Furnace processing of renewable raw materials containing lead is advanced technology. Compared with the blast furnace smelting and treating waste lead storage batteries and regenerated and sintered raw materials, the electric furnace smelting has a remarkable advantage of low coke consumption. The amount of coke added to the charge only ensures the need for a reduction reaction in the furnace. Thus, the use of air to burn coke is unnecessary, and as a result, less fumes are generated, reducing the amount of dust discharged and the cost of flue gas purification. When the electric furnace is smelted, the heat loss is greatly reduced, and the heat loss with the waste gas and the waste residue is reduced by 60%.
Fig.1 Process flow diagram of reduction of smelting lead agglomerate, recycled raw materials and returning material in blast furnace
Figure 2 Process flow chart of smelting waste lead storage battery in blast furnace
The lead battery regeneration method to process the material processing is a lead-antimony alloy by the All-Union Scientific Research and Design Institute of non-ferrous metals and other units developed. The industrial-scale soda reduction electric smelting process was first adopted at the Leninorgorsk lead plant. Advantage of this method is to add soda, limestone and iron-containing materials, etc. during melting flux materials reproducing, directly in line with the production of lead-antimony alloy All-Union standard.
In the production of lead-bismuth alloys in electric furnaces, lead sulphates and oxides are simultaneously reacted with soda (or soda-sulfate mixture) and other oxide components of the charge and carbon reductant during the smelting process.
The charge is melted in the reducing environment of the electric furnace to produce a liquid phase; the crude lead is distributed in the lower part of the furnace; the melt of the copper -slag slag is in a lighter phase, forming the upper part of the melt.
The reaction history of the oxidation-reduction process carried out in an electric furnace is summarized as follows: lead oxides and sulfate compounds in the charge, which react with solid carbon and carbon monoxide in the presence of sodium carbonate upon heating; oxidation of lead Matters, sulfates and silicates interact with sulfides of lead and sodium. [next]
The process of the process carried out in the solid phase can be represented by the following process and reaction formula:
Pb+CO→PbO·CO Absorption→PbCO 2 Absorption→Pb+CO 2 (1)
PbO·SiO 2 +CO→PbO·SiO 2 ·CO aspirate →Pb·SiO 2 ·CO 2 absorption →Bb+SiO 2 +CO 2 (2)
2PbO·SiO 2 +CO→2PbO·SiO 2 ·CO aspirate→Pb+Pb·SiO 2 ·CO 2 →2Pb+SiO 2 +2CO 2 (3)
C+CO 2 →C+CO 2 absorption →CO·CO→2CO (4)
PbO+Na 2 CO 3 +C→Pb+Na 2 O+CO 2 +CO (5)
PbSO 4 +Na 2 CO 3 +3C→Pb+Na 2 S+3CO 2 +CO (6)
PbSO 4 +2C→PbS+2CO 2 (203)
Sb 2 O 3 +3CO→Sb 2 O 3 ·3CO Absorption →2Sb+3CO 2 (7)
Sodium sulfide and lead oxide interact essentially in the liquid phase by the following reactions:
Na 2 S+3PbO→3Pb+Na 2 O+SO 2 (8)
Na 2 S+3(2PbO·SiO 2 )→6Pb+Na 2 O+SO 2 +3SiO 2 +1.5O 2 (9)
Na 2 S+3(Pb·SiO 2 )→3Pb+Na 2 O+SO 2 +3SiO 2 (10)
A certain amount of chloride enters the charge as it returns to the charge. Chloride and sodium sulfate interact in the presence of carbon in the following reactions:
PbCl 2 +Na 2 CO 3 +C→Pb+2NaCl+CO 2 +CO (11)
Scrap is an essential component of the charge, ensuring the reduction of lead sulfide and barium sulfide with iron:
PbS+Feâ†â†’Pb+FeS (12)
Sb 2 S 3 +3Feâ†â†’2Sb+3FeS (13)
The matte melt consists of unreacted lead sulfide, iron sulfide and vulcanized steel. The slag component of the melt is formed by the composition of the ore-free rock (SiO 2 , CaO, Al 2 O 3 ) in interaction with sodium carbonate:
Na 2 CO 3 +nSiO 2 â†â†’Na 2 O·nSiO 2 +CO 2 (14)
Na 2 SO 4 +nSiO 2 â†â†’Na 2 O·nSiO 2 +SO 3 (15)
mNa 2 O · nSiO 2 + CaO ↠→ mNa 2 O · CaO · nSiO 2 (16)
Since the content of the mineral-free rock in the recycled raw material is not high, the single-phase slag is not formed and becomes a component of the ice-copper-slag melt.
The decomposition of the smelted product is entirely dependent on its physical properties. The sodium silicate slag melt dissolves a very small amount of lead and antimony, so the metal loses little with the sulfide slag melt during smelting. The solubility of lead and bismuth compounds in the sodium silicate slag melt is shown in Table 1.
Table 1 Table of dissolution of lead and antimony compounds in sodium silicate slag melt
Composition of slag (%) | Temperature (°C) | Equilibrium concentration of lead and antimony compounds (%) | |||
Pb | PbS | Sb | Sb 2 S 2 | ||
SiO2 36.3 | 900 | 0.03 | 0.27 | 0.09 | 1.35 |
Na2O 39.5 | 1000 | 0.038 | 0.29 | 0.99 | 2.40 |
CaO 24.2 | 1200 | 0.039 | - | 0.99 | - |
SiO2 26.2 | 900 | 0.078 | 0.28 | 0.21 | 1.85 |
Na2O 45.0 | 1000 | 0.100 | 0.29 | 0.19 | 3.80 |
CaO 20.3 | 1100 | 0.16 | - | - | - |
FeO 20.0 | 1200 | 0.18 | 1.30 | - | - |
SiO2 37.4 | 900 | 0.025 | 0.20 | 0.30 | 3.0 |
Na2O 32.4 | 1000 | 0.035 | - | - | 3.1 |
CaO 20.3 | 1100 | 0.035 | - | - | 3.4 |
FeO 9.9 | |||||
The equilibrium concentration of lead and bismuth increases with increasing temperature in systems containing these two metal sulfides. Increasing the silica content lowers the equilibrium concentration, and adding iron oxide to the slag system increases the equilibrium concentration of lead.
The qualitative separation of the smelted products makes it possible to adjust the depth of the furnace by taking into account the sulfides of the lead and bismuth metals and their slag melts. The melting of lead, antimony and copper sulfides is ensured according to the difference in melt temperature, and is effectively reacted with the matte body.
The technical specifications of the electrosmelting process are determined by the viscosity and conductivity of the slag melt. The increase in the silica content and the reduction in the levels of calcium oxide and sodium oxide in the slag increase the viscosity of the slag and make it difficult to discharge. In addition, an increase in the content of silica also lowers the electrical conductivity. [next]
The viscosity and conductivity of the slag melt are correlated with temperature (SiO 2 31.0%, Na 2 O 35.25%, CaO 8.75%, FeO 29%):
Temperature (°C) 750 900 950 1000 1050 1100 1150 1200
Viscosity (Pa·s) 84 36 24 14 11 80 5.9 3.4
Conductivity (West·cm -1 ) 0.76 1.11 1.61 1.91 — — — —
In industrial practice, the regenerated lead raw material is subjected to electric furnace melting in a soda reduction process to produce a matte-slag melt containing SiO 228 to 42%, Na 2 O 28 to 40%, CaO 15 to 24%, and FeO 10 to 20%. Such ingredients ensure a lead-lean bromide-slag solution and increase the recovery of lead and antimony.
The practice of electric furnace smelting According to the process flow chart (Fig. 3), the regenerated raw materials are treated by electrothermal method into lead containing antimony. The recycled raw materials should meet the requirements of ГOCT1639-78. The recycled raw materials smelted by the incoming call furnace are: lead and lead-containing waste, lead-acid batteries, lead slag, lead mud, and metal products for dissolving lead storage batteries. The chemical composition of lead-containing materials is listed in Table 2.
Figure 3 Process flow chart of electric furnace melting smelting lead-containing raw materials
Table 2 Chemical composition of lead-containing materials smelted in electric furnace (%)
materials | Pb | Sb | Cu | S | As | Sn | Fe | SiO2 | other |
Waste lead block | 97.0~99.0 | 0.25~0.5 | - | - | - | - | - | - | 0.5 to 2.75 |
Lead waste and block material containing antimony | 90.0~95.0 | 0.25~0.5 | - | - | - | - | 5.0 | - | 1.5 to 4.5 |
Waste lead storage battery | 73.5~88.5 | 1.2 to 4.1 | 3.4 to 3.6 | 3.2 to 7.0 | 0.02~0.01 | 0.01 | - | 1.0 to 2.0 | 1.6 to 19.2 |
Metal products after disintegration of lead-lead batteries | 90.0~92.5 | 3.0 to 4.0 | 0.2 | 0.6~0.88 | 0.01 | 0.01 | - | - | 3.9 to 6.4 |
The smelting of electric furnace into lead-bismuth alloy technology places high demands on the preparation of recycled raw materials. These requirements are to carefully carry out the following procedures: acceptance, sorting, disintegration, and preparation before smelting. During the cold of the year, the raw materials must be dried and the residual moisture should not exceed 4%.
100% of the charge smelted in an electric furnace in a factory is recycled raw material (lead content is not less than 75%). 4 to 6% of the total amount of recycled raw materials is sodium carbonate, 1.5 to 2.0% is limestone, 2 to 3 is iron filings, and 5 to 8% is metallurgical coke. The ratio of coke is calculated based on the fixed layer having a thickness of 50 to 100 mm produced on the melting surface. [next]
Determining a required slag melt composition charge - in accordance with the following ingredients produced matte: Pb3 ~ 5%, Fe 23% to 30% full. Cu 1.2 to 3.0%, S12 to 15%, Na 17 to 20%, SiO 27 to 9%, CaO 12 to 14%, and other 7.3 to 16.0%. The content of SiO 2 in the slag-ice copper is at a level of 7 to 9%, and is limited to enter with the filler in the coke ash, lead slag, and waste lead storage battery slag.
The charge is loaded into the furnace by a plate feeder or a screw feeder and sent to a uniformly distributed slag surface without forming a slope.
After the charge enters the melt, the reduction reaction of the metal and the reaction of the slag-copper melt are initiated. The charge is periodically charged and smelted in 4 to 4.5 hours. During this period, 27 to 32 tons of charge and return material (dust particles and refractory dross) were charged into the furnace.
The smelting process was carried out in a three-phase three-electrode furnace (Fig. 4) with an electrode diameter of 0.3 m. The parameters of the electric furnace are as follows:
Electric furnace power (kVA) 2300
Unit productivity of the charge (ton / meter 2 · day and night) 9.8
Electrode consumption per ton of charge (tons) 0.0096~0.011
Electricity consumption per ton of charge (kWh) 600～650
Bottom area (m 2 ) 7.37
Size of electric furnace in melting zone (m)
Figure 4 Electric furnace for melting lead-containing recycled raw materials
A-longitudinal section; δ-cross section
Width 1.86
Length 3.96
The size of the electric furnace in the flue gas zone (m)
Width 2.1
Length 4.2
The necessary temperature is maintained in the furnace, taking into account both the heat released by the current passing through the slag melt and the arc radiant heat between the electrode and the charge.
The current enters the furnace working space through three graphite electrodes, and the electrode terminal penetrates into the slag melt 180-450 mm.
The heat exchange in the furnace is ensured by the convection agitation of the slag melt. At the same time, the thermal field in the melt is rather uneven. In the vicinity of the furnace wall, the electrode zone is guaranteed to have a maximum temperature of 1,250 to 1,300 ° C, a temperature of 1000 ° C in the bottom of the furnace, and a temperature of 700 ° C in the bottom of the furnace. The uneven temperature determines the order in which the charge is loaded. Approximately 90% of the charge is loaded into the space close to the electrode, while a small portion (10-15%) is placed closer to the side of the furnace. After the molten pool reaches the level of 1.3 to 1.4 meters, iron filings are started. The temperature of the molten pool should not be lower than 1200 ~ 1300 °C. After precipitation, a smelted product is produced. The crude lead is placed in a refining workshop with a ladle of 0.7 m3 . The slag-copper melt is injected into the steel spindle mold, cooled, and separately combined into the reservoir. The yield of the smelted product is as follows: crude lead 73 to 76%, slag-ice copper 12-16%, flue gas 5 to 7%, and alkali scum 0.3%.
The technical and economic indicators for electric furnace smelting are listed below:
Recycled raw materials 100
Soda (% of raw materials) 5.5
Limestone 1.5
Scrap iron 2.9
Coke 3.8
Raw material unit melting capacity (ton / meter 2 · day and night) 8.3
Yield of smelted products (% of raw materials)
Crude lead bismuth 74.0
Slag-ice copper 13.0
Alkali dross 0.3
Recovery rate in finished battery alloy (%)
Lead 94.2
锑 89.0
Recovery in slag-copper melt (%)
Lead 0.65
锑 2.10
Electrode consumed per ton of raw material (kg) 13.0
Power consumption (kWh / ton of raw materials) 600
Temperature (°C)
Inside the furnace 1500
Furnace top 900
Produced lead 860
Negative pressure under the top of the furnace (kPa) 3.0
The electrothermal soda-reduction process is an effective method for directly producing lead-bismuth alloys with high lead and antimony recovery rates. At the same time, from the comprehensive utilization of raw materials, the process cannot guarantee sufficient extraction of copper walls and tin . The loss of copper with slag-copper is about 91%, and the loss of tin is about 8-10%.
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