HERBORISTIC
COSMETIC
VEGETAL EXTRACTORS
Rapid
extractors for medical herbs
Essential
oil extractors
Mixers
- Emulsifiers
Hammer
mill
POLLUTING
CHEMICALS
Silver
recovery units
Concentrators
evaporators
WASTE
WATERS
Chemical-phisical
plant
Depurators
Resins plant
Reverse
osmosis
Ultrafiltration
APPLICATION
EXAMPLES
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THE SILVER RECOVERY FROM PHOTOGRAPHIC SOLUTIONS
INTRODUCTION
| Since
the end of the sixties we had
built the first silver recovery unit in Europe. Until that time, the
recovery
took place through precipitation by using sodium sulphide. |
|
The
chemical reaction was absolutely easy and the silver was completely
recovered in the form of sulphide. |
RECOVERY
FROM BLEACH-FIX AND/OR MIXTURE OF LIQUIDS
It
is possible to recovery the silver also from mixture of liquids (fixer,
bleach-fix, developer etc) but it's necessary to have a rotating
cylindrical cathode electrolytic silver recovery machine with current
density adjustment. Electrolysis is an electrochemical reaction and,
like all the electrochemical reactions, there must be some conditions
to realize it and some parameters must be respected.
1. the solution must contain silver in the form of silvertiosulphate;
2. the solution must be perfectly clean and it must not have cloudiness
or precipitate;
3. the solution must contain Sodium Sulphate in quantity enough to
preserve the Ammonium Tiosulphate from the
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sulphuration
(at least 8-10
gramsxliter);
4. the solution must have an optimum pH value (only the C-41 fixer has
a tampon solution CH3COOH/CH3COONa)
5. the deposit on cathode must happen uniformly and it must not have
protuberances;
6. the liquid exchange in the electrolysis bath must have a V = 5-8
liters/minute value;
7. the electrodeposition tension must be superior to the iron one;
8. the current density must be at least 4-5 times superior to
the
one normally used for the fixer recovery.
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ELECTRODEPOSITION
CURRENT
Even
if one of these parameters is
not respected, this could cause an 'un-metallic' deposit. For example,
let's consider a recovery machine provided with one or more plates as
cathode and devoid of rotating cathode; in this case, the parameters
nr. 6.7.8. can't be respected.
If the deposit isn't metallic, the electrodeposition current supplied
to the
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plates
won't arrive to the liquid and will stop itself on the plate.
In this case, there will not be the silver recovery and there will also
be the precipitation of the bath.
The most common mistakes are the extension of recovering time and the
reduction of the ampere at the end of the working cycle. |
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