Recovery of silver from photographic films - by treating chopped film in large scale plant with fixing soln. to dissolve the silver, which is reclaimed by electrolysis

摘要

The films are chopped into small pieces and, if unexposed, are fed directly into at least one fixing bath; exposed films are first treated with a soln. pref. contg. 35 g/l CuSO4, 25 ml/l HCl and 80 g/l NaCl to convert Ag into soluble Ag salts remaining on the chopped pieces, which are then fed into the fixing bath. The fixing bath dissolves the silver, and is fed through at least one electrolysis cell for recovering the Ag by deposition on a cathode. The pref. plant can contain 500 kg chopped film and uses a main fixing soln., and a sec. fixing soln. which possesses a lower capacity for dissolving Ag, both solns. being subjected to electrolysis, to recover the Ag in separate cells. The fixing soln. contains e.g. 140 g/l ammonium thiosulphate, 25 g/l sodium metabisulphite, and 25 g/l Na2SO3. The plant pref. includes >=1 towers in which the chopped film is exposed to the fixing soln.