The smelting of organic bismuth is divided into two steps: roughing and refining. The rough refining method varies depending on the raw materials. When using bismuth sulfide concentrate, bismuth oxide and bismuth mixed ore, bismuth oxide slag, and bismuth oxychloride as raw materials for refining bismuth, a mixed smelting method is used, and an appropriate amount of iron filings and soda ash are added. , fluorite powder, coal powder, etc., are mixed and smelted in a reverberatory furnace to obtain crude bismuth, which is sent for refining.
Fire refining of crude lead
This method usually removes arsenic and antimony by smelting and adding sulfur to remove copper and oxidation refining. It consists of the steps of adding zinc to extract silver and then oxidizing or vacuum zinc removal, adding calcium and magnesium to remove bismuth. This method is used in factories such as lead and zinc smelters in northwest China.
1. Crude lead smelting and sulfur addition to remove copper
Crude lead contains Copper is generally 1.2%-2.0%, and the smelting method is used to reduce the copper content in lead. The basic principle of the smelting method is that copper in crude lead can react with arsenic and antimony to form stable refractory compounds – copper arsenide and copper antimonide. These compounds are insoluble in lead and enter the dross in a solid state to separate from the lead. The smelting method can reduce copper in crude lead to less than 0.1%.
The equipment used in the melting method includes reverberatory furnaces and melting pots, which are commonly used in large lead smelting plants. The melting pot is made of cast steel, with a capacity of 30-370t, and uses heavy oil as fuel. The melting temperature is 500-600℃, and the melting slag floats out of the lead liquid surface and is fished out with a slag bailer.
In order to further remove copper, the lead subjected to smelting treatment is then subjected to sulfur treatment. This method takes advantage of the fact that copper’s affinity for sulfur is greater than lead’s affinity for sulfur, producing Cu2S with a smaller density than lead, and Cu2S is insoluble in lead at an operating temperature of 320-340°C. Sulfur is added to the molten lead to further remove the copper. to 0.001%-0.002%.
2. Crude lead oxidation refining
The purpose of this method is to remove Impurities such as tin, arsenic, and antimony are further removed from the copper crude lead. Refining is carried out in a reverberatory furnace. The furnace temperature is controlled at 800-900°C. The furnace door is opened and the inflowing air is naturally ventilated to oxidize the impurities, so that tin, arsenic, antimony and lead form lead salt scum, which is then fished out with a machine.
3. Adding zinc to crude lead to remove silver and subsequent zinc removal
To melt Adding zinc to lead can form zinc-gold compounds and zinc-silver compounds with the gold and silver in the lead. This product has stable properties, high melting point, and lower density than lead. It is insoluble in zinc-saturated lead, so it floats on the surface of the lead liquid in solid form to form a silver-zinc shell, which separates the precious metal from the lead.
Adding zinc to extract silver is carried out in a zinc adding pot. The amount of zinc added is 1.5%-2% of the lead weight. The operating temperature is 450-480℃, It is carried out in three stages: 330-340℃ and 420-430℃. Remove the silver-zinc shell and find that the silver content in the lead liquid is less than 2g/t.
After silver removal, lead often contains 0.6%-0.7% zinc that needs to be removed. Generally, the oxidation zinc removal method is used, which utilizes the ZnO formed by zinc oxidation to be insoluble in lead and float out in lead water for removal. The process is carried out at 750-900°C. The oxidant can be air, water vapor or oxygen. Through this, the zinc content of lead oxide can be reduced to 0.0025%.
4. Bismuth removal from crude lead
This method uses calcium and magnesium smelting to Remove organic bismuth in lead. During smelting, calcium, magnesium and bismuth in lead are produced and are insoluble in lead. and Bi3Ca and Bi3Mg2 scum shells that are less dense than lead. During production, calcium is added in the form of Pb-Ca alloy, and the operating temperature is 380-390°C. After two bismuth removal operations, the bismuth in crude lead can be reduced from 0.5%-1.0% to less than 0.005%. After removing bismuth, the crude lead needs to be refined to remove calcium and magnesium. The methods include air blowing oxidation, chlorine blowing and alkaline refining. Among them, the alkaline refining method has the best effect.
