A process for the treatment and recovery of materials from the production and development of photographic and x-ray films. The process substantially includes the following operating stages: a first stage involving the shredding of the said materials; a second stage involving oxidation of the metallic silver to ionic silver; a third stage for solubilization of the silver salt in water; a fourth stage for the recovery of the metallic silver; a fifth stage for solubilization of the gelatin in an alkaline bath; a sixth stage for recovery of the gelatin; a seventh stage involving the washing, rinsing and drying of the polyester; an eighth stage for drying the polyester.
The present invention relates to a process for the treatment and recovery of materials from the production and development of photographic and x-ray films. In particular, it relates to a process for the recovery, by means of chemical/physical treatments, of the materials of which photographic films and x-ray plates are made, more precisely the recovery of silver, polyester, which forms the base of the photo-x-ray film, and the animal gelatin which coats one or both surfaces of the aforementioned polyester base.
The present invention, therefore belongs to the sector of industrial chemical processes designed to recover materials which, when recycled, are suitable for further use.
As is known, the recovery of materials from the production and development of photographic and x-ray films currently regards only the metallic part (including the oxidised form) of the said films, that is to say, silver. Obviously, this is due to the intrinsic value of the said metal.
The rest, that is to say, the polyester and gelatin, is currently discarded, this being an undoubted disadvantage from the economic (and environmental) viewpoint, considered that recycled polyester and gelatin have excellent possibilities for re-use. For example, polyester in the textiles sector, and animal gelatin as feed for the bacterial flora in purification plant.
In accordance with conventional techniques, the silver may be recovered using dry or wet systems.
The dry system envisages that the starting material, i.e.: photosensitive plates or films, be subjected to combustion. In this case, the silver evaporates or remains as an unburned base body, which may then be gathered. In contrast, the polyester and gelatin are lost.
As is known, the wet system envisages the use of developing and fixing baths. The fixing bath is used to extract the "superfluous" silver from the fixed silver.
The object of the present invention is, therefore, to recover all of the material, that is to say, the silver, polyester and animal gelatin.
A further object is to effect the said recovery in a relatively simple, low cost manner. These objects, together with others, are all fulfilled by the process for the treatment and recovery of materials from the production and development of photographic and x-ray films, the main characteristics of said process being described in the claims herein. Further characteristics and advantages of the present invention are more clearly illustrated in the following description of the process, by way of example only, and not limited only to the sector protected by the present patent right.
The following is an example of the process.
The material to be treated consists of a base which is a polyester film, coated on one or both surfaces with a gelatin of animal origin, in which metallic silver or silver salt is dispersed.
The material normally arrives in bales of waste or sheets, not yet exposed, or in the form of x-ray plates in envelopes.
The first step, which is manual, consists in undoing the bales and separating the plates from the paper. The film is then shredded in a special machine and reduced to pieces whose size is 0.3 - 3 cm2. It is essential that the material be shredded, in order to allow the completion of the chemical reactions which must take place on both surfaces of the film. Larger dimensions would promote adhesion of the surfaces, preventing completion of the reactions and reducing the overall efficiency of the process. In particular, recovery of the silver would be compromised.
The material containing metallic silver is then subjected to a "bleaching" action, that is to say, oxidation of the metallic silver to ionic silver. This action occurs in an aqueous bath, kept at ambient temperature (10 - 25 °C), containing: copper sulphate (to oxidise the silver); hydrogen peroxide (to re-oxidise the copper); sodium chloride (to provide a counter-ion to the silver ion). The reaction occurs at pH 0.5 - 3. Lower pH values could cause the gelatin to be detached; whilst higher pH values would make the bleaching action less effective.
The treatment time varies from 3 to 15 minutes: lower times would be insufficient to complete the reaction; higher times could cause the gelatin to be detached.
The use of copper as an oxidising agent is determined by process economy and final quality of the polyester recovered: other oxidising agents would be more difficult to remove and would, as a result, pollute the final product. The following are the concentrations of the reagents: copper sulphate 5 - 12 %; sodium chloride 5 - 15 %; hydrogen peroxide 0.1 - 1 %.
The material containing bleached silver, that is to say, silver salt, is then treated in a fixing bath containing sodium thiosulphate. During this stage, the silver salt contained in the gelatin, and insoluble in water, is solubilized by the presence of the thiosulphate.
The reaction occurs at pH 4.5 - 5.5; lower pH values would render the thiosulphate unstable, whilst higher values would slow down the extraction-solubilization of the silver salt.
The treatment time is 3 - 15 minutes at a temperature of 10 - 25 °C; the concentration of the sodium thiosulphate may vary from 50 to 200 g/l. The fixing solution, enriched with silver, is then sent to the electrolytic recuperator; once the silver has been deposited, the bath is put into circulation again.
The material - now consisting of polyester coated with gelatin - is sent to the gelatin removal tank, which consists of a bath containing sodium hydrate 5 - 25 % and is kept at 55 - 80 °C. The gelatin solubilizing process occurs within 5 - 20 minutes.
The polyester is then sent to the washing, rinsing and centrifugation plant.
Afterwards, it is dried until the residual humidity is 0.1 - 3 % and packaged according to market requirements.
Obviously, the practical execution of the process in question may be subject to procedural variations, although these are all encompassed by the scope of the present patent.
In particular, product washing stages may be envisaged upstream of those operating stages which require unpolluted products from the operating stage upstream.
Moreover, all components may be substituted with technically equivalent parts to meet the various requirements.