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Production of electrolytic nickel from nickel-chromium alloy scrap
I. Overview
Nichrome scrap, nickel-chromium alloy mainly waste processing and the production process, such as nickel-chromium alloy cast scrap, machining cuttings, shavings, cuttings, tailings, and related components, like waste defective element . Due to the different sources of nickel-chromium alloy scrap, its composition is more complicated. Generally, it contains 35% to 65% of nickel and 15% to 25% of chromium. The chemical composition examples are shown in Table 1.
Table 1 Examples of chemical composition of nichrome scrap, %
Material name
Ni
Cr
Fe
Mn
Mo
Cu
Co
scrap
35
19
37
0.50
0.45
0.12
0.10
scrap
37
25
42
4.50
3.0
0.12
0.10
wood shavings
38.5
14.5
37
2.73
0.25
wood shavings
66.1
14.6
0.50
1.0
2.80
Waste
61.7
17.8
0.50
0.80
2.20
Waste
68.7
16.6
0.50
0.25
0.10
Nickel-chromium scrap steel containing more than 55% nickel can be directly smelted into an anode plate in an electric arc furnace. When the nickel content is less than 55%, an air blowing method is required, and after enriching to about 60% of nickel, it can be cast into a crude nickel anode plate.
Nickel-chromium alloy waste production electrolytic nickel process is divided into electric furnace smelting to obtain crude nickel anode plate and electrolytic refining two sections. Since the electrolytic refining process is similar to the production of electrolytic nickel by nickel- phosphorus iron , only the electric furnace melting section will be described here.
Second, raw materials
(1) Most of the raw materials containing more than 55% nickel are shavings and drill cuttings. The raw material composition is as follows (%):
Ni
Co
Cu
Fe
Cr
Pb
Zn
55～70
0.01 to 0.9
0.1 to 2.3
3~8
5~20
0.002
<0.01
(2) Examples of raw material components containing less than 55% nickel are as follows (%):
Ni
Co
Cu
Fe
Cr
35～50
0.10
0.12
37~42
14.50~25
Third, electric furnace smelting technology operating conditions
Nickel-chromium scrap electric furnace melting, including feeding, melting, chromium removal, zinc evaporation, deoxidation, casting and other operations.
(1) Feeding
The 1.5t/set electric furnace treats the nickel-chromium alloy scrap 1.5~2.5t per furnace, and the block material is added once. The crumb material is added twice, first half, and after the electricity is melted, the remaining half is added.
(two) melting
After the material is added, continue to electrify for 1 h to melt the material.
(three) in addition to chromium
After the material is melted, it is oxidized by blowing air to remove impurities such as iron and chromium, and some nickel is oxidized. However, the formed oxidized nickel is reduced by metal iron and chromium in the nickel melt to form corresponding iron and chromium oxide. Object. At this time, 80 to 100 kg of limestone and 70 to 100 kg of fluorite are successively added to carry out slagging. As the chromium is oxidized and slag, the slag is sticky, that is, 30 to 50 kg of quartz sand is added, and the air is oxidized for about 10 minutes to improve the fluidity of the slag. Each oxidation time is 30 to 45 minutes. After the air blow is stopped, the power is raised for about 20 minutes, and then the slag is discharged. After the air-conditioning is carried out 2 to 3 times according to the above operation, the nickel content of the alloy can reach 60% or more.
The temperature gradually rises during the blowing process. The temperature at the start of blowing is about 1600 ° C, and the temperature at the end of the blowing is above 1700 ° C. Quartz sand can dilute the slag, but the fluidity of the slag cannot be fundamentally improved. Therefore, the slag cannot be completely discharged when the slag is discharged, and some of the slag must be discharged with raft or iron.
(4) Steamed zinc
Nickel-chromium alloy scrap contains very low zinc, but some zinc-containing impurities are often entrained in scraps such as shavings and drill cuttings. Therefore, after oxidizing and removing chromium, steaming of zinc is required. Before steaming, add 30 to 50 kg of petroleum coke or electrode powder to carry out carburization, and control the nickel melt to have a carbon content of 0.2% to 0.3%. The temperature of the steamed zinc is controlled at 1650 ~ 1700 ° C, and the time of inserting wood is about 10 min. After the first insertion, the power is warmed up, and then inserted a second time. After 2 to 3 times of wood insertion, the zinc content in the furnace is reduced to 0.004%.
(5) Deoxidation
Since a large amount of gas (especially oxygen) is dissolved in the nickel melt during dechromation and zinc smelting, deoxidation is carried out with petroleum coke 10 minutes before the tapping. Add petroleum coke can not be excessive, generally plus about 10kg.
(6) Casting
When the alloy contains more than 65% nickel, the crude nickel anode can be cast out. The tapping temperature is controlled at around 1650 °C. The anode plate mold is made of pig iron, and a layer of bone powder is coated in the mold. During casting, the melt flows into the intermediate control package through the launder and is then injected into the vertical anode mold to obtain a nickel-iron anode plate for electrolytic refining.
Each furnace is treated with nickel-chromium alloy scrap of 1.5 to 2.5 tons, and the smelting time is controlled according to the nickel content of the molten sample. The molten sample contains about 50% nickel and the smelting time is 10-12h. The molten sample contains about 30% nickel and the smelting time is 12-15h.
The relationship between the direct yield of nickel and the grade of the tapping is shown in Table 2.
Table 2 Relationship between grade of alloy and nickel into alloy rate, %
Raw material containing nickel
Furnace alloy containing nickel
Nickel alloy rate
45.17
77.55
73.94
35.37
73.34
72.24
43.34
65.29
86.61
47.61
68.42
79.78
48.51
62.68
79.12
45.06
65.89
79.25
The direct yield of nickel is low, the main reason is that the chromium-containing oxide in the slag is higher, and thus the melting point of the slag is higher. Therefore, rational selection of slag type, improvement of slag flowability, and reduction of nickel content in slag are the key to improving the direct yield of nickel. Table 3 shows the relationship between the chromium content of the slag and the nickel content of the slag.
Table 3 Relationship between chromium content in slag and nickel in slag, %
Slag containing chromium
Slag containing nickel
23.93
2.56
22.13
2.98
10.09
1.04
5.31
0.56
Table 4 shows the distribution of nickel chromium in the blown product. After the blowing, the alloy retains more than 90% of the chromium removed.
Table 4 Distribution of nickel and chromium in the product of blowing, %
element
Input material
Output alloy
Output slag
Loss rate
content
Distribution rate
content
Distribution rate
content
Distribution rate
Ni
45.06
100
65.89
79.75
1.86
3.05
17.20
Cr
18.50
100
1.60
4.75
22.52
89.90
5.37
According to the data in Tables 11 to 16, it is preferable that the alloy contains nickel in an amount of 60% to 65%.
Fourth, the product
The blown product has a crude nickel anode plate and slag.
Examples of the composition of the crude nickel anode plate are as follows (%)
Ni
Co
Fe
Cu
65~70
0.01~0.10
10~15
0.02~0.30
Pb
Cr
Mo
C
Zn
<0.002
2 to 10
1 to 6
1 to 2
0.001 to 0.004
Examples of slag composition are as follows (%):
Ni
Cr
CaO
SiO 2
FeO
1.54~2.98
17.09~24.47
5~10
2-8
7 to 10
V. Technical and economic indicators
Electric furnace smelting nickel direct yield 80%~90%
When the furnace is 10~15h
Electricity consumption is about 1800kW·h/t
Electrode consumption 30 ~ 40kg / t material
Limestone about 70kg/t
Fluorite about 80kg/t
Quartz sand about 40kg / t material
Slag formation rate 0.7~1.1kg/t