Abstract:
The present invention relates to a treatment method for treating effluents from a photographic development process, particularly a redox amplification (RX) development process, which is operated at an alkaline pH and is buffered with a phosphate buffer, said treatment method being characterized by the addition to the effluents of a Group II or Group III metal cation which forms an aqueous insoluble or substantially insoluble phosphate salt, thereby to precipitate phosphate salt from the effluent, and to reduce the pH of the effluent.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a treatment method for treating effluents from a photographic development process, particularly a redox amplification (RX) development process. The treatment method of the present invention can be applied to individual stages of the process separately, or the effluents from each stage can be combined together, and the treatment method applied to the combined effluents. 
     BACKGROUND OF THE INVENTION 
     At the time of writing, RX development processes are known in the photographic art but are not used commercially. They are particularly useful for processing colour photographic papers. In such processes, the photographic materials on which images are to be captured comprise silver halide emulsions which have significantly lower lay-down densities of silver halide as compared with silver halide emulsions used in conventional (non-amplified) development processes; for paper applications the silver halide normally employed is silver chloride. 
     Redox amplification processes have been described in GB-A-1268126, GB-A-1399481, GB-A-1560572, and GB-A-1403418. GB-A-1560572, for example, discloses silver coverages of up to 3.25 mg/dm 2 , preferably from 0.001 to 3.25 mg/dm 2  and more preferably from 0.01 to 1.6 mg/dm 2  for use in RX processes. 
     Cobalt(III) complexes have been used in RX processes to oxidise phenylenediamine colour developers in the presence of image-wise exposed silver halide grains. Although peroxy amplifiers were proposed as early as 1972 in GB-A-1268126, the inherent instability of hydrogen peroxide has meant that cobalt (III) has been the preferred oxidising agent until relatively recently. 
     It is well known that colour developers require for their operation alkaline conditions, and for this reason, hydrogen peroxide amplifier-developers for RX processes have been buffered as alkaline solutions using carbonate or bicarbonate buffers. More recently it has been found that the stability of hydrogen peroxide RX developer solutions is improved if their pH is increased to 11.0 or more. For this phosphate buffers may be employed. 
     Alkaline sulphite fixers and peroxide bleaches for use in conjunction with RX developers have also been disclosed in the prior art; see for example WO-A-90/13060 and WO-A-92/07300. 
     Whilst the disposal of photographic effluents containing hydrogen peroxide/phosphate is more acceptable from an environmental point of view as compared with the disposal of cobalt solutions, the former is undesirable in view of the alkalinity of the solutions as discussed above, and as bulk disposal of phosphates leads to eutrophy of lakes and other bodies of water at sewage outfalls. The concentration of phosphates in photo-effluents from the combined overflow of the tank can be up to about 6000 ppm (measured as phosphorus). 
     PROBLEM TO BE SOLVED BY THE INVENTION 
     Accordingly, there is a requirement for a treatment method for treating effluents from photographic development processes, including developer, bleach and fixer effluents, which method can significantly reduce the phosphate contents of the effluents and can also reduce the pH of the effluents to an acceptable level for disposal, towards pH 7.0. Furthermore it would be desirable for such treatment method to be susceptible of being employed as a single step, particularly as part of an automated photographic development operation. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention there is provided a treatment method for treating effluent from a photographic development process stage, particularly a redox amplification (RX) development process, which is operated at an alkaline pH and is buffered with a phosphate buffer, said treatment method being characterised by the addition to the effluent of a Group II or Group III metal cation which forms an aqueous insoluble or substantially insoluble phosphate salt, thereby to precipitate phosphate salt from the effluent, and to reduce the pH of the effluent. Thereafter the precipitate may be removed from the effluent. 
     According to another aspect of the invention there is provided a development method for the development of an image-wise exposed silver halide photographic emulsion comprising the steps of developing the emulsion, and thereafter bleaching and fixing, wherein at least one of the developing, bleaching and fixing stages comprises treatment with a phosphate buffered, alkaline treatment solution; characterised in that effluent from said at least one stage is treated using a treatment method in accordance with the present invention. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The present invention thus provides a treatment method for development effluents which can be used as a single step to reduce the pH of the effluents and to reduce the phosphates content thereof, so as to render the effluent more acceptable from an environmental stand-point for sewering in a public utilities sewerage system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The effluent treated may be from the developing, fixing or bleaching stages of a development process. In some embodiments the effluent from two or more of these stages may be combined and treated together. Preferably however the treatment method is carried out separately on at least the developer effluent. 
     The developer may have a pH in the range 9.0 to 14.0, preferably 10.0 to 12.0; for example a typical pH for an RX developer is 11.7. Said developer may be an RX type and in some embodiments include hydrogen peroxide as an oxidising agent for oxidising a phenylenediamine developing agent such as, for example, CD3 in the presence of image-wise exposed silver halide grains as catalyst. The high pH of the developer solution may assist in stabilising the solution. 
     The developing agent may be selected from p-phenylenediamines; typically the agent may be selected from: 
     4-amino N,N-diethylaniline hydrochloride, 
     4-amino-3-methyl-N,N-diethylaniline hydrochloride, 
     4-amino-3-methyl-N-ethyl-N-(2-methanesulfonamidoethyl)aniline sesquisulfate hydrate, (CD3) 
     4-amino-3-methyl-N-ethyl-N-(2-hydroxyethyl)aniline-sulfate, 
     4-amino-3-(2-methanesulfonamido ethyl)-N,N-diethyl-aniline hydrochloride and 
     4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonic acid. 
     As RX development processes are particularly suitable for print materials, the developing agent will typically be CD3. 
     The RX developer may contain from 0.5-10 ml/liter of 30% H 2  O 2 . Said RX developer may further comprise additional stabilising agents of the kind known in the art, including preservatives for protecting the peroxide from air or from premature reaction with the developing agent, and metal-sequestrating agents. 
     As preservatives may be employed one or more compounds selected from hydrazines, hydroxylamines, hydroxamic acids, oximes, nitrory radicals, hydrazides, phenols, saccharides, monoamines, dissines, tertiary amines, polyamines, quaternary ammonium salts, alpha-hydroxy ketones, alcohols, diamides and disulfonamides. The preferred antioxidants are hydroxylamine compounds, especially hydroxylamine itself. Many antioxidants are described in EP-A-0410375. The developer solution may also contain other compounds which increase its stability such, for example, as a long-chain compound which can adsorb silver, e.g. dodecylamine. 
     As metal-sequestrating agents may be used for example 1-hydroxyethylidene-1,1&#39;-diphosphonic acid which is a chelating agent for nickel and manganese ions or diethyltriamine-pentaacetic acid which chelates inter alia with iron ions. 
     The treatment method of the invention may also be used for treating separately the fixing or bleaching effluents. The bleach may be a peroxide bleach comprising typically hydrogen peroxide, and may be buffered with a phosphate buffer at an alkaline pH in accordance with WO-A-92/07300. 
     Said fixing solution may comprise an alkali metal sulphite fixing agent in accordance with WO-A-90/13060, and further in accordance with that disclosure the fix may be worked at a pH greater than 6.0, typically 9.0. 
     The phosphate buffer used in the invention may be any suitable buffering agent which is known in the art, but byway of example only may be an alkali metal hydrogen phosphate e.g. dipotassiumhydrogen phosphate. 
     Said Group II or Group III metal cation may be selected from any such cation which forms an insoluble phosphate, but will typically be calcium or aluminium. In some embodiments magnesium or strontium may be used. Of course it is desirable that the cation selected should be environmentally acceptable for sewering. 
     The cation may be added in the treatment method in the form of an aqueous solution. In particular soluble metal halide salts may be used, such as, for example, the chlorides, bromides or iodides; the chloride salts have been found to be particularly useful. Particularly preferred reagents are calcium chloride and especially aluminium chloride. 
     The amount of precipitating agent added to the effluents is selected to ensure precipitation of a substantial proportion of the phosphates in the effluents, and also to reduce the pH of the effluents to an acceptable level. Of course what is acceptable will depend on the environment where the effluents are to be sewered. Nevertheless, as a rough guide, the pH should be reduced below about pH 9.0, and after treatment the pH should preferably be in the range 5.0-8.0, typically about 7.0. 
     Generally, the concentration of phosphates in the effluents should be reduced below the 4000 ppm as phosphorus level, preferably below 3000 ppm and ideally below 1000 ppm. Typically, the treatment method of the invention may reduce the phosphates concentration of say an RX developer, having an initial concentration of about 6000.ppm phosphate, to about 700-800 ppm. 
     In a particular aspect of the invention the amount of cation added is selected to precipitate a desired proportion of the phosphate in the effluents and to reduce the pH of the effluents, without requiring any excess cation for either purpose. In other words, the amount added to reduce the pH to an acceptable level as described above should be about just enough to precipitate the required amount of phosphate, and vice versa. 
     Naturally the actual amount or volume of cation added will depend on the cation itself and, when used in solution, on the concentration of the solution used. Typically however up to about 50 ml of a 10-20% solution may be added per liter of effluent, preferably up to 20 ml and ideally 5-15 ml or an equivalent amount. 
     Following precipitation of the phosphate salt(s) in the effluent, the precipitate may be removed from the effluent in any convenient manner known to a person skilled in the art, such, for example, as by filtration or centrifugation. 
     Following is a description by way of example only of methods of carrying the present invention into effect. 
     An RX developer with the following formulation was made up: 
     
         ______________________________________Dipotassium hydrogen phosphate                     40.0   gHydroxylamine sulphate    1.0    gCD3                       4.5    gHydrogen peroxide (30%)   2      ml1-hydroxyethylidene-1,1&#39;-diphosphonic acid                     0.6    gDiethyltriamine-pentaacetic acid                     2.0    gWater to                  11pH adjusted to 11.70______________________________________ 
    
     To separate aliquots of 100 ml of this developer were added different treatment solutions as described in the table below. The mixtures were stirred for 10 minutes and then filtered. The level of phosphate was determined in the effluent filtrates by atomic absorption spectroscopy and the results included in the table. The pH of the final filtrate was also determined using a Radionmeter pH-meter fitted with a Corning glass electrode and a sleeved EIL reference electrode. 
     
         ______________________________________            Phosphate                     FinalTreatment        (ppm P)  pH______________________________________None             5960     11.70    Comp.Add 12 ml water  5315     11.69    Comp.Add 12 ml 20% aluminium            785      5.15     Inv.chloride solutionAdd 10 ml 10% calcium            3730     11.41    Inv.chloride solutionAdd 20 ml 10% calcium            2105     10.57    Inv.chloride solutionAdd 30 ml 10% calcium            585      7.40     Inv.chloride solutionAdd 20 ml 10% magnesium            413      11.06    Inv.chloride solutionAdd 40 ml 10% strontium            982      10.63    Inv.chloride solution______________________________________ 
    
     All treatments involving the addition of a group II or group III metal salt resulted in the reduction in phosphate content and could be used to reduce the phosphate in photo-effluent as described above. Simultaneously the pH was reduced. By a careful choice of the amount of addition considerable amounts of phosphate can be removed and at the same time the pH reduced towards more acceptable levels. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.