The Removal of Metals from Photographic Effluent by Sodium Sulfide Precipitation

The two most commonly used methods for silver removal — metallic replacement and electrolytic plating — can remove better than 95% of the silver but are not effective in removing any other metals which may be present in photographic effluents. The method of chemical precipitation with sodium sulfide can remove virtually 100% of the silver and most other metals from dilute or concentrated photographic effluents using one-step treatment. A sulfide precipitation process has been developed using automatic pH control, automatic detection of the precipitation endpoint, and two-stage filtration which is capable of safely and efficiently treating photographic effluents of varying pH and metals concentration.