Aerospace
Continued...
On exhaustion of the
demineraliser resins, highlighted by a detectable rise in
conductivity, a regeneration is required. The resultant
regenerant waste is high in contaminants and requires additional
treatment before discharge to drain. This is typically carried
out on a batch basis and may include cyanide oxidation or
chromium reduction stages.
Many aerospace companies are now
looking to evaporation to reduce the volume of regenerant waste
before off-site disposal. Vacuum evaporation applies a negative
pressure to the boiling chamber allowing water to boil and lower
temperatures. This type of approach is often referred to as “zero
discharge” and has the major benefit of not having to operate
and police a discharge to drain.
Other technologies are often employed within the aerospace finishing
area to remove a specific contaminant at point of source. For example,
electro-winning cells can be used for plating out metals from dragouts,
thereby reducing the levels carried forward to other rinse stages.
An example of this might be on a static rinse post cadmium plating
where the operation of an electro-winning cell also facilitates
the electrolytic oxidation of cyanide.
Ion exchange polishing columns
are also used to remove metals at point of source or before final
discharge to drain. This type of system often employs highly selective
resins which can facilitate removal of metals even under difficult
operating conditions.
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