Metallurgical Safety Occupational Hazards in the Lead Smelting Process

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Metallurgical Safety Occupational hazards in the lead smelting process (1) Lead poisoning. Lead has a low melting point (327.5°C), and it volatilizes significantly at 400 to 550°C, and increases as the temperature increases. When lead ore is reduced and smelted in a blast furnace, because the temperature in the blast furnace reaches over 1200°C, lead volatilizes greatly. The slag also contains about 2% lead, which also volatilizes when it flows out. ； Lead ore contains a certain amount of lead, arsenic, and antimony to form lead matte and arsenic matte. When matte is discharged, lead volatilizes more ； The outflow of molten metallic lead also causes the formation of lead vapor. Lead vapor quickly condenses and oxidizes in the air to form lead oxide (PbO), which is dispersed in the working environment as aerosols. Lead and its compounds are highly toxic poisons. Lead and its compounds exist in the form of steam, smoke and dust during production, and mainly enter the human body through the respiratory tract. The absorption in the respiratory tract is much more complete and rapid than that in the digestive tract. Because it often enters and accumulates in the human body, it causes lead poisoning in operators. Lead poisoning can cause disorders of nervous system function and decrease in hematopoietic function. * * Regulations allow lead dust concentration to be 0.05 mg/m3 and lead soot concentration to be 0.03 mg/m3. (2) Arsenic poisoning. Because lead ore contains a certain amount of arsenide. Arsenic matte can also be produced during reduction smelting in a blast furnace. When arsenic matte is released, a large amount of arsenic vapor and arsenic trioxide will disperse to the operating site, causing arsenic poisoning in operators and causing lesions in capillaries, metabolism, nervous system, etc. * * The specified allowable concentration of arsenic trioxide is 0.3 mg/m3. (3) Carbon monoxide poisoning. Due to the strong reducing atmosphere in the blast furnace, carbon monoxide sometimes emits outwards from the top and belly of the furnace. ； When dealing with the air outlet fault, the air outlet overflows. ； During the smelting process of the blast furnace, furnace knots will inevitably occur. When dealing with furnace knots, it is necessary to increase the amount of coke added, lower the material level, and stop the blast, which also creates conditions for the generation of carbon monoxide. The treatment of furnace knots is done manually at the furnace mouth, which is labor-intensive and increases breathing volume. Therefore, carbon monoxide poisoning can occur if you are not careful. (4) Pulverized coal explosion. The blast furnace slag is processed using the fumigation method. During the processing, a large amount of pulverized coal needs to be injected into the slag layer. During the drying, crushing, storage, pipeline transportation and use of coal, there may be a hidden danger of explosion. (5) The hazards of hydrogen fluoride and silicon tetrafluoride. During lead electrolytic refining, the electrolyte used is an aqueous solution of fluorosilicate (H2SiF6) and lead fluorosilicate (PbSiF6). Fluorosilicic acid is made from hydrofluoric acid (H2F2) plus quartz stone powder (SiO2) ； Hydrofluoric acid is made from fluorite (CaF2) and sulfuric acid. ； Lead fluorosilicate is produced by adding lead to fluorosilicate. During the preparation of the above products, hydrogen fluoride and silicon tetrafluoride overflow, causing damage to respiratory mucosa, teeth and skin. In severe cases, skeletal fluorosis may occur. If the operator's skin is in direct contact with hydrofluoric acid, it will not only damage the skin and muscles, but also damage the bones in severe cases. (6) Asphalt hazards. The electrolytic cell used for the electrolytic refining of lead is first made of wood or reinforced concrete into a groove shape, and then the inside and outside are lined with a thick mixture of asphalt and talcum powder as a protective layer. This method is used to solve the corrosion problem. The floor of the electrolytic plant, electrolyte flow trough, liquid storage tank, etc. are all soldered with a thick layer of asphalt mixture using a red-hot soldering iron. Before soldering, heat the asphalt to melt it, mix it with a certain proportion of talcum powder, mix it thoroughly, and then send it to the place where the asphalt needs to be soldered and solder it evenly with a soldering iron. This operation is called "burning oil". There are three ways in which asphalt comes into contact with the human body:: ①Volatile substances in asphalt produce steam during heating, which can pollute the skin or enter the body through the respiratory tract. ； ②Asphalt dust adheres to the epidermis and enters the hair follicles, blocking the hair follicles and causing pathological changes. The dust can also enter the body through the respiratory tract. ； ③Molten asphalt can cause poisoning if it comes into direct contact with the skin. The main components of asphalt are polycyclic hydrocarbons, which may cause skin cancer. It is also a photosensitive material that produces radiation with longer wavelengths, which is harmful to the human body. 2. Preventive measures The preventive measures for occupational hazards in lead smelting are as follows:: (1) Prevent lead and arsenic poisoning. Commonly used measures include: ①During the transportation, transfer and production process of lead materials with flying dust and poison, measures such as sealing, exhaust and purification should be taken. ②In lead workplaces, vacuum cleaning devices should be installed to regularly clean equipment, floors, side walls and roofs to reduce the flying of dust and secondary dust. ③The work clothes and masks of lead workers must be washed in the factory, and work clothes with lead dust must not be taken out of the factory to prevent secondary pollution, especially lead poisoning of employees' family members. Wearing work clothes is not allowed in the cafeteria. ④Rinse your mouth, face, and hands before meals and when drinking water. Smoking and eating in the workplace are prohibited. It is also forbidden to use hot lead slag, lead matte and lead ingots to cook food. ⑤Regular physical examinations should be carried out for those working with lead ； For employees engaged in smelting operations, a six-hour work system and regular recuperation are implemented. ⑥Strictly prohibit the operation of the lead blast furnace with low material column, lower the temperature of the top of the lead blast furnace and reduce the generation of lead vapor. (2) Prevent carbon monoxide poisoning. Strengthen ventilation in production plants, conduct regular carbon monoxide concentration testing, and strengthen maintenance to prevent leaks. (3) Prevent pulverized coal explosion. The following measures are often taken: Explosion-proof valves should be installed on the pipelines of the pulverized coal system. Explosion-proof doors should be installed on coal separation bins, separators, cyclones and other equipment. The area of ​​the explosion-proof door and the volume of the equipment should be set at 0.4 m2/m3, but shall not be less than 90 cm2. The explosion-proof disc used should be a thin iron plate with a thickness of no more than 0.5 mm, and should have cross notches on it. The scored side should face outward when installed. Except for the section leading to the burner, the pipeline conveying pulverized coal must not have horizontal sections, let alone be bag-shaped. The mechanical equipment of the pulverized coal preparation system should have well-maintained interlocking devices ； Electrical equipment should be explosion-proof. All pipelines transporting pulverized coal and equipment for preparing pulverized coal should be well grounded, and their grounding resistance should be checked regularly. The pulverized coal on the outside of the equipment system, the surface of the pipes, and the floor and walls of the factory building should be regularly cleaned to prevent spontaneous combustion and secondary explosions. Smoking and fire are strictly prohibited in places where pulverized coal is prepared. If fire is required for maintenance, it must be thoroughly cleaned, inspected and approved by relevant departments, and a fire permit must be obtained. When cleaning and repairing in the warehouse, there should be supervision. If the pulverized coal remaining in the warehouse spontaneously ignites, the cleaning personnel should exit immediately, seal the warehouse, use steam or carbon dioxide to extinguish the fire, and only enter the warehouse after confirming that there are no fire sources and harmful gases. When using hot air, if the coal type has high volatile content, the hot air temperature must not exceed 160°C. When stopping feeding pulverized coal, the air pressure of the coal feeding machine should be maintained at 0.2 kgf/cm2 (1.96×104 Pa). After all the pulverized coal is fed, the air compressor should be stopped. (4) Prevent the hazards of hydrogen fluoride and silicon tetrafluoride. Specific measures are as follows: When carrying out the above operations, they should be carried out in a closed container. Each storage tank must be covered and water-sealed. Strengthen the natural ventilation in the lead electrolysis plant, and the fresh air sent in winter needs to be preheated. Distribute acid-proof overalls, boots, and acid-proof gloves to prevent direct skin contact. In summer, operators are given skin care ointment to avoid causing rashes. (5) Prevent the hazards of asphalt. The specific method is: Transport asphalt at night, on cloudy days or at dusk, and avoid operating in daylight. Boiling asphalt should be done outdoors in a well-ventilated environment, and the temperature should be controlled to prevent sudden boiling and overflow, causing fires and burns. When burning asphalt in the container, frequent rotations are required, the working time is changed to a 6-hour working day, and protective ointment is applied to the skin surface. Provide dust hats with shawls, protective glasses, canvas gloves and shoe covers, and filter masks to prevent skin contact and reduce respiratory inhalation.