Chemistry of inorganic compounds – Sulfur or compound thereof – Binary compound
Patent
1992-08-05
1997-09-30
Lewis, Michael
Chemistry of inorganic compounds
Sulfur or compound thereof
Binary compound
423 37, 423 48, 4221863, 20415715, B01J 1912
Patent
active
056723288
DESCRIPTION:
BRIEF SUMMARY
REFERENCE TO RELATED APPLICATION
This results from a national stage application under 35 USC .sctn. 371, of PCT/DK/91/00038, filed Feb. 8, 1991.
1. Technical Field
The invention relates to a method for removing silver in the form of silver sulfide from a solution containing a silver thiosulfate complex in a photographic fix or rinsing fluid solution by means of preparation, which method comprises subjecting said solution to electromagnetic radiation with a wavelength of 375 nm or less.
2. Background Art
U.S. Pat. No. 4,088,552 discloses the conversion of silver thiosulfate complexes in a liquid into silver sulfide by irradiating a liquid by means of UV radiation or other high-energy radiation. Said patent specification discloses how by irradiation of the liquid with a relatively large amount of energy it is possible to precipitate silver sulfide as a solid matter which is subsequently removed by filtering. It is stated by way of example that by irradiating 50 g of fix solution with 1200 g UV radiation for 12 minutes 90% of the silver will precipitate. It is further described how by irradiating liquids containing silver thiosulfate complexes with electron radiation from a 0.3 to 2 MW accelerator an almost momentary precipitation of silver sulfide is achieved. None of the above methods are however suited for conventional use because of the very large amount of energy necessary to carry out the methods.
DISCLOSURE OF THE INVENTION
The object of the invention is to provide a method of the type mentioned above which enables a rapid and safe removal of silver compounds from a photographic solution while using only small amounts of energy.
The method according to the invention is characterised in that the liquid is irradiated with such an amount of energy that substantially no crystalline silver sulfide is formed and in that the irradiated liquid is passed through a filter-like means which binds the silver sulfide to its surface as crystalline silver sulfide. As a result, the silver sulfide is precipitated and deposited on the surface of the means as solid silver sulfide which in its turn acts as a catalyst for further precipitation and depositing of solid silver sulfide on the surface of the means. By binding the silver sulfide to the surface of the means, the required capacity of a possible subsequent filter is reduced.
A filter-like means is broadly to be understood as a means by which the relationship between the surface area in contact with the liquid and the flow area is large or expressed differently a means with a very large surface.
It has surprisingly been found that by irradiating a rinsing fluid containing silver thiosulfate complexes by means of UV light at for instance 254 nm and by using energy levels in the order of 1% of the levels stated in U.S. Pat. No. 4,088,552, the silver thiosulfate solution is substantially completely converted into an oversaturated solution of silver sulfide in which substantially no silver sulfide is found in solid form. Tests have thus shown that by filtering the irradiated liquid through a 1 micrometer filter immediately after the irradiation, substantially no silver sulfide will be removed by filtering.
Furthermore according to the invention the liquid may be filtered after having passed through the means. Crystalline silver sulfide, which has not been deposited on the means or which has been detached therefrom, is thereby removed from the liquid.
In addition, according to the invention the means may be formed of a granular or fibrous material. In practice said embodiment has proved especially advantageous for obtaining a very large surface.
Further according to the invention the means may be of glass. Said embodiment has proved particularly advantageous in practice, especially when the means comprises glass wool.
The apparatus according to the invention for carrying out the method according to the invention and which comprises a irradiation means adapted to irradiate a liquid by means of electro magnetic radiation to convert silver thiosulfat dissolved in the liq
REFERENCES:
patent: 3865714 (1975-02-01), Warner
patent: 4088552 (1978-05-01), Morrison et al.
patent: 4857204 (1989-08-01), Joklik
Eskofot A/S
Lewis Michael
Vanoy Timothy C.
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