1.
INTRODUCTION
Description of vacuum evaporation treatment for photographic liquids,
x-ray, graphic arts, etc
The purpouse is reducing the dsposal costs by separating the water from
the polluting substances. Every developer, fixer, bleach-fix,
stabilizer, etc. solution can be treated by vacuum concentrators plant.
2. DEVELOPER AND FIXING PROCESS
The photosensitive material (photographic, x-ray films, graphic arts,
and so on) is usually made by a film covered with the silver bromide
and other chemical substances.
The silver salt, hit by the light, are
exposed becoming unsoluble. In black/white, x-ray and graphic arts
treatments the developer takes place in a hydroquinone base and it
create the latent image by turning in silver the silver salts hit by
the light.
The ammonium thiosulphate, contained in the following fixer bath, will
take the silver off and create the image. The black part of the film is
made by metallic silver; in the light part the silver has passed in the
solution. In the colours treatment all the silver contained in the film
will be melted in the fixer or bleach-fix bath.
3. TYPE
OF POLLUTION
The black and white fixer baths contain above all hydroquinone, sodium
carbonate, sodium sulphite;
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the
developer colour contains ethylene
glycol, formic aldehyde and potassium carbonate; whereas the substances
in the bleach fix are Fe-EDTA, sodium sulphite and acetic acid.
4. THE VACUUM EVAPORATION PROCES
In the following scheme we have separate the substances containing
silver from the others devoid of it (usually developer with an alkaline
pH).
It is possible to recover in advance the silver from the fixer and
bleach-fix baths, even if it is mixed (but it is necessary however to
have in this case a rotating cylindrical chathode recovery machine).
Before the evaporation treatment it is necessary to adjust pH to 5,5
for turning ammonia into ammonium salt and avoiding the transport of
large ammonia quantities in the distilled water.
The evaporator produces a concentrate and a distillate; the
distillation yield is about 80% (the concentrate density is about 1,3).
The concentrates, after being stored, are sent for the disposal.
The distillates, according to their chemical characteristics, can
undergo some post-treatment like, for example, a chemical oxidation for
sulphites treatment, a èH check or a treatment to eliminate
the
ammonia.
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