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Recovering silver from your photoprocessing effluent is good business; it is a source of extra revenue. In addition, most environmental regulations specify limits on the amount of silver that can be discharged. So unless you process only very small amounts of photographic material, you'll want to consider some means of silver recovery.

Basically, there are two methods in general use: metallic replacement and electroplating. Other methods that involve ion exchange technology are less commonly used because they sometimes require a larger capital investment and/or greater technical expertise. An ion exchange method may be needed where environmental considerations are a factor.

How Do These Recovery Methods Differ ?

Both metallic replacement and electrolytic methods recover silver efficiently and are simple to operate. However, there are significant differences in these two methods that you'll want to consider before choosing the method that is best for you. In addition, there may be good reasons for you to consider using ion exchange to recover silver. First, let's talk about metallic replacement.

Metallic Replacement

In this method, a metal (usually iron) reacts with the silver thiosulfate and goes into solution. The less active metal (silver) settles out as a solid. To bring the silver into contact with the iron, the used fixer or bleach-fix is passed through a container filled with steel wool. The steel wool provides the source of iron to replace the silver.

The main advantages of this method are the very low initial cost (cartridges cost $30 to $60) and the simplicity of installation; only a few simple plumbing connections are required.

The disadvantages, compared to the electrolytic method, are that the silver is recovered as a sludge, making it more difficult to determine the exact amount recovered, and that the sludge requires more refining than the plate silver obtained with electrolytic methods.

Also, cartridges cannot be reused; they must be replaced when they are exhausted. The effluent from the cartridges contains high amounts of iron. This is a problem in localities with sewer codes that limit the iron concentration in the effluent.

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