GB673058A - Regeneration of exhausted photographic silver bleaching solutions - Google Patents

Abstract

673,058. Regenerating photographic bleaching solutions. GENERAL ANILINE & FILM CORPORATION. Dec. 27, 1950 [Dec. 30, 1949], No. 31393/50. Class 98 (ii). An exhausted photographic bleaching solution containing an alkali metal ferricyanide, ferrocyanide ions, and an alkali metal bromide is regenerated by adding thereto an amount of either an alkali metal hypobromite, a mixture of an alkali metal bromate and hydrobromic acid in the molar ratio of 1 to 6, or a mixture of an alkali metal bromate and an alkali metal bromide in the molar ratio of 1 to 5 such that it will release one molar equivalent of bromine for each molar equivalent of ferrocyanide ion present in the exhausted bleaching solution. The regenerating mixture may also contain sulphamic acid or anhydrous alkali metal bisulphate, or may contain sulphuric acid. The bleaching solution may contain, in addition to the ferricyanide and bromide, a buffering agent such as a dialkali metal phosphate and a corrosion preventative such as an alkali metal tetraphosphate. In example 1, a solution of sodium hypobromite prepared by adding bromide to sodium hydroxide solution is added to an exhausted bleaching solution containing potassium ferricyanide and bromide, dibasic sodium phosphate, and sodium bisulphate. In example 2, potassium bromate and hydrobromic acid are successively added to the bleaching solution, in example 3 a mixture of potassium bromate and bromide followed by anhydrous sodium bisulphate, and in example 4, as in example 3 with the replacement of the bisulphate by sulphuric acid.