Refining dross is the
result of lead refining process where impurities like Cu, Te, As-Sb-Sn, Ag, Zn and Bi in sequence from lead
bullion. Composition of each type of dross varies and is subjected to specific
refining steps and raw material contents. Conversely, lead refining processes are
taken in account for the convenience of refining dross recovery.
In general, the copper dross is treated by reverberatory furnace or rotary
furnace. In case of copper dross with high arsenic, tin and antimony, caustic
soda plus iron filings are used. In reaction with caustic soda, the arsenic,
tin and antimony report to sodium salt as slag to be recovered by
hydrometallurgy consequently. After removal of arsenic, tin and antimony, iron
fillings is added to reduce lead content in the copper matte which later is
directed to copper converting system. Complete separation of Te, As, Sn and Sb
is accomplished by chemical methods in a leaching plant.
Apart
from conventional dross treatment methods, Metalcess focuses on treating tin slag
from Harris refining process, silver-zinc crust/silver foam from Parkes process
and lead anode slime treatment. With Metalcess solution, high purity tin is
obtained by combining fire-refining and vacuum distillation.
Metalcess
provides an integrated system combining liquation and distillation technology
to treat silver-zinc crust/silver foam from Parkes process, in which zinc, lead
and silver are separated efficiently at the cost of low energy consumption.
Noticeably, the zinc recovered from silver-zinc crust can be used as
desilvering agent again for the Parkes process. While the lead alloy can be
charged to lead refining pot before bismuth-removing step. This system is
superior in reducing energy consumption, shortening process flow and improving
working environment.