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The purpose of blast furnace smelting is to remove most of the zinc and a part of lead and tin to produce black copper . The raw materials processed by the blast furnace are mixed copper and copper-containing slag.
(1) Copper
Table 1 Chemical composition of yellow copper and white copper
       (2) Copper-containing slag
1. The slag produced by the refining of the crude copper fire method.
3. The quartz slag produced in other stages of the black copper fire refining process.
4. The converter slag is produced by blowing the secondary blister copper. [next] The chemical composition of various copper-containing slags is shown in Table 2. Smelting slag purpose is copper oxide from its decomposition ferrite and silicate out, and allowed for the reduction of the lower metallic copper, copper grade, generally 60% to 70%, so called Black copper.
In the solid copper, copper forms a solid liquid with various metal impurities, and is mainly in a free state in a molten state. In addition, there are in the form of a metal compound such as arsenic compound, antimony compound, tin compound and zinc and the like exist.
Zinc has a melting point of 692.4K and a boiling point of 1180K.
Table 2 Chemical composition table of copper slag
When the temperature is 1180 K, the vapor pressure of zinc is 101.3 kPa. Therefore, in the blast furnace temperature, zinc is volatilized a lot, but the furnace must be controlled to a reducing atmosphere, otherwise the oxygen in the furnace gas will oxidize zinc to ZnO. When the melting point of ZnO is as high as 2248K, it is easy to form a furnace knot in the furnace, which affects the normal operation of the furnace. When the temperature is higher than 1573K, the lead begins to strongly evaporate. In the blast furnace, only the temperature in the focus zone can reach 1573K, and the residence time of the charge in this zone is short, so the amount of lead volatilization is large.
At the temperature of the blast furnace smelting, tin does not substantially evaporate in the form of a metal. The vapor pressure of SnO at 1533K can reach 101.3 kPa, and SnO 2 starts to volatilize a little at 1073 K, but it cannot be completely melted at 1673 to 1773 K. Therefore, when tin is present in the form of a suboxide in a reducing atmosphere, Remove a small portion.
Most of the copper in the copper-containing slag exists in the form of free oxides, ferrites and silicates of copper, and some are mechanically intercalated in the slag. The purpose of smelting copper-containing slag in a blast furnace is to try to reduce the copper in the slag from the copper oxide, ferrite and silicate, and produce it in the form of metallic copper, and the oxide and slag in the slag. The silica is still removed in the form of slag.
When the metal oxide is reduced at 1,273 K, the order from easy to difficult is Cu 2 O, PbO, NiO, SnO, Fe 3 O 4 , FeO, ZnO, MnO, or the like. It can be seen that Cu 2 O is easily reduced to metallic copper. The reduction of copper ferrite and silicate requires a higher temperature and a stronger reducing atmosphere in the furnace. When a strong alkaline oxide is present in the charge, copper can be completely precipitated from these compounds.
When smelting copper-containing slag, the high-valence oxide of iron should be reduced to FeO for slag formation, but it cannot be reduced to metallic iron. Otherwise, not only the quality of the metal copper is lowered, but also the iron in the furnace is easily formed to form a furnace. The amount of coke added during smelting is the minimum consumption, and there is enough quartz flux in the charge to prevent the formation of the furnace. [next] Third, physical and chemical changes in blast furnace smelting
(1) Blast furnace melting smelting copper When the blast furnace is used to smelt copper, several complicated physical and chemical changes such as drying, volatilization, slagging and combustion are carried out according to the law. According to the temperature and physical chemistry in the furnace, it is divided into four zones according to the height of the furnace, namely the upper zone, the middle zone, the focus zone and the hearth zone. There are no obvious boundaries in each zone of the furnace, and the physical and chemical reactions in each zone are not absolute. The physicochemical processes of each zone are as follows.
1. The temperature in the upper area is 873~1073K. The charge and coke are added by the charging furnace door. In this area, the furnace gas is dried and some limestone is decomposed according to the following.
CaCO 3 =CaO+CO 2
2. Central area With the smelting process proceeding, the charge and coke gradually move downward and enter the central area, with a temperature of 1073~1273K. In this area, zinc begins to volatilize, and the more volatile it is, the more intense it is; the limestone is strongly decomposed, and the decomposition pressure as a function of temperature is shown in Table 3.
Table 3 Table of relationship between decomposition pressure and temperature of limestone
It can be seen from the table that at a temperature of 1173 K, the decomposition pressure of limestone has exceeded 101.3 kPa, and the partial pressure of CO 2 in the furnace gas in this zone is very low, and it is seen that limestone is largely decomposed in this zone. At the same time, part of the low melting point material begins to melt.
3. Focus area The charge continues to move downwards to the lower part of the furnace, the focus area. The focal area is slightly higher than the tuyere, and the temperature in this area is very high, up to 1623 ~ 1673K. At this time, zinc is largely volatilized, and lead and tin are partially volatilized. The slagging reaction of CaO, FeO and SiO 2 is mainly carried out in this area.
2FeO+SiO 2 =2FeO·SiO 2
CaO+SiO2=CaO·SiO2
2FeO·SiO 2 +CaO=CaO·SiO 2 +2FeO
Copper and non-volatile metal impurities Zinc, lead, tin, nickel and other molten materials, together with the slag, pass through the hot coke layer as a filter, and then flow into the hearth after superheating, clarifying the stratification and discharging it regularly.
After the metal vapor such as zinc or lead volatilized from the middle and lower parts escapes from the surface, the air sucked by the feed gate is oxidized to oxide.
2Zn ( g ) +O 2 =2ZnO (dust)
2Pb ( g ) +O 2 =2PbO (dust)
Part of the zinc and lead vapors are oxidized by CO 2 in the furnace gas
Zn ( g ) +CO 2 =ZnO (dust) +CO
Pb ( g ) +CO 2 =PbO (dust) +CO[next]
When zinc and lead vapor are oxidized, a large amount of heat is released, so that the temperature of the furnace space in the material space is as high as about 1273K.
The ZnO and PbO dust enters the flue with the furnace gas, and after cooling, it enters the dust collector for recovery. The combustion of coke is carried out in the focal zone. When air is blown from the tuyere into the hot coke layer, the coke is burned down and released a lot of heat, which raises the temperature inside the furnace.
C+O 2 =CO 2
When the remaining oxygen in the furnace gas and the CO 2 produced by the reaction move upward, the following reaction with the red hot coke occurs as follows.
2C+O 2 =2CO
C+CO 2 = 2CO
The CO produced maintains a reducing atmosphere in the furnace.
(2) Blast furnace smelting copper-containing slag When blast furnace smelting copper-containing slag, it can be divided into dissociation, reduction, slagging and combustion processes.
1. Dissociation In the upper part of the furnace, the charge is heated by the furnace gas, first removing the adsorbed water, then removing the structural water.
CuO·SiO 2 ·nH 2 O=CuO·SiO 2 +nH 2 O↑
CaCO 3 ·nH 2 O=CaCO 3 +nH 2 O↑
Part of the limestone begins to decompose and CuOg begins to decrease.
2, restore
The reduction process mainly occurs in the central part of the furnace. The limestone is strongly decomposed here, and the copper oxide is reduced by CO. The reaction is as follows
2CuO+CO=Cu 2 O+CO 2
CuO+CO=Cu+CO 2
Cu 2 O+CO=2Cu+CO 2
The relationship between the equilibrium constant of the reaction Cu 2 O+CO=2Cu+CO 2 and temperature is shown in Table 4.
Table 4 Table of relationship between equilibrium constant of Cu 2 O+CO=2Cu+CO 2 and temperature
As can be seen from the data in the table, when the concentration of CO in the furnace gas is very low, the reduction reaction can proceed. Therefore, the reduction and smelting of the blast furnace easily reduces the free copper and its oxides into metallic copper.
Copper oxides can also be reduced by solid carbon, and the reaction is as follows
2CuO+C=2Cu+CO 2
2Cu 2 O+C=4Cu+CO 2
Copper in the form of silicate or ferrite can be substituted in the presence of CaO, and the reduction reaction is as follows
CuSiO 2 +CaO+CO=Cu+CaO·SiO 2 +CO 2
CuO·Fe 2 O 3 +CaO+CO=Cu+CaO·Fe 2 O 3 +CO 2
The above reaction indicates that when the blast furnace is used to treat the copper-containing slag, a certain amount of limestone is added to make the alkali slag, that is, the high calcium slag, which is advantageous for improving the recovery rate of copper and reducing the copper content of the slag. However, when the CaO content in the slag is too high, the melting temperature of the slag rises, making operation difficult. Usually, the content of CaO in the slag is controlled within the range of 28% to 33%.
3. Slag formation and melting The slagging and melting process is mainly in the focus area. Like the molten copper, the molten metal copper and slag are heated into the hearth for clarification and separation. The reduction of the copper oxide is thoroughly carried out in the central portion of the furnace. Otherwise, the unreduced copper oxide will slag in the focal zone, thereby increasing the loss of copper.
4. Combustion Mainly refers to the burning of coke. Like smelting copper, the combustion reaction of coke is also carried out in the tuyere area.
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The basic principle of blast furnace melting
First, the raw material of the blast furnace
      Â
The copper is mainly yellow copper and white copper. The impurities are mainly zinc, followed by lead, tin and nickel . The chemical composition is shown in Table 1. The copper grade produced by the lysing of yellow copper and white copper is relatively high, about 85%, called black copper. Â
Copper name
chemical composition(%)
Cu
Zn
Pb
Sn
Ni
Fe
Yellow copper
White copper
55～85
55～70
8~30
18~22
0.3 to 6
4~6
1 to 3
1 to 3
0.2 to 1.0
2.5 to 15
0.1~1.0
0.5 to 1.0
The blast furnace can also handle copper-containing slag. The common slags are as follows.
2. The zinc slag produced in the zinc removal stage during the refining of the black copper fire method.
Second, the physical and chemical basis of blast furnace smelting
name
chemical composition
Cu
Pb
Sn
SiO 2
CaO
FeO
Al 2 O 3
HgO
Steamed zinc slag
Quartz slag
Copper slag
Converter slag
15~18
25~35
10~22
30~40
1 to 4
0.2 to 1
micro-
4~10
2 to 5
1 to 2
micro-
1~8
14-20
12~22
30~45
4~8
1 to 2
0.5 to 1
2 to 4
0.5 to 1
20~25
5~8
7~9
7~9
3~8
4~5
9 to 13
4~8
1 to 3
1 to 2
2 to 4
0.5 to 1
|
Temperature / K
973
1023
1073
1133
1173
Decomposition pressure / kPa
3.3
7.7
22.4
36.4
103.1
Temperature / K
1173
1323
1356
lgK
Pcl/Pa
-4.56
2.7
-4.05
9.1
-3.95
11.3