APPENDIX I
SILVER RECOVERY
Recovering silver from the photographic process
saves the government money. These savings can come
from two sources: the monetary value of recovered
silver and avoiding fines from the Environmental
Protection Agency.
Like most natural resources, silver is a valuable and
diminishing resource. In photography, silver forms the
image on most types of photographic films. Unlike
many other natural resources, silver is not destroyed in
the photographic process. Much of this silver can be
recovered, refined, and used again.
In photography, silver is recovered from two main
sources: photographic solutions and black-and-white
scraps (film and paper). When most films and papers
are processed, some of the silver they contain are
removed in the fixing bath. With positive types of
black-and-white film, as much as 80 percent of the
silver that was in the emulsion may be removed during
fixing. With color film and paper, close to 100 percent
of the silver is removed in the fixer.
When black-and-white negative film or black-
and-white paper with a high percentage of exposed area
is processed, most of the silver remains in the emulsion.
Most of the silver that remains in film or paper can be
recovered.
ENVIRONMENTAL ISSUES
The awareness and concern for polluting our
environment has brought about new legislation and
stricter enforcement of existing environmental codes.
Silver is one of the heavy metals that is controlled by
federal, state, and local legislation. These government
agencies monitor the amount of silver that is discharged
into the sewer system. Each Navy imaging facility is
subject to environmental codes and restrictions of the
state and local area. Each state has a similar set of codes
that may differ somewhat, so it is important for you to
become familiar with them. For example, the
maximum silver concentration limit for an imaging
facility in Gulfport, Mississippi, may be 5.0 mg/L
(ppm), whereas an imaging facility in San Diego,
California, may be 0.05 mg/L (ppm).
Compliance with these strictly enforced local sewer
code ordinances is of greater concern today than
economic gain. Violations can result in severe fines.
Individual violators may also be held personally
responsible for such fines. An excessive concentration
of silver in the effluent of a photographic processor can
cause an imaging facility to be closed until the silver
concentration is within acceptable limits. A copy of the
sewer codes for your local area may be obtained from
the sewer authority or from Navy Public Works.
SILVER RECOVERY TECHNOLOGY
A number of different methods for recovering silver
from used photographic solutions are in use today. Two
methods that are used commonly in Navy imaging
facilities are metallic replacement and electrolytic
plating.
METALLIC REPLACEMENT
The metallic replacement method uses a plastic
cartridge packed tightly with steel wool. The cartridge
resembles a 5-gallon bucket with tubes protruding from
the cover. The system is inexpensive and well-suited
for the small-volume user.
A silver recovery cartridge operates on the principle
of metal ion exchange. When the fixer containing silver
is passed through the cartridge, the iron in the steel wool
or wire screen replaces the silver ions in the fixer. The
silver then drops to the bottom of the cartridge as impure
metallic silver sludge. The iron ions in the fixer are
drained from the cartridge with the fixer into a drain or
holding container (fig. AI-1).
In time, the filter material in the cartridge dissolves
and the cartridge must be replaced. After about 80
percent of the steel wool is dissolved, the cartridge
becomes inefficient and silver passes through the
system. The cartridge is actually exhausted before the
filter is completely dissolved. A metallic-replacement
unit is capable of desilvering to a lower level than an
electrolytic plating unit; therefore, some imaging
facilities use electrolytic plating unit first and then send
the solution through the metallic-replacement cartridge
for final treatment.
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