Chromate Recovery by Ion Exchange
C.   F.   PAULSON
Special Applications  Dept.
The Permutit Company
New York, New York
Electroplaters and anodizers have recognized for many years the
high cost and difficult disposal problems connected with the use of
chromic acid. It has frequently been necessary to dump baths containing a large amount of free chromic acid when a small amount
of the chromic acid became neutralized with the metallic cations.
Recently increased water pollution control has made the disposal of
untreated chromate solutions very difficult, due to their high toxicity.
Various disposal methods have been proposed and many are in use
today, but these frequently involve large capital expenditures and
high operating costs, as well as often providing a serious sludge disposal problem of the detoxified material.
Many experimenters, including Professor Bloodgood, have investigated ion exchange for chromate recovery in the past, but always
encountered difficulties due to the poor resistance to oxidation of
resins which  have been available until  recently.
The Permutit Company recognized this problem and did considerable work on it in the past, but it was only recently with the advent
of the new styrene base ion exchangers that a satisfactory solution
was found. A considerable amount of work has been conducted on
the removal of metals from acids such as phosphoric, acetic and comparatively dilute sulfuric and it was only natural to extend these
tests to chromic acid when the resistance of Permutit Q to oxidation
had been explored. Tests showed that Permutit Q was resistant to
oxidation by chromic acid solutions up to approximately 10 per
cent concentration, and that it was possible to remove metallic cations
from such solutions.
Although the removal of metallic cations from anodizing and
plating solutions, so that they do not need to be dumped, overcomes
the bulk of the chromate waste disposal problem, the persistent
question arose as to how to recover this chromate in useful form from
the rinse water. This also had been investigated utilizing anion
exchange, but the anion exchangers were not sufficiently resistant
to oxidation.
When Permutit S, a highly basic anion exchanger, was developed
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