Figure AI-1.Silver recovery cartridge.
An electrolytic plating silver recovery unit is more
complex than a silver recovery cartridge, but it is
actually much easier to operate and control than the
processing machines that generate the used solutions.
The initial cost is higher than a cartridge; however, the
cost is not exorbitant and the electrolytic plating unit
should be considered as the primary means for
recovering silver from fixers and bleach fixers. Navy
imaging facilities are not charged for silver recovery
equipment. Procedures for obtaining silver recovery
equipment are located in the Defense Reutilization and
Marketing Manual (NOTAL), DoD 4160.21-M.
The electrolytic plating method of silver recovery
uses two electrodes: a cathode and an anode. They are
placed in the silver bearing solution and an electric
current is passed between them, causing almost pure
silver to plate onto the cathode (fig. AI-2). The silver
recovery capacity of the unit is determined by the direct
current density and the size of the cathodes; that is,
(amperes) in relation to the surface area of the cathode.
Tank size is another measure of recovery capacity.
Smaller tanks have less plating capacity because of a
proportionately smaller cathode surface area.
An agitation or recirculation system provides a
continuous supply of silver-laden solution to the
cathode. Without this system, the current density would
become too high for the amount of silver present in the
solution near the cathode and result in the formation of
silver sulfide. This silver sulfide decreases the
efficiency of the unit.
The cathodes in various electrolytic plating units
vary in design. Some units have a simple flat plate;
others may have several circular disks mounted on a
shaft or use a rotating cylinder (fig. AI-3). Cathodes are
made of metal and there are two types: flexible and
nonflexible. The flexibility of the cathode makes it easy
to remove the silver flake. Those cathodes that are not
flexible can be tapped lightly on a flat surface to remove