Decomposition of Thiocyanates During Electrolysis

The fate of thiocyanate ion during electrolytic silver recovery operations was studied. The experimental conditions for these laboratory tests were chosen to simulate conditions that might be applied in the recovery of silver in the photographic industry. A photographic fixer solution spiked with a one molar concentration of ammonium thiocyanate was electrolyzed in a commercially available rotating cathode silver recovery cell at a current density of 20 mA/cm2. A low concentration of hydrogen cyanide gas (generally <1 ppm)was detected in the headspace of the electrolytic cell during the constant current electrolysis. Analysis of the fixer solution after electrolysis also confirmed the presence of cyanide in the liquid phase.