Plating Waste Treatment
C. F. PAULSON
Special Applications Department
The Permutit Company
New York, New York
Treatment of electroplating rinse waters by ion exchange has been
one of the most attractive methods considered in recent years for the
elimination of a very serious water pollution problem. First attempts
at this problem go back approximately 12 years, but until recently, all
attempts have been uniformly unrewarding. Most of the difficulties
were due to shortcomings in the properties of the ion exchange resins
themselves. With the recent advent of a broader range of ion exchangers,
these shortcomings have been virtually eliminated.
The most successful of the ion exchange processes applied to electroplating waste recovery has been the use of cation and anion exchangers
in the recovery of chromic acid. This was discussed at the Seventh
Purdue Industrial Waste Conference by the author and several others.
There are really two separate ion exchange processes. One is the use
of a cation exchanger to remove metallic cations from strong chromic
acid solutions such as are used for bright dipping, stripping, chromium
plating, chromic acid anodizing, etc. The second is the use of an anion
exchanger in series with a cation exchanger to recover the chromic acid
from the rinse solutions following the above treatments. The rinse
water may be reused virtually indefinitely and the chromic acid is
eventually returned to the treatment bath. Since the announcement of
the cation exchange process several years ago, this process has developed
rapidly, and there are now more than a dozen large plants throughout
the country applying either all or a part of this process successfully.
In this connection, it can now be reported that it is now feasible to
remove metallic cations from chromic acid solutions all the way up to
the 40 percent plating tanks by cation exchange. Whether for any given
installation this is economically attractive depends upon the overall
layout and scale of operation. The anion exchange process has recently
been extended to the treatment of mixed chromate rinse water.
A process for the recovery of cyanide from cyanide plating rinse
baths, very similar in operation to the chromate rinse recovery process,
has been developed under one of the research projects of the American
Electroplaters Society.   In essence, the process consists of passing all of
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