Removal of Hexacyanoferrate from Selected Photographic Process Effluents by Ion Exchange
Donald J. Brugger
An ion-exchange process has achieved almost complete removal of hexacyanoferrate anion Fe(CN)6 from the bleach wash of Eastman color-print processes that use ferricyanide bleaches. A weak-base, gel-type resin column that has an adsorption capacity of approximately 50 g of Fe(CN)6 per liter of wet resin was used. For resin regeneration, the hexacyanoferrate was eluted from the resin with sodium hydroxide, and the resulting solution was then oxidized for use as a bleach replenisher. This technique provides a route to complete recovery and recycling of the ferricyanide. Similar treatment was also applied to a final wash of Process K-14 for Kodachrome films, with equal success in removal of the hexacyanoferrate. However, reuse of the ferrocyanide recovered by this process is complicated by the presence of thiosulfate anion which is also removed from the effluent by the resin.