CS268732B1 - A method of treating a bleach fixer in photochemistry to regenerate it - Google Patents

Abstract

The solution consists in removing silver ions from the fixer by precipitating them with sulfide ions so that the precipitation is only carried out to the so-called protective concentration of silver in the fixer. This prevents the precipitation, separation or destruction of the remaining amount of effective fixer blocks. Their amount is then simply replenished to its original content by adding the appropriate chemicals.

Description

The invention relates to a method of treating a bleaching fixer in photochemistry for its regeneration. Bleaching fixers are used in color photography to convert microcrystals of metallic silver, which have precipitated in the developer (developing bath) on the colored material, back to silver halide (i.e. to the original form of silver present on the photo*, material), which is already soluble in a solution of thioethers. The actual bleaching is an oxidation-reduction reaction in which Ag° is converted into Ag* by means of an oxidizing agent which is part of the bleaching fixer.

The composition and ratio of individual substances in bleaching fixers varies. The presence of an oxidizing component · a complexing agent capable of dissolving the resulting silver halide in the bleaching fixer is crucial for the chemistry of silver. In some cases (reap. methods) oxidation and fixing are separated by two baths.

A variety of substances are used as an oxidizing agent in the bleach fixer: very often, sodium ferric chelate, ammonium ferric chelate are applied, other substances can be used, e.g. potassium hexacyanoferrate (red blood salt), potassium dichromate, ammonium dichromate and others.

The most commonly used complexing salt in bleaching fixatives is sodium thiosulfate or ammonium thiosulfate, which are capable of converting the resulting silver halide into water-soluble double salts of sodium silver thiosulfates of various compositions, e.g. 31^8^03, NagSgC^.Ag^SgC^, SHtgSgOj.31^8283, 3Η*2θ2®3· ,Ag ₂ S ₂ C ₃ and others.

In the bleaching process, the spent bleach fixer is discarded, the yield of which is around 408 to 588 ml per 1 m ² of the processed material and emerges from the developing process with a silver content of around 1 g/1, sometimes the silver concentration is significantly higher, the Ag content of 2 g/1 is no exception. In practice, the spent bleach fixer is poured into wastewater, which it contaminates with organic substances, high salinity, high content of sulfur substances (thiosulfates, sulfites, etc.), when the usual concentration is 160 g of sulfur substances per 1 liter; last but not least, contamination with ionic silver also occurs. Therefore, methods of its purification, utilization or regeneration come to the fore. A number of methods have been proposed for this purpose, but most of them have various disadvantages. When displacing silver from the fixer with powdered zinc, it requires a scarce raw material and, moreover, the fixer is no longer usable in photochemistry after this operation. After displacing silver with iron, the fixer can be used again and the displacing metal is more available, but the speed and efficiency of silver separation is low. When using ion exchangers, high efficiency is achieved, but high demands are made on the equipment (large volume of the ion exchanger * its difficult regeneration, expensive operation). Other procedures and possibilities of regeneration are based on dividing the bleaching fixer into two consecutive processes - bleaching (1st bath) and fixing (2nd bath). The first bath can be regenerated by supplying chemicals (although after regeneration they no longer reach their original efficiency), the second bath is most often subjected to electrolysis of silver thiosulfate complexes. During electrolysis, sulfur compounds are destroyed by anodic oxidation and the fixer is completely destroyed; When unusable residues are discharged, the wastewater is polluted again, ' ·

The above-mentioned shortcomings are eliminated by the method of treating a bleaching fixer in photochemistry for its regeneration according to the invention, characterized in that silver ions from the fixer are precipitated by sulfide ions in such a way that the precipitation is carried out only to such a residual concentration of silver in the fixer that, after separation of the silver sulfide precipitate, the fixer can be regenerated simply by replenishing the components depleted by its previous use.

^£ CS 268 732 Bl

The dosage of sulfide, or rather an aqueous solution of this sulfide (it is appropriate to use an aqueous solution of sodium sulfide) of known concentration, consists in measuring the sulfide solution and pouring it (slow pouring is appropriate) into a known volume of spent bleach fixer with a specified silver concentration and at a normal temperature of about 20 °C (a higher temperature is more suitable - the upper limit is determined by the thermal stability of the bleach fixer according to its chemical composition), and with constant stirring. The conditions for the precipitation of silver sulfide - slow pouring of the sulfide solution, increased temperature, constant stirring and after mixing the mixture affect the size of its entering particles and thus the ease of its separation from the bleach fixer solution. The precipitation of silver with the sulfide solution is carried out within a previously permitted limit of the residual silver content in the bleach fixer. The residual silver content serves as protection against oxidation-reduction ions of the bleaching fixer - most often Fe - from precipitation by sulfide. It is more advantageous and more efficient to allow a low residual silver concentration in the bleaching fixer (e.g. 0.05 g/1). If the dosage of the sulfide solution is determined by calculation, by a table of silver, it can be carried out in various ways. For example, by shot blasting, free sedimentation, filtration, etc., or by combining the above methods. Free sedimentation is considered a very advantageous method, when after sedimentation the bleaching fixer is sucked off through a filter candle (above the sediment) into a container where the bleaching fixer will be replenished for new use. The advantage of this case of separation lies in the low investment requirements and in the fact that the precipitation process can be repeated several times without cleaning the equipment until the amount of sediment is sufficient. Dried silver sulfide is then a suitable raw material for the production of silver. The bleaching fixer, free from the precipitated silver sulfide and containing silver in the vicinity of the permitted protective concentration (e.g. 0.05 g Ag/l), is supplemented with chemicals exhausted by its previous use (losses caused by dilution in the developing process, or caused by consumption during the actual photochemical process). These are usually amounts of 10 to 50% of their original weights in the bleaching fixer (depending on the type and method of developing). Finally, the pH is adjusted.

Advantages of the method according to the invention:

- silver is captured in the form of sulfide, which can be used as a raw material for metallurgical production of silver (the efficiency of silver extraction is around 90 to 95%)

- the costs of performing the precipitation operation are low

- separating the precipitate is simple and does not require complex technological equipment

- the consumption of treated water for the preparation of bleach fixers will be reduced by as many times as the number of regeneration cycles performed

- the laboriousness in handling chemicals for the preparation of bleaching fixatives is significantly reduced (around 30% of the weight), for substances of the thiosulfate type, the weight of which is the highest (for the preparation of bleaching fixatives), is reduced to up to 10% of the original weight when using the invention

- significant savings in chemicals required for the preparation of bleaching fixatives are achieved (chemical savings are around 70%)

- contamination of wastewater is avoided (or significantly reduced); wastewater is not burdened by high salinity of bleaching fixatives, sulfur substances and silver wicks.

Example

For 110 l of bleach fixer with the original composition (based on 1 l) 10 g of Chelaton 3, 10 g of sodium carbonate, 40 g of sodium ferric chelate, 4 g of sulfite

CS 268 732 Bl sodium, 1.5 g 1,4*-sulfophenyl-3,4 dimethyl-5-pyrazolone, 0.25 g 3-mercapto-1,2,4-triazole and 160 g sodium thiosulfate pentahydrate, after its use (silver content 1.8 Ag/1 1) 2.53 l of saturated sodium sulfide solution was added. Silver sulfide precipitated, with a residual silver content of 0.05 g.Ag/1. After separation of the precipitate by sedimentation, the liquid phase was sucked off through a filter candle and thus prepared for regeneration. This was done by adding 340 g of Chelaton 3, 60 g of sodium carbonate, 1360 g of sodium ferric chelate, 220 g of sodium sulfite, 160 g of 1,4'-sulfophenyl-3,4-dimethyl-5-pyrazolone, 8.5 g of 3-mercapto-1,2,4-triazole and 2200 g of sodium thiosulfate pentahydrate. The fixer regenerated in this way was further used in the photochemical process, where it provided the same results as the original fixer.

Claims (1)

A method of treating a bleaching fixer in photochemistry for its regeneration, characterized in that silver ions from the fixer are precipitated with sulfide ions in such a way that the precipitation is only carried out to such a residual concentration of silver in the fixer that it is possible, after separation of the silver sulfide precipitate, to regenerate the fixer by replenishing the components depleted by its previous use.