g. The horizontal retort smelter (Figure 2-14), is used exclusively for the
reduction of zinc. Zinc has the unusual property of vaporizing only a few degrees
above its melting temperature and is, therefore, obtained from ores by vaporization
in a retort furnace. Both electrolytic and blast furnace methods may also be used
for zinc production.
(1) The ore is received and stored prior to roasting, in which process sulfur
is removed from the ore and zinc sulfide is converted into zinc oxide. Some plants
may also sinter the ore before proceeding to the reduction process.
NOTE: Flue gasses from the processes may be treated to remove either zinc oxide or
cadmium metal, or in some plants, both. A sulfuric acid plant may also use
the flue gases for acid production.
(2) The treated ore is then moved to a mixing building, where is it is mixed
with pulverized coke or coal and stored to await reduction.
(3) The prepared ore and fuel mix is then placed in the retort furnace, and
zinc is obtained by vaporization and from its ore's condensation. In this process
a slag is formed, and this will frequently be visible in association with each
: As both the retorts and condensers
of clay and
subject to constant
thermal stress and handling, they frequently need replacing. Many horizontal
retort smelters will, therefore, have their own pottery plants for the
production of these items.
Figure 2-14. Ore Reduction Plant (Horizontal Retort Smelters).