Process for processing spent photographic baths

Details Process for processing spent photographic baths Process for processing spent photographic baths

1997-05-15

1999-01-26

Woo, Jay H.

Liquid purification or separation

Processes

Making an insoluble substance or accreting suspended...

210721, 210724, 210726, 210759, 210767, C02F 120

Patent

active

058634428

ABSTRACT:
A process for the processing of spent photographic baths of black and white processes, namely developing baths with a preponderant content of alkali sulphite, particularly sodium sulphite, and fixing baths with a preponderant content of thiosulphates, particularly ammonium thiosulphate and/or sodium thiosulphate is proposed and is characterized in that following the deposition of the silver contained in the baths, the spent fixing baths are brought to a pH of approximately 0.5 with concentrated HCl and the elementary sulphur resulting from the decomposition of the thiosulphates is separated, whilst the remaining sulphurous acid intermediate solution is mixed with the spent developing baths and adjusted to a pH of approximately 2 and the resulting, SO.sub.2 -supersaturated solution is heated and pure SO.sub.2 is drawn off in a vacuum. Finally, the residual solution is adjusted to a pH of approximately 10 with Ca(OH).sub.2 and the liberated ammonia is drawn off.

REFERENCES:
patent: 3829549 (1974-08-01), Anderson et al.
patent: 4755453 (1988-07-01), Kunda et al.
patent: 4874530 (1989-10-01), Kobayashi
patent: 5085836 (1992-02-01), Booker
patent: 5160417 (1992-11-01), Neale
WPI Database section Ch, week 9527, Derwent Publications Ltd. Class D15 An 9 XP002036614 & JP 07 116 670 Ko Eng KK May 9, 1995.
WPI Database section CH, week 7626, Derwent Publications Ltd Class D15 AN 76-48533X XP002036615 & JP 51 052 666 (S. Inoue) May 10, 1976.

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