Silver bleach baths regeneration - by oxidising ferrocyanide complexes with hydrogen peroxide, using ruthenium/osmium catalyst

摘要

Fe(II) cyanide complexes in spent photographic Ag bleach baths are oxidised by treating the baths with H2O2 at pH above 5 in the presence of Ru or Os or their cpds. This process makes it possible to regenerate the spent baths without changing the pH value, which pref. is 5.5-8. Suitable reagents are H2O2 and its addn. cpds., e.g. 2Na2CO3.3H2O2 or NaBO2.H2O2.3H2O and, as catalyst, RuCl3, OsO4 and Ru on a carrier, e.g. active C, SiO2 or pumice. The H2O2 requirement is easily determined from the redox potential of the bath. The process can be operated batchwise or continuously.