Pyro-metallurgy is still the main process for lead production and a lot of lead direct smelting
processes have been developed in recent years. All the processes will experience two steps in
common. The first is the oxidisation of PbS to PbO and then reduction from PbO to Pb, furthermore,
from ZnO to Zn. So, the composition of melts, especially the slag composition at reduction step
change continuously. Up to now, there are few systematic results on the slag physical-chemical
properties with its composition change. In this work, the typical lead direct smelting processes were
analysed from theoretical and practical standpoints. The full-period slag composition and slag
melting point change were compared. Especially, to the PbO and ZnO reduction steps, based on the
full-period slag composition change, the slag properties were predicted. Based on dust composition
and test results, the mechanism of Pb compound evaporation and its effect on practice and
measurement of high PbO bearing slag physical-chemical property is discussed. It is suggested that
to restrain the evaporation in practice and to obtain more accurate measurement results of
physicochemical properties of smelting slag are the key problem not only to set high efficiency,
energy saving process, but also to environmental pollution control.