Patent ID: 6074812
Filing Date: 2000-06-13
Classification: G03C

Abstract:
In a method for desalting and dewatering a silver halide emulsion comprising removing soluble salts from the silver halide emulsion by electrodialysis, wherein said electrodialysis is carried out by passing a feed stream of the emulsion between an anion-exchange membrane and a cation-exchange membrane while a direct current voltage is applied between the anion-exchange and cation-exchange membranes so that ions are removed from the feed stream and transferred to a waste stream on the sides of the anion-exchange and cation-exchange membranes opposite to the feed stream,the improvement wherein a soluble salt is added to the waste stream at an initial higher concentration with respect to the feed stream so as to establish a concentration gradient between the waste stream and the feed stream which drives osmotic dewatering of the feed stream during electrodialysis.