N. Sathaiyan et al., Simultaneous electrolytic recovery of silver from spent fixer solution andregeneration of bleach solution, T I INST ME, 51(5), 1998, pp. 393-398
In colour photography, the film is first treated with bleach solution so th
at the reduced silver is oxidised to soluble silver ion which is subsequent
ly dissolved in sodium thiosulphate bringing all silver into the solution.
During bleaching, the wferricynanide bleach is reduced to ferrous state aff
ecting its efficacy leading to its disposal. Similarly the build up of silv
er concentration in the thiosulfate complex also leads to its rejection. Th
e disposal of large quantities of chemicals not only poses environmental ha
zard but also loss of valuable chemicals. This necessitates the recovery of
silver From thiosulfate complex and regeneration of bleach solution which
facilitate the recycling of the regenerated bleach and fixer solution in th
e system, thereby avoiding the pollution problem.
Even though various methods are available for the recovery of silver and re
generation of bleach, electrolytic method offers the advantage of not alter
ing the composition of solution and totally avoiding the use of unwanted ch
emicals, thereby making the solution suitable for efficient reuse.
In this paper an attempt has been made to recover silver at the cathode and
regenerate bleach solution at the anode by the adoption of a divided cell
configuration. It was observed that electrolytic production of two useful p
roducts one at the cathode and the other at the anode simultaneously reduce
s the electrical energy requirements by half in comparision to the power re
quirement of individual electrolytic process.