Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2000-11-03
2004-05-18
Cintins, Ivars C. (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S669000, C210S688000, C210S729000, C210S912000, C588S256000
Reexamination Certificate
active
06736977
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the disposal of processing solutions used to process silver halide photographic materials.
BACKGROUND OF THE INVENTION
Color photographic processing typically includes the processing steps of development, bleaching, fixing, washing and stabilizing. For color negative materials these steps are practiced using a color developer that generates the dye image and, as a side product, metallic silver; a bleach containing a heavy metal bleaching agent that converts any metallic silver into silver ion; and a fixing solution containing a fixing agent that forms soluble silver ion complexes which arc subsequently removed in the washing steps. Finally, the photographic element may be treated to a stabilization step that renders the material stable for storage and includes agents, such as surfactants, that allow water to sheet off the surface without streaking.
The overflow from such a photographic process may consist of environmentally regulated substances such as the reduced form of the color developing agent and its oxidized derivatives, heavy metal ions including silver ion, sequestering agents, and substances that have high oxygen demand. Environmental regulations in some locations restrict the discharge of the reduced form of color developer and solutions which contain any leachable silver greater than 5 ppm. Thus it is typical that this waste is collected in receiver tanks using either one receiver for each solution or one receiver for all solutions. A qualified hauler then picks up the liquid waste for disposal. If the pH of the waste solutions exceeds 12.5 or is less than 2, other environmental regulations may apply.
One alternative to such a “haul away” process by a qualified hauler is to convert the waste by chemical or physical means into a residual solid that can be removed to a place of safe and legal disposal. U.S. Pat. No. 5,457,272 describes a method that solidifies photographic effluent by adding a water-soluble silicate to the effluent in an amount that renders the mixture glass-like and less permeable to water. Unfortunately this reaction occurs over days, which increases the expense to the user because it requires an on-site treatment and storage area. In addition, the effluent cannot contain ammonium ions, since the effluent might release free ammonia when the alkaline earth compound, such as calcium hydroxide, is added. This restriction limits the manufacturer's formulation options.
U.S. Pat. No. 5,275,509 describes a method of disposing of photographic fixer and developer using an absorbing polymer which is substantially insoluble in the mixture of equal parts fixer and developer. The expectation is that the silver ion in this mixture is immobilized and precipitates as insoluble silver sulfide. The mixture can then be disposed of in a landfill or similar site designed to receive nontoxic waste. This practice, however, when applied to the combined color photographic processing effluent, would not address the issue of the reduced color developing agent. In addition, it has been discovered by the inventors herein that the silver ion is not immobilized by the absorbing polymer but can leach from the absorbent, making the resultant mixture subject to environmental regulation.
One method to reduce the silver ion concentration below 5 ppm is to precipitate it from the solution. A particularly efficient precipitating agent is trimercato-s-triazine (TMT) as described in patents U.S. Pat. Nos. 5,288,278; 5,437,792; 5,476,593; 5,496,474; 5,563,267; 5,759,410; and 5,961,939 and references sited therein. These patents describe how to reduce the silver ion concentration below 5 ppm in effluent mixtures that are then discharged to the drain. No consideration is given to managing the reduced form of the color developing agent or the conversion of the liquid waste to apparently dry waste. Other methods of isolation convert the silver ion to silver metal such as electrolytic reduction or use of galvanic cells such as used in the steel wool containing chemical recovery cartridges.
There is still needed a means of waste disposal of combined waste photoprocessing solutions which is simple, less expensive and which is not subject to environmental regulation.
SUMMARY OF THE INVENTION
This invention provides a method of disposing of photographic silver halide processing solutions including developer solution, bleach solution and at least one silver bearing solution comprising a) combining the developer and bleach solutions to oxidize the developing agent in the developer and form a developer/bleach waste solution, b) treating the silver bearing solution(s) to reduce the silver ion level and form a low silver waste solution; and c) contacting the developer/bleach waste solution and the low silver waste solution with an absorbent material to form an apparently dry waste material having a leachable silver ion level below 5 ppm.
The present invention provides a process to use the natural chemistry of the color photographic solution reactions to lower their hazard rating and to add absorbent material to convert the aqueous waste to apparently dry waste. Combining the bleach and developer waste solutions results in the complete oxidation of the reduced developer. Contacting this combined solution with an absorbing material converts the solution to an apparently dry waste that can be discharged to a common waste receptacle. A general hauler can now dispose of this apparently dry, nontoxic waste. This invention also provides the means to reduce the level of leachable silver ion from silver bearing waste solutions to below 5 ppm. The liquid mixture can then be rendered apparently dry and shipped to a refiner to extract the silver. Alternatively, the silver ion can be separately removed from the effluent stream to a level below 5 ppm and the residual liquid rendered apparently dry for easy waste disposal to a landfill or similar site designed to receive nontoxic waste.
DETAILED DESCRIPTION OF THE INVENTION
The first step in the method of the invention is to combine the overflow or waste developer and bleach solutions to oxidize the developing agents in the developer and form a developer/bleach waste solution. The function of the developer in the photochemical process is to reduce the silver halide in the silver halide photographic material to silver metal. In so doing, the developing agent is oxidized. With color photographic materials, the useful image consists of one or more organic dye images produced by color couplers which react with the oxidized color developing agent formed wherever silver halide is reduced to metallic silver. After the completion of the color developing step the unused color developing agent is in a reduced state.
The function of the bleach bath in the photochemical process is to convert metallic silver formed in the developer to an ionic state. The bleach reaction requires that the silver be oxidized by an oxidizing agent. The overflow or waste bleach solution contains a certain amount of unreacted oxidizing agent. By combining the waste bleach and developer solutions the reduced developer is oxidized to an environmentally benign developer/bleach waste solution. Additionally the pH of the waste developer is often quite high, generally about 9 to 12. Combining it with the bleach solution which generally has a pH of 2 to 6.5 neutralizes the alkaline developer. Combining the bleach and developer may be done in any manner known to those skilled in the art such as by mixing, agitation, spraying or any other means. It may be done at a separate waste processing station with the developer/bleach waste solution then being transported to a waste processing station containing the absorbent or it could be done, for example, by combining the solutions at a processing station and then adding the absorbent at the same station. The waste processing station may be any area wherein a waste solution is processed. The various stations may be part of the same apparatus or piece of equipment or they may be in separate pieces of equipment. Th
Hall Jeffrey L.
Lobo Lloyd A.
Transvalidou Faye
Cintins Ivars C.
Eastman Kodak Company
Meeks Roberts Sarah
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