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.
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