Lead Refining

The process of removing unwanted contaminants by various treatments carried out on a bath of molten Lead is known as Lead refining.

Primary Lead production is usually viewed in terms of two distinct operations converting Lead concentrate to bullion and refining the bullion.

Depending on the nature of the concentrate, the bullion exiting the smelting furnace contains a particularly broad range of impurities. For example, smelters of complex concentrates may have iron, copper, nickel, cobalt, zinc, arsenic, antimony, tin, bismuth, selenium, tellurium, silver, and gold, as well as Sulphur and oxygen.

In conventional Lead refining, the bullion from the smelting unit must invariably be drossed. Drossing (or rough drossing) is accomplished by cooling the bullion to within 50°C of the freezing point of Lead.

By crystallization, iron, copper, and many impurities from the bullion are rejected in part or fully. A fine drossing process is conducted where Sulphur or, less commonly, phosphorus is used to scavenge residual copper.

Crude Lead produced during smelting operations is remelted in cast iron kettles and refined by the addition of reagents, such as Sulphur and caustic soda. The purified Lead is then cast into molds or ingots.

Typically, metal from the smelting furnace is melted in an indirect-fired kettle or pot and the trace elements are combined to produce the desired alloy. Employees may be exposed to Lead fume and particulate during the refining process.

Lead Casting Machine

The refined or alloyed finished lead is generally cast in 23-25 kg ingots in a continuous chain casting machine with cast iron moulds which are cooled in the bottom with a spray of water. The molten refined or alloyed lead is pumped out from kettle with Lead pump of which discharge pipe is connected with pouring trough of Lead casting machine. Speed of lead casting machine is such that before releasing from ingot mould each of ingot get solidify. A fast cooling of lead is particularly important for the lead alloys to avoid the possibility of metals migration.
 

Refining Process

Lead particulate may become airborne due to updrafts created by thermal rise from the surface of the refining kettle during preheating and cleaning.

Lead fumes or particulate may be emitted from the surface of the molten Lead during the transfer of Lead to the kettle and from the kettle during melting, adding refining agents, and stirring of molten alloy.

• Lead emissions may occur while drossing Lead kettles.
• Settled dust may be reentrained due to vibrating equipment and vehicular traffic in the area.
• Provide exhaust ventilated enclosure for refining kettles.
• Enclose and exhaust ventilates all launders.
• Pump rather than pour molten Lead when possible.
• Keep molten Lead temperatures to a minimum to reduce Lead fume generation.
• Provide local exhaust ventilation hoods and ductwork that does not interfere with the use of overhead cranes.
• Provide roll back access doors to allow the addition of refining agents.
• Provide a supplied air island near the refining kettle.