of 1400 ° C.)

  According to a third aspect of the present invention, there is provided the slag fuming method according to the first aspect, wherein a lead splash condenser is used when collecting the fumes.

The slag fuming method of the present invention is a slag fuming method that volatilizes and separates zinc and lead from slag produced from a zinc and / or lead smelting furnace. By collecting the fumes containing them and collecting them in the molten lead in the metallic state, it is possible to recover zinc with a low content of arsenic and antimony, so that the recovery cost of zinc can be reduced.
Furthermore, when collecting the fumes, the cost can be further reduced by using existing equipment such as a lead splash condenser used in ISP.
Moreover, since the slag which can satisfy the soil environment standard stably can be produced | generated, it is used for various uses, such as a cement material. As described above, its industrial value is extremely large.

Hereinafter, the slag fuming method of the present invention will be described in detail.
The slag fuming method of the present invention is a slag fuming method for volatilizing and separating zinc and lead from slag produced from a zinc and / or lead smelting furnace, and after adding a copper source to the slag, Fuming is performed, and the produced fumes containing zinc and lead are collected in molten lead in a metallic state.

  In the present invention, it is important to perform fuming of the slag after adding a copper source to the slag and to collect the generated fumes containing zinc and lead in the molten lead in the metallic state. Have As a result, a fume containing zinc and lead with a low content of arsenic and antimony and a slag that can stably satisfy the soil environmental standards can be obtained, and the fume can be efficiently recovered in a metallic state. .

  That is, by adding a copper source, it is possible to distribute arsenic and antimony in a uniform melt of a Cu—Fe—Pb—As-based copper alloy in which they are stably contained, thereby suppressing volatilization due to fuming. it can. Therefore, reducing the distribution of arsenic and antimony in the fumes containing zinc and lead produced by fuming and the slag after fuming is achieved. Further, by collecting the fumes in the molten lead in a metal state, zinc and lead can be efficiently recovered from the molten lead. On the other hand, in the conventional slag fuming method, the fumes are oxidized and recovered as dust containing zinc and lead in an oxide form.

Here, generation of a uniform melt of a Cu—Fe—Pb—As-based copper alloy accompanying the addition of the copper source will be described in more detail with reference to the drawings. FIG. 1 shows a copper-iron binary system phase diagram.
From FIG. 1, it can be seen that, for example, at 1350 ° C., iron melts to about 15% in copper to form a uniform melt. That is, when the iron spice coexists with metallic copper, the iron spice melts in the copper and forms a uniform melt of a copper-based Cu—Fe—Pb—As-based copper alloy together with some lead. It will be. In the high copper grade region, the amount of iron dissolved in copper forming a uniform melt varies with temperature, and the amount of dissolution increases as the temperature increases. Therefore, there is a merit that the treatment can be performed with a small amount of copper as the temperature is increased.

In the method of the present invention, fuming can be performed as follows.
For example, using a slag fuming furnace equipped with a lance for gas injection, immerse the lance in the slag and copper melt charged in the furnace and contain heavy oil, natural gas, pulverized coal, etc. from the lance tip and oxygen content Gas blowing is performed to eject gas, and these are mixed and agitated, and zinc, lead, arsenic, antimony, and the like are reduced to a metallic state with the melt inside a predetermined reducing atmosphere. Here, most of the metallized zinc and a part of lead are volatilized to form a fume.

  On the other hand, metallized arsenic and antimony have the property of high vapor pressure and the property of strong affinity for iron and copper. Therefore, when the copper melt coexists, arsenic and antimony react with copper. Here, the activity of arsenic in copper is remarkably small when the arsenic concentration is low, so if arsenic melts or dissolves in copper, the vapor pressure of arsenic becomes sufficiently small, and the copper does not volatilize An alloy will be formed. Antimony also exhibits the same behavior as arsenic and is contained in the homogeneous melt of the copper alloy.

  The slag used in the above method is not particularly limited, and is produced in a reducing atmosphere containing arsenic or arsenic and antimony in addition to zinc and lead produced from a zinc and / or lead smelting furnace. The formed slag is used. For example, in the above-mentioned ISP blast furnace, iron and copper reduced to metal react with arsenic and antimony to form a high melting point intermetallic compound called spice, and between the slag layer and the metal layer. It exists in semi-molten or solid form.

That is, the slag can be operated at a slag temperature of 1200 to 1350 ° C. by mixing raw materials and flux, for example, FeO—SiO ₂ —Al ₂ O ₃ —CaO—ZnO—PbO-based relatively It is prepared to have a low melting point slag composition. Therefore, this slag contains a large amount of iron as an oxide. For example, in a reducing atmosphere such as an ISP smelting furnace, metallic iron produced by local strong reduction, Arsenic and antimony form spices.

  It is known that arsenic and antimony in this iron spice have a significantly reduced activity and are in a very stable state. Therefore, arsenic and antimony exist in a turbid state in the slag as a spice phase, despite the fact that the slag temperature of the ISP blast furnace is 1200 to 1350 ° C., which is higher than the boiling point of those metals.

  The copper source used in the above method is not particularly limited, and a copper-containing material capable of forming a uniform melt with iron at a temperature of 1075 to 1500 ° C. in a reducing atmosphere during slag fuming is used. However, intermediates, such as copper scrap obtained from a copper scrap and a copper smelting process (copper quality 98-99 weight%), can be used, for example.

  The amount of copper used with respect to the slag used in the above method is not particularly limited, and reacts with spices contained in the slag to form a uniform Cu—Fe—Pb—As copper alloy in a temperature range of 1075 to 1500 ° C. The conditions for forming the melt are selected. For example, the amount of iron dissolved in the uniform melt in this temperature range is 5 to 50% by weight with respect to copper, and the temperature used and the spices contained in the slag Depending on the amount of iron, it is desirable to use more than the amount of copper determined from the amount of iron dissolved in copper.

Specifically, by changing the amount of copper according to the amount of iron in the spices contained in the slag, or by changing the amount of slag to be processed with a constant amount of copper, Cu-Fe-Pb-As-based copper A uniform melt of the alloy can be stably formed.
In addition, in the formation of the homogeneous melt, there is a concern about the formation of a copper spice phase, but under the condition of adding an excess amount of copper selected based on the amount of iron dissolved, the formation of a copper spice phase does not occur. In practice, it is prepared based on the amount of iron dissolved.

  Here, the generation of spices and lead-rich phases will be described in more detail with reference to the drawings. FIG. 2 is a phase diagram of a ternary system of copper, lead and arsenic at 1200 ° C. (see, for example, “Resources and Materials” 1998, No. 4, p. 218, FIG. 7). FIG. 2 shows that a two-liquid phase separation range of a spice phase and a lead-rich phase is formed within the composition of an elliptical region. Outside this region, a homogeneous phase is formed. For example, when lead is contained in an amount of about 10% by weight, the spice phase is not formed until a composition containing about 20% by weight of arsenic. It can be seen that if the amount of lead is less than that, spices are not generated in the vicinity of copper metal.

  In the above method, the temperature of the slag in fuming is preferably 1075 to 1500 ° C, more preferably 1200 to 1400 ° C. In order to sufficiently volatilize zinc and lead in the slag and react copper and spices to form a uniform melt of the copper alloy, the above temperature range is used. That is, when the temperature of the slag is less than 1075 ° C., the formation of zinc vapor from the Zn—ZnO equilibrium is insufficient, so that the volatilization efficiency of zinc from the slag deteriorates, or the formation of stable slag containing FeO from the Fe—FeO equilibrium. Is insufficient, there is a problem that the viscosity of the slag is too high or solidifies. On the other hand, when the temperature of the slag exceeds 1500 ° C., there arises a problem that the amount of damage to the refractory increases or the required thermal energy increases.

In the above method, the fuming atmosphere is not particularly limited, and an atmosphere capable of reducing zinc, lead, arsenic, and antimony to a metal state is used. In particular, −8> logPo ₂ > -11. It is preferable to control the oxygen partial pressure within a range of 5 (wherein Po ₂ represents the oxygen partial pressure in the slag in units of atm and is converted to a temperature reference of 1400 ° C.).

That is, when Po ₂ exceeds 10 ⁻⁸ atm, the reducing property is weakened, so that the volatilization of metallic zinc is difficult to occur. Further, by Fe ₃ O ₄ which is a refractory by Po ₂ dependent FeO-Fe ₃ O ₄ equilibrium deteriorates the fluidity of the slag was increased in the slag, a stable slag fuming operation becomes difficult . On the other hand, if Po ₂ is less than 10 ^−11.5 atm, iron becomes stable in the metal state due to Po ₂ dependence of the Fe—FeO equilibrium, which is not preferable because generation of furnace iron occurs and hinders operation.

  Therefore, in the fuming, it is preferable that the temperature of the slag is 1075 to 1500 ° C., and the oxygen partial pressure of the slag satisfies the above requirements. As a result, generation of furnace iron can be suppressed, and most of zinc can be volatilized and recovered.

Next, a method for recovering fumes containing zinc and lead obtained from the fuming furnace will be described.
In the above method, zinc and lead in the fumes obtained from the fuming furnace are collected in the molten lead in the metal state without being oxidized. The means for collecting is not particularly limited, and means for collecting zinc and lead in the fume in the molten lead in a metal state is used. For example, lead used in ISP A splash condenser can be applied efficiently.

  The condenser has one end coupled to a fume inlet from the fuming furnace and a smoke exhaust path at the other end, a condenser main body having a lead splash rotor at the center of the condenser, and molten lead ( (Circulating lead) The circulating part is composed of a cooling tank for cooling the molten lead, a flux furnace for adding ammonium chloride to the circulating lead, a separation furnace for separating zinc from the circulating lead, and a return furnace for returning the circulating lead to the capacitor body. Yes. In addition, a heating furnace is provided to keep the temperature of the separated zinc constant.

  During the operation of the above condenser, exhaust gas (fuming product gas) from the fume furnace is introduced into the condenser main body from the fume inlet, and the circulating lead circulating at a temperature lower than the temperature of the exhaust gas is splashed using a lead splash rotor. And circulating lead is brought into contact with the exhaust gas. Thereby, the zinc fume in the exhaust gas is cooled and dissolved in the circulating lead. Subsequently, the circulating lead in which zinc is dissolved is cooled with a cooling bath to precipitate zinc dissolved in the circulating lead. Thereafter, zinc is separated from the circulating lead in a separation furnace, and the zinc is cast into crude zinc after being introduced into a heating furnace to a predetermined temperature. Then, the circulating lead is returned to the capacitor body through the return furnace.

In the operation of the condenser, it is important to maintain good efficiency (condenser efficiency) for transferring zinc fume in the fuming product gas into the circulating lead. In order to obtain high capacitor efficiency, in addition to mechanical and equipment factors such as the state of lead splash, chemical factors such as the temperature of the fuming gas and oxygen partial pressure (CO ₂ / CO ratio) Control is required.

That is, zinc becomes an oxide when the gas temperature decreases even at the same oxygen partial pressure. Therefore, it is necessary to maintain the oxygen partial pressure and temperature at which zinc does not oxidize, such as the top of the blast furnace of the blast furnace method. For example, the temperature of the fuming product gas is preferably 1000 to 1400 ° C., and the CO ₂ / CO ratio is preferably about 0.5 to 0.8.

  Also, the fumes produced in accordance with the present invention have very low arsenic and antimony content, so there is little contamination of lead circulated in the condenser. On the other hand, when arsenic and antimony are accompanied in the fume, arsenic and antimony are accumulated in the circulating lead, so that the ability to collect zinc is significantly reduced. Moreover, since the amounts of arsenic and antimony mixed in the product zinc obtained from the separation furnace increase, the product specifications cannot be satisfied.

Next, the copper alloy and slag obtained from the fuming furnace in the above method will be described.
In the above method, the uniform melt of the copper alloy obtained from the fume furnace can be repeated until arsenic or iron does not dissolve in copper or a uniform melt cannot be formed. At this time, regarding the amount of arsenic, the content in the slag is usually 0. Since it is as low as n% by weight or less, it is practically limited by the amount of iron. Moreover, even when iron in a copper alloy is saturated, the copper alloy can be continuously used by adding copper.

  The homogeneous melt of the copper alloy obtained in the fume furnace in the above method is separated from the slag by the specific gravity difference, and can be easily recovered as a copper alloy by tilting or tapping the furnace. In addition, the recovered copper alloy is, for example, put into a copper smelting converter process in an oxidizing atmosphere to recover copper, remove iron as slag, and treat lead, arsenic and antimony as dust Is possible. Thus, since the process in the existing process step is possible, the cost increase in the recovered copper process is very small.

  The slag obtained in the above method is a slag that can stably satisfy the soil environmental standards and can be used as a cement raw material or the like.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the analysis method of the metal used by the Example and the comparative example was performed by the ICP emission analysis method.
Moreover, the slag produced from the blast furnace was used for the raw material slag used in the Examples. Table 1 shows the chemical composition.

Moreover, the slag fuming method used by the Example and the comparative example is as follows.
[Slag fuming method]
The slag fuming device of FIG. 3 was used. The slag fuming device includes an electric resistance type crucible furnace 9 (fuming part) that performs slag fuming and an electric resistance type tubular furnace 10 (condenser part) that absorbs the fumes placed thereon. A heat insulating material 17 is installed between the two.
The fuming section is heated by an electric resistance type crucible furnace 9, and the temperature and the atmosphere in the electric furnace are controlled by the temperature control thermocouple 6 and the atmosphere-supporting nitrogen blowing tube 1. First, the raw material composition is charged into the alumina crucible 7 used for the reaction, and the alumina crucible 7 is charged into the ceramic outer crucible 5 installed on the crucible holding brick 8. Next, nitrogen is blown into the melt that has been heated and melted through the stirring nitrogen blowing tube 3, and slag fuming is performed while measuring the reaction temperature with the thermocouple 4 for temperature measurement. The generated fumes are sent to the condenser section through the fume collecting ceramic tube 2.

The condenser portion is heated by the electric resistance type tubular furnace 10, and the temperature is controlled by the temperature control thermocouple 6. The generated fumes are blown together with the gas into the molten lead inserted in the alumina tamman tube 15 installed in the atmosphere-backing ceramic tube 14 through the fume collecting ceramic tube 2. The atmosphere-backing ceramic tube 14 is sealed at the top with a rubber plug 12 and at the bottom with a high-purity graphite seal cap. In addition, a high-purity graphite tube is used as an intermediate portion (U-shaped bent portion) of the fume collecting ceramic tube 2.
First, nitrogen gas is blown in while adjusting the flow rate from the atmosphere-assuring nitrogen blowing pipe 1 so that the inside of the atmosphere-proofing ceramic pipe 14 is sucked and exhausted by a pump through the exhaust ceramic pipe 13 and the inside of the pipe is not depressurized. . The reaction temperature is measured with a thermocouple 4 for temperature measurement. The position of the Tamman tube is adjusted so that the gas temperature from the fuming portion is 1000 ° C. or higher, and the lead melt is 800 ° C.

Example 1
First, the first slag fuming operation was performed. In an alumina crucible, a raw material formulation consisting of 500 g of the above slag, 100 g of metallic copper (copper grade 99.99 wt%) and 12 g of coke (total carbon 87.5 wt%) was put. Moreover, 1500 g of metal lead (lead quality 99.9 wt%) was put in an alumina-made Tamman tube. Next, according to the slag fuming method, the temperature inside the electric resistance type crucible furnace was raised to 1400 ° C. and the inside of the electric resistance type tubular furnace was raised to 800 ° C. in a nitrogen atmosphere. After the slag in the alumina crucible melted, the tube was held for 30 minutes, and then the melt in the alumina crucible was stirred with nitrogen gas for 50 minutes to fume the slag and absorb the fume. After maintaining for 30 minutes after the completion of stirring, the mixture was cooled, and then the slag and copper alloy in the alumina crucible and the zinc recovery lead in the alumina tamman tube were separated and recovered.

  Subsequently, the recovered lead was repeatedly used, and the same operation as the slag fuming operation was further repeated four times. Note that the weight of lead for zinc recovery increased by 80 g after 5 operations. This increase represents the weight of zinc and lead recovered by fume slag. That is, it can be seen that zinc can be recovered in a metallic state in the capacitor portion using lead as an absorbent.

  Then, the chemical composition of the obtained slag, copper alloy, and lead for zinc recovery was analyzed. The results are shown in Table 2. In addition, the analytical value of the obtained slag and copper alloy represents the average value of five operations. In addition, a dissolution test was conducted on the slag according to Environment Agency Notification No. 46 to measure the amount of lead and arsenic dissolved. The results are shown in Table 3.

From Table 2, since Example 1 was performed based on the present invention, arsenic and antimony were concentrated in the copper alloy, lead and arsenic in the slag were reduced, and arsenic and antimony were used as lead for zinc recovery. It can be seen that there is no distribution. That is, zinc with low arsenic and antimony can be recovered.
From Table 3, Example 1 was conducted based on the present invention using copper-containing soot as a copper source, so the amount of lead and arsenic eluted was reduced, and the soil environment standard (Pb, As Elution amount: 0.01 mg / L or less for each) can be satisfied.

(Comparative Example 1)
As a raw material formulation, the same procedure as in Example 1 was carried out except that metallic copper was not added, and then the chemical composition of the obtained zinc recovery lead was analyzed. As a result, arsenic in the obtained zinc recovery lead showed a high value of 0.21%. That is, in Comparative Example 1, since slag fuming was performed without adding copper, satisfactory results were not obtained with arsenic in lead for zinc recovery.

  As is clear from the above, the slag fuming method of the present invention can be applied to slag produced from a smelter in zinc and / or lead smelting, for example, zinc from slag produced from a smelter by a blast furnace method. In slag fuming method for volatile separation and recovery of lead, it is useful as a method of directly recovering zinc with low arsenic and antimony contents, and also reduces lead and arsenic in slag containing lead and arsenic It is suitable as a slag reforming method. The modified slag is used for various purposes such as cement materials.

It is a copper-iron binary system phase diagram. It is a phase diagram of the copper-lead-arsenic ternary system at 1200 ° C. It is a conceptual diagram of the slag fuming apparatus used for the Example and the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nitrogen blowing tube for atmosphere guarantee 2 Ceramic tube for fume collection 3 Stirring nitrogen blowing tube 4 Thermocouple for temperature measurement 5 Graphite crucible 6 Temperature control thermocouple 7 Alumina crucible 8 Crucible holding brick 9 Electric resistance type crucible furnace 10 Electricity Resistance tube furnace 11 High-purity graphite 12 Rubber plug 13 Exhaust ceramic tube 14 Atmosphere-supporting ceramic tube 15 Alumina tanman tube 16 High-purity graphite seal cap 17 Thermal insulation

Claims (3)

In a slag fuming method for volatile separation of zinc and lead from slag produced from a smelting furnace for zinc and / or lead smelting,
A slag fuming method comprising: performing slag fuming after adding a copper source to the slag; and collecting the generated fumes containing zinc and lead in a molten state in molten lead. 2. The slag fuming method according to claim 1, wherein the fuming is performed while maintaining the temperature at 1075 to 1500 ° C. and controlling the oxygen partial pressure of the slag within a range represented by the following equation.
−8> logPo ₂ > −11.5
(However, in the formula, Po ₂ represents the partial pressure of oxygen in the slag in units of atm and is converted to a temperature reference of 1400 ° C.)   The slag fuming method according to claim 1, wherein a lead splash condenser is used when collecting the fumes.

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