Barbara B Booker

US Patent:

50858360, Feb 4, 1992

Filed:

Dec 3, 1990

Appl. No.:

7/620890

Inventors:

Barbara T. Booker - Spartanburg SC

Assignee:

E. I. du Pont de Nemours and Company - Wilmington DE

International Classification:

C22D 1104

US Classification:

423 34

Abstract:

A method to reduce dissolved silver present in spent, waste, photographic processing fluids containing thiosulfate, is described. This process involves adjusting the pH to a low level prior to the addition of finely ground steel to the solution. With the pH at the low level, e. g. 2. 5, the reaction of dissolved silver to precipitated silver, is facilitated. However, the pH must then be raised or neutralized, e. g. 7-8. 5, in order to insure that the dissolved silver is essentially all precipitated. This material can now be safely shipped without treatment as a hazardous material and, after filtering the solids therefrom, can be safely disposed.