United States Patent (19) [11] 3,912,514 Bulloch et al. (45) Oct. 14, 1975

54) METHOD OF REGENERATING ASPENT OTHER PUBLICATIONS PHOTOGRAPHIC SILVER BLEACH Def. Pub. T878,007, Walsh, 9-8-1970. SOLUTION Treatise on Inorg. Chem. by H. Remy. Vol. 1, 1956, (75. Inventors: David K. Bulloch, Hillsdale; Ronald pp. 810-81 l. A. Klein, Palisades Park, both of N.J. Primary Examiner-Mary F. Kelley 73 Assignee: Philip A. Hunt Chemical Attorney, Agent, or Firm-Kirschstein, Kirschstein, Corporation, Palisades Park, N.J. Ottinger & Frank 22 Filed: May 21, 1973 57 ABSTRACT 21 Appl. No.: 362,243 In a spent photographic silver bleach solution the ratio of ferrocyanide to ferricyanide has attained a value at 52) U.S. Cl...... 96/60 R; 96/50 A; 423/367 which the efficacy of bleaching is so greatly impaired I51) Int. C.’...... G03C 5/32; CO1C 3/12 that the solution must be either discarded or regener 58 Field of Search...... 96/60 R, 50 A; 423/367, ated. According to the present disclosure, regenera- . 423/473, 472; 252/186, 187 R tion is accomplished with an alkali metal halite that reacts with the ferrocyanide to oxidize it to a ferricya 56) References Cited nide. The reaction takes place at a pH between about UNITED STATES PATENTS 6 and about 8. An acid preferably is present to pre 2,515,930 7/1950 Seary...... 96/50 A vent the reaction conditions from becoming so alka 2,61 1,699 9/1952 Zappert...... 96/50 A line as to materially inhibit the oxidation. 2.6 t 1,700 9/1952 Brunner...... 96/50 A 8 Claims, No Drawings 3,770,437 1 1/1973 Brugger et al...... 96/60 R 3,912,514 2 METHOD OF REGENERATING ASPENT cessity for regeneration long has been recognized in the PHOTOGRAPHIC SILVER BLEACH, SOLUTION photographic art and the specific regeneration of ferro cyanide to ferricyanide has been practiced for many BACKGROUND OF THE INVENTION years. 1. Field of the Invention At one time, an electrolytic method was employed Regeneration of a spent photographic silver bleach for this purpose, but because of its high maintenance solution. costs and operational problems it was abandoned. 1. Description of the Prior Art A number of chemical agents have been proposed to Bleach solutions are widely used in certain branches oxidize ferrocyanide to ferricyanide. Thus, liquid bro of photography. They are employed to remove metallic O mine is disclosed for this purpose in U.S. Pat. No. silver grains from an emulsion in which they were 2,515,930. But bromine is caustic and corrosive and, formed by development of exposed particles of silver hence, great caution must be exercised when it is em halide. Typically, the bleaching is performed in color ployed. As a variant of the bromine oxidation it has film processes to remove metallic silver grains the pres been proposed to use bromine releasing agents as, for ence of which is necessary to permit the formation of 15 example, those disclosed in U.S Pat. No. 2,61 1,700 for colored dye images, and in reversal black and white this purpose. Also, the use of hypobromides or mix processes to remove the silver grains which formed the tures of bromate ions and hydrobromic acid have been negative image prior to the re-exposure of film for ac disclosed as in U.S. Pat. No. 2,61 1,699. None of these tinically sensitizing the remaining particles of silver hal methods has found wide application, either because of ide. The purpose of bleaching is to convert the metallic 20 the caustic and corrosive nature of the compounds or silver into a silver salt which thereafter is made water the bromine released or because of their high cost or soluble by fixation (treatment with thiosulfate) and because of the involved manipulation required. subsequently removed from the film by washing with Recently ozone oxidation has come into commercial water. Although the conversion of metallic silver to the usage (see T. W. Bober and T. J. "The Regeneration of silver salt occurs in several steps the particular reaction 25 Ferricyanide Bleach Using Ozone" - Parts I and II, is not important to the discussion of this invention and, Image Technology, Vol. 14, No. 4-p. 13; No. 5-p. 19 therefore, only the overall simplified ionic equation is (1972)). The article describes large scale regeneration given below: trials on Process CRI-1 and Process K-12 bleaches using ozone, and suppliers of complete factory-built Fe(CN) + Ag+ Br - AgBr -- Fe(CNs' 30 systems for bleach regeneration are given. However, A commonly and widely used bleach solution con there is a difficulty with the ozone oxidation in that the tains as the oxidizing agent an alkali metal ferricyanide equipment used for generation of ozone has a high ini and an alkali metal bromide to effect the reaction tial capital cost and a high operation cost. Moreover, above given, and usually other ingredients such as generation of ozone is inefficient in terms of energy bleach accelerators (see, for example, British Pat. No. 35 conversion. Still further, the formulations for ozone 1,150,466), buffers (see, for example, U.S. Pat. No. generation are rapidly being changed so that often gen 3,342,598), corrosion inhibitors (see, for example, erating equipment is obsoleted before its initial cost British Pat. 872,275), anti-sludge agents, and biocides can be fully amortized. (see, for example, British Pat. 1,177,048). The particu Another approach to the regeneration of ferrocya lar constitution of the bleach solution is of no particular 40 nides has been by the use of peroxides and per-acids, importance to the present invention as long as it con but in such cases the bleach must be made very acidic tains ferricyanide which is in part reduced to ferrocya for the reaction to proceed rapidly and to completion. nide during the bleaching process. As just implied, the The high acidity results in undesirable side reactions ferricyanide oxidizes metallic silver to silver in its ionic and unduly complicates the regeneration of ferricya form which thereupon reacts with the bromide ion to 45 nide. form the sparsely soluble silver bromide. As the ferricy At the present time the most widely practiced anide oxidizes the metallic silver, the ferricyanide itself method for converting ferrocyanide to ferricyanide uti is reduced to ferrocyanide. lizes a water-soluble persulfate as the regenerating Ferrocyanide accumulates in the bleach solution. agent. The latter method has several advantages. Capi The decrease in ferricyanide and the corresponding in 50 tal outlay is low, the method is relatively safe and it is crease in ferrocyanide gradually impairs the efficacy of simple to use. However, it suffers several drawbacks, the bleach until finally a point is reached where the so the most serious of which is the formation of sulfate lution no longer is commercially effective and either ions as a by-product of regeneration. These ions reduce must be discarded or it must be regenerated. the efficacy of the bleaching action of the ferricyanide At this point there still is a preponderance of ferricy 55 on metallic silver grains, the reduction being so serious anide. It is only the ferrocyanide which must be regen that after four or five regeneration cycles the bleach erated by converting the same back to ferricyanide. has to be discarded. It is not currently feasible to inex The actual ratio between the two cyanides has no bear pensively remove the sulfate ions so as to restore the ing upon the use of the present invention and, indeed, usefulness of the bleach. As the sulfate ion concentra the limiting ratio beyond which the solution should not 60 tion increases, saturation eventually is approached and be used will depend upon various other factors such, in some portions of the system, e.g. a tank, or in some for example, as the solution temperature and the of the lines, crystallization occurs. To avoid this, users bleach accelerators employed. Mention has been made of persulfate for silver bleach regeneration frequently of the spending of ferricyanide simply in order to un 65 discard a portion of each batch of recycled bleach and derstand the manner in which the ferrocyanide came replace it with an equal volume of sulfate-free bleach. into being and the necessity of restoring ferrocyanide Typically, the loss incurred in 10% or more of an aver to ferricyanide when the occasion requires. Such ne age recycled volume of bleach. Perhaps a more impor 3,912,514 3 4 tant consequence of a high sulfate concentration in the the spent photographic silver bleach solution being re bleach is the necessity for a higher equilibrium concen generated. To prevent these two alkalizing effects, it is tration of ferricyanide than would be necessary if sul desirable to compensate for the rise in pH by including fate ions were not present. A cursory comparison of an acid in the regenerating reaction. Any acid is useful sulfate-free with sulfate-containing bleaches indicates 5 for example, a 10% water solution of an orthophos that the ferricyanide concentration for a sulfate-ion phoric acid. A preferred acid is hydrobromic acid be free bleach for an equivalent rate of bleaching is about cause it does not add any extraneous ions to the system 30% less than for a bleach containing a saturation and, indeed, provides a bromide ion which is useful in quantity of sulfate ions. the system. Also involved in connection with ferricyanide silver O It is of passing interest to observe that the same reac bleaches and in which the spent bleaches contain ferro tion, which essentially is an oxidation of the ferrocya cyanide as well, and which, for example, with the per nide constituent of the spent photographic silver sulfate regenerating process require discarding of bleaching can be used for the manufacture of an alkali bleach fractions to keep the sulfate ion concentration metal ferricyanide starting from an alkali metal ferro at an acceptable level, is that economic and conve 15 cyanide, or as a method of preparing a fresh ferricya nience factors are not the only governing consider nide bleach starting with a composition including an ations as they once were. In the present day, the de alkali metal ferrocyanide as all or part of the amount mands of ecology require that pollution be kept to a of cyanide eventually desired to be present as a ferricy minimum. Ferricyanide and ferrocyanide can decom anide. pose to form cyanide when such solutions are dumped 20 The invention consists in the series of steps which will either into a sewer or a running or quiescent body of be exemplified in the method hereinafter described and water. Due to the large concentration of these ions in of which the scope of application will be indicated in bleach effluent, maximum allowable cyanide concen the appended claims. trations which represent the limits for the sewer codes in many municipalities are exceeded far too easily, so 25 PREFERRED EMBODIMENT OF THE INVENTION that given the present state of affairs, pollution abate A spent photographic bleach solution, this being a ment has become the deciding factor and regeneration solution in which the amount of ferrocyanide is great is often the only acceptable alternative. enough, as is well known, to reduce the rate of bleach SUMMARY OF THE INVENTION ing to an unacceptable level, is regenerated in accor-. 30 dance with the present invention by treating such a so 1. Purposes of the Invention lution with a water solution containing an alkali metal It is an object of this invention to provide for regener halite, preferably in the presence of an acid, desirably ating spent photographic silver bleaching solutions a a mineral acid, and most desirably hydrobromic acid so method which avoids all the foregoing drawbacks. as not to unnecessarily introduce extraneous ions into It is another object of the invention to provide a 35 the bleaching solution. The regenerated bleach formed method of the character described which will regener is substantially equivalent to the fresh bleach of a like ate spent ferricyanide/ferrocyanide-containing photo composition. By selecting a preferred halite, to wit, a graphic bleaching solutions with a low capital outlay bromite, and a preferred acid, undesirable foreign ions and low maintenance costs, and with an ability to be are not added to the bleach solution, minimum time is operated by personnel of low skill. 40 required for completion of the regeneration, the regen It is another object of the invention to provide a eration is relatively safe and inexpensive and the method of the character described which can be prac method virtually eliminates bleach overflow disposal ticed economically and safely and, withal, is rapid and problems. The presumed overall ionic reaction is: efficient. 45 Other objects of the invention in part will be obvious BrO +4Fe(CN)4+2HO - 4Fe(CN) --Br +' and in part will be pointed out hereinafter. 4OH 2. Brief Description of the Invention In accordance with the present invention, a spent Experimental evidence suggests a two-step reaction photographic silver bleach solution is regenerated by 50 expressed ionically as follows: reacting such solution with an alkali metal halite to oxi dize ferrocyanide ions to ferricyanide ions. The desired BrO +4Fe(CN) + HO - BrO +4Fe(CN) + halite is a bromite. The reaction proceeds best at a pH in the neighborhood of neutrality. More specifically, it 2OH. BrO--- HO-> Br- 2CH will proceed rapidly and apparently stoichiometrically 55 between a pH of about 6 and a pH of about 8. It has The conversion of ferrocyanide to ferricyanide pro been observed that at a pH of above 8.5 the regenerat ceeds quite rapidly and apparently stoichiometrically ing reaction approaches a standstill. between a pH of about 6 and a pH of about 8. The oxidation reaction of the halite on the ferrocya To practice the conversion of an alkali metal ferrocy nide ions generates hydroxyl ions which tend to raise 60 anide to an alkali metal ferricyanide, pursuant to the the pH of the solutions beyond the acceptable range. instant invention there is added to an aqueous ferrocya Moreover, sodium bromite is not considered stable nide solution a stoichiometric amount of bromite, for enough to store in dry form. It can decompose violently example, in the form of sodium bromite. As indicated on contact with organic matter and acids, so that for previously, the sodium bromite which is a very strong safe handling it is customary to ship it diluted in a dilute 65 oxidizing agent is not sufficiently stable to be safely aqueous solution of sodium hydroxide, for instance, at stored dry and, therefore, is supplied commercially as 3.5% sodium hydroxide water solution containing an alkalized dilute water solution of sodium bromite, about 6 to 8% of sodium bromite. This, too, therefore, for example, a 6 to 8% sodium bromite water solution is strongly alkaline and tends to raise further the pH of containing 3.5% sodium hydroxide. Such a solution is 3,912,514 S 6 commercially available from Olin Corporation under in mind the quantity and constitution of the buffering the trademark “Preptone'. Where such a stoichiomet agent which is present in the bleach being regenerated. ric amount of bromite is added to an unbuffered ferro For example, if the bleach being regenerated contains cyanide solution and the pH is adjusted to neutrality a phosphate buffer system therein, the preferred acid with hydrobromic acid, the conversion of ferrocyanide utilized in the regenerating system of the present inven to ferricyanide is essentially complete within about 15 tion for the neutralization of excess alkalinity desirably minutes. It has been observed, however, that the pH of would be orthophosphoric acid. Another desirable acid the regenerated solution rises and continues to rise for use for the foregoing purpose is hydrobromic acid. up to about 6 hours, suggesting that the first-mentioned The following example has been set forth to aid in un reaction of the above twostage reaction is rapid and the 10 derstanding the use of the present invention. second one is slow. A typical standard photographic bleach for the The invention is practiced in connection with a pho bleaching of color reversal film has the following for tographic ferrocyanide/ferricyanide spent bleach solu mula: tion by adding to such a spent solution wherein the 15 amount of ferrocyanide has previously been ascer Potassium ferricyanide 56 g tained a stoichiometric amount of bromite, again in the Potassium bromide 16.5 g form of sodium bromite, e.g. supplied as "Preptone,' Sodium phosphate 22g Water to one liter and again adjusting the pH to between about 6 to about pH 6.90 8 with hydrobromic acid. The amount of hydrobromic acid employed will depend upon the specific composi 20 This bleach was used to replace the conventional tion of the particular bleach solution and the degree of bleach used in the Ektachrome E-3 process. The above its exhaustion. formula gave photographic sensitometric results equiv Where a buffered bleach is regenerated the pH rise alent to those employed with the replaced formula. The is greatly depressed, that is to say, does not rise as rap film used was Ektachrome sheet film. The aforesaid idly as where the method is practiced with an unbuf 25 film after having been exposed in a camera was pro fered ferrocyanide solution, and the recorded pH cessed at a rate of 2 square feet per gallon per process changes usually are complete within approximately 30 cycle using conventional solutions that are employed in minutes. The conversion of the ferrocyanide ions to the Ektachrome E-3 process except for the bleach solu ferricyanide ions is complete within 10 minutes or less. tion which was replaced, as just indicated, with the The invention may be used with any of the conven 30 above solution. All other solutions were replenished in tional ferricyanide bleach solutions that commonly are accordance with Eastman Kodak instructions which used for photographic processing such, for example, as are standard and well known in the art. those employed in color film processing for the bleach After eight process cycles, which is the equivalent of ing step and those employed in reversal black and white approximately 17 square feet of film per gallon of the processing for the bleaching step. These bleaches typi 35 substituted bleach, the bleach was analyzed and there cally include aqueous solutions containing an alkali after regenerated with the aforesaid sodium bromite metal ferricyanide such as potassium ferricyanide (Ka solution ("Preptone' which has been described ear Fe CNJ), sodium ferricyanide (Naa Fe (CNJ), lith lier). A certain amount of dilution occurred from wash ium ferricyanide (Lia Fe (CN)6) or ammonium ferricy water carried over from the processing step previous to anide (NHa Fe CNs), and an alkali metal bromide. 40 the bleach step; such dilution losses were made up be Mixtures of these ferricyanide salts also may be used. fore or after each regeneration by adding potassium As mentioned above, the alkaline halite salts usable ferricyanide and potassium bromide and the pH was in the instant regeneration process are not available or adjusted during each regeneration with orthophos safe in dry form but they are commercially available as phoric acid. aqueous solutions thereof, usually dilute aqueous solu 45 The aforesaid sequence was repeated until 47 square tions, typical solutions having from about 6% to about feet of film per gallon of bleach had been processed; 8% of the halite salt dissolved therein. Such is the case this, of course, included intermediate regeneration with sodium bromite which is the desired halite of this steps with sodium bromite solution. invention. Moreover, for the purpose of maximizing the The following table is a summary of the chemical chemical stability of alkali metal and sodium halites, it 50 composition of the bleach at the various processing is customary to make such solutions very alkaline, e.g. stages: with sodium hydroxide, a typical amount of sodium hy droxide employed being 3%% by weight. Such com Potassium Potas mercially available halite aqueous solutions are quite 55 Potassium Ferricyanide sium satisfactory for use in connection with the method of Ferri- added to make Bro the present invention. cyanide up for dilu- mide The excess alkalinity of the available commercial so (g/l) tion (g/l) (g/l) lutions, as well as the alkalinity produced during the Start 56.0 16.5 Before first regeneration 38.3 9.4 course of the reaction, which tend to raise the pH of the 60 After first regeneration 55.5 16.2 reacting solutions to above 8 this being in excess of the Before second regeneration 4.0 9:6 After second regeneration 56.8 17. range at which the change from ferrocyanide to ferricy Before third regeneration 46.5 7.5 anide proceeds rapidly, can be and, pursuant to the After third regeneration 56.3 17.9 present invention, is offset with either a mineral acid or an organic acid or an acid buffering agent. Inasmuch as conventional ferricyanide bleaches normally contain 65 The pH of the bleach was adjusted to 6.9 + 0.1 during buffering agents to control the pH of the bleach, the Se and after each regeneration. Sensitometric gray-scale lection of the neutralizing acid should be done bearing control strips were processed with each process cycle 3,912,514 7 8 and, other than normal run-to-run variability, no signif 0.1 mg) to one liter in a 2% sodium bicarbonate solu icant density differences occurred during the course of tion of distilled or deionized water; and a reagent grade the test. The dye maximum density area of the control potassium persulfate solution prepared by diluting 1.2 strips were also read on a Westrex RA 1 100B sound g. of potassium persulfate to one liter with a 2% sodium densitometer and no significant differences in density bicarbonate solution of distilled or deionized water. readings appeared over the duration of the test. Chemi The method for analyzing for potassium ferricyanide cally, the bleach at the end of the regeneration series constitutes diluting the spent bleach sample in two was essentially the same as at the beginning of process steps, the first of which consists in pipetting 3 ml. of the ing with no build-up of interferring foreign ions. sample into a flask and diluting to 100 ml. with the 2% The quantitative details of the aforesaid example in 10 sodium bicarbonate solution; the second step consists cluded first assaying the sodium bromite solution. in pipetting 5 ml. of the resulting dilute solution into a Commercial sodium bromite solutions contain 60-80 flask and diluting a second time to 100 ml. with the 2% grams per liter of active ingredient and 32-34 grams sodium bicarbonate solution. The absorbance of the per liter of sodium hydroxide; the carrier is water. twice-diluted spent bleach sample is read on the spec These solutions are moderately stable but should be an 15 trophotometer at 420 nm. using a 10 mm. cuvette and alyzed for bromite prior to use because some decompo using the 2% sodium bicarbonate solution as a blank. sition may occur. The absorbance of the standard potassium ferricyanide Materials used to analyze for bromite are: a water so solution is read in a similar manner, i.e. after double di lution of a reagent grade potassium iodide prepared by lution as aforesaid. dissolving 100 grams of potassium iodide in water and 20 The calculation for potassium ferricyanide employs diluting with water to one liter (the water is either dis the following equation: tilled water or deionized water); a reagent grade of a phosphate buffer prepared by dissolving 300 grams of crystalline monobasic sodium phosphate (NaH2PO4 Potassium 25 ferricyanide see HO) in water and diluting with water to one liter, the grams/liter) water again being distilled or deionized; and a reagent grade of 0.1000N aqueous solution of sodium thiosul fate. sample gll KafeCNs in standard solution 10,000 The method of sodium bromite analysis constitutes absorbance standard absorbance 15 pipetting 1 ml. of sodium bromite solution into a 250 ml. Erlenmeyer flask containing 100 ml. of water which is distilled or deionized and adding thereto 20 ml. of the 10% potassium iodide solution and 20 ml. of the phos phate buffer solution. Next, the mixture is titrated with the 0.1000N sodium thiosulfate solution until the mix 35 The method for analyzing for sodium ferrocyanide ture is lemon yellow. Finally, a drop or two or a reagent decahydrate constitutes diluting the spent bleach sam grade soluble starch indicator is added and the mixture ple in two steps, the first of which consists in pipetting is titrated to a colorless endpoint. 3 ml. of the sample into a flask and diluting to 100 ml. The general equation employed for calculating for with the 2% sodium bicarbonate solution; the second 40 step consists in pipetting 20 ml. of the resulting solution sodium bromite content is as follows: into a bottle and adding by use of a pipette 20 ml. of the potassium persulfate solution. The bottle is closed with a glass stopper, shaken well and allowed to stand g/liter NaBrO, = at 20-25°C for one hour, whereupon 10 ml. of the re 45 action mixture is pipetted into a flask and diluted to . Iml NaySOs. In Na2SOs) Equivalent wt. of NaBro 100 ml. with the 2% sodium bicarbonate solution. Now volume of sample the absorbance of the reaction mixture is read on the spectrophotometer at 420 nm. using a 10 mm. cuvette and using the 2% sodium bicarbonate solution as a 50 blank. Particularizing the above general equation to the The absorbance of a similarly twice-diluted and simi aforesaid parameters, the sodium bromite assay in larly treated standard potassium ferricyanide solution grams per liter equals: is read in the same fashion. ml Na2SON Na2S2O3)33.7 After having determined the potassium ferricyanide 55 content of the bleach by the previous method, the total It also is necessary in carrying out the present inven ferricyanide present after full conversion of the ferro tion to assay the spent bleach for ferrocyanide and fer cyanide is obtained by the following formula: ricyanide content before regenerating the same. This may be done spectrophotometrically by the following method. The equipment and reagents used are: a Beckman 60 Total g/ KFe(CN) in DB spectrophotometer or an equivalent device potassium st standard solution equipped with 10 mm. cuvettes; a reagent grade 2% so ferricyanide absorbancexe standard absorbance dium bicarbonate solution prepared by dissolving 20 g. grams/liter of sodium bicarbonate in distilled or deionized water and diluting with distilled or deionized water to one li 65 ter; a reagent grade potassium ferricyanide solution 40 100 prepared by diluting 0.2 g of potassium ferricyanide (t ge3 x 2 x f) 3,912,514 9 10 To determine the sodium ferrocyanide decahydrate were added), and a pH of 7.86, there were added 36 content, the following formula is employed: ml. (a stoichiometric quantity) of a 7% solution of so dium bromite, pH 13 to 14 (Preptone) and 24 milli liters of 4N hydrobromic acid. The sodium ferrocya nide, NaFe CNo. 10H2O, was added to raise the even grams/liter sodium ferrocyanide decahydrate = tual concentration of ferricyanide in the exhausted 484 E. potassium initial RE 329 bleach to the concentration normally found in a fresh ferricyanide ferricyanide gll bleach. After one hour at room temperature the bleach solution was analyzed and found to have a volume of After completion of the assays, a calculation is made 10 500 milliliters and contain 132 grams per liter of so of the volume of sodium bromite (in liters) required for dium ferricyanide, NaFe CNJs.H.O, as compared to regeneration. 133 grams per liter of sodium ferricyanide, NaFe This amount is equal to the number of grams of so (CN)6H2O, if all the ferrocyanide in the exhausted dium ferrocyanide decahydrate to be regenerated mul bleach had been converted to ferricyanide. The pH of tiplied by the equivalent weight of sodium bromite 15 the regenerated solution was 7.92 as compared to a pH . (33.7) and divided by the multiple of the equivalent of 8.0 for a fresh bleach. weight of sodium ferricyanide decahydrate (484) and The step of halitizing as described in detail above can the grams per liter of sodium bromite found by the be employed to produce an alkaline ferricyanide from aforementioned assay. The equation employed is: an alkaline ferrocyanide as a method for producing so 20 dium ferricyanide apart from a bleach, and the same halitizing step can be used to prepare a ferricyanide bleach starting from a ferrocyanide base, i.e. a bleach Vol. bromite = sodium ferocyanide decahydrate gll x 0.0696 in which the cyanide is present principally as a ferrocy liters bromite assay g/l) 25 anide and is converted to a ferricyanide for commercial use of the bleach. Certain bleach addenda react with alkali halites. For Next in the practice of the invention the quantity of example, sodium thiocyanate is completely destroyed sodium bromite solution required to oxidize all the fer by reaction upon the addition of a bromite to a bleach rocyanide to ferricyanide, e.g. calculated in the forego 30 containing the same. Hence, this compound must be ing manner is added to the spent bleach solution and eliminated from any bleach formula regenerated by the the pH of the solution in which the ferrocyanide is technique of the present invention. Carbowax 1,540 (a being oxidized is adjusted to neutrality with an acid, polyethylene glycol) is not noticeably affected by so e.g. an orthophosphoric acid or hydrobromic acid. The dium bromite. It has been observed that when a sodium acid employed preferably is added in a water solution 35 bromite solution is mixed with a 50% Carbowax 1,540 and may be quite concentrated. For example, when solution for a week, there is some slight oxidation of the using hydrobromic acid a 48% aqueous solution Carbowax; but sine this is not a procedure which would thereof is employed. The neutralizing acid is not pre be followed with the use of the present invention, it is mixed with the alkaline sodium bromite solution. not necessary to employ bleach formulations with Car The bleach is now regenerated and as a check for ef 40 bowax eliminated. ficient reuse the regenerated bleach is assayed for each The use of the invention has not appeared to cause of its constituents such, for example, as ferricyanide, any dye degradation on color film which has been bromide and other addenda normally present in a fresh bleached by a regenerated bleach solution. bleach. Standard analytical assay methods are em The present invention also is useful to regenerate po ployed. It will be recalled that during the bleaching 45 tassium ferricyanide bleaches such, for instance, as an method the bleach solution in the bleaching tank is di ME-4 type of ferricyanide bleach. An ME-4 ferricya luted by carry-over of solution from the preceding tank nide bleach replenisher and fresh bleach usually con and it is this which necessitates the aforesaid assay of tains about 160 g/l of potassium ferricyanide. The aver the constituents of the regenerated bleach. age concentration of potassium ferricyanide present in Finally, additional compounds are added to make up 50 a tank of spent bleach following the ME-4 process is the differences caused by dilution or use, the added l 12 g/l and the equilibrium tank concentration of fer compounds being solid or water solutions of potassium rocyanide is about 30 g/l as potential potassium ferricy ferricyanide, sodium bromide and other addenda as are anide. In the practice of the invention enough bromite required. is added to convert about two-thirds of the ferrocya The foregoing description of the method of the in 55 vention provides all the instructions necessary to carry nide to ferricyanide, to wit, about 20 g/l, and about 30 out said method. Nevertheless, to complete the de g/1 of dry potassium ferricyanide is added to raise the scription, there is set forth below an example of a quan total potassium ferricyanide concentration after regen titatively described series of steps for regenerating a eration to the desired 160 g/l level. spent ferricyanide bleach solution, i.e. one containing 60 The cost of using a halite such as sodium bromite for some ferrocyanide: regeneration of a spent ferricyanide photographic sil To 440 milliliters of an exhausted ferricyanide ver bleach solution is higher than that for regeneration bleach, found by analysis to contain 101 grams per liter with a persulfate solution, but the additional cost is of sodium ferricyanide, NaFe CNJ.H.O, and 84 largely negated by eliminating the need for discarding grams per liter of sodium ferrocyanide, NaFe 65 a portion of bleach solution when persulfate regenera (CNJ. 10HO 47 grams per liter of sodium ferrocya tion is utilized in order to prevent a build-up of sulfate. mide, NaFe CNJ. 10HO, were present and 37 grams Moreover, by using a halite for regeneration ferricya per liter of sodium ferrocyanide, NaFe (N)-10H2O, nide losses to the environment can be minimized and 3,912,514 11 12 substantially eliminated because the system is amena 3. A method as set forth in claim 1 wherein the pH ble to closedloop operation. is maintained in the range of between about 6 and It thus will be seen that there is provided a method about 8 by the addition to the spent silver bleach solu which achieves the various objects of the invention and tion in which the ferrocyanide is being oxidized of an which is well adapted to meet the conditions of practi acid selected from the group consisting of orthophos cal use. phoric acid and hydrobromic acid. As various possible embodiments might be made of 4. A method as set forth in claim 3 wherein the alkali the above invention, and as various changes might be metal bromite is in water solution and wherein said made in the embodiment above set forth, it is to be un water solution also contains an alkalizing agent. derstood that all matter herein described is to be inter O 5. A method as set forth in claim 4 wherein the alkal preted as illustrative and not in a limiting sense. izing agent is an alkali metal hydroxide. Having thus described the invention there is claimed 6. A method as set forth in claim 5 wherein the alkali as new and desired to be secured by Letters Patent: metal hydroxide is sodium hydroxide. 1. A method of regenerating a photographic aqueous 7. A method as set forth in claim 6 wherein the pH spent silver bleach solution containing an alkali ferro 5 of the alkaline water solution of the alkali metal bro cyanide, said method comprising adding to the silver mite is at least 13. bleach solution an aqueous solution containing an al 8. A method as set forth in claim 1 wherein the kali metal bromite to oxidize ferrocyanide ions to ferri amount of alkali metal bromite added to the spent sil cyanide ions, the oxidation being carried out at a pH of ver bleach solution is about equal to that necessary to between about 6 and about 8 at room temperature. 20 stoichiometrically react with all the ferrocyanide ions 2. A method as set forth in claim 1 wherein the alkali to convert them to ferricyanide ions. metal is sodium. ck k k >k :k

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