Patent Publication Number: US-4840717-A

Title: Silver recovery cell

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to silver recovery devices for silver laden solutions; more particularly to a silver recovery device used to recover silver obtained during photographic processes; and still more particularly to an improved silver recovery cell therefor. 
     2. Description of the Prior Art 
     It is well known that silver based compounds are a major constituent of photographic film. After the film has been exposed to light, it is subjected to a &#34;developer&#34; solution. The light exposure combined with a bath in the developer solution results in some of the silver in the silver compounds being converted to metallic silver, resulting in an image of the film. In order to prevent any remaining silver compounds from being affected by further exposure to light, the film is chemically processed by a &#34;fixer&#34; solution to remove the remaining silver compounds that were not affected by the aforesaid light exposure. This &#34;fixes&#34; the film and allows it to be subsequently viewed in lighted environments without the image thereon being affected. This developing process of photographic film is very well known in the art and results in large amounts of silver being released into the fixer solution. For both environmental and economic reasons, it is very desirable to recover as much of this released silver as is possible. 
     It is known in the prior art to recover silver from photographic solutions by use of an electrical silver plating system. An example of such a system is described in U.S. Pat. No. 3,875,032 to Thompson, where a power supply is electrically connected to an anode and cathode, each being immersed in a photographic fixer solution. When electricity is applied to the electrodes, silver, present in the solution as either suspended metallic silver or as suspended or dissolved silver compounds, is caused to plate on the cathode. In Thompson, the photographic fixer solution is contained in a tank rendering the process awkward and inefficient. 
     An improved type of electrical silver plating system is described in U.S. Pat. No. 4,612,102 to Brimo et al. Brimo et al teach that the silver plating process may be performed utilizing a cell having a cylindrically shaped canister for containing the photographic fixer solution. Brimo et al teach that a rod shaped anode of graphite material is connected to a removable top and that a cylindrically shaped cathode having a longitudinal slit encircles the anode and is resident in the canister. Terminals connect a power supply to the cathode and the anode. While this cell is an improvement over the tank of Thompson, it suffers from inability to visually inspect the status of the silver plating that is occurring on the cathode, a factor that is critical in controlling quality of the operation. Further, because the anode is connected to the top, silver tends to plate mainly adjacent to the top, where the fixer solution is entering the canister, rather than along the entire longitudinal length of the cathode, resulting in inefficient operation. 
     Accordingly, what is needed is a silver recovery device which incorporates a cell having the structural features of visual inspection of silver plating at the cathode and uniform plating of the cathode surface. 
     SUMMARY OF THE INVENTION 
     The present invention is a silver recovery device incorporating a recovery cell structured to permit visual inspection of the status of silver plating on the cathode and to ensure uniform silver plating on the surface of the cathode. 
     A clear cylindrical canister is provided having a closed bottom and an open top. A graphite, rod is secured to the bottom at the axial center of the clear canister, and a terminal is provided to connect the graphite rod to a power supply. The graphite rod serves as the anode. A cylindrically shaped cathode of stainless steel is provided which inserts into the clear canister and surrounds the anode. A longitudinal slit subtending an angel of approximately 60 degrees is provided in the cathode. A terminal in the side of the clear canister connects the cathode to the power supply. A removable top is provided through which fixer solution enters and leaves the clear canister. It is preferred that the fixer solution enter the canister in a manner so as to cause general agitation of the fixer solution in the clear canister. In operation, the condition of silver plating can be ascertained by looking through the clear canister and the slit in the cathode. A light may be provided in the removable top to facilitate seeing the plated silver on the cathode. 
     It is, therefore, an object of the present invention to provide a silver recovery device for silver laden solutions having a recovery cell that permits visual inspection of the plated silver on the cathode. 
     It is an additional object of the present invention to provide a silver recovery cell of the aforesaid type having a predetermined relationship between the cathode and anode and the silver laden solution entry and exit ports so as to cause silver to be uniformly plated on the cathode. 
     It is a further object of the present invention to provide a silver recovery device having improved silver laden solution flow characteristics. These, and additional objects, advantages, features and benefits of the invention will become apparent from the following specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1. is a schematic view of the preferred environment of use of the present invention. 
     FIG. 2. is a part sectional side view of the recovery cell according to the present invention. 
     FIG. 3 is a plan view of the recovery cell according to the present invention, shown along lines 3--3 of FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the figures, FIG. 1 shows the present invention in its preferred environment of use. Two identical recovery cells 10 are connected in series through appropriate piping 12 to a photographic fixer solution bath 14. The piping includes a conventional valve 16 for selectively directing the flow of photographic fixer solution so as to either flow through the recovery cells 10 or to by-pass them. A conventional pump 18 is included to enhance flow of photographic fixer solution when the valve 16 is adjusted to cause flow through the recovery cells 10. A conventional power supply 20 provides electrical power to the recovery cells 10 in a manner to be discussed hereinbelow. In this preferred environment of use, the recovery cells 10 according to the present invention selectively remove silver from the photographic fixer solution. 
     Referring now to FIGS. 2 and 3, the structure and operation of the recovery cell 10 according to the present invention may be understood. 
     A clear canister 22 of cylindrical shape is provided. The top 24 of the clear canister 22 is open and provided with threads 26. A preferred material for the clear canister 22 is a clear plastic or glass. The bottom 28 of the clear canister is closed. Attached to the bottom 28 at the axial center of the clear canister, an anode rod 30 is provided. The anode rod projects upwardly into the clear canister 22 along its axial center. An anode terminal 32 is connected to the end of the anode rod. Threads 34 and 34&#39; are provided, respectively, on the bottom 28 and the anode terminal 32 to secure the anode rod to the clear canister. Alternatively, the anode rod may be secured to the clear canister by an adhesive being applied to the bottom 28 and the anode terminal 32. The anode rod 30 is preferred to be constructed of graphite. It is further preferred that there be a cylindrically shaped mounting portion 36 in the bottom 28 so that the anode rod will be rigidly secured to the bottom 28 by engagement therewith. A cathode cylinder 38 is provided in the clear canister 22. The cathode cylinder is preferred to be structured to have a diameter substantially similar to that of the inside diameter of the clear canister. Further, the cathode cylinder 38 is provided with a longitudinal slot 40, the slot preferably subtending an arc A of approximately 60 degrees. The cathode cylinder surrounds the anode rod 30 along the entire length of the anode rod. A cathode terminal 42 is provided through the side of the clear canister 22. The cathode terminal terminates interior of the clear canister in a contact 43 which touches against the cathode cylinder 38 so as to provide good electrical connection between the cathode cylinder 38 and the cathode terminal 42. It is preferred that the cathode cylinder be constructed of stainless steel. 
     The top 44 is structured to releasably thread onto the clear canister 22, via threads 46. A resilient gasket 48 seals the top 44 with respect to the clear canister 22. The top 44 includes passageways for the photographic fixer solution 50 to flow into and out of the clear canister 22. An inlet passageway 52 is provided which connects with the piping 12. Photographic fixer solution flows through the top 44 as indicated by arrows B. The photographic fixer solution 50 flows into an inlet port 54 before entering the clear canister 22. The inlet port 54 is structured to cause constriction of the fluid flow therethrough so as to cause a fluid flow velocity increase when the photographic fixer solution leaves the inlet port 54 and enters the clear canister. The fluid flow velocity is preferred to be such as to cause a general agitation and mixing of the photographic fixer solution in the clear canister so that a maximum opportunity is provided for the photographic fixer solution to swirl along the entire length of the anode rod 30. The top 44 further includes an exit passageway 56 through which photographic fix solution 48 may exit, along arrows C, from the clear canister 22 and return to the piping 12. A spring loaded air bleed 58 is provided at the uppermost part of the exit passageway 56 so that air may be selectively bled out of the recovery cell 10. By allowing air to bleed during filling of the silver recovery cell 10, filling time is considerably reduced as compared to a system not incorporating an air bleed 58. 
     In operation, the anode terminal and the cathode terminal are connected to a suitable conventional power supply. Such a power supply is described, for example, in the aforesaid U.S. Pat. Nos. 3,875,032 and 4,612,102; it is to be understood that a suitable conventional power supply is not intended to be limited to the types described in the aforesaid patents. When electrical power is supplied to the anode and cathode terminals and there is a silver laden photographic fixer solution present within the clear canister, silver will be caused to plate onto the cathode cylinder. The status of this plating may be observed at any time by looking through both the clear canister and the slot in the cathode cylinder. When it is determined by such inspection that either plating is not occurring as expected or that a maximum acceptable amount of plating has occurred, steps may thereupon be taken to ensure continued maximum efficiency of the recovery cell 10. Because the anode rod is secured in the recovery cell 10 remote from the top where photographic fixer solution enters the clear canister, there is general uniformity of plating of silver over the inside surface 60 of the cathode cylinder 38. 
     To facilitate inspection of the plated silver on the interior surface 60 of the cathode cylinder 22, a light 52 may be provided in the top 44 at a location adjacent the inlet port 54. The light 52 is illuminated by electricity supplied into the top and a switch (not shown) is used to selectively actuate the light when viewing into the clear canister. 
     To facilitate silver removal, recovery cells 10 may be connected serially, as shown in FIG. 1, where the exit pasageway of one connects to the inlet passageway of the next. 
     To facilitate fluid flow of the photographic fixer solution through the recover cell 10, a pump 18 is attached to the piping 12. This is especially advantageous when a recovery cell 10 is connected in series with one of more recovery cells 10, as shown in FIG. 1. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such changes or modifications can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.