Simultaneous electrolytic recovery of silver from spent fixer solution and regeneration of bleach solution

In colour photography, the film is first treated with bleach solution so that the reduced silver is oxidized to soluble silver ion which is subsequently dissolved in sodium thiosulphate bringing all silver into the solution. During bleaching, the ferricyanide bleach is reduced to ferrous state affecting its efficacy leading to its disposal. Similarly the build up of silver concentration in the thiosulfate complex also leads to its rejection. The disposal of large quantities of chemicals not only poses environmental hazard 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 the system, thereby avoiding the pollution problem. Eventhough various methods are available for the recovery of silver and regeneration of bleach, electrolytic method offers the advantage of not altering the composition of solution and totally avoiding the use of unwanted chemicals, 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 products one at the cathode and the other at the anode simultaneously, reduces the electrical energy requirements by half in comparison to the power requirement of individual electrolytic process