Characteristics of crude lead refining and refining product treatment
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Figure 1. Lead-copper system state diagrams I, IIIII - liquid The complete removal of copper by this method was unsuccessful because the low melting mixture (eutectic) solidified at 326 ° C and still contained 0.06% copper. In practice, lead contains about 0.1% copper after ingot casting.
The basic component of scum is mechanically carried away by lead. At low temperatures, more lead is mixed into the scum, so it is called fertilizer residue. At high temperatures, dry scum containing a small amount of lead is obtained.
Liquid crude lead is injected into the refining pot. Use electric preheat to maintain the necessary temperature. The temperature of the lead liquid at the time of removing the dry scum is 500 to 550 °C. The removal of dry scum from the liquid lead pan is accomplished by means of a bridge crane with a slag colander. The output of dry scum is 15-20% of the total amount of crude lead. The composition of the dry scum is (%): lead 57-68, copper 13-23, sulfur 2.3-4.5, 锑0.5-1.1, arsenic 3.1-4.6.
After the dry scum is taken out, the crude lead is sent to the next step of the refining pot, and the fertilizer is taken out when the temperature drops to 300 to 335 °C. The slag output is 6 to 8% of the total amount of crude lead. The composition of the slag is (%): lead is nearly 95, copper is 3 to 5.
Remove the copper immediately after the fertilizer residue is taken out. In the tank for refining lead, elemental sulfur is mixed with a mechanical mixer for 25 to 30 minutes. The temperature of lead in the refining pot is 315 to 335 °C. The ground sulfur has a particle size of about 3 mm.
Copper dissolved in the lead wall iron wall interactions with the molten elemental sulfur:
[Cu] lead + S liquid = CuS solid (1)
[Cu] lead + CuS = Cu 2 S solid (2)
Due to the high melting point (1170 ° C), cuprous sulfide does not actually dissolve in the crude lead and floats on the surface with a density of 5.6 g/cm 3 .
When the copper is refined, the vulcanization of lead is carried out:
[Pb] lead + S liquid = [PbS] liquid (3)
At the same time, it is determined that the vulcanization reaction rate of copper at a low temperature is much higher than that of lead, so that it is safer and more intense to remove copper from lead.
The sulfide scum floating on the surface is placed in a steel ingot mold and charged into a pot. To completely remove the copper, an additive of 2 to 3 kinds of sulfur is added.
The output of sulfide scum is nearly 12% of the total crude lead. Lead in addition to copper contains no more than 0.05% copper and arsenic and antimony no more than 1.7%.
The crude lead-bismuth alloy obtained after smelting in the furnace is melted and simultaneously incorporated into the melt into the wood block and the wood chip, so that the scum of the sulfide is well separated from the melt. Sulfur scum (dry scum) contains sulfides of copper, lead, antimony and arsenic. The output of dry scum is about 14.5% of total crude lead. The composition of dry scum is (%): lead is nearly 85, 锑 is nearly 4.9, and sulfur is nearly 9. The consumption of wood chips is 1.5 to 2.0 kilograms of wood chips per 1 ton of refined alloy. The high levels of lead and antimony in the scum make it necessary to treat it in an electric furnace in accordance with the soda flow chart.
The purpose of the alkaline refined lead-bismuth alloy is to oxidize impurities with oxygen in the air, and when it interacts with the molten caustic soda, it is followed by the formation of stannate, arsenate and sodium citrate. The consumption of caustic sodium depends on the composition and temperature of the refined alloy, and consumes 2 to 3 kg of caustic soda per ton of commercial lead-bismuth alloy.
The order in which the impurities are oxidized and subsequently transferred to the alkaline slag is: arsenic-tin-bismuth-lead. The alkaline refining process takes place in the diffusion control zone. What has a huge impact on this process is the saturation and agitation speed of the impurities in the melt. In practice, the machine is stirred with a mechanical mixer. The duration of the addition of caustic soda is 2.0 to 2.5 hours.
When refining the alloy, it is not desirable to completely remove the ruthenium. To remove tin and arsenic, the necessary amount of base is added. The process is often controlled by the residual content of tin and arsenic.
The alkaline melt is produced in an amount of 0.25% of the total amount of the refined alloy. The alkaline slag containing 41 to 46% of lead and 3.5 to 9.2% of bismuth is sent to an electric furnace for treatment.
At the time of production, after the alloy having a low content of alkaline refining bismuth (less than 2%), a calculated amount of metal ruthenium is incorporated into the refined lead at a temperature of 450 to 480 °C.
The finished lead-bismuth alloy of the brand CCyAA is poured into a cast iron spindle mold on a horizontal conveyor belt. The ingot casting machine has a production capacity of 7.5 tons/hour and a casting weight of 35 to 40 kilograms.