(2) There are a number of secondary features in the alumina process that may
cause some confusion and complicate analysis. These features include:
(a) Waste reprocessing facility for the capture of alumina that has slipped
through the original processing and might have been discarded.
This reprocessing
facility will be readily identifiable by the presence of a second set of rotary
kilns and settling tanks.
(b) Reprocessing of the diluted sodium hydroxide (caustic soda) solution
left in the precipitator tanks after the removal of aluminum hydroxide crystals.
This diluted solution is held temporarily in storage tanks near the precipitator
building. The storage tanks may be confused with the seed tanks though the former
are shorter and wider.
(c) From the storage tanks the diluted caustic soda solution is piped into
evaporators where excess water is removed. These evaporators will be close to the
storage tanks and will appear as small boilers complete with small stacks.
(d) After being treated in an evaporator, the newly concentrated caustic
soda is pumped back into the concentrated caustic soda tanks near the autoclave
building.
Figure 2-9.
Alumina Processing Plant Flow.
IT 0673
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