RU2002835C1 - Process for recovering silver from spent photosolutions - Google Patents

Abstract

Use: relates to the recovery of silver from spent photographic solutions. SUBSTANCE: photographic solutions are treated with acid, heated and the precipitate is filtered, moreover, the mixture of photographic solutions taken in an arbitrary ratio is treated with mineral acid to form phte 1, the acidified solution is heated to 95-100 ° C and kept at this temperature for 30 minutes before filtration minutes With this invention, it is possible to bring into the circulation a mixture of various spent photographic solutions, taken in an arbitrary ratio of 1 table

Description

The invention relates to non-ferrous metallurgy, in particular to the recovery of silver from spent photographic solutions.

Known methods of processing spent photographic solutions fixer and bleaching-fixing.

According to the known method, silver is extracted from bleaching-fixing solutions by adding reducing substances to the solution: dithionites, halophosphites, borohydrites, hydrazine salts, hydroxylamine, semicarbazide, carbon monoxide. Then silver is cemented, for example with iron wire

1.

The disadvantage of this method is that fixative solutions, as well as sulfate fixative solutions from the treatment of reversible black-and-white film, are excluded from the scope of its application. In addition, the method involves the use of scarce, expensive reducing agents, many of which are also toxic compounds.

According to the method, silver is removed from fixative solutions, as well as from bleaching-fixing solutions for color photo paper: Orvocolor, Agfacolor and NIKOI, by introducing a sulfur-containing precipitant, formamidindi sulfinic acid, into the solution and heating the solution to 95-100 ° C. 2.

The disadvantage of this method is that sulfuric acid fixative solutions from the treatment of reversible black-and-white photographic films, as well as the use of a scarce and expensive reagent, formzmidine disulfinic acid, which is a product of the mild oxidation of thiourea (thiourea), are excluded from its scope of application.

Closest to the proposed method is the extraction of silver from spent fixative solutions by treating them with a mixture of nitric and sulfuric acids, taken in a ratio of 1: 1 in volume in an amount of 20 ml per 1 liter of solution (Rabah MA, El Barawy KA, Aly FH / Int. I. Miner. Process. - 1989. - 26, No. 1-2 - C. 17-27. Storage location of the SPSL USSR).

The disadvantage of this method is the narrow scope of its application - only for fixative solutions, as well as the need for the joint use of two reagents: nitric acid - an oxidizing agent and sulfuric acid, which are also taken in a strictly specified ratio.

The essence of the method is that it is possible to extract silver by processing a mixture of spent photographic solutions of any type, taken in an arbitrary ratio, by acidifying the mixture of photographic solutions with any strong mineral acid (or mixture of acids) to a pH value of 1 (for example, in the case of sulfuric acid, this corresponds to its concentration of 30 g / l), followed by exposure at a temperature of 95-100 ° C for 30 minutes.

Bringing the acidity to pH 1 creates the necessary conditions for the intraspheric decomposition of thiosulfate

ligand in the inner sphere of silver. The temperature of 95-100 ° C provides the most rapid and quantitative course of acid hydrolysis of silver thiosulfate complexes under the conditions of the presence in the solutions of complexing components, for example, chelates, derivatives of ethymidiamine polyacetic acid. Temporary exposure for 30 minutes provides the maximum degree of acid hydrolysis of silver thiosulfate complexes.

The use of strong acids is due to their high degree of acid dissociation, i.e., the largest in comparison with

acids of medium strength by the formation of hydrated hydrogen ions per unit mass of acid. Together, these distinguishing features create the necessary and sufficient conditions for

recovering silver from a mixture of spent photographic solutions of any type taken in an arbitrary ratio.

The chemical essence of the method lies in the high temperature acid

hydrolysis of the silver thiosulfate complex quantitatively proceeding under the catalytic effect of hydration of other hydrogen ions.

The proposed method is carried out on

pilot plant.

The results of testing by the known and proposed methods are shown in the table.

For testing, a mixture of spent photographic solutions is used: fixative, bleaching-fixing and sulfate fixative solution for reversible black and white film, which are taken in a ratio that corresponds to their real

education. As the mineral acid, the most affordable and cheap sulfuric acid is used.

PRI me R. 4.0 liters of concentrated sulfuric acid (density - 1.83 kg) are added to 222 l of a mixture of solutions: fixative, bleaching-fixing and fixative sulphate, taken in a ratio of 10: 1: 0.1 and containing 3.33 g / l of silver / l), the pH of the solution is 0.95. Next, the solution is heated in an indirectly heated reactor to a temperature of 98 ° C and maintained at this temperature for 30 minutes. After cooling the solution to 60 ° C, the latter is filtered off on a suction filter. The residual silver content in the filtrate was 40 mg / L. The precipitate accumulated on the suction filter is a silver sulfosulfide concentrate (silver content in terms of dry weight is 21.0%).

Using the proposed method makes it possible to involve in the processing industry the currently untreated bleaching-fixing solutions from the processing of color photographic paper, as well as sulfuric fixative solutions from the processing of reversible black-and-white film.

(56) UK patent No. 1371568. cl. In 1 C, 1974.

USSR copyright certificate No. 1249471.cl. G 03 C 11/24, 1986.

Rabat M.A .. El. Barawy K.A. Aly F.H. Int I Miner Process, 1989.

Claims (1)

The claims METHOD FOR REMOVING SILVER FROM WASTE PHOTO SOLUTIONS, including treating them with acid and heating, filtering the precipitate, different by treating the photo-solutions with mineral acid to create a pH of 1. The acidified solution is heated to 95 - 10 ° C, held at this temperature for 30 minutes and then filtered.