SILVER EXTRACTION FOR POLLUTION-CONTROL OF PHOTOGRAPHIC FIXING SOLUTION WITH TETRAMETHYLTHIURAM DISULFIDE

Silver recovery from photographic fixing solutions can be performed by solvent extraction with thiuram disulfides. Tetramethylthiuram disulf ide (TMTDS) was selected for further studies because it had the highes t distribution ratio among the three extractants. Its selectivity for silver extraction from a thiosulfate medium and from an analytical pho tographic fixing solution were evaluated. A 1:1 silver(I)-TMTDS comple x is formed. For a one-stage and one-hour silver(I) extraction process , a 96% recovery was obtained from an analytical fixing solution conta ining 1 gdm(-3) silver(I), starting with a 0.02 M (1 M=mol dm(-3)) TMT DS solution. The possible extraction mechanism involves the reduction of TMTDS in the presence of thiosulfate ions, followed by chelation of the silver(I) with the reduced TMTDS. Effective stripping can be perf ormed by using 3 M hydrochloric acid. By dilution of the fixing soluti on with water (1 :1), and the use of 0.1 M TMTDS, recycling of the org anic phase between the extraction and stripping stages for silver extr action can be achieved in a few times. The results for the analytical solutions were further shown to be applicable to a black and white pho tographic industrial solution.