Recycling silver from photo films
Extraction of silver from fixing baths and X-rays.
Photographic silver is contained in three recoverable sources: undeveloped silver halide film emulsions, used fixer baths (silver thiosulfate in solution) and medical and industrial X-rays.
The Fixer Bath: In a darkroom, used fixer contains 3 to 8g of silver per liter in the form of thiocyanate complexes. Recovery is by electrolysis (desilverization cell) or by chemical exchange with iron filings (cementation).
X-rays: A standard X-ray contains 0.3 to 0.8g of silver per sheet. Hospitals and radiological practices that destroy their archives represent significant deposits. Recovery is regulated — specialized companies (e.g., Retriev Technologies) buy these stocks.
Antique Silver — Refining Process: The nitric acid method is the most accessible in the workshop: dissolve the alloy in diluted HNO3 (1/3), precipitate the silver with sodium chloride (table salt) to form AgCl (white precipitate), filter, dry, and reduce to silver metal with zinc or by electrolysis.
Regulatory Warning: In Switzerland, the handling of nitric acid and effluent discharge are strictly regulated. Depleted acid baths must be handed over to an approved collector (SUVA lists certified companies by canton). Never pour down the drain.